Laminate and packaging bag

Abstract

To provide a laminate capable of being subjected to high-temperature retort treatment when formed into a packaging bag even if mainly composed of a polyolefin-based film.SOLUTION: There is provided a laminate which comprises a first base material layer, a second base material layer and a sealant layer in this order, wherein all of the first base material layer, the second base material layer and the sealant layer contain a polyolefin film, the polyolefin film of the first base material layer and the second base material layer comprise an inorganic oxide layer on at least one surface and the heat shrinkage rate in the traveling direction after heating at 120°C for 15 minutes in each of the first base material layer, the second base material layer and the sealant layer satisfies the following expressions: the heat shrinkage rate of the second base material layer≤5% (Expression 1), the heat shrinkage rate of the second base material layer≥the heat shrinkage rate of the first base material layer (Expression 2) and the heat shrinkage rate of the second base material layer≥the heat shrinkage rate of the sealant layer (Expression 3).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a laminate and a packaging bag. [Background technology]

[0002] BACKGROUND ART Laminates are known that include a biaxially oriented PET (polyethylene terephthalate) film, which has excellent heat resistance and toughness, as a base film, and a polyolefin film such as polyethylene or polypropylene as a sealant layer (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-178357 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, growing environmental awareness stemming from the problem of marine plastic waste has led to calls for further improvements in the efficiency of the sorted collection and recycling of plastic materials. In other words, there is a growing demand for mono-materialization of packaging laminates, which have traditionally been made by combining various different materials to achieve high performance.

[0005] To achieve a mono-material laminate, the constituent films must be made of the same material. However, if a laminate is made using polyolefin-based films, the resulting packaging bag may not be able to withstand high-temperature retort treatment.

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a laminate that can be subjected to high-temperature retort treatment when made into a packaging bag, even when the laminate is mainly composed of a polyolefin-based film. Another object of the present invention is to provide a packaging bag using the laminate. [Means for solving the problem]

[0007] One aspect of the present invention provides a laminate comprising a first base material layer, a second base material layer, and a sealant layer in this order, wherein the first base material layer, the second base material layer, and the sealant layer all comprise a polyolefin film, and the polyolefin film of the first base material layer or the second base material layer has an inorganic oxide layer on at least one surface, and the heat shrinkage rate in the machine direction (MD) of each of the first base material layer, the second base material layer, and the sealant layer after heating at 120°C for 15 minutes satisfies the following formula: Heat shrinkage rate of the second base layer ≦ 5% (Equation 1) Heat shrinkage rate of the second base material layer ≧ Heat shrinkage rate of the first base material layer (Equation 2) Heat shrinkage rate of the second base layer ≧ Heat shrinkage rate of the sealant layer (Equation 3) (Heat shrinkage rate (%) = (length in the running direction before heating - length in the running direction after heating) / length in the running direction before heating x 100)

[0008] In one embodiment, the heat shrinkage rate may satisfy the following formula: Heat shrinkage rate of the second base layer - Heat shrinkage rate of the first base layer ≥ 0.3% (Equation 4) Heat shrinkage rate of the second base layer - Heat shrinkage rate of the sealant layer ≥ 0.5% (Equation 5)

[0009] In one embodiment, the heat shrinkage rate may satisfy the following formula: Heat shrinkage rate of sealant layer ≦ 2% (Equation 6)

[0010] In one embodiment, the polyolefin film of the first base layer or the second base layer has the inorganic oxide layer on at least one surface and a gas barrier coating layer on the inorganic oxide layer, and the gas barrier coating layer may be formed using a composition for forming a gas barrier coating layer containing at least one selected from the group consisting of a hydroxyl group-containing polymer compound, a metal alkoxide, a silane coupling agent, and a hydrolyzate thereof.

[0011] In one embodiment, the inorganic oxide layer may include silicon oxide.

[0012] In one embodiment, the laminate may be for use in a retort pouch.

[0013] Another aspect of the present invention provides a packaging bag produced by forming the above-described laminate into a bag. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a laminate that can be subjected to high-temperature retort treatment when made into a packaging bag, even when the laminate is mainly composed of a polyolefin-based film.Furthermore, according to the present invention, it is possible to provide a packaging bag using the laminate. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a laminate according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Preferred embodiments of the present disclosure will be described in detail below, with reference to the drawings where appropriate. In the drawings, identical or corresponding parts are designated by the same reference numerals, and duplicate explanations will be omitted. Furthermore, the dimensional ratios of the drawings are not limited to those shown.

[0017] <Laminate> FIG. 1 is a schematic cross-sectional view showing a laminate according to one embodiment. The laminate 100 shown in FIG. 1 comprises a first substrate layer 11, a second substrate layer 12, and a sealant layer 13, in this order. The first substrate layer 11 and the second substrate layer 12, and the second substrate layer 12 and the sealant layer 13 may each be bonded with an adhesive layer S. The first substrate layer, the second substrate layer, and the sealant layer all comprise a polyolefin film. The polyolefin film of the first substrate layer or the second substrate layer comprises an inorganic oxide layer on at least one surface to improve gas barrier properties against, for example, water vapor and oxygen. Because a polyolefin film comprising an inorganic oxide layer has gas barrier properties, such a first substrate layer or second substrate layer can be referred to as a gas barrier substrate layer. Each layer will be described below.

