Multilayer structure

Abstract

To provide a multilayer structure capable of forming a packaging body that has excellent releasing properties even for foodstuffs that release gas during storage, such as roasted coffee beans, and that can prevent the bag from breaking due to rise in an internal pressure, and that can control odor leakage from contents even when being subjected to impacts such as falling.SOLUTION: There is provided a multilayer structure comprising: a sealant layer (A), a paper layer (B), and a barrier layer. The sealant layer (A) has oxygen permeability of 100 cc / (m2 day atm) or greater measured at a temperature of 23°C, and relative humidity of 50% according to JIS-K 7126 -2. The paper layer has basis weight of less than 50 g / m2, and density of less than 1.00 g / cm3. The barrier layer (C) includes at least one selected from a polyvinylalcohol-based resin and a modified starch.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a multilayer structure used for food packaging containers and the like, and to a package and a food package each including the multilayer structure. [Background technology]

[0002] With the recent rise in environmental awareness and calls to reduce plastic use, the demand for paper packaging is on the rise. Although paper is a material with excellent biodegradability and recyclability, it has low barrier properties and strength, and in order to fulfill the same functions as plastic packaging, it needs to be laminated or composited with other functional materials.

[0003] Roasted coffee beans are one of the foods for which there is a high demand for paper packaging, but after packaging, the coffee beans release gases such as carbon dioxide, which increases the internal pressure and can cause the beans to burst if they are sealed. Conventionally, measures have been taken to prevent this, such as providing check valves or holes in the surface and heat-sealed parts of the packaging (e.g., Patent Document 1). Similar problems can also occur with fermented foods such as miso. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-167335 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional check valves are an obstacle to recycling, and when holes are provided, not only do costs increase, but it is not easy to achieve a barrier property as well. On the other hand, according to the inventor's research, even if a package without a valve or hole is provided with barrier properties, the internal pressure may increase during storage due to gas released from the food, causing the bag to break (sometimes called bag breakage) or causing odor leakage from the contents, and odor leakage from the contents is particularly noticeable when the package is subjected to an impact such as being dropped. It was also found to be difficult to prevent bag breakage and achieve both odor leakage and disintegration properties.

[0006] Therefore, an object of the present invention is to provide a multilayer structure capable of forming a package that has excellent disintegration properties even for foods that release gas during storage, such as roasted coffee beans, and that can prevent bags from breaking due to an increase in internal pressure and suppress odor leakage from the contents even if the bag is subjected to an impact such as being dropped, as well as a package and a food package that include the multilayer structure. [Means for solving the problem]

[0007] As a result of intensive research into solving the above problems, the present inventors have found that in a multilayer structure comprising a sealant layer (A), a paper layer (B) and a barrier layer (C) in this order, the above problems can be solved if the oxygen permeability of the sealant layer (A) is within a specific range, the paper layer (B) has specific basis weight and density, and the barrier layer (C) contains specific components, and have completed the present invention. That is, the present invention includes the following aspects.

[0008] [1] A multilayer structure including a sealant layer (A), a paper layer (B) and a barrier layer (C) in this order, wherein the sealant layer (A) has an oxygen permeability of 100 cc / (m2) measured at a temperature of 23°C and a humidity of 50% in accordance with JIS K 7126-2. 2 ·day·atm) or more, and the basis weight of the paper layer (B) is 50g / m 2 and density is less than 1.00g / cm 3 and the barrier layer (C) comprises at least one selected from the group consisting of polyvinyl alcohol-based resins and modified starches. [2] The multilayer structure according to [1], wherein the sealant layer (A) contains at least one selected from the group consisting of polyolefin-based resins and biodegradable polyester-based resins. [3] The multilayer structure according to [1] or [2], comprising a sealant layer (A), a paper layer (B), a barrier layer (C) and a paper layer (D) in this order. [4] A package having a sealant layer (A) contained in the multilayer structure according to any one of [1] to [3] adhered thereto. [5] A food package comprising a food product that releases carbon dioxide inside the package described in [4]. [6] The food packaging body described in [5], wherein the food that releases carbon dioxide is roasted coffee beans or a fermented food. Effect of the Invention

[0009] The present invention can provide a multilayer structure capable of forming a package that has excellent disintegration properties, can prevent bag breakage due to an increase in internal pressure, and can suppress odor leakage from the contents even when the package is subjected to an impact such as being dropped, even for foods that release gas during storage, such as roasted coffee beans, and a package and food package including the multilayer structure. In particular, the package can be suitably used for food packaging materials that release gas during storage, such as roasted coffee beans. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a twin-screw extruder used in the examples. [Diagram 2] FIG. 2 is a schematic diagram of a laminate manufacturing apparatus used in the examples. [Diagram 3] FIG. 2 is a schematic diagram of a manufacturing apparatus for a multilayer structure used in the examples.

[0011] [Multilayer structure] The multilayer structure of the present invention comprises a sealant layer (A), a paper layer (B) and a barrier layer (C) in this order, and the sealant layer (A) has an oxygen permeability of 100 cc / (m2) measured at a temperature of 23°C and a humidity of 50% in accordance with JIS K 7126-2. 2·day·atm) or more, and the basis weight of the paper layer (B) is 50g / m 2 and density is less than 1.00g / cm 3 The present inventors have studied a multilayer structure used for packaging containing food that releases gas during storage, such as roasted coffee beans, and have found that the barrier layer (C) has a basis weight of 50 g / m2 or less on the sealant layer (A) side rather than the barrier layer (C). 2 and density is less than 1.00g / cm 3 They found that by providing a paper layer having an oxygen permeability of less than 100 cc / (m2), the gas escapes to the outside through the paper layer (B) without the bag breaking, even though the internal pressure of the packaging bag increases due to the gas released from the food. Surprisingly, the leakage of odor from the contents itself is suppressed, making it possible to provide a packaging body that is simpler and has higher performance than conventional techniques such as those in Patent Document 1. Furthermore, when the oxygen permeability of the sealant layer (A) is less than 100 cc / (m2, 2 By providing a barrier layer (C) containing at least one selected from the group consisting of polyvinyl alcohol resins and modified starches, high disintegration properties can be achieved, providing a package with high recyclability.

[0012] The phrase "comprising a sealant layer (A), a paper layer (B) and a barrier layer (C) in this order" means that the sealant layer (A), the paper layer (B) and the barrier layer (C) are laminated in this order, and other layers such as adhesive layers may be present between each layer. It is preferable that the sealant layer (A), the paper layer (B) and the barrier layer (C) are directly laminated.

[0013] <Sealant layer (A)> The multilayer structure of the present invention contains a sealant layer (A), and therefore when producing the package of the present invention, the sealant layers (A) of the multilayer structure of the present invention can be bonded together to easily produce the package. In addition, the package of the present invention has an oxygen transmission rate (sometimes abbreviated as OTR) of 100 cc / (m2) or more, measured at a temperature of 23°C and a humidity of 50% in accordance with JIS K 7126-2.2 ·day·atm) or more, bag breakage caused by an increase in the internal pressure of the package can be suppressed. From the viewpoint of suppressing bag breakage caused by an increase in the internal pressure of the package, the OTR of the sealant layer (A) is set to 200 cc / (m 2 ·day·atm) or more is preferable, and 300cc / (m 2 The OTR of the sealant layer (A) is usually 100,000 cc / (m 2 ·day·atm) or less, and 50000cc / (m 2 ·day · atm) or less, 30000cc / (m 2 ·day · atm) or less, or 15000cc / (m 2 The oxygen permeability of the sealant layer (A) can be measured, for example, by the method described in the Examples. In this specification, the upper limit and the lower limit of the numerical range can be combined in any combination.

[0014] The material constituting the sealant layer (A) must have an oxygen transmission rate (OTR) of 100cc / (m2) measured at a temperature of 23°C and a humidity of 50% in accordance with JIS K 7126-2. 2The thermoplastic resin is not particularly limited as long as it has a thermal conductivity of 1000 MPa (days) or more, but usually contains a thermoplastic resin. One or more types of thermoplastic resins may be contained. Examples of the thermoplastic resin include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polybutylene succinate (PBS), poly(ethylene glycol-co-1,4-cyclohexane dimethanol terephthalate) (PETG), and polybutylene succinate adipate (PBSA); polyolefin resins such as polyethylene and polypropylene; polystyrene resins; polymethylpentene resins; polyvinyl chloride resins; polyacetal resins; polycarbonate resins; polylactic acid (PLA); esterified starch; cellulose acetate resins; polyurethane resins such as biopolyurethane; poly(meth)acrylic resins such as polymethylmethacrylic; ionomer resins; and copolymers thereof. Examples of the copolymers include styrene-(meth)acrylic copolymers, acrylonitrile-butadiene-styrene copolymers, and acrylonitrile-styrene copolymers. These thermoplastic resins can be used alone or in combination of two or more. The (meth)acrylic resin includes methacrylic resin and acrylic resin. The thermoplastic resin may be a fossil resource-derived resin or a biological resin. Among the thermoplastic resins exemplified above, examples of the biological resin include polylactic acid (PLA), esterified starch, cellulose acetate, polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), biopolyethylene, biopolyethylene terephthalate, and biopolyurethane. The biological resin includes a substance derived from a renewable organic resource as a raw material, and is preferably a polymer material having a number average molecular weight (Mn) of 1,000 or more obtained by chemical or biological synthesis. The use of biodegradable resins such as PLA, esterified starch, cellulose acetate, PBS, and PBSA can improve biodegradability, and biodegradable polyester resins such as PBS and PBSA are particularly preferred. The term "biodegradable resin" refers to a resin that can be decomposed to the molecular level by the action of microorganisms, and ultimately circulates back into nature as carbon dioxide and water.

