Porous cellulose particles

Abstract

Porous cellulose particles having a compression modulus of 50 MPa or less, a specific surface area of from 100 m2 / g to less than 500 m2 / g, and a pore volume of 1.5 mL / g or more.

Description

Porous cellulose particles

[0001] The present invention relates to porous cellulose particles.

[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 properties. 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 attracted attention as particles that do not fall under the category of microplastic beads. One type of such polymer particles is chemically unmodified cellulose particles.

[0004] Porous cellulose particles are known as functional cellulose particles used in cosmetics. Porous cellulose particles are preferred because they allow functional substances in cosmetics to be encapsulated inside the particles. For example, Patent Document 1 describes porous cellulose particles with a crystal form of Type I and a specific surface area of ​​20 m ２ / g or more and the volume of pores with a diameter of 0.01 μm or more is 0.3 cm ３ Patent Document 2 discloses porous cellulose particles formed by aggregation of crystalline cellulose of type I crystal form, which have a porous structure of 0.1 to 1.5 micrometers per 1000 micrometers and an average particle size of at most 100 μm, and which are used as additives for cosmetics. １ is 0.5 to less than 50 μm, and the specific surface area is 25 to 1000 m ２ The document discloses porous cellulose particles having a sphericity of 0.85 or more and a viscosity of 0.1 / g, and states that cosmetics containing the porous cellulose particles have excellent feel characteristics.

[0005] Methods for producing porous cellulose particles have also been investigated. For example, Patent Document 3 describes a method for producing porous cellulose particles, which includes dissolving cellulose diacetate in a solvent to prepare a cellulose diacetate solution, dispersing the cellulose diacetate solution in a medium immiscible with the cellulose diacetate solution to obtain a dispersion, cooling the dispersion, adding a poor solvent to the cooled dispersion to precipitate cellulose diacetate particles, and saponifying the cellulose diacetate particles. This method allows porous cellulose particles to be produced more easily without using multiple harmful solvents. Patent Document 4 discloses a method for producing porous cellulose beads, which is characterized by mixing cellulose with an alkaline aqueous solution at a predetermined temperature range to prepare a cellulose dispersion, and contacting the resulting cellulose dispersion with a coagulation solvent. It describes that porous cellulose beads with high mechanical strength can be produced without using highly toxic and corrosive auxiliary materials and without undergoing complicated processes that are industrially disadvantageous. Patent Document 5 discloses that cellulose is dissolved in an alkali-containing aqueous solution in a predetermined temperature range to prepare a cellulose solution, which is then heated under predetermined conditions to prepare an emulsion, precipitate cellulose beads, and then crosslinked, thereby enabling the simple and efficient production of porous crosslinked cellulose beads having a pore structure suitable for antibody adsorption without using highly toxic or corrosive auxiliary materials and without undergoing industrially disadvantageous and complicated processes. Patent Document 6 discloses a method for producing porous crosslinked cellulose beads having a particle size of 1 to 2,500 μm, an average pore size of 200 to 1,000 μm, and a specific surface area of ​​500 to 800 m ２ / g, water content of 86 to 93%, pore volume of 1.00 to 5.00 ml / g, and porosity of 90 to 95%, and a method for producing the same.

[0006] Japanese Patent Publication No. 2-84401 International Publication No. 2020 / 004604 International Publication No. 2015 / 029790 Japanese Patent Publication No. 2017-14528 Japanese Patent Publication No. 2021-161246 Chinese Patent Application Publication No. 101250267

[0007] Functional particles to be incorporated into cosmetics are required to provide excellent texture, such as a soft feel and minimal roughness upon application, etc. Furthermore, in the case of porous particles, it is desirable that the particles be capable of encapsulating functional substances, and that when the cosmetic is applied to an object, the particles disintegrate during application, allowing the functional substances to be gradually released onto the object.

[0008] The porous cellulose particles described in Patent Document 1 are crystalline cellulose of type I crystal form, and are therefore hard particles, which are thought to cause a squeaky feeling when the particles collapse during application. Furthermore, the pore volumes of the porous cellulose particles disclosed in the examples are all 1 mL / g or less, which is thought to indicate insufficient encapsulation of functional substances. The porous cellulose particles described in Patent Document 2 are also aggregates of crystalline cellulose of type I crystal form. While the porous cellulose particles are described as having good tactile properties, there is no mention or suggestion of their encapsulation or sustained release of functional substances. Furthermore, the pore volumes of the porous cellulose particles disclosed in the examples of Patent Document 2 are all 1 mL / g or less, which is thought to indicate insufficient encapsulation of functional substances. The porous cellulose particles described in Patent Document 3 and the porous cellulose beads described in Patent Document 4 are both used as chromatography packing materials, and due to their large average particle size, are thought to provide poor tactile sensation when used in cosmetics. Furthermore, since particles used as chromatography packing materials preferably have high strength, these documents do not suggest porous cellulose particles that collapse during application. The porous cross-linked cellulose beads described in Patent Document 5 are hard particles due to the cross-linking treatment. Furthermore, the cellulose beads are also described as being suitable for use as adsorbents for chromatography, affinity adsorbents, etc., and have a lower porosity than particles for cosmetic applications, which are expected to disintegrate during application. The cellulose microparticles described in Patent Document 6 have a large specific surface area and a high water content.

[0009] The present invention relates to the provision of porous cellulose particles that can impart a soft feel to cosmetics when incorporated therein, are less rough when applied, and are excellent in the ability to encapsulate functional substances and in the disintegration of particles.

[0010] The present inventors have found that the above problems can be solved by using porous cellulose particles having a compressive modulus of elasticity of 50 MPa or less, a specific surface area, and a pore volume within a predetermined range. ２ / g or more 500m ２ / g and a pore volume of 1.5 mL / g or more. [2] A cosmetic preparation containing the porous cellulose particles described in [1] above. [3] A method for producing the porous cellulose particles described in [1] above, which comprises the following steps (I) to (V) in order: Step (I): mixing raw cellulose with an alkaline aqueous solution to prepare a cellulose aqueous solution; Step (II): mixing the cellulose aqueous solution with an organic solvent to prepare a cellulose emulsion; Step (III): mixing the cellulose emulsion with a cellulose non-solvent to precipitate coarse cellulose particles and obtain a suspension containing the coarse cellulose particles; Step (IV): performing solid-liquid separation of the suspension containing the coarse cellulose particles, and then washing the obtained coarse cellulose wet particles to obtain purified cellulose wet particles; and Step (V): drying the purified cellulose wet particles to obtain porous cellulose particles.

[0011] According to the present invention, it is possible to provide porous cellulose particles that can impart a soft feel when incorporated into cosmetics, are less rough when applied, and have excellent capabilities for encapsulating functional substances and excellent particle disintegration properties.

[0012] 1 is an X-ray diffraction profile of raw cellulose (cellulose type I crystals) used in the examples. 2 is an X-ray diffraction profile of porous cellulose particles (cellulose type II crystals) obtained in Example 1. 3 is an X-ray diffraction profile of porous cellulose particles (amorphous) obtained in Example 4.

[0013] [Porous Cellulose Particles] The porous cellulose particles of the present invention have a compressive modulus of elasticity of 50 MPa or less and a specific surface area of ​​100 m２ / g or more 500m ２ The porous cellulose particles of the present invention have a specific surface area of ​​less than 1.5 mL / g and a pore volume of 1.5 mL / g or more. By virtue of the above-described configuration, the porous cellulose particles of the present invention can impart a soft feel to a cosmetic when incorporated therein, have little roughness upon application, and exhibit excellent encapsulation of functional substances and particle disintegration properties. The reasons for this are unclear, but are thought to be as follows: Having a compressive modulus of elasticity of the porous cellulose particles equal to or less than a predetermined value is thought to impart a soft feel to the cosmetic, reduce roughness upon application to a target object, and facilitate disintegration upon application to the target object. Furthermore, having both a specific surface area and pore volume of the porous cellulose particles equal to or greater than a predetermined value is thought to improve encapsulation of functional substances.