[0018] [First base layer 11] The first base layer is a film that serves as one of the supports and includes a polyolefin film. The first base layer may be made of a polyolefin film. Examples of polyolefin films include polyethylene film (PE), polypropylene film (PP), and polybutene film (PB). Examples of polyolefin films include acid-modified polyolefin films obtained by graft-modifying polyolefin with unsaturated carboxylic acid, acid anhydride of unsaturated carboxylic acid, ester of unsaturated carboxylic acid, etc.

[0019] The polyolefin film constituting the first base layer may be a stretched film or a non-stretched film. However, from the viewpoints of impact resistance, heat resistance, water resistance, dimensional stability, etc., the polyolefin film may be a stretched film. This makes it possible to more suitably use the laminate in applications that require retort treatment or boiling treatment. The stretching method is not particularly limited, and any method may be used, such as inflation stretching, uniaxial stretching, or biaxial stretching, as long as it can provide a dimensionally stable film.

[0020] The thickness of the polyolefin film is not particularly limited and can be set to 6 to 200 μm depending on the application, but may be 9 to 50 μm or 12 to 38 μm from the viewpoint of obtaining excellent impact resistance and excellent gas barrier properties.

[0021] The polyolefin film may be subjected to various pretreatments such as corona treatment, plasma treatment, and flame treatment on its lamination surface, as long as the barrier performance is not impaired, or may be provided with a coating layer such as an easy-adhesion layer.

[0022] (adhesion layer) When the polyolefin film has an inorganic oxide layer, an adhesive layer (anchor coat layer) may be provided on the surface of the polyolefin film on which the inorganic oxide layer is to be laminated. The adhesive layer is provided on the polyolefin film, and can achieve two effects: improving the adhesion performance between the polyolefin film and the inorganic oxide layer, and improving the smoothness of the polyolefin film surface. The improved smoothness makes it easier to form the inorganic oxide layer uniformly without defects, and thus makes it easier to exhibit high barrier properties. The adhesive layer can be formed using an anchor coat agent.

[0023] Examples of anchor coating agents include polyester-based polyurethane resins, polyether-based polyurethane resins, etc. As the anchor coating agent, polyester-based polyurethane resins are preferred from the viewpoints of heat resistance and interlayer adhesive strength.

[0024] The thickness of the adhesive layer is not particularly limited, but is preferably in the range of 0.01 to 5 μm, more preferably in the range of 0.03 to 3 μm, and particularly preferably in the range of 0.05 to 2 μm. If the thickness of the adhesive layer is equal to or greater than the lower limit, more sufficient interlayer adhesive strength tends to be obtained, while if the thickness is equal to or less than the upper limit, desired gas barrier properties tend to be easily exhibited.

[0025] The method for applying the adhesive layer to the polyolefin film can be any known application method without any particular limitation, and examples thereof include a dipping method, a method using a spray, a coater, a printer, a brush, etc. In addition, examples of the types of coaters and printers used in these methods and the application methods thereof include gravure coaters such as direct gravure, reverse gravure, kiss reverse gravure, and offset gravure, reverse roll coaters, microgravure coaters, coaters combined with a chamber doctor, air knife coaters, dip coaters, bar coaters, comma coaters, and die coaters.

[0026] The amount of adhesive layer applied is 1m after applying and drying the anchor coating agent. 2 Mass per unit is 0.01 to 5 g / m 2 It is preferable that the density is 0.03 to 3 g / m 2 It is more preferable that the thickness is 1m after the anchor coating agent is applied and dried. 2 When the mass per unit area is equal to or greater than the lower limit, film formation tends to be sufficient, whereas when the mass per unit area is equal to or less than the upper limit, the film tends to be sufficiently dried and the solvent tends not to remain.

[0027] The method for drying the adhesive layer is not particularly limited, but examples thereof include natural drying, drying in an oven set at a predetermined temperature, and using a dryer attached to the coater, such as an arch dryer, floating dryer, drum dryer, infrared dryer, etc. Furthermore, the drying conditions can be appropriately selected depending on the drying method, and for example, in the method of drying in an oven, drying at a temperature of 60 to 100°C for about 1 second to 2 minutes is preferred.

[0028] Instead of the polyurethane resin, a polyvinyl alcohol resin can be used for the adhesive layer. The polyvinyl alcohol resin may be any resin having a vinyl alcohol unit formed by saponifying a vinyl ester unit, such as polyvinyl alcohol (PVA) or ethylene-vinyl alcohol copolymer (EVOH).

[0029] Examples of PVA include resins prepared by homopolymerizing vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versatate, followed by saponification. PVA may also be modified PVA, which has been copolymerized or post-modified. Modified PVA can be obtained, for example, by copolymerizing a vinyl ester with an unsaturated monomer copolymerizable with the vinyl ester, followed by saponification. Examples of unsaturated monomers copolymerizable with vinyl esters include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxyl-containing α-olefins such as 3-buten-1-ol, 4-pentyn-1-ol, and 5-hexen-1-ol; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, and undecylenic acid; nitriles such as acrylonitrile and methacrylonitrile; diacetone acrylamide, acrylic acid, and the like. olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid; vinyl compounds such as alkyl vinyl ether, dimethyl allyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxane, glycerin monoallyl ether, and 3,4-diacetoxy-1-butene; vinylidene chloride, 1,4-diacetoxy-2-butene, and vinylene carbonate.

