Title of Invention	RESIN COATED METAL SHEET
Abstract	A resin coated metal sheet according to the present invention is a resin coated metal sheet coated with a resin film comprising a surface treatment composition, in which the surface treatment composition contains: an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes and a resin component comprising an olefin- α , β -unsaturated carboxylic acid copolymer, an α , β -unsaturated carboxylic acid polymer, and an acrylic modified epoxy resin; and further a glycidoxy radical containing silane coupling agent and metavanadate. By the configuration, it is possible to obtain a resin coated metal sheet having not only corrosion resistance but also roll-formability and coating adhesiveness after post-coating.

Title of Invention

RESIN COATED METAL SHEET

Abstract

A resin coated metal sheet according to the present invention is a resin coated metal sheet coated with a resin film comprising a surface treatment composition, in which the surface treatment composition contains: an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes and a resin component comprising an olefin- α , β -unsaturated carboxylic acid copolymer, an α , β -unsaturated carboxylic acid polymer, and an acrylic modified epoxy resin; and further a glycidoxy radical containing silane coupling agent and metavanadate. By the configuration, it is possible to obtain a resin coated metal sheet having not only corrosion resistance but also roll-formability and coating adhesiveness after post-coating.

Full Text	TITLE OF THE INVENTION RESIN COATED METAL SHEET FIELD OF THE INVENTION The present invention relates to a resin coated metal sheet excellent in roll-formability and coating adhesiveness after post-coating. BACKGROUND OF THE INVENTION Hot dip galvanized steel sheets used for building material applications include a hot dip galvanized steel sheet (GI sheet) produced by plating a steel sheet with pure zinc, an alloyed hot-dip galvanized steel sheet (GA sheet) produced by alloying it, and the like. A GI sheet is: formed (roll-formed) from a flat sheet into a formed product having an intended cross-sectional shape by running continuously between plural pairs of rolls aligned in a row (forming speed: approximately 20 to 70 m/min) and passing through forming processes sequentially; and thereafter used nakedly (without the application of post-coating) for a deck, a lightweight steel member, or the like. Meanwhile, a GA sheet is, after the surface is post-coated with a calcium plumbate anticorrosive paint, a lead-free paint, an electrodeposition paint, or the like, used for a door, a shutter, or the like. Conventionally, chromate treatment has been applied on the surface of a GI sheet, a GA sheet, or the like with an aim to improve corrosion resistance. Under the recent growth of environmental awareness however, a treatment method other than a chromate treatment (non-chromate treatment) has been studied and a resin coated metal sheet produced by forming a chromate-free resin film on a hot dip galvanized steel sheet has heretofore been developed. For example, JP-A No. 61608/2009 discloses a resin coated metal sheet coated with a resin film comprising a surface treatment composition containing: an inorganic component comprising lithium silicate and colloidal silica,- α resin component containing an olefin- α , β -unsaturated carboxylic acid copolymer, an α , β -unsaturated carboxylic acid polymer, and an oxazoline radical containing copolymer; and further a glycidyl radical containing silane coupling agent and metavanadate. The resin film described in the above literature is preferably used for a GI sheet. The reason is that, although a GI sheet undergoes severe contact pressure during roll-forming, the resin film described in the above literature can be thinned due to its heavy specific gravity (about 2), hence roll-damage on the resin film during roll-forming can be mitigated, and the exfoliation of the resin film from the GI sheet surface caused by sliding from rolls (generation of film crumbs) hardly occurs. Another reason is that, in roll-forming: a coolant is supplied on the surface of a GI sheet in order to secure lubricity and cool down processing heat and used repeatedly; and on the occasion, even if a resin film (film crumbs) peels off from the GI sheet and is mixed into the coolant, the resin film described in the above literature contains an inorganic component abundantly, has a large specific gravity, and thus settles in the coolant, and hence the film crumbs are prevented from floating in the coolant and accompanying the coolant. As a result, it is possible to avoid the possibilities that, when the coolant is wiped off from the surface of the GI sheet with a drain pad (a drainage process) : the film crumbs build up on the surface of the drain pad; friction occurs between the build-up film crumbs and the surface of a formed product and generates unusual noises; the formed product cannot pass through the drain pad section at a uniform traveling speed; the shape and the size of the product get out of order; and thus the yield deteriorates. On the other hand, when the aforementioned resin film is applied to a GA sheet, coating adhesiveness and corrosion resistance after post-coating have been insufficient in some cases. The reason of the insufficient coating adhesiveness is presumably that, whereas the surface of a GA sheet is originally unleveled and rough and thus has an excellent coating adhesiveness due to an anchor effect, the resin film causes the unevenness of the GA sheet surface to level or covers only the outermost surface of the GA sheet and thus the anchor effect of the GA sheet is lost. Further, the reason of the insufficient corrosion resistance is presumably that only the outermost surface of the GA sheet is covered with the aforementioned resin film, the film is not formed at the bottom portions of the recesses, the plated zinc is exposed, and thereby under film corrosion appears when a corrosion resistance test is carried out by applying cross-cut on the coated surface after post-coating. Furthermore, additional problems have been: that blisters (swellings of a coated film) are generated around the cross-cut portions in the corrosion resistance test because of vacancies formed at the bottom portions of the recesses; and that lithium silicate having a water absorbing property is used as a resin film component. SUMMERY OF THE INVENTION The present invention has been achieved in view of the aforementioned situation and an object of the present invention is to obtain: a chromate-free surface treatment composition which has not only corrosion resistance but also roll-formability required of a GI sheet and coating adhesiveness after post-coating required of a GA sheet; and a resin coated metal sheet coated with a resin film comprising the surface treatment composition. A resin coated metal sheet according to the present invention acquired by solving the aforementioned problems is a resin coated metal sheet coated with a resin film comprising a surface treatment composition, in which the surface treatment composition contains: an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes by 60 to 80 parts by mass,- α resin component comprising an olefin- α , β -unsaturated carboxylic acid copolymer, an α , β -unsaturated carboxylic acid polymer, and an acrylic modified epoxy resin by 20 to 40 parts by mass; and further a glycidoxy radical containing silane coupling agent by 5 to 15 parts by mass and metavanadate by 0.5 to 3 parts by mass per 100 parts by mass in total of the inorganic component and the resin component. A preferable embodiment of the present invention is that: the inorganic component contains colloidal silica (A) having a surface area average particle size of 4 to 6 nm and colloidal silica (B) having a surface area average particle size of 10 to 20 nm; and a mix ratio of the (A) to the (B) is 70:30 to 40:60 (in mass ratio). Here, in the present specification, colloidal silica having a surface area average particle size of 4 to 6 nm means colloidal silica in which colloidal silica having a surface area particle size of 5 nm accounts for 90% or more (preferably 95% or more). Likewise, colloidal silica having a surface area average particle size of 10 to 20 nm means colloidal silica in which colloidal silica having a surface area particle size of 12 nm accounts for 90% or more (preferably 95% or more) . A surface area average particle size can be measured generally by the Sears method or the BET method. An electron microscope that can directly measure a particle size is effectively used in order to measure a surface area average particle size more accurately. Another preferable embodiment is that the resin component contains the acrylic modified epoxy resin by 2 to 15% by mass. Further, other preferable embodiments are that: the surface tension of the surface treatment composition is 50 dyn/cm or less; the coating weight of the resin film is 0.2 to 1 g/m2 by dry mass; and the metal sheet coated with the resin film is a hot dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet. A resin coated metal sheet according to the present invention: is coated with a resin film comprising a prescribed surface treatment composition; and hence can satisfy not only corrosion resistance but also roll-formability required of a GI sheet and coating adhesiveness after post-coating required of a GA sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A resin coated metal sheet according to the present invention is a resin coated metal sheet coated with a resin film comprising a surface treatment composition and is characterized in that the surface treatment composition contains: an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes by 60 to 80 parts by mass; a resin component comprising an olefin- α, β -unsaturated carboxylic acid copolymer, an α, β-unsaturated carboxylic acidpolymer, and an acrylic modified epoxy resin by 2 0 to 40 parts by mass ; and further a glycidoxy radical containing silane coupling agent by 5 to 15 parts by mass and metavanadate by 0.5 to 3 parts by mass per 100 parts by mass in total of the inorganic component and the resin component. A resin coated metal sheet according to the present invention is hereinafter explained in detail. Meanwhile, although a film in the present invention contains an inorganic component far more than a resin component, the term "resin film" is mostly used in this specific field and hence the term "resin film" is used also in the present invention. (Inorganic component) In the present invention, lithium silicate is not used as an inorganic component. By not using lithium silicate having a water absorbing property, it is possible to inhibit coating adhesiveness from deteriorating even when severe corrosion resistance tests such as a saltwater immersion test and a salt spray test are applied after post-coating and cross-cutting are applied on the surface of a resin coated metal sheet. One of the characteristics of the present invention is that plural kinds of colloidal silica having different surface area average particle sizes are used as an inorganic component. By so doing, it is possible to enhance affinity (fitting capability) of a binder resin (a resin component) with colloidal silica, improve film-formability of a formed resin film (bonding force between colloidal silica particles), and form a dense film. More specifically, it is preferable that an inorganic component: contains colloidal silica (A) having a surface area average particle size of 4 to 6 nm and colloidal silica (B) having a surface area average particle size of 10 to 20 nm; and comprises the colloidal silica (A) and the colloidal silica (B). It is estimated that colloidal silica: is dissolved and eluted at film defective portions in a corrosive environment; inhibits the dissolution and elusion of a metal sheet by the buffering effect and the passivation-film forming effect of pH; and thus improves the corrosion resistance of the metal sheet. In order to exhibit these effects sufficiently, it is effective to use colloidal silica (A). On the other hand, the problem has been that, since colloidal silica (A) has a high surface activity, when only colloidal silica (A) is used, it sometimes happens that the liquid stability of a surface treatment composition deteriorates with the passage of time (viscosity increases after about 48 hours) or a dense film cannot be formed, and it is impossible to increase the content of an inorganic component in a resin film and thereby increase the specific gravity of the resin film. To cope with the problem, the present inventors, as a result of earnest studies, have found that, by using colloidal silica (B) having a low surface activity and a surface area average particle size of 10 to 2 0 nm in combination, the content of an inorganic component can be increased without deteriorating the liquid stability of a surface treatment composition. Here, a surface area average particle size of colloidal silica described in the present specification means: a value measured by the Sears method in the case where a surface area average particle size is about 1 to 10 nm and by the BET method in the case where the size is about 10 to 100 nm; or a nominal value described in a brochure of a maker. A mix ratio of colloidal silica (A) to colloidal silica (B) is preferably 70:30 to 40:60 by mass and yet preferably 65:35 to 45:55. If a mass ratio of colloidal silica (A) exceeds 70, it sometimes happens that: the affinity with a resin component deteriorates; the liquid stability of a surface treatment composition deteriorates; and a uniform and dense film cannot be formed. As a result, the bare corrosion resistance and the coating adhesiveness after post-coating of a resin coated metal sheet deteriorate. If the mass ratio of colloidal silica (A) is less than 40, the quantity of Si ions dissolved and eluted at film defective portions in a corrosive environment may decrease and bare corrosion ' resistance may deteriorate undesirably. Colloidal silica is commercially available and, as colloidal silica having a surface area average particle size of 4 to 6 nm, "SNOWTEX (registered trademark) XS" made by NISSAN CHEMICAL INDUSTRIES, LTD. is named for example. Further, as colloidal silica having a surface area average particle size of 10 to 20 nm, "SNOWTEX (registered trademark) 40", "SNOWTEX (registered trademark) N", "SNOWTEX (registered trademark) SS", and "SNOWTEX (registered trademark) O" made likewise by NISSAN CHEMICAL INDUSTRIES, LTD. and "ADELITE (registered trademark) AT-30" and "ADELITE (registered trademark) AT-30A" made by ADEKA CORPORATION are named. In the case where a surface treatment composition used for forming a resin film is water-based, it is preferable to select the type of colloidal silica in conformity with the pH of the surface treatment composition in order to disperse colloidal silica well. An inorganic component comprising the aforementioned colloidal silica is set at 60 to 80 parts by mass per 100 parts by mass in total with a resin component described below. Since a surface treatment composition containing an inorganic component within the range described above shows a good film-formability in forming a resin film, the film hardly peels off and the roll-formability of a resin coated metal sheet improves. Further, the surface tension of the surface treatment composition lowers (preferably 50 dyn/cm or lower), the surface treatment composition intrudes even into the surface (recesses) of a GA sheet that has a rough surface and is inferior in water wettability, a resin film is formed along the rough surface of the GA sheet, and hence corrosion resistance and coating adhesiveness also improve. If the content of an inorganic component exceeds 80 parts by mass, a resin component is insufficient, hence the film-formability of a formed film is also insufficient, and a normal film cannot