Method for producing composite cellulose particles

Abstract

To provide a method for producing composite cellulose particles that exhibit excellent encapsulation stability of a functional substance.SOLUTION: A method for producing composite cellulose particles having the following steps in this order: (1) mixing a cellulose emulsion containing cellulose, water, and an organic solvent with a cellulose non-solvent to obtain a suspension containing crude cellulose particles; (2) washing crude cellulose wet particles obtained by solid-liquid separation of the suspension to obtain purified cellulose wet particles; (3) mixing the purified cellulose wet particles with an azeotropic solvent having an azeotropic point with water, removing water by azeotropy to obtain a dehydrated cellulose particle dispersion in which dehydrated cellulose particles are dispersed in the azeotropic solvent; and (4) mixing the dehydrated cellulose particle dispersion or a cake obtained by solid-liquid separation of the dispersion with a functional substance and removing a solvent including the azeotropic solvent to obtain composite cellulose particles containing the functional substance.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing composite cellulose particles. [Background technology]

[0002] It is known that functional polymer particles are used as additives in cosmetics to impart a soft feel (elasticity), a smooth feel, or sebum-trapping functionality. Many of these polymer particles contain synthetic polymers (microplastic beads) with a particle size of a few micrometers. However, due to environmental considerations, the use of microplastic beads is expected to be restricted in the future.

[0003] Therefore, biodegradable polymer particles made from natural polymer materials have been attracting attention as particles that do not fall under the category of microplastic beads. One example of such polymer particles is cellulose particles. Such cellulose particles are known to be blended into cosmetics to improve the softness and feel on the skin when the cosmetics are used, and to carry various functional substances, thereby enabling the functions of the functional substances to be exerted.

[0004] Cellulose particles are also attracting attention as medical adsorbents and adsorbents for purifying high molecular weight pharmaceuticals such as antibody drugs, and various methods for producing porous cellulose beads are being investigated that do not use highly corrosive or toxic secondary materials or that do not require industrially complicated processes.

[0005] For example, Patent Document 1 discloses porous cellulose particles capable of carrying functional substances, which have a particle size of 0.1 to 1.0 mm, have a plurality of surface openings on part or all of the outer surface, the maximum opening size being 1 / 10 to 1 / 3 of the particle size, and the surface openings are separated from adjacent surface openings by partitions having a thickness of 20 μm or less.The document describes that the particles are easily deformed when swollen, can cause only moderate irritation to the skin, and can easily carry functional substances due to the presence of surface openings. Patent Document 2 discloses a cellulose composite powder having an average particle size of 1 to 100 μm and a value based on a shear test falling within a predetermined range, and describes that the powder has a good feel on the skin.

[0006] Patent Document 3 describes a method for producing porous cellulose particles by bringing a cellulose dispersion prepared by mixing a low-temperature aqueous alkaline solution with cellulose into contact with a coagulation solvent. Patent Document 4 also describes a method for producing porous cellulose beads, which includes a step of cooling a cellulose dope prepared by mixing an alkaline aqueous solution with raw cellulose powder to a temperature lower than -12°C, and a step of adjusting the temperature of the cellulose dope to a temperature higher than 15°C after the cooling step. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-323095 [Patent Document 2] Japanese Patent Publication No. 2023-2552 [Patent Document 3] International Publication No. 2012 / 121258 [Patent Document 4] International Publication No. 2018 / 186222 Summary of the Invention [Problem to be solved by the invention]

[0008] The cellulose particles containing the functional substance contain the functional substance to add a specific function, but in order to effectively exhibit the function of the functional substance, it is desirable that the cellulose particles can sufficiently retain and encapsulate the functional substance and be stable without agglomeration.

[0009] However, the porous cellulose particles described in Patent Document 1 have a large maximum surface pore size of 1 / 10 to 1 / 3 of the particle size, so that they can support functional substances with poor wettability.In addition, the pore volumes of the porous cellulose particles disclosed in the examples are all 1 mL / g or less, which suggests that the ability to encapsulate functional substances and the encapsulation stability are insufficient. Furthermore, the cellulose particles described in Patent Document 2 are considered to be essentially solid particles, making it difficult to encapsulate functional substances, and further improvement is required from the viewpoint of the stability of encapsulating functional substances. Patent Documents 3 and 4 describe a method for producing porous cellulose particles by adding a coagulation solvent to a dispersion of cellulose particles in an alkaline aqueous solution, and although the cellulose particles obtained by these methods are considered to be sufficiently porous, they only describe a ligand that interacts with the target substance to be adsorbed as a substance to be introduced into the cellulose particles. This ligand is introduced by chemical bonding to the hydroxyl groups of the cellulose, and therefore the process is complicated. The present invention relates to a method for producing composite cellulose particles, which allows various functional substances to be encapsulated by a simple operation and which provides good encapsulation stability of the functional substances in the resulting composite cellulose particles. [Means for solving the problem]

[0010] The present inventors have discovered that composite cellulose particles that solve the above-mentioned problems can be obtained by mixing a water-in-oil emulsion containing cellulose with a cellulose non-solvent to obtain crude cellulose particles, washing and dehydrating the crude cellulose particles, and then mixing the particles with a functional substance while they are still wet with an azeotropic solvent that has an azeotropic point with water to form a composite. That is, the present invention relates to the following. [1] A method for producing composite cellulose particles, comprising the following steps (1) to (4) in this order: Step (1): A step of mixing a water-in-oil cellulose emulsion containing cellulose, water, and an organic solvent with a cellulose non-solvent to precipitate coarse cellulose particles and obtain a suspension containing the coarse cellulose particles. Step (2): A step of subjecting the suspension containing the crude cellulose particles obtained in step (1) to solid-liquid separation, and then washing the obtained crude cellulose wet particles to obtain purified cellulose wet particles. Step (3): A step of mixing the purified wet cellulose particles obtained in step (2) with an azeotropic solvent having an azeotropic point with water, and distilling off the water contained in the purified wet cellulose particles by azeotropy to obtain a dehydrated cellulose particle dispersion in which the dehydrated cellulose particles are dispersed in the azeotropic solvent. Step (4): A step of obtaining composite cellulose particles by the following step (4a) or step (4b): Step (4a): A step of mixing the dehydrated cellulose particle dispersion obtained in step (3) with a functional substance, and then removing the solvent containing the azeotropic solvent used in step (3) to obtain composite cellulose particles containing the functional substance. Step (4b): A step of obtaining composite cellulose particles containing the functional substance by subjecting the dehydrated cellulose particle dispersion obtained in the step (3) to solid-liquid separation to obtain a cake, mixing the cake with a functional substance, and then removing the solvent containing the azeotropic solvent used in the step (3) to obtain composite cellulose particles containing the functional substance. [Effects of the Invention]

[0011] According to the present invention, a method for producing composite cellulose particles can be provided, which allows various functional substances to be incorporated into particles by simple operations, and the resulting composite cellulose particles have good inclusion stability of the functional substances. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Method of manufacturing composite cellulose particles] The method for producing composite cellulose particles of the present invention is a method for producing composite cellulose particles comprising the following steps (1) to (4) in this order. Step (1): A step of mixing a water-in-oil cellulose emulsion containing cellulose, water, and an organic solvent with a cellulose non-solvent to precipitate coarse cellulose particles and obtain a suspension containing the coarse cellulose particles. Step (2): A step of subjecting the suspension containing the crude cellulose particles obtained in step (1) to solid-liquid separation, and then washing the obtained crude cellulose wet particles to obtain purified cellulose wet particles. Step (3): A step of mixing the purified wet cellulose particles obtained in step (2) with an azeotropic solvent having an azeotropic point with water, and distilling off the water contained in the purified wet cellulose particles by azeotropy to obtain a dehydrated cellulose particle dispersion in which the dehydrated cellulose particles are dispersed in the azeotropic solvent. Step (4): A step of obtaining composite cellulose particles by the following step (4a) or step (4b): Step (4a): A step of mixing the dehydrated cellulose particle dispersion obtained in step (3) with a functional substance, and then removing the solvent containing the azeotropic solvent used in step (3) to obtain composite cellulose particles containing the functional substance. Step (4b): A step of obtaining composite cellulose particles containing the functional substance by subjecting the dehydrated cellulose particle dispersion obtained in the step (3) to solid-liquid separation to obtain a cake, mixing the cake with a functional substance, and then removing the solvent containing the azeotropic solvent used in the step (3) to obtain composite cellulose particles containing the functional substance.

[0013] In the method for producing composite cellulose particles of the present invention, in step (4), the functional substance to be mixed with the dehydrated cellulose particle dispersion obtained in step (3) or the cake obtained by solid-liquid separation of the dehydrated cellulose particle dispersion obtained in step (3) may be used without pretreatment, or may be used as a functional substance dispersion in which the functional substance is dispersed in an organic solvent or as a functional substance solution in which the functional substance is dissolved in an organic solvent. When the functional substance is used as a functional substance dispersion or functional substance solution, the solvent containing the azeotropic solvent to be removed in step (4) is the azeotropic solvent used in step (3) and the organic solvent used in step (4).

[0014] The method for producing composite cellulose particles of the present invention has the above-mentioned configuration, and thus various functional substances can be incorporated into the particles by simple operations, and the inclusion stability of the functional substances in the obtained composite cellulose particles is good. The reason for this is not clear, but is thought to be as follows. As in the above step (1), the coarse cellulose particles obtained by mixing a water-in-oil cellulose emulsion with a cellulose non-solvent are thought to be porous particles with a relatively large pore volume. The crude cellulose particles thus obtained are then purified by removing impurities in step (2), and then mixed with an azeotropic solvent having an azeotropic point with water in step (3), and the water is distilled off by azeotropy, resulting in particles with a high cellulose content from which impurities have been sufficiently removed, and dehydrated cellulose particles that can sufficiently suppress aggregation between particles are thought to be obtained. Furthermore, by dispersing these dehydrated cellulose particles in an azeotropic solvent without drying them or mixing them with a functional substance while wetted with the azeotropic solvent, the functional substance can be efficiently impregnated into the formed pores without causing deformation, shrinkage, etc. of the particles due to drying. The azeotropic solvent is then removed to precipitate or leave the functional substance in the pores. At this time, the functional substance is concentrated and composited by the removal of the azeotropic solvent, so the functional substance easily penetrates into the dehydrated cellulose particles, and it is thought that composite cellulose particles with good encapsulation stability of the functional substance can be obtained with a simple operation.

[0015] <Process (1)> Step (1) is a step of mixing a water-in-oil cellulose emulsion containing cellulose, water, and an organic solvent with a cellulose non-solvent to precipitate crude cellulose particles and obtain a suspension containing the crude cellulose particles. A water-in-oil cellulose emulsion containing cellulose, water, and an organic solvent can be obtained by the following steps (1-1) and (1-2). Step (1-1): A step of mixing raw cellulose with an alkaline aqueous solution to prepare an aqueous cellulose solution. Step (1-2): A step of mixing the aqueous cellulose solution obtained in the step (1-1) with an organic solvent to prepare a cellulose emulsion. The cellulose aqueous solution prepared in step (1-1) is different from a cellulose suspension and is a solution in which cellulose is dissolved in an alkaline aqueous solution. Here, the state in which the cellulose is "dissolved" means that the cellulose aqueous solution is transparent to the naked eye. Note that the cellulose may be partially dispersed. It is believed that by preparing an aqueous cellulose solution in step (1-1) and subjecting the aqueous solution to step (1-2) and thereafter, it becomes easier to control the morphology inside the cellulose particles, and carrier cellulose particles with the desired physical properties can be easily produced.

[0016] <Process (1-1)> Step (1-1) is a step of mixing raw cellulose with an aqueous alkaline solution to prepare an aqueous cellulose solution.

[0017] (raw cellulose) From the viewpoint of environmental considerations, the raw cellulose used in step (1-1) is preferably chemically unmodified and chemically pure cellulose. Examples of the raw cellulose include wood such as various wood chips, pruned branches of various trees, thinned wood, branches, construction waste, and industrial waste; wood pulp produced from wood, pulp such as cotton linter pulp obtained from fibers surrounding cotton seeds; paper such as newspaper, cardboard, magazines, and fine paper; plant stems and leaves such as rice straw and corn stalks; and plant shells such as rice husks, palm shells, and coconut shells. Among these, from the viewpoints of cellulose purity in the raw cellulose, degree of polymerization of cellulose, and ease of availability, pulp such as various wood chips, pruned branches of various trees, thinned wood, branches, construction waste, and industrial waste; wood pulp produced from wood, and cotton linter pulp obtained from fibers surrounding cotton seeds are preferred. Examples of the form of the raw material cellulose include powder, sheet, cotton, etc. Among these, the raw material cellulose is preferably in powder form from the viewpoint of excellent solubility in an alkaline aqueous solution.

[0018] From the viewpoint of improving the production efficiency of composite cellulose particles, the degree of polymerization of the starting cellulose is preferably 10 or more, more preferably 50 or more, even more preferably 100 or more, and even more preferably 150 or more, and from the viewpoint of improving solubility in an alkaline aqueous solution, it is preferably 1000 or less, more preferably 500 or less, and even more preferably 300 or less. The degree of polymerization of the starting cellulose is preferably 10 or more and 1000 or less, more preferably 50 or more and 500 or less, even more preferably 100 or more and 500 or less, and even more preferably 150 or more and 300 or less. The degree of polymerization of raw cellulose is generally controlled by the conditions of acid hydrolysis of raw pulp. For example, a longer acid hydrolysis time will result in a raw cellulose with a lower degree of polymerization.