[0014] The compressive modulus of the porous 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, from the viewpoint of a soft feel, minimal roughness when applied to an object, and improved disintegration during application to an object. Furthermore, from the viewpoint of suppressing disintegration during the production process of the porous cellulose particles, it is preferably 1.0 MPa or more, more preferably 2.0 MPa or more, still more preferably 3.0 MPa or more, still more preferably 4.0 MPa or more, and still more preferably 4.9 MPa or more. The compressive modulus of the porous cellulose particles is 50 MPa or less, preferably 1.0 MPa to 50 MPa, more preferably 1.0 MPa to 40 MPa, even more preferably 1.0 MPa to 30 MPa, still more preferably 1.0 MPa to 20 MPa, still more preferably 2.0 MPa to 10 MPa, still more preferably 2.0 MPa to 7.0 MPa, still more preferably 3.0 MPa to 6.0 MPa, still more preferably 4.0 MPa to 5.3 MPa, still more preferably 4.0 MPa to 5.2 MPa, and still more preferably 4.9 MPa to 5.0 MPa. The compressive modulus is the apparent compressive modulus of a single particle measured using a microcompression tester, and can be measured specifically by the method described in the Examples. The compressive modulus of the porous cellulose particles can be adjusted, for example, by changing the degree of polymerization of the raw cellulose used in step (I) and the cellulose concentration in the aqueous solution prepared in step (I) in the method for producing porous cellulose particles described below. Specifically, the compressive modulus of the resulting porous cellulose particles is increased by using raw cellulose with a high degree of polymerization in step (I) or by increasing the cellulose concentration in the aqueous solution. Furthermore, porous cellulose particles with a low compressive modulus can be obtained by using raw cellulose with a low degree of polymerization in step (I) or by decreasing the cellulose concentration in the aqueous solution.

[0015] The median diameter (D) of porous cellulose particles measured by a dry method ５０ ) is preferably 75 μm or less, more preferably 70 μm or less, even more preferably 65 μm or less, even more preferably 55 μm or less, even more preferably 40 μm or less, and even more preferably 30 μm or less, from the viewpoint of suppressing roughness when applied to an object. Furthermore, from the viewpoint of improving disintegration properties during application to an object, 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 porous cellulose particles measured by a dry method is preferably 5 μm or more and 75 μm or less, more preferably 5 μm or more and 70 μm or less, even more preferably 5 μm or more and 65 μm or less, even more preferably 5 μm or more and 55 μm or less, even more preferably 10 μm or more and 40 μm or less, and even more preferably 15 μm or more and 30 μm or less. The median diameter of porous cellulose particles measured by a dry method is the 50% median diameter measured using a particle size distribution analyzer based on the laser diffraction / scattering method using dried particles as a measurement sample, and can be measured specifically by the method described in the Examples. The median diameter of porous cellulose particles can be adjusted, for example, by changing the stirring speed when mixing the aqueous cellulose solution and the organic solvent in step (II) in the method for producing porous cellulose particles described below. Specifically, by increasing the stirring speed when mixing the aqueous cellulose solution and the organic solvent in step (II), the emulsion droplet diameter of the resulting cellulose emulsion becomes smaller, resulting in porous cellulose particles with a small median diameter. Furthermore, by decreasing the stirring speed, the emulsion droplet diameter of the resulting cellulose emulsion becomes larger, resulting in porous cellulose particles with a large median diameter.

[0016] The specific surface area of ​​the porous cellulose particles is set to 100 m from the viewpoint of improving the inclusion of functional substances. ２ / g or more, preferably 110m ２ / g or more, more preferably 120m ２ / g or more, more preferably 130m ２ / g or more, and even more preferably 135m ２ / g or more, and even more preferably 140m ２ / g or more, and even more preferably 144m ２ / g or more. From the viewpoint of suppressing the collapse of the porous 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 porous cellulose particles is 100 m / g or less. ２ / g or more 500m ２ / g, preferably less than 100m ２ / g or more 200m ２ / g or less, more preferably 110m ２ / g or more 180m ２ / g or less, more preferably 120m ２ / g or more 180m ２ / g or less, and even more preferably 130m ２ / g or more 150m ２ / g or less, and even more preferably 135m ２ / g or more 150m ２ / g or less, and even more preferably 140m ２ / g or more 150m ２ / g or less, and even more preferably 144m ２ / g or more 150m ２ / g or less. The specific surface area is determined by dividing the sum of the surface areas of the fine surfaces inside the porous cellulose particles and the particle surfaces, measured by mercury intrusion porosimetry, by the mass of the particles and then normalizing the result. Specifically, it can be measured by the method described in the Examples. The specific surface area of ​​porous cellulose particles can be controlled, for example, by selecting the surface tension of the dispersion medium (organic solvent) used in the dispersion medium replacement, which is performed as necessary in step (IV), and the drying method in step (V) in the method for producing porous cellulose particles described below. Specifically, if the surface tension of the organic solvent used in the dispersion medium replacement in step (IV) is low, the capillary force associated with the evaporation of the organic solvent is small, and shrinkage of the cellulose particles during drying can be suppressed, thereby obtaining porous cellulose particles with a large specific surface area. Furthermore, in step (V), even if a drying method in which capillary force due to the surface tension of the organic solvent does not act, such as freeze-drying, can suppress shrinkage of the cellulose particles during drying, thereby obtaining porous cellulose particles with a large specific surface area.

[0017] From the viewpoint of improving the encapsulation of functional substances, the pore volume of the porous cellulose particles is 1.5 mL / g or more, preferably 2.0 mL / g or more, more preferably 2.5 mL / g or more, even more preferably 3.0 mL / g or more, still more preferably 3.5 mL / g or more, and even more preferably 4.0 mL / g or more. From the viewpoint of suppressing disintegration during the production process of the porous 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 porous cellulose particles is 1.5 mL / g or more, preferably 1.5 mL / g to 8.0 mL / g, more preferably 2.0 mL / g to 7.0 mL / g, even more preferably 2.5 mL / g to 6.0 mL / g, even more preferably 3.0 mL / g to 5.0 mL / g, even more preferably 3.5 mL / g to 5.0 mL / g, and even more preferably 4.0 mL / g to 5.0 mL / g. The pore volume is a value determined by standardizing the total volume of mercury that has penetrated into the pores and interparticle gaps of the porous cellulose particles, as measured by mercury intrusion porosimetry, by dividing the total volume by the mass of the particles, and can be measured specifically by the method described in the Examples. The pore volume of the porous cellulose particles can be adjusted, for example, by the surface tension of the dispersion medium (organic solvent) used in the dispersion medium replacement, which is carried out as necessary in step (IV), the selection of the drying method in step (V), and also by the emulsion droplet size of the cellulose emulsion obtained in step (II) in the method for producing porous cellulose particles described below. Specifically, if the emulsion droplet size of the cellulose emulsion is small, the median diameter and pore volume of the obtained porous cellulose particles will also be small.

[0018] The porous cellulose particles of the present invention are preferably chemically unmodified from the viewpoint of environmental consideration. In this specification, "unmodified" means (1) that substantially no substituents have been introduced into the hydroxy groups in the cellulose constituting the porous cellulose particles, and (2) that the surface of the porous cellulose particles is not coated with a surface treatment agent. The amount of substituents introduced into the hydroxy groups in the cellulose constituting the porous cellulose particles is preferably 0.5 mol% or less, more preferably 0.1 mol% or less, and even more preferably 0 mol%, based on the total hydroxy groups. Furthermore, the porous cellulose particles are preferably uncrosslinked particles from the viewpoints of imparting a soft feel, improving the encapsulation of functional substances, and improving disintegration properties upon application to an object. "Uncrosslinked particles" refers to particles that are produced without intentional crosslinking and have substantially no crosslinked structure.

[0019] The surface pore diameter of the porous cellulose particles is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more from the viewpoint of improving the encapsulation of functional substances, and is preferably 800 nm or less, more preferably 600 nm or less, and even more preferably 500 nm or less from the viewpoint of having high particle strength and maintaining the particle shape. The surface pore diameter of the porous cellulose particles is preferably 50 nm or more and 800 nm or less, more preferably 100 nm or more and 600 nm or less, and even more preferably 200 nm or more and 500 nm or less. The surface pore diameter can be determined by mercury intrusion porosimetry, and specifically can be measured by the method described in the Examples.

[0020] The sphericity of the porous cellulose particles is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more, from the viewpoint of improving the feel when applied to an object and imparting appropriate particle disintegration properties. The upper limit of the sphericity is 100%, and it may be 90% or less. The sphericity of the porous cellulose particles is a value defined by the following formula, and can be determined by measurement using a dynamic image analyzer CAMSIZER X2 (manufactured by MICROTRAC MRB). Specifically, the sphericity can be measured by the method described in the Examples. Sphericity (%) = 4π × particle area (m 2 ) / (particle circumference (m)) ２ ×100

[0021] From the viewpoint of imparting a soft feel and improving disintegration properties when applied to an object, the cellulose constituting the porous cellulose particles is preferably cellulose II type crystalline cellulose or amorphous cellulose rather than cellulose I type crystalline cellulose. The crystalline form of the cellulose constituting the porous cellulose particles can be identified from the diffraction angle and diffraction intensity by X-ray diffraction. Cellulose II type crystalline cellulose exhibits a diffraction peak derived from the (11-0) plane at a diffraction angle 2θ = 12.5° and a diffraction peak derived from the (110) plane at 2θ = 20.0°, and can be easily distinguished from cellulose I type crystalline cellulose. Cellulose II type crystallinity is defined by the following formula, but the value is not particularly limited. Cellulose II type crystallinity (%) = [(I ２０．０ -I １５．０ ) / I ２０．０ ]×100 (where I ２０．０ is the diffraction intensity of the lattice plane (110 plane) (diffraction angle 2θ = 20.0°) in X-ray diffraction, and I １５．０is the diffraction intensity of the amorphous portion (diffraction angle 2θ = 15.0). The cellulose type II crystallinity can be measured by X-ray diffraction, specifically by the method described in the Examples. The crystalline form of porous 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 drying treatment is carried out in step (V) in the method for producing porous cellulose particles described below. Although the reason is unclear, if the drying treatment is carried out in step (V) when the purified wet cellulose particles contain an aqueous solvent, the crystallinity will be high, and if the drying treatment is carried out in step (V) when the purified wet cellulose particles contain a non-aqueous solvent, the crystallinity will be low.

