Title of Invention	"BIAXIALLY ORIENTED MATTE FILM AND 4 PROCESS THEREOF"
Abstract	An improved matte film comprising a core layer of polypropylene sandwiched between a pair of thinner skin layers of thickness, wherein at least one skin layer comprises metallocene linear low density polypropylene (mLLDPE) and a process to prepare the matte film thereof.

Full Text

FIELD OF THE INVENTION The subject invention relates to a biaxially oriented matte film, and a process thereof. More specifically, the subject invention relates to an improved matte film comprising a core layer of polypropylene of thickness from 75 to 80%, sandwiched between a pair of thinner skin layers of thickness from 10 to 15% and 5-7% respectively, wherein the haze value of the film is at least 35-45% and the gloss value is 30-40 units. The film has silky matte finish which is quite different from normal matte and glossy film. The film is used for lamination of printed paper board or another plastic web. The object of the present invention is to provide an improved matte biaxially oriented polypropylene film having better mar resistance. Another object of the present invention is to provide an improved matte film which has silky matte finish. Further object of the present invention is to provide an improved process for the preparation of the matte film employing coextrusion process, wherein the film has at least three layers. Yet another object of the present invention is to provide an improved process for the preparation of biaxially oriented polypropylene matte film employing Polypropylene (PP) as the base layer and silica in the other (skin) layer The object of the invention is also to provide a cost-effective matte film having better optical properties and finish as compared to the conventionally available biaxially oriented polypropylene films. BACKGROUND OF THE INVENTION Conventionally oriented matte polyolefin films are used in large quantities as packaging material. They are mostly used as laminates. Lamination process namely solvent lamination, water based lamination, dry lamination and the like combine this film with printed products like, printed paper board. BOPP films that are normally used for lamination are of two types. One is a high glossy, transparent film with a haze value less than 2% and a gloss value of more than 90 units. The other variety is matte finished one that has a gloss value of less than 10 units and a haze value of more than 70%. The latter variety when laminated gives natural, glare-free look whereas the former gives scintillating look. Both these have their advantages and disadvantages like glare, aesthetics, and the like. Moreover with matte film, mar resistance of the matte surface is very poor as even a slight scratch damages the matte skin thereby resulting in a shiny spot. Resistance of film surface to such scratches is called mar resistance. In order to achieve a matte surface with excellent optics having a perfect combination between glossy and matte surface this invention depicts a BOPP film which has combined both the properties. Moreover, its mar resistance is also improved to quite an extent. In European Patent EP-A-27 586 it is described that finely divided silica (SiO2) is used to a very large extent as an antiblocking agent, in a concentration of 500 to 5000 ppm, preferably 1000 to 4000 ppm. These antiblocking agents (which are also known, for example, under the trade names SYLOBLOC 44 & 45 supplied by Grace GmbH, of Worms), which have average particle sizes of 1.0 to 6.0m, preferably 2.5 to 5.0m, improved the frictional behavior of the film and thus improve its running properties on machines. This also aids the migration of additives like anti static agents, slip agents through to the surface. However, silica particles impair optical properties like haze. Conventional matte films suffer from the drawback that the films are either too dull or too shiny. To achieve both the natural looks and surface smoothness a novel process has been evolved by which a biaxially oriented polypropylene film is prepared which has excellent and unique optical properties. Polyolefines are usually stablized against thermal decomposition during their production and processing to for films as it involves high temperatures and shears. Examples of preferred compounds with a stablizing effect and their combination thereof for ethylene, propylene and other a-olefin polymers are described in EP-A-263 882. With respect to the layer concerned, amount of stablizers needed is generally 0.1 to 2.0% by weight. In one embodiment, the invention resides in a multi layer, precisely three layered, transparent consisting of polypropylene polymer. Out of the three layers, core layer accounts for 50-85% of the total thickness, preferably 75-80%. Minor layers are called skin layers, namely skin I, comprising 2.5 to 25% of the total thickness, preferably 