Multilayer packaging film

Abstract

The present disclosure relates to a multilayer packaging film having a first base layer, a second base layer on the first base layer, and a sealing layer on the second base layer. In some embodiments, the second base layer has a shrinkage value less than a shrinkage value of the first base layer. In some embodiments, the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the first base layer. In some embodiments, the second base layer has a shrinkage value greater than 5%, and the shrinkage value of the second base layer is less than the shrinkage value of the first base layer. Also disclosed are methods of producing the multilayer packaging films and hermetically sealed packages (e.g., thermoformed trays or cups and retort pouches) formed from the multilayer packaging films.

Description

Technical Field

[0001] The present invention relates to multilayer film structures. Embodiments of the present invention relate to flexible multilayer films for packaging applications. Background Art

[0002] A typical packaging application involving exposure of a multilayer film structure to thermal stress is retort packaging. In retort packaging, the packaged product undergoes an extended heat and pressure treatment process. Similarly, the package or packaged product may undergo a pasteurization process at about 80°C. In yet another application, the multilayer film structure may be used as a heat shrink wrap foil at a temperature of 80°C or lower.

[0003] Food products are increasingly being packaged in flexible retort packages (i.e., flexible stand-up pouches) as an alternative to metal cans and glass jars. Packaging materials for flexible retort packages typically include an embedded barrier layer, an outer polymer layer adhered to one side of the barrier layer and forming the outer surface of the package, and an inner polymer film layer adhered to the other side of the gas barrier layer and forming the inner surface of the package. This combination of layers is designed to withstand the retort process without melting or substantial degradation (i.e., leakage, delamination). In general, retort consists of heating the packaging container to a temperature of 100 to 135° C. at an overpressure of 0.5 to 1.1 bar for a period of 15 to 100 minutes.

[0004] Examples of laminates for retort packaging are disclosed in US 4,310,578 A; US 4,311,742 A; US 4,308,084 A; US 4,309,466 A; US 4,402,172 A; US 4,903,841 A; US 5,273,797 A; US 5,731,090 A; EP 1 466 725 A1; JPH 09 267 868 A; JP 2002 096 864 A; JP 2015066 721 A; JP 2018 053 ​​180 A; JP 2017 144 648 A; JPS 62 279 944 A; JPS 6 328 642; and JPH 10 244 641 A.

[0005] A typical option for designing a flexible retort packaging multilayer film structure is to use an aluminum barrier layer with a thickness of at least 5 μm, preferably a thickness of more than 12 μm. However, aluminum is expensive, has a high density, can develop pinholes at smaller thicknesses after flexing, and has the disadvantage of being opaque. Aluminum is also known to cause problems with reheating packaged food products in microwave ovens. Furthermore, the presence of a metal layer is generally undesirable in terms of recycling possibilities and metal detection during the packaging process.

[0006] A typical example of a multilayer film structure for a standard retort pouch comprises an outer polyethylene terephthalate layer, a barrier layer and an inner sealing layer, wherein the outer layer comprises a print layer, the barrier layer comprises a metal foil or inorganic oxide coated polymer film, and the inner layer is a heat sealable polyolefin layer. The packaging material may also contain additional polymer film layers, such as a polyamide layer, etc.

[0007] The diversity of polymer layers that make up multilayer barrier film structures introduces the additional challenge of making these multilayer film structures recyclable and able to withstand retort processes without melting or substantial degradation (ie, leakage, delamination).

[0008] Without questioning the relative merits of prior art systems, there exists a need for improved multilayer film structures for packaging, wherein the multilayer film structures are recyclable and are capable of withstanding the retort process without melting or substantially degrading (ie, leaking, delamination). Summary of the invention

[0009] Embodiments of the present invention advantageously provide a multilayer packaging film that can withstand a cooking process without melting or substantial degradation (i.e., leaking, delamination). In some embodiments, the multilayer packaging film structure is heat treated, for example, during a pasteurization or cooking process. In some embodiments, the multilayer packaging film structure comprises one or more inorganic coatings that remain substantially crack-free during and after the heat treatment, thereby limiting the increase in oxygen and water vapor transmission rates of the multilayer packaging film.

[0010] Additional embodiments of the present invention advantageously provide a more sustainable, transparent multilayer packaging film that exhibits excellent oxygen transmission rate (low transmission rate, high barrier properties), has thermoelasticity, and the thermoelastic multilayer packaging film structure is relatively easier to recycle than typical high barrier packaging film structures.

[0011] The present disclosure provides a multilayer packaging film having a first base layer, a second base layer on the first base layer, and a sealing layer on the second base layer. In some embodiments, one or more of the first base layer, the second base layer, or the sealing layer comprises a polyolefin film.

[0012] In some embodiments, the polyolefin film of each of the first base layer and the second base layer is an oriented polyethylene (OPE) film or an oriented polypropylene (OPP) film. In some embodiments, one or more of the oriented polyethylene (OPE) film or the oriented polypropylene (OPP) film is formed by one or more of a sequential stretching process or a simultaneous stretching process. In some embodiments, the simultaneous stretching process is one or more of a linear motor simultaneous stretching process, a double bubble process, or a triple bubble process.

[0013] In some embodiments, the oriented polypropylene (OPP) film is a coextruded OPP film having a treated, non-sealable first side and a sealable second side.

[0014] In some embodiments, the oriented polypropylene (OPP) film is a coextruded OPP film having a treated and non-sealable first side and a treated and non-sealable second side.

[0015] In some embodiments, the polyolefin film comprises a biaxially oriented polypropylene (BOPP) film. In some embodiments, the biaxially oriented polypropylene (BOPP) film is formed by a linear motor simultaneous stretching process, and the biaxially oriented polypropylene (BOPP) film has a treated and non-sealable first side and a sealable second side. In some embodiments, the biaxially oriented polypropylene (BOPP) film is formed by a triple bubble process, and the biaxially oriented polypropylene (BOPP) film has a treated and non-sealable first side and a sealable second side.

[0016] In some embodiments, one or more of the first base layer or the second base layer has an inorganic coating thereon. The inorganic coating may be on one or more sides of the first base layer and / or the second base layer. In some embodiments, the inorganic coating of one or more of the first base layer or the second base layer comprises silicon oxide. In some embodiments, the inorganic coating of one or more of the first base layer or the second base layer has a gas barrier coating thereon. In one or more embodiments, the gas barrier coating comprises one or more of a hydroxyl-containing polymer compound, a metal alkoxide, a silane coupling agent, and a hydrolyzate thereof. In some embodiments, the inorganic coating improves the gas barrier properties of one or more of the first base layer or the second base layer to water vapor and oxygen.

[0017] Some embodiments of the multilayer packaging film further include an adhesive layer on one or more of the first base layer, the second base layer, or the sealing layer. In one or more embodiments, the adhesive layer includes polyurethane. In some embodiments, the adhesive layer includes one or more of a polyester-based polyurethane resin or a polyether-based polyurethane resin.

[0018] In some embodiments, the adhesive layer includes a polyvinyl alcohol-based resin having a vinyl alcohol unit, in which a vinyl ester unit is saponified, and examples thereof include polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH).

[0019] In some embodiments, the adhesive layer is heat resistant and provides adhesion to each layer in contact with the adhesive layer.

[0020] In some embodiments, the adhesive layer is located between one or more of the first base layer and the second base layer, or between the second base layer and a sealing layer. In some embodiments, the adhesive layer is located between the first base layer and one or more of the inorganic coating layers thereon, between the second base layer and the inorganic coating layer thereon, or between the inorganic coating layer on the second base layer and the sealing layer.

[0021] In the embodiment where the multilayer packaging film comprises the inorganic coating, the adhesive layer may be located on the surface of the polyolefin film laminated with the inorganic coating. Without intending to be bound by theory, in such embodiments, it is believed that the adhesive layer improves the adhesion between the polyolefin film and the inorganic coating and improves the smoothness of the polyolefin film surface.

