Block copolymer, resin composition, and heat sealing material

Abstract

This block copolymer comprises a block structural unit (A) containing a polylactic acid unit (a) as a main component and a block structural unit (B) containing a polyester unit (b) as a main component, wherein: the polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2); the aliphatic diol (b1) is an aliphatic diol having at least 4 carbon atoms and having an alkyl group as a branched chain; the content of a D-lactic acid unit in 100 mass% of the polylactic acid unit (a) is 1-50 mass%; the content of an aromatic carboxylic acid unit in 100 mass% of the polyester unit (b) is at most 20 mass%; and the melting point of the block copolymer is at most 175ºC.

Description

Block copolymer, resin composition and heat sealing material

[0001] The present invention relates to a block copolymer, a resin composition containing the block copolymer, and a heat-sealing material formed using the resin composition.

[0002] From the perspective of environmental protection, there has been active development of bioplastics with excellent biodegradability. Polylactic acid, a bioplastic, is made from renewable plant-derived resources such as corn, which are produced through photosynthesis, and is expected to be used in a wide range of fields.

[0003] For example, Patent Document 1 describes a polylactic acid film or sheet that is useful as a substrate for adhesive tapes or sheets. Patent Document 2 describes a transparent packaging material made of a polylactic acid resin. Patent Documents 3 and 4 describe a toner containing a resin that includes a polylactic acid skeleton. Patent Document 5 describes a polyester resin that is a block copolymer (I) mainly composed of a polylactic acid unit (a) and a polyester unit (b) and is characterized by being a stereocomplex, and that has a high melting point and excellent flexibility and mechanical properties, and is therefore applicable to fibers, medical materials, etc.

[0004] JP 2014-001261 ​​A JP 2015-169881 A JP 2003-268125 A JP 2013-160914 A JP 2011-153275 A

[0005] Patent Documents 1 to 5 do not disclose the application of polylactic acid resins to heat-sealing materials. Polylactic acid resins are bioplastics with excellent biodegradability. Therefore, the present inventors considered it highly useful to use polylactic acid resins to obtain heat-sealing materials that are highly biodegradable, suppress the progression of aging degradation due to hydrolysis, and have excellent low-temperature heat-sealing properties. The present inventors investigated the application of the polylactic acid resins described in Patent Documents 1 to 5 to heat-sealing materials, but were unable to obtain heat-sealing materials with excellent biodegradability, hydrolysis resistance, low-temperature heat-sealing properties, and blocking resistance. The present invention aims to provide a block copolymer that can be used to obtain heat-sealing materials with excellent biodegradability, hydrolysis resistance, low-temperature heat-sealing properties, and blocking resistance, a resin composition containing the block copolymer, and a heat-sealing material formed from the resin composition.

[0006] As a result of intensive research to solve the above problems, the present inventors have conceived the following invention and found that the above problems can be solved.

[0007] [1] A block copolymer comprising block structural units (A) primarily composed of polylactic acid units (a) and block structural units (B) primarily composed of polyester units (b), wherein the polyester units (b) contain units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), wherein the aliphatic diol (b1) is an aliphatic diol having 4 or more carbon atoms and an alkyl group as a branched chain, wherein the content of D-lactic acid units in 100% by mass of the polylactic acid units (a) is 1% by mass or more and 50% by mass or less, wherein the content of aromatic carboxylic acid units in 100% by mass of the polyester units (b) is 20% by mass or less, and wherein the melting point of the block copolymer is 175°C or less. [2] The block copolymer according to [1] above, wherein the content of block structural units (B) in 100% by mass of the block copolymer is 35% by mass or more and 90% by mass or less. [3] The block copolymer according to [1] or [2] above, wherein the content of the block structural unit (A) is 5% by mass or more and 65% by mass or less, based on 100% by mass of the total of the block structural units (A) and the block structural units (B). [4] The block copolymer according to any of [1] to [3] above, wherein the aliphatic diol (b1) is at least one selected from 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, and 2,4-diethyl-1,5-pentanediol. [5] The block copolymer according to any of [1] to [4] above, wherein the aliphatic dicarboxylic acid (b2) is at least one selected from adipic acid and succinic acid. [6] The block copolymer according to any of [1] to [5] above, wherein the melting point is 100°C or more and 130°C or less. [7] The block copolymer according to any of [1] to [6] above, wherein the number average molecular weight is 30,000 or less. [8] The block copolymer according to any one of [1] to [7] above, having a number average molecular weight of 11,000 or more. [9] The block copolymer according to any one of [1] to [8] above, wherein the number average molecular weight of the block structural unit (B) is 2,500 or more.

[10] The block copolymer according to any one of [1] to [9] above, having a glass transition temperature of -80°C or more and -15°C or less.

[11] The block copolymer according to any one of [1] to

[10] above, wherein the polylactic acid unit (a) is a random structural unit containing an L-lactic acid unit and a D-lactic acid unit.

[12] A resin composition comprising the block copolymer according to any one of [1] to

[11] above.

[13] The resin composition according to

[12] above, wherein sodium lactate is contained in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the block copolymer.

[14] A heat-sealing material formed using the resin composition according to

[12] or

[13] above.

[15] A laminate having at least two layers, a layer (1) and a layer (2), wherein the layer (1) is directly laminated on the layer (2), and the layer (1) comprises the resin composition according to

[12] or

[13] above.

[16] A laminate having at least two layers, a layer (1) and a layer (2), wherein the layer (1) is directly laminated on the layer (2), and the layer (1) comprises the heat-sealing material according to

[14] above.

[0008] According to the present invention, it is possible to provide a block copolymer from which a heat-sealing material having excellent biodegradability, hydrolysis resistance, low-temperature heat-sealing properties, and blocking resistance can be obtained, a resin composition containing the block copolymer, and a heat-sealing material formed from the resin composition. Here, "excellent low-temperature heat-sealing properties" means that seal strength is achieved with less energy. Specifically, this means that heat-sealing can be achieved at low temperature, low pressure, and in a short time.

[0009] The following describes an embodiment of the present invention. However, the embodiment described below is merely an example for embodying the technical concept of the present invention, and the present invention is not limited to the following description. In this specification, preferred embodiments are shown, but a combination of two or more of the individual preferred embodiments is also a preferred embodiment. For matters indicated as numerical ranges, when there are several numerical ranges, the lower and upper limits can be selectively combined to create a preferred embodiment. Furthermore, when a numerical range is described as "XX to YY," it means "XX or more and YY or less." In this specification, "~ unit" (where "~" indicates a polymer) means "a structural unit derived from ~." For example, "polylactic acid unit" means "a structural unit derived from polylactic acid," and "polyester unit" means "a structural unit derived from polyester." In this specification, "main chain" refers to the longest molecular chain in a molecule. Furthermore, "branched chain" refers to a molecular chain other than the main chain in a molecule. In this specification, "main component" in a structural unit refers to the unit with the highest content (by mass%) among the units constituting the structural unit. The "main component" in the structural unit has a content of, for example, 50% by mass or more, in one embodiment 70% by mass or more, in one embodiment 80% by mass or more, in one embodiment 85% by mass or more, in one embodiment 90% by mass or more, and in one embodiment 100% by mass. In this specification, the "solid content" refers to components excluding the solvent. The solid content of a resin composition refers to components excluding the solvent and dispersion medium from the resin composition. In this specification, the L-lactic acid unit refers to a unit derived from L-lactic acid in the block structural unit (A). Note that, in the lactide-derived unit in the block structural unit (A), the portion corresponding to L-lactic acid in the lactide-derived unit is also included in the L-lactic acid unit. In this specification, the D-lactic acid unit refers to a unit derived from D-lactic acid in the block structural unit (A). In the lactide-derived units in the block structural unit (A), the portion corresponding to D-lactic acid in the lactide-derived units is also included in the D-lactic acid unit.As used herein, poly DL-lactic acid refers to polylactic acid containing L-lactic acid units and D-lactic acid units. Examples of poly DL-lactic acid include block copolymers containing poly L-lactic acid blocks and poly D-lactic acid blocks, and random copolymers containing L-lactic acid units and D-lactic acid units at random. As used herein, DL-lactic acid refers to a mixture of D-lactic acid and L-lactic acid. As used herein, DL-lactide refers to a mixture of D-lactide and L-lactide. As used herein, meso-lactide refers to lactide formed from one D-lactic acid unit and one L-lactic acid unit. As used herein, "melting point" refers to the melting peak temperature, and in the case of multiple melting peaks, refers to the melting peak temperature of the melting point peak that is highest in the range of 100 to 200°C. The melting point can be determined using a differential scanning calorimeter, specifically, by the method described in the Examples.

