JP7702269B2 - Natural rubber particles, their manufacturing method, and cosmetics - Google Patents

Description

The present invention relates to natural rubber particles with high elasticity and good biodegradability, and a method for producing the same.

Currently, synthetic polymers (plastics) derived from petroleum are used in a variety of industries. Synthetic polymers are often developed with the aim of long-term stability, and do not decompose in the natural environment. This has led to various environmental problems. For example, plastic products that have been discharged into the water environment have accumulated for long periods of time, causing major impacts on the ecosystems of oceans and lakes. In addition, in recent years, microplastics with lengths ranging from 5 mm or less to the nm level have become a major problem. Examples of microplastics include fine particles contained in cosmetics, small lumps of plastic resin before processing, and large products that have become finer as they float in the ocean.

Because plastic particles have a low true density, they are difficult to remove at sewage treatment plants and tend to end up in rivers, oceans, ponds, etc. Furthermore, because plastic particles tend to adsorb chemical substances such as pesticides, there is a risk that they may affect the human body through bioaccumulation. This issue has been pointed out by the United Nations Environment Programme and other organizations, and various countries and industry groups are considering regulating them. For example, guidelines for labeling the natural/organic index for cosmetics (ISO 16128) have been established. According to these guidelines, the ingredients in a product are classified into natural ingredients, naturally derived ingredients, and non-natural ingredients, and an index is calculated based on the content of each ingredient. This index is already displayed on products, and naturally derived ingredients and even natural ingredients are being required.

In light of this background, biodegradable plastics that are decomposed into water and carbon dioxide by microorganisms in the natural environment and are incorporated into the natural carbon cycle have been attracting attention. In particular, cellulose particles, a natural raw material derived from plants, do not float on water even if they are released into the environment, and have good biodegradability, so there is little concern that they will cause environmental problems. For example, porous cellulose particles formed from type I cellulose, which has good biodegradability, are known (see, for example, Patent Document 1). When these particles are blended into cosmetics, good tactile characteristics are obtained. In addition, particles containing cellulose acetate, which has excellent biodegradability, tactile feel, and lipophilicity, are known (see, for example, Patent Document 2). Furthermore, starch particles with excellent biodegradability, with an amylopectin content of 90% by weight or more, are known (see, for example, Patent Document 3).

WO2020/004604 publication WO2020/188698 publication WO2021/033742 publication

The particles disclosed in these patent documents are highly biodegradable and have the same soft and smooth feel as plastic beads such as PMMA and Nylon. However, since the material itself is relatively hard, it does not have high elasticity and is not suitable as a replacement material for silicone beads or polyurethane beads.

Therefore, the object of the present invention is to create particles made from natural materials that have high elasticity and good biodegradability.

The natural rubber particles according to the present invention have an average particle diameter _d1 of 0.01 to 20 μm, a maximum particle diameter _d2 of less than 30 μm and within 3.0 times the average particle diameter _d1 , a CV value of less than 40%, a sphericity of 0.80 or more, and a glass transition temperature of −53 to 10° C.

The method for producing natural rubber particles according to the present invention includes a purification step of adding an alkaline component to a solution containing uncrosslinked natural rubber latex and hydrolyzing lipids to obtain a purified natural rubber solid, a step of adding an organic solvent to the purified natural rubber and dissolving the purified natural rubber to obtain a solution, a step of mixing the solution, a surfactant, and water to prepare an emulsion containing emulsified droplets, a crosslinking step of irradiating the emulsion with ionizing radiation to crosslink the natural rubber particles, an organic solvent removal step of removing the organic solvent from the emulsified droplets, and a solid-liquid separation step of performing solid-liquid separation on the aqueous dispersion obtained through the crosslinking step and the organic solvent removal step to obtain the natural rubber particles as a solid.

Alternatively, the crosslinking step may be carried out after removing the organic solvent from the emulsion.

The present invention relates to natural rubber particles formed by crosslinking a natural rubber component, which have an average particle size _d1 of 0.01 to 20 μm, a maximum particle size _d2 of less than 30 μm, a particle size ratio ( _d2 / _d1 ) of 3.0 or less, a particle variation coefficient 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.

