Adhesive resin composition

Abstract

The present invention relates to an adhesive resin composition comprising a biodegradable polyester-based resin (A) and a poly(vinyl alcohol)-based resin (B) and satisfying expression (1): 0.30<Y / X<0.99 [wherein X indicates the mass of the poly(vinyl alcohol)-based resin (B) contained in a film of the adhesive resin composition having a thickness of 300 μm, and Y indicates the mass of the poly(vinyl alcohol)-based resin (B) which, when the film is immersed in 80°C pure water for one hour, is extracted with the hot water].

Description

adhesive resin composition

[0001] This patent application claims priority under the Paris Convention to Japanese Patent Application No. 2022-200517 (filing date: December 15, 2022) and Japanese Patent Application No. 2023-104831 (filing date: June 27, 2023), the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to an adhesive resin composition, a laminate comprising an adhesive layer comprising the adhesive resin composition, and a food packaging material or agricultural film comprising the adhesive layer or the laminate.

[0003] Plastics are widely used as packaging materials due to their excellent moldability, strength, water resistance, transparency, and other properties. However, plastics are poorly biodegradable, and if discarded in nature after use, they can remain for long periods of time and cause environmental damage. In response to this, biodegradable resins that biodegrade or hydrolyze in soil or water and are useful for preventing environmental pollution have recently attracted attention, and the practical application of packaging materials and the like using biodegradable resins has been progressing. Examples of such packaging materials include laminates comprising a biodegradable resin layer, an adhesive layer, and a polyvinyl alcohol-based resin layer. For example, Patent Document 1 describes a biodegradable laminate in which a polyvinyl alcohol-based resin layer is laminated on at least one side of a biodegradable resin layer via an adhesive layer made of an adhesive composition obtained by graft polymerizing a biodegradable polyester-based resin with an α,β-unsaturated carboxylic acid or its anhydride.

[0004] JP 2013-212682 A

[0005] However, according to the investigations of the present inventors, it was found that it was difficult for the adhesive layer in conventional biodegradable laminates to exhibit sufficient adhesive strength to both the polyvinyl alcohol-based resin layer and the biodegradable resin layer.

[0006] Therefore, an object of the present invention is to provide an adhesive resin composition having excellent adhesive strength to both a polyvinyl alcohol-based resin layer and a biodegradable resin layer, a laminate including an adhesive layer comprising the adhesive resin composition, and a food packaging material or agricultural film including the adhesive layer or the laminate.

[0007] As a result of extensive research aimed at achieving the above object, the present inventors have found that the above problems can be solved when a specific parameter (Y / X) is within a specific range in an adhesive resin composition containing a biodegradable polyester resin (A) and a polyvinyl alcohol resin (B), and have thus completed the present invention. That is, the present invention includes the following preferred embodiments.

[0008] [1] An adhesive resin composition comprising a biodegradable polyester resin (A) and a polyvinyl alcohol resin (B), the adhesive resin composition satisfying the following formula (1): 0.30≦Y / X≦0.99 (1) [wherein X represents the mass of the polyvinyl alcohol resin (B) contained in a 300 μm-thick film made of the adhesive resin composition, and Y represents the mass of the polyvinyl alcohol resin (B) extracted into hot water when the film is immersed in pure water at 80°C for 1 hour and the soluble components are extracted.] [2] The adhesive resin composition according to [1], wherein the polyvinyl alcohol resin (B) has a degree of saponification of 75 to 96 mol%. [3] The adhesive resin composition according to [1] or [2], wherein the biodegradable polyester resin (A) has a breaking elongation of 50% or more as measured in accordance with ISO 527-1. [4] The adhesive resin composition according to any one of [1] to [3], wherein the polyvinyl alcohol resin (B) has a viscosity-average degree of polymerization of 100 to 5,000. [5] The adhesive resin composition according to any one of [1] to [4], wherein the biodegradable polyester resin (A) has a melting point of 70°C or higher. [6] The adhesive resin composition according to any one of [1] to [5], wherein the biodegradable polyester resin (A) comprises an aromatic-aliphatic copolymer polyester resin. [7] The adhesive resin composition according to [6], wherein the aromatic-aliphatic copolymer polyester resin is polybutylene adipate terephthalate. [8] The adhesive resin composition according to any one of [1] to [7], wherein a 300 μm-thick film made of the adhesive resin composition is immersed in pure water at 80°C for 1 hour to extract the soluble matter, and the diameter of the holes formed is 10 μm or less. [9] An adhesive resin composition comprising a biodegradable polyester resin (A) and a polyvinyl alcohol resin (B), the adhesive resin composition having a bicontinuous structure formed from at least a phase consisting of the biodegradable polyester resin (A) and a phase consisting of the polyvinyl alcohol resin (B).

[10] A laminate comprising an adhesive layer comprising the adhesive resin composition according to any one of [1] to [9].

[11] The laminate according to

[10] , comprising, in this order, a biodegradable resin layer, the adhesive layer, and a polyvinyl alcohol resin layer.

[12] The laminate according to

[11] , wherein the biodegradable resin layer, the adhesive layer, and the polyvinyl alcohol-based resin layer all satisfy the biodegradability standard in accordance with ISO 14855.

[13] A food packaging material comprising an adhesive layer comprising the adhesive resin composition according to any one of [1] to [9], or the laminate according to any one of

[10] to

[12] .

[14] An agricultural film comprising an adhesive layer comprising the adhesive resin composition according to any one of [1] to [9], or the laminate according to any one of

[10] to

[12] .

[0009] The adhesive resin composition of the present invention has excellent adhesive strength to both polyvinyl alcohol-based resin layers and biodegradable polyester-based resin layers, and is therefore suitable for use as packaging materials for food and agricultural films.

[0010] 1 is an image taken with an SEM of an adhesive resin composition film after hot water treatment in Example 2. 2 is an image taken with an SEM of an adhesive resin composition film after hot water treatment in Comparative Example 1. 3 is an image taken with an SEM of an adhesive resin composition film after hot water treatment in Example 13.

[0011] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0012] [Adhesive Resin Composition] The adhesive resin composition of the present invention comprises a biodegradable polyester resin (A) and a polyvinyl alcohol resin (B), and satisfies the following formula (1): 0.30≦Y / X≦0.99 (1) [wherein X represents the mass of the polyvinyl alcohol resin (B) contained in a 300 μm thick film (sometimes referred to as an adhesive resin composition film) made of the adhesive resin composition, and Y represents the mass of the polyvinyl alcohol resin (B) extracted into hot water when the film is immersed in pure water at 80° C. for 1 hour]. In this specification, the biodegradable polyester resin (A) may be referred to as "component (A)," the polyvinyl alcohol resin (B) may be referred to as "component (B)," and polyvinyl alcohol may be abbreviated as PVA. In this specification, the upper and lower limits may be combined in any combination.

[0013] In formula (1), the adhesive resin composition film for determining X and Y is prepared, for example, by preheating pellets of the adhesive resin composition at 180°C for 5 minutes using a compression molding machine, and then compressing the film under a load of 50 kgf / cm. ２ The sample was compression molded for 30 seconds under the conditions of

[0014] X in formula (1) represents the mass of the polyvinyl alcohol-based resin (B) contained in the adhesive resin composition film, and can be calculated by, for example, cutting the adhesive resin composition film into 10 mm squares to obtain a mass measurement sample measuring 10 mm long x 10 mm wide x 300 μm thick, and then using the following calculation formula (2). The proportion of the polyvinyl alcohol-based resin (B) contained in the adhesive resin composition can be calculated, for example, by freeze-pulverizing the adhesive resin composition film, treating it with hot water, and measuring the mass of the polyvinyl alcohol-based resin (B) contained in the extract. X = (mass of the mass measurement sample) x (proportion (mass %) of the polyvinyl alcohol-based resin (B) contained in the adhesive resin composition) / 100 (2)

[0015] Y in formula (1) represents the mass of polyvinyl alcohol resin (B) extracted into hot water when an adhesive resin composition film is immersed in pure water at 80°C for 1 hour and the soluble components are extracted. Specifically, when the only component eluted by hot water treatment is polyvinyl alcohol (B), a sample for mass measurement is immersed in hot water at 80°C for 1 hour to obtain a sample (sometimes referred to as a sample after hot water treatment), and the mass can be calculated using the following calculation formula (3): Y = (mass of sample for mass measurement) - (mass of sample after hot water treatment) (3) For example, the hot water treatment is carried out by placing the sample for mass measurement (approximately 0.03 g) in a 50 cc screw tube, followed by the addition of 20 ml of distilled water at 23°C. The screw tube is placed in a hot air dryer set at 80°C, and after 30 minutes, the distilled water is confirmed to have reached 80°C, and then allowed to stand for another hour. The sample is then gently shaken with tweezers to remove any eluted components from the pores and surface, and the sample for mass measurement is then removed from the screw tube and placed in a hot air dryer set at 80°C for 1 hour.

[0016] Y / X in formula (1) can be determined by substituting the values ​​of X and Y obtained above. X and Y are expressed in the same unit, for example, when the unit of X is grams (g), the unit of Y is grams (g). Y / X in formula (1) can be determined, for example, by the method described in the Examples.

[0017] The adhesive resin composition of the present invention contains a biodegradable polyester-based resin (A) and a PVA-based resin (B). The component (A) is insoluble in pure water. Therefore, Y / X can be said to be substantially the ratio of the PVA-based resin (B) contained in the adhesive resin composition that is extracted as a soluble component when the adhesive resin composition is immersed in hot water at 80°C for 1 hour.

[0018] The present inventors have further studied the interlayer adhesive strength of laminates and have surprisingly found that when the specific parameter Y / X is within the range of 0.30 to 0.99, the adhesive strength to both the PVA-based resin layer and the biodegradable resin layer is significantly improved. Although the reason for this effect is unclear, it is presumed that this effect is achieved because, when the ratio of the PVA-based resin (B) that decreases upon immersion in hot water at 80°C for one hour is within a specific range, a structure is formed in which a well-balanced mixture of sea-island structure moieties (where the PVA-based resin (B) corresponds to islands) and co-continuous structure moieties of the PVA-based resin (B) is formed. More specifically, the co-continuous structure moieties are structures in which the PVA-based resin (B) is connected, thereby enhancing the adhesive strength to the PVA-based resin layer that is the adherend. Meanwhile, the sea-island structure moieties are structures in which the PVA-based resin (B) is not connected, thereby enhancing the strength and toughness of the composition itself and facilitating the development of good adhesive strength to the biodegradable resin layer. Therefore, it is presumed that a well-balanced mixture of these structures results in improved adhesive strength to the PVA-based resin layer and the biodegradable resin layer. Furthermore, it is presumed that the PVA-based resin (B) dissolves more easily in co-continuous structure regions where the PVA-based resin (B) is connected than in sea-island structure regions when immersed in hot water, whereas the PVA-based resin (B) dissolves less easily in sea-island structure regions where the PVA-based resin (B) is not connected than in co-continuous structure regions when immersed in hot water. Therefore, it is presumed that the proportion of co-continuous structure regions tends to increase as the value of Y / X increases, and the proportion of sea-island structure regions tends to increase as the value of Y / X in formula (1) decreases.