[0022] The physical properties of the porous 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.

[0023] The porous cellulose 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 porous cellulose particles is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably substantially 100% by mass.

[0024] [Method for producing porous cellulose particles] The porous cellulose particles of the present invention can be produced by a production method preferably comprising the following steps (I) to (V) in order: Step (I): mixing raw cellulose with an alkaline aqueous solution to prepare a cellulose aqueous solution; Step (II): mixing the cellulose aqueous solution with an organic solvent to prepare a cellulose emulsion; Step (III): mixing the cellulose emulsion with a cellulose non-solvent to precipitate coarse cellulose particles and obtain a suspension containing the coarse cellulose particles; Step (IV): subjecting the suspension containing the coarse cellulose particles to solid-liquid separation, and then washing the obtained coarse wet cellulose particles to obtain purified wet cellulose particles; Step (V): drying the purified wet cellulose particles to obtain porous cellulose particles. The above production method makes it possible to easily produce porous cellulose particles having the above physical properties.

[0025] <Step (I)> In step (I), starting cellulose and an alkaline aqueous solution are mixed to prepare an aqueous cellulose solution. The aqueous cellulose solution prepared in step (I) 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 aqueous cellulose 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 (I) and subjecting the aqueous solution to step (II) and subsequent steps, it becomes easier to control the internal morphology of cellulose particles, and porous cellulose particles with desired physical properties can be easily produced.

[0026] (Raw Cellulose) From the viewpoint of environmental consideration, the raw cellulose used in step (I) 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 cellulose polymerization, 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 pulp such as cotton linter pulp obtained from fibers surrounding cotton seeds are preferred. The raw cellulose may be in the form of, for example, powder, sheet, or cotton. Among these, the starting cellulose is preferably in a powder form from the viewpoint of excellent solubility in an alkaline aqueous solution.

[0027] 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, from the viewpoint of the strength of the resulting porous cellulose particles, and is preferably 1000 or less, more preferably 500 or less, and even more preferably 300 or less, from the viewpoint of improving solubility in an alkaline aqueous solution. 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 the starting cellulose is generally controlled by the conditions for acid hydrolysis of the starting pulp. For example, a starting cellulose with a low degree of polymerization can be obtained by extending the acid hydrolysis time.

[0028] Either crystalline cellulose or amorphous cellulose can be used as the raw material cellulose, but from the viewpoint of obtaining porous 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.

[0029] When the starting cellulose is in a powdered form, the median diameter of the starting cellulose is preferably 10 μm or more, more preferably 20 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 starting cellulose can be measured by the same method as described above.

[0030] (Alkaline aqueous solution) The alkaline aqueous solution used in step (I) is not particularly limited as long as it is alkaline and can dissolve cellulose. Here, "capable of dissolving cellulose" means, for example, mixing cellulose with an alkaline aqueous solution in an amount that results in a 4% by mass solution, and visually confirming dissolution. The alkaline compound used in the alkaline aqueous solution can be either an inorganic alkaline compound or an organic alkaline compound, and examples thereof include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide; ammonia; and tertiary amines such as trimethylamine and triethylamine. Among these, from the viewpoints of availability and economy, alkali metal hydroxides are preferred, and one or more selected from the group consisting of sodium hydroxide and potassium hydroxide are more preferred, with sodium hydroxide being even more preferred. The above alkaline compounds can be used alone or in combination of two or more.

[0031] 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, and is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 25% 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.

[0032] In step (I), from the viewpoint of improving production efficiency, the solubility of the starting cellulose, and the stability of the resulting aqueous cellulose solution, alkaline aqueous solutions of different concentrations may be mixed with the starting cellulose in multiple batches. Specifically, in step (I), the starting cellulose is preferably mixed with an alkaline aqueous solution A having an alkali compound concentration of 1% by mass or more and 10% by mass or less, and then an alkaline aqueous solution B having an alkali compound concentration of more than 10% by mass or less and 40% by mass or less is added and mixed to prepare an aqueous cellulose solution. The alkaline compound concentration 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 alkaline compound concentration 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 (I), 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.

[0033] The mixing of the starting cellulose and the aqueous alkali solution in step (I) can be carried out by adding the starting cellulose to the aqueous alkali solution and stirring using a known device. The temperature during mixing of the starting cellulose and the aqueous alkali 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 alkali 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 aqueous alkali solution A and aqueous alkali solution B are used, it is preferable to add the starting cellulose to aqueous alkali solution A and stir and mix them, then adjust the temperature of the mixture to the above-mentioned range, and then add aqueous alkali solution B and mix them.

[0034] 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 can be set appropriately. Usually, stirring is continued until the starting cellulose is dissolved as can be seen visually.

[0035] The cellulose concentration in the cellulose aqueous solution obtained in step (I) 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 improving the strength of the obtained porous cellulose particles. Furthermore, from the viewpoint of making the viscosity of the cellulose aqueous solution easy to prepare a cellulose emulsion when subjected to step (II), it is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and even more preferably 6% by mass or less. The cellulose concentration in the cellulose aqueous solution obtained in step (I) 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 8% by mass or less, and even more preferably 2% by mass or more and 6% by mass or less.

[0036] 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 (I) 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, still 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 (I) 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.

[0037] <Step (II)> In step (II), the cellulose aqueous solution obtained in step (I) is mixed with an organic solvent to prepare a cellulose emulsion. Step (II) makes it possible to prepare a water-in-oil cellulose emulsion that can produce porous cellulose particles having a desired median diameter. The organic solvent is not particularly limited as long as it is an organic solvent that is immiscible with water and can be mixed with the cellulose aqueous solution to prepare a cellulose emulsion.

[0038] Preferred organic solvents used in step (II) include hydrocarbon solvents, ester solvents, halogenated solvents, and the like.

[0039] Examples of hydrocarbon solvents include chain aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons. The number of carbon atoms in the chain aliphatic hydrocarbons is preferably 6 or more, more preferably 8 or more, and preferably 18 or less, more preferably 12 or less. The chain aliphatic hydrocarbons may be either linear aliphatic hydrocarbons or branched aliphatic hydrocarbons. The number of carbon atoms in the alicyclic hydrocarbons and aromatic hydrocarbons is preferably 6 or more and 18 or less, more preferably 6 or more and 12 or less. 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.

[0040] The ester solvent is preferably an ester having 4 to 10 carbon atoms, such as ethyl acetate, butyl acetate, etc. The halogen-based solvent is, for example, dichloromethane, dichloroethane, dichlorobenzene, etc.

[0041] The organic solvents may be used alone or in combination of two or more. From the viewpoint of easily preparing a water-in-oil cellulose emulsion, the organic solvent is preferably a hydrocarbon solvent, more preferably a chain aliphatic hydrocarbon, further 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.

[0042] In step (II), 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, relative to 100 parts by mass of the aqueous cellulose solution, from the viewpoint of improving the emulsion stability of the water-in-oil cellulose emulsion; from the viewpoint of easily obtaining porous cellulose particles having a desired median diameter, it 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. And, in step (II), 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, relative to 100 parts by mass of the aqueous cellulose solution.

[0043] In step (II), 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, and amphoteric surfactants. Among these, from the viewpoint of improving the emulsifying ability of the water-in-oil cellulose emulsion, nonionic surfactants are preferred.

[0044] From the viewpoint of improving the emulsion stability of water-in-oil cellulose emulsions, 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, even more preferably 1 or more and 5 or less, even more preferably 1 or more and 4 or less, and even more preferably 1 or more and 3 or less. Here, HLB is an index representing the ratio of the relative affinity of a surfactant for both liquids in an oil-water system, and can be calculated from the following formula using the Griffin 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 hydrophilic groups contained in surfactants include hydroxyl groups and ethyleneoxy groups. The HLB of two or more types of nonionic surfactants can be determined as a weighted average obtained by multiplying the HLB of each nonionic surfactant by the mass fraction of each nonionic surfactant (i.e., the value obtained by dividing the mass of each nonionic surfactant by the total mass of the nonionic surfactants).

