JP7540191B2 - Composite particles, methods for producing composite particles, and personal care products containing composite particles - Google Patents

Description

The present invention relates to composite particles, a method for making composite particles, and personal care products containing composite particles.

Water-absorbent polymer particles are particles of water-absorbent polymers that have been made insoluble in water by slightly cross-linking hydrophilic or water-soluble polymers, and have the property of absorbing water, swelling, and becoming gel-like when they come into contact with water. By utilizing the intermediate cross-linked regions of both water-soluble and hydrophilic polymers, they can be controlled to exhibit high water absorption. Water-absorbent polymers were invented in the 1970s, and polymers obtained by hydrolyzing graft copolymers of starch and acrylonitrile were announced as having amazing water absorption capabilities. After that, new highly water-absorbent polymers were developed one after another, mainly in Japan and the United States, and the world's first commercial production began in 1978.

Water-absorbent polymer particles are used in a wide range of applications. For example, in the field of sanitary products, they are used in disposable diapers, etc.; in the field of agriculture and horticulture, they are used as soil water-retaining materials, seedling sheets, seed coatings, disintegration aids for pesticides, liquid seeding, and culture media for mushrooms; in the field of food and distribution, they are used as freshness-preserving materials, drip absorbers, and food dehydration materials; in the field of civil engineering and construction, they are used as dew prevention materials, water-retaining agents for spraying on slopes, to prevent lost circulation, and as sealing materials; in the field of personal care products and toiletry products, they are used as gel air fresheners, sweat pads, disposable hand warmers, ice packs, deodorants, and control It is used in skin care products such as sweat removers, portable toilets, cleansing agents, lotions, milky lotions, and packs; in the medical product field, wound protection dressings and poultices; in the electrical and electronic materials field, inkjet recording paper, waterproofing materials for communication cables, alkaline batteries, lead-acid batteries, etc.; in the paint and adhesive field, water-wet paints, water-swelling paints, anti-fouling paints for ship bottoms, emulsion paints, and also for removing water from oil, water-swelling toys, gasket packing, fire extinguishing water, etc.

Water-absorbent polymer particles are required to have various functions such as water absorption and retention, suction and swelling, gelling, and thickening. Water-absorbent polymer particles must have excellent water absorption, but highly water-absorbent particles are prone to collapse due to external forces such as compression. In addition, particles tend to aggregate when they absorb water, making dispersibility and dispersion stability an issue. Furthermore, safety to the environment and human body is important when used in fields such as hygiene, horticulture and agriculture, civil engineering and construction, food and distribution, personal care products and toiletry products, and medical products. Furthermore, the feel of use is important in cosmetic applications that come into contact with the human body.

On the other hand, in recent years, active efforts have been made to use chitin and/or chitosan, which constitute the cellulose fibers in wood and the shells of crustaceans such as crabs, as new materials by micronizing at least one side of the structure to the nanometer order.

For example, Patent Document 1 discloses that wood cellulose can be repeatedly mechanically treated with a blender or grinder to obtain fine cellulose, i.e., cellulose nanofibers (hereinafter also referred to as CNF). It has been reported that the CNF obtained by this method has a minor axis diameter of 10-50 nm and a major axis diameter of 1 μm to 10 mm. This CNF is one-fifth the weight of steel, yet more than five times stronger, and has a huge specific surface area of more than 250 ^m2 /g, so it is expected to be used as a filler for reinforcing resins and as an adsorbent.

In addition, active efforts are being made to produce CNF by chemically treating the cellulose fibers in wood in advance to facilitate finer processing, and then finer processing using low-energy mechanical processing such as a household mixer. The above-mentioned chemical treatment method is not particularly limited, but a method in which anionic functional groups are introduced into cellulose fibers to facilitate finer processing is preferred. The introduction of anionic functional groups into cellulose fibers makes it easier for solvents to penetrate between the cellulose microfibril structures due to the osmotic effect, and the energy required for finer processing of cellulose raw materials can be significantly reduced.
The method for introducing the anionic functional group is not particularly limited. For example, Non-Patent Document 1 discloses a method in which the surface of cellulose fine fibers is selectively phosphoric acid esterified using a phosphoric acid esterification treatment.

Patent Document 2 discloses a method for carboxymethylation by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a highly concentrated alkaline aqueous solution. Carboxy groups may also be introduced by directly reacting cellulose with a carboxylic anhydride compound such as maleic acid or phthalic acid that has been gasified in an autoclave.

A method has also been reported in which the relatively stable N-oxyl compound 2,2,6,6-tetramethylpiperidinyl-1-oxy radical (TEMPO) is used as a catalyst to selectively oxidize the surface of cellulose fine fibers (see, for example, Patent Document 3). The oxidation reaction using TEMPO as a catalyst (TEMPO oxidation reaction) allows for environmentally friendly chemical modification that proceeds in an aqueous system at room temperature and pressure. When applied to cellulose in wood, the reaction does not proceed inside the crystals, and only the alcoholic primary carbons in the cellulose molecular chains on the crystal surface can be selectively converted to carboxy groups.

Due to the osmotic pressure effect caused by the ionization of carboxyl groups selectively introduced to the crystal surface by TEMPO oxidation, it is possible to obtain cellulose single nanofibers (hereinafter referred to as CSNF, TEMPO oxidized cellulose nanofibers, or TEMPO oxidized CNF) dispersed in a solvent as individual cellulose microfibril units. CSNF exhibits high dispersion stability derived from the carboxyl groups on the surface. Wood-derived CSNF obtained from wood by TEMPO oxidation reaction is a structure with a high aspect ratio, with a minor axis diameter of around 3 nm and a major axis diameter ranging from several tens of nm to several μm, and it has been reported that its aqueous dispersion and molded body have high transparency. In addition, Patent Document 4 reports that a laminated film obtained by applying and drying a CSNF dispersion has gas barrier properties.

Furthermore, studies are being conducted to impart further functionality to CNF or CSNF. For example, further functionality can be imparted by utilizing the carboxyl groups on the CSNF surface. Patent Document 5 discloses a composite (metal nanoparticle-supported CSNF) in which metal nanoparticles are supported on CSNF by reducing and precipitating metals in a state in which metal ions are adsorbed on the carboxyl groups on the CSNF surface. Patent Document 5 discloses an example in which metal nanoparticle-supported CSNF is used as a catalyst, and reports that catalytic activity is improved by making it possible to disperse and stabilize metal nanoparticles in a state in which the specific surface area is high.

Patent Document 6 discloses that chitin nanofibers can be obtained by crushing chitin and/or chitosan extracted from crab shells, etc., into ultrafine fibers. Chitin nanofibers are a recyclable resource that has antibacterial and biodegradable properties, and are expected to be used as an additive to foods and cosmetics, as reinforcing fibers for films, as agricultural resources, and for medical purposes.
Since chitin and/or chitosan are tightly bound to each other by strong hydrogen bonds, it is not easy to prepare completely individual nanofibers from chitin and/or chitosan. According to the chitin nanofiber and its production method described in Patent Document 6, a dispersion containing chitin nanofibers separated into individual fibers can be obtained in a simple process.

As such, various studies are being conducted regarding the development of high-performance components that impart new functionality to fine fibers derived from natural materials, such as cellulose nanofibers and chitin nanofibers.
However, in order to put these fine fibers into practical use, the solids concentration of the resulting fine fiber dispersion is low, at about 0.1 to 5%. For example, when attempting to transport the fine fiber dispersion, this is equivalent to transporting a large amount of solvent, which leads to a rise in transportation costs and significantly impairs business viability.

However, if the solvent in the dispersion of fine fibers is simply removed by heat drying or the like, the fine fibers will aggregate and keratinize, or form a membrane, making it difficult to effectively utilize the high specific surface area characteristic of the fine fibers and making it difficult to achieve stable functionality. Furthermore, because the solid concentration of the fine fibers is low, the process of removing the solvent by drying itself requires a large amount of energy, which is also a factor that impairs commercial viability.
In this way, handling fine fibers such as cellulose nanofibers and chitin nanofibers in the form of a dispersion liquid is itself a cause of loss of commercial viability. Therefore, there is a strong demand for composite particles in which fine fibers are bonded to the surface of particles, which have a new handling mode that can effectively utilize the characteristics of the fine fibers, that is, the high specific surface area, and which can be easily washed and separated from the solvent.

JP 2010-216021 A International Publication No. 2014/088072 JP 2008-001728 A International Publication No. 2013/042654 International Publication No. 2010/095574 JP 2010-180309 A International Publication No. 2017/155054

Noguchi Y, Homma I, Matsubara Y. Complete nanofibrillation of cellulose prepared by phosphorylation. Cellulose. 2017;24:1295.10.1007/s10570-017-1191-3

The objective of the present invention is to provide composite particles that not only have excellent water absorption, but also have a high recovery rate without collapsing when subjected to external forces such as compression, have good dispersibility and dispersion stability in various solvents such as water and oil, and have excellent skin compatibility and moisture retention, a method for producing the same, and a personal care product using the composite particles.