be formed. As a result, barrier effect in a corrosive environment may lower and corrosion resistance may deteriorate in some cases. Further, the film comes to be too hard and brittle, cracks are generated, and film exfoliation tends to happen during roll-forming. Furthermore, since colloidal silica (amorphous silica particles are dispersed in water in a colloidal state) has a high surface tension (about 66 to 73 dyn/cm), if the content of an inorganic component exceeds 80 parts by mass, it sometimes happens that the surface tension of a surface treatment composition increases, wettability with a metal sheet on which a resin film is formed deteriorates, and a uniform thin film is hardly formed. Inparticular, it comes to be difficult to form a uniform ultra-thin film at uneven portions on the surface of a GA sheet and hence coating adhesiveness and bare corrosion resistance deteriorate. If the content of an inorganic component is less than 60 parts by mass, the corrosion resistance of an obtained resin coated metal sheet may be insufficient in some cases. Further, the hardness of a film is insufficient, the specific gravity of the film does not increase so much as intended, hence a resin film is hardly thinned, and film exfoliation tends to occur during roll-forming. Moreover, because the specific gravity of a resin film does not increase, it sometimes happens that film crumbs cannot settle out in a coolant receiving tank, the effect of inhibiting build-up on a drain pad surface is insufficient, and resultantly operability and the shape of a product deteriorate. Furthermore, when a resin film is formed on a metal sheet (specifically a GAsheet) by using a surface treatment composition containing an inorganic component by less than 60 parts by mass, although the content of a resin component increases and film-formability improves, the quantity of eluted Si ions to inhibit corrosion decreases and hence it sometimes happens that corrosion (underfilm corrosion) proceeds between a resin film and a metal sheet surface (plated layer interface), resultantly coating adhesiveness after post-coating deteriorates, and blisters are generated in the vicinities of cross-cut portions in a corrosion test after post-coating. In the present invention, the content of an inorganic component is preferably 65 to 75 parts by mass per 100 parts by mass in total of an inorganic component and a resin component. On this occasion, the mix ratio of colloidal silica (A) to (B) is preferably 50:50(in mass ratio) and thereby it is particularly possible to improve the bare corrosion resistance and the coating adhesiveness of a GA sheet to good levels. (Resin component) A surface treatment composition used in the present invention contains, in addition to the aforementioned inorganic component, a resin component comprising an olefin- α , β -unsaturated carboxylic acid copolymer (hereunder referred to as "olefin-acid copolymer" occasionally), an α , β-unsaturated carboxylic acid polymer (hereunder referred to as "carboxylic acid polymer" occasionally), and an acrylic modified epoxy resin. The corrosion resistance of a resin coated metal sheet produced by forming a resin film with a surface treatment composition containing both the olefin-acid copolymer and the carboxylic acid polymer improves. The accurate mechanism is nonobvious but it is estimated that, by using both the substances, a dense resin film is formed and the permeation of water and oxygen is effectively inhibited. Here, the "olefin-acid copolymer" in the present invention means a substance that: is a copolymer of olefin and α , β -unsaturated carboxylic acid; and contains a constituent component derived from olefin by 50% by mass or more (namely, a constituent component derived from α, β-unsaturated carboxylic acid is 50% by mass or less) in the copolymer. Meanwhile, the "carboxylic acid polymer" means a substance that: is a polymer (including a copolymer) obtained by using α , β-unsaturated carboxylic acid as a monomer; and contains a constituent component derived from α , β -unsaturated carboxylic acidby 90% bymass or more in the polymer. Then the " α, β-unsaturated carboxylic acid" includes " α, β -unsaturated carboxylic salt" formed by neutralizing a part of a carboxyl radical with a neutralized that will be stated later. An olefin-acid copolymer used in the present invention can be produced by copolymerizing olefin and α , β -unsaturated carboxylic acid by a known method and is commercially available. One or more kinds of olefin-acid copolymers can be used in the present invention. Olefin used in the production of an olefin-acid copolymer is not particularly limited but ethylene, propylene, or the like is preferably used and ethylene is yet preferably used. For the olefin-acid copolymer, either a constituent component of olefin that is derived from only one kind of olefin or a constituent component of olefin that is derived from two or more kinds of olefin can be used. α, β -unsaturated carboxylic acid used in the production of an olefin-acid copolymer is also not particularly limited but, for example, monocarboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, or isocrotonic acid and dicarboxylic acid such as maleic acid, fumaric acid, or itaconic acid are named. Among those, acrylic acid is preferably used. For the olefin-acid copolymer, either a constituent component of α , β -unsaturated carboxylic acid that is derived from only one kind of α , β-unsaturated carboxylic acid or a constituent component of α , β -unsaturated carboxylic acid that is derived from two or more kinds of α , β-unsaturated carboxylic acid can be used. An olefin-acid copolymer used in the present invention may have a constituent component derived from another monomer within the range where corrosion resistance that is an effect of the present invention and the like are not adversely affected. In an olefin-acid copolymer, the content of a constituent component derived from another monomer is preferably 10% by mass or less, yet preferably 5% by mass or less, and the most desirable olefin-acid copolymer is a copolymer comprising only olefin and α , β –unsaturated carboxylic acid. An ethylene-acrylic acid copolymer is named as a preferable olefin-acid copolymer. α , β -unsaturated carboxylic acid in an olefin-acid copolymer is used for improving adhesiveness between a resin film and a metal sheet and the content of the α ,β -unsaturated carboxylic acid is preferably 5% by mass or more and yet preferably 10% by mass or more in the copolymer. If the content of the α , β -unsaturated carboxylic acid is excessive however, corrosion resistance may deteriorate undesirably and hence the content of the α, β -unsaturated carboxylic acid is preferably 30% by mass or less and yet preferably 25% by mass or less in the copolymer. The mass-average molecular weight (Mw) of an olefin-acid copolymer used in the present invention is preferably 1, 000 to 100, 000, yet preferably 3,000 to 70,000, and still yet preferably 5,000 to 3 0,000 in polystyrene equivalent. The Mw can be measured by GPC in which polystyrene is used as the standard. As a carboxylic acid polymer used in the present invention, a monopolymer or a copolymer comprising one or more kinds of α , β -unsaturated carboxylic acid, or a copolymer produced by further copolymerizing another monomer is named. Such a carboxylic acid polymer can be produced by a known method and is commercially available. In the present invention, one ormore kinds of carboxylic acidpolymers can be used. As α , β -unsaturated carboxylic acid used for producing a carboxylic acid polymer, any of the α , β -unsaturated carboxylic acid exemplified as a substance that can be used for synthesizing the aforementioned olefin-acid copolymer can be used. Among those, acrylic acid or maleic acid is preferably used and maleic acid is particularly preferably used. A carboxylic acid polymer may contain a constituent component derived from a monomer other than α , β -unsaturated carboxylic acid but the content of a constituent component derived from another monomer is limited to 10% by mass or less and preferably 5% by mass or less in the polymer, and a carboxylic acid polymer comprising only α , β -unsaturated carboxylic acid is yet preferably used. As a preferable carboxylic acid polymer, polyacrylic acid, polymethacrylic acid, acrylic acid-maleic acid copolymer, polymaleic acid, or the like can be named for example. Among those, polymaleic acid is preferably used from the viewpoints of coating adhesiveness, resin film adhesiveness, and corrosion resistance. By using polymaleic acid, the particle size of a generated resin emulsion reduces (20 to 60 ran), thus a formed film comes to be dense, and hence corrosion resistance and the like improve. Further, since the content of a carboxyl radical is large, adhesiveness between a resin film and a metal sheet improves and corrosion resistance further improves accordingly. Mw of a carboxylic acid polymer used in the present invention is, in polystyrene equivalent, preferably 500 to 3 0,000, yet preferably 800 to 10,000, still yet preferably 900 to 3,000, and most desirably 1,000 to 2,000. The Mw can be measured by GPC in which polystyrene is used as the standard. The content ratio of an olefin-acid copolymer to a carboxylic acid polymer in a surface treatment composition is 1,000:1 to 10:1, preferably 200:1 to 20:1, and yet preferably 100:1 to 100:3. If the content ratio of a carboxylic acid polymer is too low, the effect in the combination of an olefin-acid copolymer and a carboxylic acid polymer is exhibited insufficiently. If the content ratio of a carboxylic acid polymer is excessive in contrast, an olefin-acid copolymer and a carboxylic acid polymer separate into different phases in a surface treatment composition and a uniform resin film may not be formed undesirably. An acrylic modified epoxy resin is also contained in the aforementioned resin component. As a method for improving the adhesiveness of post-coating, a technology of containing block isocyanate (a heat sensitive crosslinker) as a resin component in a film, dissociating a blocking agent in the block isocyanate and reproducing an active isocyanate radical by using heat at baking after post-coating (at a baking temperature), and hardening and bridging the film and the coating film has heretofore been known. A calcium plumbate anticorrosive paint used as a paint for post-coating in the building material field is mostly an air-drying type not requiring baking (drying) by heat however and the above technology cannot be used. The present inventors, as a result of earnestly working on the above problems, have found that the coating adhesiveness of a resin film improves by concurrently using an acrylic modified epoxy resin allowing a film to be formed at a low temperature as a resin component. Precise mechanism of improving coating adhesiveness by concurrently using an acrylic modified epoxy resin is not obvious. It is estimated however that an acrylic modified epoxy resin does not function as a binder of an inorganic component (colloidal silica) but, by forming a film on the outermost surface of a resin film (scattering in the form of stripes), contributes to the improvement of coating adhesiveness after post-coating though it does not contribute to the improvement of bare corrosion resistance. The reason why an acrylic modified epoxy resin forms a film on the outermost surface of a resin film is presumably that, whereas the emulsion particle sizes of an olefin-acid copolymer and a carboxylic acid polymer are in the range of 20 to 60 nm, the emulsion particle size of an acrylic modified epoxy resin is as large as about 100 nm or more. An acrylic modified epoxy resin used in the present invention can be produced by, for example: copolymerizing a polymerizable unsaturated radical containing epoxy resin obtained by reacting an epoxy resin with unsaturated fatty acid and (meth) acrylic acid; or copolymerizing a polymerizable unsaturated radical containing epoxy resin obtained by reacting an epoxy resin and a glycidyl radical containing vinyl monomer with amines and (meth) acrylic acid. In particular, a water-based acrylic modified epoxy resin is commercially available and, for example, "MODEPICS (registered trademark) 301", "MODEPICS (registered trademark) 302", "MODEPICS (registered trademark) 303", and "MODEPICS (registered trademark) 304" made by Arakawa Chemical Industries, Ltd. are named. The acrylic modified epoxy resin may be used either individually or by combining two or more kinds. An acrylic modified epoxy resin may be contained by preferably 2% by mass or more (yet preferably 3% by mass or more) and also by preferably 15% by mass or less (yet preferably 7% by mass or less) in a resin component of 100% by mass. In the range, it is possible to improve coating adhesiveness after post-coating without hindering the roll-formability and the bare corrosion resistance of a resin coated metal sheet. If the content of an acrylic modified epoxy resin is less than 2% by mass, the effect of improving coating adhesiveness after post-coating is not recognized. In contrast, if the content of an acrylic modified epoxy resin exceeds 15% by mass, corrosion resistance tends to deteriorate. Ina GA sheet inparticular, coating adhesiveness may deteriorate considerably and blisters may be generated in some cases. The precise mechanism of deteriorating bare corrosion resistance and corrosion resistance and coating adhesiveness after post-coating when the content of an acrylic modified epoxy resin exceeds 15% by mass is not obvious, but it is estimated that an excessively contained acrylic modified epoxy resin hinders an emulsion of an olefin-acid copolymer and a carboxylic acid polymer from forming a film. A glycidoxy radical containing silane coupling agent (more specifically, a silane coupling agent having a glycidoxy radical at a terminal) is contained in a surface treatment composition of the present invention. Adhesiveness between a metal sheet and a resin film improves by using a glycidoxy radical containing silane coupling agent. Further, it is estimated that the glycidoxy radical containing silane coupling agent has also the effect of improving a bonding force between an inorganic component and a resin component in a resin film, and the glycidoxy radical containing silane coupling agent shows large effects of improving roll-formability and bare corrosion resistance. Further, by adding a glycidoxy radical containing silane coupling agent, the surface tension of a surface treatment composition lowers, hence wettability with a metal sheet improves, the coating performance of the surface treatment composition improves, and it comes to be possible to form a uniform resin film. Furthermore, when a surface treatment composition is cyclically used by a spray-wringer method (a method of spraying a surface treatment composition on the surface of a metal sheet and thereafter squeezing the surface with wringer rolls), the effect of inhibiting foaming caused by a surfactant in the composition appears. As a glycidoxy radical containing silane coupling agent, Y-glycidoxypropylmethyl diethoxysilane, y-glycidoxypropyl trimethoxysilane (KBM403 made by Shin-Etsu Chemical Co., Ltd.), or Y-glycidoxymethyl dimethoxysilane is named for example. The content of a glycidoxy radical containing silane coupling agent in a surface treatment composition is 5 parts or more by mass, preferably 7 parts or more by mass and 15 parts or less by mass, preferably 13 parts or less by mass per 100 parts by mass in total of an inorganic component and a resin component. If the content of a silane coupling agent is less than 5 parts by mass, the effect of improving adhesiveness between a metal sheet and a resin film is not recognized. Further, it sometimes happens that: a bonding force between an inorganic component and a resin component in a resin film component lowers; the hardness of a film lowers; the denseness of a film deteriorates; and roll-formability, coating adhesiveness, and bare corrosion resistance deteriorate. Even if the content of a glycidoxy radical containing silane coupling agent exceeds 15 parts by mass, the effect of improving adhesiveness between a metal sheet and a resin film and the effect of improving a bonding force between an inorganic component and a resin component in a resin film component are saturated and hence that causes a cost to increase. On the contrary, it sometimes happens that: roll-formability, coating adhesiveness, and bare corrosion resistance deteriorate; and the liquid stability of a surface treatment composition deteriorates and gelation and the settlement of colloidal silica are caused. Further, metavanadate is contained in a surface treatment composition of the present invention. Metavanadate, by being eluted similarly to colloidal silica, exhibits the effects of inhibiting the dissolution and elusion of a metal sheet and improving corrosion resistance. Metavanadate exhibits the effect of improving bare corrosion resistance particularly in the case of a GA sheet. In order to effectively exhibit the effects, metavanadate may be used by 0. 