[0019] Either crystalline cellulose or amorphous cellulose can be used as the raw material cellulose, but from the viewpoint of obtaining composite cellulose particles with the desired physical properties and from the viewpoint of ease of availability, crystalline cellulose is preferred, and cellulose type I crystalline cellulose is more preferred.

[0020] When the starting cellulose is in a powdered form, the median diameter of the starting cellulose is preferably 1 μm or more, more preferably 5 μm or more, from the viewpoint of improving handleability, and is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 200 μm or less, and still more preferably 150 μm or less, from the viewpoint of improving solubility in an alkaline aqueous solution. The median diameter of the raw cellulose (D 50 ) is the median diameter measured by a dynamic image analyzer, and specifically, can be measured by the method described in the Examples.

[0021] (alkaline aqueous solution) The alkaline aqueous solution used in step (1-1) is not particularly limited as long as it is alkaline and can dissolve cellulose. The alkaline compound used in the alkaline aqueous solution may be either an inorganic alkaline compound or an organic alkaline compound, and examples thereof include alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide; ammonia; and tertiary amines such as trimethylamine and triethylamine. Among these, the alkaline compound is preferably an alkali metal hydroxide from the viewpoints of availability and economy, and more preferably at least one selected from the group consisting of sodium hydroxide and lithium hydroxide, and even more preferably sodium hydroxide, from the viewpoint of improving the solubility of cellulose. The alkaline compounds may be used alone or in combination of two or more.

[0022] From the viewpoint of improving the solubility of the starting cellulose and the stability of the resulting cellulose aqueous solution, the concentration of the alkali compound in the aqueous alkali solution is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, still more preferably 4% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and still more preferably 20% by mass or less. The concentration of the alkali compound in the aqueous alkali solution is preferably 1% by mass or more and 40% by mass or less, more preferably 2% by mass or more and 30% by mass or less, even more preferably 3% by mass or more and 25% by mass or less, and still more preferably 4% by mass or more and 20% by mass or less.

[0023] In step (1-1), from the viewpoint of improving production efficiency, the solubility of the starting cellulose, and the stability of the resulting aqueous cellulose solution, aqueous alkaline solutions of different concentrations may be mixed with the starting cellulose in multiple batches. Specifically, in step (1-1), it is preferable to prepare an aqueous cellulose solution by mixing the starting cellulose with an aqueous alkali solution A having an alkali compound concentration of 1% by mass or more and 10% by mass or less, and then adding and mixing an aqueous alkali solution B having an alkali compound concentration of more than 10% by mass and 40% by mass or less. The concentration of the alkaline compound in the alkaline aqueous solution A is more preferably 2% by mass or more and 8% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less. The concentration of the alkaline compound in the alkaline aqueous solution B is more preferably 15% by mass or more and 30% by mass or less, and even more preferably 20% by mass or more and 25% by mass or less. When alkaline aqueous solution A and alkaline aqueous solution B are used in step (1-1), their ratio is not particularly limited. However, from the viewpoint of improving production efficiency and improving the stability of the resulting cellulose aqueous solution, the mass ratio of alkaline aqueous solution A to alkaline aqueous solution B (A / B) is preferably in the range of 1 or more and 10 or less, more preferably 2 or more and 8 or less, and even more preferably 3 or more and 6 or less.

[0024] The mixing of the starting cellulose with the alkaline aqueous solution in step (1-1) can be carried out by adding the starting cellulose to the alkaline aqueous solution and stirring the mixture using a known device. The temperature during mixing of the starting cellulose and the aqueous alkaline solution is preferably 10°C or lower, more preferably 5°C or lower, and even more preferably 0°C or lower, from the viewpoint of uniformly dispersing the starting cellulose and efficiently dissolving it. Furthermore, from the viewpoint of improving the solubility of cellulose without freezing, the temperature is preferably -20°C or higher, more preferably -10°C or higher, and even more preferably -5°C or higher. The temperature during mixing of the starting cellulose and the aqueous alkaline solution is preferably -20°C or higher and 10°C or lower, more preferably -10°C or higher and 5°C or lower, and even more preferably -5°C or higher and 0°C or lower. When the alkaline aqueous solution A and the alkaline aqueous solution B are used, it is preferable to add the starting cellulose to the alkaline aqueous solution A and mix them with stirring, and then adjust the temperature of the mixture to within the above range, after which the alkaline aqueous solution B is added and mixed.

[0025] The stirring time is not particularly limited as it depends on the production scale, the concentration of the alkaline compound in the alkaline aqueous solution, and the temperature, and is set appropriately. Usually, stirring is continued until the starting cellulose is dissolved as can be seen visually.

[0026] The cellulose concentration in the cellulose aqueous solution obtained in step (1-1) is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of the production efficiency of the resulting composite cellulose particles. Furthermore, from the viewpoint of achieving a viscosity that facilitates the preparation of a cellulose emulsion when the cellulose aqueous solution is subjected to step (1-2), the cellulose concentration is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 9% by mass or less, and even more preferably 8% by mass or less. The cellulose concentration in the cellulose aqueous solution obtained in step (1-1) is preferably 0.5% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 10% by mass or less, even more preferably 1% by mass or more and 9% by mass or less, and even more preferably 2% by mass or more and 8% by mass or less.

[0027] From the viewpoint of improving the solubility of the starting cellulose and the stability of the resulting aqueous cellulose solution, the alkali compound concentration in the aqueous cellulose solution obtained in step (1-1) is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 2% by mass or more, still more preferably 3% by mass or more, even more preferably 5% by mass or more, and is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less. The alkali compound concentration in the aqueous cellulose solution obtained in step (1-1) is preferably 0.5% by mass or more and 15% by mass or less, more preferably 1% by mass or more and 15% by mass or less, even more preferably 2% by mass or more and 12% by mass or less, still more preferably 3% by mass or more and 10% by mass or less, and even more preferably 5% by mass or more and 10% by mass or less.

[0028] <Process (1-2)> In step (1-2), the cellulose aqueous solution obtained in step (1-1) is mixed with an organic solvent to prepare a water-in-oil cellulose emulsion. Step (1-2) makes it possible to prepare a water-in-oil cellulose emulsion capable of producing cellulose particles having a desired median diameter for use in composite synthesis.

[0029] The organic solvent used in this step (1-2) is not particularly limited as long as it is an organic solvent that is immiscible with water and can be mixed with the aqueous cellulose solution to prepare a cellulose emulsion. The octanol / water partition coefficient ClogP of the organic solvent used here is preferably 0.5 or more, more preferably 1.0 or more, even more preferably 2.0 or more, and even more preferably 2.8 or more, from the viewpoint of obtaining a water-in-oil emulsion in step (1-2). The upper limit of the octanol / water partition coefficient ClogP of the organic solvent used in step (1-2) is not particularly limited, but is preferably 10.0 or less, more preferably 8.5 or less, and even more preferably 7.0 or less, from the viewpoint of solubility in a cellulose non-solvent, which will be described later. In the method for producing composite cellulose particles of the present invention, when the organic solvent used in step (1-2) is a mixed solvent, the octanol / water partition coefficient ClogP of the organic solvent can be a weighted average of the ClogP of each organic solvent, with the volume of each solvent constituting the mixed solvent being used as a weight.

[0030] In this specification, the octanol / water partition coefficient ClogP refers to a measure of the partitioning of a substance between an octanol phase and an aqueous phase, and is an index of the hydrophobicity of a chemical substance. ClogP represents the calculation formula for the octanol-water partition coefficient (logP) defined as follows, calculated in accordance with EPIWEB4.1 (US EPA): logP = log([substance]octanol / [substance]water) In the above formula, "[substance] octanol" indicates the molar concentration of the substance in the 1-octanol phase, and "[substance] water" indicates the molar concentration of the substance in the water phase.

[0031] Preferred organic solvents used in step (1-2) include hydrocarbon solvents, ester solvents, halogenated solvents, and the like. Examples of hydrocarbon solvents include chain aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons. The number of carbon atoms in the chain aliphatic hydrocarbon is preferably 6 or more, more preferably 8 or more, and preferably 18 or less, more preferably 12 or less. The chain aliphatic hydrocarbon may be either a linear aliphatic hydrocarbon or a branched aliphatic hydrocarbon. The alicyclic hydrocarbons and aromatic hydrocarbons preferably have 6 or more and 18 or less carbon atoms, more preferably 6 or more and 12 or less carbon atoms. Specific examples of hydrocarbon solvents include n-pentane, n-hexane, n-heptane, n-octane, isooctane, n-decane, isodecane, n-dodecane, isododecane, tetradecane, hexadecane, octadecane, cyclohexane, methylcyclohexane, cycloheptane, methylcycloheptane, toluene, and xylene.

[0032] The ester solvent is preferably an ester having 4 to 10 carbon atoms, and examples thereof include ethyl acetate and butyl acetate. Examples of halogen-based solvents include dichloromethane, chloroform, dichloroethane, and dichlorobenzene.

[0033] The organic solvents may be used alone or in combination of two or more. The organic solvent is preferably a hydrocarbon solvent, more preferably a chain aliphatic hydrocarbon, from the viewpoint of facilitating the preparation of a water-in-oil cellulose emulsion, and from the viewpoint of production, even more preferably one or more selected from the group consisting of n-pentane, n-hexane, n-heptane, n-octane, isooctane, decane, isodecane, dodecane, isododecane, tetradecane, hexadecane, and octadecane, and even more preferably one or more selected from the group consisting of n-octane, isooctane, n-decane, isodecane, n-dodecane, and isododecane.

[0034] In step (1-2), the amount of organic solvent mixed with the aqueous cellulose solution is preferably 80 parts by mass or more, more preferably 100 parts by mass or more, and even more preferably 120 parts by mass or more, per 100 parts by mass of the cellulose aqueous solution, from the viewpoint of improving the emulsion stability of the water-in-oil cellulose emulsion, and is preferably 1000 parts by mass or less, more preferably 800 parts by mass or less, even more preferably 500 parts by mass or less, and even more preferably 300 parts by mass or less, from the viewpoint of easily obtaining carrier cellulose particles having the desired median diameter. In step (1-2), the amount of organic solvent mixed with the aqueous cellulose solution is preferably 80 parts by mass or more and 1000 parts by mass or less, more preferably 100 parts by mass or more and 800 parts by mass or less, even more preferably 120 parts by mass or more and 500 parts by mass or less, and even more preferably 120 parts by mass or more and 300 parts by mass or less, per 100 parts by mass of the cellulose aqueous solution.

[0035] In the step (1-2), from the viewpoint of improving the emulsion stability of the water-in-oil cellulose emulsion, it is preferable to further mix an emulsifier in addition to the aqueous cellulose solution and the organic solvent. Examples of the emulsifier include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, etc. Among these, nonionic surfactants are preferred from the viewpoint of improving the emulsion stability of the water-in-oil cellulose emulsion.

[0036] From the viewpoint of improving the emulsion stability of a water-in-oil cellulose emulsion, the HLB (Hydrophile-Lipophile Balance) of the nonionic surfactant used as an emulsifier is preferably 1 or more and 10 or less, more preferably 1 or more and 8 or less, even more preferably 1 or more and 6 or less, still more preferably 1 or more and 5 or less, still more preferably 1 or more and 4 or less, and still more preferably 1 or more and 3 or less. Here, HLB is an index that represents the ratio of the relative affinity of a surfactant to both liquids in an oil-water system, and can be calculated using the following formula by Griffin's method (J. Soc. Cosm. Chem., 1954, 5:249-256). HLB = 20 × [(molecular weight of hydrophilic group contained in surfactant) / (molecular weight of surfactant)] Examples of the hydrophilic group contained in the surfactant include a hydroxy group and an ethyleneoxy group. The HLB of two or more nonionic surfactants can be calculated as a weighted average obtained by multiplying the HLB of each nonionic surfactant by the mass fraction of each nonionic surfactant (i.e., the mass of each nonionic surfactant divided by the total mass of the nonionic surfactants).

[0037] Examples of nonionic surfactants used as emulsifiers include sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbit fatty acid esters, polyoxyethylene hydrogenated castor oil, polyglycerin fatty acid esters, sucrose fatty acid esters, and polyether-modified silicones, and these can be used alone or in combination of two or more. The number of carbon atoms in the alkyl group in the fatty acid units constituting these nonionic surfactants, such as sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerin fatty acid esters, polyoxyethylene sorbitol fatty acid esters, polyglycerin fatty acid esters, and sucrose fatty acid esters, and in the polyoxyethylene alkyl ethers, is preferably 12 or more, more preferably 16 or more, even more preferably 18 or more, and is preferably 24 or less, more preferably 22 or less, from the viewpoint of maintaining the HLB in the above-mentioned range.

[0038] Examples of sorbitan fatty acid esters include sorbitan monooleate, sorbitan monostearate, sorbitan sesquioleate, coconut oil fatty acid sorbitan, sorbitan monopalmitate, sorbitan tristearate, and sorbitan trioleate. Examples of polyoxyethylene sorbitan fatty acid esters include polyoxyethylene sorbitan monooleate and polyoxyethylene sorbitan trioleate. Examples of polyoxyethylene alkyl ethers include polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, and polyoxyethylene stearyl ether. Examples of polyoxyethylene glycerin fatty acid esters include polyoxyethylene glyceryl monooleate. Examples of polyoxyethylene sorbitol fatty acid esters include polyoxyethylene sorbitol tetraoleate. Examples of sucrose fatty acid esters include sucrose palmitate, sucrose oleate, sucrose stearate, sucrose erucate, and sucrose behenate.

