The present invention relates to heat-sealable multi-layer biaxially oriented polypropylene (BOPP) films used for packaging, decorative and label applications. More particularly, the present invention relates to a transparent and a metalized multi-layer BOPP film with high heat seal integrity and low kinetic friction coefficient.
BACKGROUND OF THE INVENTION
Biaxially-oriented polypropylene (BOPP) films are widely used in packaging owing to the high stiffness, strength, optical properties (low haze and high gloss), and moisture barrier properties. BOPP is also used for several other functions for example, in laminations they provide printability, transparent or matte appearance, and/or slip properties. They are used to provide a surface suitable for receiving organic or inorganic coatings for gas and moisture barrier properties. They are also used to provide a heat-sealable layer for bag forming and sealing, or a layer that is suitable for receiving an adhesive either by coating or laminating.
For some applications of BOPP films, it is desirable to have very high heat seal strength. When heat sealing is used, it is important that the plastic film be readily heat sealable while also possessing other good physical and mechanical properties such as resistance to tearing, high tensile strength, and good process ability in high speed equipment. In cases, where food packages are transported to very high altitudes, the gas-filled packages can expand due to the lower ambient air pressure, stressing the sealed areas greatly, and thereby causing bursting. In addition, in food packaging applications, especially snack food packages, the packages can be subjected to much abuse during shipping and handling, moreover, a common consumer perception is that highly inflated bags ("pillow packs") are of higher quality package and then the snack food package often requires extremely strong seals to withstand high gas pressure inside the bag. Such multi-layer films

must also have the ability to resist peeling at the interface between the layers of the multi-layered film.
Typical multi-layered films include at least a core layer, typically comprised of polypropylene (PP), an outer layer typically known as a skin/surface layer, typically comprised of polar polymers, and a tie/intermediate layer located intermediate the core layer and the skin layer. Conventional tie layers are mostly maleic anhydride (MAH) grafted polypropylene (PP-g-MAH) homopolymers, copolymers, or combinations of PP-g-MAH with non-grafted polyolefms. In general, these maleated adhesive tie layers lack peel resistance at their interfaces with other adjacent layers. This is because they are poor in stress dissipation and reactivity due to their high chain rigidity and interfacial tension.
Several prior art provides various combinations of materials for use in multi-layer packaging which have been discussed below along with the disadvantages associated with them.
US5888648A describes a multi-layer hermitically sealable film which comprises of a substrate layer and a sealant layer, wherein the sealant layer itself comprises of an intermediate layer and a sealing layer. The intermediate layer can be formed of compositions such as LDPE (low density polyethylene), LLDPE (linear low density polyethylene), EPB (ethylene-propylene-butene) terpolymer, EP (ethylene-propylene) copolymer, plastomers, or blends thereof. Such a structure provides high heat seal strengths and hermetic seals, but the structure can be expensive due to the use of a thick intermediate layer (5-9 |im) in conjunction with a thinner sealant layer (ca. 1.5 |im) and also requires the use of an in-line extrusion coater in conjunction with 3-layer co-extrusion of the film.
US8617717B2 describes a heat-sealable film structure comprising (a) a base layer comprising a metallocene-catalyzed isotactic polypropylene homopolymer having an isotacticity from about 80 to 99%; and (b) a heat-seal layer comprising of 80-90% of a first polymer component (FPC), and 10-20% of a second polymer component (SPC). The FPC comprises of a polypropylene copolymer 2 to 5 wt % co-monomer, and 75 wt % to about 95 wt % propylene and from about 8 wt % to