[0019] Fig. 1 is a scanning electron microscope (SEM) image of the cross section of the adhesive resin composition film after hot water treatment in Example 2 of the present specification, Fig. 2 is a SEM image of the adhesive resin composition film after hot water treatment in Comparative Example 1, and Fig. 3 is a SEM image of the adhesive resin composition film after hot water treatment in Example 13. Many voids are present in the SEM images of Figs. 1, 2, and 3, and it can be said that the PVA-based resin (B) extracted and removed by hot water was originally present in these voids. As can be seen from these SEM images, in the embodiments of Figs. 1 and 3 where Y / X is within the above range, both cocontinuous structure portions in which voids are continuously connected and sea-island structure portions in which voids form islands coexist, whereas in the embodiment of Fig. 2 where Y / X is less than 0.30, the sea-island structure accounts for the majority of the film. The present invention requires that Y / X be within a specific range, and the structure of the adhesive resin composition is not limited as long as the effects of the present invention are achieved.

[0020] In this way, the adhesive resin composition of the present invention can exhibit excellent adhesive strength because the value of Y / X in formula (1) is adjusted to an appropriate value of 0.30 to 0.99. In this specification, adhesive strength can be evaluated by a peel test and means the peel strength between the adhesive resin composition (adhesive layer) and other layers such as a PVA-based resin layer and a biodegradable resin layer.

[0021] When Y / X in formula (1) is less than 0.30 and exceeds 0.99, the adhesive strength to the PVA-based resin layer is likely to decrease. In the present invention, Y / X in formula (1) is 0.3 or more, preferably 0.4 or more, more preferably 0.5 or more, even more preferably 0.6 or more, even more preferably 0.66 or more, particularly preferably 0.7 or more, and particularly preferably 0.8 or more, and may be, for example, 0.85 or more or 0.90 or more. The upper limit of Y / X in formula (1) is 0.99 or less, preferably 0.98 or less. When Y / X is equal to or greater than the above-mentioned lower limit, the adhesive strength to the PVA-based resin layer can be increased. Furthermore, when Y / X is equal to or less than the above-mentioned upper limit, the strength and toughness of the adhesive resin composition itself can be increased, and good adhesive strength to the biodegradable resin layer can also be exhibited. As a result, when Y / X is equal to or greater than the above-mentioned lower limit and equal to or less than the above-mentioned upper limit, the adhesive strength to the PVA-based resin layer and the biodegradable resin layer can be improved.

[0022] The ratio Y / X in formula (1) can be controlled within the above range by adjusting the values ​​of X and Y. Here, X can be adjusted by the amount of PVA-based resin (B) added during the preparation of the adhesive resin composition film. Y essentially represents the amount of PVA-based resin (B) lost after immersion in hot water for 1 hour, and can be adjusted within the above range by adjusting the types and contents of components (A) and (B), the degree of saponification and polymerization of component (B), and the manufacturing conditions of the adhesive resin composition. For example, the ratio Y / X in formula (1) can be adjusted within the above range by appropriately adjusting the types and contents of preferred components (A) and (B), the preferred degree of saponification and polymerization of component (B), and the preferred manufacturing conditions described herein.

[0023] In one embodiment of the present invention, the diameter of the pores formed when a 300 μm thick film made of the adhesive resin composition is immersed in pure water at 80°C for 1 hour is preferably 10 μm or less, more preferably 5 μm or less, even more preferably 3 μm or less, and even more preferably 1 μm or less. When the pore diameter is below the above upper limit, the adhesive strength to the polyvinyl alcohol-based resin layer and the biodegradable resin layer is likely to be improved. Furthermore, the lower limit of the pore diameter is preferably 0.01 μm or more. The 300 μm thick film made of the adhesive resin composition is the same as that described above in the description of formula (1), and the treatment of immersion in pure water at 80°C for 1 hour is the same as the hot water treatment described above in the description of formula (1). The pore diameter can be measured using a SEM after the hot water treatment, for example, by the method described in the Examples.

[0024] <Biodegradable Polyester Resin (A)> The adhesive resin composition of the present invention contains a biodegradable polyester resin (A). In this specification, "biodegradable" refers to a material that has the property of being chemically decomposable, for example, by hydrolysis, enzymatic degradation, or microbial degradation, and preferably refers to a material that meets the biodegradability standards specified in EN 13432, ASTM 6400, or ISO 14855. That is, a material is considered to be biodegradable if, when placed in a compost environment, 90% of the material disintegrates into particles with an average size of less than 2 mm within 12 weeks, and after 6 months, at least 60% of the material has decomposed into carbon dioxide and / or water in accordance with ASTM 6400, or at least 90% of the material has decomposed into carbon dioxide and / or water in accordance with EN 13432.

[0025] The biodegradable polyester resin is not particularly limited as long as it is a polyester resin having the above-mentioned biodegradability, and may be a petroleum-derived biodegradable resin or a biologically derived biodegradable resin. Examples of biodegradable polyester resins include aliphatic polyester resins, aromatic-aliphatic copolymer polyester resins, and aromatic polyester resins. The biodegradable polyester resin preferably contains at least one selected from the group consisting of aliphatic polyester resins and aromatic-aliphatic copolymer polyester resins. From the viewpoint of having high biodegradability and easily increasing adhesive strength and thermoformability, it is more preferable to contain an aromatic-aliphatic copolymer polyester resin.

[0026] Examples of aliphatic polyester resins include polyhydroxyalkanoates (abbreviated as PHA), polyalkylene monocarboxylates, and polyalkylene dicarboxylates.

[0027] PHA is a polymer containing hydroxyalkanoic acid as a monomer unit. More specific examples include polyglycolic acid, polylactic acid (sometimes abbreviated as PLA), poly(3-hydroxyalkanoate) (abbreviated as P3HA), and poly(4-hydroxyalkanoate).

[0028] P3HA is a polymer whose main monomer unit is 3-hydroxyalkanoic acid. Examples of 3-hydroxyalkanoic acid include 3-hydroxybutyrate, 3-hydroxypropionate, 3-hydroxyvalerate, 3-hydroxyhexanoate, 3-hydroxyheptanoate, and 3-hydroxyoctanoate. P3HA may be a homopolymer or a copolymer containing two or more types of monomer units. Furthermore, when P3HA is a copolymer, it may be a copolymer obtained by copolymerizing two or more types of 3-hydroxyalkanoic acid, or a copolymer obtained by copolymerizing one or more types of 3-hydroxyalkanoic acid with a 4-hydroxyalkanoic acid such as 4-hydroxybutyrate.

[0029] Specific examples of P3HA include poly(3-hydroxybutyrate) homopolymer (abbreviated as PHB), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviated as PHBH), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviated as PHBV), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviated as 3HB4HB).

[0030] Examples of polyalkylene monocarboxylates include ring-opening polymers of lactones (cyclic esters), and specific examples thereof include polycaprolactone (abbreviated as PCL).

[0031] Polyalkylene dicarboxylate is a polycondensate of an aliphatic diol (or a derivative thereof) and an aliphatic dicarboxylic acid (or a derivative thereof). Examples include polybutylene succinate (abbreviated as PBS), polyethylene succinate (abbreviated as PES), and poly(butylene succinate-co-butylene adipate).

[0032] The aliphatic polyester resin is preferably at least one selected from the group consisting of PHA, polyalkylene monocarboxylate, and polyalkylene dicarboxylate, and from the viewpoint of easily increasing adhesive strength, it is more preferably at least one selected from the group consisting of polyalkylene monocarboxylate and polyalkylene dicarboxylate, and from the viewpoint of thermoformability, it is more preferably PHA.

[0033] Aromatic-aliphatic copolymer polyester resins are polyester resins having both aromatic and aliphatic moieties, and are condensates of an aliphatic or aromatic diol (or a derivative thereof) with an aromatic or aliphatic dicarboxylic acid (or a derivative thereof). Examples include polybutylene adipate terephthalate (abbreviated as PBAT), polybutylene succinate terephthalate (PBST), and polyethylene adipate terephthalate (PEAT). PBAT is preferred because it has high biodegradability and is easy to improve adhesive strength and thermoformability. These biodegradable polyester resins may be used alone or in combination of two or more.

[0034] The biodegradable polyester resin (A) may be produced by a conventional method, or a commercially available product may be used. Commercially available biodegradable polyester resins (A) include polycaprolactone (PCL) sold by Union Carbide under the trade name Tone™ (e.g., Tone P-300, P-700, P-767, and P-787, each having a weight average molecular weight of about 10,000, 40,000, 43,000, and 80,000), or by Perstorf under the trade names CAPA 6800 and CAPAFB 100 (each having a molecular weight of 80,000 and 100,000 Daltons); polylactic acid (PLA) sold by Cargill under the trade name Natureworks™ PLA; and polylactic acid (PLA) sold by Biomer (Germany) under the trade names Biocycle™ or Biomer™. Polyhydroxybutyrate (PHB) sold under the trade name Bionolle™ by Showa Highpolymer Co., Ltd.; polyethylene succinate (PES) and polybutylene succinate (PBS) sold under the trade name Bionolle™ (e.g., Bionolle™ 1001 (PBS) and Bionolle™ 6000 (PES)) by Showa Highpolymer Co., Ltd.; polybutylene adipate (PBA) sold under the trade name Skygreen™ SG100 by SK Chemicals (Korea); polybutylene adipate terephthalate (PBAT) aliphatic / aromatic copolyesters such as Ecoflex™ by BASF (Germany), or EnPOL™ G8060 and EnPOL™ 8000 by IreChemical Ltd (Seoul); Poly(hydroxybutyrate valerate) (PHBV) by Polyethylene Glycol (USA); and the like.

[0035] The biodegradable polyester resin (A) may be a modified biodegradable polyester resin or an unmodified biodegradable polyester resin. The modified biodegradable polyester resin is not particularly limited, but may be, for example, a modified biodegradable polyester resin obtained by graft-modifying a biodegradable polyester resin with an unsaturated carboxylic acid and / or its derivative. The unsaturated carboxylic acid used as the modifier is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, etc. Furthermore, the derivative of the unsaturated carboxylic acid is not particularly limited, but examples thereof include acid anhydrides, esters, amides, imides, metal salts, etc.

[0036] Specific examples of the derivatives of unsaturated carboxylic acids include maleic anhydride, himic anhydride, itaconic anhydride, citraconic anhydride, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, glycidyl acrylate, maleic acid monoethyl ester, maleic acid diethyl ester, itaconic acid monomethyl ester, itaconic acid diethyl ester, acrylamide, methacrylamide, maleic acid monoamide, maleic acid diamide, maleic acid-N-monoethylamide, maleic acid-N,N-diethylamide, maleic acid-N,N-monobutylamide, maleic acid-N,N-dibutylamide, fumaric acid monoamide, fumaric acid diamide, fumaric acid-N-monobutylamide, fumaric acid-N,N-dibutylamide, maleimide, N-butylmaleimide, N-phenylmaleimide, sodium acrylate, sodium methacrylate, potassium acrylate, and potassium methacrylate. These unsaturated carboxylic acids and / or their derivatives can be used singly or in any combination and ratio of two or more. Among these, maleic acid or its anhydride is particularly preferred because of its low electron density and high reactivity.

[0037] The content of the modifier is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more, relative to the mass of the modified biodegradable polyester resin, and is preferably 3.0% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.2% by mass or less.