5 to 3 parts by mass per 100 parts by mass in total of an inorganic component and a resin component. If metavanadate is less than 0.5 part by mass, the effect of improving bare corrosion resistance is insufficient. If metavanadate is added in excess of 3 parts by-mass in contrast, bare corrosion resistance tends to deteriorate to some extent. This is presumably because excessive metavanadate inhibits the hydrolytic reaction of a glycidoxy radical containing silane coupling agent and slightly influences a bonding force between an inorganic component and a resin component. Further, coating adhesiveness tends to deteriorate conspicuously and the liquid stability of a surface treatment composition also tends to deteriorate. The content of metavanadate is preferably 0.7 to 1.5 parts by mass. Here, the preferable content of metavanadate is represented in V element equivalent. As metavanadates, sodium metavanadate (NaV03), ammonium metavanadate (NH4V03), and potassium metavanadate (KV03) are named for example. They may be used either individually or in combination of two or more kinds. Such metavanadates are easily available in the market. A surface treatment composition of the present invention may further contain a carbodiimide radical containing compound. A carbodiimide radical reacts with a carboxyl radical in an olefin-acid copolymer and a carboxylic acid polymer, reduces the quantity of the carboxyl radical in a resin film, and can improve alkali resistance. In the present invention, one or more kinds of carbodiimide radical containing compounds can be used. A carbodiimide radical containing compound: can be produced by heating isocyanate such as hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (HXDI), 4,4-diphenylmethane diisocyanate (MDI), or tolylene diisocyanate (TDI) under the existence of a carbodiimidizing catalyst; and can be aqueous (water-soluble, water-emulsifiable, or water-dispersible) by denaturalization. When a surface treatment composition is water-based, an aqueous carbodiimide radical containing compound is preferably used. Further, a compound containing plural carbodiimide radicals in one molecule is preferably used. By containing plural carbodiimide radicals in one molecule, it is possible further to improve bare corrosion resistance and the like by crosslinking reaction with a carboxyl radical in a resin component. As commercially available carbodiimide radical containing compounds, N,N-dicyclohexyl carbodiimide, N,N-diisopropyl carbodiimide, and "CARBODILITE (registered trademark) " series that is polycarbodiimide (a polymer containing plural carbodiimide radicals in a molecule) made by Nisshinbo Chemical Inc. can be named for example. As the grades of "CARBODILITE (registered trademark) ", "SV-02", "V-02", "V-02-L2", and "V-04" of a water-soluble type and "E-01" and "E-02" of an emulsion type are named. The content of a carbodiimide radical containing compound is decided in response to the contents of an olefin-acid copolymer and a carboxylic acid polymer to be crosslinked with. That is, the content of a carbodiimide radical containing compound is preferably 0.1 part or more by mass, yet preferably 0.5 part or more by mass, and still yet preferably 8 parts or more by mass per 100 parts by mass in total of an olefin-acid copolymer and a carboxylic acid polymer. If the content of a carbodiimide radical containing compound is excessive however, the effect of the combination of an olefin-acid copolymer and a carboxylic acid polymer lowers. Further, if an aqueous carbodiimide radical containing compound is used excessively in a water-based surface treatment composition, water resistance and corrosion resistance maybe adversely affected. From such a viewpoint, the content of a carbodiimide radical containing compound is preferably 30 parts or less by mass, yet preferably 2 0 parts or less by mass, and still yet preferably 16 parts or less by mass per 100 parts by mass stated above. A surface treatment composition in the present invention may contain a wax, a crosslinker, a diluent, an anti-skinning agent, a surfactant, an emulsifier, a disperser, a leveling agent, an antifoaming agent, a penetrating agent, a film-forming auxiliary agent, a dye, a pigment, a thickening agent, a lubricant, and others within the range not hindering the effects of the present invention. It is preferable to lower the surface tension of a surface treatment composition used in the present invention by appropriately adjusting the blend ratio of an inorganic component to a resin component (more specifically inorganic component: resin component = 60:40 to 80:20). More specifically, the surface tension is set at 50 dyn/cm or less and preferably 48 dyn/cm or less. By so doing, a surface treatment composition intrudes even into the surface (recesses) of a GA sheet that has a rough surface and is inferior in water wettability and the bare corrosion resistance and the coating adhesiveness of the GA sheet can be improved. A method for measuring the surface tension of a surface treatment composition will be described later. A surface treatment composition used in the present invention has heretofore been explained in detail and a method for producing a surface treatment composition is explained hereunder. A surface treatment composition in the present invention: may be either a solvent-based composition or a water-based composition, both being able to be applied on the surface of a metal sheet; and, from environmental concerns however, is preferably a water-based composition. A surface treatment composition can be prepared by: blending prescribed quantities of an organic solvent (in the case of a solvent-based composition) or water, preferably deionized water (in the case of a water-based composition), colloidal silica, an olefin-acid copolymer, a carboxylic acid polymer, an acrylic modified epoxy resin, a glycidoxy radical containing silane coupling agent, metavanadate, and if necessary a carbodiimide radical containing compound or another component; and stirring them. When a surface treatment composition is prepared, it is preferable to: add a part of a glycidoxy radical containing silane coupling agent and a carbodiimide radical containing compound to an emulsion of an olefin-acid copolymer and a carboxylic acid polymer and thereby prepare the mixture beforehand; and add colloidal silica (preferably added in the increasing order of surface area average particle sizes) , the remaining glycidoxy radical containing silane coupling agent, metavanadate, and an acrylic modified epoxy resin in this order to the mixture. If metavanadate is added before a glycidoxy radical containing silane coupling agent is added, it sometimes happens that the hydrolytic reaction of the silane coupling agent is inhibited and the effect of the silane coupling agent is hindered. Here, it is preferable to add a glycidoxy radical containing silane coupling agent in two additions as stated above. The reason is that: the firstly added silane coupling agent contributes to the fractionization of emulsion particles and the resultant densification of a resin film and the improvement of corrosion resistance; and the secondary added silane coupling agent contributes to the securement of adhesiveness with a metal sheet and the improvement of film properties. Here, the content of the firstly added silane coupling agent is preferably 0 .1 part or more by mass (yet preferably 2 parts or more by mass) and preferably 10 parts or less by mass (yet preferably 7 parts or less by mass) per 100 parts by mass in total of an olefin-acid copolymer and a carboxylic acid polymer. Then the content of the secondary added silane coupling agent is the same as the content stated earlier. Heat may be applied when the aforementioned components are stirred. It is preferable to apply heat particularly when an olefin-acid copolymer is emulsified under the existence of a carboxylic acid polymer. When a water-based surface treatment composition is produced, it is preferable to emulsify an olefin-acid copolymer that is the main component in a resin component. An olefin-acid copolymer can be emulsified by either using an emulsifier or neutralizing a carboxyl radical in the copolymer. By using an emulsifier, it is possible to: reduce the average particle size of aqueous emulsion of an olefin-acid copolymer; and improve film-formability, the denseness of a resin film caused by it, and the like. However, it is preferable to neutralize and thus emulsify a carboxyl radical in an olefin-acid copolymer. The reason is that, by neutralizing and thus emulsifying a carboxyl radical, it is possible to: reduce the quantity of an emulsifier used or avoid using an emulsifier; and reduce or eliminate the adverse influence of an emulsifier on the water resistance and the corrosion resistance of a resin film. When a carboxyl radical in an olefin-acid copolymer is neutralized, it is preferable to use a base by preferably about 0.5 to 0.95 and yet preferably about 0.6 to 0.8 in carboxyl radical equivalent. If the degree of neutralization is too low, emulsifiability does not improve much and, if the degree of neutralization is too high in contrast, it sometimes happens that the viscosity of a composition including an olefin-acid copolymer comes to be excessively high. As a base for neutralization: a strong base comprising a group consisting of hydroxides of alkali metals and alkali earth metals (for example, NaOH, KOH, Ca(OH)2, and others, preferably NaOH); ammonia water; primary amine; secondary amine; or tertiary amine (preferably triethylamine) can be named for example . When a strong base such, as NaOH is used, emulsif iability improves but, if it is excessively used, the corrosion resistance of a resin film may deteriorate undesirably. Meanwhile, amine of a low boiling point (preferably amine having a boiling point of 100°C or lower in atmospheric pressure; for example triethylamine) does not much deteriorate the corrosion resistance of a resin film. The reason is presumably that low melting point amine evaporates when a resin film is formed by heating and drying after a surface treatment composition is applied. Since the effect of amine on improving emulsifiability is small however, it is preferable to neutralize a carboxyl radical by using the strong base and amine in combination. An optimum combination is a combination of NaOH and triethylamine. When a strong base and amine are used in combination, it is preferable to use a strong base of about 0.01 to 0.3 and amine of about 0.4 to 0.8 in the equivalent of a carboxyl radical of an olefin-acid copolymer. When a water-based surface treatment composition is used, a small amount of organic solvent may be blended in order to lower an interface tension and improve wettability to a metal sheet. As anorganic solvent for the purpose, methanol, ethanol, isopropanol, butanol, hexanol, 2-ethylhexanol, ethylene glycol ethyl ether, ethylene glycol butyl ether, diethylene glycol, or propylene glycol can be named for example. The solid content of a surface treatment composition used in the present invention is not particularly limited and may be adjusted in conformity with a method for coating a metal sheet with the surface treatment composition. The solid content of a surface treatment composition: is generally about 5 to 20% by mass; and, when a spray-wringer method (a method of spraying a surface treatment composition on the surface of a metal sheet and thereafter squeezing the surface with wringer rolls) is adopted for coating for example, is preferably about 10 to 18% by mass. In the present invention, a method and a condition for forming a resin film on a metal sheet are not particularly limited and it is possible to produce a resin coated metal sheet by coating one surface or both the surfaces of a metal sheet with a surface treatment compos it ion by a known coating method and applying heating and drying. As a coating method of a surface treatment composition, a bar coater method, a curtain flow coater method, a roll coater method, a spray method, or a spray-wringer method can be named for example. Among those methods, a bar coater method or a spray-wringer method is preferably used from the viewpoint of costs and the like. Further, heating and drying conditions are not particularly limited but a heating and drying temperature of about 50 °C to 120 °C and preferably about 70°Ctol00°C can be exemplified. A too high heating and drying temperature is not desired because the temperature causes a resin film to deteriorate. The coating weight of a resin film in a resin coated metal sheet is preferably 0.2 to 1 g/m2 and yet preferably 0.3 to 0.7 g/m2 in dry mass. If a coating weight is less than 0.2 g/m2, a metal sheet surface is hardly covered and roll-formability, coating adhesiveness, and bare corrosion resistance are hindered largely. If a coating weight exceeds 1 g/m2 in contrast, although corrosion resistance improves, the quantity of a film peeling-off during roll-forming increases, hence the quantity of the film crumbs building up on a drain pad increases, and that causes troubles undesirably. Further, coating adhesiveness is damaged largely. Here, a resin film in the present invention contains an inorganic component abundantly and has a large specific gravity. Consequently, even when the coating weight is identical, a film thickness is successfully reduced in comparison with a conventional resin film containing a rich resin component. This also contributes to the reduction of film crumbs. A metal sheet used in the present invention is not particularly limited and, as a metal sheet, a non-plated cold-rolled steel sheet, a hot dip galvanized steel sheet (GI), an alloyed hot-dip galvanized steel sheet (GA) , an electro-galvanized steel sheet (EG) , analuminum sheet, or a titanium sheet can be named for example. Among those, the present invention is preferably applied to a hot dip galvanized steel sheet (GI) and an alloyed hot-dip galvanized steel sheet (GA) which are not subjected to chromate treatment. [Examples] The present invention is hereunder described in detail on the basis of examples. The present invention is not limited to the following examples however and modifications in the range not deviating from the above- and after-mentioned tenors are all included in the technological scope of the present invention. Firstly, evaluation methods used in test examples are explained hereunder. (Roll-formability) A specimen of 4 0 mm x 300 mm is cut out from a resin coated metal sheet and set vertically on a tensile tester, and a tabular die (material: SKD11) is abutted on the rear surface of the specimen. Successively, a tool (a semicircular columnar die, material: SKD11) having a convex