Rice wax fine particles and process for producing the same

Abstract

To provide rice wax fine particles substantially free from an emulsifier.SOLUTION: The rice bran wax fine particles have a polydispersion index of 0.25 or less in particle size distributions measured by a dynamic light scattering method, and absolute values of peak tops of zeta potentials of surfaces of the rice bran wax fine particles are 10mV or less.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present disclosure relates to rice wax microparticles. [Background technology]

[0002] Conventionally, wax microparticles have been used in various fields such as cosmetics, paints, etc. For example, Patent Document 1 discloses a method for producing wax microparticles, in which wax is emulsified in a solvent using an emulsifier, and then the solvent is removed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-166756 Summary of the Invention [Problem to be solved by the invention]

[0004] Rice wax microparticles, a type of wax microparticle, are in high demand as a natural wax. However, the method for producing wax microparticles described in Patent Document 1 contains an emulsifier in the wax microparticles, leaving room for improvement as rice wax microparticles made from naturally derived ingredients. For this reason, there has been a demand for rice wax microparticles that are substantially free of emulsifiers. [Means for solving the problem]

[0005] The present invention can be realized as the following aspects.

[0006] (1) According to one embodiment of the present disclosure, rice wax microparticles are provided. These rice wax microparticles have a polydispersity index of 0.25 or less in particle size distribution measured by dynamic light scattering, and an absolute value of the peak top of the surface zeta potential of 10 mV or less. Because the absolute value of the peak top of the surface zeta potential of the rice wax microparticles of this embodiment is 10 mV or less, rice wax microparticles that are substantially free of emulsifiers can be provided.

[0007] (2) According to another aspect of the present disclosure, there is provided a method for producing the rice wax microparticles described in (1) above. This method for producing rice wax microparticles includes an emulsification step in which rice wax is emulsified using water and an emulsifier to obtain a dispersion, and a removal step in which the emulsifier contained in the dispersion is removed by washing with a solvent. According to this aspect of the method for producing rice wax microparticles, the emulsifier can be removed in the removal step, making it possible to produce rice wax microparticles that are substantially free of emulsifier.

[0008] (3) In the method for producing rice wax microparticles described in (2) above, the solvent may contain ethanol. According to this form of the method for producing rice wax microparticles, the rice wax microparticles are washed with ethanol in the removal step, which prevents the safety of the rice wax microparticles from being reduced.

[0009] The present invention can be realized in various forms, such as cosmetics containing rice wax microparticles and methods for producing the same, pharmaceuticals containing rice wax microparticles and methods for producing the same, foods containing rice wax microparticles and methods for producing the same, liquid marble containing rice wax microparticles and methods for producing the same, Pickering emulsions containing rice wax microparticles and methods for producing the same, use of rice wax microparticles for producing cosmetics, use of rice wax microparticles for producing liquid marble, use of rice wax microparticles for producing Pickering emulsion, etc. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an optical microscope image of a rice wax microparticle dispersion. [Figure 2] FIG. 2 is an explanatory diagram showing the particle size distribution of microparticles contained in a rice wax microparticle dispersion. [Figure 3] FIG. 1 is an explanatory diagram showing the measurement results of the zeta potential of a rice wax microparticle dispersion. [Figure 4] FIG. 1 is an explanatory diagram showing a 1H nuclear magnetic resonance spectrum. [Figure 5] FIG. 1 is an explanatory diagram showing the results of water contact angle evaluation. [Figure 6] FIG. 1 is an explanatory diagram showing the results of X-ray diffraction measurements. [Figure 7] FIG. 1 is an explanatory diagram showing the results of a thermal profile in DSC. [Figure 8] FIG. 1 is an explanatory diagram showing the particle size distribution of microparticles contained in a dispersion of rice wax microparticles from which the emulsifier has been removed. [Figure 9] FIG. 1 is an explanatory diagram showing the measurement results of the zeta potential of rice wax microparticles from which the emulsifier has been removed. [Figure 10] This is a photographic image of liquid marble. [Figure 11] 1 is an observation image of a Pickering emulsion. DETAILED DESCRIPTION OF THE INVENTION

[0011] According to one embodiment of the present disclosure, there is provided rice wax microparticles having a polydispersity index (PDI) of 0.25 or less in particle size distribution measured by dynamic light scattering (DLS) and a surface zeta potential peak top absolute value of 10 mV or less.

[0012] Rice wax is a vegetable wax that is primarily produced as a by-product during the process of extracting and refining rice bran oil.