In order to solve the above problems, the first and second aspects of the present invention have the following configurations.
[First aspect]
A core particle having at least a hydrophilic polymer;
The core particles have fine fibers inseparably bonded thereto and covering the surfaces of the core particles,
The fine fibers are composite particles made of at least one of cellulose nanofibers and chitin nanofibers.

[Second Aspect]
A step of dispersing fine fibers, which are at least one of cellulose nanofibers and chitin nanofibers, in a hydrophobic solvent to obtain a hydrophobic solvent dispersion of the fine fibers;
a step of dispersing droplets containing core particle precursors in the hydrophobic solvent dispersion and coating the surfaces of the droplets with the fine fibers;
a step of solidifying the core particle precursor inside the droplets to obtain a dispersion of composite particles in which the surfaces of the core particles are covered with the fine fibers;
purifying the composite particles;
A method for producing a composite particle having the following structure:

The personal care product according to the present invention also contains the composite particles according to the first aspect.

The present invention provides composite particles that are not only excellent in water absorption, but also have a high recovery rate and are resistant to collapse due to external forces such as compression, have good dispersibility and dispersion stability in various solvents such as water and oil, and have excellent skin compatibility and moisture retention, as well as a manufacturing method thereof and a personal care product using the composite particles.

FIG. 1 is a schematic diagram showing a composite particle according to one embodiment of the present invention. 1A to 1C are diagrams illustrating a method for producing a composite particle according to an embodiment. 1 is a graph showing the results of measuring the spectral transmission spectrum of the aqueous dispersion of cellulose nanofiber obtained in Example 1. 1 is a graph showing the results of steady-state viscoelasticity measurement, using a rheometer, for the aqueous dispersion of cellulose nanofibers obtained in Example 1.

Below, an embodiment of the present invention will be described with reference to the drawings. However, in each of the drawings described below, parts corresponding to each other will be given the same reference numerals, and explanations of overlapping parts will be omitted as appropriate. Furthermore, this embodiment is merely an example of a configuration for embodying the technical idea of the present invention, and the material, shape, structure, arrangement, dimensions, etc. of each part are not specified as described below. The technical idea of the present invention may be modified in various ways within the technical scope defined by the claims.

1, the composite particle 1 of the present embodiment is a composite particle 1 having a core particle 2 having at least a hydrophilic polymer, and fine fibers 3 which are at least one of cellulose nanofibers and chitin nanofibers and are inseparably bonded to the surface of the core particle 2. The fine fibers 3 may contain both cellulose nanofibers and chitin nanofibers.
In this embodiment, the fine fibers 3 are preferably formed as a coating layer that covers the surface of the core particle 2 .

The method for producing the composite particles 1 is not particularly limited, and any known method can be used, including chemical preparation methods and physicochemical preparation methods.
Examples of chemical preparation methods include polymerization granulation methods (emulsion polymerization, suspension polymerization, seed polymerization, radiation polymerization, etc.) in which particles are formed during the polymerization process from polymerizable monomers.
Examples of physicochemical preparation methods include dispersion granulation methods (spray drying, in-liquid hardening, solvent evaporation, phase separation, solvent dispersion cooling, etc.) in which particles are formed from fine droplets of a polymer solution.

Examples of the method for producing the composite particle 1 include an aqueous solution polymerization method and a reversed-phase suspension polymerization method. Examples of the aqueous solution polymerization method include a method in which an aqueous solution of a water-soluble ethylenically unsaturated monomer is polymerized in the presence of fine fibers 3 to obtain a hydrous gel-like material, which is then pulverized and dried to obtain a dry powder. Examples of the reversed-phase suspension polymerization method include a method in which an aqueous solution of a core particle precursor such as a water-soluble ethylenically unsaturated monomer is dispersed in a hydrophobic solvent dispersion of fine fibers 3 in which fine fibers 3 are dispersed in a hydrophobic solvent such as a hydrocarbon solvent, and the dispersion is suspended to obtain a hydrous gel-like composite particle 1, which is then dehydrated and dried to obtain a dry powder. In view of the ease of controlling the particle size of the composite particle 1, it is preferable to use the reversed-phase suspension polymerization method.

Specifically, in the reversed-phase suspension polymerization method, as described later in Fig. 2, droplets 4 containing a core precursor are formed into a W/O type Pickering emulsion using fine fibers 3, and the core particle precursor inside the droplets is polymerized and/or crosslinked to obtain a dispersion of composite particles 1 in which the core particles 2, the surfaces of which are covered with fine fibers 3, are bonded to the fine fibers 3 and are in an inseparable state. By using the fine fibers 3, it is possible to form stable droplets 4 without using additives such as surfactants, and it is possible to obtain composite particles 1 that can maintain a true sphericity, have sufficient strength, have good dispersion stability, are smooth, and are compatible with the skin.
Here, the W/O type emulsion is also called water-in-oil type, and has oil as a continuous phase in which hydrophilic droplets (water droplets, water particles) are dispersed.

The core particle precursor may be any precursor that can produce a solid hydrophilic polymer. In particular, a precursor that can produce a water-absorbent polymer is preferable. Examples of core particle precursors include polymerizable monomers, molten polymers, and dissolved polymers. A hydrophilic polymer can be obtained by polymerizing the polymerizable monomer through heating or the like. A solid hydrophilic polymer can be obtained by cooling the molten polymer. A solid hydrophilic polymer can be obtained by removing the solvent from the dissolved polymer.

Personal care products are products such as cosmetics and toiletries that keep people's skin clean and groomed and beautify them. These include hair care, oral care, scent care, nail care, body care, skin care, and makeup-related products, such as toothpaste, perfume, nail lacquer, skin lotion, milky lotion, cleansing agent, eye shadow, eyeliner, foundation, blush, hair gel, hair spray, shampoo, conditioner, hair growth agent, lotion, cream, and soap.

The composite particle 1 of this embodiment can be produced by the production method shown in FIG.
The manufacturing method shown in FIG. 2 corresponds to the manufacturing method of the second embodiment described above, and includes a first step, a second step, a third step, and a fourth step.
The first step is a step of dispersing fine fibers 3, which are either cellulose nanofibers or chitin nanofibers, in a hydrophobic solvent 5 to obtain a hydrophobic solvent dispersion of the fine fibers 3, as shown in FIG. 2(a).

2(b), the second step is a step of dispersing droplets 4 containing core particle precursors in a hydrophobic solvent dispersion of fine fibers 3, and coating the surfaces of the droplets 4 with the fine fibers 3. Through this step, a W/O type Pickering emulsion is obtained in which the hydrophobic solvent dispersion of fine fibers 3 serves as the continuous phase, and the droplets 4 containing the core precursors serve as the dispersed phase.
The third step is a step of solidifying the core particle precursor inside the droplets 4 to obtain a dispersion of composite particles 1 in which the surfaces of core particles 2 are covered with fine fibers 3, as shown in FIG. 2(c).
2C, to obtain a dry powder of the composite particle 1. By this step, the dry powder of the composite particle 1 is obtained.

In other words, the W/O type Pickering emulsion is stabilized by the fine fibers 3 adsorbing to the interface of the droplets 4 containing the core particle precursors dispersed in the hydrophobic solvent 5. Then, while maintaining this stabilized state, the core particle precursors inside the emulsion droplets 4 are solidified to obtain composite particles 1. Composite particles 1 in a dry state are called dry powder, and composite particles 1 in a wet state that has absorbed water are called swollen gel.

The term "inseparable" here means that even after the operation of purifying and washing the composite particle 1 by centrifuging the dispersion liquid containing the composite particle 1 to remove the supernatant and then adding a solvent to redisperse the composite particle 1, or the operation of repeatedly washing the composite particle 1 with a solvent by filtration and washing using a membrane filter, the core particle 2 and the fine fiber 3 do not separate, and the coating state of the core particle 2 with the fine fiber 3 is maintained. The coating state can be confirmed by observing the surface of the composite particle 1 with a scanning electron microscope. The bonding mechanism between the fine fiber 3 and the core particle 2 in the composite particle 1 is not clear, but since the composite particle 1 is produced using a W/O type emulsion stabilized by the fine fiber 3 as a template, it is presumed that the fine fiber 3 is physically fixed to the surface of the core particle 2 in order to solidify the core particle precursor to form the core particle 2 in a state in which the fine fiber 3 is in contact with the core particle precursor inside the droplet 4 of the emulsion, and the core particle 2 and the fine fiber 3 are finally inseparably fixed.

Although not particularly limited, when the composite particles 1 are produced using a template of a W/O type emulsion stabilized by the fine fibers 3, the W/O type emulsion is stabilized, so that it is possible to obtain spherical composite particles 1 derived from the W/O type emulsion. In detail, it is preferable that a coating layer made of the fine fibers 3 is formed with a relatively uniform thickness on the surface of the spherical core particles 2.
By covering the surface of the core particle 2 with the fine fibers 3, the core particle 2 is less likely to disintegrate due to external forces during transportation, etc., and a smooth feel in use, as well as excellent water absorbency, water retention, and dispersibility can be achieved.

