Description:FORM 2

THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENT RULES, 2003

COMPLETE SPECIFICATION
[See section 10, Rule 13]

AN AQUEOUS COATING COMPOSITION TO OBTAIN A HIGH BARRIER TRANSPARENT BOPP FILM, AND THE METHODS THEREOF

UFLEX LIMITED,
A COMPANY INCORPORATED UNDER THE LAWS OF INDIA,
OF 305, III FLOOR, BHANOT CORNER, PAMPOSH ENCLAVE,
GK-1, NEW DELHI-110048 (INDIA);

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:
AN AQUEOUS COATING COMPOSITION TO OBTAIN A HIGH BARRIER TRANSPARENT BOPP FILM, AND THE METHODS THEREOF
FIELD OF THE PRESENT INVENTION
[001] The present invention relates to the field of food packaging. More particularly, it pertains to an aqueous polyvinyl alcohol (PVOH) coating composition and method thereof, which is a heat sealable, and offers high barrier property, when coated on a variety of film / laminate, particularly on a biaxially oriented polypropylene (BOPP) film. The present invention also discloses a high barrier BOPP film, coated with said PVOH based composition, and its method thereof.
BACKGROUND OF THE PRESENT INVENTION
[002] A composite barrier packaging film typically comes in a laminated structure of either polyester (biaxially oriented polyester (BOPET) or polyolefin (biaxially oriented polypropylene (BOPP)). In a multilayer composite packaging film, either BOPP or BOPET film forms a base layer to provide structural integrity for containment function. The base layer supports other layers, that have useful properties, related to packaging, such as barrier layer to resist water vapour and moisture etc. a heat seal layer for forming a heat sealable container, and to provide features like printability etc.
[003] In recent years, the increasing pressure of modern fast-paced lifestyle leaves less time and inclination to prepare proper meals. This places a lot of importance on storage of food products and other edible items for longer duration, which requires to be warmed before consuming. Polypropylene (PP) is the only notable plastic recommended for microwave heating, and hence, materials based on Polypropylene (PP) are the most desirable food packaging material, which can be visually checked and pre-heated on microwave, before consuming the product. Further, metallization on the BOPP film is not desirable.
[004] Multilayer packaging films composed of different materials such as polyolefin-polyester (BOPP-BOPET) based laminates although provide the desired barrier properties, but are tedious to recycle. Hence, there exists a need of the hour to develop films with excellent barrier properties, which can be comfortably recycled.
[005] Further, there have been intensive efforts to develop suitable transparent packaging films for food products, to satisfy consumer’s desire to look at the product within the package, before procuring. Hence, mandatorily the food packaging multi-layered films / laminates must exhibit excellent reluctance towards atmospheric moisture and gas, to maintain freshness of the product, especially for sensitive and perishable goods or products.
[006] To achieve the desirable barrier properties, a thin layer of metal or foil, such as aluminium is effectively coated / laminated on BOPP and BOPET films. These metalized films inherently possess certain advantages such as impart desired resistance for atmospheric moisture, gases and light. Even these metallized films are used for packaging of light sensitive products, but these metalized films are expensive and non-transparent (Blackish) in nature and hence, prevent viewing the contents inside the package.
[007] Thus, there is a demand to develop a clear and transparent packaging films, that provide excellent resistance to transmission of water vapour or oxygen gas with either no metallization or optionally ultra-thin, non-hazy or non-opaque metallization. Commercial clear metalizing techniques, such as aluminium oxide (Al2O3) or silicon dioxide (SiO2), can provide certain barrier protections, but make the film very brittle with poor resistance to flex cracking.
[008] Further, a window can be provided on the package to verify the freshness of the product present inside the package, by the consumers, without compromising barrier properties and without the use of metal oxides or metal foils. A thin layer of Polyvinylidene chloride (PVdC), coated on polyolefin or polyester films, serves the cause. PVdC-coated polyolefin or polyester films demonstrates good resistance to water vapour and most gases and also has superior lamination bond, without the need of priming or additives or changes to lamination process. However, PVdC coated films have potential negative long-term effect on the environment, due to the presence of carcinogenic chlorine atoms. These films also turn yellow as it ages, become brittle and are prone to flex cracking and most importantly these films might generate hydrochloric acid fumes from the chlorine.
[009] A thin layer, coated with polyvinyl alcohol (PVOH) or ethylene vinyl alcohol (EVOH) or combination of both on polyester or polyolefin films, may provide resistance for moisture (or vapour) and oxygen transmission, however, the resultant multilayer packaging films were not successful in providing the required moisture (or vapour) and oxygen resistance, desired for products that need to be stored for extended durations. Further, under high humid atmosphere, PVOH or EVOH coatings have high affinity to absorb moisture, which in result, swell the layers and hence deteriorate effective barrier properties.
[0010] Therefore, there remains an urgent need to have a transparent packaging film with outstanding barrier properties, which can be cost effectively manufactured.
[0011] Further, it is known that the water vapour transmission rate (WVTR) and oxygen transmission rate (OTR) values are irreversible. If we want to improve the WVTR, then OTR gets deteriorated or if we want to improve OTR, then WVTR gets deteriorated. Thus, there is also a need to provide improved WVTR and OTR simultaneously.
[0012] The present invention addresses the above-mentioned concerns in the field of food packaging, by providing a water based PVOH coating composition to develop a high barrier, cost-effective, halogen-free packaging film. The high barrier coating of the present invention provides an exceptional barrier to oxygen, water vapour, moisture resistance and see through packaging.
[0013] The PVOH coated transparent film of the present invention extends the shelf-life of the stored products, maintains its flavours, and aroma, when used in flexible packaging. The present invention also provides an economic and innovative solution to the problem of inversely proportional properties of OTR and WVTR, for food packaging, apart from being optionally recyclable.
OBJECT OF THE PRESENT INVENTION
[0014] The main object of the present invention is to provide an especially formulated aqueous PVOH coating composition and method of making said composition that is applied on a polypropylene film, specifically on a biaxially oriented polypropylene (BOPP) film.
[0015] Yet another object of the present invention is to provide an aqueous coating composition, that is transparent and can be applied by inline or offline method on BOPP film surface(s).
[0016] Another object of the present invention to provide a PVOH based coating composition that is not affected by relative humidity and temperature, due to perfect crosslinking of coating molecules throughout Matrix Polymer.
[0017] Further object of the present invention is to provide a high barrier transparent BOPP packaging film coated with an aqueous PVOH based coating composition, which is suitable for printing and lamination, heat sealable, and thermally stable during and after the manufacturing process.
[0018] Another object of the present invention to provide a PVOH coated BOPP film that provides a high barrier property by improving both the barrier parameters i.e. OTR and WVTR simultaneously.
[0019] Another object of the present invention to provide a coated BOPP film having improved OTR and WVTR values in varying environmental conditions of temperature and relative humidity, mainly for packaging of dry ready-to-eat food products or microwave oven cooking / pre-heating products.
[0020] Another object of the present invention to provide a high barrier BOPP film having OTR value of 0.2 ~ 1.0 cc/m2-day at 23°C temperature and 0% relative humidity and WVTR value of 2 ~ 5 gm/m2-day at 38°C temperature and 90% relative humidity.
[0021] Yet another object of the present invention is to provide a high barrier packaging film or a laminate having a PVOH coated BOPP film, as a core layer.
