Natural rubber particles, a method for producing the same, and a cosmetic

Abstract

To achieve highly elastic substitute materials for silicone beads and polyurethane beads by using natural rubber having high elasticity and good biodegradability.SOLUTION: Natural rubber particles have an average particle size d1 of 0.01-20 μm, a maximum particle diameter d2 that is up to three times 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.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Currently, petroleum-derived synthetic polymers (plastics) 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 period, 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 cosmetics and the like, small lumps of plastic resin before processing, and those that have been refined while large products are floating in the sea.

[0003] Plastic particles are difficult to remove in sewage treatment plants because of their low true specific gravity and are likely to flow into rivers, the ocean, ponds, etc. Furthermore, plastic particles are likely to adsorb chemical substances such as pesticides, and thus may affect the human body through bioaccumulation. This has also been pointed out by the United Nations Environment Programme and others, and various countries and industrial 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 origin 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 origin 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 also 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. Also, 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 a substitute material for silicone beads and polyurethane beads.

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

Means for Solving the Problems

[0008] 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.

[0009] 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 to hydrolyze a lipid to obtain a solid of purified natural rubber, a step of adding an organic solvent to the purified natural rubber to dissolve the purified natural rubber to obtain a solution, a step of mixing the solution, a surfactant, and water to prepare an emulsion containing emulsion droplets, a crosslinking step of irradiating the emulsion with ionizing radiation to crosslink the natural rubber particles, an organic solvent removing step of removing the organic solvent from the emulsion droplets, and a solid-liquid separation step of subjecting the aqueous dispersion obtained through the crosslinking step and the organic solvent removing step to solid-liquid separation to obtain the natural rubber particles as a solid.

[0010] Alternatively, the crosslinking step may be performed after removing the organic solvent from the emulsion.

Embodiments for Carrying Out the Invention

[0011] The present invention relates to natural rubber particles formed by crosslinking a natural rubber component, having an average particle diameter d1 of 0.01 to 20 μm, a maximum particle diameter d2 of less than 30 μm, a particle size ratio (d2 / d1) 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.

[0012] The shape of the particles affects the tactile properties of the powder. For particles with an average particle diameter d1 greater than 20 μm or particles with a maximum particle diameter d2 of 30 μm or more, a rough feeling is felt, 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. Particles with an average particle diameter d1 less than 0.01 μm are difficult to manufacture industrially. When using the particles (powder) as a tactile improvement material, the average particle diameter d1 is preferably 1 to 20 μm, and most optimally 5 to 15 μm. If it is less than 1 μm, the tactile properties such as the rolling feeling, the persistence of the rolling feeling, and the uniform spreading property decrease. Particles with an average particle diameter d1 of less than 0.01 to 1 μm are suitable as a soft focus material because of their high light scattering effect.

[0013] 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 possibility that uniform rollability 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, it can be manufactured without particular problems.

[0014] Also, the glass transition temperature is related to the degree of cross-linking of natural rubber. Natural rubber in a state where the glass transition temperature is lower than -53°C has insufficient cross-linking and stickiness, so it cannot be taken out as a 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.

[0015] The sphericity is 0.80 or more. The higher the sphericity, the better the rolling feeling of the powder (particles). The sphericity is particularly preferably 0.90 or more.

[0016] Furthermore, the protein content is preferably less than 10 ppm. There is less risk of developing immediate-type allergy (latex allergy) caused by proteins. Furthermore, the phosphorus content derived from phospholipids is preferably less than 100 ppm. Also, it is preferably free of fatty acids. Odor, bacterial growth, deterioration, and spoilage can be suppressed. In the infrared absorption spectrum of natural rubber particles, absorption near 1710 cm -1 characteristic of fatty acids, and absorption near 1740 cm -1 characteristic of fatty acid esters are not substantially observed, it can be determined that no fatty acids are contained.

[0017] By forming particles with natural rubber having a cis molecular structure as a component, high elasticity can be obtained. Examples of cis-type natural resources include Ficus elastica, guayule, Russian dandelion, etc. Particles obtained from trans-type gum arabic may not obtain high elasticity.

[0018] Crosslinked natural rubber has a slower biodegradation rate compared to uncrosslinked natural rubber. However, the natural rubber 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), 60% or more is decomposed. Such natural rubber particles do not fall under the definition proposal of microplastics proposed by the European Chemicals Agency.

