Polyisoprene particles, a method for producing the same, and a cosmetic

Abstract

To provide substitute materials for silicone beads and polyurethane beads, having high elasticity, by using high-purity polyisoprene.SOLUTION: A polyisoprene particle has an average particle size d1 of 1-20 μm, a maximum particle size d2 of less than 30 μm, a particle size ratio (d2 / d1) of 3.0 or less, a coefficient of variation of less than 40%, a sphericity of 0.80 or more, and a glass transition temperature of -53 to 10°C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to polyisoprene particles having high elasticity and good biodegradability, a method for producing the same, and cosmetics.

Background Art

[0002] Currently, synthetic polymers (plastics) derived from petroleum are used in various industries. Synthetic polymers are often developed for long-term stability and do not decompose in the natural environment. Therefore, various environmental problems have occurred. For example, plastic products flowing into the water environment are accumulated for a long time, and the ecosystems of the ocean and lakes are greatly affected. In recent years, microplastics with lengths from 5 mm or less to the nm level have become a major problem. Examples of those corresponding to microplastics include fine particles contained in cosmetic products, small pieces of plastic resin before processing, and those that are refined while large products are floating in the sea.

[0003] Plastic particles are difficult to remove at sewage treatment plants because of their low true specific gravity and easily flow into rivers, the ocean, ponds, etc. Furthermore, since plastic particles easily adsorb chemical substances such as pesticides, there is a risk of affecting the human body through bioaccumulation. This has also been pointed out by the United Nations Environment Programme, etc., and various countries and industry groups are considering regulations. For example, guidelines (ISO16128) regarding the natural / organic index display of cosmetics have been established. According to these guidelines, raw materials in products are classified into natural raw materials, natural-derived raw materials, and non-natural raw materials, and an index is calculated based on the content of each raw material. Already, this index is displayed on products, and natural-derived raw materials, and furthermore, natural raw materials are required.

[0004] Against such a background, biodegradable plastics that are decomposed into water and carbon dioxide by microorganisms or the like in the natural environment and incorporated into the natural carbon cycle have attracted attention. In particular, cellulose particles, which are natural raw materials derived from plants, do not float in water even if they flow out into the environment, and have good biodegradability, so there are few concerns about causing environmental problems. For example, porous cellulose particles formed of type I cellulose having good biodegradability are known (see, for example, Patent Document 1). When these particles are blended into cosmetics, good tactile properties can be obtained. In addition, particles containing cellulose acetate, which are excellent in biodegradability, touch, and lipophilicity, are known (see, for example, Patent Document 2). Furthermore, starch particles having excellent biodegradability with an amylopectin content of 90% by weight or more are known (see, for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] The particles disclosed in these patent documents are excellent in biodegradation and have soft and smooth tactile properties similar to plastic beads such as PMMA and Nylon. However, since the material itself is relatively hard, high elasticity cannot be obtained, and it is not suitable as an alternative material for silicone beads and polyurethane beads.

[0007] Therefore, an object of the present invention is to realize particles having high elasticity and good biodegradability.

Means for Solving the Problems

[0008] The polyisoprene particles according to the present invention have an average particle diameter d 1 of 1 to 20 μm, a maximum particle diameter d 2 of less than 30 μm, a particle size ratio (d 2 / d 1 ) of 3.0 or less, a coefficient of variation of less than 40%, a sphericity of 0.80 or more, and a glass transition temperature of -53 to 10°C.

[0009] The method for producing polyisoprene particles according to the present invention comprises a step of mixing liquid polyisoprene, a surfactant, and water to prepare an emulsion containing emulsion droplets, a step of irradiating the emulsion with ionizing radiation, and a step of subjecting the emulsion to solid-liquid separation to obtain polyisoprene particles as a solid. Further, the liquid polyisoprene may be diluted with an organic solvent to prepare an emulsion. At this time, the aqueous dispersion obtained by removing the organic solvent from the emulsion may be irradiated with ionizing radiation.