[0045] 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 sorbitol 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 fatty acids in the 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 alkyl groups in the polyoxyethylene alkyl ethers, is preferably 12 or more, more preferably 16 or more, and even more preferably 18 or more, from the viewpoint of maintaining the HLB in the above-mentioned range, and is preferably 24 or less, more preferably 22 or less.

[0046] Examples of sorbitan fatty acid esters include sorbitan monooleate, sorbitan monostearate, sorbitan sesquioleate, sorbitan coconut oil fatty acid, 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.

[0047] Among the above, from the viewpoint of further improving the emulsion stability of the water-in-oil cellulose emulsion, 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 still more preferably one or more selected from the group consisting of sucrose erucate and sucrose behenate.

[0048] In step (II), when an emulsifier is further mixed, the amount of the emulsifier mixed is, from the viewpoint of further improving the emulsion stability of the water-in-oil cellulose emulsion, preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, even more preferably 1.0 parts by mass or more, and preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5.0 parts by mass or less, relative to 100 parts by mass of the organic solvent. The amount of the emulsifier mixed is preferably 0.1 parts by mass or more and 20 parts by mass or less, more preferably 0.5 parts by mass or more and 10 parts by mass or less, even more preferably 1.0 parts by mass or more and 5.0 parts by mass or less, relative to 100 parts by mass of the organic solvent.

[0049] 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.

[0050] 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 during mixing of the aqueous cellulose solution and the organic solvent is preferably 20°C or lower, more preferably 10°C or lower, and even more preferably 5°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 a 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 during mixing of the aqueous cellulose solution and the organic solvent is preferably −20°C or higher and 20°C or lower, more preferably −10°C or higher and 10°C or lower, and even more preferably −5°C or higher.

[0051] The stirring speed when mixing the aqueous cellulose solution and 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 porous cellulose particles having a desired median size, it is preferably 1000 rpm or more, more preferably 3000 rpm or more, even more preferably 5000 rpm or more, still more preferably 5500 rpm or more, and preferably 15000 rpm or less, more preferably 12000 rpm or less, even more preferably 10000 rpm or less, still more preferably 8500 rpm or less. The stirring speed when mixing the aqueous cellulose solution and the organic solvent is preferably 1000 rpm or more and 15000 rpm or less, more preferably 3000 rpm or more and 12000 rpm or less, even more preferably 5000 rpm or more and 10000 rpm or less, still more preferably 5500 rpm or more and 8500 rpm or less.

[0052] 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.

[0053] <Step (III)> In step (III), the cellulose emulsion obtained in step (II) is mixed with a cellulose nonsolvent to precipitate coarse cellulose particles, thereby obtaining a suspension containing the coarse cellulose particles. The cellulose nonsolvent is a so-called cellulose nonsolvent that does not dissolve cellulose, and is a solvent that is compatible with the alkaline aqueous solution and organic solvent. By mixing the solvent with the cellulose emulsion, the cellulose nonsolvent flows into the cellulose and the organic solvent inside the cellulose flows out, forming a phase-separated structure. This allows for control of the morphology inside the cellulose particles, coagulating the cellulose in a state where a desired porous structure is formed, and precipitating the cellulose as particles. The cellulose nonsolvent is preferably an alcohol-based solvent, more preferably an alcohol having 4 or less carbon atoms. Examples of alcohols that can be used as cellulose nonsolvents include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, and tert-butyl alcohol. These can be used alone or in combination of two or more.

[0054] Among the above, the cellulose non-solvent is preferably at least one selected from the group consisting of ethanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-1-propanol, more preferably ethanol, from the viewpoint of easily precipitating crude cellulose particles and controlling the internal morphology of the cellulose particles to obtain porous cellulose particles having desired physical properties.

[0055] The amount of the cellulose non-solvent mixed is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 200 parts by mass or more, and preferably 1000 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 400 parts by mass or less, relative to 100 parts by mass of the cellulose emulsion, from the viewpoints of easily precipitating the crude cellulose particles, controlling the internal morphology of the cellulose particles to obtain porous cellulose particles having the desired physical properties, and maintaining the stability of the emulsion. The amount of the cellulose non-solvent mixed is preferably 50 parts by mass or more and 1000 parts by mass or less, more preferably 100 parts by mass or more and 500 parts by mass or less, even more preferably 200 parts by mass or less, relative to 100 parts by mass of the cellulose emulsion.

[0056] In step (III), it is preferable to further mix an acid from the viewpoint of neutralizing the alkaline compound 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, it is preferably an organic acid, more preferably a carboxylic acid having 4 or less carbon atoms. 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 the cellulose emulsion and the cellulose non-solvent, it is preferably one or more selected from the group consisting of acetic acid, lactic acid, malic acid, and succinic acid, more preferably acetic acid.

[0057] When an acid is used in step (III), the amount of acid mixed 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 (I) 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 mixed in step (III) 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 (I).

[0058] 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 the cellulose emulsion while stirring the cellulose non-solvent so as not to cause the emulsion droplets to bond together. The temperature when mixing the cellulose emulsion and the cellulose non-solvent is preferably 0°C or higher, more preferably 5°C or higher, even more preferably 15°C or higher, and preferably 50°C or lower, more preferably 40°C or lower, even more preferably 30°C or lower. The temperature when mixing the cellulose emulsion and the cellulose non-solvent 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.

[0059] When an acid is mixed in step (III), 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.

[0060] 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 porous cellulose particles with 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 coarse cellulose particles and controlling the internal morphology of the cellulose particles to obtain porous 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.

[0061] <Step (IV)> In step (IV), the suspension containing the coarse cellulose particles obtained in step (III) is subjected to solid-liquid separation, and the resulting coarse cellulose wet particles are then washed to obtain purified cellulose wet particles. Solid-liquid separation of the suspension containing coarse cellulose particles can be carried out by centrifugation, filtration, decantation, or a combination thereof. Next, the coarse cellulose wet particles obtained after solid-liquid separation are washed to remove impurities such as the organic solvent and emulsifier used in step (II) and the neutralization salt generated in step (III). The washing of the coarse cellulose wet particles can be carried out using water, an organic solvent, or a combination thereof. It is preferable to use an organic solvent to remove hydrophobic impurities such as the organic solvent and emulsifier used in step (II), and it is preferable to use water to remove water-soluble impurities such as the neutralization salt.

[0062] The organic solvent used in the washing treatment of the wet crude cellulose particles in step (IV) is preferably a solvent that can dissolve the organic solvent and emulsifier used in step (II) and that can be easily dried. Examples of such a solvent 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.

[0063] When drying by reduced pressure is performed, from the viewpoint of suppressing shrinkage of the resulting porous cellulose particles during drying after the above-mentioned washing treatment, it is preferable to further disperse the cellulose particles after the washing treatment in a dispersion medium to perform dispersion medium replacement. From the viewpoint of suppressing shrinkage of the resulting porous cellulose particles during drying, the dispersion medium used for dispersion medium replacement is preferably an organic solvent with low surface tension, and an organic solvent having a surface tension at 25°C of preferably 20 mN / m or less, more preferably 18 mN / m or less. The above surface tension is a surface tension value measured at 25°C using an automatic surface tensiometer (K100 manufactured by KRUSS).

[0064] Examples of the low surface tension organic solvent include aliphatic hydrocarbons having 7 or less carbon atoms, such as pentane, hexane, and heptane, as well as ether compounds having 4 or less carbon atoms, such as ethyl methyl ether and diethyl ether, which can be used alone or in combination of two or more. Among these, pentane is preferred from the viewpoint of suppressing shrinkage of the resulting porous cellulose particles during drying.

[0065] The amount of the dispersion medium used for the dispersion medium substitution is preferably 100 parts by mass or more, more preferably 200 parts by mass or more, and preferably 2000 parts by mass or less, more preferably 1000 parts by mass or less, and even more preferably 600 parts by mass or less, relative to 100 parts by mass of the cellulose particles after the washing treatment. The amount of the dispersion medium used for the dispersion medium substitution is preferably 100 parts by mass or more and 2000 parts by mass or less, more preferably 200 parts by mass or more and 1000 parts by mass or less, and even more preferably 200 parts by mass or more and 600 parts by mass or less, relative to 100 parts by mass of the cellulose particles after the washing treatment.