[0030] The degree of polymerization of PVA is preferably 300 to 3000. If the degree of polymerization is less than 300, the barrier properties tend to decrease, while if it exceeds 3000, the viscosity becomes too high and the coating suitability tends to decrease. The saponification degree of PVA is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 99 mol% or more. The saponification degree of PVA may be 100 mol% or less, or 99.9 mol% or less. The polymerization degree and saponification degree of PVA can be measured in accordance with the method described in JIS K 6726 (1994).

[0031] EVOH is generally obtained by saponifying a copolymer of ethylene and an acid vinyl ester such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, or vinyl versatate.

[0032] The degree of polymerization of EVOH is preferably 300 to 3000. If the degree of polymerization is less than 300, the barrier properties tend to decrease, while if it exceeds 3000, the viscosity becomes too high and the coatability tends to decrease. The saponification degree of the vinyl ester component of EVOH is preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 99 mol% or more. The saponification degree of EVOH may be 100 mol% or less, or 99.9 mol% or less. The saponification degree of EVOH is determined by nuclear magnetic resonance (H-NMR) measurement, from the peak area of ​​the hydrogen atoms contained in the vinyl ester structure and the peak area of ​​the hydrogen atoms contained in the vinyl alcohol structure.

[0033] The ethylene unit content of EVOH is 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, and particularly preferably 25 mol% or more. The ethylene unit content of EVOH is preferably 65 mol% or less, more preferably 55 mol% or less, and even more preferably 50 mol% or less. When the ethylene unit content is 10 mol% or more, good gas barrier properties or dimensional stability can be maintained under high humidity conditions. On the other hand, when the ethylene unit content is 65 mol% or less, good gas barrier properties can be achieved. The ethylene unit content of EVOH can be determined by NMR.

[0034] When a polyvinyl alcohol resin is used as the adhesive layer, the adhesive layer may be formed by coating a polyvinyl alcohol resin solution or by multi-layer extrusion.

[0035] (inorganic oxide layer) When the polyolefin film has an inorganic oxide layer, examples of the inorganic oxide contained in the inorganic oxide layer include aluminum oxide, silicon oxide, magnesium oxide, and tin oxide. From the viewpoint of transparency and barrier properties, the inorganic oxide may be selected from the group consisting of aluminum oxide, silicon oxide, and magnesium oxide. Furthermore, from the viewpoint of excellent tensile stretchability during processing, it is preferable that the inorganic oxide layer be a layer using silicon oxide. By using an inorganic oxide layer, high barrier properties can be obtained with a very thin layer that does not affect the recyclability of the laminate.

[0036] The O / Si ratio of the inorganic oxide layer is desirably 1.7 or higher. When the O / Si ratio is 1.7 or higher, the content of metallic Si is suppressed, making it easier to achieve good transparency. Furthermore, the O / Si ratio is preferably 2.0 or lower. When the O / Si ratio is 2.0 or lower, the crystallinity of SiO is increased, preventing the inorganic oxide layer from becoming too hard and achieving good tensile strength. This makes it possible to suppress the occurrence of cracks in the inorganic oxide layer when laminating a gas barrier coating layer. Furthermore, even after forming into a packaging bag, polyolefin films may shrink due to heat during boiling or retort treatment. However, when the O / Si ratio is 2.0 or lower, the inorganic oxide layer can easily follow this shrinkage, making it possible to suppress a decrease in barrier properties. To more fully achieve these effects, the O / Si ratio of the inorganic oxide layer is preferably 1.75 to 1.9, more preferably 1.8 to 1.85.

[0037] The O / Si ratio of the inorganic oxide layer can be determined by X-ray photoelectron spectroscopy (XPS). For example, an X-ray photoelectron spectrometer (manufactured by JEOL Ltd., product name: JPS-90MXV) is used as the measurement device, and measurements can be performed using a non-monochromated MgKα (1253.6 eV) X-ray source with an X-ray output of 100 W (10 kV-10 mA). For quantitative analysis to determine the O / Si ratio, relative sensitivity factors of 2.28 for O1s and 0.9 for Si2p can be used.

[0038] The thickness of the inorganic oxide layer is preferably 10 nm or more and 50 nm or less. A thickness of 10 nm or more can provide sufficient water vapor barrier properties. Furthermore, a thickness of 50 nm or less can prevent cracks from occurring due to deformation caused by internal stress in the thin film, thereby preventing a decrease in water vapor barrier properties. Note that a thickness exceeding 50 nm is undesirable from an economic standpoint, as it increases costs due to an increase in the amount of material used and a longer film formation time. From the same viewpoint as above, the thickness of the inorganic oxide layer is more preferably 20 nm or more and 40 nm or less.

[0039] The inorganic oxide layer can be formed, for example, by vacuum deposition. Vacuum deposition can be performed using physical vapor deposition or chemical vapor deposition. Examples of physical vapor deposition include, but are not limited to, vacuum deposition, sputtering, and ion plating. Examples of chemical vapor deposition include, but are not limited to, thermal CVD, plasma CVD, and photo-CVD.

