阅读说明：本技术 乙酸纤维素粒子、化妆品组合物、以及乙酸纤维素粒子的制造方法 (Cellulose acetate particle, cosmetic composition, and method for producing cellulose acetate particle ) 是由 小林慧子 大村雅也 于 2019-02-06 设计创作，主要内容包括：本发明的目的在于提供一种生物分解性及触感优异的微粒。本发明涉及的乙酸纤维素粒子的平均粒径为80nm以上且100μm以下,且正球度为0.7以上且1.0以下、表面平滑度为80％以上且100％以下,所述乙酸纤维素的乙酰基总取代度为0.7以上且2.9以下。(The purpose of the present invention is to provide microparticles having excellent biodegradability and excellent tactile sensation. The cellulose acetate particles according to the present invention have an average particle diameter of 80nm or more and 100 μm or less, a normal sphericity of 0.7 or more and 1.0 or less, a surface smoothness of 80% or more and 100% or less, and a total degree of substitution with acetyl groups of 0.7 or more and 2.9 or less.)

1. Cellulose acetate particles having an average particle diameter of 80nm to 100 μm, a positive sphericity of 0.7 to 1.0, and a surface smoothness of 80% to 100%,

the cellulose acetate has a total degree of substitution of acetyl groups of 0.7 to 2.9.

2. The cellulose acetate particle according to claim 1,

the cellulose acetate has a total degree of substitution of acetyl groups of 2.0 or more and less than 2.6.

3. The cellulose acetate particle according to claim 1 or 2,

the cellulose acetate particles contain a plasticizer and,

the content of the plasticizer is 2 to 40 wt% based on the weight of the cellulose acetate particles.

4. The cellulose acetate particle according to claim 3,

the plasticizer is at least 1 or more selected from citric acid plasticizer, glyceride plasticizer, adipic acid plasticizer, and phthalic acid plasticizer.

5. A cosmetic composition comprising the cellulose acetate particles according to any one of claims 1 to 4.

6. A method for producing cellulose acetate particles, comprising:

a step for obtaining a cellulose acetate impregnated with a plasticizer by mixing a cellulose acetate having a total acetyl substitution degree of 0.7 to 2.9 with the plasticizer;

a step in which the cellulose acetate impregnated with the plasticizer and a water-soluble polymer are kneaded at 200 ℃ to 280 ℃ to obtain a dispersion in which the cellulose acetate impregnated with the plasticizer is a dispersoid; and

and a step of removing the water-soluble polymer from the dispersion.

7. The method for producing cellulose acetate particles according to claim 6,

the mixing comprises the following steps: the cellulose acetate and the plasticizer are mixed at a temperature of 20 ℃ or higher and less than 200 ℃ and then melt-kneaded.

8. The method for producing cellulose acetate particles according to claim 6 or 7,

the plasticizer is at least 1 or more selected from citric acid plasticizer, glyceride plasticizer, adipic acid plasticizer, and phthalic acid plasticizer.

9. The method for producing cellulose acetate particles according to claim 6 or 7,

the plasticizer is at least 1 selected from triethyl citrate, acetyl tributyl citrate, triacetin and diisononyl adipate.

10. The method for producing cellulose acetate particles according to claim 6 or 7,

the plasticizer is at least 1 selected from acetyl triethyl citrate, triacetin, diacetin and diethyl phthalate.

11. The method for producing cellulose acetate particles according to any one of claims 6 to 10, wherein,

the water-soluble polymer is polyvinyl alcohol or thermoplastic starch.

Technical Field

The present invention relates to cellulose acetate particles, a cosmetic composition, and a method for producing cellulose acetate particles.

Background

In the past, various kinds of polymer fine particles have been proposed according to the application. For example, the purpose of fine particles contained in cosmetics is also various. The purpose of containing fine particles in cosmetics is: improving the extensibility of the cosmetic; imparting a change to the feel; imparting a wrinkle-lightening effect; and improving smoothness of foundation and the like.

