Title of Invention	CHROME-FREE RESIN COMPOSITION HAVING GOOD ALKALINE RESISTANCE AND PROCESSIBILITY, METHOD FOR SURFACE-TREATED STEEL SHEET USING THE SAME AND SURFACE-TREATED STEEL SHEET
Abstract	There is provided a chrome-free resin composition for surface-treating a steel sheet having excellent corrosion resistance, alkaline resistance, processibilities and conductivity, chemical resistance, a method for manufacturing a steel sheet using the same, and a surface-treated steel sheet manufactured according to the method. The surface-treated steel sheet is prepared by coating a steel sheet with a resin composition including a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet,  an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition, and the soft urethane resin is present in a content of 5 to 95 % by weight, and the hard urethane resin is present in a content of 5 to 95 % by weight , based on the total amount of the urethane resin mixture.

Title of Invention

CHROME-FREE RESIN COMPOSITION HAVING GOOD ALKALINE RESISTANCE AND PROCESSIBILITY, METHOD FOR SURFACE-TREATED STEEL SHEET USING THE SAME AND SURFACE-TREATED STEEL SHEET

Abstract

There is provided a chrome-free resin composition for surface-treating a steel sheet having excellent corrosion resistance, alkaline resistance, processibilities and conductivity, chemical resistance, a method for manufacturing a steel sheet using the same, and a surface-treated steel sheet manufactured according to the method. The surface-treated steel sheet is prepared by coating a steel sheet with a resin composition including a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet,  an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition, and the soft urethane resin is present in a content of 5 to 95 % by weight, and the hard urethane resin is present in a content of 5 to 95 % by weight , based on the total amount of the urethane resin mixture.