[0022] Another object of the present invention to provide a packaging film / laminate, comprising at least a high barrier BOPP film, as a core layer, having OTR value of less than 0.2 cc/m2-day at 23°C temperature and 0% relative humidity (RH) and WVTR value of less than 2.9 gm/m2-day at 38°C temperature and 90% relative humidity (RH).
[0023] Yet another object of the present invention is to provide a coated BOPP film that is heat sealable with non-coated BOPP films on its coated surfaces.
[0024] Yet another object of the present invention is to provide a coated BOPP film that is heat sealable with variety of other films such as CPP, BOPET films etc. on its coated surfaces.
[0025] Yet another object of the present invention is to provide a high barrier BOPP packaging film, which has excellent flex crack resistance, does not form pin holes and have excellent abrasion resistance and scratch resistance.
[0026] Further, another object of the present invention is to provide a PVOH containing coating composition, which has high oxygen and flavour / odour barrier characteristics, is moisture resistant and is directly applicable to hydrophobic polymeric substrates, without the requirement of a primer coating.
[0027] Further, another object of the present invention is to provide a PVOH containing coating composition, which not only adheres tenaciously to hydrophobic polymeric substrates, but is also tacky and can be used as a primer coating for subsequently applied coatings.
[0028] Further, another object of the present invention is to provide a high barrier multilayer film / laminate which is easy to manufacture, easy to recycle and have environmental sustainability.
SUMMARY OF THE PRESENT INVENTION
[0029] One aspect of the present invention is to provide an aqueous PVOH based coating composition. The aqueous coating composition comprises PVOH in the range of 5 ~ 10 wt%; Isopropyl alcohol in the range of 5 ~ 10 wt %; demineralized water (DM water) in the range of 60 ~ 90 wt%; and cross linker and / or adhesion promoter in the range of 0.2 ~ 2 wt%; wherein said wt% (weight percents) are based on the total wt% of the coating composition. The aqueous coating is essentially transparent.
[0030] Another aspect of the present invention is to provide a method of obtaining an aqueous PVOH based coating composition. The details of which are given in the detailed description part.
[0031] Another aspect of the present invention is to provide a heat sealable, high barrier and transparent biaxially oriented polypropylene (BOPP) film, coated with an aqueous coating, having high barrier properties. The film of the present invention comprises a BOPP base film having a core layer and one or more skin layers, wherein at least one skin layer is sealable and coated with an aqueous PVOH based coating composition of the present invention on at least one of its surfaces i.e. top surface. The high barrier BOPP film is coated in-line or offline, on its any sealable skin layer(s) with the aqueous PVOH based coating composition.
[0032] The high barrier BOPP film has a top surface and a bottom surface. Top and bottom surface herein refers to a top and bottom surface of a skin layer(s), toward the respective surfaces. Any one surface which has sealable skin layer at its side is coated with the aqueous PVOH based coating composition. The coated surface / side of the BOPP base film laminated with a coated BOPP film or an uncoated BOPP film or any other polymer / plastic film with adhesive or by coextrusion lamination to form a high barrier BOPP film or a laminate. Both surfaces / sides of the BOPP base film can be coated with the aqueous PVOH based coating composition, for increased barrier properties, if required. High barrier BOPP film obtained from transparent BOPP base film remains transparent.
[0033] The PVOH coated BOPP film of the present invention, improves both the barrier parameters i.e. OTR and WVTR simultaneously. OTR is improved from 2000 cc/m2-day to 0.2 cc/m2-day and WVTR is improved from 8 gm/m2-day to 4.8 gm/m2-day, when compared with BOPP base film or uncoated BOPP film.
[0034] In yet another aspect of the present invention, a method for preparing a heat sealable high barrier BOPP film with an aqueous PVOH based coating composition is also disclosed. The details of which are given in the detailed description part.
[0035] Additional aspects will be provided in part in the detailed description that follows, and in part will be obvious from the description, or may be learned from the practice of the embodiments described below. It is to be understood that both the foregoing general description and the following detailed description are exemplary, explanatory and not restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The foregoing summary and/or other objects, features and advantages, of the present invention will become more apparent from the following description of the preferred embodiment with reference to the accompanying drawings, in which reference numerals designate the elements of the invention and wherein;
[0037] FIG. 1 illustrates a high barrier coated BOPP film in accordance with an exemplary embodiment of the present invention.
[0038] FIG. 2 illustrates a high barrier coated BOPP film with skin layers in accordance with an exemplary embodiment of the present invention.
[0039] FIG. 3 illustrates a high barrier laminate having a coated BOPP film as a base film in accordance with an exemplary embodiment of the present invention.
[0040] FIGS. 4A & 4B show flowcharts depicting methods (100, 200) for obtaining a PVOH based coating, and a heat sealable high barrier BOPP film, respectively, in accordance with the exemplary embodiments of the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0041] For a thorough understanding of the present invention, reference is to be made to the following description in connection with the above-mentioned drawings. Although the invention is described in connection with exemplary embodiments, the invention is not intended to be limited to the specific forms set forth herein. It is understood that various omissions and substitutions of equivalents are contemplated as circumstances may suggest or render expedient, but these are intended to cover the application or implementation without departing from the spirit or scope of the invention. Further, it will nevertheless be understood that no limitation in the scope of the invention is thereby intended, such alterations and further modifications in the figures and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. In other instances, detailed descriptions of well-known methods, layout and procedures, and devices are omitted so, not to obscure the description of the present invention with unnecessary detail. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
[0042] As used herein, the singular forms “a”, “an”, “the” include plural referents unless the context clearly dictates otherwise. Further, the terms “like”, “as such”, “for example”, are meant to introduce examples, which further clarify more general subject matter and should be contemplated for the persons skilled in the art, to understand the subject matter.
[0043] Further, reference herein to “one embodiment” or “an embodiment” or “another embodiment” means that a particular feature, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the disclosure. Furthermore, the appearances of such phrase at various places herein are not necessarily all referring to the same embodiment. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
[0044] The terminology used in the description of the invention herein is for the purpose of describing embodiments only and is not intended to be limiting of the invention. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a range of “1 to 10” or a range of “1 ~ 10” includes any and all subranges between (and including) the minimum value of 1 and the maximum value of 10, that is, any and all subranges having a minimum value of equal to or greater than 1 and a maximum value of equal to or less than 10, e.g., 5.5 to 10.
[0045] The reference in this specification to any prior art publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgement or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavours to which this specification relates.
[0046] The term “composition” refers to a mixture of materials which comprise the composition, as well as reaction products and decomposition products formed from the materials of the composition.
[0047] As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. To avoid any doubt, all compositions claimed through use of the term “comprising” may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless stated to the contrary.
[0048] The term “flexible packaging” herein relates to any packaging or a part thereof whose shape can be changed readily. For example, bags, packages, pouches, flexible containers, tubes, etc., in any shape and design. The term “food product” herein relates to edible products for human being and for animals, require storage and / or pre-heating before ready to consume.
[0049] The term “polypropylene” herein defines a form of polyolefins, which can be extruded, cast, and stretched bidirectional to form a thin film for packaging for the purposes of packaging food products and / or other items.
[0050] The term “film” herein relates to a polymeric film / laminate having at least one or a combination of suitable single or multilayer polymeric films, or laminate in various combinations of layers of single or multilayer polymeric films thereof.
[0051] The term “heat sealability” herein relates to making at least two thermoplastic surfaces by application of heat and pressure, sealing thereof.