about 16 wt % ethylene. Further, 50 to 99 % of the heat sealable film thickness is the base layer, and the base layer further comprises a slip agent, and the heat seal layer further comprises a slip agent and an anti-blocking agent. However, the document only provides a heat seal film with heat-seal strength around 200 g/25.4 mm. Moreover, the compositions of anti-block agent constitutes around 0.4%, whereas, slip agent constitutes around 0.07%.
US 13/649,793 provides a bi-axially oriented coextruded multilayer film comprising first layer of film made of a polypropylene homopolymer; a second layer of film formed to the first layer of film, wherein the film is made from a mixture of a polypropylene homopolymer and a migratory antistatic and slip additive; and a third layer of film formed to the second layer of film, wherein the third layer of film is made of a polypropylene homopolymer. The second layer comprises of 3% of antistatic and slip additives, which is relatively high than other documented reports. Moreover, the coefficient of friction is in the range of 0.25-0.45 us.
Though, there are several documents citing varying compositions of biaxially oriented polypropylene films, several variations in the compositions, and inclusion of additives sequentially improves the quality of the films in the form of heat-seal strength, coefficient of friction, haziness, and other factors. Taking into consideration the drawbacks of prior art, the invention provides a novel composition for making biaxially oriented polypropylene films for packaging.
State of the art bag grade BOPP films are generally non heat-sealable films and hence they are not recommended replacement for Polyethylene and zippers can't be attached to such films due to no heat-sealability property. Thus there is a need for a quality replacement of polyethylene bags that could have zippers, high gloss and heat sealability required in many applications.

OBJECT OF THE INVENTION
The main object of the invention is to provide a heat-sealable multi-layer biaxially oriented polypropylene (BOPP) films used for packaging, decorative, and label applications.
Another main object of the present invention is to provide a transparent and a metalized multi-layer biaxially oriented polypropylene film with high heat seal integrity and low kinetic friction coefficient.
Yet another object of the present invention is to provide a transparent multi-layer biaxially oriented polypropylene film comprising of polypropylene homopolymer, random polypropylene copolymer, antistatic and slip additives, propylene based elastomer and silica/organic anti-block.
Yet another object of the present invention is to provide a metalized multi-layer biaxially oriented polypropylene film comprising of polypropylene homopolymer, random polypropylene copolymer, propylene based elastomer, inorganic/organic anti-block and inorganic/organic anti-block based on acrylate.
Still another object of the present invention is to provide a transparent and a metalized multi-layer biaxially oriented polypropylene film with a zipper and high gloss level.
SUMMARY OF THE INVENTION
The present invention relates to a heat-sealable multi-layer biaxially oriented polypropylene (BOPP) films used for packaging, decorative and label applications. More particularly, the present invention relates to a transparent and a metalized multi-layer BOPP film with high heat seal integrity and low kinetic friction coefficient.
In a main embodiment, the present invention provides a two variant multi-layer BOPP film comprising of an outer layer, a plurality of intermediate layer, a core

layer and an inner layer wherein the two variants are transparent BOPP and metalized BOPP; the multi-layer film is a five layer film; one intermediate layer is between the core layer and an inner layer and other intermediate layer is between the core layer and an outer layer; the two variant BOPP film has a heat-seal strength in the range of 500gm/25mm to 2000gm/25 mm; and the two variant BOPP film has a kinetic coefficient of friction in the range of 0.15-0.35 |is.
In yet another embodiment, the present invention provides a transparent multi¬layer BOPP film comprising an outer layer and an inner layer preferably made from a blend of polypropylene copolymer, ethylene and silica/organic antiblock, a core layer preferably made from blend of antistatic and slip content and random polypropylene copolymer, an inner layer and an intermediate layer near to inner layer preferably made from a blend of propylene based elastomer and random polypropylene copolymer, an intermediate layer near the outer layer preferably made of antistatic and slip content; wherein the polypropylene homopolymer content is in the range of 80% to 99%; the random polypropylene copolymer content is in the range of 1% to 18%; the antistatic and slip content is in the range of 0.005% to 0.10%; the propylene based elastomer preferably olefmic elastomer is primarily composed of isotactic propylene repeat units with random ethylene distribution is in the range of 0.5% to 10%;and the silica/organic antiblock is in the range of 0.001% to 0.05%.
Still in another embodiment, the present invention provides a metalized BOPP film comprising an outer layer preferably made from a blend of inorganic/organic antiblock and random polypropylene copolymer, a core layer preferably made of a polypropylene homopolymer, an inner layer preferably made from a blend of polypropylene copolymer, propylene based elastomer and antiblock, an outer layer preferably made from a blend of anti-block and random polypropylene copolymer, an intermediate layer near inner layer preferably made from a blend of propylene based elastomer and polypropylene homopolymer and an intermediate layer near outer layer preferably made of polypropylene homopolymer; wherein the anti-block used is inorganic/organic antiblock based on acrylate; the polypropylene homopolymer content is in the range of 80% to 99%; the random polypropylene

