Directional tear packaging with polypropylene film

Abstract

This disclosure relates to a sealant film comprising one or more polypropylene layers and a sealing layer comprising a polypropylene terpolymer and one or more polymers selected from polybutene-1 or plastomer. The sealant film is a mechanically oriented (MDO) film comprising at least 95% by weight of polypropylene. Also disclosed are multilayer packaging films comprising such sealant films, and hermetically sealed packages (e.g., retort pouches) formed from multilayer packaging films.

Description

Technical Field

[0001] The present invention relates to a sealant film (e.g., a machine direction oriented (MDO) film) and a multilayer film structure incorporating such a sealant film. Embodiments of the present invention are directed to multilayer films having straight-line tear performance 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 is subjected to a long-term heat and pressure treatment process.

[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. 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 substantially decomposing (i.e., leaking, peeling). Generally, the retort process consists of heating the packaging container to a temperature in the range of 100 - 135 °C with an overpressure in the range of 0.5 - 1.1 bar for a time in the range of 15 - 100 minutes.

[0004] Examples of laminates for retort packaging are US No. 4,310,578A, US No. 4,311,742A, US No. 4,308,084A, US No. 4,309 ,466A, US No. 4,402,172A, US No. 4,903,841A, US No. 5,273,797A, US No. 5,731,090A, EP No. 1 466 725A1, JPH No. 09 267 868A, JP 2002 096 864A, JP 2015 066 721A, JP 2018 053 ​​180A, JP 2017 144 648A, JPS No. 62 279 944A, JPS No. 6 328 This is disclosed in Patent No. 642 and JPH No. 10 244 641A.

[0005] A typical example of a multilayer film structure for a standard retort pouch includes a polyethylene terephthalate outer layer, a barrier layer, and an inner sealing layer, where the outer layer includes a printed 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 similar.

[0006] However, without dispute the advantages associated with state-of-the-art systems, there is a need for improved sealant films and multilayer film structures for packaging that are recyclable and offer linear tear performance. [Overview of the Initiative]

[0007] Embodiments of the present invention advantageously provide sealant films having easy tearing and linear tearing properties, a low sealing initiation temperature, recyclability, and / or compatibility with retort processing, and multilayer packaging films incorporating them.

[0008] This disclosure provides a sealant film comprising co-extrusion of one or more polypropylene layers and a sealing layer comprising a polypropylene terpolymer and one or more polymers selected from polybutene-1 or plastomer.

[0009] In some embodiments, the sealant film is a mechanically oriented (MDO) film containing at least 90% by weight of polypropylene. In some embodiments, the MDO film contains at least 95% by weight of polypropylene.

[0010] In some embodiments, the sealant film comprises co-extrusion of a sealing layer comprising a polypropylene terpolymer and one or more polymers selected from polybutene-1 or plastomer, a core layer comprising polypropylene, and a lamination layer comprising polypropylene.

[0011] In some embodiments, the core layer comprises a polypropylene homopolymer. In some embodiments, the core layer further comprises a heterogeneous polypropylene copolymer.

[0012] In some embodiments, the lamination layer comprises a heterogeneous polypropylene copolymer.

[0013] In some embodiments, the sealant film comprises a sealing layer of 15-40% by weight, a core layer of 70-20% by weight, and a lamination layer of 15-40% by weight.

[0014] In some embodiments, the sealing layer comprises at least 20% by weight of polypropylene terpolymer.

[0015] In some embodiments, the terpolymer has a melting temperature in the range of 120 to 140°C, such as 120 to 130°C. Exemplary melting temperatures include about 120°C, about 125°C, about 130°C, about 135°C, and about 140°C.

[0016] In some embodiments, the MDO film is stretched at least twice in the flow direction.

[0017] In some embodiments, the sealant film provides a seal strength of 4 N / 15 mm at a seal start temperature of 140°C or lower, such as 130°C or lower. Exemplary seal start temperatures include about 120°C, about 125°C, about 130°C, about 135°C, and about 140°C.

[0018] In some embodiments, the sealant film provides straight-line tearability in the flow direction.

[0019] In some embodiments, the sealant film provides a seal strength of at least 10 N, such as at least 15 N or at least 20 N.

[0020] In some embodiments, the sealant film is retortable up to a temperature of at least 130°C.

[0021] The present disclosure also provides a multilayer packaging film comprising the sealant film described herein.

[0022] In some embodiments, the multilayer packaging film comprises a sealant film and a first base layer comprising a polypropylene film.

[0023] In some embodiments, the multilayer packaging film comprises at least 90 wt% polypropylene, such as at least 95 wt% polypropylene.

[0024] In some embodiments, the multilayer packaging film further comprises a second base layer comprising a polypropylene film.

[0025] In some embodiments, one or both of the first base layer and the second base layer comprise a barrier layer.