with a tip diameter R of 9.1 mm is abutted on the surface (front face) of the specimen opposite to the surface on which the tabular die abuts and the tool is pulled downward at 3 00 mm/min within the range where the tabular die is abutting on the rear surface of the specimen while a load of 4,900 N (500 kgf) is imposed on the tool in the horizontal direction. Thereafter, the semicircular columnar die is separated from the specimen and returned to the position before the sliding and then the same sliding operation as stated above is repeated nine times (ten times in total). Thereafter, the coating weights of a portion (W1) where the semicircular columnar die is repeatedly slid and a portion (W0) to which the sliding is not applied are analyzed respectively with a fluorescent X-ray analyzer, a film residual ratio is computed from Formula 1 below, and evaluation is made on the basis of the following criterion; Film residual ratio (%) = W1/ W0 x 100 (Formula 1), ©: Film residual ratio 95% or more, o: Film residual ratio 90% or more and less than 95 %, ∆: Film residual ratio 80% or more and less than 90%, and x: Film residual ratio less than 80%. Here, a coating weight is obtained by analyzing a Si element in colloidal silica (Si02) contained in a film and computing the coating weight from the proportion of the Si element contained in the film on the basis of Formula 2 below; Coating weight (g/m2) = Si (mg/m2) x(60/28)x(100/C) /l, 000 (Formula 2), C: Proportion of colloidal silica (Si02) in a film. (Bare corrosion resistance (SST, flat plate) On the basis of JIS Z2371, salt spray test is applied to a resin coated metal sheet and a time spent until a white rust ratio (area where white rust appears/total area of a resin coated metal sheet x 100) reaches 5% is measured. Here, with regard to bare corrosion resistance in building material applications of a GI sheet and a GA sheet, there is no problem in practical use as long as a white rust ratio is within 5% after SST lapsed time of 48 hours, which is comparable to a chromate treatment. Further, for other applications too, there is no problem as long as the time is 96 hours or longer in the case of a GI sheet and 72 hours or longer in the case of a GA sheet. (Bare corrosion resistance in JASO cycle test (flat plate)) JASO cycle test is applied on the basis of JIS H8502. One cycle is as follows in time sequence; salt spraying (temperature 35°C x 2 hours) → drying (temperature 35°C x humidity 30% or less x 4 hours) → wetting (temperature 50°C x humidity 95% or more x 2 hours) (the times include transfer times respectively) . After 20 cycles are repeated, a white rust ratio (area where white rust appears/total area of a resin coated metal sheet x 100) is evaluated on the basis of the following criterion; ©: White rust ratio less than 5%, o: White rust ratio 5% or more and less than 10%, ∆: White rust ratio 10% or more and less than 20%, and x: White rust ratio 20% or more. (Surface tension) In conformity with JIS K2241, an aqueous solution of 23% surface treatment composition is prepared with ion-exchanged water and the surface tension of the aqueous solution is obtained by the Du Nouy method using a metal ring as a probe under a room temperature condition with a surface tension measuring device (made by Shimadzu Corporation). (Coating adhesiveness) Firstlyacalciumplumbateanticorrosivepaint (HELGONCP Light Gray, made by NIPPON PAINT Co., Ltd.) is diluted with a thinner (Paint Thinner A, made by NIPPON PAINT Co., Ltd.), the viscosity is adjusted (20 seconds with a Ford cup #4) , thereafter spray coating is applied to a resin coated metal sheet at a spray pressure of 39 N (4 kgf), the resin coated metal sheet is aged for 12 hours and thereafter dried for 60 minutes at a temperature of 80°C, and thereby a coated sheet having a coating thickness of 35 to 40 μm is produced. Successively, the rear surface and the edges of a coated sheet are sealed, thereafter cross-cutting is applied with a cutter knife, salt spray test (SST) is applied in conformity with JIS Z2371, the maximum bulge width on one side from the cross-cut portion is measured after a lapse of 3 60 hours, and thereby the maximum bulge width is evaluated on the basis of the following criterion; ©: Bulge width less than 1.0 mm, o: Bulge width 1.0 mm or more and less than 1.5 mm, ∆: Bulge width 1.5 mm or more and less than 2.0 mm, and x: Bulge width 2.0 mm or more. The rear surface and the edges of a coated sheet are sealed, thereafter cross-cutting is applied with a cutter knife, the coated sheet is immersed in a sodium chloride aqueous solution (30 g/L) at a solution temperature of 23°C ± 2°C for 96 hours and thereafter rinsed with water, successively the moisture on the surface is wiped off, and immediately thereafter tape peel test is applied to the cross-cut portion. With regard to a coated sheet after subjected to the peel test, the maximum exfoliation width on one side from the cross -cut portion is measured and thereby the maximum exfoliation width is evaluated on the basis of the following criterion; ©: Exfoliation width less than 1.0 mm, o: Exfoliation width 1.0 mm or more and less than 1.5 mm, ∆: Exfoliation width 1.5 mm or more and less than 2.0 mm, and x: Exfoliation width 2.0 mm or more. (Preparation of emulsion of olefin-acid copolymer and carboxylic acid polymer) 200.0 parts by mass of ethylene-acrylic acid copolymer (PRIMACOR (registered trademark) 59901, constituent component derived from acrylic acid: 20%bymass, mass-average molecular weight (Mw) : 20,000, melt index-. 1,300, acid value: 150, made by The Dow Chemical Company) as an olefin-acid copolymer, 8.0 parts by mass of a polymaleic acid aqueous solution ("NONPOL (registered trademark) PMA-50W", Mw: about 1,100 (polystyrene equivalent) , 50% by mass product, made by NOF CORPORATION) as a carboxylic acidpolymer, 35.5 parts by mass of triethylamine (0.63 in the equivalent of a carboxyl radical of an ethylene-acrylic acid copolymer) ,6.9 parts by mass of a 48% NaOH aqueous solution (0.15 in the equivalent of a carboxyl radical of an ethylene-acrylic acid copolymer) ,3.5 parts by mass of tall oil fatty acid (HARTALL FA3 , made by Harima Chemicals , Inc.), and 792.6 parts by mass of ion-exchanged water are: added and sealed in an autoclave having an emulsifier equipped with an agitator, a thermometer, and a temperature controller; stirred at a high speed for 3 hours at 150°C in 5 atmospheres,- and thereafter cooled to 30°C. Successively, 10.4 parts by mass of a glycidoxy radical containing silane coupling agent (TSL8350, γ-glycidoxypropyl trimethoxysilane, made by Momentive Performance Materials Inc. (former company name: GE Toshiba Silicone Inc.)), 31.2 parts by mass of a carbodiimide radical containing compound ("CARBODILITE (registered trademark) SV-02" made by Nisshinbo Chemical Inc., polycarbodiimide, Mw: 2,700, solid content: 40% by mass) , and 72.8 parts by mass of ion-exchanged water are added and stirred for 10 minutes, and thereby an emulsion of an olefin-acid copolymer and a carboxylic acid polymer is prepared (solid content concentration is about 20% by mass, measured in conformity with JIS K6833). (Test Examples 1-1 to 1-10) Colloidal silica (A) (SNOWTEX (registered trademark) XS (solid content concentration 20%) made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 4 to 6 nm (nominal value) and colloidal silica (B) (SNOWTEX (registered trademark) 40 (solid content concentration 40%) made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 10 to 2 0 nm (nominal value) are added sequentially to the above emulsion and mixed well. Thereafter, a glycidoxy radical containing silane coupling agent (KBM403 (solid content concentration 100%) made by Shin-Etsu Chemical Co., Ltd.) and successively sodium metavanadate (sodium metavanadate (solid content concentration about 66%) made by Shinko Chemical Co., Ltd.) as metavanadate are added. Further, acrylic modified epoxy resin (MODEPICS (registered trademark) 302 (solid content concentration 33.5%) made by Arakawa Chemical Industries, Ltd.) is added to the mixture and thereby a surface treatment composition is produced. Here, the mix quantities (or the mix ratios) of components in the production of the surface treatment composition stated above are as follows; mass ratio of colloidal silica (A) to (B) 50:50, mass ratio of an inorganic component to a resin component (the mix quantity of the total solid content and an acrylic modified epoxy resin in an emulsion, the same is applied hereunder) 30:70 to 95:5, mix quantity of acrylic modified epoxy resin 5 parts by mass per 95 parts by mass of the total solid content in an emulsion (5% by mass in a resin component), mix quantity of a glycidoxy radical containing silane coupling agent 10 parts by mass per 100 parts by mass in total of an inorganic component and a resin component, and mix quantity of metavanadate 1 part by mass per 100 parts by mass in total of an inorganic component and a resin component. A resin coated metal sheet having a resin coating weight of 0 .5 g/m2 is produced by: using an alkali-degreased hot dip galvanized steel sheet GI sheet (Zn coating weight 45 g/m2) or an alloyed hot-dip galvanized steel sheet GA sheet (Zn coating weight 45 g/m2) as a metal sheet; coating the surface of the steel sheet with a surface treatment composition by bar coating (bar No. 3 or 4) ; and heating and drying the steel sheet for about 12 seconds at a sheet temperature of 90°C. The evaluation results of the obtained resin coated metal sheets are shown in Table 1. (Test Example 1-11) An inorganic component is prepared by mixing lithium silicate ("Lithium Silicate 45" made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a Si02/Li20 molar ratio of 4 .5 with colloidal silica (SNOWTEX (registered trademark) XS made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 4 to 6 nm (nominal value) so that the mass ratio may be 90:10. The obtained inorganic component is added to the aforementioned emulsion, both are mixed well, thereafter a glycidoxy radical containing silane coupling agent (KBM403, y-glycidoxypropyl trimethoxysilane, made by Shin-Etsu Chemical Co., Ltd.) and successively sodiummetavanadate (sodiummetavanadatemadeby Shinko Chemical Co., Ltd.) are added. An oxazoline radical containing copolymer (EPOCROS (registered trademark) K-2030E, solid content 40% by mass, made by NIPPON SHOKUBAI CO., LTD.) is further added to the mixture and thereby a surface treatment composition is prepared. Here, the mix quantities (or the mix ratios) of components in the production of the surface treatment composition stated above are as follows; mix ratio of an inorganic component to the mixture of the total solid content and an oxazoline radical containing copolymer in an emulsion 70:30, mix quantity of an oxazoline radical containing copolymer 5 parts by mass per 95 parts by mass of the total solid content in an emulsion, mix quantity of a glycidyl radical containing silane coupling agent 15 parts by mass per 100 parts by mass in total of an inorganic component and a mixture of the total solid content and an oxazoline radical containing copolymer in an emulsion, and mix quantity of sodium metavanadate 5 parts by mass per 100 parts by mass in total of an inorganic component and a mixture of the total solid content and an oxazoline radical containing copolymer in an emulsion. A resin coated metal sheet is produced in the same way as Test Example 1-1 except that the surface treatment composition prepared in Test Example 1-11 is used. The evaluation results of the obtained resin coated metal sheet are shown in Table 1. (Test Examples 2-1 to 2-10) Surface treatment compositions are produced in the same way as Test Example 1-3 except that the ratio by mass of colloidal silica (A) to colloidal silica (B) is changed to 100:0 to 0:100. Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 2-1 to 2-10 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 2. (Test Examples 2-11 to 2-12) Surface treatment compositions are produced in the same way as Test Example 2-1 except that, in place of colloidal silica (B) , colloidal silica (SNOWTEX (registered trademark) 50 made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 2 0 to 30 nm (nominal value) or colloidal silica (SNOWTEX (registered trademark) 2 0L made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 40 to 50 nm (nominal value) is used. Resin coated metal sheets are produced in the same way as Test Example 2-1 except that the surface treatment compositions prepared in Test Examples 2-11 to 2-12 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 2. (Test Examples 3-1 to 3-11) Surface treatment compositions are produced in the same way as Test Example 1-3 except that the mix quantity of an acrylic modified epoxy resin is set at 0 to 20 parts by mass (0 to 2 0% by mass in a resin component) per 80 to 100 parts by mass of the total solid content in the aforementioned demulsion. Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 3-1 to 3-11 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 3. (Test Examples 4-1 to 4-9) Preparation of surface treatment composition> Surface treatment compositions are produced in the same way as Test Example 1-3 except that the mix quantity of a glycidoxy radical containing silane coupling agent is set at 0 to 2 0 parts by mass per 100 parts by mass in total of an inorganic component and a resin component. Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 4-1 to 4-9 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 4. (Test Examples 5-1 to 5-10) Surface treatment compositions are produced in the same way as Test Example 1-3 except that the mix quantity of metavanadate is set at 0 to 5 parts by mass per 100 parts by mass in total of an inorganic component and a resin component. Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 5-1 to 5-10 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 5. (Test Examples 6-1 to 6-8) Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the resin coating weight is set at 0.1 to 1. 5 g/m2. The evaluation results of the obtained resin coated metal sheets are shown in Table 6. The present invention makes it possible to provide a resin coated metal sheet satisfying not only corrosion resistance but also roll-formability required of a GI sheet and coating adhesiveness after post-coating required of a GA sheet. What is claimed is: 1. Aresin coatedmetal sheet coated with a resin film comprising a surface treatment composition, wherein the surface treatment composition contains: an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes by 60 to 80 parts by mass; a resin component comprising an olefin- α, β -unsaturated carboxylic acid copolymer, an α , β-unsaturated carboxylic acid polymer, and an acrylic modified epoxy resin by 20 to 40 parts by mass; and further a glycidoxy radical containing silane coupling agent by 5 to 15 parts by mass and metavanadate by 0.5 to 3 parts by mass per 100 parts by mass in total of the inorganic component and resin component. 2. A resin coated metal sheet according to Claim 1, wherein: the inorganic component contains colloidal silica (A) having a surface area average particle size of 4 to 6 nm and colloidal silica (B) having a surface area average particle size of 10 to 20 nm; and the mix ratio of the (A) to the (B) is 70:30 to 40:60 (in mass ratio) . 3. A resin coated metal sheet according to Claim 1 or 2, wherein the resin component contains the acrylic modified epoxy resin by 2 to 15% by mass. 4. A resin coated metal sheet according to Claim 1 or 2, wherein the surface tension of the surface treatment composition is 50 dyn/cm or less. 5 A resin coated metal sheet according to Claim 1 or 2 , wherein the coating weight of the resin film is 0.2 to 1 g/m2 by dry mass. 6 A resin coated metal sheet according to Claim 1 or 2, wherein the metal sheet coated with the resin film is a hot dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet.