Mode for Carrying Out the Invention

[0010] The present invention relates to polyisoprene particles formed by crosslinking chain polyisoprene, having an average particle diameter d 1 of 1 to 20 μm, a maximum particle diameter d 2 of less than 30 μm, a particle size ratio (d 2 / d 1 ) of 3.0 or less, a particle coefficient of variation of less than 40%, a sphericity of 0.80 or more, and a glass transition temperature of -53 to 10°C. Such particles have high elasticity and good biodegradability.

[0011] The shape of the particles affects the tactile properties of the powder. Particles with an average particle diameter d 1 greater than 20 μm, or particles with a maximum particle diameter d 2 of 30 μm or more feel rough, and the soft and moist feelings decrease. When the maximum particle diameter exceeds 3.0 times the average particle diameter, the uniform spreading property decreases. When using the particles (powder) as a tactile improvement material, the average particle diameter d 1 is preferably 1 to 20 μm, and most preferably 5 to 15 μm. If it is less than 1 μm, the tactile properties such as rolling feeling, persistence of rolling feeling, and uniform spreading property decrease. The average particle diameter d 1Particles with a size of 0.01 to less than 1 μm are suitable as soft focus materials because of their high light scattering effect.

[0012] Also, the particle coefficient of variation (CV value) is less than 40%. If the particle coefficient of variation is 40% or more, there is a risk that uniform rolling properties cannot be obtained. The particle coefficient of variation is preferably 30% or less. Although the smaller the particle coefficient of variation, the more suitable it is, it is industrially difficult to obtain particles with a narrow distribution. Generally, if it is 3% or more, there will be no particular problem in manufacturing.

[0013] Also, the glass transition temperature is related to the degree of cross-linking of polyisoprene. Polyisoprene with a glass transition temperature lower than -53°C has insufficient cross-linking and adhesiveness, so it cannot be taken out as powder (particles). When the cross-linking progresses and the temperature reaches 10°C or more, the elasticity decreases and the biodegradability also decreases. The glass transition temperature is preferably -50 to 0°C, and most optimally -40 to -10°C.

[0014] The sphericity is 0.80 or more. The higher the sphericity, the better the rolling feeling of the powder (particles). A sphericity of 0.90 or more is particularly preferred.

[0015] Furthermore, the residual monomer contained in the polyisoprene particles is preferably less than 100 ppm. If the residual monomer is 100 ppm or more, the unique odor of city gas is strong and it is not acceptable as a cosmetic material. More preferably, it is less than 20 ppm.

[0016] By forming particles with cis-type polyisoprene as a component of the molecular structure, high elasticity can be obtained. Examples of cis-type polyisoprene include synthetic polyisoprene obtained by solution polymerization and biomass polyisoprene obtained by fermentation. Particles obtained from trans-type polyisoprene may not be able to obtain high elasticity.

[0017] Crosslinked polyisoprene has a slower biodegradation rate compared to uncrosslinked polyisoprene. However, the polyisoprene particles of the present invention have a fine particle size and a large specific surface area. Therefore, when exposed for 28 days in a biodegradability test according to OECD TG301F (ready biodegradability), more than 60% is decomposed. Such polyisoprene particles do not meet the definition proposal of microplastics proposed by the European Chemicals Agency.

[0018] Also, the specific gravity of polyisoprene is lighter than water and it is likely to float on water. Therefore, there is concern that it cannot be removed in wastewater treatment facilities and is directly released into the environment. However, since polyisoprene has photodegradability, it is easily incorporated into the cycle of the material circulation in nature.

[0019] Also, although polyisoprene particles are hydrophobic, they can be incorporated into aqueous cosmetics by surface treatment to make them hydrophilic. The surface treatment method may be any method that can modify the surface of polyisoprene particles to be hydrophilic. For example, treatment with nonionic or anionic surfactants with an HLB value of 8 to 18, treatment with amino acids or lipoamino acids, treatment with water-soluble polymers such as alginic acid or polyacrylic acid, etc. can be mentioned.