[0010] The block copolymer of this embodiment is a block copolymer containing block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b), wherein the polyester units (b) contain units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), wherein the aliphatic diol (b1) is an aliphatic diol having 4 or more carbon atoms and an alkyl group as a branched chain, wherein the content of D-lactic acid units in 100% by mass of the polylactic acid units (a) is 1% by mass or more and 50% by mass or less, wherein the content of aromatic carboxylic acid units in 100% by mass of the polyester units (b) is 20% by mass or less, and wherein the melting point of the block copolymer is 175°C or less.

[0011] The block copolymer of this embodiment makes it possible to obtain a heat-sealing material that is excellent in biodegradability, hydrolysis resistance, low-temperature heat-sealing property, and blocking resistance. Although the details of the reason for this are unknown, it is presumed that the multiple specific structural elements possessed by the combination of the specific block structural unit (A) and the specific block structural unit (B) act in a composite manner on various properties of the block copolymer, such as steric hindrance, crystalline melting enthalpy, and melting point, making it possible to obtain a heat-sealing material that is excellent in biodegradability, hydrolysis resistance, low-temperature heat-sealing property, and blocking resistance.

[0012] [Block structural unit (A)] <Polylactic acid unit (a)> The block structural unit (A) is composed mainly of polylactic acid units (a), and the content of D-lactic acid units in 100% by mass of the polylactic acid units (a) (100% by mass of the total amount of L-lactic acid units and D-lactic acid units) is 1% by mass or more and 50% by mass or less. The "major component" refers to the unit having the highest content among the units constituting the block structural unit (A). The content of polylactic acid units (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 even be 100% by mass. There is no upper limit to the amount of polylactic acid units (a) contained in the block structural unit (A), and it may be, for example, 100% by mass or less.

[0013] The content of D-lactic acid units in 100% by mass of polylactic acid units (a) is 1% by mass or more and 50% by mass or less. A content of 1% by mass or more results in excellent low-temperature heat-sealability and biodegradability. A content of 1% by mass or more and 50% by mass or less results in excellent economic efficiency (cost), improved blocking resistance, and improved adhesion retention between heat-sealable layers at high temperatures. From these viewpoints, the content is preferably 2 to 40% by mass, more preferably 2 to 30% by mass, even more preferably 2 to 20% by mass, still more preferably 2 to 15% by mass, even more preferably 2 to 13% by mass, still more preferably 2 to 12% by mass, still more preferably 2 to 10% by mass, still more preferably 2 to 9% by mass, still more preferably 3 to 8% by mass, and still more preferably 4 to 8% by mass.

[0014] The content of L-lactic acid units in 100% by mass of polylactic acid units (a) is 50% by mass or more and 99% by mass or less. A content of 50% by mass or more results in excellent economic efficiency (cost), excellent hydrolysis resistance, improved blocking resistance, and improved adhesion retention between heat-sealable layers at high temperatures. Furthermore, a content of 99% by mass or less results in excellent low-temperature heat-sealability and biodegradability. From these viewpoints, the content is preferably 60 to 98% by mass, more preferably 70 to 98% by mass, even more preferably 80 to 98% by mass, even more preferably 85 to 98% by mass, even more preferably 87 to 98% by mass, even more preferably 88 to 98% by mass, even more preferably 90 to 98% by mass, even more preferably 91 to 98% by mass, even more preferably 92 to 97% by mass, and even more preferably 92 to 96% by mass.

[0015] Examples of the polylactic acid unit (a) include a random structural unit containing L-lactic acid units and D-lactic acid units arranged randomly, and a block structural unit containing a poly-L-lactic acid block and a poly-D-lactic acid block. In the case of the block structural unit containing a poly-L-lactic acid block and a poly-D-lactic acid block, a stereocomplex may occur depending on the ratio, order, etc. of the poly-L-lactic acid block and the poly-D-lactic acid block. Among these, a random structural unit containing an L-lactic acid unit and a D-lactic acid unit is preferred from the viewpoint of obtaining a heat-sealing material that is excellent in biodegradability, hydrolysis resistance, and low-temperature heat-sealing property. The present inventors compared a first block copolymer having a poly-L-lactic acid block and a branched polyester block with a second block copolymer in which the poly-L-lactic acid block was replaced with a poly-L-lactic acid block having a lower molecular weight to lower the melting point, and a third copolymer in which the poly-L-lactic acid block was replaced with a poly-DL-lactic acid block having a random structural unit containing L-lactic acid units and D-lactic acid units randomly to lower the melting point to the same level as the second block copolymer, and discovered a new finding that the third block copolymer had significantly improved seal strength. Furthermore, the present inventors discovered a new finding that, in the third block copolymer, by adjusting the content of D-lactic acid units in the poly-DL-lactic acid block, the type and content of polyester units in the polyester block, and the melting point to fall within specific ranges, it is possible to obtain a heat-sealing material with even better biodegradability, hydrolysis resistance, and low-temperature heat-sealing properties. Therefore, the polylactic acid unit (a) is preferably a random structural unit containing L-lactic acid units and D-lactic acid units arranged randomly.

[0016] The polylactic acid constituting the polylactic acid unit (a) may be produced by a direct condensation method of lactic acid or by a ring-opening polymerization method of lactide. The lactic acid may be, for example, at least one selected from the group consisting of L-lactic acid and D-lactic acid, and DL-lactic acid. The lactide may be, for example, at least one selected from the group consisting of L-lactide and D-lactide, DL-lactide, and meso-lactide.

[0017] <Units (a') Other Than Polylactic Acid Units (a)> The block structural units (A) may or may not contain units (a') other than the polylactic acid units (a). The monomer constituting the units (a') is not particularly limited as long as the effects of the present invention are not impaired. The content of units (a') in the block structural units (A) is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0018] <Number Average Molecular Weight of Block Structural Unit (A)> From the viewpoints of even better handleability, cost, low-temperature heat sealability, and biodegradability, the number average molecular weight of the block structural unit (A) may be preferably 100,000 or less, more preferably 25,000 or less, and even more preferably 15,000 or less. From the viewpoint of even better hydrolysis resistance and blocking resistance, the number average molecular weight of the block structural unit (A) may be preferably 1,000 or more, more preferably 4,000 or more, and even more preferably 5,000 or more. From these viewpoints, the number average molecular weight of the block structural unit (A) is 1,000 to 100,000, more preferably 4,000 to 25,000, and even more preferably 5,000 to 15,000. When a block copolymer has multiple block structural units (A), the number average molecular weight of the block structural unit (A) refers to the sum of all blocks. 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).

