Multi-layer 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 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 equal to or greater than 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 a method of manufacturing the multilayer packaging film and a hermetically sealed package (e.g., a thermoformed tray or cup and a retort pouch) formed from the multilayer packaging film.

Description

Technical Field

[0001] The present invention relates to a multilayer film structure. Embodiments of the present invention are directed 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 a long-term heat and pressure treatment process. Similarly, the package or the packaged product may undergo a pasteurization process at about 80°C. In yet another application, the multilayer film structure can be used as a heat shrink wrap foil at temperatures below 80°C.

[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 bottles. Packaging materials for flexible retort packaging typically include an encapsulating 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 substantially decomposing (i.e., leaking, delaminating). Generally, the retort process consists of heating the packaging container to a temperature in the range of 100 to 135°C, with an overpressure in the range of 0.5 to 1.1 bar, for a time in the range of 15 to 100 minutes.

[0004] Examples of laminates for retort packaging are disclosed in US 4,310,578A, US 4,311,742A, US 4,308,084A, US 4,309,466A, US 4,402,172A, US 4,903,841A, US 5,273,797A, US 5,731,090A, EP 1 466 725A1, JP 09 267 868A, JP 2002 096 864A, JP 2015 066 721A, JP 2018 053 180A, JP 2017 144 648A, JPS 62 279 944A, JPS 6 328 642, and JP 10 244 641A.

[0005] One typical option for designing an elastic retort packaging multilayer film structure is the use of an aluminum barrier layer having a thickness of at least 5 μm, preferably more than 12 μm. However, aluminum is expensive and has a high density, is prone to pinholes after bending at lower thicknesses, and has the drawback of opacity. Aluminum is also known to cause problems when reheating foods packaged in a microwave oven. Furthermore, the presence of a metal layer is generally undesirable from the viewpoints of recyclability and metal detection within the packaging process.

[0006] Typical examples of multilayer film structures for standard retort pouches include a polyethylene terephthalate outer layer, a barrier layer, and an inner sealing layer, where the outer layer includes a printing layer, the barrier layer includes a metal foil or an inorganic oxide-coated polymer film, and the inner layer is a heat-sealable polyolefin layer. The packaging material may also include additional polymer film layers such as a polyamide layer or the like.

[0007] The diversity of the polymer layers constituting the multilayer barrier film structure poses further challenges in making these multilayer film structures recyclable and capable of withstanding the retort process without melting or substantially deteriorating (i.e., leaking, peeling).

[0008] There is a need for an improved multilayer film structure for packaging without countering the associated advantages of state-of-the-art systems, where the multilayer film structure is recyclable and can withstand retort processes without melting or substantially deteriorating (i.e., leaking, peeling). SUMMARY OF THE INVENTION

[0009] Embodiments of the present invention advantageously provide a multilayer packaging film that can withstand retort processes without melting or substantially deteriorating (i.e., leaking, peeling). In some embodiments, the multilayer packaging film structure is heat-treated, for example, during pasteurization or retort processing. In some embodiments, the multilayer packaging film structure includes one or more inorganic coating layers that remain substantially crack-free during and after heat treatment, thereby limiting an increase in the oxygen transmission rate and water vapor transmission rate of the multilayer packaging film.

[0010] Additional embodiments of the present invention advantageously provide a more sustainable transparent multilayer packaging film that is heat-resistant and exhibits excellent oxygen transmission rate (low transmission rate, high barrier), and the heat-resistant 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 includes a polyolefin film.

[0012] In some embodiments, each of the first and second polyolefin films is a stretched polyethylene (OPE) film or a stretched polypropylene (OPP) film. In some embodiments, one or more of the stretched polyethylene (OPE) film or the stretched polypropylene (OPP) film are 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 stretched polypropylene (OPP) film is a coextruded OPP film having a first side that has been treated but is not sealable and a second side that is sealable.

[0014] In some embodiments, the stretched polypropylene (OPP) film is a coextruded OPP film having a first side that has been treated but is not sealable and a second side that has been treated but is not sealable.

[0015] In some embodiments, the polyolefin film includes a biaxially stretched polypropylene (BOPP) film. In some embodiments, the biaxially stretched polypropylene (BOPP) film is formed by a linear motor simultaneous stretching process, and the biaxially stretched polypropylene (BOPP) film has a first side that has been treated but is not sealable and a second side that is sealable. In some embodiments, the biaxially stretched polypropylene (BOPP) film is formed by a triple bubble process, and the biaxially stretched polypropylene (BOPP) film has a first side that has been treated but is not sealable and a second side that is sealable.

[0016] In some embodiments, one or more of the first layer or the second layer have an inorganic coating layer thereon. The inorganic coating layer may be on one or more sides of the first layer and / or the second layer. In some embodiments, the inorganic coating of one or more of the first layer or the second layer contains silicon oxide. In some embodiments, the inorganic coating of one or more of the first layer or the second layer has a gas barrier coating thereon. In one or more embodiments, the gas barrier coating contains one or more of a hydroxyl group-containing polymer compound, a metal alkoxide, a silane coupling agent, and their hydrolyzates. In some embodiments, the inorganic coating layer improves the gas barrier performance of one or more of the first layer or the second layer against water vapor and oxygen.

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

[0018] In some embodiments, the adhesive layer contains a polyvinyl alcohol-based resin having a vinyl alcohol unit in which the vinyl ester unit is saponified, examples of which 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 with which the adhesive layer is in contact.

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

[0021] In embodiments where the multilayer packaging film includes an inorganic coating, the adhesive layer may be located on the surface of the polyolefin film on which the inorganic coating layer is laminated. Without intending to be bound by theory, in such embodiments, the adhesive layer is thought to improve the adhesion between the polyolefin film and the inorganic coating layer and to improve the smoothness of the surface of the polyolefin film.

[0022] In one or more specific embodiments, the multilayer packaging film includes a first base layer and a second base layer, each having an inorganic coating layer 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 layer 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 layer on the second base layer. In one or more specific embodiments, the sealing layer is on the inorganic coating layer on the second base layer.

[0023] In some embodiments, the multilayer packaging film has a total composition that includes 80 wt% or more polyolefin, 90 wt% or more polyolefin, or 95 wt% or more polyolefin. In some embodiments, the multilayer packaging film has a total composition that includes 80 wt% or more polypropylene, 90 wt% or more polypropylene, or 95 wt% or more polypropylene. In some embodiments, the multilayer packaging film has a total composition that includes 80 wt% or more polyethylene, 90 wt% or more polyethylene, or 95 wt% or more 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 equal to or greater than 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 greater than the shrinkage value of the first base layer. In some embodiments, the second base layer has a shrinkage value of 5% or less. In some embodiments, the shrinkage value of the second base layer is equal to or greater than 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 0.3% or more. In some embodiments, the difference in shrinkage values between the second base layer and the sealing layer is 0.5% or more. In some embodiments, the shrinkage value of the sealing layer is 2% or more.