copolymer content is in the range of 1% to 18%;-the propylene based elastomer preferably olefmic elastomer primarily composed of isotactic propylene repeat units with random ethylene distribution in the range of 0.5% to 10%; inorganic/organic antiblock is in the range of 0.001% to 0.05%; and inorganic/organic antiblock based on acrylate is in the range of 0.00% to 0.1%.
BRIEF DESCRIPTION OF THE DRAWINGS
Acompleteunderstandingofthedeviceandmethodofthepresentinventionmaybe obtained by reference to the following drawing:
Fig. 1(a) and 1(b) shows a transparent and metalized multi-layer BOPP film respectively in accordance to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention now will be described hereinafter with reference to the detailed description, in which some, but not all embodiments of the invention are indicated. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.
The present invention relates to heat-sealable multi-layer biaxially oriented polypropylene (BOPP) films used for packaging, decorative, and label applications. More particularly, the present invention relates to a transparent and metalized multi-layer BOPP film with high heat seal integrity and low kinetic friction coefficient.
In a most preferred embodiment, the present invention relates to a multi-layer biaxially oriented polypropylene (BOPP) film comprising of an outer layer, a plurality of intermediate layer, a core layer and an inner layer wherein the multi¬layer film is a five layer film; one intermediate layer is between a core layer and an

inner layer and other intermediate layer is between a core layer and an outer layer; said BOPP film has a heat-seal strength in the range of 500gm/25mm to 2000gm/25 mm; said BOPP film has a kinetic coefficient of friction in the range of 0.15-0.35 u; and said BOPP film has gloss level in the range of 85-95..
Here, the outer layer is made from a blend of polypropylene copolymer, ethylene and silica/organic antiblock or a blend of inorganic/organic antiblock and random polypropylene copolymer. The core layer is made from blend of antistatic and slip content and random polypropylene copolymer or polypropylene homopolymer. The inner layer is made from a blend of polypropylene copolymer, ethylene and silica/organic antiblock or a blend of polypropylene copolymer, propylene based elastomer and antiblock. The intermediate layer is made from a blend of propylene based elastomer and random polypropylene copolymer or antistatic and slip content or a blend of propylene based elastomer and polypropylene homopolymer or polypropylene homopolymer. The multi-layer BOPP film is either transparent BOPP film or metalized BOPP film.
In another preferred embodiment, the present invention provides a transparent multi-layer BOPP film comprising an outer layer and an inner layer preferably made from a blend of polypropylene copolymer, ethylene and silica/organic antiblock, a core layer preferably made from blend of antistatic and slip content and random polypropylene copolymer, an inner layer and an intermediate layer near to inner layer preferably made from a blend of propylene based elastomer and random polypropylene copolymer, an intermediate layer near the outer layer preferably made of antistatic and slip content.
In yet another preferred embodiment, the present invention provides a metalized BOPP film comprising an outer layer preferably made from a blend of inorganic/ organic antiblock and random polypropylene copolymer, a core layer preferably made of a polypropylene homopolymer, an inner layer preferably made from a blend of polypropylene copolymer, propylene based elastomer and antiblock, an outer layer preferably made from a blend of anti-block and random polypropylene copolymer, an intermediate layer near inner layer preferably made from a blend of

