Title of Invention

"A BIAXIALLY ORIENTED TRANSPARENT HOLOGRAPHIC FILM"

Abstract

An improved biaxially oriented transparent holographic film comprising an upper skin layer of high crystalline polypropylene, a core layer of polypropylene polymer sandwiched between the said upper and lower skin layers and a lower skin layer of high crystalline polypropylene having antiblocking agents and additionally polar polymers with silcone resins. The said film is coextruded and oriented along its one axis by applying tension and anealed while maintaining tension. A diffraction pattern into a surface of the film is embossed and the film is cooled.

Full Text

FIELD OF THE INVENTION The present invention relates to a novel bioxially oriented, transparent polypropylene holofilm consisting of polypropylene polymer and the process for the manufacture of the said biaxially oriented, transparent holofilm to be used for packaging to avoid the piracy of the said package. The film presents a magnificient colour rainbow under any form of light, not only attracting immediate attention but also complimenting the product. Other than packaging application the film can also be used as labels. More particularly, the subject invention relates to an improved biaxially oriented multilayer holofilm with unique property of being directly embossable and also suitable for mechanical engineering followed by matelization. The object of the invention is to provide an improved biaxially oriented holofilm having excellent optical properties, enhanced durability and dimentional stability. Another object of the invention is to provide an improved biaxially oriented holofilm having polar polymers and excellent hot slip properties. Yet another object of the invention is to provide a novel process for manufacturing a biaxially oriented holofilm comprising co-extruding at least one polypropylene layer and having a third layer containing polar polymers. BACKGROUND OF THE INVENTION Conventionally transparent oriented polyolefin films are used widely as packaging materials. Since the film have excellent optical properties, they are used in large quantities in graphic industries for lamination namely solvent lamination, water based lamination, dry lamination etc. of printed products. In order to avoid counterfiting, imprinting of typical image in packaging structure was introduced. The film as known conventionally for holography are polyester or BOPP based. These films are provided with specialty coating so that the film can be engraved and metallized for holographic effect. Generally the embossing is done in a two-stage process, namely, coating and embossing. Coating is done to increase or facilitate the process of embossing. Nature of coating is secretly held and belongs to the family of acrylics. After coating, film is passed through an air oven to expel solvent from coating. Schematic description of the process. (Formula Removed) Embossing is done on the coated side. Embossing unit consists of a hot drum with the required pattern engraved onto the surface, a nip roll and a cooling drum. Film from oven is passed between hot drum and the nip roll. Typically, temperatures are kept between 100 and 150° C and the pressure is around 2-3 kgs / sq.cm. Because of temperature and pressure, engraved pattern is transferred on the film surface and it acts like a grating. That is, lines embossed on the surface start diffracting, refracting light with multiple reflections. As soon as embossing is done, film is cooled so that no post-embossing distortion takes place. This gives a rainbow effect. This effect becomes exponentially stronger by subsequent metallization. US patent 5,164,227 describes thermoplastic coating of sheets or paper before embossing to give good embossing effect. Therefore, quality of coating directly influences quality of embossing. This suffers from the draw back that if coating thickness variation is more, then improper embossing is resulted. US patent 5,932,150 depicts the process of coating oriented film to effect embossing at lower temperature. Since coating is done off-line, the ultimate embossing operation is seriously affected by this offline process quality. The other prior arts include embossing uncoated, oriented film at higher temperature. But such a process gives unfavorable results like dimensional distortion of oriented films. To eliminate the above drawbacks a novel process has been involved by which a biaxially oriented transparent polypropylene film is prepared which has excellent optical properties and an improved surface to enable embossing without coating. In order to achieve the desired transparency and surface the biaxially oriented holofilm of the present invention is made from a polypropylene having a crystallinity more than 65% and isotacticity more than 95%. Polyolefines are usually stabilized against thermal decomposition during their production and processing to for films as it involves high temperatures and shear. Examples of preferred compounds with a stabilizing effect and their combination thereof for ethylene, propylene and other α-olefine polymers, are described in EP-A-27 586 and EP-A-263 882. With respect to the layer concerned, amount of stabilizers needed is generally 0.1 to 2.0% by weight. The film needs good hot