[0013] The polydispersity index of the particle size distribution measured by dynamic light scattering can be calculated as follows: The relationship between the particle diffusion rate and particle size is given by the Stokes-Einstein equation (D = k B T / 6πηR H ) where D is the translational diffusion coefficient (m 2 / s) - "particle diffusion rate" and k B is the Boltzmann constant (m 2 kg / Ks 2 ), T is temperature (K), η is viscosity (Pa s), and R H indicates the hydrodynamic radius (m). In dynamic light scattering, a single-frequency laser is irradiated onto a sample, and the change in scattered light over time is measured at a specified angle. This signal is used to calculate the diffusion coefficient and particle size using the Stokes-Einstein equation. The fluctuations of the scattered light over time are expressed as an autocorrelation function, and the translational diffusion coefficient is determined. The Stokes diameter can be calculated from the determined diffusion coefficient, and the average particle size of the particles dispersed in the solution can be derived. In addition, the polydispersity index can be determined by cumulant analysis of the autocorrelation function (JIS Z8826 / ISO 013321). The surface zeta potential can be determined using electrophoretic light scattering, more specifically, using an Anton Paar Litesizer.

[0014] The rice wax microparticles of the present disclosure have a polydispersity index of 0.25 or less, resulting in excellent particle size uniformity. Furthermore, the rice wax microparticles of the present disclosure have a surface zeta potential peak top absolute value of 10 mV or less, resulting in substantial emulsifier-free content. Therefore, the rice wax microparticles of the present disclosure are substantially free of emulsifiers and have excellent particle size uniformity. In this disclosure, "substantially free of emulsifiers" means that the surface zeta potential peak top absolute value of the rice wax microparticles is 10 mV or less. The polydispersity index of the rice wax microparticles is preferably 0.20 or less, more preferably 0.15 or less, and even more preferably 0.10 or less. Furthermore, the surface zeta potential peak top absolute value of the rice wax microparticles is preferably 8 mV or less, more preferably 6 mV or less, and even more preferably 4 mV or less.

[0015] The average particle size of the rice wax microparticles of the present disclosure is not particularly limited, but from the viewpoint of stabilizing the structure of the Pickering emulsion, the average particle size measured by dynamic light scattering is preferably 0.1 μm to 10 μm, more preferably 0.3 μm to 5 μm, and even more preferably 0.5 μm to 3 μm. The average particle size can be determined by the method described above.

[0016] The rice wax microparticles of the present disclosure can be used in a variety of applications, including cosmetics, pharmaceuticals, foods, beverages, and paints. Because the rice wax microparticles of the present disclosure are substantially free of emulsifiers, they are suitable for preparing, for example, liquid marble and Pickering emulsions. Furthermore, because the rice wax microparticles of the present disclosure are substantially free of emulsifiers, their surfaces are hydrophobic, making them particularly suitable for preparing water-in-oil (W / O) Pickering emulsions.

[0017] Liquid marbles are liquid droplets coated with particles that have hydrophobic surfaces. Because the wax microparticles of the present disclosure have hydrophobic surfaces, they can stabilize the droplets by adsorbing to the gas-liquid interface, producing liquid marbles, which are liquid / gas dispersions. The liquid that coats the liquid marbles is not particularly limited, but examples include water and glycerol.

[0018] The oil agent used in preparing the Pickering emulsion is not particularly limited and examples thereof include liquid oils, hydrocarbon oils, ester oils, silicone oils, etc., and preferably includes liquid oils. One type of oil agent may be used alone, or two or more types may be used in combination.

[0019] The liquid oils and fats are not particularly limited, but examples thereof include emu oil, avocado oil, camellia oil, turtle oil, macadamia nut oil, corn oil, mink oil, olive oil, rapeseed oil, egg yolk oil, sesame oil, persic oil, wheat germ oil, camellia oil, castor oil, linseed oil, safflower oil, cottonseed oil, perilla oil, meadowfoam oil, soybean oil, peanut oil, tea seed oil, Japanese kaya oil, rice bran oil, Chinese tung oil, Japanese tung oil, jojoba oil, germ oil, triglycerin, glycerin trioctanoate (triethylhexanoin), glycerin triisopalmitate, and the like.

[0020] The hydrocarbon oil is not particularly limited, but examples thereof include liquid paraffin, pristane, paraffin, squalene, and petrolatum.

