WO2021074927A1 - Biaxially oriented polypropylene film with enhanced heat seal strength and method of manufacturing thereof - Google Patents

Biaxially oriented polypropylene film with enhanced heat seal strength and method of manufacturing thereof Download PDF

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Publication number
WO2021074927A1
WO2021074927A1 PCT/IN2020/050886 IN2020050886W WO2021074927A1 WO 2021074927 A1 WO2021074927 A1 WO 2021074927A1 IN 2020050886 W IN2020050886 W IN 2020050886W WO 2021074927 A1 WO2021074927 A1 WO 2021074927A1
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WIPO (PCT)
Prior art keywords
layer
polypropylene
film
bopp film
bopp
Prior art date
Application number
PCT/IN2020/050886
Other languages
French (fr)
Inventor
Sanjeev Kumar Pathak
Original Assignee
Max Speciality Films Ltd.
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Filing date
Publication date
Application filed by Max Speciality Films Ltd. filed Critical Max Speciality Films Ltd.
Publication of WO2021074927A1 publication Critical patent/WO2021074927A1/en

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B25/00—Layered products comprising a layer of natural or synthetic rubber
    • B32B25/04—Layered products comprising a layer of natural or synthetic rubber comprising rubber as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B25/08—Layered products comprising a layer of natural or synthetic rubber comprising rubber as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B25/00—Layered products comprising a layer of natural or synthetic rubber
    • B32B25/16—Layered products comprising a layer of natural or synthetic rubber comprising polydienes homopolymers or poly-halodienes homopolymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/16—Layered products comprising a layer of synthetic resin specially treated, e.g. irradiated
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • B32B27/20—Layered products comprising a layer of synthetic resin characterised by the use of special additives using fillers, pigments, thixotroping agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
    • B32B27/306—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl acetate or vinyl alcohol (co)polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J7/00—Chemical treatment or coating of shaped articles made of macromolecular substances
    • C08J7/04—Coating
    • C08J7/052—Forming heat-sealable coatings
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
    • C23C14/14—Metallic material, boron or silicon
    • C23C14/20—Metallic material, boron or silicon on organic substrates
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/03—3 layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/05—5 or more layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00—Layers arrangement
    • B32B2250/24—All layers being polymeric
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2255/00—Coating on the layer surface
    • B32B2255/10—Coating on the layer surface on synthetic resin layer or on natural or synthetic rubber layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2255/00—Coating on the layer surface
    • B32B2255/20—Inorganic coating
    • B32B2255/205—Metallic coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2255/00—Coating on the layer surface
    • B32B2255/26—Polymeric coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2270/00—Resin or rubber layer containing a blend of at least two different polymers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/30—Properties of the layers or laminate having particular thermal properties
    • B32B2307/31—Heat sealable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/514—Oriented
    • B32B2307/518—Oriented bi-axially
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/54—Yield strength; Tensile strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/558—Impact strength, toughness
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/582—Tearability
    • B32B2307/5825—Tear resistant
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/744—Non-slip, anti-slip
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/746—Slipping, anti-blocking, low friction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2439/00—Containers; Receptacles
    • B32B2439/70—Food packaging
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
    • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
    • C08J2323/10—Homopolymers or copolymers of propene
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2475/00—Characterised by the use of polyureas or polyurethanes; Derivatives of such polymers
    • C08J2475/04—Polyurethanes
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D7/00—Electroplating characterised by the article coated
    • C25D7/06—Wires; Strips; Foils
    • C25D7/0614—Strips or foils

Definitions

  • the present invention relates to a BOPP film. Specifically, the invention relates to BOPP film with enhanced heat seal properties, high moisture barrier, high oxygen barrier and outstanding metal adhesion properties.
  • BOPP film has a surface suitable for receiving various coatings for oxygen and moisture barrier properties.
  • the film also provides good heat-sealable layers for forming closed structures like packs/pouches/bags. Because of all these properties, BOPP film proves to be ideal for packaging chips and snacks, biscuits, noodles, frozen food, etc.
  • BOPP films are sealed together in the form of a package/bag to hold food items. Heat sealing is used to seal surfaces BOPP films with each other. In heat sealing, heat and pressure are applied to the sealing surfaces, thus forming a bond between the two surfaces, and sealing the two surfaces.
  • the packaging used for food requires protection of the delicate food inside packaging from both air and physical damages.
  • Nitrogen flushing is a method used in the packaging to cushion the food and to protect the food from both air and physical damages. Also, nitrogen does not react with food, keeping the food fresh for a long duration.
  • Metalizing is the process of deposition of a metal layer to a BOPP film. This metallization protects the food items inside the packaging from light and UV damages. Further, metallization enhances the oxygen and moisture barrier properties of the BOPP film. For metalizing, the BOPP film must have good metal adhesion properties. Existing BOPP films lack good metal adhesion properties and such films pose issue of poor lamination bond during adhesive and extrusion lamination process that can hamper the shelf life of food stored in such laminate with poor lamination bond.
  • a B OPP film with enhanced heat seal strength comprising: a core layer; two skin layers deposited on either side of the core layer, wherein the one skin layer is metalizable layer and the other skin layer is heat sealable layer; wherein the BOPP film has a heat seal strength in the range of 1.2 to 3 kg/inch, a water vapor transmission rate in the range of 0.05 to 0.30gm/m 2 /day and an oxygen transmission rate in the range of 0.05- 40cc/m 2 /day.
  • the core layer comprises polymer selected from the group consisting of homo polypropylene, a polypropylene based elastomer, terpolymer, and/or combination thereof.
  • the core layer comprises 90% to 95% homo polypropylene and 5% to 10% of polypropylene based elastomer or terpolymer.
  • the skin layer comprises polymer selected from the group consisting of: terpolymer or co-polymer and a polypropylene based elastomer, butene or ethylene base co-polymer and Maleic anhydride grafted polypropylene, Ethylene-vinyl alcohol co-polymer, and/or combination thereof.
  • At least one skin layer comprises 21 to 65% of Terpolymer or Co-Polymer, 20 to 50% of Polypropylene based elastomers, 5 to 15% of Tafmer and 10-14% of antiblock additive.
  • At least one skin layer comprises 50 to 70% of Butene and ethylene base Co-Polymer and 30 to 50% of Maleic anhydride grafted Polypropylene, or 100% of Maleic anhydride grafted Polypropylene, or 100% of Ethylene- vinyl alcohol co-polymer.
  • the BOPP film further comprises a tie layer disposed between the core layer and the at least one skin layer.
  • the tie layer comprising polymer selected from the group consisting of homo polypropylene, polypropylene based elastomer, co polymer, Terpolymer, Maleic anhydride grafted polypropylene, and/or combination thereof.
  • the tie layer comprising 30-60% of homo polypropylene and 40 to 70 % PP based elastomer, or 100% of homo polypropylene.
  • the BOPP film has metal adhesion in the range of 100 to 1200 gm/25mm.
  • a method of forming a BOPP film having enhanced heat seal strength comprising: Coextmding a core layer, two skin layers to form a polypropylene film; Orienting the polypropylene film in machine direction orientation (MDO) to obtain an oriented polypropylene film; Coating the oriented polypropylene film with polyurethane to obtain a polyurethane coated polypropylene film; Orienting the polyurethane coated polypropylene film in transverse direction orientation (TDO) to obtain a BOPP film; and Depositing a metal layer on atleast one of skin layer, wherein the BOPP film has a heat seal strength in the range of 1.2 to 3kg/inch, a water vapor transmission rate in the range of 0.05 to 0.30gm/m2/day, an oxygen transmission rate in the range of 0.05 -40cc/m2/day .
  • MDO machine direction orientation
  • TDO transverse direction orientation
  • the present invention solves the problems of the existing biaxially oriented polypropylene (BOPP) metalized films by providing a novel BOPP film comprising the following layers: a) a core layer b) at least one tie layer c) two skin layers.
