Laminate for packaging

Abstract

Provided is a laminate for packaging, the laminate having good gas barrier performance even after retort sterilization treatment. The laminate comprises a gas barrier substrate layer 2 in which at least a gas barrier layer 4 is laminated on a substrate 3 composed of a thermoplastic resin, wherein after the retort sterilization treatment, the elastic modulus of the gas barrier layer 4 as measured using a SPM is less than 3.3 GPa.

Description

Packaging laminate

[0001] The present invention relates to a packaging laminate, and more particularly to a packaging laminate that has good gas barrier properties even after retort sterilization.

[0002] Conventionally, a packaging laminate having a gas barrier layer containing a metal alkoxide or the like laminated thereon has been known as a packaging material used for packaging foods, etc. (See, for example, Patent Document 1.) It is also known that retort sterilization is effective in enabling the storage of packaged foods, etc. at room temperature.

[0003] Japanese Patent Application Laid-Open No. 2020-37187

[0004] However, packaging laminates having a gas barrier layer laminated thereon have a problem in that the gas barrier performance is reduced by retort sterilization. The present inventors have conducted extensive research in light of this background technology and have completed the present invention.

[0005] The packaging laminate according to the present invention is a packaging laminate including a gas barrier substrate layer in which at least a gas barrier layer is laminated on a substrate made of a thermoplastic resin, and after the packaging laminate is subjected to retort sterilization treatment, the elastic modulus of the gas barrier layer measured using SPM is less than 3.3 GPa.

[0006] According to the present invention, it is possible to provide a packaging laminate that has good gas barrier properties even after retort sterilization.

[0007] 1 is an explanatory diagram schematically illustrating an example of a packaging laminate according to an embodiment of the present invention.

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is an explanatory diagram that schematically illustrates an example of a packaging laminate according to this embodiment.

[0009] In this embodiment, the packaging laminate 1 includes a gas barrier substrate layer 2 in which at least a gas barrier layer 4 is laminated on a substrate 3 made of a thermoplastic resin, and various layers can be laminated as needed on the gas barrier substrate layer 2. In the example shown in the figure, a sealant layer 6 is laminated on the gas barrier substrate layer 2 via an adhesive layer 5 laminated adjacent to the gas barrier layer 4, so that a bag-shaped package such as a packaging pouch can be made by heat sealing.

[0010] Furthermore, by ensuring that the elastic modulus of the gas barrier layer 4, as measured using SPM after retort sterilization, is less than 3.3 GPa, preferably 3.0 GPa or less, and more preferably 2.5 GPa or less, the packaging laminate 1 tends to have excellent gas barrier performance even after retort sterilization. The lower limit of the elastic modulus of the gas barrier layer 4 is not limited to this, but is preferably 0.1 GPa or more, and more preferably 0.5 GPa or more.

[0011] Furthermore, by controlling the elastic modulus of the gas barrier layer 4 and the ratio of the elastic modulus of the substrate 3 on which the gas barrier layer 4 is laminated, the packaging laminate 1 can exhibit superior gas barrier performance even after retort sterilization. In this case, by adjusting the ratio (E1 / E2) of the elastic modulus of the gas barrier layer 4 (E1) to the elastic modulus of the substrate 3 (E2) measured using SPM after retort sterilization to preferably 0.5 to 2.4, more preferably 0.7 to 2.0, and even more preferably 1.0 to 1.9, it is possible to alleviate the stress generated between the substrate 3 and the gas barrier layer 4, and to prevent a decrease in gas barrier performance even after retort sterilization.

[0012] The elastic modulus can be measured using an SPM as follows.

[0013] First, a slice cut from the packaging laminate 1 is embedded in an epoxy resin or the like. Next, a sample for observation is prepared by cutting the slice using a microtome equipped with a diamond knife, with the constituent layers of the packaging laminate 1 having a smooth cross section. By measuring this cross section, the elastic modulus of the constituent layers of the packaging laminate in its practical state, i.e., after retort sterilization, can be accurately measured.

[0014] Next, a scanning probe microscope (SPM) is used to observe the surface profile and align the sample, followed by measurement in quantitative nanomechanical mapping (PF-QNM) mode to obtain an elastic modulus image. The measurement area is 1.5 μm × 1.5 μm, and the measurement environment is room temperature and atmospheric air.