slip properties while running over the hot rollers. The present film contains silicone resins for providing good hot slip properties. The film also needs polar characteristics during embossing operation, therefore polar polymers are added to the film for achieving desired property of embossing. Polarity can be introduced by corona treatment of the film surface. But this supports from the fact that embossing is hampered due to physical and chemical modification of film surface. Corona treatment gives stickiness during mechanical engraving and this is undesirable to the customer. Therefore the objective of the present invention is to provide a biaxially oriented polypropylene film which process permanent polarity for good embossing as well as hot ship properties. In one embodiment the invention resides in a biaxially oriented transparent holographic film having an upper skin layer of high crystalline polypropylene having 5-25% of total film thickness, lower slow layer of copolymers having 5-25% of total film thickness and a core layer of polypropylene polymer sandwiched between the said upper and lower skin layer having 50-90 of the total film thickness wherein the skin layers contain 1 to 20% of antiblocking agents. Another embodiment of the invention resides in a process for manufacturing a biaxially oriented transparent holofilm comprising co-extruding at least one polypropylene layer with high crystallinity more than 65% and isotacticity more than 95% Rochwell hardness measured accordingly to ASTMD 785 in the unit of R Scale is more than 90. The core layer is of polypropylene. The biaxial orientation of polypropylene increases its stiffness and enhances both its optical and other physical properties such as tensile strength, tear strength and other mechanical properties. In order to achieve the permanent polarity for the pupose of embossing polar polymers are added in the lower skin of the film. These Polar polymers help good metal adhesion without affecting embossing. Polar polymers like acrylic modified or meleic anyhydride modified polypropylene are used. The film also contains silicone resins for good hot slip properties. Addition level of such resins are may vary from. 0.25 to 1.25%, preferably 0.5 to 1.0% of the lower stain. The polar polymers are added in the lower layer in the range of 12-13%. In the process for manufacture a biaxially oriented at least three layered composite film consists of polypropylene core and skin layer with polar polymers and silicone layers are co extruded to obtain film. The biaxially oriented film of the subject invention is much superior as compared to the conventionally available films and is having better quality of use in packaging. Accordingly this invention here, depicts an oriented polyolefin film, preferably, an oriented polypropylene (BOPP) film, hereinafter be referred to as BOPP film, which has excellent optical hot slip properties and a modified surface to enable embossing without coating. In the preferred embodiment, the film is a multi layer, precisely three layered, transparent consisting of polypropylene polymer. Out of the three layers, core layer accounts for 50-90 % of the total thickness, preferably 75-85%. Minor layers are called skin layers, namely skin I or upper layer, comprising 5 to 25% of the total thickness, preferably 5-12.5% of total film thickness and skin II or the lower layer, comprising 5 to 25% of the total thickness, preferably 10 -12.5% of total film thickness. In a further preferred embodiment, core layer consists, predominantly of polypropylene polymer with melt flow index of 0.2 to 7 g/10 min., preferably 1 to 6 g/10 min and more preferably 2.5 to 4.5 g/10 min. The selected polypropylene polymer for core layer has a crystallinity of more than 60% and isotactic index of more than 80%, preferably more than 90%. Melting point of the subject polypropylene is not less than 160°C. Polypropylene selected for core layer is a commonly available commercial grade such as PD 382 from Montell for an example. Skin I, the upper layer, comprising 5 to 25% of the total thickness, preferably 5-12.5% of total film thickness, is made of high crystalline polypropylene with crystallinity of at least 60%, preferably, more than 65 % and isotactic index of 90, preferably more than 95%. Rockwell hardness, measured according to ASTM D 785 in the unit of R scale, is more than 75, preferably 85 and more preferably more than 90. In a further modified version, the said skin may also contain copolymers like ethylene-propylene random copolymer or propylene-alpha olefin copolymer or ethylene-alpha olefin copolymer or an appropriate blend of these copolymers. Skin I also contains anti blocking agents that are either spherical, organic compounds such as polymethyl methacrylate, Nylon, Polyisobutyl methacrylate, to name a few or inorganic molecules like silica, silicates, etc. These antiblocking agents may be present in the range of 0.1 to 2.0%, preferably 0.2 to 1.0%. Skin II, lower layer, comprising 5 to 25% of the total thickness, preferably 10-12.5% of total film thickness. In a preferred embodiment, said skin comprises copolymers like ethylene-propylene random copolymer or propylene-alpha olefin copolymer or ethylene-alpha olefin copolymer or an appropriate blend of