Packaging materials and packaging bags

Abstract

To provide packaging materials and packaging bags that ensure a high proportion of polyolefin resin in the overall packaging material while also providing sufficient resistance to external impacts (impact resistance) even when stored in a cold place for a long period of time. [Solution] A packaging material comprising a base material made of unstretched polyethylene, a polyvinyl alcohol resin layer, a vapor-deposited layer, and a sealant layer, wherein the cross-sectional indentation hardness of the polyvinyl alcohol resin layer, as measured by a nanoindenter, is 50 to 100 MPa, and a packaging bag comprising the packaging material.

Description

[Technical Field]

[0001] This disclosure relates to packaging materials and packaging bags. [Background technology]

[0002] In recent years, the monomaterialization of packaging materials has been progressing from the perspective of facilitating material recycling. On the other hand, packaging materials are also required to maintain functions such as gas barrier properties, and as disclosed in Patent Document 1, monomaterial packaging materials are known that have a vapor-deposited layer, a base layer made of polyolefin resin, and a base layer containing polyurethane resin on the base layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2022 / 220200 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The base layer provided in the packaging material disclosed in Patent Document 1 is intended to improve the adhesion between the base material layer and the vapor-deposited layer. However, when the packaging material is stored in a cold place such as a refrigerator for a long period of time, the base layer hardens due to the low temperature, making it more susceptible to damage when subjected to external impacts such as dropping. When the base layer is damaged, cracks also occur in the vapor-deposited layer, and the barrier properties of the packaging material are no longer guaranteed.

[0005] This disclosure is made in view of the above points, and aims to provide a packaging material and a packaging bag that ensure a large proportion of polyolefin resin in the overall packaging material, while also ensuring sufficient resistance to external impacts (impact resistance) even when stored in a cold place for a long period of time. [Means for solving the problem]

[0006] One aspect of this disclosure is a packaging material comprising a base material made of unstretched polyethylene, a polyvinyl alcohol resin layer, a vapor-deposited layer, and a sealant layer, wherein the cross-sectional indentation hardness of the polyvinyl alcohol resin layer, as measured by a nanoindenter, is 50 to 100 MPa. This packaging material ensures a large proportion of polyolefin resin in the overall packaging material, while also being less susceptible to deterioration of barrier properties due to external impacts even when stored in a cold place for a long period of time. In other words, it has high cold impact resistance.

[0007] In one embodiment, the sealant layer may contain polyethylene. In this case, since both the sealant layer and the substrate are mainly composed of polyethylene, the entire packaging material is easily recyclable.

[0008] In one embodiment, the thickness of the polyvinyl alcohol resin layer may be 0.05 to 10 μm. A thickness within this range results in superior cold shock resistance.

[0009] In one embodiment, the polyvinyl alcohol resin layer may contain ethylene vinyl alcohol. In another embodiment, the ethylene unit content in the ethylene vinyl alcohol may be 30 to 50 mol%. In yet another embodiment, the vapor-deposited layer may be an inorganic oxide layer made of silicon oxide or aluminum oxide.

[0010] In one embodiment, the substrate and the polyvinyl alcohol resin layer may be co-extruded layers formed by a co-extrusion method. Being co-extruded layers enhances adhesion between the substrate and the polyvinyl alcohol resin layer, making it easier for the packaging material to maintain gas barrier properties.

[0011] Another aspect of this disclosure is a packaging bag comprising any of the packaging materials described above. Because the packaging bag is formed using a packaging material with high cold shock resistance while ensuring a large proportion of polyolefin resin in the overall packaging material, its barrier properties are less likely to deteriorate due to external impacts even when stored in a cold place for a long period of time. [Effects of the Invention]

[0012] According to this disclosure, it is possible to provide packaging materials and packaging bags that ensure a large proportion of polyolefin resin in the overall packaging material while also ensuring sufficient resistance to external impacts (impact resistance) even when stored in a cold place for a long period of time. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1 is a schematic cross-sectional view showing one embodiment of the packaging material of this disclosure. [Figure 2] Figure 2 is a schematic cross-sectional view showing one embodiment of the packaging of the present disclosure. [Modes for carrying out the invention]

[0014] Embodiments of this disclosure are described below. The same reference numerals are used for identical components, and redundant descriptions are omitted. Furthermore, the dimensional ratios in the drawings are not limited to those shown.

