Sealant material

Abstract

To provide a sealant material having satisfactory biodegradability.SOLUTION: A sealant material including block copolymer includes a block structural unit (A) including a polylactic acid unit (a) as a main unit, and a block structural unit (B) including a polyester unit (b) as a main unit, where a melting point is 110°C or more and 185°C or less, where the polyester unit (b) contains a unit derived from aliphatic diol (b1) and aliphatic dicarboxylic acid (b2), and the aliphatic diol (b1) is diol having an alkyl group as a branched chain.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a sealant material having good biodegradability. [Background technology]

[0002] From the viewpoint of environmental protection, bioplastics have been actively developed. For example, polylactic acid, a bioplastic, is made from renewable resources derived from plants such as corn, which are produced by photosynthesis, and is expected to be used in a wide range of fields. For example, Patent Document 1 describes a heat seal film consisting of a base layer made of a crystallized lactic acid-based polyester composition (A) that satisfies specific requirements, and a heat seal layer made of an amorphous lactic acid-based polyester composition (B) that satisfies specific requirements. Patent Document 2 describes a heat-sealable lactic acid-based polymer laminate having a base layer (I) made of a crystallized lactic acid-based polymer (A) and a seal layer (II) made of an amorphous lactic acid-based polymer (B) having a softening point lower than the melting point of the lactic acid-based polymer (A). Patent Document 3 describes a polylactic acid resin film that contains a polylactic acid resin having a hard segment containing a specific polylactic acid repeating unit and a soft segment containing a specific polyurethane polyol repeating unit, and that has a total Young's modulus in the length direction and the width direction and a total initial tensile strength in the length direction and the width direction each within a specific range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-94585 A [Patent Document 2] Japanese Patent Application Publication No. 10-151715 [Patent Document 3] Special Publication No. 2014-507524 Summary of the Invention [Problem to be solved by the invention]

[0004] It can be assumed that the resins or resin compositions containing polylactic acid described in Patent Documents 1 to 3 have a certain degree of biodegradability. Here, "biodegradability" refers to the property of being ultimately decomposed into water and carbon dioxide by organisms such as microorganisms, and it is known that resins containing polylactic acid exhibit biodegradability in compost. However, due to increasing environmental awareness, there is a demand for better biodegradability. As mentioned above, various applications of bioplastics are being considered, but in recent years, from the standpoint of environmental protection, there has also been a demand for better biodegradability for sealant materials. Therefore, an object of the present invention is to provide a sealant material having good biodegradability. [Means for solving the problem]

[0005] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by providing a sealant material containing a block copolymer that satisfies specific requirements. That is, the present invention includes the following inventions. [1] A sealant material comprising a block copolymer including a block structural unit (A) containing a polylactic acid unit (a) as a main unit and a block structural unit (B) containing a polyester unit (b) as a main unit, and having a melting point of 110°C or higher and 185°C or lower, The polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), and the aliphatic diol (b1) is a diol having an alkyl group as a branched chain. [2] The sealant material according to [1], wherein the glass transition point of the block copolymer is -80°C or higher and -15°C or lower. [3] The sealant material according to [1] or [2], wherein the two hydroxyl groups in the aliphatic diol (b1) are primary hydroxyl groups, and the aliphatic diol (b1) is a diol having no quaternary carbon. [4] The sealant material according to any one of the above [1] to [3], wherein the aliphatic diol (b1) has 4 or more carbon atoms. [5] The sealant material according to any one of [1] to [4] above, wherein the block structural unit (A) accounts for 5 mass% or more and 95 mass% or less relative to 100 mass% of the total of the block structural unit (A) and the block structural unit (B). [6] The sealant material according to any one of the above [1] to [5], wherein the aliphatic diol (b1) has 10 or less carbon atoms. [7] The sealant material according to any one of the above [1] to [6], wherein the branched chain of the aliphatic diol (b1) is a methyl group. [8] The sealant material according to any one of [1] to [7], wherein in the polylactic acid units (a), the proportion of units derived from D-lactic acid or D-lactide is less than 10 mass% relative to 100 mass% of the total of the units derived from L-lactic acid or L-lactide and the units derived from D-lactic acid or D-lactide, or the proportion of units derived from L-lactic acid or L-lactide is less than 10 mass% relative to 100 mass% of the total of the units derived from L-lactic acid or L-lactide and the units derived from D-lactic acid or D-lactide. [9] A laminate comprising a substrate and a sealing layer comprising the sealant material according to any one of [1] to [8] above.

[10] The laminate according to [9], wherein the substrate is paper. Effect of the Invention

[0006] According to the present invention, a sealant material having good biodegradability can be provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] The present invention will be described below based on one embodiment (hereinafter, also referred to as "one aspect of the present invention"). However, the embodiment described below is an example for embodying the technical idea of ​​the present invention, and the present invention is not limited to the following description. In addition, although preferred embodiments are shown in the present specification, a combination of two or more of the individual preferred embodiments is also a preferred embodiment. In addition, in the present specification, when there are several numerical ranges for matters indicated by numerical ranges, the lower limit values ​​and upper limit values ​​can be selectively combined to form a preferred embodiment. In other words, in this specification, the lower limit and upper limit described in stages for numerical ranges can be combined independently. For example, the description of "preferably 10 to 90, more preferably 30 to 60" for the same item can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60." Furthermore, with regard to a numerical range, for example, based on the description of "preferably 10 to 90, more preferably 30 to 60," the upper limit value can be not particularly specified and only the lower limit value can be specified as "10 or more" or "30 or more," and similarly, the lower limit value can be not particularly specified and only the upper limit value can be specified as "90 or less" or "60 or less." In this specification, unless otherwise specified, when a numerical range is stated, for example, "XX to YY", it means "not less than XX and not more than YY" (XX represents the lower limit and YY represents the upper limit). As above, for example, from the description of "preferably 10 or more, more preferably 30 or more" and the description of "preferably 90 or less, more preferably 60 or less" for the same item, the "preferable lower limit (10)" and the "more preferable upper limit (60)" can be combined to form "10 or more and 60 or less." Also, as above, only the lower limit can be specified as "10 or more" or "30 or more," and similarly, only the upper limit can be specified as "90 or less" or "60 or less." In addition, in this specification, "units" (where "units" refers to a polymer) means "structural units derived from." For example, a "polylactic acid unit" means "structural units derived from polylactic acid," and a "polyester unit" means "structural units derived from polyester." In this specification, unless otherwise specified, the "main chain" of a polymer means the longest molecular chain in the polymer molecule. In addition, in this specification, the term "solid content" refers to the total content of the polymer and raw material components of the polymer in a solution or dispersion obtained by dissolving or dispersing at least one selected from the group consisting of a polymer and raw material components of the polymer in a medium containing at least one selected from an organic solvent and water, excluding the medium. In addition, in this specification, unless otherwise specified, the terms "biodegradable" and "hydrolysis resistance" refer to the sealant material which is one embodiment of the present invention, and the "biodegradability" and "hydrolysis resistance" of the block copolymer contained in the sealant material. In addition, in this specification, unless otherwise specified, the expression "sealing strength" refers to the "sealing strength" of the sealant material which is one embodiment of the present invention.

[0008] [Sealant material] A sealant material according to one embodiment of the present invention is a block copolymer comprising a block structural unit (A) containing a polylactic acid unit (a) as a main unit and a block structural unit (B) containing a polyester unit (b) as a main unit, and having a melting point of 110°C or higher and 185°C or lower, wherein the polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), and the aliphatic diol (b1) is a diol having an alkyl group as a branched chain. The block copolymer contained in the sealant will now be described.