In particular, fine particles having a high sphericity have excellent touch feeling, and can obtain a light scattering (soft focus) effect depending on the physical properties and shape thereof. When such fine particles are used for foundation or the like, effects of filling in the unevenness of the skin to make it smooth and making wrinkles or the like inconspicuous (soft focus) by scattering light in various directions can be expected.

For the purpose and effect of such cosmetics, fine particles having a narrow particle size distribution and a high sphericity are required as fine particles to be blended in the cosmetics, and as such fine particles, fine particles made of polyamide such as nylon 12, or synthetic polymer such as polymethyl methacrylate (PMMA) or Polystyrene (PS) have been proposed.

However, since the fine particles formed of these synthetic polymers have a specific gravity of 1 or less, are light, and have a small particle diameter, they tend to float in water and cannot be removed by a drainage facility, and sometimes they flow into a river directly or further into the sea through a river. Therefore, there is a problem that the sea and the like are contaminated with particles formed of these synthetic polymers.

Further, since the fine particles formed of these synthetic polymers have a property of adsorbing a trace amount of chemical pollutants in the environment, there is a possibility that plankton and fish ingest the fine particles adsorbing the chemical pollutants and may also have adverse effects on the human body, and various effects may be exerted.

In view of such a risk, attempts have been made to replace synthetic polymer fine particles for various uses with particles having biodegradability.

A representative biodegradable resin includes cellulose acetate. Cellulose acetate is excellent in that it can be obtained from natural materials such as wood, cotton, etc. which do not compete with food and feed. It would therefore be beneficial if particles of synthetic polymer could be replaced by particles of cellulose acetate. However, polymers applicable to a method for producing synthetic polymer microparticles are limited, and it is difficult to apply the polymers to the production of cellulose acetate microparticles.

Patent document 1 describes a method including: forming a polysaccharide ester product comprising a polysaccharide ester and a solvent by polysaccharide synthesis; diluting the polysaccharide ester product to obtain a polysaccharide ester coating; and forming a plurality of polysaccharide ester microspheres from the polysaccharide ester coating. Among them, cosmetic compositions are exemplified as articles that can contain polysaccharide ester microspheres.

Patent document 2 describes a cellulose acylate having a volume average particle diameter D50 of 72 μm or more and 100 μm or less, a polymerization degree of 131 or more and 350 or less, and a substitution degree of 2.1 or more and 2.6 or less, which are measured by a laser diffraction particle size distribution measuring apparatus, and a method for producing the cellulose acylate preferably including the following steps: an acylation step of acylating cellulose in the presence of sulfuric acid; and a deacylation step of deacylating the acylated cellulose in a polar solvent in the presence of acetic acid.

Patent document 3 describes that a molded article (for example, a porous body or spherical particles) composed of a resin component (a) is produced by kneading the resin component (a) such as a thermoplastic resin and a water-soluble auxiliary component (B) to prepare a dispersion and eluting the auxiliary component (B) from the dispersion; as the resin component (a), cellulose derivatives such as cellulose acetate are described.

Disclosure of Invention

Problems to be solved by the invention

However, the polysaccharide ester microspheres of patent document 1 are porous particles having a large particle diameter and a wide particle size distribution, and are not sufficient as a substitute for synthetic polymer microparticles blended in cosmetics and the like. Cellulose acylate obtained by the production method described in patent document 2 is also porous particles having an irregular shape. The granular molded body obtained by the production method described in patent document 3 is also a granular body having a low spherical shape and a substantially spherical shape.

The purpose of the present invention is to provide microparticles having excellent biodegradability and tactile sensation.

Means for solving the problems

The first aspect of the present invention relates to cellulose acetate particles having an average particle diameter of 80nm or more and 100 μm or less, a positive sphericity of 0.7 or more and 1.0 or less, a surface smoothness of 80% or more and 100% or less, and a total degree of substitution of acetyl groups of the cellulose acetate of 0.7 or more and 2.9 or less.

In the cellulose acetate particle, the total degree of substitution with acetyl groups of the cellulose acetate may be 2.0 or more and less than 2.6.