[0038] The adhesive resin composition of the present invention is an alloy of a biodegradable polyester-based resin (A) and a PVA-based resin (B) that satisfies formula (1), and therefore can exhibit excellent adhesive strength to a PVA-based resin layer and a biodegradable resin layer without modifying the biodegradable polyester-based resin. Therefore, in a preferred embodiment of the present invention, the biodegradable polyester-based resin (A) is preferably an unmodified biodegradable polyester-based resin. When the biodegradable polyester-based resin (A) is unmodified, it is possible to prevent a decrease in biodegradability due to modification and also to avoid the complicated production process due to modification.

[0039] In a preferred embodiment of the present invention, the biodegradable polyester resin (A) has a breaking elongation measured in accordance with ISO 527-1 of preferably 50% or more, more preferably 100% or more, even more preferably 200% or more, even more preferably 400% or more, particularly preferably 600% or more, particularly more preferably 750% or more, particularly more preferably 850% or more, and particularly more preferably 1000% or more. When the breaking elongation is equal to or greater than the above lower limit, toughness increases, and adhesive strength tends to improve. The upper limit of the breaking elongation is usually 5000% or less, preferably 3000% or less, and more preferably 2000% or less. When the breaking elongation is equal to or less than the above upper limit, a decrease in the elastic modulus and maximum strength of the adhesive resin composition can be suppressed, and therefore a decrease in adhesive strength is easily suppressed. The breaking elongation can be measured in accordance with ISO 527-1, for example, by the method described in the Examples.

[0040] In a preferred embodiment of the present invention, the melting point of the biodegradable polyester resin (A) is preferably 70°C or higher, more preferably 80°C or higher, even more preferably 90°C or higher, even more preferably 100°C or higher, and particularly preferably 105°C or higher. When the melting point of the biodegradable polyester resin (A) is above the above-mentioned lower limit, the thermoformability is more easily improved, so that the occurrence of wrinkles and the like in the obtained laminate is more easily suppressed or prevented, and the appearance is more likely to be good. The upper limit of the melting point is preferably 300°C or lower, more preferably 200°C or lower, even more preferably 150°C or lower, even more preferably 140°C or lower, and particularly preferably 130°C or lower. When the melting point is below the above-mentioned upper limit, the thermoformability is easily improved, so that the obtained laminate can be easily molded into a predetermined shape. The melting point can be measured using a differential scanning calorimeter (DSC), for example, by the method described in the examples.

[0041] In one embodiment of the present invention, the melt mass flow rate (MFR) of the biodegradable polyester resin (A) is preferably 1.0 g / 10 min or more, more preferably 3.0 g / 10 min or more, even more preferably 5.0 g / 10 min or more, even more preferably 7.0 g / 10 min or more, and particularly preferably 10 g / 10 min or more, and is preferably 30 g / 10 min or less, more preferably 25 g / 10 min or less, and even more preferably 20 g / 10 min or less. Having the MFR of the biodegradable polyester resin (A) in the above range facilitates improving adhesive strength and thermoformability. The MFR can be measured in accordance with JIS K 7210:2014 at a temperature of 200°C and a load of 2.16 kg.

[0042] In one embodiment of the present invention, the weight average molecular weight (Mw) of the biodegradable polyester resin (A) is preferably 10,000 or more, more preferably 30,000 or more, even more preferably 50,000 or more, and is preferably 500,000 or less, more preferably 200,000 or less, even more preferably 100,000 or less. When the Mw of the biodegradable polyester resin (A) is within the above range, the adhesive strength and thermoformability are easily improved.

[0043] In one embodiment of the present invention, the number average molecular weight (Mn) of the biodegradable polyester resin (A) is preferably 5,000 or more, more preferably 10,000 or more, even more preferably 20,000 or more, and preferably 200,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less. Having the Mn of the biodegradable polyester resin (A) within the above range makes it easy to improve adhesive strength and thermoformability. The Mw and Mn of the biodegradable polyester resin (A) can be determined by gel permeation chromatography (GPC) measurement and converted into standard polystyrene, for example, by the method described in the examples.

[0044] The content of the biodegradable polyester resin (A) is preferably 42 parts by mass or more, more preferably 45 parts by mass or more, even more preferably 48 parts by mass or more, based on 100 parts by mass of the total of components (A) and (B); and is preferably 90 parts by mass or less, more preferably 85 parts by mass or less, even more preferably 80 parts by mass or less, even more preferably 77 parts by mass or less, particularly preferably 75 parts by mass or less, especially more preferably 73 parts by mass or less or 70 parts by mass or less, especially more preferably 67 parts by mass or less or 65 parts by mass or less, and extremely preferably 63 parts by mass or less. When the content of the biodegradable polyester resin (A) is at or above the above-mentioned lower limit, biodegradability is easily improved and adhesive strength to the biodegradable resin layer is easily increased. When the content of the biodegradable polyester resin (A) is at or below the above-mentioned upper limit, adhesive strength to the PVA-based resin layer is easily increased. The content of the biodegradable polyester resin (A) relative to the mass of the adhesive resin composition can also be selected from the above-mentioned range.

[0045] <Polyvinyl Alcohol Resin (B)> The adhesive resin composition of the present invention contains a PVA resin (B).

[0046] The PVA-based resin (B) is a resin containing a vinyl ester polymer or copolymer (collectively referred to as a vinyl alcohol-based polymer). The vinyl alcohol-based polymer is a polymer containing vinyl alcohol units as monomer units. The vinyl alcohol-based polymer is obtained by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester monomer, which is the raw material monomer for the vinyl alcohol-based polymer. The saponified vinyl alcohol-based polymer may contain vinyl ester units in addition to vinyl alcohol units.

[0047] The vinyl alcohol polymer may be a modified vinyl alcohol copolymer containing monomer units other than vinyl alcohol units and vinyl ester units, which is obtained by saponifying a copolymer obtained by copolymerizing a vinyl ester monomer, which is a raw material monomer, with another monomer. Also, the PVA resin (B) may contain multiple types of vinyl alcohol polymers having different physical properties.

[0048] Examples of vinyl ester monomers used as raw material monomers for vinyl alcohol polymers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate. Among these, vinyl acetate is preferred from the viewpoints of ease of production and availability, cost, and the like.

[0049] The vinyl alcohol polymer may be a modified vinyl alcohol copolymer containing, in addition to vinyl alcohol units and vinyl ester units, other monomer units other than the vinyl ester units, as described above. The other monomers can be appropriately selected depending on the type of the PVA resin layer to be adhered, and examples thereof include α-olefins such as ethylene, propylene, n-butene, and isobutylene; acrylic acid and its salts; acrylic acid esters; methacrylic acid and its salts; methacrylic acid esters; acrylamide; acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N,N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts thereof, and N-methylolacrylamide and its derivatives; methacrylamide; methacrylamide derivatives such as N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts or quaternary salts thereof, and N-methylolmethacrylamide and its derivatives; methylvinyl vinyl ethers such as ethyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids and salts or esters thereof such as maleic acid, itaconic acid, and fumaric acid; vinyl silyl compounds such as vinyltrimethoxysilane; isopropenyl acetate; vinyl compounds such as dimethylallyl vinyl ketone, N-vinylpyrrolidone, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerin monoallyl ether, and 3,4-diacetoxy-1-butene; and the like. Among these, from the viewpoint of ease of industrial production, it is preferable that the other monomer is an α-olefin such as ethylene. The content (modification amount) of these other monomer units varies depending on the purpose and application of use.In one embodiment, the content (modification amount) of other monomer units is preferably 10 mol % or less, more preferably 5 mol % or less, and may be preferably 0 mol % or more, more preferably 0.1 mol % or more.

[0050] The vinyl alcohol polymer may or may not have some of its hydroxyl groups crosslinked, and may have some of its hydroxyl groups reacted with an aldehyde compound such as acetaldehyde or butylaldehyde to form an acetal structure, or may not react with these compounds to form an acetal structure.

[0051] The PVA-based resin (B) preferably contains, as a vinyl alcohol-based polymer, at least one selected from the group consisting of unmodified vinyl alcohol polymers and α-olefin-vinyl alcohol copolymers, and more preferably contains an unmodified vinyl alcohol polymer, from the viewpoint of easily increasing adhesive strength and thermoformability, although this depends on the type of PVA-based resin layer that is the adherend.

[0052] The saponification degree of the PVA-based resin (B) contained in the adhesive resin composition of the present invention is preferably 75 mol% or more, more preferably 77 mol% or more, even more preferably 79 mol% or more, and even more preferably 80 mol% or more, and may be, for example, 81 mol% or more or 82 mol% or more. The saponification degree of the PVA-based resin (B) is preferably 96 mol% or less, more preferably 94 mol% or less, even more preferably 92 mol% or less, even more preferably 90 mol% or less, particularly preferably 89 mol% or less, and especially preferably 88 mol% or less, and may be, for example, 85 mol% or less. When the saponification degree of the PVA-based resin (B) is equal to or greater than the above-mentioned lower limit, it is easy to form hydrogen bonds with the PVA-based resin layer as an adherend, thereby improving the adhesive strength and gas barrier properties to the PVA-based resin layer. When the saponification degree of the PVA-based resin (B) is equal to or less than the above-mentioned upper limit, it is easy to exhibit appropriate fluidity during adhesion, and therefore it is easy to improve the adhesive strength and thermoformability. In this specification, the saponification degree of the PVA-based resin (B) refers to the ratio (mol %) of the number of moles of vinyl alcohol units to the total number of moles of structural units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification contained in the vinyl alcohol-based polymer and vinyl alcohol units. The saponification degree of the PVA-based resin (B) can be measured in accordance with JIS K 6726:1994. When the PVA-based resin (B) contains only one type of vinyl alcohol-based polymer, the saponification degree of the vinyl alcohol-based polymer is the saponification degree of the PVA-based resin (B). When the PVA-based resin (B) contains two or more types of vinyl alcohol-based polymers, the saponification degree refers to the average saponification degree calculated from the saponification degrees of each vinyl alcohol-based polymer and the blending ratio. When the PVA-based resin (B) contains two or more vinyl alcohol-based polymers, the vinyl alcohol-based polymers having different degrees of saponification may be mixed in an appropriate mixing ratio to adjust the degree of saponification of the PVA-based resin (B) to fall within the above-mentioned range.

[0053] In one embodiment of the present invention, the viscosity-average degree of polymerization (sometimes referred to as "degree of polymerization") of the PVA-based resin (B) contained in the adhesive resin composition of the present invention may be preferably 5,000 or less, 4,000 or less, 3,000 or less, or 2,000 or less, more preferably 1,500 or less, even more preferably 1,200 or less, even more preferably 900 or less, particularly preferably 700 or less, especially more preferably 600 or less, and especially more preferably 480 or less, 400 or less, or 350 or less. When the degree of polymerization is below the above upper limit, the adhesive strength to the PVA-based resin layer and thermoformability are likely to be improved. This is presumably because the PVA-based resin (B), which is a polar component, easily migrates to the interface during adhesion and easily forms a co-continuous structural portion. The viscosity-average degree of polymerization of the PVA-based resin (B) is preferably 100 or more, more preferably 150 or more, even more preferably 200 or more, even more preferably 220 or more, especially preferably 250 or more, and especially preferably 270 or more. When the polymerization degree is equal to or higher than the above lower limit, the mechanical strength of the adhesive resin composition and the adhesive strength to the biodegradable resin layer are easily increased. This is presumably because a sea-island structure is easily formed. The polymerization degree of the PVA-based resin (B) can be measured in accordance with JIS K 6726:1994. When the PVA-based resin (B) contains only one vinyl alcohol-based polymer, the polymerization degree of the vinyl alcohol-based polymer is the polymerization degree of the PVA-based resin (B). When the PVA-based resin (B) contains two or more vinyl alcohol-based polymers, the polymerization degree of the PVA-based resin (B) refers to the average polymerization degree calculated from the polymerization degrees and blending ratios of the respective vinyl alcohol-based polymers. When the PVA-based resin (B) contains two or more vinyl alcohol-based polymers, the polymerization degree of the PVA-based resin (B) may be adjusted to fall within the above-mentioned range by mixing vinyl alcohol-based polymers with different polymerization degrees at an appropriate blending ratio.