[0019] Also, the specific gravity of natural rubber is lighter than water and is likely to float in water. Therefore, there is concern that it cannot be removed in wastewater treatment facilities and is directly released into the environment. However, since natural rubber has photodegradability, it is easily incorporated into the cycle of the material circulation in nature.

[0020] Also, although natural rubber particles are hydrophobic, by performing surface treatment to make them hydrophilic, they can be incorporated into aqueous cosmetics. The surface treatment method may be any method that can modify the surface of natural rubber particles to be hydrophilic. For example, treatment with nonionic or anionic surfactants having 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.

[0021] <Method for Producing Natural Rubber Particles> First, an alkali is added to an uncrosslinked natural rubber latex solution to hydrolyze lipids and then washed with water. Acid is added thereto to coagulate the latex, followed by further washing with water and drying (purification step). Thereby, a solid of purified natural rubber with reduced lipids is obtained. Next, this solid of natural rubber is added to an organic solvent and dissolved until it becomes completely transparent (dissolution step). Thereby, a solution in which natural rubber is dissolved in the organic solvent is obtained. Next, this solution, a surfactant, and water are mixed to prepare an emulsion containing emulsion droplets (emulsification step). Thereby, an O / W emulsion containing emulsion droplets composed of an inner layer of a solution in which natural rubber is dissolved in an organic solvent and an outer layer of water is obtained. This emulsion is irradiated with ionizing radiation to crosslink the natural rubber (crosslinking step). Thereby, a three-dimensional network structure in which the constituent components (chain-like polyisoprene) of natural rubber are crosslinked is obtained. Subsequently, the organic solvent is removed from the emulsion droplets in the O / W emulsion (organic solvent removal step). Thereby, an aqueous dispersion of crosslinked natural rubber particles is obtained. Next, this aqueous dispersion is subjected to solid-liquid separation, further washed with water, and a cake-like substance is taken out (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 interchanged. That is, after removing the organic solvent from the emulsion obtained in the emulsification step, it may be irradiated with ionizing radiation.

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

[0023] [Purification Step] An alkali is added to unvulcanized natural rubber latex, and it is heated at room temperature to 200 °C to hydrolyze lipids. Natural rubber latex mainly consists of cis-polyisoprene contained in the sap of rubber trees such as Hevea brasiliensis. Furthermore, it contains about 6% by weight of non-rubber components such as proteins, fatty acids, and phospholipids. By reducing the lipids, the amount of gel components insoluble in organic solvents in the subsequent dissolution process is reduced, and the yield is improved. 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 5% or more is preferred.

[0024] After hydrolysis, the rubber component and lipids are separated by ultrafiltration, centrifugation, etc. Next, an acidic component such as a mineral acid is added, and the rubber component is separated by solid-liquid separation and washed with water. Then, vacuum drying is performed to obtain a solid of natural rubber.

[0025] Also, on the market, products in which ammonia is added to natural rubber latex and concentrated to about 60% by centrifugation, etc. are in circulation, and these may be used as raw materials.

[0026] Furthermore, it is desirable to reduce proteins by enzyme treatment using enzymes, modification treatment using modifiers, or extraction with acetone, etc. On the market, deproteinized natural rubber latex (for example, enzyme-treated latex (Ceraltex manufactured by Sumitomo Rubber Industries, Ltd.), aluminum hydroxide-treated latex (manufactured by Thailand MMG Polymer, etc.) are in circulation, and these may be utilized. Those with residual protein reduced to less than 1% are preferred. On the other hand, rubber in the form of sheets (visually graded rubber) and blocks (technologically graded rubber) that are in circulation as solid rubber contain a large amount of non-rubber components and are difficult to purify.

[0027] [Dissolution process] Next, add the solid content of natural rubber into an organic solvent, and heat it from room temperature to below the boiling point of the solvent to dissolve it. The SP value of the organic solvent is preferably 6 - 10 (in the range of approximately ±2 with respect to the SP value of natural rubber, which is 8). Cyclohexane, etc. are suitable. The gel component does not dissolve even when high temperature and high pressure are applied in an autoclave. Therefore, the solution is ultrafiltered to separate the gel. Thereby, a transparent natural rubber solution is obtained. Since proteins and lipids are water-soluble, they can be reduced by this ultrafiltration. It is economical that the solid content in the natural rubber solution is 50% or more.

