Emulsion

Abstract

Provided is an emulsion containing a block copolymer (I) and a dispersant (II), wherein the block copolymer (I) contains block structural units (A) containing polylactic acid units (a) as a main component and block structural units (B) containing polyester units (b) as a main component.

Description

emulsion

[0001] The present invention relates to an emulsion having excellent biodegradability.

[0002] From the viewpoint of environmental protection, there has been active development of biodegradable resins, which are plastics that are ultimately decomposed into water and carbon dioxide and return to nature after being involved in biomass formation by organisms such as microorganisms in nature, and which also reduce the generation of carbon dioxide.In addition, in order to apply biodegradable resins to a wide range of fields such as paints, adhesives, printing, fibers, and films, there has been active development of techniques for microparticulating biodegradable resins and dispersions in which microparticulated biodegradable resins are dispersed.

[0003] Such techniques have been proposed, for example, in Patent Documents 1 to 3. Patent Document 1 discloses biodegradable polyester resin microparticles such as polylactic acid resins and a method for producing the same. Patent Document 2 discloses an aqueous dispersion of a hydrolytically unstable polymer that is substantially free of volatile organic compounds, the hydrolytically unstable polymer containing a biodegradable polymer. Patent Document 3 discloses an aqueous dispersion in which a biodegradable resin is dispersed in water, the aqueous dispersion containing a specific polyvinyl alcohol as a dispersant.

[0004] JP 2005-2302 A JP 2019-507229 A JP 2004-99883 A

[0005] It is assumed that the biodegradable resin microparticles and dispersions of biodegradable resins described in Patent Documents 1 to 3 have a certain degree of biodegradability. However, with increasing environmental awareness, there has been a demand for products with even better biodegradability.

[0006] Therefore, an object of the present invention is to provide an emulsion that is highly biodegradable.

[0007] 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.

[0008] [1] An emulsion containing a block copolymer (I) and a dispersant (II), wherein the block copolymer (I) comprises block structural units (A) containing polylactic acid units (a) as a main component and block structural units (B) containing polyester units (b) as a main component. [2] The emulsion according to [1] above, wherein the block copolymer (I) accounts for 50% by mass or more and 99% by mass or less, relative to 100% by mass of the total of the block copolymer (I) and the dispersant (II). [3] The emulsion according to [1] or [2] above, wherein the polyester units (b) contain 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. [4] The emulsion according to [3] above, wherein the aliphatic diol (b1) has 10 or less carbon atoms. [5] The emulsion according to [3] or [4] above, wherein the aliphatic diol (b1) has 5 or more carbon atoms. [6] The emulsion according to any one of [3] to [5] above, wherein the branched chain of the aliphatic diol (b1) is a methyl group. [7] The emulsion according to any one of [1] to [6] above, wherein the block structural unit (A) accounts for 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). [8] The emulsion according to any one of [1] to [7] above, wherein the dispersant (II) is a vinyl alcohol-based polymer. [9] The emulsion according to any one of [1] to [8] above, wherein the particle size is 100 to 1,000 nm.

[10] A method for producing the emulsion according to any one of the above [1] to [9], comprising a step of dispersing the block copolymer (I) dissolved in an organic solvent in an aqueous medium in the presence of the dispersant (II).

[11] A method for producing the emulsion according to the above

[10] , further comprising a step of removing the organic solvent.

[0009] According to the present invention, an emulsion having excellent biodegradability can be provided.

[0010] 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, unless otherwise specified, the "main chain" of a polymer refers to the longest molecular chain in the polymer molecule. In this specification, "solid" means non-fluidity at room temperature (23°C) and under no pressure.

[0011] [Emulsion] The emulsion of this embodiment contains a block copolymer (I) and a dispersant (II). The block copolymer (I) contains block structural units (A) containing polylactic acid units (a) as a main component and block structural units (B) containing polyester units (b) as a main component. The present inventors have conducted various studies on formulations for imparting excellent biodegradability to emulsions. As a result, the present inventors have found that an emulsion containing a block copolymer (I) containing block structural units (A) and block structural units (B) and a dispersant (II) is an effective formulation for achieving excellent biodegradability.

[0012] <Block Copolymer (I)> The block copolymer (I) contains 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. The inclusion of the polylactic acid unit (a) facilitates adjustment of the melting point to room temperature or higher, improving the handleability of the block copolymer (I). Furthermore, the inclusion of the block structural unit (B) containing a polyester unit (b) as a main component improves the biodegradability and hydrolysis resistance of the block copolymer (I).

[0013] <Block structural unit (A)> <Polylactic acid unit (a)> The block structural unit (A) is mainly composed of polylactic acid unit (a). The "main component" refers to the unit that is contained in the block structural unit (A) at the highest content ratio. The content ratio of 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 amount of polylactic acid unit (a) contained in the block structural unit (A), and it may be, for example, 100% by mass or less.