Full Text	[DESCRIPTION] [invention Title] CHROME-FREE RESIN COMPOSITION HAVING GOOD ALKALINE RESISTANCE AND PROCESSIBILITY, METHOD FOR SURFACE-TREATED STEEL SHEET USING THE SAME AND SURFACE-TREATED STEEL SHEET [Technical Field] The present invention relates to a chrome-free resin composition for surface-treating a steel sheet having excellent alkaline resistance and processibilities, as well as excellent corrosion resistance, conductivity and chemical resistance, a method for manufacturing a steel sheet using the same, and a surface-treated steel sheet manufactured according to the method. [Background Art] Recently, the controls over the use of environmental pollutants, for example Cr, Pb, Cd, Hg, PBB, PBDE, etc. have been strengthened all over the world with an increasing concern in environmental issues. As representative examples of the controls, there are, in particular, Restriction of Hazardous Substances (RoHS, enforced on July 01, 2006), Waste from Electrical and Electronic Equipment (WEEE, enforced on July 01, 2006), Registration, Evaluation and Authorization of Chemicals (REACH), End-of-Life Vehicles (ELV, enforced on January 01, 2007), etc., all of which were adopted by EU. These require all enterprises all over the world to positively cope with new policies for environmental management such as development of environment-friendly product, reduction of wastes in factories, green purchasing, etc. In the past, a surface-treating method for coating a surface of a steel sheet with chromate film including chrome as a major component has been [DESCRIPTION] [invention Title] CHROME-FREE RESIN COMPOSITION HAVING GOOD ALKALINE RESISTANCE AND PROCESSIBILITY, METHOD FOR SURFACE-TREATED STEEL SHEET USING THE SAME AND SURFACE-TREATED STEEL SHEET [Technical Field] The present invention relates to a chrome-free resin composition for surface-treating a steel sheet having excellent alkaline resistance and processibilities, as well as excellent corrosion resistance, conductivity and chemical resistance, a method for manufacturing a steel sheet using the same, and a surface-treated steel sheet manufactured according to the method. [Background Art] Recently, the controls over the use of environmental pollutants, for example Cr, Pb, Cd, Hg, PBB, PBDE, etc. have been strengthened all over the world with an increasing concern in environmental issues. As representative examples of the controls, there are, in particular, Restriction of Hazardous Substances (RoHS, enforced on July 01, 2006), Waste from Electrical and Electronic Equipment (WEEE, enforced on July 01, 2006), Registration, Evaluation and Authorization of Chemicals (REACH), End-of-Life Vehicles (ELV, enforced on January 01, 2007), etc., all of which were adopted by EU. These require all enterprises all over the world to positively cope with new policies for environmental management such as development of environment-friendly product, reduction of wastes in factories, green purchasing, etc. In the past, a surface-treating method for coating a surface of a steel sheet with chromate film including chrome as a major component has been widely used to give corrosion resistance and paint adhesion to galvanized steel sheets, galvannealed steel sheets, aluminized steel sheets, aluminum alloy coated steel sheets, cold-rolled steel sheets and hot-rolled steel sheets, which have been used for automotive materials, home appliances, building materials, etc. Major chromate treatments are carried out using electrolytic chromate and coating-type chromate. Among them, an electrolytic chromate treatment is generally carried out by cathodically electrolyzing a metal plate with a treatment solution that includes hexavalent chrome as a major component and also include various negative ions such as sulfuric acid, phosphoric acid, boric acid and halogen as the other components. Meanwhile, the coating-type chromate treatment is generally carried out by dipping a metal plate into a treatment solution, or spraying a treatment solution onto a metal plate, wherein the treatment solution is prepared by adding inorganic colloids and inorganic ions to a solution in which some of hexavalent chrome is reduced into trivalent chrome in advance. These methods require a variety of countermeasures against work environments, sewage disposals, etc. due to the toxicity of hexavalent chrome in the chromate treatment solution. Also, the recycling and waste disposal of automobiles, electronic appliances, building materials, all of which use the surface-treated metals, cause problems regarding harmfulness to human body and environmental pollutions. Furthermore, the use of trivalent chrome is also problematic since some of the trivalent chrome is converted into hexavalent chrome by surrounding conditions such as temperature, microorganisms, etc. Therefore, steel companies have concentrated their efforts on developing a chrome-free, surface-treated steel sheet that does not include hexavalent chrome and simultaneously satisfies various requirements of desired characteristics such as corrosion resistance, alkaline resistance, conductivity, etc. In the prior art, a chrome-free, surface-treated metal sheet was manufactured by primarily coating a surface of a steel sheet with a metal salt film containing phosphate as a major component and secondarily coating the primarily coated steel sheet surface with a resin film containing acryl, epoxy and urethane resin as a major component, or forming each of the primary and secondary films with a resin film. However, the products have problems that it is not suitable to suppress electromagnetic waves and inner noises from photocopiers, printers, VCRs, computers and the like, and ensure their processibilities since the electrical conductivity and weldability of the metal sheet are often deteriorated according to the thickness of metal salt or film. With a recent increasing demand for a chrome-free, surface-treated steel sheet having excellent conductivity, there have been attempts to develop a chrome-free coated steel sheet using a method of primarily coating the resin film in the field of most home appliances companies. However, as far as a resin-based surface treating composition does not have especially excellent components, the quality characteristics (i.e. corrosion resistance, etc) of the surface-treated steel sheet are more highly deteriorated than that in conventional steel sheets that are not treated with chrome or phosphate. However, the major foreign and domestic home appliances companies have recently established their own quality standard and purchased only certified products in the case of the chrome-free, surface-treated steel sheet as an alternative to develop their own environment-friendly products. Japanese Patent Laid-open Publication No. Hei8-92479 and Japanese Patent Laid-open Publication No. Hei8-500770 disclose a method for coating a metal plate with a polyaniline coating composition that does not contain hexavalent chrome at all in consideration of the conductivity. However, since the polyaniline having high rigidity and low adhesion is present between the metal and a resin film, the resin film may be easily peeled out from interfaces between the polyaniline and the metal, and between the polyaniline and the resin. Therefore, problems occur when an upper surface of a steel sheet is painted in order to give designs, corrosion resistance and other functions to the steel sheet. Films having low adhesion have been generally known to have a low corrosion resistance. Also, the low solution stability may cause precipitates and bad smell, which leads to the deteriorated workability such as general impediments to the work environment, etc. A Zn- coated layer shows its excellent effect to improve characteristics such as conductivity, corrosion resistance, alkaline resistance, resistance to high temperature and high humidity by using the method of only primarily coating the Zn-coated layer with resin, and since some severely processed products lack processibilities, damages are caused to a resin layer and a coating layer of a processed friction portion, which leads to the loss of the resin layer and the change of a surface into a black surface. Furthermore, US Publication No. 2004-54044 discloses a composition prepared by mixing a hexafluoro complex (i.e. titanium, zirconium, etc.) and at least one inorganic compound with an organic film forming agent in water. However, the composition adversely affects the environment since it contains a fluorine complex, and should be also carefully handled due to its acidity. Also, Japanese Patent Laid-open Publication No. 2002-030460 discloses a composition prepared by mixing a vanadium compound and Zi and Ti with a mixed resin. However, the problem is that an etching process on a surface of a steel sheet should be carried out in an acidic solution so as to reduce a vanadium compound and ensure the adhesion. Also, Korean Patent Publication No. 2006-76953 discloses a surface-treating composition including an antirust agent and a metal chelating agent, in which a complex of organic resin and inorganic binder is prepared using a silane coupling agent, etc. However, the problem is that the complex of organic resin and inorganic binder should be prepared in advance. Also, some products whose alkaline resistance is necessarily required have problems that a resin layer is damaged due to the lack of alkaline resistance when it is in contact with an alkali solution, which leads to the loss of the resin layer or the severely discolored surface of the product. Furthermore, Japanese Patent No. 3706518 discloses a resin composition including an organic resin and a phosphate compound selected from the group consisting of ammonium phosphate, sodium phosphate and potassium phosphate. However, the use object of the phosphate compound is restricted to play a role in improving corrosion resistance by forming a thin passivation layer on a steel sheet. [Disclosure] [Technical Problem] An aspect of the present invention provides a resin composition for surface-treating a steel sheet capable of providing a chrome-free coating layer having excellent alkaline resistance and processibilities, as well as excellent corrosion resistance, conductivity and chemical resistance by coating a steel sheet with the resin composition. Another aspect of the present invention provides a surface-treated steel sheet coated with the resin composition for surface-treating a metal sheet. Still another aspect of the present invention provides a method for manufacturing a surface-treated steel sheet by forming a resin coating layer from the resin composition according to one embodiment of the present invention. The objects of the present invention are not limited to the above-mentioned objects, and other objects of the invention will become apparent from the following description of embodiments. [Technical Solution] Various aspects of the present invention provide a resin composition applied onto a steel sheet and/or a Zn-coated layer, a method for manufacturing a surface-treated steel sheet using the same, and a surface-treated steel sheet manufactured according to the method. According to one aspect of the present invention, there is provided a resin composition for surface-treating a steel sheet, including a urethane resin mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent. According to another aspect of the present invention, there is provided a resin composition for surface-treating a steel sheet, including a urethane resin mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based. organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition. In this case, the urethane resin mixture may include 5 to 95 % by weight of a soft urethane resin and 5 to 95 % by weight of a hard urethane . resin, based on the total solid content of the urethane resin mixture. Also, the soft urethane resin may include polyurethane prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, or polyurethane prepared from acryl polyol and pooyisocyanate. In addition, the polyhydric alcohol may be selected from the group consisting of acrylpolyol, polyesterpolyol, polyetherpolyol, polyolefin polyol, and mixtures thereof. Additionally, the soft urethane resin may have a number-average molecular weight of 5,000 to 300,000. Also, the hard urethane resin may be selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond. In addition, the hard urethane resin may have a number-average molecular weight of 200,000 to 2,000,000. Additionally, the hard urethane resin may have a Shore A hardness of 40 to 90. Furthermore, the diisocyanate may be p-phenylene diisocyanate. Also, the Ti or Zr-based organic oxide may be selected from the group consisting of titanium diisopropoxide bis(acetylacetonate), titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2- ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and mixtures thereof. Here, the solvent may be water. Also, the solvent may further include an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof. In this case, the resin composition may further include at least one additive selected from the group consisting of a wetting agent, a cross-linking agent, a lubricant and an antifoaming agent. According to still another aspect of the present invention, there is provided a method for surface-treating a steel sheet, including: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2. According to still another aspect of the present invention, there is provided a method for surface-treating a steel sheet, including: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition. In this case, the urethane resin mixture may include 5 to 95 % by weight of a soft urethane resin and 5 to 95 % by weight of a hard urethane resin, based on the total solid content of the urethane resin mixture. Also, the method may further include: drying the resin composition-coated steel sheet at a peak metal temperature (PMT) of 80 to 200D. In addition, the steel sheet may be selected from the group consisting of a galvanized steel sheet, an electrogalvanized steel sheet, a galvannealed steel sheet, an aluminized steel