[0054] The content of the PVA-based resin (B) in the adhesive resin composition of the present invention is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, even more preferably 20 parts by mass or more, even more preferably 23 parts by mass or more, particularly preferably 25 parts by mass or more, especially more preferably 27 parts by mass or more or 30 parts by mass or more, extremely preferably 33 parts by mass or more or 35 parts by mass or more, extremely preferably 37 parts by mass or more, and is preferably 58 parts by mass or less, more preferably 55 parts by mass or less, and even more preferably 52 parts by mass or less, based on 100 parts by mass of the total of components (A) and (B). When the content of the PVA-based resin (B) is equal to or greater than the above-mentioned lower limit, the adhesive strength to the PVA-based resin layer is easily increased, and the adhesive strength is easily improved. When the content of the PVA-based resin (B) is equal to or less than the above-mentioned upper limit, the adhesive strength to the biodegradable resin layer is easily increased. The content of the PVA-based resin (B) relative to the mass of the adhesive resin composition can also be selected from the above-mentioned range.

[0055] In one embodiment of the present invention, it is presumed that the higher the content of component (B), the easier it is to form co-continuous structural moieties, and the value of Y / X tends to be larger. On the other hand, it is presumed that the lower the content of component (B), the easier it is to form sea-island structural moieties, and the value of Y / X tends to be smaller. Furthermore, it is presumed that if the degree of saponification of component (B) is too high or too low, it is difficult to form co-continuous structural moieties, and an appropriate degree of saponification tends to be large. Furthermore, it is presumed that the lower the degree of polymerization of component (B), the easier it is to form co-continuous structural moieties, and the value of Y / X tends to be large. On the other hand, it is presumed that the higher the degree of polymerization of component (B), the easier it is to form sea-island structural moieties, and the value of Y / X tends to be small.

[0056] <Method for Producing Polyvinyl Alcohol Resin (B)> As described above, the PVA resin (B) contains a vinyl alcohol polymer. The vinyl alcohol polymer can be obtained, for example, by polymerizing a vinyl ester monomer, or a vinyl ester monomer with another monomer, to obtain a vinyl ester polymer or copolymer, followed by saponification. Methods for polymerizing vinyl ester monomers include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these, bulk polymerization and solution polymerization, in which polymerization is performed without a solvent or in a solvent such as alcohol, are preferred. Examples of alcohols used as solvents during solution polymerization include lower alcohols such as methanol, ethanol, and propanol. Examples of initiators used in copolymerization include known azo initiators or peroxide initiators, such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), benzoyl peroxide, and n-propyl peroxydicarbonate. The polymerization temperature is not particularly limited, but is preferably in the range of 0° C. to 150° C. Furthermore, for example, when the vinyl alcohol polymer is an ethylene-vinyl alcohol copolymer or the like, it is preferable to copolymerize a vinyl ester monomer with a monomer such as ethylene by the above method.

[0057] The vinyl ester polymer obtained in the polymerization step can be saponified in an organic solvent by alcoholysis or hydrolysis in the presence of a catalyst. Examples of catalysts used in the saponification step include basic catalysts such as sodium hydroxide, potassium hydroxide, and sodium methoxide; or acidic catalysts such as sulfuric acid, hydrochloric acid, and p-toluenesulfonic acid. The organic solvent used in the saponification step is not particularly limited, but examples include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene. These can be used alone or in combination. Among these, it is preferable to use methanol or a mixed solution of methanol and methyl acetate as the solvent and carry out the saponification reaction in the presence of sodium hydroxide as a basic catalyst, as this is simple and convenient. The amount of saponification catalyst used is preferably 0.001 to 0.5 in molar ratio to the vinyl ester monomer units in the vinyl ester polymer. This molar ratio is more preferably 0.002 or more, and more preferably 0.4 or less, more preferably 0.3 or less.

[0058] A preferred embodiment of the saponification step is as follows. First, a saponification catalyst such as sodium hydroxide is added to the vinyl ester polymer solution obtained in the polymerization step and mixed. The solvent used here is preferably methanol. Initially, the mixture is a homogeneous liquid. However, as the saponification reaction progresses and the vinyl ester units in the polymer are saponified and converted to vinyl alcohol units, the solubility in the solvent decreases, causing the polymer to precipitate in the solution. At this time, the solution contains methyl acetate produced by alcoholysis with methanol. As the saponification reaction progresses, the amount of polymer precipitated gradually increases, forming a slurry, which then loses fluidity. Therefore, to ensure that the saponification reaction proceeds uniformly, it is preferable to mix thoroughly until fluidity is lost.

[0059] The method for mixing the vinyl ester polymer solution and the saponification catalyst is not particularly limited, and various methods such as a static mixer, a kneader, or a stirring blade can be used, but the use of a static mixer is preferred because it allows continuous, uniform mixing. In this case, it is preferable to add the saponification catalyst to the vinyl ester polymer solution after the polymerization step in a pipe connected to the polymerization tank, and then pass the mixture through a static mixer to mix and obtain a paste. The temperature of the reaction solution in the static mixer is usually 20 to 80°C.

[0060] The method for promoting the saponification reaction of the vinyl ester polymer in the paste that has passed through the static mixer is not particularly limited. A preferred method is to place the paste on a moving belt and promote the saponification reaction while moving the belt in a tank maintained at a constant temperature. The paste on the belt loses its fluidity and becomes solid, and the saponification reaction then proceeds in the solid state. This method allows the saponification reaction to proceed continuously in the solid state, resulting in a solid block containing the vinyl alcohol polymer and the solvent. The saponification temperature is preferably 20 to 60°C, preferably 25°C or higher, more preferably 30°C or higher, and preferably 55°C or lower, more preferably 50°C or lower. A saponification temperature above the lower limit mentioned above can easily prevent a decrease in the reaction rate. A saponification temperature below the upper limit mentioned above can easily prevent a decrease in the solvent content in the resulting solid block and a deterioration in the solubility of the resulting vinyl alcohol polymer. The saponification time is preferably 5 minutes to 2 hours. The saponification time is more preferably 8 minutes or longer, even more preferably 10 minutes or longer, more preferably 1.5 hours or shorter, and even more preferably 1 hour or shorter.

[0061] If necessary, a washing step may be added to wash the vinyl alcohol polymer for the purpose of removing impurities such as sodium acetate. Examples of washing liquids include methanol, acetone, methyl acetate, ethyl acetate, hexane, and water. Among these, methanol, methyl acetate, and water, alone or in combination, are more preferred. The amount of washing liquid is typically 30 to 10,000 parts by mass, and more preferably 50 to 3,000 parts by mass, per 100 parts by mass of the vinyl alcohol polymer. The washing temperature is preferably 5 to 80°C, and more preferably 20 to 70°C. The washing time is preferably 20 minutes to 10 hours, and more preferably 1 to 6 hours. Known washing methods, such as a batch method and a countercurrent washing method, can be used. Commercially available vinyl alcohol polymers can also be used.

[0062] <Adhesive Resin Composition> The adhesive resin composition of the present invention contains the biodegradable polyester-based resin (A) and the polyvinyl alcohol-based resin (B) and satisfies formula (1), and therefore has excellent adhesive strength to both a PVA-based resin layer and a biodegradable resin layer. Therefore, it is useful as an adhesive layer between a PVA-based resin layer and a biodegradable polyester-based resin layer. Furthermore, the adhesive resin composition of the present invention also has excellent thermoformability, and the resulting laminate can be easily molded into a predetermined shape. Furthermore, it also has excellent biodegradability. Therefore, the adhesive resin composition of the present invention can be suitably used as a packaging material for food, etc., or an agricultural film.

[0063] The adhesive strength of the adhesive resin composition of the present invention to a PVA-based resin is preferably 4 N / 25 mm or more, more preferably 5 N / 25 mm or more, even more preferably 7 N / 25 mm or more, even more preferably 10 N / 25 mm or more, particularly preferably 15 N / 25 mm or more, and particularly preferably 20 N / 25 mm or more, and may be, for example, 25 N / 25 mm or more, 27 N / 25 mm or more, or 30 N / 25 mm or more. When the adhesive strength is equal to or greater than the above-mentioned lower limit, the strength of the resulting laminate is easily improved. The adhesive strength to a PVA-based resin is usually 100 N / 25 mm or less. The adhesive strength to a PVA-based resin refers to the peel strength between an adhesive layer made of the adhesive resin composition and a PVA resin layer in a multilayer sheet comprising the adhesive layer and the PVA resin layer. The peel strength can be measured in accordance with JIS K 6854-1:1999 using a peel tester under conditions of a peel angle of 90°, a tensile speed of 50 mm / min, and an ambient temperature of 23° C. The adhesive strength to a PVA-based resin can be determined, for example, by the method described in the examples.

[0064] The adhesive strength of the adhesive resin composition of the present invention to a biodegradable resin (preferably PLA) is preferably 9 N / 25 mm or more, more preferably 15 N / 25 mm or more, even more preferably 20 N / 25 mm or more, even more preferably 30 N / 25 mm or more, particularly preferably 40 N / 25 mm or more, particularly preferably 50 N / 25 mm or more, and especially preferably 55 N / 25 mm or more. When the adhesive strength is above the lower limit, the strength of the resulting laminate can be improved. The adhesive strength to a biodegradable resin is typically 150 N / 25 mm or less. The adhesive strength to a biodegradable resin refers to the peel strength between an adhesive layer made of the adhesive resin composition and a biodegradable resin layer in a multilayer sheet comprising the adhesive layer and the biodegradable resin layer. The peel strength can be measured using a peel tester in accordance with JIS K 6854-1:1999, at a peel angle of 90°, a tensile speed of 50 mm / min, and an ambient temperature of 23°C. The adhesive strength to the biodegradable resin can be determined, for example, by the method described in the Examples.

[0065] The adhesive resin composition of the present invention may contain additives other than component (A) and component (B) as long as the additives do not impair the objects and effects of the present invention. Examples of additives include fillers, processing stabilizers, weathering stabilizers, colorants, UV absorbers, heat stabilizers, light stabilizers, antioxidants, antistatic agents, flame retardants, plasticizers, lubricants, fragrances, foaming agents, deodorizers, extenders, release agents, mold release agents, reinforcing agents, mildew inhibitors, preservatives, crystallization rate retarders, and resins other than the biodegradable polyester-based resin (A) and the PVA-based resin (B). These additives can be used alone or in combination of two or more. The content of the additives is not particularly limited, but may be, for example, 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and preferably 0% by mass or more, more preferably 0.1% by mass or more, relative to the mass of the adhesive resin composition. The adhesive resin composition of the present invention may contain, among the above additives, additives that are insoluble in hot water. The term "hot water insoluble" refers to a material that does not lose mass when subjected to the above-mentioned hot water treatment. In one embodiment of the present invention, the adhesive resin composition of the present invention may comprise component (A), component (B), and any additive that is insoluble in hot water.