[0022] In one or more specific embodiments, the multilayer packaging film comprises a first base layer and a second base layer, each base layer having an inorganic coating thereon. In one or more specific embodiments, the adhesive layer is between and in direct contact with the first base layer and the inorganic coating on the first base layer. In one or more specific embodiments, the adhesive layer is between and in direct contact with the second base layer and the inorganic coating on the second base layer. In one or more specific embodiments, the sealing layer is on the inorganic coating on the second base layer.

[0023] In some embodiments, the total composition of the multilayer packaging film comprises greater than or equal to 80% by weight of polyolefins, greater than or equal to 90% by weight of polyolefins, or greater than or equal to 95% by weight of polyolefins. In some embodiments, the total composition of the multilayer packaging film comprises greater than or equal to 80% by weight of polypropylene, greater than or equal to 90% by weight of polypropylene, or greater than or equal to 95% by weight of polypropylene. In some embodiments, the total composition of the multilayer packaging film comprises greater than or equal to 80% by weight of polyethylene, greater than or equal to 90% by weight of polyethylene, or greater than or equal to 95% by weight of polyethylene.

[0024] In some embodiments, the shrinkage value of the second base layer is less than the shrinkage value of the first base layer. In some embodiments, the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the first base layer. In some embodiments, the shrinkage value of the second base layer is greater than 5%, and the shrinkage value of the second base layer is greater than the shrinkage value of the first base layer. In some embodiments, the shrinkage value of the second base layer is less than or equal to 5%. In some embodiments, the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealing layer.

[0025] In some embodiments, the difference in shrinkage values ​​between the first base layer and the second base layer is greater than or equal to 0.3%. In some embodiments, the difference in shrinkage values ​​between the second base layer and the sealing layer is greater than or equal to 0.5%. In some embodiments, the shrinkage value of the sealing layer is greater than or equal to 2%.

[0026] In some embodiments, each of the first base layer and the second base layer has a thickness in a range of 6 microns to 100 microns, including in a range of 6 microns to 50 microns or 10 microns to 40 microns.

[0027] In some embodiments, the thickness of the sealing layer is less than or equal to 120 microns, including less than or equal to 110 microns, less than or equal to 100 microns, less than or equal to 90 microns, less than or equal to 80 microns, less than or equal to 70 microns, less than or equal to 60 microns, less than or equal to 50 microns, less than or equal to 40 microns, less than or equal to 30 microns, less than or equal to 20 microns, less than or equal to 10 microns or less than or equal to 5 microns.

[0028] In some embodiments, the inorganic coating has a thickness in a range from 0.005 micrometers to 0.1 micrometers.

[0029] In some embodiments, the thickness of the adhesive layer is in the range of 0.5 micrometers to 10 micrometers. In some embodiments, the thickness of the adhesive layer is in the range of 2 micrometers to 4 micrometers.

[0030] Some embodiments of the present disclosure relate to hermetically sealed packages (e.g., thermoformed trays and cups with lids and retort pouches) formed from multilayer packaging films. In some embodiments, the package further comprises at least one lap seal that bonds the first base layer of the multilayer packaging film to the sealing layer.

[0031] Additional embodiments relate to methods for producing multilayer packaging films. The methods for producing multilayer packaging films may include any suitable process known to those skilled in the art that does not change the shrinkage values ​​of the corresponding layers as described herein. In some embodiments, the methods for producing multilayer packaging films include one or more of extrusion lamination, lacquer lamination, or thermal calendering. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present disclosure may be more fully understood by considering the following detailed description of various embodiments of the present disclosure in conjunction with the accompanying drawings, in which:

[0033] Figure 1 , 2 , 3, 4 and 5 are cross-sectional views of different embodiments of multilayer packaging films; and

[0034] Figure 6and 7 is a perspective view of an embodiment of a hermetically sealed package comprising a multi-layer packaging film.

[0035] The accompanying drawings show some but not all embodiments. The elements depicted in the drawings are illustrative and are not necessarily drawn to scale, and the same (or similar) reference numerals represent the same (or similar) features throughout the drawings. DETAILED DESCRIPTION

[0036] It is believed that the packaging industry is turning to more sustainable options, including streamlining the materials used to narrow categories. For example, one option is to design a packaging structure with a high polyolefin content so that the film is classified as recyclable. Removing non-olefin polymers from the packaging structure usually results in insufficient overall performance of the packaging structure. In the case where the packaging is intended for thermal processing applications (such as cooking or pasteurization), polyolefin polymers are more sensitive to application temperature. Specifically, at high temperatures, polyolefin materials may shrink more than other polymer materials and may become unsuitable as structural components of inorganic coatings because polyolefins will approach their melting points under cooking or even pasteurization conditions compared to more traditional, non-recyclable oPET films used to support barrier oxide coatings in retortable applications. Introducing the material selection as described herein into the packaging film can reduce the negative impact of using a group of more recyclable polymer materials. Therefore, due to the high polyolefin content, the barrier packaging film described herein is more easily recycled, but maintains high performance properties such as oxygen and moisture barriers.

[0037] As used herein, layers or films that are "directly in contact" or "immediately adjacent" to each other have no intervening materials therebetween.

[0038] As used herein, the term "inorganic coating" refers to a layer comprising a metal layer or an oxide coating. The inorganic coating can act as a barrier layer. The inorganic coating can be directly vacuum deposited (i.e., vacuum coated, vapor coated, vacuum metallized) on the surface of the first or second substrate. Alternatively, the inorganic coating can be deposited by wet chemical methods, such as solution coating, or applied by reactive coating techniques, such as chemical vapor deposition.

[0039] As used herein, the term "polyolefin" generally includes polypropylene and polyethylene polymers. Alternatively, the term "polyolefin" includes polybutylene films. The polyolefin film may, for example, include an acid-modified polyolefin film obtained by grafting and modifying a polyolefin polymer with an unsaturated carboxylic acid, an unsaturated carboxylic acid anhydride, an unsaturated carboxylic acid ester, or the like. The polyolefin film may be subjected to various pretreatment processes. The pretreatment process may include any suitable process known to those skilled in the art that does not impair barrier properties. The pretreatment process includes, but is not limited to, corona treatment, plasma treatment, or flame treatment, or other similar processes. The polyolefin film may include an adhesive reinforcement layer.

[0040] As described herein, one or more polyolefin films of multilayer packaging film can be oriented. Orientation can be the result of film uniaxial orientation (machine direction or transverse direction) or biaxial orientation (machine direction and transverse direction) stretching, thereby increasing machine direction and / or transverse direction dimensions, and subsequently reducing the thickness of the material. Biaxial orientation can be given to the film simultaneously or continuously. In certain embodiments, the film is stretched in one direction or two directions at a temperature just below the melting temperature of the polymer in the film. In this way, stretching "orients" the polymer chain, thereby changing the physical properties of the film. At the same time, stretching makes the film thinner. The resulting oriented film is thinner and can have significant changes in mechanical properties such as toughness, heat resistance, stiffness, tear strength and barrier properties. Orientation is usually achieved by a double bubble or triple bubble process, a tenter process or an MDO process using a heated roller. Typical blown film processes do impart some stretching of the film, but are not enough to be considered as oriented as described herein. The oriented film may be heat set (i.e., annealed) after orientation so that the film is relatively dimensionally stable (i.e., less than 10% free shrink) under elevated temperature conditions that may be experienced during conversion (i.e., printing or lamination) of a retort film laminate or during use (i.e., heat sealing or retort sterilization) of the laminate. As used herein, the terms "unoriented" and "non-oriented" refer to monolayer or multilayer films, sheets, or webs that are substantially free of post-extrusion orientation.

[0041] As used throughout this application, the term "copolymer" refers to a polymer product obtained by polymerization or copolymerization of at least two monomeric species. The term "copolymer" also includes polymerization reactions of three, four or more monomeric species with reaction products known as terpolymers, tetrapolymers, etc.