[0015] Among these thermoplastic resins, from the viewpoints of heat sealing properties and preventing the package from breaking, at least one resin selected from the group consisting of polyolefin resins, polyester resins, polystyrene resins, poly(meth)acrylic resins, and copolymers thereof is preferred, and at least one resin selected from the group consisting of polyethylene, polypropylene, PBS, PBSA, PETG, and styrene-(meth)acrylic copolymers (acrylic emulsions) is more preferred.

[0016] In a preferred embodiment of the present invention, from the viewpoints of improving heat sealability and preventing rupture of the package, the sealant layer (A) preferably contains at least one selected from the group consisting of polyolefin resins and biodegradable polyester resins, and more preferably contains at least one selected from the group consisting of polyethylene, polypropylene, PBS, and PBSA.

[0017] In one embodiment of the present invention, the glass transition temperature (also referred to as Tg) of the sealant layer (A) is preferably -150°C or higher, more preferably -130°C or higher, even more preferably -120°C or higher, even more preferably -110°C or higher, and preferably 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower. When the Tg of the sealant layer (A) is within the above range, it is easy to maintain heat sealability suitable for food packaging materials. The Tg of the sealant layer (A) can be measured by a differential scanning calorimeter (DSC). The above Tg indicates the Tg of the sealant layer (A) itself, but it may be the Tg of the resin contained in the sealant layer (A). That is, the Tg of the resin contained in the sealant layer (A) can be selected from the above Tg range of the sealant layer (A). In addition, when the sealant layer (A) contains two or more resins, the Tg of the resin can be the average value of all the resins.

[0018] In one embodiment of the present invention, the weight average molecular weight (also referred to as Mw) of the sealant layer (A) is preferably 10,000 or more, more preferably 20,000 or more, and preferably 1,000,000 or less, more preferably 800,000 or less. When the Mw of the sealant layer (A) is within the above range, it is easy to achieve both melt moldability and mechanical strength. The above Mw indicates the Mw of the sealant layer (A) itself, but it may also be the Mw of the resin contained in the sealant layer (A). That is, the Mw of the resin contained in the sealant layer (A) can be selected from the above Mw range of the sealant layer (A). In addition, when the sealant layer (A) contains two or more resins, the Mw of the resin can be the average value of all the resins. The Mw can be determined by performing gel permeation chromatography (GPC) measurement and converting it into standard polystyrene.

[0019] The sealant layer (A) may further contain an additive. Examples of the additive include additives exemplified in the section <Barrier layer (C)> described later. These additives may be used alone or in combination of two or more. The sealant layer (A) may be provided in one or more, and may be a single layer or multilayer. When the multilayer structure has two or more sealant layers (A), at least one sealant layer (A) may be disposed on the side of the barrier layer (C) opposite to the side where the paper (B) is located. The thickness and type of the two or more sealant layers (A) may be the same or different. When the sealant layer (A) contains an additive other than the thermoplastic resin, the content thereof is preferably 30% by mass or less, more preferably 20% by mass or less, and may be 10% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less, based on the mass of the sealant layer (A).

[0020] The sealant layer (A) may be a layer having sealing properties (e.g., heat sealing properties), water vapor barrier properties, light blocking properties, etc., and is preferably a layer having sealing properties. When the sealant layer (A) has sealing properties, it enhances the airtightness, protects the contents from deterioration due to oxidation by oxygen, etc., and tends to enable the storage period to be extended.

[0021] The form of the sealant layer (A) is not particularly limited, but is preferably a film or sheet. The thickness of the sealant layer (A) is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, particularly preferably 10 μm or more, from the viewpoint of easily improving the barrier property, foaming resistance, and deformation resistance, and is preferably 1000 μm or less, more preferably 500 μm or less, even more preferably 200 μm or less, even more preferably 100 μm or less, particularly preferably 70 μm or less, and particularly preferably 50 μm or less. When the thickness of the sealant layer (A) is within the above range, the bag breakage of the package of the present invention tends to be more suppressed. When the multilayer structure has two or more sealant layers (A), the thickness of the sealant layer (A) indicates the thickness of one sealant layer (A). The thickness of the sealant layer (A) can be measured by microscopic observation of a cross-sectional image obtained by cutting the multilayer structure perpendicular to the thickness direction, and can be measured, for example, by the method described in the Examples.

[0022] A commercially available product can also be used as the sealant layer (A). When forming the sealant layer (A), if the extrusion coating described below is used, a composition capable of forming a resin layer by extrusion coating (e.g., resin pellets) can be used, if the solution coating described below is used, a composition capable of forming a resin layer by solution coating (e.g., a resin emulsion, etc.) can be used, and if the attachment method described below is used, a film or sheet can be used as the sealant layer (A).

[0023] <Paper layer (B)> The multilayer structure of the present invention can prevent bag breakage caused by an increase in the internal pressure of the package of the present invention by including the paper layer (B). The paper layer (B) is laminated on the sealant layer (A) side of the barrier layer (C), and this allows the gas inside the package to be appropriately released to the outside.

[0024] The basis weight of the paper layer (B) is 50 g / m 2 The basis weight of the paper layer (B) is less than 50 g / m 2If the weight is more than this, the odor leakage from the contents in the package of the present invention may not be suppressed. The basis weight of the paper layer (B) is preferably 1 g / m 2 More preferably, 10 g / m 2 More preferably, 20 g / m 2 More preferably, 30 g / m 2 More preferably, it is 45 g / m 2 Less than 40 g / m 2 Less than 40 g / m, more preferably 2 less than 38 g / m 2 The basis weight of the paper layer (B) is within the above range, the multilayer structure of the present invention has good disintegration properties, and the package of the present invention can suppress odor leakage from the contents. When there are two or more paper layers (B), the basis weight of the paper layer (B) means the basis weight of one paper layer (B). The basis weight of the paper layer (B) can be measured by the method described in the Examples.

[0025] The density of the paper layer (B) is 1.00 g / cm 3 The density of the paper layer (B) is less than 1.00 g / cm 3 When the density of the paper layer (B) is less than 0.90 g / cm, the bag breakage caused by the increase in the internal pressure in the package of the present invention can be suppressed. 3 Less than or equal to 0.80 g / cm 3 More preferably, 0.75 g / cm 3 The density of the paper layer (B) is preferably 0.30 g / cm or less from the viewpoint of suppressing odor leakage of the contents. 3 More preferably, 0.40 g / cm 3 More preferably, 0.50 g / cm 3 That's all.

[0026] The paper constituting the paper layer (B) may be, for example, a film or sheet containing pulp, a filler, a chemical, or a pigment. Examples of pulp include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood pulp (NUKP), and sulfite pulp; mechanical pulps such as stone grind pulp and thermomechanical pulp; wood fibers such as deinked pulp and waste paper pulp; and non-wood fibers obtained from kenaf, bamboo, hemp, and the like. These pulps can be used alone or in combination of two or more. Among these, chemical pulp, mechanical pulp, and wood fiber are preferred, and chemical pulp is more preferred, from the viewpoints of easily suppressing the occurrence of foreign matter contamination in the base paper and the occurrence of discoloration over time when recycling used paper containers, and of easily improving the surface texture when printed.

[0027] Examples of the filler include known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers. The fillers can be used alone or in combination of two or more. Examples of the chemicals include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents (e.g., neutral sizing agents), water-resistant agents, water retention agents, thickeners, lubricants, retention improvers, drainage improvers, and paper strength enhancers, and these may be used alone or in combination of two or more. Examples of the retention improvers include aluminum sulfate and various anionic, cationic, nonionic, or amphoteric ones. Examples of the dry strength enhancers include polyacrylamide and cationized starch, and examples of the wet strength enhancers include polyamidoamine epichlorohydrin. These chemicals are added within a range that does not affect the formation or runnability. Examples of neutral sizing agents include alkyl ketene dimers, alkenyl succinic anhydrides, and neutral rosin sizing agents. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate salts, colloidal silica, and satin white, and organic pigments such as solid, hollow, and core-shell types, which can be used alone or in combination. Furthermore, dyes, fluorescent whitening agents, pH adjusters, defoamers, pitch control agents, slime control agents, and the like can also be added as necessary. The surface of the paper may be treated with various chemicals or pigments.