[0040] In the vacuum film formation, resistance heating vacuum deposition, EB (Electron Beam) heating vacuum deposition, induction heating vacuum deposition, sputtering, reactive sputtering, dual magnetron sputtering, plasma enhanced chemical vapor deposition (PECVD), and the like are particularly preferably used. However, in terms of productivity, vacuum deposition is currently the most superior. As a heating means for vacuum deposition, it is preferable to use any of the electron beam heating method, resistance heating method, and induction heating method.

[0041] (Gas barrier coating layer) The polyolefin film may have a gas barrier coating layer on the inorganic oxide layer, the gas barrier coating layer being formed using a gas barrier coating layer-forming composition containing at least one selected from the group consisting of a hydroxyl group-containing polymer compound, a metal alkoxide, a silane coupling agent, and a hydrolyzate thereof.

[0042] The gas barrier coating layer is a coating layer with gas barrier properties and is formed using a composition for forming a gas barrier coating layer (hereinafter also referred to as a coating agent) whose main component is an aqueous solution or a water / alcohol mixed solution containing at least one selected from the group consisting of a hydroxyl-containing polymeric compound, a metal alkoxide, a silane coupling agent, and their hydrolysates. To maintain sufficient gas barrier properties after hot water treatment such as retort treatment, the coating agent preferably contains at least a silane coupling agent or its hydrolysate, more preferably at least one selected from the group consisting of a hydroxyl-containing polymeric compound, a metal alkoxide, and their hydrolysates, and a silane coupling agent or its hydrolysate, and even more preferably a hydroxyl-containing polymeric compound or its hydrolysate, a metal alkoxide or its hydrolysate, and a silane coupling agent or its hydrolysate. The coating agent can be prepared, for example, by mixing a metal alkoxide and a silane coupling agent directly, or after prior hydrolysis, with a solution of a hydroxyl-containing polymeric compound, which is a water-soluble polymer, dissolved in an aqueous solvent (water or a water / alcohol mixture).

[0043] Each component contained in the coating agent for forming the gas barrier coating layer will be described in detail. Examples of hydroxyl group-containing polymer compounds used in the coating agent include polyvinyl alcohol, polyvinylpyrrolidone, starch, methyl cellulose, carboxymethyl cellulose, and sodium alginate. Among these, polyvinyl alcohol (PVA) is preferred when used in the coating agent for the gas barrier coating layer, as it provides particularly excellent gas barrier properties.

[0044] From the viewpoint of obtaining excellent gas barrier properties, the gas barrier coating layer is preferably formed from a composition containing at least one selected from the group consisting of metal alkoxides represented by the following general formula (I) and hydrolysates thereof: M(OR 1 ) m (R 2 ) n-m …(I) In the above general formula (I), R 1 and R 2 are each independently a monovalent organic group having 1 to 8 carbon atoms, and are preferably an alkyl group such as a methyl group or an ethyl group. M represents an n-valent metal atom such as Si, Ti, Al, or Zr. m is an integer from 1 to n. 1 or R 2 If there are multiple, R 1 Comrades or R 2 They may be the same or different.

[0045] Specific examples of metal alkoxides include tetraethoxysilane [Si(OC2H5)4], triisopropoxyaluminum [Al(O-2'-C3H7)3], etc. Tetraethoxysilane and triisopropoxyaluminum are preferred because they are relatively stable in aqueous solvents after hydrolysis.

[0046] The silane coupling agent includes a compound represented by the following general formula (II). Si(OR 11 ) p (R 12 ) 3-p R 13…(II) In the above general formula (II), R 11 represents an alkyl group such as a methyl group or an ethyl group, and R 12 represents a monovalent organic group such as an alkyl group, an aralkyl group, an aryl group, an alkenyl group, an alkyl group substituted with an acryloxy group, or an alkyl group substituted with a methacryloxy group, and R 13 represents a monovalent organic functional group, and p represents an integer of 1 to 3. 11 or R 12 If there are multiple, R 11 Comrades or R 12 R may be the same or different. 13 Examples of the monovalent organic functional group represented by the formula (I) include a monovalent organic functional group containing a glycidyloxy group, an epoxy group, a mercapto group, a hydroxyl group, an amino group, an alkyl group substituted with a halogen atom, or an isocyanate group.

[0047] Specific examples of the silane coupling agent include vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyldimethoxysilane.

[0048] The silane coupling agent may also be a polymer formed by polymerization of a compound represented by the general formula (II). A trimer is preferred as the polymer, and 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate is more preferred. This is a condensation polymer of 3-isocyanatoalkylalkoxysilane. It is known that 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate has no chemical reactivity in the isocyanate moiety, but the reactivity is ensured by the polarity of the nurate moiety. It is generally added to adhesives, similar to 3-isocyanatoalkylalkoxysilane, and is known as an adhesion improver. Therefore, adding 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate to a hydroxyl group-containing polymer compound can improve the water resistance of a gas barrier coating layer through hydrogen bonding. While 3-isocyanate alkyl alkoxysilanes are highly reactive and have low liquid stability, 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurates are not water-soluble due to the polarity of the nurate moiety, but they are easily dispersed in aqueous solutions and can maintain stable liquid viscosity. Furthermore, the water resistance of 3-isocyanate alkyl alkoxysilanes and 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurates is equivalent.

