Title of Invention

DIRECT EMBOSSABLE POLYETHYLENETEREPHTHALATE FILM

Abstract

This invention relates to a mono or co-extruded, coated polyester film that is directly embossable, solvent resistant and exhibits low haze, wherein, the film is a two layered film of AB structure, A being 5-25% of a layer comprising a blend of homopolyesters and copolyesters containing inorganic particles, B being 75-95% homo-polyester containing inorganic particles, the film being longitudinally & transversely stretched, the film optionally containing an antistatic agent, a surface coating, wherein the said coating gets crosslinked to the PET surface during heat setting thereby rendering the film surface susceptible to embossing under pressure and temperature. Further the invention discloses process for the preparation of such films.

Full Text

F0RM2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE SPECIFICATION (See section 10; rule 13) 1. Title of the invention.: Direct Embossable Polyethyleneterephthalate Film 2. Applicant - (a) Garware Polyester Ltd (b) Garware House, 50-A Swami Nityananda Marg, Western Express Highway, Vile Parle, Mumbai 400057, India (c) An Indian Company. The following specification particularly describes the nature of this invention and the manner in which it is to be performed ORIGINAL 317/MUM/2006 Field of the invention This invention relates to a mono or co-extruded, coated polyester film that is directly embossable, solvent resistant and exhibits low haze. Background of the invention The art of producing holograms by embossing on substrates such as polyvinylchloride (PVC), polyethyleneterephthalate (PET), biaxially oriented polypropylene (BOPP), polystyrene (PS), polyamides (PA) such as Nylon or other plastic materials is well documented. Substrates such as BOPP or PET are generally pre-coated with a relatively thick acrylic layer prior to embossing holograms. An off-line process is generally used to coat PET based substrates. Directly embossable solvent resistant films have been a longstanding need of the industry. However production of directly embossable films have eluded film manufacturers as most of the available base materials suffer due to problems of low crystallinity, low density and the ease with which they are heat-sealable. Such heat sealable materials are unsuitable for direct embossing as they stick to the embossing shims during processing thereby negatively impacting the embossed texture and line speeds / productivity. In the case of inline or offline coating of PET film, the thickness deemed necessary to produce embossable holographic substrates are difficult to achieve using conventional film making processes. To achieve thick-coated layer on PET films using conventional film making machines, the line speeds have to be substantially reduced. Further the processing requires higher loads on tenter ovens and recycling of the coated PET film in conventional lines is difficult, or in many cases not commercially feasible. A polyester film before or after metallization is directly embossed with holographic patterns at a relatively slow rate of travel, such as 25-30 feet per minute. The film is softened in order to accept an embossing pattern. However this process suffers from, weaknesses of image distortion due to over softening of the film. To address this shortcoming, the softening temperature needs to be as low as possible to avoid softening of the film. Such films are typically embossed at rates below 50 feet per minute. U. S. Pat. No. 5155604 describes conditions for an offline coating for holographic embossing and use of polysiloxane release agent to emboss the film at relatively high speed. U.S. Pat. No. 3,758,649 describes an apparatus for direct embossing a thermoplastic cast vinyl tape. US Pat. No. 4,734,335 describes biaxially stretched and heatset multilayer embossable film comprising of a polyester core sandwiched between two external layers of another polyester having higher - melting temperature than that 2 of the polyester core. The limitation of this is that the lower melting point of the core negatively impacts the mechanical properties of the film resulting in poor machinability during converting operation such as lamination, metallization and printing. U.S. Pat. No. 4,913,858 describes