Full Text

TITLE OF THE INVENTION

RESIN COATED METAL SHEET

FIELD OF THE INVENTION

The present invention relates to a resin coated metal sheet excellent in roll-formability and coating adhesiveness after post-coating.

BACKGROUND OF THE INVENTION

Hot dip galvanized steel sheets used for building material applications include a hot dip galvanized steel sheet (GI sheet) produced by plating a steel sheet with pure zinc, an alloyed hot-dip galvanized steel sheet (GA sheet) produced by alloying it, and the like. A GI sheet is: formed (roll-formed) from a flat sheet into a formed product having an intended cross-sectional shape by running continuously between plural pairs of rolls aligned in a row (forming speed: approximately 20 to 70 m/min) and passing through forming processes sequentially; and thereafter used nakedly (without the application of post-coating) for a deck, a lightweight steel member, or the like. Meanwhile, a GA sheet is, after the surface is post-coated with a calcium plumbate anticorrosive paint, a lead-free paint, an electrodeposition paint, or the like, used for a door, a shutter, or the like.

Conventionally, chromate treatment has been applied on the surface of a GI sheet, a GA sheet, or the like with an aim to improve corrosion resistance. Under the recent growth of environmental awareness however, a treatment method other than a chromate treatment (non-chromate treatment) has been studied and a resin coated metal sheet produced by forming a chromate-free resin film on a hot dip galvanized steel sheet has heretofore been developed. For example, JP-A No. 61608/2009 discloses a resin coated metal sheet coated with a resin film comprising a surface treatment composition containing: an inorganic component comprising lithium silicate and colloidal silica,- α resin component containing an olefin- α , β -unsaturated carboxylic acid copolymer, an α , β -unsaturated carboxylic acid polymer, and an oxazoline radical containing copolymer; and further a glycidyl radical containing silane coupling agent and metavanadate.

The resin film described in the above literature is preferably used for a GI sheet. The reason is that, although a GI sheet undergoes severe contact pressure during roll-forming, the resin film described in the above literature can be thinned due to its heavy specific gravity (about 2), hence roll-damage on the resin film during roll-forming can be mitigated, and the exfoliation of the resin film from the GI sheet surface caused by sliding from rolls (generation of film crumbs) hardly occurs. Another reason is that, in roll-forming: a coolant is supplied on the surface of a GI sheet in order to secure lubricity and cool down processing heat and used repeatedly; and on the occasion, even if a resin film (film crumbs) peels off from the GI sheet and is mixed into the coolant, the resin film described in the above literature contains an inorganic component abundantly, has a large specific gravity, and thus settles in the coolant, and hence the film crumbs are prevented from floating in the coolant and accompanying the coolant.

As a result, it is possible to avoid the possibilities that, when the coolant is wiped off from the surface of the GI sheet with a drain pad (a drainage process) : the film crumbs build up on the surface of the drain pad; friction occurs between the build-up film crumbs and the surface of a formed product and generates unusual noises; the formed product cannot pass through the drain pad section at a uniform traveling speed; the shape and the size of the product get out of order; and thus the yield deteriorates.

On the other hand, when the aforementioned resin film is applied to a GA sheet, coating adhesiveness and corrosion resistance after post-coating have been insufficient in some cases. The reason of the insufficient coating adhesiveness is presumably that, whereas the surface of a GA sheet is originally unleveled and rough and thus has an excellent coating adhesiveness due to an anchor effect, the resin film causes the unevenness of the GA sheet surface to level or covers only the outermost surface of the GA sheet and thus the anchor effect of the GA sheet is lost. Further, the reason of the insufficient corrosion resistance is presumably that only the outermost surface of the GA sheet is covered with the aforementioned resin film, the film is not formed at the bottom portions of the recesses, the plated zinc is exposed, and thereby under film corrosion appears when a corrosion resistance test is carried out by applying cross-cut on the coated surface after post-coating. Furthermore, additional problems have been: that blisters (swellings of a coated film) are generated around the cross-cut portions in the corrosion resistance test because of vacancies formed at the bottom portions of the recesses; and that lithium silicate having a water absorbing property is used as a resin film component.

SUMMERY OF THE INVENTION

The present invention has been achieved in view of the aforementioned situation and an object of the present invention is to obtain: a chromate-free surface treatment composition which has not only corrosion resistance but also roll-formability required of a GI sheet and coating adhesiveness after post-coating required of a GA sheet; and a resin coated metal sheet coated with a resin film comprising the surface treatment composition.

A resin coated metal sheet according to the present invention acquired by solving the aforementioned problems is a resin coated metal sheet coated with a resin film comprising a surface treatment composition, in which the surface treatment composition contains: an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes by 60 to 80 parts by mass,- α resin component comprising an olefin- α , β -unsaturated carboxylic acid copolymer, an α , β -unsaturated carboxylic acid polymer, and an acrylic modified epoxy resin by 20 to 40 parts by mass; and further a glycidoxy radical containing silane coupling agent by 5 to 15 parts by mass and metavanadate by 0.5 to 3 parts by mass per 100 parts by mass in total of the inorganic component and the resin component.

A preferable embodiment of the present invention is that: the inorganic component contains colloidal silica (A) having a surface area average particle size of 4 to 6 nm and colloidal silica (B) having a surface area average particle size of 10 to 20 nm; and a mix ratio of the (A) to the (B) is 70:30 to 40:60 (in mass ratio).

Here, in the present specification, colloidal silica having a surface area average particle size of 4 to 6 nm means colloidal silica in which colloidal silica having a surface area particle size of 5 nm accounts for 90% or more (preferably 95% or more). Likewise, colloidal silica having a surface area average particle size of 10 to 20 nm means colloidal silica in which colloidal silica having a surface area particle size of 12 nm accounts for 90% or more (preferably 95% or more) . A surface area average particle size can be measured generally by the Sears method or the BET method. An electron microscope that can directly measure a particle size is effectively used in order to measure a surface area average particle size more accurately.

Another preferable embodiment is that the resin component contains the acrylic modified epoxy resin by 2 to 15% by mass.

Further, other preferable embodiments are that: the surface tension of the surface treatment composition is 50 dyn/cm or less; the coating weight of the resin film is 0.2 to 1 g/m2 by dry mass; and the metal sheet coated with the resin film is a hot dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet.

A resin coated metal sheet according to the present invention: is coated with a resin film comprising a prescribed surface treatment composition; and hence can satisfy not only corrosion resistance but also roll-formability required of a GI sheet and coating adhesiveness after post-coating required of a GA sheet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A resin coated metal sheet according to the present invention is a resin coated metal sheet coated with a resin film comprising a surface treatment composition and is characterized in that the surface treatment composition contains: an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes by 60 to 80 parts by mass; a resin component comprising an olefin- α, β -unsaturated carboxylic acid copolymer, an α, β-unsaturated carboxylic acidpolymer, and an acrylic modified epoxy resin by 2 0 to 40 parts by mass ; and further a glycidoxy radical containing silane coupling agent by 5 to 15 parts by mass and metavanadate by 0.5 to 3 parts by mass per 100 parts by mass in total of the inorganic component and the resin component. A resin coated metal sheet according to the present invention is hereinafter explained in detail.

Meanwhile, although a film in the present invention contains an inorganic component far more than a resin component, the term "resin film" is mostly used in this specific field and hence the term "resin film" is used also in the present invention. (Inorganic component)

In the present invention, lithium silicate is not used as an inorganic component. By not using lithium silicate having a water absorbing property, it is possible to inhibit coating adhesiveness from deteriorating even when severe corrosion resistance tests such as a saltwater immersion test and a salt spray test are applied after post-coating and cross-cutting are applied on the surface of a resin coated metal sheet.

One of the characteristics of the present invention is that plural kinds of colloidal silica having different surface area average particle sizes are used as an inorganic component. By so doing, it is possible to enhance affinity (fitting capability) of a binder resin (a resin component) with colloidal silica, improve film-formability of a formed resin film (bonding force between colloidal silica particles), and form a dense film.

More specifically, it is preferable that an inorganic component: contains colloidal silica (A) having a surface area average particle size of 4 to 6 nm and colloidal silica (B) having a surface area average particle size of 10 to 20 nm; and comprises the colloidal silica (A) and the colloidal silica (B).

It is estimated that colloidal silica: is dissolved and eluted at film defective portions in a corrosive environment; inhibits the dissolution and elusion of a metal sheet by the buffering effect and the passivation-film forming effect of pH; and thus improves the corrosion resistance of the metal sheet. In order to exhibit these effects sufficiently, it is effective to use colloidal silica (A). On the other hand, the problem has been that, since colloidal silica (A) has a high surface activity, when only colloidal silica (A) is used, it sometimes happens that the liquid stability of a surface treatment composition deteriorates with the passage of time (viscosity increases after about 48 hours) or a dense film cannot be formed, and it is impossible to increase the content of an inorganic component in a resin film and thereby increase the specific gravity of the resin film. To cope with the problem, the present inventors, as a result of earnest studies, have found that, by using colloidal silica (B) having a low surface activity and a surface area average particle size of 10 to 2 0 nm in combination, the content of an inorganic component can be increased without deteriorating the liquid stability of a surface treatment composition. Here, a surface area average particle size of colloidal silica described in the present specification means: a value measured by the Sears method in the case where a surface area average particle size is about 1 to 10 nm and by the BET method in the case where the size is about 10 to 100 nm; or a nominal value described in a brochure of a maker.

A mix ratio of colloidal silica (A) to colloidal silica (B) is preferably 70:30 to 40:60 by mass and yet preferably 65:35 to 45:55. If a mass ratio of colloidal silica (A) exceeds 70, it sometimes happens that: the affinity with a resin component deteriorates; the liquid stability of a surface treatment composition deteriorates; and a uniform and dense film cannot be formed. As a result, the bare corrosion resistance and the coating adhesiveness after post-coating of a resin coated metal sheet deteriorate. If the mass ratio of colloidal silica (A) is less than 40, the quantity of Si ions dissolved and eluted at film defective portions in a corrosive environment may decrease and bare corrosion ' resistance may deteriorate undesirably.

Colloidal silica is commercially available and, as colloidal silica having a surface area average particle size of 4 to 6 nm, "SNOWTEX (registered trademark) XS" made by NISSAN CHEMICAL INDUSTRIES, LTD. is named for example. Further, as colloidal silica having a surface area average particle size of 10 to 20 nm, "SNOWTEX (registered trademark) 40", "SNOWTEX (registered trademark) N", "SNOWTEX (registered trademark) SS", and "SNOWTEX (registered trademark) O" made likewise by NISSAN CHEMICAL INDUSTRIES, LTD. and "ADELITE (registered trademark) AT-30" and "ADELITE (registered trademark) AT-30A" made by ADEKA CORPORATION are named. In the case where a surface treatment composition used for forming a resin film is water-based, it is preferable to select the type of colloidal silica in conformity with the pH of the surface treatment composition in order to disperse colloidal silica well.

An inorganic component comprising the aforementioned colloidal silica is set at 60 to 80 parts by mass per 100 parts by mass in total with a resin component described below. Since a surface treatment composition containing an inorganic component within the range described above shows a good film-formability in forming a resin film, the film hardly peels off and the roll-formability of a resin coated metal sheet improves. Further, the surface tension of the surface treatment composition lowers (preferably 50 dyn/cm or lower), the surface treatment composition intrudes even into the surface (recesses) of a GA sheet that has a rough surface and is inferior in water wettability, a resin film is formed along the rough surface of the GA sheet, and hence corrosion resistance and coating adhesiveness also improve.

If the content of an inorganic component exceeds 80 parts by mass, a resin component is insufficient, hence the film-formability of a formed film is also insufficient, and a normal film cannot be formed. As a result, barrier effect in a corrosive environment may lower and corrosion resistance may deteriorate in some cases. Further, the film comes to be too hard and brittle, cracks are generated, and film exfoliation tends to happen during roll-forming. Furthermore, since colloidal silica (amorphous silica particles are dispersed in water in a colloidal state) has a high surface tension (about 66 to 73 dyn/cm), if the content of an inorganic component exceeds 80 parts by mass, it sometimes happens that the surface tension of a surface treatment composition increases, wettability with a metal sheet on which a resin film is formed deteriorates, and a uniform thin film is hardly formed. Inparticular, it comes to be difficult to form a uniform ultra-thin film at uneven portions on the surface of a GA sheet and hence coating adhesiveness and bare corrosion resistance deteriorate.

If the content of an inorganic component is less than 60 parts by mass, the corrosion resistance of an obtained resin coated metal sheet may be insufficient in some cases. Further, the hardness of a film is insufficient, the specific gravity of the film does not increase so much as intended, hence a resin film is hardly thinned, and film exfoliation tends to occur during roll-forming. Moreover, because the specific gravity of a resin film does not increase, it sometimes happens that film crumbs cannot settle out in a coolant receiving tank, the effect of inhibiting build-up on a drain pad surface is insufficient, and resultantly operability and the shape of a product deteriorate. Furthermore, when a resin film is formed on a metal sheet (specifically a GAsheet) by using a surface treatment composition containing an inorganic component by less than 60 parts by mass, although the content of a resin component increases and film-formability improves, the quantity of eluted Si ions to inhibit corrosion decreases and hence it sometimes happens that corrosion (underfilm corrosion) proceeds between a resin film and a metal sheet surface (plated layer interface), resultantly coating adhesiveness after post-coating deteriorates, and blisters are generated in the vicinities of cross-cut portions in a corrosion test after post-coating.

In the present invention, the content of an inorganic component is preferably 65 to 75 parts by mass per 100 parts by mass in total of an inorganic component and a resin component. On this occasion, the mix ratio of colloidal silica (A) to (B) is preferably 50:50(in mass ratio) and thereby it is particularly possible to improve the bare corrosion resistance and the coating adhesiveness of a GA sheet to good levels.
(Resin component)

A surface treatment composition used in the present invention contains, in addition to the aforementioned inorganic component, a resin component comprising an olefin- α , β -unsaturated carboxylic acid copolymer (hereunder referred to as "olefin-acid copolymer" occasionally), an α , β-unsaturated carboxylic acid polymer
(hereunder referred to as "carboxylic acid polymer" occasionally), and an acrylic modified epoxy resin.