[0042] As used throughout this application, unless otherwise specified, the term "polypropylene" or "PP" refers to a propylene homopolymer or copolymer. Such propylene copolymers include copolymers of propylene with at least one alpha-olefin and copolymers of propylene with other units or groups. The term "polypropylene" or "PP" is used without regard to the presence or absence of substituent branched groups or other modifiers. Polypropylene includes, but is not limited to, homopolymer polypropylene, polypropylene impact copolymers, polypropylene random copolymers, propylene-ethylene copolymers, ethylene-propylene copolymers, maleic anhydride grafted polypropylene, and blends thereof. Various polypropylene polymers can be recycled as recycled polypropylene or recycled polyolefins.

[0043] As used throughout this application, unless otherwise specified, the term "polyethylene" or "PE" refers to an ethylene homopolymer or copolymer. Such ethylene copolymers include copolymers of ethylene and at least one alpha-olefin and copolymers of ethylene and other units or groups such as vinyl acetate, acid groups, acrylate groups or others. The term "polyethylene" or "PE" is used regardless of the presence or absence of substituent branched groups. Polyethylene includes, but is not limited to, medium density polyethylene, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra-low density polyethylene, ethylene alpha-olefin copolymers, ethylene vinyl acetate, ethylene acid copolymers, ethylene acrylate copolymers, neutralized ethylene copolymers such as ionomers, maleic anhydride grafted polyethylene and blends thereof. Various polyethylene polymers can be recycled as regenerated polyethylene or regenerated polyolefins.

[0044] As used throughout this application, the term "polyester" or "PET" refers to a homopolymer or copolymer having ester bonds between monomer units. The ester bonds can be represented by the general formula [OR-OC(O)-R'-C(O)] n It represents, wherein R and R' are the same or different alkyl (or aryl) groups, and can be generally formed by the polymerization of dicarboxylic acid and diol monomers.

[0045] As used herein, the term "polyamide" refers to a high molecular weight polymer having amide bonds (--CONH--)n occurring along the molecular chain and includes "nylon" resins, which are well-known polymers with a large number of uses, including utility as packaging films. Examples of nylon polymer resins used for food packaging and processing include: nylon 66, nylon 610, nylon 66 / 610, nylon 6 / 66, nylon 11, nylon 6, nylon 66T, nylon 612, nylon 12, nylon 6 / 12, nylon 6 / 69, nylon 46, nylon 6-3-T, nylon MXD-6, nylon MXDI, nylon 12T, and nylon 6I / 6T. Examples of polyamides include nylon homopolymers and copolymers, such as: nylon 4,6 (poly(tetramethylene adipamide)), nylon 6 (polycaprolactam, nylon 6,6 (poly(hexamethylene adipamide)), nylon 6,9 (poly(hexamethylene nonane diamide)), nylon 6,10 (poly(hexamethylene sebacamide)), nylon 6,12 (poly(hexamethylene dodecanedioamide)), nylon 6 / 12 (poly(caprolactam-co-dodecanedioamide)), nylon 6,6 / 6 (poly(hexamethylene adipamide-co-caprolactam)), nylon 66 / 610 (e.g., made by condensation of a mixture of nylon 66 salt and nylon 610 salt), nylon 6 / 69 resin (e.g., made by condensation of ε-caprolactam, hexamethylenediamine and azelaic acid), nylon 11 (polyundecyl bridged) lactam), nylon 12 (polylaurolactam), and copolymers or mixtures thereof. Polyamides are used in films for food packaging and other applications because of their unique physical and chemical properties. Polyamides are selected as materials for improving the temperature resistance, abrasion resistance, puncture strength and / or barrier properties of the films. The properties of polyamide-containing films can be modified by selecting various variables including copolymer selection and conversion methods (e.g., coextrusion, orientation, lamination and coating).

[0046] As used herein, "polyurethane" generally refers to a polymer having organic units connected by urethane bonds (-NH-(C=O)-O-).

[0047] As used herein, "polylactic acid" is a polymer made from lactic acid and has a backbone of [-C(CH3)HC(=O)O-] n .

[0048] As used throughout this application, the term "vinyl alcohol copolymer" refers to a film-forming copolymer of vinyl alcohol (CH2CHOH). Examples include, but are not limited to, ethylene vinyl alcohol copolymer (EVOH), butene glycol vinyl alcohol copolymer (BVOH), and polyvinyl alcohol (PVOH).

[0049] As used throughout this application, the term "ethylene vinyl alcohol copolymer", "EVOH copolymer" or "EVOH" refers to a copolymer composed of repeating units of ethylene and vinyl alcohol. Ethylene vinyl alcohol copolymer can be represented by the following general formula: [(CH2-CH2) n -(CH2-CH(OH))] n . Ethylene vinyl alcohol copolymers may include saponified or hydrolyzed ethylene vinyl acetate copolymers. EVOH refers to vinyl alcohol copolymers having ethylene comonomers and prepared by, for example, hydrolysis of vinyl acetate copolymers or by chemical reaction with vinyl alcohol. Ethylene vinyl alcohol copolymers may contain 28 mole percent (or less) to 48 mole percent (or more) ethylene.

[0050] As used herein, the term "layer" refers to the building block of a film, which is a structure of a single material type or a uniform blend of materials. A layer can be a single polymer, a blend of materials within a single polymer type, or a blend of various polymers, can contain metallic materials, and can have additives. A layer can be continuous with the film, or can be discontinuous or patterned. Compared with the length and width (xy direction), a layer has an insignificant thickness (z direction), and is therefore defined as having two major surfaces, whose area is defined by the length and width of the layer. An outer layer is a layer connected to another layer only at one of the major surfaces. In other words, one major surface of the outer layer is exposed. An inner layer is a layer connected to another layer at two major surfaces. In other words, the inner layer is between two other layers. A layer may have a sublayer.

[0051] Similarly, as used herein, the term "film" refers to a web constructed of layers and / or films, all of which are immediately adjacent to and connected to each other. A film can be described as having a thickness that is insignificant compared to the length and width of the film. The film has two major surfaces, whose areas are defined by the length and width of the film.

[0052] As used herein, the term "external" is used to describe a film or layer that is located on one of the major surfaces of the film it contains. As used herein, the term "internal" is used to describe a film or layer that is not located on the surface of the film it contains. An internal film or layer is adjacent to another film or layer on both sides.

[0053] As used herein, "barrier" or "barrier film" or "barrier layer" or "barrier material" refers to providing a reduced transmission rate to gases such as oxygen (i.e., containing an oxygen barrier material). Barrier materials can provide a reduced transmission rate to moisture (i.e., containing a moisture barrier material). Barrier properties can be provided by one or more barrier materials or a blend of multiple barrier materials. Inorganic coatings can act as barrier layers. Barrier layers can provide the specific barrier needed to preserve the product within the package over an extended shelf life, which can be several months or even more than a year.

[0054] During the shelf life of the packaged product (i.e., when the package is hermetically sealed), the barrier layer can reduce the influx of oxygen through the barrier packaging film. The oxygen transmission rate (OTR) of a multilayer packaging film is an indication of the barrier provided and can be measured according to ASTM F1927 using conditions of 1 atmosphere, 23°C, and 50% RH.

[0055] As used herein, "multilayer packaging film" or "hermetically sealed packaging" or "retort packaging" is a film structure, or packaging made from a film structure, that maintains a high oxygen or moisture barrier level with little degradation after exposure to or above a heat treatment temperature. The package can be filled with a product, sealed and maintained hermetically sealed, thereby maintaining excellent barrier properties.