[0014] The polylactic acid constituting the polylactic acid unit (a) may be prepared by direct condensation of lactic acid or by ring-opening polymerization of lactide. The lactic acid may be, for example, at least one selected from the group consisting of L-lactic acid, D-lactic acid, and DL-lactic acid. The lactide may be, for example, at least one selected from the group consisting of L-lactide, D-lactide, DL-lactide, and meso-lactide. Furthermore, 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 (I), poly-L-lactic acid, poly-D-lactic acid, and poly-DL-lactic acid are preferred, with poly-L-lactic acid and poly-D-lactic acid being more preferred. On the other hand, from the viewpoint of the cost and complexity of synthesis, it is preferable that the polylactic acid is not a stereocomplex polylactic acid. From the viewpoint of exhibiting even better biodegradability, the block structural units (A) preferably contain 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, of structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid. For example, in one preferred embodiment, the block structural units (A) are composed of structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid, i.e., the structural units derived from poly-L-lactic acid or structural units derived from poly-D-lactic acid account for 100% by mass.

[0015] <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.

[0016] <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 100,000, more preferably 5,000 to 25,000, even more preferably 8,200 to 15,000, and particularly preferably 5,200 to 15,000. Within the above numerical range, the productivity is excellent and the viscosity range tends to be easy to handle as an emulsion. When the block copolymer (I) has multiple block structural units (A), the number average molecular weight of the block structural unit (A) refers to the total 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 (I) described below and the mass content of the block structural unit (A).

[0017] <Block structural unit (B)> The block structural unit (B) is mainly composed of polyester units (b). The term "main component" refers to the unit having 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, and may even be 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.

[0018] From the viewpoint of exhibiting even better biodegradability, the polyester unit (b) preferably contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2). Specifically, the polyester unit (b) preferably 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 a monomer 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 it does 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, and may even be 100 mol%.

[0019] <Aliphatic Diol (b1)> The number of carbon atoms in the aliphatic diol (b1) is preferably 5 or more, more preferably 6 or more, from the viewpoint of exhibiting excellent hydrolysis resistance, and is preferably 10 or less, more preferably 9 or less, even more preferably 8 or less, and particularly preferably 7 or less, from the viewpoint of exhibiting even more excellent biodegradability.

[0020] The aliphatic diol (b1) preferably has an alkyl group as a branched chain from the viewpoints of suppressing crystallization of the block structural unit (B) and exhibiting even better biodegradability, and from the viewpoint of improving the hydrolysis resistance of the block structural unit (B) as an emulsion. That is, it is preferable that the polyester unit (b) contains units derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), and the aliphatic diol (b1) has an alkyl group as a branched chain. Here, the "branched chain" in the aliphatic diol (b1) refers to a partial structure branching from the "main chain" in the aliphatic diol (b1), and no hydroxyl groups are bonded to its terminals. The "main chain" in the aliphatic diol (b1) refers to a partial structure that is a molecular chain composed of two hydroxyl groups in the molecule at both ends and multiple atoms, preferably carbon atoms, connecting the two hydroxyl groups. Therefore, 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) has a branched chain that is an alkyl group, the block structural unit (B) is more likely to become an amorphous polymer. This presumably makes it easier for microorganisms to penetrate into the polymer structure during biodegradation, resulting in even better biodegradability. However, being an amorphous polymer is only one factor affecting biodegradability. This is because biodegradation is thought to be a combination of various factors, such as whether microorganisms recognize the amorphous structure as food, whether enzymes and microorganisms can easily access it, steric hindrance of the main chain, melting point, and crystallinity. Therefore, the effects of the present invention cannot be achieved simply by using an amorphous polymer. Note that when the aliphatic diol (b1) has an alkyl group as a branched chain, the "number of carbon atoms" of the aliphatic diol (b1) refers to the total number of carbon atoms in the aliphatic diol (b1), including the number of carbon atoms constituting the alkyl group.

[0021] The number of branched chains in the aliphatic diol (b1) is preferably one or two, more preferably one. The branched chains are preferably methyl, ethyl, and propyl groups, more preferably methyl and ethyl groups, and even more preferably methyl groups. When the aliphatic diol (b1) has multiple branched chains, the branched chains may be the same or different. From the viewpoint of easy reaction with dicarboxylic acids and easy production of triblock copolymers, it is preferable that the branched chains of the aliphatic diol (b1) are at least the γ-position away from the hydroxyl group and are methyl groups with little steric hindrance. Furthermore, from the viewpoint of even better biodegradability, it is preferable that the aliphatic diol (b1) has hydroxyl groups at both ends of the main chain.