sheet, a coated steel sheet whose coating layer includes cobalt, molybdenum, tungsten, nickel, titanium, aluminum, manganese, iron, magnesium, tin, copper, and mixtures thereof, an aluminum alloy plate including silicon, copper, magnesium, iron, manganese, titanium, zinc, and mixtures thereof, a phosphate-coated galvanized steel sheet, a cold-rolled steel sheet, and a hot-rolled steel sheet. Additionally, the soft urethane resin may have a number-average molecular weight of 5,000 to 300,000, and may be prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol. Also, the hard urethane resin may have a number-average molecular weight of 200,000 to 2,000,000, and may be selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4, 4 ' -bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond. In addition, the hard urethane resin may have a Shore A hardness of 4 0 to 90. Additionally, the Ti or Zr-based organic oxide may be selected from the group consisting of titanium diisopropoxide bis(acetylacetonate) , titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and mixtures thereof. Also, the solvent may be water. Furthermore, the solvent may further include an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof. According to still another aspect of the present invention, there is provided a surface-treated steel sheet including a steel sheet; and a resin coating layer, wherein the resin coating layer is prepared by coating the steel sheet with a resin composition comprising a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1, 800 mg/m2. According to yet another aspect of the present invention, there is provided a surface-treated steel sheet including a steel sheet; and a resin coating layer, wherein the resin coating layer is prepared by coating the steel sheet with a resin composition comprising a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition, and the soft urethane resin is present in a content of 5 to 95 % by weight, and the hard urethane resin is present in a content of 5 to 95 % by weight , based on the total amount of the urethane resin mixture. [Advantageous Effects] As described above, the chrome-free resin composition for surface treating a steel sheet and the surface-treated steel sheet including a coating layer having excellent alkaline resistance and corrosion resistance have processibilities, conductivity, water resistance, solution stability, etc., as well and therefore may be easily used as materials to be processed. [Description of Drawings] FIG. 1 is a schematic configuration view illustrating a steel sheet including a resin coating layer according to one exemplary embodiment of the present invention. FIG. 2 is a diagram illustrating a level of damaged surfaces of the steel sheet according to one exemplary embodiment of the present invention and a conventional steel sheet after their machining characteristics are measured using a draw bead friction tester. FIG. 3 is a diagram illustrating appearances of the steel sheet according to one exemplary embodiment of the present invention and the conventional steel sheet after their alkaline resistances are determined in a degreasing solution. [Best Mode] Hereinafter, exemplary embodiments of the present invention will be described in detail. The present invention is related to a resin composition for surface-treating a steel sheet capable of improving alkaline resistance and processibilities and manufacturing a metal sheet having physical properties such as conductivity, corrosion resistance and chemical resistance by coating a steel sheet with a chrome-free resin composition including a urethane resin mixture of soft urethane resin and hard urethane resin, a corrosion-resistant curing agent (such as Ti or Zr organic oxides), at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent. The urethane resin mixture of soft urethane resin and hard urethane resin is used for the resin composition according to one exemplary embodiment of the present invention. Here, the urethane resin has strong physical properties such as water resistance, chemical resistance, acid resistance and alkaline resistance, and include soft and tough coating film, and therefore the urethane resin is used to prevent scratches of a surface of a steel sheet or an aluminum plate by painting the steel sheet or the aluminum plate, or widely used to give chemical resistance to the steel sheet or the aluminum plate. The urethane resin mixture is present in a solid concentration of 10 to 90 % by weight, based on the total solid content of the resin composition. When the total solid concentration of the urethane resin mixture is less than 10 % by weight, the urethane resin does not show salt water resistance against the penetration of corrosive ions and chemical resistance against the penetration of chemical substances, which leads to the deteriorated chemical resistance and alkaline resistance of the resin composition. Therefore, a resin film may be discolored or peeled off when the resin film was degreased at 60▒ for 5 minutes in an alkali solution with pH 10 or higher. On the contrary, when the total solid concentration of the urethane resin mixture exceeds 90 % by weight, the solution stability of the resin composition is deteriorated due to its agglomeration, and the manufacturing cost may be increased due to the use of the excessive urethane resin. However, since the exclusive use of the urethane resin has its limits to realize a soft and tough property of the resin film, the urethane resin mixture of soft urethane resin and hard urethane resin is used in the present invention. The soft urethane resin is present in a content of 5 to 95 % by weight, based on the solid concentration of the urethane resin mixture. When the solid concentration of the soft urethane resin is less than 5 % by weight, the processibilities of a surface-treated steel sheet are improved, but its heat resistance and water resistance are deteriorated, whereas the corrosion resistance of the surface-treated steel sheet is highly degraded without improving its processibilities when the solid concentration of the soft urethane resin exceeds 95 % by weight. Also, a molecular weight of the soft urethane resin is preferably in a range of 5,000 to 300,000. When the molecular weight of the soft urethane resin is less than 5,000, the processibilities of the surface-treated steel sheet are highly degraded, but the solution stability of the resin composition becomes low when the molecular weight of the soft urethane resin exceeds 300,000. The soft urethane resin that may be used herein includes, but is not particularly limited to, a polyurethane dispersion resin, a polyurethane resin (i.e. polyethylene-modified polyurethane resin, etc.) prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, and a polyurethane resin (i.e. an acryl-urethane resin, a polyethylene-acryl-modified polyurethane resin, etc.) prepared from acryl polyol and pooyisocyanate. Here, acryl polyol, polyesterpolyol, polyetherpolyol, polyolefin polyol and the like may be used as the polyhydric alcohol. Also, a molecular weight of the hard urethane resin is preferably is in a range of 200,000 to 2,000,000. When the molecular weight of the hard urethane resin is less than 200,000, the processibilities of the surface-treated steel sheet are not improved, whereas, when the molecular weight of the hard urethane resin exceeds 2,000,000, the low solution stability of the resin composition and the increased viscosity of the resin solution results in the deteriorated workability of the resin composition. The hard urethane resin that may be used herein includes, but is not particularly limited to, a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and isocyanate (in particular, p-phenylenediisocyanate) , a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, a polyurethane resin having an acetal bond, etc. Also, the hard urethane resin having a Shore A hardness of 40 to 90 is used preferably to manufacture a dried film. When the Shore A hardness of the hard urethane resin is less than 40, the processibilities of the resin composition are not improved, whereas, when the Shore A hardness of the hard urethane resin exceeds 90, a thin film is too hard to broke during its processing, and therefore the resin composition has no effect to improve processibilities. As a result, the hard urethane resin preferably has a hardness within the range. Ti or Zr organic oxide as a corrosion-resistant curing agent is added to the urethane resin. The corrosion-resistant curing agent is present in a content of 1 to 20 % by weight, based on the total solid content of the resin composition. In this case, when the content of the corrosion-resistant curing agent is less than 1 % by weight, its addition effect is not sufficient due to the deteriorated corrosion resistance. On the contrary, when the content of the corrosion-resistant curing agent exceeds 20 % by weight, the corrosion-resistant curing agent may be abundantly precipitated due to its saturated concentration in the resin composition, and the properties (such as corrosion resistance, alkaline resistance and water resistance) of the resin composition are degraded with deterioration of the solution stability. Desirable examples of the Ti or Zr-based organic oxide include, but is not particularly limited to, titanium diisopropoxide bis(acetylacetonate), titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, etc. The resin composition may include at least one compound selected from the listed compounds. Also, the resin composition for surface-treating a steel sheet according to one exemplary embodiment of the present invention includes at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate, hydrated manganese phosphate, etc. These compounds are added to improve adhesion between a resin (particularly, a zinc coating layer) and a steel sheet, and has effects to improve corrosion resistance, as well as conductivity and heat resistance owing to the metal salt effect by forming a passivation film on the zinc coating layer. The compounds such as monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is preferably added in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition. When the compounds are added in a content of less than 0.1 % by weight, they have a low adhesion to a steel sheet, and therefore the resin film may be easily peeled off during processes such as alkali degreasing, etc. On the contrary, when the compounds are added in a content of greater than 10.0 % by weight, the solution stability of the resin composition may be deteriorated since the excessive compounds do not improve the adhesion between the resin and the steel sheet, but promote the agglomeration of the resin, and also the adhesion between the resin and the steel sheet may be rather deteriorated. A component except for the solid content in the resin composition is a solvent, and water may be used as the solvent. In addition, an alcohol solvent and an aqueous alkaline solution may be further separately added to the resin composition in order to enhance wetting and dispersing properties of the coating composition. Ethanol, methanol, propanol, isopropanol, glycerol and the like may be used as the alcohol solvent, amine compound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium hydroxide and the like may be used as the aqueous alkaline solution. The resin composition has excellent resin solution stability and shows its effects to further improve corrosion resistance, conductivity, alkaline resistance, resistance to high temperature and high humidity of an anticorrosive coating layer since particles of the corrosion-resistant curing agent are uniformly dispersed by its reaction with organic functional groups of the resin. Also, the resin composition for surface-treating a steel sheet according to one exemplary embodiment of the present invention may further include at least one additive such as a wetting agent, a cross-linking agent, a lubricant, an antifoaming agent, etc. The wetting agent has an effect to form stripes and improve the adhesion, the cross-linking agent has an effect to improve the corrosion resistance and alkaline resistance, the lubricant has an effect on a coefficient of friction and the processibilities, and the antifoaming agent has an effect to further improve the workability. These additives are preferably used in a content of 5 to 25 % by weight, based on the solid content of the resin composition. When the content of the additive is less than 5 % by weight, an effect of the additive on the corrosion resistance, alkaline resistance, etc. is not shown, but when the content of the additive exceeds 25 % by weight, an insignificant effect on the addition of the additive is shown due to its saturation, and the solution stability may be also degraded. The wetting agent includes a deflocculating wetting and dispersing agent, polymeric wetting and dispersing gent, etc. Desirable examples of the wetting agent include, but are not particularly limited to, wetting and dispersing agents commercially available from EFKA and Tego, EFKA 3580 (Ciba), BW-W500 (Buhmwoo Chemical), WET 500 (Ciba), etc. The cross-linking agent that may be used herein includes, but is not particularly limited to, vinylsilane, methoxysilane, acrylsilane, epoxysilane, chlorosilane, alkoxysilane, silazane, silylating agent, melamine, melamine resin, alkylmelamine, alkylmelamine resin, fluorinated melamine and fluorinated melamine resin, polyamine-based, alkylated aromatic polyamine-based, polyamide-based or acid anhydride-based curing agent, etc. The lubricant includes, but is not particularly limited to, silicon wax, polyethylene wax, polypropylene wax, amide wax, polytetrafluoroethylene (PTFE) wax, paraffin wax, etc. The antifoaming agent that may be used herein includes, but is not particularly limited to, oil-type, modified oil-type, solution-type, powder-type, emulsion-type silicon antifoaming agents. An amount of an attached coating layer coated with the resin composition according to one exemplary embodiment of the present invention is preferably in a range of 300 to 1, 800mg/m2 after the