[0052] The terms “seal layer”, “sealable” and “heat seal layer”, as used herein, refer to a “film” layer, or layers, involved in the sealing of the film: to itself, to another film layer of the same film or another film, and/or to another article which is not a film, for example, a tray. In general, the heat seal layer is a surface layer, that is, an exterior or an interior layer of any suitable thickness, that provides for the sealing of the film to itself or another layer.
[0053] The term “high barrier packaging film”, “packaging film” and “coated film” herein relates to a “film” coated with a coating composition of the present invention.
[0054] The term “coating” herein relates to a thin layer of a covering applied on a substrate. Further the term “coating solution” or “coating composition” herein relates to same component. Both can be interchangeable.
[0055] “Polyvinyl alcohol (PVOH)” as used herein means a normally solid polymeric material, soluble in water, but insoluble in most organic solvents and characterized by the presence of (--CH2 --CHOH--) units in the polymer chain. These polymers are ordinarily prepared by the replacement of the acetate groups of polyvinyl acetate with hydroxyl groups as by hydrolysis or alcoholysis. The percentage of acetate groups replaced by hydroxyl groups is the degree of hydrolysis of the PVOH thus formed and indicates the percent of hydroxyl groups present in PVOH out of the total possible hydroxyl groups. As explained herein below the crosslinking reaction by which the superior barrier coatings of this invention are obtained proceeds through the hydroxyl groups of PVOH. Therefore, the PVOH useful in the present invention is partially or fully hydrolyzed.
[0056] The term “PVOH coating” herein relates to polyvinyl alcohol-based coating prepared from this disclosure.
[0057] As used herein, the phrase “halogen-free packaging film” designates a “film” having polymers that are free of halogens in the polymer backbones.
[0058] As used herein, the term “barrier” refers to a material that controls permeability of one or more elements including, moisture, chemicals, heat, odour, and oxygen or other gases. As it relates to multilayer films, the barrier can be provided by a single layer or multiple layers acting in concert or individually. For example, a moisture barrier refers to a material that limits the permeability of water vapor through the material.
[0059] The methods described herein, including quantities of materials, temperatures, pressures, times, etc. are not intended to be limiting and are included merely as examples of suitable conditions / compositions for use in forming some embodiments the present structure.
[0060] The present invention discloses an aqueous coating composition (4) and method (100) of obtaining thereof. The present invention also discloses a high barrier BOPP film (10) as which is produced by applying an aqueous coating composition (4), based on PVOH, for improving its barrier properties.
[0061] The aqueous coating composition (4) of the present invention comprises PVOH in the range of 5 ~ 10 wt%; Isopropyl alcohol in the range of 5 ~ 10 wt %; demineralized water (DM water) in the range of 60 ~ 90 wt%; and a cross linker and / or adhesion promoter in the range of 0.2 ~ 2 wt%; wherein said wt% (weight percents) are based on the total wt% of the coating composition (4).
[0062] Typical PVOH compounds or resins used in the present invention may be partially or fully hydrolysed grade of water-soluble ethylene-modified Polyvinyl alcohol such as EXCEVAL AQ104 (PVOH Compound A) or Polyvinyl alcohol such as POVAL 28-98 (PVOH Compound B) or POVAL 5-98 (PVOH Compound C), manufactured by KURARAY.
[0063] The cross linker Polyethyleneimine (PEI) is a linear or branched synthetic cationic polymer, available in a broad range of molecular weights. PEI has one nitrogen in every three atoms in the backbone, which provides characteristic positive charges upon protonation.
[0064] In one of the embodiments, the crosslinker is polyethylene imine (PEI) such as Loxanol MI 6730, which is a branched polyethyleneimine aqueous dispersion of cationic polymer with solid content concentration of 50% and average molecular weight ~ 750.000 g/mole, viscosity ~ 25.000 mPa. s (Millipascal-second) and has density @ 20oC approx. ~ 1.09 g/cm3, obtained from BASF. Crosslinker Loxanol MI 6730 serves to improve the shelf-life and stability of the polymer compositions. Further, Polyethyleneimine (PEI) based Loxanol MI 6730, also serves as an adhesive promoter to enhance molecular bonding. The cross linker and / or adhesion promoter is added to the PVOH coating composition (4) in the range of 0.2 ~ 2 wt%.
[0065] The aqueous PVOH coating composition (4) based on PEI crosslinker and /or adhesive promoter, of the present invention (Composition 1) comprises the below mentioned ingredients in specific ranges, tabulated as TABLE 1:
Particular PVOH Compound
A / B / C (wt%) DM Water (wt%) IPA (wt%) PEI Crosslinker and / or Adhesive Promoter (wt%) Solids (%)
Composition 1 5 ~ 10 60 ~ 90 5 ~10 0.2 ~ 2
6.5 ~ 7.5
[0066] FIGS. 1 & 2 show a heat sealable and high barrier transparent biaxially oriented polypropylene (BOPP) film (10), comprising a base film (2) having at least a core layer (1) and one or more skin layers (3A, 3B), wherein at least one skin layer (3A or 3B) is a sealable skin layer (3A) having a top surface (5) and bottom surface (5’-not shown) wherein at least one surface (5) is coated with an aqueous PVOH based coating composition (4). The present invention also provides a method (100) to obtain an aqueous coating composition (4), as shown in FIG. 4A, described in later part of the description.
[0067] The present invention also discloses a PVOH coated BOPP film / laminate (10, 20) that provides a high barrier property by improving both the barrier parameters i.e. OTR and WVTR simultaneously.
[0068] The present invention also provides a method (200) of applying an aqueous coating composition (4), as shown in FIG. 4B on a base film (2) of polypropylene, especially biaxially oriented polypropylene film (2) to obtain a high barrier BOPP film (10). The base film (2) can be a multi-layer film / laminate or a combination thereof. Further, the base film (2) is co-extruded. In some embodiments the base film (2) can include two or more layers. The base film (2) is bi-axially oriented by any known methods.
[0069] Typically, there are four main types of polypropylenes (PP): homopolymer, random copolymer, block copolymer and impact copolymer. Homopolymer polypropylene is solely composed of propylene monomer units. Whereas a random copolymer polypropylene is a type of polypropylene that is produced by the copolymerization of propylene with a small amount of another monomer, typically ethylene (alpha olefins). Thus, the two monomers are randomly distributed along the polymer chain. This results in a polymer with a combination of properties from both monomers. Homopolymer PP is often compared to random copolymer PP because both of them are relatively inexpensive and exhibit good mechanical properties. However, random copolymer has the advantage of being more impact-resistant, which makes it a better choice for some applications. Further, Random copolymer polypropylene is more transparent than homopolymer PP when it contains a higher proportion of the other monomer.
[0070] Oriented polypropylene films are formed from coextrusion of three layers; the outer layer herein refers as skin layers which can also be act as sealing layer, are made of homopolymers or copolymers, and the core or middle layer is a homopolymer containing small particles.
[0071] As shown in FIGS. 1 & 2, the high barrier BOPP film (10) of the present invention comprises at least a base film (2). The base film (2) has a top surface (2A) and a bottom surface (2B). Any one or both the surface (2A, 2B) can be coated with the aqueous PVOH based coating composition (4). As shown in FIG. 2, the base film (2) is a multilayer film, comprises a core layer (1); and one or more skin layers (3A, 3B), towards top surface and bottom surfaces (2A, 2B) of the base film (2), respectively. At least one skin layer (3A) is a sealable layer, involved in the sealing or laminating of the base film (2) to itself, to another film layer of the same film or another film. The core layer (1) is coated with an aqueous PVOH based coating (4) on a top surface (5) of the sealable skin layer (3A).