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

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

[0028] In some embodiments, the inorganic coating layer has a thickness in the range of 0.005 microns to 0.1 microns.

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

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

[0031] Further embodiments are directed to a method of manufacturing a multilayer packaging film. The method of manufacturing a multilayer packaging film may include any suitable process known to those skilled in the art that does not change the shrinkage value of each layer described herein. In some embodiments, the method of manufacturing a multilayer packaging film includes one or more of extrusion lamination, lacquer lamination, or high temperature calendar processing.

Brief Description of the Drawings

[0032] The present disclosure may be more fully understood in consideration of the following detailed description of various embodiments of the present disclosure in connection with the accompanying drawings.

[0033]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

[0034] The drawings illustrate some embodiments but not all embodiments. The elements illustrated in the drawings are exemplary and not necessarily to scale, and the same (or similar) reference numerals indicate the same (or similar) features throughout the drawings.

Best Mode for Carrying Out the Invention

[0035] The packaging industry is thought to be moving towards more sustainable options, including the rationalization into a narrow category of materials used. For example, one option is to design a packaging structure with a high polyolefin content in order to classify the film as recyclable. The exclusion of non-olefin polymers from the packaging structure often presents a defect in the overall performance of the packaging structure. In the case of packaging intended for heat treatment applications such as retorting or pasteurization, polyolefin polymers are more sensitive to the application temperature. Specifically, at high temperatures, polyolefin materials may shrink more than other polymer materials and may become inappropriate as a component of the structure of the inorganic coating layer, which is because polyolefin, compared to more conventional non-recyclable oPET films used to support barrier oxide coatings in retortable applications, even under retorting or pasteurization conditions, is closer to their melting points. The introduction of the selected materials described herein into the packaging film can reduce the adverse effects by utilizing a set of more recyclable polymer materials. As a result, the barrier packaging film described herein is more easily recyclable due to its high polyolefin content, but retains high performance characteristics such as oxygen and moisture barrier.

[0036] As used herein, layers or films that are "in direct contact" with each other, or "directly adjacent" to each other, do not have intervening materials therebetween.

[0037] As used herein, an "inorganic coating layer" refers to a layer including a metal layer or an oxide coating layer. The inorganic coating layer can act as a barrier layer. The inorganic coating layer may be directly vacuum deposited (i.e., vacuum coated, vapor deposited, vacuum metallized) on the surface of the first base layer or the second base layer. Alternatively, the inorganic coating layer may be deposited by a wet chemical method such as solution coating, or may be applied through a reactive coating technique such as chemical vapor deposition.

[0038] As used herein, the term "polyolefin" generally includes polypropylene polymers and polyethylene polymers. Alternatively, the term "polyolefin" includes polybutene films. Polyolefin films can include, for example, acid-modified polyolefin films obtained by graft-modifying polyolefin polymers with unsaturated carboxylic acids, unsaturated carboxylic anhydrides, unsaturated carboxylic esters, etc. Various pretreatment processes can be carried out on the polyolefin film. The pretreatment process can include any suitable process known to those skilled in the art that does not impair the barrier performance. 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 adhesion enhancing layer.

[0039] As described herein, one or more of the polyolefin films of the multilayer packaging film may be oriented. The orientation may be the result of uniaxial stretching (in the machine direction or the transverse direction) or biaxial stretching (in the machine direction and the transverse direction) of the film, and when the dimensions in the machine direction and / or the transverse direction are increased, the thickness of the material then decreases. The biaxial stretching may be applied to the film simultaneously or continuously. In some embodiments, the film is stretched in one or both directions at a temperature slightly below the melting temperature of the polymer of the film. In this way, the stretching "orients" the polymer chains and changes the physical properties of the film. At the same time, the stretching thins the film. The resulting oriented film is thinner and may have significant changes in mechanical properties such as toughness, heat resistance, rigidity, tear strength, and barrier. Orientation is typically achieved by a double bubble process or a triple bubble process, by a tenter frame process or an MDO process using heated rolls. A typical blown film process imparts some stretching of the film but is not sufficient to be considered 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 shrinkage) under the high temperature conditions that may be experienced during conversion (i.e., printing or lamination) of the retort film laminate or during use of the laminate (i.e., heat sealing or retort sterilization). As used herein, the terms "non-oriented" and "unoriented" refer to single-layer or multilayer films, sheets or webs that are substantially free of orientation after extrusion.

[0040] As used throughout this application, the term "copolymer" refers to a polymer product obtained by a polymerization reaction or copolymerization of at least two monomer species. The term "copolymer" also includes polymerization reactions of three, four, or more monomer species having reaction products called terpolymers, quarterpolymers, etc.

[0041] When used throughout this application, the term "polypropylene" or "PP" refers to propylene homopolymers or copolymers, unless otherwise indicated. Such copolymers of propylene include copolymers of propylene and at least one alpha-olefin, and copolymers of propylene and other units or groups. The term "polypropylene" or "PP" is used regardless of the presence or absence of substituent branching groups or other modifiers. Polypropylene includes, but is not limited to, homopolymer polypropylene, polypropylene impact copolymer, polypropylene random copolymer, propylene-ethylene copolymer, ethylene-propylene copolymer, maleic anhydride grafted polypropylene, and mixtures thereof. Various polypropylene polymers can be recycled as recycled polypropylene or recycled polyolefin.

[0042] When used throughout this application, the term "polyethylene" or "PE" refers to ethylene homopolymers or copolymers, unless otherwise indicated. Such copolymers of ethylene include copolymers of ethylene and at least one alpha-olefin, and copolymers of ethylene and vinyl acetate, acid groups, acrylate groups, or other other units or groups. The term "polyethylene" or "PE" is used regardless of the presence or absence of substituent branching 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 copolymer, ethylene vinyl acetate, ethylene acid copolymer, ethylene acrylate copolymer, neutralized ethylene copolymers such as ionomers, maleic anhydride grafted polyethylene, and mixtures thereof. Various polyethylene polymers can be recycled as recycled polyethylene or recycled polyolefin.