[0066] Fillers may be added from the viewpoints of easily increasing hardness and rigidity, easily preventing blocking, etc. Examples of fillers include inorganic fillers such as mica, kaolin, kaolinite, clay, talc, acid clay, silica, alumina, diatomaceous earth, bentonite, montmorillonite, kibushi clay, gairome clay, rose stone, alumite, china clay, feldspar, perlite, calcium carbonate, magnesium hydroxide, carbon black, vermiculite, titanium oxide, mica, zirconium oxide, boron nitride, aluminum nitride, shirasu, glass, and glass fiber, and organic fillers such as urea-formalin-based resins and melamine-formalin-based resins. These fillers can be used alone or in combination of two or more.

[0067] Examples of the other resins include polyphenylene ether resins, polycarbonate resins, polyamide resins such as nylon 66 and nylon 11, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, styrene resins such as polystyrene, and (meth)acrylate resins such as polymethyl methacrylate resins. The other resins can be used alone or in combination of two or more.

[0068] The adhesive resin composition of the present invention may be in the form of a pellet, sheet, or film without any particular limitation. That is, the adhesive resin composition may be in the form of a pellet, sheet, or film containing or consisting of the adhesive resin composition. The thickness of the sheet or film can be appropriately selected depending on the application, and is preferably 5 to 1,000 μm, more preferably 10 to 500 μm. The thickness of the film or sheet can be measured using a thickness gauge, for example, by the method described in the Examples. The adhesive resin composition of the present invention may also contain a solvent and may be in the form of a solution or dispersion. Known solvents capable of dissolving or dispersing the components in the composition can be used as the solvent.

[0069] The method for producing the adhesive resin composition of the present invention is not particularly limited, and may be, for example, a method of mixing the biodegradable polyester resin (A), the PVA resin (B), and optional additives. A conventional mixer, preferably a melt kneader, can be suitably used for mixing. In a preferred embodiment of the present invention, the adhesive resin composition can be obtained by melt kneading using an extruder.

[0070] As the extruder, a twin-screw extruder can preferably be used. The twin-screw extruder may be either co-rotating or counter-rotating. The screw rotation speed (rotational speed) is preferably 20 rpm or more, more preferably 70 rpm or more, even more preferably 150 rpm or more, and usually 1000 rpm or less. The cylinder temperature is preferably 40°C or more, more preferably 80°C or more, even more preferably 100°C or more, and preferably 300°C or less, more preferably 200°C or less. Each component can be directly introduced into the extruder. Alternatively, these components may be premixed using a mixer or the like and then introduced into the extruder.

[0071] The molten mixture that has been forced through the extruder while being melt-kneaded is extruded through a die, the temperature of which may be preferably 100 to 200°C, more preferably 100 to 150°C.

[0072] The specific mechanical energy (SME) (unit: kJ / kg) during melt-kneading is not particularly limited, but is preferably 400 kJ / kg or more, more preferably 500 kJ / kg or more, and preferably 900 kJ / kg or less, more preferably 800 kJ / kg or less. When the specific mechanical energy is within the above range, it is easy to adjust X / Y within the above range, and the adhesive strength of the adhesive resin composition is easy to increase. The specific mechanical energy (Ψ) can be calculated by the following formula: Ψ=N(RUN) / N(MAX)×Φ / φ(MAX)×Kw / Q (4) (In formula 1, N(RUN) represents the screw rotation speed (unit: rpm), N(MAX) represents the maximum screw rotation speed (unit: rpm), Φ represents the motor torque (unit: N m) during the test, φ(MAX) represents the maximum motor torque (unit: N m), Kw represents the motor power (unit: kJ / h), and Q represents the discharge rate (unit: kg / h).)

[0073] The extruded mixture (melt) can be extruded into a sheet, film or strand shape, and in this case, the mixture (melt) is cooled and dried.

[0074] When the mixture is extruded into strands, it can be extruded through a strand nozzle with multiple holes and cut with a rotary cutter to form pellets. To prevent the pellets from sticking together, vibration can be applied periodically or constantly, and moisture in the pellets can be removed using hot air, dehumidified air, or an infrared heater.

[0075] When the mixture is extruded into a sheet or 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. Cooling is preferably performed between the die and the roller to prevent the mixture from adhering to the roller. The solution or dispersion of the adhesive resin composition of the present invention may also be formed into a sheet or film by a conventional film-forming method (e.g., cast film formation).

[0076] [Adhesive Resin Composition Having a Co-Continuous Structure] The present invention also encompasses an adhesive resin composition comprising a biodegradable polyester-based resin (A) and a polyvinyl alcohol-based resin (B), the adhesive resin composition having a co-continuous structure formed from (or consisting of) at least a phase consisting of the biodegradable polyester-based resin (A) and a phase consisting of the PVA-based resin (B). Because the adhesive resin composition of the present invention has a specific co-continuous structure, it exhibits excellent adhesive strength to both a PVA-based resin layer and a biodegradable resin layer. Therefore, it is useful as an adhesive layer between a PVA-based resin layer and a biodegradable polyester-based resin layer. Furthermore, the adhesive resin composition of the present invention also exhibits excellent thermoformability, allowing the resulting laminate to be easily molded into a predetermined shape. Furthermore, it also exhibits excellent biodegradability. Therefore, the adhesive resin composition of the present invention is suitable for use as a packaging material for food, etc., or an agricultural film.

[0077] In this specification, the term "co-continuous structure" refers to a network structure (or three-dimensional continuous structure) in which two or more components are mixed together while forming continuous phases, and can be distinguished from a sea-island structure, a cylindrical structure, and a lamellar structure. The network structure (or three-dimensional continuous structure) does not necessarily have to be entirely connected, and may be partially disconnected.

[0078] In the present invention, the co-continuous structure is formed of at least two phases, the first phase being made of the biodegradable polyester-based resin (A) and the second phase being made of the PVA-based resin (B). When the adhesive resin composition contains additives such as the above-mentioned other resins, the co-continuous structure may contain other phases. However, from the viewpoint of improving the adhesive strength and thermoformability of the adhesive resin composition, it is preferred that the co-continuous structure be formed only from a phase made of the biodegradable polyester-based resin (A) and a phase made of the PVA-based resin (B).

[0079] In one embodiment of the present invention, the adhesive resin composition of the present invention preferably has both the co-continuous structure and the sea-island structure, and more preferably has the co-continuous structure mainly and a partial sea-island structure. In the sea-island structure, the sea portion is the biodegradable polyester-based resin (A) and the island portion is the PVA-based resin (B). This structure allows the composition to exhibit excellent adhesive strength to both the PVA-based resin layer and the biodegradable resin layer. The co-continuous structure portion has continuous PVA-based resin (B) molecules, thereby enhancing adhesive strength to the PVA-based resin layer as an adherend. Meanwhile, the sea-island structure portion has no continuous PVA-based resin (B) molecules, thereby enhancing the strength and toughness of the composition itself and facilitating the development of excellent adhesive strength to the biodegradable resin layer. The co-continuous structure can be measured using a SEM after platinum deposition on a cross section of the sample (adhesive resin composition film) subjected to the hot water treatment described above, for example, by the method described in the Examples.

[0080] In the SEM image obtained, as described above, the PVA-based resin (B) is eluted by the hot water treatment, and the portions where the PVA-based resin (B) was present become voids. For example, in Fig. 13, it can be seen that the phase consisting of the biodegradable polyester-based resin (A) other than the voids and the phase consisting of the PVA-based resin (B) corresponding to the voids form a bicontinuous structure. It can also be seen that the phase consisting of the biodegradable polyester-based resin (A) other than the voids forms a sea portion, and the phase consisting of the PVA-based resin (B) corresponding to the voids partially forms a sea-island structure.

[0081] Examples of methods for preparing a co-continuous structure include methods similar to those for adjusting Y / X in formula (1). That is, by adjusting the types and contents of component (A) and component (B), the degree of saponification and degree of polymerization of component (B), and the manufacturing conditions of the adhesive resin composition, for example, by appropriately using the types and contents of preferred components (A) and (B), the degree of saponification and degree of polymerization of preferred component (B), and preferred manufacturing conditions described herein, an adhesive resin composition having a co-continuous structure can be obtained. In one embodiment of the present invention, the higher the content of component (B), the more moderate the degree of saponification of component (B), or the lower the degree of polymerization, the more likely it is that a co-continuous structure will be formed.

[0082] [Laminate] The present invention encompasses a laminate comprising an adhesive layer comprising the adhesive resin composition of the present invention. The laminate of the present invention may comprise one or more adhesive layers of the present invention, and when two or more layers are comprised, the adhesive layers may have the same or different compositions. The form of the adhesive layer is not particularly limited, and may be, for example, a film or sheet. The laminate may comprise layers other than the adhesive layer of the present invention. Examples of such layers include a resin layer, paper, and other adhesive layers. The resin layer is a resin layer having a different composition from the adhesive layer. Furthermore, it is preferable that the adhesive layer has "biodegradability" as defined above.

[0083] The resin constituting the resin layer is not particularly limited, and examples thereof include polyester-based resins such as polyethylene terephthalate (PET); polyolefin-based resins such as polypropylene (PP) [preferably biaxially oriented polypropylene (BOPP)] and polyethylene (PE) [preferably low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE)]; ethylene-vinyl acetate copolymers; polyvinyl alcohol-based resins such as polyvinyl alcohol and ethylene-α-olefin copolymers; biodegradable resins such as biodegradable polyester-based resins; and resins obtained by modifying these with modifiers such as maleic anhydride. The resin layers can be used alone or in combination of two or more. The adhesive layer in the laminate of the present invention comprises an adhesive resin composition satisfying formula (1), and therefore can exhibit excellent adhesive strength to both the biodegradable resin layer and the polyvinyl alcohol-based resin layer. Therefore, the laminate of the present invention preferably includes a biodegradable resin layer and / or a polyvinyl alcohol-based resin layer as the resin layer, and more preferably includes a biodegradable resin layer and a polyvinyl alcohol-based resin layer. In order to achieve excellent biodegradability, the resin layer in the laminate of the present invention preferably consists of only a biodegradable resin layer and a polyvinyl alcohol-based resin layer. Furthermore, by including an adhesive layer, the laminate of the present invention can improve thermoformability, biodegradability, and gas barrier properties.

[0084] The biodegradable resin layer is a resin layer having biodegradability, and biodegradability is as defined above. The biodegradable resin layer is preferably a layer containing a biodegradable resin as a main component. Examples of the biodegradable resin include the biodegradable polyester resins described above in the section <Biodegradable polyester resin (A)>, as well as casein, modified starch, cellulose acetate, and the like. Among these, the biodegradable resin is preferably the biodegradable polyester resin described above from the viewpoint of easily increasing the adhesive strength with the adhesive layer and biodegradability. Furthermore, from the viewpoints of versatility, biodegradability, and mechanical properties, the biodegradable resin is more preferably at least one selected from the group consisting of PLA, PHB, PHBV, 3HB4HB, PHBH, PBAT, PBS, and PCL. Furthermore, from the viewpoints of strength, heat resistance, and water resistance, PLA and / or PBAT are even more preferable.