[0028] The method for producing paper (papermaking) is not particularly limited, and paper can be produced by acidic papermaking, neutral papermaking, or alkaline papermaking using a known Fourdrinier former, on-top hybrid former, gap former machine, or the like.

[0029] The method for treating the paper surface is not particularly limited, but known coating devices such as a rod metering size press, a pond type size press, a gate roll coater, a spray coater, a blade coater, and a curtain coater can be used.

[0030] Examples of the paper obtained in this manner include fine paper, medium quality paper, coated paper, one-sided glossy paper, kraft paper, one-sided glossy kraft paper, bleached kraft paper, unbleached kraft paper, one-sided glossy bleached kraft paper, rayon paper, tissue paper, glassine paper, paperboard, white paperboard, waterproof paper, cellophane, liner, etc. The papers can be used alone or in combination of two or more kinds.

[0031] The paper may have a transparent coating layer on one or both sides of the base paper as a part of the paper. By applying a transparent coating to the base paper, the surface strength and smoothness of the base paper can be easily improved, and the coatability when applying a pigment can be easily improved. The transparent coating layer may contain a starch-derived polymer compound as a binder. The amount of the transparent coating is 0.1 to 4.0 g / m2 in solids per side. 2 is preferable, and 0.5 to 2.5 g / m 2 is more preferable. For example, a coating liquid mainly composed of starch, various starches such as oxidized starch, polyacrylamide, polyvinyl alcohol, and other water-soluble polymers may be applied onto the base paper using a coater (coating machine) such as a size press, a gate roll coater, a premetering size press, a curtain coater, or a spray coater. In order to make the coating layer uniform after coating, it is preferable to pre-calender the base paper before coating using an online soft calender, online chilled calender, or the like to smooth the base paper in advance.

[0032] The paper may be smoothed as necessary. For the smoothing treatment, a normal smoothing treatment device such as a super calendar, a gloss calendar, a soft calendar, a heat calendar, or a shoe calendar can be used. The smoothing treatment device is used on-machine or off-machine as appropriate, and the shape of the pressure device, the number of pressure nips, heating, etc. are also appropriately adjusted.

[0033] <Barrier layer (C)> The multilayer structure of the present invention can suppress odor leakage from the package of the present invention by including a barrier layer (C), and the paper layer of the multilayer structure of the present invention has excellent disintegration properties. The barrier layer (C) includes at least one selected from the group consisting of polyvinyl alcohol resins and modified starches, and preferably includes polyvinyl alcohol resins and modified starch. In this specification, the term "barrier properties" refers to properties that can prevent or suppress odor leakage from the contents of the package, in addition to properties that can prevent or suppress gas permeation.

[0034] (Modified starch) From the viewpoint of easily improving the barrier properties, foaming resistance, deformation resistance, disintegration property and biodegradability, the modified starch is preferably at least one selected from the group consisting of etherified starch, esterified starch, cationized starch and crosslinked starch.

[0035] Examples of starches include starches derived from cassava, corn, potato, sweet potato, sago, tapioca, sorghum, beans, bracken, lotus, water chestnut, wheat, rice, oats, arrowroot, peas, etc. Among these, starches derived from corn and cassava are preferred, and starches derived from corn with high amylose are more preferred. The starches can be used alone or in combination of two or more kinds.

[0036] Examples of the etherified starch include alkyl-etherified starches such as methyl-etherified starch, carboxyalkyl-etherified starches such as carboxymethyl-etherified starch, and hydroxyalkyl-etherified starches such as etherified starches having a hydroxyalkyl group having 2 to 6 carbon atoms. Allyl-etherified starch can also be used.

[0037] Examples of the esterified starch include esterified starches having structural units derived from carboxylic acids, such as esterified starches having structural units derived from acetic acid; esterified starches having structural units derived from dicarboxylic anhydrides, such as esterified starches having structural units derived from maleic anhydride, esterified starches having structural units derived from phthalic anhydride, and esterified starches having structural units derived from octenylsuccinic anhydride; and esterified starches having structural units derived from oxo acids, such as nitrate-esterified starch, phosphate-esterified starch, and urea-phosphate-esterified starch. Other examples include xanthate-esterified starch, acetoacetate-esterified starch, and the like.

[0038] Examples of the cationic starch include a reaction product of starch with 2-diethylaminoethyl chloride, and a reaction product of starch with 2,3-epoxypropyltrimethylammonium chloride.

[0039] Examples of the crosslinked starch include formaldehyde crosslinked starch, epichlorohydrin crosslinked starch, phosphate crosslinked starch, and acrolein crosslinked starch.

[0040] From the viewpoint of easily improving the barrier property, foaming resistance, deformation resistance, disintegration property and biodegradability, the modified starch is preferably at least one selected from the group consisting of etherified starch having a hydroxyalkyl group having 2 to 6 carbon atoms and esterified starch having a structural unit derived from dicarboxylic acid anhydride, more preferably at least one selected from the group consisting of hydroxyethyl etherified starch, hydroxypropyl etherified starch, hydroxybutyl etherified starch, esterified starch having a structural unit derived from maleic anhydride, esterified starch having a structural unit derived from phthalic anhydride and esterified starch having a structural unit derived from octenylsuccinic anhydride, and even more preferably at least one selected from the group consisting of hydroxyethyl etherified starch, hydroxypropyl etherified starch and hydroxybutyl etherified starch. The modified starch (A) can be used alone or in combination of two or more kinds. In this specification, the number of carbon atoms described before "starch" refers to the number of carbon atoms in a group substituted with one hydroxyl group in starch (a group formed by modifying one hydroxyl group in starch). For example, etherified starch having a hydroxyalkyl group with 2 to 5 carbon atoms indicates that the hydroxyalkyl group formed by modifying one hydroxyl group in the starch has 2 to 5 carbon atoms.

[0041] The etherified starch having a hydroxyalkyl group having 2 to 6 carbon atoms may be obtained by reacting starch with an alkylene oxide such as ethylene oxide, propylene oxide, butylene oxide, etc. The average number of hydroxy groups used for modification is preferably 0.05 to 2 per glucose unit in the starch.

[0042] The average amylose content of the modified starch contained in the barrier layer (C) is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, and particularly preferably 65% ​​by mass or more, from the viewpoint of improving the barrier property. When the average amylose content is equal to or more than the above lower limit, the barrier property and the deformation resistance are likely to be improved. The average amylose content in the modified starch is usually 90% by mass or less. In this specification, the amylose content can be measured, for example, by the iodine coloring method described in "Starch 50 No.4 158-163 (1998)". In addition, when one type of modified starch is used, the average amylose content indicates the amylose content of the one type of modified starch, and when two or more types of modified starch are used, it is the weighted average of the amylose contents of the two or more types of modified starches.

[0043] The moisture content in the modified starch may be 5 to 15% by mass.

[0044] The modified starch may be commercially available. Representative examples of commercially available modified starches include ECOFILM (trademark) and National 1658 (trademark), which are hydroxypropyl etherified starches manufactured by Ingredión.

[0045] The content of the modified starch is preferably 30 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, particularly preferably 70 parts by mass or more, particularly preferably 75 parts by mass or more, and is preferably 99.5 parts by mass or less, more preferably 99 parts by mass or less, even more preferably 98 parts by mass or less, particularly preferably 95 parts by mass or less, based on 100 parts by mass of the total of the modified starch and the polyvinyl alcohol resin. When the content of the modified starch is equal to or more than the lower limit, the biodegradability and disintegrability are easily improved, and when the content of the modified starch is equal to or less than the upper limit, the barrier property, oil resistance, and deformation resistance are easily improved. The content of the modified starch can be selected from the above range even when based on the mass of the barrier layer (C).

[0046] (Polyvinyl alcohol resin) Polyvinyl alcohol resins are polymers that are compatible with modified starch.

[0047] The saponification degree of the polyvinyl alcohol resin is preferably 80 mol% or more, and may be 100 mol% or less, 99.9 mol% or less, or 99.8 mol% or less. When the saponification degree of the polyvinyl alcohol is within the above range, the barrier property, foaming resistance, and deformation resistance are easily improved. The saponification degree is more preferably 85 mol% or more, further preferably 88 mol% or more, and particularly preferably 90 mol% or more. The saponification degree indicates the molar fraction of hydroxyl groups relative to the total of hydroxyl groups and ester groups in the polyvinyl alcohol resin. The saponification degree can be measured in accordance with JIS K 6726 (polyvinyl alcohol test method).