[0020] <Method for producing polyisoprene particles> First, liquid polyisoprene, a surfactant, and water are mixed to prepare an emulsion containing emulsion droplets (first step). Thereby, an O / W emulsion containing emulsion droplets composed of an inner layer of a solution in which polyisoprene is dissolved in an organic solvent and an outer layer of water is obtained. This emulsion is irradiated with ionizing radiation to crosslink polyisoprene (second step). Thereby, a three-dimensional network structure in which chain-like polyisoprene is crosslinked is obtained. Subsequently, this aqueous dispersion is subjected to solid-liquid separation, further washed with water, and a cake-like substance is taken out (third step). This cake-like substance is dried and crushed to obtain a powder of polyisoprene particles.

[0021] Here, the liquid polyisoprene may be diluted with an organic solvent and then an emulsion is prepared. At this time, the emulsion containing the organic solvent may be irradiated with ionizing radiation, or after removing the organic solvent from the emulsion, it may be irradiated with ionizing radiation.

[0022] Hereinafter, each step will be described in detail.

[0023] [First Step] First, a liquid polyisoprene, water, and a surfactant are mixed (preparation of a mixed solution). The surfactant is added to form O / W-type emulsion droplets. An HLB value of 8 to 18 is suitable for the surfactant. Next, this mixed solution is emulsified by an emulsifying device to obtain an emulsion. At this time, the emulsifying conditions are set so as to obtain an emulsion containing emulsion droplets with an average diameter of about 1 to 40 μm. Liquid polyisoprene is present in the emulsion droplets. As the emulsifying device, a general high-speed shearing device can be used. In addition, known devices such as a membrane emulsifying device and a microchannel emulsifying device that can obtain more uniform emulsion droplets can be applied according to the purpose. The liquid polyisoprene may be diluted with an organic solvent and then the mixed solution is prepared. As the liquid polyisoprene, synthetic polyisoprene obtained by solution polymerization or biomass polyisoprene obtained by an enzymatic method is used. Note that the synthetic polyisoprene does not contain non-rubber components such as proteins and lipids contained in natural rubber, but slightly contains residual monomers, residual solvents, and polymerization terminators. As such liquid polyisoprene, for example, commercially available products with a molecular weight of 10,000 to 50,000 such as Kuraprene manufactured by Kuraray Co., Ltd., Nipol manufactured by Zeon Corporation, and IR manufactured by JSR Corporation can be exemplified. If necessary, it can be diluted with an organic solvent and used.

[0024] The average diameter of the emulsion droplets was measured as follows. The emulsion was dropped onto a slide glass and covered with a cover glass from above. Using a digital microscope (manufactured by Keyence Corporation, VHX-600), photographs were taken through the cover glass at magnifications from 30 times to 2000 times to obtain a photographic projection diagram of the emulsion droplets. From this photographic projection diagram, 50 droplets were arbitrarily selected, and the equivalent circle diameter was calculated using the attached software. The average value of these 50 equivalent circle diameters was taken as the average diameter (average droplet diameter).

[0025] [Second Step] In this step, this emulsion is placed in a metal container and irradiated with ionizing radiation. Thereby, the polyisoprene contained in the emulsion droplets can be crosslinked. When irradiating with ionizing radiation to such an extent that the glass transition temperature of the uncrosslinked polyisoprene rises by about 10 °C, the adhesiveness of the particles is suppressed and they can be taken out as a powder. Also, it is considered that the residual monomers slightly contained in the liquid polyisoprene polymerize by the irradiation of ionizing radiation. After irradiation, the residual monomers become 100 ppm or less, and the odor is substantially imperceptible. The ionizing radiation is any one of X-rays, γ-rays, and electron beams, and the irradiation dose is preferably in the range of 50 to 500 kGy. When it is less than 50 kGy, since crosslinking is underdeveloped, when the emulsion is subjected to solid-liquid separation, the polyisoprene particles stick to each other and solidify, and cannot be taken out as individual powders. Also, when it exceeds 500 kGy, the crosslinking density is too high, the elasticity decreases, and the biodegradation rate decreases.