[0056] As used herein, "free shrinkage" or "shrinkage value" is the unrestrained linear shrinkage that a film or layer undergoes due to exposure to elevated temperatures. Shrinkage is irreversible and relatively rapid (i.e., noticeable within seconds or minutes). Shrinkage values ​​are expressed as a percentage of the original size, (i.e., 100x (size before shrinkage - size after shrinkage) / (size before shrinkage)). Free shrinkage can be measured using any suitable method capable of measuring a difference in shrinkage values ​​of at least 0.2%. Free shrinkage can be measured using ASTM D2732-03. As described in ASTM D2732-03, free shrinkage is a value obtained by measuring the unrestrained (i.e., free) shrinkage of a 10 square centimeter sample immersed in 90°C water for five seconds. ASTM D2732-03 includes at least the following steps:

[0057] 1. Embossed and cut out the embossed portion of the film.

[0058] 2. Place the sample in a free-shrink holder so that it does not touch the edges of the holder.

[0059] i. A minimum of two samples are required for each temperature.

[0060] 3. Before immersing each specimen, observe and record the temperature of the bath.

[0061] 4. Immerse the specimen in the bath for 10 seconds or a time determined to be sufficient for the material to reach thermal equilibrium and experience maximum contraction.

[0062] 5. Remove the sample from the bath and quickly immerse it in a liquid medium at room temperature, preferably miscible with the bath medium.

[0063] After 6.5 seconds, remove the sample from the cooling medium and measure and record the linear dimensions of the sample in the machine (longitudinal) and transverse directions.

[0064] 7. Determine the percentage of free shrinkage in each direction as follows:

[0065] Unrestricted linear shrinkage, % = [(L0-L f ) / L0]×100 (1)

[0066] in:

[0067] L o = initial length of the side (100 mm), and

[0068] L f = length of the side after contraction.

[0069] 8. The report should include the following:

[0070] i. Average linear free shrinkage percentage in both machine (longitudinal) and transverse directions,

[0071] ii. Bath temperature,

[0072] iii. Complete sample identification, and

[0073] iv. Number of samples tested.

[0074] ASTM D2732-03, Standard Test Method for Unrestrained Linear Thermal Shrinkage of Plastic Film and Sheeting, available at https: / / petro-pack.com / wp-content / uploads / D-2732-Shrinkage.pdf.

[0075] Without intending to be bound by any particular theory, it is believed that one of ordinary skill in the art would measure free shrink using the protocol in ASTM D2732-03.

[0076] Alternatively, free shrinkage can be measured by using the test method described in ASTM D2732-03, modified to use hot air as the heating source rather than a hot fluid bath. If the hot air method is used, place the unrestrained sample in an oven set to the specified temperature for at least 1 minute, allowing ample time for the oven interior and the sample to reach thermal equilibrium.

[0077] Alternatively, the shrinkage value is calculated after measuring the linear dimension in the machine direction (MD) before and after shrinkage according to Formula 1:

[0078]

[0079] The shrinkage value may be measured after heating at 120° C. for 15 minutes. Alternatively, the shrinkage value may be measured after heating at 127° C. for 50 minutes.

[0080] Multilayer packaging film as described herein can be used as boiling or pasteurization packaging film.As used herein, "boiling packaging film" or "boiling packaging" is a film or a packaging made of film, which can be filled with product, sealed, and keep airtight seal after being exposed to typical boiling sterilization process.Typical boiling sterilization is a batch process, using a temperature of about 100 ℃ to about 150 ℃, an overpressure of about 70psi (483kPa) at most, and the duration can be from a few minutes to several hours.Common boiling processes for products packaged in flexible films include steam or water soaking.Food or other products packaged in boiling packaging films and boiled and sterilized can be stored for extended periods of time (that is, shelf-stable) under ambient conditions, keeping aseptic.Because the boiling process can degrade the film or the packaging made of film, a very dedicated flexible packaging film has been designed to withstand the boiling process.

[0081] As used herein, the term "adhesive layer" refers to a layer having the primary function of bonding two adjacent layers together. The adhesive layer can be positioned between two layers of a multilayer film to maintain the two layers in a relative position to each other and prevent undesirable delamination. Unless otherwise indicated, the adhesive layer can have any suitable composition that provides a desired level of adhesion to one or more surfaces in contact with the adhesive layer material.

[0082] The adhesive layer can be deposited on the polyolefin film of one or more in the first base layer or the second base layer by any suitable method known to those skilled in the art. In certain embodiments, the deposited adhesive layer includes but is not limited to immersion method (dipping method) and the method using sprayer, coater, printer, brush, etc. In addition, the type of coater and printer used in these methods and the example of its coating method can include gravure coater, reverse roll coater, micro gravure coater, combination chamber and blade coater, air knife coater, dip coater, rod coater, dot coater and the mold coater for direct gravure printing method, reverse gravure printing method, contact reverse gravure printing method, offset gravure printing method, etc.

[0083] The adhesive layer can be dried by any suitable method known to those skilled in the art. The method of drying the adhesive layer includes, but is not limited to, a method of natural drying, a method of drying in an oven set to a predetermined temperature, and a method of using a dryer such as an arch dryer, a floating dryer, a drum dryer, and an infrared dryer attached to a coater. Drying conditions can be selected based on the drying method. For example, in a method of drying in an oven, the adhesive layer can be dried at a temperature in the range of 60°C to 100°C for about 1 second to 2 minutes.

[0084] As used herein, the term "sealing layer" refers to a layer of a film, sheet, etc. that involves sealing the film, sheet, etc. to itself and / or another layer of the same or another film, sheet, etc. As used herein, the terms "heat seal," "heat-sealed," "heat seal," "heat sealable," etc. refer both to a film layer that can be heat-sealed to itself or another thermoplastic film layer, and to the formation of a fusion bond between two polymer surfaces by conventional indirect heating means. It should be understood that conventional indirect heating generates sufficient heat on at least one film contact surface to be conducted to an adjacent film contact surface so that the formation of a bonding interface therebetween is achieved without loss of film integrity.

[0085] An embodiment of a multi-layer packaging film structure is Figure 1-7 Although the embodiment of the multilayer packaging film structure can be referred to Figure 1-7 Although not limited to any particular embodiment, the method 500 may be used to form a multilayer packaging film structure. Figure 1-7 An embodiment of a multi-layer packaging film structure is shown in .

[0086] Figure 1 A cross-sectional view of an embodiment of a multilayer packaging film 10 is shown. The multilayer packaging film 10 includes a first base layer 13 on a second base layer 14. The second base layer 14 has an inorganic coating layer 15 on one side. The multilayer packaging film 10 includes an adhesive layer 16 between and in direct contact with the first base layer 13 and the second base layer 14, and an adhesive layer 16 between and in direct contact with the inorganic coating layer 15 on the second base layer 14 and the sealing layer 11. Figure 1 In the embodiment, the first base layer 13 forms an outer layer of the multilayer packaging film 10 , and the sealant layer 11 forms an opposite outer layer of the multilayer packaging film 10 .

[0087] Figure 2 There is shown a cross-sectional view of an embodiment of a multilayer packaging film 10. The multilayer packaging film 10 comprises a first base layer 13 on a second base layer 14. The second base layer 14 has an inorganic coating 15 on one side. Figure 2 The inorganic coating 15 is shown, which is on the second base layer 14. Figure 1 The multilayer packaging film 10 includes an adhesive layer 16 between the first base layer 13 and the inorganic coating 15 on the second base layer 14 and in direct contact with them, and an adhesive layer 16 between the second base layer 14 and the sealing layer 11 and in direct contact with them. Figure 2In the embodiment, the first base layer 13 forms an outer layer of the multilayer packaging film 10 , and the sealant layer 11 forms an opposite outer layer of the multilayer packaging film 10 .