[0022] Examples of the aliphatic diol (b1) having 5 to 10 carbon atoms and having an alkyl group as a branched chain include 2,2-dimethyl-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2-methyl-1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 2,3-pentanediol, 2,4-pentanediol, and 2-methyl-2,4-pentanediol. 1,4-pentanediol, 2-methyl-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, 2-methyl-1,8-octanediol, 2,7-dimethyl-1,8-octanediol, and 2-methyl-1,9-nonanediol. The aliphatic diol (b1) is preferably 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, 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, more preferably 5 or more, and even more preferably 6 or more, from the viewpoint of exhibiting excellent hydrolysis resistance, and is preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less, from the viewpoint of exhibiting even more excellent biodegradability.

[0024] Examples of the aliphatic dicarboxylic acid (b2) having from 4 to 12 carbon atoms 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, adipic acid, or sebacic acid, more preferably adipic acid or sebacic acid, and even more preferably adipic acid. The aliphatic dicarboxylic acid (b2) may be used alone or in combination of two or more.

[0025] <Preferred Combinations of Aliphatic Diol (b1) and Aliphatic Dicarboxylic Acid (b2)> From the viewpoint of exhibiting even better biodegradability, the combination of 3-methyl-1,5-pentanediol and adipic acid, the combination of 2-methyl-1,3-propanediol and succinic acid, and the combination of 2,4-diethyl-1,5-pentanediol and adipic acid are preferred examples of an embodiment, and the combination of 3-methyl-1,5-pentanediol and adipic acid is a more preferred example of an embodiment.

[0026] <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, and even more preferably 1.15 / 1 to 1 / 1.15.

[0027] <Units (b') Other Than Polyester Units (b)> The block structural unit (B) may 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.

[0028] <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 less than 100,000, more preferably less than 50,000, even more preferably less than 30,000, still more preferably less than 20,000, particularly preferably less than 15,000, and most preferably less than 10,000. Within the above numerical range, the block copolymer (I) tends to have excellent productivity. 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.

[0029] <Structural Unit Proportion> The proportion of the block structural unit (A) is preferably 5% by mass or more, more preferably 15% by mass or more, even more preferably 25% by mass or more, and particularly preferably 35% by mass or more, based on 100% by mass of the total of the block structural unit (A) and the block structural unit (B). Furthermore, the proportion of the block structural unit (A) is preferably 95% by mass or less, more preferably 85% by mass or less, even more preferably 75% by mass or less, and particularly preferably 60% by mass or less, based on 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 (I) tends to be even more excellent. When the proportion of the block structural unit (A) is 95% by mass or less, the block copolymer (I) tends to be excellent in flexibility, biodegradability, and the like. From the viewpoint of handleability, the proportion of the block structural unit (A) is more preferably 10% by mass or more, even more preferably 15% by mass or more. From the viewpoints of flexibility, biodegradability, etc., the proportion of the block structural unit (A) is more preferably 80% by mass or less, even more preferably 75% by mass or less, still more preferably 70% by mass or less, and particularly preferably 60% by mass or less. １ It can be determined by H-NMR, specifically by the method described in the Examples.

[0030] The total content of the block structural unit (A) and the block structural unit (B) in the block copolymer (I) 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 (I), and it may be, for example, 100% by mass or less.

[0031] The block copolymer (I) 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 (I) is preferably 10% by mass or less, more preferably 5% by mass or less.

[0032] <Number Average Molecular Weight of Block Copolymer (I)> From the viewpoints of handleability and hydrolysis resistance, the number average molecular weight of the block copolymer (I) is preferably 5,000 or more, more preferably 8,000 or more, and even more preferably 10,000 or more. From the viewpoint of productivity, the number average molecular weight of the block copolymer (I) is preferably less than 200,000, more preferably less than 100,000, even more preferably less than 60,000, still more preferably 50,000 or less, particularly preferably 40,000 or less, and most preferably 20,000 or less. The number average molecular weight of the block copolymer (I) can be determined by gel permeation chromatography (GPC), and specifically, can be measured by the method described in the Examples.

[0033] <<Bonding Form of Block Copolymer (I)>> The bonding form of the block copolymer (I) is preferably a triblock type or a diblock type, and more preferably a triblock type. The block copolymer (I) 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)].

[0034] <Dispersant (II)> The dispersant (II) is not particularly limited as long as it can form an emulsion containing the block copolymer (I) and does not impair the effects of the present invention. Examples of the dispersant (II) 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. From the viewpoints of improving dispersion stability and exhibiting even more excellent biodegradability, the dispersant (II) is preferably a water-soluble polymer or an anionic surfactant, more preferably a water-soluble polymer. From the viewpoints of improving dispersion stability and exhibiting even more excellent biodegradability, the water-soluble polymer is preferably a vinyl alcohol polymer.The anionic surfactant is preferably an alkylbenzenesulfonate, more preferably sodium dodecylbenzenesulfonate, from the viewpoint of improving dispersion stability and exhibiting even better biodegradability.