[0026] Also, when the above-mentioned emulsification is carried out in a dilute system and irradiated with ionizing radiation, particles with higher elasticity can be obtained. Note that the glass transition temperature of the polyisoprene particles can be adjusted in this crosslinking step. A 200 L drum can is also suitable for handling as the metal container.

[0027] [Organic Solvent Removal Step] When preparing an emulsion using polyisoprene diluted with an organic solvent, the organic solvent is removed from the emulsion before or after the crosslinking step. By heating under normal pressure or reduced pressure, the organic solvent is evaporated. As a result, the organic solvent is removed from the emulsion droplets, and an aqueous dispersion containing polyisoprene particles with a particle size of about 1 to 40 μm is obtained.

[0028] For example, in the heating removal method under normal pressure, a separable flask equipped with a condenser is heated to remove the organic solvent. In the heating removal method under reduced pressure, heating under reduced pressure is carried out using a rotary evaporator, an evaporator, etc. to remove the organic solvent.

[0029] [Third Step] Next, the solid content is separated from the aqueous dispersion obtained in the second step or the organic solvent removal step by a known method such as filtration or centrifugation. As a result, a cake-like substance of polyisoprene particles is obtained. By washing the obtained cake-like substance, the surfactant can be reduced. When polyisoprene particles are blended into a liquid preparation such as an emulsion, the surfactant may inhibit long-term stability. Therefore, the residual amount of the surfactant contained in the polyisoprene particles is preferably 100 ppm or less. To reduce the surfactant, it is good to wash with an organic solvent.

[0030] [Drying Step] In the drying step, the water contained in the cake-like substance obtained in the solid-liquid separation step is evaporated by heating under normal pressure or reduced pressure. Then, by crushing with a mixer or the like, a powder of polyisoprene particles with an average particle size of 1 to 20 μm is obtained.

[0031] [Cosmetics] The above polyisoprene particles and various cosmetic ingredients can be blended to prepare a cosmetic. According to such a cosmetic, the same flexibility as silicone beads or polyurethane beads can be felt, and at the same time, a rolling feeling, the persistence of the rolling feeling, and a uniform spreading property, a soft feeling and a moist feeling can be obtained. That is, it can satisfy the typical tactile characteristics required for a tactile improver for cosmetics.

[0032] Specific cosmetics are exemplified in Table 1 by category. Such cosmetics can be manufactured by conventional general methods. Cosmetics are used in various forms such as powder, cake, pencil, stick, cream, gel, mousse, liquid, cream, etc.

[0033] Typical classifications and components of various cosmetic ingredients are exemplified in Table 2. Furthermore, cosmetic ingredients listed in the Pharmaceutical Excipient Standards 2006 (published by Yakujutsu Nippo Co., Ltd., June 16, 2006) and International Cosmetic Ingredient Dictionary and Handbook (published by The Cosmetic, Toiletry, and Fragrance Association, Eleventh Edition 2006) etc. may be blended.

[0034] [Table 1]

[0035] [Table 2] [Examples]

[0036] Hereinafter, the examples of the present invention will be specifically described.

[0037] [Example 1] 200 g of liquid polyisoprene (Kuraray's Kuraprene KL-10) was added to a mixed solution of 3346 g of water and 25 g of a surfactant (Kao's Leodol TW-O120V). This mixed solution was stirred at 12,000 rpm for 10 minutes using an emulsifying and dispersing machine (Primix's T.K. Robomix). As a result, an emulsion containing emulsion droplets was obtained.

[0038] Approximately 1.8 L of this emulsion was filled into a 4 L metal square can (manufactured by AS ONE Corporation) and irradiated with γ-rays at a dose of 270 kGy.

[0039] This emulsion was filtered through quantitative filter paper (Advantec Toyo No. 2) using a Büchner funnel (3.2 L, manufactured by Sekiguchi Rika Glass Kikai Co., Ltd.). Subsequently, washing with 1 L of heptane was repeated three times to remove the surfactant. The cake-like substance thus obtained was dried at 60 °C for 12 hours. After crushing this dried powder with a juicer mixer, it was sieved through a 250-mesh sieve (JIS test standard sieve) to obtain polyisoprene particles.