[0015] [Packaging material] Embodiments of the packaging material of this disclosure will now be described. The packaging material can be called a packaging film. Figure 1 is a schematic cross-sectional view showing one embodiment of the packaging material of this disclosure. As shown in Figure 1, the packaging material 100 comprises a base material 10 made of unstretched polyethylene, a polyvinyl alcohol resin layer 20, a vapor deposition layer 40, and a sealant layer 30. The side of the sealant layer 30 opposite to the base material 10 is the sealing surface 30a, which is the surface that comes into contact with the contents. The packaging material 100 may further include adhesive layers between each layer as needed.

[0016] The packaging material 100 contains a polyolefin resin. The content of the polyolefin resin in the packaging material 100 is not particularly limited, but is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more. In this case, the packaging material 100 can be said to be a packaging material made of substantially a single material (monomaterial), and the recyclability of the packaging material 100 can be improved. The upper limit of the content is 100% by mass. Here, the "content of the polyolefin resin" means the content of polyolefin (for example, polyethylene, polypropylene) contained in the packaging material 100.

[0017] From the viewpoint of further improving the recyclability, it is preferable that the base material 10 and the sealant layer 30 contain a polyolefin resin.

[0018] (Base material layer) The base material 10 is a layer that supports the polyvinyl alcohol resin layer 20, the vapor deposition layer 40, and the sealant layer 30, and is made of unstretched polyethylene. By using polyethylene for the base material 10, recycling becomes easy.

[0019] Specific examples of the polyethylene resin include low density polyethylene resin (LDPE), medium density polyethylene resin (MDPE), linear low density polyethylene resin (LLDPE), high density polyethylene resin (HDPE), ethylene vinyl acetate copolymer (EVA), ethylene - α - olefin copolymer, ethylene - (meth)acrylic acid copolymer, and the like.

[0020] The base material 10 is an unstretched film. In other words, the base material 10 is an unstretched film. Because the base material 10 is an unstretched film, the degree of crystallinity of the film is less than 35%, may be 30% or less, or may be 26% or less. Because the base material 10 is an unstretched film, it has more flexibility compared to when a stretched film is used as the base material. Therefore, even if the resin hardens after being stored in a cold place for a long period of time, it can maintain relatively good flexibility, so when external impact is applied, the stress is distributed and it is less likely to break, and as a result it is easier to maintain the barrier properties of the packaging material.

[0021] The surface of the substrate 10 on the side facing the sealant layer 30 may be subjected to various pretreatments such as corona treatment, plasma treatment, ozone treatment, or flame treatment, or a coating layer such as an easy-adhesion layer or a gas barrier layer as described later may be provided. The substrate 10 may contain resins other than polyethylene. Examples of resins other than polyethylene include polypropylene. The substrate 10 may also contain at least one additive selected from fillers, antistatic agents, plasticizers, lubricants, antioxidants, etc., as needed.

[0022] The thickness of the base material 10 can be 15 μm or more, and may be 20 μm or more, from the viewpoint of heat resistance (thermal shrinkage during heat welding). On the other hand, from the viewpoint of reducing carbon dioxide emissions in the manufacturing process, it can be 50 μm or less, may be 40 μm or less, and may be 30 μm or less. Therefore, the thickness of the base material 10 can be 15 to 50 μm, and more preferably 25 to 35 μm.