[0035] When a vinyl alcohol polymer is used as the dispersant (II), the degree of saponification of the vinyl alcohol polymer is preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 85 mol% or more. The upper limit is preferably 100 mol% or less, more preferably 99 mol% or less, more preferably 98 mol% or less, even more preferably 95 mol% or less, and particularly preferably 90 mol% or less. The degree of saponification 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.

[0036] When a vinyl alcohol polymer is used as the dispersant (II), the viscosity of the vinyl alcohol polymer as a 4% by mass aqueous solution (20°C) is preferably 3 to 120 mPa s, more preferably 4 to 70 mPa s, even more preferably 8 to 60 mPa s, and particularly preferably 20 to 50 mPa s. The viscosity can be measured by the viscosity measurement method described in JIS-K6726 (1994).

[0037] <Dispersion medium> The dispersion medium is preferably an aqueous medium containing water as the main component. The aqueous medium containing water as the main component may contain a water-soluble organic solvent (alcohols, ketones, etc.) that is soluble in water at any ratio. Here, "aqueous medium containing water as the main component" refers to a dispersion medium containing 50% by mass or more of water. From the viewpoints of cost and environmental impact, the dispersion medium is preferably an aqueous medium containing 90% by mass or more of water, and more preferably water. From the viewpoints of productivity, handleability, and dispersion stability, the content of the dispersion medium in the emulsion is preferably 50% by mass or more, more preferably 65% ​​by mass or more, even more preferably 75% by mass or more, still more preferably 80% by mass or more, and preferably 99% by mass or less, more preferably 97% by mass or less, and even more preferably 95% by mass or less.

[0038] <Components other than block copolymer (I), dispersant (II), and dispersion medium> The emulsion may contain components other than the block copolymer (I), dispersant (II), and dispersion medium. Examples of components other than the block copolymer (I), dispersant (II), and dispersion medium include polymers other than the block copolymer (I), colorants (pigments or dyes), antifoaming agents, antioxidants, and ultraviolet absorbers. The content of components other than the block copolymer (I), dispersant (II), and dispersion medium in the emulsion is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0039] <Ratio of Block Copolymer (I) and Dispersant (II)> From the viewpoint of the active ingredient, the block copolymer (I) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, still more preferably 70% by mass or more, and particularly preferably 75% by mass or more, relative to 100% by mass of the total of the block copolymer (I) and the dispersant (II). From the viewpoint of improving dispersion stability and a viscosity range that is easy to handle, the block copolymer (I) is 99% by mass or less, more preferably 97% by mass or less, even more preferably 96% by mass or less, still more preferably 90% by mass or less, and particularly preferably 85% by mass or less. That is, the block copolymer (I) is preferably 50 to 99% by mass, more preferably 60 to 97% by mass, even more preferably 65 to 96% by mass, still more preferably 70 to 90% by mass, and particularly preferably 75 to 85% by mass, relative to 100% by mass of the total of the block copolymer (I) and the dispersant (II). The content of the dispersant (II) is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, even more preferably 5% by mass or more, particularly preferably 10% by mass or more, and most preferably 15% by mass or more, based on the total 100% by mass of the block copolymer (I) and the dispersant (II), from the viewpoint of improving dispersion stability and achieving a viscosity range that is easy to handle. From the viewpoint of increasing productivity and the amount of the active ingredient, the content of the dispersant (II) is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less, particularly preferably 28% by mass or less, and most preferably 25% by mass or less. That is, the content of the dispersant (II) is preferably 1 to 50% by mass, more preferably 3 to 40% by mass, even more preferably 4 to 35% by mass, even more preferably 5 to 30% by mass, particularly preferably 10 to 28% by mass, and most preferably 15 to 25% by mass, based on the total 100% by mass of the block copolymer (I) and the dispersant (II).

[0040] The total content of the block copolymer (I) and the dispersant (II) in the emulsion is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more from the viewpoint of increasing the amount of the active ingredient, and is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less from the viewpoint of making the emulsion have a viscosity that is easy to handle. That is, the total content of the block copolymer (I) and the dispersant (II) in the emulsion is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, and even more preferably 5 to 20% by mass.

[0041] [Solid content in emulsion] The solid content in the emulsion is preferably 1 to 50% by mass, more preferably 3 to 30% by mass, and even more preferably 5 to 20% by mass. When the solid content in the emulsion is within the above range, better dispersion stability tends to be obtained. The solid content in the emulsion means the value measured for the residue after heating and drying at 140°C using a heat-drying moisture content meter until no weight change occurs.

[0042] Furthermore, the total content of the block copolymer (I) and the dispersant (II) in the solid content of the emulsion is, from the viewpoint of the effective ingredients, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, and still more preferably 90% by mass or more, and may even contain 100% by mass.

[0043] [Emulsion Particle Size] From the viewpoint of dispersion stability, the emulsion particle size is preferably 100 to 1,000 nm, more preferably 130 to 800 nm, even more preferably 150 to 600 nm, still more preferably 180 to 400 nm, and particularly preferably 200 to 350 nm. In this specification, the term "particle size" refers to the average particle size measured with a dynamic light scattering measurement device described below.