[0021] The ester oil is not particularly limited, but examples thereof include isopropyl myristate, cetyl octanoate, octyldodecyl myristate, isopropyl palmitate, butyl stearate, hexyl laurate, myristyl myristate, decyl oleate, hexyldecyl dimethyloctanoate, isocetyl stearate, isocetyl isostearate, ethylene glycol di-2-ethylhexanoate, neopentyl glycol dicaprate, diisostearyl malate, glycerin di-2-heptylundecanoate, trimethylolpropane tri-2-ethylhexanoate, trimethylolpropane triisostearate, pentaneerythritol tetra-2-ethylhexanoate, glycerin tri-2-ethylhexanoate, triisostearate, Examples of suitable oils include methylolpropane, cetyl 2-ethylhexanoate, 2-ethylhexyl palmitate, glycerin trimyristate, tri-2-heptylundecanoic acid glyceride, oleic acid oil, cetostearyl alcohol, acetoglyceride, 2-heptylundecyl palmitate, cetyl palmitate, diisobutyl adipate, N-lauroyl-L-glutamic acid-2-octyldodecyl ester, di-2-heptylundecyl adipate, ethyl laurate, di-2-ethylhexyl sebacate, 2-hexyldecyl myristate, 2-hexyldecyl palmitate, 2-hexyldecyl adipate, diisopropyl sebacate, 2-ethylhexyl succinate, ethyl acetate, butyl acetate, amyl acetate, and triethyl citrate.

[0022] The silicone oil is not particularly limited, but examples thereof include linear siloxanes, cyclic siloxanes, etc. The linear siloxane is not particularly limited, but examples thereof include dimethylpolysiloxane, methylphenylpolysiloxane, methylhydrogenpolysiloxane, diphenyltrimethicone, diphenylsiloxyphenyltrimethicone, etc. The cyclic siloxane is not particularly limited, but examples thereof include pentasiloxane, decamethylpolysiloxane, dodecamethylpolysiloxane, tetramethyltetrahydrogenpolysiloxane, etc.

[0023] The method for producing the rice wax microparticles of this embodiment is not particularly limited, but they can be produced, for example, by the method described below. According to another aspect of the present disclosure, there is provided a method for producing rice wax microparticles.

[0024] The method for producing rice wax microparticles of the present disclosure includes an emulsification step in which rice wax is emulsified using water and an emulsifier to obtain a dispersion, and a removal step in which the emulsifier contained in the dispersion is removed by washing with a solvent.

[0025] The emulsifier used in the emulsification step is not particularly limited and includes, for example, nonionic emulsifiers, amphoteric emulsifiers, etc. However, from the viewpoint of narrowing the particle size distribution of the rice wax microparticles, it is preferable to use a nonionic emulsifier. Nonionic emulsifiers include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, condensates of polyethylene glycol and polypropylene glycol, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, fatty acid monoglycerides, polyglyceric acid esters, alkyl polyglucosides, sucrose fatty acid esters, etc. As the nonionic emulsifier, it is preferable to use at least one of fatty acid monoglycerides and polyglyceric acid esters. As the amphoteric emulsifier, it is not particularly limited and includes, for example, lecithin, betaine ester-type emulsifiers, etc. One emulsifier may be used alone, or two or more may be used in combination.

[0026] The emulsification step is preferably carried out at a temperature equal to or higher than the melting point of the rice wax, in order to narrow the particle size distribution of the rice wax microparticles. More specifically, a temperature of 80°C or higher is preferred, 85°C or higher is more preferred, and 90°C or higher is even more preferred. Furthermore, in order to narrow the particle size distribution of the rice wax microparticles, the emulsification step is preferably carried out by applying sufficient shear force. More specifically, stirring may be carried out using, for example, a liquid phase stirring method using a stirring blade, a stirring method using a continuous twin-screw mixer, a stirring method using a homomixer, or a stirring method using ultrasonic irradiation, and shear force is preferably applied using a homomixer. The stirring time is not particularly limited, but is preferably 3 minutes or more, more preferably 5 minutes or more, and even more preferably 7 minutes or more.

[0027] In order to narrow the particle size distribution of the rice wax microparticles, the emulsification process preferably includes a step of mixing a solution (hereinafter also referred to as the "first solution") obtained by heating and dissolving rice wax and an emulsifier (hereinafter also referred to as the "second emulsifier") into a solution (hereinafter also referred to as the "first solution") obtained by mixing water and an emulsifier (hereinafter also referred to as the "first emulsifier").