The corrosion resistance of a resin coated metal sheet produced by forming a resin film with a surface treatment composition containing both the olefin-acid copolymer and the carboxylic acid polymer improves. The accurate mechanism is nonobvious but it is estimated that, by using both the substances, a dense resin film is formed and the permeation of water and oxygen is effectively inhibited.

Here, the "olefin-acid copolymer" in the present invention means a substance that: is a copolymer of olefin and α , β -unsaturated carboxylic acid; and contains a constituent component derived from olefin by 50% by mass or more (namely, a constituent component derived from α, β-unsaturated carboxylic acid is 50% by mass or less) in the copolymer. Meanwhile, the "carboxylic acid polymer" means a substance that: is a polymer (including a copolymer) obtained by using α , β-unsaturated carboxylic acid as a monomer; and contains a constituent component derived from α , β -unsaturated carboxylic acidby 90% bymass or more in the polymer. Then the " α, β-unsaturated carboxylic acid" includes " α, β -unsaturated carboxylic salt" formed by neutralizing a part of a carboxyl radical with a neutralized that will be stated later.

An olefin-acid copolymer used in the present invention can be produced by copolymerizing olefin and α , β -unsaturated carboxylic acid by a known method and is commercially available. One or more kinds of olefin-acid copolymers can be used in the present invention.

Olefin used in the production of an olefin-acid copolymer is not particularly limited but ethylene, propylene, or the like is preferably used and ethylene is yet preferably used. For the olefin-acid copolymer, either a constituent component of olefin that is derived from only one kind of olefin or a constituent component of olefin that is derived from two or more kinds of olefin can be used.

α, β -unsaturated carboxylic acid used in the production of an olefin-acid copolymer is also not particularly limited but, for example, monocarboxylic acid such as acrylic acid, methacrylic acid, crotonic acid, or isocrotonic acid and dicarboxylic acid such as maleic acid, fumaric acid, or itaconic acid are named. Among those, acrylic acid is preferably used. For the olefin-acid copolymer, either a constituent component of α , β -unsaturated carboxylic acid that is derived from only one kind of α , β-unsaturated carboxylic acid or a constituent component of α , β -unsaturated carboxylic acid that is derived from two or more kinds of α , β-unsaturated carboxylic acid can be used.

An olefin-acid copolymer used in the present invention may have a constituent component derived from another monomer within the range where corrosion resistance that is an effect of the present invention and the like are not adversely affected. In an olefin-acid copolymer, the content of a constituent component derived from another monomer is preferably 10% by mass or less, yet preferably 5% by mass or less, and the most desirable olefin-acid copolymer is a copolymer comprising only olefin and α , β –unsaturated carboxylic acid. An ethylene-acrylic acid copolymer is named as
a preferable olefin-acid copolymer.

α , β -unsaturated carboxylic acid in an olefin-acid copolymer is used for improving adhesiveness between a resin film and a metal sheet and the content of the α ,β -unsaturated carboxylic acid is preferably 5% by mass or more and yet preferably 10% by mass or more in the copolymer. If the content of the α , β -unsaturated carboxylic acid is excessive however, corrosion resistance may deteriorate undesirably and hence the content of the α, β -unsaturated carboxylic acid is preferably 30% by mass or less and yet preferably 25% by mass or less in the copolymer.

The mass-average molecular weight (Mw) of an olefin-acid copolymer used in the present invention is preferably 1, 000 to 100, 000, yet preferably 3,000 to 70,000, and still yet preferably 5,000 to 3 0,000 in polystyrene equivalent. The Mw can be measured by GPC in which polystyrene is used as the standard.

As a carboxylic acid polymer used in the present invention, a monopolymer or a copolymer comprising one or more kinds of α , β -unsaturated carboxylic acid, or a copolymer produced by further copolymerizing another monomer is named. Such a carboxylic acid polymer can be produced by a known method and is commercially available. In the present invention, one ormore kinds of carboxylic acidpolymers can be used.

As α , β -unsaturated carboxylic acid used for producing a carboxylic acid polymer, any of the α , β -unsaturated carboxylic acid exemplified as a substance that can be used for synthesizing the aforementioned olefin-acid copolymer can be used. Among those, acrylic acid or maleic acid is preferably used and maleic acid is particularly preferably used.

A carboxylic acid polymer may contain a constituent component derived from a monomer other than α , β -unsaturated carboxylic acid but the content of a constituent component derived from another monomer is limited to 10% by mass or less and preferably 5% by mass or less in the polymer, and a carboxylic acid polymer comprising only α , β -unsaturated carboxylic acid is yet preferably used.

As a preferable carboxylic acid polymer, polyacrylic acid, polymethacrylic acid, acrylic acid-maleic acid copolymer, polymaleic acid, or the like can be named for example. Among those, polymaleic acid is preferably used from the viewpoints of coating adhesiveness, resin film adhesiveness, and corrosion resistance. By using polymaleic acid, the particle size of a generated resin emulsion reduces (20 to 60 ran), thus a formed film comes to be dense, and hence corrosion resistance and the like improve. Further, since the content of a carboxyl radical is large, adhesiveness between a resin film and a metal sheet improves and corrosion resistance further improves accordingly.
Mw of a carboxylic acid polymer used in the present invention is, in polystyrene equivalent, preferably 500 to 3 0,000, yet preferably 800 to 10,000, still yet preferably 900 to 3,000, and most desirably 1,000 to 2,000. The Mw can be measured by GPC in which polystyrene is used as the standard.

The content ratio of an olefin-acid copolymer to a carboxylic acid polymer in a surface treatment composition is 1,000:1 to 10:1, preferably 200:1 to 20:1, and yet preferably 100:1 to 100:3. If the content ratio of a carboxylic acid polymer is too low, the effect in the combination of an olefin-acid copolymer and a carboxylic acid polymer is exhibited insufficiently. If the content ratio of a carboxylic acid polymer is excessive in contrast, an olefin-acid copolymer and a carboxylic acid polymer separate into different phases in a surface treatment composition and a uniform resin film may not be formed undesirably.

An acrylic modified epoxy resin is also contained in the aforementioned resin component. As a method for improving the adhesiveness of post-coating, a technology of containing block isocyanate (a heat sensitive crosslinker) as a resin component in a film, dissociating a blocking agent in the block isocyanate and reproducing an active isocyanate radical by using heat at baking after post-coating (at a baking temperature), and hardening and bridging the film and the coating film has heretofore been known. A calcium plumbate anticorrosive paint used as a paint for post-coating in the building material field is mostly an air-drying type not requiring baking (drying) by heat however and the above technology cannot be used.

The present inventors, as a result of earnestly working on the above problems, have found that the coating adhesiveness of a resin film improves by concurrently using an acrylic modified epoxy resin allowing a film to be formed at a low temperature as a resin component. Precise mechanism of improving coating adhesiveness by concurrently using an acrylic modified epoxy resin is not obvious. It is estimated however that an acrylic modified epoxy resin does not function as a binder of an inorganic component (colloidal silica) but, by forming a film on the outermost surface of a resin film (scattering in the form of stripes), contributes to the improvement of coating adhesiveness after post-coating though it does not contribute to the improvement of bare corrosion resistance. The reason why an acrylic modified epoxy resin forms a film on the outermost surface of a resin film is presumably that, whereas the emulsion particle sizes of an olefin-acid copolymer and a carboxylic acid polymer are in the range of 20 to 60 nm, the emulsion particle size of an acrylic modified epoxy resin is as large as about 100 nm or more.

An acrylic modified epoxy resin used in the present invention can be produced by, for example: copolymerizing a polymerizable unsaturated radical containing epoxy resin obtained by reacting an epoxy resin with unsaturated fatty acid and (meth) acrylic acid; or copolymerizing a polymerizable unsaturated radical containing epoxy resin obtained by reacting an epoxy resin and a glycidyl radical containing vinyl monomer with amines and (meth) acrylic acid.

In particular, a water-based acrylic modified epoxy resin is commercially available and, for example, "MODEPICS (registered trademark) 301", "MODEPICS (registered trademark) 302", "MODEPICS (registered trademark) 303", and "MODEPICS (registered trademark) 304" made by Arakawa Chemical Industries, Ltd. are named. The acrylic modified epoxy resin may be used either individually or by combining two or more kinds.

An acrylic modified epoxy resin may be contained by preferably 2% by mass or more (yet preferably 3% by mass or more) and also by preferably 15% by mass or less (yet preferably 7% by mass or less) in a resin component of 100% by mass. In the range, it is possible to improve coating adhesiveness after post-coating without hindering the roll-formability and the bare corrosion resistance of a resin coated metal sheet.

If the content of an acrylic modified epoxy resin is less than 2% by mass, the effect of improving coating adhesiveness after post-coating is not recognized. In contrast, if the content of an acrylic modified epoxy resin exceeds 15% by mass, corrosion resistance tends to deteriorate. Ina GA sheet inparticular, coating adhesiveness may deteriorate considerably and blisters may be generated in some cases. The precise mechanism of deteriorating bare corrosion resistance and corrosion resistance and coating adhesiveness after post-coating when the content of an acrylic modified epoxy resin exceeds 15% by mass is not obvious, but it is estimated that an excessively contained acrylic modified epoxy resin hinders an emulsion of an olefin-acid copolymer and a carboxylic acid polymer from forming a film.

A glycidoxy radical containing silane coupling agent (more specifically, a silane coupling agent having a glycidoxy radical at a terminal) is contained in a surface treatment composition of the present invention. Adhesiveness between a metal sheet and a resin film improves by using a glycidoxy radical containing silane coupling agent. Further, it is estimated that the glycidoxy radical containing silane coupling agent has also the effect of improving a bonding force between an inorganic component and a resin component in a resin film, and the glycidoxy radical containing silane coupling agent shows large effects of improving roll-formability and bare corrosion resistance. Further, by adding a glycidoxy radical containing silane coupling agent, the surface tension of a surface treatment composition lowers, hence wettability with a metal sheet improves, the coating performance of the surface treatment composition improves, and it comes to be possible to form a uniform resin film. Furthermore, when a surface treatment composition is cyclically used by a spray-wringer method (a method of spraying a surface treatment composition on the surface of a metal sheet and thereafter squeezing the surface with wringer rolls), the effect of inhibiting foaming caused by a surfactant in the composition appears.

As a glycidoxy radical containing silane coupling agent, Y-glycidoxypropylmethyl diethoxysilane, y-glycidoxypropyl trimethoxysilane (KBM403 made by Shin-Etsu Chemical Co., Ltd.), or Y-glycidoxymethyl dimethoxysilane is named for example.

The content of a glycidoxy radical containing silane coupling agent in a surface treatment composition is 5 parts or more by mass, preferably 7 parts or more by mass and 15 parts or less by mass, preferably 13 parts or less by mass per 100 parts by mass in total of an inorganic component and a resin component. If the content of a silane coupling agent is less than 5 parts by mass, the effect of improving adhesiveness between a metal sheet and a resin film is not recognized. Further, it sometimes happens that: a bonding force between an inorganic component and a resin component in a resin film component lowers; the hardness of a film lowers; the denseness of a film deteriorates; and roll-formability, coating adhesiveness, and bare corrosion resistance deteriorate. Even if the content of a glycidoxy radical containing silane coupling agent exceeds 15 parts by mass, the effect of improving adhesiveness between a metal sheet and a resin film and the effect of improving a bonding force between an inorganic component and a resin component in a resin film component are saturated and hence that causes a cost to increase. On the contrary, it sometimes happens that: roll-formability, coating adhesiveness, and bare corrosion resistance deteriorate; and the liquid stability of a surface treatment composition deteriorates and gelation and the settlement of colloidal silica are caused.

Further, metavanadate is contained in a surface treatment composition of the present invention. Metavanadate, by being eluted similarly to colloidal silica, exhibits the effects of inhibiting the dissolution and elusion of a metal sheet and improving corrosion resistance. Metavanadate exhibits the effect of improving bare corrosion resistance particularly in the case of a GA sheet. In order to effectively exhibit the effects, metavanadate may be used by 0. 5 to 3 parts by mass per 100 parts by mass in total of an inorganic component and a resin component. If metavanadate is less than 0.5 part by mass, the effect of improving bare corrosion resistance is insufficient. If metavanadate is added in excess of 3 parts by-mass in contrast, bare corrosion resistance tends to deteriorate to some extent. This is presumably because excessive metavanadate inhibits the hydrolytic reaction of a glycidoxy radical containing silane coupling agent and slightly influences a bonding force between an inorganic component and a resin component. Further, coating adhesiveness tends to deteriorate conspicuously and the liquid stability of a surface treatment composition also tends to deteriorate. The content of metavanadate is preferably 0.7 to 1.5 parts by mass. Here, the preferable content of metavanadate is represented in V element equivalent.

As metavanadates, sodium metavanadate (NaV03), ammonium metavanadate (NH4V03), and potassium metavanadate (KV03) are named for example. They may be used either individually or in combination of two or more kinds. Such metavanadates are easily available in the market.

A surface treatment composition of the present invention may further contain a carbodiimide radical containing compound. A carbodiimide radical reacts with a carboxyl radical in an olefin-acid copolymer and a carboxylic acid polymer, reduces the quantity of the carboxyl radical in a resin film, and can improve alkali resistance. In the present invention, one or more kinds of carbodiimide radical containing compounds can be used.

