Biodegradable resin composition

Abstract

The purpose of the present invention is to provide a biodegradable resin composition which is excellent in terms of biodegradability, low-temperature moldability, and oxygen barrier properties under high humidity.　A biodegradable resin composition according to the present invention contains a polyvinyl alcohol-based resin (A), a modified starch (B), and a polyol plasticizer (C). The melting point of the composition is 180°C or less, and the temperature at which the storage elastic modulus of the composition is less than 1,000 MPa is not less 35°C but less than 180°C.

Description

Biodegradable resin composition

[0001] This patent application claims priority under the Paris Convention to Japanese Patent Application No. 2023-218158 (filing date: December 25, 2023), the entire contents of which are incorporated herein by reference. The present invention relates to a biodegradable resin composition, a molded article comprising the biodegradable resin composition, a laminate and a film for food packaging or agricultural use that include a biodegradable barrier layer made of the biodegradable resin composition, and coated paper obtained by coating paper with the biodegradable resin composition.

[0002] Plastics are widely used as packaging materials due to their high moldability, strength, water resistance, transparency, etc. However, plastics are poorly biodegradable, and if discarded in nature after use, they may remain for a long time and cause environmental damage. In response to this, biodegradable resins that are biodegraded or hydrolyzed in soil or water and are useful for preventing environmental pollution have recently attracted attention, and packaging materials using biodegradable resins have been put to practical use. For example, Patent Document 1 describes a biodegradable composition containing starch, polyvinyl alcohol, a plasticizer, etc.

[0003] Patent No. 5669906

[0004] However, conventional biodegradable resin compositions have a high molding temperature, and there has been a demand for a reduction in the molding temperature. However, when an attempt is made to lower the melting point of a biodegradable resin composition from the viewpoint of lowering the molding temperature, the oxygen barrier property is reduced under high humidity conditions such as those to which food packaging materials are exposed, and it has been found that it is difficult to achieve both moldability at low temperatures (for example, about 180°C) and oxygen barrier property under high humidity conditions.

[0005] Therefore, an object of the present invention is to provide a biodegradable resin composition that is excellent in biodegradability, low-temperature formability, and oxygen barrier property under high humidity conditions, a molded article containing the biodegradable resin composition, a laminate and a film for food packaging or agricultural use that include a biodegradable barrier layer made of the biodegradable resin composition, and coated paper obtained by coating paper with the biodegradable resin composition.

[0006] As a result of extensive research to achieve the above object, the present inventors have found that the above problems can be solved when a biodegradable resin composition containing a polyvinyl alcohol resin (A), a modified starch (B), and a polyol plasticizer (C) has a melting point and a temperature at which the storage modulus falls below 1,000 MPa within a specific range, and have thus completed the present invention. That is, the present invention includes the following aspects.

[0007] [1] A biodegradable resin composition comprising a polyvinyl alcohol-based resin (A), a modified starch (B), and a polyol plasticizer (C), wherein the melting point of the composition is 180°C or lower, and the temperature at which the storage modulus of the composition falls below 1,000 MPa is 35°C or higher and lower than 180°C. [2] The biodegradable resin composition according to [1], wherein the melting point of the polyvinyl alcohol-based resin (A) is 200°C or lower. [3] The biodegradable resin composition according to [1] or [2], wherein the content of the modified starch (B) is 0.5% by mass or higher relative to the mass of the biodegradable resin composition. [4] The biodegradable resin composition according to any of [1] to [3], wherein the Tg of the polyol plasticizer (C) is 50°C or higher. [5] The biodegradable resin composition according to any of [1] to [4], wherein the polyol plasticizer (C) contains trehalose. [6] The biodegradable resin composition according to any one of [1] to [5], wherein the content of the polyol plasticizer (C) is 5 to 80 mass% relative to the mass of the biodegradable resin composition. [7] A molded article comprising the biodegradable resin composition according to any one of [1] to [6]. [8] The molded article according to [7], which is a film. [9] A laminate comprising a biodegradable barrier layer made of the biodegradable resin composition according to any one of [1] to [6]. [9] Coated paper obtained by coating paper with the biodegradable resin composition according to any one of [1] to [6].

[10] A film for food packaging or agricultural use, comprising a biodegradable barrier layer made of the biodegradable resin composition according to any one of [1] to [6].

[0008] According to the present invention, it is possible to provide a biodegradable resin composition that is excellent in biodegradability, low-temperature moldability, and oxygen barrier property under high humidity conditions.

[0009] 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 within the scope that does not impair the spirit of the present invention. Note that the multiple upper and lower limit values ​​described in this specification can be arbitrarily combined to form a suitable numerical range.

[0010] [Biodegradable Resin Composition] The biodegradable resin composition of the present invention comprises a polyvinyl alcohol-based resin (A), a modified starch (B), and a polyol plasticizer (C), and the melting point of the composition is 180° C. or lower, and the temperature at which the storage modulus of the composition falls below 1,000 MPa is 35° C. or higher and lower than 180° C. In this specification, the polyvinyl alcohol-based resin (A) may be referred to as the "PVA-based resin (A)," and the biodegradable resin composition may be simply referred to as the "composition."

[0011] In this specification, "biodegradable" refers to a property that allows chemical decomposition, for example, by the action of hydrolysis, enzymatic decomposition, microbial decomposition, etc. In addition, in this specification, a "biodegradable resin composition" refers to a material that meets the biodegradability standards specified in ISO 14851, and is a material with a biodegradability of 70% or more as measured by the method described in the examples.

[0012] The present inventors have unexpectedly discovered that, in a biodegradable resin composition containing a PVA-based resin (A), a modified starch (B), and a polyol plasticizer (C), adjusting the melting point of the composition to 180°C or lower and the temperature at which the storage modulus of the composition falls below 1,000 MPa to 35°C or higher but lower than 180°C can improve biodegradability, low-temperature moldability, and oxygen barrier property under high humidity. While the reason for this is unclear, a composition with a melting point of 180°C or lower has relatively low crystallinity, improving low-temperature moldability. While reduced crystallinity typically leads to a decrease in oxygen barrier property under high humidity, adjusting the temperature at which the storage modulus falls below 1,000 MPa to 35°C or higher but lower than 180°C can suppress the mobility of amorphous portions while maintaining low-temperature moldability, thereby improving oxygen barrier property under high humidity.

[0013] The melting point of the composition of the present invention is 180°C or lower, preferably 178°C or lower, preferably 175°C or lower, preferably 173°C or lower, more preferably 170°C or lower, and preferably 150°C or higher, preferably 155°C or higher, preferably 160°C or higher, and more preferably 165°C or higher. The melting point of the composition of the present invention is preferably 150 to 180°C, more preferably 160 to 170°C. When the melting point of the composition is below the upper limit, the low-temperature moldability of the composition can be improved. When the melting point of the composition is above the lower limit, the gas barrier properties, strength, and stability can be easily improved. The melting point of the composition can be measured by DSC (differential scanning calorimetry) using the method described in the examples. The melting point of the composition can be adjusted to the above range by selecting the types, contents, and production method of the PVA-based resin (A), modified starch (B), and polyol plasticizer (C), for example, by using the PVA-based resin (A), modified starch (B), and polyol plasticizer (C) in the preferred forms described below, by using the preferred contents described below, by employing the preferred production method described below, etc. In particular, the melting point of the composition tends to decrease as the saponification degree of the PVA-based resin (A) decreases and / or the content of the polyol plasticizer (C) increases.