drying of the coating layer, and a drying temperature (PMT) is in a range of 80▒ to 200▒, which are similar to the drying temperature of the conventional resin surface-treating solution. In this case, when the amount of the attached coating layer is less than 300mg/m2, the corrosion resistance and processibilities of the resin composition are not improved, whereas when the amount of the attached coating layer exceeds 1,800mg/m2, an effect on the corrosion resistance is saturated, and the economical efficiency is low due to the low conductivity and the high manufacturing cost. Also, although the corrosion resistance of the resin film is increasingly improved as the drying temperature increases, it is reasonable to satisfy clients' requirements for products when the products are manufactured within the drying temperature of 80 to 200▒. Also, a metal plate that is applicable in the present invention includes, but is not particularly limited to, a galvanized steel sheet, an electrogalvanized steel sheet such as a zinc/nickel-coated steel sheet, a zinc/iron-coated steel sheet, a zinc/titanium-coated steel sheet, a zinc/magnesium-coated steel sheet, a zinc/manganese-coated steel sheet, a zinc/aluminized-steel sheet and the like, a hot-dip-coated steel sheet, an aluminized steel sheet, a coated steel sheet whose coating layer includes different metals or impurities, for example, cobalt, molybdenum, tungsten, nickel, titanium, aluminum, manganese, iron, magnesium, tin, copper, etc., a coated steel sheet having a coating layer dispersed with inorganic substances such as silica and alumina, an aluminum alloy plate including silicon, copper, magnesium, iron, manganese, titanium, zinc, etc., a phosphate-coated galvanized steel sheet, a cold-rolled steel sheet, a hot-rolled steel sheet, etc. Also, a multilayer coating layer in which at least two coated steel sheets are sequentially stacked is applicable in the present invention. [Mode for Invention] Hereinafter, the present invention will be described in more detail referring to the exemplary embodiments of the present invention. However, it should be understood that the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention. Examples 1-13 and Comparative examples 1-14 1-1. Preparation of Resin Composition A urethane resin having a number-average molecular weight of 100,000, composed of isoprene diisocyanate, adipic acid and polyhydric alcohol monomers, was prepared as the soft urethane resin monomer. Also, an urethane resin having a number-average molecular weight of 1,000,000 was prepared from p-phenylene diisocyanate and polycarbonatepolyol monomers as the hard urethane resin monomer. Ti organic oxide (Tyzor TE® titanium(IV) (triethanolaminato) isopropoxide) commercially available from Dupont was used as the corrosion-resistant curing agent. Aluminum dihydrogen phosphate commercially available from Junsei was used as the aluminum phosphate. In this case, contents of the soft urethane resin, the hard urethane resin, the Ti-based corrosion-resistant curing agent, the aluminum dihydrogen phosphate and other additives were adjusted to content levels as listed in Table 1, and the quality characteristics of the resin composition were evaluated. As the additives, 10 % by weight of colloidal silica (Snowtex-40 commercially available from Nissan Chemical), 0.5 % by weight of a siloxane wetting agent (EFKA 3580 from Ciba), 1.2 % by weight of a silane cross-linking agent (Aldrich, 3-glycidoxypropyl trimethoxy silane), 2.5 % by weight of an amine curing agent (Cymel 303 from Cytec) , and 1.5 % by weight of a polyethylene lubricant (Lanco PE 1500 from Noveon) were added in bulk. A solid concentration of the resin composition for surface-treating a steel sheet was adjusted to a concentration level of approximately 15 % by weight. For reference, water was used as the major component except for the solid content, and approximately 3 % by weight of ethanol and approximately 0.5 % by weight of an amine compound were added as the alcohol solvent and the aqueous alkaline solution, respectively. 1-2. Manufacture of Coated Steel Sheet 1) Test specimen: An electrogalvanized steel sheet (EG) having an attachment amount of 20g/mI (based on a single surface of the steel sheet) was used as a base steel sheet to be coated with the resin composition for surface-treating a steel sheet. 2) Coating method: A test sample was coated with a resin composition using a continuous roll coating simulator, and dried under PMT conditions as listed in Table 1. The attachment amount of a film was 1,000 mg/m2. 1-3. Performance Evaluation (1) Processibilities: A coefficient of friction was measured using a draw bead friction tester (a load of 1,000 kgf, a speed of 1,000 mm/min, and a distance of 100 mm) , and a resin film of the test specimen was evaluated based on the following damage levels when the resin film of the test specimen was scratched on a bead surface of the draw bead friction tester, o: Damaged area of less than 5% □ : Damaged area of 5 to 10% x : Damaged area of greater than 10% (2) Corrosion resistance: A salt spray test on a test specimen was performed for 96 hours according to JIS-Z2371 standard, and the test specimen was evaluated based on the following corrosion levels. o : White rust of less than 5% □ : White rust of 5 to 20% x : White rust of greater than 20% (3) Conductivity: a surface of a test specimen coated with a resin film was measured for conductivity using a surface resistance meter (Loresta-GP) , and evaluated based on the following surface resistance levels. o : Surface resistance of less than lmΩ ▒ : Surface resistance of in or less x : Surface resistance of more than 1Ω ( very poor in conductivity or weldability) (4) Alkaline resistance: A test specimen was dipped into an alkali solution (Gardoclean 4292L, pH 12) at 50▒ for 5 minutes, and washed with water. Then, the test specimen was observed with the naked eye for changes in color and peeling of a resin coating layer, and evaluated based on the following levels. o : No peel, and color change of less than 2.0 ▒ : No peel, and color change of 2.0 or more x : Peels (5) Water resistance: A test specimen was dipped into water for 30 minutes, and rubbed 30 times with a finger. Then, the changes in color of the test specimen was measured and evaluated based on the following color change levels. o : Color change of less than 1.0 ▒ : Color change of 1.0 or more x : Peels (6) Solution stability: 100 g of the resin composition for surface- treating a steel sheet was kept at 50▒ for 10 days in an oven, and the precipitation, gelation and separation of the resin composition were evaluated, as follows. o : Not precipitated, gelled or separated ▒ : Either slightly precipitated, gelled or separated x : Some precipitated, gelled and/or separated The evaluation results are listed in the following Table 1. [Table 1] (Table Removed) Examples 14-19 and Comparative examples15-17 2-1. Manufacture of Coated Steel Sheet 1) Test specimen: An electrogalvanized steel sheet (EG) having an attachment amount of 20g/m2 (based on a single surface of the steel sheet) was used as a base steel sheet to be coated with the resin composition for surface-treating a steel sheet. 2) Coating method: A test specimen was dipped into a pretreatment solution for 3 seconds and dried under PMT conditions as listed in Table 2. Also, a resin composition of Example was prepared according to the components and their contents of Example 4 as listed in Table 1, and a steel sheet was coated with the resin composition using a continuous roll coating simulator, and dried at an amount of the attached resin under PMT conditions as listed in the following Table 2. 2-2. Performance Evaluation The processibilities, conductivity and corrosion resistance of the test specimen prepared under the above-mentioned conditions were evaluated using the evaluation method as listed in the Table 1. 2-3. Evaluation Results The performance of the resin composition for surface-treating a steel sheet was measured under the above-mentioned conditions, and listed in the following Table 2 . [Table 2] (Table Removed) As listed in the Table 2, it was revealed that the surface-treated steel sheets of Examples 14 to 19 according to one exemplary embodiment of the present invention show their excellent quality characteristics, but the surface-treated steel sheets of Comparative examples 17 to 19 show their degraded characteristics. [We claim:—] [Claim 1] A resin composition for surface-treating a steel sheet, comprising: a urethane resin mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent. [Claim 2] A resin composition for surface-treating a steel sheet, comprising: a urethane resin mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition. [ Claim 3] The resin composition of claim 2, wherein the urethane resin mixture comprises 5 to 95 % by weight of a soft urethane resin and 5 to 95 % by weight of a hard urethane resin, based on the total solid content of the urethane resin mixture. [Claim 4] The resin composition of any one of claims 1 to 3, wherein the soft urethane resin comprises polyurethane prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, or polyurethane prepared from acryl polyol and pooyisocyanate. [Claim 5l The resin composition of claim 4, wherein the polyhydric alcohol is selected from the group consisting of acrylpolyol, polyesterpolyol, polyetherpolyol, polyolefin polyol, and mixtures thereof. [Claim 6] The resin composition of claim 4, wherein the soft urethane resin has a number-average molecular weight of 5,000 to 300,000. [Claim 7] The resin composition of any one of claims 1 to 3, wherein the hard urethane resin is selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond. [Claim 8] The resin composition of claim 7, wherein the hard urethane resin has a number-average molecular weight of 200,000 to 2,000,000. [Claim 9] The resin composition of claim 7, wherein the hard urethane resin has a Shore A hardness of 40 to 90. [Claim 10] The resin composition of claim 7, wherein the diisocyanate is p-phenylene diisocyanate. [Claim 11] The resin composition of any one of claims 1 to 3, wherein the Ti or Zr-based organic oxide is selected from the group consisting of titanium diisopropoxide bis(acetylacetonate) , titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and mixtures thereof. [Claim 12] The resin composition of any one of claims 1 to 3, wherein the solvent is water. [claim 13] The resin composition of claim 12, wherein the solvent further comprises an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof. [ Claim 14 ] The resin composition of any one of claims 1 to 3, further comprising at least one additive selected from the group consisting of a wetting agent, a cross-linking agent, a lubricant and an antifoaming agent. [Claim 15] A method for surface-treating a steel sheet, comprising: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2. [Claim 16] A method for surface-treating a steel sheet, comprising: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition. [ Claim 17 ] The method of claim 16, wherein the urethane resin mixture comprises 5 to 95 % by weight of a soft urethane resin and 5 to 95 % by weight of a hard urethane resin, based on the total solid content of the urethane resin mixture. [claim 18] The method of any one of claims 15 to 17, further comprising: drying the resin composition-coated steel sheet at a peak metal temperature (PMT) of 80 to 200▒. [Claim 19] The method of any one of claims 15 to 17, wherein the steel sheet is selected from the group consisting of a galvanized steel sheet, an electrogalvanized steel sheet, a galvannealed steel sheet, an aluminized steel sheet, a coated steel sheet whose coating layer includes cobalt, molybdenum, tungsten, nickel, titanium, aluminum, manganese, iron, magnesium, tin, copper, and mixtures thereof, an aluminum alloy plate including silicon, copper, magnesium, iron, manganese, titanium, zinc, and mixtures thereof, a phosphate-coated galvanized steel sheet, a cold-rolled steel sheet, and a hot-rolled steel sheet. [Claim 20] The method of any one of claims 15 to 17, wherein the soft urethane resin has a number-average molecular weight of 5,000 to 300,000, and comprises polyurethane prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, or polyurethane prepared from acryl polyol and pooyisocyanate. [Claim 21] The method of any one of claims 15 to 17, wherein the hard urethane resin has a number-average molecular weight of 200,000 to 2,000,000, and is selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond. [Claim 22] The method of claim 21, wherein the hard urethane resin has a Shore A hardness of 40 to 90. [claim 23] The method of any one of claims 15 to 17, wherein the Ti or Zr-based organic oxide is selected from the group consisting of titanium diisopropoxide bis (acetylacetonate) , titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and mixtures thereof. [Claim 24] The method of any one of claims 15 to 17, wherein the solvent is water. [claim 25] The method of claim 24, wherein the solvent further comprises an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof. [Claim 26 1 A surface-treated steel sheet comprising a steel sheet; and a resin coating layer, wherein the resin coating layer is prepared by coating the steel sheet with a resin composition comprising a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2. [claim 27 ] A surface-treated steel sheet comprising a steel sheet; and a resin coating layer, wherein the resin coating layer is prepared by coating the steel sheet with a resin composition comprising a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of 300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition, and the soft urethane resin is present in a content of 5 to 95 % by weight, and the hard urethane resin is present in a content of 5 to 95 % by weight , based on the total amount of the urethane resin mixture. [ Claim 28 ] A resin composition for surface-treating a steel sheet substantially as herein described with reference to the foregoing description, tables, examples and the accompanying drawings.