[0072] The high barrier BOPP film (10) is coated in-line or offline with the aqueous PVOH based coating composition, on at least one sealable skin layer (3A). The base film (2) is a biaxially oriented polypropylene (BOPP). Coating (4) can be performed on roll-to-roll bases.
[0073] The thickness of the high barrier BOPP film is in range of 12 µ to 30 µ. More preferably, thickness of the base film is in range of 18 µ – 26 µ. Where µ is microns.
[0074] The PVOH coating on any one of the sealable skin layers (3A) of BOPP film (2) is ranging from 0.5 ~1.5 GSM (gram per square meter).
[0075] As shown in FIG. 3, the present invention also discloses a high barrier laminate (20) having single layer films or multilayer films or a combination thereof. The high barrier laminate (20) comprises a high barrier BOPP film (10) having a top surface (10A) and a bottom surface (10B), any one or both surface (10A, 10B) is sealable and at least one sealable surface (10A) is coated with the aqueous PVOH based high barrier coating (4); optionally a printing layer (6) over the coated surface(s) of the base film (10A); at least an adhesive layer (8) over the printing layer (6) or directly on the coated surface(s) of the base film (10A); and at least a transparent film / laminate (12) to be laminated with the sealable and coated surface (10A) of the high barrier coated base film (10), by using adhesive layer or by extrusion lamination (8).
[0076] The transparent film / laminate (12) may comprise any of films such as coated BOPP film, an uncoated BOPP film, CPP, BOPET or any other polymer film.
[0077] The coated side of the biaxially oriented polypropylene (BOPP) film (10) may be unprinted or surface printed or reverse printed. The printing is performed by PU based inks, however other inks such as vinyl-based inks, nitrocellulose-based inks etc., may also be used. The coated surface(s) of the high barrier BOPP film (10A) laminates / seals to a coated BOPP film or an uncoated BOPP film or any other polymer film (12) with the adhesive layer or by coextrusion (8) to form the high barrier BOPP film or a laminate (20). Both surfaces (10A, 10B) of the base film (10) can be coated with the aqueous PVOH based coating composition (4), for increased barrier properties. The range of oxygen transmission rate (OTR) of the said coated film after lamination is less than 0.2 cc/m2/day and the water vapour transmission rate (WVTR) of the said coated film after lamination is less than 2.9 gm/m2/day. Further, the total thickness of the laminate (20) after laminating with the coated film (10) is more than 50 microns, more preferably in the range of 50 to 90 microns.
[0078] The web of a BOPP base film (2, 10) has a top surface (2A, 10A) and a bottom surface. (2B, 10B) In the present invention, optionally primers are applied to any one sealable or both surfaces (2A, 2B,10A, 10B) of the base film (2, 1) before coating with the PVOH coating composition (4) of the present disclosure. The primers can be any of copolyester, Polyurethane primer based on polyurethane dispersions, polyurethane solutions, solvent-free or solvent based reactive polyurethane, poly acrylates or a combination thereof. These primers are applied to increase the surface energy of the BOPP film (10).
[0079] Optionally the surface energy of the BOPP base film (10) can also be increased by Plasma surface treatment, Corona treatment, Flame treatment, Acid etching, UV treatment, primers known to a person skilled in the art or adhesion promoters, individually or a combination thereof
[0080] The most preferred way to increase the surface energy of the BOPP base film (2, 10) is corona treatment of the BOPP film substrate on the preferred coating surface i.e. top or bottom surface (2A) (10A). In this process, the BOPP film (2, 10) surface is exposed to ozone produced by electric discharge of the electrodes. Optionally corona treatment can be provided on other surface (bottom or top surface) (2B, 10B) for excellent adhesion of various suitable adhesive (8) during further process of making laminates (20) by laminating multiple layers of films. The web of corona treated BOPP film (2, 10) is then passed on to a winder for winding on to steel rolls. PVOH coating composition (4) of the present invention can be applied inline or offline method, on the web of corona treated BOPP film / laminate (2,10).
[0081] All the said layers in the laminate (20), such as the skin layers, and the core layer(s) are laminated together by suitable adhesive layer (8) or by using hot extrusion lamination, as shown in the FIG 3. Adhesive (8) can be solvent less such as DOWSIL 899 and LOCTITE CAC 1580 / LOCTITE CAC 1511A or solvent based such as DOW 811 and LOCTITE CAC 2511 / LOCTITE CAC 1511A or extrusion coating for example LDPE or LLDPE. The adhesive (8) is based on any or combination of the above, can also be used. The PVOH coating composition (4) of the present invention is coated on the BOPP film (2). In the processing, PVOH coating solution (4) applies and dries on a variety of BOPP film substrates like heat sealable on any one surface / side, heat sealable & treated on any one surface / side, heat sealable on both surfaces / sides, heat sealable & treated on both the surfaces / sides or heat sealable & treated on any one of the surfaces / sides and the other surface / side is plain or treated. Further, the high barrier laminate (20) can be transparent, opaque or translucent, depending upon the requirement.
[0082] As shown in FIG. 4A, the present invention also discloses a method (100) to obtain an aqueous PVOH based coating (4) comprising below steps:
(a) demineralized (DM) water is heated at a temperature in the range of 50 °C ~ 60°C in the vessel;
(b) adding PVOH polymer solids in the above DM water;
(c) stirring the mixture of step (b) at a temperature in the range of 85~95°C for 1 to 5 hours, to obtain a homogenous aqueous solution;
(d) cooling the homogenous aqueous solution of step (c) at an ambient temperature to obtain a Solution A;
(e) Separately preparing an aqueous solution by mixing isopropyl alcohol (IPA) and DM water in the ratio of 1:1;
(f) adding a Polyethylene imine (PEI) based cross linker and / or adhesion promoter to the mixture of step (e) at an ambient temperature;
(g) stirring the mixture of step (f) at a temperature in the range of 45~55°C for 30 to 60 minutes to obtain a Solution B;
(h) Solution A and Solution B are added to a mixture of IPA and DM water having the ratio of 1:1;
(i) stirring the mixture of step (h) at a temperature in the range of 45~55°C for 30 to 60 minutes; and
(j) filtering the above solution of step (i), to obtain the final coating solution of the PVOH aqueous coating composition (4) as shown at step (k).
[0083] According to the method (100) of the present invention, at step (b) diluting PVOH solids in the range of 5 ~ 10 wt% in DM water of step (a) and initially water heated from ambient temperature to 50 °C ~ 60°C, preferably 60°C then PVOH solids are mixed in the hot water and stirred at high speed for proper mixing and when the temperature reached in the range of 85°C ~ 95°C, preferably 90°C, then holding the material, for approx. 1 ~ 5, preferably 3 hours to obtain a homogeneous aqueous solution, as mentioned at step (c). The homogeneous aqueous solution was cooled to an ambient temperature, which is in the range of 20oC ~ 35oC to obtain Solution A, of step (d).
[0084] Separately 20 gm of (isopropyl alcohol and DM water) solution with 1:1 ratio is added as mentioned in step (e) to form a solution. Further, Polyethylene imine based (PEI) cross linker and / or adhesion promoter in the range of 0.2 ~ 2 wt% is added at an ambient temperature in the range of 20oC ~ 35oC, to the above solution having DM water and isopropyl alcohol, as mentioned in step (f). Then, this mixture is stirred at temperature for a duration as mentioned in step (g) to obtain the Solution B.