[0066] The dispersion medium replacement can be carried out, for example, by adding the washed cellulose particles to a dispersion medium and stirring the mixture using a known device. The temperature at which the washed cellulose particles and the dispersion medium are mixed is preferably 0° C. or higher, more preferably 5° C. or higher, even more preferably 15° C. or higher, and preferably 50° C. or lower, more preferably 40° C. or lower, and even more preferably 30° C. or lower. The temperature at which the washed cellulose particles and the dispersion medium are mixed is preferably 0° C. or higher and 50° C. or lower, more preferably 5° C. or higher and 40° C. or lower, and even more preferably 15° C. or higher and 30° C. or lower.

[0067] The stirring speed during mixing of the washed cellulose particles with the dispersion medium depends on the production scale and temperature and is set as appropriate, but from the viewpoint of sufficiently dispersing the cellulose particles, 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 washed cellulose particles with the dispersion medium 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 during mixing of the washed cellulose particles with the dispersion medium depends on the production scale and temperature and is set as appropriate, but is usually 0.2 hours or more and 12 hours or less, preferably 0.5 hours or more and 6 hours or less.

[0068] By carrying out the above-mentioned dispersion medium substitution, a suspension containing purified cellulose particles is obtained. The suspension can be subjected to solid-liquid separation in the same manner as above to recover purified wet cellulose particles.

[0069] <Step (V)> In step (V), the purified wet cellulose particles obtained in step (IV) are dried to obtain dry porous cellulose particles. As a method for drying the purified wet cellulose particles, freeze-drying is preferably used from the viewpoint of suppressing shrinkage of the particles during drying and maintaining the porous structure. In addition, when the dispersion medium is replaced in step (IV), drying treatment can also be performed by vacuum drying, drying with supercritical carbon dioxide, etc.

[0070] The freeze-drying preferably involves pre-freezing the purified wet cellulose particles, followed by primary and secondary drying. Pre-freezing is preferably rapid freezing at a temperature of −200° C. or higher and −50° C. or lower under normal pressure. The primary drying is preferably carried out under a vacuum of 0.1 Pa or higher and 100 Pa or lower and at a temperature of −20° C. or higher and −5° C. or lower, in which ice in the pre-frozen product is sublimated, and then the secondary drying is preferably carried out under a vacuum of 0.1 Pa or higher and 100 Pa or lower and at a temperature of 20° C. or higher and 40° C. or lower.

[0071] [Cosmetics] The present invention further provides a cosmetic comprising the porous cellulose particles. By including the porous cellulose particles, the cosmetic of the present invention can impart a pleasant feel to the skin. Furthermore, since porous cellulose particles have excellent encapsulation properties for functional substances and excellent particle disintegration properties, a cosmetic comprising the porous cellulose particles can sustainably release functional substances onto a target object upon application. To effectively achieve the above-described effects, the cosmetic of the present invention is preferably a skin cosmetic. Examples of such skin cosmetic include foundations, makeup bases, sunscreens, emulsions, and lotions. The content of the porous cellulose particles in the cosmetic may be any amount that can achieve the desired performance, and can be selected appropriately depending on the type and form of the cosmetic. However, the content is typically in the range of 0.01% by mass to 80% by mass in the cosmetic.

[0072] <Applications> The porous cellulose particles of the present invention can be incorporated or used in applications other than cosmetics, such as toiletries, oral care products, quasi-drugs, pharmaceuticals, household products, agricultural products, etc. Furthermore, since the porous cellulose particles of the present invention are made from cellulose derived from natural plants, they are environmentally friendly and can be suitably used as an alternative material to microplastics.

[0073] In addition to the above-described embodiments, the present invention discloses the following: <1> A compressive elastic modulus of 50 MPa or less, a specific surface area of ​​100 m ２ / g or more 500m ２ / g or less, and a pore volume of 1.5 mL / g or more. <2> The porous cellulose particles of <1>, wherein the compressive modulus of the porous cellulose particles is 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 5.0 MPa or less, still more preferably 5.3 MPa or less, and still more preferably 5.2 MPa or less. <3> The porous cellulose particles of <1> or <2>, wherein the compressive modulus of the porous cellulose particles is preferably 1.0 MPa or more, more preferably 2.0 MPa or more, still more preferably 3.0 MPa or more, still more preferably 4.0 MPa or more, and still more preferably 4.9 MPa or more. <4> The porous cellulose particles of any one of <1> to <3>, wherein the median diameter of the porous cellulose particles measured by a dry method is 75 μm or less. <5> The median diameter (D ５０ <6> The porous cellulose particles according to any one of <1> to <4>, wherein the median diameter (D ５０<7> The porous cellulose particles according to any one of <1> to <5>, wherein the specific surface area of ​​the porous cellulose particles is preferably 110 m or more, more preferably 10 m or more, and even more preferably 15 m or more. ２ / g or more, more preferably 120m ２ / g or more, more preferably 130m ２ / g or more, and even more preferably 135m ２ / g or more, and even more preferably 140m ２ / g or more, and even more preferably 144m ２ <8> The porous cellulose particles according to any one of <1> to <6>, wherein the specific surface area of ​​the porous cellulose particles is preferably 200 m / g or more. ２ / g or less, more preferably 180m ２ / g or less, more preferably 150m ２ <9> The porous cellulose particles of any one of <1> to <8>, wherein the pore volume of the porous cellulose particles is preferably 2.0 mL / g or more, more preferably 2.5 mL / g or more, even more preferably 3.0 mL / g or more, still more preferably 3.5 mL / g or more, and still more preferably 4.0 mL / g or more. <10> The porous cellulose particles of any one of <1> to <9>, wherein the pore volume of the porous cellulose particles 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 still more preferably 5.0 mL / g or less.

[0074] <11> Porous cellulose particles according to any one of <1> to <10>, wherein the sphericity of the porous cellulose particles is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. <12> Porous cellulose particles according to any one of <1> to <11>, wherein the surface pore diameter of the porous cellulose particles is preferably 50 nm or more, more preferably 100 nm or more, and even more preferably 200 nm or more. <13> Porous cellulose particles according to any one of <1> to <12>, wherein the surface pore diameter of the porous cellulose particles is preferably 800 nm or less, more preferably 600 nm or less, and even more preferably 500 nm or less. <14> Porous cellulose particles according to any one of <1> to <13>, wherein the porous cellulose particles are not chemically modified. <15> Porous cellulose particles according to any one of <1> to <14>, wherein the porous cellulose particles are non-crosslinked particles. <16> Porous cellulose particles according to any one of <1> to <15>, wherein the cellulose constituting the porous cellulose particles is cellulose II type crystalline cellulose or amorphous cellulose. <17> Porous cellulose particles according to any one of <1> to <16>, wherein the cellulose content in the porous cellulose particles is preferably 95% by mass or more, more preferably 99% by mass or more, and even more preferably substantially 100% by mass. <18> A cosmetic preparation comprising the porous cellulose particles according to any one of <1> to <17>. <19> A method for producing porous cellulose particles according to any one of <1> to <17>, comprising the following steps (I) to (V) in this order:Step (I): mixing a raw cellulose solution with an alkaline aqueous solution to prepare a cellulose aqueous solution; Step (II): mixing the cellulose aqueous solution with an organic solvent to prepare a cellulose emulsion; Step (III): mixing the cellulose emulsion with a cellulose non-solvent to precipitate coarse cellulose particles and obtain a suspension containing the coarse cellulose particles; Step (IV): subjecting the suspension containing the coarse cellulose particles to solid-liquid separation, and then washing the obtained coarse cellulose wet particles to obtain purified cellulose wet particles; Step (V): drying the purified cellulose wet particles. <20> The method for producing porous cellulose particles according to <19>, wherein the raw cellulose used in the step (I) is preferably chemically unmodified, chemically pure cellulose, and more preferably wood or pulp.

[0075] <21> The method for producing porous cellulose particles according to <19> or <20>, wherein the starting cellulose used in the step (I) is in the form of a powder, a sheet, or a cotton, preferably in the form of a powder. <22> The method for producing porous cellulose particles according to any one of <19> to <21>, wherein the starting cellulose used in the step (I) has a degree of polymerization of preferably 10 or more, more preferably 50 or more, even more preferably 100 or more, still more preferably 150 or more, and preferably 1000 or less, more preferably 500 or less, and even more preferably 300 or less. <23> The method for producing porous cellulose particles according to any one of <19> to <22>, wherein the starting cellulose used in the step (I) is preferably crystalline cellulose, more preferably cellulose type I crystalline cellulose. <24> The method for producing porous cellulose particles according to any one of <19> to <23>, wherein the starting cellulose used in step (I) is in a powdery form, and the median diameter of the starting cellulose is preferably 10 μm or more, more preferably 20 μm or more, and 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. <25> The method for producing porous cellulose particles according to any one of <19> to <24>, wherein the alkali compound used in the alkaline aqueous solution in step (I) is preferably an alkali metal hydroxide, more preferably one or more selected from the group consisting of sodium hydroxide and potassium hydroxide, and even more preferably sodium hydroxide. <26> The method for producing porous cellulose particles according to any one of <19> to <25>, wherein the concentration of the alkali compound in the alkaline aqueous solution used in step (I) is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less. <27> The method for producing porous cellulose particles according to any one of <19> to <26>, wherein in the step (I), aqueous alkaline solutions of different concentrations are mixed with the starting cellulose in multiple batches.<28> The method for producing porous cellulose particles according to any one of <19> to <27>, wherein in step (I), the starting cellulose is mixed 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 an aqueous alkali solution B having an alkali compound concentration of more than 10% by mass and 40% by mass or less is added and mixed to prepare an aqueous cellulose solution. <29> The method for producing porous cellulose particles according to <28>, wherein the concentration of the alkali compound in the aqueous alkali 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. <30> The method for producing porous cellulose particles according to <28> or <29>, wherein the concentration of the alkali compound in the aqueous alkali 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.