[0048] The polyvinyl alcohol resin preferably has a viscosity of 1 to 50 mPa·s at 20°C of a 4% aqueous solution of the polyvinyl alcohol resin measured in accordance with JIS Z 8803. When the viscosity of the polyvinyl alcohol is within the above range, the barrier property, foaming resistance, and deformation resistance tend to be easily improved. The viscosity is more preferably 2 mPa·s or more, even more preferably 3 mPa·s or more, more preferably 45 mPa·s or less, even more preferably 40 mPa·s or less.

[0049] The polyvinyl alcohol resin may further contain other monomer units other than the vinyl alcohol unit. Examples of the other monomer units include monomer units derived from ethylenically unsaturated monomers. Examples of the ethylenically unsaturated monomer include α-olefins such as ethylene, propylene, n-butene, isobutylene, and 1-hexene; acrylic acid and its salts; unsaturated monomers having an acrylic acid ester group; methacrylic acid and its salts; unsaturated monomers having a methacrylic acid ester group; acrylamide, N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts (e.g., quaternary salts); methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate, 2,3-diacetoxy-1-allyloxypropane and allyl chloride; unsaturated dicarboxylic acids and their salts or esters such as maleic acid, itaconic acid and fumaric acid; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate; and vinyl ester monomers such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl caproate, vinyl carboxylate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate and vinyl benzoate. The content of other monomer units is preferably 10 mol % or less, and more preferably 5 mol % or less, based on the total molar amount of the structural units constituting the polyvinyl alcohol resin.

[0050] The method for producing the polyvinyl alcohol resin is not particularly limited. For example, a method of polymerizing vinyl acetate monomer and any other monomer, and saponifying the resulting polymer to convert it into vinyl alcohol units can be mentioned. Examples of the polymerization method include batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization. Examples of the polymerization method include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. The saponification of the polymer can be performed by a known method. For example, the saponification can be performed in a state where the polymer is dissolved in alcohol or water-containing alcohol. The alcohol that can be used at this time is, for example, a lower alcohol such as methanol or ethanol. The polyvinyl alcohol resin can be used alone or in combination of two or more kinds.

[0051] The content of the polyvinyl alcohol resin is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, even more preferably 2 parts by mass or more, particularly preferably 5 parts by mass or more, particularly more preferably 10% by mass or more, based on 100 parts by mass of the total of the modified starch and the polyvinyl alcohol resin, and is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, even more preferably 40 parts by mass or less, particularly preferably 30 parts by mass or less, and particularly preferably 25 parts by mass or less. When the content of the polyvinyl alcohol resin is equal to or more than the above lower limit, the barrier property, oil resistance, and deformation resistance are easily improved, and when the content of the polyvinyl alcohol resin is equal to or less than the above upper limit, the biodegradability and disaggregability are easily improved. The content of the polyvinyl alcohol resin can be selected from the above range even when based on the mass of the barrier layer (C).

[0052] In the barrier layer (C), the total proportion of the modified starch and the polyvinyl alcohol-based resin is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, and may be 90% by mass or more, 95% by mass or more, or 98% by mass or more, based on the mass of the barrier layer (C). The total proportion of the modified starch (A) and the polyvinyl alcohol-based resin may be 100% by mass or less. When the total proportion of the modified starch (A) and the polyvinyl alcohol-based resin is within the above range, the barrier property, foaming resistance, deformation resistance, biodegradability, and disaggregability are easily improved.

[0053] The total proportion of the modified starch (A) and the polyvinyl alcohol-based resin is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more, and may be 90% by mass or more, 95% by mass or more, 98% by mass or more, or 99% by mass or more, based on the mass of the resin constituting the barrier layer (C). The total proportion of the modified starch (A) and the polyvinyl alcohol-based resin may be 100% by mass or less.

[0054] (Other ingredients) In the multilayer structure of the present invention, the barrier layer (C) may further contain a fatty acid having 12 to 22 carbon atoms and / or a fatty acid salt thereof. Examples of fatty acids having 12 to 22 carbon atoms and fatty acid salts thereof include stearic acid, calcium stearate, sodium stearate, palmitic acid, lauric acid, myristic acid, linoleic acid, and behenic acid. Among these, stearic acid, calcium stearate, and sodium stearate are preferred from the viewpoint of processability. The fatty acids having 12 to 22 carbon atoms and fatty acid salts thereof can each be used alone or in combination of two or more kinds.

[0055] When the barrier layer (C) contains a fatty acid having 12 to 22 carbon atoms and / or a fatty acid salt thereof, the content in the barrier layer (C) is preferably 0.01 to 3 mass%, more preferably 0.03 to 2 mass%, and even more preferably 0.1 to 1 mass%, based on the mass of the barrier layer (C). If the content of the fatty acid having 12 to 22 carbon atoms and / or a fatty acid salt thereof is within the above range, it tends to be advantageous in terms of processability.

[0056] The barrier layer (C) may further contain clay. Examples of the clay include synthetic or natural layered silicate clays, such as montmorillonite, bentonite, beidellite, mica, hectorite, saponite, nontronite, sauconite, vermiculite, ledikite, magadite, kenyaite, stevensite, and vulkonskoite. The clays may be used alone or in combination.

[0057] When the barrier layer (C) contains clay, the content in the barrier layer (C) is preferably 0.1 to 5 mass%, more preferably 0.1 to 3 mass%, and further preferably 0.5 to 2 mass%, based on the mass of the barrier layer (C). If the clay content is within the above range, it tends to be advantageous in terms of transparency and strength.

[0058] The barrier layer (C) may contain a plasticizer from the viewpoint of film-forming property and coating property. Examples of the plasticizer include water, sorbitol, glycerol, maltitol, xylitol, mannitol, glycerol trioleate, epoxidized linseed oil, epoxidized soybean oil, tributyl citrate, acetyl triethyl citrate, glyceryl triacetate, 2,2,4-trimethyl-1,3-pentanediol diisobutyrate, polyethylene oxide, and polyethylene glycol. The plasticizers can be used alone or in combination of two or more kinds. Among these plasticizers, water is preferred from the viewpoint of enhancing the barrier property. When the barrier layer (C) contains water, the total proportion of the modified starch, the polyvinyl alcohol resin and the water in the barrier layer (C), relative to the mass of the barrier layer (C), is preferably 70 mass% or more, more preferably 80 mass% or more, and even more preferably 85 mass% or more, and may be 90 mass% or more, 95 mass% or more, 98 mass% or more, 99 mass% or more, or 99.9 mass% or more.

[0059] The moisture content (water content) in the barrier layer (C) is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 7% by mass or more, and is preferably 20% by mass or less, more preferably 18% by mass or less, and even more preferably 15% by mass or less, based on the mass of the barrier layer (C). When the moisture content is equal to or more than the above lower limit, the barrier layer (C) is likely to have an appropriate bending resistance as a food packaging material, and when the moisture content is equal to or less than the above upper limit, the foaming resistance, deformation resistance, and barrier properties are likely to be improved. The moisture content is measured by crushing the powder to a maximum particle size of 1 mm or less using a Wonder Blender WB-1 and measuring the moisture content at 130°C for 60 minutes using a heat-drying moisture meter.

[0060] The barrier layer (C) may further contain additives, as necessary, such as fillers, processing stabilizers, weathering stabilizers, colorants, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, other thermoplastic resins, lubricants, fragrances, antifoaming agents, deodorants, extenders, release agents, mold releasing agents, reinforcing agents, crosslinking agents, mildew inhibitors, preservatives, crystallization rate retarders, etc. These additives may be used alone or in combination of two or more.

[0061] The barrier layer (C) may be one or more, and may be a single layer or multiple layers. When the barrier layer (C) is two or more, the position of the other barrier layer (C) is not particularly limited as long as the sealant layer (A), the paper layer (B) and the barrier layer (C) are laminated in this order, and the thickness and type of each layer may be the same or different.

[0062] The barrier layer (C) is preferably in the form of a film or sheet. From the viewpoint of improving the barrier property, foaming resistance, deformation resistance and biodegradability, the thickness of the barrier layer (C) is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, particularly preferably 10 μm or more, and is preferably 600 μm or less, more preferably 500 μm or less, even more preferably 400 μm or less, even more preferably 300 μm or less, particularly preferably 250 μm or less. Particularly more preferably 150 μm or less, particularly more preferably 80 μm or less. When the multilayer structure has two or more barrier layers (C), the thickness of the barrier layer (C) indicates the thickness of one barrier layer (C). The thickness of the barrier layer (C) can be measured by microscopic observation, for example, by the method described in the Examples.