[0085] Now the Solution A and Solution B, are added to a mixture of IPA and DM water having the ratio of 1:1, at step (h) and this mixture of step (h) is stirred at a temperature in the range of 45~55°C, preferably 45°C for 30 to 60 minutes, preferably 45 minutes, as mentioned at step (i). Now this solution is filtered at step (j) to obtain the final coating solution of the PVOH aqueous coating composition (4).
[0086] According to the present invention, the aqueous solution of isopropyl alcohol at above-mentioned step (e) may be in 1:1 ratio solution of isopropyl alcohol & DM water. According to the method (100) of the PVOH based coating composition (4) of the present invention, adding demineralized water (DM water) dilutes the alcohol, which reduces the burn and allows other properties to reveal themselves. Meanwhile there's also something significant happening on a molecular level. Aroma molecules share more chemical likenesses with alcohol than they do with water. As such, they tend to bind with alcohol. When we mix DM water and isopropyl alcohol (IPA), it forms a homogenous solution, as they are both polar solvents, with an area of slight positive and negative charges. The homogenous solution will have properties of both water and IPA. The homogenous solution will have a lower freezing point, and a higher boiling point as compared to pure water.
[0087] IPA plays a crucial role as it is more effective for reducing the viscosity of the mixture, compared to water. Also, IPA's surface energy 21~23 mN/m (milliNewton per Metre) helps to reduce the surface energy of the coating, which is essential for even wetting or coating. In contrast, water has a surface energy of 70 mN/m. Surface energy of the coating composition of the present invention would be around 65-70 mN/m, without adding IPA, leading to uneven wetting and pinholes. Therefore, the addition of IPA in the homogenous aqueous solution of PVOH and DM water helps to achieve more even wetting or coating. The surface energy of the most films is around 40-50 mN/m without IPA. It is essential to add IPA after the initial mixing process, as adding it initially during the heating process, may cause it to evaporate.
[0088] Polyethylene imine based (PEI) cross linker and / or adhesive promoter, in the range of 0.2 ~ 2 wt%, is added at above-mentioned step (f). Polyethylene imine based (PEI) acts as a cross-linker as well as an adhesive promoter. When it works as a crosslinker, it increases the molecular bonding in the presence of DM water and IPA, whereas at higher temperature, it acts as an adhesive promoter and increases the surface energy of the film surface.
[0089] Another embodiment of the present invention, as shown in flowchart of FIG. 4B, is to provide a method (200) for preparing a heat sealable and high barrier biaxially oriented polypropylene base film (BOPP) with an aqueous coating, comprising below steps:
(a) applying the coating solution of the PVOH based aqueous coating (4) on a biaxially oriented polypropylene base film (BOPP) (2) on a top surface (2A);
(b) drying or curing the coated BOPP film;
(c) cooling the coated and dried BOPP film at an ambient temperature; and
(d) winding the cooled coated and dried high barrier transparent BOPP film (10) over a winder.
[0090] The above-mentioned high barrier PVOH based coating composition (4) at above-mentioned step (a) of method (200) is coated preferably but not limited to by using an offline reverse gravure coating process / method. This coating method (200) relies on an engraved roller running in a high barrier PVOH based coating (4) bath, which fills the engraved dots or lines of the engraved roller with the coating solution (4). The excess coating (4) on the engraved roller is wiped off by a doctor blade and the coating in the engraved roller, is then deposited onto a desired surface of a substrate, preferably a web of BOPP film (2), as it passes between the engraved roller and a pressure roller. In this method, the web of BOPP film (2) is firstly loaded onto an unwinder, where it travels through plurality of various path rollers, bow rollers, gravure rollers and nip rollers, to smoothly guide the web of the BOPP film (2) and to apply appropriate pressure to hold the web for coating process (200).
[0091] In one of the embodiments of the present invention, the PVOH based coating composition (4) may be coated twice on the BOPP film (2) substrate, wherein the first coating (4) act as a primer for the second coating. Coating of the primer on the BOPP film substrate results in excellent printability (6) characteristics of the BOPP film, particularly to vinyl-based inks, nitrocellulose-based inks and polyurethane (PU) based inks.
[0092] In some embodiments of the present invention, the PVOH based coating (4) is coated on any one surfaces (top or bottom surface) or both surfaces (top and bottom surfaces) of the sealable skin layers (3A, 3B) of the base film (2) for heat sealing.
[0093] The high barrier BOPP film (10) thus prepared, is then, coated again with fully or partially hydrolysed PVOH based solution (4), which renders the film highly resistant against Oxygen, gas, aroma and moisture (water vapour).
[0094] The PVOH coating (4) composition of the present invention is hydrophilic in nature and can be processed by coating technology like gravure / rotogravure / air knife. The processing methods may be a kiss coating or a nip where the uniformity and consistency of the applied pressure is important, with forward or reverse methods. The best method to apply the coating (4), can be gravure processing technology or air knife coating method, which gives the final BOPP film (10) with high clarity. In some extents, coating coverage is best when it is dried in a hot air oven after applying coating composition on the surface (2A) of the base film (2) by rotogravure nip forward method. Further, Temperature plays an important role in defining adhesion of dried chemicals of the coating composition (4) on the film surface (5, 2A, 10A). In the present invention case, the aqueous PVOH based coating (4) is dried at a temperature in the range of 95°C to 125°C.
[0095] The resulting weight of the PVOH based solution coating (4) is of 0.5~1.5 GSM, after step (c).
[0096] In some processing methods (200), the best barrier property is achieved when coating is done with reverse rotating gravure, with continuous supply of coating chemical, at coating head through a lacquer pump feeding system.
[0097] The coated wet base BOPP film (10) started to get dry, when entered in a hot air dryer or an infrared irradiation apparatus at step (b), having sufficient length for proper curing. The coated and dried BOPP film (10) is then passed over a cooling roll, to get cool at ambient temperature in the range of 20 ~ 35oC, as mentioned in step (c), and finally wound up.
[0098] The coated BOPP film (10) of the present invention is heat sealable to other BOPP films (12).
[0099] The final PVOH coating on the top surface (5) of one sealable skin layer (3A) of BOPP base film (2) is ranging from 0.5-1.5 GSM (gram per square meter). The thickness of the high barrier coated BOPP film (10) is ranging from 12 µ ~30 µ, preferably 18 µ – 26 µ.
[00100] As shown in FIGS. 4A & 4B, the methods (100, 200) may include a number of steps; sequence thereof may be exemplary for the persons skilled in the art to better understand the present invention.
[00101] Testing has been performed to measure OTR and WVTR at different relative humidity i.e. 0%, 50%, 70%, 90% and 100%. PVOH based coating composition (4) of the present invention, is not affected by relative humidity (RH) and temperature, due to perfect crosslinking of the coating molecules throughout the Matrix polymer.
EXAMPLES OF PVOH BASED COATING COMPOSITION (4) COMPOSITION
[00102] FIG. 4A & 4B shows flowcharts illustrating the steps of a method (100, 200) to obtain the PVOH based coating composition (4) and to obtain a high barrier BOPP film (10), respectively.
[00103] To better explain the present coating composition (4), example is taken to better explain the invention, which should be consider as a non-limiting example.