[0088] Figure 3 A cross-sectional view of an embodiment of a multilayer packaging film 10 is shown. The multilayer packaging film 10 includes a first base layer 13 on a second base layer 14. The first base layer 13 has an inorganic coating 15 on one side. The multilayer packaging film 10 includes an adhesive layer 16 between and in direct contact with the first base layer 13 and the second base layer 14, and an adhesive layer 16 between and in direct contact with the second base layer 14 and the sealing layer 11. Figure 3 In the embodiment, the first base layer 13 forms an outer layer of the multilayer packaging film 10 , and the sealant layer 11 forms an opposite outer layer of the multilayer packaging film 10 .

[0089] Figure 4 There is shown a cross-sectional view of an embodiment of a multilayer packaging film 10. The multilayer packaging film 10 comprises a first base layer 13 on a second base layer 14. The first base layer 13 has an inorganic coating 15 on one side. Figure 4 The inorganic coating 15 is shown, which is on the first base layer 13 and Figure 3 The multilayer packaging film 10 includes an adhesive layer 16 between and in direct contact with the first base layer 13 and the second base layer 14, and an adhesive layer 16 between and in direct contact with the second base layer 14 and the sealing layer 11. Figure 3 In the embodiment, the inorganic coating layer 15 on the first base layer 13 forms an outer layer of the multilayer packaging film 10 , and the sealing layer 11 forms an opposite outer layer of the multilayer packaging film 10 .

[0090] Figure 5 A cross-sectional view of an embodiment of a multilayer packaging film 10 is shown. Figure 5 In the illustrated alternative embodiment, the multilayer packaging film 10 includes a first base layer 13 and a second base layer 14, each base layer having an inorganic coating 15 thereon. Figure 5 In the embodiment, the inorganic coating layer 15 is interposed between the first base layer 13 and the adhesive layer 16 and is in indirect contact therewith, and the inorganic coating layer 15 is interposed between the second base layer 14 and the adhesive layer 16 and is in indirect contact therewith. The sealing layer 11 is directly adjacent to the adhesive layer 16 on the inorganic coating layer 15 on the second base layer 14. Figure 5 In the embodiment, the first base layer 13 forms an outer layer of the multilayer packaging film 10, and the sealing layer 11 forms an opposite outer layer of the multilayer packaging film 10. Figure 1-4 As shown, the inorganic coating 15 may be positioned on one or more sides of the first base layer 13 and the second base layer 14 .

[0091] The first base layer 13 and the second base layer 14 have a thickness 13A, 14A measured in the z direction. In some embodiments, each of the first base layer 13 and the second base layer 14 has a thickness 13A, 14A in the range of 6 microns to 100 microns, including in the range of 6 microns to 50 microns or 10 microns to 40 microns.

[0092] The adhesive layer 16 has a thickness 16A measured in the z-direction. In some embodiments, the thickness 16A of the adhesive layer 16 is in a range of 0.5 micrometers to 10 micrometers.

[0093] The inorganic coating 15 has a thickness 15A measured in the z-direction. The thickness 15A of the inorganic coating 15 is in the range of 0.005 micrometers to 0.1 micrometers, in the range of 0.005 micrometers to 0.06 micrometers, in the range of 0.01 micrometers to 0.1 micrometers, or in the range of 0.01 micrometers to 0.06 micrometers. Inorganic coatings having thicknesses greater than these ranges may result in the inability of the layer to flex to accommodate changes in surface area without cracking or otherwise failing.

[0094] The sealing layer 11 has a thickness 11A measured in the z direction. In some embodiments, the thickness 11A of the sealing layer 11 is less than or equal to 120 microns, including less than or equal to 110 microns, less than or equal to 100 microns, less than or equal to 90 microns, less than or equal to 80 microns, less than or equal to 70 microns, less than or equal to 60 microns, including less than or equal to 50 microns, less than or equal to 40 microns, less than or equal to 30 microns, less than or equal to 20 microns, less than or equal to 10 microns, less than or equal to 5 microns, or less than or equal to 1 micron.

[0095] The free shrinkage of the first base layer at 95°C or another elevated processing temperature to which the multilayer packaging film is exposed results in a reduction in the surface area of ​​the first base layer. It is believed that any layer adjacent to or proximate to the contracted first base layer is subjected to contraction forces in the xy direction due to the reduction in surface area. The free shrinkage of each respective layer / film may be measured individually. Alternatively, the free shrinkage of each respective layer / film may be measured on a combination of one or more layers / films (including any intermediate layers that may be present).

[0096] The first base layer and / or the second base layer can be a film, and the film can be produced by any known process, such as a blown film or a cast film. The first base layer and / or the second base layer can be a uniaxially oriented polypropylene film (MDOPP), a biaxially oriented polypropylene film (BOPP), a uniaxially oriented polyethylene film (MDOPE) or a biaxially oriented polyethylene film (BOPE). The first base layer and / or the second base layer can be produced using a specific polymer, and can be oriented using specific conditions that optimize the heat resistance of the film.

[0097] In some embodiments, the polyolefin film of each of the first base layer and the second base layer is an oriented polyethylene (OPE) film or an oriented polypropylene (OPP) film. In some embodiments, one or more of the oriented polyethylene (OPE) film or the oriented polypropylene (OPP) film is formed by one or more of a sequential stretching process or a simultaneous stretching process. In some embodiments, the simultaneous stretching process is one or more of a linear motor simultaneous stretching process, a double bubble process, or a triple bubble process.

[0098] In one or more embodiments, the oriented polypropylene (OPP) film is a coextruded OPP film.In one or more embodiments, the oriented polypropylene (OPP) film is a coextruded OPP film having a treated first side and a treated second side.

[0099] In some embodiments, the polyolefin film comprises a biaxially oriented polypropylene (BOPP) film. In one or more embodiments, the biaxially oriented polypropylene (BOPP) film is formed by a linear motor simultaneous stretching process, and the biaxially oriented polypropylene (BOPP) film has a treated and non-sealable first side and a sealable second side. In one or more embodiments, the biaxially oriented polypropylene (BOPP) film is formed by a three-bubble process, and the biaxially oriented polypropylene (BOPP) film has a treated and non-sealable first side and a sealable second side.

[0100] Inorganic coatings provide a significant contribution to the oxygen barrier (OTR reduction) of multilayer packaging films.

[0101] In one or more embodiments, the inorganic coating of the multilayer packaging film comprises one or more of an oxide, a metal oxide, a nitride, or a metal nitride. In some embodiments, the inorganic coating comprises one or more of aluminum (Al) or silicon (Si). In some embodiments, the inorganic coating comprises an alloy of aluminum (Al) and any suitable metal oxide known to those skilled in the art. In some embodiments, the inorganic coating comprises an alloy of silicon (Si) and any suitable metal oxide known to those skilled in the art.

[0102] In some embodiments, the inorganic coating comprises a transparent oxide coating such as one or more of aluminum oxide (AlOx) or silicon oxide (SiOx). The inorganic coating may comprise any transparent ceramic known to those skilled in the art, including but not limited to oxides, nitrides or carbides.

[0103] In some embodiments, the inorganic coating comprises silicon oxide (SiOx). In embodiments where the inorganic coating comprises silicon oxide (SiOx), the ratio of the weight of oxygen (O) atoms to the weight of silicon (Si) atoms is measured. In embodiments where the inorganic coating comprises silicon oxide (SiOx), the ratio of the weight of oxygen (O) atoms to the weight of silicon (Si) atoms is in the range of 1 to 3. In embodiments where the inorganic coating comprises silicon oxide (SiOx), the ratio of the weight of oxygen (O) atoms to the weight of silicon (Si) atoms is measured using any suitable analytical technique known to those skilled in the art, such as x-ray photoelectron spectroscopy.

[0104] In alternative embodiments, the inorganic coating comprises one or more of magnesium oxide (MgOx) or tin oxide (SnOx).

[0105] The inorganic coating can be applied by any suitable process known to those skilled in the art. In some embodiments, the inorganic coating is applied by a vacuum deposition process, such as chemical vapor deposition or physical vapor deposition. Alternatively, the inorganic coating can be applied using wet chemical techniques.