[0028] From the viewpoint of narrowing the particle size distribution of the rice wax microparticles, it is preferable that both the first emulsifier and the second emulsifier are nonionic emulsifiers. The first emulsifier and the second emulsifier may be the same type of emulsifier, but are preferably different types of emulsifiers. The first emulsifier is preferably a hydrophilic emulsifier with an HLB value of less than 10, and the second emulsifier is preferably a lipophilic emulsifier with an HLB value of 10 or more. The dispersion obtained by the emulsification step may contain any component in addition to water and the emulsifier.

[0029] The method for producing rice wax microparticles may include a step of cooling the resulting dispersion after the emulsification step. In the cooling step, the dispersion is preferably cooled to a temperature below the melting point of the rice wax. More specifically, the dispersion is preferably cooled to 70°C or below, more preferably to 60°C or below, and even more preferably to 50°C or below. The cooling method in the cooling step is not particularly limited, but air cooling is preferred from the viewpoint of preventing the rice wax microparticle production process from becoming too complicated.

[0030] The solvent used in the removal step (hereinafter also referred to as "cleaning solution") is not particularly limited, and examples thereof include alcohol, acetone, ethyl acetate, hexane, petroleum ether, etc., but it is preferable to include alcohol in order to prevent a decrease in the safety of the rice wax microparticles. The alcohol is not particularly limited, and examples thereof include ethanol, methanol, 1-propanol, 2-propanol, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, dibutylene glycol, etc., but it is preferable to include ethanol in order to prevent a decrease in the safety of the rice wax microparticles. The concentration of the cleaning solution is not particularly limited, but in order to effectively remove the emulsifier, it is preferably 2% by volume or more and 98% by volume or less, and more preferably 5% by volume or more and 95% by volume or less. Therefore, it is even more preferable that the cleaning solution be 2% by volume or more and 98% by volume or less of ethanol, and even more preferably 5% by volume or more and 95% by volume or less of ethanol. The cleaning solution may contain any optional components.

[0031] In the removal step, it is preferable to mix the dispersion with a washing liquid to generate insoluble matter, and then dry the insoluble matter. Furthermore, from the viewpoint of efficiently removing the emulsifier, it is preferable to repeatedly mix the dispersion with the washing liquid and dry the insoluble matter. More specifically, it is preferable to perform this process twice or more, and more preferably three or more times. When mixing the dispersion with the washing liquid, it is preferable to mix the washing liquid in an amount at least twice as large as the volume of the dispersion, more preferably at least four times as large as the volume of the washing liquid, and even more preferably at least eight times as large as the volume of the washing liquid. When generating insoluble matter, filtration is preferably performed. The filtration method is not particularly limited, but filter filtration is preferred, and membrane filter filtration is more preferred. The method for drying the insoluble matter is not particularly limited, and examples include vacuum drying (reduced-pressure drying), freeze drying, and air drying. However, vacuum drying is preferred from the viewpoint of suppressing the incorporation of impurities. When mixing the dispersion or insoluble matter with the washing liquid, it is preferable to perform ultrasonic irradiation from the viewpoint of efficiently removing the emulsifier. The duration of ultrasonic irradiation is not particularly limited, but is preferably 10 minutes or more, more preferably 20 minutes or more, and even more preferably 30 minutes or more. [Example]

[0032] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0033] (1) Preparation of rice wax microparticle dispersion 43 g of distilled water and 1.0 g of decaglycerin stearate (manufactured by Nikko Chemicals Co., Ltd.) were added to a 100 mL beaker and heated and dissolved in a water bath at 90°C. A mixture of 5.0 g of rice wax SS-II (manufactured by Boso Oil & Fats Co., Ltd.) and 1.0 g of lipophilic monostearate glyceride (manufactured by Nikko Chemicals Co., Ltd.), which had been separately mixed by heating and dissolving, was added to the beaker with manual stirring to prepare a preliminary emulsion. Next, the mixture was heated in a water bath at 90-95°C and stirred at 32,000 rpm for 8 minutes using an LR-1G homomixer (manufactured by Mizuho Kogyo Co., Ltd.), and then cooled to 40°C under air cooling to prepare the rice wax microparticle dispersion of Example 1.

[0034] The rice wax microparticle dispersion of Example 2 was prepared in the same manner as in Example 1, except that decaglycerin stearate ester (manufactured by Nikko Chemicals Co., Ltd.) was replaced with decaglycerin myristate ester (manufactured by Nikko Chemicals Co., Ltd.).