[0049] Some 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurates are produced by thermal condensation of 3-isocyanatepropylalkoxysilane, and although the raw material 3-isocyanatepropylalkoxysilane may be contained, this does not pose any particular problems. 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate is more preferred, and 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is even more preferred. Because the methoxy group hydrolyzes quickly and those containing the propyl group are relatively inexpensive, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is practically advantageous.

[0050] Furthermore, known additives such as an isocyanate compound, a dispersant, a stabilizer, a viscosity adjuster, and a colorant can be added to the coating agent as needed, provided that the gas barrier properties are not impaired.

[0051] The thickness of the gas barrier coating layer is preferably 50 to 1000 nm, more preferably 100 to 500 nm. When the thickness of the gas barrier coating layer is 50 nm or more, more sufficient gas barrier properties tend to be obtained, and when it is 1000 nm or less, sufficient flexibility tends to be maintained.

[0052] The coating liquid for forming the gas barrier coating layer can be applied by, for example, dipping, roll coating, gravure coating, reverse gravure coating, air knife coating, comma coating, die coating, screen printing, spray coating, gravure offset, etc. The coating film obtained by applying this coating liquid can be dried by, for example, hot air drying, hot roll drying, high frequency irradiation, infrared irradiation, UV irradiation, or a combination thereof.

[0053] The temperature at which the coating film is dried can be, for example, 50 to 150° C., and preferably 70 to 100° C. By keeping the drying temperature within the above range, the occurrence of cracks in the inorganic oxide layer and the gas barrier coating layer can be further suppressed, and excellent barrier properties can be achieved.

[0054] The gas barrier coating layer may be formed using a coating agent containing a polyvinyl alcohol resin and a silane compound. The coating agent may contain an acid catalyst, an alkali catalyst, a photopolymerization initiator, etc., as needed.

[0055] The polyvinyl alcohol resin is as described above. Examples of the silane compound include a silane coupling agent, polysilazane, and siloxane, and specific examples thereof include tetramethoxysilane, tetraethoxysilane, glycidoxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, and hexamethyldisilazane.

[0056] (Printing layer) A printing layer can be provided on the second substrate layer side of the first substrate layer. The printing layer is provided in a position visible from the outside of the laminate for the purpose of displaying information about the contents, identifying the contents, or improving the design of the packaging bag. The printing method and printing ink are not particularly limited, and are appropriately selected from known printing methods and printing inks taking into consideration printability on the film, design such as color tone, adhesion, and safety as a food container. Examples of printing methods that can be used include gravure printing, offset printing, gravure offset printing, flexographic printing, and inkjet printing. Among these, gravure printing is preferably used from the viewpoints of productivity and high-resolution images.

[0057] To improve the adhesion of the printed layer, the surface of the first substrate layer facing the second substrate layer may be subjected to various pretreatments such as corona treatment, plasma treatment, and flame treatment, or a coating layer such as an easy-adhesion layer may be provided. Examples of the surface of the first substrate layer facing the second substrate layer include the surface of a polyolefin film (when the first substrate layer is not a gas barrier substrate layer) and the surface of a gas barrier coating layer (when the first substrate layer is a gas barrier substrate layer).

[0058] [Second base layer 12] For the configuration of the second substrate layer, the above description of the configuration of the first substrate layer can be referred to as appropriate. When the first substrate layer is a gas barrier substrate layer, the second substrate layer does not need to be a gas barrier substrate layer, and conversely, when the second substrate layer is a gas barrier substrate layer, the first substrate layer does not need to be a gas barrier substrate layer.

[0059] (Adhesive layer S) The first base material layer and the second base material layer can be laminated via an adhesive layer. Examples of adhesive materials that can be used include polyester-isocyanate resins, urethane resins, and polyether resins. For use of the packaging bag in retort pouch applications, a two-component curing urethane adhesive that is retort-resistant is preferably used.

[0060] [Sealant layer 13] The sealant layer is a layer that provides heat-sealing properties to the laminate, and includes a polyolefin film. The sealant layer may be made of a polyolefin film.

[0061] Among thermoplastic resins, polyolefin resins are commonly used as the material for the sealant layer.Specific examples include ethylene resins such as low-density polyethylene resin (LDPE), medium-density polyethylene resin (MDPE), linear low-density polyethylene resin (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-α-olefin copolymer, and ethylene-(meth)acrylic acid copolymer, as well as blends of polyethylene and polybutene, and polypropylene resins such as homopolypropylene resin (PP), propylene-ethylene random copolymer, propylene-ethylene block copolymer, and propylene-α-olefin copolymer.These thermoplastic resins can be selected appropriately depending on the intended use and temperature conditions such as boiling and retort processing.

[0062] The polyolefin film constituting the sealant layer may contain various additives such as a flame retardant, a slip agent, an antiblocking agent, an antioxidant, a light stabilizer, and a tackifier.

[0063] The thickness of the sealant layer is determined depending on the weight of the contents, the shape of the packaging bag, etc., but is preferably about 30 to 150 μm.