  • BOPP biaxially oriented polypropylene
  • a BOPP film having: a) high heat seal strength, b) low seal initiation temperature, c) high oxygen barrier, d) high moisture barrier, e) high metal adhesion.
  • a BOPP film wherein the film is having a five-layered structure which comprises a skin layer, a tie layer, a core layer, a tie layer, and another skin layer.
  • a BOPP film wherein the film is having a three-layered structure which comprises a core layer and two skin layers.
  • a BOPP film having at least one skin layer comprising a combination of a terpolymer or Co-polymer and a polypropylene based elastomer.
  • a BOPP film having atleast one skin layer comprising a butene or ethylene base co-polymer and Maleic anhydride grafted polypropylene.
  • a BOPP film having a skin layer comprising Maleic anhydride grafted polypropylene.
  • a BOPP film having a skin layer comprising Ethylene- vinyl alcohol copolymer (EVOH).
  • EVOH Ethylene- vinyl alcohol copolymer
  • a BOPP film wherein the skin layer may further comprise TAFMER.
  • a BOPP film wherein the skin layer may further comprise organic antiblock agents.
  • a BOPP film wherein the skin layer may further comprise inorganic antiblock agents.
  • a BOPP film having a core layer comprising homo polypropylene and a polypropylene based elastomer.
  • a BOPP film having a core layer comprising a homo polypropylene and a terpolymer.
  • a BOPP film having a tie layer comprising homo polypropylene.
  • a BOPP film having a tie layer comprising polypropylene based elastomer and homopolypropylene or co-polymer or Terpolymer.
  • a BOPP film having a tie layer comprising MAH Grafted polypropylene.
  • Fig.1 is a schematic cross-sectional view of the process/apparatus used for the manufacturing of Biaxially Oriented Polypropylene film according to an embodiment of the present invention
  • Fig.2 is a schematic cross-sectional view of the Biaxially Oriented Polypropylene film according to another embodiment of the present invention.
  • Fig.3 is a schematic cross-sectional view of the Biaxially Oriented Polypropylene film according to yet another embodiment of the present invention.
  • This disclosure is generally directed to products and methods describing a “BOPP film”, exhibiting high heat seal strength, low seal initiation temperature, high oxygen barrier, high moisture barrier, and high metal adhesion properties.
  • Reference to “layer” or “film” as used herein refers to a structure of a single polymer type or a blend of polymers.
  • BOPP film refers to a Biaxially Oriented Polypropylene Film which are produced by stretching polypropylene film in both machine direction and transverse direction. These films are preferred substrate for food packaging globally. Other than food packaging, BOPP films are also used for laminating and printing applications.
  • skin layer refers to the portion of BOPP film that is located outermost of all the layers of the BOPP film.
  • core layer refers to the portion of BOPP film that is located in the center of all the layers or being sandwich between the skin layers of the BOPP film.
  • tie layer refers to a material placed on one or more layers, partially or entirely, to promote the adhesion of one layer to another surface.
  • tie layers are the adhesive layers or coatings which positioned between skin layers and the core layer of the multi-layered BOPP film.
  • anti-block additive refers to additives which are used to minimize the interaction between two layers.
  • Suitable anti-blocking additive include, Organic anti blocking agents selected from, but not limited to, PMMA, silicones, silicon gum and PDMS etc; or Inorganic anti-blocking selected from, but not limited to, synthetic silica, silicates, aluminum silicates, etc.
  • Multilayered BOPP film of the present invention is manufactured by using a co-extrusion process followed by a biaxial orientation process.
  • the co-extrusion process involves the usage of multiple extruders to form multilayer flat film.
  • Co-extruded film contains most of the characteristics of laminated films, however, all the layers are formed by extrusion at the same time.
  • Biaxial orientation is the stretching of film in two perpendicular directions. Biaxial orientation improves the tensile strength, impact strength, tear strength, optical and barrier properties, stiffness, and resistance to crazing.
  • a method of forming a BOPP film is provided. The method comprises coextruding a core layer, two skin layers to form a polypropylene film.
  • the polypropylene film is then oriented in machine direction orientation (MDO) to obtain an oriented polypropylene film.
  • MDO machine direction orientation
  • the oriented polypropylene film is then coated with water-based polyurethane to obtain a polyurethane coated polypropylene film followed by orienting the polyurethane coated polypropylene film in transverse direction orientation (TDO) to obtain a BOPP film.
  • TDO transverse direction orientation
  • a metal layer is deposited over at least one skin layer.
  • Fig.l shows an apparatus (100) for carrying out the manufacturing of the BOPP film.
  • the raw material (not shown) is first delivered to a hopper unit (1).
  • the raw material used for making BOPP film is polypropylene resins with other additional additives. Different types of resins may be used for different layers of BOPP film.
  • the hopper unit ( 1 ) helps in feeding the raw material to a co-extrusion unit.
  • the co-extrusion unit comprises of a main extruder (2), first co-extruder (4) and a second co-extruder (5). Any number of co-extruders can be used depending on the number of layers required.
  • the main extruder (2) can be a screw-type extruder with a screw drive (3). The thickness of different layers of the BOPP film is controlled by the relative speeds and sizes of the main extruder (2), first co-extruder (4), and second co-extruder (5).
  • the raw material is subjected to heat and pressure which results in melting of the raw material. This molten raw material is then pushed to an extruder head (not shown) with the help of the screw drive (3).
  • screw extruders are used in the present invention, however, other suitable extruders, for example, twin- screw extruder, piston extruder, ram extruder, etc, as obvious to a person skilled in the art, can also be used.
  • the main extruder (2), first co-extruder (4) and second co-extruder (5) are maintained at a temperature ranging from about 220° C to about 260° C.
  • the T-die (6) can comprise multiple openings that take the melted raw material from the extruder head of the main extruder (2), first co-extruder (4) and second co-extruder (5).
  • the bottom of the T-die (6) comprises a long slit (not shown).
  • the long slit of the T-die (6) converts the molten raw material into a film.
  • the T-die (6) is kept at a temperature of about 240° C to 250° C.
  • the T-die (6) is used here as an exemplary die, however, other suitable dies available in the market and obvious to a person skilled in the art, can also be utilized.
  • the film undergoes a quenching process, which solidifies the film.
  • the film from the T-die (6) is delivered to a chilled roller (7).
  • the chilled roller (7) brings the film in contact with a water bath (8).
  • the chilled roller (7) and water bath (8) are maintained at a temperature of about 25-42 ° C.
  • the solidified film from the water bath (8) goes to a machine direction orientation (MDO) unit (9) where it is stretched in the machine direction.
  • the machine direction is the direction parallel to the direction of the movement of the film on a film-making machine.
  • the machine direction orientation unit (MDU) (9) comprises a set of preheating rollers (10), machine direction stretching rollers (11) and annealing rollers (12).
  • the film from the water bath (8) first moves over the set of preheating rollers (10) of the machine direction orientation (MDO) unit (9).
  • the set of preheating rollers (10) are maintained at a temperature ranging from about 100° C to 150° C.
  • the film passes over the machine direction stretching rollers (11), which are arranged in series.
  • the temperature of the machine direction stretching rollers (11) are kept at about 70° C to 90° C.
  • the film passes over the annealing rollers (12), which are maintained at a temperature of about 100° C to 120 0 C.
  • the stretching in machine direction orientation (MDO) unit (9) reduces the thickness of the film and enhances its mechanical properties.
  • the film undergoes water based polyurethane coating through a coating unit.
  • the Polyurethane based coating enhances the metal adhesion, OTR and WVTR properties of the BOPP film.
  • a dispersion of acrylic and/or polyurethane (PU) is used for coating.
  • water based polyurethane coating is done in an inline coating unit (13).
  • the polyurethane coating unit (13) is integrated with the main assembly line. This process improves the surface chemistry of the BOPP film and helps in achieving superior metal adhesion, oxygen transmission rate (OTR) and water vapor transmission rate (WVTR), luster and other optical properties.
  • the polyurethane coating process is carried out in an offline coating unit (not shown).