[0014] The temperature at which the storage modulus of the composition of the present invention falls below 1,000 MPa (or the temperature at which the storage modulus becomes less than 1,000 MPa) is 35°C or higher, preferably 40°C or higher, more preferably 50°C or higher, even more preferably 60°C or higher, still more preferably 70°C or higher, and particularly preferably 80°C or higher, and may be lower than 180°C, preferably 165°C or lower, preferably 160°C or lower, more preferably 155°C or lower, more preferably 150°C or lower, more preferably 145°C or lower, more preferably 140°C or lower, even more preferably 135°C or lower, still more preferably 130°C or lower, and particularly preferably 120°C or lower, 110°C or lower, or 100°C or lower. The temperature at which the storage modulus falls below 1,000 MPa is 35°C or higher and lower than 180°C, preferably 40°C or higher and lower than 180°C, more preferably 50 to 165°C, even more preferably 60 to 150°C, still more preferably 70 to 135°C, and particularly preferably 80 to 130°C, and may be, for example, 80 to 120°C, 80 to 110°C, or 80 to 100°C. When the temperature at which the storage modulus falls below 1,000 MPa is equal to or higher than the lower limit, the mobility of the amorphous portion of the composition can be further suppressed, thereby further improving the oxygen barrier property under high humidity. When the temperature at which the storage modulus falls below 1,000 MPa is equal to or lower than the upper limit, the deterioration of the low-temperature moldability of the composition can be suppressed. The temperature at which the storage modulus of the composition falls below 1,000 MPa refers to the temperature at which the storage modulus falls below 1,000 MPa when measured using a dynamic viscoelasticity analyzer under conditions of heating from −50° C. to 200° C. at a rate of 3° C. / min, and can be measured by the method described in the Examples. The temperature at which the storage modulus of the composition falls below 1,000 MPa can be adjusted to fall within the above range by adjusting the types, contents, and production method of the PVA-based resin (A), modified starch (B), and polyol plasticizer (C). For example, the temperature may be adjusted to fall within the above range by using the PVA-based resin (A), modified starch (B), and polyol plasticizer (C) in the preferred forms described below, by using the preferred contents described below, by employing the preferred production method described below, or by other means. In particular, the use of a polyol plasticizer (C) with a higher Tg tends to increase the temperature at which the storage modulus falls below 1,000 MPa.

[0015] [Polyvinyl Alcohol-Based Resin (A)] The biodegradable resin composition of the present invention contains a PVA-based resin (A). The PVA-based resin (A) may be a single type of PVA-based resin or a mixture of two or more types of PVA-based resins. The saponification degree of the PVA-based resin (A) is preferably 73 mol% or more, more preferably 80 mol% or more, preferably 83 mol% or more, more preferably 85 mol% or more, and preferably 99.9 mol% or less, more preferably 95 mol% or less, and even more preferably 90 mol% or less. The saponification degree of the PVA-based resin (A) is preferably 73 to 99.9 mol%, more preferably 80 to 95 mol%, more preferably 83 to 95 mol%, more preferably 83 mol% to 90 mol% or less, and particularly preferably 85 mol% to 90 mol%. A saponification degree within the above ranges can improve the low-temperature moldability and oxygen barrier properties of the composition under high humidity conditions. In this specification, the saponification degree means the molar fraction of hydroxyl groups relative to the total of hydroxyl groups and ester groups in the PVA-based resin (A), and can be measured in accordance with JIS K 6726. When two or more PVA-based resins are used, the saponification degree of the PVA-based resin (A) can be determined by measuring the saponification degree after mixing the two or more PVA-based resins.

[0016] The PVA-based resin (A) may be a polyvinyl alcohol having a vinyl alcohol unit or a modified polyvinyl alcohol containing a monomer unit other than a vinyl alcohol unit (also referred to as a constituent unit derived from another monomer), as long as the effect of the present invention is not impaired.

[0017] In one embodiment of the present invention, the melting point of the PVA-based resin (A) is preferably 200°C or lower, more preferably 195°C or lower, even more preferably 190°C or lower, and preferably 160°C or higher, more preferably 170°C or higher, and even more preferably 180°C or higher. The melting point of the PVA-based resin (A) is preferably 160 to 200°C, more preferably 170 to 195°C, and even more preferably 180 to 190°C. When the melting point of the PVA-based resin (A) is below the upper limit, the low-temperature moldability of the composition can be improved. When the melting point is above the lower limit, the gas barrier properties are likely to be improved. The melting point of the PVA-based resin (A) can be measured by DSC (differential scanning calorimetry) using the method described in the Examples. When two or more PVA-based resins are used, the melting point of the PVA-based resin (A) can be determined by measuring the melting point of the two or more PVA-based resins after mixing.

[0018] The viscosity-average degree of polymerization (sometimes referred to as "degree of polymerization") of the PVA-based resin (A) is preferably 200 to 3,000, more preferably 300 to 2,000, even more preferably 300 to 1,500, and particularly preferably 500 to 1,000. When the degree of polymerization is equal to or higher than the lower limit, the oxygen barrier property under high humidity conditions can be improved, while when the degree of polymerization is equal to or lower than the upper limit, the low-temperature moldability can be improved. The degree of polymerization of the PVA-based resin (A) can be measured in accordance with JIS-K6726. Specifically, the PVA-based resin is resaponified and purified, and then the intrinsic viscosity [η] (dl / g) measured in water at 30°C is calculated by the following formula (P: viscosity-average degree of polymerization): P=([η]×10 ３ When two or more PVA-based resins are used, the viscosity-average polymerization degree of the PVA-based resin (A) can be determined by measuring the viscosity-average polymerization degree of the PVA-based resins after mixing the two or more PVA-based resins.

[0019] The method for producing the PVA-based resin (A) is not particularly limited, but examples thereof include a method in which a vinyl alcohol monomer is copolymerized with any of the other monomers described above, and the resulting copolymer is saponified to convert it into vinyl alcohol units. Polymerization methods include batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization. Polymerization methods include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. The saponification of the copolymer can be carried out by known methods. For example, the saponification can be carried out in a state in which the copolymer is dissolved in alcohol or aqueous alcohol. The alcohol that can be used in this case is preferably a lower alcohol such as methanol or ethanol.

[0020] In one embodiment of the present invention, the content of the PVA-based resin (A) is preferably 0.5% by mass or more, more preferably 5% by mass or more, more preferably 8% by mass or more, more preferably 15% by mass or more, more preferably 25% by mass or more, particularly preferably 35% by mass or more, and is preferably 80% by mass or less, preferably 70% by mass or less, preferably 60% by mass or less, preferably 55% by mass or less, more preferably 50% by mass or less, and even more preferably 45% by mass or less, based on the mass of the composition. The content of the PVA-based resin (A) is preferably 0.5 to 80% by mass, more preferably 1 to 70% by mass, even more preferably 5 to 65% by mass, even more preferably 15 to 60% by mass, particularly preferably 25 to 55% by mass, particularly more preferably 35 to 50% by mass, and especially more preferably 35 to 45% by mass, based on the mass of the composition. When the content of the PVA-based resin (A) is equal to or more than the lower limit, the oxygen barrier property under high humidity, low-temperature moldability, and mechanical strength can be improved. When the content of the PVA-based resin (A) is equal to or less than the upper limit, the biomass ratio can be increased.

[0021] In one embodiment of the present invention, the amount of the PVA-based resin (A) is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, more preferably 15 parts by mass or more, more preferably 25 parts by mass or more, more preferably 35 parts by mass or more, even more preferably 45 parts by mass or more, still more preferably 55 parts by mass or more, particularly preferably 65 parts by mass or more, and is preferably 98 parts by mass or less, more preferably 95 parts by mass or less, more preferably 90 parts by mass or less, particularly preferably 85 parts by mass or less, based on 100 parts by mass in total of the PVA-based resin (A) and the modified starch (B). The content of the PVA-based resin (A) is preferably 5 to 98 parts by mass or 10 to 98 parts by mass, more preferably 15 to 95 parts by mass, even more preferably 25 to 95 parts by mass or 35 to 95 parts by mass, still more preferably 45 to 90 parts by mass or 55 to 90 parts by mass, and particularly preferably 65 to 85 parts by mass or 75 to 85 parts by mass, based on 100 parts by mass of the total of the PVA-based resin (A) and the modified starch (B). When the content of the PVA-based resin (A) is equal to or greater than the lower limit, the oxygen barrier property under high humidity, low-temperature moldability, and mechanical strength can be improved. When the content of the PVA-based resin (A) is equal to or less than the upper limit, the biodegradability can be improved.