[0063] <Multilayer structure> Since the multilayer structure of the present invention includes a sealant layer (A), a paper layer (B), and a barrier layer (C) in this order, when a package is produced by bonding the sealant layers (A) of the multilayer structure of the present invention together, even if the contents are foods that release gas during storage, such as roasted coffee beans, the gas is released to the outside through the sealant layer (A) and the paper layer (B), so that the bag can be prevented from breaking. In addition, although the reason is unclear, odor leakage can also be suppressed, so that the package can be suitably used as a package for packaging foods that release gas during storage. In particular, the package formed of the multilayer structure of the present invention can effectively suppress odor leakage of the contents even if it is subjected to an impact such as being dropped. It is preferable that the multilayer structure of the present invention has the sealant layer (A), the paper layer (B), and the barrier layer (C) directly laminated in this order.

[0064] The multilayer structure of the present invention preferably includes a sealant layer (A), a paper layer (B), a barrier layer (C) and a paper layer (D) in this order. The paper layer (D) can be made of the same material as that described for the paper layer (B). The paper layer (D) may be the same as or different from the paper layer (B). The basis weight and density of the paper layer (D) are not particularly limited, and generally available paper can be used. The multilayer structure of the present invention is provided with the paper layer (D), which makes it easy to suppress defects such as curling during molding of the multilayer structure and distortion of the package caused thereby. Furthermore, the paper is exposed on the outer surface of the package, which has the effect of making it easier to recognize it as a paper package, and it is possible to suppress the barrier property from decreasing when the barrier layer (C), which is highly water-soluble, gets wet with water.

[0065] The multilayer structure of the present invention may contain layers other than the sealant layer (A), the paper layer (B), the barrier layer (C), and the paper layer (D).

[0066] Examples of other layers include an adhesive layer, a primer layer, an inorganic vapor deposition layer, a heat seal layer, a moisture-proof layer, and a light-shielding layer. Examples of adhesives constituting the adhesive layer include acrylic adhesives, urethane adhesives, epoxy adhesives, vinyl acetate adhesives, ethylene-vinyl acetate adhesives, vinyl chloride adhesives, silicone adhesives, nitrile cellulose adhesives, phenol adhesives, polyvinyl alcohol adhesives, melamine adhesives, and styrene adhesives, and from the viewpoint of adhesiveness, urethane adhesives and the like are preferred. The thickness of the adhesive layer is preferably 0.1 to 30 μm, more preferably 1 to 20 μm. The thickness of the adhesive layer can be measured using an optical microscope, a film thickness gauge, or the like.

[0067] Examples of the inorganic vapor deposition layer include layers formed by vapor deposition of inorganic oxides such as silicon oxide and aluminum oxide. The heat seal layer is a layer capable of thermal adhesion (heat sealing) different from the sealant layer (A) in the present invention, and the moisture-proof layer is a layer having a moisture-proof effect.

[0068] The lamination position of the other layers is not particularly limited as long as the sealant layer (A), paper layer (B) and barrier layer (C) are laminated in this order, but it is preferable to laminate the other layers so as not to impede the release of internal gas by the sealant layer (A) and paper layer (B). The multilayer structure may have one or more other layers, and when it has two or more layers, the thicknesses and types of the other layers may be the same or different.

[0069] Specific examples of the layer configuration of the multilayer structure of the present invention are shown below. Note that " / / " means that the layers may be laminated via an adhesive layer or directly, but a direct laminate configuration may be preferable in some cases. Sealant layer (A) / / paper layer (B) / / barrier layer (C), sealant layer (A) / / paper layer (B) / / barrier layer (C) / / paper layer (D), sealant layer (A) / / paper layer (B) / / barrier layer (C) / / paper layer (D) / / barrier layer (C), sealant layer (A) / / paper layer (B) / / barrier layer (C) / / paper layer (D) / / barrier layer (C) / / paper layer (D).

[0070] In addition, the multilayer structure having the above-mentioned layer configuration may contain the other layers at any position.

[0071] The multilayer structure of the present invention has excellent oxygen barrier properties. In one embodiment of the present invention, the oxygen transmission rate (OTR) of the multilayer structure is preferably 100 cc / (m 2 ·day·atm) or less, preferably 50cc / (m 2 ·day·atm) or less, and more preferably 30cc / (m 2 ·day·atm) or less, and even more preferably 10cc / (m 2 ·day·atm) or less, and especially preferably 5cc / (m 2 ·day·atm). The lower limit of the oxygen permeability of the multi-layer structure is 0cc / (m 2 The oxygen transmission rate (OTR) of the multilayer structure can be measured by the method described in the Examples.

[0072] The multilayer structure of the present invention has excellent disintegration properties. In one embodiment of the present invention, the disintegration degree of the multilayer structure is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and even more preferably 85% or more, and may be, for example, 88% or more or 90% or more. The upper limit of the disintegration degree of the multilayer structure is 100% or less. The disintegration degree of the multilayer structure can be measured, for example, by the method described in the Examples. In this specification, disintegration property refers to the property of being able to disintegrate, more specifically, the property of pulp being easily separated and suspended in a disintegrating liquid, and can be evaluated by the disintegration degree.

[0073] [Method of manufacturing multilayer structure] The method for producing the multilayer structure of the present invention is not particularly limited, but examples thereof include a method including a step of directly laminating a barrier layer (C) on a paper layer (B) to obtain a laminate (referred to as step (X)); and a step of laminating a sealant layer (A) on the exposed surface side of the paper layer (B) in the obtained laminate to obtain a multilayer structure (referred to as step (Y)). As another method, each layer may be formed and then laminated by dry lamination.

[0074] <Process (X)> Step (X) is a step of directly laminating a barrier layer (C) on a paper layer (B) to obtain a laminate, and preferably includes a step of coating the paper layer (B) with a water-containing composition containing modified starch and the polyvinyl alcohol-based resin (referred to as step (i)), and more preferably includes a step of using an extruder to coat the paper layer (B) conveyed by a take-off machine with the water-containing composition. Including such a step makes it easier to improve the barrier property, foaming resistance, and deformation resistance of the resulting multilayer structure. When the paper layer (D) is included, it is preferable to coat the water-containing resin composition between the paper layer (B) and the paper layer (D). That is, it is preferable to prepare a laminate (paper layer (B) / barrier layer (C) / paper layer (D)) in such a way that the water-containing resin composition coating layer is sandwiched between the paper layer (B) and the paper layer (D).

[0075] (Production of Water-Containing Composition) The water-containing composition includes a resin composition containing modified starch and a polyvinyl alcohol resin, and has a water content of 1 to 50% by mass. The water content is preferably 5% by mass or more, more preferably 8% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less. When the water content is within the above range, the coating property and film-forming property when the water-containing composition is coated on the paper (B) are easily improved, and the adhesion between the paper layer (B) and the barrier layer (C) in the obtained multilayer structure is easily improved, so that the barrier property is easily improved. The water content of the water-containing composition is, for example, the water content measured at a temperature of 130°C for 60 hours using a heat-dry type moisture meter. In this specification, the water-containing composition means all resin compositions containing water and having a water content of 1 to 50% by mass measured by the above method. That is, the water-containing composition is preferably a resin composition whose water content is adjusted to the above range by adding water to the resin composition, but also includes resin compositions whose water content is within the above range at the time of production.

[0076] The resin composition can be produced, for example, by a method including at least the steps of: (1) mixing modified starch and a polyvinyl alcohol resin to obtain a mixture; (2) extruding the mixture; and (3) cooling and drying the extruded mixture. The components contained in the resin composition are the same as those contained in the barrier layer (C), but their moisture contents may be the same or different from each other, and can be preferably selected from the same range as the moisture content of the barrier layer (C).

[0077] Step (1) is a step of mixing at least modified starch and a polyvinyl alcohol resin, and optionally other components, such as the fatty acid having 12 to 22 carbon atoms and / or the fatty acid salt thereof, the clay, the plasticizer, and the additives, can be mixed together.

[0078] Step (1) is usually carried out using an extruder in which the components are mixed homogeneously while being subjected to shear stress by the screw and heated by application of external heat to the barrel.

[0079] As the extruder, for example, a twin screw extruder can be used. The twin screw extruder may be either co-rotating or counter-rotating. The screw diameter may be, for example, 20 to 150 mm, and the ratio L / D ratio of the extruder length (L) to the screw diameter (D) may be, for example, 20 to 50. The screw rotation speed is preferably 80 rpm or more, more preferably 100 rpm or more. The extrusion molding pressure is preferably 5 bar (0.5 MPa) or more, more preferably 10 bar (1.0 MPa) or more. Each component can be directly introduced into the extruder. Also, each component may be premixed using a mixer and introduced into the extruder.