[0039] Among the above, from the viewpoint of further improving the emulsion stability of water-in-oil cellulose emulsions, the nonionic surfactant used as an emulsifier is preferably one or more selected from the group consisting of sorbitan fatty acid esters, polyoxyethylene alkyl ethers, sucrose fatty acid esters, and polyether-modified silicones, more preferably sucrose fatty acid esters, even more preferably one or more selected from the group consisting of sucrose palmitate, sucrose oleate, sucrose stearate, sucrose erucate, and sucrose behenate, and even more preferably one or more selected from the group consisting of sucrose erucate and sucrose behenate.

[0040] When an emulsifier is further mixed in step (1-2), the amount of emulsifier mixed is, from the viewpoint of further improving the emulsion stability of the water-in-oil cellulose emulsion, preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.03 parts by mass or more, and preferably 2.5 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.5 parts by mass or less, relative to 100 parts by mass of the organic solvent. The amount of emulsifier mixed is preferably 0.01 parts by mass or more and 2.5 parts by mass or less, more preferably 0.02 parts by mass or more and 2.0 parts by mass or less, even more preferably 0.03 parts by mass or less, relative to 100 parts by mass of the organic solvent.

[0041] The emulsifier may be added to either the aqueous cellulose solution or the organic solvent before mixing, or may be added after mixing the aqueous cellulose solution and the organic solvent.

[0042] The cellulose emulsion can be prepared, for example, by adding an organic solvent and an emulsifier to an aqueous cellulose solution and stirring the mixture using a known mixer such as a homomixer or a high-speed emulsifying disperser. The temperature at which the aqueous cellulose solution and the organic solvent are mixed is preferably 40°C or lower, more preferably 30°C or lower, and even more preferably 25°C or lower, from the viewpoint of further improving the emulsion stability of the water-in-oil cellulose emulsion. Furthermore, from the viewpoint of preparing the water-in-oil cellulose emulsion without freezing, the temperature is preferably -20°C or higher, more preferably -10°C or higher, and even more preferably -5°C or higher. The temperature at which the aqueous cellulose solution and the organic solvent are mixed is preferably -20°C or higher and 40°C or lower, more preferably -10°C or higher and 30°C or lower, and even more preferably -5°C or higher and 25°C or lower.

[0043] The stirring speed when mixing the aqueous cellulose solution with the organic solvent is appropriately selected depending on the production scale, the equipment used, the viscosity of the cellulose emulsion, etc., but from the viewpoint of controlling the emulsion droplet size and obtaining carrier cellulose particles with the desired median size, it is preferably 1000 rpm or more, more preferably 3000 rpm or more, even more preferably 3500 rpm or more, still more preferably 4000 rpm or more, and preferably 15000 rpm or less, more preferably 14000 rpm or less, even more preferably 13000 rpm or less, and still more preferably 12000 rpm or less. The stirring speed when mixing the aqueous cellulose solution with the organic solvent is preferably 1000 rpm or more and 15000 rpm or less, more preferably 3000 rpm or more and 14000 rpm or less, even more preferably 3500 rpm or more and 13000 rpm or less, and still more preferably 4000 rpm or more and 12000 rpm or less.

[0044] The time for mixing the aqueous cellulose solution with the organic solvent is appropriately selected depending on the production scale, the equipment used, the viscosity of the cellulose emulsion, and the like.

[0045] 〈Process (1-3)〉 Next, the cellulose emulsion obtained in step (1-2) is mixed with a cellulose non-solvent to precipitate coarse cellulose particles, thereby obtaining a suspension containing the coarse cellulose particles. The cellulose nonsolvent is a solvent that does not dissolve cellulose, i.e., a nonsolvent for cellulose, and is compatible with the alkaline aqueous solution and the organic solvent. By mixing the solvent with a cellulose emulsion, the cellulose nonsolvent flows into the cellulose and the organic solvent flows out from the cellulose, forming a phase-separated structure. This allows the morphology inside the cellulose particles to be controlled, and the cellulose can be coagulated in a state where a desired porous structure is formed, and precipitated as particles (porous cellulose particles).

[0046] In the method for producing composite cellulose particles of the present invention, the cellulose nonsolvent preferably has an octanol / water partition coefficient ClogP of less than 0.5, more preferably 0.3 or less, even more preferably 0.1 or less, still more preferably -0.2 or less, and preferably -1.0 or more, from the viewpoints of easily precipitating crude cellulose particles and controlling the internal morphology of the cellulose particles to obtain carrier cellulose particles with desired physical properties. From the same viewpoints as above, the cellulose nonsolvent preferably has an octanol / water partition coefficient ClogP of -1.0 or more and less than 0.5, more preferably -1.0 or more and 0.3 or less, even more preferably -1.0 or more and 0.1 or less, and still more preferably -1.0 or more and -0.2 or less. In the method for producing composite cellulose of the present invention, the cellulose non-solvent may be used alone or in a mixture of two or more solvents. When a mixture of two or more solvents is used, the octanol / water partition coefficient ClogP of the cellulose non-solvent can be a weighted average of the ClogP of each solvent, where the volume of each solvent constituting the mixture of cellulose non-solvents is weighted. When the octanol / water partition coefficient of the cellulose non-solvent is less than 0.5, separation of the water and the cellulose non-solvent in a water-in-oil cellulose emulsion can be suppressed even with a small amount of the cellulose non-solvent, allowing cellulose to be precipitated efficiently and further improving the productivity of cellulose particles.

[0047] The cellulose non-solvent is preferably an alcohol solvent, more preferably an alcohol having 4 or less carbon atoms. Examples of alcohols that can be used as cellulose non-solvents include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, and tert-butyl alcohol, and these can be used alone or in combination of two or more.

[0048] Among the above, from the same viewpoint as above, the cellulose non-solvent is preferably one or more selected from the group consisting of methanol, ethanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-1-propanol, and more preferably one or more selected from the group consisting of methanol (ClogP -0.77) and ethanol (ClogP -0.31).

[0049] The amount of cellulose non-solvent mixed is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 15 parts by mass or more, and preferably 200 parts by mass or less, more preferably 150 parts by mass or less, and even more preferably 100 parts by mass or less, per 100 parts by mass of cellulose emulsion, from the viewpoints of easily precipitating crude cellulose particles, controlling the internal morphology of the cellulose particles to obtain carrier cellulose particles with desired properties, and maintaining emulsion stability. The amount of cellulose non-solvent mixed is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of cellulose emulsion, and more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more, per 100 parts by mass of cellulose emulsion.

[0050] In step (1), it is preferable to further mix an acid in order to neutralize any alkaline compounds remaining in the crude cellulose particles. The acid may be either an inorganic acid or an organic acid, but from the viewpoint of solubility in the cellulose emulsion and the cellulose non-solvent, an organic acid is preferred, and a carboxylic acid having 4 or less carbon atoms is more preferred. Examples of carboxylic acids having 4 or less carbon atoms include monocarboxylic acids, dicarboxylic acids, and hydroxycarboxylic acids having 4 or less carbon atoms, such as formic acid, acetic acid, propionic acid, butyric acid, lactic acid, citric acid, malic acid, and succinic acid. Among these, from the viewpoint of solubility in a cellulose emulsion and a cellulose non-solvent, preferred are one or more selected from the group consisting of acetic acid, lactic acid, malic acid, and succinic acid, and more preferred are one or more selected from the group consisting of acetic acid and malic acid.

[0051] When an acid is used in step (1), the amount of acid added is preferably 1.0 equivalent or more, more preferably 1.2 equivalents or more, and even more preferably 1.4 equivalents or more relative to the alkali compound used in step (1-1) from the viewpoint of neutralizing the alkali compound remaining in the crude cellulose particles, and from the viewpoint of economy, it is preferably 3.0 equivalents or less, more preferably 2.0 equivalents or less, and even more preferably 1.8 equivalents or less. The amount of acid added in step (1) is preferably 1.0 equivalent or more and 3.0 equivalents or less, more preferably 1.2 equivalents or more and 2.0 equivalents or less, and even more preferably 1.4 equivalents or more and 1.8 equivalents or less relative to the alkali compound used in step (1-1). The pH after neutralization with acid is preferably 6 to 8, more preferably 6.5 to 7.5.

[0052] The cellulose emulsion and the cellulose non-solvent can be mixed, for example, by adding the cellulose emulsion to the cellulose non-solvent and stirring using a known device. When adding the cellulose emulsion to the cellulose non-solvent, it is preferable to add and mix the cellulose emulsion while stirring the cellulose non-solvent so as to prevent the emulsion droplets from bonding together. The temperature when the cellulose emulsion and the cellulose non-solvent are mixed is preferably 0° C. or higher, more preferably 5° C. or higher, even more preferably 15° C. or higher, and is preferably 50° C. or lower, more preferably 40° C. or lower, even more preferably 30° C. or lower. The temperature when the cellulose emulsion and the cellulose non-solvent are mixed is preferably 0° C. or higher and 50° C. or lower, more preferably 5° C. or higher and 40° C. or lower, even more preferably 15° C. or higher and 30° C. or lower.

[0053] When an acid is mixed in step (1), the acid may be mixed simultaneously with the cellulose emulsion and the cellulose non-solvent, or may be mixed after the cellulose emulsion and the cellulose non-solvent are mixed. From the viewpoint of efficiently neutralizing the alkaline compounds remaining in the crude cellulose particles (containing the neutralization salt and the emulsifier as impurities), it is preferable to mix the acid after the cellulose emulsion and the cellulose non-solvent are mixed.

[0054] The stirring speed during mixing of the cellulose emulsion and the cellulose non-solvent depends on the production scale and temperature and is set appropriately, but from the viewpoint of sufficiently precipitating the coarse cellulose particles and controlling the internal morphology of the cellulose particles to obtain carrier cellulose particles with the desired physical properties, it is preferably 100 rpm or more, more preferably 200 rpm or more, and also preferably 2000 rpm or less, more preferably 1500 rpm or less, even more preferably 1000 rpm or less, and even more preferably 800 rpm or less. The stirring speed during mixing of the cellulose emulsion and the cellulose non-solvent is preferably 100 rpm or more and 2000 rpm or less, more preferably 200 rpm or more and 1500 rpm or less, even more preferably 200 rpm or more and 1000 rpm or less, and even more preferably 200 rpm or more and 800 rpm or less. The stirring time when mixing the cellulose emulsion and the cellulose non-solvent depends on the production scale and temperature and is set appropriately, but from the viewpoint of sufficiently precipitating the coarse cellulose particles and controlling the internal morphology of the cellulose particles to obtain carrier cellulose particles with the desired physical properties, it is usually 0.2 hours or more and 12 hours or less, preferably 0.5 hours or more and 6 hours or less.

[0055] <Process (2)> Step (2) is a step in which the suspension containing the crude cellulose particles obtained in step (1) is subjected to solid-liquid separation, and the obtained crude wet cellulose particles are then washed to obtain purified wet cellulose particles. The solid-liquid separation of the suspension containing the coarse cellulose particles can be carried out by centrifugation, filtration, decantation, or a combination thereof. Next, the crude cellulose wet particles obtained after solid-liquid separation are washed to remove impurities such as the organic solvent and emulsifier used in step (1-2) and the neutralized salt generated in step (1). The washing treatment of the crude cellulose wet particles can be carried out using water, an organic solvent, or a combination thereof. An organic solvent is preferably used to remove hydrophobic impurities such as the organic solvent and emulsifier used in step (1-2), and water is preferably used to remove water-soluble impurities such as the neutralized salt.

[0056] The organic solvent used in the washing treatment of the wet crude cellulose particles in step (2) is preferably a solvent that can dissolve the organic solvent and emulsifier used in step (1-2) and that can be easily dried, and examples thereof include ketone solvents having 6 or less carbon atoms, such as acetone and methyl isobutyl ketone, and alcohol solvents having 6 or less carbon atoms, such as ethanol and 2-propanol.

[0057] <Process (3)> Step (3) is a step of mixing the purified wet cellulose particles obtained in step (2) with an azeotropic solvent having an azeotropic point with water, and distilling off the water contained in the purified wet cellulose particles by azeotropy to obtain a dehydrated cellulose particle dispersion in which the dehydrated cellulose particles are dispersed in the azeotropic solvent.

[0058] In step (3), purified wet cellulose particles are mixed with an azeotropic solvent having an azeotropic point with water, and azeotropic distillation is carried out. This allows the efficient and gradual removal of water, mainly present within the cellulose particles, along with the azeotropic solvent, to obtain dehydrated cellulose particles that retain the shape of the purified wet cellulose particles. The amount of the azeotropic solvent mixed is preferably 1 part by mass or more, more preferably 10 parts by mass or more, and even more preferably 30 parts by mass or more, per 1 part by mass of the solid content of the cellulose particles, from the viewpoint of distilling off water, and is preferably 1,000 parts by mass or less, more preferably 300 parts by mass or less, and even more preferably 100 parts by mass or less, from the viewpoint of production efficiency. From the same viewpoint as above, the amount is preferably 1 part by mass or more and 1,000 parts by mass or less, more preferably 10 parts by mass or more and 300 parts by mass or less, and even more preferably 30 parts by mass or more and 100 parts by mass or less. The amount of the azeotropic solvent mixed described here is the total amount, and it may be added and mixed all at once or in portions. The present invention includes step (3), which allows water contained in the purified wet cellulose particles to be distilled off. The cellulose particles obtained in step (3) are cellulose particles containing an azeotropic solvent that has an azeotropic point with water.