[00104] EXAMPLE 1: 90 g of DM water was heated from ambient temperature to 60°C and 10 g of EXCEVAL AQ4104 (PVOH Compound A) was added to this heated DM water. It was stirred at 90°C for 3 hours to obtain a homogeneous aqueous solution. The aqueous solution was cooled to ambient temperature to obtain Solution A. Separately 20 gm of 1:1 aqueous ratio solution of isopropyl alcohol and DM water was prepared. DM water is added in IPA to improve the stability of the final coating solution. Further, 0.2-0.5 g of Loxanol MI 6730 (a PEI based cross linker and / or adhesive promoter) was added to this solution of isopropyl alcohol (IPA) and DM water. The resultant liquid having isopropyl alcohol (IPA); DM water and Loxanol MI 6730 was continuously stirred for 45 minutes with a constant speed of 250 rpm at 45°C, to obtain a Solution B. Then Solution A was mixed with Solution B with further addition of DM water and isopropyl alcohol (IPA), in 1: 1 of DM water and IPA. The resultant liquid was continuously stirred for 45 minutes with a constant speed of 250 rpm at 45°C. The final solution was filtered to obtain the final solution of the PVOH based coating composition (based on PVOH Compound A) (4) and is ready to be coated on the sealable surface (5) of the skin layer (3A) of the BOPP film (2). After applying this coating composition (4) on the film (2), the film (2) was dried at a temperature in the range of 95 to 125°C to obtain the sealable and high barrier transparent BOPP film (10) coated with PVOH based coating composition based on PVOH Compound A (4).
[00105] The dried coating weight was 0.5-1.5 in GSM. The solid content concentration of the composition was 6.5 to 7.5%.
[00106] In this coating applications, it is generally preferred to provide environment friendly, water-based, odourless and perfect crosslinking agent, when mixed in coating solution, as described above.
[00107] Similarly, by using the PVOH compound B: POVAL 28-98 and PVOH compound C: POVAL 5-98, PVOH based coating composition (4) based on PVOH Compound B and PVOH Compound C are obtained respectively, in a similar manner, as described above and are ready to be coated on the desired BOPP film (2), respectively, to obtain sealable and high barrier transparent BOPP films (10).
[00108] The PVOH based aqueous coating (4) is transparent.
[00109] Below is the summary of Polyurethane (PUD) and Co-polyester coatings and their properties, which are available without PVOH coating, to compare the heat sealable and high barrier BOPP film (10) coated with PVOH based coating composition of the present invention and tabulated as TABLE 2:
Properties UOM (Unit of Measurement) Test Method Substrate - BOPP Film
PUD Coating Co-polyester Coating

OTR cc/m2/day ASTM D3985 90.1 110.2
WVTR gm/m2/day ASTM F1249 38.02 42.48
Surface Tension Dynes/cm ASTM F2578 48 60
Heat Seal Strength gm/inch D2029 200 ~ 300 300 ~ 400
Gloss@45° GU ASTM D2457 78-85 115-119
[00110] COMAPARATIVE STUDY AND RESULT: When we tested the high barrier BOPP film (10), having BOPP Film (2) as a base film having a core layer (1) and a coating, on a top surface (5) of any of a sealable skin layer(s) (3A or 3B), comprising of PVOH based coating of the present invention, it is found that the OTR of the high barrier BOPP film (10) of the present invention is in the range of 0.2 ~1.0 cc/m2/day, measured by ASTM D3985 and the WVTR of the film (10) is in the range of 2 ~5 gm/m2/day, as measured by ASTM F1249. The glossiness (GLOSS@45°) of the high barrier BOPP film (10) of the present invention is in the range of 80 - 120 and additionally the heat seal strength of the high barrier BOPP film (10) of the present invention is in the range of 350 - 650 gm/inch. Surface Tension of the high barrier BOPP film (10) of the present invention is in the range 54-56 dyne/cm, like given in prior art in the above table.
[00111] Below is the summary of various properties of the high barrier BOPP film (10) of the present invention by using different grades of PVOH compound (A, B, C) tabulated as TABLE 3:

S. No. Properties UOM Test Method

PVdC
(Prior art)
(without cross linker) Substrate - BOPP Film;
Cross linker - PEI
PVOH Compound
EXCEVAL AQ4104 (Compound A) POVAL
28-98
(Compound B) POVAL
5-98
(Compound C)
1 OTR cc/m2/day ASTM D3985 8.0 0.289 0.224 0.281
2 WVTR gm/m2/day ASTM F1249 8.0 4.486 4.782 4.843
3 Surface Tension dynes/cm ASTM F2578 54 56 56 54
4 Heat Seal Strength gm/inch D2029 250-350 350-450 375-612 400-500
5 Gloss@45° GU ASTM D2457 75-85 112-120 85-90 83-85
[00112] EXAMPLE 2 (PVOH coated CPP film & PVOH coated BOPET film for Comparative analysis): Testing was performed by applying the PVOH coating solution (4) of the present invention on CPP and BOPET base films. Below is the summary of various properties of the PVOH coated CPP film and PVOH coated BOPET film, to compare the desired OTR and WVTR properties of the high barrier BOPP film (10) of the present invention and tabulated herein as TABLE 4:
S. No. Properties ASTM Values of coated CPP film Values of coated BOPET film Values of coated BOPP film Measuring Unit
1 OTR D3985 1.328 1.354 .2 -1.0 cc/m2/day
2 WVTR F1249 10.806 44.712 2-5 gm/m2/day
3 Surface Tension F2578 46 54 54-56 Dynes/cm
4 Heat Seal Strength D2029 1587-1746 Not Sealable 350-650 gm/inch
5 Gloss@45° D2457 80-85 111-125 80-120 GU
6 Thickness Inhouse 25-50 12-18 12-36 microns
[00113] From the above Table it is evident that high barrier transparent BOPP film (10) coated with PVOH coating composition (4) of the present invention, results better and improved barrier properties such as OTR and WVTR, in comparison to the other base film such as CPP and BOPET, when coated with the PVOH based coating composition (4) of the present invention.
[00114] TESTING METHODS: PVOH coated BOPP film (10) is subjected to many testing to evaluate film performance in final application. The test methods involved are:
a. Coating GSM determination by dry coating wash methods:
b. OTR
c. WVTR
d. Dyne’s value
e. Heat Sealing Strength
[00115] COATING GSM (GRAM PER SQUARE METER) DETERMINATION: Coating weight is a property of prime importance, which determines permeability rate of gas, water vapor, aroma & flavour, oil & grease molecules. Sample (substrate BOPP film) from Operating, Drive and Centre side taken by cutting specimen in size of 100mm × 100mm in square shape. One specimen from each three position (Operating, Drive and Centre) is weighed in an analytical weighing balance, which has the capacity to measure from 0.0001 gm to 220 gm. This is called an initial value. Sample is taken and put in boiling water for approx. 2~3 minutes and removal of the PVOH based coating of the present invention, by rubbing with cotton. Weigh the sample again, which will be the final value. Now use the following formula to calculate coating gsm (gram per square meter).
Coating GSM: (Initial weight - Final weight) × 100
[00116] OTR TESTING (OXYGEN TRANSMISSION RATE) DETERMINATION: OTR means oxygen transmission rate. The standard test method used for testing OTR is ASTM D3985 at 23°C at 0% RH value. Unit of OTR value is cc/m2/day. Following parameters are selected to test in MOCON OX-TRAN 2/22(H): 100% permeant concentration, 740 mmHg active Barometer pressure at temperature of 23°C and 0% RH (relative humidity) with conditioning time and re-zero Exam Minutes of 60 minutes and 30 minutes respectively. The number of testing cycles was 3 with convergence period of 3 cycles. Test specimen size was 50 cm2. Specimen was mounted on the test cell in such a way that the test gas passes through the surface of un-coated side. Carrier gas is on the side of coated surface. After completion of test, the OTR value reflects under Test Result header as Transmission @100.0%. Gases used for oxygen transmission testing has purity of 99.99% in case of Oxygen gas and purity of Nitrogen gas was 99.999%.