[0023] (Polyvinyl alcohol resin layer) The polyvinyl alcohol resin layer 20 is provided between the base layer 10 and the vapor-deposited layer 40. The polyvinyl alcohol resin layer 20 can improve the adhesion between the base layer 10 and the vapor-deposited layer 40 by planarizing the surface of the base layer 10. The polyvinyl alcohol resin can be any resin having vinyl alcohol units formed by saponification of vinyl ester units, such as polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH). EVOH can be suitably used from the viewpoint of heat resistance and gas barrier properties.

[0024] Examples of PVA include resins obtained by polymerizing vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versaticate individually, and then saponifying them.

[0025] PVA may be copolymerized or post-modified modified PVA. Copolymerized modified PVA can be obtained, for example, by copolymerizing a vinyl ester with an unsaturated monomer copolymerizable with the vinyl ester, followed by saponification. Post-modified PVA can be obtained by copolymerizing PVA obtained by polymerizing a vinyl ester and then saponifying it with an unsaturated monomer in the presence of a polymerization catalyst. The amount of modification in modified PVA can be less than 50 mol% from the viewpoint of exhibiting sufficient gas barrier properties, and can be 10 mol% or more from the viewpoint of obtaining the effect of modification.

[0026] Examples of the unsaturated monomers mentioned above include olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxyl group-containing α-olefins such as 3-buten-1-ol, 4-pentin-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; amides such as diacetone acrylamide, acrylamide, and methacrylamide; and Examples include olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid; vinyl compounds such as alkyl vinyl ethers, dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinylethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerol monoallyl ether, and 3,4-diacetoxy-1-butene; and vinylidene chloride, 1,4-diacetoxy-2-butene, vinylene carbonate, polyoxypropylene, and polyoxypropylene vinylamine. From the viewpoint of gas barrier properties, the unsaturated monomer can be an olefin, and ethylene may be particularly suitable.

[0027] Examples of polymerization catalysts include radical polymerization catalysts such as azobisisobutyronitrile, benzoyl peroxide, and lauryl peroxide. The polymerization method is not particularly limited, and bulk polymerization, emulsion polymerization, solvent polymerization, etc., can be employed.

[0028] The degree of polymerization of PVA is preferably 300 to 3000. A degree of polymerization of 300 or higher tends to result in superior barrier properties, while a degree of polymerization of 3000 or lower tends to result in superior coating suitability. The degree of saponification of PVA is preferably 80 mol% or higher, more preferably 90 mol% or higher, and even more preferably 98 mol% or higher. Furthermore, the degree of saponification of PVA may be 100 mol% or lower, or 99.9 mol% or lower. The degree of polymerization and saponification of PVA can be measured in accordance with the method described in JIS K6726 (1994).

[0029] EVOH is generally obtained by saponifying copolymers of ethylene with vinyl acid esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, and vinyl versatate.

[0030] The ethylene unit content of EVOH is 30-50 mol%, more preferably 40-50 mol%, and even more preferably 45-50 mol%. When the ethylene unit content is 30 mol% or more, the hardness of the polyvinyl alcohol resin layer becomes sufficiently soft, making it less susceptible to breakage even when subjected to external impact, and thus preventing a decrease in the barrier properties of the packaging material. On the other hand, when the ethylene unit content is 50 mol% or less, sufficient hardness can be ensured for the polyvinyl alcohol resin layer, thus preventing the layer from being too soft, which could lead to excessive transmission of external impact to the vapor-deposited layer and subsequent cracking. The ethylene unit content of EVOH can be determined by NMR spectroscopy.

[0031] Saponification can be carried out with alkali or acid, but alkali is preferred from the standpoint of saponification rate. Examples of alkalis include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and alkali metal alkoxides such as sodium ethylate, potassium ethylate, and lithium methylate.

[0032] The thickness of the polyvinyl alcohol resin layer 20 is not particularly limited, but from the viewpoint of barrier properties and processability, it can be 0.05 to 10 μm, may be 0.2 to 10 μm, may be 0.25 to 2.5 μm, or may be 0.3 to 1.5 μm.