[0080] In step (1), from the viewpoint of enhancing the film-forming property and the gas barrier property, it is preferable to mix a plasticizer, preferably water, in an amount of preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, particularly preferably 20% by mass or more, and preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less, based on the mass of the mixture. Here, the mass of the mixture indicates the total mass of the mixture including the plasticizer. In step (1), the plasticizer may be introduced at the initial stage of extrusion, and the plasticizer can be introduced before the heating temperature is reached, for example, when the temperature is 100°C or less. The modified starch is subjected to a cooking treatment by a combination of moisture, heat, and shear stress, and can be gelatinized (gelated). In addition, by separately introducing a plasticizer, preferably water, the polyvinyl alcohol resin can be dissolved, the resin composition can be softened, and the modulus and brittleness can be reduced.

[0081] In step (1), the cooking treatment is preferably performed by heating to a temperature of more than 100°C and not more than 150°C, more preferably from 115°C to 140°C. Here, the cooking treatment is a treatment for crushing and gelling starch granules. Heating can be performed by applying heat from the outside to the barrel of the extruder. By applying a stepwise changed temperature to each barrel, heating to the desired temperature can be achieved. When the cooking treatment is performed at a temperature of more than 120°C, it is advantageous in terms of processability.

[0082] To prevent foaming, the cooked mixture is preferably forced toward the die while the temperature is lowered to preferably 85 to 120° C., more preferably 90 to 110° C. In addition, foaming can be prevented and moisture can be removed by venting the barrel.

[0083] The residence time in the extruder can be set depending on the temperature profile and the screw speed, and is preferably 1 to 2.5 minutes.

[0084] In the step (2) of extruding the mixture, the molten mixture that has been forced through the extruder while being melt-kneaded is extruded through a die. The die temperature is preferably 85 to 120°C, more preferably 90 to 110°C.

[0085] In step (3) of cooling and drying the extruded mixture (melt), the mixture (melt) can be extruded into a film or sheet, or into a strand.

[0086] When the mixture is extruded into a film, the mixture can be extruded through a film forming die and then cooled and dried while being taken up by a take-up roller. Between the die and the roller, cooling is preferably performed to prevent the mixture from adhering to the roller. A forming roll may be installed between the die and the roller. The forming roll may be made of, for example, rubber, resin, or metal. For drying, the roll may be heated, and dehumidified air may be supplied during the take-up. In the case of the blown tube method, the dehumidified air can be used to expand the film as it exits the die. Talc can also be entrained in the air flow to prevent the film from blocking.

[0087] When the mixture is extruded in the form of strands, it can be extruded through a strand nozzle with multiple holes and cut with a rotary cutter to form the strands into pellets. To prevent the pellets from sticking together, vibration can be applied periodically or constantly, and moisture in the pellets can be removed by hot air, dehumidified air, or an infrared heater.

[0088] In a preferred embodiment of the present invention, since water is added to form a water-containing composition after the resin composition is formed, the resin composition is preferably in the form of pellets.

[0089] In a preferred embodiment of the present invention, water is added to the obtained resin composition (preferably a pellet-shaped resin composition), and the mixture is stirred to obtain a water-containing composition. In order to prevent the resin composition from sticking together and to allow the entire pellet to absorb water, it is preferable to add water in two or more portions while stirring. In order to keep the water content constant, the water-containing composition may be stored in a sealed container.

[0090] (Manufacture of laminates) In step (X), the water-containing composition is preferably fed into an extruder. Examples of the extruder include a single screw extruder and a twin screw extruder. The extruder has a screw diameter of, for example, 20 to 150 mm, a ratio (L / D) of the extruder length (L) to the screw diameter (D) of, for example, 15 to 50, and a screw rotation speed of, preferably, 80 rpm or more, more preferably 100 rpm or more. The cylinder temperature in the extruder may be, for example, 80 to 120°C, preferably 90 to 110°C.

[0091] The water-containing composition fed into the extruder is plasticized and discharged from the die outlet. Meanwhile, the paper layer (B) is conveyed by a take-up machine, preferably a roller-type take-up machine. The paper layer (B) is conveyed by coating the water-containing composition discharged from the die outlet onto the conveyed paper layer (B), to obtain a laminate. The obtained laminate is conveyed while being pressed against the paper layer (B) between a plurality of rolls including a metal roll, and can be wound into a roll by a winding machine. Examples of the plurality of rolls include a pressure roll, a cast roll, and a touch roll. In this way, a laminate of the paper layer (B) / barrier layer (C) can be obtained. In the present invention, since the water of the water-containing composition evaporates during the above-mentioned manufacturing process, the moisture content of the barrier layer (C) in the obtained laminate is reduced to that of the water-containing composition. The obtained laminate may also be dried to adjust the moisture content. When a paper layer (D) is included, the laminate (paper layer (B) / barrier layer (C) / paper layer (D)) can be prepared in the same manner as above, except that the paper layer (D) is transported from the side opposite the paper layer (B) and stacked so that it sandwiches the barrier layer (C).

[0092] <Process (Y)> The step (Y) is a step of laminating a sealant layer (A) on the exposed surface side of the paper layer (B) in the obtained laminate to obtain a multilayer structure.

[0093] Examples of the lamination method of the sealant layer (A) in step (Y) include an extrusion coating method, an extrusion lamination method, a solution coating method, and a film attachment method. The extrusion coating method may be, for example, a method of extrusion coating or extrusion laminating a thermoplastic resin and optional additives onto a paper layer (B) in a laminate (e.g., paper (B) / barrier layer (C)). The solution coating method may be, for example, a method of applying a solution in which a resin is dissolved or dispersed in a solvent onto a paper layer (B) in a laminate, followed by drying. The film attachment method may be, for example, a method of dry laminating or sandlaminating a film-like sealant layer (A) onto a paper layer (B) in a laminate.

[0094] When the multilayer structure of the present invention contains other layers, the method for laminating the other layers may be, for example, the methods exemplified above for laminating the sealant layer (A).

[0095] The multilayer structure of the present invention can be used, for example, as a barrier packaging material used for packaging applications such as packaging materials for food, containers, cups, etc., or as industrial materials. Among these, it can be used as a barrier packaging material used for packaging applications such as packaging materials for food, containers, cups, etc., and can be used as a soft packaging material for food, etc. In particular, from the viewpoint of utilizing the effects of the present invention, it is preferable that the package contains a food that releases gas inside, and the gas is preferably carbon dioxide. Examples of foods that release carbon dioxide include roasted coffee beans and fermented foods.

[0096] [Packaging and food packaging] The present invention encompasses a package in which the sealant layer (A) contained in the multilayer structure of the present invention is bonded. The package of the present invention may be arranged in the order of the sealant layer (A), paper layer (B) and barrier layer (C) from the inside to the outside, or in the reverse order, but from the viewpoint of suppressing bag breakage due to an increase in internal pressure, suppressing odor leakage of the contents in the package, and from the viewpoint of gas barrier properties, it is preferable to arrange the sealant layer (A), paper layer (B) and barrier layer (C) in that order from the inside to the outside, that is, the sealant layer (A) side of the multilayer structure is arranged on the inside (inside) of the package. The shape of the package of the present invention is not particularly limited as long as the sealant layer (A) is bonded to form a package, and may be, for example, a two-sided bag, a three-sided bag, a three-sided bag with a zipper, a palm-shaped bag, a gusset bag, a bottom gusset bag, a stand bag, a stand zipper bag, a four-column flat-bottom gusset bag, a side seal bag, a bottom seal bag, or the like, or may be in the form of a container or cup. In the package of the present invention, the sealant layer (A) may be bonded to a layer other than the sealant layer (A), but it is preferable that the sealant layers are bonded to each other from the viewpoint of barrier properties, etc. Furthermore, in the package of the present invention, it is preferable that the sealant layer is thermally bonded (heat sealed or heat fused) from the viewpoint of adhesiveness, barrier properties, etc. The present invention encompasses a food package containing a food that releases carbon dioxide inside the package of the present invention. The food package of the present invention is prevented from breaking due to an increase in internal pressure, has a simple structure and excellent disintegration properties, and can prevent odor leakage even if it is subjected to an impact such as being dropped. The food that releases carbon dioxide is not particularly limited, but is preferably roasted coffee beans or fermented foods, and even with these foods, the food package of the present invention can effectively prevent bag breakage and odor leakage due to an increase in internal pressure. EXAMPLES

[0097] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto.

[0098] [Test Method] (1) Oxygen permeability The films and multilayer structures for measuring the oxygen permeability of the sealant layer (A) obtained in the examples and comparative examples were stored for 2 weeks under conditions of 20°C and 65% RH, and then attached to an oxygen permeability measuring device to measure the oxygen permeability. The measurement conditions were as follows. Equipment: Modern Controls "MOCON OX-TRAN2 / 20" Temperature: 20℃ Humidity on oxygen supply side and carrier gas side: 65% RH Oxygen pressure: 1.0atm Carrier gas pressure: 1.0atm

[0099] (2) Basis weight of paper The basis weights of the paper layer (B) and the paper layer (D) used in the examples and comparative examples were measured by a method conforming to ISO 536:2019 (Paper and paperboard-Method of determining basis weight).