[0015] Furthermore, from the acquired elastic modulus image, a portion near the center of the thickness of the constituent layer to be measured is arbitrarily selected, and an elastic modulus line profile is obtained with an analysis range of 1 μm and a sampling interval of 3 nm. The average elastic modulus calculated from this profile is taken as the elastic modulus of the constituent layer. The elastic modulus obtained by this method can accurately measure the elastic modulus while eliminating the influence of adjacent layers, even when an extremely thin constituent layer with a thickness of 1 μm or less is the measurement target.

[0016] The substrate 3 may be a film obtained by forming a thermoplastic resin using an inflation method, a T-die method, or the like. From the viewpoint of heat resistance and mechanical strength, it is preferable to use a stretched film as the film. The stretching method is not particularly limited, and may be a tubular method or a tenter method, or may be uniaxial stretching, sequential biaxial stretching, or simultaneous biaxial stretching. In this case, the thermoplastic resin used for the substrate 3 is preferably an olefin-based resin, a polyester-based resin, a polyamide-based resin, or the like.

[0017] Examples of olefin-based resins include ethylene-based resins such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and copolymers of ethylene and an α-olefin other than ethylene; propylene-based resins such as polypropylene (homopolypropylene), random copolymers of propylene and ethylene, block copolymers of propylene and ethylene, and copolymers of propylene and an α-olefin other than propylene; α-olefin homopolymers such as cyclic olefin polymers (COP); and α-olefin copolymers such as cyclic olefin copolymers (COP). In this case, examples of the α-olefin include α-olefins having 2 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 3-methyl-1-butene, and 4-methyl-1-pentene.

[0018] Examples of polyester resins include polyethylene terephthalate resin, polybutylene terephthalate resin, and polyethylene naphthalate resin.

[0019] Examples of polyamide resins include nylon 6, nylon 6,6, nylon 6,10, nylon 11, and nylon 12.

[0020] Among these, from the viewpoint of heat resistance in retort sterilization, it is preferable to use a biaxially oriented film made of a propylene-based resin or a biaxially oriented film made of a polyethylene terephthalate resin for the substrate 3. In particular, when a propylene-based resin is used, a random copolymer is preferable from the viewpoint of transparency, a homopolymer is preferable when importance is placed on the rigidity and heat resistance of the package, and a block copolymer is preferable when importance is placed on the impact resistance of the package.

[0021] The α-olefins used as raw materials for olefin-based resins, such as ethylene and propylene, may be derived from conventional petroleum fuels, but may also be partially or entirely derived from plants. In this case, the use of olefin-based resins made from plant-derived raw materials can increase the biomass content. Furthermore, the olefin-based resin may be an α-olefin derived from chemical recycling, or may be partially or entirely derived from recycled olefin-based resins.

[0022] In order to enhance the recyclability of the packaging laminate 1, when these olefin-based resins are used for the substrate 3, it is preferable that they are contained in the thermoplastic resin in an amount of 80% by weight or more, and more preferably 90% by weight or more. In addition to the above olefin-based resins, as long as the high content of such olefin-based resins is not impaired, for example, ethylene vinyl compound copolymers such as ethylene vinyl acetate copolymer, ethylene vinyl alcohol copolymer, and ethylene vinyl chloride copolymer; styrene-based resins such as polystyrene, acrylonitrile styrene copolymer, ABS, and α-methylstyrene styrene copolymer; polyvinyl-based resins such as polyvinyl chloride, polyvinylidene chloride, vinyl chloride vinylidene chloride copolymer, polymethyl acrylate, and polymethyl methacrylate; polyamide-based resins such as nylon 6, nylon 6,6, nylon 6,10, nylon 11, and nylon 12; thermoplastic polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polycarbonate, polyphenylene oxide, polyimide resin, polyamide-imide resin, polyetherimide resin, fluororesin, allyl resin, polyurethane resin, cellulose resin, polysulfone resin, polyethersulfone resin, ketone resin, amino resin, polylactic acid, and the like may be contained.

[0023] The substrate 3 may have a single-layer structure or a multi-layer structure. The thickness of the substrate 3 is preferably 10 μm or more, more preferably 15 μm or more, and also preferably 100 μm or less, more preferably 50 μm or less, for example, 10 μm or more and 100 μm or less. A laminate including a stretched substrate having a thickness equal to or greater than the above lower limit has excellent heat resistance and mechanical strength, for example. A laminate including a stretched substrate having a thickness equal to or less than the above upper limit has excellent processability, for example.