The particle size of the composite particles 1 can be confirmed by observation with an optical microscope. For example, the diameters of 100 randomly selected composite particles 1 are measured, and the average particle size can be calculated by averaging the particle diameters D.
The average particle size of the dry powder of the composite particle 1 is not particularly limited, but is preferably 0.1 μm or more and 1000 μm or less. The volume of the composite particle 1 may increase when it absorbs water. The average particle size of the swollen gel of the composite particle 1 that has absorbed water is not particularly limited, but is preferably 0.2 μm or more and 2000 μm or less.

The coefficient of variation of the particle size distribution of the dry powder and swollen gel of the composite particle 1 is preferably 0.7 or less, and more preferably 0.5 or less. By using the fine fibers 3, a stable W/O type emulsion can be formed, narrowing the particle size distribution and decreasing the coefficient of variation. The narrowing of the particle size distribution allows for a wet gel with a smoother texture to be obtained.
From the viewpoint of dispersion stability, the fine fibers 3 preferably form a coating layer on the surface of the core particle 2. The coating layer preferably covers the entire surface of the core particle 2, but does not necessarily have to cover the entire surface.

The thickness of the coating layer formed of the fine fibers 3 is not particularly limited, but is preferably 3 nm or more and 1000 nm or less.
The average thickness of the coating layer can be calculated by cutting the composite particle 1 fixed in an embedding resin with a microtome, observing the cut surface with a scanning electron microscope, measuring the thickness of the coating layer in the cross-sectional image of the composite particle 1 in the image at 100 random points on the image, and calculating the average value.
In addition, it is preferable that the composite particle 1 is uniformly coated with a coating layer having a relatively uniform thickness. A uniform thickness of the coating layer leads to high dispersion stability. Specifically, the coefficient of variation of the thickness of the coating layer described above is preferably 0.5 or less, and more preferably 0.4 or less.

In a wet gel load-unloading test, the composite particle 1 preferably has a recovery rate of 20% or more after unloading at a minimum test force of 0.01 mN, a maximum test force of 0.5 mN, and a rate of 0.045 mN/s. More preferably, the recovery rate is 30% or more, and more preferably, 50% or more. Since the composite particle 1 is covered with the fine fibers 3, it is less likely to collapse due to external forces and exhibits a high recovery rate.
The loading and unloading test is carried out as follows. Using a micro-compression tester MCT-510 (Shimadzu Corporation), the wet gel is placed on the sample stage, and a flat indenter is used to measure each wet gel. The displacement when a load is applied from a minimum test force of 0.01 mN to a maximum test force of 0.5 mN at a loading rate of 0.045 mN/s, and the displacement when the load is similarly unloaded to the minimum test force at an unloading rate of 0.045 mN/s are obtained. The recovery rate is calculated as "L/D x 100", where D is the diameter of the particle and L is the displacement from the time of loading to the time of unloading. The recovery rates of 10 composite particles are measured and the average value is calculated.

The water absorption per unit mass of the dry powder of the composite particle 1 of the present invention is preferably 10 g/g or more and 800 g/g or less, more preferably 20 g/g or more and 500 g/g or less, and more preferably 30 g/g or more and 300 g/g or less. As described later, by including a hydrophilic polymer in the core particle 2, a composite particle 1 having excellent water absorption ability can be obtained.
The water absorption can be measured as follows. 500 g of 0.9% by mass saline (physiological saline) was placed in a beaker and stirred, while adding 5.0 g of dry powder while taking care not to cause lumps. The mixture was left for 24 hours with stirring to allow the dry powder to swell sufficiently to obtain a swollen gel. The mixture was poured into a cotton bag, the top was tied with a rubber band, and the mixture was dehydrated for 1 minute using a dehydrator, and the mass of the cotton bag containing the swollen gel after dehydration was measured. The same operation was performed without adding the dry powder, and the mass of the cotton bag after wetting was measured, and the mass of the swollen gel was obtained by the following calculation, and the water absorption per 1 g of dry powder was calculated.
Water absorption amount = (mass of cotton bag containing swollen gel - mass of cotton bag without swollen gel - mass of dry powder) / mass of dry powder

The composite particle 1 of the present invention is preferably spherical, and particularly preferably true spherical. A true spherical shape can provide a smooth feel when used as a cosmetic product such as a cleansing agent or skin care product. The index of sphericity can be evaluated from the circularity measured by an image analysis type particle size distribution meter. The circularity is preferably 0.6 or more, more preferably 0.7 or more, and even more preferably 0.9 or more. If the circularity is less than 0.6, it is difficult to obtain a smooth feel when used. The average circularity can be calculated as the average value of the circularities of 1,000 or more particles measured by an image analysis type particle size distribution meter. In addition, when the area of the composite particle on the image is S and the perimeter is L, the circularity can be calculated by the formula "circularity = 4πS / L ² ", and the closer the circularity is to 1, the higher the sphericity.

The fine fibers 3 in this embodiment are cellulose nanofibers and/or chitin nanofibers.
Cellulose nanofibers are fibers made of cellulose or cellulose derivatives with a number average minor axis diameter of 1 nm to 1000 nm. Chitin nanofibers are fibers made of chitin and/or chitosan or chitin and/or chitosan derivatives with a number average minor axis diameter of 1 nm to 1000 nm.
Cellulose nanofibers (CNF) are fine fibers 3 that can be obtained by crushing cellulose raw materials obtained from wood and the like into extremely fine fibers, and are safe and biodegradable.

Chitin nanofibers (chitin NF) are fine fibers 3 that can be obtained by grinding chitin and/or chitosan (hereinafter chitin/chitosan) raw materials extracted from crab shells, etc., into ultrafine fibers, and are safe, biodegradable, and antibacterial. In particular, chitin nanofibers produced by the method of Patent Document 6 are made of chitin and/or chitosan that have not been chemically modified, and do not require safety confirmation, making it much easier to apply them in applications where they are taken into the body, such as food, medical care, pharmaceuticals, and personal care.

The fine fibers 3 in the present invention are preferably dispersed in a hydrophobic solvent 5. By dispersing in a hydrophobic solvent 5, a stable W/O type Pickering emulsion can be formed. The fine fibers 3 are preferably chemically modified cellulose nanofibers and/or chitin nanofibers. Introducing a modifying group into the fine fibers 3 by chemical modification makes them more likely to disperse in the solvent 5. The modifying group can be introduced by a known method. For example, the modifying group can be introduced via a covalent bond such as an ether bond, an ester bond, an amide bond, or a urethane bond, or via an ionic bond.

The modifying group of the fine fibers 3 is not particularly limited, and any known modifying group, for example, a hydrocarbon group, can be introduced. Examples of the hydrocarbon group include a chain saturated hydrocarbon group, a chain unsaturated hydrocarbon group, a cyclic saturated hydrocarbon group, and an aromatic hydrocarbon group.
The fine fibers 3 preferably have an ionic functional group on the crystal surface. In particular, when the fine fibers 3 have an anionic functional group, it is possible to introduce a modifying group by ionic bonding via the anionic functional group. Examples of the anionic functional group include, but are not limited to, a carboxy group, a phosphate group, and a sulfo group. Among these, the carboxy group and the phosphate group are preferred, and the carboxy group is preferred because of the ease of selective introduction to the cellulose crystal surface.

The content of the ionic functional group is preferably 0.1 mmol or more and 5.0 mmol or less per 1 g of the fine fiber raw material and/or the fine fiber 3. If it is less than 0.1 mmol, the dispersion stability of the composite particle 1 may deteriorate, and if it exceeds 5.0 mmol, it may become difficult to stably manufacture the composite particle 1.

The chain saturated hydrocarbon group may be linear or branched. Examples of the chain saturated hydrocarbon group include methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl, isobutyl, pentyl, tert-pentyl, isopentyl, hexyl, isohexyl, heptyl, octyl, 2-ethylhexyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl, octadecyl, docosyl, and octacosanyl groups. These may be introduced alone or in any combination of two or more.

The chain unsaturated hydrocarbon group may be linear or branched. Specific examples of the chain unsaturated hydrocarbon group include, for example, an ethylene group, a propylene group, a butene group, an isobutene group, an isoprene group, a pentene group, a hexene group, a heptene group, an octene group, a nonene group, a decene group, a dodecene group, a tridecene group, a tetradecene group, and an octadecene group. These may be introduced alone or in any ratio of two or more.
Examples of the cyclic saturated hydrocarbon group include a cyclopropane group, a cyclobutyl group, a cyclopentane group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group, a cyclododecyl group, a cyclotridecyl group, a cyclotetradecyl group, a cyclooctadecyl group, etc. These may be introduced alone or in any combination of two or more kinds at any ratio.

The aromatic hydrocarbon group is, for example, selected from the group consisting of an aryl group and an aralkyl group. Examples of the aryl group include a phenyl group, a naphthyl group, an anthryl group, a phenanthryl group, a biphenyl group, a triphenyl group, a terphenyl group, and groups in which these groups are substituted with the substituents described below, and one or more of these groups may be introduced. Examples of the aralkyl group include a benzyl group, a phenethyl group, a phenylpropyl group, a phenylpentyl group, a phenylhexyl group, a phenylheptyl group, a phenyloctyl group, and groups in which the aromatic group of these groups is substituted with the substituents described below, and one or more of these groups may be introduced.