[0022] [Modified Starch (B)] The biodegradable resin composition of the present invention contains modified starch (B). The starch used as the raw material for modified starch (B) may be derived from, for example, corn, cassava, potato, sweet potato, sago, tapioca, sorghum, beans, bracken, lotus, water chestnut, wheat, rice, oats, arrowroot, or pea. Among these, from the viewpoint of amylose content, the starch used as the raw material for modified starch (B) is preferably derived from corn (maize) or cassava, and more preferably from corn. The modified starch (B) may be composed of one or more types of starch. The modified starch (B) contains a modified group in which a hydroxyl group contained in starch is modified.

[0023] In one embodiment of the present invention, the average amylose content of the modified starch (B) is preferably 0.1 to 95% by mass, more preferably 0.3 to 90% by mass, even more preferably 0.3 to 85% by mass, even more preferably 0.5 to 80% by mass, even more preferably 0.7 to 75% by mass, particularly preferably 0.7 to 70% by mass, particularly preferably 0.7 to 65% by mass, and particularly preferably 0.7 to 10% by mass. When the average amylose content is within the above range, the oxygen barrier properties and low-temperature moldability of the composition under high humidity conditions can be improved. In this specification, the amylose content can be measured, for example, by the iodine coloration method described in "Starch 50 No. 4 158-163 (1998)." Furthermore, in this specification, the average amylose content refers to the amylose content of one type of modified starch when one type of modified starch is used, and refers to the weighted average of the amylose contents of the two or more types of modified starches when two or more types of modified starches are used. Therefore, for example, when two or more types of modified starches are used and the average amylose content is less than 50% by mass, modified starches with an amylose content of 50% by mass or more may be included.

[0024] In one embodiment of the present invention, the weight-average molecular weight (Mw) of the modified starch (B) is preferably 5,000 to 800,000, more preferably 10,000 to 650,000, even more preferably 20,000 to 550,000, and particularly preferably 25,000 to 100,000. When the Mw of the modified starch (B) is equal to or greater than the lower limit, the oxygen barrier property under high humidity conditions can be improved, and when the Mw is equal to or less than the upper limit, the low-temperature moldability can be improved. In this specification, the weight-average molecular weight can be measured using GPC (gel permeation chromatography) and can be measured by the method described in the examples.

[0025] The modified starch (B) preferably contains a hydrophobically modified starch having a modified group (sometimes referred to as a hydrophobic compound-modified group) modified with a hydrophobic compound having an SP value of 11.3 or less. In this case, this is advantageous in terms of oxygen barrier properties under high humidity conditions and low-temperature moldability. In this specification, the SP value refers to the solubility parameter calculated by the Fedors equation (Polym. Eng. Sci., 14[2], 147 (1974)).

[0026] The hydrophobic compound-modified group is a group in which a hydroxyl group contained in starch is modified by a reaction between the reactive group of the hydrophobic compound and the hydroxyl group, and is preferably bound to the starch by etherification, esterification, or amidation. The reactive group may be, for example, at least one selected from the group consisting of a halogen group, a halohydrin group, an epoxy group, a glycidyl group, an acid anhydride group, and an amino group. The hydrophobically modified starch is preferably, for example, at least one selected from the group consisting of etherified starch, esterified starch, and amidated starch.

[0027] When a hydrophobic compound is etherified, i.e., bonded to starch via an ether bond, the reactive group contained in the hydrophobic compound may be, for example, a halogen group, a halohydrin group, an epoxy group, or a glycidyl group, and the hydrophobic compound is preferably a hydrophobic compound having 6 to 24 carbon atoms. Specific examples of the hydrophobic compound include cetyl bromide, lauryl bromide, epoxidized soybean fatty alcohol, epoxidized linseed fatty alcohol, and glycidyl ethers having 2 to 24 carbon atoms, preferably glycidyl ethers having 6 to 24 carbon atoms, such as allyl glycidyl ether, propyl glycidyl ether, butyl glycidyl ether, decane glycidyl ether, lauryl phenyl glycidyl ether, myristoyl glycidyl ether, cetyl glycidyl ether, palmityl glycidyl ether, stearyl glycidyl ether, and linolyl glycidyl ether.

[0028] When a hydrophobic compound is esterified, i.e., bound to starch via an ester bond, the reactive group contained in the hydrophobic compound may be, for example, an acid anhydride group, and the hydrophobic compound is preferably a carboxylic acid anhydride having 6 to 24 carbon atoms, preferably 7 to 20 carbon atoms. Specific examples of the carboxylic acid anhydride include alkanoic acid carboxylic acid anhydrides such as octanoic acid acetic anhydride, decanoic acid acetic anhydride, lauric acid acetic anhydride, and myristic acid acetic anhydride; and alkyl or alkenyl dicarboxylic acid anhydrides such as alkyl or alkenyl succinic anhydride and alkyl or alkenyl maleic anhydride. As the alkyl or alkenyl dicarboxylic acid anhydride, octenylsuccinic anhydride (SP value: 10.4), nonylsuccinic anhydride, decylsuccinic anhydride, dodecenylsuccinic anhydride, octenylmaleic anhydride, nonylmaleic anhydride, decylmaleic anhydride, and dodecenylmaleic anhydride are preferred, and octenylsuccinic anhydride or octenylmaleic anhydride are more preferred.

[0029] When a hydrophobic compound is amidated, i.e., bonded to starch via an amide bond, the reactive group contained in the hydrophobic compound may be, for example, an amino group. The hydrophobic compound may suitably be an aliphatic amine containing a saturated or unsaturated hydrocarbon group having 6 to 24 carbon atoms. The aliphatic amine may contain a branched chain, but is preferably linear. Specific examples of the aliphatic amine include n-dodecylamine, n-hexadecylamine, n-octadecylamine, cocoamine, tallow amine, hydrogenated N-tallow-1,3-diaminopropane, N-hydrogenated tallow-1,3-diaminopropane, and N-oleyl-1,3-diaminopropane.

[0030] Among these, from the viewpoint of improving the oxygen barrier property and low-temperature moldability of the composition under high humidity conditions, the hydrophobically modified starch is preferably at least one selected from the group consisting of etherified starch having a glycidyl ether-modified group having 6 to 24 carbon atoms (etherified starch having a structural unit derived from glycidyl ether) and esterified starch having a carboxylic acid anhydride-modified group having 6 to 24 carbon atoms (esterified starch having a structural unit derived from carboxylic acid anhydride).

[0031] In one embodiment of the present invention, when the modified starch (B) comprises a hydrophobically modified starch, the content of the hydrophobically modified starch may be, for example, 10% by mass or more, preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, preferably 75% by mass or more, preferably 80% by mass or more, more preferably 85% by mass or more, more preferably 90% by mass or more or 100% by mass, based on the mass of the modified starch (B).

[0032] In one embodiment of the present invention, the content of the modified starch (B) is 0.5% by mass or more, more preferably 1% by mass or more, more preferably 3% by mass or more, more preferably 5% by mass or more, and particularly preferably 8% by mass or more, relative to the mass of the biodegradable resin composition; and is preferably 80% by mass or less, preferably 70% by mass or less, preferably 60% by mass or less, preferably 50% by mass or less, preferably 45% by mass or less, preferably 35% by mass or less, preferably 25% by mass or less, and more preferably 15% by mass or less. The content is preferably 0.5 to 80% by mass, more preferably 1 to 70% by mass, even more preferably 3 to 60% by mass, even more preferably 3 to 50% by mass, particularly preferably 5 to 45% by mass or 5 to 35% by mass, and particularly preferably 7 to 25% by mass or 8 to 15% by mass. When the content of the modified starch (B) is at least the lower limit, biodegradability can be improved, while when the content of the modified starch (B) is at most the upper limit, oxygen barrier properties under high humidity, low-temperature moldability, and mechanical strength can be improved.