The shape of the particles affects the tactile properties of the powder. Particles with an average particle diameter _d1 of more than 20 μm or particles with a maximum particle diameter _d2 of 30 μm or more feel rough and have a reduced soft and moist feel. If the maximum particle diameter exceeds 3.0 times the average particle diameter, uniform spreadability decreases. Particles with an average particle diameter _d1 of less than 0.01 μm are difficult to manufacture industrially. When particles (powders) are used as a feel improver, the average particle diameter _d1 is preferably 1 to 20 μm, and optimally 5 to 15 μm. If it is less than 1 μm, tactile properties such as rolling feel, duration of rolling feel, and uniform spreadability decrease. Particles with an average particle diameter _d1 of 0.01 to less than 1 μm are suitable as soft focus materials because of their high light scattering effect.

The particle variation coefficient (CV value) is less than 40%. If the particle variation coefficient is 40% or more, uniform rolling properties may not be obtained. The particle variation coefficient is preferably 30% or less. Although a smaller particle variation coefficient is more preferable, it is industrially difficult to obtain particles with a narrow distribution. If it is approximately 3% or more, production can be carried out without any particular problems.

The glass transition temperature is also related to the degree of cross-linking of natural rubber. Natural rubber with a glass transition temperature below -53°C is not sufficiently cross-linked and is sticky, so it cannot be extracted as a powder (particles). When cross-linking progresses to above 10°C, elasticity decreases and biodegradability also decreases. A glass transition temperature of -50 to 0°C is preferable, with -40 to -10°C being optimal.

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

Furthermore, the protein content is preferably less than 10 ppm. There is little risk of developing immediate-type allergies (latex allergies) due to proteins. Furthermore, the phosphorus content derived from phospholipids is preferably less than 100 ppm. It is also preferable that the rubber is free of fatty acids. This can suppress odor, bacterial growth, deterioration, and decay. If the infrared absorption spectrum of natural rubber particles does not substantially show absorption near 1710 cm ^-1 , which is specific to fatty acids, and absorption near 1740 cm ^-1 , which is specific to fatty acid esters, then it can be determined that the rubber does not contain fatty acids.

High elasticity can be achieved by forming particles from natural rubber with a cis molecular structure. Examples of natural sources of cis rubber include rubber trees, guayule, and Russian dandelion. Particles made from trans gum arabic may not be able to achieve high elasticity.

Cross-linked natural rubber has a slower rate of biodegradation than uncross-linked natural rubber. However, the natural rubber particles of the present invention have a fine particle size and a large specific surface area. As a result, more than 60% of the particles are decomposed after 28 days of exposure in a biodegradability test according to OECD TG301F (easily degradable). Such natural rubber particles do not fall under the proposed definition of microplastics proposed by the European Chemicals Agency.

In addition, the specific gravity of natural rubber is lighter than water, making it easy to float on water. This means that it cannot be removed by wastewater treatment facilities, and there are concerns that it will be released directly into the environment. However, because natural rubber is photodegradable, it can easily be incorporated into the material circulation cycle in nature.

Although natural rubber particles are hydrophobic, they can be made hydrophilic by surface treatment, allowing them to be incorporated into aqueous cosmetics. Any surface treatment method can be used as long as it can modify the surface of the natural rubber particles to make them hydrophilic, and examples of such surface treatment methods include treatment with nonionic or anionic surfactants with an HLB value of 8 to 18, treatment with amino acids or lipoamino acids, and treatment with water-soluble polymers such as alginic acid or polyacrylic acid.

<Method of producing natural rubber particles>
First, an alkali is added to an uncrosslinked natural rubber latex solution to hydrolyze lipids, and the solution is washed with water. An acid is added to the solution to coagulate the latex, and the solution is then washed with water and dried (refining step). This results in a solid purified natural rubber with reduced lipids. Next, the solid natural rubber is added to an organic solvent and dissolved until it is completely transparent (dissolving step). This results in a solution in which natural rubber is dissolved in an organic solvent. Next, this solution is mixed with a surfactant and water to prepare an emulsion containing emulsified droplets (emulsifying step). This results in an O/W emulsion containing emulsified droplets in which the inner layer is a solution in which natural rubber is dissolved in an organic solvent, and the outer layer is water. This emulsion is irradiated with ionizing radiation to crosslink the natural rubber (crosslinking step). This results in a three-dimensional network structure in which the constituent component of natural rubber (chain polyisoprene) is crosslinked. Next, the organic solvent is removed from the emulsified droplets in the O/W emulsion (organic solvent removing step). This results in an aqueous dispersion of crosslinked natural rubber particles. Next, this aqueous dispersion is subjected to solid-liquid separation and further washed with water to extract a cake-like substance (solid-liquid separation step). Next, this cake-like substance is dried and crushed to obtain a powder of natural rubber particles (drying step). Here, the order of the crosslinking step and the organic solvent removal step may be reversed. That is, the emulsion obtained in the emulsification step may be irradiated with ionizing radiation after removing the organic solvent.