[0033] The mass per unit area of ​​the polyvinyl alcohol resin layer 20 is 0.1 to 10 g / m². 2 This can be done if the mass is 0.1 g / m 2As described above, even if the surface smoothness of the substrate layer is insufficient, the surface of the polyvinyl alcohol resin layer 20 can be formed to be sufficiently smooth, and a vapor-deposited layer with excellent gas barrier properties can be formed on the surface. On the other hand, if this mass is 10 g / m 2 The following is advantageous in terms of realizing monomaterial packaging and reducing material costs.

[0034] The cross-sectional indentation hardness of the polyvinyl alcohol resin layer 20 is 50 to 100 MPa. It may also be 55 to 80 MPa or 58 to 72 MPa. The cross-sectional indentation hardness is the hardness measured by a nanoindenter across the cross-section of the polyvinyl alcohol resin layer 20, and is measured by the nanoindentation method. The nanoindentation method is a measurement method that obtains the mechanical properties of a sample by performing a quasi-static indentation test on the target object. One specific measurement method is described in the examples below.

[0035] The cross-sectional indentation hardness of the polyvinyl alcohol resin layer 20, as measured by a nanoindenter, can be controlled, for example, by adjusting the ethylene content (%) in the polyvinyl alcohol resin layer 20. It is known that the cross-sectional indentation hardness tends to decrease (become softer) as the ethylene content (%) increases, and conversely, tends to increase (become harder) as the ethylene content (%) decreases.

[0036] The base material 10 and the polyvinyl alcohol resin layer 20 may be co-extruded layers formed by a co-extrusion method. When these layers are co-extruded layers, the laminate tends to adhere well and maintain gas barrier properties. In the case of co-extrusion, an adhesive resin such as maleic anhydride graft-modified polyethylene may be sandwiched between the base material 10 and the polyvinyl alcohol resin layer 20.

[0037] (deposited layer) The vapor-deposited layer 40 is a layer formed by vapor deposition, and the vapor-deposited layer 40 is composed of inorganic materials. Examples of inorganic materials include metals and metal oxides.

[0038] The inorganic compounds that make up the inorganic oxide layer include aluminum as a metal and silicon dioxide (SiO₂) as a metal oxide. X ), aluminum oxide (AlO X Examples include the following. By using aluminum as the metal, a packaging material with excellent light-shielding properties can be obtained. From the viewpoint of excellent transparency and excellent tensile stretchability during processing, silicon oxide is preferred as the inorganic compound. By using an inorganic oxide layer, high gas barrier properties can be obtained with a very thin layer that does not affect the recyclability of the packaging material. The vapor-deposited layer 40 may consist of a single layer or multiple layers.

[0039] The inorganic oxide layer is made of metals such as aluminum, or SiO2. X or AlO X It can be formed by vacuum deposition using inorganic compounds such as the above. The thickness of the deposited layer 40 is not particularly limited, but is preferably 5 nm or more. In this case, compared to the case where the thickness of the deposited layer 40 is less than 5 nm, the decrease in gas barrier properties can be suppressed more effectively even after moist heat treatment such as boiling of the packaging material 100. The thickness of the deposited layer 40 is more preferably 8 nm or more, and particularly preferably 10 nm or more. Furthermore, the thickness of the deposited layer 40 is preferably 300 nm or less. In this case, compared to the case where the thickness of the deposited layer 40 exceeds 300 nm, the decrease in gas barrier properties can be suppressed more effectively even after moist heat treatment such as boiling of the packaging material 100. In addition, the proportion of polyolefin resin in the overall packaging material 100 can be increased, and the recyclability of the packaging material 100 can be improved. The thickness of the deposited layer 40 is more preferably 200 nm or less, and particularly preferably 100 nm or less.