Full Text

[DESCRIPTION]
[invention Title]
CHROME-FREE RESIN COMPOSITION HAVING GOOD ALKALINE RESISTANCE AND PROCESSIBILITY, METHOD FOR SURFACE-TREATED STEEL SHEET USING THE SAME AND SURFACE-TREATED STEEL SHEET
[Technical Field]
The present invention relates to a chrome-free resin composition for surface-treating a steel sheet having excellent alkaline resistance and processibilities, as well as excellent corrosion resistance, conductivity and chemical resistance, a method for manufacturing a steel sheet using the same, and a surface-treated steel sheet manufactured according to the method.
[Background Art]
Recently, the controls over the use of environmental pollutants, for example Cr, Pb, Cd, Hg, PBB, PBDE, etc. have been strengthened all over the world with an increasing concern in environmental issues. As representative examples of the controls, there are, in particular, Restriction of Hazardous Substances (RoHS, enforced on July 01, 2006), Waste from Electrical and Electronic Equipment (WEEE, enforced on July 01, 2006), Registration, Evaluation and Authorization of Chemicals (REACH), End-of-Life Vehicles (ELV, enforced on January 01, 2007), etc., all of which were adopted by EU. These require all enterprises all over the world to positively cope with new policies for environmental management such as development of environment-friendly product, reduction of wastes in factories, green purchasing, etc.
In the past, a surface-treating method for coating a surface of a steel sheet with chromate film including chrome as a major component has been
[DESCRIPTION]
[invention Title]
CHROME-FREE RESIN COMPOSITION HAVING GOOD ALKALINE RESISTANCE AND PROCESSIBILITY, METHOD FOR SURFACE-TREATED STEEL SHEET USING THE SAME AND SURFACE-TREATED STEEL SHEET
[Technical Field]
The present invention relates to a chrome-free resin composition for surface-treating a steel sheet having excellent alkaline resistance and processibilities, as well as excellent corrosion resistance, conductivity and chemical resistance, a method for manufacturing a steel sheet using the same, and a surface-treated steel sheet manufactured according to the method.
[Background Art]
Recently, the controls over the use of environmental pollutants, for example Cr, Pb, Cd, Hg, PBB, PBDE, etc. have been strengthened all over the world with an increasing concern in environmental issues. As representative examples of the controls, there are, in particular, Restriction of Hazardous Substances (RoHS, enforced on July 01, 2006), Waste from Electrical and Electronic Equipment (WEEE, enforced on July 01, 2006), Registration, Evaluation and Authorization of Chemicals (REACH), End-of-Life Vehicles (ELV, enforced on January 01, 2007), etc., all of which were adopted by EU. These require all enterprises all over the world to positively cope with new policies for environmental management such as development of environment-friendly product, reduction of wastes in factories, green purchasing, etc.
In the past, a surface-treating method for coating a surface of a steel sheet with chromate film including chrome as a major component has been
widely used to give corrosion resistance and paint adhesion to galvanized steel sheets, galvannealed steel sheets, aluminized steel sheets, aluminum alloy coated steel sheets, cold-rolled steel sheets and hot-rolled steel sheets, which have been used for automotive materials, home appliances, building materials, etc. Major chromate treatments are carried out using electrolytic chromate and coating-type chromate. Among them, an electrolytic chromate treatment is generally carried out by cathodically electrolyzing a metal plate with a treatment solution that includes hexavalent chrome as a major component and also include various negative ions such as sulfuric acid, phosphoric acid, boric acid and halogen as the other components. Meanwhile, the coating-type chromate treatment is generally carried out by dipping a metal plate into a treatment solution, or spraying a treatment solution onto a metal plate, wherein the treatment solution is prepared by adding inorganic colloids and inorganic ions to a solution in which some of hexavalent chrome is reduced into trivalent chrome in advance.
These methods require a variety of countermeasures against work environments, sewage disposals, etc. due to the toxicity of hexavalent chrome in the chromate treatment solution. Also, the recycling and waste disposal of automobiles, electronic appliances, building materials, all of which use the surface-treated metals, cause problems regarding harmfulness to human body and environmental pollutions. Furthermore, the use of trivalent chrome is also problematic since some of the trivalent chrome is converted into hexavalent chrome by surrounding conditions such as temperature, microorganisms, etc.
Therefore, steel companies have concentrated their efforts on
developing a chrome-free, surface-treated steel sheet that does not include
hexavalent chrome and simultaneously satisfies various requirements of
desired characteristics such as corrosion resistance, alkaline resistance, conductivity, etc. In the prior art, a chrome-free, surface-treated metal sheet was manufactured by primarily coating a surface of a steel sheet with a metal salt film containing phosphate as a major component and secondarily coating the primarily coated steel sheet surface with a resin film containing acryl, epoxy and urethane resin as a major component, or forming each of the primary and secondary films with a resin film.
However, the products have problems that it is not suitable to suppress electromagnetic waves and inner noises from photocopiers, printers, VCRs, computers and the like, and ensure their processibilities since the electrical conductivity and weldability of the metal sheet are often deteriorated according to the thickness of metal salt or film.
With a recent increasing demand for a chrome-free, surface-treated steel sheet having excellent conductivity, there have been attempts to develop a chrome-free coated steel sheet using a method of primarily coating the resin film in the field of most home appliances companies. However, as far as a resin-based surface treating composition does not have especially excellent components, the quality characteristics (i.e. corrosion resistance, etc) of the surface-treated steel sheet are more highly deteriorated than that in conventional steel sheets that are not treated with chrome or phosphate. However, the major foreign and domestic home appliances companies have recently established their own quality standard and purchased only certified products in the case of the chrome-free, surface-treated steel sheet as an alternative to develop their own environment-friendly products.
Japanese Patent Laid-open Publication No. Hei8-92479 and Japanese
Patent Laid-open Publication No. Hei8-500770 disclose a method for coating a
metal plate with a polyaniline coating composition that does not contain
hexavalent chrome at all in consideration of the conductivity. However, since
the polyaniline having high rigidity and low adhesion is present between the
metal and a resin film, the resin film may be easily peeled out from
interfaces between the polyaniline and the metal, and between the polyaniline
and the resin. Therefore, problems occur when an upper surface of a steel
sheet is painted in order to give designs, corrosion resistance and other
functions to the steel sheet. Films having low adhesion have been generally
known to have a low corrosion resistance. Also, the low solution stability
may cause precipitates and bad smell, which leads to the deteriorated
workability such as general impediments to the work environment, etc. A Zn-
coated layer shows its excellent effect to improve characteristics such as
conductivity, corrosion resistance, alkaline resistance, resistance to high
temperature and high humidity by using the method of only primarily coating
the Zn-coated layer with resin, and since some severely processed products
lack processibilities, damages are caused to a resin layer and a coating
layer of a processed friction portion, which leads to the loss of the resin
layer and the change of a surface into a black surface.
Furthermore, US Publication No. 2004-54044 discloses a composition
prepared by mixing a hexafluoro complex (i.e. titanium, zirconium, etc.) and
at least one inorganic compound with an organic film forming agent in water.
However, the composition adversely affects the environment since it contains
a fluorine complex, and should be also carefully handled due to its acidity.
Also, Japanese Patent Laid-open Publication No. 2002-030460 discloses a
composition prepared by mixing a vanadium compound and Zi and Ti with a mixed
resin. However, the problem is that an etching process on a surface of a
steel sheet should be carried out in an acidic solution so as to reduce a
vanadium compound and ensure the adhesion. Also, Korean Patent Publication No.
2006-76953 discloses a surface-treating composition including an antirust agent and a metal chelating agent, in which a complex of organic resin and inorganic binder is prepared using a silane coupling agent, etc. However, the problem is that the complex of organic resin and inorganic binder should be prepared in advance. Also, some products whose alkaline resistance is necessarily required have problems that a resin layer is damaged due to the lack of alkaline resistance when it is in contact with an alkali solution, which leads to the loss of the resin layer or the severely discolored surface of the product. Furthermore, Japanese Patent No. 3706518 discloses a resin composition including an organic resin and a phosphate compound selected from the group consisting of ammonium phosphate, sodium phosphate and potassium phosphate. However, the use object of the phosphate compound is restricted to play a role in improving corrosion resistance by forming a thin passivation layer on a steel sheet.
[Disclosure]
[Technical Problem]
An aspect of the present invention provides a resin composition for surface-treating a steel sheet capable of providing a chrome-free coating layer having excellent alkaline resistance and processibilities, as well as excellent corrosion resistance, conductivity and chemical resistance by coating a steel sheet with the resin composition.
Another aspect of the present invention provides a surface-treated steel sheet coated with the resin composition for surface-treating a metal sheet.
Still another aspect of the present invention provides a method for manufacturing a surface-treated steel sheet by forming a resin coating layer
from the resin composition according to one embodiment of the present invention.
The objects of the present invention are not limited to the above-mentioned objects, and other objects of the invention will become apparent from the following description of embodiments.
[Technical Solution]
Various aspects of the present invention provide a resin composition applied onto a steel sheet and/or a Zn-coated layer, a method for manufacturing a surface-treated steel sheet using the same, and a surface-treated steel sheet manufactured according to the method.
According to one aspect of the present invention, there is provided a resin composition for surface-treating a steel sheet, including a urethane resin mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent.
According to another aspect of the present invention, there is provided a resin composition for surface-treating a steel sheet, including a urethane resin mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based. organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated
manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition.
In this case, the urethane resin mixture may include 5 to 95 % by weight of a soft urethane resin and 5 to 95 % by weight of a hard urethane . resin, based on the total solid content of the urethane resin mixture.
Also, the soft urethane resin may include polyurethane prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, or polyurethane prepared from acryl polyol and pooyisocyanate.
In addition, the polyhydric alcohol may be selected from the group consisting of acrylpolyol, polyesterpolyol, polyetherpolyol, polyolefin polyol, and mixtures thereof.
Additionally, the soft urethane resin may have a number-average molecular weight of 5,000 to 300,000.
Also, the hard urethane resin may be selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond.