Each step is explained in detail below.

[Purification process]
An alkali is added to uncrosslinked natural rubber latex, and the latex is heated to room temperature to 200°C to hydrolyze the lipids. Natural rubber latex is mainly composed of cis-polyisoprene, which is contained in the sap of rubber trees and the like. It also contains about 6% by weight of non-rubber components such as proteins, fatty acids, and phospholipids. By reducing the lipid content, the amount of gel components that are insoluble in organic solvents in the subsequent dissolution process is reduced, improving the yield. Examples of the alkali used here include ammonia, sodium hydroxide, and potassium hydroxide. The higher the concentration of the alkali, the more effective it is, and a concentration of 5% or more is preferable.

After hydrolysis, the rubber components are separated from the lipids by ultrafiltration, centrifugation, etc. Next, an acidic component such as a mineral acid is added, and the rubber components are separated into solid and liquid and washed with water. After that, it is vacuum dried to obtain a solid natural rubber product.

In addition, there are products on the market in which ammonia is added to natural rubber latex and concentrated to about 60% by centrifugation, etc., and these can also be used as raw materials.

It is further desirable to reduce the protein content by enzyme treatment using an enzyme, denaturation treatment using a denaturant, extraction with acetone, etc. Deproteinized natural rubber latex (for example, enzyme-treated latex (Seratex, manufactured by Sumitomo Rubber Industries, Ltd.) and aluminum hydroxide-treated latex (manufactured by MMG Polymer, Thailand) are available on the market, and these may be used. Latex with residual protein reduced to less than 1% is preferable. On the other hand, sheet-shaped (visually graded rubber) and block-shaped (technically graded rubber) rubbers available as solid rubber contain a large amount of non-rubber components and are difficult to purify.

[Dissolution process]
Next, the natural rubber solids are added to an organic solvent and dissolved by heating from room temperature to below the boiling point of the solvent. The SP value of the organic solvent is preferably 6 to 10 (approximately within a range of ±2 with respect to the SP value of natural rubber of 8). Cyclohexane is preferable. The gel component does not dissolve even when subjected to high temperature and pressure in an autoclave. Therefore, the solution is ultrafiltered to separate the gel. This results in a transparent natural rubber solution. Since proteins and lipids are water-soluble, they can be reduced by this ultrafiltration. It is economical for the solids content in the natural rubber solution to be 50% or more.

[Emulsification process]
The natural rubber solution is mixed with water and a surfactant. The surfactant is added to form O/W type emulsion droplets. The HLB value of the surfactant is preferably 8 to 18. Next, this mixed solution is emulsified using an emulsifier. At this time, the emulsification conditions are set so as to obtain an emulsion containing emulsion droplets with an average diameter of about 0.02 to 40 μm. The natural rubber solution is present in the emulsion droplets. A general high-speed shear device can be used as the emulsifier. In addition, known devices such as a high-pressure emulsifier that can obtain finer nano-sized emulsion droplets, a membrane emulsifier that can obtain more uniform emulsion droplets, and a microchannel emulsifier can be used depending on the purpose.

The average diameter of the emulsion droplets was measured as follows: The emulsion was dropped onto a glass slide, and a cover glass was placed over it. Using a digital microscope (Keyence, VHX-600), a photograph was taken through the cover glass at magnifications of 30 to 2000 times to obtain a photographic projection of the emulsion droplets. From this photographic projection, 50 droplets were randomly selected, and the circular equivalent diameter was calculated using the accompanying software. The average of the circular equivalent diameters of these 50 droplets was taken as the average diameter (average droplet diameter).

[Crosslinking process]
The emulsion is placed in a metal container and irradiated with ionizing radiation. When ionizing radiation is applied to the extent that the glass transition temperature of uncrosslinked natural rubber is increased by about 10°C, the adhesion of the particles is suppressed, and the natural rubber can be taken out as a powder. Furthermore, the remaining non-rubber components are decomposed and transferred to the water layer by the irradiation of ionizing radiation. Therefore, the purity of the natural rubber is increased. The ionizing radiation is applied in the form of either x-rays, gamma rays, or electron beams, and the irradiation dose is preferably in the range of 50 to 500 kGy. When the dose is less than 50 kGy, the crosslinking is underdeveloped, so that when the emulsion is subjected to solid-liquid separation, the rubber particles stick together and form a mass, and it is not possible to take out the rubber particles as individual powders. Furthermore, when the dose exceeds 500 kGy, the crosslinking density is too high, and the elasticity and the biodegradation rate decrease.