  • an offline coating unit not shown.
  • a dedicated separate apparatus for polyurethane coating is used.
  • the polyurethane coating varies in the range of about 0.05 gram/sqm to 0.20 gram/sqm dry coating.
  • Mitsui Takelac WPB341 is used for polyurethane coating.
  • the polyurethane coated film is then stretched in a transverse direction i.e. direction perpendicular to the machine direction, in a transverse direction orientation (TDO) unit (14).
  • TDO transverse direction orientation
  • the film first passes over a preheating zone (not shown).
  • the preheating zone is maintained at a temperature ranging from about 160 0 C to 180° C.
  • the preheated film is then stretched in a transverse direction with the help of chain clips or jaws (not shown).
  • the chain clips or jaws are kept at a temperature of about 158 0 C/ fan speed about 90%.
  • the film is then transferred to a set of annealing rollers (not shown).
  • the annealing rollers are maintained at a temperature ranging from about 160 0 C to 165 0 C/ fan speed about 80%. This transverse direction orientation further decreases the film -thickness and enhances its mechanical properties.
  • MDSR may be defined as the length of a portion of the film after stretching divided by the initial length of that portion.
  • TDSR may be defined as the width of a portion of the film after stretching divided by the initial width of that portion.
  • MDSR/TDSR ratio for the above-mentioned BOPP film is 4.2 to 5.5/ 8.5 to 10.
  • Pull roll (15) takes the film from the TDO unit (14) and transfers them to a winder (17).
  • a thickness gauge (16) is located between the pull roll (15) and winder (17) for quality inspection.
  • the film wound on the winder (17) subsequently undergoes the metallization process in a metallization unit (not shown).
  • a layer of metal is deposited on one side of the BOPP film.
  • Metallization processes are known in the art and can be any of the known methods, but not limited to, vacuum deposition, electroplating, sputtering, spraying. Metallization is generally done on the heat-sealable skin layer of the film.
  • Metal used for metallization can be selected from, but not limited to, aluminum, gold, silver, copper.
  • the apparatus described in previous embodiment results in the formation of a BOPP film.
  • the BOPP film comprises a core layer; two skin layers deposited on either side of the core layer, wherein the one skin layer is metalizable layer and the other skin layer is heat sealable layer.
  • the BOPP film further comprises a tie layer disposed between the core layer and the at least one skin layer.
  • the tie layer comprises polymer selected from the group comprising: homo polypropylene, polypropylene based elastomer, co-polymer, Terpolymer, Maleic anhydride grafted polypropylene, and/or combination thereof.
  • the BOPP film of the invention has a water vapor transmission rate in the range of 0.05 to 0.20gm/m2/day and an oxygen transmission rate in the range of 5-10cc/m2/day.
  • the BOPP film has heat seal strength in the range of 1.2 to 3 kg/inch.
  • Fig.2 shows a BOPP film (20) having a five layered structure.
  • the five layered structure comprises an upper skin layer (21), an upper tie layer (22), a core layer (23), a lower tie layer (24), and a lower skin layer (25).
  • the upper skin layer (21) comprises a combination of a co-polymer or terpolymer and a polypropylene based elastomer.
  • polypropylene based elastomer primarily comprises isostatic propylene repeat units with random ethylene distribution. Thickness of the upper skin layer ranges from 1 micron to 4 microns.
  • Vistamaxx is used as polypropylene based elastomer. Vistamaxx enhances the heat-sealing properties of the upper skin layer (21). In an embodiment, Vistamaxx 3980 is used as polypropylene based elastomer. In another embodiment, Vistamaxx 3588 is used as polypropylene based elastomer.
  • the upper skin layer (21) can further comprise TAFMER.
  • TAFMER easily blends with homo polypropylene or polypropylene based elastomer or co-polymer or Terpolymer, and other thermoplastics to enhance the characteristics such as low-temperature heat sealability, hot tack and heat seal strength of the BOPP film.
  • TAFMER XM 7070 is used in the upper skin layer (21).
  • the upper skin layer (21) comprises DP- 8220 M as alternate of TAFMER XM7070.
  • DP-8220 M is a random copolymer of butene- 1 with medium ethylene content. The addition of DP- 8220 M reduces the seal initiation temperature of the sealing layer of the BOPP film.
  • the upper skin layer (21) can further comprise an organic or inorganic anti-blocking agent.
  • anti-blocking agents helps in preventing sticking of the film on rollers or onto itself during winding (known as blocking).
  • organic anti -blocking agents are used in the upper skin layer (21).
  • Organic anti-blocking agents can be selected from but not limited to PMMA, silicones, silicon gum and PDMS etc.
  • inorganic anti-blocking agents are used in the upper skin layer (21).
  • Inorganic anti-blocking can be selected from, but not limited to, synthetic silica, silicates, aluminum silicates, etc.
  • a mixture of both organic and inorganic anti blocking agents is used in the upper skin layer (21).
  • the Upper tie layer (22) comprises a combination of a Homo polypropylene and a polypropylene based elastomer.
  • Tafmer PN 3560 is selected as polypropylene based elastomer.
  • the thickness of the upper tie layer (22) ranges from 2 micron to 5 microns.
  • the core layer (23) comprises a combination of a homo polypropylene and polypropylene based elastomer.
  • the core layer (23) comprises a combination of a homo polypropylene and a terpolymer.
  • the core layer (23) comprises a combination of terpolymer, polypropylene based elastomer and homo polypropylene.
  • polypropylene based elastomer primarily composes of isostatic propylene repeat units with random ethylene distribution.
  • the Lower tie layer (24) comprises a homo polypropylene.
  • the Lower tie layer (24) comprises of MAH Grafted polypropylene.
  • Admer QF 500T is selected as MAH Grafted polypropylene.
  • the thickness of the lower tie layer (24) ranges from 0.5 micron to 2 microns.
  • the lower skin layer (25) comprises of a combination of Butene or ethylene base Co- Polymer and Maleic anhydride grafted polypropylene.
  • PKS 607 is selected as butene base co-polymer.
  • 3C30F HP is selected as butene base co-polymer.
  • PKS407 HP is selected as ethylene base co-polymer.
  • Admer AT 3177 E is selected as Maleic anhydride grafted polypropylene.
  • the lower skin layer (25) comprises 100% of Maleic anhydride grafted polypropylene.
  • Admer AT 3177 E is selected as Maleic anhydride grafted polypropylene.
  • the lower skin layer (25) comprises ethylene vinyl alcohol (EVOH).
  • EVOH enhances the barrier properties of the film.
  • Eval G156B or G-Soamol GH3804B or Soarnol H4815B is selected as an EVOH.
  • the metallization is performed on this lower skin layer (25) where a metal layer is deposited on the lower skin layer.
  • the thickness of the lower skin layer (25) ranges from 0.6 micron to 2.0 microns.
  • anti-blocking agents are used in the top skin layer, however, any of the above-mentioned skin layers can comprise an anti-blocking agent.
  • upper skin layer (21) may further comprise other processing aids or additives such as, slip agents, and combinations thereof.
  • upper skin layer (21) and lower skin layer (25) can further undergo various surface treatment processes selected from, but not limited to, flame treatment, corona treatment, plasma treatment or any other process before metallization, coatings, printing inks, and/or lamination.
  • the upper tie layer (22) and the lower tie layer (24) and core layer (23) can further comprise of various additives such as, opacifying agents, pigments, slip or antistatic agents, antioxidants, fillers, moisture barrier additives, gas barrier additives, hydrocarbon waxes, fillers such as calcium carbonate, and combinations thereof. Further, any of the above-mentioned additives can be used and added in core layer
  • Fig.3 shows a BOPP film (20), having a three-layered structure.
  • the three-layered structure comprises an upper skin layer (21), a core layer (23) and a lower skin layer (25).
  • the multilayered BOPP film described in previous embodiments are exemplary BOPP film only and therefore should not be construed as a limitation to the present invention. It may be obvious for the person skilled in the art, to use any combination of the above mentioned upper skin layer (21), upper tie layer (22), core layer (23), lower tie layer (24) and lower skin layer (25) to form a BOPP film.