[0106] The sealing layer may comprise a polyolefin material. In some embodiments, the sealing layer comprises polypropylene. In some embodiments, the sealing layer comprises one or more of the following: a polypropylene copolymer, a polypropylene terpolymer, polybutene, polyethylene, a polyethylene copolymer, a polyethylene terpolymer, LLDPE, mLLDPE, MDPE, or HDPE. The sealing layer may comprise a polymer formulation designed to reduce the initial heat seal temperature to supplement the heat resistance of the relative outer layer. Even though the temperature softening point of the sealing layer may be quite low, the sealing layer may have sufficient integrity to withstand the high temperatures of the high temperature sterilization process and other abuses that the packaging may suffer during distribution and use.

[0107] In some embodiments, the sealing layer of the multilayer packaging film has a composition that will allow a heat seal to be formed, thereby forming an airtight package. As used herein, the term "heat seal" or "heat sealed" refers to two or more surfaces that have been bonded together by applying both heat and pressure in a short period of time or by an ultrasonic energy sealing process. Heat sealing and ultrasonic sealing are well-known and commonly used processes for making packaging and are familiar to those skilled in the art.

[0108] The sealing layer must be on the surface of the multilayer packaging film to facilitate the function of sealing. During the use of the multilayer packaging film in packaging, the sealing layer can be heat-sealed to itself or another packaging component. During heat sealing, the sealing layer softens at a sealing temperature lower than the temperature resistance of the relative outer layer of the multilayer packaging film, thereby allowing the formation of a heat-sealed bond. The sealing layer softens at a sealing temperature lower than the temperature resistance of the relative outer layer. The sealing layer softens and forms a heat seal under sealing conditions (time, temperature and pressure) that do not cause excessive shrinkage or damage to the outer surface of the multilayer packaging film.

[0109] The multilayer packaging film is intended to contain a large amount of polyolefins, particularly polypropylene or polyethylene, so that the multilayer packaging film is acceptable for recycling process. Compared with the materials (that is, polyester, aluminum foil, polyamide) traditionally used for packaging films, polyolefins have relatively low heat resistance. Due to lower heat resistance, packaging will be formed using a heat sealing process with a lower temperature to avoid any shrinkage or burn-through. The challenge faced by the multilayer packaging film disclosed herein is to incorporate a sealing layer with a low heat seal initiation temperature (HSIT) and high seal strength and seal toughness, to withstand both cooking or pasteurization and normal distribution and processing (that is, drop strength and burst strength). In certain embodiments, the sealing layer also contains materials approved for contact with food under cooking conditions, as specified by government agencies for food safety.

[0110] The seal layer may contain a material having a low heat seal initiation temperature (HSIT).In some embodiments of the retort packaging film, the seal layer contains a polypropylene copolymer having a melting temperature equal to or less than 135°C.

[0111] The sealing layer can be a single layer film, such as a non-oriented cast polypropylene film. The sealing layer can be the outer layer of a multilayer coextruded film (such as a blown film). The entire multilayer coextruded film is attached to the second base layer, and the sealing layer is positioned opposite to the second base layer so as to be exposed.

[0112] The multilayer packaging film may have a total thickness of about 30 microns to about 180 microns.

[0113] Although the structure of multilayer packaging film and any packaging made therefrom contain several different elements (sealing layer, first base layer, second base layer, inorganic coating, adhesive, etc.), the total composition of film or packaging should have a high level of single material type (polyolefin or specifically, polypropylene or polyethylene) to promote recycling. As used herein, the term "total composition" is used to describe the entire film structure or packaging. Any material, layer or component interconnected in any way is a part of the total composition of the article. Multilayer packaging film can have a high level of polymers based on polyolefin. Multilayer packaging film can have a high level of polymers based on polypropylene. Multilayer packaging film can have a high level of polymers based on polyethylene. When the article contains a large amount of polymers based on polypropylene, the multilayer packaging film described herein and any packaging made therefrom can be recycled in a polypropylene recycling process. When the article contains a large amount of polymers based on polyethylene, the multilayer packaging film described herein and any packaging made therefrom can be recycled in a polyethylene recycling process. The mixed polyolefin recycling process can also accept the relatively high level of polyolefins present in the multilayer packaging film described herein and any packaging made therefrom.

[0114] The total composition of multilayer packaging film as herein described can contain at least 80 % by weight, at least 85 % by weight, at least 90 % by weight or at least 95 % by weight of a polymer based on polyolefin, thereby promote the recyclability of using the film and / or packaging.The material of the polymer not based on polyolefin is minimized.For example, the inorganic coating of multilayer packaging film is a material of the material not based on the polymer of polyolefin, and therefore provides with the thinnest possible layer, to suitably play the effect of barrier.Multilayer packaging film can also have other non-polyolefin materials, such as those materials arranged in the adhesive layer.

[0115] In a specific embodiment of the multilayer packaging film, the total composition of the film contains at least 80 wt%, at least 85 wt%, or at least 90 wt%, or at least 95 wt% of a polypropylene-based polymer. In a specific embodiment of the multilayer packaging film, the total composition of the film contains at least 80 wt%, at least 85 wt%, or at least 90 wt%, or at least 95 wt% of a polyethylene-based polymer.

[0116] Using the combination of film structure design elements described herein, a more heat-resistant multilayer packaging film can be achieved. Due to the high polyolefin content, the film can be suitable for recycling in a polyolefin-based recycling process. The film can have a low level (i.e., ≤5% by weight) or substantially free of materials such as polyester, polyamide, chlorinated polymers, and aluminum foil. As used herein, the term "substantially free" means that there is less than about 5%, including less than about 4%, less than about 3%, less than about 2%, less than about 1%, and less than about 0.5% of materials, such as polyester, polyamide, chlorinated polymers, and aluminum foil, in terms of atoms.

[0117] The film may contain non-polyolefin-based polymers, such as those used in the adhesive layer, but the amount of non-polyolefin-based polymers is minimized and generally constitutes less than or equal to 10 wt % or less than 5 wt % of the total composition. The film may contain non-polymeric materials, such as barrier materials, but the amount of non-polymeric materials is minimized and generally constitutes less than 10 wt % or less than 5 wt % of the total composition.

[0118] As previously described herein, the rise in ambient temperature may cause the first base layer, the second base layer and / or the sealing layer to shrink slightly in one or more directions. As the temperature rises, the polymer material softens, releasing the tension that may have been embedded in the layer during production. The release of tension may cause the movement and rearrangement of the polymer chains, as well as the final change (increase or decrease) in the size of the layer. A common result of increasing the temperature on the first base layer, the second base layer and / or the sealing layer is that the first base layer, the second base layer and / or the sealing layer are slightly reduced (i.e., shrunk) in at least one direction parallel to the xy plane of the layer.

[0119] When the first base layer, the second base layer and / or the sealing layer shrink, compressive forces are applied to other layers in the multilayer packaging film, wherein the greatest forces are applied to adjacent layers. Other layers may also have a tendency to shrink at elevated temperatures, and the free shrinkage of each layer may be slightly different. When any polymer layer is compared with an inorganic coating of a multilayer packaging film, the greatest difference in free shrinkage may be found. Most inorganic coatings will not shrink at temperatures (e.g., 95°C or other temperatures) at which the first base layer, the second base layer and / or the sealing layer will shrink. In addition, inorganic coatings also have very high moduli (high stiffness) at these elevated temperatures.

[0120] In some embodiments, the multilayer packaging film may have an average oxygen transmission rate (OTR) value of less than or equal to 2 cm prior to exposure to elevated heat conditions. 3 / m 2 / day, less than or equal to 1cm 3 / m 2 / day, less than or equal to 0.5cm 3 / m 2 / day or less than or equal to 0.1cm 3 / m 2 / day (measured according to ASTM F1927 using conditions of 1 atmosphere, 23°C and 50% RH).