[0085] The PVA-based resin layer is not particularly limited as long as it contains a PVA-based resin as the main component, and examples thereof include the polyvinyl alcohol-based resins described in the above section <Polyvinyl Alcohol-Based Resin (B)>. In one embodiment of the present invention, the PVA-based resin layer may contain a plasticizer, such as a polyol (e.g., trehalose), in addition to the PVA-based resin. In this specification, the term "main component" refers to a component that accounts for 40% by mass or more, preferably 50% by mass or more, of the mass of the layer. The amount may be, for example, 55% by mass or more, 70% by mass or more, or 90% by mass or more. The PVA-based resin layer preferably has biodegradability as defined above.

[0086] The paper is not particularly limited, and examples thereof include kraft paper, unglazed kraft paper, fine paper, construction paper, glassine paper, parchment paper, synthetic paper, white cardboard, Manila cardboard, milk carton base paper, cup base paper, ivory paper, and silver paper.

[0087] Examples of the laminate of the present invention include a laminate including a biodegradable resin layer / adhesive layer in this order; a laminate including a PVA-based resin layer / adhesive layer in this order; and a laminate including a biodegradable resin layer / adhesive layer / PVA-based resin layer in this order. Among these, the laminate of the present invention is preferably a laminate including a biodegradable resin layer / adhesive layer / PVA-based resin layer in this order (sometimes referred to as laminate A). These laminates may include layers other than the biodegradable resin layer and the PVA-based resin layer between or on the outside of each layer, but it is preferable that no such layers are included between each layer, i.e., that each layer is adjacent. For example, laminate A preferably has the biodegradable resin layer, adhesive layer, and PVA-based resin arranged adjacently (i.e., in contact) in this order. Laminate A has excellent adhesive strength and biodegradability between the biodegradable resin layer and the adhesive layer, and between the adhesive layer and the PVA-based resin layer.

[0088] The thickness of the adhesive layer in the laminate of the present invention can be appropriately selected depending on the type of laminate and is not particularly limited, but is preferably 1 μm or more, more preferably 3 μm or more, even more preferably 5 μm or more, even more preferably 10 μm or more, particularly preferably 15 μm or more, and 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 50 μm or less. When the thickness of the adhesive layer is within the above range, it is easy to improve the adhesive strength, thermoformability, biodegradability, and gas barrier properties. When two or more adhesive layers are included in the laminate, the thickness of the adhesive layer refers to the thickness of one layer.

[0089] The thickness of the layers other than the adhesive layer in the laminate of the present invention (e.g., biodegradable resin layer or PVA-based resin layer) can be appropriately selected depending on the type of laminate and is not particularly limited, but is preferably 15 to 1000 μm, more preferably 20 to 500 μm, and even more preferably 30 to 400 μm. When the thickness of the other layers is within the above range, adhesive strength, thermoformability, biodegradability, and gas barrier properties are likely to be improved. When two or more other layers are included in the laminate, the thickness of the other layers refers to the thickness of one layer.

[0090] The thickness of the laminate of the present invention is not particularly limited, but is preferably 50 μm or more, more preferably 70 μm or more, even more preferably 100 μm or more, particularly preferably 200 μm or more, especially preferably 300 μm or more, and is preferably 5000 μm or less, more preferably 3000 μm or less, even more preferably 1000 μm or less. When the thickness of the laminate is within the above range, the strength, thermoformability, biodegradability, and gas barrier properties of the laminate are easily improved.

[0091] In one embodiment of the present invention, the thickness of the adhesive layer in the laminate A of the present invention is the same as the thickness of the adhesive layer described above. The thickness of the biodegradable resin layer in the laminate A is not particularly limited, but is preferably 30 μm or more, more preferably 50 μm or more, even more preferably 100 μm or more, even more preferably 200 μm or more, and preferably 1000 μm or less, more preferably 500 μm or less. The thickness of the PVA-based resin layer in the laminate A is not particularly limited, but is preferably 15 μm or more, more preferably 20 μm or more, even more preferably 25 μm or more, and 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, and particularly preferably 50 μm or less. When the thickness of each layer is within the above range, the adhesive strength, thermoformability, biodegradability, and gas barrier properties are easily improved. The thickness of each layer (biodegradable resin layer, adhesive layer, and PVA-based resin layer) in the laminate A indicates the thickness of one layer when two or more of the same layer are present in the laminate A. The thickness of each layer and the thickness of the laminate can be measured using a thickness meter, for example, by the method described in the Examples.

[0092] Specific examples of the layer configuration of the laminate A of the present invention include the following: biodegradable resin layer / adhesive layer / PVA-based resin layer; biodegradable resin layer / adhesive layer / PVA-based resin layer / adhesive layer / biodegradable resin layer; biodegradable resin layer / regrind layer / adhesive layer / PVA-based resin layer / adhesive layer / regrind layer / biodegradable resin layer; biodegradable resin layer / adhesive layer / PVA-based resin layer / adhesive layer / paper.

[0093] In one embodiment of the present invention, in the laminate of the present invention, it is preferred that at least one layer selected from the group consisting of a biodegradable resin layer, an adhesive layer, and a PVA-based resin layer is biodegradable in accordance with the ISO 14855 standard, more preferably at least two layers, and even more preferably all layers are biodegradable in accordance with the ISO 14855 standard.

[0094] The laminate of the present invention can be produced by laminating another layer such as a resin layer and an adhesive layer by a conventional method such as coextrusion molding (coextrusion lamination, coextrusion sheet molding, coextrusion inflation molding, coextrusion blow molding, etc.), coinjection molding, extrusion lamination, or dry lamination. For example, the laminate may be produced by coextruding or laminating the other layer and the adhesive layer, or by forming a film of an adhesive resin composition on the other layer. When laminating, the adhesive resin composition may be applied to the surface of the other layer or extrusion coated on the surface of the other layer.

[0095] The method for producing the laminate A, which is a preferred embodiment of the present invention, is not particularly limited, but a preferred method is to co-extrude a pellet-shaped adhesive resin composition that forms the adhesive layer, a pellet-shaped biodegradable resin (or biodegradable resin composition) that forms the biodegradable resin layer, and a pellet-shaped PVA-based resin (or PVA-based resin composition) that forms the PVA-based resin layer using a co-extruder. More specifically, the resins (or resin compositions) can be introduced into the hoppers of each extruder, melt-kneaded, and co-extruded using a feed block die. The cylinder temperature of each extruder can be appropriately selected depending on the melting temperature of the resin (or resin composition). Although not limited, the cylinder temperature of the extruder for the adhesive layer may be, for example, 120 to 300°C, preferably 150 to 250°C. The cylinder temperature of the extruder for the biodegradable resin layer may be, for example, 150 to 300°C, preferably 180 to 250°C. The cylinder temperature of the extruder for the PVA-based resin layer may be, for example, 150 to 300°C, preferably 190 to 260°C.

[0096] In one embodiment of the present invention, a crosslinking agent may be added to the adhesive resin composition of the present invention when obtaining the laminate of the present invention. Examples of crosslinking agents include epoxy compounds, isocyanate compounds, aldehyde compounds, silica compounds, aluminum compounds, zirconium compounds, and boron compounds. Among these, silica compounds such as colloidal silica and alkyl silicates are preferred. The amount of crosslinking agent added may be 5 to 60 parts by mass, preferably 10 to 40 parts by mass, and more preferably 15 to 30 parts by mass, per 100 parts by mass of the PVA-based resin. In one embodiment of the present invention, the laminate of the present invention may be subjected to a stretching treatment for the purpose of improving gas barrier properties and mechanical properties.

[0097] The laminate of the present invention also has excellent thermoformability and can be easily molded into a desired shape. In a preferred embodiment, the thermoforming process does not result in wrinkles or other imperfections, resulting in excellent appearance. The molding method is preferably melt molding. Examples of the melt molding method include, but are not limited to, extrusion molding, injection molding, T-die extrusion film formation, inflation film formation, compression molding, transfer molding, reinforced plastic molding, hollow molding, press molding, blow molding, calendar molding, foam molding, vacuum molding, and pressure molding. If desired, other thermoplastic resins can be laminated by methods such as coextrusion molding and lamination molding. These methods can produce molded articles of any shape, such as films, sheets, tubes, bottles, capsules, nonwoven fabrics, and fibers. In one embodiment of the present invention, when molding by vacuum molding, the laminate can be heated and then molded into the desired shape using a vacuum forming machine. The molding temperature is not limited and can be appropriately selected depending on the type of laminate, and is preferably 100° C. or higher, more preferably 130° C. or higher, and even more preferably 150° C. or higher, and is preferably 300° C. or lower, and more preferably 200° C. or lower. When the molding temperature is in this range, a molded product with excellent thermoformability is easily formed.

[0098] [Food Packaging Materials] The adhesive resin composition and laminate of the present invention are not particularly limited in their applications, but can be suitably used as packaging materials, particularly food packaging materials. Therefore, the present invention encompasses food packaging materials including an adhesive layer comprising the adhesive resin composition of the present invention or a laminate of the present invention. Because the food packaging material of the present invention includes the adhesive layer or laminate of the present invention, it has excellent adhesive strength, thermoformability, biodegradability, and gas barrier properties. Food packaging materials are not particularly limited, but examples include containers for packaging foods such as meat, fresh noodles, processed foods, tea, coffee powder, coffee beans, and pickles. In a preferred embodiment of the present invention, the food packaging material may be garbage bags for organic waste, containers used at various events, tea bags, coffee capsules, etc., and is particularly suitable for use as coffee capsules.

[0099] [Agricultural Films] The adhesive resin composition and laminate of the present invention are degradable in the natural environment and have excellent gas barrier properties, making them suitable for use as agricultural films. Therefore, the present invention encompasses agricultural films that include an adhesive layer comprising the adhesive resin composition of the present invention or a laminate of the present invention. Examples of agricultural films include mulch films, fumigation films, seedling raising films, and covering films, and among these, the present invention is particularly useful as a fumigation film.

[0100] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The measurement methods and evaluation methods used in the following examples and comparative examples are shown below.

[0101] [Saponification Degree] The saponification degree of the PVA-based resin (B) was determined by the method described in JIS K 6726:1994.

[0102] [Viscosity-average degree of polymerization] The viscosity-average degree of polymerization of each PVA-based resin (B) was determined by the method described in JIS K 6726:1994. Specifically, each polymer was resaponified and purified, and then calculated from the intrinsic viscosity [η] (l / g) measured in water at 30°C using the following formula. In the following formula, the degree of polymerization is represented as P. P = ([η] x 10 ４ / 8.29)（１／０．６２）

[0103] [Elongation at Break] A sheet obtained by hot press molding the biodegradable polyester resin (A) was cut into a width of 15 mm and a length of 100 mm, and the elongation at break was measured in accordance with ISO 527-1.

[0104] [Melting Point] 10 mg of the adhesive resin composition pellets obtained in each Example and Comparative Example were sealed in an aluminum pan (manufactured by TA Instruments), heated from -30°C to 220°C at a rate of 10°C / min, then rapidly cooled to -30°C at a rate of 10°C / min, and heated again from -30°C to 220°C at a rate of 10°C / min to perform DSC measurement. In the obtained DSC curve, the melting point Tm (°C) was determined from the apex temperature of the peak in the temperature range from the start to the end of melting during the second heating.

[0105] [MFR] The MFR of the biodegradable polyester resin (A) was measured at 200°C under a load of 2.16 kg in accordance with JIS K 7210:2014.