10-15% of total film thickness and skin II, comprising 2.5 to 25% of the total thickness, preferably 5-7% of total film thickness. Another embodiment of the subject application resides in the process for manufacturing a biaxially oriented silky matte film comprising co-extruding three layers of polyolefinic compounds namely, core layer, skin I & skin II. Core layer is predominantly of Polypropylene with crystallinity of more than 60% and isotacticity of more than 90%. Skin consists primarily of Polypropylene with properties being the same as that of core. Skin I comprises a compound of high density polyethylene (HDPE) from 10-70% and crystallinity of which is more than 80% and 30-90% of ethylenepropylene random copolymer or a terpolymer of ethylene, propylene and an α-olefine. The biaxial orientation of polypropylene increases its stiffness and enhances other physical properties such as tensile strength, tear strength and other mechanical properties. 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. The propylene homopolymer layer is having a melt flow index value from 2-4 and melting point between 160 and 170°C and copolymer or terpolymer is having the melt flow index from 5 to 8 g/ 10 min. Compound giving matte effect is having a melt flow index between 3 & 6 g/10 min. In order to improve slip properties of the film slip agents such as, erucamide, Oleamide, glycerol mono strearate (GMS), waxes and metallic greases are added at a concentration between 10 and 1000 ppm, preferably 20-500 ppm and more preferably, 50-150 ppm. In addition, polymers from the polysiloxane group are used. To minimize static charge anti static agents comprising alkali alkanesulphonates, polyether-modified i.e. ethoxylated and/or propoxylated polysiloxanes and/or straight chain, saturated aliphatic tertiary amines, which contain an aliphatic radical with 10 to 20 carbon atoms and which contain two hydroxyalkyl (C1-C4) groups as substituents, among which N, N-bis(2-hydroxyethyl)-alkylamines with C10-C20, preferably C12-C18, as the alkyl groups are particularly suitable. The effective amount of antistatic agent falls within the range of 0.05 to 3.0% by weight with respect to the weight of polypropylene. Skin I, comprising 2.5 to 25% of the total thickness, preferably 10-15% of total film thickness, comprises a compound of high density polyethylene (HDPE) from 10-70% and crystallinity of which is more than 80% and 30-90% of propylene-ethylene random copolymer or a terpolymer of ethylene, propylene and an α-olefine. Skin II, comprising 2.5 to 25% of the total thickness, preferably 5-7% of total film thickness, 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. Skin II also contains anti blocking agents that are spherical, organic compounds such as polymethyl methacrylate, Nylon, Polyisobutyl methacrylate, Polydimethyl siloxanes or simply silicones to name a few. These organic antiblocks may be used separately or in combination and in the range of 0.01 to 2.0%, preferably 0.02 to 1.0%. Also, conventional anti blocking agents like silica can also be used. The matte film, thus prepared by the process of the present invention is much superior than the conventionally available films and is having better use in packaging. In the process of manufacturing a biaxially oriented polypropylene film, the composite sheet, consisting of polypropylene in core and in one of the skin layers and d skin I comprising matte compound, co-polymer or terpolymer is co-extruded through a slit die after combining in the feedblock. In the said feedblock, the materials are layered to form the multi-layer melt stream. The said coextruded sheet emerging from the die is cooled in a set up comprising Chill roll and water bath at a temperature sufficient to maintain a minimum crystallinity for machine direction stretching. The said composite sheet after cooling is fed into an apparatus adapted for biaxial orientation. In the said apparatus the composite sheet is fed to a set of differential speed heated rollers to stretch the sheet longitudinally at a degree of about 2:1 to 6:1. The sheet is then fed to a tenter frame, where it is stretched in the transverse direction at a degree of about 7:1 to about 10:1. The biaxially oriented sheet is then subjected to a heat setting treatment allowing the matte compound to crystallize. The crystallization of the skin imparts matte properties to the composite film. The heat setting treatment is carried out preferably at annealing temperature of between 160-170°C. The film thus produced is tested for gloss on Gardinar gloss meter and haze on haze mater. Matte skin with altered recipe has improved mar resistance over the normal mate film. Mar resistance was observed visibly and the relative performance was observed qualitatively after scratching the surface. According to the present invention there is provided a biaxially oriented matte film