  • the BOPP film of the present invention exhibit improved heat-seal strength.
  • the heat seal strength measured for BOPP film is in the range of 1.2 kg/inch to 3.0 kg/inch.
  • Seal initiation temperature of the BOPP film measured at 30 psi and 1 sec dwell time ranges from 70° C to 115° C.
  • Oxygen transmission rate is the measure of the amount of oxygen gas that passes through a substance (BOPP film in the present case) over a given period. OTR values for the BOPP film of the present invention, vary in the range of 0.05cc/m 2 /day to 40 cc/m 2 /day.
  • Water vapour transmission rate is the measure of the amount of water vapour/moisture that passes through a substance (BOPP film in the present case) over a given period.
  • WVTR of the BOPP film vary in the range of 0.05 gm/sqm/day to 0.3 gm/sqm/day.
  • Metal adhesion of the BOPP film through AIMCAL ref method (with EAA film) vary in the range of 100 gm/25mm to 1200 gm/25mm.
  • BOPP film of the present invention The food items stored in the BOPP film of the present invention have a great shelf life. Further, BOPP film manufactured from the above described method are suitable for both adhesive as well as extrusion lamination. No metal cracking takes place during extrusion lamination of the BOPP film of the present invention.
  • the BOPP film prepared using the above described method are typically used as inner web of laminate in 3 Ply as sandwich layer and as sealant layer in 2 Ply laminate structures for VFFS (Vertical Form Fill Seal) machine and HFFS (Horizontal Form Fill Seal) machines.
  • VFFS Very Form Fill Seal
  • HFFS Horizontal Form Fill Seal
  • Skin layer (Heat Sealable Side): 21 to 65% Terpolymer or Co-Polymer + 20 to 50% PP based elastomer (Vistamaxx 3980 or Vistamaxx 3588) + 5-15% Tafmer XM7070or DP-8220 M + 8 to 10 % Organic and 2 to 4 % Inorganic antiblock or only organic antiblock. Layer thickness is in the range from 1.5 to 3 microns
  • Tie layer 30 to 60% Homo PP + 40% to 70 % PP based elastomer (Tafmer PN 3560). Layer thickness is in the range from 3 to 5 microns
  • Skin layer 50 to 70% Butene or ethylene base Co-Polymer (PKS 607 or 3C30L HP or PKS407 HP) and 30 to 50% of Maleic anhydride grafted PP (Admer AT 3177 E.
  • Layer thickness is in the range from 0.6 to 1.5mic
  • Skin layer top-coat Polyurethane dispersion (Mitsui Takelac WPB341) coating on aforementioned metalisable surface. With 0.05 to 0.20 gram/sqm dry coating.
  • Skin layer 21 to 65% Terpolymer or Co-Polymer + 20 to 50% PP based elastomeric (Vistamaxx 3980 or Vistamaxx 3588) + 5 to 15% Tafmer XM7070 or DP-8220 M + 8 to 10 % Organic and 2 to 4 % Inorganic antiblock or only organic antiblock. Layer thickness is on the range from 1.5 to 4 micron
  • Tie layer 30 to 40% Homo PP + 60% to 70 % PP based elastomer (Tafmer PN 3560). Layer thickness is in the range from 2 to 5 micron
  • Skin layer 21-65% Terpolymer or Co-Polymer + 20-50% PP based elastomeric (Vistamaxx 3980 or Vistamaxx 3588) + 5- 15% Tafmer XM7070 or DP-8220 M + 8-10 % Organic and 2-4 % Inorganic antiblock or only organic antiblock. Layer thickness is in the range from 2 to 5 micron
  • Tie layer 30 to 60% Homo PP + 40 to 70 % PP based elastomer (Tafmer PN 3560). Layer thickness is in the range from 2 to 5 mic
  • Core layer 90 to 95% Homo PP + 5-10% of PP based elastomer or Terpolymer
  • Tie layer 100% MAH Grafted PP (Admer QL 500T). Layer thickness is in the range from 0.5 to 2.0 mic
  • Skin layer 100% EVOH (EVAL G 156 B). Layer thickness is in the range from 0.6 to 2.0 mic
  • Table 1 shows the values of various properties measured of the above-mentioned BOPP film.

Abstract

The present invention relates to a method of manufacturing biaxially oriented polypropylene (BOPP) film with high heat seal strength, low seal initiation temperature, high metal adhesion, high moisture barrier, and high oxygen barrier. The BOPP film with enhanced heat seal strength comprises a core layer; two skin layers deposited on either side of the core layer, wherein the one skin layer is metalizable layer and the other skin layer is heat sealable layer.

Description

BIAXIALLY ORIENTED POLYPROPYLENE FILM WITH ENHANCED HEAT SEAL STRENGTH AND METHOD OF MANUFACTURING THEREOF
CROSS-REFERENCE TO RELATED APPLICATION
[001] This application claims the benefit of IN Provisional Application No 201911041959, filed October 16, 2019, the contents of which are incorporated herein by reference in its entirety.
FIELD OF INVENTION
[002] The present invention relates to a BOPP film. Specifically, the invention relates to BOPP film with enhanced heat seal properties, high moisture barrier, high oxygen barrier and outstanding metal adhesion properties.
BACKGROUND OF THE INVENTION
[003] BOPP film has a surface suitable for receiving various coatings for oxygen and moisture barrier properties. The film also provides good heat-sealable layers for forming closed structures like packs/pouches/bags. Because of all these properties, BOPP film proves to be ideal for packaging chips and snacks, biscuits, noodles, frozen food, etc. BOPP films are sealed together in the form of a package/bag to hold food items. Heat sealing is used to seal surfaces BOPP films with each other. In heat sealing, heat and pressure are applied to the sealing surfaces, thus forming a bond between the two surfaces, and sealing the two surfaces.
[004] The packaging used for food requires protection of the delicate food inside packaging from both air and physical damages. Nitrogen flushing is a method used in the packaging to cushion the food and to protect the food from both air and physical damages. Also, nitrogen does not react with food, keeping the food fresh for a long duration.
[005] Traditional BOPP films have heat seal strength range of 300 gm/25mm - 500 gm/25mm and thus is not suitable enough for nitrogen flushing. Further, these films require a high seal initiation temperature and thus a large amount of heat energy for heat sealing is required. Heat seal-oriented films with optical, heat-seal, barrier and hot tack properties have been described in US 11/003,269; US09/810,956. These patent applications are incorporated here by reference.
[006] Metalizing is the process of deposition of a metal layer to a BOPP film. This metallization protects the food items inside the packaging from light and UV damages. Further, metallization enhances the oxygen and moisture barrier properties of the BOPP film. For metalizing, the BOPP film must have good metal adhesion properties. Existing BOPP films lack good metal adhesion properties and such films pose issue of poor lamination bond during adhesive and extrusion lamination process that can hamper the shelf life of food stored in such laminate with poor lamination bond.
[007] There is a need for developing a BOPP film, with higher heat seal strength, low seal initiation temperature, superior metal adhesion, high moisture barrier and high oxygen barrier to overcome the above-mentioned shortcomings.
SUMMARY OF THE INVENTION
[008] According to an aspect of the present invention, there is provided a B OPP film with enhanced heat seal strength comprising: a core layer; two skin layers deposited on either side of the core layer, wherein the one skin layer is metalizable layer and the other skin layer is heat sealable layer; wherein the BOPP film has a heat seal strength in the range of 1.2 to 3 kg/inch, a water vapor transmission rate in the range of 0.05 to 0.30gm/m2/day and an oxygen transmission rate in the range of 0.05- 40cc/m2/day.
[009] According to another aspect of the present invention, the core layer comprises polymer selected from the group consisting of homo polypropylene, a polypropylene based elastomer, terpolymer, and/or combination thereof.
