JP2007204672A - Poly(hydroxycarboxylic acid) fine particles and process for production thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide poly(hydroxycarboxylic acid) spherical fine particles derived from regeneratable vegetable sources, excellent in biocompatibility and suitable for cosmetics and a process for their production. <P>SOLUTION: The poly(hydroxycarboxylic acid) spherical fine particles have an average particle size of 0.1-100 μm and are surface coated with silicone oil. The poly(hydroxycarboxylic acid) spherical fine particles are produced by the dispersion polymerization of a 10-50 mass% of a cyclic ester monomer relative to 100 mass% of the total amount of the heating medium and the monomer at temperatures from 100°C to the melting point of poly(hydroxycarboxylic acid) in the silicone oil heating medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to poly (hydroxycarboxylic acid) fine particles whose surface is coated with silicone oil and a method for producing the same.

  Nylon 12 spherical fine particles generally used as a cosmetic base are produced by a suspension anionic polymerization method. However, in this method, it is necessary to use a paraffinic heat medium and an alkali catalyst, and the heat medium is removed after the completion of the polymerization, and further, an extraction operation with an organic solvent is necessary. It was. Furthermore, it was necessary to add silicone oil again in order to improve the slipperiness of the fine particles (Patent Documents 1 and 2). On the other hand, polymethylmethacrylate spherical fine particles are produced at a relatively low cost. However, since the raw material is derived from petroleum resources, there is a risk of depletion and a problem that causes global warming.

  Poly (hydroxycarboxylic acid) typified by polylactic acid has been cited as a renewable plant resource-derived resin that does not depend on petroleum resources as a raw material, and has attracted much attention in recent years. Regarding the production method of polylactic acid spherical fine particles, polylactic acid microcapsules by the in-liquid drying method (solvent evaporation method) have been known (Non-patent Document 1). There was a safety problem. Further, there is a method (Patent Document 3) in which a polylactic acid resin is melt-kneaded with polyacrylic acid or the like and re-precipitated in water, but acrylic odor is a problem.

  Further, although dispersion polymerization using a 1,4-dioxane / heptane mixed solvent as a heat medium (Non-patent Document 2) has been studied, the use of an organic solvent has been a problem. Furthermore, although dispersion polymerization using non-critical carbon dioxide as a heat medium (Non-patent Document 3) has been studied, a special reaction vessel is required, which is a problem in terms of versatility and mass productivity.

Japanese Patent Publication No. 7-17833 JP 2002-220474 A Japanese Patent Laid-Open No. 2005-200663 Hideto Tsuji, Yoshito Tsuji, "Polylactic acid-for medical treatment, pharmaceutical preparation, and environment", pages 24-25, Polymer publication society, 1997 Macromolecules, 1996, 29, 13, p. 4556 Macromolecules, 2003, 36, 16, p. 5908

  The present invention is intended to solve the above-mentioned problems, and is a poly (hydroxycarboxylic acid) spherical fine particle derived from a renewable plant resource, excellent in biocompatibility, and suitable for cosmetics, etc. Is to provide fine particles coated with silicone oil.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention obtained homogeneous spherical fine particles such as polylactic acid by carrying out dispersion polymerization of lactide or the like in a silicone oil heat medium, and the heat medium. It has been found that the separation operation is extremely easy, and it is not necessary to add silicone oil separately to improve the slipperiness. That is, the gist of the present invention is as follows.

[1] Poly (hydroxycarboxylic acid) spherical fine particles having an average particle diameter of 0.1 to 100 μm and a surface coated with silicone oil.
[2] A cosmetic base material using the poly (hydroxycarboxylic acid) spherical fine particles according to [1]. [3] 10 to 50% by mass of cyclic ester monomer in a silicone oil heating medium at a temperature not lower than 100 ° C. and not higher than the melting point of poly (hydroxycarboxylic acid) with respect to 100% by mass of the total amount of the heating medium and monomer. A method for producing poly (hydroxycarboxylic acid) spherical fine particles, wherein the polymer is dispersed and polymerized.
[4] The method for producing poly (hydroxycarboxylic acid) spherical fine particles according to [3], wherein after the synthesis of the poly (hydroxycarboxylic acid) fine particles, the separation operation from the heat medium is performed only by filtration.