[0100] (3) Paper density The density of the paper layer (B) used in the examples and comparative examples was measured by a method in accordance with ISO 534:2011 (Paper and paperboard -- Determination of thickness, density and specific volume).

[0101] (4) Thickness of the sealant layer (A) and the barrier layer (C) A small piece of 1 x 1 cm was cut from the multilayer structure obtained in the examples and comparative examples, and the cross section was cut smoothly with a microtome. The cross section of the sample piece was measured using a field emission scanning electron microscope (SU-8010 manufactured by Hitachi High-Technologies Corporation), and the thicknesses of the sealant layer (A) and the barrier layer (C) were measured. When the interface was unclear, the barrier layer (C) was pretreated by potassium iodide staining before measurement.

[0102] (5) Disintegratability The multilayer structures obtained in the examples and comparative examples were evaluated for disintegrability by a method conforming to the CEPI recyclability laboratory test method-Version 2020. The disintegration degree was defined by the following formula. Dissociation degree (%)=100-Coarse reject(%)-Fine reject(%)

[0103] (6) Storage test of roasted coffee beans Using the multilayer structures obtained in the examples and comparative examples, gusset bags with inner dimensions of 90 mm in width, 50 mm in depth, and 260 mm in height were produced. In making the bags, the sealant layers (A) were heat-sealed to each other, and it was confirmed that each seal strength was greater than the material destruction of the sealant when peeled off. 200 g of coffee beans that had been cooled for 5 minutes immediately after roasting to the second crack were placed in each gusset bag, and the top was sealed under the same heat sealing conditions as in making the bag. Some of the gusset bags in which the coffee beans were sealed were dropped in a random direction from a height of 1 m. The gusset bags after the coffee beans were sealed that were not subjected to the drop test and the gusset bags after the coffee beans were sealed after the drop were each placed in a glass container with an internal volume of 3 L, the top was sealed, and the bag was stored for one week in an environment of 23°C and 50% RH. After storage, the sensor part of a portable odor sensor (Shin Cosmos Electric, XP-329m) was inserted into the gap of the glass container to measure the odor intensity, and the odor intensity of the gusset bag after the coffee beans were sealed in that was not subjected to the drop test was evaluated as "odor leakage when left still," and the odor intensity of the gusset bag after the coffee beans were sealed in that was dropped was evaluated as "odor leakage after dropping." In addition, the gusset bag in the glass container was visually checked for any breakage.

[0104] [Materials used] (1) Starch ECOFILM™: Corn starch modified with propylene oxide, amylose content 70% by weight, Ingredion

[0105] (2) PVOH Kuraray Poval (trademark) 4-98: polyvinyl alcohol resin, saponification degree 98 mol%, viscosity 4 mPa·s (20°C, 4% aqueous solution), manufactured by Kuraray Co., Ltd.

[0106] (3) Modified PVOH - Exeval (trademark) AQ-4104: Modified polyvinyl alcohol resin, manufactured by Kuraray Co., Ltd.

[0107] (4)PE Novatec (registered trademark) LC600A: Low-density polyethylene resin, manufactured by Japan Polyethylene Corporation

[0108] (5)PP Novatec (registered trademark) FL02A: Polypropylene resin, manufactured by Japan Polypropylene Corporation

[0109] (6) PETG SKYGREEN® K2012: PETG resin, manufactured by SK Chemicals Co., Ltd.

[0110] (6) PBS resin BioPBS FZ92AC: Polybutylene succinate (PBS) resin, manufactured by PTTMCC

[0111] (7) Acrylic emulsion HYDRECT: Acrylic emulsion, non-volatile content 40%, manufactured by DIC Graphics

[0112] (8)PVDC Saran™ Film 700: Polyvinylidene chloride (PVDC) film, 43 μm thick, manufactured by Asahi Kasei Corporation

[0113] (9)EVOH EVAL(TM) EF-XL: Biaxially oriented ethylene-vinyl alcohol copolymer (EVOH) film, 12 μm thick, manufactured by Kuraray Co., Ltd.

[0114] (10) Vapor-deposited PET VM-PET1310: Aluminum-deposited polyethylene terephthalate film, 12 μm thick, manufactured by Toray Advanced Film Co., Ltd.

[0115] (11) Paper layer (B) and paper layer (D) Unbleached kraft paper, basis weight 23g / m 2 , density 0.59g / cm 3 Unbleached kraft paper, basis weight 35g / m 2 , density 0.69g / cm 3 Unbleached kraft paper, basis weight 45g / m 2 , density 0.69g / cm 3 Unbleached kraft paper, grammage 50g / m 2 , density 0.69g / cm 3 Bleached kraft paper, basis weight 40g / m 2 , density 0.84g / cm 3 Glassine paper, basis weight 40g / cm 2 , density 1.00g / cm 3 The basis weight and density of the paper layer were measured according to the methods described in the above test methods (2) and (3).

[0116] <Example 1> As raw materials, 8,000 kg of ECOFILM (trademark) (starch) and 2,000 kg of Kuraray Poval (trademark) 4-98 (PVOH) were mixed in a tumbler mixer for 2 hours, and the resulting mixture was fed to a twin-screw extruder connected to a liquid pump. Figure 1 shows a schematic diagram of the twin-screw extruder used in Example 1, and the screw diameter, L / D ratio, screw rotation speed, operation method, and temperature profile (Table 1) of the extruder are shown below.

[0117] [Table 1]

[0118] Screw diameter: 27mm L / D ratio: 48 Screw rotation speed: 500 rpm Operation method: Co-rotation (meshing self-wiping) method

[0119] Specifically, the obtained mixture was fed into the barrel through a hopper in C1 at a rate of 3.5 kg / hr via a weight feeder of the twin-screw extruder. Water was injected into the barrel at a flow rate of 26 g / min through a liquid pump (L) in C4. The temperature ranges of C5 to C9 were cooking ranges, and starch was completely gelatinized within these ranges. The mixture was extruded from a multi-hole strand nozzle installed after C11 and cut with a rotary cutter to form pellets. Since the pellets contained excess moisture, the moisture was removed with hot air while constantly vibrating to prevent sticking.

[0120] Water was added to the obtained resin composition in the form of pellets until the water content reached 35% by mass relative to the mass of the resin composition. When adding water, in order to prevent the pellets from sticking together and to allow the entire pellet to absorb water uniformly, the water was added in several batches while stirring for 15 minutes with a tumbler mixer. After stirring, the pellets were placed in a polyethylene bag to prevent water from evaporating, sealed, and left at room temperature for 6 hours. In this way, a water-containing composition (water-containing pellets) with a water content of 35% by mass was obtained. The water content was confirmed by measuring for 60 minutes at 130°C using a Mettler Toledo heat-drying moisture meter "HR73".

[0121] The obtained hydrous pellets were then put into a single-screw extruder 2 shown in FIG. 2 and extruded from a film-forming die 3. Next, the hydrous composition 4 extruded from the outlet of the die 3 was coated between the paper 5 and the paper 5' conveyed by a roller-type take-up machine (not shown) so that the thickness of the resin composition layer (barrier layer (C)) was 20 μm. The laminate 6 (also called a coating) obtained by coating was immediately pressed through a pressure roll (made of rubber) 7a, a cast roll (made of metal) 7b, and a touch roll (made of rubber) 7c, and then wound up in a roll by a winder (not shown). In this way, a laminate in which the paper layer (B) / barrier layer (C) / paper layer (D) were laminated in this order was obtained. Details of the single-screw extruder used and the operating conditions, as well as the temperature profile (Table 2) are shown below. · Single screw extruder: Extruder manufactured by the Institute of Plastics Engineering (40mm diameter, L / D=25) ·Set temperature: [Table 2] ·Discharge amount: 20kg / hr Die: 450mm wide coat hanger die, lip opening 0.2mm -Die-to-cast roll distance (air gap): 150mm Paper: Unbleached kraft paper, basis weight 35g / m 2 , density 0.69g / cm 3

[0122] The obtained laminate had a good appearance without any uneven thickness or foreign matter.