[0028] [Emulsification step] Mix the natural rubber solution, water, and a surfactant. The surfactant is added to form O / W type emulsion droplets. An HLB value of 8 - 18 is suitable for the surfactant. Next, emulsify this mixed solution using an emulsifying device. At this time, set the emulsification conditions so that an emulsion containing emulsion droplets with an average diameter of about 0.02 - 40 μm is obtained. The natural rubber solution exists in the emulsion droplets. As the emulsifying device, a general high-speed shearing device can be used. In addition, known devices such as a high-pressure emulsifying device that can obtain finer nano-sized emulsion droplets, a membrane emulsifying device that can obtain more uniform emulsion droplets, and a microchannel emulsifying device can be applied according to the purpose.

[0029] Note that the average diameter of the emulsion droplets was measured as follows. Drop the emulsion onto a slide glass and cover it with a cover glass from above. Take a photograph of the emulsion droplets through the cover glass at a magnification of 30 to 2000 times using a digital microscope (manufactured by Keyence Corporation, VHX - 600) to obtain a photographic projection diagram of the emulsion droplets. From this photographic projection diagram, arbitrarily select 50 droplets and calculate the equivalent circle diameter using the attached software. The average value of these 50 equivalent circle diameters was taken as the average diameter (average droplet diameter).

[0030] [Crosslinking step] Put this emulsion into a metal container and irradiate it with ionizing radiation. When irradiating with ionizing radiation to raise the temperature by about 10 °C relative to the glass transition temperature of the uncrosslinked natural rubber, the adhesiveness of the particles can be suppressed and they can be taken out as powder. Also, due to the irradiation of ionizing radiation, the remaining non-rubber components are decomposed and transferred to the aqueous layer. Therefore, the purity of natural rubber increases. 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 - 500 kGy. When it is less than 50 kGy, since crosslinking is underdeveloped, when the emulsion is subjected to solid-liquid separation, the rubber 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.

[0031] 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. In addition, the glass transition temperature of natural rubber particles can be adjusted in this crosslinking process. A 200L drum can is also suitable for handling as the metal container.

[0032] [Organic solvent removal step] Remove the organic solvent from the emulsion obtained in the crosslinking step. By heating under normal pressure or reduced pressure, the organic solvent is evaporated. Thereby, the organic solvent is removed from the emulsion droplets, and an aqueous dispersion containing natural rubber particles with a particle size of about 0.02 - 40 μm is obtained.

[0033] For example, in the heating removal method under normal pressure, a separable flask equipped with a condenser is heated to remove the organic solvent. Also, in the heating removal method under reduced pressure, reduced pressure heating is carried out using a rotary evaporator or an evaporator to remove the organic solvent.

[0034] [Solid-liquid separation step] Next, the solid content is separated from the aqueous dispersion obtained in the organic solvent removal step by a known method such as filtration or centrifugation. As a result, a cake-like substance of natural rubber particles is obtained. By washing the obtained cake-like substance, the surfactant can be reduced. When the natural rubber particles are incorporated 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 natural rubber particles is preferably 100 ppm or less. To reduce the surfactant, it is advisable to wash with an organic solvent.

[0035] [Drying step] In the drying step, the moisture 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 natural rubber particles with an average particle size of 0.01 to 20 μm is obtained.

[0036] [Cosmetics] The above-mentioned natural rubber particles and various cosmetic components can be blended to prepare cosmetics. According to such cosmetics, a flexibility similar to that of silicone beads or polyurethane beads can be felt. At the same time, excellent tactile properties (rolling feeling, persistence of the rolling feeling, and uniform spreading property, soft feeling and moist feeling) possessed by the powder of natural rubber particles can be obtained. That is, the typical tactile properties required for a tactile improver for cosmetics can be satisfied. As the tactile improver, natural rubber particles with an average particle size d1 of 1 to 20 μm are particularly suitable.

[0037] 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, and cream.

[0038] Table 2 illustrates typical classifications and components as various cosmetic ingredients. Furthermore, cosmetic ingredients listed in Pharmaceutical Excipients Standards 2006 (published by Yakujitsu Shimbun Co., Ltd., June 16, 2006), International Cosmetic Ingredient Dictionary and Handbook (published by The Cosmetic, Toiletry, and Fragrance Association, Eleventh Edition 2006), etc. may be blended.

[0039]

Table 1

[0040]

Table 2

Examples

[0041] Hereinafter, examples of the present invention will be specifically described.