[0026] In some embodiments, one or both of the first base layer and the second base layer comprise a biaxially oriented polypropylene film (BOPP).

[0027] In some embodiments, one or both of the first and second layers comprise metallized biaxially oriented polypropylene film (met BOPP).

[0028] In some embodiments, the multilayer packaging film provides in-line tearability in the flow direction.

[0029] In some embodiments, the multilayer packaging film provides a seal strength of 4 N / 15 mm at a seal start temperature of 140 °C or less.

[0030] In some embodiments, the multilayer packaging film provides a seal strength of at least 10 N, such as at least 15 N or at least 20 N.

[0031] The present disclosure also provides a retort pouch formed from the multilayer packaging film.

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 1A] Shows the seal curve of the MDO-stretched film according to an embodiment of the present invention compared to an unstretched film and a comparative MDO-stretched film. [Figure 1B] Shows the tear resistance of the MDO-stretched film according to an embodiment of the present invention compared to an unstretched film. [Figure 1C] Shows the tear resistance of a laminate incorporating the MDO-stretched film according to an embodiment of the present invention compared to a laminate incorporating an unstretched film. [Figure 2] Shows a cross-sectional view of an embodiment of a sealant film. [Figure 3] Shows a cross-sectional view of an embodiment of the multilayer packaging film. [Figure 4] Shows a cross-sectional view of an embodiment of the multilayer packaging film. [Figure 5]A perspective view of an embodiment of an hermetically sealed package including a multilayer packaging film is shown.

[0034] The drawings illustrate some, but not all, embodiments. The elements shown in the drawings are illustrative and not necessarily to exact scale, and the same (or similar) reference numbers represent the same (or similar) features throughout the drawings. [Modes for carrying out the invention]

[0035] The packaging industry is moving towards more sustainable options, including streamlining the materials used into narrower categories. For example, one option is to design packaging structures with a high polyolefin (e.g., polypropylene) content to classify the film as recyclable. Eliminating non-olefin polymers from packaging structures often results in deficiencies in the overall performance of the packaging structure. For packaging intended for heat treatment applications such as retort or pasteurization, polyolefin polymers are more sensitive to the applied temperature.

[0036] Furthermore, while easy tearing and linear tearing properties can be provided by mechanical orientation (MDO), this technique increases the sealing onset temperature (SIT). Thus, it is difficult to combine sealing and tearing properties simultaneously in polypropylene films.

[0037] The inventors discovered that mixing a polymer (e.g., polybutene-1 and / or plastomer) into a polypropylene film provides enhanced film properties. For example, Figure 1A shows the seal curve of an MDO film. As can be seen, incorporating a polymer (e.g., polybutene-1 and / or plastomer) into a polypropylene film, as shown in samples 1-3, lowers the sealing onset temperature compared to a standard stretched polypropylene film. Figure 1B shows that these samples 1-3 also had approximately three times lower tear resistance compared to a standard stretched polypropylene film. Figure 1C shows that laminates incorporating samples 1-3 had approximately twice as low tear resistance compared to a standard stretched polypropylene film, and that the lower tear resistance was retained after retorting.

[0038] Accordingly, embodiments of the present invention relate to mixing a polymer (e.g., polybutene-1 and / or plastomer) with a polypropylene-based film and subjecting such film to MDO treatment to provide low SIT and linear tear performance.

[0039] definition As used herein, the term "polyolefin" generally includes polypropylene polymers and polyethylene polymers. Polyolefin films may include acid-modified polyolefin films obtained by grafting polyolefin polymers with, for example, unsaturated carboxylic acids, unsaturated carboxylic acid anhydrides, unsaturated carboxylic acid esters, etc. Various pretreatment processes may be carried out on polyolefin films. Pretreatment processes may include any suitable process known to those skilled in the art that does not impair barrier properties. Pretreatment processes include, but are not limited to, corona treatment, plasma treatment, or flame treatment, or other similar processes. Polyolefin films may include an adhesion-enhancing layer.

[0040] As described herein, the films described herein can be oriented. Orientation may be the result of uniaxial stretching (in the flow direction or transverse direction) or biaxial stretching (in the flow direction and transverse direction), where increasing the dimensions in the flow direction and / or transverse direction subsequently decreases the thickness of the material. Biaxial stretching may be applied to the film simultaneously or sequentially. In some embodiments, the film is stretched in one or both directions at a temperature slightly below the melting temperature of the film's polymer. In this way, stretching "orients" the polymer chains and alters the physical properties of the film. At the same time, stretching thins the film. The resulting oriented film is thinner and may have significant changes in mechanical properties such as toughness, heat resistance, stiffness, tear strength, and barrier properties. Orientation is typically achieved by an MDO process using heated rolls. Oriented films may be heat-set (i.e., annealed) after orientation so that the film is relatively dimensionally stable (i.e., less than 10% free shrinkage when heated to 130°C for 10 minutes) under high-temperature conditions that may be experienced during the conversion (i.e., printing or lamination) of retort film laminates or during the use of laminates (i.e., heat sealing or retort sterilization). As used herein, “free shrinkage” is the unconstrained linear shrinkage that a film or layer undergoes upon exposure to high temperatures. 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 dimensions (i.e., 100 × (pre-shrinkage dimensions - post-shrinkage dimensions) / (pre-shrinkage dimensions)). Free shrinkage can be measured using any suitable method capable of measuring a difference in shrinkage value 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 cm square sample immersed in 90°C water for 5 seconds.