[0059] The azeotropic solvent used in step (3) is an azeotropic solvent having an azeotropic point with water, and this azeotropic solvent is preferably one or more selected from the group consisting of azeotropic solvent 1 and azeotropic solvent 2 below.

[0060] The azeotropic solvent 1, which has an azeotropic point with water, has an octanol / water partition coefficient ClogP of 0.5 or more, preferably 1.0 or more, and more preferably 2.0 or more. When the octanol / water partition coefficient ClogP of the azeotropic solvent 1 is equal to or greater than the lower limit, water present within (near the surface of) and between the cellulose particles can be efficiently removed by azeotropy. Furthermore, the solvent and water separate in the resulting fraction, making it easy to remove water. That is, in step (3), the purified wet cellulose particles obtained in step (2) are mixed with the azeotropic solvent 1, and water and the azeotropic solvent 1 are distilled off by azeotropy. The azeotropic solvent 1 is then refluxed, thereby continuously distilling off water. By refluxing the azeotropic solvent 1 and returning it to the system, water can be repeatedly distilled off by azeotropy. Therefore, water present within and between the purified wet cellulose particles can be removed in a short time, ultimately yielding dehydrated cellulose particles that retain the shape of the purified wet cellulose particles. There is no particular upper limit to the octanol / water partition coefficient ClogP of the azeotropic solvent 1 as long as it can be separated from water. From the viewpoint of ease of handling, however, it is preferably 10.0 or less, more preferably 7.0 or less, and even more preferably 5.0 or less.

[0061] The azeotropic solvent 1 can be, for example, the same organic solvent as exemplified in step (1-2), and is preferably at least one selected from the group consisting of hydrocarbon solvents, ester solvents, and halogenated solvents, more preferably at least one selected from the group consisting of hydrocarbon solvents and halogenated solvents. Among these, from the viewpoint of efficiently removing water from within and between the hydrous cellulose particles, preferably at least one selected from the group consisting of aliphatic hydrocarbons having from 5 to 12 carbon atoms, alicyclic hydrocarbons having from 5 to 12 carbon atoms, aromatic hydrocarbons having from 6 to 12 carbon atoms, and esters having from 4 to 12 carbon atoms, more preferably at least one selected from the group consisting of alicyclic hydrocarbons, even more preferably at least one selected from the group consisting of cyclohexane, methylcyclohexane, cycloheptane, and methylcycloheptane, and even more preferably at least one selected from the group consisting of cyclohexane. That is, preferably, the cellulose non-solvent in step (1) contains one or more solvents selected from the group consisting of methanol and ethanol, and the azeotropic solvent 1 in step (3) contains one or more solvents selected from the group consisting of aliphatic hydrocarbons having 5 to 12 carbon atoms, alicyclic hydrocarbons having 5 to 12 carbon atoms, aromatic hydrocarbons having 6 to 12 carbon atoms, and esters having 4 to 12 carbon atoms.

[0062] The azeotropic solvent 2 having an azeotropic point with water preferably has an octanol / water partition coefficient ClogP of less than 0.5. When azeotropic solvent 2 is used in step (3), the purified wet cellulose particles obtained in step (2) are mixed with azeotropic solvent 2 and azeotropically distilled to distill off both azeotropic solvent 2 and water. Since azeotropic solvent 2 does not separate from water, if water still remains in the cellulose particles, fresh azeotropic solvent 2 is added and mixed, and the azeotropic solvent 2 and water are distilled off again by azeotropy. By repeating this step, dehydrated cellulose particles from which water has been distilled can be obtained. The azeotropic solvent 2 preferably contains one or more selected from the group consisting of 1-propanol and 2-propanol, and more preferably contains 2-propanol. That is, preferably, the cellulose non-solvent in step (1) contains one or more selected from the group consisting of methanol and ethanol, and the azeotropic solvent 2 in step (3) contains one or more selected from the group consisting of 1-propanol and 2-propanol.

[0063] The boiling point (1 atm) of the azeotropic solvent used in step (3) is preferably 100°C or lower, more preferably 90°C or lower, and is preferably 30°C or higher, more preferably 40°C or higher. Furthermore, in this azeotropic solvent, the azeotropic point with water (azeotropic point of the azeotropic mixture with water) is preferably 100°C or less, more preferably 95°C or less, even more preferably 90°C or less, and even more preferably 85°C or less, from the viewpoint of efficiently removing water from within and between cellulose particles, and is also preferably 30°C or more, more preferably 40°C or more, even more preferably 50°C or more, and even more preferably 60°C or more.

[0064] In step (3), the heating temperature when water is distilled off by azeotropy is the azeotropic temperature or higher, specifically, preferably 30°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, still more preferably 60°C or higher, and preferably 100°C or lower.

[0065] In step (3), the water contained in the purified wet cellulose particles is distilled off to obtain dehydrated cellulose particles. In step (3), the dehydrated cellulose particles are obtained as a dispersion in the azeotropic solvent.

[0066] <Replacement process> The method for producing composite cellulose of the present invention may include a substitution step, performed after step (2) and before step (3), in which water contained in the purified wet cellulose particles obtained in step (2) is substituted with a solvent having an octanol / water partition coefficient ClogP of less than 0.5. This substitution step allows the water present within (near the surface) and between the particles of the purified wet cellulose particles obtained in step (2) to be removed by solvent substitution. This substitution step can suppress aggregation of the cellulose particles when mixed with an azeotropic solvent having an azeotropic point with water in step (3), and also facilitates the removal of water present within the purified wet cellulose particles, allowing for more efficient dehydration. That is, the primary purpose of this substitution step is to remove water present on the particle surface and between the particles of the purified wet cellulose particles. This facilitates the removal of water remaining inside the purified wet cellulose particles in step (3), thereby enabling the production of dehydrated cellulose particles with a reduced water content.

[0067] The octanol / water partition coefficient ClogP of the solvent used in the substitution step (hereinafter also referred to as "substitution solvent") is preferably less than 0.5, more preferably 0.3 or less, even more preferably 0.1 or less, and preferably -1.0 or more, from the viewpoint of reducing the water content of the resulting cellulose particles. As a solvent having an octanol / water partition coefficient ClogP of less than 0.5, alcohol is preferred from the same viewpoint as above. From the viewpoint of efficiently replacing the water present within and between the purified wet cellulose particles obtained in step (2) with the substitution solvent, it is preferable to use the same alcohol as exemplified as the azeotropic solvent 2 in steps (1) and (3) above, and specifically, it is preferable to use one or more alcohols selected from the group consisting of methanol, ethanol, 1-propanol, and 2-propanol, more preferably one or more alcohols selected from the group consisting of methanol, ethanol, and 2-propanol. Furthermore, it is also preferable to use the same alcohol as the azeotropic solvent in step (3) as the substitution solvent.

[0068] From the viewpoint of efficiently replacing and removing water present within and between the purified wet cellulose particles, the amount of the substitution solvent used is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 10 parts by mass or more, per 1 part by mass of the solid content of the purified wet cellulose particles obtained in step (2), and is also preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and even more preferably 30 parts by mass or less. This substitution method involves mixing and stirring the purified wet cellulose particles with the substitution solvent, and then subjecting the substitution solvent to solid-liquid separation to obtain purified wet cellulose particles. The solid-liquid separation can be performed by centrifugation, filtration, decantation, or a combination thereof. The obtained purified wet cellulose particles are subjected to the above-described step (3) to obtain a dehydrated cellulose particle dispersion.

[0069] <Process (4)> Step (4) is a step of obtaining composite cellulose particles by the above step (4a) or step (4b).

[0070] In step (4a), first, a dehydrated cellulose particle dispersion in which dehydrated cellulose particles are dispersed is prepared. Here, the dehydrated cellulose particle dispersion obtained in step (3) may be used as is, or the concentration may be adjusted appropriately. The content of solids (dehydrated cellulose particles) in the dehydrated cellulose particle dispersion is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, from the viewpoint of enabling functional substances to be encapsulated by a simple procedure and efficiently encapsulating the functional substances in the dehydrated cellulose particles. It is also preferably 6% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less. From the same viewpoints as above, it is preferably 1% by mass or more to 6% by mass or less, more preferably 2% by mass or more to 5% by mass or less, even more preferably 3% by mass or less.

[0071] Next, in step (4a), the dehydrated cellulose particle dispersion is mixed with a functional substance. The functional substance used here is not particularly limited as long as it is a known functional substance. The functional substance may be, for example, one that is blended into cosmetics or the like, and is released to the outside of the composite cellulose particles by the application operation when applied to an object, and can exhibit its function. Either organic or inorganic substances can be used as the functional substance, and can be appropriately selected depending on the function to be imparted. More specific functional substances will be described in the description of composite cellulose particles below.

[0072] In this step (4a), the dehydrated cellulose particles and the functional substance are mixed together. If the functional substance is an organic substance that dissolves in the azeotropic solvent, the functional substance can easily penetrate into the pores of the cellulose particles in a dissolved state. In other words, a relatively large amount of the functional substance can be impregnated into the pores of the cellulose particles, allowing the functional substance to penetrate deeper, closer to the center of the particles. On the other hand, when the functional substance is an organic or inorganic substance insoluble in an azeotropic solvent, the particulate functional substance is allowed to pass through the surface pores of the cellulose particles and diffuse into the interior of the cellulose particles for composite formation. Therefore, the particle size (dispersion diameter) of such a functional substance in the functional substance dispersion during composite formation must be smaller than the surface pore diameter of the dehydrated cellulose particles. To efficiently incorporate the functional substance into the dehydrated cellulose particles, the average particle size (average dispersion diameter) of the particulate functional substance is preferably less than 400 nm, more preferably 300 nm or less, even more preferably 250 nm or less, and even more preferably 200 nm or less. For ease of handling, the average particle size (average dispersion diameter) is preferably 20 nm or more, more preferably 50 nm or more, even more preferably 80 nm or more, and even more preferably 100 nm or more. The average particle size is preferably 20 nm or more but less than 400 nm, more preferably 50 nm or more but less than 300 nm, even more preferably 80 nm or more but less than 250 nm, and even more preferably 100 nm or more. The average particle size (average dispersion diameter) of this particulate functional material is a hydrodynamic diameter measured by a dynamic light scattering measuring instrument and is expressed as a volume average diameter. Specifically, it can be measured by the following method. The average particle size (average dispersion diameter) of the functional material in the dispersion is measured using a Zetasizer measuring instrument ("Zetasizer Nano ZS" manufactured by Malvern) according to the following procedure. 1. 0.5 g of a functional substance is mixed with 49.5 g of a dispersion medium to prepare a functional substance dispersion. 2. The functional substance dispersion is placed in the measurement container of the aforementioned measuring device, and measurement is carried out using dynamic light scattering (DLS) to obtain the volume distribution of particle diameters. 3. The particle size at 50% of the volume distribution of the obtained particle sizes (nm) is taken as the measurement result for the average particle size (average dispersed diameter) (nm) of the functional material in the dispersion.

[0073] In step (4a), the dehydrated cellulose particle dispersion contains a sufficient amount of azeotropic solvent to disperse or dissolve the functional substance. Therefore, a functional substance dispersion or a functional substance solution in which the functional substance is dissolved in an organic solvent may be used for mixing. Alternatively, the functional substance may be directly mixed with the dehydrated cellulose particle dispersion without using an organic solvent. In other words, this mixing results in the functional substance being dispersed or dissolved in the dehydrated cellulose particle dispersion. When a functional substance dispersion or a functional substance solution is used in this step, it is preferable that the organic solvent be the same as the azeotropic solvent used in step (3).

[0074] In this step (4a), the amount of functional substance used may be determined depending on the content of the functional substance to be contained in the composite cellulose particles and its content under the production conditions. That is, at least the amount of functional substance desired to be contained in the composite cellulose particles is used and mixed with the dehydrated cellulose particle dispersion. In the method for producing composite cellulose particles of the present invention, a relatively high proportion of the functional substance can be encapsulated in the composite cellulose particles. Therefore, the amount of functional substance used is preferably in the range from the same amount to an excess of about 10% by mass relative to the amount to be contained in the composite cellulose particles.

[0075] The dehydrated cellulose particle dispersion and the functional substance can be mixed, for example, by stirring using a known device. The stirring speed during mixing is preferably 100 rpm or higher, more preferably 200 rpm or higher, from the viewpoint of efficiently incorporating the functional substance into the dehydrated cellulose particles, and is preferably 2000 rpm or lower, more preferably 1500 rpm or lower, even more preferably 1000 rpm or lower, and even more preferably 800 rpm or lower. From the same viewpoint as above, the stirring speed is preferably 100 rpm or higher and 2000 rpm or lower, more preferably 200 rpm or higher and 1500 rpm or lower, even more preferably 200 rpm or higher and 1000 rpm or lower, and even more preferably 200 rpm or higher and 800 rpm or lower.