these copolymers or blend of hydrocarbon resins with polypropylene. Skin II also contains anti blocking agents that are either spherical, organic compounds such as polymethyl methacrylate, Nylon, Polyisobutyl methacrylate, to name a few or inorganic molecules like silica, silicates, etc. These antiblocking agents may be present in the range of 0.1 to 2.0%, preferably 0.2 to 1.0%. In a preferred embodiment, skin II contains silicone resins for providing good hot slip properties while running over the hot rollers. This may be added in the range of 0.25% to 1.25%, preferably, 0.5 to 1.0% of skin II. In a more preferred embodiment, skin II also contains polar polymers like acrylic modified or maleic anhydride modified polypropylene to give permanent polarity. Polarity is also introduced by corona treatment of the film surface. But, this suffers from the fact that embossing is hampered due to the physical and chemical modifications of film surface. Permanent polarity induced by way of adding polar polymers help good metal adhesion without affecting embossing. The films according to the invention may be produced by monoaxial orientation or preferably biaxial orientation both by double bubble process and sequential stretching on a tenter frame followed by melt extrusion. Three melt streams from three extruders, namely main extruder giving the core layer, satellite I for skin I and satellite II for skin II, are pressed together in the slit die and are extruded as a single sheet. This is quenched on a chill roll and/or water bath and/or a combination of both and is stretched at least mono axially, preferably biaxially. In the course, the film is stretched in the machine direction or longitudinally at a ratio of 4:1 to 7:1, preferably 5:1 to 6:1, at a temperature of 110 to 150°C, preferably 120 to 145°C. This monoaxially oriented polymeric film is reheated and stretched in the cross direction or transverse direction with a stretch ratio of 8:1 to 12:1, preferably 9:1 to 11:1. Transverse orientation is carried out in a tenter frame consisting of numerous clips on an endless metallic belt. Tenter frame is divided in to three regions, viz, preheating, stretching and annealing region. Stretching is effected at a temperature range of 130 to 190°C, preferably 145 to 170°C. So produced biaxially oriented polypropylene film is heat set or annealed or thermally fixed at a temperature 1 to 35°C below transverse stretching temperature. At the end of this operation, final film thickness is 8 to 30µ, preferably 10 to 25µ. Before taking the film on winder, edges of the film carried by the clips of transverse direction orienter is trimmed and recycled. The film so produced is then oriented along a first axis by passing the film through a series of powered calender rollers which tension the film in the longitudinal direction. The film is the orientd along a second axis, normal to the first axis, by clamping the edges of the film in a tenter frame which tensions the film in the transverse direction. The temperature of the film is raised to a desired annealing temperature above room temperature and a diffraction pattern into a surface of the film is embossed while the film is continuously maintained at a temperature above room temperature at desired annealing temperature and under tension along at least one of said first and second axis. The film is cooled to room temperature and a metallic layer is deposited over the diffraction pattern embossed into the surface of the film. A more complete appreciation of the invention and the attendant advantages thereof will be more clearly understood by reference to the accompanying drawings, which are for illustrative purposes, hence the same should not be construed to restrict the scope of the invention. Accordingly the present invention relates to a biaxially oriented transparent holographic film comprising: - an upper skin layer of high crystalline polypropylene of at least 60% crystallinity having 5 to 25% of the total film thickness; - a core layer of polypropylene polymer sandwiched between the said upper and lower skin layers being more than 80% of the total film thickness; - a lower skin layer of copolymers selected from propylene-ethylene random copolymers, propylene-α-olefin copolymers or ethylene-alpha olefin copolymer or an appropriate blend thereof having 5 to 25% of the total film thickness, wherein the said upper skin and lower skin layers contain antiblocking agents in 0.2 - 1.0% while the lower skin layer contains polar polymers as herein described in the range of 12-13% and additionally with silicone resins in the range of 0.25% to 1.25%. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig. 1 depicts a general lay out of the manufacture of biaxially oriented polypropylene (BOPP) film on a tenter frame. Fig. 2 depicts the process of embossing on the film. DETAILED DESCRIPTION OF THE INVENTION As shown in Fig. 1 extrusion of the three layer is done through three separate extruders 1, 2 and 3 on a tenter frame followed by melt extrusion. Three melt streams from three extruders, namely main extruder giving the core layer, satellite I for skin I and satellite II for skin II, are pressed together in the slit die (5) and are extruded as a single sheet. The said composite sheet after cooling is fed into an apparatus adapted for monoaxial orientation. The film is quenched on a chill roll and/or water bath and/or a combination of the both and is stretched at least mono axially, preferably biaxially. In the course, the film is stretched in the machine direction of longitudinally at a ratio of 4:1 to 7:1, preferably 5:1 to 6:1, at a temperature of 110 to 150°C, preferably 120 to 145°C. This monoaxially oriented polymeric film is subjected to heat treatment and stretched in the cross direction or transverse direction with a stretch ratio of 8:1 to 12:1, preferably 9:1 to 11:1. This is effected at a temperature range of 130 to 190°C, preferably 145 to 170°C. So produced baixially oriented polypropylene film is heat set or annealed or thermally fixed at a temperature 1 to 35°C below transverse stretching temperature. As shown in Fig. 2 the film is passed through film unwind (1). Hot drum(2) is provided with the required pattern engraved onto the surface. A nip roll (3) is placed adjacent to the hot roller. Film from oven is passed between hot drum (2) and the nip roll (3). Because of temperature and pressure, engraved pattern is transferred on the film surface. The film is then passed through the idler roller (4) and cooled so that no post-embossing distortion takes place. A metallic layer is deposited over the diffracted pattern embossed into the surface of the film. A biaxially oriented polypropylene multilayer holo film embodiment of the present invention is illustrated by the following examples: Example 1 A biaxially oriented polypropylene multi layer film was produced by means of the coextrusion process as described elsewhere, with the preferred stretching ratios (machine direction 5:1 and transverse direction 9.5:1) at an average machine direction stretching temperature of 135°C and at an average transverse direction stretching temperature of 165°C. After stretching in the transverse direction, film is annealed at a temperature range of 150 to 160 degree C. This facilitates crystallization of polypropylene, thereby, tensilization of film. This process is called heat setting, which reduces the tendency of film to shrink under heat application. The external surfaces of the skin layers are corona treated to 44 dyne/cm. The entire film thickness is 20 µ or 80 gauge and its composition is as under (Table Removed) Example 2 A three layer film with a total thickness of 20µ was produced by the process depicted in example I, but the raw material composition was altered as follows 86.86 % by weight of a polypropylene polymer with a density of 0.91 g/cc and a melt flow index of 3 g/10 min at 230°C and at a loading of 2.16 kg as determined by ASTM D 1238 12.58 % by weight A blend of ethylene-propylene random copolymer, propylene-alpha olefin copolymer. longitudinal direction. The film is the orientd along a second axis, normal to the first axis, by clamping the edges of the film in a tenter frame which tensions the film in the transverse direction. The temperature of the film is raised to a desired annealing temperature above room temperature and a diffraction pattern into a surface of the film is embossed while the film is continuously maintained at a temperature above room temperature at desired annealing temperature and under tension along at least one of said first and second axis. The film is cooled to room temperature and a metallic layer is deposited over the diffraction pattern embossed into the surface of the film. A more complete appreciation of the invention and the attendant advantages thereof will be more clearly understood by reference to the accompanying drawings, which are for illustrative purposes, hence the same should not be construed to restrict the scope of the invention. (Table Removed) Example 5 A three layer film with a total thickness of 20µ was produced by the process depicted in example II and the film composition is as stated below 86.86 % by weight of a polypropylene polymer with a density of 0.91 g/cc and a melt flow index of 3 g/10 min at 230°C and at a loading of 2.16 kg as determined by ASTM D 1238 12.72% by weight A blend of ADMER, ethylene-propylene random copolymer, propylene-alpha olefin copolymer. 0.42% by weight Of synthetic silica anti block in the skin layers The properties of the three-layered, biaxially oriented polypropylene films of examples and comparison have been compared and summarized in a table A. Embossing process Embossing of films produced in accordance with the said examples was done at temperatures between 100 and 110 degree C, pressure of 2-3.5 k g/ sq.cm. Embossing was done at a speed of 30-40 ft/min. And, the results have been tabulated below. Table A (Table Removed) P: Poor; G: Good; E: Excellent Haze Haze is the fraction of light that is scattered by angle of more than 2.50 in the medium. Scattering in the film is basically resulted out of particles distributed on the surface and interior of the film such as slip additives, anti blocking agents and impurities. It is also due to surface roughness and interface between core layer and skin layers. The measurement was made according to the ASTM D 1003 test method for % haze, after calibrating the instrument with standard haze samples between 0.3 and 34 % haze. 45° Gloss Gloss is a measure of specular