[0041] As used herein, the terms “unoriented” and “non-oriented” refer to monolayer or multilayer films, sheets, or webs that are substantially unoriented after extrusion.

[0042] As used throughout this application, the term “copolymer” refers to a polymer product obtained by the polymerization or copolymerization of at least two monomer species. The term “copolymer” also includes polymerization reactions of three, four, or more monomer species, which have reaction products called terpolymers, quarterpolymers, and so on.

[0043] As used throughout this application, the terms “polypropylene” or “PP” refer to propylene homopolymers or copolymers unless otherwise indicated. Such copolymers of propylene include copolymers of propylene with at least one alpha-olefin, and copolymers of propylene with other units or groups. The terms “polypropylene” or “PP” are used with or without substituted branched 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.

[0044] As used herein, the term “terpolymer” refers to a copolymer produced from three different monomers. The term “polypropylene terpolymer” refers to a polypropylene molecular chain modified with two additional comonomers during the polymerization process. Examples of the two additional comonomers may include ethylene and / or C4-C16α-olefins, ethylene and / or C4-C8α-olefins, and ethylene and butylene.

[0045] As used herein, the term “other phase” refers to a copolymer having a second phase.

[0046] Where used throughout this application, the terms “polyethylene” or “PE” refer to ethylene homopolymers or copolymers unless otherwise indicated. Such copolymers of ethylene include copolymers of ethylene with at least one alpha-olefin, and copolymers of ethylene with vinyl acetate, acid groups, acrylate groups, or other units or groups. The terms “polyethylene” or “PE” are used with or without substituted 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 mixtures thereof. Various polyethylene polymers can be recycled as recycled polyethylene or recycled polyolefins.

[0047] As used throughout this application, the terms "polyester" or "PET" refer to homopolymers or copolymers having ester bonds between monomer units. Ester bonds are represented by the general formula [OR-OC(O)-R'-C(O)] n It may also be represented as such, where R and R' are the same or different alkyl (or aryl) groups, and can generally be formed from the polymerization of dicarboxylic acids and diol monomers.

[0048] As used herein, the term "polyamide" refers to the amide bonds (--CONH--) that occur along the molecular chain. n This refers to high molecular weight polymers having a specific property, including nylon resin, a well-known polymer with numerous applications, including as a packaging film. As used herein, "polyurethane" generally refers to polymers having organic units linked by urethane bonds (-NH-(C=O)-O-).

[0049] 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), butenediol vinyl alcohol copolymer (BVOH), and polyvinyl alcohol (PVOH).

[0050] As used throughout this application, the terms “ethylene vinyl alcohol copolymer,” “EVOH copolymer,” or “EVOH” refer to copolymers consisting of repeating units of ethylene and vinyl alcohol. Ethylene vinyl alcohol copolymers may 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, prepared, for example, by hydrolysis of vinyl acetate copolymers or by chemical reaction with vinyl alcohol. Ethylene vinyl alcohol copolymers may contain 28 mol percent (less than) to 48 mol percent (more than). The term "layer," as used herein, refers to a component of a film that is a structure of a single material type 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 or additives. Layers may be continuous with the film, or discontinuous or patterned. A layer has a thickness (z direction) relative to its length and width (x and y directions), and is therefore defined to have two main surfaces, the area of ​​which is defined by the length and width of the layer. An outer layer is a layer connected to another layer by only one of its main surfaces. In other words, one main surface of the outer layer is exposed. An inner layer is a layer connected to another layer at both main surfaces. In other words, an inner layer lies between two other layers. A layer may have sublayers.

[0051] 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 one another. A film can be described as having a thickness only slightly relative to its length and width. A film has two main surfaces, the area of ​​which is defined by the length and width of the film.

[0052] As used herein, the term “barrier layer” refers to a layer of film containing any material that controls the permeability elements of the film. The barrier layer may provide, for example, an oxygen barrier, a moisture barrier, a chemical barrier, a thermal barrier, and / or an odor barrier. In one or more embodiments, the barrier layer is vacuum-deposited.