[0076] The stirring time of the dehydrated cellulose particle dispersion and the functional substance is preferably 0.2 hours or more, more preferably 0.5 hours or more, even more preferably 0.8 hours or more, from the viewpoint of efficiently incorporating the functional substance into the dehydrated cellulose particles, and is preferably 12 hours or less, more preferably 6 hours or less, even more preferably 3 hours or less. From the same viewpoint as above, the stirring time is preferably 0.2 hours or more and 12 hours or less, more preferably 0.5 hours or more and 6 hours or less, even more preferably 0.8 hours or more and 3 hours or less.

[0077] The dehydrated cellulose particle dispersion and the functional substance are thoroughly mixed to impregnate the dehydrated cellulose particles with the functional substance, and then the solvent containing the azeotropic solvent is removed to obtain composite cellulose particles containing the functional substance. The solvent containing the azeotropic solvent is removed by a drying treatment, preferably by heat drying, vacuum drying, or a combination of these.

[0078] The heating temperature in the removal treatment of solvents containing an azeotropic solvent may be a temperature equal to or higher than the azeotropic point of the azeotropic solvent used, or, if an organic solvent other than the azeotropic solvent is used, a temperature equal to or higher than the boiling point of the organic solvent. Specific temperature conditions are preferably 30°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and even more preferably 60°C or higher, from the viewpoint of rapidly reducing the amount of remaining solvent. Furthermore, from the viewpoint of ease of temperature control, the temperature is preferably 90°C or lower, more preferably 85°C or lower, even more preferably 80°C or lower, and even more preferably 75°C or lower. The temperature is preferably 30°C or higher but 90°C or lower, more preferably 40°C or higher but 85°C or lower, even more preferably 50°C or higher but 80°C or lower, and even more preferably 60°C or higher but 75°C or lower. The pressure in the drying treatment may be any pressure that promotes the evaporation of the solvent, including the azeotropic solvent used. Specific pressures are preferably 800 hPa or less, more preferably 700 hPa or less, even more preferably 600 hPa or less, and even more preferably 500 hPa or less. The lower limit may be a vacuum (0 hPa), and considering ease of pressure adjustment, the pressure is preferably 10 hPa or more, more preferably 20 hPa or more, and even more preferably 30 hPa or more. When drying is performed under reduced pressure, it can be performed at room temperature (25° C.), or the above-mentioned heating temperature and pressure may be combined to perform drying under reduced pressure.

[0079] In the step (4b), a cake is first prepared by subjecting a dehydrated cellulose particle dispersion in which dehydrated cellulose particles are dispersed to solid-liquid separation. The cake obtained by solid-liquid separation of the dispersion may be obtained by subjecting the dehydrated cellulose particle dispersion obtained in step (3) to a known solid-liquid separation method, such as centrifugation, filtration, decantation, or a combination thereof. The cake obtained here contains the azeotropic solvent and dehydrated cellulose particles used in step (3). This cake contains a relatively large amount of azeotropic solvent so that the functional substance can be efficiently encapsulated in the dehydrated cellulose particles by subsequent mixing with the functional substance. That is, the content of solids (dehydrated cellulose particles) in the cake is preferably 5% by mass or more, more preferably 6% by mass or more, even more preferably 7% by mass or more, from the viewpoint of efficiently encapsulating the functional substance in the dehydrated cellulose particles, and is preferably 20% by mass or less, more preferably 18% by mass or less, even more preferably 15% by mass or less. From the same viewpoints as above, the content is preferably 5% by mass or more and 20% by mass or less, more preferably 6% by mass or more and 18% by mass or less, even more preferably 7% by mass or more and 15% by mass or less.

[0080] Next, in step (4b), the cake is mixed with a functional substance. The functional substance used is the functional substance described in the composite cellulose particles. In step (4b), the cake contains a sufficient amount of azeotropic solvent to disperse or dissolve the functional substance. Therefore, as in step (4a), a functional substance dispersion or functional substance solution may be used for mixing, or the functional substance may be mixed directly into the cake without using an organic solvent. In other words, the functional substance is dispersed or dissolved in the cake by this mixing. When a functional substance dispersion or functional substance solution is used in this step, it is preferable that the organic solvent be the same as the azeotropic solvent used in step (3).

[0081] In this step (4b), the amount of the functional substance used can be the same as that described in step (4a). The cake and the functional substance can be mixed under the same conditions as in step (4a), using the same equipment, stirring speed, and stirring time.

[0082] The cake and the functional substance are thoroughly mixed to impregnate the dehydrated cellulose particles with the functional substance, and then the solvent containing the azeotropic solvent used in step (3) is removed to obtain composite cellulose particles containing the functional substance. The solvent containing the azeotropic solvent is removed by a drying treatment, preferably by heat drying, vacuum drying, or a combination of these, namely, heat and vacuum drying.

[0083] [Composite cellulose particles] The composite cellulose particles obtained by the method for producing composite cellulose particles of the present invention are composite cellulose particles containing cellulose and a functional substance.

[0084] <Cellulose> The cellulose contained in the composite cellulose particles obtained by the production method of the present invention is not particularly limited as long as it is a known cellulose. 10 O5) n It is a carbohydrate (polysaccharide) represented by the formula, and is a polymer formed by the polymerization of β-glucose. From the viewpoint of environmental consideration, it is preferable that the cellulose contained in the composite cellulose particles has a small amount of substituents substituted on the hydroxy groups of the cellulose. The amount of substituents introduced into the hydroxy groups of the cellulose is preferably 0.5 mol % or less, more preferably 0.1 mol % or less, and even more preferably substantially 0 mol %, based on the total hydroxy groups (the sum of the hydroxy groups and the substituents introduced into the hydroxy groups). From the viewpoint of efficiently incorporating a functional substance into the dehydrated cellulose particles, the cellulose contained in the composite cellulose particles preferably does not have a crosslinked structure intentionally introduced by the composite.

[0085] From the viewpoint of efficiently incorporating a functional substance into the dehydrated cellulose particles, the cellulose is preferably made of crystalline cellulose of cellulose type II or amorphous cellulose, rather than crystalline cellulose of cellulose type I. The crystalline form of the cellulose constituting the composite cellulose particles can be identified from the diffraction angle and diffraction intensity by X-ray diffraction. Cellulose type II crystalline cellulose exhibits a diffraction peak at a diffraction angle 2θ = 12.5° derived from the (110) plane and a diffraction peak at 2θ = 20.0° derived from the (110) plane, and can be easily distinguished from cellulose type I crystalline cellulose. The degree of crystallinity of cellulose type II is defined by the following formula, but the value is not particularly limited. Cellulose type II crystallinity (%) = [(I 20.0 -I 15.0 ) / I 20.0 ] x 100 (Here I 20.0 is the diffraction intensity of the lattice plane (110 plane) (diffraction angle 2θ = 20.0°) in X-ray diffraction, and I 15.0 is the diffraction intensity of the amorphous part (diffraction angle 2θ = 15.0). The cellulose type II crystallinity can be measured by the X-ray diffraction method as described below. The X-ray diffraction intensity is measured using an X-ray diffractometer ("MiniFlex-II" manufactured by Rigaku Corporation) under the following conditions. X-ray source:Cu / Kα-radiation Measurement range: 2θ=5~50° The measurement sample has an area of ​​320 mm 2 The specimen is compressed into a pellet with a thickness of 1 mm. The X-ray scanning speed is 5° / min. The crystalline form of cellulose in the composite cellulose particles (cellulose type II crystallinity) can be adjusted, for example, by the type of solvent contained in the purified wet cellulose particles when the azeotropic solvent removal treatment is carried out in step (3) in the method for producing composite cellulose particles of the present invention. Although the reason is unclear, the crystallinity increases when the azeotropic solvent removal treatment is carried out when the purified wet cellulose particles contain an aqueous solvent, and decreases when the azeotropic solvent removal treatment is carried out when the purified wet cellulose particles contain a non-aqueous solvent.

[0086] From the viewpoint of improving the encapsulation stability and release property of the functional substance, the cellulose contained in the composite cellulose particles is preferably particulate cellulose in whole or in part, and more preferably is a component that forms the base particle of the composite cellulose particles. In the present invention, the carrier cellulose particles of the composite cellulose particles are cellulose particles that support a functional substance. Note that these carrier cellulose particles are made of cellulose and do not contain a functional substance as a constituent component. Here, the particulate cellulose may be such that multiple particulate cellulose particles form one composite cellulose particle via a functional substance, or such that one particulate cellulose particle alone forms the base particle of one composite cellulose particle. In addition, when cellulose (particulate cellulose or cellulose particles) forms the base particle of a composite cellulose particle, it means that one particulate cellulose (cellulose particle) alone forms one composite cellulose particle, and the diameter of the area where the particulate cellulose exists is approximately equal to the particle diameter of the composite cellulose particle. When some or all of the cellulose contained in this composite cellulose particle is particulate cellulose, the presence of many void spaces between or within the particulate cellulose not only makes it possible to stably retain functional substances in the void spaces, but also makes it possible to keep the compressive elastic modulus of the composite cellulose particle below a predetermined value, thereby improving the release of functional substances. From the viewpoint of being able to stably retain the functional substance and from the viewpoint of good release of the functional substance, the carrier cellulose particles are preferably porous particles (porous cellulose particles) having a large number of pores within the carrier cellulose particles (particulate cellulose), and more preferably, one porous particle forms the base particle of the composite cellulose particle. When the carrier cellulose particles are porous particles and a functional substance is held in the pores of the carrier cellulose particles, at least a portion of the functional substance held in the pores can be released to the outside of the particles through openings on the surface of the composite cellulose particles that are connected to the pores, for example, by applying external pressure to the composite cellulose particles. Furthermore, when the carrier cellulose particles are porous particles (porous cellulose particles), when pressure loads or the like are repeatedly applied, the functional substance held near the surface of the composite cellulose particles is released by the initial load, and the functional substance held further inside can be released by the later load, and the functional substance also has sustained release properties, gradually releasing the functional substance.

[0087] <Functional substances> The functional substance used here is not particularly limited as long as it is a known functional substance, as described above. Examples of functional substances include those that are blended into cosmetics and the like, and are released to the outside of the composite cellulose particles by the application operation when applied to an object, and can exhibit their functions, and may be organic or inorganic. When the functional substance is organic, it is preferably one or more selected from the group consisting of silicone, fatty acid, ester oil, alcohol, nonionic polymer, organic acid having 8 or less carbon atoms, chroman derivative, vitamin and vitamin derivative, and elastomer.

[0088] Silicones are water-insoluble compounds whose main chain consists of a repeating structure of silicon and oxygen atoms, and when they are incorporated into cosmetics and applied to the skin, they provide a sustained smooth feel and form a film on the skin surface, reducing irritation from the external environment. Examples of silicones used here include polydimethylsiloxane, polysiloxane, and modified polysiloxane.

[0089] Fatty acids have a carboxy group at the end of a hydrocarbon structure and are incorporated as oily components into cosmetics and the like. Fatty acids may be saturated or unsaturated. The number of carbon atoms in the fatty acids used here is preferably 6 or more, more preferably 8 or more, even more preferably 10 or more, and preferably 22 or less, more preferably 20 or less, even more preferably 18 or less. Specific examples of fatty acids include palm kernel oil fatty acid, lauric acid, palmitic acid, stearic acid, myristic acid, oleic acid, behenic acid, eicosapentaenoic acid, docosahexaenoic acid, and isostearic acid.

[0090] Ester oils are esters made from fatty acids and alcohols, and are used in cosmetics as low-viscosity oily bases, emollients that reduce moisture loss from the skin, maintain moisture, and soften the skin, etc. Examples of ester oils include synthetic ester oils and natural fats and oils. The number of carbon atoms in the fatty acid used as the raw material is preferably 4 or more, more preferably 8 or more, even more preferably 10 or more, and preferably 22 or less, more preferably 20 or less, even more preferably 18 or less. The number of carbon atoms in the fatty acid is preferably 4 or more and 22 or less, more preferably 8 or more and 20 or less, even more preferably 10 or more and 18 or less. The number of carbon atoms in the alcohol used as a raw material is preferably 1 or more, more preferably 3 or more, even more preferably 5 or more, and is preferably 22 or less, more preferably 20 or less, even more preferably 18 or less. Specific examples of ester oils include isopropyl myristate, octyldodecyl myristate, myristyl myristate, isopropyl palmitate, 2-ethylhexyl stearate, butyl stearate, stearyl stearate, cholesteryl isostearate, cetyl 2-ethylhexanoate, glyceryl tri-2-ethylhexanoate, and isotridecyl isononanoate.

[0091] The alcohol is a compound having a hydroxyl group, and either a monohydric alcohol or a polyhydric alcohol can be used. The monohydric alcohol is a component that forms a lamellar liquid crystal structure outside the oil droplets together with a nonionic surfactant in an oil-in-water emulsion, stabilizing the emulsion. The number of carbon atoms in the monohydric alcohol is preferably 6 or more, more preferably 8 or more, even more preferably 10 or more, and preferably 24 or less, more preferably 22 or less, even more preferably 20 or less. Specific examples of the monohydric alcohol include behenyl alcohol, cetearyl alcohol, stearyl alcohol, isostearyl alcohol, cholesterol, jojoba alcohol, etc.

[0092] Polyhydric alcohols are alcohols (polyols) with two or more hydroxyl groups, and are components that maintain the viscosity of cosmetics and adjust the moisturizing properties and feel on the skin. The number of carbon atoms in polyhydric alcohols is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, and preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Specific examples of polyhydric alcohols include sugar alcohols such as polyethylene glycol, polypropylene glycol, dipropylene glycol, 1,3-butylene glycol, glycerin, xylitol, and sorbitol.