[0019] [Block structural unit (B)] The block structural unit (B) is mainly composed of polyester units (b). The term "main component" refers to the unit with the highest content among the units constituting the block structural unit (B). The content of polyester units (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, even more preferably 85% by mass or more, and particularly preferably 90% by mass or more. It may even contain 100% by mass. There is no upper limit to the amount of polyester units (b) contained in the block structural unit (B), and it may be, for example, 100% by mass or less. The polyester units (b) contain units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2). Specifically, the polyester units (b) contain 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 monomers other than the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) are not particularly limited as long as they do not impair the effects of the present invention. The total amount of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) in the polyester unit (b) is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 99 mol% or more, or even 100 mol%. The total amount of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) in the polyester unit (b) is preferably 90 mol% or more, more preferably 95 mol% or more, even more preferably 99 mol% or more, or even 100 mol%.

[0020] <Aliphatic diol (b1)> The aliphatic diol (b1) is an aliphatic diol having 4 or more carbon atoms and an alkyl group as a branched chain. If the aliphatic diol (b1) has 3 or fewer carbon atoms, hydrolysis resistance may be poor. The "number of carbon atoms" refers to the total number of carbon atoms in the aliphatic diol (b1), including the number of carbon atoms constituting the alkyl group. The number of carbon atoms in the aliphatic diol (b1) is preferably 10 or less. Having 10 or fewer carbon atoms results in excellent biodegradability. From these viewpoints, the number of carbon atoms in the aliphatic diol (b1) is preferably 4 to 10, more preferably 4 to 9, even more preferably 4 to 8, and even more preferably 4 to 6.

[0021] If the aliphatic diol (b1) does not have a branched chain that is an alkyl group, the block structural unit (B) tends to crystallize, and the hydrolysis resistance of the block structural unit (B) tends to deteriorate, so the block copolymer cannot exhibit a wide range of biodegradability and excellent hydrolysis resistance. Furthermore, the number of branched chains in the aliphatic diol (b1) is preferably one or two, more preferably one. The branched chain is preferably selected from methyl groups, ethyl groups, and propyl groups, more preferably methyl groups and ethyl groups, and even more preferably methyl groups. Furthermore, when the aliphatic diol (b1) has multiple branched chains, the branched chains may be the same or different. From the viewpoints of easily reacting with dicarboxylic acids, facilitating the production of a triblock copolymer, and achieving even better biodegradability and hydrolysis resistance, it is preferable that the aliphatic diol (b1) have hydroxyl groups at both ends of the main chain.

[0022] 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, and 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 2-methyl-1,3-propanediol, 3-methyl-1,5-pentanediol, or 2,4-diethyl-1,5-pentanediol, more preferably 3-methyl-1,5-pentanediol. The aliphatic diol (b1) may be used alone or in combination of two or more.

[0023] <Aliphatic dicarboxylic acid (b2)> The number of carbon atoms in the aliphatic dicarboxylic acid (b2) is preferably 4 or more and 12 or less. When the carbon atom number in the aliphatic dicarboxylic acid (b2) is 4 or more, the aliphatic dicarboxylic acid (b2) has excellent hydrolysis resistance. Furthermore, when the carbon atom number in the aliphatic dicarboxylic acid (b2) is 12 or less, the aliphatic dicarboxylic acid (b2) has excellent biodegradability. From these viewpoints, the number of carbon atoms in the aliphatic dicarboxylic acid (b2) is preferably 4 to 10, more preferably 4 to 8, and even more preferably 4 to 6.

[0024] 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. The aliphatic dicarboxylic acid (b2) is preferably succinic acid or adipic acid, and more preferably adipic acid. The aliphatic dicarboxylic acid (b2) may be used alone or in combination of two or more.

[0025] <Content of aromatic carboxylic acid units in polyester units (b)> The content of aromatic carboxylic acid units in 100% by mass of polyester units (b) is 20% by mass or less. When the content is 20% by mass or less, biodegradability is improved. Here, the aromatic carboxylic acid units also include heteroaromatic carboxylic acid units containing heteroatoms. The aromatic carboxylic acid units may contain one or both of heteroaromatic carboxylic acid units containing heteroatoms and aromatic carboxylic acid units not containing heteroatoms, or may contain only one of both, or may contain only the aromatic carboxylic acid unit not containing heteroatoms of both. From this viewpoint, the content of aromatic carboxylic acid units in 100% by mass of polyester units (b) is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, still more preferably 3% by mass or less, and even more preferably 1% by mass or less, and the polyester units (b) may not contain aromatic carboxylic acid units.

[0026] <Preferred Combinations of Aliphatic Diol (b1) and Aliphatic Dicarboxylic Acid (b2)> From the viewpoint of exhibiting even better biodegradability and hydrolysis resistance, a combination of 2-methyl-1,3-propanediol (MPDiol) and succinic acid (SA), a combination of 3-methyl-1,5-pentanediol (MPD) and adipic acid (AA), and a combination of 2,4-diethyl-1,5-pentanediol (DEPD) and adipic acid (AA) are examples of preferred embodiments, and a combination of 3-methyl-1,5-pentanediol and adipic acid is an example of a more preferred embodiment.

[0027] <Ratio of Aliphatic Diol (b1) and Aliphatic Dicarboxylic Acid (b2)> The molar ratio of the aliphatic diol (b1) and the aliphatic dicarboxylic acid (b2) charged when reacting them [aliphatic diol (b1) / aliphatic dicarboxylic acid (b2)] is preferably 1.4 / 1 to 1 / 1.4, more preferably 1.2 / 1 to 1 / 1.2.

[0028] <Units (b') Other Than Polyester Units (b)> The block structural unit (B) may or may not contain units (b') other than the polyester units (b). The monomer constituting the units (b') is not particularly limited as long as the effects of the present invention are not impaired. The content of the units (b') in the block structural unit (B) is preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 20% by mass or less, still more preferably 15% by mass or less, and particularly preferably 10% by mass or less.

[0029] <Number Average Molecular Weight of Block Structural Unit (B)> The number average molecular weight of the block structural unit (B) is preferably 2,500 or more, more preferably 4,000 or more, and even more preferably 5,000 or more. The number average molecular weight of the block structural unit (B) is preferably 100,000 or less, more preferably 50,000 or less, even more preferably 40,000 or less, still more preferably 36,000 or less, and still more preferably 25,000 or less, and may be 20,000 or less, or may be 15,000 or less. The number average molecular weight of the block structural unit (B) is preferably 2,500 to 100,000, more preferably 4,000 to 50,000, even more preferably 5,000 to 40,000, even more preferably 5,500 to 36,000, even more preferably 5,500 to 25,000, even more preferably 5,500 to 20,000, and even more preferably 6,000 to 15,000. Within these numerical ranges, the block copolymer tends to have excellent flexibility and impact resistance. 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.

[0030] [Structural Unit Proportion] The proportion of the block structural unit (A) is preferably 5% by mass or more and 65% 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 handleability of the block copolymer tends to be even better. Furthermore, when the proportion of the block structural unit (A) is 65% by mass or less, the flexibility and impact resistance of the block copolymer tends to be excellent. 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. Furthermore, from the viewpoint of flexibility and impact resistance, the proportion of the block structural unit (A) is more preferably 60% by mass or less, and even more preferably 55% by mass or less. From these viewpoints, the proportion of the block structural unit (A) is more preferably 10 to 60% by mass, even more preferably 15 to 55% by mass, and even more preferably 30 to 55% by mass. The proportion of the block structural unit (A) is １ It can be determined by H-NMR, specifically by the method described in the Examples.