[0053] Examples of materials for the barrier layer include metals and silicon oxide (SiO₂). x Examples include metal barrier materials, or polymer barrier materials. Exemplary metal barrier materials include aluminum (Al). Exemplary polymer barrier materials include, but are not limited to, ethylene-vinyl alcohol (EVOH) copolymers, polyvinyl alcohol (PVOH) copolymers, polyvinyl chloride, polyvinylidene polymers and copolymers including polyvinylidene polymers and polyvinylidene chloride, polyamides including amorphous polyamides, acrylonitrile polymers including acrylonitrile-methyl acrylate copolymers, polyurethane engineering plastics, poly(methylpentene) resins, ethylene-carbon monoxide copolymers, liquid crystal polymers, polyesters such as polyethylene terephthalate, polyimides including polyetherimide and polyacrylimide, and other such polymer materials known to have relatively low gas permeability.

[0054] As used herein, the term “external” is used to describe a film or layer located on one of the main 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 on both sides to another film or layer.

[0055] As used herein, “multilayer packaging film,” “hermetic sealed package,” or “retort-stable package” refers to a film structure or packaging made from a film structure that exhibits little degradation after exposure to temperatures above the heat treatment temperature and maintains a high oxygen barrier level or moisture barrier level. The package may remain filled, sealed, and hermetic sealed with the product, and thus maintain excellent barrier properties.

[0056] The multilayer packaging films described herein may be useful as retort or pasteurized packaging films. Where used herein, “retort packaging film” or “retort packaging” refers to a film or package made from a film that is filled with a product, sealed, and may remain airtight after exposure to a typical retort sterilization process. Typical retort sterilization is a batch process using temperatures in the range of approximately 100°C to approximately 150°C and overpressures up to approximately 70 psi (483 kPa), and can last from several minutes to several hours. Common retort processes used for products packaged in flexible films include steam or water immersion. Food or other products packaged in retort packaging films and retort-sterilized can be stored for extended periods under ambient conditions (i.e., are storage stable) and retain their sterility. Because the retort process degrades films or packages made from films, very specialized flexible packaging films have been designed to withstand the retort process.

[0057] 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 a multilayer film to maintain the two layers in place relative to each other and prevent undesirable delamination. Unless otherwise indicated, the adhesive layer may have any preferred composition that provides a desired level of adhesion to one or more surfaces in contact with the adhesive layer material.

[0058] The adhesive layer can be deposited on a polyolefin film, which is one or more of a first or second base layer, by any suitable method known to those skilled in the art. The adhesive layer may bond the first base layer to the sealing layer, the second base layer to the sealing layer, and / or the first base layer to the second base layer. If two adhesive layers are present in the packaging film, they may be identical or different in composition and thickness.

[0059] The adhesive layer may be any conventional laminating material and may include, but is not limited to, polymer adhesives applied by a one-component or two-component bonding system (i.e., adhesive lamination) or extrusion (i.e., extrusion lamination process).

[0060] As used herein, the term “sealing layer” refers to a layer such as a film, sheet, etc., that is involved in sealing itself and / or to another layer such as the same or another film, sheet, etc. As used herein, the terms “heat-sealed,” “heat-sealed,” “heat-sealable,” and “heat-sealable” refer to both a film layer that is heat-sealable to itself or another thermoplastic film layer, and the formation of a fusion bond between two polymer surfaces by conventional indirect heating means. It will be understood that conventional indirect heating generates enough heat on at least one film contact surface for conduction to a continuous film contact surface so that the formation of a bonding interface between the films is achieved without loss of film integrity.

[0061] As used herein, the term “seal onset temperature” refers to the seal temperature at which a seal strength of approximately 4 N / 15 mm is achieved. The seal onset temperature and seal strength may be evaluated using ASTM F2029.

[0062] As used herein, the term “linear tear property” refers to a property of a film, sheet, web, etc., that allows it to be easily torn in a substantially linear manner. In one or more embodiments, a sealant film provides linear tear property in the flow direction. Linear tear property can be evaluated by measuring the angle at which the tear occurs, using the tearing method outlined in ASTM D1938. The test specimen should be prepared such that the initial cut between tongue A and tongue B of the test specimen is in the flow direction of the sample film. Once the test is complete, the angle between the flow direction and the tear propagation direction can be measured. As used herein, linear tear property is defined by a tear propagation angle of 5° or less from the flow direction.

[0063] Figure 2 shows a cross-sectional view of one embodiment of the sealant film 10. The sealant film 10 includes a sealing layer 11, a core layer 12, and a lamination layer 13. In Figure 2, the lamination layer 13 forms the outer layer of the sealant film 10, and the sealing layer 11 forms the opposing outer layer of the sealant film 10.