[0035] The rice wax microparticle dispersions of Examples 1 and 2 were observed under an optical microscope. An OLYMPUS U-CMAD3 was used for the observations. The particle size distribution of the microparticles contained in the rice wax microparticle dispersions of Examples 1 and 2 was measured using a Litesizer TM700 (manufactured by Anton Paar) to determine the polydispersity index. The rice wax microparticle dispersions of Examples 1 and 2 were also subjected to zeta potential measurement using a Litesizer TM700 (manufactured by Anton Paar).

[0036] Figure 1 shows optical microscope images of rice wax microparticle dispersions. Figure 1(a) shows the results of Example 1, and Figure 1(b) shows the results of Example 2. As shown in Figure 1, the diameters of the microparticles contained in the rice wax microparticle dispersions of Examples 1 and 2 were found to be in the submicron to several μm range.

[0037] Figure 2 is an explanatory diagram showing the particle size distribution of microparticles contained in a rice wax microparticle dispersion. Figure 2(a) shows the results of Example 1, and Figure 2(b) shows the results of Example 2. As shown in Figure 2, in both Example 1 and Example 2, the particle size distribution had little variation and the polydispersity index was small. More specifically, the polydispersity index of the rice wax microparticles in Example 1 was 0.24, and the polydispersity index of the rice wax microparticles in Example 2 was 0.25.

[0038] Figure 3 is an explanatory diagram showing the measurement results of the zeta potential of rice wax microparticle dispersions. Figure 3(a) shows the results of Example 1, and Figure 3(b) shows the results of Example 2. As shown in Figure 3, in both Examples 1 and 2, the zeta potential of the rice wax microparticle dispersions was negative, with a peak top of approximately -40 mV. This result was thought to be due to the surface of the rice wax microparticles being coated with an emulsifier (surfactant).

[0039] (2) Removal of emulsifiers The emulsifier contained in the rice wax microparticle dispersion of Example 1 was removed by washing with a solvent. Specifically, ethanol was added in an amount nine times the volume of the rice wax microparticle dispersion, and the mixture was filtered through a membrane filter to obtain the insoluble portion as a powder. The mixture was then air-dried on filter paper and further vacuum-dried using a bell-jar vacuum oven BV-001 (manufactured by SIBATA) to obtain a dry powder. The obtained dry powder was transferred to a sample tube, to which a large amount of ethanol (10,000% by mass) was added. Ultrasonic irradiation was then performed for 30 minutes using an ultrasonic cleaner (MCS-6, manufactured by AS ONE), yielding a rice wax microparticle dispersion in which the dispersion medium was ethanol. This was then filtered through a membrane filter again to prepare rice wax microparticles.

[0040] The rice wax microparticles were analyzed using a nuclear magnetic resonance spectroscopy system (ECA-600, JEOL) with deuterated DMSO as the solvent. The samples were dissolved at 85°C and mixed with d6-DMSO for analysis. The refined rice wax (Rice Wax SS-II, Boso Oil & Fat Co., Ltd.) used to prepare the rice wax microparticles was also analyzed. The water contact angle of the microparticle powder film was evaluated to confirm that the emulsifier (surfactant) had been removed from the surface of the rice wax microparticles. The water contact angle was measured by observing the contact angle of a water droplet on a powder bed containing the rice wax microparticles. The rice wax microparticles were also analyzed by X-ray diffraction using a RINT 2000 (Rigaku). Differential scanning calorimetry (DSC) was also performed on the rice wax microparticles using a DSC 8230 (Rigaku).

[0041] Figure 4 shows 1 FIG. 4 is an explanatory diagram showing H nuclear magnetic resonance spectroscopy spectra. The upper panel of FIG. 4 shows the spectrum of refined rice wax, and the lower panel of FIG. 4 shows the spectrum of rice wax microparticles. As shown in FIG. 4, the spectrum of the rice wax microparticles was similar to that of refined rice wax. This result indicated that the emulsifier used in preparing the rice wax microparticles was absent from the washed rice wax microparticles. Therefore, it can be said that the emulsifier was successfully removed by the above-mentioned washing procedure.

[0042] Figure 5 is an explanatory diagram showing the results of the water contact angle evaluation. As shown in Figure 5, the water contact angle was approximately 124°, indicating that the surface of the rice wax microparticles was hydrophobic. This is thought to be due to the rice wax being exposed on the surface of the rice wax microparticles from which the emulsifier had been removed.

[0043] Figure 6 is an explanatory diagram showing the results of X-ray diffraction measurements. As shown in Figure 6, the rice wax microparticles showed clear X-ray diffraction peaks. This confirmed that the rice wax microparticles were in a crystalline state.