comprising a core layer sandwiched between a skin II and a skin I wherein: said skin II is 2.5 to 25% w/w comprising high crystalline polypropylene and 0.01 to 2.0% of anti block agents; said core layer is 50-85%) w/w comprising polypropylene polymer, 10-1000 ppm slip agents, and 0.05-3.00% antistatic agents such as herein described; said skin I is 2.5 to 25%> w/w comprising 10-70% high density Polyethylene and 30-90% of ethylene propylene copolymer or terpolymer of ethylene, propylene or α-olefin. The present invention also provides a process for preparation of a biaxially oriented matte film having the following steps: three layered composite sheet, consisting of polypropylene core, skin layer along with Polypropylene layer with high crystallinity and isotacticity is co-extruded through extruders; co-extruding three layered composite sheet, consisting of polypropylene core, skin layer along with Polypropylene layer with high crystallinity and isotacticity through extruders; passing the coextruded material through a combining feed block to form the multi-layer melt stream, feeding the melt steam into a slot cast sheet die or other type of die to form the multi-layer sheet; quenching the multilayer sheet after cooling at conventional chill roll and stretching it in the machine direction longitudinally at 120-145°C to form monoaxially oriented film; stretching the said monoaxially film in the transverse direction at 145-170°C to form biaxially oriented film; subjecting the film to annealing at a temperature of 160°C-170°C; treating the film surface by conventional corona discharge or plasma treatment to obtain said matte film. Hence, it would be advantageous to manufacture such a matte film which has optimum coefficient of friction, desired optical properties and sufficient sealing strength if sealing layer is used as one of the layers out of the three layers. The biaxially oriented film of the present invention comprises a synergistic composition, the ingredients of which are not reacting chemically, but interacting synergistically to provide the desired exceptional results and properties. SUMMARY OF THE INVENTION In the present invention there is provided a process for the preparation of an improved biaxially oriented silky matte polypropylene (BOPP) film which is of a core layer and at least one skin layer comprising a compound of high density polyethylene (HDPE) from 10-70% and crystallinity of which is more than 80% and 30-90% of ethylene-propylene random copolymer or a terpolymer of ethylene, propylene and an a-olefin and biaxially stretching the resultant coextruded layer by known methods. The embodiment of the invention resides in the co-extrusion of polypropylene . Other embodiment of the invention resides in providing an improved matte biaxially oriented polypropylene film having better mar resistance. Yet another embodiment of the invention resides in providing an improved matte film which has silky matte finish. 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. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig. 1 depicts a general lay out of the manufacture of biaxially oriented polypropylene (BOPP) film on a pleare defene 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 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 20µ. Before taking the film on winder edges of the film carried by the clips of transverse direction orienter is trimmed and recycled. The BOPP films are considerably non polar which make the spreading of inks, adhesives exempli gratia on the film surface difficult or impossible. In order to increase the surface energy or wettability of the film by known processes such as corona treatment, flame treatment, plasma treatment and fluorine pretreatment. The subject film surface is exposed to corona discharge or beam of electrons which in effect deposit the atmospheric oxygen on the surface in the form of carbonyl, epoxide, ether and/or alcohol groups. These groups increase the surface energy of film and hence the affinity for inks or adhesives. Treatment intensities fall in the range of 36 to 42 dynes/cm. Films thus produced is laminated to printed paper board on both the sides. The invention is described in detail in the Examples given below which are provided by way of illustration only and therefore should not be construed as limitation to the present invention. 