[0009] <Block copolymer> The block copolymer contains a block structural unit (A) containing a polylactic acid unit (a) as a main unit and a block structural unit (B) containing a polyester unit (b) as a main unit, and has a melting point of 110° C. to 185° C. The polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), and the aliphatic diol (b1) is a diol having an alkyl group as a branched chain. Although the reason why good biodegradability can be realized by using a block copolymer satisfying the above requirements is not clear, it is presumed that since the block structural unit (B) easily forms an amorphous structure, when the block copolymer biodegrades, microorganisms easily enter the polymer structure, realizing good biodegradability, and thus the sealant material also has good biodegradability. In addition, it is considered that biodegradability is further improved by the aliphatic diol (b1) having an alkyl group as a branched chain. On the other hand, if the block structural unit (B) does not form an amorphous structure, it is considered that microorganisms are less likely to enter the polymer structure when the block copolymer biodegrades, and it is considered that it is difficult to obtain the effect of the present invention. However, the fact that a polymer has an amorphous structure is only one factor that affects biodegradability. This is because it is considered that various factors such as whether microorganisms recognize the amorphous structure as food, whether enzymes and microorganisms are easily accessible, steric hindrance of the main chain, melting point, crystallinity, etc. affect biodegradability in combination. Therefore, it is not the case that the effect of the present invention can be obtained simply by the polymer having an amorphous structure.

[0010] (Block Structure Unit (A)) <Polylactic acid unit (a)> The block structural unit (A) has a polylactic acid unit (a) as a main unit. The term "main unit" refers to the unit that is contained at the highest content among the units that constitute the block structural unit (A). The content of the polylactic acid unit (a) in the block structural unit (A) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, and even more preferably 90% by mass or more, and may be 100% by mass. There is no upper limit to the content of the polylactic acid unit (a) in the block structural unit (A), and it is, for example, 100% by mass or less.

[0011] The polylactic acid constituting the polylactic acid unit (a) may be prepared by a direct condensation method of lactic acid, or may be prepared by a ring-opening polymerization method of lactide. As the lactic acid, for example, at least one selected from the group consisting of L-lactic acid, D-lactic acid, and DL-lactic acid can be used. From the viewpoint of easy availability, L-lactic acid is preferable. As the lactide, for example, at least one selected from the group consisting of L-lactide, D-lactide, DL-lactide, and meso-lactide can be used. From the viewpoint of easy availability, L-lactide is preferable. In addition, the polylactic acid may be poly-L-lactic acid, poly-D-lactic acid, poly-DL-lactic acid, or a stereocomplex polylactic acid obtained by mixing poly-L-lactic acid and poly-D-lactic acid. From the viewpoints of cost, availability of raw materials, and ease of handling of the block copolymer, the polylactic acid constituting the polylactic acid unit (a) is preferably at least one selected from the group consisting of poly-L-lactic acid, poly-D-lactic acid, and poly-DL-lactic acid, more preferably at least one selected from poly-L-lactic acid and poly-D-lactic acid, and even more preferably poly-L-lactic acid from the viewpoint of availability of raw materials. On the other hand, from the viewpoints of synthesis cost, complexity, and processability of the block copolymer, it is preferable that the polylactic acid constituting the polylactic acid unit (a) does not form a stereocomplex. For example, it is more preferable that the ratio of units derived from D-lactic acid or D-lactide in the polylactic acid unit (a) is less than 10% by mass relative to the total 100% by mass of units derived from L-lactic acid or L-lactide and units derived from D-lactic acid or D-lactide, or that the ratio of units derived from L-lactic acid or L-lactide is less than 10% by mass relative to the total 100% by mass of units derived from L-lactic acid or L-lactide and units derived from D-lactic acid or D-lactide. It is more preferable that in the polylactic acid units (a), the proportion of units derived from D-lactic acid or D-lactide is less than 5% by mass relative to 100% by mass of the total of the units derived from L-lactic acid or L-lactide and the units derived from D-lactic acid or D-lactide, or that the proportion of units derived from L-lactic acid or L-lactide is less than 5% by mass relative to 100% by mass of the total of the units derived from L-lactic acid or L-lactide and the units derived from D-lactic acid or D-lactide. Furthermore, in the polylactic acid units (a), the proportion of units derived from D-lactic acid or D-lactide is more preferably less than 10% by mass, and even more preferably less than 5% by mass, relative to 100% by mass of the total of the units derived from L-lactic acid or L-lactide and the units derived from D-lactic acid or D-lactide.

[0012] In addition, from the viewpoint of facilitating obtaining even better biodegradability, the polylactic acid unit (a) contains preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of constitutional units derived from L-lactic acid or L-lactide; or, the polylactic acid unit (a) contains preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of constitutional units derived from D-lactic acid or D-lactide. In addition, there is no upper limit to the content of constitutional units derived from L-lactic acid or L-lactide in the polylactic acid unit (a), and it is, for example, 100% by mass or less. Similarly, there is no upper limit to the content of constitutional units derived from D-lactic acid or D-lactide in the polylactic acid unit (a), and it is, for example, 100% by mass or less. In addition, as an embodiment of the polylactic acid unit (a), the polylactic acid unit (a) is preferably composed of a constitutional unit derived from L-lactic acid or L-lactide, or a constitutional unit derived from D-lactic acid or D-lactide, that is, the content of the constitutional unit derived from L-lactic acid or L-lactide, or the content of the constitutional unit derived from D-lactic acid or D-lactide in the polylactic acid unit (a) is preferably 100% by mass. In addition, as an embodiment of the polylactic acid unit (a), the content of the constitutional unit derived from L-lactic acid or L-lactide in the polylactic acid unit (a) is more preferably 100% by mass.

[0013] <Units (a') other than polylactic acid units (a)> The block structural unit (A) may or may not contain a unit (a') other than the polylactic acid unit (a). The monomer constituting the unit (a') is not particularly limited as long as it does not impair the effects of the present invention. The content of units (a') in the block structural unit (A) is preferably 30 mass % or less, more preferably 20 mass % or less, even more preferably 15 mass % or less, and still more preferably 10 mass % or less.

[0014] <Number average molecular weight of block structural unit (A)> The number average molecular weight of the block structural unit (A) is preferably 1,000 to 150,000, more preferably 3,000 to 100,000, and even more preferably 4,000 to 25,000. Within the above numerical range, the block copolymer has an excellent balance between ease of production and better hydrolysis resistance. When the block copolymer has a plurality of block structural units (A), the number average molecular weight of the block structural unit (A) means the total number average molecular weight of all the block structural units (A). The number average molecular weight of the block structural unit (A) can be determined from the number average molecular weight of the block copolymer described below and the mass content of the block structural unit (A).

[0015] (Block Structure Unit (B)) <Polyester unit (b)> The block structural unit (B) has a polyester unit (b) as a main unit. The term "main unit" refers to the unit that is contained at the highest content among the units that constitute the block structural unit (B). In this specification, polylactic acid is a unit constituting the polylactic acid unit (a), and is not included as a unit constituting the polyester unit (b). The content of the polyester unit (b) in the block structural unit (B) is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 85% by mass or more, still more preferably 90% by mass or more, and may be 100% by mass. There is no upper limit to the content of the polyester unit (b) in the block structural unit (B), and it is, for example, 100% by mass or less. The polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2). Specifically, the polyester unit (b) contains units derived from a polyester obtained by reacting an aliphatic diol (b1) with an aliphatic dicarboxylic acid (b2). The polyester unit (b) may or may not contain units derived from monomers other than the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2). The monomer other than the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) is not particularly limited as long as the effects of the present invention are not impaired. The total amount of the units derived from the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) in the polyester unit (b) is preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 99% by mass or more, and may be 100% by mass. There is no upper limit to the total amount of the units derived from the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) contained in the polyester unit (b), and it is, for example, 100% by mass or less.