  According to the poly (hydroxycarboxylic acid) spherical fine particles of the present invention, since the surface is coated with silicone oil, there is no need to separately add silicone oil for the purpose of improving slipperiness when used for cosmetics and the like. Is economical. The polylactic acid and polyglycolic acid of the present invention are derived from plant resources and have good biocompatibility. Furthermore, lactic acid and glycolic acid, which are hydrolysates thereof, are known to have a high whitening effect due to the suppression of tyrosinase production in lactic acid, and glycolic acid has a skin peeling effect and is suitable for cosmetic use. ing.

  According to the production method of the present invention, since the separation operation of the obtained spherical fine particles can be only filtration, the operation is simple.

  Hereinafter, the present invention will be described in detail.

  As the poly (hydroxycarboxylic acid) constituting the poly (hydroxycarboxylic acid) spherical fine particles of the present invention, poly (L-lactic acid), poly (D-lactic acid), from the viewpoint of heat resistance, biocompatibility and plant origin, Examples include poly (glycolic acid) and copolymers or mixtures thereof, with poly (L-lactic acid) being most preferred. Other polymer components may be copolymerized or mixed in a small amount, but the melting point (Tm) is preferably 120 ° C. or higher. When Tm is less than 120 ° C., fusion between fine particles in the drying step or the like may be a problem. The melting points of the homopolymers of polylactic acid and polyglycolic acid are about 180 ° C. and about 230 ° C., respectively.

  Specific examples of the cyclic ester monomer that is a raw material for the poly (hydroxycarboxylic acid) resin of the present invention include cyclic dimer esters of hydroxycarboxylic acids such as L-lactide, D-lactide, and glycolide. Other components such as cyclic esters and cyclic ester-ethers may be used in small amounts.

  The weight average molecular weight of the poly (hydroxycarboxylic acid) resin is preferably 10,000 or more, and more preferably 20,000 or more. When the weight average molecular weight is less than 10,000, there are problems such that the fine particles become brittle and are easily hydrolyzed. The upper limit of the weight average molecular weight is not particularly limited, and in some cases, the molecular weight may be increased by a crosslinking agent or a chain extender.

  The surface of the poly (hydroxycarboxylic acid) spherical fine particles of the present invention is coated with silicone oil. Those that are not coated with silicone oil are uneconomical because it is necessary to add silicone oil separately when used in applications requiring slipperiness such as cosmetics.

  The silicone oil coated on the surface of the poly (hydroxycarboxylic acid) spherical fine particles is preferably represented by the following formula (1) or (2).

Wherein R ₁ is an alkyl group having 1 to 6 carbon atoms, R ₂ is hydrogen, an alkyl group having 1 to 6 carbon atoms or a phenyl group, R ₃ is an alkyl group having 1 to 6 carbon atoms, and n is 2 or more. number)

(Wherein R ₄ is an alkyl group having 1 to 6 carbon atoms, R ₅ is hydrogen, an alkyl group having 1 to 6 carbon atoms or a phenyl group, and n is a number of 3 or more)

  Specific examples of the silicone oil include polydimethylsiloxane, dimethylsiloxane-methylphenylsiloxane copolymer, cyclic dimethylsiloxane, and epoxy-modified silicone oil, carboxyl-modified silicone oil, methacryl-modified silicone oil, alcohol-modified silicone oil, and mercapto-modified silicone. Examples thereof include modified silicone oils such as oil, vinyl-modified silicone oil, amino-modified silicone oil, polyether-modified silicone oil, higher fatty acid-modified silicone oil, and terminal-reactive silicone oil. Of these, polydimethylsiloxane, dimethylsiloxane-methylphenylsiloxane copolymer, and cyclic dimethylsiloxane are preferably used.

  The poly (hydroxycarboxylic acid) spherical fine particles of the present invention must have a particle size in the range of 0.1 to 100 μm, and a preferred range is 10 to 50 μm. If it is less than 0.1 μm, the fluidity of the fine particles is lowered, and if it exceeds 50 μm, it may cause graininess such as roughness.

  The poly (hydroxycarboxylic acid) spherical fine particles of the present invention can be produced, for example, by subjecting a cyclic ester monomer to dispersion polymerization in a silicone oil heat medium.