In addition, the hard urethane resin may have a number-average molecular weight of 200,000 to 2,000,000.
Additionally, the hard urethane resin may have a Shore A hardness of 40 to 90.
Furthermore, the diisocyanate may be p-phenylene diisocyanate.
Also, the Ti or Zr-based organic oxide may be selected from the group consisting of titanium diisopropoxide bis(acetylacetonate), titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato)
isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-
ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and mixtures thereof.
Here, the solvent may be water.
Also, the solvent may further include an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof.
In this case, the resin composition may further include at least one additive selected from the group consisting of a wetting agent, a cross-linking agent, a lubricant and an antifoaming agent.
According to still another aspect of the present invention, there is provided a method for surface-treating a steel sheet, including: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a
range of 300 to 1,800 mg/m2.
According to still another aspect of the present invention, there is provided a method for surface-treating a steel sheet, including: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated
manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a
range of 300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition.
In this case, the urethane resin mixture may include 5 to 95 % by weight of a soft urethane resin and 5 to 95 % by weight of a hard urethane resin, based on the total solid content of the urethane resin mixture.
Also, the method may further include: drying the resin composition-coated steel sheet at a peak metal temperature (PMT) of 80 to 200D.
In addition, the steel sheet may be selected from the group consisting of a galvanized steel sheet, an electrogalvanized steel sheet, a galvannealed steel sheet, an aluminized steel sheet, a coated steel sheet whose coating layer includes cobalt, molybdenum, tungsten, nickel, titanium, aluminum, manganese, iron, magnesium, tin, copper, and mixtures thereof, an aluminum alloy plate including silicon, copper, magnesium, iron, manganese, titanium, zinc, and mixtures thereof, a phosphate-coated galvanized steel sheet, a cold-rolled steel sheet, and a hot-rolled steel sheet.
Additionally, the soft urethane resin may have a number-average molecular weight of 5,000 to 300,000, and may be prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol.
Also, the hard urethane resin may have a number-average molecular
weight of 200,000 to 2,000,000, and may be selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4, 4 ' -bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond.
In addition, the hard urethane resin may have a Shore A hardness of 4 0 to 90.
Additionally, the Ti or Zr-based organic oxide may be selected from the group consisting of titanium diisopropoxide bis(acetylacetonate) , titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and mixtures thereof.
Also, the solvent may be water.
Furthermore, the solvent may further include an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof.
According to still another aspect of the present invention, there is
provided a surface-treated steel sheet including a steel sheet; and a resin
coating layer, wherein the resin coating layer is prepared by coating the
steel sheet with a resin composition comprising a mixture of soft urethane
resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one
compound selected from the group consisting of monoaluminum phosphate,
aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese
phosphate; and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of
300 to 1, 800 mg/m2.
According to yet another aspect of the present invention, there is provided a surface-treated steel sheet including a steel sheet; and a resin coating layer, wherein the resin coating layer is prepared by coating the steel sheet with a resin composition comprising a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a range of
300 to 1,800 mg/m2, wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition, and the soft urethane resin is present in a content of 5 to 95 % by weight, and the hard urethane resin is present in a content of 5 to 95 % by weight , based on the total amount of the urethane resin mixture.
[Advantageous Effects]
As described above, the chrome-free resin composition for surface
treating a steel sheet and the surface-treated steel sheet including a
coating layer having excellent alkaline resistance and corrosion resistance
have processibilities, conductivity, water resistance, solution stability,
etc., as well and therefore may be easily used as materials to be processed. [Description of Drawings]
FIG. 1 is a schematic configuration view illustrating a steel sheet including a resin coating layer according to one exemplary embodiment of the present invention.
FIG. 2 is a diagram illustrating a level of damaged surfaces of the steel sheet according to one exemplary embodiment of the present invention and a conventional steel sheet after their machining characteristics are measured using a draw bead friction tester.
FIG. 3 is a diagram illustrating appearances of the steel sheet according to one exemplary embodiment of the present invention and the conventional steel sheet after their alkaline resistances are determined in a degreasing solution.
[Best Mode]
Hereinafter, exemplary embodiments of the present invention will be described in detail.
The present invention is related to a resin composition for surface-treating a steel sheet capable of improving alkaline resistance and processibilities and manufacturing a metal sheet having physical properties such as conductivity, corrosion resistance and chemical resistance by coating a steel sheet with a chrome-free resin composition including a urethane resin mixture of soft urethane resin and hard urethane resin, a corrosion-resistant curing agent (such as Ti or Zr organic oxides), at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent.
The urethane resin mixture of soft urethane resin and hard urethane resin is used for the resin composition according to one exemplary embodiment of the present invention. Here, the urethane resin has strong physical properties such as water resistance, chemical resistance, acid resistance and alkaline resistance, and include soft and tough coating film, and therefore the urethane resin is used to prevent scratches of a surface of a steel sheet or an aluminum plate by painting the steel sheet or the aluminum plate, or widely used to give chemical resistance to the steel sheet or the aluminum plate.
The urethane resin mixture is present in a solid concentration of 10 to 90 % by weight, based on the total solid content of the resin composition. When the total solid concentration of the urethane resin mixture is less than 10 % by weight, the urethane resin does not show salt water resistance against the penetration of corrosive ions and chemical resistance against the penetration of chemical substances, which leads to the deteriorated chemical resistance and alkaline resistance of the resin composition. Therefore, a resin film may be discolored or peeled off when the resin film was degreased at 60▒ for 5 minutes in an alkali solution with pH 10 or higher. On the contrary, when the total solid concentration of the urethane resin mixture exceeds 90 % by weight, the solution stability of the resin composition is deteriorated due to its agglomeration, and the manufacturing cost may be increased due to the use of the excessive urethane resin.
However, since the exclusive use of the urethane resin has its limits
to realize a soft and tough property of the resin film, the urethane resin
mixture of soft urethane resin and hard urethane resin is used in the present
invention. The soft urethane resin is present in a content of 5 to 95 % by
weight, based on the solid concentration of the urethane resin mixture. When
the solid concentration of the soft urethane resin is less than 5 % by weight, the processibilities of a surface-treated steel sheet are improved, but its heat resistance and water resistance are deteriorated, whereas the corrosion resistance of the surface-treated steel sheet is highly degraded without improving its processibilities when the solid concentration of the soft urethane resin exceeds 95 % by weight.
Also, a molecular weight of the soft urethane resin is preferably in a range of 5,000 to 300,000. When the molecular weight of the soft urethane resin is less than 5,000, the processibilities of the surface-treated steel sheet are highly degraded, but the solution stability of the resin composition becomes low when the molecular weight of the soft urethane resin exceeds 300,000.
The soft urethane resin that may be used herein includes, but is not particularly limited to, a polyurethane dispersion resin, a polyurethane resin (i.e. polyethylene-modified polyurethane resin, etc.) prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, and a polyurethane resin (i.e. an acryl-urethane resin, a polyethylene-acryl-modified polyurethane resin, etc.) prepared from acryl polyol and pooyisocyanate. Here, acryl polyol, polyesterpolyol, polyetherpolyol, polyolefin polyol and the like may be used as the polyhydric alcohol.
Also, a molecular weight of the hard urethane resin is preferably is in a range of 200,000 to 2,000,000. When the molecular weight of the hard urethane resin is less than 200,000, the processibilities of the surface-treated steel sheet are not improved, whereas, when the molecular weight of the hard urethane resin exceeds 2,000,000, the low solution stability of the resin composition and the increased viscosity of the resin solution results
in the deteriorated workability of the resin composition.
The hard urethane resin that may be used herein includes, but is not particularly limited to, a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and isocyanate (in particular, p-phenylenediisocyanate) , a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, a polyurethane resin having an acetal bond, etc.
Also, the hard urethane resin having a Shore A hardness of 40 to 90 is used preferably to manufacture a dried film. When the Shore A hardness of the hard urethane resin is less than 40, the processibilities of the resin composition are not improved, whereas, when the Shore A hardness of the hard urethane resin exceeds 90, a thin film is too hard to broke during its processing, and therefore the resin composition has no effect to improve processibilities. As a result, the hard urethane resin preferably has a hardness within the range.
Ti or Zr organic oxide as a corrosion-resistant curing agent is added to the urethane resin. The corrosion-resistant curing agent is present in a content of 1 to 20 % by weight, based on the total solid content of the resin composition. In this case, when the content of the corrosion-resistant curing agent is less than 1 % by weight, its addition effect is not sufficient due to the deteriorated corrosion resistance. On the contrary, when the content of the corrosion-resistant curing agent exceeds 20 % by weight, the corrosion-resistant curing agent may be abundantly precipitated due to its saturated concentration in the resin composition, and the properties (such as corrosion resistance, alkaline resistance and water resistance) of the resin composition are degraded with deterioration of the solution stability.
Desirable examples of the Ti or Zr-based organic oxide include, but is
not particularly limited to, titanium diisopropoxide bis(acetylacetonate),
titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, etc. The resin composition may include at least one compound selected from the listed compounds.
Also, the resin composition for surface-treating a steel sheet according to one exemplary embodiment of the present invention includes at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate, hydrated manganese phosphate, etc. These compounds are added to improve adhesion between a resin (particularly, a zinc coating layer) and a steel sheet, and has effects to improve corrosion resistance, as well as conductivity and heat resistance owing to the metal salt effect by forming a passivation film on the zinc coating layer.
The compounds such as monoaluminum phosphate, aluminum dihydrogen
phosphate, monozinc phosphate and hydrated manganese phosphate is preferably
added in a content of 0.1 to 10.0 % by weight, based on the total solid