[0093] Nonionic polymers are components that adjust the moisturizing properties and usability of the skin. They are incorporated as emulsifiers into cosmetics and other products to improve water vapor barrier properties and usability in low-humidity environments, and examples of such components include cellulose derivatives such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose. These cellulose derivatives differ from the celluloses described above in that the degree of substitution of the cellulose derivatives (i.e., the ratio of the number of substituents introduced to hydroxy groups to the total number of hydroxy groups and substituents introduced to hydroxy groups) is preferably greater than 0.5 mol %, more preferably 1 mol % or greater, from the viewpoint of solubility in solvents.

[0094] Organic acids having 8 or less carbon atoms are components that have the effects of increasing the moisture retention capacity of the skin, increasing flexibility, promoting the adhesion and detachment of stratum corneum cells, and expelling unnecessary stratum corneum. The number of carbon atoms in these organic acids is 8 or less, preferably 7 or less, more preferably 6 or less, even more preferably 5 or less, and preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more. Specific examples of organic acids having 8 or less carbon atoms include butyric acid, lactic acid, citric acid, malic acid, succinic acid, malonic acid, tartaric acid, salicylic acid, etc.

[0095] Chroman derivatives have the molecular formula CH 10 It is a compound with a heterocyclic structure (chroman structure) of O, and is a component with antioxidant properties. Examples of chroman derivatives include tocopherol acetate, which has vitamin E-like properties.

[0096] The functional substance may also be one or more selected from the group consisting of vitamins and vitamin derivatives. The vitamin or vitamin derivative may be any known compound without any particular limitation, and is preferably vitamin A, vitamin C, vitamin E, or derivatives thereof.

[0097] Further, examples of functional substances include elastomers, which are materials with rubber elasticity. By compounding the elastomer with cellulose, composite cellulose particles with a desired range of elastic recovery can be obtained. From the viewpoint of improving the softness of cosmetics and the like blended with the composite cellulose particles, such functional substances are preferably materials that become elastomers at room temperature (25° C.) By using a material that becomes elastomers at room temperature (25° C.), the properties of the elastomer can be effectively exhibited in cosmetics and the like blended with the composite cellulose particles, and the cosmetics and the like can be made to feel a sufficient softness when in use.

[0098] The elastomer is not particularly limited and can be selected from known elastomers. Specifically, it is natural rubber or synthetic rubber. Examples of synthetic rubber include silicone-based elastomers, fluorine-based elastomers, urethane-based elastomers, styrene-based elastomers, olefin-based elastomers, vinyl chloride-based elastomers, ester-based elastomers, and amide-based elastomers. Among these, from the viewpoint of environmental friendliness, it is preferable to use at least one selected from the group consisting of silicone-based elastomers, urethane-based elastomers, and natural rubber, and more preferably a silicone-based elastomer. Examples of silicone elastomers include dimethylpolysiloxane, polymethylsilsesquioxane, methylphenylpolysiloxane, polyether-modified silicone, amino-modified silicone, and oxazoline-modified silicone. Among these, from the viewpoint of being able to impart a soft feel to the skin when blended into cosmetics and the like, it is preferable to include at least one type selected from the group consisting of polyethersilicone, amino-modified silicone, and oxazoline-modified silicone, and more preferably oxazoline-modified silicone.

[0099] In addition, when the functional substance is an organic substance, dissolving it and compounding it with cellulose in step (4) is preferable because the content of the functional substance in the compounded cellulose particles can be increased. The solubility parameter (SP value) of the functional substance can be used as an indicator of solubility in an organic solvent. In this specification, the solubility parameter (SP value) is a value calculated by inputting the SMILES of the functional substance using the Hansen Solubility Parameter software "Hansen Solubility Parameter in Practice (HSPiP 4th Edition 4.1.07)." The SP value of multiple organic substances is calculated as a weighted average of the SP values ​​of each organic substance, with the volume of each organic substance used as the weight when each organic substance dissolves. The solubility parameter (SP value) of the functional substance used in the present invention is preferably 10 MPa from the viewpoint of solubility in organic solvents. 1 / 2 More preferably, 12 MPa 1 / 2 More preferably, 13 MPa 1 / 2 and preferably 40 MPa or more. 1 / 2 Less than or equal to 38 MPa, preferably 1 / 2 or less, more preferably 36 MPa 1 / 2 Preferably, the pressure is 10 MPa or less. 1 / 2 More than 40MPa 1 / 2 or less, preferably 12 MPa 1 / 2 More than 38MPa 1 / 2 or less, more preferably 13 MPa 1 / 2 More than 36MPa 1 / 2 The following is the result.

[0100] When the functional substance is an inorganic substance, the functional substance is preferably one or more selected from the group consisting of zinc oxide, titanium oxide, barium sulfate, calcium carbonate, talc, mica, and titanium oxide-coated mica.

[0101] Zinc oxide and titanium oxide are used as white pigments with high covering power. Furthermore, zinc oxide has a sebum-absorbing effect, which helps prevent shine and makeup from coming off due to sebum. Talc and mica are used as extender pigments to adjust texture, such as spreadability and lubricity, and to improve physical properties such as adhesion and gloss. Titanium dioxide-coated mica is also used as a pearlescent pigment, producing various interference colors and imparting a glossy appearance.

[0102] <Characteristics of composite cellulose particles> From the viewpoint of efficiently encapsulating a functional substance in the carrier cellulose particles, the compressive modulus of the composite cellulose particles is 50 MPa or less, preferably 40 MPa or less, more preferably 30 MPa or less, even more preferably 20 MPa or less, still more preferably 10 MPa or less, still more preferably 8.0 MPa or less, still more preferably 7.5 MPa or less, still more preferably 7.1 MPa or less, still more preferably 6.5 MPa or less, and still more preferably 6.0 MPa or less. From the viewpoint of suppressing disintegration during the production process of the composite cellulose particles, the compressive modulus is preferably 0.9 MPa or more, more preferably 1.5 MPa or more, even more preferably 1.9 MPa or more, still more preferably 2.1 MPa or more, and still more preferably 2.3 MPa or more. The compressive modulus of the composite cellulose particles is preferably 0.9 MPa or more and 50 MPa or less, more preferably 0.9 MPa or more and 40 MPa or less, even more preferably 0.9 MPa or more and 30 MPa or less, even more preferably 0.9 MPa or more and 20 MPa or less, even more preferably 1.5 MPa or more and 10 MPa or less, even more preferably 1.5 MPa or more and 8.0 MPa or less, even more preferably 1.9 MPa or more and 7.5 MPa or less, even more preferably 2.1 MPa or more and 7.1 MPa or less, even more preferably 2.1 MPa or more and 6.5 MPa or less, and even more preferably 2.3 MPa or more and 6.0 MPa or less.

[0103] The compressive elastic modulus is the apparent compressive elastic modulus of a single particle measured by a microcompression tester, and specifically can be measured by the following method. The compressive elastic modulus of the particles is measured using a microcompression tester ("MCT-510" manufactured by Shimadzu Corporation), and the average value is calculated as the measurement result according to the following procedure. 1. Particles are placed on the measurement stage attached to the device, and the particle size d (μm) is measured. 2. The indenter (Φ50 μm) is lowered at a constant loading rate (mN / sec) to compress the particles (displacement x (μm)) until the test force P (mN) reaches the specified value (0.98 mN). 3. Calculate the compressive stress using the following formula from the particle size d (μm) and the test force P (mN). Compressive stress (MPa) = 2.48 × P (mN) / (π × (d (μm)) 2 ) 4. Calculate the compressive strain from the displacement x (μm) and particle size d (μm) using the following formula. Compressive strain (%) = x (μm) / d (μm) × 100 5. Create a stress-strain curve from the calculated compressive stress and compressive strain, and calculate the compressive modulus (MPa) from the slope of the elastic region (0-10%). 6. Repeat steps 1 to 5 seven times, and use the arithmetic mean value of the five measurements excluding the maximum and minimum values ​​of the compressive elastic modulus as the measurement result of the compressive elastic modulus of the particles. The compressive modulus of the composite cellulose particles can be adjusted, for example, by changing the type of cellulose particles (dehydrated cellulose particles used in step (4)) used for composite formation and the type and / or content of the functional substance in the composite cellulose particle production method of the present invention. For example, when cellulose particles with a low compressive modulus are composited with a functional substance with a low compressive modulus using the composite cellulose particle production method of the present invention, increasing the content of the functional substance decreases the compressive modulus of the resulting composite cellulose particles, while decreasing the content of the functional substance increases the compressive modulus of the composite cellulose particles.

[0104] The median diameter of the composite cellulose particles (D 50) is preferably 250 μm or less, more preferably 200 μm or less, even more preferably 150 μm or less, even more preferably 120 μm or less, even more preferably 110 μm or less, and even more preferably 100 μm or less, from the viewpoint of efficiently incorporating a functional substance into the dehydrated cellulose particles. Also, from the same viewpoint as above, it is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more. The median diameter of the composite cellulose particles is preferably 5 μm or more and 250 μm or less, more preferably 5 μm or more and 200 μm or less, even more preferably 5 μm or more and 150 μm or less, even more preferably 5 μm or more and 120 μm or less, even more preferably 10 μm or more and 110 μm or less, and even more preferably 15 μm or more and 100 μm or less. Here, the median diameter of the composite cellulose particles (D 50 ) is the median diameter measured by a dynamic image analyzer, and specifically, can be measured by the method described in the Examples. The median diameter of the composite cellulose particles can be adjusted, for example, by changing the stirring speed when mixing the aqueous cellulose solution with the organic solvent when preparing the cellulose emulsion used in step (1) in the method for producing composite cellulose particles of the present invention. Specifically, by increasing the stirring speed when mixing the aqueous cellulose solution with the organic solvent in step (1), the emulsion droplet size of the resulting cellulose emulsion becomes smaller, resulting in cellulose particles with a small median diameter. Furthermore, by decreasing the stirring speed, the emulsion droplet size of the resulting cellulose emulsion becomes larger, resulting in cellulose particles with a large median diameter. Furthermore, the median diameter can be adjusted by changing the content of the functional substance in step (4) of the method for producing composite cellulose particles of the present invention. Specifically, by increasing the content of the functional substance, the voids in the carrier cellulose particles are filled and the particles are less likely to shrink when the organic solvent or azeotropic solvent dries, making it easier for the median diameter of the resulting composite cellulose particles to maintain the median diameter of the carrier cellulose particles; by reducing the content of the functional substance, the voids in the carrier cellulose particles are not filled and the particles are more likely to shrink when the organic solvent or azeotropic solvent dries, making it easier for the median diameter of the resulting composite cellulose particles to decrease.

[0105] The composite cellulose particles obtained by the method for producing composite cellulose particles of the present invention are composite cellulose particles constituted by the composite of cellulose and a functional substance, as described above, and are preferably composite cellulose particles comprising particulate cellulose as the cellulose, with at least a portion of the functional substance contained within the particulate cellulose. That is, they are composite cellulose particles in which at least a portion of the functional substance is contained within carrier cellulose particles, and from the viewpoint of ease of production, more preferably, the carrier cellulose particles are porous cellulose particles, and at least a portion of the functional substance is contained within the porous cellulose particles. In the composite cellulose particles of the present invention, all of the functional substance may be contained within the carrier cellulose particles, or a portion of the functional substance may be contained within the carrier cellulose particles, with the remainder attached to the outer surface of the carrier cellulose particles. In the composite cellulose particles of the present invention, it is preferable that at least a part of the functional substance is retained in a state that allows it to be released to the outside of the composite cellulose particles by application of pressure or the like.

[0106] From the viewpoint of improving the encapsulation stability and release property of the functional substance, the composite cellulose particles of the present invention preferably contain a single particulate cellulose (carrier cellulose particle) as the cellulose alone (i.e., forming the base particle of the composite cellulose particle), and the functional substance is contained within the carrier cellulose particle (base particle).

[0107] The content of the functional substance in the composite cellulose particles is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, and even more preferably 70 parts by mass or more, per 100 parts by mass of the carrier cellulose particles, from the viewpoint of efficiently encapsulating the functional substance in the dehydrated cellulose particles, and from the viewpoint of improving the encapsulation stability of the functional substance, it is preferably 600 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 400 parts by mass or less. From the same viewpoint as above, the content of the functional substance is preferably 10 parts by mass or more and 600 parts by mass or less, more preferably 30 parts by mass or more and 500 parts by mass or less, and even more preferably 50 parts by mass or more and 400 parts by mass or less.

[0108] <Carrier cellulose particles> From the viewpoint of environmental considerations, it is preferable that the surface of the cellulose carrier particles used in the present invention is not coated with a surface treatment agent. The carrier cellulose particles can be produced, for example, by carrying out steps (1) to (3) in the method for producing composite cellulose particles of the present invention.

[0109] To form these carrier cellulose particles as porous particles, for example, in the method for producing composite cellulose particles of the present invention, when precipitating crude cellulose particles in step (1), a solvent type can be selected as the cellulose non-solvent to be used so as to form the desired pores.