[0044] [Long-term dispersion stability of emulsion] From the viewpoint of long-term storage, it is desirable that the dispersion stability of the emulsion is such that the resin does not settle for preferably 2 weeks or more, more preferably 1 month or more, and even more preferably 3 months or more at 23° C. In this specification, the term "long-term dispersion stability" refers to the stability evaluated by the method described in "(7) Long-term dispersion stability of emulsion" in the examples.

[0045] [Hydrolysis Resistance of Block Copolymer (I) in Emulsion] When the block copolymer (I) in the emulsion undergoes hydrolysis over time, the number average molecular weight of the block copolymer (I) decreases. The higher the hydrolysis resistance of the block copolymer (I), the more suppressed the decrease in the number average molecular weight (Mn) over time. The hydrolysis resistance of the block copolymer (I) in the emulsion can be measured using the retention rate of the number average molecular weight (Mn) calculated by the following formula: Retention rate of number average molecular weight (Mn) = (number average molecular weight (Mn) of block copolymer (I) after standing for 1,000 hours at 23°C / number average molecular weight (Mn) of block copolymer (I) within 6 hours of emulsion production) × 100 (%). From the viewpoint of long-term storage stability, the retention rate of the number average molecular weight (Mn) of the block copolymer (I) in the emulsion is preferably 60% or more, more preferably 70% or more, even more preferably 80% or more, and particularly preferably 90% or more. In this specification, the "number average molecular weight (Mn)" is a value determined by gel permeation chromatography (GPC), and specifically, can be measured by the method described in the examples.

[0046] [Viscosity of emulsion] From the viewpoint of ease of handling, the viscosity of the emulsion is preferably 10 to 1,000 mPa s, more preferably 100 to 500 mPa s, and even more preferably 200 to 350 mPa s. In this specification, "viscosity" refers to the viscosity measured at 23°C using an E-type viscometer described below.

[0047] [Method for Producing Block Copolymer (I)] The block copolymer (I) can be produced by a known production method. The known production method for the block copolymer (I) 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.

[0048] Another known method for producing the block copolymer (I) 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, etc.). The polymerization reaction may be solution polymerization, melt polymerization, interfacial polycondensation, etc., and known polymerization reaction conditions can be set for each.

[0049] [Method for producing emulsion] A known production method can be used for producing the emulsion. The emulsion can be obtained by dispersing the block copolymer (I) in a dispersion medium by a pressurized dispersion method, for example, in which a block copolymer (I), a dispersant (II), and a dispersion medium are simultaneously charged into a sealed vessel having a stirrer, and pressurized while heating and stirring to disperse the block copolymer (I); a direct dispersion method in which the block copolymer (I) is added to a heated dispersion medium containing a dispersant (II) maintained under normal pressure or pressure and stirred to disperse; a method in which the block copolymer (I) dissolved in an organic solvent is added to a dispersion medium containing a dispersant (II) and stirred to disperse; or a phase inversion method in which the block copolymer (I) is heated and melted, and the dispersion medium is added thereto and stirred to disperse the block copolymer (I) in the dispersion medium. Methods other than those mentioned above can also be appropriately used as long as they can obtain an aqueous dispersion of a biodegradable resin. From the viewpoint of easy synthesis, the method for producing the emulsion preferably comprises adding and stirring the block copolymer (I) dissolved in an organic solvent to a dispersion medium containing a dispersant (II) to disperse the block copolymer (I). That is, the method preferably comprises a step of dispersing the block copolymer (I) dissolved in an organic solvent in an aqueous medium in the presence of the dispersant (II). When preparing the emulsion, a dispersing device such as a high-pressure homogenizer may be used in combination as necessary. Furthermore, from the viewpoint of environmental load, the method preferably further comprises a step of removing the organic solvent after the dispersing step. The organic solvent removal step is preferably carried out by, for example, heating the solution obtained in the dispersing step to remove the organic solvent.

[0050] Furthermore, if necessary, components other than the block copolymer (I), the dispersant (II), and the dispersion medium may be added to the dispersion medium in advance before dispersing the block copolymer (I), may be added together with the block copolymer (I) when dispersing the block copolymer (I), or may be added after dispersing the block copolymer (I).

[0051] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these.