propylene based elastomer and polypropylene homopolymer and an intermediate layer near outer layer preferably made of polypropylene homopolymer. The outer layer is deposited with aluminium metal by offline vacuum metalizing process.
The present invention provides a multi-layer biaxially oriented polypropylene film (BOPP) in metalized form and transparent form. The BOPP film is a five layer film with the heat-seal strength of the film in the range of 500 gm/25 mm to 2000 gm/25 mm. The gloss level of the film in the range of 85-95 and the kinetic coefficient of friction of the film is in the range of 0.15-0.35.
The transparent multi-layer BOPP is used in applications where transparency and aesthetics are the primary requirements comprising of five layers having a core layer, an inner and an outer layer, an intermediate layer between an outer layer and a core layer and an intermediate layer between a core layer and an inner layer. The layers are made of preferably polypropylene homopolymer in the range of 80% to 99%; random polypropylene copolymer in the range of 1% to 18%; of antistatic and slip content in the range of 0.005% to 0.10%; the propylene based elastomer is in the range of 0.5 % to 10%;the silica or organic anti-block in the range of 0.001% to 0.05%;the propylene based elastomer is an olefinic elastomer primarily composed of isotactic propylene repeat units with random ethylene distribution. The antistatic and slip agents tend to reduce the treatment retention.
The metalized multi-layer BOPP film is used where oxygen and moisture barrier is utilized with special characteristics of C.O.F.in the range of 0.15 to 0.35 which facilitates high speed packaging comprising of five layers having a core layer, an inner and an outer layer, an intermediate layer between an outer layer and a core layer and an intermediate layer between a core layer and an inner layer. The layers are made of preferably polypropylene homopolymer in the range of 80% to 99%; the random polypropylene copolymer in the range ofl% to 18%; an antistatic and slip content in the range of 0.005% to 0.10%; the propylene based elastomer in the range of 0.5% to 10%; inorganic or organic anti-block in the range of 0.001% to 0.05% and organic/inorganic anti-block based on acrylate in the range of 0.00% to 0.1%.

The invention provides a biaxially oriented polypropylene film with improved heat seal strength to replace polyethylene-based films and cast polypropylene films. The high seal strength of the films makes them lap-sealable with Poly-olefmic films as well. Addition of a zipper at a low temperature is also enabled. Polypropylene zipper and universal zipper are joined with N1-BGS/N1-BGR by means of heat sealing jaws. The temperature range of attaching zipper with BOPP film ranges from 150 degrees to 200 degrees. The universal zipper is polypropylene film with bonding modifier. The heat-sealing side of metalized film enables to increase the output of packaging machine by two ways i.e. allowing better heat-seal integrity at lower dwell time of heat-sealing jaws; and by exhibiting very low kinetic coefficient of friction, which makes the film excellent in adaptability to machine processing, obviating difficulties in handling.
Now referring to Fig. 1(a) and 1(b), the transparent BOPP film is shown. The film comprises of five layers having outer layer 10, intermediate layer 11, core layer 12, intermediate layer 13 and inner layer 14. The outer layer 10 and inner layer 14 is preferably made from a blend of polypropylene copolymer, ethylene and silica/organic antiblock, a core layerl2 is preferably made from blend of antistatic and slip content and random polypropylene copolymer, the inner layer 14 and the intermediate layer 13is preferably made from a blend of propylene based elastomer and random polypropylene copolymer and the intermediate layer 11 is preferably made of antistatic and slip content.
The metalized BOPP film, as shown in Fig. 1(b), comprises of five layers having outer layer 20, intermediate layer 21, core layer 22, intermediate layer 23 and inner layer 24. The outer layer 20 is preferably made from a blend of inorganic/organic antiblock and random polypropylene copolymer, the core layer 22 is preferably made of a polypropylene homopolymer, the inner layer 24 is preferably made from a blend of polypropylene copolymer, propylene based elastomer and antiblock, the outer layer 20 is preferably made from a blend of anti-block and random polypropylene copolymer, the intermediate layer 23 is preferably made from a blend of propylene based elastomer and polypropylene homopolymer and the

intermediate layer 21 is preferably made of polypropylene homopolymer. The anti-block used is inorganic/organic antiblock based on acrylate.
The transparent and metalized films have low coefficient of friction and high seal strength.
Moreover, the enhanced gloss level of the films makes them suitable for both transparent and metalized versions of the films. The enhanced gloss levels enable reverse printing and bulk packaging.
Due to less density, BOPP film is preferred over polyethylene in light weight bulk packaging. Therefore, in the present invention BOPP film has higher gloss level with minimum of 85 while maintaining high seal strength than regular BOPP films. Further, the BOPP composition in the present invention allows for zipper to be applied in the packaging bag due to high heat sealing characteristics.
Many modifications and other embodiments of the invention set forth herein will readily occur to one skilled in the art to which the invention pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