The cellulose acetate particles may contain a plasticizer, and the content of the plasticizer is 2 wt% or more and 40 wt% or less with respect to the weight of the cellulose acetate particles.

In the cellulose acetate particles, the plasticizer may be at least 1 or more selected from the group consisting of a citric acid plasticizer, a glycerin ester plasticizer, an adipic acid plasticizer, and a phthalic acid plasticizer.

The second aspect of the present invention relates to a cosmetic composition containing the above cellulose acetate particles.

A third aspect of the present invention relates to a method for producing cellulose acetate particles, the method comprising: a step for obtaining a cellulose acetate impregnated with a plasticizer by mixing a cellulose acetate having a total degree of substitution with acetyl groups of 0.7 to 2.9 with the plasticizer; a step of kneading the plasticizer-impregnated cellulose acetate and a water-soluble polymer at 200 ℃ to 280 ℃ to obtain a dispersion in which the plasticizer-impregnated cellulose acetate is a dispersoid; and a step of removing the water-soluble polymer from the dispersion.

In the method for producing cellulose acetate particles, the mixing may include: the cellulose acetate and the plasticizer are mixed at a temperature of 20 ℃ or higher and less than 200 ℃ and then melt-kneaded.

In the method for producing cellulose acetate particles, the plasticizer may be at least 1 or more selected from the group consisting of a citric acid plasticizer, a glycerin ester plasticizer, an adipic acid plasticizer, and a phthalic acid plasticizer.

In the above method for producing cellulose acetate particles, the plasticizer may be at least 1 or more selected from the group consisting of triethyl citrate, acetyl tributyl citrate, triacetin, and diisononyl adipate.

In the method for producing cellulose acetate particles, the plasticizer may be at least 1 or more selected from the group consisting of acetyl triethyl citrate, triacetin, diacetin, and diethyl phthalate.

In the method for producing cellulose acetate particles, the water-soluble polymer may be polyvinyl alcohol or thermoplastic starch.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, fine particles having excellent biodegradability and excellent tactile sensation can be provided.

Drawings

Fig. 1 is a diagram illustrating a method of evaluating surface smoothness (%).

Fig. 2 is a diagram illustrating a method of evaluating surface smoothness (%).

Detailed Description

[ cellulose acetate particles ]

The cellulose acetate particles of the present invention have an average particle diameter of 80nm to 100 [ mu ] m, a positive sphericity of 0.7 to 1.0, a surface smoothness of 80% to 100%, and a total degree of substitution of acetyl groups of 0.7 to 2.9.

When the cellulose acetate particles of the present invention have an average particle diameter of 80nm or more and 100 μm or less, the average particle diameter may be 100nm or more, 1 μm or more, 2 μm or more, and 4 μm or more. The particle size may be 80 μm or less, may be 40 μm or less, may be 20 μm or less, and may be 14 μm or less. When the average particle size is too large, the feeling is poor and the light scattering (soft focus) effect is also reduced. In addition, when the average particle size is too small, the production becomes difficult. The texture may be, for example, skin feel and texture when incorporated in a cosmetic composition, in addition to the case where the cellulose acetate particles are directly contacted.

The average particle size can be measured using dynamic light scattering. Specifically, the following is described. First, a sample was prepared by making a pure water suspension of cellulose acetate particles at a concentration of 100ppm using an ultrasonic vibration device. The average particle diameter can be measured by measuring the volume frequency particle size distribution by a laser diffraction method (laser diffraction/scattering particle size distribution measuring device LA-960 "manufactured by horiba, Ltd., ultrasonic treatment for 15 minutes, refractive index (1.500, medium (water; 1.333)).

The coefficient of variation of the particle size of the cellulose acetate particles of the present invention may be 0% to 60%, or 2% to 50%.

The particle diameter variation coefficient (%) can be calculated by the standard deviation of particle diameter/average particle diameter × 100.

The cellulose acetate particle of the present invention may have a positive sphericity of 0.7 or more and 1.0 or less, preferably 0.8 or more and 1.0 or less, and more preferably 0.9 or more and 1.0 or less. When the amount is less than 0.7, the feeling is poor, and for example, when the composition is blended in a cosmetic composition, the skin feeling and soft focus effect are also reduced.