[0040] (Sealant layer) The sealant layer 30 is a layer that provides sealing properties to the packaging material 100 by heat welding (e.g., heat sealing), and includes, for example, a polyolefin resin. Specifically, examples of polyolefin resins include polyethylene resins and polypropylene resins. Since the base material 10 is made of polyethylene, using a polyethylene resin in the sealant film 30 increases the polyethylene ratio of the overall packaging material, making recycling easier, and also reduces the melting point difference with the resin constituting the base material 10, thus simplifying temperature control during heat welding. On the other hand, using a polypropylene resin in the sealant layer 30 provides excellent heat resistance.

[0041] Polyethylene resins include, specifically, low-density polyethylene resin (LDPE), medium-density polyethylene resin (MDPE), linear low-density polyethylene resin (LLDPE), high-density polyethylene resin (HDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-α-olefin copolymer, and ethylene-(meth)acrylic acid copolymer.

[0042] Furthermore, from the viewpoint of facilitating the recycling of the packaging material 100, it is preferable that the resin mainly constituting the sealant layer 30 is the same type of resin as the resin mainly constituting the base material 10. Here, "mainly constituting" means that the resin makes up 50% by mass when the total amount of components of the layer made up of resin is used as the basis. From the viewpoint of simplifying recycling and improving sealing performance by heat welding, it is preferable that the sealant layer 30 be a low-density polyethylene film.

[0043] The thickness of the sealant layer 30 can be 40 μm or more, may be 50 μm or more, or may be 60 μm or more, from the viewpoint of minimizing shrinkage and distortion during heat sealing. On the other hand, from the viewpoint of reducing the amount of heat required for heat sealing, making it easier to reduce thermal damage to other layers of the packaging material 100, and from the viewpoint of reducing resources and costs, the thickness can be 150 μm or less, may be 100 μm or less, may be 90 μm or less, or may be 80 μm or less. Therefore, the thickness of the sealant layer 30 can be 40 to 150 μm, more preferably 40 to 120 μm, and more preferably 60 to 110 μm. Furthermore, from the viewpoint of widening the heat sealing temperature margin during heat sealing, the thickness of the sealant layer 30 is preferably 65 μm or more.

[0044] (Printing layer) The packaging material 100 may have a printed layer. The printed layer enhances the visual appeal of the contents the packaging material packages, attracting consumer attention, and also allows for the provision of information that consumers need, such as ingredient information. The printed layer can be provided on at least one surface of the substrate 10. The thickness of the printed layer may be 0.1 to 10 μm.

[0045] The printed layer is formed using an ink made by adding various pigments, plasticizers, drying agents, and stabilizers to a binder resin such as urethane, acrylic, nitrocellulose, or rubber. This printed layer can display characters, patterns, symbols, and combinations thereof.

[0046] The ink may be water-based or oil-based, but water-based ink is preferred. Water-based inks use water or alcohol as a solvent, thus further reducing the environmental impact. The ink may be biomass ink or not, but from the viewpoint of reducing the environmental impact, biomass ink is preferred. Here, biomass ink refers to ink that contains components obtained from biological resources (biomass) such as cotton, pulp, rice bran, vegetable oil, and angiosperm seeds. Examples of methods for forming the printed layer include conventionally known printing methods such as gravure printing, offset printing, and flexographic printing.

[0047] (adhesive layer) The adhesive layer is provided between each of the above layers as needed, and is a layer that adheres each layer together. Examples of adhesives that can be used to constitute the adhesive layer include polyester-isocyanate resins, urethane resins, and polyether resins. For use in boil sterilization applications of the packaging bag, a boil-resistant, two-component curing urethane adhesive is preferably used.

[0048] The adhesive may be an adhesive capable of exhibiting gas barrier properties after curing (a gas barrier adhesive). That is, the adhesive layer may contain a gas barrier adhesive and can be said to be a cured product of a gas barrier adhesive. In particular, forming an adhesive layer that comes into contact with the vapor-deposited layer using an adhesive that exhibits gas barrier properties makes it possible to further suppress the decrease in gas barrier properties due to crack formation in the vapor-deposited layer. This further improves the gas barrier performance of the packaging material 100. Examples of gas barrier adhesives include epoxy adhesives, polyester / polyurethane adhesives, and polyamine adhesives. Specific examples include "Maxive" (registered trademark) from Mitsubishi Gas Chemical Company and "Paslim" (registered trademark) from DIC Corporation.