[0010] According to another aspect of the present invention, the core layer comprises 90% to 95% homo polypropylene and 5% to 10% of polypropylene based elastomer or terpolymer.
[0011] According to yet another aspect of the present invention, the skin layer comprises polymer selected from the group consisting of: terpolymer or co-polymer and a polypropylene based elastomer, butene or ethylene base co-polymer and Maleic anhydride grafted polypropylene, Ethylene-vinyl alcohol co-polymer, and/or combination thereof.
[0012] According to another aspect of the present invention, at least one skin layer comprises 21 to 65% of Terpolymer or Co-Polymer, 20 to 50% of Polypropylene based elastomers, 5 to 15% of Tafmer and 10-14% of antiblock additive.
[0013] According to another aspect of the present invention, at least one skin layer comprises 50 to 70% of Butene and ethylene base Co-Polymer and 30 to 50% of Maleic anhydride grafted Polypropylene, or 100% of Maleic anhydride grafted Polypropylene, or 100% of Ethylene- vinyl alcohol co-polymer.
[0014] According to another aspect of the present invention, wherein a metal layer deposited over the at least one skin layer.
[0015] According to yet another aspect of the present invention, the BOPP film further comprises a tie layer disposed between the core layer and the at least one skin layer. [0016] According to yet another aspect of the present invention, the tie layer comprising polymer selected from the group consisting of homo polypropylene, polypropylene based elastomer, co polymer, Terpolymer, Maleic anhydride grafted polypropylene, and/or combination thereof.
[0017] According to yet another aspect of the present invention, the tie layer comprising 30-60% of homo polypropylene and 40 to 70 % PP based elastomer, or 100% of homo polypropylene.
[0018] According to another aspect of the present invention, the BOPP film has metal adhesion in the range of 100 to 1200 gm/25mm.
[0019] According to yet another aspect of the present invention, there is provided a method of forming a BOPP film having enhanced heat seal strength, the method comprising: Coextmding a core layer, two skin layers to form a polypropylene film; Orienting the polypropylene film in machine direction orientation (MDO) to obtain an oriented polypropylene film; Coating the oriented polypropylene film with polyurethane to obtain a polyurethane coated polypropylene film; Orienting the polyurethane coated polypropylene film in transverse direction orientation (TDO) to obtain a BOPP film; and Depositing a metal layer on atleast one of skin layer, wherein the BOPP film has a heat seal strength in the range of 1.2 to 3kg/inch, a water vapor transmission rate in the range of 0.05 to 0.30gm/m2/day, an oxygen transmission rate in the range of 0.05 -40cc/m2/day .
[0020] According to yet another aspect, the present invention solves the problems of the existing biaxially oriented polypropylene (BOPP) metalized films by providing a novel BOPP film comprising the following layers: a) a core layer b) at least one tie layer c) two skin layers.
[0021] According to yet another aspect of the present invention, there is provided a BOPP film having: a) high heat seal strength, b) low seal initiation temperature, c) high oxygen barrier, d) high moisture barrier, e) high metal adhesion.
[0022] According to yet another aspect of the present invention, there is provided a BOPP having excellent nitrogen flushing properties.
[0023] According to yet another aspect of the present invention, there is provided a BOPP film, wherein the film is having a five-layered structure which comprises a skin layer, a tie layer, a core layer, a tie layer, and another skin layer. [0024] According to yet another aspect of the present invention, there is provided a BOPP film, wherein the film is having a three-layered structure which comprises a core layer and two skin layers.
[0025] According to yet another aspect of the present invention, there is provided a BOPP film, having at least one skin layer comprising a combination of a terpolymer or Co-polymer and a polypropylene based elastomer.
[0026] According to yet another aspect of the present invention, there is provided a BOPP film, having atleast one skin layer comprising a butene or ethylene base co-polymer and Maleic anhydride grafted polypropylene.
[0027] According to yet another aspect of the present invention, there is provided a BOPP film, having a skin layer comprising Maleic anhydride grafted polypropylene.
[0028] According to yet another aspect of the present invention, there is provided a BOPP film, having a skin layer comprising Ethylene- vinyl alcohol copolymer (EVOH).
[0029] According to yet another aspect of the present invention, there is provided a BOPP film, wherein the skin layer may further comprise TAFMER.
[0030] According to yet another aspect of the present invention, there is provided a BOPP film, wherein the skin layer may further comprise organic antiblock agents.
[0031] According to yet another aspect of the present invention, there is provided a BOPP film, wherein the skin layer may further comprise inorganic antiblock agents.
[0032] According to yet another aspect of the present invention, there is provided a BOPP film, having a core layer comprising homo polypropylene and a polypropylene based elastomer.
[0033] According to yet another aspect of the present invention, there is provided a BOPP film, having a core layer comprising a homo polypropylene and a terpolymer.
[0034] According to yet another aspect of the present invention, there is provided a BOPP film, having a tie layer comprising homo polypropylene.
[0035] According to yet another aspect of the present invention, there is provided a BOPP film, having a tie layer comprising polypropylene based elastomer and homopolypropylene or co-polymer or Terpolymer.
[0036] According to yet another aspect of the present invention, there is provided a BOPP film, having a tie layer comprising MAH Grafted polypropylene. DETAILED DESCRIPTION OF DRAWINGS
The foregoing and other features and advantages of the invention will be more fully understood from the following descriptions made with reference to the drawings.
[0037] Fig.1 is a schematic cross-sectional view of the process/apparatus used for the manufacturing of Biaxially Oriented Polypropylene film according to an embodiment of the present invention;
[0038] Fig.2 is a schematic cross-sectional view of the Biaxially Oriented Polypropylene film according to another embodiment of the present invention; and
[0039] Fig.3 is a schematic cross-sectional view of the Biaxially Oriented Polypropylene film according to yet another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Aspects of the present invention are best understood by reference to the description set forth herein. All the aspects described herein will be better appreciated and understood when considered in conjunction with the following descriptions. It should be understood, however, that the following descriptions, while indicating preferred aspects and numerous specific details thereof, are given by way of illustration only and should not be treated as limitations. Changes and modifications may be made within the scope herein without departing from the spirit and scope thereof, and the present invention herein includes all such modifications.
[0041] Several aspects of the present invention are disclosed herein. It is to be understood that these aspects may or may not overlap with one another. Thus, part of one aspect may fall within the scope of another aspect, and vice versa. Each aspect is illustrated by several embodiments, each of which in turn, can include one or more specific embodiments. It is to be understood that the embodiments may or may not overlap with each other. Thus, part of one embodiment, or specific embodiments thereof, may or may not fall within the ambit of another, or specific embodiments thereof, and vice versa.
[0042] A broad framework of the principles will be presented by describing various embodiments of this invention using exemplary aspects. The terms "one embodiment" or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosure. For clarity and ease of description, each aspect includes only a few embodiments. Different embodiments from different aspects may be combined or practiced separately, to design a customized process or product depending upon application requirements. Many different combinations and sub-combinations of a few representative processes or structures shown within the broad framework of this invention, that may be apparent to those skilled in the art but not explicitly shown or described, should not be construed as precluded.
[0043] This disclosure is generally directed to products and methods describing a “BOPP film”, exhibiting high heat seal strength, low seal initiation temperature, high oxygen barrier, high moisture barrier, and high metal adhesion properties.
Definitions:
[0044] Reference to “layer” or “film” as used herein refers to a structure of a single polymer type or a blend of polymers.
[0045] Reference to “BOPP film” as used herein refers to a Biaxially Oriented Polypropylene Film which are produced by stretching polypropylene film in both machine direction and transverse direction. These films are preferred substrate for food packaging globally. Other than food packaging, BOPP films are also used for laminating and printing applications.
[0046] Reference to "skin layer" as used herein refers to the portion of BOPP film that is located outermost of all the layers of the BOPP film.
[0047] Reference to "core layer" as used herein refers to the portion of BOPP film that is located in the center of all the layers or being sandwich between the skin layers of the BOPP film.