[0110] The surface pore diameter of the cellulose carrier particles is not particularly limited, but from the viewpoint of efficiently incorporating a functional substance into the dehydrated cellulose particles, the surface pore diameter is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more, and from the viewpoint of maintaining the particle shape of the composite cellulose particles, the surface pore diameter is preferably 800 nm or less, more preferably 700 nm or less, and even more preferably 600 nm or less. The surface pore diameter of the cellulose carrier particles is preferably 50 nm or more and 800 nm or less, more preferably 100 nm or more and 700 nm or less, and even more preferably 200 nm or more and 600 nm or less. The surface pore diameter can be determined by mercury intrusion porosimetry, specifically by the method described in the examples. The surface pore diameter of the carrier cellulose particles is measured by the mercury intrusion method using a mercury porosimeter ("Auto Pore IV 9500" manufactured by Shimadzu Corporation) according to the following method. 1. The pore volume of the particles is determined using the method described above, and the horizontal axis is pore diameter (nm) and the vertical axis is pore volume (mL / g) to plot the pore volume to obtain an integrated pore distribution curve. 2. The (integrated) pore volume is differentiated by the pore diameter, i.e., the increase in pore volume at each pore diameter is taken as the differential pore volume (mL / g), and the horizontal axis is plotted as the pore diameter (nm) and the vertical axis is plotted as the differential pore volume (mL / g) to obtain a pore distribution curve. 3. In the obtained pore distribution curve, the mode of pore diameter in the region of pore diameters of 1000 nm or less is taken as the surface pore diameter (nm) of the particle.

[0111] From the viewpoint of efficiently incorporating a functional substance into the dehydrated cellulose particles, the pore volume of the carrier cellulose particles is preferably 1.5 mL / g or more, more preferably 2.0 mL / g or more, even more preferably 2.3 mL / g or more, and even more preferably 2.4 mL / g or more. Furthermore, from the viewpoint of suppressing disintegration during the production process of the composite cellulose particles, the pore volume is preferably 8.0 mL / g or less, more preferably 7.0 mL / g or less, even more preferably 6.0 mL / g or less, and even more preferably 5.0 mL / g or less. The pore volume of the carrier cellulose particles is preferably 1.5 mL / g or more and 8.0 mL / g or less, more preferably 2.0 mL / g or more and 7.0 mL / g or less, even more preferably 2.3 mL / g or more and 6.0 mL / g or less, and even more preferably 2.4 mL / g or more and 5.0 mL / g or less. The pore volume is a value obtained by dividing the total volume of mercury that has penetrated into the pores inside the carrier cellulose particles and the gaps between the particles, as measured by mercury intrusion porosimetry, by the mass of the particles and normalizing it.Specifically, it can be measured by the following method. The pore volume of the carrier cellulose particles is measured by the mercury intrusion method using a mercury porosimeter ("Auto Pore IV 9500" manufactured by Shimadzu Corporation) according to the following method. 1. Approximately 0.05 g of particles (Y(g)) are placed in the cell of a mercury porosimeter. 2. Mercury is forced into the particles, and the volume Z (mL) of mercury that penetrates into the pores within the particles and the gaps between the particles is calculated at measurement pressures ranging from 0.01 MPa to 210 MPa. 3. The value obtained from the particle mass Y (g) and the volume Z (mL) of the mercury that penetrates using the following formula is the measurement result of the particle pore volume (mL). Pore ​​volume (mL / g) = Z (mL) / Y (g) In the method for producing composite cellulose particles of the present invention, the pore volume of the carrier cellulose particles can be adjusted, for example, by the surface tension of the azeotropic solvent used in step (3) as well as the emulsion droplet size of the cellulose emulsion used in step (1). Specifically, if the emulsion droplet size of the cellulose emulsion is small, the median diameter and pore volume of the resulting carrier cellulose particles also become small.

[0112] The specific surface area of ​​the carrier cellulose particles was set at 85m from the viewpoint of improving the encapsulation stability of functional substances. 2 / g or more, preferably 90m 2 / g or more, more preferably 95m 2 / g or more, more preferably 100m 2 / g or more, and even more preferably 103m 2 / g or more. In addition, from the viewpoint of suppressing the collapse of the carrier cellulose particles during the manufacturing process, 2 / g, preferably less than 200m 2 / g or less, more preferably 180m 2 / g or less, more preferably 150m 2 The specific surface area of ​​the carrier cellulose particles is 85 m 2 / g or more 500m 2 / g, preferably less than 90m 2 / g or more 200m 2 / g or less, more preferably 95m 2 / g or more 180m 2 / g or less, more preferably 100m 2 / g or more 150m 2 / g or less, even more preferably 103m 2 / g or more 150m 2 / g or less. The specific surface area is a value obtained by dividing the total surface area of ​​the fine surface inside the carrier cellulose particle and the particle surface, measured by mercury intrusion porosimetry, by the mass of the particle and normalizing it, and can be specifically measured by the method described in the examples. The specific surface area of ​​the carrier cellulose particles is measured by the mercury intrusion method using a mercury porosimeter ("Auto Pore IV 9500" manufactured by Shimadzu Corporation) according to the following method. 1. Approximately 0.05 g of particles (Y(g)) are placed in the cell of a mercury porosimeter. 2. Mercury is injected into the particles, and the total surface area of ​​the microsurface inside the particle and the particle surface is measured in the range of pressure from 0.01 MPa to 210 MPa. 2 ) value. 3. The mass of a particle Y (g) and the total surface area of ​​the microsurface inside the particle and the particle surface X (m 2 ) and the value obtained by the following formula is used as the specific surface area (m 2 / g) as the measurement result. Specific surface area (m 2 / g)=X(m 2 ) / Y(g) The specific surface area of ​​the carrier cellulose particles can be controlled, for example, by selecting the surface tension of the azeotropic solvent used in the azeotropic distillation performed in step (3) in the method for producing composite cellulose particles of the present invention. Specifically, if the surface tension of the azeotropic solvent used in step (3) is low, the capillary force associated with its evaporation is small, which can suppress shrinkage of the cellulose particles during drying, thereby enabling the production of carrier cellulose particles with a large specific surface area.

[0113] From the viewpoint of efficiently encapsulating a functional substance in the dehydrated cellulose particles, the compressive modulus of the carrier cellulose particles is 50 MPa or less, preferably 40 MPa or less, more preferably 30 MPa or less, even more preferably 20 MPa or less, still more preferably 10 MPa or less, still more preferably 7.0 MPa or less, still more preferably 6.0 MPa or less, still more preferably 5.3 MPa or less, still more preferably 5.2 MPa or less, and still more preferably 5.0 MPa or less. Furthermore, from the viewpoint of suppressing disintegration during the production process of the carrier cellulose particles, the compressive modulus is preferably 0.9 MPa or more, more preferably 2.0 MPa or more, even more preferably 2.5 MPa or more, still more preferably 2.8 MPa or more, and still more preferably 3.0 MPa or more. The compressive modulus of the composite cellulose particles is 50 MPa or less, preferably 1.0 MPa or more and 50 MPa or less, more preferably 1.0 MPa or more and 40 MPa or less, even more preferably 1.0 MPa or more and 30 MPa or less, even more preferably 0.9 MPa or more and 20 MPa or less, even more preferably 2.0 MPa or more and 10 MPa or less, even more preferably 2.0 MPa or more and 7.0 MPa or less, even more preferably 2.5 MPa or more and 6.0 MPa or less, even more preferably 2.8 MPa or more and 5.3 MPa or less, even more preferably 2.8 MPa or more and 5.2 MPa or less, and even more preferably 3.0 MPa or more and 5.0 MPa or less.

[0114] The compressive elastic modulus is the apparent compressive elastic modulus of a single particle measured by a microcompression tester, and specifically can be measured by the method described in the description of the composite cellulose particles. The compressive modulus of the carrier cellulose particles can be adjusted, for example, in step (1) of the method for producing composite cellulose particles of the present invention by changing the degree of polymerization of the raw cellulose used, the cellulose concentration in the aqueous solution prepared for cellulose emulsion formation, the type of cellulose non-solvent used, etc. Specifically, the compressive modulus of the carrier cellulose particles is increased by using a raw cellulose with a high degree of polymerization or by increasing the cellulose concentration in the aqueous solution. On the other hand, the compressive modulus of the carrier cellulose particles is decreased by using a raw cellulose with a low degree of polymerization or by decreasing the cellulose concentration in the aqueous solution.

[0115] The physical properties of the carrier cellulose particles can be adjusted, for example, by selecting suitable production conditions for the cellulose particles, the type of raw cellulose used to produce the cellulose particles, etc., as specifically described above.

[0116] The cellulose carrier particles preferably have a low content of compounds other than cellulose, such as impurities contained in the raw cellulose, solvents used during production, additives, etc. That is, the cellulose content in the cellulose carrier particles is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably substantially 100% by mass.

[0117] In the method for producing composite cellulose particles, when the functional substance is composited in step (4), the upper limit of the amount of functional substance that can be contained in the composite cellulose particles varies depending on whether the functional substance is dissolved in an azeotropic solvent and composited, or whether the functional substance is dispersed in an azeotropic solvent and composited.

[0118] In the method for producing composite cellulose particles of the present invention, when a functional substance is dissolved and composited in step (4), the solution containing the dissolved functional substance easily penetrates the interior of the cellulose particles, allowing a relatively large amount of functional substance to be encapsulated in the cellulose particles. The content of the functional substance is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, even more preferably 200 parts by mass or more, and even more preferably 250 parts by mass or more, per 100 parts by mass of cellulose, and is preferably 600 parts by mass or less, more preferably 500 parts by mass or less, and even more preferably 400 parts by mass or less. The content of the functional substance is preferably 100 parts by mass or more and 600 parts by mass or less, more preferably 150 parts by mass or more and 500 parts by mass or less, and even more preferably 200 parts by mass or more and 400 parts by mass or less, per 100 parts by mass of cellulose.

[0119] On the other hand, in the method for producing composite cellulose particles of the present invention, when a functional substance is dispersed and composited in step (4), the particulate functional substance passes through the surface pores of the cellulose particles and diffuses into the interior of the cellulose particles, resulting in a smaller amount of functional substance encapsulated in the cellulose particles than when dissolved. In this case, the content of the functional substance is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 40 parts by mass or more, even more preferably 50 parts by mass or more, per 100 parts by mass of cellulose, and preferably 100 parts by mass or less, more preferably 95 parts by mass or less, even more preferably 90 parts by mass or less, and even more preferably 85 parts by mass or less. Furthermore, the content is preferably 10 parts by mass or more to 100 parts by mass or less, more preferably 30 parts by mass or more to 95 parts by mass or less, even more preferably 40 parts by mass or more to 90 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of cellulose.

[0120] [Application] The composite cellulose particles obtained by the method for producing composite cellulose particles of the present invention can be incorporated into or used in, for example, cosmetics, toiletries, oral care products, quasi-drugs, pharmaceuticals, household products, agricultural products, etc. Furthermore, the composite cellulose particles obtained by the method for producing composite cellulose particles of the present invention are made of cellulose derived from natural plants, and therefore are environmentally friendly and can be suitably used as an alternative material to microplastics. Among these, their use as cosmetics, which require a good feel to the touch, is preferred.

[0121] <Cosmetics> The composite cellulose particles obtained by the method for producing composite cellulose particles of the present invention can be used as a cosmetic containing the composite cellulose particles. The cosmetic contains the composite cellulose particles, which provide a pleasant feel to the touch. Furthermore, the composite cellulose particles have excellent stability in encapsulating functional substances and excellent release properties, so that the cosmetic containing the composite cellulose particles can effectively release the functional substances onto the target object by application. From the viewpoint of effectively exerting the above-mentioned effects, the cosmetic of the present invention is preferably a cosmetic for skin, and examples of such cosmetic for skin include foundation, makeup base, sunscreen, emulsion, lotion, etc. The content of the composite cellulose particles in the cosmetic may be any amount that can exhibit the desired performance and can be selected appropriately depending on the type, form, etc. of the cosmetic, but is usually in the range of 0.01% by mass or more and 80% by mass or less in the cosmetic. [Example]

[0122] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way. The various measurement and evaluation methods are as follows. Unless otherwise specified, particle size refers to the diameter of the particle.

[0123] <Median diameter> The median diameter of the composite cellulose particles (D 50) is measured using a dynamic image analyzer (CAMSIZER X2, manufactured by Microtrac MRB). Specifically, 20 mg of dried composite cellulose particles are placed in the device feeder, and the particles are dispersed at an air dispersion pressure of 30 kPa. The cumulative particle size distribution and volume frequency distribution are determined from 10,000 images measured in the dynamic image analyzer. The particle size at which the cumulative value reaches 50% is calculated as the median size.

[0124] <Inclusion stability> The encapsulation stability of the composite cellulose particles was evaluated by using an electromagnetic sieve AS-200 (manufactured by Letze) to classify the particles using a 150 μm test sieve specified in JIS Z 8801 and measure the amount of agglomeration. The measurement sample was 10 to 20 g and was classified for 5 minutes at an amplitude of 1.5 mm. The powder remaining on the 150 μm test sieve was collected and its mass was measured, and the mass was divided by the mass charged into the sieve to determine the amount of agglomeration. Therefore, the smaller the amount of agglomeration, the higher the encapsulation stability. The test sieves used were utility model types manufactured by Iida Seisakusho Co., Ltd.