content of the resin composition. When the compounds are added in a content
of less than 0.1 % by weight, they have a low adhesion to a steel sheet, and
therefore the resin film may be easily peeled off during processes such as
alkali degreasing, etc. On the contrary, when the compounds are added in a
content of greater than 10.0 % by weight, the solution stability of the resin
composition may be deteriorated since the excessive compounds do not improve
the adhesion between the resin and the steel sheet, but promote the
agglomeration of the resin, and also the adhesion between the resin and the
steel sheet may be rather deteriorated.
A component except for the solid content in the resin composition is a
solvent, and water may be used as the solvent. In addition, an alcohol solvent and an aqueous alkaline solution may be further separately added to the resin composition in order to enhance wetting and dispersing properties of the coating composition. Ethanol, methanol, propanol, isopropanol, glycerol and the like may be used as the alcohol solvent, amine compound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate, ammonium hydroxide and the like may be used as the aqueous alkaline solution.
The resin composition has excellent resin solution stability and shows its effects to further improve corrosion resistance, conductivity, alkaline resistance, resistance to high temperature and high humidity of an anticorrosive coating layer since particles of the corrosion-resistant curing agent are uniformly dispersed by its reaction with organic functional groups of the resin.
Also, the resin composition for surface-treating a steel sheet
according to one exemplary embodiment of the present invention may further
include at least one additive such as a wetting agent, a cross-linking agent,
a lubricant, an antifoaming agent, etc. The wetting agent has an effect to
form stripes and improve the adhesion, the cross-linking agent has an effect
to improve the corrosion resistance and alkaline resistance, the lubricant
has an effect on a coefficient of friction and the processibilities, and the
antifoaming agent has an effect to further improve the workability. These
additives are preferably used in a content of 5 to 25 % by weight, based on
the solid content of the resin composition. When the content of the additive
is less than 5 % by weight, an effect of the additive on the corrosion
resistance, alkaline resistance, etc. is not shown, but when the content of
the additive exceeds 25 % by weight, an insignificant effect on the addition
of the additive is shown due to its saturation, and the solution stability
may be also degraded.
The wetting agent includes a deflocculating wetting and dispersing agent, polymeric wetting and dispersing gent, etc. Desirable examples of the wetting agent include, but are not particularly limited to, wetting and dispersing agents commercially available from EFKA and Tego, EFKA 3580 (Ciba), BW-W500 (Buhmwoo Chemical), WET 500 (Ciba), etc.
The cross-linking agent that may be used herein includes, but is not particularly limited to, vinylsilane, methoxysilane, acrylsilane, epoxysilane, chlorosilane, alkoxysilane, silazane, silylating agent, melamine, melamine resin, alkylmelamine, alkylmelamine resin, fluorinated melamine and fluorinated melamine resin, polyamine-based, alkylated aromatic polyamine-based, polyamide-based or acid anhydride-based curing agent, etc.
The lubricant includes, but is not particularly limited to, silicon wax, polyethylene wax, polypropylene wax, amide wax, polytetrafluoroethylene (PTFE) wax, paraffin wax, etc.
The antifoaming agent that may be used herein includes, but is not particularly limited to, oil-type, modified oil-type, solution-type, powder-type, emulsion-type silicon antifoaming agents.
An amount of an attached coating layer coated with the resin composition according to one exemplary embodiment of the present invention is
preferably in a range of 300 to 1, 800mg/m2 after the drying of the coating
layer, and a drying temperature (PMT) is in a range of 80▒ to 200▒, which are similar to the drying temperature of the conventional resin surface-treating solution. In this case, when the amount of the attached coating
layer is less than 300mg/m2, the corrosion resistance and processibilities of the resin composition are not improved, whereas when the amount of the
attached coating layer exceeds 1,800mg/m2, an effect on the corrosion
resistance is saturated, and the economical efficiency is low due to the low conductivity and the high manufacturing cost. Also, although the corrosion resistance of the resin film is increasingly improved as the drying temperature increases, it is reasonable to satisfy clients' requirements for products when the products are manufactured within the drying temperature of 80 to 200▒.
Also, a metal plate that is applicable in the present invention includes, but is not particularly limited to, a galvanized steel sheet, an electrogalvanized steel sheet such as a zinc/nickel-coated steel sheet, a zinc/iron-coated steel sheet, a zinc/titanium-coated steel sheet, a zinc/magnesium-coated steel sheet, a zinc/manganese-coated steel sheet, a zinc/aluminized-steel sheet and the like, a hot-dip-coated steel sheet, an aluminized steel sheet, a coated steel sheet whose coating layer includes different metals or impurities, for example, cobalt, molybdenum, tungsten, nickel, titanium, aluminum, manganese, iron, magnesium, tin, copper, etc., a coated steel sheet having a coating layer dispersed with inorganic substances such as silica and alumina, an aluminum alloy plate including silicon, copper, magnesium, iron, manganese, titanium, zinc, etc., a phosphate-coated galvanized steel sheet, a cold-rolled steel sheet, a hot-rolled steel sheet, etc. Also, a multilayer coating layer in which at least two coated steel sheets are sequentially stacked is applicable in the present invention.
[Mode for Invention]
Hereinafter, the present invention will be described in more detail referring to the exemplary embodiments of the present invention. However, it should be understood that the description proposed herein is just a
preferable example for the purpose of illustrations only, not intended to limit the scope of the invention.
Examples 1-13 and Comparative examples 1-14
1-1. Preparation of Resin Composition
A urethane resin having a number-average molecular weight of 100,000, composed of isoprene diisocyanate, adipic acid and polyhydric alcohol monomers, was prepared as the soft urethane resin monomer. Also, an urethane resin having a number-average molecular weight of 1,000,000 was prepared from p-phenylene diisocyanate and polycarbonatepolyol monomers as the hard urethane resin monomer. Ti organic oxide (Tyzor TE® titanium(IV) (triethanolaminato) isopropoxide) commercially available from Dupont was used as the corrosion-resistant curing agent. Aluminum dihydrogen phosphate commercially available from Junsei was used as the aluminum phosphate. In this case, contents of the soft urethane resin, the hard urethane resin, the Ti-based corrosion-resistant curing agent, the aluminum dihydrogen phosphate and other additives were adjusted to content levels as listed in Table 1, and the quality characteristics of the resin composition were evaluated.
As the additives, 10 % by weight of colloidal silica (Snowtex-40 commercially available from Nissan Chemical), 0.5 % by weight of a siloxane wetting agent (EFKA 3580 from Ciba), 1.2 % by weight of a silane cross-linking agent (Aldrich, 3-glycidoxypropyl trimethoxy silane), 2.5 % by weight of an amine curing agent (Cymel 303 from Cytec) , and 1.5 % by weight of a polyethylene lubricant (Lanco PE 1500 from Noveon) were added in bulk. A solid concentration of the resin composition for surface-treating a steel sheet was adjusted to a concentration level of approximately 15 % by weight. For reference, water was used as the major component except for the solid
content, and approximately 3 % by weight of ethanol and approximately 0.5 %
by weight of an amine compound were added as the alcohol solvent and the aqueous alkaline solution, respectively.
1-2. Manufacture of Coated Steel Sheet
1) Test specimen: An electrogalvanized steel sheet (EG) having an
attachment amount of 20g/mI (based on a single surface of the steel sheet)
was used as a base steel sheet to be coated with the resin composition for surface-treating a steel sheet.
2) Coating method: A test sample was coated with a resin composition
using a continuous roll coating simulator, and dried under PMT conditions as
listed in Table 1. The attachment amount of a film was 1,000 mg/m2.
1-3. Performance Evaluation
(1) Processibilities: A coefficient of friction was measured using a
draw bead friction tester (a load of 1,000 kgf, a speed of 1,000 mm/min, and a
distance of 100 mm) , and a resin film of the test specimen was evaluated
based on the following damage levels when the resin film of the test specimen was scratched on a bead surface of the draw bead friction tester, o: Damaged area of less than 5%
□ : Damaged area of 5 to 10%
x : Damaged area of greater than 10%
(2) Corrosion resistance: A salt spray test on a test specimen was
performed for 96 hours according to JIS-Z2371 standard, and the test specimen
was evaluated based on the following corrosion levels.
o : White rust of less than 5%
□ : White rust of 5 to 20%
x : White rust of greater than 20%
(3) Conductivity: a surface of a test specimen coated with a resin film
was measured for conductivity using a surface resistance meter (Loresta-GP) ,
and evaluated based on the following surface resistance levels.
o : Surface resistance of less than lmΩ ▒ : Surface resistance of in or less
x : Surface resistance of more than 1Ω ( very poor in conductivity or weldability)
(4) Alkaline resistance: A test specimen was dipped into an alkali
solution (Gardoclean 4292L, pH 12) at 50▒ for 5 minutes, and washed with
water. Then, the test specimen was observed with the naked eye for changes in
color and peeling of a resin coating layer, and evaluated based on the
following levels.
o : No peel, and color change of less than 2.0 ▒ : No peel, and color change of 2.0 or more x : Peels
(5) Water resistance: A test specimen was dipped into water for 30
minutes, and rubbed 30 times with a finger. Then, the changes in color of the
test specimen was measured and evaluated based on the following color change
levels.
o : Color change of less than 1.0 ▒ : Color change of 1.0 or more x : Peels
(6) Solution stability: 100 g of the resin composition for surface-
treating a steel sheet was kept at 50▒ for 10 days in an oven, and the
precipitation, gelation and separation of the resin composition were
evaluated, as follows.
o : Not precipitated, gelled or separated
▒ : Either slightly precipitated, gelled or separated
x : Some precipitated, gelled and/or separated
The evaluation results are listed in the following Table 1.
[Table 1]
(Table Removed)
Examples 14-19 and Comparative examples15-17 2-1. Manufacture of Coated Steel Sheet
1) Test specimen: An electrogalvanized steel sheet (EG) having an
attachment amount of 20g/m2 (based on a single surface of the steel sheet) was used as a base steel sheet to be coated with the resin composition for surface-treating a steel sheet.
2) Coating method: A test specimen was dipped into a pretreatment
solution for 3 seconds and dried under PMT conditions as listed in Table 2.
Also, a resin composition of Example was prepared according to the components and their contents of Example 4 as listed in Table 1, and a steel sheet was coated with the resin composition using a continuous roll coating simulator, and dried at an amount of the attached resin under PMT conditions as listed in the following Table 2.
2-2. Performance Evaluation
The processibilities, conductivity and corrosion resistance of the test specimen prepared under the above-mentioned conditions were evaluated using the evaluation method as listed in the Table 1.
2-3. Evaluation Results
The performance of the resin composition for surface-treating a steel sheet was measured under the above-mentioned conditions, and listed in the following Table 2 .
[Table 2]
(Table Removed)
As listed in the Table 2, it was revealed that the surface-treated steel sheets of Examples 14 to 19 according to one exemplary embodiment of the present invention show their excellent quality characteristics, but the surface-treated steel sheets of Comparative examples 17 to 19 show their degraded characteristics.