[0048] Reference to "tie layer," as used herein refers to a material placed on one or more layers, partially or entirely, to promote the adhesion of one layer to another surface. Preferably, tie layers are the adhesive layers or coatings which positioned between skin layers and the core layer of the multi-layered BOPP film.
[0049] Reference to "anti-block additive," as used herein refers to additives which are used to minimize the interaction between two layers. Suitable anti-blocking additive include, Organic anti blocking agents selected from, but not limited to, PMMA, silicones, silicon gum and PDMS etc; or Inorganic anti-blocking selected from, but not limited to, synthetic silica, silicates, aluminum silicates, etc.
[0050] Multilayered BOPP film of the present invention is manufactured by using a co-extrusion process followed by a biaxial orientation process. The co-extrusion process involves the usage of multiple extruders to form multilayer flat film. Co-extruded film contains most of the characteristics of laminated films, however, all the layers are formed by extrusion at the same time. Biaxial orientation is the stretching of film in two perpendicular directions. Biaxial orientation improves the tensile strength, impact strength, tear strength, optical and barrier properties, stiffness, and resistance to crazing. [0051] According to an embodiment of the invention, a method of forming a BOPP film is provided. The method comprises coextruding a core layer, two skin layers to form a polypropylene film. The polypropylene film is then oriented in machine direction orientation (MDO) to obtain an oriented polypropylene film. The oriented polypropylene film is then coated with water-based polyurethane to obtain a polyurethane coated polypropylene film followed by orienting the polyurethane coated polypropylene film in transverse direction orientation (TDO) to obtain a BOPP film. After obtaining the BOPP film, a metal layer is deposited over at least one skin layer.
[0052] According to another embodiment of the invention, Fig.l shows an apparatus (100) for carrying out the manufacturing of the BOPP film. The raw material (not shown) is first delivered to a hopper unit (1). In a preferred embodiment, the raw material used for making BOPP film is polypropylene resins with other additional additives. Different types of resins may be used for different layers of BOPP film.
[0053] The hopper unit ( 1 ), helps in feeding the raw material to a co-extrusion unit. The co-extrusion unit comprises of a main extruder (2), first co-extruder (4) and a second co-extruder (5). Any number of co-extruders can be used depending on the number of layers required. The main extruder (2) can be a screw-type extruder with a screw drive (3). The thickness of different layers of the BOPP film is controlled by the relative speeds and sizes of the main extruder (2), first co-extruder (4), and second co-extruder (5).
[0054] In the main extruder (2), first co-extruder (4) and second co-extruder (5), the raw material is subjected to heat and pressure which results in melting of the raw material. This molten raw material is then pushed to an extruder head (not shown) with the help of the screw drive (3). Preferably screw extruders are used in the present invention, however, other suitable extruders, for example, twin- screw extruder, piston extruder, ram extruder, etc, as obvious to a person skilled in the art, can also be used. The main extruder (2), first co-extruder (4) and second co-extruder (5), are maintained at a temperature ranging from about 220° C to about 260° C.
[0055] From the extruder head the melted raw material is transferred to a T-die (6). The T-die (6) can comprise multiple openings that take the melted raw material from the extruder head of the main extruder (2), first co-extruder (4) and second co-extruder (5). The bottom of the T-die (6) comprises a long slit (not shown). The long slit of the T-die (6) converts the molten raw material into a film. The T-die (6) is kept at a temperature of about 240° C to 250° C. The T-die (6) is used here as an exemplary die, however, other suitable dies available in the market and obvious to a person skilled in the art, can also be utilized. [0056] After the conversion of raw material to a film by the T-die (6), the film undergoes a quenching process, which solidifies the film. The film from the T-die (6) is delivered to a chilled roller (7). The chilled roller (7) brings the film in contact with a water bath (8). In a preferred embodiment, the chilled roller (7) and water bath (8) are maintained at a temperature of about 25-42 ° C.
[0057] The solidified film from the water bath (8) goes to a machine direction orientation (MDO) unit (9) where it is stretched in the machine direction. The machine direction is the direction parallel to the direction of the movement of the film on a film-making machine. The machine direction orientation unit (MDU) (9) comprises a set of preheating rollers (10), machine direction stretching rollers (11) and annealing rollers (12).
[0058] The film from the water bath (8) first moves over the set of preheating rollers (10) of the machine direction orientation (MDO) unit (9). The set of preheating rollers (10) are maintained at a temperature ranging from about 100° C to 150° C. After preheating, the film passes over the machine direction stretching rollers (11), which are arranged in series. In a preferred embodiment, the temperature of the machine direction stretching rollers (11) are kept at about 70° C to 90° C. Subsequently, the film passes over the annealing rollers (12), which are maintained at a temperature of about 100° C to 120 0 C. The stretching in machine direction orientation (MDO) unit (9) reduces the thickness of the film and enhances its mechanical properties.
[0059] After machine direction orientation, the film undergoes water based polyurethane coating through a coating unit. The Polyurethane based coating enhances the metal adhesion, OTR and WVTR properties of the BOPP film. In another embodiment, a dispersion of acrylic and/or polyurethane (PU) is used for coating.
[0060] In another embodiment, water based polyurethane coating is done in an inline coating unit (13). In the inline coating process, the polyurethane coating unit (13) is integrated with the main assembly line. This process improves the surface chemistry of the BOPP film and helps in achieving superior metal adhesion, oxygen transmission rate (OTR) and water vapor transmission rate (WVTR), luster and other optical properties.
[0061] In another embodiment, the polyurethane coating process is carried out in an offline coating unit (not shown). In the off-line coating process, a dedicated separate apparatus for polyurethane coating is used.
[0062] The polyurethane coating varies in the range of about 0.05 gram/sqm to 0.20 gram/sqm dry coating. In a preferred embodiment, Mitsui Takelac WPB341 is used for polyurethane coating. [0063] The polyurethane coated film is then stretched in a transverse direction i.e. direction perpendicular to the machine direction, in a transverse direction orientation (TDO) unit (14). In the transverse direction orientation (TDO) unit (14), the film first passes over a preheating zone (not shown). The preheating zone is maintained at a temperature ranging from about 160 0 C to 180° C. The preheated film is then stretched in a transverse direction with the help of chain clips or jaws (not shown). In a preferred embodiment, the chain clips or jaws are kept at a temperature of about 158 0 C/ fan speed about 90%. The film is then transferred to a set of annealing rollers (not shown). In a preferred embodiment, the annealing rollers are maintained at a temperature ranging from about 160 0 C to 165 0 C/ fan speed about 80%. This transverse direction orientation further decreases the film -thickness and enhances its mechanical properties.
[0064] MDSR may be defined as the length of a portion of the film after stretching divided by the initial length of that portion. TDSR may be defined as the width of a portion of the film after stretching divided by the initial width of that portion. MDSR/TDSR ratio for the above-mentioned BOPP film is 4.2 to 5.5/ 8.5 to 10.
[0065] Pull roll (15) takes the film from the TDO unit (14) and transfers them to a winder (17). A thickness gauge (16) is located between the pull roll (15) and winder (17) for quality inspection.
[0066] The film wound on the winder (17) subsequently undergoes the metallization process in a metallization unit (not shown). In the metallization process, a layer of metal is deposited on one side of the BOPP film. Metallization processes are known in the art and can be any of the known methods, but not limited to, vacuum deposition, electroplating, sputtering, spraying. Metallization is generally done on the heat-sealable skin layer of the film. Metal used for metallization can be selected from, but not limited to, aluminum, gold, silver, copper.
[0067] In another embodiment of the present invention, the apparatus described in previous embodiment results in the formation of a BOPP film. The BOPP film comprises a core layer; two skin layers deposited on either side of the core layer, wherein the one skin layer is metalizable layer and the other skin layer is heat sealable layer.
[0068] In yet another embodiment, the BOPP film further comprises a tie layer disposed between the core layer and the at least one skin layer. The tie layer comprises polymer selected from the group comprising: homo polypropylene, polypropylene based elastomer, co-polymer, Terpolymer, Maleic anhydride grafted polypropylene, and/or combination thereof.