  The polymerization temperature needs to be 100 ° C. or higher and Tm or lower of the poly (hydroxycarboxylic acid) to be generated. If it is lower than 100 ° C., the polymerization reaction itself is slow, and there are problems such as low yield and low productivity, which is not preferable. If it is higher than Tm, poly (hydroxycarboxylic acid) fine particles are hardly formed, which is not preferable. A suitable reaction temperature is 100 ° C. or more and (Tm−10) ° C. or less, more preferably 120 ° C. or more and (Tm−20) ° C. or less.

The amount of the cyclic ester monomer in the dispersion polymerization needs to be 10 to 50% by mass, preferably 15 to 35% by mass with respect to 100% by mass of the total amount of the heat medium and the monomer. If the amount is less than 10% by mass, the yield decreases. On the other hand, if the amount exceeds 40% by mass, the poly (hydroxycarboxylic acid) tends to be in the form of a mass rather than a fine particle.

  The silicone oil used as the heat medium is preferably one represented by the above formula (1) or (2). Specific examples thereof include polydimethylsiloxane, dimethylsiloxane-methylphenylsiloxane copolymer, cyclic Dimethylsiloxane, epoxy-modified silicone oil, carboxyl-modified silicone oil, methacryl-modified silicone oil, alcohol-modified silicone oil, mercapto-modified silicone oil, vinyl-modified silicone oil, amino-modified silicone oil, polyether-modified silicone oil, higher fatty acid-modified silicone oil And modified silicone oils such as terminal-reactive silicone oils. Of these, polydimethylsiloxane, dimethylsiloxane-methylphenylsiloxane copolymer, and cyclic dimethylsiloxane are preferably used.

The kinematic viscosity of the silicone oil heat transfer medium is preferably 1-1000 mm ² / s (cSt) (25 ° C.), more preferably 20-200 mm ² / s (cSt) (25 ° C.). When the kinematic viscosity is less than 1 mm ² / s, the resulting poly (hydroxycarboxylic acid) spherical fine particles have a too small particle size, which is undesirable from the viewpoint of fluidity and the like. A kinematic viscosity exceeding 1000 mm ² / s is not preferable because it makes it difficult to isolate the poly (hydroxycarboxylic acid) spherical fine particles.

  The boiling point of the silicone oil heating medium is preferably 150 ° C. or higher, more preferably 180 ° C. or higher, and further preferably 200 ° C. or higher. When the boiling point is less than 150 ° C., it is necessary to lower the polymerization temperature, and there is a problem that the polymerization rate becomes very small.

  As the catalyst used in the present invention, a general cyclic ester ring-opening polymerization catalyst or transesterification catalyst is used. Specifically, tin-based catalysts such as tin octylate, tin dimethylmaleate, tin lactate, tin dilaurate, tin distearate, and tin powder, aluminum trisacetylacetonate, aluminum triisopropoxide, aluminum-salen type complex , Etc., tetraisopropyl titanate, tetrabutyl titanate, antimony oxide, germanium oxide, zinc acetate, etc. are used, and tin and aluminum catalysts are particularly preferably used. The addition amount of the catalyst is preferably 0.01 to 0.5 parts by mass, more preferably 0.02 to 0.2 parts by mass with respect to 100 parts by mass of the cyclic ester monomer.

  As the polymerization apparatus, any apparatus capable of stirring and temperature control may be used. What is equipped with the stirring blade, the raw material inlet, and the product discharge outlet is preferable.

  The stirring speed in the dispersion polymerization of the present invention differs depending on the polymerization apparatus and the shape of the stirring blade and cannot be clearly defined, but is preferably 10 to 1,000 rpm, more preferably 20 to 500 rpm. If the stirring speed is less than 10 rpm, agglomerates may be generated, and if it exceeds 1,000 rpm, the particle size of the produced poly (hydroxycarboxylic acid) spherical fine particles may be too small, and the fluidity as a cosmetic may be reduced. Absent.

In the production method of the present invention, when the kinematic viscosity of the silicone oil heat medium is low, for example, when the kinematic viscosity of the silicone oil is 20 mm ² / s or less, it is preferable to use a dispersion stabilizer. If the dispersion stabilizer is not used, the produced resin may be agglomerated.