[0033] In one embodiment of the present invention, the content of the modified starch (B) is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, more preferably 8 parts by mass or more, more preferably 10 parts by mass or more, more preferably 15 parts by mass or more, and is preferably 95 parts by mass or less, preferably 90 parts by mass or less, preferably 85 parts by mass or less, preferably 75 parts by mass or less, more preferably 65 parts by mass or less, more preferably 55 parts by mass or less, more preferably 45 parts by mass or less, more preferably 35 parts by mass or less, and more preferably 25 parts by mass or less, based on 100 parts by mass of the total of the PVA-based resin (A) and the modified starch (B). The content is preferably 2 to 95 parts by mass or 2 to 90 parts by mass, more preferably 5 to 85 parts by mass, even more preferably 5 to 75 parts by mass or 5 to 65 parts by mass, even more preferably 10 to 55 parts by mass or 10 to 45 parts by mass, and particularly preferably 15 to 35 parts by mass or 15 to 25 parts by mass. When the content of modified starch (B) is equal to or greater than the lower limit, biodegradability can be improved, and when the content of modified starch (B) is equal to or less than the upper limit, oxygen barrier properties under high humidity, low-temperature moldability, and mechanical strength can be improved.

[0034] [Polyol Plasticizer (C)] The biodegradable resin composition of the present invention contains a polyol plasticizer (C). By containing the polyol plasticizer (C), the melting point of the composition can be lowered and low-temperature moldability can be improved.

[0035] In one embodiment of the present invention, the glass transition temperature (Tg) of the polyol plasticizer (C) is not limited as long as the melting point of the composition and the temperature at which the storage modulus falls below 1,000 MPa are within the above-mentioned ranges, but is preferably 50°C or higher. By including a polyol plasticizer (C) with a Tg of 50°C or higher, the mobility of the amorphous portion of the composition can be suppressed, thereby improving the oxygen barrier property under high humidity conditions. The Tg of the polyol plasticizer (C) is preferably 50°C or higher, more preferably 70°C or higher, even more preferably 90°C or higher, and even more preferably 110°C or higher, and is preferably 250°C or lower, more preferably 200°C or lower, even more preferably 180°C or lower, and even more preferably 150°C or lower. The Tg of the polyol plasticizer (C) is preferably 50 to 250°C, more preferably 70 to 200°C, even more preferably 90 to 180°C, and even more preferably 110 to 150°C. When the Tg of the polyol plasticizer (C) is equal to or higher than the lower limit, the oxygen barrier property under high humidity conditions can be further improved, and when the Tg of the polyol plasticizer (C) is equal to or lower than the upper limit, the low-temperature moldability can be further improved.

[0036] The polyol plasticizer (C) may be any type of polyol plasticizer as long as the melting point of the composition and the temperature at which the storage modulus falls below 1,000 MPa are within the above-mentioned ranges. Examples include polyhydric alcohols such as trehalose and maltitol. Trehalose is preferred because it enhances low-temperature moldability while exhibiting excellent oxygen barrier properties under high humidity. When the polyol plasticizer (C) contains trehalose, the content thereof may be, for example, 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, 90% by mass or more, or 100% by mass, based on the mass of the polyol plasticizer (C). The polyol plasticizer (C) may be used alone or in combination of two or more types. In one embodiment of the present invention, when the crystallinity of a composition is reduced and its low-temperature solubility is enhanced, for example, by adjusting the degree of saponification or the amount of modification of the PVA-based resin, the oxygen barrier property tends to decrease. However, when a polyol plasticizer (C), preferably having a Tg of 50°C or higher, more preferably trehalose, is used, it is surprising that the polyol plasticizer suppresses the mobility of the amorphous portion of the composition and effectively prevents the oxygen barrier property from decreasing under high humidity. Therefore, when a polyol plasticizer, preferably having a Tg of 50°C or higher, more preferably trehalose, is used, it is possible to achieve both high levels of low-temperature solubility and high-humidity oxygen barrier property. Alternatively, even if the number of hydrogen bonds in the composition is reduced by, for example, adjusting the degree of saponification or the amount of modification of the PVA-based resin in order to lower the melting point of the composition, the polyol plasticizer, preferably having a Tg of 50°C or higher, more preferably trehalose, penetrates into the portions that can no longer block oxygen through hydrogen bonds, effectively preventing oxygen penetration, and it is therefore believed that the above-mentioned effects of the present invention can be effectively achieved.

[0037] In one embodiment of the present invention, the content of the polyol plasticizer (C) is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 20% by mass or more, more preferably 30% by mass or more, particularly preferably 40% by mass or more, and even more preferably 45% by mass or more, relative to the mass of the biodegradable resin composition, and is preferably 80% by mass or less, preferably 70% by mass or less, preferably 65% ​​by mass or less, preferably 60% by mass or less, and even more preferably 55% by mass or less. Furthermore, the content of the polyol plasticizer (C) is preferably 5 to 80% by mass, more preferably 10 to 75% by mass, even more preferably 20 to 70% by mass, even more preferably 30 to 65% by mass, particularly preferably 40 to 60% by mass, and especially preferably 45 to 55% by mass, relative to the mass of the biodegradable resin composition. When the content of the polyol plasticizer (C) is within the above range, the low-temperature solubility of the composition and the oxygen barrier properties at high humidity can be improved.

[0038] In one embodiment of the present invention, the content of the polyol plasticizer (C) is, based on 100 parts by mass of the total of the modified starch (A) and the polyvinyl alcohol-based resin (B), preferably 5 parts by mass or more, more preferably 10 parts by mass or more, more preferably 25 parts by mass or more, more preferably 40 parts by mass or more, more preferably 50 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 90 parts by mass or more, and is preferably 400 parts by mass or less, preferably 300 parts by mass or less, preferably 250 parts by mass or less, preferably 200 parts by mass or less, preferably 150 parts by mass or less, more preferably 130 parts by mass or less, more preferably 120 parts by mass or less, and more preferably 110 parts by mass or less. The content of the polyol plasticizer (C) is preferably 5 to 400 parts by mass, more preferably 10 to 300 parts by mass, even more preferably 25 to 250 parts by mass, still more preferably 50 to 200 parts by mass, particularly preferably 70 to 150 parts by mass, and especially preferably 90 to 110 parts by mass, based on 100 parts by mass of the total of the modified starch (A) and the polyvinyl alcohol-based resin (B). When the content of the polyol plasticizer (C) is within the above range, the low-temperature solubility and oxygen barrier property under high humidity conditions of the composition can be improved.

[0039] [Biodegradable Resin Composition] The biodegradable resin composition of the present invention contains a PVA-based resin (A), a modified starch (B), and a polyol plasticizer (C), and has a melting point of 180° C. or lower and a temperature at which the storage modulus falls below 1,000 MPa of 35° C. or higher but lower than 180° C., thereby exhibiting excellent biodegradability, low-temperature formability, and oxygen barrier properties under high humidity. Therefore, the biodegradable resin composition of the present invention can be suitably used as a food packaging material, etc.

[0040] The biodegradable resin composition of the present invention may contain plasticizers other than the polyol plasticizer, such as water, epoxidized linseed oil, epoxidized soybean oil, tributyl citrate, acetyltriethyl citrate, glyceryl triacetate, and plasticizer resins.

[0041] The biodegradable resin composition of the present invention may further contain additives such as clay, fatty acid salts, fillers, processing stabilizers such as copper compounds, weathering stabilizers, colorants, UV absorbers, heat stabilizers, light stabilizers, antioxidants, antistatic agents, flame retardants, lubricants, fragrances, foaming agents, deodorizers, extenders, release agents, mold release agents, reinforcing materials, antifungal agents, preservatives, and crystallization rate retarders, as needed, within the scope of the present invention. These additives may be used alone or in combination of two or more. In one embodiment of the present invention, the content (or total content) of the additives is not particularly limited and can be selected appropriately depending on the type of additive. For example, the content may be 0 to 10% by mass, 0 to 5% by mass, 0 to 1% by mass, 0 to 0.1% by mass, or 0 to 0.01% by mass, based on the mass of the biodegradable resin composition.