[0031] The proportion of the block structural unit (B) is preferably 35% by mass or more and 90% 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 (B) is 35% by mass or more, the flexibility and impact resistance of the block copolymer tend to be even better. Furthermore, when the proportion of the block structural unit (B) is 90% by mass or less, the handleability and blocking resistance of the block copolymer tend to be excellent. From the viewpoints of flexibility and impact resistance, the proportion of the block structural unit (B) is more preferably 40% by mass or more, and even more preferably 45% by mass or more. Furthermore, from the viewpoints of handleability and blocking resistance, the proportion of the block structural unit (B) is more preferably 80% by mass or less, and even more preferably 70% by mass or less. From these viewpoints, the proportion of the block structural unit (B) is preferably 40 to 90% by mass, more preferably 45 to 85% by mass, and even more preferably 45 to 70% by mass. The proportion of the block structural unit (B) is １It can be determined by H-NMR, specifically by the method described in the Examples.

[0032] 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, 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 may be, for example, 100% by mass or less.

[0033] 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 the effects of the present invention are not impaired. The content of units other than the block structural unit (A) and the block structural unit (B) in the block copolymer is preferably 10% by mass or less, more preferably 5% by mass or less. The block copolymer may or may not contain a polyester block structural unit having an anionic group, but from the viewpoints of hydrolysis resistance and productivity, it is preferable that the block copolymer does not contain such a polyester block structural unit.

[0034] [Number-Average Molecular Weight of Block Copolymer] The number-average molecular weight of the block copolymer is preferably 30,000 or less. When the number-average molecular weight is 30,000 or less, a heat-sealing material having excellent biodegradability and low-temperature heat-sealing properties can be obtained. Furthermore, the number-average molecular weight of the block copolymer is preferably 11,000 or more. When the number-average molecular weight is 11,000 or more, a heat-sealing material having excellent hydrolysis resistance and impact resistance can be obtained. From this viewpoint, the number-average molecular weight of the block copolymer is preferably 11,000 to 30,000, more preferably 11,000 to 28,000, even more preferably 11,000 to 25,000, still more preferably 11,000 to 22,000, and even more preferably 11,000 to 19,000. 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.

[0035] [Bonding Form of Block Copolymer] 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)].

[0036] <Melting Point of Block Copolymer> The melting point of the block copolymer is 175°C or lower. When the melting point of the block copolymer is 175°C or lower, the block copolymer has excellent low-temperature heat-sealing properties and biodegradability. Furthermore, from the viewpoint of hydrolysis resistance, the melting point of the block copolymer is preferably 110°C or higher. From these viewpoints, the melting point of the block copolymer is preferably 100 to 175°C, more preferably 100 to 135°C, even more preferably 100 to 130°C, and even more preferably 110°C or higher but lower than 130°C. The melting point of the block copolymer can be determined using a differential scanning calorimeter, specifically, by the method described in the Examples. The melting point of the block copolymer increases when the polylactic acid unit (a) described above forms a stereocomplex compared to when the stereocomplex does not form, and typically has a highest melting point exceeding 175°C.

[0037] <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 this range, the block copolymer tends to have excellent flexibility and impact resistance. From the viewpoint of low-temperature properties such as low-temperature impact resistance, the glass transition temperature of the block copolymer is more preferably −20° C. or lower, even more preferably −25° C. or lower, and may be −30° C. or lower, −35° C. or lower, −40° C. or lower, −45° C. or lower, or −50° 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, −65° C. or higher, or −60° C. or higher. From these viewpoints, the glass transition temperature of the block copolymer is more preferably −80° C. to −20° C., even more preferably −80 to −25° C., still more preferably −75° C. to −25° C., still more preferably −70° C. to −30° C., still more preferably −70° C. to −35° C., still more preferably −65 to −40° C., still more preferably −65 to −45° C., and still more preferably −60 to −50° C. The glass transition temperature of the block copolymer can be determined by differential scanning calorimetry, and specifically, can be measured by the method described in the examples.

[0038] <Crystalline Melting Enthalpy of Block Copolymer> From the viewpoint of more easily obtaining a heat-sealing material having excellent biodegradability and low-temperature heat-sealing property, the crystalline melting enthalpy of the block copolymer is preferably 20 J / g or less, more preferably 18 J / g or less, even more preferably 15 J / g or less, and particularly preferably 10 J / g or less. Furthermore, from the viewpoints of heat resistance, adhesive strength retention, and blocking resistance, the crystalline melting enthalpy is preferably 1 J / g or more, more preferably 2 J / g or more, and even more preferably 3 J / g or more. The crystalline melting enthalpy of the block copolymer tends to decrease by increasing the content of D-lactic acid units in 100% by mass of polylactic acid units (a) or by decreasing the content of block structural units (A) in 100% by mass of the total of block structural units (A) and block structural units (B). The crystalline melting enthalpy of the block copolymer can be determined using a differential scanning calorimeter, specifically, by the method described in the Examples.

[0039] <Hydrolysis Resistance of Block Copolymer> The hydrolysis resistance of the block copolymer is preferably 80 hours or more. A hydrolysis resistance of 80 hours or more tends to make it easier to obtain a heat-sealing material that is excellent in hydrolysis resistance and easy to handle during storage. From this viewpoint, the hydrolysis resistance of the block copolymer is preferably 100 hours or more, more preferably 200 hours or more, and even more preferably 300 hours or more. The hydrolysis resistance of the block copolymer is expressed as the time it takes for the number average molecular weight to decrease to less than 90% of the original value when immersed in neutral water, and can be measured specifically by the method described in the Examples.

[0040] [Method for Producing Block Copolymer] The block copolymer can be produced by a known method, such as the production methods (1) and (2) described below. Method (1) is preferred from the viewpoint of productivity. (1) A known method for producing a block copolymer may be, for example, a method of synthesizing a polyester constituting the polyester unit (b) and polymerizing the polyester with lactide. The polyester can be synthesized by a known method. For example, a polyester can be synthesized by reacting an aliphatic diol (b1) with an aliphatic dicarboxylic acid (b2) using an esterification catalyst (e.g., tin octoate, tin chloride, tin oxide). When polymerizing a polyester with lactide, it is preferable to use a ring-opening polymerization catalyst (e.g., tin octoate, tin chloride, tin oxide). Examples of the polymerization reaction include solution polymerization, melt polymerization, and interfacial polycondensation, and known polymerization reaction conditions can be set for each method.

[0041] (2) Furthermore, a known method for producing a block copolymer may be, for example, a method in which 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. 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 polymerizing polylactic acid and polyester, it is preferable to use an esterification catalyst (e.g., tin octoate, tin chloride, tin oxide). Examples of the polymerization reaction include solution polymerization, melt polymerization, and interfacial polycondensation, and known polymerization reaction conditions can be set for each.

[0042] [Resin Composition] The resin composition according to this embodiment includes the block copolymer according to this embodiment. The resin composition may or may not include a dispersant. The resin composition may or may not include a solvent and / or a dispersion medium. The resin composition may or may not include a hydroxycarboxylic acid salt. The resin composition may or may not include other components.

[0043] (Block Copolymer) Details of the block polymer contained in the resin composition are as described above. From the viewpoint of obtaining a heat-sealing material excellent in biodegradability, hydrolysis resistance, and low-temperature heat-sealing property, the content of the block polymer in 100% by mass of the solid content of the resin composition is preferably 60 to 100% by mass, more preferably 80 to 100% by mass, even more preferably 90 to 100% by mass, and still more preferably 92 to 95% by mass.