[0043] When used throughout this application, the term "polyester" or "PET" refers to a homopolymer or copolymer having ester linkages between monomer units. The ester linkage may be represented by the general formula [O-R-OC(O)-R'-C(O)] n wherein R and R' are the same or different alkyl (or aryl) groups and can generally be formed from the polymerization of dicarboxylic acid and diol monomers.

[0044] As used herein, the term "polyamide" refers to high molecular weight polymers having amide linkages (--CONH--)n occurring along the molecular chain, and includes "nylon" resins, which are well-known polymers having numerous uses, including utility as packaging films. Examples of nylon polymer resins for use in 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 nonanediamide)), nylon 6,10 (poly(hexamethylene sebacamide)), nylon 6,12 (poly(hexamethylene dodecanediamide)), nylon 6 / 12 (poly(caprolactam-co-dodecanediamide)), nylon 6,6 / 6 (poly(hexamethylene adipamide-co-caprolactam)), nylon 66 / 610 (produced, for example, by condensation of a mixture of nylon 66 salt and nylon 610 salt), nylon 6 / 69 resin (produced, for example, by condensation of epsilon-caprolactam, hexamethylenediamine, and azelaic acid), nylon 11 (polyundecanolactam), nylon 12 (polylauryl lactam), and copolymers or mixtures thereof. Polyamides are used in films for food packaging and other applications due to their unique physical and chemical properties. Polyamides are selected as materials to improve the temperature resistance, abrasion resistance, puncture strength, and / or barrier of the film. The properties of polyamide-containing films can be changed by a wide range of variable selections, including the selection of copolymers, and conversion methods such as coextrusion, orientation, lamination, and coating.

[0045] As used herein, "polyurethane" generally refers to a polymer having organic units linked by urethane bonds (-NH-(C=O)-O-).

[0046] As used herein, "polylactic acid" is a polymer made from lactic acid and having a backbone of [-C(CH3)HC(=O)O-] n .

[0047] 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), butanediol vinyl alcohol copolymer (BVOH), and polyvinyl alcohol (PVOH).

[0048] As used throughout this application, the term "ethylene vinyl alcohol copolymer", "EVOH copolymer", or "EVOH" refers to a copolymer consisting of repeating units of ethylene and vinyl alcohol. The ethylene vinyl alcohol copolymer can be represented by the following general formula: [(CH2-CH2) n -(CH2-CH(OH))] n . The ethylene vinyl alcohol copolymer can include saponified or hydrolyzed ethylene vinyl acetate copolymer. EVOH refers to a vinyl alcohol copolymer having an ethylene comonomer and prepared, for example, by hydrolysis of a vinyl acetate copolymer or by a chemical reaction with vinyl alcohol. The ethylene vinyl alcohol copolymer may contain from 28 mole percent or less to 48 mole percent or more of ethylene.

[0049] As used herein, the term "layer" refers to a component of a film that is a single material type structure or a homogeneous mixture of materials. A layer may be a single polymer, a mixture of materials within a single polymer type, or a mixture of various polymers, and may contain metallic materials and may have additives. A layer may be continuous with the film or may be discontinuous or patterned. A layer has a small thickness (z-direction) as compared to the length and width (x-y direction), and is thus defined to have two major surfaces, the area of which is defined by the length and width of the layer. An outer layer is a layer that is connected to another layer by only one of its major surfaces. In other words, one major surface of the outer layer is exposed. An inner layer is a layer that is connected to another layer by both of its major surfaces. In other words, the inner layer is between two other layers. A layer may have sub-layers.

[0050] Similarly, as used herein, the term "film" refers to a web constructed of layers and / or films, all of which are directly adjacent to and connected to each other. A film can be described as having a small thickness as compared to the length and width of the film. A film has two major surfaces, the area of which is defined by the length and width of the film.

[0051] As used herein, the term "outer" is used to describe a film or layer that is located on one of the major surfaces of the film in which it is included. As used herein, the term "inner" is used to describe a film or layer that is not located on the surface of the film in which it is included. An inner film or layer has another film or layer adjacent to it on both sides.

[0052] As used herein, "barrier" or "barrier film" or "barrier layer" or "barrier material" refers to providing a reduction in the permeation of gases such as oxygen (i.e., containing an oxygen barrier material). The barrier material may provide a reduction in the permeation of moisture (i.e., including a moisture barrier material). The barrier properties may be provided by one or more barrier materials, or a mixture of multiple barrier materials. An inorganic coating layer may act as a barrier layer. The barrier layer may provide the specific barrier necessary to store the product within the package over a long-term shelf life that can be several months or even over a year.

[0053] The barrier may reduce the influx of oxygen through the barrier packaging film during the shelf life of the packaged product (i.e., while the package is hermetically sealed). The oxygen transmission rate (OTR) of the multilayer packaging film is an indicator of the barrier provided and can be measured in accordance with ASTM F1927 using conditions of 1 atmosphere, 23 °C, and 50% RH.

[0054] As used herein, "multilayer packaging film", or "hermetically sealed package", or "retort stable package" is a film structure, or a package made from a film structure, that has little degradation and maintains a high oxygen barrier level or moisture barrier level after exposure to heat treatment temperatures. The package may be filled with the product, sealed, and remain hermetically sealed, and thus maintain excellent barrier properties.

[0055] As used herein, "free shrinkage" or "shrinkage value" is the unconstrained linear shrinkage that a film or layer undergoes upon exposure to high temperature. The shrinkage is irreversible and relatively rapid (i.e., evident within seconds or minutes). The shrinkage value is expressed as a percentage of the original dimension (i.e., 100×(dimension before shrinkage - dimension after shrinkage) / (dimension before shrinkage)). Free shrinkage can be measured using any suitable method having the ability to measure a shrinkage value difference of at least 0.2%. Free shrinkage can be measured using ASTM D2732-03. As described in ASTM D2732-03, free shrinkage is the value obtained by measuring the unconstrained (i.e., free) shrinkage of a 10 cm square sample immersed in water at 90°C for 5 seconds. ASTM D2732-03 includes at least the following steps: 1. Press a stamp onto the film and cut out the stamped portion. 2. Place the sample in a free shrinkage holder such that the sample does not contact the edges of the holder. i. At least two samples are required for each temperature. 3. Observe and record the temperature of the bath before immersing each sample. 4. Immerse the sample in the bath for 10 seconds or for a time determined to be sufficient for the material to reach thermal equilibrium and undergo maximum shrinkage. 5. Remove the sample from the bath and quickly immerse it preferably in a liquid medium at room temperature that is miscible with the bath medium. 6. After 5 seconds, remove the sample from the cooling medium and measure and record the linear dimensions of the sample in both the flow (long axis) and transverse directions. 7. Determine the free shrinkage rate in each direction as follows: 8. The report shall include the following:

Number

[0056] While not intending to be bound by any particular theory, one of ordinary skill in the art would measure free shrinkage using the protocol of ASTM D2732 - 03.