[0064] Figure 3 shows a cross-sectional view of one embodiment of a multilayer packaging film 20. The multilayer packaging film 20 includes a first base layer 14 and a sealant film 10. The sealant film 10 includes a sealing layer 11, a core layer 12, and a lamination layer 13. The multilayer packaging film 20 may also include an adhesive layer (not shown) located between the first base layer 14 and the lamination layer 13 and in direct contact with them. In Figure 2, the first base layer 14 forms the outer layer of the multilayer packaging film 20, and the sealing layer 11 forms the opposing outer layer of the multilayer packaging film 20.

[0065] Figure 4 shows a cross-sectional view of one embodiment of a multilayer packaging film 20. The multilayer packaging film 20 includes a first base layer 14, a second base layer 15, and a sealant film 10. The sealant film 10 includes a sealing layer 11, a core layer 12, and a lamination layer 13. The multilayer packaging film 20 includes an adhesive layer 16 located between the first base layer 14 and the second base layer 15 and in direct contact with them, and an adhesive layer 16 located between the first base layer 14 and the lamination layer 13 and in direct contact with them. In Figure 4, the second base layer 15 forms the outer layer of the multilayer packaging film 20, and the sealing layer 11 forms the opposing outer layer of the multilayer packaging film 10. In some embodiments, one or both of the first layer 14 and the second base layer 15 have a barrier layer on any surface.

[0066] In some embodiments, one or both of the first base layer 14 and the second base layer 15 have a thickness in the range of 6 to 100 microns, including a range of 6 to 50 microns or 10 to 40 microns.

[0067] In some embodiments, the adhesive layer 16 has a thickness in the range of 2 to 4 microns. In some embodiments, the adhesive layer 16 has a thickness of 2 microns or less, including 1.9 microns or less, 1.8 microns or less, 1.7 microns or less, 1.6 microns or less, 1.5 microns or less, 1.4 microns or less, 1.3 microns or less, 1.2 microns or less, 1.1 microns or less, 1.0 micron or less, 0.9 microns or less, 0.8 microns or less, 0.7 microns or less, or 0.6 microns or less.

[0068] In some embodiments, the sealing layer 11 has a thickness of 120 microns or less, including thicknesses of 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 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.

[0069] The first and / or second base layer may be a film, which may be manufactured by any well-known process, such as blow film or cast film. The first and / or second base layer may be a uniaxially oriented polypropylene film (MDOPP) or a biaxially oriented polypropylene film (BOPP). The first and / or second base layer may be manufactured using a specific polymer and may be oriented using specific conditions that optimize the heat resistance of the film. In some embodiments, the oriented polypropylene (OPP) film is formed by one or more continuous stretching processes or co-stretching processes. In some embodiments, the co-stretching process is one or more linear motor co-stretching processes, double bubble processes, or triple bubble processes.

[0070] In some embodiments, the polyolefin film includes 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 first side that is processed but not sealable and a second side that is sealable. In one or more embodiments, the biaxially oriented polypropylene (BOPP) film is formed by a triple bubble process, and the biaxially oriented polypropylene (BOPP) film has a first side that is processed but not sealable and a second side that is sealable.

[0071] In various embodiments, the sealing layer comprises polypropylene having additional polymers. In some embodiments, the sealing layer comprises polypropylene terpolymer and one or more polymers selected from polybutene-1 and / or plastomers.

[0072] In one or more embodiments, the sealing layer comprises 10% to 40% by weight of polybutene-1 and / or plastomer. In some embodiments, the sealing layer comprises 10% by weight of plastomer. In some embodiments, the sealing layer comprises 20% by weight of plastomer. In some embodiments, the sealing layer comprises 10% by weight of polybutene-1. In some embodiments, the sealing layer comprises 20% by weight of polybutene-1.

[0073] The sealing layer may include a polymer formulation designed to reduce the heat-seal initiation temperature, thereby enhancing the heat resistance of the opposing outer layer. While the sealing layer may have a relatively low softening point, it may possess sufficient integrity to withstand the high temperatures of the retort sterilization process, as well as other aggravating stresses that the package may endure during distribution and use.

[0074] In some embodiments, the sealing layer of a multilayer packaging film has a composition that allows for the formation of a heat seal, and therefore allows for 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 heat and pressure for 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 producing packages and are well known to those skilled in the art.

[0075] The sealing layer is always located on the surface of the multilayer packaging film to facilitate its sealing function. During the 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, allowing for the formation of a heat-seal bond at a sealing temperature lower than the temperature resistance of the opposite outer layer 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 on the outer surface of the multilayer packaging film under sealing conditions (time, temperature, and pressure) that do not cause excessive shrinkage or abrasion.