[0076] <31> The method for producing porous cellulose particles according to any one of <28> to <30>, wherein the mass ratio (A / B) of the alkaline aqueous solution A to the alkaline aqueous solution B is preferably 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. <32> The method for producing porous cellulose particles according to any one of <19> to <31>, wherein in the step (I), the temperature when mixing the starting cellulose and the alkaline aqueous solution is preferably 10°C or less, more preferably 5°C or less, even more preferably 0°C or less, and preferably -20°C or more, more preferably -10°C or more, and even more preferably -5°C or more. <33> The method for producing porous cellulose particles according to any one of <28> to <30>, wherein in the step (I), the starting cellulose is added to the alkaline aqueous solution A and mixed with stirring, and then the temperature of the mixture is adjusted to preferably 10°C or less, more preferably 5°C or less, even more preferably 0°C or less, and preferably -20°C or more, more preferably -10°C or more, and even more preferably -5°C or more, before adding the alkaline aqueous solution B and mixing. <34> The method for producing porous cellulose particles according to any one of <19> to <33>, wherein the cellulose concentration in the aqueous cellulose solution obtained in the step (I) is 1% by mass or more and 8% by mass or less. <35> The method for producing porous cellulose particles according to any one of <19> to <34>, wherein the alkali compound concentration in the aqueous cellulose solution obtained in the step (I) 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, still 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.<36> The method for producing porous cellulose particles according to any one of <19> to <35>, wherein the organic solvent used in the step (II) is a hydrocarbon solvent, more preferably a chain aliphatic hydrocarbon, 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. <37> The method for producing porous cellulose particles according to any one of <19> to <36>, wherein an emulsifier is further mixed in the step (II). <38> The method for producing porous cellulose particles according to <37>, wherein the emulsifier is a nonionic surfactant, 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 a sucrose fatty acid ester, 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. <39> The method for producing porous cellulose particles according to <38>, wherein the HLB of the nonionic surfactant used as the 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 even more preferably 1 or more and 3 or less. <40> The method for producing porous cellulose particles according to any one of <37> to <39>, wherein the amount of the emulsifier mixed in the step (II) is preferably at least 0.1 part by mass, more preferably at least 0.5 part by mass, even more preferably at least 1.0 part by mass, and is preferably at most 20 parts by mass, more preferably at most 10 parts by mass, even more preferably at most 5.0 parts by mass, relative to 100 parts by mass of the organic solvent.

[0077] <41> The method for producing porous cellulose particles according to any one of <19> to <40>, wherein in the step (II), the temperature during mixing of the aqueous cellulose solution and the organic solvent is preferably 20° C. or lower, more preferably 10° C. or lower, even more preferably 5° C. or lower, and preferably −20° C. or higher, more preferably −10° C. or higher, and even more preferably −5° C. or higher. <42> The method for producing porous cellulose particles according to any one of <19> to <41>, wherein in the step (II), the stirring speed during mixing of the aqueous cellulose solution and the organic solvent is preferably 1,000 rpm or higher, more preferably 3,000 rpm or higher, even more preferably 5,000 rpm or higher, still more preferably 5,500 rpm or higher, and preferably 15,000 rpm or lower, more preferably 12,000 rpm or lower, even more preferably 10,000 rpm or lower, and still more preferably 8,500 rpm or lower. <43> The method for producing porous cellulose particles according to any one of <19> to <42>, wherein the cellulose non-solvent used in the step (III) is an alcohol having 4 or less carbon atoms. <44> The method for producing porous cellulose particles according to any one of <19> to <43>, wherein the cellulose non-solvent used in the step (III) is preferably one or more selected from the group consisting of ethanol, 2-propanol, 1-butanol, 2-butanol, and 2-methyl-1-propanol, more preferably ethanol. <45> The method for producing porous cellulose particles according to any one of <19> to <44>, wherein the amount of the cellulose non-solvent used in the step (III) is preferably 50 parts by mass or more, more preferably 100 parts by mass or more, even more preferably 200 parts by mass or more, and is preferably 1,000 parts by mass or less, more preferably 500 parts by mass or less, even more preferably 400 parts by mass or less, relative to 100 parts by mass of the cellulose emulsion. <46> The method for producing porous cellulose particles according to any one of <19> to <45>, wherein an acid is further mixed in the step (III). <47> The method for producing porous cellulose particles according to <46>, wherein the acid mixed in the step (III) is preferably an organic acid, more preferably a carboxylic acid having 4 or less carbon atoms.<48> The method for producing porous cellulose particles according to <46> or <47>, wherein the amount of acid mixed in the step (III) is preferably 1.0 equivalent or more, more preferably 1.2 equivalents or more, even more preferably 1.4 equivalents or more, and preferably 3.0 equivalents or less, more preferably 2.0 equivalents or less, and even more preferably 1.8 equivalents or less, relative to the amount of the alkali compound used in the step (I). <49> The method for producing porous cellulose particles according to any one of <46> to <48>, wherein in the step (III), the cellulose emulsion and the cellulose non-solvent are mixed and then the acid is mixed. <50> The method for producing porous cellulose particles according to any one of <19> to <49>, wherein in the step (III), the temperature during mixing of the cellulose emulsion and the cellulose non-solvent is preferably 0°C or more, more preferably 5°C or more, even more preferably 15°C or more, and preferably 50°C or less, more preferably 40°C or less, and even more preferably 30°C or less.

[0078] <51> The method for producing porous cellulose particles according to any one of <19> to <50>, wherein in the step (III), the stirring speed during mixing of the cellulose emulsion and the cellulose non-solvent is preferably 100 rpm or more, more preferably 200 rpm or more, and preferably 2000 rpm or less, more preferably 1500 rpm or less, even more preferably 1000 rpm or less, and still more preferably 800 rpm or less. <52> The method for producing porous cellulose particles according to any one of <19> to <51>, wherein in the step (III), the stirring time during mixing of the cellulose emulsion and the cellulose non-solvent is 0.2 hours or more and 12 hours or less, preferably 0.5 hours or more and 6 hours or less. <53> The method for producing porous cellulose particles according to any one of <19> to <52>, wherein in the step (IV), solid-liquid separation of the suspension containing the coarse cellulose particles obtained in the step (III) is carried out by centrifugation, filtration, decantation, or a combination thereof. <54> The method for producing porous cellulose particles according to any one of <19> to <53>, wherein in the step (IV), the washing treatment of the crude wet cellulose particles obtained after the solid-liquid separation is carried out using water, an organic solvent, or a combination thereof. <55> The method for producing porous cellulose particles according to <54>, wherein the organic solvent is a ketone solvent having 6 or less carbon atoms or an alcohol solvent having 6 or less carbon atoms, preferably acetone, methyl isobutyl ketone, ethanol, or 2-propanol. <56> The method for producing porous cellulose particles according to any one of <19> to <55>, wherein in the step (IV), the cellulose particles obtained after the washing treatment are dispersed in a dispersion medium to replace the dispersion medium, and then dried under reduced pressure. <57> The method for producing porous cellulose particles according to <56>, wherein in the step (IV), the dispersion medium used for the dispersion medium replacement is an organic solvent having a surface tension at 25°C of preferably 20 mN / m or less, more preferably 18 mN / m or less, and is preferably pentane.<58> The method for producing porous cellulose particles according to <56> or <57>, wherein in the step (IV), the amount of the dispersion medium used for the dispersion medium substitution is preferably 100 parts by mass or more, more preferably 200 parts by mass or more, and preferably 2,000 parts by mass or less, more preferably 1,000 parts by mass or less, and even more preferably 600 parts by mass or less, relative to 100 parts by mass of the cellulose particles after the washing treatment. <59> The method for producing porous cellulose particles according to any one of <56> to <58>, wherein in the step (IV), the temperature at which the cellulose particles after the washing treatment and the dispersion medium are mixed is preferably 0°C or more, more preferably 5°C or more, even more preferably 15°C or more, and preferably 50°C or less, more preferably 40°C or less, and even more preferably 30°C or less. <60> The method for producing porous cellulose particles according to any one of <56> to <59>, wherein in the step (IV), the stirring speed when mixing the washed cellulose particles with the dispersion medium is preferably 100 rpm or more, more preferably 200 rpm or more, and is preferably 2000 rpm or less, more preferably 1500 rpm or less, even more preferably 1000 rpm or less, and still more preferably 800 rpm or less.