[0064] The sealant layer can be formed by any of the known lamination methods, such as a dry lamination method in which a film-like sealant layer made of the above-mentioned thermoplastic resin is bonded with an adhesive such as a one-component curing or two-component curing urethane adhesive, a non-solvent dry lamination method in which a film-like sealant layer is bonded with a solvent-free adhesive, and an extrusion lamination method in which the above-mentioned thermoplastic resin is heated and melted, extruded into a curtain shape, and bonded together.

[0065] Among the above-mentioned forming methods, the dry lamination method is preferred because it has high resistance to retort treatment, particularly high-temperature hot water treatment at 120° C. or higher. On the other hand, if the packaging bag is used for an application in which it will be treated at a temperature of 85° C. or lower, the lamination method is not particularly limited.

[0066] [Thermal shrinkage rate of each layer] In the laminate, the thermal shrinkage rate in the machine direction (MD) after heating at 120° C. for 15 minutes in each of the first base material layer, the second base material layer, and the sealant layer satisfies the following formula. Heat shrinkage rate of the second base layer ≦ 5% (Equation 1) Heat shrinkage rate of the second base material layer ≧ Heat shrinkage rate of the first base material layer (Equation 2) Heat shrinkage rate of the second base layer ≧ Heat shrinkage rate of the sealant layer (Equation 3)

[0067] Here, the heat shrinkage rate (%) is a value calculated by the following formula. (Length in the running direction before heating - Length in the running direction after heating) / Length in the running direction before heating x 100 The procedure for measuring the heat shrinkage rate is as follows. (1) The layer to be measured is cut into a 20 cm x 20 cm sample. (2) Draw a 10 cm line in the running direction of the measurement sample (the running direction length before heating). (3) Heat the measurement sample at 120°C for 15 minutes. (4) The length of the written line in the running direction is measured (length in the running direction after heating). (5) Calculate the thermal shrinkage rate using the above formula.

[0068] The heat shrinkage rate of the second base layer is 5% or less. This makes it difficult for cracks to occur in the gas barrier coating layer during barrier processing, resulting in good barrier properties. From this perspective, the heat shrinkage rate can be 4% or less, and may be 3% or less. However, producing a film with a very small heat shrinkage rate requires a long time for heat setting (thermal fixation), which significantly reduces productivity. From this perspective, the lower limit of the heat shrinkage rate of the second base layer can be 1.5% or more.

[0069] The heat shrinkage rate of the second base layer is equal to or greater than the heat shrinkage rate of the first base layer and equal to or greater than the heat shrinkage rate of the sealant layer. By sandwiching and laminating the second base layer between a first base layer and a sealant layer, each of which has a heat shrinkage rate lower than that of the second base layer, the heat shrinkage rate of the laminate can be reduced. This prevents the gas barrier function from decreasing during retort processing, thereby maintaining the barrier properties after retort processing. From this perspective, the heat shrinkage rate of the second base layer minus the heat shrinkage rate of the first base layer can be 0.3% or more, and may be 0.5% or more. If the heat shrinkage rate of the second base layer is greater than that of the first base layer by a certain amount, it becomes difficult to achieve the effect of reducing the shrinkage rate of the laminate. This makes it difficult to prevent the gas barrier function from decreasing, so the upper limit of the heat shrinkage rate of the second base layer minus the heat shrinkage rate of the first base layer can be 1.5% or less. Furthermore, the heat shrinkage rate of the second base layer minus the heat shrinkage rate of the sealant layer can be 0.5% or more, and may be 1.0% or more. If the heat shrinkage rate of the second base layer is greater than that of the sealant layer by a certain amount, it becomes difficult to obtain the effect of reducing the shrinkage rate of the laminate, which makes it difficult to prevent a decrease in the gas barrier function. Therefore, the upper limit of the heat shrinkage rate of the second base layer minus the heat shrinkage rate of the sealant layer can be set to 3.0%.

[0070] The heat shrinkage rate of the sealant layer can be 2% or less, which makes it easier to suppress the heat shrinkage of the laminate. From this perspective, the heat shrinkage rate may be 1% or less.

[0071] As described above, all of the films constituting the laminate can be polyolefin films. Such a laminate can be considered a monomaterial packaging material with excellent recyclability. From this perspective, the total mass of components other than the polyolefin component (e.g., adhesives and ink components) can be 10% by mass or less, and may be 7.5% by mass or less, of the total mass of the laminate.

[0072] Furthermore, when the laminate is made into a packaging bag, it can be subjected to high-temperature retort treatment, and can be suitably used for retort pouch applications.

[0073] <Packaging bag> The packaging bag is obtained by forming the above-described laminate into a bag. The packaging bag may be formed by folding one laminate in half so that the sealant layers face each other and then heat-sealing three sides to form a bag, or may be formed by stacking two laminates so that the sealant layers face each other and then heat-sealing four sides to form a bag. The packaging bag can contain contents such as food, medicine, etc., and can be subjected to heat sterilization treatment such as retort treatment or boiling treatment.