[0016] {Aliphatic diol (b1)} The aliphatic diol (b1) is an aliphatic diol having an alkyl group as a branched chain. Here, the "branched chain" in the aliphatic diol (b1) refers to a partial structure branching off from the "main chain" in the aliphatic diol (b1), and no hydroxyl group is bonded to the end thereof. The "main chain" of the aliphatic diol (b1) refers to a molecular chain consisting of a plurality of atoms, preferably carbon atoms, connecting two hydroxyl groups in the molecule at both ends. Therefore, the two hydroxyl groups in the aliphatic diol (b1) are located at both ends of the "main chain" of the aliphatic diol (b1). When the aliphatic diol (b1) does not have an alkyl group as a branched chain, the block structural unit (B) is likely to crystallize, and the block copolymer cannot exhibit good biodegradability. In the aliphatic diol (b1), the number of branched chains is preferably 1 or 2, more preferably 1. The branched chain of the aliphatic diol (b1) is preferably at least one selected from the group consisting of a methyl group, an ethyl group, and a propyl group, more preferably at least one selected from a methyl group and an ethyl group, and even more preferably a methyl group. In the case where the aliphatic diol (b1) has a plurality of branched chains, the respective branched chains may be the same or different.

[0017] In addition, from the viewpoint of facilitating the production of a block copolymer by easily reacting with a dicarboxylic acid, the two hydroxyl groups of the aliphatic diol (b1) are preferably primary hydroxyl groups. In addition, from the viewpoint of easily reacting with a dicarboxylic acid and facilitating the production of a block copolymer, as well as facilitating obtaining good biodegradability, the aliphatic diol (b1) is preferably a diol having no quaternary carbon. Therefore, it is more preferable that the two hydroxyl groups in the aliphatic diol (b1) are primary hydroxyl groups and the aliphatic diol (b1) is a diol having no quaternary carbon.

[0018] The aliphatic diol (b1) preferably has 4 or more carbon atoms. The "number of carbon atoms" mentioned above refers to the total number of carbon atoms in the aliphatic diol (b1), including the number of carbon atoms constituting the alkyl group. The aliphatic diol (b1) preferably has 4 or more carbon atoms since it has excellent hydrolysis resistance. From the viewpoint of achieving even better hydrolysis resistance, the aliphatic diol (b1) preferably has 5 or more carbon atoms, more preferably 6 or more carbon atoms. From the viewpoint of availability, the aliphatic diol (b1) preferably has 10 or less carbon atoms, more preferably 9 or less carbon atoms.

[0019] Examples of the aliphatic diol (b1) include 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 2-methyl-1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 2,3-pentanediol, 2,4-pentanediol, 2-methyl-2,4-pentanediol, 1,4-pentanediol, 2-methyl- Examples of the aliphatic diol (b1) include 1,5-pentanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,5-pentanediol, 2,4-dimethyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 2-ethyl-1,6-hexanediol, and 2-methyl-1,8-octanediol. The aliphatic diol (b1) is preferably at least one selected from the group consisting of 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, and 2,4-diethyl-1,5-pentanediol, and more preferably 3-methyl-1,5-pentanediol. The aliphatic diol (b1) may be used alone or in combination of two or more kinds.

[0020] {Aliphatic dicarboxylic acids (b2)} The number of carbon atoms of the aliphatic dicarboxylic acid (b2) is not limited as long as it does not impair the effects of the present invention. On the other hand, for example, from the viewpoint of easily improving hydrolysis resistance, the number of carbon atoms of the aliphatic dicarboxylic acid (b2) is preferably 4 or more, more preferably 5 or more, and even more preferably 6 or more. In addition, from the viewpoint of availability, the number of carbon atoms of the aliphatic dicarboxylic acid (b2) is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less.

[0021] Examples of the aliphatic dicarboxylic acid (b2) include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, and decanedicarboxylic acid. At least one selected from the group consisting of succinic acid, adipic acid, and sebacic acid is preferred, at least one selected from succinic acid and adipic acid is more preferred, and adipic acid is even more preferred. The aliphatic dicarboxylic acid (b2) may be used alone or in combination of two or more kinds.

[0022] <Preferable combination of aliphatic diol (b1) and aliphatic dicarboxylic acid (b2)> A preferred embodiment of the combination of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) is, for example, from the viewpoint of exhibiting good biodegradability and superior seal strength, at least one combination selected from the group consisting of a combination of 2-methyl-1,3-propanediol and succinic acid, a combination of 3-methyl-1,5-pentanediol and succinic acid, a combination of 2,4-diethyl-1,5-pentanediol and succinic acid, a combination of 2-methyl-1,3-propanediol and adipic acid, a combination of 3-methyl-1,5-pentanediol and adipic acid, and a combination of 2,4-diethyl-1,5-pentanediol and adipic acid. is preferred, at least one combination selected from the group consisting of 2-methyl-1,3-propanediol and adipic acid, 3-methyl-1,5-pentanediol and succinic acid, 3-methyl-1,5-pentanediol and adipic acid, and 2,4-diethyl-1,5-pentanediol and adipic acid is more preferred, at least one combination selected from the group consisting of 3-methyl-1,5-pentanediol and succinic acid, and 3-methyl-1,5-pentanediol and adipic acid is even more preferred, and the combination of 3-methyl-1,5-pentanediol and adipic acid is even more preferred.

[0023] <Ratio of aliphatic diol (b1) and aliphatic dicarboxylic acid (b2)> The molar ratio of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) fed in the reaction is preferably 1.4 / 1 to 1 / 1.4, more preferably 1.2 / 1 to 1 / 1.2.

[0024] <Units (b') other than polyester units (b)> The block structural unit (B) may or may not contain a unit (b') other than the polyester unit (b). The monomer constituting the unit (b') is not particularly limited as long as it does not impair the effects of the present invention. The content of units (b') in the block structural unit (B) is preferably 50 mass % or less, more preferably 30 mass % or less, even more preferably 20 mass % or less, still more preferably 15 mass % or less, and particularly preferably 10 mass % or less.

[0025] <Number average molecular weight of block structural unit (B)> The number average molecular weight of the block structural unit (B) is preferably 2,000 or more, more preferably 2,500 or more, even more preferably 4,000 or more, and still more preferably 5,000 or more. From the viewpoint of ease of production of the block copolymer, the number average molecular weight of the block structural unit (B) is preferably 180,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, and still more preferably 40,000 or less, and may be 30,000 or less, 20,000 or less, or 15,000 or less. The number average molecular weight of the block structural unit (B) can be determined by gel permeation chromatography (GPC), specifically, by the method described in the Examples.

