Title of Invention	"A MULTILAYER BIAXIALLY ORIENTED FILM"
Abstract	This invention relates to a multilayer biaxially oriented film comprising a core layer having polypropylene and a modifier that reduces crystallinity of polypropylene matrix and skin layers on either side of the core layer comprising propylene-ethylene copolymer, propylene-α-olefin copolymer, silicone resin, silica antiblock.

Full Text

FIELD OF THE INVENTION This present invention relates to a biaxially oriented film, having excellent runnability on packing machines, superior hot slip, and optical properties. This film is distinguished by its ability to give tighter packs by way of heat shrinkage. Prior Art Transparent, oriented polypropylene films are used in large quantities as over-wrapping substrate since many years. A tobacco over wrap is supposed to have very good optical properties, sealability-should seal at low temperature on high speed machines, good slip properties at elevated temperatures & provide excellent aesthetics. In order to meet these requirements, the present invention deals with a heat shrinkable tobacco over wrap BOPP film. Shrink film is one, which shrinks under heat to give tight wraps U.S.Pat. 5292561 discloses a process for producing polyolefin shrink films, which shrink in only one direction. EPA 047742 discloses a transparent polypropylene film that exhibits shrinkage at 100°C of at least 10% in MD (machine direction) and less than 2% in TD (transverse direction). These patents describe only uniaxially shrinkable film, where as the present invention describes a biaxially oriented polypropylene film that shrinks in both the directions for better aesthetics after wrapping. Objects of the Invention The main object of this invention is to prepare a biaxially oriented cigarette overwrap film. Another object of this invention is to prepare a film having excellent optical properties. Yet another object of this invention is to prepare a film having superior shrinkage characteristics. Still another object of this invention is to prepare a film that is heat shrinkable in both directions namely machine direction and transverse direction for better aesthetics after wrapping. Yet further object of this invention is to prepare a film which seals at low temperature on high speed machine. Still another object of this invention is to prepare a film which shrinks under heat to give tight wraps. Yet another object of this invention is to prepare a film which has grid slip properties at elevated temperatures. Further object and advantages of the invention will be more apparent from the ensuing description. According to the present invention there is provided a multilayer biaxialiy oriented film comprising a core layer having polypropylene and a modifier that reduces crystallinity of polypropylene matrix and skin layers on either side of the core layer comprising propylene-ethylene copolymer, propylene-α-olefin copolymer, silicone resin, silica antiblock. The ingecientsof multilayer biaxially oriented film are interacting synergistically, but not reacting, to produce the desired results and properties. The ingredients do not form a mere admixture. Statement of the Invention The present invention relates to a multilayer biaxially oriented film comprising a core layer, skin I on one surface of the core layer and skin II on other surface of core layer, wherein the core layer comprises of a modifier that reduces crystallinity of polypropylene matrix and wherein skin I comprises propylene-ethylene copolymer, propylene-a-olefin copolymer, silicone resin, silica antiblock; wherein skin II comprises propylene-ethylene copolymer, silicone resin, silica antiblock; and wherein the core layer comprises 50-95% of total thickness and each of the two skin layers comprise 2.5 - 25% of the total thickness of the film. 'Description of the Invention The present invention depicts a biaxiaily oriented polypropylene (BOPP) film, here in after be referred to as BOPP film, which has excellent optical properties and superior shrinkage characteristics. At the outset of the description which follows it is to be understood that the ensuing description only illustrates a particular form of this invention. However, such particular form is only an exemplary embodiment and without intending to be understood as exemplary teaching of the invention and not intended to be taken restrictively. In the preferred embodiment, the film is a multilayer, precisely three layered, transparent consisting of polypropylene polymer. Out of the three layers, core layer accounts for 50-95 % of the total thickness, preferably 75-90%. Minor layers are called skin layers, namely skin I, comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness and skin II, comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness. In a further preferred embodiment, core layer consists, predominantly of polypropylene polymerwith melt flow index of 0.2 to 