[0074] Retort processing is a method of sterilizing microorganisms such as mold, yeast, and bacteria under pressure, typically for the preservation of food, pharmaceuticals, etc. Typically, food packaging bags are sterilized at 105–140°C and 0.15–0.30 MPa for 10–120 minutes. Retort processing equipment is available in two types: steam and hot water, which utilize heated steam and pressurized water, respectively, depending on the sterilization conditions of the food contents. Boiling is a moist heat sterilization method for preserving food, pharmaceuticals, etc. Typically, food packaging bags are sterilized at 60–100°C and atmospheric pressure for 10–120 minutes, depending on the contents. Boiling is typically performed in a hot water bath at temperatures below 100°C. Methods include a batch method, in which the bag is immersed in a hot water bath at a constant temperature for a set time and then removed, and a continuous method, in which the bag is passed through a tunnel-type hot water bath for processing.

[0075] The packaging bag is particularly suitable for use in applications where retort treatment is performed at a temperature of 120° C. or higher. A packaging bag using the laminate can maintain excellent barrier properties even when subjected to retort treatment. [Example]

[0076] The present disclosure will be explained in more detail by the following examples, but the present disclosure is not limited to these examples.

[0077] <Preparation of the first base layer and the second base layer> The following stretched polypropylene films were prepared as the first and second base layers. Note that the "shrinkage rate" below refers to the heat shrinkage rate in the machine direction (MD) after heating at 120°C for 15 minutes. [First base layer] OPP (shrinkage rate 2.0%): thickness 20 μm OPP (shrinkage rate 3.1%): thickness 20 μm OPP (shrinkage rate 4.1%): thickness 20 μm EVOH-OPP (shrinkage rate 2.0%): 18 μm thick. An EVOH layer (adhesion layer) is provided on top of the OPP film. [Second base layer] OPP (shrinkage rate 2.6%): thickness 20 μm OPP (shrinkage rate 2.6%): thickness 18 μm OPP (shrinkage rate 3.8%): thickness 20 μm EVOH-OPP (shrinkage rate 2.6%): 18 μm thick. An EVOH layer (adhesion layer) is provided on top of the OPP film.

[0078] The gas barrier substrate layer is produced by the following method.

[0079] [Preparation of Adhesion Layer-Forming Composition] Acrylic polyol and tolylene diisocyanate were mixed so that the number of OH groups in the acrylic polyol was equal to the number of NCO groups in the tolylene diisocyanate, and the mixture was diluted with ethyl acetate to a total solids content (total amount of acrylic polyol and tolylene diisocyanate) of 5% by mass. β-(3,4-epoxycyclohexyl)trimethoxysilane was further added to the diluted mixture in an amount of 5 parts by mass per 100 parts by mass of the total amount of acrylic polyol and tolylene diisocyanate, and these were mixed to prepare a composition for forming an adhesion layer (anchor coating agent).

[0080] [Preparation of composition for forming gas barrier coating layer] A composition for forming a gas barrier coating layer was prepared by mixing the following liquids A, B, and C in a mass ratio of 65 / 25 / 10, respectively. Solution A: A hydrolysis solution with a solid content of 5% by mass (SiO2 equivalent) obtained by adding 72.1 g of 0.1N hydrochloric acid to 17.9 g of tetraethoxysilane (Si(OC2H5)4) and 10 g of methanol and stirring for 30 minutes. Solution B: 5% by mass of polyvinyl alcohol in water / methanol (water:methanol mass ratio 95:5). Liquid C: A hydrolysis solution prepared by diluting 1,3,5-tris(3-trialkoxysilylpropyl) isocyanurate with a water / isopropyl alcohol mixture (water:isopropyl alcohol mass ratio 1:1) to a solids content of 5 mass%.

[0081] [Manufacturing of gas barrier OPP] The above-mentioned adhesive layer-forming composition was applied to the corona-treated surface of a stretched polypropylene film by gravure roll coating, and then dried and cured at 60°C to give a coating amount of 0.1 g / m 2An adhesive layer made of a polyester-based polyurethane resin was then formed. Next, a 30-nm-thick transparent inorganic oxide layer (silica vapor deposition layer) made of silicon oxide was formed using an electron beam heating vacuum deposition system. The vapor deposition material type was adjusted to form a vapor deposition layer with an O / Si ratio of 1.8. The O / Si ratio was measured using an X-ray photoelectron spectrometer (manufactured by JEOL Ltd., product name: JPS-90MXV) using a non-monochromated MgKα X-ray source (1253.6 eV) at an X-ray output of 100 W (10 kV-10 mA). Quantitative analysis to determine the O / Si ratio was performed using relative sensitivity factors of 2.28 for O1s and 0.9 for Si2p, respectively.

[0082] When an alumina vapor deposition layer was formed as an inorganic oxide layer, it was carried out as follows: Aluminum was evaporated while introducing oxygen by electron beam vacuum deposition to form an AlOx vapor deposition film with a thickness of 10 nm.

[0083] Next, the composition for forming a gas barrier coating layer was applied onto the inorganic oxide layer by gravure roll coating, and the applied composition was heated and dried in an oven under conditions of a tension of 20 N / m and a drying temperature of 120°C to form a gas barrier coating layer with a thickness of 0.3 µm. This resulted in a gas barrier film having a laminated structure of film substrate / adhesion layer / inorganic oxide layer / gas barrier coating layer.