[0042] In one embodiment of the present invention, the oxygen permeability (unit: cc·20 μm / (m)) of the biodegradable resin composition of the present invention at a temperature of 23° C. and a relative humidity of 75% is ２The oxygen permeability (%) is preferably 10 or less, more preferably 5.0 or less, even more preferably 3.0 or less, even more preferably 2.0 or less, particularly preferably 1.0 or less, and particularly preferably 0.5 or less. When the oxygen permeability at a temperature of 23°C and a relative humidity of 75% is not more than the upper limit, excellent oxygen barrier properties can be exhibited under high humidity conditions. The oxygen permeability can be measured using a gas permeability measuring device in accordance with JIS K 7126-1:2006 after conditioning for one week under conditions of a temperature of 23°C and a relative humidity of 75%, and is the amount of permeation when converted to a thickness of 20 μm, and can be measured by the method described in the examples.

[0043] The biodegradable resin composition of the present invention has a degree of biodegradation of 70% or more, preferably 80% or more, and more preferably 90% or more in a biodegradability test in accordance with ISO 14851. The degree of biodegradation can be measured in accordance with ISO 14851 by the method described in the examples.

[0044] The biodegradable resin composition of the present invention may be in the form of a molded article, such as a pellet, a film, or a sheet, as described below.

[0045] [Method for Producing Biodegradable Resin Composition] The method for producing the biodegradable resin composition of the present invention is not particularly limited, but preferably includes the steps of (1) mixing the PVA-based resin (A), the modified starch (B), and the polyol plasticizer (C) to obtain a mixture, and (2) extruding, cooling, and drying the mixture.

[0046] Step (1) is a step of mixing the PVA-based resin (A), the modified starch (B), and the polyol plasticizer (C), and optionally other components, such as the above-mentioned additives, can also be mixed together.

[0047] Step (1) is usually carried out using an extruder, in which the components are mixed homogeneously while being subjected to shear stress by the screw and heated by applying external heat to the barrel.

[0048] As the extruder, for example, a twin-screw extruder can be used. The twin-screw extruder may be either co-rotating or counter-rotating. The screw diameter may be, for example, 15 to 150 mm, and the L / D ratio, which is the ratio of the extruder length (L) to the screw diameter (D), may be, for example, 20 to 60. The screw rotation speed is preferably 80 to 500 rpm, more preferably 150 to 300 rpm. The extrusion molding pressure is preferably 5 bar (0.5 MPa) or more, more preferably 10 bar (1.0 MPa) or more. Each component can be directly introduced into the extruder. Alternatively, these components may be premixed using a mixer and then introduced into the extruder.

[0049] In step (1), water can be added from the viewpoint of improving the mixability of the composition. However, in one embodiment of the present invention, the biodegradable resin composition has excellent melt-moldability, and therefore can be melt-molded, for example, without adding water as a plasticizer to an extruder.

[0050] The modified starch (B) can be gelatinized (gelled) by a cooking treatment using a combination of heat, shear stress and, optionally, water. Here, cooking treatment is a treatment for crushing and gelling starch granules.

[0051] The temperature of the extruder (temperature during kneading) is preferably 30 to 250°C, more preferably 45 to 200°C, and the temperature during cooking treatment is preferably 100 to 220°C, more preferably 150 to 200°C, and even more preferably 170 to 190°C. Heating can be carried out by applying heat to the barrel of the extruder from the outside. By applying a temperature that is changed stepwise to each barrel, heating to the desired temperature can be achieved. Cooking treatment at a temperature of 120°C or higher is advantageous in terms of processability.

[0052] The residence time in the extruder can be set depending on the temperature profile and the screw speed, and is preferably 1 to 10 minutes.

[0053] In step (2) of extruding, cooling, and drying the mixture, the molten mixture that has been forced through the extruder while being melt-kneaded is extruded through a die, and then cooled and dried. The die temperature is preferably 100 to 220° C., more preferably 150 to 200° C., and even more preferably 170 to 190° C. The mixture (melt) can be extruded into, for example, a film or sheet, or a strand.

[0054] When the mixture is extruded into a film or sheet, it can be cooled and dried while being extruded through a film-forming die and then wound up on a take-up roller. Cooling between the die and the roller is preferred to prevent the mixture from sticking to the roller. For drying, the roll may be heated, and dehumidified air may be supplied during winding. In the case of the blown tube method, dehumidified air can be used to expand the film as it exits the die. Talc can also be entrained in the air stream to prevent film blocking.

[0055] 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.

[0056] The biodegradable resin composition of the present invention, preferably pellets of the biodegradable resin composition, can be melt-molded to form molded articles of any shape, such as films, sheets, tubes, bottles, etc. Examples of melt-molding methods include conventional methods such as extrusion molding, injection molding, extrusion film formation from a T-die, 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.

[0057] In one embodiment of the present invention, when a biodegradable resin composition (e.g., pellets) is compression molded, a molded product can be produced using a conventional compression molding machine. The temperature during compression molding can be adjusted appropriately depending on the application, and may be, for example, 100 to 300°C, preferably 120 to 250°C, and the load is, for example, 50 to 200 kgf / cm. ２ , preferably 70 to 150 kgf / cm ２ may be.

[0058] In one embodiment of the present invention, when the biodegradable resin composition (e.g., pellets) is extruded, a molded product can be produced using a conventional extruder, preferably a twin-screw extruder. The extrusion conditions can be the same as those described in Example 1 [Method for producing a biodegradable resin composition].

[0059] [Molded Article] The present invention encompasses a molded article comprising the biodegradable resin composition of the present invention. The molded article of the present invention comprises the biodegradable resin composition, and therefore has excellent biodegradability, low-temperature moldability, and oxygen barrier properties under high humidity. The molded article may be in any form obtained by molding the composition, and examples include pellets, films, sheets, tubes, bottles, and the like. From the viewpoint of ease of use as food packaging materials, etc., films are preferably used. The molding methods exemplified above can be used as molding methods.

[0060] In one embodiment of the present invention, the content of the biodegradable resin composition in the molded body is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, and even more preferably 90 to 100% by mass, relative to the mass of the molded body. It is particularly preferable that the molded body consists of the biodegradable resin composition.

[0061] When the molded article is a film, the thickness of the film is not particularly limited, but is preferably 5 to 500 μm, more preferably 50 to 450 μm, and even more preferably 100 to 400 μm.

[0062] [Laminate] The present invention encompasses a laminate comprising a biodegradable barrier layer made of a biodegradable resin composition. Because the laminate of the present invention comprises a biodegradable barrier layer, it has excellent biodegradability, low-temperature formability, and oxygen barrier properties under high humidity. The laminate of the present invention may comprise one or more biodegradable barrier layers, and when two or more layers are comprised, the biodegradable barrier layers may have the same or different compositions. The form of the biodegradable barrier layer is not particularly limited, and may be, for example, a film or sheet. The laminate may also comprise another layer (a) in addition to the biodegradable barrier layer of the present invention. Examples of the other layer (a) include a resin layer, paper, and an adhesive layer. The resin layer has a different composition from the adhesive layer.

[0063] 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), linear low-density polyethylene (LLDPE)]; ethylene-vinyl acetate copolymers; polyvinyl alcohol-based resins such as polyvinyl alcohol resins and ethylene-α-olefin copolymers; biodegradable resins such as biodegradable polyester-based resins; and resins obtained by modifying these with a modifier such as maleic anhydride. The resin layer can be used alone or in combination of two or more types. From the viewpoint of increasing the biodegradability of the laminate, it is preferable to use a biodegradable polyester resin as the resin constituting the resin layer.

[0064] The biodegradable polyester resin may be a petroleum-derived resin or a biologically derived resin, and examples thereof include polycaprolactone (abbreviated as PCL), polybutylene succinate (abbreviated as PBS), polyethylene succinate (abbreviated as PES), poly(butylene succinate-co-butylene adipate), polybutylene adipate terephthalate (abbreviated as PBAT), polybutylene succinate terephthalate (PBST), and polyethylene terephthalate (PES). Examples of suitable biodegradable polyester resins include ethylene adipate terephthalate (PEAT), polylactic acid (PLA), 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), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (abbreviated as 3HB4HB), etc. Biodegradable polyester resins can be used alone or in combination of two or more.

[0065] The paper is not particularly limited, and examples thereof include kraft paper, double-bleached 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.