[0079] <61> The method for producing porous cellulose particles according to any one of <56> to <60>, wherein in the step (IV), the suspension obtained by the dispersion medium substitution is subjected to solid-liquid separation to recover purified wet cellulose particles. <62> The method for producing porous cellulose particles according to any one of <19> to <61>, wherein in the step (V), the drying method is a freeze-drying method. <63> The method for producing porous cellulose particles according to <62>, wherein the freeze-drying method is a method in which the purified wet cellulose particles are pre-freezed, followed by primary drying and secondary drying. <64> The method for producing porous cellulose particles according to <63>, wherein the pre-freezing comprises rapid freezing at a temperature of −200° C. or higher and −50° C. or lower under normal pressure, followed by primary drying in which ice in the pre-frozen product is sublimated under a vacuum of 0.1 Pa or higher and 100 Pa or lower at a temperature of −20° C. or higher and −5° C. or lower, and then secondary drying in which the product is heated to a temperature of 20° C. or higher and 40° C. or lower under a vacuum of 0.1 Pa or higher and 100 Pa or lower.

[0080] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Various measurement and evaluation methods are as follows.

[0081] <X-ray diffraction intensity> The X-ray diffraction intensity is measured using an X-ray diffractometer (MiniFlex-II manufactured by Rigaku Corporation) under the following conditions. The measurement conditions are as follows: X-ray source: Cu / Kα-radiation Measurement range: 2θ = 5 to 50° The measurement sample has an area of ​​320 mm ２ The cellulose type II crystals were compressed into pellets with a thickness of 1 mm. The X-ray scanning speed was 5° / min. The cellulose type II crystals had a peak corresponding to the 110 plane at a diffraction angle 2θ = 20.0° (I ２０．０ The cellulose type II crystallinity (X [%]) is determined by the peak intensity (I １５．０ ) and can be calculated using the following formula: X = [(I ２０．０ -I １５．０ ) / I ２０．０ ]×100

[0082] <Compressive modulus> The compressive modulus of cellulose particles is measured using a microcompression tester ("MCT-510" manufactured by Shimadzu Corporation). Specifically, cellulose particles are placed on a measurement stage attached to the above-mentioned device, and the diameter d is measured. An indenter (Φ50 μm) is lowered at a constant loading rate (mN / sec) to compress the particles until a specified test force (0.98 mN) is reached. The compressive stress is calculated from the particle size d (μm) and the test force P (mN) using the following formula: Compressive stress (MPa) = 2.48 × P (mN) / (π × (d (μm)) ２ ) The compressive strain is calculated from the displacement x (μm) and particle size d (μm) using the following formula: Compressive strain (%) = x (μm) / d (μm) x 100 A stress-strain curve is created from the calculated compressive stress and compressive strain, and the compressive modulus is calculated from the slope of the elastic region (0-10%). Measurements are carried out seven times, and the average of the five measurements excluding the maximum and minimum values ​​is used as the test result.

[0083] <Median diameter> The median diameter (D ５０) is measured using a laser scattering particle size distribution analyzer ("LS 13 320" manufactured by Beckman Coulter, Inc.). Specifically, 50 mg of dried cellulose particles are weighed into a measurement cell and measured using a Tornado dry powder module to determine the particle size at 50% in the volume distribution of particle sizes. During the measurement, the actual refractive index of cellulose, 1.469, is entered.

[0084] <Specific Surface Area> The specific surface area of ​​cellulose particles is measured by the following method. Mercury is injected into cellulose particles by mercury intrusion porosimetry using a mercury porosimeter ("Auto Pore IV 9500" manufactured by Shimadzu Corporation), and the total surface area of ​​the fine surfaces inside the cellulose particles and the particle surfaces, X (m ２ Specifically, about 0.05 g of cellulose particles is placed in the cell of a mercury porosimeter, and measurement is carried out by mercury intrusion porosimetry in the range of measurement pressure from 0.01 MPa to 210 MPa. ２ The mass of the cellulose particles used as the measurement sample is defined as Y (g), and the value of X (m ２ The value of Y (g) / Y (g) is the specific surface area of ​​the cellulose particles.

[0085] <Pore Volume> The pore volume of cellulose particles is measured by the following method. Mercury is injected into cellulose particles by mercury intrusion porosimetry using a mercury porosimeter (Shimadzu Corporation's "Auto Pore IV 9500"), and the total volume Z (mL) of mercury that has infiltrated into the pores within the cellulose particles and the gaps between the cellulose particles is determined. Specifically, approximately 0.05 g of cellulose particles is placed in the cell of the mercury porosimeter, and measurement is performed by mercury intrusion porosimetry at measurement pressures ranging from 0.01 MPa to 210 MPa to determine the value of Z (mL). The mass of the cellulose particles used as the measurement sample is defined as Y (g), and the value Z (mL) / Y (g) is the pore volume of the cellulose particles.

[0086] <Surface Pore Diameter> The surface pore diameter of cellulose particles is measured by the following method. Mercury is injected into cellulose particles by mercury intrusion porosimetry using a mercury porosimeter (Shimadzu Corporation, "Auto Pore IV 9500"), and the pore distribution within the cellulose particles is determined. Specifically, approximately 0.05 g of cellulose particles is first placed in the cell of the mercury porosimeter, and measurement is performed by mercury intrusion porosimetry at measurement pressures ranging from 0.01 MPa to 210 MPa. The pore volume of the cellulose particles: Z (mL) / Y (g) is determined in the same manner as above. The horizontal axis is plotted as pore diameter (nm) and the vertical axis is plotted as pore volume (mL / g), to obtain an integrated pore distribution curve. Next, the (integral) pore volume is differentiated by pore diameter, i.e., the increase in pore volume at each pore diameter is determined as the differential pore volume (mL / g). The horizontal axis represents the pore diameter (nm) and the vertical axis represents the differential pore volume (mL / g) to obtain a pore distribution curve. In the obtained pore distribution curve, the mode of the pore diameter in the pore diameter range of 1000 nm or less is defined as the surface pore diameter of the particle.

[0087] <Sphericity> The sphericity of cellulose particles is measured using a dynamic image analyzer (CAMSIZER X2 manufactured by MICROTRAC MRB). Specifically, 20 mg of dried cellulose particles are placed in the device feeder, and the particles are dispersed at an air dispersion pressure of 30 kPa. The dispersion is placed in the dynamic image analyzer, and an image is obtained. From the image, the sphericity (%) of one particle is calculated using the following formula. The average value of approximately 5,000 images obtained is taken as the sphericity. Sphericity (%) = 4π × particle area (m 2 ) / (particle circumference (m)) ２ ×100

[0088] <Sensation> Approximately 5 mg of cellulose particles were applied to the right forearm of a specialist panelist in an area of ​​4 cm x 5 cm at a dose of 0.25 mg / cm. ２ The softness and the lack of roughness at this time are evaluated by sensory evaluation according to the following criteria: 5: Very soft and smooth, 4: Soft and smooth, 3: No hardness or roughness, 2: Hard and rough, 1: Very hard and rough

[0089] <Encapsulation rate of functional substance (Nile Red)> Approximately 50 mg of cellulose particles is weighed and mixed with a solution prepared by dissolving approximately 50 mg of the functional substance Nile Red (manufactured by Tokyo Chemical Industry Co., Ltd.) in 20 mL of ethanol. After stirring overnight, the mixture is vacuum dried at 60°C to evaporate the ethanol, yielding composite particles composed of cellulose particles and Nile Red. The composite particles obtained are removed, and the Nile Red encapsulated within the particles is extracted using 50 mL of o-xylene. The amount of extracted Nile Red is quantified by ultraviolet-visible absorption measurement, and the encapsulation rate is calculated using the following formula: Encapsulation rate (%) = (amount of extracted Nile Red (mg)) / (amount of Nile Red used (mg)) × 100 The encapsulation rate is scored according to the following criteria: 5: 80% or more, 4: 60% or more but less than 80%, 3: 40% or more but less than 60%, 2: 20% or more but less than 40%, 1: less than 20%