7g/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. In a further preferred embodiment of this invention, core layer also consists of modifiers to aid getting better heat shrinkage. These modifiers may be propylene-ethylene copolymers or propylene-a-olefin copolymers or atactic polypropylene or syndiotactic polypropylene or hydrogenated hydrocarbon resins or an appropriate blend of such modifiers. Modifiers help processing of polymer matrix under extreme conditions of temperatures & stretch ratios. They also help to get excellent heat sensitive shrinkage during conversion operations. In this invention, hydrocarbon resin is present in the range of 4 to 20%. In a preferred embodiment of this invention, resin is present in the range of 6 to 15%. In a more preferred embodiment, Propylene-ethylene copolymer is present in the range of 4 to 16 % and in a more preferred embodiment of the invention, propylene-ethylene copolymer is present in the range of 6-12%. In order to improve slip properties of the film slip agents such as, erucamide, Oleamide, glycerol mono stearate (GMS), waxes and metallic greases are added at a concentration between 10 and 1000ppm, preferably 20-500 ppm and more preferably, 50-150ppm. 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 1 0 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 concerned. Skin I, comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness, is made of propylene-ethylene copolymer, with an ethylene percentage of 2-6, preferably, 2-4%. Skin I also contains propylene a-olefin copolymer to enable low seal initiation. In an embodiment of this invention, skin I contains 3-15% of propylene a-olefin copolymer preferably, 5-8% of propylene a-olefin copolymer. Skin II, comprising 2.5 to 25% of the total thickness, preferably 5-12.5% of total film thickness, is made of propylene-ethylene copolymer, with an ethylene percentage of 2-6.preferably, 2-4%. Skin II also contains propylene a-olefin copolymer to enable low seal initiation. In an embodiment of this invention, skin I contains 3-15% of propylene α-olefin copolymer preferably, 5-8% of propylene a-olefin copolymer. It is also one of the intentions of this invention that the said film has good slip properties at higher temperatures. In a preferred embodiment of this invention, skin I has spherical shaped silicone beads to the tune of 500 to 2000ppm. In a more preferred embodiment of this invention, silicone resin is present between 750 and 1500ppm In a more preferred embodiment of this invention skin I & skin II have differential CoF for efficient running on the machine. The films according to the invention may be produced by 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 biaxiaily. in the course, the film is stretched in the machine direction or longitudinally at a ratio of 4:1 to 10:1, preferably 5:1 to 8:1, at a temperature of 90 to 150°C, preferably 100 to 130°C. This monoaxially oriented polymeric film is reheated and stretched in the cross direction or transverse direction with a stretch ratio of 7:1 to 12:1, preferably 8:1 to 9:1. This is effected at a temperature range of 130 to 190°C, preferably 145 to 170°C. So produced biaxiaily oriented polypropylene film is not allowed to heat-set at higher temperatures in TDO, in contrast, it is done at lower temperatures. 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. Such films are characterized by differential coefficient of friction (CoF), high heat shrinkage in both MD (8-10%) and TD (8-10%) at 120°C in 5 minutes. Example 1 A biaxiaily oriented polypropylene multilayer film was produced by means of the coextrusion process as described elsewhere, with the preferred stretching ratios (machine direction 6.9:1 and transverse direction 9.0:1) at an average machine direction stretching temperature of 110°C and at an average transverse direction stretching temperature of 155°C. After stretching in the transverse direction, film is annealed at a temperature range of 150 to 160°C. Thickness of this film is 20 microns. (Table Removed) Comparison 1 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: (Table Removed) Comparison 2 A three layer film with a total thickness of 20µ was produced by the process depicted in example II with the following recipe. 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. Shrinkage The said film is cut into the size of 10cm * 10cm and is kept in an hot air oven at 120°C for five minutes. Then the film is taken out and cooled to the room temperature and change in dimensions is measured. From the following formula, the percent shrinkage is calculated. % shrinkage = (Change in dimension/original dimensions) * 100 We Claim: 1. A multilayer biaxially oriented film comprising a core layer, skin I on one surface of the core layer and skin I1 on other surface of core layer, wherein the core layer comprises of polypropylene polymer and a modifier that reduces crystallinity of polypropylene polymer and wherein skin I comprises propylene-ethylene copolymer, propylene-a-olefin copolymer, silicone resin, silica antiblock; wherein skin I1 comprises propylene-ethylene copolymer, silicone resin, silica antiblock; and wherein the core layer comprises 50-95% of total thickness and each of the two skin layers comprise 2.5 - 25% of the total thickness of the film. 2. The multilayer film as claimed in claim 1, wherein said modifier is selected from a group consisting of atactic polypropylene, propylene-a-olefin copolymer, propyleneethylene copolymer, syndiotactic polypropylene and hydrocarbon resin or a mixture thereof. 