[0069] The BOPP film of the invention has a water vapor transmission rate in the range of 0.05 to 0.20gm/m2/day and an oxygen transmission rate in the range of 5-10cc/m2/day. The BOPP film has heat seal strength in the range of 1.2 to 3 kg/inch. [0070] According to yet another embodiment of the invention, Fig.2 shows a BOPP film (20) having a five layered structure. The five layered structure comprises an upper skin layer (21), an upper tie layer (22), a core layer (23), a lower tie layer (24), and a lower skin layer (25).
[0071] The upper skin layer (21) comprises a combination of a co-polymer or terpolymer and a polypropylene based elastomer. In an embodiment, polypropylene based elastomer primarily comprises isostatic propylene repeat units with random ethylene distribution. Thickness of the upper skin layer ranges from 1 micron to 4 microns.
[0072] In a preferred embodiment, Vistamaxx is used as polypropylene based elastomer. Vistamaxx enhances the heat-sealing properties of the upper skin layer (21). In an embodiment, Vistamaxx 3980 is used as polypropylene based elastomer. In another embodiment, Vistamaxx 3588 is used as polypropylene based elastomer.
[0073] The upper skin layer (21) can further comprise TAFMER. TAFMER easily blends with homo polypropylene or polypropylene based elastomer or co-polymer or Terpolymer, and other thermoplastics to enhance the characteristics such as low-temperature heat sealability, hot tack and heat seal strength of the BOPP film. In a preferred embodiment, TAFMER XM 7070 is used in the upper skin layer (21).
[0074] In another embodiment, the upper skin layer (21) comprises DP- 8220 M as alternate of TAFMER XM7070. DP-8220 M is a random copolymer of butene- 1 with medium ethylene content. The addition of DP- 8220 M reduces the seal initiation temperature of the sealing layer of the BOPP film.
[0075] The upper skin layer (21) can further comprise an organic or inorganic anti-blocking agent. The addition of anti-blocking agents helps in preventing sticking of the film on rollers or onto itself during winding (known as blocking).
[0076] In an embodiment, organic anti -blocking agents are used in the upper skin layer (21). Organic anti-blocking agents can be selected from but not limited to PMMA, silicones, silicon gum and PDMS etc. In another embodiment, inorganic anti-blocking agents are used in the upper skin layer (21). Inorganic anti-blocking can be selected from, but not limited to, synthetic silica, silicates, aluminum silicates, etc. In another embodiment, a mixture of both organic and inorganic anti blocking agents is used in the upper skin layer (21).
[0077] The Upper tie layer (22) comprises a combination of a Homo polypropylene and a polypropylene based elastomer. In a preferred embodiment, Tafmer PN 3560 is selected as polypropylene based elastomer. The thickness of the upper tie layer (22) ranges from 2 micron to 5 microns. [0078] The core layer (23) comprises a combination of a homo polypropylene and polypropylene based elastomer. In another embodiment, the core layer (23) comprises a combination of a homo polypropylene and a terpolymer. In another embodiment, the core layer (23) comprises a combination of terpolymer, polypropylene based elastomer and homo polypropylene. In an embodiment, polypropylene based elastomer primarily composes of isostatic propylene repeat units with random ethylene distribution.
[0079] The Lower tie layer (24) comprises a homo polypropylene. In another embodiment, the Lower tie layer (24) comprises of MAH Grafted polypropylene. In a preferred embodiment, Admer QF 500T is selected as MAH Grafted polypropylene. The thickness of the lower tie layer (24) ranges from 0.5 micron to 2 microns.
[0080] The lower skin layer (25) comprises of a combination of Butene or ethylene base Co- Polymer and Maleic anhydride grafted polypropylene. In a preferred embodiment, PKS 607 is selected as butene base co-polymer. In another embodiment, 3C30F HP is selected as butene base co-polymer. In another embodiment, PKS407 HP is selected as ethylene base co-polymer. In a preferred embodiment, Admer AT 3177 E is selected as Maleic anhydride grafted polypropylene.
[0081] According to yet another embodiment, the lower skin layer (25) comprises 100% of Maleic anhydride grafted polypropylene. In a preferred embodiment, Admer AT 3177 E is selected as Maleic anhydride grafted polypropylene.
[0082] According to yet another embodiment, the lower skin layer (25) comprises ethylene vinyl alcohol (EVOH). EVOH enhances the barrier properties of the film. In a preferred embodiment, Eval G156B or G-Soamol GH3804B or Soarnol H4815B is selected as an EVOH.
[0083] The metallization is performed on this lower skin layer (25) where a metal layer is deposited on the lower skin layer. The thickness of the lower skin layer (25) ranges from 0.6 micron to 2.0 microns.
[0084] According to yet another embodiment of the invention, anti-blocking agents are used in the top skin layer, however, any of the above-mentioned skin layers can comprise an anti-blocking agent.
[0085] According to yet another embodiment, upper skin layer (21) may further comprise other processing aids or additives such as, slip agents, and combinations thereof.
[0086] According to yet another embodiment, upper skin layer (21) and lower skin layer (25) can further undergo various surface treatment processes selected from, but not limited to, flame treatment, corona treatment, plasma treatment or any other process before metallization, coatings, printing inks, and/or lamination. [0087] According to yet another embodiment, the upper tie layer (22) and the lower tie layer (24) and core layer (23) can further comprise of various additives such as, opacifying agents, pigments, slip or antistatic agents, antioxidants, fillers, moisture barrier additives, gas barrier additives, hydrocarbon waxes, fillers such as calcium carbonate, and combinations thereof. Further, any of the above-mentioned additives can be used and added in core layer
[0088] According to yet another embodiment of the invention, Fig.3 shows a BOPP film (20), having a three-layered structure. The three-layered structure comprises an upper skin layer (21), a core layer (23) and a lower skin layer (25).
[0089] The multilayered BOPP film described in previous embodiments are exemplary BOPP film only and therefore should not be construed as a limitation to the present invention. It may be obvious for the person skilled in the art, to use any combination of the above mentioned upper skin layer (21), upper tie layer (22), core layer (23), lower tie layer (24) and lower skin layer (25) to form a BOPP film.
[0090] The BOPP film of the present invention, exhibit improved heat-seal strength. The heat seal strength measured for BOPP film is in the range of 1.2 kg/inch to 3.0 kg/inch. Seal initiation temperature of the BOPP film measured at 30 psi and 1 sec dwell time ranges from 70° C to 115° C.
[0091] Oxygen transmission rate (OTR) is the measure of the amount of oxygen gas that passes through a substance (BOPP film in the present case) over a given period. OTR values for the BOPP film of the present invention, vary in the range of 0.05cc/m2/day to 40 cc/m2/day.
[0092] Water vapour transmission rate (WVTR) is the measure of the amount of water vapour/moisture that passes through a substance (BOPP film in the present case) over a given period. WVTR of the BOPP film vary in the range of 0.05 gm/sqm/day to 0.3 gm/sqm/day.
[0093] Metal adhesion of the BOPP film through AIMCAL ref method (with EAA film) vary in the range of 100 gm/25mm to 1200 gm/25mm.
[0094] The food items stored in the BOPP film of the present invention have a great shelf life. Further, BOPP film manufactured from the above described method are suitable for both adhesive as well as extrusion lamination. No metal cracking takes place during extrusion lamination of the BOPP film of the present invention.