[0042] [Example 1] De-proteinized natural rubber (SELATEX-1101 manufactured by Sumitomo Rubber Industries, Ltd.) was used as 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 obtained aqueous dispersion was 13.5. This aqueous dispersion was heated to 40°C and stirred for 24 hours to hydrolyze the lipid. Next, it was washed using an ultrafiltration membrane until the electrical conductivity became 10 mS / m or less. Next, vacuum drying was performed using a rotary evaporator to obtain a solid of purified natural rubber.

[0043] Cyclohexane was added to this solid to a solid content of 50% by weight, and then stirred at 60°C for 2 hours to obtain a transparent solution of natural rubber.

[0044] To 200 g of this dissolution solution, a mixed solution of 3346 g of water and 25 g of a surfactant (Leodol TW-O120V manufactured by Kao Corporation) was added. This mixed solution was stirred at 10,000 rpm for 10 minutes using an emulsifying and dispersing machine (T.K. Robomix manufactured by Primix Corporation). As a result, emulsification occurred, and an emulsion containing emulsion droplets was obtained.

[0045] This emulsion was packed into a 4 L metal square can (manufactured by AS ONE Corporation) and irradiated with γ-rays at a dose of 270 kGy to crosslink the natural rubber in the emulsion droplets.

[0046] Next, cyclohexane was distilled off and removed from this emulsion using a rotary evaporator. The obtained aqueous dispersion was filtered through quantitative filter paper (No. 2 manufactured by Advantec Toyo Kaisha Ltd.) using a Buchner funnel (3.2 L manufactured by Sekiyama Rika Kikai Kogyo Co., Ltd.). Then, washing with water was performed until the electric conductivity reached 1 mS / m to remove non-rubber components. 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. This dried powder was crushed with a juicer mixer and sieved through a 250 mesh sieve (JIS test standard sieve) to obtain natural rubber particles.

[0047] The preparation conditions of the natural rubber particles were summarized in Table 3. Also, the physical properties of the powder of the natural rubber particles were measured by the following method. The same measurements were performed for other examples and comparative examples, and the results are shown in Table 4.

[0048] (1) Average particle diameter, maximum particle diameter, coefficient of variation of particles Using a laser diffraction apparatus (LA-950v2 manufactured by Horiba, Ltd.), the particle size distribution of the natural rubber particles was measured. From this particle size distribution, the median value was obtained and taken as the average particle diameter d1. Also, the largest particle diameter detected in the particle size distribution was taken as the maximum particle diameter d2. Furthermore, the standard deviation σ and the population mean μ were obtained from the particle size distribution (population), and the coefficient of variation of particles (CV = σ / μ) was obtained. In Table 4, it is expressed as a percentage. Also, the ratio of the maximum particle diameter to the average particle diameter (d2 / d1) was obtained by dividing the maximum particle diameter d2 by the average particle diameter d1.

[0049] (2) Sphericity Photographs were taken at magnifications ranging from 2,000 to 250,000 times using a transmission electron microscope (Hitachi, Ltd., H-8000) to obtain photographic projection diagrams. From these photographic projection diagrams, 50 arbitrary particles were selected, and the maximum diameter DL and the minor axis DS perpendicular to it were measured for each particle, and the ratio (DS / DL) was determined. The average value of these ratios was defined as the sphericity.

[0050] (3) Protein content It was measured by the Kjeldahl method. Specifically, the sample was decomposed by heating with sulfuric acid, and the nitrogen contained in the sample was converted into ammonium sulfate. Next, the decomposition solution 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 defined as the protein content. In this example, as a result of quantifying N, it was less than 1 ppm, the detection limit. Therefore, the protein amount was judged to be less than 6 ppm.

[0051] (4) Phosphorus quantification Approximately 1 g of natural rubber particle powder was collected in a platinum dish. 5 ml of nitric acid and 10 ml of hydrofluoric acid were added, and it was heated on a sand bath. After drying, a small amount of water and 50 ml of nitric acid were added to dissolve it, and it was put into a 100-ml volumetric flask and diluted to 100 ml with water. Next, the operation of collecting 10 ml of this solution into a 20-ml volumetric flask was repeated 5 times to obtain 5 aliquots of 10 ml. Then, using these, phosphorus was measured by the standard addition method with an ICP plasma emission spectrometer (SPS5520 manufactured by SII).

[0052] (5) Confirmatory test for fatty acids and fatty acid esters In the infrared absorption spectrum, the absorption near 1710 cm attributed to the carbonyl group characteristic of fatty acids and the absorption near 1740 cm attributed to the carbonyl group characteristic of fatty acid esters were confirmed for their presence or absence. -1 near, and the absorption near 1740 cm -1 attributed to the carbonyl group characteristic of fatty acid esters.