The sphericity can be determined by the following method. Using an image of the particles observed by a Scanning Electron Microscope (SEM), the major and minor diameters of 30 particles selected at random were measured, and the minor diameter/major diameter ratio of each particle was determined, and the average of the minor diameter/major diameter ratio was defined as the sphericity. The closer to 1 the positive sphericity is, the more the ball can be determined to be positive.

When the surface smoothness of the cellulose acetate particle of the present invention is 80% or more and 100% or less, it is preferably 85% or more and 100% or less, and more preferably 90% or more and 100% or less. When the amount is less than 80%, the feeling is poor. The closer to 100%, the more preferable is the touch feeling.

The surface smoothness can be determined by taking a scanning electron micrograph of the particles, observing the irregularities on the particle surface, and based on the area of the recesses,

the cellulose acetate particles of the present invention preferably have a total degree of substitution of acetyl groups of 0.7 or more and 2.9 or less, 0.7 or more and less than 2.6, more preferably 1.0 or more and less than 2.6, still more preferably 1.4 or more and less than 2.6, and most preferably 2.0 or more and less than 2.6.

When the total substitution degree of acetyl groups is less than 0.7, the water solubility is high, and in a step of extracting particles in the production of cellulose acetate particles described later, particularly in a step of removing a water-soluble polymer from a dispersion, cellulose acetate may be easily eluted, and the sphericity of the particles may be reduced, and thus the feel may be poor. On the other hand, if it is larger than 2.9, the biodegradability of the cellulose acetate particles is poor.

The total degree of substitution of acetyl groups in cellulose acetate can be determined by the following method. First, the total degree of substitution with acetyl groups means the sum of the degrees of substitution with acetyl groups at the 2,3, and 6 positions of the glucose ring of cellulose acetate, and the degrees of substitution with acetyl groups at the 2,3, and 6 positions of the glucose ring of cellulose acetate particles can be measured by NMR method according to the method of Otsuka (Tezuka, Carboydr. Res.273,83 (1995)). That is, in pyridine, using propionic anhydride on a sample of cellulose acetateThe free hydroxyl group undergoes propionylation. The obtained sample was dissolved in deuterated chloroform and measured¹³C-NMR spectrum. The carbon signals of acetyl group appear in the order of 2-, 3-and 6-positions from the high magnetic field in the region of 169ppm to 171ppm, and the signals of carbonyl group carbon of propionyl group appear in the same order in the region of 172ppm to 174 ppm. The substitution degrees of the acetyl groups at the 2,3 and 6 positions of the glucose ring in the original cellulose acetate can be determined from the presence ratio of the acetyl group to the propionyl group at each corresponding position. Except that¹³The degree of substitution with acetyl groups may be determined by C-NMR¹H-NMR.

The total degree of substitution with acetyl groups can be determined by converting the degree of acetylation determined by the method of measurement of the degree of acetylation in ASTM D-817-91 (test method for cellulose acetate, etc.) into the following formula. This is the most common method for calculating the degree of substitution of cellulose acetate.

DS＝162.14×AV×0.01/(60.052-42.037×AV×0.01)

In the above formula, DS is the total degree of substitution of acetyl groups, and AV is the degree of acetylation (%). The value of the degree of substitution obtained by conversion usually has a certain error from the above-mentioned NMR measurement value. When the converted value is different from the NMR measurement value, the NMR measurement value is used. In addition, when the values differ depending on the specific method of NMR measurement, the NMR measurement value based on the above-mentioned manual Iuka method was used.

The outline of the method for measuring the degree of acetylation in ASTM D-817-91 (test method for cellulose acetate and the like) is as follows. First, 1.9g of dried cellulose acetate was accurately weighed and dissolved in 150mL of a mixed solution of acetone and dimethyl sulfoxide (volume ratio: 4:1), 30mL of a 1N-sodium hydroxide aqueous solution was added, and the mixture was saponified at 25 ℃ for 2 hours. Phenolphthalein was added as an indicator and the excess sodium hydroxide was titrated with 1N-sulfuric acid (concentration factor: F). In addition, a blank test was performed in the same manner as described above, and the acetylation degree was calculated according to the following formula.