[00117] WVTR (WATER VAPOR TRANSMISSION RATE) DETERMINATION: WVTR means water vapor transmission rate. The standard test method used for testing WVTR is ASTM F1249 at 38°C at 90% RH value. Unit of WVTR value is gm/m2/day. Following parameters are selected to test in MOCON PERMATRAN-W 3/34 (G): with 740 mmHg active Barometer pressure, at temperature of 37.8°C and 90% RH (relative humidity) with conditioning time and re-zero Exam Minutes of 60 minutes and 30 minutes respectively. The number of testing cycles was 3 with convergence period of 3 cycles. Test specimen size was 50 cm2. After completion of test, the WVTR value reflects under Test Result header as Transmission@90.0%.
[00118] HEAT SEALING STRENGTH DETERMINATION: The other side of PVOH coated (BOPP) film is uncoated and special co-polymer based to impart heat sealing property. The heat sealing is a property in which un-coated to un-coated side is sealed using heat sealer machine then sealing strength is checked with the help of UTM (Universal Testing Machine). Test specimen is cut in one-inch width and 175 mm length. Un-coated sides of samples are kept in touch with each other and get sealed in heat sealer at a temperature of 120°C, 2.1 Bar pressure and dwelling time of 1 second. The sealed sample is cooled at 23° ± 2°C for 3 ~ 5 minutes. The sealed sample is mounted in jaw of UTM and tested at speed of 100 mm/min. The value is either in gm/25mm or gm/inch.
[00119] SURFACE TENSION DETERMINATION: Surface tension of the PVOH coated side is measured as per testing standard of D-2578. A chemical solution is made from chemical of formamide and Cellosolve. Different combination gives a different solution with different surface tension. The solution is picked up by cotton with stick and applied on the coated side of film in 1 inch. The solution, which stays in applied area and doesn’t shrink before 2 seconds, is the surface tension of the film.
[00120] ADVANTAGES OF THE PRESENT INVENTION: The present invention serves to solve several of the problems of the currently available packaging films. Some of the mentionable advantages of the present invention are:
1. The PVOH coated BOPP film (of the present invention demonstrates excellent barrier properties against oxygen, water vapor and aroma, and oil, resulting in extended self-life of the packaged food.
2. The PVOH coated BOPP film of the present invention ensures similar or superior barrier properties in comparison to metallized films and also allows see through packaging owing to its clarity, transparency, which is not possible with the metallized films.
3. The PVOH coated BOPP film of the present invention can be used in microwave ovens and remains stable due to non-metallic nature.
4. The PVOH coated BOPP film of the present invention can be easily recycled as no metallization or metal foil is used.
5. The PVOH coated BOPP film of the present invention is halogen-free packaging films.
6. The coating of the present invention is a superior alternative to PVDC coatings which have high chlorine content, which leaches out in the packaged food with time, resulting hazardous consequence for the consumer’s health.
7. The PVOH coating used in the present invention is transparent and chlorine free while offering superior or similar barrier properties when compared to PVDC coatings.
8. The present invention is suitable for further processes like printing and lamination, and suitable for high graphics printing as well. The film of the present invention possesses excellent flex resistance, abrasion and scratch resistance and does not form pin holes.
9. The heat sealable and high barrier polypropylene film / laminate (10, 20) is used to manufacture a flexible product whose shape can be changed readily for example flexible pouch, bag, sachet, flexible container, shaped pouches, etc.
10. It can be seen from the above results, the PVOH coated films of the present invention significantly improved the OTR, WVTR simultaneously by covering a layer of PVOH based aqueous coating, and the modified polyvinyl alcohol coated films provided by the present invention have higher bonding strength to various types of inks and good printability.
[00121] Specific examples are used herein to illustrate the principle and embodiments of the present invention. The description of the above examples is used only for facilitating the understanding of the methods and the core idea of the present invention. It should be noted that for the skilled in the art, a number of variations and modifications can be made to the present invention without departing from the principles of the present invention, such variations and modifications also fall within the scope claimed by the present invention as set forth in the claims.
[00122] REFERENCE NUMERALS:
1 Core layer of a Base Film
3A, 3B Skin layer(s) of a Base Film
5 Top Surface of a Sealable Skin layer (3A)
2 BOPP Base Film
2A and 2B Top and Bottom Surface of a Base Film
4 PVOH Aqueous Coating Composition
6 Printing Layer
8 Adhesive / Extrusion Lamination
10 High Barrier Transparent BOPP Film
10A and 10B Top and Bottom Surface of the High Barrier BOPP Film
12 Transparent film
20 High Barrier Laminate
100 Method of obtaining PVOH Aqueous Coating Composition (4)
200 Method of obtaining a High Barrier Transparent BOPP Film (10)
, Claims:WE CLAIM:
1. An aqueous coating composition (4) comprising:
Polyvinyl alcohol (PVOH) in the range of 5 ~ 10 wt%;
Isopropyl alcohol in the range of 5 ~ 10 wt %;
Demineralized water (DM water) in the range of 60 ~ 90 wt%; and
a crosslinker and / or adhesion promoter in the range of 0.2 ~ 2 wt%;
wherein the wt% are based on the total wt% of the coating composition (4),
wherein the aqueous coating composition (4) is coated on a biaxial oriented polypropylene (BOPP) base film (2) to obtain a heat sealable and high barrier transparent BOPP film (10).
2. The high barrier BOPP film (10) as claimed in claim 1, wherein the BOPP base film (2) is a multilayer film having a core layer (1); and one or more skin layers (3A, 3B); wherein at least one skin layer (3A) is coated with the aqueous coating composition (4).
3. The heat sealable and high barrier BOPP film (10) as claimed in claim 1, wherein at least one skin layer of the base film (2) is sealable and is coated with the aqueous coating composition (4) on at least one surface (5) of the sealable skin layer (3A).
4. The aqueous coating composition (4) as claimed in claim 1, wherein the PVOH is partially or fully hydrolyzed and water-soluble ethylene-vinyl alcohol such as EXCEVAL AQ104 or Polyvinyl alcohol such as POVAL 28-98 or POVAL 5-98.
5. The aqueous coating composition (4) as claimed in claim 1, wherein the crosslinker and / or adhesive promoter is polyethylene imine (PEI) based Loxanol MI 6730.
6. The aqueous coating composition (4) as claimed in claim 1, wherein the solid content concentration of the composition is in the range of 6.5 to 7.5%.
7. The aqueous coating composition (4) as claimed in claim 1, wherein the aqueous coating composition (4) is transparent and chlorine free.
8. The high barrier BOPP film (10) as claimed in claim 1, wherein the weight of the coating composition (4) is in the range of 0.5 ~ 1.5 GSM.
9. The high barrier BOPP film (10) as claimed in claim 1, wherein the thickness of the film (10) is in the range of 12 µ ~ 30 µ, more preferably in the range of 18 µ ~ 26 µ.
10. The high barrier BOPP film (10) as claimed in claim 1, wherein the BOPP base film (2) is transparent.
11. The high barrier BOPP film (10) as claimed in claim 1, wherein the oxygen transmission rate (OTR) of the said coated film (10) is in range of 0.2 ~1.0 cc/m2/day.