Furthermore, if the above-mentioned emulsification is carried out in a dilute system and then irradiated with ionizing radiation, particles with higher elasticity can be obtained. Furthermore, the glass transition temperature of the natural rubber particles can be adjusted in this crosslinking process. As for the metal container, a 200 L drum can is suitable for ease of handling.

[Organic solvent removal process]
The organic solvent is removed from the emulsion obtained in the crosslinking step. The organic solvent is evaporated by heating under normal pressure or reduced pressure. This removes the organic solvent from the emulsion droplets, and an aqueous dispersion containing natural rubber particles with particle sizes of about 0.02 to 40 μm is obtained.

For example, in the normal pressure heating removal method, a separable flask equipped with a cooling tube is heated to remove the organic solvent. In the reduced pressure heating removal method, the organic solvent is removed by heating under reduced pressure using a rotary evaporator or evaporator.

[Solid-liquid separation process]
Next, solids are separated from the aqueous dispersion obtained in the organic solvent removal step by known methods such as filtration and centrifugation. This results in a cake-like material of natural rubber particles. The amount of surfactant can be reduced by washing the resulting cake-like material. When natural rubber particles are blended into a liquid preparation such as an emulsion, the surfactant may inhibit long-term stability. For this reason, the amount of residual surfactant contained in the natural rubber particles is preferably 100 ppm or less. In order to reduce the amount of surfactant, washing with an organic solvent is preferable.

[Drying process]
In the drying process, the water contained in the cake-like material obtained in the solid-liquid separation process is evaporated by heating under normal or reduced pressure, and then the cake-like material is crushed in a mixer or the like to obtain a powder of natural rubber particles with an average particle size of 0.01 to 20 μm.

<Cosmetics>
Cosmetics can be prepared by blending the above-mentioned natural rubber particles with various cosmetic ingredients. Such cosmetics provide a feeling of softness similar to that of silicone beads or polyurethane beads. At the same time, it is possible to obtain the excellent tactile properties (rolling feel, sustained rolling feel, uniform spreadability, soft feel and moist feel) that powder of natural rubber particles has. In other words, it is possible to satisfy the typical tactile properties required for a cosmetic feel improver. Natural rubber particles with an average particle diameter _d1 of 1 to 20 μm are particularly suitable as a feel improver.

Specific examples of cosmetics are shown in Table 1 by classification. Such cosmetics can be produced by conventional methods. Cosmetics are used in various forms, such as powder, cake, pencil, stick, cream, gel, mousse, liquid, and cream.

Representative classifications and ingredients of various cosmetic ingredients are shown in Table 2. In addition, cosmetic ingredients listed in the Standards for Quasi-Drug Ingredients 2006 (published by Yakuji Nippo Co., Ltd., June 16, 2006) and the International Cosmetic Ingredient Dictionary and Handbook (published by The Cosmetic, Toiletry, and Fragrance Association, Eleventh Edition 2006) may also be blended.

The following is a detailed description of an embodiment of the present invention.

[Example 1]
Deproteinized natural rubber (SELATEX-1101 manufactured by Sumitomo Rubber Industries, Ltd.) was used as the natural rubber latex. This was diluted with pure water to a rubber concentration of 30% by weight, and sodium hydroxide was added thereto so that the concentration became 5%. The pH of the resulting aqueous dispersion was 13.5. This aqueous dispersion was heated to 40°C and stirred for 24 hours to hydrolyze the lipids. Next, the mixture was washed using an ultrafiltration membrane until the electrical conductivity was 10 mS/m or less. Next, the mixture was vacuum dried using a rotary evaporator to obtain a purified natural rubber solid.

Cyclohexane was added to this solid to make the solid content 50% by weight, and the mixture was stirred at 60°C for 2 hours to obtain a transparent solution of natural rubber.

200 g of this solution was added to a mixed solution of 3,346 g of water and 25 g of a surfactant (Reodol TW-O120V, manufactured by Kao Corporation). This mixed solution was stirred at 10,000 rpm for 10 minutes using an emulsifier/disperser (T.K. Robomix, manufactured by Primix Corporation). This resulted in emulsification, and an emulsion containing emulsion droplets was obtained.

This emulsion was packed into a 4 L metal can (manufactured by AS ONE Corporation) and irradiated with 270 kGy of gamma rays to crosslink the natural rubber in the emulsion droplets.