[0106] [Mw, Mn] The Mw and Mn of the biodegradable polyester resin (A) were measured using the relative molecular weight analysis method by GPC analysis shown below. <Sample Preparation> Approximately 5 mg of a powder sample of the biodegradable polyester resin (A) was collected and precisely weighed. 1 ml of hexafluoroisopropanol (HFIP) containing 20 mM sodium trifluoroacetate was added per 0.1 mg of sample to the collected sample, and the solution was dissolved by heating at 40°C for 3 hours. GPC analysis was performed using this solution under the following conditions. The relative molecular weight distribution curve was calculated by converting the relative molecular weight determined from the RI detector using the analysis software attached to the analyzer. The analysis was performed three times for the same sample, and the average value was used as the analysis result.

[0107] <GPC analysis conditions> Measurement device: HLC-8320GPC (manufactured by TOSOH Corporation) Analysis software: Empower (manufactured by Waters Corporation) Sample concentration: 0.1 mg / ml Mobile phase solvent: hexafluoroisopropanol with 20 mM sodium trifluoroacetate added Injection volume: 10 μl Flow rate: 0.2 ml / min Measurement temperature: 40°C Sample dissolution conditions: 40°C x 3 hours Filtration: 0.45 μm PTFE filter Column: GMMHR-H(S) (manufactured by TOSOH Corporation) x 2 Detector: RI detector included with the device Device calibration sample: PMMA (manufactured by Agilent Corporation)

[0108] [Thickness] The thickness of the film made of the adhesive resin composition, the laminate, and each layer in the laminate in the examples and comparative examples was measured with a digital micrometer.

[0109] [Measurement of (Y / X)] Y / X was measured as follows: First, pellets of the adhesive resin compositions obtained in the examples and comparative examples were preheated at 180°C for 5 minutes using a compression molding machine, and then subjected to a load of 50 kgf / cm. ２ The film was compression molded under the conditions of for 30 seconds to obtain a film made of the adhesive resin composition having a thickness of 300 μm. The film was cut into 10 mm squares to obtain samples for mass measurement having dimensions of 10 mm length x 10 mm width x 300 μm thickness. At this time, the value calculated by the following calculation formula (2) was defined as X. X = (mass of the sample for mass measurement) x (proportion (mass %) of the polyvinyl alcohol-based resin (B) contained in the adhesive resin composition) / 100 (2)

[0110] The obtained mass measurement sample (approximately 0.03 g) was placed in a 50 cc screw cap, and 20 ml of distilled water at 23°C was added. The screw cap containing the mass measurement sample and 20 ml of distilled water was placed in a hot air dryer set at 80°C. After 30 minutes, the distilled water was confirmed to be at 80°C, and then the sample was left to stand for another hour. The sample was then gently shaken with tweezers to remove any eluted components from the pores and surface. The mass measurement sample was then removed from the screw cap and placed in a hot air dryer set at 80°C and left to stand for another hour to obtain a post-hot water treatment sample. At this time, the value calculated using the following formula (3) was designated Y. In the examples and comparative examples, the only component eluted by hot water treatment was polyvinyl alcohol (B), so the value Y calculated using the following formula (3) can be considered to be the mass of polyvinyl alcohol (B) extracted into the hot water. Y = (mass of the mass measurement sample) - (mass of the post-hot water treatment sample) (3)

[0111] Using the obtained values ​​of X and Y, Y / X, which indicates the ratio of the polyvinyl alcohol resin (B) contained in the adhesive resin composition reduced by the hot water treatment, was calculated. The results are shown in Table 2.

[0112] [SEM Images] In Examples 2, 13, and Comparative Example 1, SEM images of the samples after the hot water treatment were taken under the following conditions. The hot water treatment samples, with platinum vapor-deposited on the cross section, were placed on the sample stage of an SEM (VE9800, manufactured by Keyence Corporation) and observed at an accelerating voltage of 5 kV. The SEM images are shown in Figures 1 to 3. In Example 2 (Figure 1) and Example 13 (Figure 3), it was confirmed that a bicontinuous structure was formed between a phase consisting of the biodegradable polyester-based resin (A) other than the voids and a phase consisting of the PVA-based resin (B) corresponding to the voids. It was also confirmed that a sea-island structure (sea: biodegradable polyester-based resin (A), islands: PVA-based resin (B)) partially coexisted. In Comparative Example 1 (Figure 2), it was confirmed that a sea-island structure was formed.

[0113] [Hole diameter] In addition to Example 2, Example 13, and Comparative Example 1, SEM images were also obtained by the above method for Examples 1, 4, and 5. Ten holes were randomly selected from the SEM images observed in Examples 1, 2, 4, and 5 and Comparative Example 1, and their diameters were measured, and the average value was used as the hole diameter. In the case of a structure such as Example 2 in Figure 1, multiple holes may be connected, but the diameters of holes that appear circular in the SEM image were measured.

[0114] [Adhesion Strength of Adhesive Resin Composition to PVA-Based Resin Layer] Pellets of the adhesive resin compositions obtained in the Examples and Comparative Examples were preheated at 180°C for 5 minutes using a compression molding machine, and then subjected to a load of 50 kgf / cm. ２ A film (also referred to as an adhesive layer) made of the adhesive resin composition was obtained by compression molding for 30 seconds under the conditions. A film made of the adhesive resin composition (150 mm long x 150 mm wide x 0.3 mm thick), a polyimide film ("Kapton Film" manufactured by Toray DuPont Co., Ltd., 75 mm long x 150 mm wide x 0.05 mm thick), and a film made of a polyvinyl alcohol resin (also referred to as a PVA resin layer) ("Mobiflex C17" manufactured by Kuraray Co., Ltd., 150 mm long x 150 mm wide x 0.5 mm thick) were stacked in this order and placed at the center of a metal spacer with inner dimensions of 150 mm x 150 mm and a thickness of 0.8 mm. The stacked film and metal spacer were sandwiched between polytetrafluoroethylene sheets and further sandwiched between metal plates from the outside, and compressed using a compression molding machine at 180 ° C. and a load of 50 kgf / cm. ２ The multilayer sheet was then compression molded at 25°C for 30 seconds to obtain a multilayer sheet containing an adhesive layer and a PVA resin layer. The multilayer sheet was cut into 25 mm wide specimens for measuring adhesive strength, and the peel strength between the adhesive layer and the PVA resin layer was measured in accordance with JIS K 6854-1:1999 using a peel tester (Shimadzu Corporation's "AGS-X") at a peel angle of 90°, a tensile speed of 50 mm / min, and an ambient temperature of 23°C, and this was taken as the adhesive strength of the adhesive resin composition. The adhesive strength was evaluated using the following indices. The results are shown in Table 2. ⊚: Peel strength of 20 N / 25 mm or more; ○: Peel strength of 10 N / 25 mm or more but less than 20 N / 25 mm; △: Peel strength of 4 N / 25 mm or more but less than 10 N / 25 mm; ×: Peel strength of less than 4 N / 25 mm.

[0115] [Adhesive Strength of Adhesive Resin Composition to Biodegradable Resin Layer] Pellets of the adhesive resin compositions obtained in the Examples and Comparative Examples were preheated at 180°C for 5 minutes using a compression molding machine, and then subjected to a load of 50 kgf / cm. ２ A film (also referred to as an adhesive layer) made of the adhesive resin composition was obtained by compression molding for 30 seconds under the conditions. A film made of the adhesive resin composition (150 mm long x 150 mm wide x 0.3 mm thick), a polyimide film ("Kapton film" manufactured by Toray DuPont Co., Ltd., 75 mm long x 150 mm wide x 0.05 mm thick), and a film made of a biodegradable resin (also referred to as a biodegradable resin layer) ("Ingeo (registered trademark) biopolymer 2003D" manufactured by Natureworks, 150 mm long x 150 mm wide x 0.5 mm thick) were stacked in this order and placed at the center of a metal spacer with inner dimensions of 150 mm x 150 mm and a thickness of 0.8 mm. The stacked film and metal spacer were sandwiched between polytetrafluoroethylene sheets and further sandwiched between metal plates from the outside, and compressed at 180 ° C. under a load of 50 kgf / cm using a compression molding machine. ２ The multilayer sheet was then compression molded at 25°C for 30 seconds to obtain a multilayer sheet comprising an adhesive layer and a biodegradable resin layer. The multilayer sheet was cut into 25 mm wide specimens for measuring adhesive strength, and the peel strength between the adhesive layer and the biodegradable resin layer was measured in accordance with JIS K 6854-1:1999 using a peel tester (Shimadzu Corporation's "AGS-X") at a peel angle of 90°, a tensile speed of 50 mm / min, and an ambient temperature of 23°C, and this was taken as the adhesive strength of the adhesive resin composition. The adhesive strength was evaluated using the following indices. The results are shown in Table 2. ⊚: Peel strength of 55 N / 25 mm or more; ○: Peel strength of 15 N / 25 mm or more but less than 55 N / 25 mm; △: Peel strength of 9 N / 25 mm or more but less than 15 N / 25 mm; ×: Peel strength of less than 9 N / 25 mm.

[0116] [Thermoformability] The laminates obtained in the examples and comparative examples were heated to 160°C using a vacuum forming machine ("Formech 508DT" manufactured by Formech) and then molded into capsule shapes with a diameter of 5 cm and a depth of 3 cm. The molded products obtained were visually observed, and the thermoformability was evaluated using the following criteria: ◯: Forming possible without problems Δ: Capsule shape formed, but some wrinkles occurred ×: Forming difficult

[0117] [Production Example 1] [Production of vinyl alcohol polymer (B1)] 630 parts by mass of vinyl acetate and 2520 parts by mass of methanol were charged into a 250 L reaction vessel equipped with a stirrer, a nitrogen inlet, and an initiator addition port. After heating to 60 ° C, the system was purged with nitrogen by nitrogen bubbling for 30 minutes. The internal temperature of the flask was adjusted to 60 ° C, and 0.5 parts by mass of AIBN was added to initiate polymerization. 3.2 hours after the start of polymerization, when the polymerization rate reached 60%, 1000 parts by mass of methanol was added and the mixture was cooled to terminate the polymerization. Unreacted vinyl acetate monomer was removed to obtain a methanol solution of PVAc. Methanol was added to the resulting PVAc solution to adjust the concentration to 25% by mass. To this methanol solution (400 parts by mass of PVAc in 100 parts by mass of PVAc in solution), 4.6 masses (molar ratio [MR] relative to vinyl acetate units in PVAc: 0.01) of an alkali solution (10 mass% NaOH in methanol) were added, and saponification was carried out at 40°C. After alkali addition, the gel was pulverized in a grinder and the saponification reaction was carried out for a total of 1 hour. Then, 1000 mass parts of methyl acetate were added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, 1000 mass parts of methanol was added to the white solid PVA polymer obtained by filtration, and the mixture was left to stand at room temperature for 3 hours for washing. The washing procedure was repeated three times, and the resulting PVA polymer was centrifuged for dewatering. The resulting PVA polymer was then left to dry in a dryer at 70°C for two days, yielding a vinyl alcohol polymer (B1) (referred to as PVA1) having a viscosity-average degree of polymerization of 300 and a degree of saponification of 88.0 mol%.