[0121] In some embodiments, after exposure to a representative retort sterilization process, the average OTR value of the barrier packaging film is less than or equal to 2.5 cm 3 / m 2 / day, less than or equal to 2cm 3 / m 2 / day, less than or equal to 1cm 3 / m 2 / day, less than or equal to 0.5cm 3 / m 2 / day or less than or equal to 0.1cm 3 / m 2 / day. The average OTR value may be close to, equal to or below the minimum detection level of the test device. A representative retort sterilization process is accomplished by cutting DIN A4 sized sections of the packaging film and exposing them to a steam sterilization process at 128°C and 2.5 bar overpressure for 60 minutes, followed by water shower cooling.

[0122] The multilayer packaging film 10, 110, 210 can be formed into a package with or without other packaging components. For example, the multilayer packaging film 210 can be formed into a flexible stand-up bag 200, such as Figure 7 In another embodiment of the hermetically sealed package 100, the multilayer packaging film 110 may be a lid material sealed to a thermoformed tray or cup, such as Figure 6 shown.

[0123] The multilayer packaging films disclosed herein maintain excellent barrier properties and visual appearance even after the film has been formed into a package, filled, hermetically sealed, and subjected to a retort sterilization process.

[0124] The present disclosure will now be described with reference to the following examples.

[0125] Examples and data

[0126] Several membrane structures were generated as summarized in Table 1 below.

[0127] Table 1: Identification and properties of the substrate and free shrinkage values ​​of the substrate in the machine direction (MD)

[0128]

[0129]

[0130] Table 1 identifies and lists the properties of each of Base Layers AF. Table 1 also lists the free shrink value for each of Base Layers AF measured in the machine direction at 120°C.

[0131] Table 2: Comparative shrinkage values ​​of the first and second substrates and average oxygen transmission rate data of the example and comparative example structures

[0132]

[0133]

[0134] *OTR unit is cm 3 / m 2 / day is measured according to ASTM F1927 using the conditions of 1 atmosphere pressure, 23°C temperature and 50% relative humidity (RH).

[0135] Table 2 lists the surface treatment (e.g., "bare" or "primed + SiOx") of each of the base layers AF. As a general convention, base layers AF with 1 (e.g., A1) are bare, and base layers AF with 2 (e.g., A2) are primed and have a silicon oxide coating thereon.

[0136] Table 2 lists the OTR of the multilayer packaging film structure of each of A1-F2 before and after heating. The oxygen transmission rate (OTR) of a multilayer packaging film is an indication of the barrier provided and can be measured according to ASTM F1927 using conditions of 1 atmosphere, temperature of 23°C and relative humidity (RH) of 50%.

[0137] Table 3: Identification and properties of base layers in multilayer packaging films

[0138]

[0139] In Table 3, the multilayer packaging film structure comprises base layers AF identified above. The multilayer packaging film structure of Table 3 comprises a first base layer, a second base layer, one or more adhesive layers, one or more inorganic oxide coating layers, and a sealant layer. The figures illustrate multilayer packaging film structures having base layers AF.

[0140] The multilayer packaging film structure of each of AF was prepared by applying an aqueous polyurethane (PU) dispersion (primer) to the surface of each of the first and second base layers to form a 1.7 micron primer coating after drying the dispersion. As applicable above, the inorganic coating on each of the first and second base layers comprises a silicon oxide coating (SiOx) applied to the primer surface by vapor deposition. A 60 micron polypropylene sealant layer was then adhesively laminated to the silicon oxide coating.

[0141] Example:

[0142] Embodiment 1: A multilayer packaging film comprising: a first base layer, the first base layer comprising a polyolefin film; a second base layer on the first base layer, the second base layer comprising a polyolefin film; and a sealing layer on the second base layer, the sealing layer comprising a polyolefin film, wherein one or more of the first base layer or the second base layer comprises an inorganic coating thereon, and wherein the shrinkage value of the second base layer is greater than 5%.

[0143] Embodiment 2: The multilayer packaging film of Embodiment 1, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the first base layer.

[0144] Embodiment 3: The multilayer packaging film of any one of the preceding embodiments, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealant layer.

[0145] Embodiment 4: A multilayer packaging film comprising: a first base layer, the first base layer comprising a polyolefin film; a second base layer on the first base layer, the second base layer comprising a polyolefin film; and a sealing layer on the second base layer, the sealing layer comprising a polyolefin film, wherein one or more of the first base layer or the second base layer comprises an inorganic coating thereon, and the shrinkage value of the second base layer is less than the shrinkage value of the first base layer.

[0146] Embodiment 5: The multilayer packaging film of Embodiment 4, wherein the shrinkage value of the second base layer is less than or equal to 5%.

[0147] Embodiment 6: The multilayer packaging film of any one of Embodiments 4 to 5, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealant layer.

[0148] Embodiment 7: A multilayer packaging film comprising: a first base layer, the first base layer comprising a polyolefin film; a second base layer on the first base layer, the second base layer comprising a polyolefin film; and a sealing layer on the second base layer, the second base layer comprising a polyolefin film, wherein one or more of the first base layer or the second base layer comprises an inorganic coating thereon, wherein the shrinkage value of the second base layer is greater than 5%, and the shrinkage value of the second base layer is less than the shrinkage value of the first base layer.

[0149] Embodiment 8: The multilayer packaging film of Embodiment 8, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealant layer.

[0150] Embodiment 9: The multilayer packaging film of any one of the preceding embodiments, wherein the shrinkage value of the second base layer is less than or equal to 5%.

[0151] Embodiment 10: The multilayer packaging film of any one of the preceding embodiments, wherein the difference in shrinkage values ​​between the first substrate and the second substrate is greater than or equal to 0.3%.

[0152] Embodiment 11: The multilayer packaging film of any one of the preceding embodiments, wherein the difference in shrinkage values ​​between the second base layer and the sealant layer is greater than or equal to 0.5%.

[0153] Embodiment 12: The multilayer packaging film of any one of the preceding embodiments, wherein the shrinkage value of the sealant layer is greater than or equal to 2%.

[0154] Embodiment 13: The multilayer packaging film according to any one of the preceding embodiments, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealant layer is measured in the machine direction (MD) according to Formula 1:

[0155]

[0156] Embodiment 14: The multilayer packaging film of any of the preceding embodiments, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealant layer is measured using the method disclosed in ASTM D2732-03.

[0157] Embodiment 15: The multilayer packaging film of any one of the preceding embodiments, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealant layer is measured after heating at 120°C for 15 minutes.

[0158] Embodiment 16: The multilayer packaging film of any preceding embodiment, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealant layer is measured after heating at 127°C for 50 minutes.

[0159] Embodiment 17: The multilayer packaging film of any one of the preceding embodiments, wherein the polyolefin film of each of the first and second substrates is an oriented polyethylene (OPE) film or an oriented polypropylene (OPP) film.

[0160] Embodiment 18: The multilayer packaging film according to Embodiment 17, wherein one or more of the oriented polyethylene (OPE) film or the oriented polypropylene (OPP) film is formed by one or more of a sequential stretching process or a simultaneous stretching process.

[0161] Embodiment 19: The multilayer packaging film according to Embodiment 18, wherein the simultaneous stretching process is one or more of a linear motor simultaneous stretching process, a double bubble process, or a triple bubble process.

[0162] Embodiment 20: The multilayer packaging film of Embodiment 17, wherein the polyolefin film comprises a biaxially oriented polypropylene (BOPP) film.

[0163] Embodiment 21: The multilayer packaging film according to Embodiment 20, wherein the biaxially oriented polypropylene (BOPP) film is formed by a linear motor simultaneous stretching process.

[0164] Embodiment 22: The multilayer packaging film of Embodiment 17, wherein the polyolefin film comprises one or more of a machine direction oriented polyethylene (MDOPE) film, a machine direction oriented polypropylene (MDOPP) film, a cast film, or a blown film.