[We claim:—]
[Claim 1] A resin composition for surface-treating a steel sheet, comprising:
a urethane resin mixture of soft urethane resin and hard urethane resin;
a Ti or Zr-based organic oxide;
at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and
a solvent.
[Claim 2] A resin composition for surface-treating a steel sheet, comprising:
a urethane resin mixture of soft urethane resin and hard urethane resin;
a Ti or Zr-based organic oxide;
at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and
a solvent,
wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition.
[ Claim 3] The resin composition of claim 2, wherein the urethane resin mixture comprises 5 to 95 % by weight of a soft urethane resin and 5 to 95 %
by weight of a hard urethane resin, based on the total solid content of the urethane resin mixture.
[Claim 4] The resin composition of any one of claims 1 to 3, wherein the soft urethane resin comprises polyurethane prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, or polyurethane prepared from acryl polyol and pooyisocyanate.
[Claim 5l The resin composition of claim 4, wherein the polyhydric alcohol is selected from the group consisting of acrylpolyol, polyesterpolyol, polyetherpolyol, polyolefin polyol, and mixtures thereof.
[Claim 6] The resin composition of claim 4, wherein the soft urethane resin has a number-average molecular weight of 5,000 to 300,000. [Claim 7] The resin composition of any one of claims 1 to 3, wherein the hard
urethane resin is selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond.
[Claim 8] The resin composition of claim 7, wherein the hard urethane resin has a number-average molecular weight of 200,000 to 2,000,000.
[Claim 9] The resin composition of claim 7, wherein the hard urethane resin has a Shore A hardness of 40 to 90.
[Claim 10] The resin composition of claim 7, wherein the diisocyanate is p-phenylene diisocyanate. [Claim 11] The resin composition of any one of claims 1 to 3, wherein the Ti
or Zr-based organic oxide is selected from the group consisting of titanium diisopropoxide bis(acetylacetonate) , titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and mixtures thereof.
[Claim 12] The resin composition of any one of claims 1 to 3, wherein the solvent is water.
[claim 13] The resin composition of claim 12, wherein the solvent further comprises an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof.
[ Claim 14 ] The resin composition of any one of claims 1 to 3, further comprising at least one additive selected from the group consisting of a wetting agent, a cross-linking agent, a lubricant and an antifoaming agent.
[Claim 15] A method for surface-treating a steel sheet, comprising: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a
range of 300 to 1,800 mg/m2.
[Claim 16] A method for surface-treating a steel sheet, comprising: coating a steel sheet with a resin composition comprising a urethane resin mixture of soft urethane resin and hard urethane resin, a Ti or Zr-based organic oxide, at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate, and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a
range of 300 to 1,800 mg/m2,
wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition.
[ Claim 17 ] The method of claim 16, wherein the urethane resin mixture
comprises 5 to 95 % by weight of a soft urethane resin and 5 to 95 % by weight of a hard urethane resin, based on the total solid content of the urethane resin mixture.
[claim 18] The method of any one of claims 15 to 17, further comprising: drying the resin composition-coated steel sheet at a peak metal temperature (PMT) of 80 to 200▒.
[Claim 19] The method of any one of claims 15 to 17, wherein the steel sheet is selected from the group consisting of a galvanized steel sheet, an electrogalvanized steel sheet, a galvannealed steel sheet, an aluminized steel sheet, a coated steel sheet whose coating layer includes cobalt,
molybdenum, tungsten, nickel, titanium, aluminum, manganese, iron, magnesium, tin, copper, and mixtures thereof, an aluminum alloy plate including silicon, copper, magnesium, iron, manganese, titanium, zinc, and mixtures thereof, a phosphate-coated galvanized steel sheet, a cold-rolled steel sheet, and a hot-rolled steel sheet.
[Claim 20] The method of any one of claims 15 to 17, wherein the soft
urethane resin has a number-average molecular weight of 5,000 to 300,000, and comprises polyurethane prepared from isoprene diisocyanate, adipic acid and polyhydric alcohol, or polyurethane prepared from acryl polyol and pooyisocyanate.
[Claim 21] The method of any one of claims 15 to 17, wherein the hard urethane resin has a number-average molecular weight of 200,000 to 2,000,000, and is selected from the group consisting of a polyurethane resin prepared from polycaprolactone polyol or polycarbonate polyol and diisocyanate, a polyurethane resin prepared from 4,4'-bis(ω-hydroxyalkyleneoxy)biphenyl and methyl-2,6-diisocyanatehexanoate, and a polyurethane resin having an acetal bond.
[Claim 22] The method of claim 21, wherein the hard urethane resin has a Shore A hardness of 40 to 90.
[claim 23] The method of any one of claims 15 to 17, wherein the Ti or Zr-based organic oxide is selected from the group consisting of titanium diisopropoxide bis (acetylacetonate) , titanium orthoester, titanium (IV) butoxide, titanium (IV) (triethanolaminato) isopropoxide, tetrakis (triethanolaminato) zirconium (IV), titanium (IV) 2-ethylhexoxide, titanium (IV) isopropoxide, zirconium (IV) bis(diethyl citrato)-dipropoxide, and
mixtures thereof.
[Claim 24] The method of any one of claims 15 to 17, wherein the solvent is water.
[claim 25] The method of claim 24, wherein the solvent further comprises an alcohol solvent selected from the group consisting of ethanol, methanol, propanol, isopropanol and glycerol, an aqueous alkaline solution selected from the group consisting of aminecompound, N-methylpyrrolidone, sodium hydroxide, potassium hydroxide, sodium carbonate and ammonium hydroxide, and mixtures thereof.
[Claim 26 1 A surface-treated steel sheet comprising a steel sheet; and a resin coating layer, wherein the resin coating layer is prepared by coating the steel sheet with a resin composition comprising a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel sheet, an amount of the resin composition attached to the steel sheet is in a
range of 300 to 1,800 mg/m2.
[claim 27 ] A surface-treated steel sheet comprising a steel sheet; and a resin coating layer, wherein the resin coating layer is prepared by coating the steel sheet with a resin composition comprising a mixture of soft urethane resin and hard urethane resin; a Ti or Zr-based organic oxide; at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate; and a solvent, wherein, after the drying of the steel
sheet, an amount of the resin composition attached to the steel sheet is in a
range of 300 to 1,800 mg/m2,
wherein the urethane resin mixture is present in a content of 10 to 90 % by weight, the Ti or Zr-based organic oxide is present in a content of 1 to 20 % by weight, and the at least one compound selected from the group consisting of monoaluminum phosphate, aluminum dihydrogen phosphate, monozinc phosphate and hydrated manganese phosphate is present in a content of 0.1 to 10.0 % by weight, based on the total solid content of the resin composition, and
the soft urethane resin is present in a content of 5 to 95 % by weight, and the hard urethane resin is present in a content of 5 to 95 % by weight , based on the total amount of the urethane resin mixture.
[ Claim 28 ] A resin composition for surface-treating a steel sheet
substantially as herein described with reference to the foregoing description, tables, examples and the accompanying drawings.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=urk/3L/ZhVuLUaSBoQBGsw==&loc=+mN2fYxnTC4l0fUd8W4CAA==

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Patent Number

271526

Indian Patent Application Number

2527/DEL/2008

PG Journal Number

09/2016

Publication Date

26-Feb-2016

Grant Date

24-Feb-2016

Date of Filing

06-Nov-2008

Name of Patentee

POSCO

Applicant Address

1 Koedong-dong Nam-ku Pohang Kyungsangbook-do 790-300 Republic of Korea

Inventors:

#	Inventor's Name	Inventor's Address
1	CHO Jae Dong	C/o Gwangyang Iron & Steel Works 700 Geumho-dong Gwangyang Cheonlanam-do Republic of Korea
2	JE Min Gyu	C/o Gwangyang Iron & Steel Works 700 Geumho-dong Gwangyang Cheonlanam-do Republic of Korea
3	OH Jong Gi	C/o Gwangyang Iron & Steel Works 700 Geumho-dong Gwangyang Cheonlanam-do Republic of Korea
4	NOH Beom Sick	C/o Gwangyang Iron & Steel Works 700 Geumho-dong Gwangyang Cheonlanam-do Republic of Korea

PCT International Classification Number

C23C22/05

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10-2007-0115600	2008-11-06	Republic of Korea