[0026] (Structural unit ratio) The content of the block structural unit (A) is preferably 5% by mass or more and 95% by mass or less relative to 100% by mass of the total of the block structural unit (A) and the block structural unit (B). When the proportion of the block structural unit (A) is 5% by mass or more, the block copolymer tends to have excellent handleability. When the proportion of the block structural unit (A) is 95% by mass or less, the block copolymer and the sealant tend to have excellent biodegradability. Here, "handleability" refers to the ease of handling as a material. For example, if the block copolymer is in a solid state at room temperature (23°C), it is easy to handle as a resin material and tends to have better handleability than a liquid block copolymer. In this specification, unless otherwise specified, the term "handleability" refers to the handleability of a block copolymer. From the viewpoint of handleability, the proportion of the block structural unit (A) is more preferably 10% by mass or more, and even more preferably 15% by mass or more. Also, from the viewpoint of facilitating obtaining better biodegradability, the proportion of the block structural unit (A) is more preferably 80% by mass or less, and even more preferably 75% by mass or less. The proportion of the block structural unit (A) is 1 The ratio of the block structural unit (A) can be determined by H-NMR, specifically, by the method described in the Examples below. In the Examples described later, the ratio of the block structural unit (A) is also referred to as the "hard ratio."

[0027] The total content of the block structural unit (A) and the block structural unit (B) in the block copolymer is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and may be 100% by mass. There is no upper limit to the total content of the block structural unit (A) and the block structural unit (B) in the block copolymer, and it is, for example, 100% by mass or less.

[0028] The block copolymer may or may not contain units other than the block structural unit (A) and the block structural unit (B). The units other than the block structural unit (A) and the block structural unit (B) are not particularly limited as long as they do not impair the effects of the present invention. In the block copolymer, the content of units other than the block structural unit (A) and the block structural unit (B) is preferably 10 mass % or less, more preferably 5 mass % or less, and even more preferably 2 mass % or less.

[0029] (Number average molecular weight of block copolymer) The number average molecular weight of the block copolymer is, for example, more preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and still more preferably 11,000 or more, from the viewpoint of handleability. Furthermore, for example, from the viewpoint of ease of production and processability of the block copolymer, the number average molecular weight of the block copolymer is preferably 450,000 or less, more preferably 200,000 or less, even more preferably 100,000 or less, still more preferably 80,000 or less, still more preferably 50,000 or less, and still more preferably 45,000 or less; and, for example, from the viewpoint of ease of synthesis, it may be 35,000 or less, 25,000 or less, or 15,000 or less. The number average molecular weight of the block copolymer can be determined by gel permeation chromatography (GPC), specifically, by the method described in the Examples.

[0030] (Block copolymer bond type) The bonding form of the block copolymer is preferably a triblock type or a diblock type, and more preferably a triblock type. The block copolymer may be a mixture of a triblock type and a diblock type. Specifically, the bonding form is preferably [block structural unit (A)]-[block structural unit (B)]-[block structural unit (A)]. As described above, the block copolymer may or may not contain units other than the block structural unit (A) and the block structural unit (B). When the block copolymer contains units other than the block structural unit (A) and the block structural unit (B), for example, in the above-mentioned bonding form, [block structural unit (A)] and [block structural unit (B)] may be bonded via a unit other than the block structural unit (A) and the block structural unit (B), or the unit other than the block structural unit (A) and the block structural unit (B) may be bonded to an end of the molecular structure.

[0031] (Melting point of block copolymer) As described above, the melting point of the block copolymer is 110° C. or higher and 185° C. or lower. When the melting point of the block copolymer is 110°C or higher, the block copolymer is unlikely to soften even at temperatures equal to or higher than the glass transition temperature thereof, and has excellent heat resistance. When the melting point of the block copolymer is 185°C or lower, the melting point is not too high, and the block copolymer has excellent processability, for example, easy melt processing. Therefore, the melting point of the block copolymer is preferably 115°C or higher, more preferably 120°C or higher, even more preferably 125°C or higher, and preferably 180°C or lower, more preferably 170°C or lower, and even more preferably 160°C or lower. The melting point of the block copolymer can be determined by a differential scanning calorimeter, specifically, by the method described in the examples.

[0032] (Glass transition temperature of block copolymer) The glass transition temperature of the block copolymer is preferably −80° C. or higher and −15° C. or lower. Within the above range, the block copolymer tends to have excellent flexibility and impact resistance. From the viewpoint of low-temperature properties such as impact resistance at low temperatures, the glass transition temperature of the block copolymer is more preferably -20°C or lower, even more preferably -25°C or lower, even more preferably -30°C or lower, and even more preferably -35°C or lower. The lower limit of the glass transition temperature of the block copolymer is preferably low, and may be, for example, -75°C or higher, -70°C or higher, or -65°C or higher. The glass transition temperature of the block copolymer can be determined by differential scanning calorimetry, specifically, by the method described in the examples.

[0033] <Method of producing block copolymer> The block copolymer can be produced by a known production method. A known method for producing a block copolymer may be, for example, a method in which a polyester constituting the polyester unit (b) is synthesized and the polyester is polymerized with lactide. The polyester can be synthesized by a known method. For example, the polyester can be synthesized by reacting an aliphatic diol (b1) with an aliphatic dicarboxylic acid (b2) using an esterification catalyst (e.g., tin octylate, tin chloride, tin oxide). When the polyester and the lactide are polymerized, it is preferable to use a ring-opening polymerization catalyst (e.g., tin octoate, tin chloride, tin oxide). The polymerization reaction may be performed by solution polymerization, melt polymerization, interfacial polycondensation, or the like, and any of the polymerization reaction conditions may be set as known in the art.

[0034] Another known method for producing a block copolymer may be, for example, a method in which a polylactic acid constituting the polylactic acid unit (a) and a polyester constituting the polyester unit (b) are separately synthesized and then the polylactic acid and the polyester are reacted with each other. Polylactic acid can be synthesized by a known method. For example, polylactic acid may be synthesized by reacting lactic acid by a direct condensation method, or polylactic acid may be synthesized by reacting lactide by a ring-opening polymerization method. When polylactic acid and polyester are polymerized, it is preferable to use an esterification catalyst (e.g., tin octoate, tin chloride, tin oxide). The polymerization reaction may be solution polymerization, melt polymerization, interfacial polycondensation, or the like, and any of these may be carried out under known polymerization reaction conditions.

[0035] <Other ingredients> Furthermore, the sealant material may or may not contain components other than the block copolymer (hereinafter also referred to as "other components"), as necessary, within the range in which the effects of the present invention are achieved. Examples of other components include polymers other than the block copolymer (hereinafter also referred to as "other polymers"); colorants such as dyes and pigments; stabilizers such as ultraviolet absorbers; antistatic agents; flame retardants; flame retardant assistants; lubricants; plasticizers; inorganic fillers; inorganic layered compounds; and inorganic layered compounds that have been subjected to an organic treatment. The other polymers are not particularly limited as long as they do not impair the effects of the present invention, and examples thereof include polylactic acid; copolymers having polylactic acid units and polyester units but not satisfying the above requirements; polyvinyl alcohol; starch; and other biodegradable resins. Furthermore, as described below, when the sealant material, which is one aspect of the present invention, is dissolved in a solvent and used as a coating liquid, it is preferable that the sealant material can be dissolved without using a halogen-based solvent, and when other polymers are contained, it is preferable that the other polymers can also be dissolved without using a halogen-based solvent.

[0036] In addition, the other components may be blended into the block copolymer when used as a sealant described later, or may be used as a sealant in a state where they are blended in advance. The method of blending the other components into the block copolymer is not particularly limited within the scope of the effect of the present invention, and may be blended using a known method, such as a method in which the block copolymer and the other components are mixed in advance using various mixers or blenders, and then melt-kneaded using various extruders, various mixers, heating rolls, various kneaders, etc.