reflection of light from the surface and the successive layers of the film at a specified angle. The gloss measurement was performed following ASTM D 2457. The gloss is in units GE, which are based on Wood's glass standard. The value of the surface gloss should be as high as possible. Blocking Blocking is the tendency of film to stick together when it is in roll form under pressure. Further, as described in earlier, embossing is done at elevated temperatures like 100 - 110 degree C. At this temperature, film doesn't slip properly and as a result film's surface sticks to the hot roller. In order to have good hot slip property, silicone resins are added. Observations were made as: G for Good, P for Poor and E for Excellent. Metal Adhesion Thus embossed film is metallized with aluminium. Metal adhesion with film surface is checked by way of the tape test. That is to say, one end of a pressure sensitive tape is pasted onto the said metallized film surface and then this tape from the other end is pulled away from the film surface. If the metal is transferred to tape, then metal adhesion is poor. While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. The present invention relates to polypropylene holographic film produced by a physical process involving extrusion and biaxial orientation and not a product of any chemical process. The desired properties of the film are due to synergy between various layers of the film. We claim: 1. A biaxially oriented transparent holographic film comprising: - an upper skin layer of high crystalline polypropylene of at least 60% crystallinity having 5 to 25% of the total film thickness; - a core layer of polypropylene polymer sandwiched between the said upper and lower skin layers being more than 80% of the total film thickness; - a lower skin layer of copolymers selected from propylene-ethylene random copolymers, propylene-α-olefin copolymers or ethylene-alpha olefin copolymer or an appropriate blend thereof having 5 to 25% of the total film thickness, wherein the said upper skin and lower skin layers contain antiblocking agents in 0.2 - 1.0% while the lower skin layer contains polar polymers as herein described in the range of 12-13% and additionally with silicone resins in the range of 0.25% to 1.25%. 2. A film as claimed in claim 1, wherein the thickness of upper skin layer is 5-12% of the total thickness. 3. A film as claimed in claim 1, wherein the thickness of lower skin layer is 10- 12.5% of the total thickness. 4. A film as claimed in claim 1, wherein thickness of said core layer is upto 90% of the total thickness. 5. A film as claimed in claim 1, wherein the said antiblocking agents are polymethylene methacrylate, Nylon, Polyisobutyl methacrylate, silica, silicates and/ or a mixture thereof. 6. A film as claimed in claim 1, wherein the said silicone resins are in the range of 0.5-1.0%. 7. A film as claimed in claim 1, wherein the said polar polymers are acrylic modified or maleic anhydride modified polypropylene. 8. A film as claimed in claim 1, wherein at least one skin layer is made of high crystalline polypropylene with a crystallinity of more than 65%. 9. A film as claimed in claim 1, wherein the isotactic index of said high crystalline polypropylene used is 90%, preferably more than 95%. 10. A process for manufacturing a biaxially oriented transparent holographic film as claimed in claim 1 comprising the steps of: - providing a body of thermoplastic film; - orienting the said film along a first axis by passing the film through a series of powered calender rollers which tension the film in the longitudinal direction; - orienting the film along a second axis, normal to the first axis, by clamping the edges of the film in a tenter frame which tensions the film in the transverse direction; - raising the temperature of the film to a desired annealing temperature above room temperature; - continuing to maintain the film at a temperature above room temperature while embossing a diffraction pattern into a surface of the film, the film being continuously maintained at a temperature above room temperature and under tension along at least one of said first and second axes from the time the film temperature is raised to the desired annealing temperature until the diffraction pattern is embossed into the film; - cooling the film to room temperature; and - depositing a metallic layer as herein described over the diffraction pattern embossed into the surface of the film. 11. A biaxially oriented transparent holographic film substantially as herein before described with reference to the accompanying drawings. 12. A process for manufacturing a biaxially oriented transparent holographic film substantially as herein before described with reference to the accompanying drawings.

Documents:

496-del-2001-abstract.pdf

496-del-2001-claims.pdf

496-DEL-2001-Correspondence Others-(26-05-2011).pdf

496-del-2001-correspondence-others.pdf

496-del-2001-correspondence-po.pdf

496-del-2001-description (complete).pdf

496-del-2001-drawings.pdf

496-del-2001-form-1.pdf

496-del-2001-form-19.pdf

496-del-2001-form-2.pdf

496-DEL-2001-Form-27-(26-05-2011).pdf

496-del-2001-form-3.pdf

496-del-2001-form-4.pdf

496-del-2001-form-5.pdf

496-del-2001-gpa.pdf

496-DEL-2001-Petition-137-(26-05-2011).pdf