[0125] <Average degree of polymerization of raw cellulose> The average degree of polymerization of the starting cellulose is measured as follows. [Preparation of measurement solution] Accurately weigh out 0.1 g (dry mass) of cellulose to be measured and place it in a 50 mL measuring flask. Add 0.5 M cuprammonium solution and make up to 50 mL. Stir overnight until the cellulose is completely dissolved to prepare the measurement solution. [Measurement of average degree of polymerization] The measurement solution obtained above is placed in an Ubbelohde viscometer (Thomas Scientific TV-3SL, viscosity coefficient = 0.03113), and after leaving it to stand in a thermostatic bath (20 ± 0.2 °C) for 1 hour, the flow time of the liquid is measured. From the flow time (t (seconds)) of cuprammonium solutions with various cellulose concentrations (g / dL) and the flow time (t0 (seconds)) of a cuprammonium aqueous solution without added cellulose, the relative viscosity η is calculated using the following formula: r Ask for. η r =t / t0 Next, the reduced viscosity (η sp / c) is calculated using the following formula. η sp / c=(η r -1) / c (c: cellulose concentration (g / dL)) Furthermore, the reduced viscosity is extrapolated to c=0 to determine the intrinsic viscosity [η] (dL / g), and the average degree of polymerization is calculated using the following formula. Average degree of polymerization=2000×[η]

[0126] <Production Example 1> (Production and Evaluation of Oxazoline-Modified Silicone) A mixture obtained by mixing 93.8 g (0.95 mol) of 2-ethyl-2-oxazoline and 203.3 g of ethyl acetate was subjected to a dehydration treatment at 28°C for 15 hours using 14.8 g of molecular sieves (trade name: Zeolum A-4, manufactured by Tosoh Corporation). In addition, a mixture of 100 g of side-chain primary aminopropyl-modified polydimethylsiloxane (AP3651, manufactured by Dow-Toray Co., Ltd., weight-average molecular weight 30,000, amine equivalent 2,000) and 203 g of ethyl acetate was dehydrated using 15.2 g of molecular sieves at 28°C for 15 hours. To the above dehydrated 2-ethyl-2-oxazoline ethyl acetate solution, 6.17 g (0.04 mol) of diethyl sulfate was added, and the mixture was heated under reflux at 80°C for 8 hours under a nitrogen atmosphere to synthesize terminal-reactive poly(N-propionylethyleneimine). This terminal-reactive poly(N-propionylethyleneimine) solution was added all at once to the above dehydrated side-chain primary aminopropyl-modified polydimethylsiloxane solution, and the mixture was heated under reflux at 80°C for 10 hours. The reaction mixture was concentrated under reduced pressure to give an N-propionylethyleneimine-dimethylsiloxane copolymer (oxazoline-modified silicone) as a pale yellow solid (190 g, 95% yield). The mass ratio of the organopolysiloxane segment in the final product was 0.50, and the weight-average molecular weight of the final product was 60,000. The obtained N-propionylethyleneimine-dimethylsiloxane copolymer (oxazoline-modified silicone) was dissolved in ethanol to a solids concentration of 50% by mass, to obtain an ethanol solution of oxazoline-modified silicone.

[0127] Example 1 (A) Process (1) (A1) Process (1-1) As the raw material cellulose, cellulose type I crystalline cellulose powder ("CEOLUS (registered trademark) FD-101" manufactured by Asahi Kasei Corporation, degree of polymerization: 170, median diameter: 50 μm) was used. 81.4 g of ion-exchanged water was added to 100 g of 8% by mass aqueous sodium hydroxide solution, followed by 18.6 g of cellulose powder (water content 6% by mass) and stirring with a spatula to obtain a cellulose dispersion. The resulting cellulose dispersion was then cooled to -2°C using a cooling water circulator (set temperature -5°C, manufactured by EYELA). Next, 50 g of 22% by mass aqueous sodium hydroxide solution at -15°C was added to the cooled cellulose dispersion to dissolve the cellulose, yielding an aqueous cellulose solution. The resulting aqueous cellulose solution had a cellulose concentration of 7.0% by mass and an NaOH concentration of 7.6% by mass.

[0128] (A2) Process (1-2) 0.2 g of a nonionic surfactant (Ryoto Sugar Ester ER-290, sucrose erucate ester, manufactured by Mitsubishi Chemical Corporation) was added to 150 g of an organic solvent (isododecane, ClogP: 5.7) and pre-stirred with a spatula. Next, 100 g of the cellulose aqueous solution obtained in step (1-1) was added, and emulsified using a continuous mixer magicLAB (manufactured by IKA Corporation) at room temperature (20°C) and 12,000 rpm to obtain a water-in-oil emulsion of cellulose. The mixed solution was passed through the emulsification section once (pass number). The particle size of the resulting water-in-oil emulsion was measured using a laser diffraction / scattering particle size distribution analyzer (LA-960V2, manufactured by Horiba, Ltd.) and was found to be 29 μm.

[0129] (A3) Process (1-3) The emulsion obtained in step (1-2) was added to a cellulose non-solvent, methanol (ClogP: -0.77), to precipitate cellulose. Precipitation was performed using 100 g of the cellulose non-solvent for 250 g of emulsion. When adding the emulsion to the cellulose non-solvent, the cellulose non-solvent was stirred at 500 rpm using a stirrer. The temperature of the cellulose non-solvent was set to room temperature (20°C). After cellulose precipitation, the resulting liquid was pressure-filtered (0.1 MPaG) using filter paper (ADVANTEC "C020A142C", 0.2 μm mesh) to obtain crude cellulose particles.

[0130] (B) Process (2) 170 g of the obtained crude cellulose particles (solid content: approximately 4 g) were dispersed in 880 g of pure water and neutralized using malic acid to a pH of approximately 7.0. The neutralized liquid was again pressure filtered, and the recovered crude cellulose particles were again dispersed in 880 g of pure water, stirred for 5 minutes, and then pressure filtered. The solid content was recovered and washed to obtain purified wet cellulose particles.

[0131] (C) Substitution process In the substitution step, the water present within and between the particles of the purified wet cellulose particles was replaced with 2-propanol (ClogP: 0.07). 170 g of the purified wet cellulose particles recovered in step (2) (solid content: approximately 17 g) was mixed with 350 g of 2-propanol, stirred for 5 minutes, and then filtered to obtain substituted purified wet cellulose particles.

[0132] (D) Process (3) 170 g (solid content: approximately 17 g) of the purified wet cellulose particles subjected to the substitution treatment was dispersed in 205 g of 2-propanol, an azeotropic solvent, to prepare a 2-propanol dispersion. The resulting 2-propanol dispersion was added to a 2-L stirring vessel and heated to 80°C in an oil bath. During this process, the water remaining in the purified cellulose wet particles that had been replaced with 2-propanol was azeotroped. The generated steam was cooled in a condenser and collected in a dropping funnel. After confirming that approximately 100 mL had accumulated in the dropping funnel, the 2-propanol and water were removed from the dropping funnel. The same amount of 2-propanol as that removed was added to the stirring vessel to remove the water from the cellulose. This procedure was repeated six times.

[0133] (E) Process (4) 2-Propanol was added to the cellulose particle dispersion obtained in step (3) to adjust the cellulose solid content to 4% by mass. To this dispersion, 300 parts by mass of modified polysiloxane represented by the following general formula (I) (manufacturer: Kao Corporation) was added as a functional substance, per 100 parts by mass of the cellulose solid content. The solution was placed in a 1-L recovery flask and heated at 80°C and 20 kPaA using an evaporator to remove the solvent. This was continued until the liquid stopped dripping from the reflux tube, and the dry powder obtained after the operation was obtained as composite cellulose particles 1. The median diameter and encapsulation stability of the obtained composite cellulose particles 1 were evaluated by the above-mentioned methods. The results are shown in Table 1. [ka] (In the formula, R 1 and R 9 are linear hydrocarbon groups having 16 to 18 carbon atoms, R 2 ~R 8 is a methyl group, R 10 and R 11 is a hydrogen atom, Q is a linear hydrocarbon group having 11 carbon atoms, p is the number of repeating units, which averages 25, and q is the number of repeating units, which averages 4.

[0134] <Examples 2 to 4> Composite cellulose particles 2 to 4 were obtained by the same procedure as in Example 1, except that the type and amount of the functional substance used in step (4) was changed as shown in Table 1. The median diameter and encapsulation stability of the obtained composite cellulose particles 2 to 4 were evaluated by the methods described above. The results are shown in Table 1. The functional substances used here were menthol ("L-menthol" (SP value 20) manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; Example 3) and the oxazoline-modified silicone obtained in Production Example 1 (Example 4).

[0135] <Comparative Example 1> Steps (1) to (3) were not carried out, and step (4) was carried out as follows. 2-Propanol was added to 6.5 g of commercially available cellulose particles ("Cellflow C-25" manufactured by JNC Corporation) to adjust the cellulose solid content to 4% by mass. To this dispersion was added 100 parts by mass of modified polysiloxane represented by the general formula (I) (manufacturer: Kao Corporation) per 100 parts by mass of the cellulose solid content. The solution was placed in a 1 L recovery flask and heated at 80°C and 20 kPaA using an evaporator to remove the solvent. This was continued until the liquid stopped dripping from the reflux tube, and the dry powder obtained after the operation was obtained as composite cellulose particles C1. The obtained composite cellulose particles C1 formed aggregates, and it was not possible to carry out tests for median diameter and encapsulation stability.

[0136] <Comparative Example 2> Composite cellulose particles C2 were obtained by the same procedure as in Comparative Example 1, except that the amount of the functional substance used in step (4) was changed as shown in Table 1. The obtained composite cellulose particles C2 were in a liquid state, and tests for median diameter and encapsulation stability could not be carried out.

[0137] [Table 1]

[0138] It can be seen from Table 1 that the composite cellulose particles obtained by the manufacturing method of this example have excellent stability of encapsulating functional substances. In contrast, the composite cellulose particles obtained by the manufacturing methods of Comparative Examples 1 and 2 became aggregates or liquid and could not be handled as composite cellulose particles. [Industrial Applicability]

[0139] According to the present invention, various functional substances can be encapsulated by a simple procedure, and the encapsulation stability of the functional substances in the resulting composite cellulose particles is good.

Claims

1. A method for producing composite cellulose particles, comprising the following steps (1) to (4) in this order: Step (1): A step of mixing a water-in-oil cellulose emulsion containing cellulose, water, and an organic solvent with a cellulose non-solvent to precipitate coarse cellulose particles and obtain a suspension containing the coarse cellulose particles. Step (2): A step of subjecting the suspension containing the crude cellulose particles obtained in the step (1) to solid-liquid separation, and then washing the obtained crude cellulose wet particles to obtain purified cellulose wet particles. Step (3): A step of mixing the purified wet cellulose particles obtained in the step (2) with an azeotropic solvent having an azeotropic point with water, and distilling off the water contained in the purified wet cellulose particles by azeotropy to obtain a dehydrated cellulose particle dispersion in which the dehydrated cellulose particles are dispersed in the azeotropic solvent. Step (4): A step of obtaining composite cellulose particles by the following step (4a) or step (4b): Step (4a): A step of mixing the dehydrated cellulose particle dispersion obtained in the step (3) with a functional substance, and then removing the solvent containing the azeotropic solvent used in the step (3) to obtain composite cellulose particles containing the functional substance. Step (4b): A step of obtaining composite cellulose particles containing the functional substance by subjecting the dehydrated cellulose particle dispersion obtained in the step (3) to solid-liquid separation to obtain a cake, mixing the cake with a functional substance, and then removing the solvent containing the azeotropic solvent used in the step (3) to obtain composite cellulose particles containing the functional substance.

2. The method for producing composite cellulose particles according to claim 1, wherein the step (1) comprises the following steps (1-1) to (1-3) in this order: Step (1-1): A step of mixing raw cellulose with an aqueous alkaline solution to prepare an aqueous cellulose solution Step (1-2): A step of mixing the aqueous cellulose solution obtained in the step (1-1) with an organic solvent to prepare a cellulose emulsion. Step (1-3): A step of mixing the cellulose emulsion obtained in Step (1-2) with a cellulose non-solvent to precipitate coarse cellulose particles and obtain a suspension containing the coarse cellulose particles.

3. 2. The method for producing composite cellulose particles according to claim 1, wherein the cellulose non-solvent used in the step (1) comprises at least one selected from the group consisting of methanol and ethanol.

4. a substitution step of bringing the purified wet cellulose particles obtained in the step (2) into contact with an azeotropic solvent having an azeotropic point with water for substitution after the step (2) and before the step (3), The method for producing composite cellulose particles according to claim 1, wherein the azeotropic point of the azeotropic solvent is 30°C or higher and 90°C or lower.

5. The method for producing composite cellulose particles according to claim 4, further comprising the step of adding an acid to the suspension containing the crude cellulose particles to neutralize the suspension after the step (1) and before the step (2).

6. 2. The method for producing composite cellulose particles according to claim 1, wherein in step (4), the content of the dehydrated cellulose particles in the dehydrated cellulose particle dispersion is 1% by mass or more and 6% by mass or less, or the content of the dehydrated cellulose particles in a cake obtained by solid-liquid separation of the dispersion is 5% by mass or more and 20% by mass or less.

7. 2. The method for producing composite cellulose particles according to claim 1, wherein the functional substance used in step (4) is an organic substance that dissolves in the azeotropic solvent used in step (3), or an organic or inorganic substance that disperses in the azeotropic solvent.

8. The method for producing composite cellulose particles according to claim 1 , wherein the dehydrated cellulose particles are porous particles.

9. 2. The method for producing composite cellulose particles according to claim 1, wherein the composite cellulose particles are composed of part or all of the cellulose being particulate cellulose, and at least a part of the functional substance being contained within the particulate cellulose.

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