[0037] In addition, for example, from the viewpoint of easily achieving both good biodegradability and better seal strength, the content of the block copolymer in the sealant is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, based on 100% by mass of the total amount of the sealant. In one embodiment of the sealant, for example, the content of the block copolymer in the sealant may be 85% by mass or more, 90% by mass or more, or 95% by mass or more, based on 100% by mass of the total amount of the sealant. There is no upper limit to the content of the block copolymer contained in the sealant, and it is, for example, 100% by mass or less, based on 100% by mass of the total amount of the sealant.

[0038] There is no particular limitation on the method of use of the sealant material. For example, the sealant material may be used by heating and melting it in pellet form, or the sealant material may be formed into a film or sheet form and used as a sealant film. In general, sealant films are widely used in packaging materials for foods, beverages, medicines, cosmetics, medical devices, etc. For example, the sealant film is disposed as a sealing layer on the innermost layer of the packaging material, and the surfaces of the sealing layers are heat sealed in contact with each other to seal the package. From the viewpoint of environmental protection, there is also an increasing need for biodegradable packaging materials, and the sealant material according to one embodiment of the present invention has good biodegradability and is therefore suitable for sealant films. The sealant film may be a monolayer film, or may be a multilayer film including two or more adjacent layers of sealant film. When the sealant film is a multilayer film, it has at least one layer formed from the sealant material which is one embodiment of the present invention, and each layer may be the same or different. From the viewpoint of obtaining good biodegradation, it is preferable that each layer is formed from the sealant material which is one embodiment of the present invention. As described above, the sealant film may be used as one or more layers of the sealant layer in a laminate having a layer such as a substrate not primarily intended for sealing performance and a sealant layer. For example, the sealant film is preferably used as a sealant layer in the following laminate, which is one embodiment of the present invention.

[0039] [Laminate] A laminate according to one embodiment of the present invention includes at least a seal layer containing the sealant material and a substrate.

[0040] <Sealing layer> The sealing layer includes the sealant material according to one embodiment of the present invention. The components contained in the sealant material contained in the sealing layer are as explained in the section on the sealant material, and the preferred embodiments thereof are also the same. As described above, when the seal layer contains other components than the block copolymer in the sealant material, the other components may be blended in advance with the block copolymer as a sealant material, or a part or all of the other components may be blended at the timing of forming the seal layer. In either case, when the finally obtained seal layer contains components that satisfy the configuration of the sealant material, the seal layer is a layer containing the sealant material.

[0041] From the viewpoint of imparting better biodegradability to the seal layer, the content of the sealant in the seal layer is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and still more preferably 98% by mass or more, based on 100% by mass of the total amount of the seal layer. There is no upper limit to the content of the sealant in the seal layer, and it is, for example, 100% by mass or less, based on 100% by mass of the total amount of the sealant. The content of the sealant material may be 100% by mass relative to the total amount of the seal layer (100% by mass). That is, the seal layer may be a layer formed only from the sealant material.

[0042] The sealing layer may be a single layer, or may be a multi-layer structure including two or more adjacent sealing layers. The laminate may include two or more layers, and may have, for example, the sealing layer on both sides of the base material, either directly or via another layer. When the laminate contains two or more sealing layers, it has at least one sealing layer formed from the sealant material which is one embodiment of the present invention, and each layer may be the same or different. From the viewpoint of obtaining good biodegradation of the laminate, it is preferable that all layers are sealing layers formed from the sealant material which is one embodiment of the present invention.

[0043] The thickness of the sealing layer is not particularly limited as long as it does not impair the effects of the present invention, but from the viewpoints of the sealing strength of the sealing layer and the laminate and economic efficiency, it is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, and preferably 100 μm or less, more preferably 80 μm or less, even more preferably 60 μm or less. The thickness of the sealing layer is the thickness of a single sealing layer.

[0044] <Base material> Examples of the substrate include paper, synthetic paper, and resin film, and preferably paper or resin film, and more preferably paper. Paper is a renewable resource and is preferable from the viewpoint of making the substrate layer easily biodegradable and from the viewpoint of environmental protection. The paper can be appropriately selected depending on the application of the laminate, and examples thereof include fine paper, craft paper, glassine paper, parchment paper, rayon paper, gravure paper, art paper, coated paper, recycled paper, and the like. The resin film can be appropriately selected depending on the application of the laminate, such as resin films formed from various polyolefin-based resins and various polyester-based resins. For example, from the viewpoint of making the base layer more easily biodegradable, preferred examples include resin films formed from biodegradable resins such as polylactic acid-based resins and polybutylene succinate-based resins.

[0045] The substrate may be a single layer or may be multi-layered. When the substrate has multiple layers, the layers may be the same or different from one another. The thickness of the substrate is not particularly limited, and can be appropriately set according to the application of the laminate obtained.When paper is used as one embodiment of the substrate, the thickness may be, for example, in the range of 5 μm or more and 3 mm or less, but as described above, the thickness can be appropriately set according to the application of the laminate obtained, and is not particularly limited.

[0046] <Other layers> The laminate may or may not have one or more layers other than the seal layer and the base material (hereinafter, also referred to as "other layers"). When the laminate has other layers, the other layers may be, for example, between the sealing layer and the substrate, or on the surface of the substrate opposite to the surface on which the sealing layer is provided. Examples of the other layers include a barrier layer, an adhesive layer for improving adhesion between the layers, a printed layer, a recycled layer, and the like.

[0047] The barrier layer is a layer provided mainly for the purpose of making it difficult for gases such as oxygen to pass through, and is preferably provided between the sealing layer and the base layer. Therefore, as one embodiment of the laminate, a laminate having a substrate, a barrier layer, and a seal layer in this order is preferred, and a laminate in which a substrate, a barrier layer, and a seal layer are directly laminated in this order is more preferred. The term "directly laminated" means that each layer is directly laminated without any other layer between each layer. Examples of materials for forming the barrier layer include polyvinyl alcohol-based resins such as polyvinyl alcohol and modified polyvinyl alcohol resins; polyvinylidene chloride resins, etc. From the viewpoint of biodegradability, polyvinyl alcohol-based resins such as polyvinyl alcohol and modified polyvinyl alcohol resins are preferably used.

[0048] The thickness of the other layers is not particularly limited and can be appropriately set depending on the purpose of providing the other layers. As an example, in a laminate having the aforementioned substrate, barrier layer, and seal layer in this order, the thickness of the barrier layer is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, and preferably 50 μm or less, more preferably 30 μm or less, even more preferably 20 μm or less. The total thickness of the laminate is not particularly limited as long as it does not impair the effects of the present invention, and can be appropriately set depending on the application of the laminate, etc.

[0049] In addition, a release material such as release paper or release film, or a protective layer such as paper or protective film may be provided on the exposed surface of the seal layer of the laminate, for example, for the purpose of protecting the surface of the seal layer, preventing the seal layer from fusing to other layers during storage and transportation, etc. These release materials or protective layers are peeled off from the exposed surface of the seal layer when the laminate is used. Similarly, a release material or a protective layer may be provided on the exposed surface of the base layer of the laminate, or on the exposed surface of another layer provided on the surface of the base layer.