[0052] The physical properties of the block copolymer (I) and polymers such as polylactic acid 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) (also referred to as Mn of the polymer) of the block copolymer (I) and polymers in the emulsion was determined by gel permeation chromatography (GPC) within 6 hours after the emulsion was produced, in terms of standard polystyrene. 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 (I) 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: differential refractive index (RI) Injection volume: 10 μL Concentration: 1 mg / 1 mL ((block copolymer (I) or polylactic acid) / THF)

[0053] (2) (A) / (B) (mass ratio) (mass of block structural units (A) mainly composed of polylactic acid units (a) / mass of block structural units (B) mainly composed of polyester units (b)) １ The (A) / (B) (mass 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 around 5.2 ppm derived from the polylactic acid unit (a) in the obtained spectrum to the signal at around 0.9 ppm derived from the structural unit (B) mainly composed of polyester unit (b). The molar ratio was multiplied by the molecular weight of the block structural unit to obtain the mass ratio, and the (A) / (B) (mass ratio) was calculated. 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

[0054] (3) Biodegradability (Compost) The emulsion was cast to a film thickness of 100 μm, air-dried for one week, dried in a vacuum dryer at 40°C for 8 hours, and then dried at 105°C for 10 minutes. Biodegradability in compost was measured according to a method in accordance with ISO 14855-2:2018. The decomposition rate after 15 days was evaluated according to the following evaluation criteria: A: Decomposition rate is 20% by mass or more B: Decomposition rate is 10% by mass or more but less than 20% by mass C: Decomposition rate is 5% by mass or more but less than 10% by mass F: Decomposition rate is less than 5% by mass

[0055] (4) Biodegradability (activated sludge) The emulsion was cast to a film thickness of 100 μm, air-dried for one week, dried in a vacuum dryer at 40°C for 8 hours, and then dried at 105°C for 10 minutes. Biodegradability in activated sludge was measured according to a method in accordance with ISO 14851:2019. The decomposition rate after 90 days was evaluated according to the following evaluation criteria: A: Decomposition rate of 30% by mass or more B: Decomposition rate of 10% by mass or more but less than 30% by mass F: Decomposition rate of less than 10% by mass

[0056] (5) Particle size The emulsion was diluted 100 times with ion-exchanged water, and the median diameter (particle size) of the particles present in the emulsion was measured by dynamic light scattering. <Conditions for measuring median diameter> Apparatus: Nanoparticle analyzer "nano Partica SZ-100" manufactured by Horiba, Ltd.

[0057] (6) Dispersion Stability After the emulsion was produced, it was left to stand at 23°C for one day, and then the presence or absence of precipitation was visually confirmed, and the dispersion stability of the emulsion was evaluated according to the following evaluation criteria: A: No precipitation was observed. B: Precipitation was observed.

[0058] (7) Long-term dispersion stability of emulsion After the emulsion was produced, it was left to stand at 23°C, and the presence or absence of precipitation at the bottom of the container was visually checked every week, and the long-term dispersion stability of the emulsion was evaluated according to the following evaluation criteria. A: No precipitation was observed for 3 months or more after the emulsion was left to stand. B: Precipitation was observed 1 month to less than 3 months after the emulsion was left to stand. C: Precipitation was observed 2 weeks to less than 1 month after the emulsion was left to stand. F: Precipitation was observed less than 2 weeks after the emulsion was left to stand.

[0059] (8) Hydrolysis Resistance After the emulsion was produced, it was left to stand at 23°C for 1,000 hours, and then the number average molecular weight (Mn) of the block copolymer (I) and the polymer (also referred to as Mn of the polymer) was determined in terms of standard polystyrene by gel permeation chromatography (GPC). Subsequently, the retention of the number average molecular weight (Mn), which serves as an indicator of hydrolysis resistance, was calculated using the following formula: Retention of number average molecular weight (Mn) = (Number average molecular weight (Mn) of block copolymer (I) or polymer after standing at 23°C for 1,000 hours / Number average molecular weight (Mn) of copolymer (I) or polymer determined in (1) above) × 100 (%). The hydrolysis resistance of the emulsion was evaluated from the calculated retention according to the following evaluation criteria. A: Retention rate of number average molecular weight (Mn) is 90% or more B: Retention rate of number average molecular weight (Mn) is 80% or more and less than 90% C: Retention rate of number average molecular weight (Mn) is 70% or more and less than 80% D: Retention rate of number average molecular weight (Mn) is 20% or more and less than 70% F: Retention rate of number average molecular weight (Mn) is less than 20% The measurement conditions for GPC are the same as those for "(1) Number average molecular weight (Mn)" above.

[0060] (9) Viscosity One day after the emulsion was produced, the viscosity of the emulsion was measured at 23°C using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd.). The viscosity of the emulsion was evaluated according to the following criteria: A: 200 to 350 mPa·s B: 100 to 500 mPa·s C: 10 to 1,000 mPa·s D: Separation or precipitation occurred, so the emulsion was not in a uniform state and measurement was not possible.