[0024] Furthermore, in order to enhance the gas barrier performance of the gas barrier substrate layer 2, the substrate 3 can be provided with a vapor deposition film formed by depositing a metal such as aluminum, or a metal oxide such as silica, silicon carbide oxide, or alumina by physical vapor deposition such as sputtering, vacuum deposition, or ion plating, or chemical vapor deposition such as thermal CVD, plasma CVD, or photo CVD, and by laminating the gas barrier layer 4 described below, a packaging laminate 1 having excellent gas barrier performance can be obtained.

[0025] Such a vapor-deposited film may be provided directly on the surface of the substrate 3, but it is preferable to provide an anchor coat layer (AC layer) on the surface of the substrate 3 in order to improve the smoothness of the vapor-deposited film and its adhesion to the substrate 3. Methods for forming the AC layer include coating or co-extrusion of a hydrophilic resin such as polyester, polyethyleneimine, acrylic resin, polyamide, ethylene-vinyl alcohol copolymer, or polyurethane, or by surface modification treatment such as corona treatment, flame treatment, or plasma treatment. It is preferable to provide the vapor-deposited film on such an AC layer. When a vapor-deposited film is provided on the substrate 3, it is preferable to laminate the gas barrier layer 4 on top of the vapor-deposited film provided on the substrate 3.

[0026] The gas barrier layer 4 can be laminated as a layer containing at least a hydroxyl group-containing polymer and an inorganic material.

[0027] Examples of the hydroxyl group-containing polymer that can be used include polyvinyl alcohol, ethylene-vinyl alcohol copolymer, methyl cellulose, and carboxymethyl cellulose. Among these, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are preferred because of their excellent gas barrier properties.

[0028] Examples of inorganic materials that can be used include alkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane, as well as metal alkoxides containing metal atoms such as zirconium, titanium, aluminum, tin, lead, and borane. Of these, alkoxysilanes such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane are preferred, and hydrolysates of these metal alkoxides may also be used.

[0029] In addition to these metal alkoxides, for example, silane coupling agents such as vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyldimethoxysilane, and aqueous polyurethane resins can also be used.

[0030] The gas barrier layer 4 is preferably a layer containing at least polyvinyl alcohol and alkoxysilane.

[0031] A composition containing these compounds is applied to the substrate 3, the AC layer, or the vapor-deposited film by roll coating, spray coating, spin coating, or the like, and then condensed by a sol-gel method to form the gas barrier layer 4. During this process, the metal alkoxide such as alkoxysilane is hydrolyzed by the catalytic action of an acid or base, and the hydroxyl-containing hydrolysis products undergo dehydration condensation with each other to form siloxane bonds, etc., which are then copolymerized by dehydration condensation with a hydroxyl-containing polymer to form a three-dimensional crosslinked structure, thereby enabling the gas barrier performance to be exhibited well. The gas barrier layer 4 has structural units derived from a hydroxyl-containing polymer such as polyvinyl alcohol and structural units derived from an inorganic material such as alkoxysilane.

[0032] The thickness of the gas barrier layer 4 is preferably 0.05 μm or more, more preferably 0.10 μm or more, even more preferably 0.15 μm or more, and most preferably 0.20 μm or more, and is preferably 2 μm or less, more preferably 1 μm or less, even more preferably 0.8 μm or less, and most preferably 0.5 μm or less, for example, 0.05 μm or more and 2 μm or less.

[0033] The adhesive layer 5 is laminated adjacent to the gas barrier layer 4 and is provided as a layer for laminating the sealant layer 6 to the gas barrier substrate layer 2. For the adhesive layer 5, for example, a urethane resin adhesive or an epoxy resin adhesive can be used. These adhesives may be one-component or two-component, and may be solvent-based dry lamination adhesives or solventless adhesives, and may be made from biomass materials from an environmental perspective. When using the package for retort applications, it is preferable to use a two-component curing urethane resin adhesive or epoxy resin adhesive that is retort-resistant.

[0034] When using a urethane resin-based two-component curing adhesive containing a polyester polyol compound as a base and an isocyanate compound as a curing agent, if a large amount of residual isocyanate compound is used, the residual isocyanate compound tends to migrate to the gas barrier layer 4 and increase the crosslink density of the gas barrier layer 4. As a result, the flexibility required for hydration swelling and dehydration shrinkage during retort sterilization cannot be ensured, and cracks may occur in the gas barrier layer 4 after retort sterilization, potentially impairing its gas barrier performance. To avoid such problems, it is preferable to set the amount of isocyanate compound so that the amount of residual isocyanate compound is as small as possible. In this way, by setting the amount of isocyanate compound in the adhesive layer 5 adjacent to the gas barrier layer 4, it is possible to effectively prevent deterioration of the gas barrier performance due to destruction of the gas barrier layer 4.