[0090] <Disintegration by Scratching> Approximately 20 mg of cellulose particles were weighed and placed on artificial leather (Laforet S2923, 5 cm x 4 cm). Using a surface property tester ("Tribogear TYPE 14" manufactured by Shinto Scientific Co., Ltd.), a vertical load of 200 g, equivalent to the application of a coating, was applied, and the particles were rubbed back and forth 20 times at a travel distance of 50 mm and a travel speed of 2000 mm / min. The cellulose particles remaining on the artificial leather surface were observed using a scanning electron microscope ("SEM" manufactured by JEOL Ltd., "JSM-IT-500HR") at an acceleration voltage of 5.0 kV and an observation magnification of 500x. Of the 20 cellulose particles in the observed image, the proportion of particles that had been flattened (disintegrated) by rubbing was calculated as the disintegration rate, and scored according to the following criteria. 5: 80% or more, 4: 60% or more but less than 80%, 3: 40% or more but less than 60%, 2: 20% or more but less than 40%, 1: Less than 20%

[0091] Example 1 (Production and evaluation of porous cellulose particles) (Step (I)) As the raw material cellulose, cellulose type I crystalline cellulose powder (Avicel PH-101 manufactured by Asahi Kasei Corporation, degree of polymerization: 170, median diameter: 50 μm, moisture content: 6%) was used. 10.6 g of the above cellulose powder was added to 189.4 g of a dilute aqueous NaOH solution (NaOH concentration: 4.2% by mass) and cooled to −2°C. Thereafter, while maintaining the temperature at −2°C, 50 g of a concentrated aqueous NaOH solution (NaOH concentration: 22% by mass) was added and stirred for 1 hour to dissolve the raw material cellulose, thereby obtaining an aqueous cellulose solution. The cellulose concentration in the obtained aqueous cellulose solution was 4% by mass, and the NaOH concentration was 7.6% by mass.

[0092] (Step (II)) 350 g of isododecane and 3.5 g of an emulsifier, sucrose erucate ester (Ryoto Sugar Ester ER-290 manufactured by Mitsubishi Chemical Corporation, HLB: 2, monoester content: approximately 2%), were added to the aqueous cellulose solution. The mixture was emulsified by stirring at 5°C and 7,000 rpm for 5 minutes using a homomixer (MARK II 2.5 manufactured by Primix Corporation), to obtain a water-in-oil emulsion of cellulose. The emulsion droplet size was measured using a laser diffraction / scattering particle size distribution analyzer (LA-960V2 manufactured by Horiba, Ltd.) and found to be 10 to 80 μm.

[0093] (Step (III)) The entire amount of the emulsion obtained in step (II) was added to 1,500 g of alcohol (ethanol), a non-solvent for cellulose, and the mixture was stirred at 400 rpm for 1 hour at room temperature (25° C.) using a stirring blade to precipitate crude cellulose particles. Next, 42.8 g of acetic acid (1.5 equivalents relative to NaOH) was added to neutralize the mixture, yielding a suspension containing crude cellulose particles.

[0094] (Step (IV)) The suspension obtained in step (III) was subjected to vacuum filtration (700 hPa) using filter paper (Millipore's "OMNIPORE DISC PTFE PHILIC 1.0 μM 90MM WH PLN 25 / PK", mesh size 1 μm) to perform solid-liquid separation. Acetone (300 parts by mass per 100 parts by mass of cellulose wet particles) was added to the recovered wet particles, and the mixture was stirred at room temperature for 1 hour, followed by solid-liquid separation again. This operation was repeated twice. Next, water (300 parts by mass per 100 parts by mass of cellulose wet particles) was added, and the mixture was stirred at room temperature for 1 hour, followed by solid-liquid separation again. This operation was repeated twice. After the above washing step, the resulting suspension was subjected to solid-liquid separation again, and the purified cellulose wet particles were recovered.

[0095] (Step (V)) The wet particles of purified cellulose recovered in step (IV) were quickly frozen in a dry ice / ethyl alcohol bath at -72°C and then freeze-dried under a vacuum of 100 Pa or less to obtain dried particles of purified porous cellulose. The obtained porous cellulose particles were evaluated by the above-mentioned method. The results are shown in Table 1.

[0096] Examples 2 to 3, 5 to 6 Porous cellulose particles were produced and evaluated in the same manner as in Example 1, except that the conditions for steps (I) to (V) in Example 1 were changed as shown in Table 1. The results are shown in Table 1.

[0097] Example 4: After steps (I) to (IV) were carried out in the same manner as in Example 1, the following procedures were further carried out to produce porous cellulose particles, which were then evaluated. The results are shown in Table 1. Pentane (300 parts by mass relative to the wet cellulose particles) was added to the purified cellulose wet particles recovered in step (IV), and the mixture was stirred at 400 rpm for 1 hour at room temperature using a stirring blade. Then, solid-liquid separation was again carried out in the same manner as above. This procedure was repeated twice. After the above procedures, the obtained purified cellulose wet particles were dried overnight under reduced pressure at a vacuum of 50 kPa or less, yielding dried purified porous cellulose particles.

[0098] Comparative Examples 1 to 3 Evaluations were carried out using commercially available cellulose particles shown in Table 1. The results are shown in Table 1.

[0099]

[0100] As can be seen from Table 1, the porous cellulose particles of this example have a good feel when applied to the skin, and are excellent in terms of the encapsulation of the functional substance and the disintegration of the particles during application. In contrast, the cellulose particles of the comparative example were inferior in all of the above performances.

[0101] 1 to 3 show the X-ray diffraction profiles of the raw cellulose (cellulose type I crystals) used in the examples, the porous cellulose particles (cellulose type II crystals) obtained in Example 1, and the porous cellulose particles (amorphous) obtained in Example 4, respectively. Fig. 2 shows a diffraction peak at a diffraction angle 2θ = 12.5° derived from the (11-0) plane and a diffraction peak at 2θ = 20.0° derived from the (110) plane, so the porous cellulose particles obtained in Example 1 can be attributed to cellulose type II crystals. Furthermore, Fig. 3 shows broad peaks, so the porous cellulose particles obtained in Example 4 can be attributed to amorphous cellulose.

[0102] According to the present invention, it is possible to provide porous cellulose particles that can impart a soft feel when incorporated into cosmetics, cause less squeaky sensation when applied, and have excellent capabilities for encapsulating functional substances and particle disintegration properties.

Claims

1. The porous cellulose particles have a compression elastic modulus of 50 MPa or less and The specific surface area is 100 m ２ / g or more and less than 500 m ２ / g, and a pore volume of 1.5 mL / g or more.

2. The porous cellulose particles according to claim 1, wherein the median diameter measured by the dry method of the porous cellulose particles is 75 μm or less.

3. The porous cellulose particles according to claim 1, wherein the porous cellulose particles are unmodified porous cellulose particles.

4. The porous cellulose particles according to claim 1, wherein the cellulose constituting the porous cellulose particles is composed of crystalline cellulose of cellulose type II or amorphous cellulose.

5. The porous cellulose particles according to claim 1, wherein the cellulose content in the porous cellulose particles is 95% by mass or more.

6. The porous cellulose particles according to claim 1, wherein the surface pore diameter of the porous cellulose particles is 50 nm or more and 800 nm or less.

7. The porous cellulose particles according to claim 1, wherein the sphericity of the porous cellulose particles is 60% or more.

8. A cosmetic containing the porous cellulose particles according to any one of claims 1 to 7.

9. A method for producing the porous cellulose particles according to any one of claims 1 to 7, comprising the following steps (I) to (V) in sequence. Step (I): A step of mixing raw material cellulose and an aqueous alkali solution to prepare an aqueous cellulose solution Step (II): A step of mixing the aqueous cellulose solution and an organic solvent to prepare a cellulose emulsion Step (III): A step of mixing the cellulose emulsion and a cellulose non-solvent to precipitate coarse cellulose particles and obtaining a suspension containing the coarse cellulose particles Step (IV): A step of solid-liquid separating the suspension containing the coarse cellulose particles, and then washing the obtained coarse cellulose wet particles to obtain purified cellulose wet particles Step (V): A step of drying the purified cellulose wet particles to obtain porous cellulose particles

10. The method for producing porous cellulose particles according to claim 9, wherein the raw material cellulose used in step (I) is crystalline cellulose of cellulose type I. [[ID= ​ ​ The method for producing porous cellulose particles according to claim 9, wherein the organic solvent used in the step (II) is a hydrocarbon solvent.

13. The method for producing porous cellulose particles according to claim 9, wherein in the step (II), an emulsifier is further mixed.

14. The method for producing porous cellulose particles according to claim 9, wherein the cellulose non-solvent used in the step (III) is an alcohol having 4 or less carbon atoms.

15. The method for producing porous cellulose particles according to claim 9, wherein in the step (III), an acid is further mixed.