[0076] The multilayer packaging film is intended to contain a large amount of polyolefin, particularly polypropylene, so that it can be accepted in recycling processes. Polyolefins have relatively lower heat resistance compared to materials conventionally used in packaging films (i.e., polyester, aluminum foil, polyamide). The challenge faced by the multilayer packaging film disclosed herein is to incorporate a sealing layer with a low sealing onset temperature (SIT) and high sealing strength and sealing toughness to withstand both retort or pasteurization processes as well as normal distribution and handling (i.e., drop strength and burst strength). In some embodiments, the sealing layer also contains a material approved for food contact during retort conditions, as directed by government agencies regarding food safety.

[0077] The multilayer packaging film may have an overall thickness of approximately 30 microns to approximately 180 microns. In some embodiments, the multilayer packaging film has an overall thickness of approximately 80 microns to approximately 140 microns.

[0078] The structure of multilayer packaging films and any packages made therefrom contains several different elements (sealing layer, primary base layer, secondary base layer, adhesive, etc.), but the total composition of the film or package should have a high level of a single material type (polyolefin or, in particular, polypropylene) to facilitate recycling. As used herein, the term “total composition” is used to describe the entire film structure or package. Any material, layer, or component connected to one another in any way is part of the total composition of the article. Multilayer packaging films may have a high level of polyolefin polymer (such as polypropylene polymer). The multilayer packaging films described herein, and any packages made therefrom, may be recyclable in a polypropylene recycling process when the article contains a large amount of polypropylene polymer.

[0079] The multilayer packaging films described herein may have a total composition containing at least 80% by weight, at least 85% by weight, at least 90% by weight, at least 95% by weight, at least 96% by weight, at least 97% by weight, at least 98% by weight, or at least 99% by weight of a polyolefin polymer, thereby promoting the recyclability of the film and / or packaging in which it is used. Non-polyolefin materials are minimized. The multilayer packaging films may also have other non-polyolefin materials, such as those located within the adhesive layer.

[0080] In a particular embodiment of the multilayer packaging film, the sealant film has a total composition containing at least 80% by weight, at least 85% by weight, at least 90% by weight, at least 95% by weight, at least 96% by weight, at least 97% by weight, at least 98% by weight, or at least 99% by weight of a polypropylene polymer.

[0081] By using the combination of film structural design elements described herein, more heat-resistant multilayer packaging films can be achieved. The films may be suitable for recycling in polyolefin-based recycling processes due to their high polyolefin content. The films may contain, or may not contain, low levels (i.e., 5% by weight or less) of materials such as polyester, polyamide, chlorine-containing polymers, and aluminum foil. As used herein, the term “not contained herein” means, on an atomic basis, that materials such as polyester, polyamide, chlorine-containing polymers, and aluminum foil constitute 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%.

[0082] The film may contain non-polyolefin polymers, such as those used in adhesive layers, but the amount of non-polyolefin polymers is minimized, generally comprising 10% by weight or less than 5% by weight of the total composition. The film may also contain non-polymer materials, such as barrier materials, but the amount of non-polymer materials is minimized, generally comprising 10% by weight or less than 5% by weight of the total composition.

[0083] The multilayer packaging film 20 can be formed into a package with or without other packaging components. For example, the multilayer packaging film 20 can be formed into a flexible stand-up pouch 200, as shown in Figure 5.

[0084] The present disclosure will now be described with reference to the following examples.

[0085] Examples and Data Several film structures were fabricated, as summarized in Table 1 below. All of the following films were fabricated on a three-layer co-extrusion line. Comparative Example 1 was unoriented, while the remaining exemplary films were oriented. The oriented films were fabricated with layer thicknesses of 45 / 90 / 45 and a 3x MDO to reach the indicated thicknesses. All oriented sealant films had final layer thicknesses of 15 microns for the sealing layer, 30 microns for the core layer, and 15 microns for the lamination layer. Comparative Example 1 had final layer thicknesses of 45 microns for the sealing layer, 90 microns for the core layer, and 45 microns for the lamination layer.

[0086] In the table below, Bormed TD109CF is a polypropylene terpolymer, Adflex Q 109 F is a random propylene heterophase copolymer, HC205TF is a nucleating polypropylene homopolymer, AB PP2049 is a polypropylene antiblock masterbatch, Moplen HP556E is a polypropylene homopolymer, Moplen EP310D HP is a low-flow polypropylene heterophase copolymer, Queo 1007 is an ethylene-based octene-1 plastomer, Queo 1001 is an ethylene-based octene-1 plastomer, Adsyl 7622 XCP is an advanced polyolefin, and PB8220 is a random copolymer of butene-1 with a moderate ethylene content.

[0087] [Table 1]

[0088] The sealant films shown in Table 1 above were tested to determine the seal curves at various temperatures. The sealing device settings are provided in Table 2 below, and the seal curves are provided in Table 3 below. The seal curves for Example 8 compared to Comparative Examples 1 and 2 are also shown in Figure 1A.