[0118] [Production Examples 2 to 8] [Production of Vinyl Alcohol Polymers (B2) to (B8)] Vinyl alcohol polymers (B2) to (B8) (referred to as PVA2 to 8) having the degrees of polymerization and saponification shown in Table 2 were obtained by changing the ratio of vinyl acetate to methanol, the polymerization conditions for the polymerization rate, and the saponification conditions for the amount of alkaline solution added.

[0119] [Production Example 9] [Production of Ethylene-Vinyl Alcohol Copolymer (B9)] A continuous polymerization vessel equipped with a reflux condenser, a raw material supply line, a reaction solution discharge line, a thermometer, a nitrogen inlet, an ethylene inlet, and a stirring blade was used. Vinyl acetate was continuously fed into the continuous polymerization vessel at 626 L / hr, methanol at 216 L / hr, and a 1% methanol solution of n-propyl peroxydicarbonate as an initiator at 30.3 L / hr, each using a metering pump. The ethylene pressure in the polymerization vessel was adjusted to 0.69 MPa. The polymerization vessel was continuously withdrawn from the continuous polymerization vessel so that the liquid level in the polymerization vessel was constant. The polymerization rate at the outlet of the continuous polymerization vessel was adjusted to 67%. The residence time in the continuous polymerization vessel was 5 hours. The temperature at the outlet of the continuous polymerization vessel was 60°C. The polymerization vessel was recovered, and the remaining vinyl acetate was removed by introducing methanol vapor into the polymerization vessel while heating it to 75°C in a hot water bath, to obtain a methanol solution of an ethylene-vinyl ester copolymer. Next, a saponification reaction was carried out for 1 hour at 40°C using sodium hydroxide as a saponification catalyst in a molar ratio of 0.02 relative to the ethylene-vinyl ester copolymer, with a water content of 0.5% in the system to be subjected to the saponification step. The resulting polymer was immersed in methanol and washed. The solvent was then removed by centrifugation, and the resulting polymer was dried to obtain an ethylene-vinyl alcohol copolymer (B9) having an ethylene unit content of 10 mol%, a viscosity-average degree of polymerization of 400, and a degree of saponification of 98.5 mol%.

[0120] Example 1 Adhesive Resin Composition 80 parts by mass of polybutylene adipate terephthalate ("Ecoflex C1200" manufactured by BASF, melting point: 118°C, elongation at break: 1012%, MFR: 15.8 g / 10 min, Mw: 72000, Mn: 24500) as the biodegradable polyester-based resin (A) and 20 parts by mass of the PVA1 obtained in Production Example 1 as the PVA-based resin (B) were melt-kneaded using a twin-screw extruder KZW15-45MG (D = 15 mmφ, L / D = 45, manufactured by Technovel Corporation) under the following conditions. The melt-kneaded mixture was extruded through a strand nozzle, and the resulting strand was cooled and cut to obtain pellets of the adhesive resin composition. The specific mechanical energy (SME) during melt-kneading was measured to be 526 kJ / kg. Screw rotation speed: 250 rpm Discharge: 3.5 kg / h Operation method: Same direction, same rotation, fully intermeshing type

[0121] <Laminate> A three-kind, five-layer laminate was produced by the following method, in which a biodegradable resin layer / adhesive layer / polyvinyl alcohol-based resin layer / adhesive layer / biodegradable resin layer were laminated in this order. Pellets of the adhesive resin composition obtained above, pellets of a polyvinyl alcohol-based resin composition (a composition obtained by kneading 100 parts by mass of ethylene-vinyl alcohol copolymer (B9) / 67 parts by mass of trehalose in a twin-screw extruder), and pellets of polylactic acid (Natureworks, Ingeo (registered trademark), biopolymer 2003D) were each placed in the hopper of a single-screw extruder (G.M. ENGINEERING, VGM25-28EX) and co-extruded at a flow rate of 5 kg / h using a feed block die to obtain a three-kind, five-layer laminate with a width of 20 cm. The cylinder temperatures set at this time were as follows: (Cylinder temperature) Adhesive layer: 180°C, polyvinyl alcohol-based resin layer: 210°C, biodegradable resin layer: 220°C

[0122] The resulting laminate had a structure of polylactic acid layer / adhesive layer / polyvinyl alcohol-based resin layer / adhesive layer / polylactic acid layer=250 μm / 20 μm / 30 μm / 20 μm / 250 μm (thickness) from the outside.

[0123] [Examples 2 to 10, 12, and 13 and Comparative Examples 1 to 4] Adhesive resin compositions and laminates were obtained in the same manner as in Example 1, except that the types and amounts of the biodegradable polyester resin (A) and the PVA resin (B) used in preparing the adhesive resin compositions were changed as shown in Table 2. In Table 2, PCL represents polycaprolactone ("Capa 6800" manufactured by Ingevity, melting point: 60°C, elongation at break: 800%, MFR: 2.4 g / 10 min), and PLA represents polylactic acid ("Ingeo™ Biopolymer 2003D" manufactured by NatureWorks, melting point: 153°C, elongation at break: 6%, MFR: 6 g / 10 min). In addition, the PBAT, PCL, and PLA used in the examples and comparative examples satisfy the biodegradability standards specified in EN13432, ASTM6400, and ISO14855. Furthermore, in the laminates obtained in the examples and comparative examples, the biodegradable resin layer, adhesive layer, and polyvinyl alcohol-based resin layer all satisfy the biodegradability standards of ISO14855.

[0124] [Example 11] An adhesive resin composition and a laminate were obtained in the same manner as in Example 1, except that the blending amounts and specific mechanical energy (SME) of the biodegradable polyester resin (A) and the PVA resin (B) when preparing the adhesive resin composition were changed as shown in Table 2. When the specific mechanical energy (SME) was changed as shown in Table 2, the discharge rate was changed to 2.0 kg / h.

[0125] According to the above-mentioned method, the adhesive strength was evaluated by measuring (Y / X) and the peel strength against the PVA-based resin layer and the biodegradable resin layer for each adhesive resin composition obtained in the Examples and Comparative Examples. Furthermore, the thermoformability of each laminate obtained in the Examples and Comparative Examples was evaluated. The results are shown in Table 2. In Table 2, *1 indicates that the film (adhesive layer) made of the adhesive resin composition was damaged before peeling in the peel test, i.e., cohesive failure occurred. The value in the *1 peel strength column indicates the strength at the time of cohesive failure, and since the peel strength is a larger value, the peel strength in the case of cohesive failure is indicated as "value <".

[0126] As shown in Table 2, it was confirmed that the adhesive resin compositions of Examples 1 to 13 were rated higher in adhesive strength to the PVA-based resin layer and the biodegradable resin layer than those of Comparative Examples 1 to 4. Therefore, the adhesive resin composition of the present invention has excellent adhesive strength. Furthermore, it was confirmed that the laminates of Examples 1 to 13 could be easily molded into desired shapes, and in particular, the laminates of Examples 1 to 8, 10, and 11 to 13 could be molded into desired shapes without the occurrence of wrinkles, etc. Therefore, laminates containing the adhesive resin composition of the present invention have excellent thermoformability.

[0127] Example 14 Laminate A three-kind, five-layer laminate was prepared by the following method, in which a biodegradable resin layer / adhesive layer / polyvinyl alcohol-based resin layer / adhesive layer / biodegradable resin layer were laminated in this order. Pellets of the adhesive resin composition obtained in Example 2, pellets of a polyvinyl alcohol-based resin composition (a composition obtained by kneading 100 parts by mass of ethylene-vinyl alcohol copolymer (B9) / 67 parts by mass of trehalose in a twin-screw extruder), and pellets of polybutylene adipate terephthalate (PBAT) (BASF Ecoflex C1200) were each placed in the hopper of a single-screw extruder (G.M. ENGINEERING, VGM25-28EX) and co-extruded at a flow rate of 1 kg / h using a feed block die to obtain a three-kind, five-layer laminate with a width of 15 cm. The cylinder temperatures set at this time were as follows: (Cylinder temperature) Adhesive layer: 180°C, polyvinyl alcohol-based resin layer: 210°C, biodegradable resin layer: 180°C

[0128] The resulting laminate had a structure of PBAT layer / adhesive layer / polyvinyl alcohol-based resin layer / adhesive layer / PBAT layer=35 μm / 5 μm / 15 μm / 5 μm / 35 μm (thickness) from the outside.

[0129] The thermoformability of the laminate obtained in Example 14 was evaluated in the same manner as in the evaluation of [Thermoformability] above, except that the heating temperature was changed from "160°C" to "110°C".

[0130]

[0131] As shown in Table 3, the laminate of Example 14 has excellent thermoformability because it can be molded into a desired shape without the occurrence of wrinkles, etc. In the laminate of Example 12, the biodegradable resin layer (PBAT layer), adhesive layer, and polyvinyl alcohol-based resin layer all meet the biodegradability standards of ISO 14855. In addition, the laminate of Example 14 has high adhesive strength to the PVA-based resin layer and biodegradable resin layer (PBAT layer).

Claims

1. An adhesive resin composition comprising a biodegradable polyester resin (A) and a polyvinyl alcohol resin (B), wherein formula (1): 0.30 ≤ Y / X ≤ 0.99 (1) [In the formula, X represents the mass of polyvinyl alcohol-based resin (B) contained in a 300 μm thick film made of the adhesive resin composition, and Y represents the mass of polyvinyl alcohol-based resin (B) extracted into hot water when the film is immersed in 80°C pure water for 1 hour and the soluble components are extracted.] An adhesive resin composition that satisfies the following conditions.

2. The adhesive resin composition according to claim 1, wherein the degree of saponification of the polyvinyl alcohol-based resin (B) is 75 to 96 mol%.

3. The adhesive resin composition according to claim 1, wherein the biodegradable polyester resin (A) has a break elongation of 50% or more as measured in accordance with ISO 527-1.

4. The adhesive resin composition according to claim 1, wherein the viscosity-average degree of polymerization of the polyvinyl alcohol-based resin (B) is 100 to 5000.

5. The adhesive resin composition according to claim 1, wherein the melting point of the biodegradable polyester resin (A) is 70°C or higher.

6. The adhesive resin composition according to claim 1, wherein the biodegradable polyester resin (A) includes an aromatic-aliphatic copolymer polyester resin.

7. The adhesive resin composition according to claim 6, wherein the aromatic-aliphatic copolymer polyester resin is polybutylene adipate terephthalate.

8. The adhesive resin composition according to claim 1, wherein the diameter of the pores formed when a 300 μm thick film made of the adhesive resin composition is immersed in pure water at 80°C for 1 hour and the soluble components are extracted is 10 μm or less.

9. An adhesive resin composition comprising a biodegradable polyester resin (A) and a polyvinyl alcohol resin (B), wherein the adhesive resin composition has a co-continuous structure formed from at least a phase consisting of the biodegradable polyester resin (A) and a phase consisting of the polyvinyl alcohol resin (B).

10. A laminate comprising an adhesive layer comprising the adhesive resin composition according to any one of claims 1 to 9.

11. The laminate according to claim 10, comprising a biodegradable resin layer, the adhesive layer, and a polyvinyl alcohol-based resin layer in this order.

12. The laminate according to claim 11, wherein the biodegradable resin layer, the adhesive layer, and the polyvinyl alcohol-based resin layer all meet the biodegradability standards in accordance with ISO 14855.

13. A food packaging material comprising an adhesive layer comprising the adhesive resin composition according to any one of claims 1 to 9.

14. An agricultural film comprising an adhesive layer comprising an adhesive resin composition according to any one of claims 1 to 9.