[0123] Next, polyethylene (PE) (Novatec (registered trademark) LC600A) 15 was put into a single-screw extruder 16 shown in FIG. 3 and extruded from a film-forming die 17. Next, the laminate 6 obtained above was transported by a roller-type take-up machine (not shown), and the laminate 6 thus transported was coated with PE 18 extruded from the outlet of the die 17. The multilayer structure 19 obtained as a coat was immediately pressed through a pressure roll (made of rubber) 7a, a cast roll (made of metal) 7b, and a touch roll (made of rubber) 7c, and then wound up in a roll by a winder (not shown). In this way, a multilayer structure in which the sealant layer (A) / paper (B) / barrier layer (C) / paper (D) were laminated in this order was obtained. Details of the single-screw extruder used and the operating conditions are shown below. The thickness of the sealant layer (A) (PE layer) was 20 μm. The obtained multilayer structure was evaluated for oxygen permeability, thickness of each layer, disintegration property, and storage test according to the above test methods (1) and (4) to (6). The results are shown in Table 3. · Single screw extruder: Extruder manufactured by the Institute of Plastics Engineering (40mm diameter, L / D=25) ·Resin temperature: 320℃ ·Discharge amount: 20kg / hr Die: 450mm wide coat hanger die, lip opening 0.6mm -Die-to-cast roll distance (air gap): 150mm

[0124] In addition, unbleached kraft paper (basis weight 35 g / m 2 , density 0.69g / cm 3 A 20 μm thick PE layer was laminated on the paper using the same method as above to prepare a film for measuring the oxygen permeability of the sealant layer (A) having a layer structure of sealant layer (A) / paper layer, and the film was evaluated according to the method described in the above test method (1). The results are shown in Table 3.

[0125] <Example 2> A multilayer structure and a film for measuring the oxygen permeability of the sealant layer (A) were produced and evaluated in the same manner as in Example 1, except that PP was used as the sealant layer (A) and the resin temperature during lamination of the sealant layer (A) was changed to 280° C. The results are shown in Table 3.

[0126] <Example 3> A multilayer structure and a film for measuring the oxygen permeability of the sealant layer (A) were produced and evaluated in the same manner as in Example 1, except that PETG was used as the sealant layer (A) and the resin temperature during lamination of the sealant layer (A) was changed to 280° C. The results are shown in Table 3.

[0127] <Example 4> A multilayer structure and a film for measuring the oxygen permeability of the sealant layer (A) were prepared and evaluated in the same manner as in Example 1, except that PBS was used as the sealant layer (A) and the resin temperature during lamination of the sealant layer (A) was changed to 170° C. The results are shown in Table 3.

[0128] <Example 5> As the sealant layer (A), an acrylic emulsion was used to coat the paper layer (B) so that the thickness after drying would be 20 μm, and a multilayer structure was produced by drying the layer at 100° C. for 3 minutes using a hot air dryer, and a film for measuring the oxygen permeability of the sealant layer (A) was also produced by coating the acrylic emulsion in the same manner as above, but a multilayer structure and a film for measuring the oxygen permeability of the sealant layer (A) were produced and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0129] <Examples 6 to 8, 12, Comparative Examples 3, 4> Except for changing the paper layer (B) and the paper layer (D) as shown in Table 3, the multilayer structure and the sealant layer (A) were prepared and evaluated as films for measuring oxygen permeability in the same manner as in Example 1. The results are shown in Table 3.

[0130] <Example 9> Except for using only modified starch as the resin composition, a multilayer structure and a film for measuring the oxygen permeability of the sealant layer (A) were prepared and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0131] <Example 10> PVOH was stirred in hot water at 95°C for 1 hour to prepare an 18 wt% aqueous solution, which was then applied to unbleached kraft paper (basis weight 35 g / m 2 , density 0.69g / cm 3 The obtained aqueous solution was applied onto a sheet of paper (B) so that the thickness after drying would be 12 μm. Unbleached kraft paper (basis weight 35 g / m) was then applied onto the coated surface of the paper (B). 2 , density 0.69g / cm 3 ) were laminated and pressed through a laminator, and then dried with hot air at 80°C for 2 minutes to obtain a laminate (paper layer (B) / barrier layer (C) / paper layer (D)). Films for measuring the oxygen permeability of the multilayer structure and sealant layer (A) were produced and evaluated in the same manner as in Example 1, except that the obtained laminate was used. The results are shown in Table 3.

[0132] <Example 11> Except for using modified PVOH instead of PVOH, a multilayer structure and a film for measuring oxygen permeability of the sealant layer (A) were prepared and evaluated in the same manner as in Example 10. The results are shown in Table 3.

[0133] <Comparative Example 1> A laminate (barrier layer (C) / paper layer (D)) was produced in the same manner as in Example 1, except that a paper layer was laminated on only one side during the production of the laminate. A 20 μm monolayer film was formed using PE, and an adhesive (a 10:1 (weight ratio) mixture of Takelac (trademark) A520 and Takenate (trademark) A50 manufactured by Mitsui Chemicals, Inc.) was applied to one side of the obtained monolayer film, which was then dried with hot air at 60° C. for 1 minute to remove the solvent and form an adhesive layer, which was then attached to the barrier layer (C) side of the laminate to obtain a multilayer structure (sealant layer (A) / adhesive layer / barrier layer (C) / paper layer (D)). Except for using the obtained multilayer structure, evaluation was performed in the same manner as in Example 1, and the results are shown in Table 3.

[0134] <Comparative Example 2> A 43 μm-thick PVDC film was laminated on the paper layer (B) of the laminate obtained in Example 1 with an adhesive layer in the same manner as in Comparative Example 1 to produce a multilayer structure (sealant layer (A) / adhesive layer / paper layer (B) / barrier layer (C) / paper layer (D)), and when producing a film for measuring the oxygen permeability of the sealant layer (A), an adhesive layer was also provided on the paper layer in the same manner as above, and the PVDC film was laminated thereon, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

[0135] <Comparative Example 5> The oxygen permeability measurement film of the sealant layer (A) obtained in Example 1 was used as it was as a multilayer structure, and evaluation was performed in the same manner as in Example 1. The results are shown in Table 3.

[0136] <Comparative Example 6> An adhesive (a 10:1 (weight ratio) mixture of Takelac A520 and Takenate A50 manufactured by Mitsui Chemicals, Inc.) was applied to one side of a 12 μm-thick EVOH film, which was then dried with hot air at 60°C for 1 minute to remove the solvent. After that, unbleached kraft paper (basis weight 35 g / m 2 , density 0.69g / cm 3 The other side of the EVOH film was then laminated with unbleached kraft paper (basis weight 35 g / m2) in the same manner. 2 , density 0.69g / cm 3) were bonded together to obtain a laminate (paper layer (B) / adhesive layer / barrier layer (C) / adhesive layer / paper layer (D)). Except for using the obtained laminate, films for measuring the oxygen permeability of the multilayer structure and the sealant layer (A) were produced and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0137] <Comparative Examples 7 and 8> Except for using the materials shown in Table 3 instead of the EVOH film, a multilayer structure and a film for measuring the oxygen permeability of the sealant layer (A) were prepared and evaluated in the same manner as in Comparative Example 6. The results are shown in Table 3.

[0138] [Table 3-1] [Table 3-2]

[0139] As shown in Table 3, the results of the roasted coffee bean storage test, including the drop test, confirmed that the multilayer structures obtained in Examples 1 to 12 were able to retain odor without risk of bag breakage. On the other hand, Comparative Examples 1 to 8 were confirmed to be inferior in at least one of the degree of disintegration and the roasted coffee bean storage test. Therefore, it was shown that the multilayer structures obtained in Examples 1 to 12 can form a package that has excellent disintegration properties even for foods that release gas during storage, such as roasted coffee beans, and can prevent bag breakage due to an increase in internal pressure, and can suppress odor leakage from the contents even if the package is subjected to an impact such as a drop. [Explanation of symbols]

[0140] 1...Water-containing composition (pellet form) 2,16…Single screw extruder 3,17…Die 4...Water-containing composition 5,5'...paper 6...Laminate 7a…Pressure roll 7b…Cast Roll 7c…Touch roll 8…Twin-screw extruder 9. Hopper 10...Liquid addition nozzle 11…Resin thermometer 12...Resin pressure gauge 13…Adapter 14…Die 15...Polyethylene (PE) 18...Extruded PE 19...Multilayer structure

Claims

1. A multilayer structure comprising a sealant layer (A), a paper layer (B), and a barrier layer (C) in this order, wherein the sealant layer (A) has an oxygen permeability of 100 cc / (m) measured at a temperature of 23°C and a humidity of 50% in accordance with JIS K 7126-2. ２ ·day·atm) or more, and the basis weight of the paper layer (B) is 50 g / m ２ and a density of 1.00 g / cm ３ and the barrier layer (C) comprises at least one selected from the group consisting of a polyvinyl alcohol-based resin and a modified starch.

2. The multilayer structure according to claim 1 , wherein the sealant layer (A) comprises at least one selected from the group consisting of polyolefin-based resins and biodegradable polyester-based resins.

3. 2. The multilayer structure according to claim 1, comprising a sealant layer (A), a paper layer (B), a barrier layer (C), and a paper layer (D) in this order.

4. A package having the sealant layer (A) contained in the multilayer structure according to any one of claims 1 to 3 adhered thereto.

5. A food package containing a food product that releases carbon dioxide inside the package of claim 4.

6. 6. The food package according to claim 5, wherein the food that releases carbon dioxide is roasted coffee beans or a fermented food.

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