Next, cyclohexane was removed from the emulsion by distillation using a rotary evaporator. The resulting aqueous dispersion was filtered through a quantitative filter paper (Advantec Toyo Co., Ltd. No. 2) using a Buchner funnel (Sekiya Rika Glass Machine Co., Ltd. 3.2 L). After that, it was washed with water until the electrical conductivity reached 1 mS/m to remove non-rubber components. Next, it was washed three times with 1 L of heptane to remove the surfactant. The cake-like material thus obtained was dried at 60°C for 12 hours. The dried powder was crushed using a juicer mixer and sieved through a 250 mesh sieve (JIS test standard sieve) to obtain natural rubber particles.

The preparation conditions for the natural rubber particles are summarized in Table 3. The physical properties of the powder of natural rubber particles were measured using the following methods. Similar measurements were also performed for other examples and comparative examples, and the results are shown in Table 4.

(1) Average particle size, maximum particle size, and particle variation coefficient The particle size distribution of natural rubber particles was measured using a laser diffraction device (LA-950v2 manufactured by Horiba, Ltd.). The median value was determined from this particle size distribution and was taken as the average particle size _d1 . The largest particle size detected in the particle size distribution was taken as the maximum particle size _d2 . Furthermore, the standard deviation σ and population mean μ were determined from the particle size distribution (population) to obtain the particle variation coefficient (CV = σ/μ). Table 4 shows the results as a percentage. The maximum particle size _d2 was divided by the average particle size _d1 to obtain the ratio of the maximum particle size to the average particle size ( _d2 / _d1 ).

(2) Sphericity A photograph was taken at a magnification of 2,000 to 250,000 times using a transmission electron microscope (Hitachi, H-8000) to obtain a photographic projection. From this photographic projection, 50 particles were randomly selected, and the maximum diameter DL and the minor diameter DS perpendicular to the maximum diameter DL were measured, and the ratio (DS/DL) was calculated. The average value of these was taken as the sphericity.

(3) Protein content Measured by Kjeldahl method. Specifically, the sample was thermally decomposed using sulfuric acid, and the nitrogen contained in the sample was converted to ammonium sulfate. Next, the decomposition liquid was made alkaline, the liberated ammonia was distilled, and the amount of N was measured by titration. The value obtained by multiplying this amount of N by 6.25 was determined as the protein content. In this example, the result of quantifying N was less than 1 ppm, which is the detection limit. Therefore, the protein amount was determined to be less than 6 ppm.

(4) Phosphorus Quantification Approximately 1 g of powder of natural rubber particles was collected on a platinum dish. 5 ml of nitric acid and 10 ml of hydrofluoric acid were added, and the mixture was heated on a sand bath. After drying, a small amount of water and 50 ml of nitric acid were added to dissolve the mixture in a 100 ml measuring flask, and water was added to make the total volume 100 ml. Next, 10 ml of the solution was collected in a 20 ml measuring flask, and this operation was repeated five times to obtain five 10 ml portions. Then, using this, phosphorus was measured by the standard addition method using an ICP plasma emission spectrometer (SII SPS5520).

(5) Identification Test of Fatty Acids and Fatty Acid Esters In the infrared absorption spectrum, the presence or absence of absorption at about 1710 cm ⁻¹ which is assigned to a carbonyl group specific to fatty acids and absorption at about 1740 cm ⁻¹ which is assigned to a carbonyl group specific to fatty acid esters was confirmed.

Specifically, 20 mg of powdered natural rubber particles was molded into a 20φ disk. This was placed in an IR cell connected to a vacuum line and subjected to evacuation at 70°C for 1 hour to remove adsorbed moisture. After evacuation, the temperature was lowered to 25°C, and the IR spectrum of the sample disk was measured with an infrared absorption spectrometer (FT/IR-4600, manufactured by JASCO Corporation).

(6) Glass Transition Temperature: The glass transition temperature was measured using a differential scanning calorimeter (DSC8230L manufactured by Rigaku Corporation) by raising the temperature from -80°C to 80°C at a rate of 10°C/min.

(7) Biodegradability The powder of natural rubber particles was subjected to a biodegradability test based on OECD TG301F (easily degradable) to measure the decomposition rate after 28 days of exposure. In this example, the decomposition rate was 90%.

[Example 2]
The preparation was carried out in the same manner as in Example 1, except that the rotation speed of the emulsifying and dispersing machine was set to 5,000 rpm.

[Example 3]
The preparation was carried out in the same manner as in Example 1, except that the rotation speed of the emulsifying and dispersing machine was set to 13,000 rpm.