[0040] The preparation conditions of the polyisoprene particles are summarized in Table 3. Also, the physical properties of the polyisoprene particle powder were measured by the following methods. The same measurements were made for other examples and comparative examples. The results are shown in Table 4.

[0041] (1) Average particle diameter, maximum particle diameter, particle coefficient of variation (CV value) Using a laser diffraction apparatus (LA-950v2, manufactured by Horiba, Ltd.), the particle size distribution of the polyisoprene particles was measured. From this particle size distribution, the median value was obtained, and the average particle diameter d 1 was determined. Also, the largest particle diameter detected in the particle size distribution was defined as the maximum particle diameter d 2 . Furthermore, the standard deviation σ and the population mean μ were obtained from the particle size distribution (population), and the particle coefficient of variation (CV = σ / μ) was obtained. In Table 4, it is expressed as a percentage. Also, the maximum particle diameter d 2 was divided by the average particle diameter d 1 to obtain the ratio of the maximum particle diameter to the average particle diameter (d 2 / d 1 ).

[0042] (2) Sphericity Using a transmission electron microscope (H-8000, manufactured by Hitachi, Ltd.), photographs were taken at magnifications from 2000 to 250,000 times to obtain a photographic projection diagram. From this photographic projection diagram, 50 arbitrary particles were selected, and for each, the maximum diameter DL and the minor axis DS orthogonal to it were measured, and the ratio (DS / DL) was obtained. The average value of these was defined as the sphericity.

[0043] (3) Glass transition temperature Using a differential scanning calorimeter (DSC8230L, manufactured by Rigaku Corporation), the temperature was raised from -80 °C to 80 °C at a rate of 10 °C / min for measurement.

[0044] (4) Residual monomer Using a spectrophotometer (U-2900 manufactured by Hitachi High-Technologies Corporation), qualitative analysis was simply performed by the photoelectric colorimetric method. Specifically, 0.01 to 3.5 g of mercuric acetate (special grade reagent), 10 ml of 1% acetic acid-acidic methyl alcohol, and 5 mg of the measurement sample were collected in a test tube and sealed. This was immersed in a water bath at 70 °C for 50 minutes to completely dissolve the mercuric acetate, and then cooled with water. The colored solution was filtered through qualitative filter paper, and the filtrate was collected. The maximum absorbance of this filtrate at 440 to 445 nm was compared with the absorbance of a THF solution with a previously prepared isoprene concentration of 100 ppm. ○: Less than 100 ppm ×: 100 ppm or more

[0045] (5) Biodegradability A biodegradability test was performed on the powder of polyisoprene particles based on OECD TG301F (ready biodegradability), and the degradation rate by 28-day exposure was measured. In this example, this degradation rate was 80%.

[0046] [Example 2] It was prepared in the same manner as in Example 1 except that the rotation speed of the emulsifying disperser was 8000 rpm.

[0047] [Example 3] It was prepared in the same manner as in Example 1 except that the rotation speed of the emulsifying disperser was 13000 rpm.

[0048] [Example 4] It was prepared in the same manner as in Example 1 except that 200 g of cyclohexane was added to 200 g of liquid polyisoprene for dilution, the rotation speed of the emulsifying disperser was 10000 rpm, and the γ-ray irradiation dose was 160 kGy.

[0049] [Example 5] It was prepared in the same manner as in Example 4 except that the γ-ray irradiation dose was 400 kGy.

[0050] [Example 6] Using 200 g of Kuraprene LIR-30 manufactured by Kuraray Co., Ltd. as the liquid polyisoprene and adding 200 g of cyclohexane for dilution, it was prepared in the same manner as in Example 1 except that the rotational speed of the emulsifying disperser was set to 11,000 rpm.

[0051] [Comparative Example 1] Powder of polyisoprene particles was obtained in the same manner as in Example 1 except that the rotational speed of the emulsifying disperser was set to 4,000 rpm.

[0052] [Comparative Example 2] It was prepared in the same manner as in Example 1 except that the rotational speed of the emulsifying disperser was set to 16,000 rpm for 60 minutes.