[0044] (Dispersant) Examples of dispersants that can be used include water-soluble polymers, surfactants, etc. Examples of water-soluble polymers include vinyl alcohol polymers such as polyvinyl alcohol, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, sodium polyacrylate, and sodium polymethacrylate. Examples of surfactants include nonionic surfactants such as sorbitan monolaurate, polyoxyethylene sorbitan monolaurate, polyoxyethylene-coconut fatty acid glyceryl, polyoxyethylene-castor oil, polyglycerin oleate, polyoxyethylene-laurylamine, and polyoxyethylene sorbit tetraoleate; alkyl benzene sulfonates such as sodium dodecyl benzene sulfonate, alkyl sulfates such as sodium dodecyl sulfate and sodium lauryl sulfate, anionic surfactants such as sodium N-cocoyl methyl taurine, sodium di-2-ethylhexyl sulfosuccinate, sodium 2-ethylhexyl sulfate, and α-sulfofatty acid methyl ester sodium salts; cationic surfactants such as benzalkonium chloride, dodecyl trimethyl ammonium chloride, tetradecylamine acetate, didecyl dimethyl ammonium chloride, and tetradecyl dimethyl benzyl ammonium chloride; and amphoteric surfactants such as coconut oil dimethylaminoacetic acid betaine, coconut oil fatty acid amidopropyl dimethylaminoacetic acid betaine, sodium lauryl diaminoethyl glycine, and monosodium lauryl aminodiacetate. The dispersant is preferably a water-soluble polymer or an anionic surfactant, more preferably a water-soluble polymer, from the viewpoint of improving dispersion stability and exhibiting even better biodegradability. The water-soluble polymer is preferably a vinyl alcohol polymer, more preferably polyvinyl alcohol, from the viewpoint of improving dispersion stability and exhibiting even better biodegradability. The anionic surfactant is preferably an alkylbenzenesulfonate, more preferably sodium dodecylbenzenesulfonate, from the viewpoint of improving dispersion stability and exhibiting even better biodegradability.

[0045] When a vinyl alcohol polymer is used as a dispersant, if the saponification degree of the vinyl alcohol polymer is 60 mol% or more, the polymer is easily soluble in water. If the saponification degree is 95 mol% or less, the emulsifying ability is further improved. Therefore, from the viewpoints of handleability and emulsifying ability, the saponification degree of the vinyl alcohol polymer is preferably 60 to 95 mol%, more preferably 70 to 95 mol%, and even more preferably 80 to 92 mol%. The saponification degree can be measured, for example, by the method for measuring saponification degree described in JIS K6726:1994. Furthermore, from the viewpoint of emulsifying ability, the vinyl alcohol polymer is preferably a partially saponified type.

[0046] When a vinyl alcohol polymer is used as a dispersant, if the 4% by mass viscosity of the vinyl alcohol polymer at 20°C is 10 mPa·s or more, the emulsifying ability is further improved. If the viscosity is 80 mPa·s or less, the vinyl alcohol polymer is easily dissolved in water. Therefore, from the viewpoint of handleability and emulsifying ability, the 4% by mass viscosity of the vinyl alcohol polymer at 20°C is preferably 10 to 80 mPa·s, more preferably 15 to 55 mPa·s, and even more preferably 20 to 50 mPa·s. Note that the viscosity in this specification refers to the viscosity measured at 20°C using a B-type viscometer (rotation speed: 12 rpm) in accordance with the rotational viscometer method of JIS K 6726:1994 for a 4% by mass aqueous solution obtained by dissolving polyvinyl alcohol in water.

[0047] The content of the dispersant is preferably 0.1 to 30 parts by mass relative to 100 parts by mass of the block copolymer. When the content is 0.1 part by mass or more, the stability of the emulsion is excellent. When the content is 30 parts by mass or less, the handleability and blocking resistance are excellent. From these viewpoints, the content is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, even more preferably 3 to 20 parts by mass, and particularly preferably 5 to 15 parts by mass.

[0048] (Dispersion medium or solvent) Examples of the dispersion medium or solvent include aqueous solvents such as water, acetone, and tetrahydrofuran; and organic solvents such as toluene, ethyl acetate, and methyl ethyl ketone. Of these, from the viewpoints of environmental load, effects on the human body, and ease of handling, aqueous solvents are preferred, and water is more preferred. When the resin composition contains a solvent, the solids concentration of the resin composition is preferably 1 to 60% by mass, more preferably 5 to 40% by mass, and even more preferably 10 to 35% by mass.

[0049] (Hydroxycarboxylate Salt) As the hydroxycarboxylate salt, salts of glycolic acid, lactic acid, etc. are preferred from the viewpoint of low-temperature heat sealing property, and alkali metal salts and alkaline earth metal salts are preferred as the salt. As the hydroxycarboxylate salt, lactate salt is more preferred from the viewpoint of its effects on the human body. Examples of lactate salts include alkali metal salts such as sodium lactate, lithium lactate, and potassium lactate; alkaline earth metal salts such as calcium lactate and magnesium lactate; and the like. Of these, from the viewpoints of availability, price, and its effects on the human body, alkali metal salts of lactic acid are preferred, and sodium lactate is more preferred. When the resin composition contains a lactate salt, the content of the lactate salt relative to 100 parts by mass of the block copolymer is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, even more preferably 1 to 4 parts by mass, and even more preferably 2 to 4 parts by mass.

[0050] (Other Components) The resin composition according to this embodiment may or may not contain other components. Examples of other components include inorganic fillers, softeners, plasticizers, heat aging inhibitors, antioxidants, hydrolysis inhibitors, light stabilizers, antistatic agents, release agents, flame retardants, foaming agents, brighteners, UV absorbers, lubricants, pigments, dyes, etc. These may be used alone or in combination of two or more.

[0051] The content of the other components is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 1 part by mass or less, based on 100 parts by mass of the block copolymer.

[0052] (Method for Producing Resin Composition) Known production methods can be used to produce the resin composition. The resin composition can be obtained by dispersing the block copolymer in a dispersion medium using a method such as a pressurized dispersion method in which a block copolymer, a dispersant, and a dispersion medium are simultaneously charged into a sealed tank equipped with a stirrer and pressurized while heating and stirring to disperse the block copolymer; a direct dispersion method in which a block copolymer is added to a heated dispersion medium containing a dispersant maintained under normal pressure or pressure and stirred to disperse; a method in which a block copolymer dissolved in an organic solvent is added to a dispersion medium containing a dispersant and stirred to disperse; or a phase inversion method in which the block copolymer is heated and melted, and then the dispersion medium is added thereto and stirred to disperse the block copolymer in the dispersion medium. When the resin composition is an emulsion, from the viewpoint of easy synthesis, a method in which a block copolymer dissolved in an organic solvent is added to a dispersion medium containing a dispersant and stirred to disperse the block copolymer is preferred as a production method for the emulsion. That is, a step of dispersing the block copolymer dissolved in an organic solvent in an aqueous medium in the presence of a dispersant is preferred. When preparing the emulsion, a dispersion device such as a high-pressure homogenizer may be used in combination as necessary. From the viewpoint of environmental load, it is preferable to further include a step of removing the organic solvent after the dispersing step, for example, by heating the solution obtained in the dispersing step.

[0053] Furthermore, if necessary, components other than the block copolymer, dispersant, and dispersion medium may be added to the dispersion medium in advance before dispersing the block copolymer, may be added together with the block copolymer when dispersing it, or may be added after dispersing the block copolymer.

[0054] (Seal Strength) The seal strength (N / 15 mm, 20°C, 5 s) of a heat seal paper using the resin composition in a heat seal layer is preferably 4.0 N / 15 mm or more, more preferably 4.5 N / 15 mm or more, and even more preferably 5.0 N / 15 mm or more. The seal strength can be measured using a desktop precision universal testing machine, and specifically, can be measured by the method described in the examples.