[0050] [Seal strength of laminate] The laminate has a seal strength, when the exposed surfaces of the sealing layers are heat-sealed and adhered together with each other in a state where they are in contact with each other, of preferably 2.0 N / 15 mm or more, more preferably 4.0 N / 15 mm or more, even more preferably 6.0 N / 15 mm or more, even more preferably 6.5 N / 15 mm or more, even more preferably 7.0 N / 15 mm or more, even more preferably 7.5 N / 15 mm or more, even more preferably 8.0 N / 15 mm or more, and even more preferably 8.5 N / 15 mm or more. The seal strength of the laminate can be specifically measured by the method described in the Examples.

[0051] [Method of manufacturing laminate] The method for producing the laminate is not particularly limited as long as the laminate can be obtained. For example, the laminate can be produced by laminating the seal layer on at least one surface side of the base material. On the surface of the base material on which the seal layer is to be laminated, other layers such as the above-mentioned barrier layer may be laminated. In this case, the seal layer can be laminated on the exposed surface of the other layer laminated on the base material to produce the laminate. Therefore, in the following description, "at least one side of the substrate" includes both the case of at least one exposed surface of the substrate and the case of the case of an exposed surface of another layer laminated on at least one side of the substrate.

[0052] Here, examples of the method for laminating the sealing layer on at least one surface side of the substrate include: (i) a method in which the sealant material is dissolved or dispersed in a medium containing at least one selected from an organic solvent and water, and the resulting coating liquid is applied to at least one surface side of the substrate to form a coating film, and the coating film is dried to form a sealing layer and laminated; (ii) a method in which the sealant material is melt-extruded to form a sealing layer on at least one surface side of the substrate, and laminated; or (iii) a method in which a previously prepared sealant film is attached as a sealing layer to at least one surface side of the substrate and laminated. Among these, method (i) is preferred from the viewpoint that the laminate can be produced at a relatively low temperature, for example.

[0053] The block copolymer contained in the sealant material can also be dissolved using a non-halogen-based organic solvent that does not contain halogen atoms such as chlorine atoms in its molecular structure. Therefore, when an organic solvent is used in the method (i) above, it is preferable to use a non-halogen-based organic solvent as the organic solvent used to dissolve the sealant material, from the viewpoints of reducing the environmental load and improving safety to living organisms. Here, the coating liquid containing the sealant material is one embodiment of the present invention. And, when the coating liquid contains an organic solvent, the content of the halogen-based organic solvent is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably, the coating liquid that does not substantially contain the halogen-based organic solvent is one preferred embodiment of the present invention. Here, "substantially free of halogen-based organic solvents" means that the content of organic solvents containing halogen atoms such as chlorine atoms in the molecular structure is, for example, preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, based on 100% by mass of the total amount of the organic solvents used. It is even more preferable that no halogen-based organic solvents are contained at all. The non-halogen organic solvent is not particularly limited as long as it does not contain a halogen atom and can dissolve the block copolymer, and examples thereof include toluene, tetrahydrofuran, etc. Among these, toluene is a preferred example.

[0054] In one embodiment of the present invention, the coating liquid containing the sealant preferably contains the sealant and water, and is preferably an aqueous coating. Here, the term "aqueous coating" refers to a coating liquid in which the content of water is preferably 50% by mass or more, more preferably 75% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and even more preferably 98% by mass or more, based on the total amount (100% by mass) of the medium used to dissolve or disperse the sealant. There is no upper limit for the water content, and it is, for example, 100% by mass or less based on the total amount (100% by mass) of the medium used to dissolve or disperse the sealant.

[0055] The content of the sealant material in the coating liquid is not particularly limited as long as the coating liquid can be applied; however, from the viewpoints of, for example, coatability and ease of drying, the content is preferably 5% by mass or more, preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 80% by mass or less, preferably 60% by mass or less, more preferably 50% by mass or less, based on 100% by mass of the total amount of the coating liquid.

[0056] The method for applying the coating liquid is not particularly limited as long as the coating liquid can be applied, and any known method can be used, such as bar coating, spray coating, roll coating, spin coating, gravure coating, die coating, knife coating, roll knife coating, and blade coating.

[0057] The method for drying the coating film is not particularly limited as long as the organic solvent can be volatilized or evaporated to form the sealing layer, and any known drying method can be used. For example, a drying device such as an oven may be used, or when an organic solvent that volatilizes even under room temperature conditions is used, natural drying may be performed without using a dryer or the like.

[0058] In addition, when the method (ii) is used, the method of melt-extruding the sealant material includes, for example, a method in which the sealant material melted using an extruder or the like is extruded from a die such as a T-die onto at least one side of the substrate to directly form a seal layer. The temperature at which the sealant material is melted may be set to a temperature higher than the melting point of the block copolymer, and may be appropriately set in consideration of the operating pressure of the extruder, the extrusion amount of the molten material, and the like. In addition, the sealant material that has been melted and extruded may be actively cooled to solidify it and form a seal layer, or the seal layer may be formed by natural cooling.

[0059] In addition, when the method (iii) is used, for example, the sealant material is formed by applying the coating liquid described in the above (i) onto a release material, drying the coating liquid, or by forming a sealant film on a release material by melt extrusion described in the above (ii), and then laminating the sealant film on the release material as a seal layer on at least one surface side of the substrate. When laminating the sealant film, a laminator or the like may be used for lamination, if necessary. EXAMPLES

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0061] The physical properties of the block copolymers and polylactic acids in the examples and comparative examples were measured or evaluated by the following methods. (1) Number average molecular weight (Mn) The number average molecular weight (Mn) of the block copolymer and polylactic acid was determined in terms of standard polystyrene by gel permeation chromatography (GPC). The Mn of the block structural unit (B) was calculated from the Mn of the block copolymer and the mass content of the block structural unit (B). <GPC measurement conditions> Equipment: Tosoh Corporation GPC equipment "HLC-8220" Separation column: Tosoh Corporation's "TSKgel SuperMultiporeHZ-M (column diameter = 4.6 mm, column length = 15 cm)" (two columns connected in series) Eluent: tetrahydrofuran (THF) Eluent flow rate: 0.35mL / min Column temperature: 40℃ Detection method: Refractive index (RI) Injection volume: 10μL Concentration: 1mg / 1mL ((block copolymer or polylactic acid) / THF)

[0062] (2) Hard ratio (mass%) (mass content of block structural unit (A) having polylactic acid unit (a) as the main unit) 1 The hard ratio of the block copolymer was calculated by H-NMR. The molar ratio of the block structural unit (A) to the block structural unit (B) was calculated from the area ratio of the signal at about 5.2 ppm derived from the polylactic acid unit (a) in the obtained spectrum to the signal at about 0.9 ppm derived from the methyl group derived from 3-methyl-1,5-pentanediol in the case of Examples 1 to 3 and 5). The molar ratio was multiplied by the molecular weight of the block structural unit to obtain a mass ratio, and the mass ratio of the block structural unit (A) when the total of the mass ratios was adjusted to 100 was determined as the hard ratio. < 1 H-NMR measurement conditions Equipment: Nuclear magnetic resonance apparatus “JNM-ECX400” manufactured by JEOL Ltd. Solvent: deuterated chloroform Measurement temperature: 50℃ Number of times accumulated: 1024

[0063] (3) Melting point (℃) The melting point of the block copolymer was measured by a differential scanning calorimeter according to the method described in JIS K7121: 2012. When multiple peaks were observed, the melting point corresponding to the highest peak was determined as the melting point of the block copolymer. Equipment: Mettler Toledo DSC822 differential scanning calorimeter Measurement conditions: Heating rate 10℃ / min