3. The multilayer film as claimed in claim 1, wherein said modifier is a mixture of propylene-ethylene copolymer and hydrocarbon resin. 4. The multilayer film as claimed in claim 1, wherein said core layer comprises an antistatic agent from the group of alkali alkanesulphonates, polyethermodified i.e., ethoxylated andlor propoxylated polysiloxanes and/or straight chain, saturated aliphatic tertiary amines 5. The multilayer film as claimed in claim 1 wherein the core layer comprises 75-90% of total thickness and each skin layer comprises 5 - 12.5% of the total thickness of the film. 6. The multilayer film as claimed in any of the preceding claims wherein the total thickness of the film is 8 to 30pm. 7. The multilayer film as claimed in claim 6 wherein the total thickness of the film is 10 to 20 pm. 8. The multilayer film as claimed in any of the preceding claims wherein the said skin I comprises 3-15% wt of propylene a-olefin copolymer. 9. The multilayer film as claimed in any of the preceding claims wherein skin I1 comprises propylene-ethylene copolymer having 2-6% ethylene. 10. The multilayer film as claimed in claim 9, wherein the propylene-ethylene copolymer has 2-4% ethylene. 11. The multilayer film as claimed in claim 1, wherein said skin I contains 5 - 8% of propylene a -olefin copolymer. 12. The multilayer film as claimed in any of the preceding claims wherein the said core layer comprises 4 to 20% wt. of hydrocarbon resin. 13. The multilayer film as claimed in claim 12, wherein the core layer comprises 6 to 15% wt. of hydrocarbon resin. 14. The multilayer film as claimed in any of the preceding claim wherein the core layer comprises antistatic agents selected from alkali alkanesulphonates, ethoxylated or propoxylated polyslilxanes, straight chain saturated aliphatic tertiary arnines with alihatic radical having 10 to 20 carbon atoms which contain two hydroxyalkyl (Cl-C4) groups as substituents or mixtures thereof. 15. The multilayer film as claimed in claim 14 wherein said substituents comprise N, N-bis (2-hydroxyethy1)-alkylamines with C10-C20. 16. The multilayer film as claimed in claim 14 wherein said substituents comprise N, N-bis (2-hydroxyethy1)-alkylamines with C12-C18. 17. The multilayer film as claimed in any of the preceding claims wherein skin I comprises 500 to 2000 ppm silicon resin consisting of silicon beads. 18. The multilayer film as claimed in claim 17, wherein the skin I comprises 750 to 1500 ppm silicon resin. 19. The multilayer film as claimed in any of the preceding claims wherein the skin I and skin I1 comprise slip agents selected from erucamide, oleamide, glycerol monostearate, waxes, metallic greases, polysiloxanes or mixtures thereof at concentration between 10 to 1000 ppm. 20. The multilayer film as claimed in claim 19, wherein said slip agents are at a concentration of 20 - 500 ppm. 21. The multilayer film as claimed in claim 19, wherein said slip agents are at a concentration of 50-150 ppm. 22. The multilayer film as claimed in claim 1, which is oriented in machine direction (MD) to the tune of 4-10 times and in transverse direction (TD) 6-12 times. 23. The multilayer film as claimed in any of the preceding claims, wherein the said film shrinks to the extent of 8-10% in MD and 8-10% in TD. 24. The multilayer film as claimed in any of the preceding claims, wherein the film shrinkage is tested at 120°C for 5 minutes.

Documents:

618-del-2003-618-del-2003-Claims-(02-01-2013).pdf

618-del-2003-618-del-2003-Correspondence Others-(02-01-2013).pdf

618-del-2003-618-del-2003-Description (Complete)-(02-01-2013).pdf

618-del-2003-618-del-2003-GPA-(02-01-2013).pdf

618-DEL-2003-Abstract-(24-06-2011).pdf

618-del-2003-abstract.pdf

618-DEL-2003-Claims-(24-06-2011).pdf

618-del-2003-claims.pdf

618-DEL-2003-Correspondence Others-(24-06-2011).pdf

618-DEL-2003-Correspondence Others-(30-06-2011).pdf

618-del-2003-correspondence-others.pdf

618-del-2003-correspondence-po.pdf

618-DEL-2003-Description (Complete)-(24-06-2011).pdf

618-del-2003-description (complete).pdf

618-del-2003-description (provisional).pdf

618-DEL-2003-Form-1-(24-06-2011).pdf

618-del-2003-form-1.pdf

618-del-2003-form-2.pdf

618-del-2003-form-26.pdf

618-del-2003-form-3.pdf

618-del-2003-form-4.pdf

618-del-2003-form-5.pdf

618-DEL-2003-GPA-(30-06-2011).pdf