[0055] The basis weight of the heat seal layer and the substrate can be appropriately selected depending on the desired qualities and handling properties, but is usually 3 g / m ３ 40g / cm or more ３ The following are preferred:

[0056] <Biodegradability in activated sludge> The biodegradability of the resin composition in activated sludge can be measured, for example, by the method described in the examples in accordance with ISO 14851:2019. There are no particular limitations on the biodegradability of the resin composition in activated sludge, but the decomposition rate after 90 days is preferably 5% by mass or more. When the biodegradability of the resin composition in activated sludge is within the above range, for example, the resin composition can be used to produce products with excellent biodegradability and low environmental impact in wastewater treatment facilities.

[0057] <Blocking Resistance> The blocking resistance of a resin composition can be evaluated, for example, by coating the resin composition on high-quality paper, bringing the coating surface into contact with the high-quality paper, and applying a predetermined load at a predetermined temperature for a predetermined period of time. Specifically, the blocking resistance can be measured by the method described in the examples.

[0058] [Heat-sealing material] The heat-sealing material of this embodiment is formed using the resin composition described above. The composition of the heat-sealing material of this embodiment is the resin composition described above except that the solvent has been removed. The preferred ranges for the seal strength, biodegradability in compost, and biodegradability in activated sludge of the heat-sealing material are the same as those for the resin composition.

[0059] [Laminate] The laminate of this embodiment has at least two layers, a layer (1) and a layer (2), the layer (1) being directly laminated on the layer (2), and the layer (1) containing the resin composition or the heat-sealing material.

[0060] The layer (2) used in the present invention may be any material as long as it is self-supporting, and examples thereof include plastic films or sheets such as polyesters (e.g., polyamide, polyethylene terephthalate), polypropylene, polyethylene, polyvinylidene chloride, polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; paper substrates (e.g., wood-free paper, Japanese paper, composite paper, kraft paper, and cup base paper); metal foils or metal plates (e.g., aluminum, iron, copper, and alloys containing these as main components); cellophane, woven fabric, and nonwoven fabrics (e.g., cotton), as single layers or laminates thereof. From the viewpoint of biodegradability, paper substrates are preferred. Layer (2) may be subjected to stretching, printing, vapor deposition, various coatings, and the like.

[0061] The method for producing the laminate is not particularly limited as long as it allows direct lamination of Layer (1) and Layer (2), but a preferred method is, for example, a method of coating Layer (2) with the emulsified resin composition or the heat seal material. Specific examples of coating methods include gravure coating, gravure reverse coating, roll coating, Mayer bar coating, blade coating, knife coating, air knife coating, comma coating, slot die coating, slide die coating, and dip coating.

[0062] The laminate of the present invention exhibits heat-sealability and is therefore useful for various types of packaging. In particular, when a paper substrate is selected for layer (2), the biodegradable laminate can be suitably used for paper processed products such as wrapping paper, packaging bags, various containers such as cups and trays, paper ties, and lid materials.

[0063] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these.

[0064] The compounds used in the examples and comparative examples are as follows: 3-methyl-1,5-pentanediol (manufactured by Kuraray Co., Ltd.) Adipic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Stannous octoate (manufactured by Tokyo Chemical Industry Co., Ltd.) Toluene (manufactured by Kishida Chemical Co., Ltd.) L-lactide (manufactured by Tokyo Chemical Industry Co., Ltd.) D-lactide (manufactured by Tokyo Chemical Industry Co., Ltd.) Methanol (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) 2,4-diethyl-1,5-pentanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 2-methyl-1,3-propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) Succinic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Propylene glycol (manufactured by Tokyo Chemical Industry Co., Ltd.) Terephthalic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Dispersant 1: "Kuraray Poval (registered trademark) 22-88", degree of saponification 87.0 to 89.0 mol, viscosity (4%, 20°C) 20.5 to 24.5 mPa·s (manufactured by Kuraray Co., Ltd.) Dispersant 2: "Kuraray Poval (registered trademark) 44-88", degree of saponification 87.0 to 89.0 mol, viscosity (4%, 20°C) 40.0 to 48.0 mPa·s (manufactured by Kuraray Co., Ltd.)

[0065] The physical properties of the block copolymers and polymers 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 copolymers and polymers (also referred to as Mn of the polymer) was determined in terms of standard polystyrene by gel permeation chromatography (GPC). The Mn of the block structural unit (B) (also referred to as Mn of the structural unit (B)) was determined from the Mn of the block copolymer and the mass content of the block structural unit (B). <GPC measurement conditions> Apparatus: GPC apparatus "HLC-8220" manufactured by Tosoh Corporation Separation column: "TSKgel SuperMultiporeHZ-M (column diameter = 4.6 mm, column length = 15 cm)" manufactured by Tosoh Corporation (two columns connected in series) Eluent: tetrahydrofuran (THF) Eluent flow rate: 0.35 mL / min Column temperature: 40°C Detection method: refractive index (RI) Injection volume: 10 μL Concentration: 1 mg / 1 mL (block copolymer or polylactic acid / THF)

[0066] (2) Mass ratio (block structural unit (A):block structural unit (B)) １ The mass ratio of the block structural unit (A) to the block structural unit (B) (block structural unit (A):block structural unit (B)) was calculated by H-NMR. １ The molar ratio of the block structural units (A) to (B) (block structural units (A):block structural units (B)) was calculated from the area ratio of the signal at around 5.2 ppm attributable to the polylactic acid unit in the spectrum obtained by H-NMR to the signal at around 0.9 ppm attributable to the block structural units (B) mainly composed of polyester units (b). The mass ratio of the block structural units (A) to (B) (block structural units (A):block structural units (B)) was determined by multiplying this molar ratio by the molecular weight of the block structural units. １ H-NMR measurement conditions> Apparatus: Nuclear magnetic resonance apparatus "JNM-ECX400" manufactured by JEOL Ltd. Solvent: deuterated chloroform Measurement temperature: 50°C Number of accumulations: 1024 Measurement conditions: Temperature rise rate 10°C / min

[0067] (3) Glass transition temperature (°C), melting point (°C), and crystalline melting enthalpy (J / g) The glass transition temperature (°C), melting point, and crystalline melting enthalpy of the block copolymer and polymer were measured in accordance with JIS K7121:2012. The melting peak temperature was taken as the melting point. Specifically, the glass transition temperature (°C), melting point (J / g), and crystalline melting enthalpy of the block copolymer and polymer were measured in accordance with JIS K7121:2012. The melting peak temperature was taken as the melting point. ｎｄ The glass transition temperature (°C), melting point (°C), and crystalline melting enthalpy (J / g) were measured in the following run. <Measurement conditions for glass transition temperature (°C), melting point (°C), and crystalline melting enthalpy (J / g)> The glass transition temperature, melting point, and crystalline melting enthalpy of the block copolymer and polymer were measured in accordance with JIS K7121:2012. Specifically, the glass transition temperature, melting point, and crystalline melting enthalpy of the block copolymer and polymer were measured in accordance with JIS K7121:2012 under the following measurement conditions. ｎｄ The glass transition temperature (°C) on the highest temperature side, the melting point (°C) on the highest temperature side, and the crystalline melting enthalpy (J / g) were measured in the test run. In this specification, the midpoint glass transition temperature in JIS K7121:2012 is defined as the glass transition temperature of the block copolymer and polymer, and the 2 ｎｄThe heat of fusion in the melting curve during the run is defined as the enthalpy of crystalline fusion.