[0057] Alternatively, free shrinkage can be measured using a modification that uses hot air as the heat source instead of a hot fluid bath, using the test method described in ASTM D2732 - 03. When using the hot - air method, place the unrestrained specimen in an oven set to the specified temperature for at least 1 minute, giving sufficient time for the interior of the oven and the specimen to reach thermal equilibrium.

[0058] Alternatively, the shrinkage value is calculated after measuring the linear dimensions in the machine direction (MD) before and after shrinkage, according to Equation 1.

[0059]

Equation

[0060] 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.

[0061] The multilayer packaging films described herein may be useful as retort or pasteurized packaging films. As used herein, "retort packaging film" or "retort packaging" is a film, or a package made from a film, that can be filled with a product, sealed, and remain hermetically sealed after being exposed to a typical retort sterilization process. Typical retort sterilization is a batch process that uses temperatures in the range of about 100°C to about 150°C and overpressure up to about 70 psi (483 kPa), and can have a duration from several minutes to several hours. Common retort processes used for products packaged in flexible films include immersion in steam or water. Foods or other products packaged in retort packaging films and retort sterilized can be stored for long periods under ambient conditions (i.e., are storage stable) and retain their sterility. Since the retort process can degrade the film, or a package made from the film, very special flexible packaging films have been designed to withstand the retort process.

[0062] As used herein, the term "adhesive layer" refers to a layer having the primary function of bonding two adjacent layers together. The adhesive layer is positioned between two layers of the multilayer film and can maintain the two layers in a predetermined position relative to each other and prevent unwanted 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.

[0063] The adhesive layer can be deposited on the polyolefin film of one or more of the first base layer or the second base layer by any suitable method known to those skilled in the art. In some embodiments, the deposition of the adhesive layer includes, but is not limited to, dipping methods (dipping methods), and methods using sprayers, coaters, printers, brushes, or the like. In addition, examples of the types of coaters and printers used in these methods, and their coating methods, include gravure coaters, reverse roll coaters, microgravure coaters, composite chamber doctor blade coaters, air knife coaters, dip coaters, bar coaters, comma coaters, and die coaters for direct gravure, reverse gravure, kiss reverse gravure, offset gravure, etc.

[0064] The adhesive layer can be dried by any suitable method known to those skilled in the art. Methods for drying the adhesive layer include, but are not limited to, natural drying, drying in an oven set at a predetermined temperature, and methods using drying machines attached to coaters such as arch dryers, floating dryers, drum dryers, and infrared dryers. The drying conditions can be selected based on the drying method. For example, in the method of drying in an oven, the adhesive layer may be dried at a temperature in the range of 60°C to 100°C for about 1 second to 2 minutes.

[0065] As used herein, the term "sealing layer" refers to a layer of film, sheet, etc. that is involved in sealing a film, sheet, etc. to itself and / or to another layer of the same or a different film, sheet, etc. As used herein, terms such as "heat seal", "heat sealed", "heat sealing", "heat sealable", etc. refer to both a film layer that is heat sealable to itself or to another thermoplastic film layer, and the formation of a fusion bond between two polymer surfaces by conventional indirect heating means. Conventional indirect heating is understood to generate sufficient heat on at least one film contact surface for conduction to a continuous film contact surface such that formation of a bond interface therebetween is achieved without loss of film integrity.

[0066] Embodiments of the multilayer packaging film structure are shown in FIGS. 1-7. Embodiments of the multilayer packaging film structure may be described with reference to FIGS. 1-7, although one or more aspects of the multilayer packaging film structure may have the same characteristics as their corresponding features in different figures. For example, the multilayer packaging film structure 10 may have the same characteristics as the multilayer packaging film structures 110, 210 of a hermetically sealed package (e.g., a thermoformed tray or cup 100 and a retort pouch 200). Without being limited to any particular embodiment, the method 500 may be used to form an embodiment of the multilayer packaging film structure illustrated in any of FIGS. 1-7.

[0067] FIG. 1 shows a cross-sectional view of an embodiment of a multilayer packaging film 10. 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 that is between and in direct contact with the first base layer 13 and the second base layer 14, and an adhesive layer 16 that is between and in direct contact with the inorganic coating layer 15 and the sealing layer 11 on the second base layer 14. In FIG. 1, the first base layer 13 forms the outer layer of the multilayer packaging film 10, and the sealing layer 11 forms the opposing outer layer of the multilayer packaging film 10.

[0068] Figure 2 shows a cross-sectional view of an embodiment of the multilayer packaging film 10. 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. In FIG. 1, the inorganic coating layer 15 is shown on the second base layer 14, and FIG. 2 illustrates the inorganic coating layer 15 as being on the opposite side of the second base layer 14. The multilayer packaging film 10 includes an adhesive layer 16 that is between and in direct contact with the first base layer 13 and the inorganic coating layer 15 on the second base layer 14, and an adhesive layer 16 that is between and in direct contact with the second base layer 14 and the sealing layer 11. In FIG. 2, the first base layer 13 forms the outer layer of the multilayer packaging film 10, and the sealing layer 11 forms the opposing outer layer of the multilayer packaging film 10.

[0069] Figure 3 shows a cross-sectional view of an embodiment of the multilayer packaging film 10. 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 layer 15 on one side. The multilayer packaging film 10 includes an adhesive layer 16 that is between and in direct contact with the first base layer 13 and the second base layer 14, and an adhesive layer 16 that is between and in direct contact with the second base layer 14 and the sealing layer 11. In FIG. 3, the first base layer 13 forms the outer layer of the multilayer packaging film 10, and the sealing layer 11 forms the opposing outer layer of the multilayer packaging film 10.

[0070] Figure 4 shows a cross-sectional view of an embodiment of the multilayer packaging film 10. 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 layer 15 on one side. In FIG. 3, the inorganic coating layer 15 is shown on the first base layer 13, and FIG. 4 illustrates the inorganic coating layer 15 as being on the opposite side of the first base layer 13. The multilayer packaging film 10 includes an adhesive layer 16 that is between and in direct contact with the first base layer 13 and the second base layer 14, and an adhesive layer 16 that is between and in direct contact with the second base layer 14 and the sealing layer 11. In FIG. 3, the inorganic coating layer 15 on the first base layer 13 forms the outer layer of the multilayer packaging film 10, and the sealing layer 11 forms the opposing outer layer of the multilayer packaging film 10.