[0035] The presence or absence of migration of the isocyanate compound into the gas barrier layer 4 can be confirmed by AFM-IR measurement, FT-IR measurement, Raman measurement, etc., based on the peak of the isocyanate group itself and the urethane bond formed by the crosslinking reaction derived from the isocyanate group.

[0036] In addition to setting the blending amount as described above, other ways to avoid the above-mentioned problems occurring in the gas barrier layer 4 include changing the type and modified form of the isocyanate compound of the curing agent. Examples of isocyanate compounds include aromatic isocyanate compounds such as tolylene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), and xylylene diisocyanate (XDI), and aliphatic isocyanate compounds such as hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI). These isocyanate compounds can be used as polyisocyanate compounds with increased molecular weight, such as adducts with trimethylolpropane, isocyanurates, and biurets. Considering retort sterilization, TDI, XDI, HDI, and IPDI are preferred, and a mixture of one or more of these compounds may also be used. By controlling the reaction rate and reaction ratio of these isocyanate compounds with the polyester polyol compound as the main component, it is possible to reduce the amount of residual isocyanate compounds, and this makes it possible to effectively prevent a decrease in gas barrier performance due to destruction of the gas barrier layer 4 after retort sterilization treatment.

[0037] Due to the migration of the isocyanate compound in the adhesive layer 5 to the gas barrier layer 4, the modulus of elasticity of the gas barrier layer 4 changes throughout a series of processes, from the step of laminating the adhesive layer 5 to the step after retort sterilization. For example, the modulus of elasticity of the gas barrier film before laminating the adhesive layer 5 is 1.6 GPa, as shown in Reference Example 2 described below. However, by laminating the adhesive layer 5, the modulus increases to 2.9 GPa, as shown in Reference Example 1 described below. Furthermore, when this laminate is subjected to retort sterilization, the modulus increases to 3.3 GPa, as shown in Comparative Example 1 described below, and the gas barrier performance is significantly reduced. This indicates that suppressing the increase in the modulus of elasticity before and after retort sterilization, i.e., keeping the modulus of elasticity after retort sterilization low, suppresses damage to the gas barrier layer 4. Furthermore, this indicates that in order to suppress the deterioration of gas barrier performance, it is important to consider the modulus of elasticity not only before retort sterilization but also after retort sterilization.

[0038] As described above, the sealant layer 6 is provided so that the packaging laminate 1 can be formed into a bag-shaped package such as a packaging pouch by heat sealing. For the sealant layer 6, a stretched or unstretched heat-sealable resin film made of an olefin-based resin such as polyethylene or polypropylene is preferably used. In this case, a conventional fossil fuel-derived olefin-based resin, a plant-derived olefin-based resin, or even a recycled olefin-based resin may be used. Among these olefin-based resins, a film made of a propylene-based resin is preferably used for the sealant layer from the viewpoint of heat resistance in retort sterilization treatment.

[0039] The sealant layer 6 can be provided by applying the adhesive used for the adhesive layer 5 to the gas barrier layer 4 by a dry lamination method or the like, and then laminating a heat-sealable resin film to the gas barrier substrate layer 2. In order to improve the recyclability of the packaging laminate 1, it is preferable to use a heat-sealable resin film made of an olefin-based resin for the sealant layer 6, and the content of the olefin-based resin in the packaging laminate 1 (the weight of the olefin-based resin used for the sealant layer 6 and the substrate 3 relative to the total weight of the packaging laminate 1) is preferably 80% by weight or more, more preferably 85% by weight or more, even more preferably 88% by weight or more, and particularly preferably 90% by weight or more. A packaging product produced using such a packaging laminate 1 has excellent recyclability, for example, and the upper limit of the content of olefin-based resin relative to the total weight of the resin material contained in the packaging laminate 1 is not particularly limited, but may be, for example, 99 wt %, 98 wt %, 97 wt %, 96 wt %, 95 wt %, 94 wt %, 93 wt %, or 92 wt %.