[0066] The adhesive layer can be selected from the resins exemplified above for the resin layer as long as it has adhesive function. For example, maleic anhydride-modified polyethylene, polyvinyl alcohol-based resin, biodegradable polyester-based resin, and mixtures thereof are used, and from the viewpoint of enhancing biodegradability, it is preferable to use a resin consisting of a polyvinyl alcohol-based resin, a biodegradable polyester-based resin, or a mixture thereof.

[0067] Examples of the layer configuration of the laminate of the present invention include layer configurations containing each layer in the following order: adhesive layer / biodegradable barrier layer; resin layer / adhesive layer / biodegradable barrier layer; resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer; resin layer / regrind layer / adhesive layer / biodegradable barrier layer / adhesive layer / regrind layer / resin layer; resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / paper; biodegradable barrier layer / paper. Among these, a configuration containing resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer in this order is preferred. Layers other than the resin layer, adhesive layer, and biodegradable barrier layer may be included between or on the outside of these layers, but it is preferred that no such layers are included between the layers, i.e., that the layers are adjacent to each other. For example, the laminate of the present invention preferably has a resin layer, adhesive layer, biodegradable barrier layer, adhesive layer, and resin layer arranged adjacent to each other (i.e., in contact) in this order. Such a laminate has excellent biodegradability, oxygen barrier properties under high humidity, and low-temperature solubility.

[0068] In one embodiment of the present invention, the thickness of the biodegradable barrier 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 to 1,000 μm, preferably 2 to 800 μm, preferably 3 to 700 μm, more preferably 5 to 500 μm, even more preferably 10 to 200 μm, still more preferably 13 to 100 μm, and particularly preferably 15 to 50 μm. When the thickness of the biodegradable barrier layer is within the above range, biodegradability, oxygen barrier properties under high humidity, and low-temperature solubility tend to be improved. When two or more biodegradable barrier layers are included in the laminate, the above thickness of the biodegradable barrier layer refers to the thickness of one layer.

[0069] In one embodiment of the present invention, the thickness of the other layer (a) 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 to 3,000 μm, more preferably 2 to 1,000 μm, and even more preferably 3 to 500 μm. When the thickness of the other layer (a) is within the above range, biodegradability, oxygen barrier properties under high humidity, and low-temperature solubility tend to be improved. When two or more other layers (a) are included in the laminate, the thickness of the other layer (a) refers to the thickness of one layer.

[0070] In one embodiment of the present invention, the thickness of the laminate of the present invention is not particularly limited, but is preferably 20 to 5000 μm, more preferably 50 to 3000 μm, and even more preferably 100 to 1000 μm. When the thickness of the laminate is within the above range, biodegradability, oxygen barrier properties under high humidity, and low-temperature solubility tend to be improved.

[0071] In one embodiment of the present invention, when the laminate of the present invention comprises a resin layer, an adhesive layer, and a biodegradable barrier layer in this order, the thickness of the biodegradable barrier layer in the laminate may be selected from the range of thicknesses of the biodegradable barrier layer described above. Furthermore, the thickness of the resin layer in the laminate may be preferably 10 to 1000 μm, more preferably 20 to 500 μm, and even more preferably 30 to 300 μm, and the thickness of the adhesive layer in the laminate may be preferably 1 to 100 μm, more preferably 2 to 50 μm, and even more preferably 3 to 30 μm. When the thickness of each layer is within the above range, biodegradability, oxygen barrier properties under high humidity, and low-temperature solubility tend to be enhanced. The thickness of each layer (biodegradable barrier layer, adhesive layer, and resin layer) in the laminate refers to the thickness of one layer when the laminate contains two or more of the same layer. Herein, the thicknesses of the monolayer film or sheet, the laminate, and each layer in the laminate can be measured using a thickness gauge and by the method described in the Examples.

[0072] The laminate of the present invention can be produced by laminating the biodegradable barrier layer with another layer such as a resin 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 biodegradable barrier layer with the other layer, or by forming a film of a biodegradable resin composition on the other layer. When laminating, the biodegradable resin composition may be applied to the surface of the other layer, or extrusion coated onto the surface of the other layer.

[0073] A laminate comprising a resin layer, an adhesive layer, and a biodegradable barrier layer in this order, which is one embodiment of the present invention, is preferably produced by co-extruding the resin forming the resin layer, the adhesive resin composition forming the adhesive layer, and the biodegradable resin composition of the present invention using a co-extruder. More specifically, the resins (or resin compositions) can be introduced into the hoppers of the extruders, 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 each resin (or resin composition). While 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 resin layer may be, for example, 150 to 300°C, preferably 170 to 250°C; and the cylinder temperature of the extruder for the biodegradable barrier layer may be, for example, 150 to 300°C, preferably 170 to 270°C.

[0074] In one embodiment of the present invention, the laminate of the present invention has excellent low-temperature formability and can be easily molded into a desired shape. In one embodiment of the present invention, thermoforming does not result in wrinkles or the like. Therefore, the laminate of the present invention has excellent appearance. The molding method is preferably melt molding. The melt molding method is not particularly limited, but examples thereof include 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 to 300° C., more preferably 130 to 250° C., and even more preferably 150 to 200° C. When the molding temperature is within this range, a molded product with excellent thermoformability is easily formed.

[0075] [Coated Paper] The present invention encompasses coated paper (or covered paper) obtained by coating (or covering) paper with the biodegradable resin composition of the present invention. The coated paper of the present invention comprises, in this order, paper and a biodegradable barrier layer made of the biodegradable resin composition. Because the coated paper of the present invention is coated with the biodegradable resin composition, it has excellent biodegradability and oxygen barrier properties under high humidity. Therefore, the coated paper of the present invention is suitable for use as a food packaging material, etc. Examples of paper include the papers exemplified in the above section [Laminate]. The biodegradable resin composition may be coated on at least one side (one side or both sides) of the paper, or may be coated in one layer or two or more layers. Conventional coating methods can be used, and for example, extrusion coating using an extruder can be suitably used. The cylinder temperature of the extruder may be, for example, 150 to 300°C, preferably 170 to 270°C.

[0076] The thickness of the paper is not particularly limited, but is preferably 10 to 1000 μm, more preferably 30 to 500 μm, and even more preferably 50 to 300 μm, and the thickness of the biodegradable barrier layer can be selected from the ranges described above. Furthermore, the thickness of the coated paper is preferably 15 to 1500 μm, more preferably 30 to 1000 μm, even more preferably 50 to 500 μm, even more preferably 80 to 400 μm, and even more preferably 100 to 300 μm. When the thickness of the paper, biodegradable barrier layer, or coated paper is within the above ranges, biodegradability and oxygen barrier properties under high humidity conditions can be improved.

[0077] The uses of the biodegradable resin composition, laminate, and coated paper of the present invention are not particularly limited, but they can be suitably used as packaging materials such as food packaging materials and agricultural applications. 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. Furthermore, the biodegradable resin composition, laminate, and coated paper of the present invention are degradable in the natural environment and have excellent gas barrier properties, making them suitable for use as agricultural films. Examples of agricultural films include mulch films, fumigation films, seedling raising films, and covering films, and among these, fumigation films are particularly useful.

[0078] The present invention encompasses a food packaging or agricultural film comprising a biodegradable barrier layer made of a biodegradable resin composition. Because the food packaging or agricultural film of the present invention comprises the biodegradable barrier layer, it has excellent biodegradability, low-temperature formability, and oxygen barrier properties under high humidity. The food packaging film of the present invention can be suitably used for the food packaging applications exemplified above, and the agricultural film can also be suitably used for the applications exemplified above. The biodegradable barrier layer made of the biodegradable resin composition is the same as that described in the above section [Laminate].