The modifying group of the fine fiber 3 may further have a substituent, and examples of the substituent include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, an isopentyloxy group, a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, an isopropoxycarbonyl group, a butoxycarbonyl group, an isobutoxycarbonyl group, a sec-butoxycarbonyl group, a tert-butoxycarbonyl group, a pentyloxycarbonyl group, an isopentyloxycarbonyl group, a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, an acetyl group, a propionyl group, an aralkyl group, and an aralkyloxy group. The above-mentioned hydrocarbon group itself may be bonded as a substituent.

The average bond amount of the modifying groups in the fine fibers 3 is preferably 0.02 mmol/g or more, more preferably 0.2 mmol/g or more, and preferably 3 mmol/g or less, more preferably 2.5 mmol/g or less, and even more preferably 2 mmol/g or less, per cellulose, from the viewpoint of dispersibility in the hydrophobic solvent 5. When any two or more types of modifying groups are simultaneously introduced into the cellulose fibers as modifying groups, it is preferable that the average bond amount of the modifying groups is such that the total amount of the modified groups introduced is within the above-mentioned range.
The introduction rate of the modifying group introduced into the fine fibers 3 can be adjusted by the amount and type of the compound for introducing the modifying group, the reaction temperature, the reaction time, the solvent, etc. The average bond amount (mmol/g) of the modifying group can be measured by a known method. For example, it can be calculated by titration, IR measurement, etc.

Specific methods for producing modifying groups on the fine fibers 3 include a method of bonding the modifying groups via carboxy groups by ionic or covalent bonds. By mixing cellulose having a carboxy group with a compound for introducing a modifying group, it is possible to chemically modify the cellulose by ionic bonds. In addition, it is possible to mix cellulose having a carboxy group with a compound for introducing a modifying group and perform an amidation reaction.
The modifying group may be introduced before or after cellulose is defibrated.

Furthermore, it is preferable that the fine fibers 3 have a fiber shape derived from a microfibril structure. Specifically, it is preferable that the fine fibers 3 are fibrous, and that the number average minor axis diameter is 1 nm or more and 1000 nm or less, the number average major axis diameter is 50 nm or more, and the number average major axis diameter is 5 times or more the number average minor axis diameter. It is also preferable that the crystallinity of the fine fibers 3 is 50% or more. The crystal structure of the cellulose nanofibers is preferably cellulose type I. The crystal structure of the chitin nanofibers may be either alpha-chitin or beta-chitin, but is preferably alpha-chitin.

The core particle 2 may have pores. That is, it may have a porous or hollow structure. The shape, size, and number of the pores can be controlled by the type and amount of a pore-forming agent used. The pores can be formed by a known method. For example, the pores can be formed by including a hydrophobic solvent inside the core particle 2 and then removing it.
The core particle 2 contains at least one kind of hydrophilic polymer. The hydrophilic polymer may be a known hydrophilic polymer, or may be a polymer obtained by polymerizing a polymerizable monomer by a known method. The hydrophilic polymer is preferably a water-absorbent polymer having water-absorbency. By containing the water-absorbent polymer in the core particle 2, it becomes possible to utilize the water-absorbency in various fields such as hygiene products, personal care products, and toiletry products.

The hydrophilic polymer is a polymer that dissolves or disperses in water, and examples thereof include polymers having at least hydrophilic groups such as a carboxyl group, an aldehyde group, a hydroxyl group, an amino group, an amide group, a sulfone group, etc. By having these hydrophilic groups, a polymer with high hydrophilicity can be obtained.
Hydrophilic polymers are classified into, for example, natural polymers, semi-synthetic polymers, synthetic polymers, etc. Natural polymers include starches such as cornstarch, sugars such as mannan and pectin, seaweeds such as agar and alginic acid, plant mucilages such as various gums, microbial mucilages such as dextran and pullulan, and proteins such as ginger and gelatin.

Examples of semi-synthetic polymers include carboxymethyl cellulose, hydroxyethyl cellulose, oxidized starch, and modified starch.
Examples of synthetic polymers include polyacrylic acid, polymaleic acid, polyvinyl alcohol, polyvinylpyrrolidone, polyvinylpyridine, polyacrylamide, polyethylene oxide, and polyvinylsulfone. In addition, mixtures of two or more of these materials incorporated into the main chain or side chain are also acceptable. Specific examples include copolymers of polyacrylic acid and polyvinyl alcohol, and copolymers of polyacrylic acid and polymaleic acid.

A water-absorbent polymer is generally a hydrophilic polymer having a crosslinked structure, and even if it absorbs water, it becomes a wet gel and can maintain its shape due to the crosslinked structure. For example, a hydrophilic polymer having a crosslinked structure can be obtained by using an ionizing radiation-curable or thermosetting polymerizable monomer, oligomer, or polymer that is dissolved or dispersed hydrophilically.
Known examples of water-absorbent polymers include crosslinked products of acrylamide-acrylate copolymers, crosslinked products of acrylamide-acrylate copolymers, crosslinked products of vinyl alcohol-acrylate copolymers, crosslinked products of acrylate-methacrylate copolymers, crosslinked products of hydrolysates of starch-acrylate graft copolymers, crosslinked products of hydrolysates of starch-acrylonitrile graft copolymers, crosslinked products of carboxymethyl cellulose, saponified products of vinyl acetate-acrylate copolymers, and partially neutralized polyacrylic acid.

The core particle 2 may contain other components such as a functional component. By containing the functional component, the core particle 2 can exhibit its function. The method of containing the functional component is to impregnate the composite particle 1 with the functional component, or to encapsulate the functional component during the production process of the composite particle 1. Also, the functional component can be contained in the pores.
The functional component is a substance that functions by affecting living organisms such as animals, plants, fungi, etc., and is not particularly limited. Examples of the functional component include, but are not limited to, fungicides, fragrances, fertilizers (biofertilizers, chemical fertilizers, organic fertilizers, etc.), pH adjusters, agricultural chemicals (insecticides, fungicides, herbicides, etc.), plant activators, plant life-extending agents, pest and animal repellents, soil penetrants, nutritional components (minerals, etc.), plant hormones, inorganic particles (titanium oxide, silica, clay, etc.), antibacterial components, etc.

In particular, it is preferable to include functional ingredients that exert their functions in personal care products. Examples include oil-based raw materials such as fats and oils and waxes, colorants, oil absorbents, light shielding agents (UV absorbers, UV scattering agents, etc.), antibacterial agents, antioxidants, antiperspirants, peeling agents, sebum suppressants, blood circulation promoting ingredients, whitening ingredients, anti-aging care ingredients, anti-inflammatory ingredients, cooling ingredients, warming ingredients, deodorizing ingredients, defoamers, antistatic agents, binders, bleaching agents, chelating agents, fragrances, perfumes, anti-dandruff active substances, skin softeners, insect repellents, preservatives, vitamins, amino acids, hormones, natural extracts, etc. Among these, it is preferable to have at least one of UV absorbers, UV scattering agents, perfumes, deodorizing ingredients, peeling agents, anti-aging care ingredients, whitening ingredients, anti-inflammatory ingredients, and colorants.

Examples of ultraviolet absorbers include homomenthyl salicylate, 2-cyano-3,3-diphenylprop-2-enoic acid 2-ethylhexyl ester, di-paramethoxycinnamate mono-2-ethylhexanoate glyceryl, paraaminobenzoic acid and its esters, 4-tert-butyl-4'-methoxydibenzoylmethane, and the like.
Examples of the ultraviolet scattering agent include titanium oxide and zinc oxide.

Fragrances include natural fragrances extracted from plants and animals, synthetic fragrances that are chemically synthesized, and compound fragrances that are a blend of multiple fragrances. Natural fragrances include, for example, flower-based fragrances such as jasmine, rose, carnation, lilac, cyclamen, lily of the valley, violet, lavender, and sweet osmanthus, citrus-based fragrances such as orange, lemon, and lime, spice-based fragrances such as cinnamon and nutmeg, and wood-based fragrances such as cypress essential oil, Japanese cedar essential oil, and so on. Examples of synthetic fragrances include hydrocarbons such as limonene, pinene, and camphene; alcohols such as linalool, geraniol, menthol, citronellol, and benzyl alcohol; aldehydes such as citral, citronellal, nonadienal, benzaldehyde, and cinnamic aldehyde; ketones such as acetophenone, methylacetophenone, methylnonylketone, irone, and menthone; phenols such as methylanisole and eugenol; lactones such as decalactone, nonyllactone, and undecalactone; and esters such as linalyl acetate, geranyl acetate, benzyl acetate, terpinyl acetate, citronellyl acetate, methyl benzoate, ethyl benzoate, isoamyl benzoate, benzyl benzoate, methyl cinnamate, and ethyl cinnamate.