[0071] Figure 5 shows a cross-sectional view of an alternative embodiment of the multilayer packaging film 10. In the alternative embodiment shown in Figure 5, the multilayer packaging film 10 includes a first base layer 13 and a second base layer 14, each having an inorganic coating layer 15 thereon. In Figure 5, the inorganic coating layer 15 is between and in indirect contact with the first base layer 13 and the adhesive layer 16, and the inorganic coating layer 15 is between and in indirect contact with the second base layer 14 and the adhesive layer 16. The sealing layer 11 is directly adjacent to the adhesive layer 16 on the inorganic coating layer 15 on the second base layer 14. In Figure 5, the first base layer 13 forms the outer layer of the multilayer packaging film 10, and the sealing layer 11 forms the opposing outer layer of the multilayer packaging film 10. As shown in Figures 1-4, the inorganic coating layer 15 may be positioned on one or more sides of the first base layer 13 and the second base layer 14.

[0072] The first base layer 13 and the second base layer 14 have thicknesses 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 the range of 6 microns to 50 microns, or 10 microns to 40 microns.

[0073] The adhesive layer 16 has a thickness 16A measured in the z-direction. In some embodiments, the adhesive layer 16 has a thickness 16A in the range of 0.5 microns to 10 microns.

[0074] The inorganic coating layer 15 has a thickness 15A measured in the z-direction. The inorganic coating layer 15 has a thickness 15A in the range of 0.005 microns to 0.1 microns, 0.005 microns to 0.06 microns, 0.01 microns to 0.1 microns, or 0.01 microns to 0.06 microns. An inorganic coating layer having a thickness greater than these ranges can result in a layer that cannot bend to accommodate changes in surface area without cracking or otherwise failing.

[0075] The sealing layer 11 has a thickness 11A measured in the z direction. In some embodiments, the sealing layer 11 has a thickness 11A of 120 microns or less, including 110 microns or less, 100 microns or less, 90 microns or less, 80 microns or less, 70 microns or less, 60 microns or less, and including 50 microns or less, 40 microns or less, 30 microns or less, 20 microns or less, 10 microns or less, 5 microns or less, or 1 micron or less.

[0076] The free shrinkage of the first base layer at 95 °C, or another elevated processing temperature to which the multilayer packaging film is exposed, causes a reduction in the surface area of the first base layer. Any layer adjacent to or near the shrinking first base layer is thought to experience a shrinkage force in the x-y direction due to the reduction in surface area. The free shrinkage of each respective layer / film may be measured alone. Alternatively, the free shrinkage of each respective layer / film may be measured together in a combination of one or more layers / films (including any intervening layers that may be present).

[0077] The first base layer and / or the second base layer may be a film, and the film may be manufactured by any well-known process, such as a blown film or a cast film. The first base layer and / or the second base layer may 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 may be manufactured using a specific polymer and may be oriented using specific conditions to optimize the heat resistance of the film.

[0078] In some embodiments, each of the first and second polyolefin films is a stretched polyethylene (OPE) film or a stretched polypropylene (OPP) film. In some embodiments, one or more of the stretched polyethylene (OPE) film or the stretched polypropylene (OPP) film are 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.

[0079] In one or more embodiments, the stretched polypropylene (OPP) film is a coextruded OPP film. In one or more embodiments, the stretched polypropylene (OPP) film is a coextruded OPP film having a treated first side and a treated second side.

[0080] In some embodiments, the polyolefin film includes a biaxially stretched polypropylene (BOPP) film. In one or more embodiments, the biaxially stretched polypropylene (BOPP) film is formed by a linear motor simultaneous stretching process, and the biaxially stretched polypropylene (BOPP) film has a treated but non-sealable first side and a sealable second side. In one or more embodiments, the biaxially stretched polypropylene (BOPP) film is formed by a triple bubble process, and the biaxially stretched polypropylene (BOPP) film has a treated but non-sealable first side and a sealable second side.

[0081] The inorganic coating layer provides a significant contribution to the oxygen barrier (OTR reduction) for the multilayer packaging film.

[0082] In one or more embodiments, the inorganic coating layer of the multilayer packaging film comprises one or more of oxides, metal oxides, nitrides, or metal nitrides. In some embodiments, the inorganic coating layer comprises one or more of aluminum (Al) or silicon (Si). In some embodiments, the inorganic coating layer comprises an alloy of aluminum (Al) and any suitable metal oxide well known to those skilled in the art. In some embodiments, the inorganic coating layer comprises an alloy of silicon (Si) and any suitable metal oxide well known to those skilled in the art.

[0083] In some embodiments, the inorganic coating layer comprises one or more of transparent oxide coatings such as aluminum oxide (AlOx) or silicon oxide (SiOx). The inorganic coating layer may include any transparent ceramic well known to those skilled in the art, including but not limited to oxides, nitrides, or carbides.

[0084] In some embodiments, the inorganic coating layer comprises silicon oxide (SiOx). In embodiments where the inorganic coating layer comprises silicon oxide (SiOx), the ratio of the oxygen (O) atomic weight to the silicon (Si) atomic weight is measured. In embodiments where the inorganic coating layer comprises silicon oxide (SiOx), the ratio of the oxygen (O) atomic weight to the silicon (Si) atomic weight ranges from 1 to 3. In embodiments where the inorganic coating layer comprises silicon oxide (SiOx), the ratio of the oxygen (O) atomic weight to the silicon (Si) atomic weight is measured using any suitable analytical technique well known to those skilled in the art, such as X-ray photoelectron spectroscopy.

[0085] In alternative embodiments, the inorganic coating layer comprises one or more of magnesium oxide (MgOx) or tin oxide (SnOx).

[0086] The inorganic coating can be applied by any suitable process well 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 layer may be applied using wet chemical techniques.

[0087] The sealing layer may include a polyolefin material. In some embodiments, the sealing layer includes polypropylene. In some embodiments, the sealing layer includes one or more of a polypropylene copolymer, a polypropylene terpolymer, polybutylene, polyethylene, a polyethylene copolymer, a polyethylene terpolymer, LLDPE, mLLDPE, MDPE, or HDPE. The sealing layer may include a polymer formulation designed to reduce the heat seal initiation temperature and thus compliment the heat resistance of the opposite outer layer. The sealing layer may have a somewhat low softening point, but the sealing layer may have sufficient integrity to withstand the high temperatures of the high temperature sterilization process as well as other abuses that the package may endure during distribution and use.