[0053] Specifically, 20 mg of natural rubber particle powder was molded into a 20φ disk. This was placed in an IR cell connected to a vacuum line and subjected to vacuum evacuation treatment at 70 °C for 1 hour to remove adsorbed moisture. After the vacuum evacuation treatment, 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).

[0054] (6) 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.

[0055] (7) Biodegradability A biodegradability test was conducted on the natural rubber particle powder based on OECD TG301F (ready biodegradability), and the degradation rate in a 28-day exposure was measured. In this example, this degradation rate was 90%.

[0056] [Example 2] It was prepared in the same manner as in Example 1, except that the rotation speed of the emulsifying disperser was set to 5000 rpm.

[0057] [Example 3] It was prepared in the same manner as in Example 1, except that the rotation speed of the emulsifying disperser was set to 13000 rpm.

[0058] [Example 4] It was prepared in the same manner as in Example 1, except that the γ-ray irradiation dose was set to 160 kGy.

[0059] [Example 5] It was prepared in the same manner as in Example 1, except that the γ-ray irradiation dose was set to 400 kGy.

[0060] [Example 6] It was prepared in the same manner as in Example 1, except that deproteinized natural rubber (SELATEX 3821 manufactured by Sumitomo Rubber Industries, Ltd.) was used as the natural rubber latex.

[0061] [Example 7] It was prepared in the same manner as in Example 1, except that the rotation speed of the emulsifying disperser was set at 16,000 rpm for 20 minutes.

[0062] [Comparative Example 1] It was prepared in the same manner as in Example 1, except that the rotation speed of the emulsifying disperser was set at 2,000 rpm.

[0063] [Comparative Example 2] When the same operations as in Example 1 were carried out except that the crosslinking step was not performed, the dried product became sheet-like and could not be crushed by the juicer mixer. Therefore, natural rubber particles could not be obtained.

[0064] [Comparative Example 3] It was prepared in the same manner as in Example 1, except that the γ-ray irradiation dose was set at 600 kGy.

[0065] [Comparative Example 4] When the same operations as in Example 1 were carried out except that the γ-ray irradiation dose was set at 40 kGy, the dried product became sheet-like and could not be crushed by the juicer mixer. Therefore, natural rubber particles could not be obtained.

[0066]

Table 3

[0067]

Table 4

[0068] 〈Tactile properties of the powder of natural rubber 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 conducted 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 the evaluation score criteria (a) were totaled, and the tactile properties were evaluated based on the evaluation criteria (b). The results are shown in Table 5. Evaluation score 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

[0069]

Table 5

[0070] 〈Feeling of using liquid foundation〉 Using powder of natural rubber particles, a W / O type liquid foundation was prepared to have the blending ratio (weight %) shown in Table 6. That is, the powder of each example was used as component (10), and was uniformly dispersed in a disper together with components (2) to (14), and then 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 disper to obtain a W / O type liquid foundation. For 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 feeling of using 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 have excellent usability both during and after application. However, the cosmetics of the comparative examples have poor usability.

[0071]

Table 6

[0072]

Table 7

Claims

Claim 1 Natural rubber particles formed by crosslinking a natural rubber component, with an average particle diameter d １ being 0.01 to 20 μm, a maximum particle diameter d ２ being less than 30 μm, a particle size ratio (d ２ / d １ ) being 3.0 or less, a coefficient of variation of particle size being less than 40%, a sphericity being 0.80 or more, and a glass transition temperature being -53 to 10°C. The natural rubber particles are characterized by these features. Claim 2 The natural rubber particles according to claim 1, wherein the protein content is less than 10 ppm. Claim 3 In the infrared absorption spectrum, no peak is observed in the vicinity of 1710 cm －１ and in the vicinity of 1740 cm －１ The natural rubber particles according to claim 1 or 2, characterized in that no peak is observed in the vicinity thereof. Claim 4 The natural rubber particles according to any one of claims 1 to 3, wherein the phosphorus content is less than 100 ppm. Claim 5 A cosmetic comprising a cosmetic ingredient and the natural rubber particles according to any one of claims 1 to 4. Claim 6 The average particle diameter d of the natural rubber particles １ The cosmetic according to claim 5, wherein the average particle diameter d is 1 to 20 μm.

Images