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. The external surfaces of the skin layers are corona treated to 44 dyne/cm. The entire film thickness is 15 or 60 gauge and its composition is as under (Table Removed) Comparison 1 A three layer film with a total thickness of 15 was produced by the process depicted in example I, but the raw material composition was altered as follows: (Table Removed) Comparison 2 A three layer film with a total thickness of 15 was produced by the process depicted in example I, but the raw material composition was altered as follows (Table Removed) The properties of the three-layered biaxially oriented polypropylene films of example and comparison have been compared and summarized in a table A. Table A (Table Removed) Haze Haze is the fraction of light that is scattered by angle of more than 2.5 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. Scratch Resistance Scratch resistance of the films was tested by rubbing it with fingernails and subsequent physical examination by holding it against light. Five different persons did the test and the result is summarized as given in table A. 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. WE CLAIM: 1. A biaxially oriented matte film comprising a core layer sandwiched between a skin II and a skin I wherein: said skin II is 2.5 to 25% w/w comprising high crystalline polypropylene and 0.01 to 2.0% of anti block agents; said core layer is 50-85% w/w comprising polypropylene polymer, 10-1000 ppm slip agents, and 0.05-3.00% antistatic agents such as herein described; said skin I is 2.5 to 25% w/w comprising 10-70% high density Polyethylene and 30-90% of ethylene propylene copolymer or terpolymer of ethylene, propylene or a-olefin. 2. A biaxially oriented matte film as claimed in claim 1, wherein the thickness of skin II is 5-7% of the total film thickness. 3. A biaxially oriented matte film as claimed in claim 1, wherein the thickness of skin I is 10-15% of the total film thickness. 4. A biaxially oriented matte film as claimed in claim 1, wherein thickness of said core layer is between 75-80% of the total film thickness. 5. A biaxially oriented matte film as claimed in claim 1, wherein crystallinity of the said skin layer made of high crystalline polypropylene is at least 60%. 6. A biaxially oriented matte film as claimed in claim 5, wherein the isotactic index of said high crystalline polypropylene used is more than 80% preferably more than 90%. 7. A biaxially oriented matte film as claimed in claim 1, wherein the said antistatic agents are selected from alkali alkanesulphonates, polyether-modified ethoxylated and/or propoxylated polysiloxanes and/or straight chain, saturated aliphatic tertiary amines. 8. A biaxially oriented matte film as claimed in claim 1, wherein the said slip agents are selected from erucamide, Oleamide, glycerol mono strearate (GMS), waxes and metallic greases. 9. A biaxially oriented matte film as claimed in claim 1, wherein the said anti blocking agents are spherical, organic compounds selected from polymethyl methacrylate, Nylon, Polyisobutyl methacrylate, Polydimethyl siloxanes, silicones or silica. 10. A biaxially oriented matte film as claimed in claim 1, wherein total thickness of the film is between 10 to 20µ.. 11. A process for preparation of a biaxially oriented matte film as claimed in claim 1 having the following steps: three layered composite sheet, consisting of polypropylene core, skin layer along with Polypropylene layer with high crystallinity and isotacticity is co-extrudcd through extruders: co-extruding three layered composite sheet, consisting of polypropylene core, skin layer along with Polypropylene layer with high crystallinity and isotacticity through extruders; passing the coextruded material through a combining feed block to form the multi-layer melt stream, feeding the melt steam into a slot cast sheet die to form the multi-layer sheet; quenching the multilayer sheet after cooling at conventional chill roll and stretching it in the machine direction longitudinally at 120-145°C to form monoaxially oriented film; stretching the said monoaxially film in the transverse direction at 145-170°C to form biaxially oriented film; subjecting the film to annealing at a temperature of 160°C-170°C; treating the film surface by conventional corona discharge or plasma treatment to obtain said matte film. 12. The process as claimed in claim 11, wherein the said film is longitudinally stretched at the ratio 5:1 to 6:1. 13. The process as claimed in claim 11, wherein the said film is transversely stretched at the ratio 9:1 to 11:1. 14. A process for the preparation of an matte film substantially as herein described with reference to the foregoing examples and accompanying drawings. 15. A matte film substantially as herein described with reference to the foregoing examples and accompanying drawings.

Documents:

1039-del-2001-abstract.pdf

1039-del-2001-claims.pdf

1039-DEL-2001-Correspondence Others-(26-05-2011).pdf

1039-del-2001-correspondence-others.pdf

1039-del-2001-correspondence-po.pdf

1039-del-2001-description (complete).pdf

1039-del-2001-drawings.pdf

1039-del-2001-form-1.pdf

1039-del-2001-form-19.pdf

1039-del-2001-form-2.pdf

1039-DEL-2001-Form-27-(26-05-2011).pdf

1039-del-2001-form-3.pdf

1039-del-2001-form-4.pdf

1039-del-2001-form-5.pdf

1039-del-2001-gpa.pdf

1039-DEL-2001-Petition-137-(26-05-2011).pdf