Average degree of acetylation (%) {6.5 × (B-a) × F }/W

In the formula, A represents the titration amount (mL) of 1N-sulfuric acid in the sample, B represents the titration amount (mL) of 1N-sulfuric acid in the blank test, F represents the concentration factor of 1N-sulfuric acid, and W represents the weight of the sample.

The cellulose acetate particle of the present invention may have a bulk specific gravity of 0.1 to 0.9, or 0.5 to 0.9. For example, in the case where the particles are blended in a cosmetic, the higher the bulk specific gravity of the particles, the better the fluidity of the cosmetic composition. The bulk specific gravity can be measured by a method based on JIS K1201-1.

The cellulose acetate particles of the present invention may or may not contain a plasticizer. In the present invention, the plasticizer is a compound which can increase the plasticity of cellulose acetate. The plasticizer is not particularly limited, and examples thereof include: adipic acid plasticizers containing adipic acid esters such as dimethyl adipate, dibutyl adipate, diisostearyl adipate, diisodecyl adipate, diisononyl adipate, diisobutyl adipate, diisopropyl adipate, diethylhexyl adipate, dioctyl adipate, dioctyldodecyl adipate, didecyl adipate, and dihexyldecyl adipate; a citric acid plasticizer containing citric acid esters such as acetyl triethyl citrate, acetyl tributyl citrate, isodecyl citrate, isopropyl citrate, triethyl citrate, triethylhexyl citrate, and tributyl citrate; glutaric acid plasticizers containing glutaric acid esters such as diisobutyl glutarate, dioctyl glutarate, and dimethyl glutarate; succinic plasticizers containing succinic acid esters such as diisobutyl succinate, diethyl succinate, diethylhexyl succinate, and dioctyl succinate; sebacic acid plasticizers containing sebacic acid esters such as diisoamyl sebacate, diisooctyl sebacate, diisopropyl sebacate, diethyl sebacate, diethylhexyl sebacate, and dioctyl sebacate; glycerin plasticizers containing glycerin alkyl esters such as triacetin, diacetin, and monoacetin; neopentyl glycol; phthalic acid plasticizers containing phthalic acid esters such as ethyl phthalate, methyl phthalate, diaryl phthalate, diethyl phthalate, diethylhexyl phthalate, dioctyl phthalate, dibutyl phthalate, and dimethyl phthalate; phosphoric acid plasticizers containing phosphoric acid esters such as triolein phosphate, tristearyl phosphate, and trihexadecyl phosphate. Further, di-2-methoxyethyl phthalate, dibutyl tartrate, ethyl benzoylbenzoate, ethyl ethylphthaloyl glycolate (EPEG), ethyl methylphthaloyl glycolate (MPEG), N-ethyltoluene sulfonamide, o-cresol p-toluenesulfonate, triethyl phosphate (TEP), triphenyl phosphate (TPP), glyceryl tripropionate, and the like can be cited. These plasticizers may be used alone, and 2 or more plasticizers may be used in combination.

Among these, preferred are citric acid plasticizers selected from citric acid esters containing triethyl citrate, acetyl tributyl citrate, and the like; glycerin plasticizers containing glycerin alkyl esters such as triacetin, diacetin, and monoacetin; adipic acid plasticizers such as diisononyl adipate; and phthalic acid plasticizers such as ethyl phthalate and methyl phthalate, more preferably at least 1 or more selected from triethyl citrate, acetyl tributyl citrate, triacetin and diisononyl adipate, and still more preferably at least 1 or more selected from acetyl triethyl citrate, triacetin, diacetin and diethyl phthalate. Among them, phthalic acid plasticizers are concerned about the similarity to environmental hormones, and therefore, attention is required for use.