[0068] <Measurement conditions for glass transition temperature (°C), melting point (°C) and crystalline melting enthalpy (J / g)> Apparatus: Mettler Toledo differential scanning calorimeter "DSC822" Block copolymers and polymers at 25°C were heated to 200°C at a temperature increase rate of 10°C / min (1 ｓｔ After holding the sample at 200°C for 5 minutes, it was cooled from 200°C at a rate of 10°C / min to 75°C and held at 75°C for 30 minutes (crystallization). It was then cooled from 75°C at a rate of 10°C / min to -50°C, then cooled from -50°C at a rate of 5°C / min to -75°C, and held at -75°C for 5 minutes. It was then heated from -75°C at a rate of 10°C / min to 250°C (2 ｎｄ Furthermore, the block copolymer used in the present invention does not have a melting point between 175°C and 250°C, and compared to a block copolymer synthesized using only L-lactide, the highest melting point temperature is lowered by copolymerizing D-lactide. This suggests that poly-D-lactic acid and poly-L-lactic acid do not form a stereocomplex, and that the polylactic acid unit (a) is a random structural unit containing L-lactic acid units and D-lactic acid units randomly.

[0069] (4) 5-Second Seal Strength: Heat-seal paper (coated paper) was left to stand for one day in a room at a temperature of 20°C ± 1°C and a humidity of 40% ± 2%. Two sheets of heat-seal paper (coated paper) were stacked with the heat-seal layers (heat-sealing materials) facing each other, and heat-sealed using a thermal gradient tester (manufactured by Toyo Seiki Seisakusho Co., Ltd., Model HG-3) at 120°C, 0.3 MPa, and 5 seconds. After standing for one hour in the same room, the heat-sealed test specimen was cut to a width of 7.5 mm and subjected to T-peel at a tensile speed of 100 mm / min using a desktop precision universal testing machine (manufactured by Shimadzu Corporation, AGS-X). The recorded maximum load was taken as the heat-seal peel strength. (5) 1-Second Seal Strength: Heat-seal paper (coated paper) was left to stand for one day in a room at a temperature of 20°C ± 1°C and a humidity of 40% ± 2%. Two sheets of heat-seal paper (coated paper) were stacked with the heat-seal layers (heat-sealing materials) facing each other, and heat-sealed using a thermal gradient tester (Model HG-3, manufactured by Toyo Seiki Seisaku-sho, Ltd.) under conditions of 120°C, 0.3 MPa, and 1 second. After leaving the test piece to stand for 1 hour in the same room, the heat-sealed test piece was cut to a width of 7.5 mm and subjected to T-peel at a tensile speed of 100 mm / min using a desktop precision universal testing machine (AGS-X, manufactured by Shimadzu Corporation). The maximum load recorded was taken as the heat-seal peel strength.

[0070] (6) Biodegradability (activated sludge) The biodegradability of the block copolymer and polymer in activated sludge was measured according to the method of ISO 14851: 2019. If the decomposition rate after 90 days was 5% by mass or more, it was evaluated as A, and if it was less than 5% by mass and 1% by mass or more, it was evaluated as B.

[0071] (7) Hydrolysis Resistance (h) The block copolymer was dissolved in chloroform at a concentration of 10% by mass, poured onto a glass plate, air-dried overnight, and then dried in a vacuum dryer at 80°C for 3 hours to obtain a film with a thickness of 200 μm. A test sample weighing 0.15 g was cut out. The obtained test sample was immersed in 50 mL of ion-exchanged water at pH 7 and left at 50°C. The number average molecular weight was measured at predetermined intervals, and the hydrolysis resistance was evaluated based on the elapsed time until the number average molecular weight became less than 90% of the initial number average molecular weight. Note that if the elapsed time exceeded 400 hours, it was indicated in the table as ">400 h."

[0072] (8) Blocking Resistance (Blocking Strength) The blocking resistance of the resin composition was evaluated according to ASTM D918-99, Standard Test Method for Blocking Resistance of Paper and Paperboard, by contacting the coating layer surface of fine paper with fine paper and storing it for 24 hours under conditions of 60±1°C, RH 75%, and 3.4 kPa, and then evaluating the degree of blocking. Blocking resistance is ranked in order of A to B. [Evaluation Criteria] A: No blocking or slight blocking, easy to peel. B: Mild blocking, making a crackling sound when peeled.

[0073] (9) D / L Ratio (D-Lactic Acid / L-Lactic Acid Ratio in Block Structural Unit (A)) After producing the emulsion, it was diluted 10-fold with THF at 23°C, stirred for 30 minutes with a shaker, allowed to stand for 30 minutes, and then filtered through No. 5C filter paper (manufactured by ADVANTEC Co., Ltd.). The obtained filtrate was air-dried overnight and then dried for 30 minutes in a hot air dryer at 110°C. The obtained solid was added to 5N NaOH in an amount 50 times the amount of the solid, and the mixture was heated and stirred under reflux for 24 hours. The obtained solution was neutralized with hydrochloric acid and then evaporated to dryness using an evaporator. To this was added a 50-fold amount of a 2 mmol copper sulfate aqueous solution / isopropanol (IPA) = 98 / 2 to form an aqueous solution, and the molar ratio (D-lactic acid / L-lactic acid) was calculated from the ratio of the peak area derived from L-lactic acid to the peak area derived from D-lactic acid using liquid chromatography (ACQUITY UPLC H-CLASS (Nihon Waters)) using a chiral ligand exchange column (SUMICHIRAL OA-5000 (Sumika Chemical Analysis Center Co., Ltd.)).

[0074] Example 1 (1) Preparation of Block Copolymer A flask equipped with a vacuum pump and an apparatus capable of distilling off the generated liquid was charged with 3-methyl-1,5-pentanediol and adipic acid in a molar ratio of 3-methyl-1,5-pentanediol / adipic acid = 1.1 / 1, and tin octoate 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 under a nitrogen atmosphere at normal pressure at 160°C for 3 hours, and then at 220°C for 3 hours, while distilling off water. The pressure was then reduced to 2,000 Pa and the mixture was reacted for 3 hours. The pressure was then reduced to 80 Pa and the mixture was reacted while appropriately checking the reaction until the number average molecular weight reached 6,000, thereby synthesizing a polymer composed of structural units (B') mainly composed of polyester units. After the reaction was completed, the pressure was returned to normal and the temperature was cooled to 80°C. Toluene was then added to dilute the mixture to a solids concentration of 40% by mass, and the toluene solution was then added to methanol in an amount twice the total volume of the solution. The supernatant was discarded, and the same amount of methanol as the amount of the toluene solution added was added again for washing. The supernatant was discarded, and the recovered insoluble matter was dried in a vacuum dryer at 40°C to remove organic volatiles, yielding a polymer composed of structural units (B') mainly composed of polyester units.

[0075] Toluene was added again to the purified polymer comprising structural unit (B'), and the toluene solution of the polymer comprising structural unit (B') was diluted so that the solids concentration of the toluene solution was 33% by mass. The temperature was then raised to 140°C, and 10% by mass of the added toluene was distilled off to dehydrate the system. Thereafter, the toluene solution of the polymer comprising structural unit (B') was cooled to 80°C, and the polymer comprising structural unit (B'), L-lactide, and D-lactide were added in a mass ratio of polymer comprising structural unit (B') / L-lactide / D-lactide = 50 / 47.5 / 2.5. Further, toluene was added in the amount of the weight of the distilled off polymer, and the solids concentration of the toluene solution of the polymer comprising structural unit (B'), L-lactide, and D-lactide was adjusted to 50% by mass. Thereafter, when the temperature of the solution was raised to 100°C, tin octoate was added in an amount of 0.1% by mass relative to the polymer consisting of structural units (B'), and the mixture was allowed to react for 4 hours to synthesize a block copolymer (block copolymer 1) consisting of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b), and a toluene solution of the block copolymer (block copolymer 1) was obtained.