[0064] (4) Glass transition temperature (℃) The glass transition temperature of the block copolymer was measured by a differential scanning calorimeter according to the method described in JIS K7121:2012. Equipment: Mettler Toledo DSC822 differential scanning calorimeter Measurement conditions: Heating rate 10℃ / min

[0065] (5) Seal strength A 5% aqueous solution of "Exceval (registered trademark) RS-2117" (manufactured by Kuraray Co., Ltd.) and "Kuraray Poval (registered trademark) 22-88" (manufactured by Kuraray Co., Ltd.) in a weight ratio of 50 / 50 was applied on the substrate "OK Prince paper (high-quality paper)" (manufactured by Oji Paper Co., Ltd.) to a coating weight of 7 g / m2 after drying. 2 After coating so that the thickness was 6 g / m2, the coating was dried at room temperature (25°C) for 1 day to form a barrier layer. After that, a polymer solution (coating liquid) prepared by dissolving the polymer polymerized in each Example or Comparative Example in a solvent was applied to the formed barrier layer so that the coating amount after drying was 6 g / m2. 2 After coating, the coating was left to dry for 3 days at room temperature (25°C) and a relative humidity of 65%RH to form a seal layer, and a sample for measuring seal strength was obtained as a laminate consisting of a base layer / barrier layer / seal layer. The seal surfaces of the obtained sample were heat sealed at 120°C, 0.3 MPa, and 5 seconds, and the seal strength was measured according to the method in accordance with JIS Z1707:2019.

[0066] (6) Biodegradable (compostable) Biodegradability in compost was measured according to the method of ISO 14855-2:2018. If the decomposition rate after 15 days was 20% or more by mass, it was rated as "A", if it was between 10% and 20% by mass, it was rated as "B", if it was between 5% and 10% by mass, it was rated as "C", and if it was less than 5% by mass, it was rated as "F".

[0067] (7) Biodegradability (activated sludge) Biodegradability in activated sludge was measured according to the method of ISO 14851:2019. If the decomposition rate was 5% or more by mass after 90 days, it was rated as "A", and if it was less than 5% by mass, it was rated as "F".

[0068] The block copolymers or polymers used as the sealant materials in the Examples and Comparative Examples were produced by the following methods: The compounds used in the synthesis of each polymer are as follows: 3-Methyl-1,5-pentanediol (Kuraray Co., Ltd.) 2-Methyl-1,3-propanediol (Tokyo Chemical Industry Co., Ltd.) 2,4-Diethyl-1,5-pentanediol (Tokyo Chemical Industry Co., Ltd.) 1,4-Butanediol (Tokyo Chemical Industry Co., Ltd.) Adipic acid (Tokyo Chemical Industry Co., Ltd.) Succinic acid (Tokyo Chemical Industry Co., Ltd.) L-lactide (Tokyo Chemical Industry Co., Ltd.) Stannous octoate (Tokyo Chemical Industry Co., Ltd.) Toluene (Kishida Chemical Co., Ltd.) Methanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) Methylene chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0069] [Example 1] In a flask equipped with a vacuum pump and an apparatus capable of distilling off the generated liquid, 3-methyl-1,5-pentanediol and adipic acid were charged in a molar ratio of 3-methyl-1,5-pentanediol / adipic acid = 1.1 / 1, and tin octylate was added in an amount of 0.1% by mass relative to the total weight of 3-methyl-1,5-pentanediol and adipic acid. The mixture was heated at normal pressure and 160 ° C for 3 hours under a nitrogen atmosphere, and then heated at 220 ° C for 3 hours to distill off water while reacting. Next, the pressure was reduced to 2,000 Pa and the mixture was reacted for 3 hours, and then the pressure was reduced to 80 Pa and the mixture was reacted while appropriately checking the number average molecular weight until it reached 6,000, thereby synthesizing a polymer composed of structural units (B') having polyester units (b) as main units. After the reaction was completed, the pressure was returned to normal pressure and the temperature was cooled to 80 ° C., and then toluene was added to dilute the solid concentration to 40% by mass, and the above toluene solution was added to methanol in an amount twice the total amount of the solution. The supernatant was discarded, and the same amount of methanol as the toluene solution added was added again for washing. The supernatant was discarded, and the recovered insoluble matter was dried at a temperature of 40°C using a vacuum dryer to remove organic volatile matter, thereby obtaining a polymer consisting of structural units (B') whose main units are polyester units (b). Toluene was added again to the purified polymer consisting of structural unit (B') to dilute the toluene solution of the polymer consisting of structural unit (B') to a solids concentration of 33 mass%, and the temperature was then raised to 140°C to distill off 10 mass% of the added toluene, thereby dehydrating the system. Thereafter, the toluene solution of the polymer consisting of the structural unit (B') was cooled to 80°C, and L-lactide was added to the toluene solution of the polymer consisting of the structural unit (B') so that the mass ratio of the polymer consisting of the structural unit (B') and L-lactide was 50 / 50, and further toluene was added in the amount of the weight of the distilled off described above, so that the solid content concentration of the toluene solution of the polymer consisting of the structural unit (B') and L-lactide was adjusted to 50 mass%. Thereafter, the temperature of the solution was raised to 100°C, and tin octylate was added in an amount of 0.1 mass% to the polymer consisting of the structural unit (B'), and the reaction was carried out at 100°C for 4 hours to synthesize a block copolymer consisting of a block structural unit (A) having a polylactic acid unit (a) as a main unit and a block structural unit (B) having a polyester unit (b) as a main unit, and a toluene solution of the block copolymer was obtained. The structure of the block structural unit (B) is the same as that of the structural unit (B'). Toluene was further added to this solution to dilute the solid content to 40% by mass, and the above-mentioned toluene solution with a solid content of 40% by mass was then added to methanol in an amount twice the total amount of the solution to precipitate a solid. The supernatant methanol was discarded, and the same amount of methanol as the amount of the toluene solution added was added again for washing. After discarding the methanol, the recovered solid was dried in a vacuum dryer at 40°C to remove organic volatiles, and a block copolymer consisting of block structural units (A) whose main unit is polylactic acid units (a) and block structural units (B) whose main unit is polyester units (b) was obtained. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1 below. When preparing the above-mentioned seal strength measurement sample, the block copolymer was dissolved in toluene at room temperature (25°C) so that the content of the block copolymer was 20 mass% and used as a polymer solution of the block copolymer.

[0070] [Examples 2 and 3] Each block copolymer consisting of a block structural unit (A) having a polylactic acid unit (a) as a main unit and a block structural unit (B) having a polyester unit (b) as a main unit was synthesized in the same manner as in Example 1, except that the number average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer consisting of the structural unit (B') having the polyester unit (b) as a main unit, and the mass ratio of L-lactide used was changed. The block copolymers thus obtained were subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1.

[0071] [Example 4] A block copolymer consisting of a block structural unit (A) having a polylactic acid unit (a) as a main unit and a block structural unit (B) having a polyester unit (b) as a main unit was synthesized in the same manner as in Example 1, except that 2-methyl-1,3-propanediol was used instead of 3-methyl-1,5-pentanediol and the number average molecular weight was adjusted by adjusting the reaction time during the synthesis of a polymer consisting of a structural unit (B') having a polyester unit (b) as a main unit. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1 below.