As the dispersion stabilizer, polysiloxane-b-poly (hydroxycarboxylic acid) diblock copolymer represented by the following formula (3), or poly (hydroxycarboxylic acid)-represented by the following formula (4): A b-polysiloxane-b-poly (hydroxycarboxylic acid) triblock copolymer is preferably used.

(In the formula, R ₆ is an aliphatic hydrocarbon having 1 to ₆ carbon atoms, R ₇ is hydrogen, an aliphatic hydrocarbon or aromatic hydrocarbon having 1 to 6 carbon atoms, and R ₈ is an alkyl group having 2 to 6 carbon atoms. Or an alkylene ether group, R ₉ is an alkyl group having 1 to 5 carbon atoms, R ₁₀ is hydrogen or an alkyl group or alkyloyl group having 1 to 20 carbon atoms, n is a number from 10 to 200, x is a number from 10 to 400, n / x is in the range of 1/4 to 4/1)

Wherein R ₁₁ is an aliphatic hydrocarbon having 1 to 6 carbon atoms, R ₁₂ is hydrogen or an aliphatic hydrocarbon or aromatic hydrocarbon having 1 to 6 carbon atoms, and R ₁₃ and R ₁₄ are 2 to 6 carbon atoms. Alkyl group or alkylene ether group, R ₁₅ is an alkyl group having 1 to 5 carbon atoms, R ₁₆ is hydrogen or an alkyl group or alkyloyl group having 1 to 20 carbon atoms, n is a number from 10 to 200, and x and y are 10 Number of ~ 200, n / x and n / y are in the range of 1/2 to 8/1)

  As a method for synthesizing the above diblock copolymer or triblock copolymer, a polysiloxane containing a hydroxyl group at one or both ends is used as a starting species, and cyclic dimer esters of hydroxycarboxylic acid or various lactones are opened. Examples thereof include a ring polymerization method and a polycondensation of a polysiloxane containing a hydroxyl group at one or both ends with a hydroxycarboxylic acid.

  In the synthesis step of the diblock copolymer or triblock copolymer, a hydroxyl group is present at one or both ends, but by adding a compound that reacts with a hydroxyl group such as acetic acid chloride or benzoic acid chloride, the end blocking is performed. It can also be used.

  From the viewpoint of the dispersion stabilizing effect, the poly (hydroxycarboxylic acid) monomer component constituting the dispersion stabilizer is preferably the same component as the constituent component of poly (hydroxycarboxylic acid) constituting the spherical fine particles. The main chain skeleton of the polysiloxane component constituting the dispersion stabilizer is preferably the same as the main chain skeleton of the silicone oil used for the heat medium.

  In the production method of the present invention, the produced poly (hydroxycarboxylic acid) spherical fine particles are filtered off from the silicone oil heating medium after the completion of the polymerization. As a filtration separation method, usual solid-liquid separation methods such as centrifugal separation, normal pressure and pressure filtration, and suction filtration can be adopted, and in particular, centrifugal separation is preferably used. As described above, in the present invention, the separation can be performed only by filtration.

  As long as the characteristics of the poly (hydroxycarboxylic acid) spherical fine particles of the present invention are not greatly impaired, pigments, heat stabilizers, antioxidants, weathering agents, plasticizers, lubricants, mold release agents, antistatic agents, fillers Etc. can also be added. As heat stabilizers and antioxidants, for example, hindered phenols, phosphorus compounds such as phosphites, hindered amines, sulfur compounds and the like can be used. Fillers include mica, talc, calcium carbonate, zinc carbonate, silica, alumina, zinc oxide, magnesium oxide, sodium aluminate, calcium aluminate, sodium aluminosilicate, calcium silicate, magnesium silicate, layered silicate, wollastonite , Hydrotalcite, zeolite and the like.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples. The measuring methods used for evaluating the examples and comparative examples are as follows.
(1) Molecular weight measurement: Using a GPC apparatus LC-VP manufactured by Shimadzu Corporation, measurement was performed at an eluent tetrahydrofuran, a temperature of 40 ° C., and a flow rate of 1 mL / min, and evaluated in terms of polystyrene.
(2) Particle shape: Scanning electron microscope observation was performed, a visual field in which 20 or more particles were present was selected, and the ratio of the minor axis / major axis of each particle was calculated. Next, an average value for 20 minor axis / major axis ratios was obtained. A sample having this ratio of 0.9 to 1.0 was rated ◎, a sample having a ratio of 0.7 or more and less than 0.9 was evaluated as ○, and a sample having a ratio of less than 0.7 was evaluated as ×. Moreover, what became the lump shape without making the form of particle | grains was set to xx. Those of 0.7 or more (以上 or ○) were accepted.
(3) Average particle diameter: An individual particle obtained by performing observation with a scanning electron microscope, selecting a visual field in which 20 or more particles exist, and measuring and averaging the major axis and minor axis of 20 particles on the image. The average value of 20 particles was defined as the average particle size.