[0079] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0080] <Test Method> (1) Oxygen Transmission Rate Under High Humidity In accordance with JIS K 7126-1:2006, the monolayer films obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were conditioned for one week under conditions of a temperature of 23°C and a relative humidity of 75%, and then the oxygen transmission rate was measured under conditions of a temperature of 23°C and a relative humidity of 75% using a gas transmission rate measuring device (OX-TRAN 2 / 22, manufactured by MOCON Co., Ltd.). The oxygen transmission rate when the measured monolayer film thickness was converted to 20 μm was expressed as oxygen transmission rate (OTR) (cc·20 μm / (m ２The oxygen barrier property was evaluated using the following index: A: OTR≦2.0 cc·20 μm / (m ２ ・day・atm) B: 2.0cc・20μm / (m ２ ・day・atm)<OTR≦5.0cc・20μm / (m ２ ・day・atm) C: 5.0cc・20μm / (m ２ ・day・atm)<OTR≦10.0cc・20μm / (m2・day・atm) D: 10.0cc・20μm / (m ２ ・day・atm)<OTR

[0081] (2) Melting Point In accordance with JIS K 7121:1987, 10 mg of pellets of the compositions obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were sealed in an aluminum pan (manufactured by TA Instruments), heated from -30°C to 230°C at a rate of 10°C / min, cooled to -30°C at a rate of 10°C / min, and then heated again from -30°C to 230°C at a rate of 10°C / min to perform DSC measurement. The melting point Tm (°C) was determined from the apex temperature of the melting peak in the temperature range from the start to the end of melting during the second heating in the obtained DSC curve. The apex temperature of the melting peak with the highest melting energy in the measurement was taken as the melting point Tm (°C). The melting point Tm (°C) was evaluated using the following index. A: 150°C≦Tm≦175°C B: 175°C<Tm≦180°C C: 180°C<Tm The melting points of the PVA resins (A) used in Examples 1 to 8 and Comparative Examples 1 to 3 were also determined by the same method.

[0082] (3) Dynamic Viscoelasticity The melt properties of the monolayer films obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were measured using a dynamic viscoelasticity apparatus (Rheogel-E4000, manufactured by UBM Co., Ltd.). Measurements were performed under conditions of a frequency of 1 Hz and a temperature increase from -50°C to 200°C at a rate of 3°C / min to obtain the storage modulus value. The temperature (Temp) at which the measured storage modulus fell below 1000 MPa was evaluated using the following index: A: 80°C≦Temp<120°C B: 60°C≦Temp<80°C, 120°C≦Temp<150°C C: 35°C≦Temp<60°C, 150°C≦Temp<180°C D: 35°C>Temp, 180°C≦Temp

[0083] (4) Thermoformability The laminates 1 obtained in Examples 1 to 8 and Comparative Examples 1 to 3 were heated to 180°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: A: Forming was possible without any problems B: A capsule shape was obtained, but some wrinkles occurred C: Forming was difficult

[0084] (5) Biodegradability For the monolayer films obtained in Examples 1 to 8 and Comparative Examples 1 to 3, in accordance with the biodegradability evaluation method described in ISO14851:2019, 300 mg of acclimated sludge (a 1:1 mixture of sludge obtained from a sewage treatment plant on the day the test started and sludge acclimated in an aqueous PVA solution for one month) and 30 mg of a sample were added to 300 ml of inorganic medium, and the mixture was cultured at 25°C for 28 days. The amount of oxygen consumed for biodegradation was measured to determine the biodegradability of the composition. A: Biodegradability ≧70% B: Biodegradability <70%

[0085] (6) Thickness The thickness of the monolayer films, laminates 1 to 4, and each layer in the laminates 1 to 4 obtained in Examples 1 to 8 and Comparative Examples 1 to 3 was measured with a digital micrometer.

[0086] (7) Weight-average molecular weight of modified starch (B) The weight-average molecular weight of modified starch (B) was calculated using GPC (gel permeation chromatography, manufactured by Tosoh Corporation, "HLC-8320GPC") and a calibration curve with pullulan.

[0087] (8) SP Value of Compound Used for Modification of Modified Starch (B) The SP value of the compound used for modification of modified starch (B) was calculated by the Fedors formula described in Polym. Eng. Sci., 14[2], 147 (1974).

[0088] (9) Glass Transition Temperature (Tg) of Polyol Plasticizer (C) The glass transition temperature (Tg) of the polyol plasticizer (C) was measured in accordance with JIS K7121: 1987 using a differential scanning calorimeter (manufactured by TA Instrument) under nitrogen at a heating rate of 10°C / min. The midpoint glass transition temperature was used.

[0089] <Polyvinyl Alcohol Resin (A)> Production Example 1 [Production of Vinyl Alcohol Polymer (A-1)] 810 parts by mass of vinyl acetate and 990 parts by mass of methanol were charged into a separable flask equipped with a stirrer, a nitrogen inlet, and an initiator addition port, and the temperature was raised to 60°C. After that, the system was purged with nitrogen by nitrogen bubbling for 30 minutes. The internal temperature of the flask was adjusted to 60°C, and then 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 parts by mass (molar ratio [MR] relative to vinyl acetate units in PVAc: 0.01) of an alkali solution (10% by mass NaOH in methanol) was 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, 1,000 parts by mass of methyl acetate was added to neutralize the remaining alkali. After confirming the completion of neutralization using a phenolphthalein indicator, 1,000 parts by mass of methanol was added to the white solid PVA 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 was then centrifuged and dewatered. The PVA was then left to dry in a dryer at 70°C for two days, yielding a vinyl alcohol polymer (A-1) having a viscosity-average degree of polymerization (sometimes abbreviated as DP) of 800, a degree of saponification of 88.0 mol%, and a melting point of 188°C.

[0090] Production Example 2 [Production of Ethylene-Vinyl Alcohol Copolymer (A-2)] A continuous polymerization vessel equipped with a reflux condenser, raw material supply lines, 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 solution 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 solution was recovered from the continuous polymerization reactor, and while heating to 75°C in a hot water bath, methanol vapor was introduced into the polymerization solution to remove residual vinyl acetate (hereinafter, sometimes abbreviated as "VAc"), yielding a methanol solution of an ethylene-vinyl ester copolymer. Subsequently, a saponification reaction was carried out for 1 hour at 40°C, with a water content of the system to be subjected to the saponification step of 0.5% and sodium hydroxide as a saponification catalyst in a molar ratio of 0.02 relative to the ethylene-vinyl ester copolymer. The resulting polymer was immersed in methanol and washed. The solvent was then removed by centrifugation, followed by drying, yielding an ethylene-vinyl alcohol copolymer (A-2) having an ethylene unit content (sometimes referred to as the Et modification amount) of 10 mol%, a viscosity-average degree of polymerization of 400, a degree of saponification (sometimes abbreviated as DS) of 98.5 mol%, and a melting point of 210°C.

[0091] Production Example 3 [Ethylene-vinyl alcohol copolymer (A-3)] EVAL (registered trademark) F171B (ethylene content 32 mol %, melting point 183° C.) was prepared as ethylene-vinyl alcohol copolymer (A-3) and used in the following experiments.

[0092] Production Example 4 [Production of Vinyl Alcohol Polymer (A-4)] 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, a vinyl alcohol polymer (A-4) having a viscosity average degree of polymerization of 1,700, a degree of saponification of 88 mol%, and a melting point of 188°C was obtained.

[0093] <Modified Starch (B)> The following were used as modified starch (B). Modified starch (B-1): CAPSUL (registered trademark) Ingredion: corn starch modified with octenylsuccinic acid, weight average molecular weight 32,000, amylose content 1% by mass, obtained from Ingredion. The SP value of the octenylsuccinic acid was 10.4. Modified starch (B-2): N-Creamer 46 (registered trademark) Ingredion: waxy corn starch modified with octenylsuccinic acid, amylose content 1% by mass, obtained from Ingredion.

[0094] <Polyol Plasticizer (C)> The following were used as the polyol plasticizer (C): Polyol plasticizer (C-1): trehalose, Tg = 120°C, obtained from Hayashibara Co., Ltd. Polyol plasticizer (C-2): sorbitol, Tg = -4°C, obtained from Fujifilm Wako Pure Chemical Industries, Ltd. Polyol plasticizer (C-3): maltitol, Tg = 47°C, obtained from Fujifilm Wako Pure Chemical Industries, Ltd.