[0053] [Comparative Example 3] When the same operation as in Example 1 was performed except that the crosslinking step (γ-ray irradiation) was not carried out, the dried product became sheet-like and could not be crushed by a juicer mixer. Therefore, polyisoprene particles could not be obtained.

[0054] [Comparative Example 4] It was prepared in the same manner as in Example 1 except that the γ-ray irradiation dose was set to 600 kGy.

[0055] [Comparative Example 5] When the same operation as in Example 1 was performed except that the γ-ray irradiation dose was set to 40 kGy, the dried product became sheet-like and could not be crushed by a juicer mixer. Therefore, polyisoprene particles could not be obtained.

[0056]

Table 3

[0057]

Table 4

[0058] 〈Touch characteristics of the powder of polyisoprene particles〉 Next, the tactile properties of the powders obtained in each example and comparative example were evaluated. For each powder, a sensory test was conducted by 20 professional panelists, and a questionnaire survey was carried out regarding seven evaluation items: smoothness, moistness, rollability, uniform spreadability, adhesion to the skin, persistence of rollability, and softness. The evaluation scores of each person based on evaluation criteria (a) were totaled, and the tactile properties were evaluated based on evaluation criteria (b). The results are shown in Table 5. Evaluation criteria (a) 5 points: Extremely excellent. 4 points: Excellent. 3 points: Ordinary. 2 points: Inferior. 1 point: Extremely inferior. Evaluation criteria (b) ◎: Total score is 80 points or more ○: Total score is 60 points or more and less than 80 points △: Total score is 40 points or more and less than 60 points ▲: Total score is 20 points or more and less than 40 points ×: Total score is less than 20 points

[0059]

Table 5

[0060] 〈Feeling of using liquid foundation〉 Using the powder of polyisoprene particles, a W / O type liquid foundation was prepared so as to have the formulation ratio (by weight %) shown in Table 6. That is, the powder of each example was used as component (10), and after being uniformly dispersed with components (2) to (14) in a disperser, it was mixed with component (1). Further, components (15) to (19) were uniformly mixed in the same manner. After heating these to 70°C to melt the components, they were emulsified, cooled, and defoamed with a disperser to obtain a W / O type liquid foundation. Regarding the liquid foundation thus obtained, a sensory test was conducted by 20 professional panelists. A questionnaire survey was conducted regarding six evaluation items: uniform spread during application to the skin, moist feeling, smoothness, and uniformity, moist feeling, and softness of the makeup film after application to the skin. The evaluation points of each person based on the above-mentioned evaluation point criteria (a) were totaled, and the usability of the foundation was evaluated based on the above-mentioned evaluation criteria (b). The results are shown in Table 7. The cosmetics according to the examples are excellent in usability both during and after application. However, the cosmetics of the comparative example do not have good usability.

[0061]

Table 6

[0062]

Table 7

Claims

1. Average particle diameter d １ is 1 to 20 μm, the maximum particle diameter d ２ is less than 30 μm, the particle size ratio (d ２ / d １ ) is 3.0 or less, the coefficient of variation is less than 40%, the sphericity is 0.80 or more, and the glass transition temperature is -53 to 10°C. The polyisoprene particles are characterized by this.

2. The polyisoprene particles according to claim 1, characterized in that the content of the residual monomer is less than 100 ppm.

3. A first step of mixing liquid polyisoprene, a surfactant, and water to prepare an emulsion containing emulsion droplets; A second step of irradiating the emulsion with ionizing radiation; A third step of solid-liquid separating the emulsion obtained in the second step to obtain polyisoprene particles as a solid matter, and a method for producing polyisoprene particles comprising the same.

4. The method for producing polyisoprene particles according to claim 3, characterized in that in the first step, the polyisoprene is diluted with an organic solvent to prepare an emulsion.

5. The method for producing polyisoprene particles according to claim 4, characterized in that in the second step, the emulsion from which the organic solvent has been removed is irradiated with the ionizing radiation to obtain an aqueous dispersion.

6. A cosmetic containing the polyisoprene particles according to any one of claims 1 to 2.

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