The structural formula of each silicone oil used in the following synthesis examples, examples and comparative examples is shown.
<KF-6003>

(In the formula, Ra is an alkylene group or alkylene ether group having 2 to 6 carbon atoms, n = about 60)

<X22-170DX>

(Wherein Rb is an alkylene group or alkylene ether group having 2 to 6 carbon atoms, n = about 60)

<KF-995>
(Kinematic viscosity = 4 mm ² / s)
(Where n = 5)

<KF-56>
(Kinematic viscosity = 15 mm ² / s)
(Where n = m = 5-10)

<KF-96>
(Kinematic viscosity = 100 mm ² / s)
(Where n = about 60)

Synthesis example 1
60 g of both-end hydroxyl group-modified silicone oil (KF-6003 made by Shin-Etsu Silicone) and 40 g of L-lactide (Musashino Chemicals, D-form content 0.1 mol%) were charged into a polymerization apparatus equipped with a stirring blade, After the nitrogen substitution, the temperature increase was started. When the internal temperature reached 180 ° C., 0.02 g of tin octylate was added to initiate polymerization. After 1 hour, the system was depressurized to remove residual lactide. The number average molecular weight of the obtained copolymer was 8,500.

Synthesis example 2
10 g of the polylactic acid-polysiloxane-polylactic acid triblock copolymer obtained in Synthesis Example 1 was dissolved in 100 mL of methylene chloride, and acetyl chloride was added dropwise thereto to acetylate the terminal hydroxyl group.

Synthesis example 3
60 g of one-end hydroxyl group-modified silicone oil (X22-170DX made by Shin-Etsu Silicone) and 40 g of L-lactide (made by Musashino Chemical Co., D mol content 0.1 mol%) were charged into a polymerization apparatus equipped with a stirring blade, After the nitrogen substitution, the temperature increase was started. When the internal temperature reached 180 ° C., 0.02 g of tin octylate was added to initiate polymerization. After 1 hour, the system was depressurized to remove residual lactide. The number average molecular weight of the obtained copolymer was 8,300.

  The presumed structural formula of each block copolymer obtained by the synthesis examples 1-3 is shown.

(Synthesis Example 1)
(In the formula, Ra is an alkylene group or alkylene ether group having 2 to 6 carbon atoms, n = about 60, x, y = average about 20)

(Synthesis Example 2)
(In the formula, Ra is an alkylene group or alkylene ether group having 2 to 6 carbon atoms, n = about 60, x, y = average about 20)

(Synthesis Example 3)
(Wherein Rb is an alkylene group or alkylene ether group having 2 to 6 carbon atoms, n = about 60, x = average about 40)

Example 1
80 g of silicone oil (KF-995 made by Shin-Etsu Silicone, kinematic viscosity 4 mm ² / s), 20 g of L-lactide (made by Musashino Chemical Co., D mol content 0.1 mol%) and 1 g of the dispersion stabilizer obtained in Synthesis Example 1 The mixture was charged into a three-necked flask equipped with a stirring blade and a reflux tube, and the system was purged with nitrogen. When the internal temperature reached 150 ° C. and the contents were dissolved, 0.02 g of tin octylate was added to initiate polymerization. When the polymerization reaction reached almost equilibrium after 2 hours, the reaction solution was filtered as it was. The other evaluation results are shown in Table 1.

Examples 2-5, Comparative Examples 1-3
Polymerization was performed in the same manner as in Example 1 under the conditions shown in Table 1. The evaluation results are also shown in Table 1.

As shown in Table 1, spherical polylactic acid fine particles were obtained in all of Examples 1 to 5. In addition, when the surface of these fine particles was washed with n-hexane and the washing solution was subjected to ¹ H-NMR measurement, a peak derived from silicone oil was observed. Therefore, it was confirmed that the fine particle surface was covered with silicone oil. Note that there was no change in the shape of the fine particles before and after washing.