[0089] [Table 2]

[0090] [Table 3] JPEG2026516385000005.jpg250160 JPEG2026516385000006.jpg130160

[0091] As can be seen from Table 3 and Figure 1A, Comparative Example 1 provides a seal of approximately 3 N / 15 mm at 120°C. This film demonstrates how an unstretched film has a low SIT. Although the SIT is good, the tear performance is not good because it is not oriented.

[0092] Comparative Example 2 is an oriented version of Comparative Example 1. This film shows how the SIT increases when oriented.

[0093] Comparative Example 3 uses 100% PP terpolymer for sealing. This film does not exhibit sufficiently low SIT when using PP terpolymer alone.

[0094] Examples 4-7 each add 10% or 20% plastomer to the sealing layer. Example 8 adds 10% elastomer and 10% plastomer. Example 9 adds 20% polybutene-1. As can be seen from Table 3, Examples 4, 5, 7, 8, and 9 have a sealing strength of at least 4 N / 15 mm at a sealing onset temperature of 130°C or below. Example 6 also has a sealing strength approaching 4 N / 15 mm at 130°C and has a sealing onset temperature of 130°C-140°C. In contrast, Comparative Examples 2 and 3 have a weak seal at 130°C. These demonstrate that incorporating polybutene-1 or plastomer results in a favorable reduction of SIT.

[0095] Figure 1A further illustrates that orientation increases SIT from Comparative Example 1 (unoriented) to Comparative Example 2 (MDO). However, incorporating the claimed polymer, as in Example 8, results in a decrease in SIT compared to the MDO film of Comparative Example 2. Thus, orientation increases SIT, but incorporating the claimed polymer helps mitigate this increase in SIT.

[0096] Figure 1B shows that the tear strength of Example 8 is approximately three times lower than that of the unoriented reference material shown in Comparative Example 1. Similarly, Figure 1C shows that the tear resistance of the laminate is still more than twice as good in Example 8 compared to Comparative Example 1. In Figure 1C, the laminate OPP40 / MDO PP60 is used to simulate the final three-layer OPP / OPP / MDO PP structure. Thus, Figures 1B and 1C show that MDO films containing the claimed polymer, and laminates incorporating such MDO films, have superior tear performance compared to unoriented films and laminates incorporating such unoriented films.

[0097] Embodiments: Sealant film embodiment A: A sealant film comprising a sealing layer comprising a polypropylene terpolymer and one or more polymers selected from polybutene-1 or plastomer, a core layer comprising polypropylene, and a lamination layer comprising polypropylene, wherein the sealant film is a mechanically oriented (MDO) film comprising at least 90% by weight of polypropylene.

[0098] Sealant film embodiment B: The sealant film according to embodiment A, wherein the core layer comprises a polypropylene homopolymer.

[0099] Sealant film embodiment C: The sealant film according to embodiment B, wherein the core layer further comprises a heterogeneous polypropylene copolymer.

[0100] Sealant film embodiment D: A sealant film according to any one of the above-described sealant film embodiments, wherein the lamination layer comprises a heterogeneous polypropylene copolymer.

[0101] Sealant film embodiment E: A sealant film according to any one of the above-described sealant film embodiments, wherein the sealant film comprises a sealing layer in the range of 15 to 40% by weight, a core layer in the range of 70 to 20% by weight, and a lamination layer in the range of 15 to 40% by weight.

[0102] Sealant film embodiment F: A sealant film according to any one of the above-described sealant film embodiments, wherein the sealing layer comprises at least 20% by weight of polypropylene terpolymer.

[0103] Sealant film embodiment G: A sealant film according to any one of the above-described sealant film embodiments, wherein the terpolymer has a melting temperature in the range of 120 to 140°C.

[0104] Sealant film embodiment H: A sealant film according to any one of the above-described sealant film embodiments, wherein the sealant film provides a sealing strength of 4 N / 15 mm at a sealing temperature of 140 °C or less, as measured by ASTM F2029.

[0105] Sealant film embodiment I: A sealant film according to any one of the above-described sealant film embodiments, wherein the sealant film provides linear tearability in the flow direction.

[0106] Sealant film embodiment J: A sealant film according to any one of the above-described sealant film embodiments, wherein the sealant film provides a sealing strength of at least 10 N as measured by ASTM F2029.

[0107] Multilayer packaging film embodiment AA: A multilayer packaging film comprising a first base layer containing a polypropylene film and one of the sealant film embodiments laminated on the first base layer, wherein the multilayer packaging film contains at least 90% by weight of polypropylene.

[0108] Multilayer packaging film embodiment BB: The multilayer packaging film according to multilayer packaging film embodiment AA, further comprising a second base layer containing a polypropylene film.

[0109] Multilayer packaging film embodiment CC: A multilayer packaging film according to any one of the above-described multilayer packaging film embodiments, wherein one or both of the first base layer and the second base layer include a biaxially oriented polypropylene film (BOPP).