[Example 4]
The preparation was carried out in the same manner as in Example 1, except that the dose of gamma rays was 160 kGy.

[Example 5]
The preparation was carried out in the same manner as in Example 1, except that the dose of gamma rays was 400 kGy.

[Example 6]
The same procedure as in Example 1 was repeated except that deproteinized natural rubber (SELATEX 3821 manufactured by Sumitomo Rubber Industries, Ltd.) was used as the natural rubber latex.

[Example 7]
The same preparation as in Example 1 was carried out except that the rotation speed of the emulsifying disperser was set to 16,000 rpm for 20 minutes.

[Comparative Example 1]
The preparation was carried out in the same manner as in Example 1, except that the rotation speed of the emulsifying and dispersing machine was set to 2000 rpm.

[Comparative Example 2]
The same procedure as in Example 1 was carried out except that the crosslinking step was not carried out, but the dried product was in a sheet form and could not be disintegrated with a juicer mixer. Therefore, natural rubber particles were not obtained.

[Comparative Example 3]
The preparation was carried out in the same manner as in Example 1, except that the dose of gamma rays was 600 kGy.

[Comparative Example 4]
The same operation as in Example 1 was carried out except that the dose of gamma rays was 40 kGy. However, the dried product was in a sheet form and could not be crushed with a juicer mixer. Therefore, natural rubber particles were not obtained.

<Tactile properties of powder made from natural rubber particles>
Next, the tactile characteristics of the powders obtained in each Example and Comparative Example were evaluated. For each powder, a sensory test was conducted by 20 expert panelists, and an interview survey was conducted on seven evaluation items, namely, smooth feeling, moist feeling, rolling feeling, uniform spreading, adhesion to skin, duration of rolling feeling, and soft feeling. The evaluation points of each person based on the evaluation point criterion (a) were totaled, and the tactile characteristics were evaluated based on the evaluation criterion (b). The results are shown in Table 5.
Evaluation criteria (a)
5 points: Very excellent.
4 points: Excellent.
3 points: Average.
2 points: Inferior.
1 point: Very poor.
Evaluation Criterion (b)
◎: Total score is 80 points or more. ○: Total score is 60 points or more but less than 80 points. △: Total score is 40 points or more but less than 60 points. ▲: Total score is 20 points or more but less than 40 points. ×: Total score is less than 20 points.

<Liquid foundation usage>
Using the powder of natural rubber particles, W/O type liquid foundations were prepared in the blending ratios (wt%) shown in Table 6. That is, the powder of each example was used as component (10), and was uniformly dispersed together with components (2) to (14) in a disperser, and then mixed with component (1). Furthermore, components (15) to (19) were similarly uniformly mixed. These were heated to 70°C to melt the components, and then emulsified, cooled, and degassed in a disperser to obtain a W/O type liquid foundation. A sensory test was conducted on the liquid foundations thus obtained by 20 expert panelists. An interview survey was conducted regarding six evaluation items, namely, uniform spread, moist feeling, and smoothness during application to the skin, and uniformity, moist feeling, and softness of the cosmetic film after application to the skin. The evaluation points of each person based on the above-mentioned evaluation point criterion (a) were totaled, and the feel of the foundation when used was evaluated based on the above-mentioned evaluation criterion (b). The results are shown in Table 7. The cosmetics according to the Examples have an excellent feeling during and after application, whereas the cosmetics according to the Comparative Examples have an unfavorable feeling during application.

Claims (6)

The natural rubber particles are formed by crosslinking a natural rubber component, and are characterized in that the natural rubber particles have an average particle diameter _d1 of 0.01 to 20 μm, a maximum particle diameter _d2 of less than 30 μm, a particle diameter ratio ( _d2 / _d1 ) of 3.0 or less, a particle variation coefficient of less than 40%, a sphericity of 0.80 or more, and a glass transition temperature of -53 to 10°C. The natural rubber particles according to claim 1, having a protein content of less than 10 ppm. 3. The natural rubber particle according to claim 1, wherein no peaks are observed near 1710 cm ⁻¹ and 1740 cm ⁻¹ in an infrared absorption spectrum. Natural rubber particles according to any one of claims 1 to 3, having a phosphorus content of less than 100 ppm. A cosmetic composition containing a cosmetic ingredient and the natural rubber particles described in any one of claims 1 to 4. The cosmetic according to claim 5 , wherein the natural rubber particles have an average particle diameter _d1 of 1 to 20 μm.