On the other hand, in Comparative Example 1, spherical particles were not generated because there was no dispersion stabilizer despite the fact that the silicone oil had a low kinematic viscosity. In Comparative Example 2, since the amount of the cyclic ester monomer was high, the obtained resin was agglomerated and spherical fine particles were not obtained. In Comparative Example 3, the yield was remarkably reduced because the amount of the cyclic ester monomer was low.

2 is a scanning electron micrograph of polylactic acid fine particles obtained in Example 2. FIG. 3 is a scanning electron micrograph of polylactic acid fine particles obtained in Comparative Example 1. FIG.

Claims (8)

Poly (hydroxycarboxylic acid) spherical fine particles having an average particle diameter of 0.1 to 100 μm and a surface coated with silicone oil. The poly (hydroxycarboxylic acid) spherical fine particles according to claim 1, wherein the silicone oil is a silicone oil represented by the following general formula (1) or (2).
Wherein R ₁ is an alkyl group having 1 to 6 carbon atoms, R ₂ is hydrogen, an alkyl group having 1 to 6 carbon atoms or a phenyl group, R ₃ is an alkyl group having 1 to 6 carbon atoms, and n is 2 or more. number)
(Wherein R ₄ is an alkyl group having 1 to 6 carbon atoms, R ₅ is hydrogen, an alkyl group having 1 to 6 carbon atoms or a phenyl group, and n is a number of 3 or more) A cosmetic base material using the poly (hydroxycarboxylic acid) spherical fine particles according to claim 1 or 2. In a silicone oil heating medium, dispersion polymerization of 10 to 50% by weight of cyclic ester monomer is carried out at a temperature not lower than 100 ° C. and not higher than the melting point of poly (hydroxycarboxylic acid) with respect to 100% by weight of the total amount of heating medium and monomer. A method for producing poly (hydroxycarboxylic acid) spherical fine particles characterized by comprising: The method for producing poly (hydroxycarboxylic acid) spherical fine particles according to claim 4, wherein the cyclic ester monomer is L-lactide, D-lactide, glycolide, or a mixture thereof. 6. The method for producing poly (hydroxycarboxylic acid) spherical fine particles according to claim 4, wherein the heat medium is a silicone oil represented by the general formula (1) or (2). It is a manufacturing method of the poly (hydroxycarboxylic acid) spherical fine particle in any one of Claims 4-6, Comprising: The triblock copolymer represented by General formula (3) as a dispersion stabilizer, or General formula (4) A method for producing poly (hydroxycarboxylic acid) spherical fine particles characterized by using a diblock copolymer represented by the formula:
(In the formula, R ₆ is an aliphatic hydrocarbon having 1 to ₆ carbon atoms, R ₇ is hydrogen, an aliphatic hydrocarbon or aromatic hydrocarbon having 1 to 6 carbon atoms, and R ₈ is an alkyl group having 2 to 6 carbon atoms. Or an alkylene ether group, R ₉ is an alkyl group having 1 to 5 carbon atoms, R ₁₀ is hydrogen or an alkyl group or alkyloyl group having 1 to 20 carbon atoms, n is a number from 10 to 200, x is a number from 10 to 400, n / x is 1
/ 4 to 4/1 range)
Wherein R ₁₁ is an aliphatic hydrocarbon having 1 to 6 carbon atoms, R ₁₂ is hydrogen or an aliphatic hydrocarbon or aromatic hydrocarbon having 1 to 6 carbon atoms, and R ₁₃ and R ₁₄ are 2 to 6 carbon atoms. Alkyl group or alkylene ether group, R ₁₅ is an alkyl group having 1 to 5 carbon atoms, R ₁₆ is hydrogen or an alkyl group or alkyloyl group having 1 to 20 carbon atoms, n is a number from 10 to 200, and x and y are 10 Number of ~ 200, n / x and n / y are in the range of 1/2 to 8/1) The method for producing poly (hydroxycarboxylic acid) spherical fine particles according to any one of claims 4 to 7, wherein after the synthesis of the poly (hydroxycarboxylic acid) fine particles, the separation operation from the heat medium is performed only by filtration.