When the cellulose acetate particles contain a plasticizer, the content of the plasticizer contained in the cellulose acetate particles is not particularly limited. For example, the content may be more than 0 wt% and 40 wt% or less, 2 wt% or more and 40 wt% or less, 10 wt% or more and 30 wt% or less, and 15 wt% or more and 20 wt% or less with respect to the weight of the cellulose acetate particles.

The content of the plasticizer in the cellulose acetate particles can be determined by¹H-NMR was measured.

The cellulose acetate particles of the present invention have excellent biodegradability. The biodegradation rate is preferably 40% by weight or more, more preferably 50% by weight or more, and further preferably 60% by weight or more within 30 days.

The biological decomposition rate can be measured by a method using activated sludge according to JIS K6950.

The cellulose acetate particles of the present invention can be produced by the production method described later.

The cellulose acetate particles of the present invention are excellent in biodegradability and touch, and therefore, can be suitably used in, for example, cosmetic compositions. Further, since the cosmetic composition has a high sphericity, it can provide an effect of filling in the irregularities of the skin to be smooth and making wrinkles inconspicuous (soft focus) by scattering light in various directions when blended in the cosmetic composition.

As cosmetic compositions, foundations such as liquid foundations and powder foundations; concealing the concealer; sun protection; isolating; priming lipstick and lipstick; body powder, solid powder, loose powder, and the like: solid powder eye shadow; anti-wrinkle cream; and skin and hair external preparations mainly for cosmetic purposes such as skin care lotions, and the dosage forms thereof are not limited. The dosage form may be aqueous solution, emulsion, suspension, etc.; semisolid agents such as gels and creams; any of solid agents such as powder, granule and solid. In addition, the emulsion can also be in the form of cream, milky lotion, etc.; oil gel formulations such as lipstick; powder formulations such as foundation; and aerosol formulations such as hair styling agents.

[ Process for producing cellulose acetate particles ]

The method for producing cellulose acetate particles of the present invention comprises: a step for obtaining a cellulose acetate impregnated with a plasticizer by mixing a cellulose acetate having a total degree of substitution with acetyl groups of 0.7 to 2.9 with the plasticizer; a step of kneading the plasticizer-impregnated cellulose acetate and a water-soluble polymer at 200 ℃ to 280 ℃ to obtain a dispersion in which the plasticizer-impregnated cellulose acetate is a dispersoid; and a step of removing the water-soluble polymer from the dispersion.

(Process for obtaining cellulose acetate impregnated with plasticizer)

In the step of obtaining a plasticizer-impregnated cellulose acetate, a cellulose acetate having a total degree of substitution of acetyl groups of 0.7 or more and 2.9 or less is mixed with a plasticizer.

Cellulose acetate having a total degree of substitution of acetyl groups of 0.7 or more and 2.9 or less can be produced by a known method for producing cellulose acetate. As such a production method, there is a so-called acetic acid method using acetic anhydride as an acetylating agent, acetic acid as a diluent, and sulfuric acid as a catalyst. The basic steps of the acetic acid process include the following steps: (1) a pretreatment step of dissociating/pulverizing a pulp raw material (dissolving pulp) having a high alpha-cellulose content and then spraying mixed acetic acid; (2) an acetylation step of reacting the pretreated pulp of (1) with a mixed acid containing acetic anhydride, acetic acid and an acetylation catalyst (e.g., sulfuric acid); (3) a ripening step of hydrolyzing cellulose acetate to produce cellulose acetate having a desired degree of acetylation; and (4) a post-treatment step of precipitating and separating the cellulose acetate from the reaction solution after the hydrolysis reaction is completed, purifying, stabilizing and drying the cellulose acetate.

The cellulose acetate preferably has a total degree of substitution of acetyl groups of 0.7 or more and 2.9 or less, 0.7 or more and less than 2.6, more preferably 1.0 or more and less than 2.6, still more preferably 1.4 or more and less than 2.6, and most preferably 2.0 or more and less than 2.6. The total substitution degree of acetyl groups can be adjusted by adjusting the conditions (such as time and temperature) of the aging step.