[0165] Embodiment 23: The multilayer packaging film of Embodiment 22, wherein the polyolefin film comprises the machine direction oriented polypropylene (MDOPP) film.

[0166] Embodiment 24: The multilayer packaging film of any preceding embodiment, wherein the inorganic coating of one or more of the first substrate or the second substrate comprises silicon oxide.

[0167] Embodiment 25: The multilayer packaging film of Embodiment 24, wherein the inorganic coating of one or more of the first substrate or the second substrate has a gas barrier coating thereon.

[0168] Embodiment 26: The multilayer packaging film according to embodiment 25, wherein the gas barrier coating comprises one or more of a hydroxyl-containing polymer compound, a metal alkoxide, a silane coupling agent, and a hydrolyzate thereof.

[0169] Embodiment 27: The multilayer packaging film of any preceding embodiment, wherein the thickness of each of the first and second base layers is in a range from 10 microns to 40 microns.

[0170] Embodiment 28: The multilayer packaging film of any preceding embodiment, wherein the sealant layer has a thickness less than or equal to 120 microns.

[0171] Embodiment 29: The multilayer packaging film of any of the preceding embodiments, wherein the oxygen transmission rate is measured before and after retorting using the method disclosed in ASTM F1927.

[0172] Embodiment 30: The multilayer packaging film of any preceding embodiment, further comprising an adhesive layer located between one or more of the first and second base layers, or the second base layer and the sealant layer.

[0173] Embodiment 31: The multilayer packaging film of Embodiment 30, wherein the adhesive layer comprises polyurethane.

[0174] Embodiment 32: The multilayer packaging film of any of Embodiments 30 to 31, wherein the adhesive layer has a thickness in a range of 2 microns to 4 microns.

[0175] Embodiment 31: The multilayer packaging film of any preceding embodiment, wherein the seal initiation temperature of the seal layer is less than or equal to 110°C.

[0176] Embodiment 32: The multilayer packaging film of any preceding embodiment, wherein the sealant layer comprises polypropylene.

[0177] Embodiment 33: A retort bag formed from the multilayer packaging film according to any one of the preceding embodiments.

Claims

1. A multilayer packaging film comprising: a first substrate, the first substrate comprising a polyolefin film; a second base layer on the first base layer, the second base layer comprising a polyolefin film; and a sealing layer on the second base layer, the sealing layer comprising a polyolefin film, wherein one or more of the first base layer or the second base layer comprises an inorganic coating thereon, and wherein the shrinkage value of the second base layer is greater than 5%.

2. The multilayer packaging film of claim 1, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the first base layer.

3. The multilayer packaging film according to any one of claims 1 to 2, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealing layer.

4. A multilayer packaging film comprising: a first substrate, the first substrate comprising a polyolefin film; a second base layer on the first base layer, the second base layer comprising a polyolefin film; and a sealing layer on the second base layer, the sealing layer comprising a polyolefin film, One or more of the first base layer or the second base layer comprises an inorganic coating thereon, and a shrinkage value of the second base layer is smaller than a shrinkage value of the first base layer.

5. The multilayer packaging film of claim 4, wherein the second base layer has a shrinkage value of less than or equal to 5%.

6. The multilayer packaging film according to any one of claims 4 to 5, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealant layer.

7. A multilayer packaging film comprising: a first substrate, the first substrate comprising a polyolefin film; a second base layer on the first base layer, the second base layer comprising a polyolefin film; and a sealing layer on the second substrate, the second substrate comprising a polyolefin film, One or more of the first base layer or the second base layer comprises an inorganic coating thereon, wherein the shrinkage value of the second base layer is greater than 5%, and the shrinkage value of the second base layer is less than the shrinkage value of the first base layer.

8. The multilayer packaging film of claim 7, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealant layer.

9. The multilayer packaging film according to any one of claims 1 to 8, wherein the shrinkage value of the second base layer is less than or equal to 5%.

10. The multilayer packaging film according to any one of claims 1 to 9, wherein the difference in shrinkage values ​​between the first substrate and the second substrate is greater than or equal to 0.3%.

11. The multilayer packaging film according to any one of claims 1 to 10, wherein the difference in shrinkage values ​​between the second base layer and the sealing layer is greater than or equal to 0.5%.

12. The multilayer packaging film according to any one of claims 1 to 11, wherein the shrinkage value of the sealing layer is greater than or equal to 2%.

13. The multilayer packaging film according to any one of claims 1 to 12, wherein the shrinkage value of each of the first base layer, the second base layer and the sealant layer is measured in the machine direction (MD) according to Formula 1:

14. The multilayer packaging film of any one of claims 1 to 13, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealant layer is measured using the method disclosed in ASTM D2732-03.

15. The multilayer packaging film according to any one of claims 1 to 14, wherein the shrinkage value of each of the first base layer, the second base layer and the sealing layer is measured after heating at 120°C for 15 minutes.

16. The multilayer packaging film of any one of claims 1 to 15, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealant layer is measured after heating at 127°C for 50 minutes.

17. The multilayer packaging film according to any one of claims 1 to 16, wherein the polyolefin film of each of the first substrate and the second substrate is an oriented polyethylene (OPE) film or an oriented polypropylene (OPP) film.

18. The multilayer packaging film of claim 17, wherein one or more of the oriented polyethylene (OPE) film or the oriented polypropylene (OPP) film is formed by one or more of a sequential stretching process or a simultaneous stretching process.

19. The multilayer packaging film according to claim 18, wherein the simultaneous stretching process is one or more of a linear motor simultaneous stretching process, a double bubble process or a triple bubble process.

20. The multilayer packaging film of claim 17, wherein the polyolefin film comprises a biaxially oriented polypropylene (BOPP) film.

21. The multilayer packaging film of claim 20, wherein the biaxially oriented polypropylene (BOPP) film is formed by a linear motor simultaneous stretching process.

22. The multilayer packaging film of claim 17, wherein the polyolefin film comprises one or more of a machine direction oriented polyethylene (MDOPE) film, a machine direction oriented polypropylene (MDOPP) film, a cast film, or a blown film.

23. The multilayer packaging film of claim 22, wherein the polyolefin film comprises the machine direction oriented polypropylene (MDOPP) film.

24. The multilayer packaging film of any one of claims 1 to 23, wherein the inorganic coating of one or more of the first substrate or the second substrate comprises silicon oxide.

25. The multilayer packaging film of claim 24, wherein the inorganic coating of one or more of the first substrate or the second substrate has a gas barrier coating thereon.

26. The multilayer packaging film according to claim 25, wherein the gas barrier coating comprises one or more of a hydroxyl-containing polymer compound, a metal alkoxide, a silane coupling agent, and a hydrolyzate thereof.

27. The multilayer packaging film of any one of claims 1 to 26, wherein the thickness of each of the first and second base layers is in the range of 10 to 40 microns.

28. The multilayer packaging film of any one of claims 1 to 27, wherein the sealant layer has a thickness less than or equal to 120 microns.

29. The multilayer packaging film according to any one of claims 1 to 28, wherein the oxygen transmission rate is measured before and after retorting using the method disclosed in ASTM F1927.

30. The multilayer packaging film of any one of claims 1 to 29, further comprising an adhesive layer located between one or more of the first and second base layers, or the second base layer and the sealant layer.

31. The multilayer packaging film of claim 30, wherein the adhesive layer comprises polyurethane.

32. The multilayer packaging film of any one of claims 30 to 31, wherein the adhesive layer has a thickness in the range of 2 to 4 microns.

33. The multilayer packaging film of any one of claims 1 to 32, wherein the seal initiation temperature of the seal layer is less than or equal to 110°C.

34. The multilayer packaging film of any one of claims 1 to 33, wherein the sealant layer comprises polypropylene.

35. A retort pouch formed from the multilayer packaging film according to any one of claims 1 to 34.

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