Deodorizing ingredients include diphenols such as catechol, 4-methylcatechol, 5-methylcatechol, resorcinol, 2-methylresorcinol, 5-methylresorcinol, and hydroquinone; biphenyldiols such as 4,4'-biphenyldiol and 3,4'-biphenyldiol; catechins such as catechin, epicatechin, epigallocatechin, and epicatechin gallate; catechol derivatives such as dopa, dopamine, chlorogenic acid, caffeic acid, paracoumaric acid, and tyrosine. Plant-derived polyphenols extracted from plants include those derived from coffee, apples, grapes, teas (green tea, roasted green tea, black tea, oolong tea, mate tea, etc.), persimmons, soybeans, cacao, rosemary, and aloe.

Peeling agents include glycolic acid, salicylic acid, and lactic acid.
Anti-aging ingredients include retinol palmitate, fullerene, acetyl hexapeptide-8, palmitoyl pentapeptide-4, ubiquinone, platinum, etc.
Examples of whitening ingredients include magnesium ascorbyl phosphate, arbutin, placenta extract, and chamomile flower extract.
Anti-inflammatory ingredients include licorice root extract, dipotassium glycyrrhizinate, stearyl glycyrrhetinate, allantoin, and coix seed extract.
Examples of colorants include organic synthetic dyes (dyes, lakes, organic pigments), natural dyes, inorganic pigments, metal particles, polymer powders, etc. Among these, it is preferable to have organic synthetic dyes, natural dyes, inorganic pigments, and metal particles.

Furthermore, when a functional material is supported on the surface of the composite particle 1, the fine fibers 3 are coated on the surface of the core particle 2, so that the dispersion stability of the functional material is high and the functional material can effectively exhibit its function. The term "supported" by the fine fibers 3 means that the functional material is physically or chemically, reversibly or irreversibly bound or adsorbed to the fine fibers 3. The functional material can be supported by a known method.
It is preferable that the functional material and the fine fibers 3 are in an "inseparable" state. The term "inseparable" between the fine fibers 3 and the functional material means that the fine fibers 3 and the functional material are not separated even after a procedure in which a dispersion liquid containing the composite particles 1 is centrifuged to remove the supernatant, and a solvent is added to redisperse the composite particles 1 to purify and wash the composite particles 1, or a procedure in which the composite particles 1 are repeatedly washed with a solvent by filtration and washing using a membrane filter is repeated.

The functional material is a material that exerts its function in personal care products, and known functional materials can be used. Examples of functional materials include oil-based raw materials such as fats and oils and waxes, colorants, oil absorbents, light shielding agents (UV absorbers, UV scattering agents, etc.), antibacterial agents, antioxidants, antiperspirants, peeling agents, sebum suppressants, blood circulation promoting ingredients, whitening ingredients, anti-aging care ingredients, anti-inflammatory ingredients, cooling ingredients, warming ingredients, deodorizing ingredients, defoamers, antistatic agents, binders, bleaching agents, chelating agents, fragrances, perfumes, anti-dandruff active substances, skin softeners, insect repellents, preservatives, vitamins, amino acids, hormones, natural extracts, etc. Among these, it is preferable to have at least one of UV absorbers, UV scattering agents, perfumes, deodorizing ingredients, and colorants.

The method of loading the functional material onto the fine fibers 3 is not particularly limited, but after loading the functional material onto the fine fibers 3 to produce functional material-loaded fine fibers, the functional material-loaded fine fibers can be used to prepare a W/O type Pickering emulsion having droplets 4 containing a non-polymerizable solvent or surfactant and a core particle precursor, and the core particle precursor inside the droplets 4 of the emulsion can be polymerized and/or crosslinked, and then filtered and washed, and the pore-forming agent can be removed to produce composite particles 1 loaded with the functional material.

The method for supporting the functional material on the fine fibers 3 is not particularly limited. For example, a commercially available or pre-prepared functional material may be added to, mixed with, and attached to a dispersion of the fine fibers 3 and the composite particles 1.
A preferred method is to prepare the functional material in a dispersion of the fine fibers 3 or the composite particles 1. By preparing the functional material in a dispersion of the fine fibers 3 or the composite particles 1, the functional material is stably supported on the fine fibers 3, and aggregation of the functional material can be suppressed.

<Method of manufacturing composite particles>
As described above, the composite particle 1 of the embodiment can be produced by the method shown in FIG.
The composite particles 1 obtained by the manufacturing method shown in Fig. 2 can be purified and dried to obtain a dry solid (dry powder), and can also be redispersed to obtain a dispersion. The composite particles 1 can be purified by filtration, centrifugation, etc., and can be further obtained as a dry solid by thermal drying in an oven or vacuum drying. In this case, the dry solid of the obtained composite particles 1 is not in the form of a film or aggregate, but is obtained as a fine-textured, smooth powder.

Although the reason for this is unclear, it is known that, usually, when the solvent is removed from a dispersion of fine fibers 3, the fine fibers 3 strongly aggregate and form a film. On the other hand, in the case of a dispersion containing composite particles 1, spherical composite particles 1 with fine fibers 3 fixed on the surface are obtained, and even when the solvent 5 is removed, the fine fibers 3 do not aggregate, and the composite particles 1 only come into contact with each other at points, so that the dried solid is thought to be obtained as a finely textured powder. Since there is no aggregation between the composite particles 1, in powder cosmetics such as foundations, cosmetics that are smooth and blend well with the skin can be obtained. In addition, in liquid cosmetics such as skin care cosmetics and liquid foundations, composite particles 1 that contain a portion of the solvent can be controlled to disintegrate when applied to the skin, which gives them a unique texture. In addition, the effect of the fine fibers 3 provides excellent shape retention and moisture retention.

By supporting the functional material on the fine fibers 3, aggregation of the functional material can be suppressed, and a uniform powder cosmetic or skin care cosmetic can be obtained.
The dry powder of the composite particle 1 can be a dry solid material that contains almost no solvent such as the hydrophobic solvent 5 and is further characterized by being redispersible in a solvent, and specifically, the solid content can be 80% or more, further 90% or more, and further 95% or more. Since the solvent 5 can be almost completely removed, favorable effects can be obtained from the viewpoints of reducing transportation costs, preventing spoilage, improving the addition rate, and improving the efficiency of kneading with the resin.

The dry powder of the composite particle 1 is resistant to deformation during transportation because the surface of the composite particle 1 is covered with the highly strong fine fibers 3. When the composite particle 1 is dispersed in a solvent and used as a cosmetic product, it can be used as a swelling gel and can be designed to disintegrate when applied to the skin, thereby providing a unique texture.
In addition, the composite particles 1 obtained as a dry powder can be easily redispersed in a solvent, and even after redispersion, the composite particles 1 exhibit dispersion stability derived from the fine fibers 3 bonded to the surfaces of the composite particles 1. Therefore, the composite particles 1 can be added to beauty serums, milky lotions, creams, and the like.

Each step is described in detail below. As described above, the manufacturing method includes steps 1, 2, 3, and 4.

(First step)
The first step is a step of dispersing fine fibers 3, which are at least one of cellulose nanofibers and chitin nanofibers, in a hydrophobic solvent 5 to obtain a hydrophobic solvent dispersion of fine fibers 3. Although not particularly limited, for example, a fine fiber raw material can be defibrated in the hydrophobic solvent 5 to obtain a hydrophobic solvent dispersion of fine fibers 3. Alternatively, the fine fiber raw material may be defibrated in water and then subjected to solvent replacement to prepare a hydrophobic solvent dispersion of fine fibers 3. The fine fiber raw material refers to a cellulose raw material or a chitin/chitosan raw material, which is a raw material for cellulose nanofibers and/or chitin nanofibers.

First, various kinds of fine fiber raw materials are dispersed in a solvent to form a suspension. The concentration of the fine fiber raw materials in the suspension is preferably 0.1% or more and less than 10%. If it is less than 0.1%, the solvent becomes excessive, which impairs productivity, and if it is 10% or more, the suspension rapidly thickens as the fine fiber raw materials are defibrated, which makes it difficult to perform a uniform defibration process, and is also not preferred.
The solvent used to prepare the suspension may be a hydrophobic solvent 5 or a hydrophilic solvent. When a hydrophilic solvent is used, the fine fiber raw material is defibrated by solvent replacement, which will be described later, and then the fine fibers 3 are dispersed in the hydrophobic solvent 5 by solvent replacement.
The hydrophilic solvent is not particularly limited, but is preferably water, alcohols such as methanol, ethanol, isopropanol, etc., cyclic ethers such as tetrahydrofuran, etc., or a mixture thereof. It is preferable that the solvent contains 50% or more of water.

If necessary, the pH of the suspension may be adjusted to increase the dispersibility of the fine fiber raw material and the resulting fine fibers 3. Examples of alkaline aqueous solutions used for pH adjustment include organic alkalis such as sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, tetrabutylammonium hydroxide aqueous solution, and benzyltrimethylammonium hydroxide aqueous solution. From the standpoint of cost, etc., sodium hydroxide aqueous solution is preferred.