The plasticizer is not particularly limited as long as it has a plasticizing effect in melt extrusion processing of cellulose acetate, and specifically, the above-mentioned plasticizers exemplified as the plasticizer contained in the cellulose acetate particles may be used alone or in combination of 2 or more kinds of plasticizers.

Among the plasticizers described as examples, preferred are citric acid plasticizers selected from the group consisting of triethyl citrate, acetyl triethyl citrate, and acetyl tributyl citrate; glycerin plasticizers containing glycerin alkyl esters such as triacetin, diacetin, and monoacetin; adipic acid plasticizers such as diisononyl adipate; and phthalic acid plasticizers such as ethyl phthalate and methyl phthalate, more preferably at least 1 or more selected from triethyl citrate, acetyl tributyl citrate, triacetin and diisononyl adipate, and still more preferably at least 1 or more selected from acetyl triethyl citrate, triacetin, diacetin and diethyl phthalate. Among them, phthalic acid plasticizers are concerned about the similarity to environmental hormones, and therefore, attention is required for use.

The amount of the plasticizer to be blended may be more than 0 part by weight and 40 parts by weight or less, 2 parts by weight or more and 40 parts by weight or less, 10 parts by weight or more and 30 parts by weight or less, and 15 parts by weight or more and 20 parts by weight or less, based on 100 parts by weight of the total amount of the cellulose acetate and the plasticizer. If the amount is too small, the regular sphericity of the obtained cellulose acetate particles tends to decrease, and if the amount is too large, the shape of the particles cannot be maintained and the regular sphericity tends to decrease.

The mixing of the cellulose acetate and the plasticizer may be carried out in a dry or wet manner using a mixer such as a henschel mixer. When a mixer such as a Henschel mixer is used, the temperature in the mixer may be a temperature at which the cellulose acetate does not melt, for example, a temperature in the range of 20 ℃ or more and less than 200 ℃.

The mixing of the cellulose acetate and the plasticizer may be carried out by melt kneading. In this case, it is preferable to perform melt kneading after mixing at a temperature condition of 20 ℃ or higher and less than 200 ℃ using a mixer such as a henschel mixer. By fusing the plasticizer and the cellulose acetate more uniformly and in a short time, the cellulose acetate particles finally produced have a high degree of sphericity, and are excellent in touch feeling and touch comfort.

The melt kneading is preferably performed by heating and mixing using an extruder. The mixing temperature (cylinder temperature) of the extruder may be in the range of 200 to 230 ℃. Even at a temperature within this range, the resulting mixture can be plasticized to obtain a uniform kneaded product. When the temperature is too low, the positive sphericity of the obtained particles is reduced, and therefore, the feeling and the touch comfort are reduced, and when the temperature is too high, the kneaded product may be thermally deteriorated or colored. In addition, the viscosity of the melt may decrease, and the kneading of the resin in the twin-screw extruder may be insufficient.

This is because the melting point of cellulose acetate is generally 230 to 280 ℃ and close to the decomposition temperature of cellulose acetate, although it depends on the degree of substitution, and therefore it is generally difficult to melt-knead the cellulose acetate in this temperature range, but the plasticizing temperature of cellulose acetate (sheet) impregnated with a plasticizer can be lowered. The kneading temperature (cylinder temperature) may be, for example, 200 ℃ in the case of using a twin-screw extruder. The kneaded product is extruded in a strand-like form and then pelletized by hot cutting or the like. The mold temperature in this case may be about 220 ℃.

(step of obtaining Dispersion)

In the step of obtaining the dispersion, the cellulose acetate impregnated with the plasticizer and the water-soluble polymer are kneaded at 200 ℃ to 280 ℃.

The cellulose acetate impregnated with the plasticizer and the water-soluble polymer can be kneaded by using an extruder such as a twin-screw extruder. The kneading temperature is the cylinder temperature.

The dispersion may be cut into pellets after being extruded in a string form from a die attached to the tip of an extruder such as a twin-screw extruder. In this case, the mold temperature may be 220 ℃ or higher and 300 ℃ or lower.