[0110] Multilayer packaging film embodiment DD: A multilayer packaging film according to any one of the above-described multilayer packaging film embodiments, wherein one or both of the first base layer and the second base layer include a barrier layer.

[0111] Multilayer packaging film embodiment EE: A multilayer packaging film according to any one of the above-described embodiments of a multilayer packaging film, wherein the multilayer packaging film provides linear tearability in the flow direction.

[0112] Embodiment FF of a multilayer packaging film: A multilayer packaging film according to any one of the above embodiments of a multilayer packaging film, wherein the multilayer packaging film provides a sealing strength of 4N / 15mm at a sealing start temperature of 140°C or lower.

[0113] Embodiment GG of a multilayer packaging film: A multilayer packaging film according to any one of the above embodiments of a multilayer packaging film, wherein the multilayer packaging film provides a sealing strength of at least 10N.

[0114] Retort pouch embodiment: A retort pouch formed from a multilayer packaging film according to any one of the multilayer packaging film embodiments.

[0115] Process embodiment: A process for producing a multilayer packaging film comprising the steps of co-extruding a sealant film comprising (i) a sealing layer comprising a polypropylene terpolymer and one or more polymers selected from polybutene-1 or plastomer, (ii) a core layer comprising polypropylene, and (iii) a lamination layer comprising polypropylene; oriented the sealant film in the flow direction; and laminating the oriented sealant film onto a first base layer comprising a polypropylene film, wherein the multilayer packaging film comprises at least 90% by weight of polypropylene.

Claims

1. A sealing layer comprising a polypropylene terpolymer and one or more polymers selected from polybutene-1 or plastomer, A core layer containing polypropylene, A sealant film comprising a lamination layer containing polypropylene, A sealant film which is a mechanically oriented (MDO) film containing at least 90% by weight of polypropylene.

2. The sealant film according to claim 1, wherein the core layer comprises a polypropylene homopolymer.

3. The sealant film according to claim 2, wherein the core layer further comprises a heterogeneous polypropylene copolymer.

4. The sealant film according to any one of claims 1 to 3, wherein the lamination layer comprises a heterogeneous polypropylene copolymer.

5. The sealant film according to any one of claims 1 to 4, wherein the sealant film comprises the sealing layer in a range of 15 to 40% by weight, the core layer in a range of 70 to 20% by weight, and the lamination layer in a range of 15 to 40% by weight.

6. A sealant film according to any one of claims 1 to 5, wherein the sealing layer comprises at least 20% by weight of polypropylene terpolymer.

7. The sealant film according to any one of claims 1 to 6, wherein the terpolymer has a melting temperature in the range of 120 to 140°C.

8. The sealant film according to any one of claims 1 to 7, wherein the sealant film provides a sealing strength of 4 N / 15 mm at a sealing temperature of 140 °C or less, as measured by ASTM F2029.

9. The sealant film according to any one of claims 1 to 8, wherein the sealant film provides linear tearability in the flow direction.

10. The sealant film according to any one of claims 1 to 9, wherein the sealant film provides a sealing strength of at least 10 N as measured by ASTM F2029.

11. A first base layer containing a polypropylene film, A multilayer packaging film comprising a sealant film according to any one of claims 1 to 10 laminated on the first base layer, A multilayer packaging film containing at least 90% by weight of polypropylene.

12. The multilayer packaging film according to claim 12, further comprising a second base layer containing a polypropylene film.

13. The multilayer packaging film according to claim 11 or claim 12, wherein one or both of the first base layer and the second base layer include a biaxially oriented polypropylene film (BOPP).

14. The multilayer packaging film according to any one of claims 11 to 13, wherein one or both of the first base layer and the second base layer include a barrier layer.

15. The multilayer packaging film according to any one of claims 11 to 14, wherein the multilayer packaging film provides linear tearability in the flow direction.

16. The multilayer packaging film according to any one of claims 11 to 15, wherein the multilayer packaging film provides a sealing strength of 4 N / 15 mm at a sealing start temperature of 140 °C or lower.

17. The multilayer packaging film according to any one of claims 11 to 15, wherein the multilayer packaging film provides a sealing strength of at least 10 N.

18. A retort pouch formed from a multilayer packaging film according to any one of claims 11 to 17.

19. A process for manufacturing multilayer packaging films, (i) a step of co-extruding a sealant film comprising a sealing layer comprising a polypropylene terpolymer and one or more polymers selected from polybutene-1 or plastomer, (ii) a core layer comprising polypropylene, and (iii) a lamination layer comprising polypropylene, The steps include orienting the sealant film in the flow direction, The process includes laminating the oriented sealant film onto a first base layer containing a polypropylene film, A process wherein the multilayer packaging film comprises at least 90% by weight of polypropylene.

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