[0049] The thickness of the adhesive layer can be, for example, 1.0 to 5.0 μm. When the adhesive layer thickness is 1.0 μm or more, it tends to be easier to ensure heat resistance that can withstand boiling treatment, while when it exceeds 5.0 μm, it tends to reduce recyclability.

[0050] In the base material and sealant layer constituting the packaging material according to the present invention, a film containing biomass-derived resin or recycled resin may be used. The recycled resin may be mechanically recycled resin or chemically recycled resin. That is, when the resin is polyethylene, biomass-derived polyethylene, recycled polyethylene (mechanically recycled resin, or chemically recycled resin) may be used in the base material and sealant layer constituting the packaging material. This makes it possible to reduce the environmental burden of production, use, and disposal of the packaging material according to the present invention.

[0051] [Packaging bag] An embodiment of a packaging bag using the packaging material of this disclosure will be described with reference to Figure 2. Figure 2 is a schematic cross-sectional view showing one embodiment of the packaging bag of this disclosure.

[0052] As shown in Figure 2, the packaging bag 400 is formed using the packaging material 100, and the sealing surface 30a constitutes the inner surface of the packaging bag 400. Specifically, the packaging bag 400 is formed by overlapping two pieces of packaging material 100 with their sealing surfaces 30a facing each other, and heat-welding the peripheral edges of the sealing surfaces 30a together. Methods for heat-welding the two pieces of packaging material 100 together include heat sealing, which involves contacting the packaging material 100 from the outside with a heat sealing bar, and ultrasonic sealing, which involves sandwiching the packaging material 100 between a horn and an anvil and generating frictional energy in the packaging material to heat-weld it.

[0053] The packaging 500 comprises a packaging bag 400 and contents C contained within the packaging bag 400. The contents C may be food (food and beverages), but may also be pharmaceuticals, etc. The packaging bag 400 comprises a main body 401 containing the contents C and a sealing portion 402 surrounding the main body 401.

[0054] In the packaging bag 500 using the above packaging material 100, the cross-sectional indentation hardness of the polyvinyl alcohol resin layer 20, as measured by a nanoindenter, is 50 to 100 MPa. As a result, even when stored for a long period of time in a cold place such as a refrigerator, the polyvinyl alcohol resin layer 20 hardens at low temperatures, which suppresses the destruction of the vapor-deposited layer 40 when subjected to external impacts such as dropping. Therefore, even when stored in a cold place for a long period of time, the barrier properties are less likely to deteriorate due to external impacts. In other words, it has high cold impact resistance.

[0055] Although a packaging bag 500 is shown as an example of a packaging container using the above-mentioned packaging material 100, the uses of the packaging material 100 are not limited to this. For example, another base material layer may be laminated onto the packaging material 100. The material constituting the base material layer used when another base material layer is laminated may be polyethylene, as with the base material 10 described above, or it may be polypropylene, nylon, polyethylene terephthalate, or paper. From the viewpoint of ease of recycling, polyethylene is preferred. Furthermore, the other base material layer may be stretched or unstretched. [Examples]

[0056] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0057] <Manufacturing of packaging materials> (Example 1) HDPE (density 0.95g / cm 3, a melting point of 130.6 °C), an adhesive resin (including maleic anhydride graft-modified polyethylene), and an EVOH resin (a melting point of 157 °C and an ethylene unit content of 48 mol%) were melted and extruded to form a three-layer film by a co-extrusion method. No stretching treatment was performed on this film, and a base material made of unstretched HDPE and a film containing an EVOH layer were obtained. At this time, the crystallinity of the base material (the layer made of HDPE) was 25% and the thickness was 32 μm, and the thickness of the EVOH layer was 1.0 μm.