Then, the suspension is subjected to a physical fiberization process to refine the fine fiber raw material. The method of physical fiberization is not particularly limited, but includes mechanical processes such as a high-pressure homogenizer, an ultra-high-pressure homogenizer, a ball mill, a roll mill, a cutter mill, a planetary mill, a jet mill, an attritor, a grinder, a juicer mixer, a homomixer, an ultrasonic homogenizer, a nanogenizer, and underwater counter-collision. By carrying out such physical fiberization, for example, the cellulose in the suspension of the cellulose raw material using a hydrophilic solvent as the solvent is refined, and a dispersion of cellulose refined to the nanometer order of at least one side of the structure can be obtained. In addition, the number average minor axis diameter and number average major axis diameter of the obtained fine fibers 3 can be adjusted by the time and number of times of the physical fiberization process.

In this manner, a dispersion (fine fiber dispersion) of fine fibers 3 is obtained, in which at least one side of the structure is finely divided to the nanometer order. When a hydrophilic solvent is used as the solvent, the obtained dispersion can be dispersed in a hydrophobic solvent 5 using a known method such as solvent substitution, or diluted, concentrated, etc., and used as a stabilizer for W/O type emulsions, which will be described later.

In addition, the dispersion of fine fibers 3 may contain other components other than cellulose and the components used for pH adjustment, as necessary, within a range that does not impair the effects of the present invention. The other components are not particularly limited and can be appropriately selected from known additives depending on the application of the composite particle 1. Specific examples include organometallic compounds such as alkoxysilanes or hydrolysates thereof, inorganic layered compounds, inorganic acicular minerals, defoamers, inorganic particles, organic particles, lubricants, antioxidants, antistatic agents, UV absorbers, stabilizers, magnetic materials, alignment promoters, plasticizers, crosslinkers, pharmaceuticals, pesticides, fragrances, adhesives, enzymes, colorants, deodorants, metals, metal oxides, inorganic oxides, preservatives, antibacterial agents, natural extracts, and marine surfactants.

Usually, the fine fibers 3 have a fiber shape derived from a microfibril structure, so that the fine fibers 3 used in the manufacturing method of this embodiment preferably have a fiber shape within the range shown below. That is, the shape of the fine fibers 3 is preferably fibrous. In addition, the number average short axis diameter of the fibrous fine fibers 3 may be 1 nm or more and 1000 nm or less, preferably 2 nm or more and 500 nm or less. Here, if the number average short axis diameter is less than 1 nm, a highly crystalline rigid fine fiber 3 fiber structure cannot be obtained, and it becomes difficult to stabilize the emulsion and form the composite particle 1 by a polymerization reaction using the emulsion as a template. On the other hand, if it exceeds 1000 nm, the size becomes too large to stabilize the emulsion, so it becomes difficult to control the size and shape of the obtained composite particle 1. In addition, there is no particular restriction on the number average major axis diameter, but it is preferably 5 times or more the number average minor axis diameter. If the number average major axis diameter is less than 5 times the number average minor axis diameter, it is not preferable because it may not be possible to sufficiently control the size and shape of the composite particle 1.

The number average minor axis diameter of the fine fibers 3 is determined by measuring the minor axis diameters (minimum diameters) of 100 fibers using a transmission electron microscope and an atomic force microscope, and taking the average value. On the other hand, the number average major axis diameter of the fine fibers 3 is determined by measuring the major axis diameters (maximum diameters) of 100 fibers using a transmission electron microscope and an atomic force microscope, and taking the average value.

The type and crystal structure of cellulose that can be used as the cellulose raw material are not particularly limited. Specifically, as the raw material consisting of cellulose type I crystals, in addition to wood-based natural cellulose, non-wood-based natural cellulose such as cotton linter, bamboo, hemp, bagasse, kenaf, bacterial cellulose, sea squirt cellulose, and valonia cellulose can be used. Furthermore, regenerated cellulose, such as rayon fiber and cupra fiber, consisting of cellulose type II crystals can also be used. In view of the ease of material procurement, it is preferable to use wood-based natural cellulose as the raw material. There are no particular limitations on the wood-based natural cellulose, and it is possible to use those that are generally used in the production of cellulose nanofibers, such as softwood pulp, hardwood pulp, and waste paper pulp. Softwood pulp is preferable because of the ease of purification and fineness.

Chitin/chitosan raw material is a linear structural polysaccharide that supports and protects the body of animals, such as crustaceans such as crabs and shrimp, insects, spiders, arthropods, and squid tendons, and is crystalline (some parts have regularly arranged molecules), and some of it is bound to proteins. Chitin is a polysaccharide whose main sugar is N-acetylglucosamine. When chitin and/or chitosan raw materials are isolated and purified, there is almost no purified chitin that is 100% N-acetylglucosamine, and some chitin and/or chitosan containing glucosamine as a component is obtained. For example, two types of chitin and/or chitosan raw materials can be used: dried king crab shells crushed to about 5 mm, and wet spear squid carapaces crushed to about 1 cm. It is preferable to purify the chitin/chitosan raw material in advance.

Furthermore, it is preferable that the above-mentioned modifying group is introduced into the fine fibers 3 by chemical modification. The introduction of the modifying group improves dispersibility in the hydrophobic solvent 5. The method for introducing the chemical modification is not particularly limited, and the modifying group can be introduced by a known method. For example, an acetyl group may be introduced as the modifying group as in Patent Document 7. Acetylation is performed by reacting cellulose with acetic anhydride in a solvent containing a solvent and acetic acid.

The type of ionic functional group introduced to the crystal surface of the fine fiber raw material is not particularly limited, and may be an anionic functional group or a cationic functional group. In particular, it is preferable to have an anionic functional group. By having an anionic functional group, it is possible to introduce a hydrophobic group into the fine fiber 3 via the anionic functional group. The type and introduction method of the anionic functional group are not particularly limited, but a carboxy group, a carboxyl group, a phosphonium group, or a sulfonium group is preferred. In the case of cellulose, a carboxy group is preferred because of the ease of selective introduction to the cellulose crystal surface.

Furthermore, it is preferable that the modifying group is introduced via an anionic functional group. By introducing the modifying group via an anionic functional group, the fine fibers 3 are easily dispersed in a hydrophobic solvent 5, and it is easy to prepare a composite particle 1 having a core particle 2 containing a hydrophilic polymer. As a bond via an anionic functional group, a known method can be used, and for example, the modifying group can be introduced by a covalent bond such as an ether bond, an amide bond, or a urethane bond, or by an ionic bond. In particular, by introducing the modifying group via an ionic bond, after preparing the composite particle 1, the modifying group can be removed by washing with an acid or alkali, and it is possible to form a surface structure suited to the application.
The compound to be modified via an anionic functional group may be a known compound, such as an organic onium compound (quaternary ammonium compound, quaternary phosphonium compound), primary to tertiary amine compound, etc.

The organic onium compound in this embodiment has a cationic structure shown in structural formula (1). Examples include quaternary ammonium compounds and quaternary phosphonium compounds.

In structural formula (1), M is any one of a nitrogen atom, a phosphorus atom, a hydrogen atom, and a sulfur atom, and R1, R2, R3, and R4 are any one of a hydrogen atom, a hydrocarbon group, and a hydrocarbon group containing a hetero atom.
For example, when M is a nitrogen atom and R1, R2, R3 and R4 are all hydrogen atoms, the organic onium compound is ammonia. When three of R1, R2, R3 and R4 are hydrogen atoms, it is a primary amine, when two are secondary amine, when one is tertiary amine, when none are quaternary amine, all of which are organic onium compounds according to the present embodiment. Examples of the hydrocarbon group containing a heteroatom include an alkyl group, an alkylene group, an oxyalkylene group, an aralkyl group, an aryl group, and an aromatic group. R1, R2, R3 and R4 may form a ring.

Examples of quaternary alkyl ammonium compounds include tetraethyl ammonium hydroxide (TEAH), tetraethyl ammonium chloride, tetrabutyl ammonium hydroxide (TBAH), tetrabutyl ammonium chloride, lauryl trimethyl ammonium chloride, dilauryl dimethyl chloride, stearyl trimethyl ammonium chloride, distearyl dimethyl ammonium chloride, cetyl trimethyl ammonium chloride, alkyl benzyl dimethyl ammonium chloride, and coconut amine.

Examples of quaternary phosphonium compounds include phosphoniums such as tetramethylphosphonium hydroxide, tetraethylphosphonium hydroxide, tetrapropylphosphonium hydroxide, tetrabutylphosphonium hydroxide, benzyltrimethylphosphonium hydroxide, benzyltriethylphosphonium hydroxide, and hexadecyltrimethylphosphonium hydroxide.

Examples of primary to tertiary alkylamine compounds include ethylamine, diethylamine, triethylamine, butylamine, dibutylamine, tributylamine, octylamine, dioctylamine, trioctylamine, dodecylamine, didodecylamine, tridodecylamine, stearylamine, distearylamine, amino-modified silicone compounds, polyetheramines, polyethylene glycol amines (PEG-NH2), and amines having ethylene oxide/propylene oxide (EO/PO) copolymerized portions.