[0061] The block copolymers and polymers in the examples and comparative examples were produced by the following methods. 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.) Succinic acid (manufactured by Tokyo Chemical Industry Co., Ltd.) Tin octoate (manufactured by Tokyo Chemical Industry Co., Ltd.) Toluene (manufactured by Kishida Chemical Co., Ltd.) L-lactide (manufactured by Tokyo Chemical Industry Co., Ltd.) Methanol (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.) 2-methyl-1,3-propanediol (manufactured by Tokyo Chemical Industry Co., Ltd.) 2,4-diethyl-1,5-pentanediol (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0062] Example 1 In a flask equipped with an apparatus capable of distilling off the generated liquid and a vacuum pump, 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 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 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. The pressure was then 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') 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 so that the solids content was 40% by mass, and the above toluene solution was then added to methanol in an amount twice the total volume of the solution. The supernatant was discarded, and methanol, in an amount equal to the amount of the toluene solution added, was added again for washing. The supernatant was discarded, and the recovered insoluble matter was dried at 40°C using a vacuum dryer to remove organic volatiles, yielding a polymer comprising structural units (B') primarily composed of polyester units (b). Toluene was added again to the purified polymer comprising structural units (B'), and the toluene solution of the polymer comprising structural units (B') was diluted to a solids content of 33% by mass. The temperature was then raised to 140°C, whereby 10% by mass of the added toluene was distilled off to dehydrate the system. Thereafter, the toluene solution of the polymer comprising structural units (B') was cooled to 80°C, and the polymer comprising structural units (B') and L-lactide were added to a ratio of polymer comprising structural units (B') / L-lactide of 50 / 50. Further addition of toluene in the amount of the weight of the distilled off solution was performed to adjust the solids content of the toluene solution of the polymer comprising structural units (B') and L-lactide to 50% by mass.After that, when the temperature of the solution was raised to 100°C, tin octylate was added in an amount of 0.1% by mass relative to the polymer consisting of structural units (B'), and the reaction was carried out for 4 hours to synthesize a block copolymer (I) 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 (I) was obtained. Toluene was further added to this solution to dilute it to a solid content of 40% by mass, and the toluene solution with a solid content of 40% by mass was then added to methanol in an amount twice the total volume of the solution to precipitate a solid. The supernatant methanol was discarded, and an equal amount of methanol to the amount of the toluene solution added 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 (I) consisting of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b). The number average molecular weight (Mn) of the resulting block copolymer (I) was 12,000. A polymer solution prepared by dissolving the resulting block copolymer (I) in toluene at a concentration of 20% by mass and an aqueous solution prepared by diluting a dispersant, "Kuraray Poval (registered trademark) 22-88" (manufactured by Kuraray Co., Ltd.), with water were mixed so that the dispersant content was 30 phr relative to the block copolymer (I) and the solid 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 disperser "Clearmix" (manufactured by M Technique Co., Ltd.) to obtain a dispersion. The dispersion was heated to a temperature of 85°C, and the toluene was removed by appropriately blowing nitrogen into the gas phase of the generated toluene vapor, thereby obtaining an emulsion containing the block copolymer (I) and the dispersant (II). The biodegradability, particle size, and dispersion stability of the resulting emulsion in activated sludge and compost are shown in Table 1-1.

[0063] [Examples 2 and 3] Each block copolymer (I) composed of a block structural unit (A) composed mainly of a polylactic acid unit (a) and a block structural unit (B) composed mainly of a polyester unit (b) was synthesized and then an emulsion was obtained in the same manner as in Example 1, except that the number average molecular weight of the structural unit (B) was adjusted by adjusting the reaction time during synthesis of the polymer composed of the structural unit (B') composed mainly of the polyester unit (b), the mass ratio of the polymer composed of the structural unit (B') to L-lactide used was changed, and the content of the dispersant (II) relative to the block copolymer (I) was changed. The obtained emulsions were subjected to the aforementioned measurements and evaluations. The results are shown in Table 1-1.

[0064] Example 4 A block copolymer (I) composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) 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, succinic acid was used instead of adipic acid, the number average molecular weight of structural units (B) was adjusted by adjusting the reaction time during synthesis of a polymer composed of structural units (B') mainly composed of polyester units (b), and the content of dispersant (II) relative to block copolymer (I) was changed. The emulsion obtained was then subjected to the aforementioned measurements and evaluations. The results are shown in Table 1-1.

[0065] Example 5 A block copolymer (I) composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) 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, the number average molecular weight of the structural units (B) was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units (b), and the content of dispersant (II) relative to the block copolymer (I) was changed. An emulsion was then obtained. The obtained emulsion was subjected to the aforementioned measurements and evaluations. The results are shown in Table 1-1.

[0066] Example 6 A block copolymer (I) composed of block structural units (A) composed mainly of polylactic acid units (a) and block structural units (B) composed mainly of polyester units (b) was synthesized in the same manner as in Example 1, except that the number-average molecular weight of the structural units (B') was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') composed mainly of polyester units (b), and the dilution concentration during synthesis was appropriately changed to a concentration that was easy to handle, and then an emulsion was obtained. The obtained emulsion was subjected to the aforementioned measurements and evaluations. The results are shown in Table 1-2.