an offline coating of film for holographic embossing. Offline coating require an additional step of coating operation after the film is produced resulting in extended processing operations and enhanced wastage. U.S. Pat. No. 5164227 discloses a polysiloxane release agent in thermoplastic coating, to increase resistance to sticking at relatively high embossing speeds. However it should be appreciated that addition of a release agent would create reduction of surface energy resulting in poor metal adhesion on the metallized film. US Pat. No. 6,761,958 describes an inline coating for holographic embossing use. This coating lacks solvent resistance, as it is not cross-linked. Summary of the invention The main object of the invention is to provide a direct embossable coated PET film with low heat sealability, low haze and solvent resistance, wherein, the film is longitudinally & transversely stretched and the coating getting crosslinked to the PET surface during the heat setting process thereby rendering the film surface susceptible to embossing under pressure and wide range of temperatures. Another object of the invention is to provide a process for the preparation of the said coated film at high speeds at the convertor's end with minimum wastage. It is yet another object of the invention to provide the said crosslinked coated monoextruded or coextruded polyethyleneterephthalate (PET), which has high solvent resistance without sticking to the embossing shim at relatively high embossing speeds. Detailed description of the invention The process of producing a direct embossable PET film involves a novel inline surface coating on a low haze polyester film. A polyester base film comprises a coextruded film with AB structure wherein the layer "B" is a homopolymer and layer "A" is a copolymer of PET or blend of homopolymer and copolymer wherein "A" is 5-25% and "B" is 75-95%. The homopolymer "B" and a copolymer of PET or blend of homopolymer and copolymer "A" are melted and the molten polymers are filtered prior to co-extrusion to form a continuous stream of molten polymer in a feed block assembly and die. The, co-extruded layer is quenched onto a cooled rotating steel drum to produce an amorphous film which is then oriented in the forward or 3 machine direction, through a set of heated rollers further treating either one or both the surfaces using corona treaters. In the case of inline coating of the film, the PET film is preferably treated to enhance adhesion of coatings to the PET substrate(s) comprising the PET film. The coating is preferably carried out on the layer A. Surface coating of the uniaxially oriented polyester film may be achieved by roll coating, gravure coating, air knife coating, rod coating and their like, the preferable one being gravure and rod coating. In the case of rod coating, thickness variations of the coating is easily achieved. Further it is possible to achieve differential coatings on two sides of the film to have one side embossable and the other side with a coating for print adhesion using a two-side rod coater. The coating liquid is preferably 1 to 20 g, especially 2 to 12 g per m2 of the running film to achieve a coating thickness of 0.005 to 3 micron, preferably 0.01 to 1 micron. The coating material is selected from a group of crossinkable polymers such as polystyrene-acrylic emulsions, polyester dispersion, methamethacrylate-acrylic emulsions and PU dispersions. The film may also be in-line coated with antistatic agents, anti-blocking agents, UV agents to impart specific properties such as reduced static charge, reduced coefficient of friction and have protection from UV light. After coating the mono-extruded or co-extruded film, the film is drawn side ways, or transverse or in cross machine direction to produce a biaxially oriented crosslinked coated film followed by winding on jumbo rolls. The co-extrusion is done at 250°C to 275°C. The group of hot rollers heated to 80°C to 120°C. Stretching in the longitudinal direction is done at a draw ratio of 2.5-7 preferably 3 to 3.5 and cooling the stretched film is done on a group of rollers at 20-50°C. The film after coating is subjected to stretching in the transverse direction at a draw ratio of not more than 2.5 to 7 preferably 3 to 5.5 at - 85 °C -90°C. The film is heat set between 200-230°C followed by winding. The film may contain regrind of 0-50%. The PET film has a thickness of about 8 microns to about 300 microns. Films produced by this method can be directly embossed for holographic applications without the need for a secondary coating step by hologram manufactures. Homo Polyesters and copolyesters may be obtained by transesterification or direct esterification by known methods as is described in D.A.Schiraldi; " New 4 Poly(Ethylene Terephthalate) copolymers" from the book "Modern Polyesters:chemistry and Technology of polyesters and copolyesters" Edited by John Scheirs and Timothy E.Long, pp.245-262. John Wiley & Sons, 2003. A melted slurry of diol or substituted diol and purified dibasic acid or with substituted diacid or with esters of diacids is heated, in the presence of a esterification catalyst, and water / methanol & excess diol are removed under vacuum leaving a residual melt of the polyester which is discharged via strand die into a cooling trough, pelletized, and then further dried to remove residual moisture. The inorganic particles slurry in diol is added prior to polycondensation step. Polyesters such as dimethyl terephthalate is preferred, more specifically polyethylene terephthalate, polybutylene terephthalate, polycyclohexane dimethanol terephthalate, polyethylene alpha beta-bis (2-chloro or 2-methoxyphenoxy) ethane - 4,4" dicarboxylate, polyethylene (tere/iso/ortho) phthalate including those produced by using more than one dibasic acid selected from terephthalic acid, isophthalic acid, adipic acid, orthophthalic acid, sebacic acid, naphthalene dicarboxylic acid, azalaic acid and the like and more than one diol selected form ethylene glycol, diethylene glycol, triethylene glycol, butane diol, neopentyl glycol, cyclohexane dimethanol and the like. The dicarboxylic esters are selected from dimethyl terephthalate, dimethyl isophthalate, dimethyle sebacate, dimethyl adipate, naphthalene dicarboxylate and their like, Inorganic particles such as silicon dioxide, calcium carbonate, talc, kaolin or mixture of thereof are optionally added prior to polycondensation stage. Inorganic particles are selected from particle sizes of 1 to 5 u preferably 2 to 4 u and are added in amounts 100 ppm -1000 ppm, preferably 300 to 500 ppm. The inorganic particles are made into dispersion in a carrier liquid such as mono-ethylene glycol or optionally added into master batches with any of the polyester. Homo polyester such as polyethylene terephthalate for the purposes of this invention was prepared using dimethyl terephthalate or purified terephthalic acid and mono ethylene glycol in presence of transesterification catalyst manganese acetate and polycondensation catalyst Sb2 03 at ~140-290°C and at pressures up to 1 mm. A co-polyester such as amorphous polyethylene terephthalate for the purposes of this was obtained by transesterification of mixture of Mono ethylene glycol, Di ethylene glycol, 1,4 cyclo hexane dimethanol and dimethyl terephthalate in the presence of preferably Manganese acetate catalyst at 140-230°C, The polycondensation reaction was carried out preferably in presence of Sb2O2 catalyst and triphenyl phosphate heat stabilizer at 260-290°C up to 1 mm Hg pressure. The base material for the film is selected from those preferably having intrinsic viscosity of 0.60 to 1.20 dl/g. One may also use a mixture of polyesters so long the polyesters used have intrinsic viscosity within the said range. 5 Characterisation of raw materials and produced films: The coated films are evaluated for embossing on an embossing machine by placing the sample on a black background to enhance the visibility of the embossed image and embossing was rated as: Excellent=Bright colors viewed from many angles with no unembossed areas. Good=Colors not as robust from different angles. Fair=Colors not as bright. Poor=Colors dull with unembossed areas. Haze of the film was measured in Haze meter by using ASTM-D-1003 standards. In the embossing machine, the film is preheated by using a heated roll and then the film comes in contact with shim under pressure for holographic impressions. The temperature at which the film sticks to the shim is called max temperature. Solvent resistance is measured by using solvent acetone. The film is immersed in the solvent for 24 hours. The appearance of the film is observed and evaluated based on the following criteria. 