The method for preparing a hydrophobic solvent dispersion of the fine fibers 3 to which a modifying group has been introduced via an anionic functional group is not particularly limited, and any known method can be used.
For example, fine fibers 3 dispersed in solvent 5 can be obtained by a process including an oxidation step of oxidizing cellulose to introduce a carboxyl group, a process of mixing a compound for introducing a modifying group with the oxidized cellulose obtained in the oxidation step, thereby introducing a modifying group into the oxidized cellulose through ionic bonding with the compound for introducing the modifying group, a solvent substitution step of subjecting the oxidized cellulose having the modifying group introduced therein to solvent substitution with a hydrophobic solvent 5, and a dispersion step of dispersing (defibrating) the cellulose obtained in the solvent substitution step in the hydrophobic solvent 5.
Alternatively, oxidized cellulose may be dispersed by a dispersion (fibrillation) treatment, and then a compound for introducing a modifying group may be mixed and introduced, followed by dispersion in the hydrophobic solvent 5.

The method for introducing carboxyl groups to the crystal surface of cellulose is not particularly limited. For example, carboxymethylation may be performed by reacting cellulose with monochloroacetic acid or sodium monochloroacetate in a high-concentration aqueous alkali solution. Alternatively, carboxyl groups may be introduced by directly reacting cellulose with a carboxylic anhydride compound such as maleic acid or phthalic acid gasified in an autoclave. Furthermore, a method using a co-oxidant in the presence of an N-oxyl compound such as TEMPO, which has high selectivity for the oxidation of alcoholic primary carbons while maintaining the structure as much as possible under relatively mild aqueous conditions, may be used. Oxidation using an N-oxyl compound is more preferable for selectivity of the carboxyl group introduction site and reduction of environmental burden.

Here, examples of N-oxyl compounds include TEMPO (2,2,6,6-tetramethylpiperidinyl-1-oxy radical), 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 4-methoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, 4-ethoxy-2,2,6,6-tetramethylpiperidine-N-oxyl, and 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl. Among these, TEMPO, which has high reactivity, is preferred. The amount of the N-oxyl compound used may be the amount used for coloring, and is not particularly limited. Usually, it is 0.01% by mass or more and 5.0% by mass or less based on the solid content of the wood-based natural cellulose to be oxidized.

An example of an oxidation method using an N-oxyl compound is a method in which wood-based natural cellulose is dispersed in water and oxidized in the presence of an N-oxyl compound. In this case, it is preferable to use a co-oxidizing agent together with the N-oxyl compound. In this case, the N-oxyl compound is sequentially oxidized by the co-oxidizing agent in the reaction system to generate an oxoammonium salt, and the cellulose is oxidized by the oxoammonium salt. This oxidation process allows the oxidation reaction to proceed smoothly even under mild conditions, improving the efficiency of introducing carboxyl groups. When the oxidation process is performed under mild conditions, the crystal structure of the cellulose is easily maintained.

As the co-oxidizing agent, any oxidizing agent can be used, such as halogens, hypohalous acids, hypohalous acids, perhalogen acids, or their salts, halogen oxides, nitrogen oxides, peroxides, etc., as long as it is capable of promoting the oxidation reaction. Sodium hypochlorite is preferred due to its ease of availability and reactivity. The amount of the co-oxidizing agent used is not particularly limited and may be an amount capable of promoting the oxidation reaction. It is usually about 1 to 200% by mass based on the solid content of the wood-based natural cellulose to be oxidized.

At least one compound selected from the group consisting of bromides and iodides may be used in combination with the N-oxyl compound and the co-oxidizing agent. This allows the oxidation reaction to proceed smoothly, improving the efficiency of introducing carboxy groups. As such a compound, sodium bromide or lithium bromide is preferred, with sodium bromide being more preferred in terms of cost and stability. The amount of the compound used is not particularly limited and may be an amount that can promote the oxidation reaction. It is usually about 1 to 50% by mass based on the solid content of the wood-based natural cellulose to be oxidized.

The reaction temperature of the oxidation reaction is preferably 4° C. or higher and 80° C. or lower, and more preferably 10° C. or higher and 70° C. or lower. If the reaction temperature is lower than 4° C., the reactivity of the reagent decreases and the reaction time becomes longer. If the reaction temperature exceeds 80° C., side reactions are promoted, the sample becomes low molecular weight, and the fiber structure of the highly crystalline rigid cellulose nanofiber collapses, making it impossible to use the sample as a stabilizer for W/O type emulsions.
The reaction time for the oxidation treatment can be appropriately set in consideration of the reaction temperature, the desired amount of carboxy groups, etc., and is not particularly limited, but is usually from 10 minutes to 5 hours.

The pH of the reaction system during the oxidation reaction is not particularly limited, but is preferably 9 or more and 11 or less. A pH of 9 or more allows the reaction to proceed efficiently. If the pH exceeds 11, side reactions may proceed, which may accelerate the decomposition of the sample. In addition, in the oxidation treatment, as the oxidation proceeds, carboxyl groups are generated, causing the pH in the system to decrease, so it is preferable to maintain the pH of the reaction system at 9 or more and 11 or less during the oxidation treatment. One method for maintaining the pH of the reaction system at 9 or more and 11 or less is to add an alkaline aqueous solution as the pH decreases.

Examples of the alkaline aqueous solution include organic alkalis such as an aqueous sodium hydroxide solution, an aqueous lithium hydroxide solution, an aqueous potassium hydroxide solution, an aqueous ammonia solution, an aqueous tetramethylammonium hydroxide solution, an aqueous tetraethylammonium hydroxide solution, an aqueous tetrabutylammonium hydroxide solution, and an aqueous benzyltrimethylammonium hydroxide solution. From the standpoint of cost, etc., an aqueous sodium hydroxide solution is preferred.

The oxidation reaction by the N-oxyl compound can be stopped by adding an alcohol to the reaction system. In this case, it is preferable to maintain the pH of the reaction system within the above range. As the alcohol to be added, low molecular weight alcohols such as methanol, ethanol, and propanol are preferable in order to quickly terminate the reaction, and ethanol is particularly preferable in view of the safety of by-products generated by the reaction.

The reaction solution after the oxidation treatment may be directly subjected to the microparticulation process, but coloration and impurities such as N-oxyl compounds are removed. In addition, the carboxyl groups introduced into the cellulose in the reaction solution after the oxidation treatment form salts with metal ions derived from the cations present in the reaction medium as counter ions. For this reason, it is preferable to recover the oxidized cellulose contained in the reaction solution and wash it with a washing solution.

The oxidized cellulose can be recovered by a known method such as filtration using a glass filter or a nylon mesh with a pore size of 20 μm.
Methods for recovering cellulose after the oxidation treatment include, for example, (a) a method in which the carboxyl groups are filtered while still forming a salt, (b) a method in which an acid is added to the reaction liquid to adjust the system to an acidic state and then the cellulose is filtered as a carboxylic acid, and (c) a method in which an organic solvent is added to cause coagulation and then the cellulose is filtered.
Among them, the method of recovering as a carboxylic acid (b) is preferable from the viewpoints of handling, recovery efficiency, and waste liquid treatment. In addition, in the counter ion replacement step described below, the method of recovering as a carboxylic acid is preferable because the generation of by-products can be suppressed and replacement efficiency is excellent when the counter ion does not contain a metal ion.

The metal ion content in the cellulose after the oxidation reaction can be examined by various analytical methods, for example, it can be easily examined by elemental analysis using the EPMA method using an electron beam microanalyzer or the fluorescent X-ray analysis method. When the cellulose is recovered by filtering the salt as it is, the metal ion content is 5 wt% or more, whereas when the cellulose is recovered by filtering the salt as it is, the content is 1 wt% or less.
The recovered cellulose can be purified by repeated washing to remove catalysts and by-products. In this case, the amount of remaining metal ions and salts can be reduced by repeatedly washing with a washing solution prepared under acidic conditions of pH 3 or less using hydrochloric acid or the like, followed by repeated washing with pure water.

(Counter ion replacement step)
Next, the counterion replacement step is carried out by adding an alkali to the suspension of cellulose into which a carboxyl group has been introduced. The amount of alkali added is preferably 0.8 to 2 equivalents relative to the carboxyl group introduced into the cellulose. In particular, it is more preferable to add 1 to 1.8 equivalents, since counterion exchange can be performed without adding an excessive amount of alkali. Here, even if the amount is less than 0.8 equivalents, it is possible to disperse the cellulose to some extent, but the dispersion treatment requires a long time and high energy, and the fiber diameter of the obtained fiber is larger than that of the present invention, and the homogeneity of the dispersion is reduced. On the other hand, if the amount exceeds 2 equivalents, it is not preferable because decomposition due to an excess amount of alkali or affinity to the dispersion medium may be reduced.

At this time, it is preferable to adjust the pH of the cellulose suspension to a range of pH 4 to pH 12 using an alkali. In particular, the pH is adjusted to an alkaline range of pH 7 to pH 12, and a carboxylate is formed with the added alkali. This makes it easier for charge repulsion between carboxyl groups to occur, improving dispersibility and making it easier to obtain a cellulose nanofiber dispersion. Here, it is possible to disperse cellulose by mechanical dispersion treatment even at a pH of less than 4, but the homogeneity of the dispersion decreases for the same reason as when the amount of alkali added is too small. On the other hand, if the pH exceeds 12, the mechanical strength and homogeneity decrease during the dispersion treatment due to the peeling reaction of oxidized cellulose and the reduction in molecular weight due to alkaline hydrolysis, and the yellowing of the dispersion due to the formation of terminal aldehydes and double bonds.