[0095] The BOPP film prepared using the above described method are typically used as inner web of laminate in 3 Ply as sandwich layer and as sealant layer in 2 Ply laminate structures for VFFS (Vertical Form Fill Seal) machine and HFFS (Horizontal Form Fill Seal) machines. [0096] The invention is described in detail in the Experiments given below which are provided by way of illustration only and therefore should not be construed as a limitation to the present invention:
Experiment- 1:
Skin layer (Heat Sealable Side): 21 to 65% Terpolymer or Co-Polymer + 20 to 50% PP based elastomer (Vistamaxx 3980 or Vistamaxx 3588) + 5-15% Tafmer XM7070or DP-8220 M + 8 to 10 % Organic and 2 to 4 % Inorganic antiblock or only organic antiblock. Layer thickness is in the range from 1.5 to 3 microns
Tie layer: 30 to 60% Homo PP + 40% to 70 % PP based elastomer (Tafmer PN 3560). Layer thickness is in the range from 3 to 5 microns
Core layer: 90 to 95% Homo PP + 5 to 10% of PP based elastomer Tie layer: 100 % Homo PP
Skin layer (metalizable surface): 50 to 70% Butene or ethylene base Co-Polymer (PKS 607 or 3C30L HP or PKS407 HP) and 30 to 50% of Maleic anhydride grafted PP (Admer AT 3177 E. Layer thickness is in the range from 0.6 to 1.5mic
Or 100% of Maleic anhydride grafted PP (Admer AT 3177 E. Layer thickness is in the range from 0.6 to 1.5microns
Skin layer top-coat: Polyurethane dispersion (Mitsui Takelac WPB341) coating on aforementioned metalisable surface. With 0.05 to 0.20 gram/sqm dry coating.
Experiment-2:
Skin layer (Heat Sealable Side): 21 to 65% Terpolymer or Co-Polymer + 20 to 50% PP based elastomeric (Vistamaxx 3980 or Vistamaxx 3588) + 5 to 15% Tafmer XM7070 or DP-8220 M + 8 to 10 % Organic and 2 to 4 % Inorganic antiblock or only organic antiblock. Layer thickness is on the range from 1.5 to 4 micron
Tie layer: 30 to 40% Homo PP + 60% to 70 % PP based elastomer (Tafmer PN 3560). Layer thickness is in the range from 2 to 5 micron
Core layer: 90 to 95% Homo PP + 5-10% of PP based elastomer Tie layer: 100% Homo PP
Skin layer (metalizable surface): 50 to 70% Butene and ethylene base Co-Polymer (PKS 607 or 3C30L HP or PKS407 HP) and 30 to 50% of Maleic anhydride grafted PP (Admer AT 3177 E) Layer thickness is in the range from 0.6 to 2.0mic Or 100% of Maleic anhydride grafted PP (Admer AT 3177 E). Layer thickness is in the range from 0.6 to 2.0 microns
Experiment-3:
Skin layer (Heat Sealable Side): 21-65% Terpolymer or Co-Polymer + 20-50% PP based elastomeric (Vistamaxx 3980 or Vistamaxx 3588) + 5- 15% Tafmer XM7070 or DP-8220 M + 8-10 % Organic and 2-4 % Inorganic antiblock or only organic antiblock. Layer thickness is in the range from 2 to 5 micron
Tie layer: 30 to 60% Homo PP + 40 to 70 % PP based elastomer (Tafmer PN 3560). Layer thickness is in the range from 2 to 5 mic
Core layer: 90 to 95% Homo PP + 5-10% of PP based elastomer or Terpolymer
Tie layer: 100% MAH Grafted PP (Admer QL 500T). Layer thickness is in the range from 0.5 to 2.0 mic
Skin layer (Lor Metalization): 100% EVOH (EVAL G 156 B). Layer thickness is in the range from 0.6 to 2.0 mic
Table 1
Figure imgf000015_0001
[0097] Table 1 shows the values of various properties measured of the above-mentioned BOPP film.
[0098] In view of the traditional BOPP films that exhibit heat seal strength upto 1 kg/inch, which is quite low as compared to the heat seal strength of the BOPP film of the present invention. Similarly, the OTR and WVTR for already existing BOPP films is in the range of 0.10 to 0.30 gm/m2/day. In the present invention, above performed experiments showed a significant increase in the values obtained for heat seal strength which is in the range of 1.2 to 3 kg/inch along with the OTR and WVTR which are recorded in the range of 0.05 to 0.30 gm/m2/day.
[0099] Although the invention has been described with regard to its embodiments, specific embodiments, and various examples, which constitute the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole. All changes that come with meaning and range of equivalency of the claims are to be embraced within their scope.
Numerals Denotation:
Hooper unit (1)
Main Extruder (2)
Screw drive (3)
First Co-extruder (4)
Second Co-extruder (5)
T-Die (6)
Chilled Roll (7)
Water Bath (8)
MDU Unit (9)
Preheat Rollers (10)
Stretching Rollers (11)
Annealing Rollers (12) polyurethane coating unit (13)
TDU unit (14)
Pull Roll (15)
Thickness Gauge (16)
Winder (17)

Claims

CLAIMS:
1. A BOPP film with enhanced heat seal strength comprises: a core layer; two skin layers deposited on either side of the core layer, wherein the one skin layer is metalizable layer and the other skin layer is heat sealable layer; and wherein the BOPP film has a heat seal strength in the range of 1.2 to 3kg/inch, a water vapor transmission rate in the range of 0.05 to 0.30gm/m2/day, an oxygen transmission rate in the range of 0.05-40cc/m2/day.
2. The BOPP film according to claim 1, wherein the core layer comprises 90% to 95% homo polypropylene and 5% to 10% of polypropylene based elastomer or terpolymer.
3. The BOPP film according to claim 1, wherein at least one skin layer comprises 21 to 65% of Terpolymer or Co-Polymer, 20 to 50% of Polypropylene based elastomers, 5 to 15% of Tafmer and 10-14% of antiblock additive.
4. The BOPP film according to claim 1, wherein at least one skin layer comprises 50 to 70% of Butene and ethylene base Co-Polymer and 30 to 50% of Maleic anhydride grafted Polypropylene, or 100% of Maleic anhydride grafted Polypropylene, or 100% of Ethylene-vinyl alcohol co polymer.
5. The BOPP film according to claim 1, wherein a metal layer deposited over the at least one skin layer.
6. The BOPP film according to claim 1, wherein the BOPP film further comprises a tie layer disposed between the core layer and the at least one skin layer.
7. The BOPP film according to claim 7, wherein the tie layer comprises 30-60% of homo polypropylene and 40 to 70% PP based elastomer, or 100% of homo polypropylene.
8. The BOPP film according to claim 1, wherein the BOPP film has metal adhesion in the range of 100 to 1200 gm/25mm.
9. A method of forming a BOPP film having enhanced heat seal strength, the method comprising:
Coextmding a core layer, two skin layers to form a polypropylene film;
Orienting the polypropylene film in machine direction orientation (MDO) to obtain an oriented polypropylene film;
Coating the oriented polypropylene film with polyurethane to obtain a polyurethane coated polypropylene film; Orienting the polyurethane coated polypropylene film in t'ransverse direction orientation (TDO) to obtain a BOPP film; and
Depositing a metal layer on atleast one of skin layer, wherein the BOPP film has a heat seal strength in the range of 1.2 to 3kg/inch, a water vapor transmission rate in the range of 0.05 to 0.30gm/m2/day, an oxygen transmission rate in the range of 0.05-40cc/m2/day.
PCT/IN2020/050886 2019-10-16 2020-10-16 Biaxially oriented polypropylene film with enhanced heat seal strength and method of manufacturing thereof WO2021074927A1 (en)

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Citations (6)

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US9120294B2 (en) * 2007-09-28 2015-09-01 Toray Plastics (America), Inc. Biaxially oriented polypropylene film with high heat seal strength

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EP1244546A1 (en) * 1999-11-08 2002-10-02 Exxonmobil Oil Corporation Metallized multi-layer film
US20040191529A1 (en) * 2003-03-25 2004-09-30 Applied Extrusion Technologies, Inc. Urethane based coating applied in-line for improved ink adhesion
WO2004094141A2 (en) * 2003-04-18 2004-11-04 Exxonmobil Oil Corporation Multi-layer oriented polypropylene films with modified core
US9120294B2 (en) * 2007-09-28 2015-09-01 Toray Plastics (America), Inc. Biaxially oriented polypropylene film with high heat seal strength
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