We claim:

1.A multi-layer biaxially oriented polypropylene (BOPP) film comprises of:
an outer layer, a plurality of intermediate layer, a core layer and an inner layer;
wherein;
one intermediate layer is between the core layer and an inner layer and other
intermediate layer is between the core layer and the outer layer;
said BOPP film has a heat seal strength in the range of 500 gm/25mm to 2000 gm/25mm;
said BOPP film has a kinetic friction in the range of 0.15-0.35 us; and said BOPP film has gloss level in the range of 85-95.
2. The film as claimed in claim 1, wherein, the outer layer is made from a blend of
polypropylene copolymer, ethylene and silica/organic antiblock or a blend of inorganic/organic antiblock and random polypropylene copolymer.
3. The film as claimed in claim 1, wherein, the core layer is made from blend of
antistatic and slip content and random polypropylene copolymer or polypropylene homopolymer.
4. The film as claimed in claim 1, wherein, the inner layer is made from a blend of
polypropylene copolymer, ethylene and silica/organic antiblock or a blend of polypropylene copolymer, propylene based elastomer and antiblock.
5. The film as claimed in claim 1, wherein, the intermediate layer is made from a
blend of propylene based elastomer and random polypropylene copolymer or antistatic and slip content ora blend of propylene based elastomer and polypropylene homopolymer or polypropylene homopolymer.

6. The film as claimed in claim 1, wherein, themulti-layer BOPP film is either
transparent BOPP film or metalized BOPP film.
7. The film as claimed in claim 6, wherein, the transparent multi-layer BOPP is having an outer layer (10) and an inner layer (14) preferably made from a blend of polypropylene copolymer, ethylene and silica/organic antiblock, a core layer (12) preferably made from blend of antistatic and slip content and random polypropylene copolymer, an inner layer (14) and an intermediate layer (13) preferably made from a blend of propylene based elastomer and random polypropylene copolymer, an intermediate layer (11) preferably made of antistatic and slip content.
8. The film as claimed in claimed in claim 7, wherein, in the transparent multi-layer BOPP film the polypropylene homopolymer content is in the range of 80% to 99%; the random polypropylene copolymer content is in the range of 1% to 18%; the antistatic and slip content is in the range of 0.005% to 0.10%; the propylene based elastomer preferably olefinic elastomer is primarily composed of isotactic propylene repeat units with random ethylene distribution is in the range of 0.5% to 10%;and the silica/organic antiblock is in the range of 0.001% to 0.05%.
9. The film as claimed in claim 6, wherein, the metalized BOPP film is having an outer layer (20) preferably made from a blend of inorganic/organic antiblock and random polypropylene copolymer, a core layer (22) preferably made of a polypropylene homopolymer, an inner layer (24) preferably made from a blend of polypropylene copolymer, propylene based elastomer and antiblock, an outer layer (20) preferably made from a blend of anti-block and random polypropylene copolymer, an intermediate layer (23) preferably made from a blend of propylene based elastomer and polypropylene homopolymer and an intermediate layer (21) preferably made of polypropylene homopolymer; wherein the anti-block used is inorganic/organic antiblock based on acrylate.
10. The film as claimed in claim 9, wherein, in the metalized BOPP film the
polypropylene homopolymer content is in the range of 80% to 99%; the random

polypropylene copolymer content is in the range of 1% to 18%;-the propylene based elastomer preferably olefmic elastomer primarily composed of isotactic propylene repeat units with random ethylene distribution in the range of 0.5% to 10%; inorganic / organic antiblock is in the range of 0.001% to 0.05%; and inorganic/organic antiblock based on acrylate is in the range of 0.00% to 0.1%.
11. The film as claimed in claim 8 and 10, wherein, the propylene based elastomer is an olefmic elastomer primarily composed of isotactic propylene repeat units with random ethylene distribution and the antistatic and slip agents tend to reduce the treatment retention.
12. The film as claimed in claim 1, wherein, said BOPP film is optionally added with a polypropylene and universal zipper by means of heat sealing jaws.