[0067] Example 7 A block copolymer (I) composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) was synthesized in the same manner as in Example 1, except that "Neopelex G-15" (manufactured by Kao Corporation) was used as the dispersant and the content of dispersant (II) relative to the block copolymer (I) was changed. An emulsion was then obtained. The obtained emulsion was subjected to the above-described measurements and evaluations. The results are shown in Table 1-2.

[0068] [Example 8] An emulsion was obtained in the same manner as in Example 1, except that the operation of heating the dispersion to remove toluene was not performed. The obtained emulsion was subjected to the above-mentioned measurements and evaluations. The results are shown in Table 1-2.

[0069] Example 9 A block copolymer (I) composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) was synthesized in the same manner as in Example 1, except that succinic acid was used instead of adipic acid, the number average molecular weight of the structural units (B) was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units (b), and the content of dispersant (II) relative to the block copolymer (I) was changed. The obtained emulsion was then subjected to the aforementioned measurements and evaluations. The results are shown in Table 1-2.

[0070] Example 10 A block copolymer (I) composed of block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b) 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, the number average molecular weight of the structural units (B) was adjusted by adjusting the reaction time during synthesis of the polymer composed of structural units (B') mainly composed of polyester units (b), and the content of dispersant (II) relative to the block copolymer (I) was changed. An emulsion was then obtained. The obtained emulsion was subjected to the aforementioned measurements and evaluations. The results are shown in Table 1-2.

[0071] Comparative Example 1: 0.1% by mass of tin octoate was added to L-lactide at 200°C, and the reaction was continued until the molecular weight reached 40,000, yielding polylactic acid. A polymer solution of the resulting polylactic acid dissolved in dichloromethane at a concentration of 20% by mass was mixed with an aqueous solution of dispersant (II) "Neopelex G-15" (manufactured by Kao Corporation) dissolved in water, with the dispersant (II) content at 5 phr relative to the polylactic acid and a solid content of 10% by mass, to yield 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 38°C, and the dichloromethane was removed by appropriately blowing nitrogen into the gas phase of the generated dichloromethane vapor, yielding an emulsion containing polylactic acid and a dispersant. The resulting emulsion was subjected to the aforementioned measurements and evaluations. The results are shown in Table 2. The obtained emulsion had poor biodegradability, which is thought to be because the polylactic acid did not contain the structural unit (B).

[0072] Comparative Example 2 An attempt was made to produce an emulsion in the same manner as in Example 1, except that no dispersant was used. However, the block copolymer could not be dispersed to form an emulsion, the particle size could not be measured, and the dispersion stability was poor.

[0073]

[0074]

[0075]

[0076] The compounds represented by the abbreviations in Tables 1-1, 1-2 and 2 are as follows: PLLA: poly-L-lactic acid MPD: 3-methyl-1,5-pentanediol DEPD: 2,4-diethyl-1,5-pentanediol MPDiol: 2-methyl-1,3-propanediol AA: adipic acid SA: succinic acid

[0077] As shown in the examples, the emulsion of this embodiment, which contains a block copolymer (I) including block structural units (A) mainly composed of polylactic acid units (a) and block structural units (B) mainly composed of polyester units (b), and a dispersant (II), has good biodegradability. Therefore, the emulsion of this embodiment is highly useful industrially.

Claims

1. An emulsion containing a block copolymer (I) and a dispersant (II), An emulsion, wherein the block copolymer (I) 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.

2. 2. The emulsion according to claim 1, wherein the block copolymer (I) is present in an amount of 50% by mass or more and 99% by mass or less relative to 100% by mass of the total of the block copolymer (I) and the dispersant (II).

3. The polyester unit (b) contains a unit derived from an aliphatic diol (b1) and an aliphatic dicarboxylic acid (b2), The emulsion according to claim 1 or 2, wherein the aliphatic diol (b1) is a diol having an alkyl group as a branched chain.

4. The emulsion according to claim 3 , wherein the aliphatic diol (b1) has 10 or less carbon atoms.

5. The emulsion according to claim 3 , wherein the aliphatic diol (b1) has 5 or more carbon atoms.

6. The emulsion according to claim 3 , wherein the branched chain of the aliphatic diol (b1) is a methyl group.

7. 3. The emulsion according to claim 1, wherein the block structural unit (A) accounts for 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).

8. The emulsion according to claim 1 or 2, wherein the dispersant (II) is a vinyl alcohol polymer.

9. 3. The emulsion according to claim 1, wherein the particle size is from 100 to 1,000 nm.

10. A method for producing the emulsion according to claim 1 or 2, comprising the steps of: A method for producing an emulsion, comprising a step of dispersing the block copolymer (I) dissolved in an organic solvent in an aqueous medium in the presence of the dispersant (II).

11. The method for producing an emulsion according to claim 10, further comprising the step of removing the organic solvent.