[0084] [Production of gas barrier EVOH-OPP] An inorganic oxide layer (silica vapor deposition layer) was formed on the EVOH layer (adhesion layer) of the EVOH-OPP film in the same manner as above. Next, a gas barrier coating layer was formed on the inorganic oxide layer using the gas barrier coating layer-forming composition in the same manner as above. This resulted in a gas barrier film having a laminated structure of film substrate / EVOH layer (adhesion layer) / inorganic oxide layer / gas barrier coating layer.

[0085] <Preparing the sealant layer> The following polypropylene films were prepared as sealant layers. CPP (shrinkage rate 0.2%): thickness 70 μm CPP (shrinkage rate 1.8%): thickness 70 μm

[0086] <Measurement of shrinkage rate of each layer> The heat shrinkage rate (%) of each layer was measured according to the following procedure. (1) The layer to be measured was cut into a 20 cm x 20 cm sample. (2) A 10 cm line was written in the running direction of the measurement sample (the running direction length before heating). (3) The measurement sample was heated at 120°C for 15 minutes. (4) The length of the written line in the running direction was measured (length in the running direction after heating). (5) The thermal shrinkage rate was calculated using the following formula. (Length in the running direction before heating - Length in the running direction after heating) / Length in the running direction before heating x 100

[0087] <Production of laminate> Based on the combination of layers shown in Table 1, each example (However, Examples 1 to 7 and 10 are reference examples.) The laminates of the present invention and comparative examples were manufactured by the following method.

[0088] [Table 1]

[0089] <Packaging bag manufacturing> The laminate obtained in each example was cut into a size of 15 cm x 10 cm, and two of the cut packaging films were stacked so that the sealant layers faced each other. After impulse sealing on three sides to form a pouch, 100 ml of tap water was added as the contents, and the remaining side was impulse sealed. This produced a pouch (packaging bag) sealed on four sides.

[0090] <Gas barrier property evaluation> The pouches obtained in each example were subjected to retort treatment in a retort apparatus at 0.2 MPa and 121°C for 30 minutes. After retort treatment, the tap water inside the pouches was discarded, and the pouches were thoroughly dried before being evaluated for gas barrier properties. Specifically, the oxygen transmission rate (OTR) and water vapor transmission rate (WTR) were measured as follows. The results are shown in Table 2. Oxygen permeability: Oxygen permeability measuring device (manufactured by MOCON, product name: OX-TRAN2 / 20) Measured at a temperature of 30°C and a relative humidity of 70% (JIS K-7126, Method B) Measurements are in units of [cc / m 2 ·day·MPa]. Water vapor transmission rate: Water vapor permeability measuring device (MOCON, product name: PERMATRAN-W 3 / 33) Measured at a temperature of 40°C and a relative humidity of 90% (JIS K-7126, Method B) Measurements are in units of [g / m 2 ·day].

[0091] [Table 2] [Industrial Applicability]

[0092] The laminate of the present invention can realize a retortable packaging bag, and the constituent films thereof can be substantially all polyolefin films. Such a laminate can be said to be a packaging material made of a single material (mono-material), and is expected to have excellent recyclability. [Explanation of symbols]

[0093] 11...first substrate layer, 12...second substrate layer, 13...sealant layer, S...adhesive layer, 100...laminated body.

Claims

1. a first substrate layer, a second substrate layer, and a sealant layer in this order; the first substrate layer, the second substrate layer, and the sealant layer all comprise a polyolefin film; the polyolefin film of the first base material layer or the second base material layer has an adhesive layer and an inorganic oxide layer in this order on at least one surface thereof; the adhesion layer contains a polyvinyl alcohol-based resin, A laminate in which the thermal shrinkage rate in the machine direction (MD direction) after heating at 120°C for 15 minutes in each of the first base material layer, the second base material layer, and the sealant layer satisfies the following formula: 1.5%≦heat shrinkage rate of second base layer≦5% (Equation 1) Heat shrinkage rate of second base material layer>Heat shrinkage rate of first base material layer (Equation 2) Heat shrinkage rate of second base material layer>Heat shrinkage rate of sealant layer (Equation 3) (Here, heat shrinkage rate (%) = (length in the running direction before heating - length in the running direction after heating) / length in the running direction before heating x 100)

2. The laminate according to claim 1 , wherein the heat shrinkage rate satisfies the following formula: 1.5%≧heat shrinkage rate of second base material layer−heat shrinkage rate of first base material layer≧0.3% (Equation 4) 3.0%≧(heat shrinkage rate of second base layer)−(heat shrinkage rate of sealant layer)≧0.5% (Equation 5)

3. The laminate according to claim 1 or 2, wherein the heat shrinkage rate satisfies the following formula: Heat shrinkage rate of sealant layer≦2% (Equation 6)

4. A laminate described in any one of claims 1 to 3, wherein the polyvinyl alcohol-based resin is polyvinyl alcohol (PVA) or ethylene-vinyl alcohol copolymer (EVOH).

5. The laminate according to any one of claims 1 to 4, which is for use in a retort pouch.

6. A packaging bag produced by producing the laminate according to any one of claims 1 to 5.

Images