[0072] [Example 5] A block copolymer consisting of a block structural unit (A) having a polylactic acid unit (a) as a main unit and a block structural unit (B) having a polyester unit (b) as a main unit was synthesized in the same manner as in Example 1, except that succinic acid was used instead of adipic acid and the number average molecular weight was adjusted by adjusting the reaction time during the synthesis of a polymer consisting of a structural unit (B') having a polyester unit (b) as a main unit. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1 below.

[0073] [Example 6] A block copolymer consisting of a block structural unit (A) having a polylactic acid unit (a) as a main unit and a block structural unit (B) having a polyester unit (b) as a main unit was synthesized in the same manner as in Example 1, except that 2,4-diethyl-1,5-pentanediol was used instead of 3-methyl-1,5-pentanediol, and the number average molecular weight was adjusted by adjusting the reaction time during the synthesis of a polymer consisting of a structural unit (B') having a polyester unit (b) as a main unit. The block copolymer thus obtained was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 1 below.

[0074] [Comparative Example 1] At 200°C, 0.1% by mass of tin octoate was added to L-lactide and the reaction was continued until the number average molecular weight reached 40,000, yielding polylactic acid. The obtained polylactic acid was subjected to the above-mentioned measurements and evaluations, and the results are shown in Table 2 below. In addition, when preparing a sample for measuring the seal strength, the obtained polylactic acid did not dissolve in toluene at room temperature (25°C) at a solid content concentration of 20% by mass, so it was dissolved in methylene chloride, a halogen-based solvent, at room temperature (25°C) at a solid content concentration of 20% by mass and used as the above-mentioned polymer solution. The polylactic acid was inferior in biodegradability and had a low seal strength compared to the block copolymer of the example. This is thought to be because the polylactic acid does not have the structural unit (B).

[0075] [Comparative Example 2] A block structural unit (B") having a polyester unit as a main unit was synthesized in the same manner as in Example 1, except that 1,4-butanediol was used instead of 3-methyl-1,5-pentanediol, succinic acid was used instead of adipic acid, and the number average molecular weight was adjusted by adjusting the reaction time during synthesis of a polymer consisting of structural units (B') having polyester units as main units. L-lactide was added to the polymer consisting of structural units (B") and L-lactide at a mass ratio of L-lactide to polymer consisting of structural units (B") / L-lactide = 50 / 50 under a condition of 200°C, and 0.1 mass% of tin octylate was added to the polymer consisting of structural units (B") to cause a reaction. L-lactide was added from time to time to cause the reaction until the number average molecular weight reached 40,000, thereby obtaining a block copolymer consisting of block structural units (A) having polylactic acid units (a) as main units and block structural units having polyester units as main units. The above-mentioned measurements and evaluations were carried out in the same manner as in Example 1, except that samples for measuring the seal strength were prepared in the same manner as in Comparative Example 1. The results are shown in Table 2 below. The block copolymer obtained in Comparative Example 2 was inferior in biodegradability and had a low seal strength compared to the block copolymers of the Examples. This is believed to be because 1,4-butanediol used as a raw material does not have an alkyl group as a branched chain.

[0076] [Table 1]

[0077] [Table 2]

[0078] The compounds represented by the abbreviations in Tables 1 and 2 are as follows. PLLA: Poly-L-lactic acid MPD: 3-methyl-1,5-pentanediol MPDiol: 2-methyl-1,3-propanediol DEPD: 2,4-diethyl-1,5-pentanediol BD: 1,4-butanediol AA: Adipic acid SA: Succinic acid

[0079] From the results of Tables 1 and 2, it was confirmed that the sealant materials of each Example, which are a block copolymer containing a block structural unit (A) containing a polylactic acid unit (a) as a main unit and a block structural unit (B) containing a polyester unit (b) as a main unit and having a melting point of 110°C to 185°C, in which the polyester unit (b) contains a unit derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), and the aliphatic diol (b1) is a diol having an alkyl group as a branched chain, have excellent biodegradability in both cases where compost and activated sludge are used. Furthermore, it was also confirmed that the sealant materials of these Examples shown in Table 1, when used as a material for a sealing layer, can provide a superior seal strength compared to the sealant materials of the Comparative Examples shown in Table 2.

[0080] It was confirmed that Comparative Example 1 had poor biodegradability compared to each of the Examples, and in particular that biodegradation was difficult to proceed in activated sludge. Furthermore, it was confirmed that Comparative Example 1 also had low sealing strength compared to each of the Examples, and it was necessary to use a halogen-based solvent to prepare the polymer solution for forming the sealing layer. These results are believed to be due to the fact that the polymer used in Comparative Example 1 does not have the block structural unit (B) in its structure. In addition, it was confirmed that Comparative Example 2 had inferior biodegradability compared to each of the Examples. Furthermore, it was confirmed that Comparative Example 2 had lower sealing strength compared to each of the Examples, and it was necessary to use a halogen-based solvent to prepare the polymer solution for forming the sealing layer. These results are believed to be due to the fact that the block structural unit (B) in the polymer used in Comparative Example 2 does not contain a unit derived from a diol having an alkyl group as a branched chain. [Industrial Applicability]

[0081] As shown in the results of the examples, the sealant according to one embodiment of the present invention has good biodegradability. The sealant according to one embodiment of the present invention also has good sealing strength. Since the melting point of the block copolymer contained in the sealant according to one embodiment of the present invention is within a predetermined range, it is expected that the sealant will have both heat resistance and handleability depending on the application of the sealant. Furthermore, it is preferable that the glass transition temperature of the block copolymer is low in the sealant according to a preferred embodiment of the present invention, and in this case, low-temperature characteristics can also be expected depending on the application of the sealant. Therefore, the sealant according to one embodiment of the present invention, the seal layer contained in the sealant, and the laminate including the seal layer are extremely useful industrially.

Claims

1. A sealant material comprising a block structural unit (A) containing a polylactic acid unit (a) as a main unit and a block structural unit (B) containing a polyester unit (b) as a main unit, and having a melting point of 110°C or higher and 185°C or lower. The sealant material, wherein the polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), and the aliphatic diol (b1) is a diol having an alkyl group as a branched chain.

2. The sealant material according to Claim 1, wherein the glass transition point of the block copolymer is -80°C or higher and -15°C or lower.

3. The sealant material according to Claim 1, wherein the two hydroxyl groups of the aliphatic diol (b1) are primary hydroxyl groups, and the aliphatic diol (b1) is a diol having no quaternary carbon.

4. The sealant material according to Claim 1, wherein the aliphatic diol (b1) has 4 or more carbon atoms.

5. The sealant material according to Claim 1, wherein the block structural unit (A) is 5% by mass or more and 95% by mass or less based on a total of 100% by mass of the block structural unit (A) and the block structural unit (B).

6. The sealant material according to Claim 1, wherein the aliphatic diol (b1) has 10 or less carbon atoms.

7. The sealant material according to Claim 1, wherein the branched chain of the aliphatic diol (b1) is a methyl group.

8. In the polylactic acid unit (a), the proportion of the unit derived from D-lactic acid or D-lactide is less than 10% by mass based on a total of 100% by mass of the unit derived from L-lactic acid or L-lactide and the unit derived from D-lactic acid or D-lactide, or the proportion of the unit derived from L-lactic acid or L-lactide is less than 10% by mass based on a total of 100% by mass of the unit derived from L-lactic acid or L-lactide and the unit derived from D-lactic acid or D-lactide. The sealant material according to Claim 1.

9. A laminate comprising a sealant layer containing the sealant material according to any one of Claims 1 to 8 and a substrate.

10. The laminate according to Claim 9, wherein the substrate is paper.