[0088] In some embodiments, the sealing layer of the multilayer packaging film has a composition that enables the formation of a heat seal and thus enables the formation of an airtight package. As used herein, the terms "heat seal" or "heat sealed" refer to two or more surfaces joined together by the application of both short-term heat and pressure or by an ultrasonic energy sealing process. Heat sealing and ultrasonic sealing are well-known commonly used processes for creating packages and are well-known to those of skill in the art.

[0089] The sealing layer is necessarily on the surface of the multilayer packaging film to facilitate the function of sealing. During use of the multilayer packaging film in a package, the sealing layer may be heat sealed to itself or to another packaging component. During heat sealing, the sealing layer softens and enables the formation of a heat seal bond at a seal temperature lower than the temperature resistance of the outer layer on the opposite side of the multilayer packaging film. The sealing layer softens at a sealing temperature lower than the temperature resistance of the opposite 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 abrasion on the outer surface of the multilayer packaging film.

[0090] The multilayer packaging film is targeted to contain a large amount of polyolefin, especially polypropylene or polyethylene, so that the multilayer packaging film can be tolerated in the recycling process. Polyolefins have relatively low heat resistance compared to the materials conventionally used in packaging films (i.e., polyester, aluminum foil, polyamide). As a result of the lower heat resistance, the package will be formed using a heat seal process at a lower temperature to avoid shrinkage or sloughing. The challenge faced by the multilayer packaging film disclosed herein is to incorporate a seal layer having a low heat seal initiation temperature (HSIT) as well as high seal strength and seal toughness in order to withstand both retort or pasteurization treatment and normal distribution and handling (i.e., drop strength and burst strength). In some embodiments, the seal layer also contains materials approved for food contact during retort conditions, as directed by government agencies regarding food safety.

[0091] 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 of 135 °C or less.

[0092] The seal layer may be a single-layer film such as an unoriented cast polypropylene film. The seal layer may be the outer layer of a multilayer coextruded film such as a blown film. The entire multilayer coextruded film is attached to a second base layer, and the seal layer is positioned on the opposite side of the second base layer and is thus exposed.

[0093] The multilayer packaging film may have an overall thickness of from about 30 microns to about 180 microns.

[0094] The structure of the multilayer packaging film and any package made therefrom contains several different elements (sealing layer, first base layer, second base layer, inorganic coating layer, adhesive, etc.), but the overall composition of the film or package should have a high level of a single material type (polyolefin or particularly polypropylene or polyethylene) to facilitate recycling. As used herein, the term "overall composition" is used to describe the entire film structure or package. Any material, layer, or component that is connected to each other in any way is part of the overall composition of the article. The multilayer packaging film may have a high level of polyolefin-based polymer. The multilayer packaging film may have a high level of polypropylene-based polymer. The multilayer packaging film may have a high level of polyethylene-based polymer. The multilayer packaging film described herein, and any package made therefrom, may be recyclable in a polypropylene recycling process when the article contains a large amount of polypropylene-based polymer. The multilayer packaging film described herein, and any package made therefrom, may be recyclable in a polyethylene recycling process when the article contains a large amount of polyethylene-based polymer. A mixed polyolefin recycling process can also accept the relatively high levels of polyolefin present in the multilayer packaging film described herein, and any package made therefrom.

[0095] The multilayer packaging film described herein may have an overall composition containing at least 80 wt%, at least 85 wt%, at least 90 wt%, or at least 95 wt% of a polyolefin-based polymer, which promotes the recyclability of the film and / or package in which it is used. Materials that are not polyolefin-based polymers are minimized. For example, the inorganic coating layer of the multilayer packaging film is a material that is not a polyolefin-based material and is therefore provided in the thinnest layer possible to function properly as a barrier. The multilayer packaging film may also have other non-polyolefin materials, such as those located within the adhesive layer.

[0096] In certain embodiments of the multilayer packaging film, the film has a total composition containing at least 80 wt%, at least 85 wt%, at least 90 wt%, or at least 95 wt% of a polypropylene-based polymer. In certain embodiments of the multilayer packaging film, the film has a total composition containing at least 80 wt%, at least 85 wt%, at least 90 wt%, or at least 95 wt% of a polyethylene-based polymer.

[0097] Using the combination of film structure design elements described herein, a more heat-resistant multilayer packaging film can be achieved. Due to its high polyolefin content, the film may be suitable for recycling in a polyolefin-based recycling process. The film may have or may be essentially free of materials such as polyester, polyamide, chlorine-containing polymers, and aluminum foil at low levels (i.e., 5 wt% or less). As used herein, the term "essentially free of" means, on an atomic basis, that materials such as polyester, polyamide, chlorine-containing polymers, and aluminum foil are 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%.

[0098] The film may contain non-polyolefin-based polymers such as those used in adhesive layers, but the amount of non-polyolefin-based polymers is minimized and generally includes 10 wt% or less of the total composition 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 includes less than 10 wt% of the total composition or less than 5 wt% of the total composition.

[0099] As described above in this specification, an increase in ambient temperature can cause the first substrate, the second substrate, and / or the sealing layer to contract slightly in one or more directions. As the temperature increases, the polymeric material softens and releases the tension that may have been embedded within the layer during manufacturing. The release of tension can result in the movement and rearrangement of polymer chains, as well as the ultimate change (increase or decrease) in the dimensions of the layer. A common result of the temperature increase on the first substrate, the second substrate, and / or the sealing layer is a slight decrease (i.e., contraction) of the first substrate, the second substrate, and / or the sealing layer in at least one direction parallel to the x-y plane of the layer.

[0100] As the first substrate, the second substrate, and / or the sealing layer contract, compressive forces are applied to the other layers within the multilayer packaging film, with the greatest force being applied to the adjacent layers. The other layers may also have a tendency to contract at elevated temperatures, and the free contraction of each layer is likely to be slightly different. The greatest difference in free contraction is likely to be found when comparing any polymer layer of the multilayer packaging film to an inorganic coating layer. Most inorganic coatings do not experience contraction at the temperature at which the first substrate, the second substrate, and / or the sealing layer contract (e.g., 95 °C, or some other temperature). In addition, inorganic coatings also have very high elasticity (high rigidity) at these elevated temperatures.