[0058] Subsequently, on the EVOH layer, using a vacuum evaporation device with an electron beam heating method, SiO with a thickness of 30 nm X The film was formed as a vapor deposition layer.

[0059] On the vapor deposition layer, an LLDPE film (density 0.92 g / cm 3 , a melting point of 115 °C, and a thickness of 100 μm) was laminated by a dry lamination method through a two-component curable urethane-based adhesive. The thickness of the adhesive layer was 2.1 μm. The packaging material was produced through the above steps.

[0060] (Example 2) A packaging material was produced in the same manner as in Example 1, except that an EVOH resin (a melting point of 165 °C and an ethylene unit content of 44 mol%) was used as the EVOH layer.

[0061] (Comparative Example 1) A packaging material was produced in the same manner as in Example 1, except that a stretched HDPE film (density 0.95 g / cm 3 , a melting point of 133.3 °C, a crystallinity of 56%, and a thickness of 25 μm) was used as the base material.

[0062] [[ID=�0]](Comparative Example 2) A packaging material was produced in the same manner as in Example 1, except that an anchor coat (AC) layer made of a barrier urethane-based resin was provided instead of the EVOH layer. Specifically, an aqueous dispersion of a polyurethane resin (manufactured by Mitsui Chemicals, Inc., Takelac WPB-341) formed from an acid group-containing polyurethane and a polyamine was applied onto the base material and dried to form the AC layer. The thickness of the AC layer was 0.2 μm.

[0063] (Comparative Example 3) A packaging material was prepared in the same manner as in Example 1, except that an EVOH resin (melting point 148°C, ethylene unit content 53 mol%) was used as the EVOH layer.

[0064] (Comparative Example 4) A packaging material was prepared in the same manner as in Example 1, except that an EVOH resin (melting point 190°C, ethylene unit content 27 mol%) was used as the EVOH layer.

[0065] <Production of packaging bags> The packaging materials of Examples 1 and 2 and Comparative Examples 1-4 were cut to 110 mm x 160 mm, and a three-sided pouch with an opening was prepared using the cut packaging material. The three-sided pouch was formed by folding the cut packaging material in the longitudinal center so that the sealant layers faced each other, and then heat-sealing the periphery of the sealant layers. The heat-sealed area is the periphery along the longitudinal direction of the packaging material. The seal width was 5 mm. The heat-seal temperature, sealing time, and sealing pressure were 150°C, 0.9 seconds, and 0.08 MPa, respectively.

[0066] <Evaluation of packaging materials and packaging bags> (1) Cross-sectional hardness of the polyvinyl alcohol resin layer The cross-sectional indentation hardness of the packaging materials in Examples 1 and 2, and Comparative Examples 1-4, was measured by nanoindentation.

[0067] The measurement samples (cross-sectional samples) were prepared as follows: After corona treatment on both sides of the packaging material, it was embedded in visible light-curable resin D-800. Then, using an ultramicrotome Leica EM UC7, the packaging material was cut perpendicular to the layering direction with a diamond knife Microstar LH. The resulting cross-section was then finished with a cutting thickness of 100 nm and a cutting speed of 1 mm / s to obtain the measurement sample.

[0068] For the measurements, a Hysitron TI-Premier (product name) manufactured by Bruker Japan Co., Ltd. was used as the measuring device, and a Bruker Japan Co., Ltd. Berkovich-type diamond indenter was used as the indenter. The measurement conditions were as follows: Temperature: normal temperature (25℃). Mode: Load control mode. Indentation and unloading: The load was indented to 15 μN at an indentation speed of 1.5 μN / second, held at the maximum load for 5 seconds, and then unloaded at a speed of 1.5 μN / second. Measurement locations: The shape measurement function of a measuring device that scans the sample surface with an indenter is used to acquire a cross-sectional shape image of the polyvinyl alcohol resin layer, and 20 points are specified on the cross-section of the polyvinyl alcohol resin layer at intervals of 1 μm or more from the shape image.