0: The appearance of the film remains unchanged visually. A : The appearance of the film is slightly whitened visually. X: There is a visually marked changed such as whitening or peeling in the appearance of the film. EXAMPLES 1) Preparation of the Homo polyester Polyethylene terephthalate was obtained by transesterification of mono ethylene glycol (11.5Kg) and dimethyl terephthalate(20 Kg). A transesterification catalyst such as manganese acetate 0.04% based on DMT was added. After transesterification at 140-230°C, the product bishydroxyethyl terephthalate was subjected to polycondensation in presence of 0.04% Sb2O2 catalyst and 0.07% triphenyl phosphate at 260-290°C by gradually decreasing the pressure from 760 to 2) Preparation of the Amorphous polyester. Amorphous Polyethylene terephthalate or co-polyester was obtained by transesterification of mixture of mono ethylene glycol (14.5 Kg), di ethylene glycol (0.5 Kg) and 1,4 cyclo hexane dimethanol (4.4 Kg) and dimethyl terephthalate (23 Kg). A transesterification catalyst such as manganese acetate 0.04% based 6 on DMT was added. After transesterification reaction at 140-230°C, the product was subjected to polycondensation in presence of 0.04% Sb2O2 catalyst and 0.07% triphenyl phosphate at 260-290°C by gradually decreasing the pressure from 760 to 3) Preparation of in-line coating formulations : a) Control Non-Crosslinkable Coating solution #1 Styrene acrylic emulsion 49.0 Parts Acetylenic Surfactant 0.01 Parts Propylene glycol phenyl ether 1.2 Parts Deionized Water 49.0 Parts b) Coating solution #2 Styrene-acrylic emulsion 49.0 Parts Hexamethoxymethylmelamine (crosslinker) 0.01 Parts Isopropyl alcohol 1.0 Part Phenyl alkyl ether (wetting agent) 0.04 Parts Colloidal silica 0.04 Parts Polyaziridine 0.01 Parts Deionized Water 94.0 Parts c) Coating Solution #3 PU dispersion Phenyl alkyl ether Colloidal silica Polyaziridine Deionized Water 50.0 Parts 0.02 Parts 0.04 Parts 4.0 Parts 50 Parts d) Coating Solution #4 Methamethacrylate-acrylic emulsion Hexamethoxymethylmelamine Isopropyl alcohol Phenyl alkyl ether Colloidal silica Polyaziridine Deionized Water 49 Parts 0.01 Parts 1.0 Parts 0.04 Parts 0.04 Parts 0.01 Parts 94 Parts Example 1 Polyester Film without any coating: The polyester film as AB structure comprised of 100% homo polyester in layer B and 50 % of homo polyester and 50% of co-polyester in layer A are extruded at a temperature of 260°C and casting the melt on a cool drum and quenching by 7 electrostatic pinning/quenching; The film is subjected to a group of hot rollers heated to 95°C with stretching in a longitudinal direction at a draw ratio of 3.5 times, cooled by a group of rollers at 38°C followed by stretching the film in a transverse direction 4.1 times 90°C. The co-extruded film is drawn transversely to produce a biaxially oriented film followed by heat setting at around 224°C and winding on a jumbo roll. The PET film has a thickness of about 12.5 micron. Example 2 The above example-l was followed but inline coating was done using the coating solution # 1 to 4 by gravure coating method. This coating was dried and crosslinked during stretching and heat setting of the film. The PET film was produced with a surface coating thickness of about 0.04 microns. The polyester film so processed was used for example 2 to 5. 8 Claims We claim: 1. A direct embossable PET film, wherein, the film is a two layered film of AB structure, A being 5-25% of a layer comprising a blend of homopolyesters and copolyesters containing inorganic particles, B being 75-95% homo-polyester containing inorganic particles, the film being longitudinally & transversely stretched, the film optionally containing an antistatic agent, a surface coating, wherein the said coating gets crosslinked to the PET surface during heat setting thereby rendering the film surface susceptible to embossing under pressure and temperature. 2. A direct embossable PET film as claimed in claim 1, wherein the uniaxially oriented polyester film is coated with crosslinkable materials such as polystyrene-acrylic aqueous emulsion, polyester dispersions, polyurethane dispersions, methyl methacrylate-acrylic emulsions. 