[0101] In some embodiments, prior to exposure to high heat conditions, the multilayer packaging film may have an average oxygen transmission rate (OTR) value of 2 cm 3 / m 2 / day or less, 1 cm 3 / m 2 / day or less, 0.5 cm 3 / m 2 / day or less, or 0.1 cm 3 / m 2 / day or less (measured in accordance with ASTM F1927 using conditions of 1 atm, 23 °C, and 50% relative humidity).

[0102] In some embodiments, after exposure to a typical retort sterilization process, the barrier packaging film may have an OTR value of 2.5 cm 3 / m 22 cm or less per day 3 / m 2 1 cm or less per day 3 / m 2 0.5 cm or less per day 3 / m 2 or 0.1 cm or less per day 3 / m 2 It has an average OTR value of 0 or less per day. The average OTR value may be close to the minimum detection level of the test apparatus, at the minimum detection level, or below it. A typical retort sterilization process is completed by cutting a DIN A4-sized portion of the packaging film, exposing it to a steam sterilization process at 128 °C and an overpressure of 2.5 bar for 60 minutes, and then cooling it with a water shower.

[0103] The multilayer packaging films 10, 110, 210 can be formed into packages with or without other packaging components. For example, as shown in FIG. 7, the multilayer packaging film 210 can be formed into a flexible stand-up pouch 200. 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, as shown in FIG. 6.

[0104] The multilayer packaging films disclosed herein maintain excellent barrier properties and visual appearance even after the film is formed into a package, filled, hermetically sealed, and subjected to a retort sterilization process.

[0105] Hereinafter, the present disclosure will be described with reference to the following examples.

Examples

[0106] [Examples and Data]

[0107] As summarized in Table 1 below, several film structures were manufactured.

[0108]

Table 1

[0109] Table 1 identifies and lists the characteristics of each of the base layers A - F. Table 1 also lists the free shrinkage values of each of the base layers A - F measured in the flow direction at 120°C.

[0110]

Table 2

[0111] Table 2 lists the surface treatment of each of the base layers A - F (e.g., "bare" or "primer + SiOx"). As a general convention, the base layers A - F with 1 (e.g., A1) are bare, and the base layers A - F with 2 (e.g., A2) are primed and have a silicon oxide coating thereon.

[0112] 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 the multilayer packaging film is an indicator of the provided barrier and can be measured according to ASTM F1927 using the conditions of 1 atmosphere, a temperature of 23°C, and a relative humidity (RH) of 50%.

[0113]

Table 3

[0114] In Table 3, the multilayer packaging film structure includes the base layers A - F 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 sealing layer. The figure illustrates the multilayer packaging film structure having the base layers A - F.

[0115] Each of the multilayer packaging film structures of A to F was prepared by applying an aqueous polyurethane (PU) dispersion (primer) to each surface of the first base layer and the second base layer, drying the dispersion, and forming a 1.7-micron primer coating. As applicable above, the inorganic coating layer on each of the first base layer and the second base layer includes a silicon oxide coating (SiOx) applied by vapor deposition on the surface of the primer. Next, a 60-micron polypropylene sealing layer was adhesively laminated to the silicon oxide coating. [Embodiment]

[0116] [Embodiment 1] A first base layer including a polyolefin film, a second base layer on the first base layer, the second base layer including a polyolefin film, and a sealing layer on the second base layer, the sealing layer including a polyolefin film, wherein one or more of the first base layer or the second base layer includes an inorganic coating thereon, and the second base layer has a shrinkage value greater than 5%, a multilayer packaging film.

[0117] [Embodiment 2] The multilayer packaging film according to Embodiment 1, wherein the shrinkage value of the second base layer is equal to or greater than the shrinkage value of the first base layer.

[0118] [Embodiment 3] The multilayer packaging film according to any one of Embodiments 1 to 2, wherein the shrinkage value of the second base layer is equal to or greater than the shrinkage value of the sealing layer.

[0119] [Embodiment 4] A first base layer including a polyolefin film, a second base layer on the first base layer, the second base layer including a polyolefin film, and a sealing layer on the second base layer, the sealing layer including a polyolefin film, wherein one or more of the first base layer or the second base layer includes an inorganic coating thereon, and the shrinkage value of the second base layer is smaller than the shrinkage value of the first base layer, a multilayer packaging film.

[0120] [Embodiment 5] The multilayer packaging film according to Embodiment 4, wherein the second base layer has a shrinkage value of 5% or less.

[0121] [Embodiment 6] The multilayer packaging film according to any one of Embodiments 4 to 5, wherein the shrinkage value of the second base layer is equal to or greater than the shrinkage value of the sealing layer.

[0122] [Embodiment 7] A first base layer including a polyolefin film, a second base layer on the first base layer, the second base layer including a polyolefin film, and a sealing layer on the second base layer, the second base layer including a polyolefin film, the multilayer packaging film comprising one or more of the first base layer or the second base layer having an inorganic coating thereon, the second base layer having a shrinkage value greater than 5%, and the shrinkage value of the second base layer being smaller than the shrinkage value of the first base layer.

[0123] [Embodiment 8] The multilayer packaging film according to Embodiment 8, wherein the shrinkage value of the second base layer is equal to or greater than the shrinkage value of the sealing layer.

[0124] [Embodiment 9] The multilayer packaging film according to any one of Embodiments 1 to 8, wherein the shrinkage value of the second base layer is 5% or less.

[0125] [Embodiment 10] The multilayer packaging film according to any one of Embodiments 1 to 9, wherein the difference in shrinkage value between the first base layer and the second base layer is 0.3% or more.

[0126] [Embodiment 11] The multilayer packaging film according to any one of Embodiments 1 to 10, wherein the difference in shrinkage value between the second base layer and the sealing layer is 0.5% or more.

[0127] [Embodiment 12] The multilayer packaging film according to any one of Embodiments 1 to 11, wherein the shrinkage value of the sealing layer is 2% or more.

[0128] [Embodiment 13] The multilayer packaging film according to any one of Embodiments 1 to 12, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealing layer is measured in the flow direction (MD) according to Formula 1.

[0129] [Number]

[0130] [Embodiment 14] The multilayer packaging film according to any one of Embodiments 1 to 13, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealing layer is measured using the method disclosed in ASTM D2732-03.

[0131] [Embodiment 15] The multilayer packaging film according to any one of Embodiments 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.

[0132] [Embodiment 16] The multilayer packaging film according to any one of Embodiments 1 to 15, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealing layer is measured after heating at 127°C for 50 minutes.

[0133] [Embodiment 17] The multilayer packaging film according to any one of Embodiments 1 to 16, wherein each of the polyolefin films of the first base layer and the second base layer is a stretched polyethylene (OPE) film or a stretched polypropylene (OPP) film.