[0069] For calculating the indentation hardness, fused silica was used as a standard sample to pre-calibrate the relationship between the indenter-sample contact depth and contact projection area. Then, the unloading curve in the 60-95% range relative to the maximum load during unloading was analyzed using the Oliver-Pharr method to calculate the indentation hardness. The measurement results are shown in Table 1.

[0070] (2) Cold shock resistance Three-sided pouches (5 of each type) prepared using the packaging materials of Examples 1 and 2 and Comparative Examples 1-4 were filled with 100 mL of 0.5% saline solution, and the openings were heat-sealed. These were stored in a refrigerator set to 0°C for 3 days, then removed and immediately subjected to a drop test. The drop test was performed at room temperature (25±1°C) by dropping the pouches vertically from a height of 0.7 m.

[0071] The oxygen permeability of the pouches after the drop test was measured. Measurements were performed using an oxygen permeability analyzer (Modern Control, OXTRAN 2 / 20) under conditions of 30°C and 70% relative humidity. The measurement method conformed to JIS K-7126, Method B (isobaric method), and ASTM D3985-81. The measurement results were evaluated according to the following criteria. The evaluation results are shown in Table 1. A: 10cc / m 2Less than 1 day at a meter B: 10cc / m 2 ·day · atm or more

[0072] [Table 1]

[0073] The summary of this disclosure is as follows: [1] A base material made of unstretched polyethylene, a polyvinyl alcohol resin layer, a vapor-deposited layer, and a sealant layer are laminated together. A packaging material wherein the cross-sectional indentation hardness of the polyvinyl alcohol resin layer, as measured by a nanoindenter, is 50 to 100 MPa. [2] The packaging material according to [1], wherein the sealant layer comprises polyethylene. [3] The packaging material according to [1] or [2], wherein the thickness of the polyvinyl alcohol resin layer is 0.05 to 10 μm. [4] The packaging material according to any one of [1] to [3], wherein the polyvinyl alcohol resin layer contains ethylene vinyl alcohol. [5] The packaging material according to [5], wherein the ethylene unit content in the ethylene vinyl alcohol is 30 to 50 mol%. [6] The packaging material according to any one of [1] to [5], wherein the vapor-deposited layer is an inorganic oxide layer made of silicon oxide or aluminum oxide. [7] The packaging material according to any one of [1] to [6], wherein the base material and the polyvinyl alcohol resin layer are co-extruded layers formed by a co-extrusion method. [8] A packaging bag comprising any one of the packaging materials described in [1] to [7]. [Explanation of Symbols]

[0074] 10...Base material, 20...Polyvinyl alcohol resin layer, 30...Sealant layer, 30a...Sealing surface, 40...Vapor deposition layer, 100...Packaging material, 400...Packaging bag, 500...Packaging body, C...Contents.

Claims

1. A base material made of unstretched polyethylene, a polyvinyl alcohol resin layer, a vapor-deposited layer, and a sealant layer are laminated together. A packaging material wherein the cross-sectional indentation hardness of the polyvinyl alcohol resin layer, as measured by a nanoindenter, is 50 to 100 MPa.

2. The packaging material according to claim 1, wherein the sealant layer contains polyethylene.

3. The packaging material according to claim 1, wherein the thickness of the polyvinyl alcohol resin layer is 0.05 to 10 μm.

4. The packaging material according to claim 1, wherein the polyvinyl alcohol resin layer contains ethylene vinyl alcohol.

5. The packaging material according to claim 4, wherein the ethylene unit content in the ethylene vinyl alcohol is 30 to 50 mol%.

6. The packaging material according to claim 1, wherein the vapor-deposited layer is an inorganic oxide layer made of silicon oxide or aluminum oxide.

7. The packaging material according to claim 1, wherein the substrate and the polyvinyl alcohol resin layer are co-extruded layers formed by a co-extrusion method.

8. A packaging bag comprising the packaging material according to any one of claims 1 to 7.

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