[0076] Toluene was further added to this solution to dilute it to a solids concentration of 40% by mass, and then the 40% by mass toluene solution was added to a volume of methanol twice the total volume of the solution to precipitate a solid. The supernatant methanol was discarded, and an equal volume of methanol was added again for washing. The methanol was discarded, and the recovered solid was dried in a vacuum dryer at 40°C to remove organic volatiles, yielding a block copolymer consisting of block structural units (A) primarily composed of polylactic acid units (a) and block structural units (B) primarily composed of polyester units (b). The obtained block copolymer was subjected to the above-described measurements and evaluations. The results are shown in Table 1.

[0077] (2) Preparation of Polymer Solution The obtained block copolymer was added to toluene to obtain a polymer solution with a solids concentration of 30% by mass. (3) Preparation of Emulsion The obtained polymer solution was mixed with an aqueous solution prepared by diluting "Kuraray Povall (registered trademark) 22-88" (manufactured by Kuraray Co., Ltd.) as a dispersant with water, so that the dispersant / block copolymer ratio was 95 / 5 and the solids content was 10% by mass, to obtain 400 g of a mixed solution. The mixed solution was stirred for 5 minutes at a peripheral speed of 17.5 m / s using a precision emulsifying and dispersing machine "Clearmix" (manufactured by M Technique Co., Ltd.) to obtain a dispersion. The dispersion was heated to a temperature of 85°C to remove the toluene, and an emulsion containing the block copolymer and dispersant was obtained. (4) Preparation of Coated Paper for Measuring 5-Second Seal Strength The obtained emulsion was used as a coating solution. The coating solution was applied at a concentration of 127.9 g / m ２ The emulsion was applied to OK Prince wood-free paper so that the film thickness after drying would be 10 μm, and the coating was dried at 25°C for at least 6 hours, followed by drying in a hot air dryer at 100°C for 5 minutes to obtain a heat-sealing material. In this way, a coated paper (heat-sealing paper) was obtained, which had paper and a heat-sealing material formed on the surface of the paper. The obtained coated paper was used to carry out the above-mentioned measurements and evaluations. The results are shown in Table 1. (5) Preparation of coated paper for measuring 1-second seal strength The obtained emulsion was used as a coating liquid. The coating liquid was applied at a thickness of 60 g / m ２ on bleached kraft paper, with a film thickness of 6 g / m after drying. ２ The coated paper was dried at 25°C for at least 6 hours, and then dried in a hot air dryer at 100°C for 5 minutes to obtain a heat-sealing material. In this way, a coated paper (heat-sealing paper) was obtained, which had paper and a heat-sealing material formed on the surface of the paper. The obtained coated paper was used to carry out the above-mentioned measurements and evaluations. The results are shown in Table 1.

[0078] Examples 2 to 11 and Comparative Examples 1 to 4 and 6 (1) Preparation of Polymers Block copolymers 2 to 16 composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) were synthesized in the same manner as in Example 1, except that the types of diol and dicarboxylic acid were as shown in Tables 1 and 2, the type and content of dispersant were as shown in Tables 1 and 2, the number average molecular weight was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units, the mass ratio of the polymer composed of structural units (B'), L-lactide, and D-lactide (polymer composed of structural units (B') / L-lactide / D-lactide) was changed, and the dilution concentration during synthesis was appropriately changed to a concentration that was easy to handle. The obtained block copolymers 2 to 16 were subjected to the above-mentioned measurements and evaluations. The results are shown in Tables 1 and 2. (2) Preparation of Polymer Solutions The resulting block copolymers 2 to 16 were added to toluene to obtain polymer solutions with solid concentrations of 30% by mass. In Example 11 and Comparative Example 6, the polymer solutions were used as coating solutions. (3) Preparation of Emulsions In Example 9, a dispersion was prepared in the same manner as in Example 1, except that the components and amounts added were as shown in Table 1. This dispersion was used as a coating solution without removing toluene. In Examples 2 to 8, 10 and Comparative Examples 1 to 4, emulsions were prepared in the same manner as in Example 1, except that the components and amounts added were as shown in Tables 1 and 2. In Examples 2 to 8, 10 and Comparative Examples 1 to 4, the emulsions were used as coating solutions. (4) Preparation of Coated Paper Coated paper was obtained in the same manner as in Example 1. The obtained coated paper was used for the measurements and evaluations described above. The results are shown in Tables 1 and 2.

[0079] Comparative Example 5 0.1% by mass of tin octoate was added to L-lactide at 200°C, and the mixture was allowed to react until the number average molecular weight reached 40,000, yielding polylactic acid (polymer 1 composed of block structural units (A) mainly composed of polylactic acid units (a)). An emulsion was prepared and coated paper was produced in the same manner as in Example 1, except that the resulting polylactic acid was used instead of the block copolymer.

[0080]

[0081]

[0082] The abbreviations in Table 1 represent the following compounds: PLLA: Poly-L-lactic acid PDLLA: Poly-DL-lactic acid MPD: 3-methyl-1,5-pentanediol DEPD: 2,4-diethyl-1,5-pentanediol MPDiol: 2-methyl-1,3-propanediol BD: 1,4-butanediol PG: Propylene glycol AA: Adipic acid SA: Succinic acid TA: Terephthalic acid

Claims

1. A block copolymer comprising a block structural unit (A) mainly composed of a polylactic acid unit (a) and a block structural unit (B) mainly composed of a polyester unit (b), wherein the polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), wherein the aliphatic diol (b1) is an aliphatic diol having 4 or more carbon atoms and an alkyl group as a branched chain, wherein the content of D-lactic acid units in 100% by mass of the polylactic acid units (a) is 1% by mass or more and 50% by mass or less, wherein the content of aromatic carboxylic acid units in 100% by mass of the polyester units (b) is 20% by mass or less, and wherein the melting point of the block copolymer is 175°C or less.

2. The block copolymer according to claim 1, wherein the content of the block structural unit (B) in 100% by mass of the block copolymer is 35% by mass or more and 90% by mass or less.

3. The block copolymer according to claim 1 or 2, wherein the content of the block structural unit (A) is 5% by mass or more and 65% by mass or less in a total of 100% by mass of the block structural unit (A) and the block structural unit (B).

4. The block copolymer according to claim 1 or 2, wherein the aliphatic diol (b1) is at least one selected from the group consisting of 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, and 2,4-diethyl-1,5-pentanediol.

5. The block copolymer according to claim 1 or 2, wherein the aliphatic dicarboxylic acid (b2) is at least one selected from the group consisting of adipic acid and succinic acid.

6. The block copolymer according to claim 1 or 2, having a melting point of 100°C or higher and 130°C or lower.

7. The block copolymer according to claim 1 or 2, having a number average molecular weight of 30,000 or less.

8. The block copolymer according to claim 1 or 2, having a number average molecular weight of 11,000 or more.

9. The block copolymer according to claim 1 or 2, wherein the number average molecular weight of the block structural unit (B) is 2,500 or more.

10. The block copolymer according to claim 1 or 2, having a glass transition temperature of -80°C or higher and -15°C or lower.

11. The block copolymer according to claim 1 or 2, wherein the polylactic acid unit (a) is a random structural unit containing an L-lactic acid unit and a D-lactic acid unit.

12. A resin composition comprising the block copolymer according to claim 1.

13. The resin composition according to claim 12, which contains 0.1 to 10 parts by mass of sodium lactate per 100 parts by mass of the block copolymer.

14. A heat seal material formed using the resin composition according to claim 12 or 13.

15. A laminate having at least two layers, a layer (1) and a layer (2), said layer (1) being laminated directly on said layer (2), said layer (1) comprising the resin composition according to claim 12 or 13.

16. A laminate having at least two layers, layer (1) and layer (2), said layer (1) being directly laminated onto said layer (2), said layer (1) comprising the heat seal material according to claim 14.

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