A carbodiimide radical containing compound: can be produced by heating isocyanate such as hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (HXDI), 4,4-diphenylmethane diisocyanate (MDI), or tolylene diisocyanate (TDI) under the existence of a carbodiimidizing catalyst; and can be aqueous (water-soluble, water-emulsifiable, or water-dispersible) by denaturalization. When a surface treatment composition is water-based, an aqueous carbodiimide radical containing compound is preferably used. Further, a compound containing plural carbodiimide radicals in one molecule is preferably used. By containing plural carbodiimide radicals in one molecule, it is possible further to improve bare corrosion resistance and the like by crosslinking reaction with a carboxyl radical in a resin component.

As commercially available carbodiimide radical containing compounds, N,N-dicyclohexyl carbodiimide, N,N-diisopropyl carbodiimide, and "CARBODILITE (registered trademark) " series that is polycarbodiimide (a polymer containing plural carbodiimide radicals in a molecule) made by Nisshinbo Chemical Inc. can be named for example. As the grades of "CARBODILITE (registered trademark) ", "SV-02", "V-02", "V-02-L2", and "V-04" of a water-soluble type and "E-01" and "E-02" of an emulsion type are named.

The content of a carbodiimide radical containing compound is decided in response to the contents of an olefin-acid copolymer and a carboxylic acid polymer to be crosslinked with. That is, the content of a carbodiimide radical containing compound is preferably 0.1 part or more by mass, yet preferably 0.5 part or more by mass, and still yet preferably 8 parts or more by mass per 100 parts by mass in total of an olefin-acid copolymer and a carboxylic acid polymer. If the content of a carbodiimide radical containing compound is excessive however, the effect of the combination of an olefin-acid copolymer and a carboxylic acid polymer lowers. Further, if an aqueous carbodiimide radical containing compound is used excessively in a water-based surface treatment composition, water resistance and corrosion resistance maybe adversely affected. From such a viewpoint, the content of a carbodiimide radical containing compound is preferably 30 parts or less by mass, yet preferably 2 0 parts or less by mass, and still yet preferably 16 parts or less by mass per 100 parts by mass stated above.

A surface treatment composition in the present invention may contain a wax, a crosslinker, a diluent, an anti-skinning agent, a surfactant, an emulsifier, a disperser, a leveling agent, an antifoaming agent, a penetrating agent, a film-forming auxiliary agent, a dye, a pigment, a thickening agent, a lubricant, and others within the range not hindering the effects of the present invention.

It is preferable to lower the surface tension of a surface treatment composition used in the present invention by appropriately adjusting the blend ratio of an inorganic component to a resin component (more specifically inorganic component: resin component = 60:40 to 80:20). More specifically, the surface tension is set at 50 dyn/cm or less and preferably 48 dyn/cm or less. By so doing, a surface treatment composition intrudes even into the surface (recesses) of a GA sheet that has a rough surface and is inferior in water wettability and the bare corrosion resistance and the coating adhesiveness of the GA sheet can be improved. A method for measuring the surface tension of a surface treatment composition will be described later.

A surface treatment composition used in the present invention has heretofore been explained in detail and a method for producing a surface treatment composition is explained hereunder.

A surface treatment composition in the present invention: may be either a solvent-based composition or a water-based composition, both being able to be applied on the surface of a metal sheet; and, from environmental concerns however, is preferably a water-based composition. A surface treatment composition can be prepared by: blending prescribed quantities of an organic solvent (in the case of a solvent-based composition) or water, preferably deionized water (in the case of a water-based composition), colloidal silica, an olefin-acid copolymer, a carboxylic acid polymer, an acrylic modified epoxy resin, a glycidoxy radical containing silane coupling agent, metavanadate, and if necessary a carbodiimide radical containing compound or another component; and stirring them.

When a surface treatment composition is prepared, it is preferable to: add a part of a glycidoxy radical containing silane coupling agent and a carbodiimide radical containing compound to an emulsion of an olefin-acid copolymer and a carboxylic acid polymer and thereby prepare the mixture beforehand; and add colloidal silica (preferably added in the increasing order of surface area average particle sizes) , the remaining glycidoxy radical containing silane coupling agent, metavanadate, and an acrylic modified epoxy resin in this order to the mixture. If metavanadate is added before a glycidoxy radical containing silane coupling agent is added, it sometimes happens that the hydrolytic reaction of the silane coupling agent is inhibited and the effect of the silane coupling agent is hindered. Here, it is preferable to add a glycidoxy radical containing silane coupling agent in two additions as stated above. The reason is that: the firstly added silane coupling agent contributes to the fractionization of emulsion particles and the resultant densification of a resin film and the improvement of corrosion resistance; and the secondary added silane coupling agent contributes to the securement of adhesiveness with a metal sheet and the improvement of film properties. Here, the content of the firstly added silane coupling agent is preferably 0 .1 part or more by mass (yet preferably 2 parts or more by mass) and preferably 10 parts or less by mass (yet preferably 7 parts or less by mass) per 100 parts by mass in total of an olefin-acid copolymer and a carboxylic acid polymer. Then the content of the secondary added silane coupling agent is the same as the content stated earlier.

Heat may be applied when the aforementioned components are stirred. It is preferable to apply heat particularly when an olefin-acid copolymer is emulsified under the existence of a carboxylic acid polymer.

When a water-based surface treatment composition is produced, it is preferable to emulsify an olefin-acid copolymer that is the main component in a resin component. An olefin-acid copolymer can be emulsified by either using an emulsifier or neutralizing a carboxyl radical in the copolymer. By using an emulsifier, it is possible to: reduce the average particle size of aqueous emulsion of an olefin-acid copolymer; and improve film-formability, the denseness of a resin film caused by it, and the like.

However, it is preferable to neutralize and thus emulsify a carboxyl radical in an olefin-acid copolymer. The reason is that, by neutralizing and thus emulsifying a carboxyl radical, it is possible to: reduce the quantity of an emulsifier used or avoid using an emulsifier; and reduce or eliminate the adverse influence of an emulsifier on the water resistance and the corrosion resistance of a resin film. When a carboxyl radical in an olefin-acid copolymer is neutralized, it is preferable to use a base by preferably about
0.5 to 0.95 and yet preferably about 0.6 to 0.8 in carboxyl radical equivalent. If the degree of neutralization is too low, emulsifiability does not improve much and, if the degree of neutralization is too high in contrast, it sometimes happens that the viscosity of a composition including an olefin-acid copolymer comes to be excessively high.

As a base for neutralization: a strong base comprising a group consisting of hydroxides of alkali metals and alkali earth metals (for example, NaOH, KOH, Ca(OH)2, and others, preferably NaOH); ammonia water; primary amine; secondary amine; or tertiary amine
(preferably triethylamine) can be named for example . When a strong base such, as NaOH is used, emulsif iability improves but, if it is excessively used, the corrosion resistance of a resin film may deteriorate undesirably. Meanwhile, amine of a low boiling point (preferably amine having a boiling point of 100°C or lower in atmospheric pressure; for example triethylamine) does not much deteriorate the corrosion resistance of a resin film. The reason is presumably that low melting point amine evaporates when a resin film is formed by heating and drying after a surface treatment composition is applied. Since the effect of amine on improving emulsifiability is small however, it is preferable to neutralize a carboxyl radical by using the strong base and amine in combination. An optimum combination is a combination of NaOH and triethylamine. When a strong base and amine are used in combination, it is preferable to use a strong base of about 0.01 to 0.3 and amine of about 0.4 to 0.8 in the equivalent of a carboxyl radical of an olefin-acid copolymer.

When a water-based surface treatment composition is used, a small amount of organic solvent may be blended in order to lower an interface tension and improve wettability to a metal sheet. As anorganic solvent for the purpose, methanol, ethanol, isopropanol, butanol, hexanol, 2-ethylhexanol, ethylene glycol ethyl ether, ethylene glycol butyl ether, diethylene glycol, or propylene glycol can be named for example.

The solid content of a surface treatment composition used in the present invention is not particularly limited and may be adjusted in conformity with a method for coating a metal sheet with the surface treatment composition. The solid content of a surface treatment composition: is generally about 5 to 20% by mass; and, when a spray-wringer method (a method of spraying a surface treatment composition on the surface of a metal sheet and thereafter squeezing the surface with wringer rolls) is adopted for coating for example, is preferably about 10 to 18% by mass.

In the present invention, a method and a condition for forming a resin film on a metal sheet are not particularly limited and it is possible to produce a resin coated metal sheet by coating one surface or both the surfaces of a metal sheet with a surface treatment compos it ion by a known coating method and applying heating and drying. As a coating method of a surface treatment composition, a bar coater method, a curtain flow coater method, a roll coater method, a spray method, or a spray-wringer method can be named for example. Among those methods, a bar coater method or a spray-wringer method is preferably used from the viewpoint of costs and the like. Further, heating and drying conditions are not particularly limited but a heating and drying temperature of about 50 °C to 120 °C and preferably about 70°Ctol00°C can be exemplified. A too high heating and drying temperature is not desired because the temperature causes a resin film to deteriorate.

The coating weight of a resin film in a resin coated metal sheet is preferably 0.2 to 1 g/m2 and yet preferably 0.3 to 0.7 g/m2 in dry mass. If a coating weight is less than 0.2 g/m2, a metal sheet surface is hardly covered and roll-formability, coating adhesiveness, and bare corrosion resistance are hindered largely. If a coating weight exceeds 1 g/m2 in contrast, although corrosion resistance improves, the quantity of a film peeling-off during roll-forming increases, hence the quantity of the film crumbs building up on a drain pad increases, and that causes troubles undesirably. Further, coating adhesiveness is damaged largely. Here, a resin film in the present invention contains an inorganic component abundantly and has a large specific gravity. Consequently, even when the coating weight is identical, a film thickness is successfully reduced in comparison with a conventional resin film containing a rich resin component. This also contributes to the reduction of film crumbs.

A metal sheet used in the present invention is not particularly limited and, as a metal sheet, a non-plated cold-rolled steel sheet, a hot dip galvanized steel sheet (GI), an alloyed hot-dip galvanized steel sheet (GA) , an electro-galvanized steel sheet (EG) , analuminum sheet, or a titanium sheet can be named for example. Among those, the present invention is preferably applied to a hot dip galvanized steel sheet (GI) and an alloyed hot-dip galvanized steel sheet (GA) which are not subjected to chromate treatment.

[Examples]
The present invention is hereunder described in detail on the basis of examples. The present invention is not limited to the following examples however and modifications in the range not deviating from the above- and after-mentioned tenors are all included in the technological scope of the present invention.

Firstly, evaluation methods used in test examples are explained hereunder.

(Roll-formability)
A specimen of 4 0 mm x 300 mm is cut out from a resin coated metal sheet and set vertically on a tensile tester, and a tabular die (material: SKD11) is abutted on the rear surface of the specimen. Successively, a tool (a semicircular columnar die, material: SKD11) having a convex with a tip diameter R of 9.1 mm is abutted on the surface (front face) of the specimen opposite to the surface on which the tabular die abuts and the tool is pulled downward at 3 00 mm/min within the range where the tabular die is abutting on the rear surface of the specimen while a load of 4,900 N (500 kgf) is imposed on the tool in the horizontal direction. Thereafter, the semicircular columnar die is separated from the specimen and returned to the position before the sliding and then the same sliding operation as stated above is repeated nine times (ten times in total). Thereafter, the coating weights of a portion (W1) where the semicircular columnar die is repeatedly slid and a portion (W0) to which the sliding is not applied are analyzed respectively with a fluorescent X-ray analyzer, a film residual ratio is computed from Formula 1 below, and evaluation is made on the basis of the following criterion;

Film residual ratio (%) = W1/ W0 x 100 (Formula 1),
©: Film residual ratio 95% or more,
o: Film residual ratio 90% or more and less than 95 %,
∆: Film residual ratio 80% or more and less than 90%, and
x: Film residual ratio less than 80%.

Here, a coating weight is obtained by analyzing a Si element in colloidal silica (Si02) contained in a film and computing the coating weight from the proportion of the Si element contained in the film on the basis of Formula 2 below;

Coating weight (g/m2) = Si (mg/m2) x(60/28)x(100/C) /l, 000
(Formula 2),

C: Proportion of colloidal silica (Si02) in a film. (Bare corrosion resistance (SST, flat plate)
On the basis of JIS Z2371, salt spray test is applied to a resin coated metal sheet and a time spent until a white rust ratio (area where white rust appears/total area of a resin coated metal sheet x 100) reaches 5% is measured. Here, with regard to bare corrosion resistance in building material applications of a GI sheet and a GA sheet, there is no problem in practical use as long as a white rust ratio is within 5% after SST lapsed time of 48 hours, which is comparable to a chromate treatment. Further, for other applications too, there is no problem as long as the time is 96 hours or longer in the case of a GI sheet and 72 hours or longer in the case of a GA sheet. (Bare corrosion resistance in JASO cycle test (flat plate))

JASO cycle test is applied on the basis of JIS H8502. One cycle is as follows in time sequence; salt spraying (temperature 35°C x 2 hours) → drying (temperature 35°C x humidity 30% or less x 4 hours) → wetting (temperature 50°C x humidity 95% or more x 2 hours) (the times include transfer times respectively) . After 20 cycles are repeated, a white rust ratio (area where white rust appears/total area of a resin coated metal sheet x 100) is evaluated on the basis of the following criterion;

©: White rust ratio less than 5%,
o: White rust ratio 5% or more and less than 10%,
∆: White rust ratio 10% or more and less than 20%, and
x: White rust ratio 20% or more.