[0040] By using the same type of thermoplastic resin for the substrate 3 and sealant layer 6 used in the packaging laminate 1, a monomaterial packaging material can be obtained that is essentially composed of a single material. Such monomaterial packaging materials are preferable because they tend to reduce the environmental impact. In this case, from the viewpoint of heat resistance in retort sterilization treatment, it is particularly preferable that the packaging laminate 1 uses a biaxially oriented polypropylene film for the substrate 3 and a non-oriented polypropylene film for the sealant layer 6.

[0041] The layer configuration of the packaging laminate 1 is not limited to these, but examples include biaxially oriented polypropylene base layer / AC layer / vapor-deposited film / gas barrier layer / adhesive layer / unstretched polypropylene sealant layer; biaxially oriented polypropylene base layer / adhesive layer / gas barrier layer / AC layer / biaxially oriented polypropylene base layer / adhesive layer / unstretched polypropylene sealant layer; biaxially oriented polypropylene base layer / adhesive layer / biaxially oriented polypropylene base layer / AC layer / gas barrier layer / adhesive layer / unstretched polypropylene sealant layer; biaxially oriented polypropylene base layer / adhesive layer / biaxially oriented polypropylene base layer / AC layer / vapor-deposited film / gas barrier layer / adhesive layer / biaxially oriented polypropylene base layer / adhesive layer / unstretched polypropylene sealant layer; bi ... and the like. Furthermore, these layer structures may have functional layers such as a print layer, a light-shielding layer, a surface protection layer, and a surface heat-resistant layer on the surface or between layers, as required.

[0042] To further enhance the gas barrier properties, the packaging laminate 1 may have a layer structure in which multiple gas barrier substrate layers 2 are laminated. In such a case, the gas barrier layers 4 in each gas barrier substrate layer 2 may be formed using materials of the same composition, or may be formed using materials of different compositions. Furthermore, the packaging laminate 1 may have a layer structure in which the gas barrier layer 4 in the gas barrier substrate layer 2 serves as a first gas barrier layer and includes a second gas barrier layer that is different from the first gas barrier layer. For example, a gas barrier coating agent may be applied to a film similar to that used for the substrate 3 in the gas barrier substrate layer 2, and this may be laminated on the gas barrier substrate layer 2.

[0043] The present invention will be described in more detail below with reference to specific examples.

[0044] <Gas barrier substrate layer> A gas barrier film used for the gas barrier substrate layer was prepared by laminating, in this order, an AC layer, a vapor-deposited film layer mainly composed of aluminum oxide, and a gas barrier layer made of a polycondensate of polyvinyl alcohol and tetraethoxysilane on one side of a biaxially stretched polypropylene film as the substrate. The thickness of this gas barrier film was 20 μm.

[0045] <Adhesive Layer> The following two-component curing adhesives composed of a main component and a curing agent were prepared as adhesives for use in the adhesive layer. In preparing these two-component curing adhesives, adhesive A was prepared with a mass ratio of main component (a):curing agent (a) of 8:1, adhesive B was prepared with a mass ratio of main component (a):curing agent (a) of 12:1, adhesive C was prepared with a mass ratio of main component (a):curing agent (a) of 32:1, adhesive D was prepared with a mass ratio of main component (a):curing agent (b) of 8.2:1, and adhesive E was prepared with a mass ratio of main component (b):curing agent (c) of 10:1. Main component (a): hydroxyl-terminated urethane resin (aliphatic ester-based monomer composition containing at least ethylene glycol and isophthalic acid; polystyrene-equivalent molecular weight Mw=18,000) / solid content 50% by mass Main component (b): hydroxyl-terminated urethane resin (aliphatic ester-based monomer composition containing at least ethylene glycol, 1,6-hexanediol, isophthalic acid, and terephthalic acid; polystyrene-equivalent molecular weight Mw=11,000) / solid content 60% by mass Curing agent (a): isocyanate-terminated urethane resin (aliphatic) containing isocyanate species, isophorone diisocyanate (IPDI) and m-xylylene diisocyanate (XDI) in a molar ratio of IPDI:XDI=1:1 / solid content 75% by mass Curing agent (b): Isocyanate group-terminated urethane resin (aliphatic) containing m-xylylene diisocyanate (XDI) as the isocyanate species / solid content 74% by mass Curing agent (c): Isocyanate group-terminated urethane resin (aliphatic) that is a mixture of isophorone diisocyanate (IPDI) and m-xylylene diisocyanate (XDI) as the isocyanate species, containing more XDI than IPDI / solid content 55% by mass

[0046] <Sealant Layer> As a heat-sealable resin film used for the sealant layer, an unstretched polypropylene film (Torayfan ZK500, manufactured by Toray Advanced Film Co., Ltd.) with one side hydrophilically treated was prepared. The thickness of this film was 70 μm.