The amount of the water-soluble polymer blended may be 55 parts by weight or more and 99 parts by weight or less based on 100 parts by weight of the total amount of the cellulose acetate impregnated with the plasticizer and the water-soluble polymer. Preferably 60 parts by weight or more and 90 parts by weight or less, and more preferably 65 parts by weight or more and 85 parts by weight or less.

The water-soluble polymer in the present specification means a polymer having an insoluble content of less than 50% by weight when 1g of the polymer is dissolved in 100g of water at 25 ℃, and examples of the water-soluble polymer include polyvinyl alcohol, polyethylene glycol, sodium polyacrylate, polyvinyl pyrrolidone, polypropylene oxide, polyglycerol, polyethylene oxide, vinyl acetate, modified starch, thermoplastic starch, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, and among these, polyvinyl alcohol, polyethylene glycol, and thermoplastic starch are preferable, and polyvinyl alcohol and thermoplastic starch are particularly preferable.

The dispersion obtained is a dispersion in which a water-soluble polymer is used as a dispersion medium and the above-mentioned cellulose acetate impregnated with the plasticizer is used as a dispersoid. In other words, the water-soluble polymer may be used as the sea component, and the cellulose acetate impregnated with the plasticizer may be used as the island component. In the dispersion, the kneaded material constituting the island component contains cellulose acetate and a plasticizer, and is mainly spherical.

(step of removing Water-soluble Polymer)

The step of removing the water-soluble polymer from the dispersion will be described.

The method for removing the water-soluble polymer is not particularly limited as long as the water-soluble polymer can be dissolved and removed from the particles, and for example, water; alcohols such as methanol, ethanol, and isopropanol; or a mixed solution thereof, and removing the water-soluble polymer of the dispersion by dissolving it in a solvent. Specifically, for example, a method of removing the water-soluble polymer from the dispersion by mixing the dispersion with the solvent, filtering the mixture, and then taking out the filtrate is exemplified.

In the step of removing the water-soluble polymer from the dispersion, the plasticizer may be removed from the dispersion together with the water-soluble polymer, or the plasticizer may not be removed. Therefore, the obtained cellulose acetate particles may or may not contain a plasticizer.

The mixing ratio of the dispersion and the solvent is preferably 0.01 wt% or more and 20 wt% or less, more preferably 2 wt% or more and 15 wt% or less, and further preferably 4 wt% or more and 13 wt% or less, based on the total weight of the dispersion and the solvent. When the amount of the dispersion is more than 20% by weight, the dissolution of the water-soluble polymer becomes insufficient and the water-soluble polymer cannot be removed by washing, and it is difficult to separate the cellulose acetate particles which are not dissolved in the solvent from the water-soluble polymer dissolved in the solvent by filtration, centrifugation or the like.

The mixing temperature of the dispersion and the solvent is preferably 0 ℃ to 200 ℃, more preferably 20 ℃ to 110 ℃, and still more preferably 40 ℃ to 80 ℃. If the temperature is lower than 0 ℃, the solubility of the water-soluble polymer becomes insufficient and the removal by washing becomes difficult, and if the temperature exceeds 200 ℃, deformation, aggregation, and the like of the particles occur, and it becomes difficult to take out the particles while maintaining a desired particle shape.

The mixing time of the dispersion and the solvent is not particularly limited, and may be, for example, 0.5 hours or more, 1 hour or more, 3 hours or more, 5 hours or more, or 6 hours or less.

The method of mixing is not limited as long as the water-soluble polymer can be dissolved, and the water-soluble polymer can be efficiently removed from the dispersion even at room temperature by using a stirring device such as an ultrasonic homogenizer or a Three-in-One Motor (Three-One Motor).

For example, when a three-in-one motor is used as the stirring device, the rotation speed at the time of mixing the dispersion and the solvent may be, for example, 5rpm or more and 3000rpm or less. This enables the water-soluble polymer to be more efficiently removed from the dispersion. In addition, the plasticizer can be efficiently removed from the dispersion.