(Surface tension)
In conformity with JIS K2241, an aqueous solution of 23% surface treatment composition is prepared with ion-exchanged water and the surface tension of the aqueous solution is obtained by the Du Nouy method using a metal ring as a probe under a room temperature condition with a surface tension measuring device (made by Shimadzu Corporation).

(Coating adhesiveness)
Firstlyacalciumplumbateanticorrosivepaint (HELGONCP Light Gray, made by NIPPON PAINT Co., Ltd.) is diluted with a thinner (Paint Thinner A, made by NIPPON PAINT Co., Ltd.), the viscosity is adjusted (20 seconds with a Ford cup #4) , thereafter spray coating is applied to a resin coated metal sheet at a spray pressure of 39 N (4 kgf), the resin coated metal sheet is aged for 12 hours and thereafter dried for 60 minutes at a temperature of 80°C, and thereby a coated sheet having a coating thickness of 35 to 40 μm is produced.

Successively, the rear surface and the edges of a coated sheet are sealed, thereafter cross-cutting is applied with a cutter knife, salt spray test (SST) is applied in conformity with JIS Z2371, the maximum bulge width on one side from the cross-cut portion is measured after a lapse of 3 60 hours, and thereby the maximum bulge width is evaluated on the basis of the following criterion;
©: Bulge width less than 1.0 mm,
o: Bulge width 1.0 mm or more and less than 1.5 mm,
∆: Bulge width 1.5 mm or more and less than 2.0 mm, and
x: Bulge width 2.0 mm or more.

The rear surface and the edges of a coated sheet are sealed, thereafter cross-cutting is applied with a cutter knife, the coated sheet is immersed in a sodium chloride aqueous solution (30 g/L) at a solution temperature of 23°C ± 2°C for 96 hours and thereafter rinsed with water, successively the moisture on the surface is wiped off, and immediately thereafter tape peel test is applied to the cross-cut portion. With regard to a coated sheet after subjected to the peel test, the maximum exfoliation width on one side from the cross -cut portion is measured and thereby the maximum exfoliation width is evaluated on the basis of the following criterion;
©: Exfoliation width less than 1.0 mm,
o: Exfoliation width 1.0 mm or more and less than 1.5 mm,
∆: Exfoliation width 1.5 mm or more and less than 2.0 mm, and
x: Exfoliation width 2.0 mm or more.

(Preparation of emulsion of olefin-acid copolymer and carboxylic acid polymer)
200.0 parts by mass of ethylene-acrylic acid copolymer (PRIMACOR (registered trademark) 59901, constituent component derived from acrylic acid: 20%bymass, mass-average molecular weight (Mw) : 20,000, melt index-. 1,300, acid value: 150, made by The Dow Chemical Company) as an olefin-acid copolymer, 8.0 parts by mass of a polymaleic acid aqueous solution ("NONPOL (registered trademark) PMA-50W", Mw: about 1,100 (polystyrene equivalent) , 50% by mass product, made by NOF CORPORATION) as a carboxylic acidpolymer, 35.5 parts by mass of triethylamine (0.63 in the equivalent of a carboxyl radical of an ethylene-acrylic acid copolymer) ,6.9 parts by mass of a 48% NaOH aqueous solution (0.15 in the equivalent of a carboxyl radical of an ethylene-acrylic acid copolymer) ,3.5 parts by mass of tall oil fatty acid (HARTALL FA3 , made by Harima Chemicals , Inc.), and 792.6 parts by mass of ion-exchanged water are: added and sealed in an autoclave having an emulsifier equipped with an agitator, a thermometer, and a temperature controller; stirred at a high speed for 3 hours at 150°C in 5 atmospheres,- and thereafter cooled to 30°C. Successively, 10.4 parts by mass of a glycidoxy radical containing silane coupling agent (TSL8350, γ-glycidoxypropyl trimethoxysilane, made by Momentive Performance

Materials Inc. (former company name: GE Toshiba Silicone Inc.)), 31.2 parts by mass of a carbodiimide radical containing compound ("CARBODILITE (registered trademark) SV-02" made by Nisshinbo Chemical Inc., polycarbodiimide, Mw: 2,700, solid content: 40% by mass) , and 72.8 parts by mass of ion-exchanged water are added and stirred for 10 minutes, and thereby an emulsion of an olefin-acid copolymer and a carboxylic acid polymer is prepared (solid content concentration is about 20% by mass, measured in conformity with JIS K6833).

(Test Examples 1-1 to 1-10)

Colloidal silica (A) (SNOWTEX (registered trademark) XS (solid content concentration 20%) made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 4 to 6 nm (nominal value) and colloidal silica (B) (SNOWTEX (registered trademark) 40 (solid content concentration 40%) made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 10 to 2 0 nm (nominal value) are added sequentially to the above emulsion and mixed well. Thereafter, a glycidoxy radical containing silane coupling agent (KBM403 (solid content concentration 100%) made by Shin-Etsu Chemical Co., Ltd.) and successively sodium metavanadate (sodium metavanadate (solid content concentration about 66%) made by Shinko Chemical Co., Ltd.) as metavanadate are added. Further, acrylic modified epoxy resin (MODEPICS (registered trademark) 302 (solid content concentration 33.5%) made by Arakawa Chemical Industries, Ltd.) is added to the mixture and thereby a surface treatment composition is produced.

Here, the mix quantities (or the mix ratios) of components in the production of the surface treatment composition stated above are as follows;
mass ratio of colloidal silica (A) to (B) 50:50,
mass ratio of an inorganic component to a resin component (the mix quantity of the total solid content and an acrylic modified epoxy resin in an emulsion, the same is applied hereunder)
30:70 to 95:5,
mix quantity of acrylic modified epoxy resin 5 parts by mass per 95 parts by mass of the total solid content in an emulsion (5% by mass in a resin component),
mix quantity of a glycidoxy radical containing silane coupling agent
10 parts by mass per 100 parts by mass in total of an inorganic component and a resin component, and
mix quantity of metavanadate 1 part by mass per 100 parts by mass in total of an inorganic component and a resin component.

A resin coated metal sheet having a resin coating weight of 0 .5 g/m2 is produced by: using an alkali-degreased hot dip galvanized steel sheet GI sheet (Zn coating weight 45 g/m2) or an alloyed hot-dip galvanized steel sheet GA sheet (Zn coating weight 45 g/m2) as a metal sheet; coating the surface of the steel sheet with a surface treatment composition by bar coating (bar No. 3 or 4) ; and heating and drying the steel sheet for about 12 seconds at a sheet temperature of 90°C. The evaluation results of the obtained resin coated metal sheets are shown in Table 1.

(Test Example 1-11)
An inorganic component is prepared by mixing lithium silicate
("Lithium Silicate 45" made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a Si02/Li20 molar ratio of 4 .5 with colloidal silica (SNOWTEX
(registered trademark) XS made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 4 to 6 nm (nominal value) so that the mass ratio may be 90:10.

The obtained inorganic component is added to the aforementioned emulsion, both are mixed well, thereafter a glycidoxy radical containing silane coupling agent (KBM403, y-glycidoxypropyl trimethoxysilane, made by Shin-Etsu Chemical Co., Ltd.) and successively sodiummetavanadate (sodiummetavanadatemadeby Shinko Chemical Co., Ltd.) are added. An oxazoline radical containing copolymer (EPOCROS (registered trademark) K-2030E, solid content 40% by mass, made by NIPPON SHOKUBAI CO., LTD.) is further added to the mixture and thereby a surface treatment composition is prepared.

Here, the mix quantities (or the mix ratios) of components in the production of the surface treatment composition stated above are as follows;
mix ratio of an inorganic component to the mixture of the total solid content and an oxazoline radical containing copolymer in an
emulsion 70:30,
mix quantity of an oxazoline radical containing copolymer 5 parts by mass per 95 parts by mass of the total solid content in an emulsion,
mix quantity of a glycidyl radical containing silane coupling agent 15 parts by mass per 100 parts by mass in total of an inorganic component and a mixture of the total solid content and an oxazoline radical containing copolymer in an emulsion, and mix quantity of sodium metavanadate 5 parts by mass per 100 parts by mass in total of an inorganic component and a mixture of the total solid content and an oxazoline radical containing copolymer in an emulsion.

A resin coated metal sheet is produced in the same way as Test Example 1-1 except that the surface treatment composition prepared in Test Example 1-11 is used. The evaluation results of the obtained resin coated metal sheet are shown in Table 1.

(Test Examples 2-1 to 2-10)
Surface treatment compositions are produced in the same way as Test Example 1-3 except that the ratio by mass of colloidal silica (A) to colloidal silica (B) is changed to 100:0 to 0:100.

Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 2-1 to 2-10 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 2. (Test Examples 2-11 to 2-12)

Surface treatment compositions are produced in the same way as Test Example 2-1 except that, in place of colloidal silica (B) , colloidal silica (SNOWTEX (registered trademark) 50 made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 2 0 to 30 nm (nominal value) or colloidal silica (SNOWTEX (registered trademark) 2 0L made by NISSAN CHEMICAL INDUSTRIES, LTD.) having a surface area average particle size of 40 to 50 nm (nominal value) is used.

Resin coated metal sheets are produced in the same way as Test Example 2-1 except that the surface treatment compositions prepared in Test Examples 2-11 to 2-12 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 2.

(Test Examples 3-1 to 3-11)

Surface treatment compositions are produced in the same way as Test Example 1-3 except that the mix quantity of an acrylic modified epoxy resin is set at 0 to 20 parts by mass (0 to 2 0% by mass in a resin component) per 80 to 100 parts by mass of the total solid content in the aforementioned demulsion.
Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 3-1 to 3-11 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 3.

(Test Examples 4-1 to 4-9)
Preparation of surface treatment composition>
Surface treatment compositions are produced in the same way as Test Example 1-3 except that the mix quantity of a glycidoxy radical containing silane coupling agent is set at 0 to 2 0 parts by mass per 100 parts by mass in total of an inorganic component and a resin component.

Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 4-1 to 4-9 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 4.

(Test Examples 5-1 to 5-10)

Surface treatment compositions are produced in the same way as Test Example 1-3 except that the mix quantity of metavanadate is set at 0 to 5 parts by mass per 100 parts by mass in total of an inorganic component and a resin component.

Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the surface treatment compositions prepared in Test Examples 5-1 to 5-10 are used. The evaluation results of the obtained resin coated metal sheets are shown in Table 5.

(Test Examples 6-1 to 6-8)

Resin coated metal sheets are produced in the same way as Test Example 1-3 except that the resin coating weight is set at 0.1 to 1. 5 g/m2. The evaluation results of the obtained resin coated metal sheets are shown in Table 6.

The present invention makes it possible to provide a resin coated metal sheet satisfying not only corrosion resistance but also roll-formability required of a GI sheet and coating adhesiveness after post-coating required of a GA sheet.

What is claimed is:

1. Aresin coatedmetal sheet coated with a resin film comprising
a surface treatment composition, wherein the surface treatment
composition contains:
an inorganic component comprising plural kinds of colloidal silica having different surface area average particle sizes by 60 to 80 parts by mass;
a resin component comprising an olefin- α, β -unsaturated carboxylic acid copolymer, an α , β-unsaturated carboxylic acid polymer, and an acrylic modified epoxy resin by 20 to 40 parts by mass; and further
a glycidoxy radical containing silane coupling agent by 5 to 15 parts by mass and metavanadate by 0.5 to 3 parts by mass per 100 parts by mass in total of the inorganic component and resin component.

2. A resin coated metal sheet according to Claim 1, wherein: the inorganic component contains colloidal silica (A) having a surface area average particle size of 4 to 6 nm and colloidal silica
(B) having a surface area average particle size of 10 to 20 nm; and the mix ratio of the (A) to the (B) is 70:30 to 40:60 (in mass ratio) .

3. A resin coated metal sheet according to Claim 1 or 2, wherein the resin component contains the acrylic modified epoxy resin by 2 to 15% by mass.

4. A resin coated metal sheet according to Claim 1 or 2, wherein the surface tension of the surface treatment composition is 50 dyn/cm or less.

5 A resin coated metal sheet according to Claim 1 or 2 , wherein the coating weight of the resin film is 0.2 to 1 g/m2 by dry mass.

6 A resin coated metal sheet according to Claim 1 or 2, wherein the metal sheet coated with the resin film is a hot dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=Hb5iRZPBsT0AI04acekV2g==&loc=egcICQiyoj82NGgGrC5ChA==

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Patent Number

279447

Indian Patent Application Number

3143/CHE/2010

PG Journal Number

04/2017

Publication Date

27-Jan-2017

Grant Date

23-Jan-2017

Date of Filing

22-Oct-2010

Name of Patentee

KABUSHIKI KAISHA KOBE SEIKO SHO(KOBE STEEL, LTD.)

Applicant Address

10-26, WAKINOHAMA-CHO 2-CHOME, CHUO-KU, KOBE-SHI, HYOGO 651-8585.

Inventors:

#	Inventor's Name	Inventor's Address
1	NAKAMOTO, TADASHIGE	C/O KAKOGAWA WORKS IN KOBE STEEL, LTD., KANAZAWA-CHO 1, KAKOGAWA-SHI, HYOGO 675-0137.
2	SHINOHARA, YOSHIAKI	C/O KAKOGAWA WORKS IN KOBE STEEL, LTD., KANAZAWA-CHO 1, KAKOGAWA-SHI, HYOGO 675-0137.

PCT International Classification Number

B32B15/00, C23C26/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2009-248033	2009-10-28	Japan