[0047] <Second Gas Barrier Layer> As a second gas barrier film including a second gas barrier layer different from the gas barrier layer (first gas barrier layer) in the gas barrier base layer, a biaxially stretched polypropylene film (Pylen Film-OT, P2261, manufactured by Toyobo Co., Ltd.) was prepared by coating one side of the film with a gas barrier coating agent (STRADER, NOH3000, manufactured by Sumitomo Chemical Co., Ltd.) to a thickness of 0.3 μm.

[0048] [Example 1] The coating solution of adhesive B had a solid content of about 4 g / m ２ The gas barrier layer side of the gas barrier film was then bonded to the hydrophilic treated side of the unstretched polypropylene film by dry lamination. The resulting laminate was then cured at 50°C for 4 days to obtain a laminate. The olefin resin content of the resulting laminate was 95% by weight.

[0049] The resulting laminate was cut into two pieces measuring 170 mm x 130 mm, and the three sides except for the opening were sealed using an impulse sealer (manufactured by Fuji Impulse Co., Ltd.) to form a flat pouch. 200 g of water was then poured into the opening, and the opening was heat-sealed to produce a water-filled package. Each side had a 5 mm seal width.

[0050] The prepared package containing water was subjected to shower-type retort sterilization at 121°C for 30 minutes.

[0051] <Elastic Modulus Measurement> 1. Preparation of Cross-Sectional Sample of Laminate A piece of film was cut out from the package after retort sterilization and embedded in epoxy resin. Next, a cross-section sample was prepared by freeze-cutting with a diamond knife using an ultramicrotome (ULTRACUT S, manufactured by LEICA) and a cryosystem (FCS, manufactured by LEICA). 2. Measurement Method After measuring the surface topography using a scanning probe microscope (SPM, MultiMode 8 scanning probe microscope, manufactured by BRUKER AXS), a DMT elastic modulus image was obtained by measurement in quantitative nanomechanical mapping (PF-QNM) mode under the following conditions: Measurement area: 1.5 μm × 1.5 μm Resolution: 512 × 512 pixels Temperature: Room temperature Humidity: In air 3. Using the analysis software attached to the SPM device, an analysis range of 1 μm and a sampling interval of 3 nm were used to obtain an elastic modulus profile on any line of each layer from the obtained elastic modulus image, and the average elastic modulus of the substrate and gas barrier layer of the gas barrier substrate layer was calculated from this elastic modulus profile. The results are shown in Table 1.

[0052] <Oxygen permeability measurement> The oxygen permeability of the package after retort sterilization was measured using an oxygen permeability measuring device (OX-TRAN2 / 22L manufactured by MOCON Corporation). The measurement conditions were a temperature of 23°C and a relative humidity of 60%. The results are shown in Table 1.

[0053] [Example 2] For a package made of a laminate obtained in the same manner as in Example 1 except that adhesive C was used, elastic modulus measurement and oxygen permeability measurement were carried out after retort sterilization treatment. The results are shown in Table 1.

[0054] [Example 3] For a package made of a laminate obtained in the same manner as in Example 1 except that adhesive D was used, elastic modulus measurement and oxygen permeability measurement were carried out after retort sterilization treatment. The results are shown in Table 1.

[0055] [Example 4] For a package made of a laminate obtained in the same manner as in Example 1 except that adhesive E was used, elastic modulus measurement and oxygen permeability measurement were carried out after retort sterilization treatment. The results are shown in Table 1.

[0056] [Example 5] The coating solution of adhesive E was prepared with a solid content of about 4 g / m ２ The gas barrier layer side of the gas barrier film and the hydrophilic treated side of the unstretched polypropylene film were bonded together by dry lamination, and similarly, the coating liquid of adhesive E was applied in an amount of about 4 g / m ２ The gas barrier coating agent was applied using a bar coater so that the thickness of the second gas barrier film was 100 μm, and the side of the second gas barrier film coated with the gas barrier coating agent was placed on the gas barrier film and laminated by dry lamination. This was then cured at 50°C for 4 days to obtain a laminate. The olefin resin content of the obtained laminate was 93 wt%. The elastic modulus and oxygen permeability of the package made of this laminate were measured after retort sterilization. The results are shown in Table 1.