[0134] [Embodiment 18] The multilayer packaging film according to Embodiment 17, wherein one or more of the stretched polyethylene (OPE) film or the stretched polypropylene (OPP) film are formed by one or more of a continuous stretching process or a simultaneous stretching process.

[0135] [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.

[0136] [Embodiment 20] The multilayer packaging film according to Embodiment 17, wherein the polyolefin film includes a biaxially stretched polypropylene (BOPP) film.

[0137] [Embodiment 21] The multilayer packaging film according to Embodiment 20, wherein the biaxially stretched polypropylene (BOPP) film is formed by a linear motor simultaneous stretching process.

[0138] [Embodiment 22] The multilayer packaging film according to Embodiment 17, wherein the polyolefin film includes 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.

[0139] [Embodiment 23] The multilayer packaging film according to Embodiment 22, wherein the polyolefin film includes a machine direction oriented polypropylene (MDOPP) film.

[0140] [Embodiment 24] The multilayer packaging film according to any one of Embodiments 1 to 23, wherein one or more inorganic coatings of the first base layer or the second base layer include silicon oxide.

[0141] [Embodiment 25] The multilayer packaging film according to Embodiment 24, wherein one or more inorganic coatings of the first base layer or the second base layer have a gas barrier coating thereon.

[0142] [Embodiment 26] The multilayer packaging film according to Embodiment 25, wherein the gas barrier coating contains one or more of a hydroxyl group-containing polymer compound, a metal alkoxide, a silane coupling agent, and their hydrolyzates.

[0143] [Embodiment 27] The multilayer packaging film according to any one of Embodiments 1 to 26, wherein each of the first base layer and the second base layer has a thickness in the range of 10 microns to 40 microns.

[0144] [Embodiment 28] The multilayer packaging film according to any one of Embodiments 1 to 27, wherein the sealing layer has a thickness of 120 microns or less.

[0145] [Embodiment 29] The multilayer packaging film according to any one of Embodiments 1 to 28, wherein the oxygen transmission rate is measured before and after retort using the method disclosed in ASTM F1927.

[0146] [Embodiment 30] The multilayer packaging film according to any one of Embodiments 1 to 29, further comprising an adhesive layer between one or more of the first base layer and the second base layer, or between the second base layer and the sealing layer.

[0147] [Embodiment 31] The multilayer packaging film according to Embodiment 30, wherein the adhesive layer contains polyurethane.

[0148] [Embodiment 32] The multilayer packaging film according to any one of Embodiments 30 to 31, wherein the adhesive layer has a thickness in the range of 2 microns to 4 microns.

[0149] [Embodiment 31] The multilayer packaging film according to any one of Embodiments 1 to 30, wherein the sealing layer has a sealing start temperature of 110°C or less.

[0150] [Embodiment 32] The multilayer packaging film according to any one of Embodiments 1 to 31, wherein the sealing layer contains polypropylene.

[0151] [Embodiment 33] A retort pouch formed from the multilayer packaging film according to any one of Embodiments 1 to 32.

Claims

**Claim 1** A multilayer packaging film comprising: a first base layer including a polyolefin film; a second base layer on the first base layer, the second base layer including a polyolefin film; a sealing layer on the second base layer, the sealing layer including a polyolefin film, wherein one or more of the first base layer or the second base layer includes an inorganic coating thereon, and the second base layer has a shrinkage value greater than 5%, the multilayer packaging film. **Claim 2** The multilayer packaging film according to 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. **Claim 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. **Claim 4** A multilayer packaging film comprising: a first base layer including a polyolefin film; a second base layer on the first base layer, the second base layer including a polyolefin film; a sealing layer on the second base layer, the sealing layer including a polyolefin film, wherein one or more of the first base layer or the second base layer includes an inorganic coating thereon, and the shrinkage value of the second base layer is smaller than the shrinkage value of the first base layer, the multilayer packaging film. **Claim 5** The multilayer packaging film according to claim 4, wherein the second base layer has a shrinkage value of 5% or less. **Claim 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 sealing layer. **Claim 7** A multilayer packaging film comprising: a first base layer including a polyolefin film; a second base layer on the first base layer, the second base layer including a polyolefin film; a sealing layer on the second base layer, the second base layer including a polyolefin film, wherein one or more of the first base layer or the second base layer includes an inorganic coating thereon, the second base layer has a shrinkage value greater than 5%, and the shrinkage value of the second base layer is smaller than the shrinkage value of the first base layer, the multilayer packaging film. **Claim 8** The multilayer packaging film according to claim 7, wherein the shrinkage value of the second base layer is greater than or equal to the shrinkage value of the sealing layer. **Claim 9** The multilayer packaging film according to any one of claims 1 to 8, wherein the shrinkage value of the second base layer is 5% or less. **Claim 10** The multilayer packaging film according to any one of claims 1 to 9, wherein the difference in shrinkage values between the first base layer and the second base layer is 0.3% or more.

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 0.5% or more.

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

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 sealing layer is measured in the machine direction (MD) according to Formula 1. 【Number 1】

14. The multilayer packaging film according to any one of claims 1 to 13, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealing 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 according to any one of claims 1 to 15, wherein the shrinkage value of each of the first base layer, the second base layer, and the sealing 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 each of the polyolefin films of the first base layer and the second base layer is a stretched polyethylene (OPE) film or a stretched polypropylene (OPP) film.

18. The multilayer packaging film according to claim 17, wherein one or more of the stretched polyethylene (OPE) film or the stretched polypropylene (OPP) film are formed by one or more of a continuous 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 according to claim 17, wherein the polyolefin film includes a biaxially oriented polypropylene (BOPP) film.

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

22. The multilayer packaging film according to claim 17, wherein the polyolefin film includes 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 according to claim 22, wherein the polyolefin film includes the machine direction oriented polypropylene (MDOPP) film.

24. The multilayer packaging film according to any one of claims 1 to 23, wherein one or more of the inorganic coatings on the first base layer or the second base layer contains silicon oxide.

25. The multilayer packaging film according to claim 24, wherein one or more of the inorganic coatings on the first base layer or the second base layer has a gas barrier coating thereon.

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

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

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

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

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

31. The multilayer packaging film according to claim 30, wherein the adhesive layer contains polyurethane.

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

33. The multilayer packaging film according to any one of claims 1 to 32, wherein the sealing layer has a sealing start temperature of 110°C or less.

34. The multilayer packaging film according to any one of claims 1 to 33, wherein the sealing layer contains polypropylene.

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

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