12. The high barrier BOPP film (10) as claimed in claim 1, wherein the water vapour transmission rate (WVTR) of the said coated film (10) is in range of 2 ~5 gm/m2/day.
13. The high barrier BOPP film (10) as claimed in claim 1, wherein the glossiness @ 45o of the film (10) is in the range of 80 ~ 120.
14. The high barrier BOPP film (10) as claimed in claim 1, wherein the OTR and WVTR of the said coated film (10) is improved simultaneously and not affected by relative humidity (RH) and temperature (T).
15. The high barrier BOPP film (10) as claimed in claim 1, wherein the heat seal strength of the film (10) is in the range of 350 ~ 650 gm/inch.
16. The high barrier BOPP film (10) as claimed in claim 1, wherein the surface tension of the film (10) is in the range of 54 ~ 56 dynes/cm.
17. The high barrier BOPP film (10) as claimed in claim 1, wherein the coated side of the biaxially oriented polypropylene (BOPP) film (10) is unprinted or surface printed (6) or reverse printed (6).
18. The high barrier BOPP film (10) as claimed in claim 17, wherein the coated and / or printed biaxially oriented polypropylene (BOPP) surface (10A) is laminated with a transparent film (12), using an adhesive layer or by coextrusion lamination (8), to obtain a high barrier laminate (20).
19. The high barrier laminate (20) as claimed in claim 18, wherein the coated and sealable surface (10A) of the base film (10) seals to the transparent film (12) comprising any of a coated BOPP film, an uncoated BOPP film, CPP, BOPET or any other polymer film.
20. The high barrier laminate (20) as claimed in claim 19, wherein the transparent film (12) or a laminate is a single or multilayer films or a combination thereof.
21. The high barrier BOPP film (10) as claimed in claim 1, wherein the oxygen transmission rate (OTR) of the said coated film (10) after lamination is less than 0.2 cc/m2/day.
22. The high barrier BOPP film (10) as claimed in claim 1, wherein the water vapour transmission rate (WVTR) of the said coated film (10) after lamination is less than 2.9 gm/m2/day.
23. The high barrier BOPP film (10) as claimed in claim 1, wherein the aqueous coating solution (4) applies and dries on a variety of film substrates having any of properties such as heat sealable on any one surface, heat sealable & treated on any one surface, heat sealable on both surfaces, heat sealable & treated on both the surfaces, heat sealable & treated on any one of the surfaces and the other surface is plain or treated.
24. The high barrier laminate (20) as claimed in claim 18, wherein the total thickness of the laminate (20) after laminating with the coated BOPP film (10) is more than 50 microns, more preferably in range of 50 to 90µ.
25. A method (100) for preparing a PVOH based aqueous coating (4) comprising below steps:
(a) demineralized (DM) water is heated at a temperature in the range of 50 °C ~ 60°C in the vessel;
(b) adding PVOH polymer solids in the above DM water;
(c) stirring the mixture of step (b) at a temperature in the range of 85~95°C for 1 to 5 hours, to obtain a homogenous aqueous solution;
(d) cooling the homogenous aqueous solution of step (c) at an ambient temperature to obtain a Solution A;
(e) separately preparing an aqueous solution by mixing isopropyl alcohol (IPA) and DM water in the ratio of 1:1;
(f) adding a Polyethylene imine (PEI) based cross linker and /or adhesion promoter to the mixture of step (e) at an ambient temperature;
(g) stirring the mixture of step (f) at a temperature in the range of 45~55°C for 30 to 60 minutes, to obtain a Solution B;
(h) Solution A and Solution B are added to a mixture of IPA and DM water having the ratio of 1:1;
(i) stirring the mixture of step (h) at a temperature in the range of 45~55°C for 30 to 60 minutes; and
(j) filtering the above solution of step (i) to obtain the final coating solution of the PVOH aqueous coating composition (4).
26. The method (100) as claimed in claim 25, wherein 10 g PVOH polymer solids is added to 90 g of preheated DM water at 60°C and stirred at 90°C for 3 hours to obtain a homogenous aqueous solution.
27. The method (100) as claimed in claim 25, wherein PVOH is partially or fully hydrolysed grade of water-soluble ethylene -modified polyvinyl alcohol such as EXCEVAL AQ104 or Polyvinyl alcohol such as POVAL 28-98 or POVAL 5-98.
28. The method (100) as claimed in claim 25, wherein the cross linker and /or adhesion promoter is Polyethylene imine (PEI) based Loxanol MI 6730.
29. The method (100) as claimed in claim 25, wherein 0.2-0.5 g of Loxanol MI 6730 is added in 20 g solution of isopropyl alcohol (IPA) and DM water in the ratio of 1:1 in step (f).
30. The method (100) as claimed in claim 25, wherein the mixture is stirred at 45°C for 45 minutes in steps (g) and (i).
31. The method (100) as claimed in claim 25, wherein demineralized water (DM water) is in the range of 60 ~ 90 wt% of the coating composition (4).
32. The method (100) as claimed in claim 25, wherein Polyvinyl alcohol (PVOH) is in the range of 5 ~ 10 wt% of the coating composition (4).
33. The method (100) as claimed in claim 25, wherein Isopropyl alcohol (IPA) is in the range of 5 ~ 10 wt % of the coating composition (4).
34. The method (100) as claimed in claim 25, wherein the crosslinker and / or adhesive promoter is in the range of 0.2 ~ 2 wt% of the coating composition (4).
35. A method (200) for preparing a heat sealable and high barrier biaxially oriented polypropylene (BOPP) film (10) as claimed in claim 1, comprising below steps:
(a) applying the coating solution of the PVOH based aqueous coating (4) as prepared in claim 24, on a biaxially oriented polypropylene (BOPP) base film (2);
(b) drying or curing the coated BOPP film (10);
(c) cooling the coated and dried BOPP film (10) at an ambient temperature; and
(d) winding the cooled coated and dried high barrier transparent BOPP film (10) over a winder.
36. The method as claimed in claim 35, wherein the PVOH based aqueous (4) at step (a) is applied by an in-line or offline method.
37. The method as claimed in claim 25 and 35, wherein the ambient temperature is in the range of 20oC ~35oC.
38. The method as claimed in claim 35, wherein drying of the film (10) is done at temperature is in the range of 95oC ~ 125oC.
39. The method as claimed in claim 35, wherein drying is done by hot air blower or infrared heaters.
40. The method (200) as claimed in claim 35, wherein additionally or optionally printing (6) is performed on the coated surface (10A) of the high barrier BOPP film (10) by a surface printing and / or reverse printing.
41. The method (200) as claimed in claim 35 and 40, wherein the coated and / or printed side of the BOPP film (10A) laminated with a transparent BOPP film or CPP film, BOPET film or any other polymer film (12) by using an adhesive or by coextrusion lamination (6), to obtain a high barrier laminate (20).
42. The high barrier BOPP film (10) as claimed in claim 18, wherein the high barrier laminate (20) is transparent, opaque or translucent.
43. The method (200) as claimed in claim 35, wherein the PVOH based aqueous coating (4) is applied to the sealable surface (10A) of the BOPP film with or without a primer.

Dated this 27th day of December 2024.

-Digitally Signed :: Filed via e-Filing-
RACHANA SONI [IN/PA-4162]
AGENT FOR THE APPLICANT