[0095] Example 1 40 parts by mass (dry mass) of the vinyl alcohol polymer (A-1) obtained in Production Example 1, 10 parts by mass (dry mass) of modified starch (B-1), and 50 parts by mass (dry mass) of polyol plasticizer (C-1) were melt-kneaded under the following conditions using a twin-screw extruder KZW15-45MG (D=15 mmφ, L / D=45, manufactured by Technovel Co., Ltd.) The melt-kneaded mixture was then extruded from a strand nozzle, and the resulting strand was cooled and cut to obtain pellets of a biodegradable resin composition.

[0096] <Single-layer film> The pellets of the biodegradable resin composition obtained above were compressed in a compression molding machine at a mold temperature of 190°C and a load of 100 kgf / cm. ２ The resulting monolayer film was subjected to compression molding for 1 minute under the conditions of

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[0097] <Laminate 1> A three-kind, five-layer laminate was produced by the following method, in which a resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer was laminated in this order. Pellets of the biodegradable resin composition obtained above, pellets of an adhesive resin composition (a composition obtained by kneading 40 parts by mass of a polyvinyl alcohol-based resin (Kuraray Poval (registered trademark) "3-88") and 60 parts by mass of polybutylene adipate terephthalate (PBAT) (manufactured by BASF, "Ecoflex C1200") in a twin-screw extruder), and polylactic acid (manufactured by Natureworks, Ingeo (registered trademark), "biopolymer 2003D") were each charged into the hopper of a single-screw extruder (manufactured by G.M. ENGINEERING, "VGM25-28EX") and co-extruded at a flow rate of 5 kg / h using a feed block die to obtain a 20 cm wide three-kind, five-layer laminate 1. The cylinder temperatures set at this time were as follows: (Cylinder temperature) Adhesive layer: 180°C, biodegradable barrier layer: 185°C, resin layer: 220°C

[0098] The resulting laminate 1 had a structure of resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer=250 μm / 20 μm / 30 μm / 20 μm / 250 μm (thickness) from the outside. There was no interfacial peeling, and the laminate had good biodegradability and barrier properties.

[0099] Comparative Example 1 Pellets of a biodegradable resin composition were obtained in the same manner as in Example 1, except that the type of polyvinyl alcohol polymer (A) and the temperature from C4 in the temperature profile to the die were changed to 195°C. Using the obtained pellets, a single-layer film was obtained in the same manner as in Example 1, except that the mold temperature was changed to 210°C. Furthermore, Laminate 1 was produced and evaluated in the same manner as in Example 1, except that the cylinder temperature of the biodegradable barrier layer was changed to 210°C. The results are shown in Table 2.

[0100] Examples 2 to 8 and Comparative Examples 2 to 3 Pellets of the biodegradable resin composition of Examples 2 to 8 and Comparative Examples 2 to 3 were obtained in the same manner as Example 1, except that the type and content of the polyvinyl alcohol polymer (A), the type and content of the modified starch (B), and the type and content of the polyol plasticizer (C) were changed as shown in Table 2. A monolayer film and a laminate 1 were produced using the obtained pellets and evaluated. The results are shown in Table 2.

[0101] <Laminate 2> A three-kind, five-layer laminate was produced by the following method, in which a resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer was laminated in this order. Pellets of the biodegradable resin composition obtained in Example 1, pellets of an adhesive resin composition (a composition obtained by kneading 40 parts by mass of a polyvinyl alcohol-based resin (Kuraray Poval (registered trademark) "3-88") and 60 parts by mass of polybutylene adipate terephthalate (PBAT) (manufactured by BASF, "Ecoflex C1200") in a twin-screw extruder), and pellets of polybutylene adipate terephthalate (PBAT) (manufactured by BASF, "Ecoflex C1200") were each placed in the hopper of a single-screw extruder (manufactured by G.M. ENGINEERING, "VGM25-28EX") and co-extruded at a flow rate of 1 kg / h using a feed block die to obtain a 20 cm wide three-kind, five-layer laminate 2. The cylinder temperatures set at this time were as follows: (Cylinder temperature) Adhesive layer: 180°C, biodegradable barrier layer: 185°C, resin layer: 180°C

[0102] The resulting laminate 2 had a structure of resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer=35 μm / 5 μm / 15 μm / 5 μm / 35 μm (thickness) from the outside. There was no interfacial peeling, and the laminate had good biodegradability and barrier properties.

[0103] <Laminate 3> A three-kind, five-layer laminate was produced by the following method, in which resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer were laminated in this order. Pellets of the biodegradable resin composition obtained in Example 1, pellets of low-density polyethylene (Novatec (registered trademark) LD and LC522 manufactured by Japan Polyethylene Corporation), and pellets of adhesive resin (Admer (registered trademark) and HE050 manufactured by Mitsui Chemicals, Inc.) were each placed in the hopper of a single-screw extruder (VGM25-28EX manufactured by G.M. ENGINEERING) and co-extruded at a flow rate of 1 kg / h using a feed block die, yielding a 20 cm-wide three-kind, five-layer laminate 3. The cylinder temperatures set at this time were as follows: (Cylinder temperatures) Adhesive layer: 200°C, Biodegradable barrier layer: 190°C, Resin layer: 200°C

[0104] The resulting laminate had a structure of resin layer / adhesive layer / biodegradable barrier layer / adhesive layer / resin layer=30 μm / 30 μm / 40 μm / 30 μm / 30 μm (thickness) from the outside. There was no interfacial peeling, and the laminate had barrier properties.

[0105] <Laminate 4 (Coated Paper)> A laminate (coated paper) in which a paper layer / biodegradable barrier layer was laminated in this order was produced by the following method. Pellets of the biodegradable resin composition obtained in Example 1 were placed in a single-screw extruder (manufactured by G.M. ENGINEERING, "VGM25-28EX"), melt-kneaded at a cylinder temperature of 185°C, and extruded through a 150 mm wide die into double-bleached kraft paper (100 μm thick, 70 g / m ２ ) was extrusion coated. The resulting laminate 4 had a structure of paper layer / biodegradable barrier layer = 100 μm / 20 μm. There was no interfacial peeling, and the laminate had good biodegradability and barrier properties.

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[0108] As shown in Table 2, the biodegradable resin compositions obtained in Examples 1 to 8 were evaluated as good in terms of biodegradability, low-temperature moldability, and oxygen barrier property under high humidity, while the biodegradable resin compositions obtained in Comparative Examples 1 to 3 were evaluated as poor in terms of any of biodegradability, low-temperature moldability, and oxygen permeability under high humidity. Therefore, it was confirmed that the biodegradable resin compositions of the present invention are excellent in biodegradability, low-temperature moldability, and oxygen barrier property under high humidity.

Claims

1. A biodegradable resin composition comprising a polyvinyl alcohol-based resin (A), a modified starch (B), and a polyol plasticizer (C), wherein the melting point of the composition is 180 °C or lower, and the temperature at which the storage elastic modulus of the composition is less than 1,000 MPa is 35 °C or higher and less than 180 °C.

2. The biodegradable resin composition according to claim 1, wherein the melting point of the polyvinyl alcohol-based resin (A) is 200 °C or lower.

3. The biodegradable resin composition according to claim 1 or 2, wherein the content of the modified starch (B) is 0.5% by mass or more based on the mass of the biodegradable resin composition.

4. The biodegradable resin composition according to claim 1 or 2, wherein the Tg of the polyol plasticizer (C) is 50 °C or higher.

5. The biodegradable resin composition according to claim 1 or 2, wherein the polyol plasticizer (C) contains trehalose.

6. The biodegradable resin composition according to claim 1 or 2, wherein the content of the polyol plasticizer (C) is 5 to 80% by mass based on the mass of the biodegradable resin composition.

7. A molded article comprising the biodegradable resin composition according to claim 1 or 2.

8. The molded article according to claim 6, which is a film.

9. A laminate comprising a biodegradable barrier layer made of the biodegradable resin composition according to claim 1 or 2.

10. A coated paper obtained by coating paper with the biodegradable resin composition according to claim 1 or 2.

11. A film for food packaging or agriculture comprising a biodegradable barrier layer made of the biodegradable resin composition according to claim 1 or 2.

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