[0057] [Example 6] The coating solution of adhesive E was prepared with a solid content of about 4 g / m ２ The gas barrier layer side of the gas barrier film and the side of the second gas barrier film coated with the gas barrier coating agent were then bonded together by dry lamination, and similarly, a coating solution of adhesive E was applied in an amount of about 4 g / m2 in a solid content. ２ The unstretched polypropylene film was coated with a bar coater so that the hydrophilic side was coated onto the gas barrier film by dry lamination. The film was then cured at 50°C for 4 days to obtain a laminate. The olefin resin content of the obtained laminate was 93% by weight. The elastic modulus and oxygen permeability of the packaged product made of this laminate were measured after retort sterilization. The results are shown in Table 1.

[0058] Comparative Example 1 A package made of a laminate obtained in the same manner as in Example 1 except that adhesive A was used was subjected to measurements of elastic modulus and oxygen permeability after retort sterilization. The results are shown in Table 1.

[0059] Furthermore, the laminate obtained in this comparative example was subjected to elastic modulus measurement and oxygen permeability measurement in the same manner as in Reference Example 1 before being subjected to retort sterilization, and the results are shown in Table 2.

[0060] The gas barrier film used in this example was also subjected to measurements of elastic modulus and oxygen permeability in the same manner as in Reference Example 2, and the results are shown in Table 2.

[0061]

[0062] These results confirm that when the elastic modulus of the gas barrier layer after retort sterilization is low, the oxygen permeability is low, i.e., the gas barrier performance is good. Furthermore, it can be confirmed that Example 5, in which the first gas barrier layer and the second gas barrier layer are not laminated facing each other, has better gas barrier performance than Example 6, in which the first gas barrier layer and the second gas barrier layer are laminated facing each other.

[0063]

[0064] The results of Reference Example 1 and Comparative Example 1 confirm that retort sterilization increases the elastic modulus of the gas barrier layer and reduces the gas barrier performance. On the other hand, in Example 2, which used Adhesive C with a reduced amount of curing agent, the elastic modulus of the gas barrier layer decreases after retort sterilization, confirming that the deterioration of gas barrier performance is suppressed. From these results, it is presumed that the amount of the isocyanate compound in the curing agent affects the elastic modulus of the gas barrier layer during retort sterilization, resulting in a difference in the elastic modulus of the gas barrier layer after retort sterilization.

[0065] The present invention has been described above by showing preferred embodiments, but it goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention.

[0066] For example, according to the present invention, a packaging laminate 1 having good gas barrier performance even after retort sterilization can be provided, and the packaging laminate 1 can also be used for boiling sterilization, microwave heating, and other purposes in addition to retort sterilization. The contents filled into the packaging laminate 1 are not particularly limited and may be food or non-food. Furthermore, the contents may be in the form of a liquid, a viscous substance, or a powder.

[0067] DESCRIPTION OF SYMBOLS 1 Packaging laminate 2 Gas barrier substrate layer 3 Substrate 4 Gas barrier layer 5 Adhesive layer 6 Sealant layer

Claims

1. A packaging laminate comprising a gas barrier substrate layer in which at least a gas barrier layer is laminated on a substrate made of a thermoplastic resin, wherein the elastic modulus of the gas barrier layer measured using an SPM after the packaging laminate is subjected to retort sterilization is less than 3.3 GPa.

2. The packaging laminate according to claim 1, wherein the gas barrier layer contains at least a hydroxyl group-containing polymer and an inorganic material.

3. The packaging laminate according to claim 1, wherein a sealant layer is laminated on the gas barrier substrate layer via an adhesive layer laminated adjacent to the gas barrier layer.

4. The packaging laminate according to claim 3, wherein the adhesive layer is made of a urethane resin adhesive.

5. The packaging laminate according to claim 1, wherein the substrate is made of an olefin-based resin.

6. The packaging laminate according to claim 3, wherein the substrate and the sealant layer are made of an olefin-based resin, and the weight of the olefin-based resin in the total weight of the packaging laminate is 80 mass % or more.

7. The packaging laminate according to claim 6, wherein the substrate is made of a biaxially oriented polypropylene film and the sealant layer is made of a non-oriented polypropylene film.

8. A packaging product comprising the packaging laminate according to any one of claims 1 to 7.

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