[0044] Figure 7 is an explanatory diagram showing the results of the thermal profile in DSC. In Figure 7, the heating process is shown on the bottom and the cooling process on the top. The results shown in Figure 7 show that a clear endothermic peak was observed during the heating process, indicating that the rice wax microparticles were present in a crystalline state.

[0045] (3) Preparation of a dispersion of rice wax microparticles from which the emulsifier has been removed A large amount of ethanol (10,000% by mass) was added to the dry powder, followed by ultrasonic irradiation for 30 minutes using an ultrasonic cleaner (MCS-6, manufactured by AS ONE) to obtain a rice wax microparticle dispersion using ethanol as the dispersion medium. The particle size distribution of the microparticles contained in the rice wax microparticle dispersion was measured using a Litesizer TM700 (manufactured by Anton Paar) to determine the polydispersity index. The rice wax microparticle dispersion was also subjected to zeta potential measurement using a Litesizer TM700 (manufactured by Anton Paar).

[0046] Figure 8 is an explanatory diagram showing the particle size distribution of microparticles contained in a dispersion of rice wax microparticles from which the emulsifier had been removed. As shown in Figure 8, the rice wax microparticles from which the emulsifier had been removed also had a small variation in particle size distribution and a small polydispersity index, similar to the results shown in Figure 2. More specifically, the polydispersity index of the rice wax microparticles from which the emulsifier had been removed was 0.24. This confirmed that rice wax microparticles not coated with an emulsifier also had good dispersibility.

[0047] Figure 9 is an explanatory diagram showing the results of measuring the zeta potential of rice wax microparticles from which the emulsifier had been removed. As shown in Figure 9, the peak top of the zeta potential on the surface of the rice wax microparticles from which the emulsifier had been removed was near 0 mV. This suggests that the surface of the dispersion was not covered with emulsifier, and that rice wax molecules with fewer polar functional groups were exposed on the surface.

[0048] (4) Making liquid marbles Liquid marbles were created using rice wax microparticles with the emulsifier removed. Liquid marbles were created by dropping water or glycerol onto a film of rice wax microparticles spread in a petri dish and gently rolling the droplets.

[0049] Figure 10 shows photographs of liquid marbles. Figure 10(a) shows an image of a liquid marble whose internal solvent is water, and Figure 10(b) shows an image of a liquid marble whose internal solvent is glycerol. As shown in Figure 10, it was confirmed that by using rice wax microparticles from which the emulsifier has been removed, it is possible to prepare liquid marbles, which are liquid / gas dispersions, in cosmetic solvents such as water and glycerol.

[0050] (5) Preparation of Pickering emulsion Pickering emulsions were prepared using rice wax microparticles from which the emulsifier had been removed. An equal volume of water (2 mL) and rice wax microparticles (50 mg) was added to 2 mL of triethylhexanoin. The mixture was then sonicated for 2 minutes using an ultrasonic cleaner (MCS-6, AS ONE) followed by vortex mixing for 1 minute. The Pickering emulsions were then prepared by high-power sonication for 3 minutes using a 450 Sonifier (Branson Ultrasonic Corp.). The formation of Pickering emulsions was observed visually and microscopically using a BZ-X800 (Keyence Corp.). Pickering emulsions were also prepared using aqueous or oil phases containing fluorescent dyes and observed microscopically.

[0051] Figure 11 shows observation images of a Pickering emulsion. Figure 11(a) is a photographic image, and Figure 11(b) is a microscope image. The results shown in Figure 11 indicate that a Pickering emulsion was formed in which rice wax microparticles coated the surface of the water and oil solution, stabilizing the emulsified state. Furthermore, investigation using a fluorescent dye revealed that the Pickering emulsion was a W / O type. This is thought to be due to the hydrophobic surface of the rice wax microparticles, which makes it easier for a W / O type to form than an O / W type.

[0052] The present invention is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in the embodiments and examples corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate.

Claims

1. Rice wax microparticles, The polydispersity index in the particle size distribution measured by dynamic light scattering is 0.25 or less, The absolute value of the peak top of the zeta potential of the surface is 10 mV or less. Rice wax microparticles.

2. 2. A method for producing the rice wax microparticles according to claim 1, comprising: an emulsification step of emulsifying rice wax using water and an emulsifier to obtain a dispersion; a removal step of removing the emulsifier contained in the dispersion by washing with a solvent; A method for producing rice wax microparticles, comprising:

3. 3. The method for producing rice wax microparticles according to claim 2, The solvent includes ethanol. Method for producing rice wax microparticles.

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