3. A direct embossable PET film as claimed in claims 1-2, wherein thickness of the coating is 0.01 u- 0.1uA. 4. A direct embossable PET film as claimed in claims 1-3, wherein the coating is crosslinked. 5. A direct embossable PET film as claimed in claims 1-4, wherein the PET base film has haze value of ~1.0 to 3.0 %. 6. A process for making direct embossable PET film as claimed in claims 1-5, comprising a two layered film of AB structure, A being 5-25% of a layer comprising a blend of homopolyester and copolyester, B being 75-95% homo-polyester, comprising: a) Extruding homo-polyester as core layer and a blend of homo-polyester and co-polyester as coextruded layer; b) Casting the melt on a cool surface followed by quenching; c) Subjecting the sheet to a group of hot rollers at 80°C - 120°C with stretching in the longitudinal direction; d) Cooling the uniaxially stretched film in a group of rollers at 20-50°C; e) Inline coating of the uniaxially stretched film; f) Stretching the film in the transverse direction with a draw ratio not more than 2.5 to 7 preferably 3 to 5.5 at 85 °C - 90°C and heat setting the film at 200 to 230°C followed by optional addition of regrind of 0-50%. 7. A process for making direct embossable PET film as claimed in claims 1-6, wherein the homo polyesters and copolyesters are obtained by transesterification or direct esterification of a diol or substituted diol and purified dibasic acid or with substituted diacid or with esters of diacids and optionally containing 100 ppm - 1000 ppm, preferably 300 to 500 ppm of 9 inorganic particles. 8. A process for making direct embossable PET film as claimed in claims 1-7, wherein the polyesters include those produced by using more than one dibasic acid selected from acids such as terephthalic acid, isophthalic acid, adipic acid, orthophthalic acid, sebacic acid, naphthalene dicarboxylic acid, azalaic acid and more than one diol such as ethylene glycol, diethylene glycol, triethylene glycol, butane diol, neopentyl glycol, cyclohexane dimethanol. 9. A process for the making of direct embossable PET film as claimed in claims 1-8, wherein the co-polyester such as amorphous polyethylene terephthalate is obtained by transesterification of mixture of mono ethylene glycol, diethylene glycol, 1,4 cyclo hexane dimethanol and dimethyl terephthalate. 10. A process for the making of direct embossable PET film as claimed in claims 1-9, wherein the base material for the film has intrinsic viscosity of 0.60 to 1.20 dl/g. 11. A process for the making of direct embossable PET film as claimed in claims 1-10, wherein the particle size of the inorganic particles are 1 to 5 u preferably 2 to 4 u selected from silicon dioxide, calcium carbonate, talc, kaolin or mixtures of thereof. 12. A process for the making of direct embossable PET film as claimed in claims 1-11, wherein the PET film is 8 microns to 300 microns. 13. A process for the making of direct embossable PET film as claimed in claims 1-12, wherein the PET base film contains 0.005 wt % to about 0.2 wt % inorganic particles based on the weight of the PET film, selected from silica, alumina, calcium carbonate and mixtures thereof. 14. A process for the making of direct embossable PET film as claimed in claims 1-13, wherein the inline coating is carried out with crosslinking agents such as styrene-acrylic aqueous emulsions, hexamethoxymethylmelamine, polyaziridine; PU dispersion, polyaziridine; or methamethacrylate-acrylic emulsion. Dated: March 5, 2005 Dr.Prabuddha Ganguli Agent on behalf of Applicant

Documents:

317-mum-2006-abstract (05-02-2008).doc

317-mum-2006-abstract (05-02-2008).pdf

317-mum-2006-cancelled page(05-02-2008).pdf

317-mum-2006-claim(granted)-(05-02-2008).pdf

317-mum-2006-claims(granted)-(05-02-2008).doc

317-mum-2006-correspondence(05-02-2008).pdf

317-mum-2006-correspondence(ipo)-(18-10-2007).pdf

317-mum-2006-form 1(05-02-2008).pdf

317-mum-2006-form 1(06-03-2006).pdf

317-mum-2006-form 18(09-11-2006).pdf

317-mum-2006-form 2(granted)-(05-02-2008).doc

317-mum-2006-form 2(granted)-(05-02-2008).pdf

317-mum-2006-form 3(27-02-2006).pdf

317-mum-2006-form 5(27-02-2006).pdf

317-mum-2006-form 9(09-11-2006).pdf

317-mum-2006-power of attorney(02-03-2006).pdf