The alkali to adjust the pH of the suspension can be an aqueous solution of sodium hydroxide, lithium hydroxide, potassium hydroxide, ammonia, etc. Also, modifying groups can be introduced by adjusting the pH using the aforementioned compound for introducing modifying groups.

As described above, by using a compound for introducing a modifying group as the alkali, the cellulose nanofibers are more easily dispersed in the solvent 5 than when an inorganic alkali having a metal ion as a counter ion is used, and the dispersion treatment can be performed with low energy and in a short time, and the homogeneity of the dispersion that is finally achieved is also high. This is thought to be because the ion diameter of the counter ion is larger and the hydrophobicity is higher when a compound for introducing a modifying group is used, and therefore the effect of separating the fine cellulose fibers from each other in the solvent 5 is greater. Furthermore, when an organic onium compound is included as a compound for introducing a modifying group, the viscosity and thixotropy of the dispersion can be reduced compared to inorganic alkali, which is advantageous in terms of ease of dispersion treatment and subsequent handling. Normally, cellulose nanofiber dispersions become gel-like and the viscosity increases as the concentration increases, so a large amount of energy is required for the dispersion treatment, making the dispersion treatment difficult, but when an organic onium compound is used, the viscosity of the dispersion is reduced, making the dispersion treatment easier. By combining an organic onium compound with a solvent, it is possible to adjust the viscosity characteristics of the dispersion, which significantly increases the range of industrial application.

(Solvent replacement process)
When oxidized cellulose having carboxyl groups introduced therein by oxidation is made into a dispersion, the cellulose can be dispersed into a homogeneous dispersion by mixing the cellulose with a dispersion medium and dispersing the mixture using the method described below. As a pretreatment for mixing with a dispersion medium, the oxidized cellulose can be subjected to solvent substitution. Here, since the reaction medium in the oxidation step of cellulose is water and the cleaning agent used for washing after the reaction is mainly water, the cellulose after the oxidation treatment is recovered in a wet state containing water. Therefore, when an organic solvent other than water is contained as the dispersion medium, it is preferable to perform solvent substitution for the purpose of removing water that becomes an impurity in the dispersion medium, for the purpose of improving dispersibility by previously bringing cellulose into affinity with the dispersion medium, or for the purpose of removing insoluble components in the dispersion medium.

It is also possible to perform solvent replacement of the oxidized cellulose with a hydrophobic solvent 5 before the counterion replacement step, but the charge repulsion of the carboxyl group is shielded by removing the contained water, or in the case of carboxylic acid, the cellulose aggregates because no charge repulsion occurs, which may adversely affect the subsequent dispersion step. Therefore, when performing solvent replacement with a hydrophobic solvent 5, it is preferable to use a cellulose modification in which the counterion of the carboxyl group of cellulose is ionically bonded to a compound for introducing a desired modifying group. Since the charge repulsion by the carboxyl group can be maintained even after the solvent replacement, the aggregation of cellulose fibers can be suppressed. Furthermore, the introduction of the modifying group improves the affinity with the hydrophobic solvent 5, making it easier to expel water and allowing for efficient solvent replacement.

The method of solvent replacement is appropriately selected according to the solvent to be replaced, the properties of the compound to be used for introducing the modifying group, and other desired properties. The cellulose that has been oxidized and washed may be mixed with a compound to introduce the modifying group, and then dehydrated or dried to introduce the modifying group. Alternatively, the cellulose that has been oxidized and washed may be dehydrated or dried and then a compound to introduce the modifying group may be used. There is no limitation on the dehydration method, and a centrifuge or various filters may be appropriately selected. There is no limitation on the drying method, and hot air drying, infrared drying, vacuum drying, freeze drying, and other methods may be appropriately selected. In order to suppress aggregation due to drying and deterioration of cellulose due to heat, various solvents and additives may be appropriately added. Furthermore, the cellulose modification product to which the compound to introduce the modifying group is ionically bonded may be directly put into the solvent 5 to be replaced with the solvent, or may be put into a solvent containing water and then sequentially replaced with the solvent.

The solvent used for the solvent replacement can be appropriately selected according to the purpose as long as it does not cause aggregation or denaturation of the cellulose fibers. In addition, the solvent may be the same as the hydrophobic solvent 5 used in preparing the cellulose nanofiber dispersion.
The obtained TEMPO oxidized cellulose is suspended in a hydrophobic solvent 5 and subjected to a defibration treatment to obtain TEMPO oxidized cellulose nanofibers (TEMPO oxidized CNF, also called cellulose single nanofibers or CSNF) having a uniform fiber width of 3 nm. When CSNF is used as the raw material for the cellulose nanofibers of the composite particles 1, the droplet size of the resulting Pickering emulsion is also uniform due to its uniform structure, and composite particles 1 with a uniform particle size can be obtained.

As described above, the CSNF used in this embodiment can be obtained by a process of oxidizing the cellulose raw material and a process of pulverizing and dispersing the cellulose. The content of carboxyl groups introduced into the CSNF is preferably 0.1 mmol/g or more and 5.0 mmol/g or less, and more preferably 0.5 mmol/g or more and 2.0 mmol/g or less. If the amount of carboxyl groups is less than 0.1 mmol/g, the solvent does not penetrate between the cellulose microfibrils due to the osmotic pressure effect, making it difficult to pulverize the cellulose and disperse it uniformly. If the amount of carboxyl groups exceeds 5.0 mmol/g, the cellulose microfibrils are depolymerized due to side reactions associated with the chemical treatment, so that the fiber structure of the highly crystalline rigid cellulose nanofibers cannot be obtained, and the cellulose nanofibers cannot be used as an emulsion stabilizer.

The solvent for the fine fiber dispersion is preferably a hydrophobic solvent 5 in order to form a stable W/O type emulsion. Although there are no particular limitations, examples of the hydrophobic solvent 5 include hydrocarbons, alcohols, ketones, ethers, ester oils, fatty acids, oils and fats, and waxes. These may be used alone or in combination.

Hydrocarbons are solvents that are composed only of carbon and hydrogen, and are further classified into chain and cyclic. Examples of hydrocarbons include aromatic hydrocarbons and aliphatic hydrocarbons. They may be saturated or unsaturated. Examples of hydrocarbons include normal hexane, cyclohexane, heptane, dodecane, toluene, benzene, paraffin, microcrystalline wax, mineral oil, petrolatum, ceresin, and squalane.
Examples of alcohols include methanol, ethanol, and isopropyl alcohol. In order to facilitate preparation of a W/O type emulsion, higher alcohols with low solubility in water are preferred. Examples of higher alcohols include lauryl alcohol, cetanol, cetearyl alcohol, stearyl alcohol, oleyl alcohol, behenyl alcohol, lanolin alcohol, hexyldecanol, octyldodecanol, and isostearyl alcohol.

Examples of ketones include methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetone, ethyl acetate, and butyl acetate.
Examples of ester oils include isopropyl myristate, isopropyl lanolate, hexyl laurate, myristyl myristate, cetyl myristate, octyldodecyl myristate, decyl oleate, octyldodecyl oleate, octyldodecyl neodecanoate (hexyldecyl dimethyloctanoate), cetyl ethylhexanoate (cetyl isooctanoate), cetyl palmitate, and triethylhexanoin.

The fatty acid is preferably a higher fatty acid. A higher fatty acid is generally a fatty acid having 12 or more carbon atoms, and includes saturated higher fatty acids and unsaturated higher fatty acids. Examples of saturated higher fatty acids include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, isostearic acid, and hydroxystearic acid. Examples of unsaturated higher fatty acids include oleic acid, linoleic acid, and undecylenic acid.
Examples of the oils and fats include vegetable oils and fats and animal oils and fats. Examples of the vegetable oils and fats include olive seed oil, coconut oil, safflower oil, linseed oil, avocado oil, almond oil, sesame oil, wheat germ oil, shea butter (shea), camellia oil, persic oil, castor oil, grape seed oil, macadamia nut oil, rosehip oil, etc. Examples of the animal oils and fats include horse oil, turtle oil, mink oil, egg yolk oil, etc.

Waxes include waxes derived from plants, animals, and minerals. Waxes derived from plants include carnauba wax, candelilla wax, jojoba seed oil, etc. Waxes derived from animals include orange roughy oil, whale wax, beeswax, and lanolin. Waxes derived from minerals include montan wax.
If necessary, a functional material may be supported on the fine fibers 3 in the dispersion of the fine fibers 3 to obtain a dispersion of the fine fibers 3 supporting the functional material. The composite particles 1 can be obtained by using the fine fibers 3 supporting the functional material.

There is no particular limitation on the method for imparting the functional material to the fine fibers 3, and any known method can be used. For example, a method is used in which the functional material is added to, mixed with, and adhered to the dispersion of the fine fibers 3. Alternatively, the functional material can be synthesized in the dispersion of the fine fibers 3 and supported thereon.
The fine fibers 3 may be defibrated after introducing a modifying group into the fine fiber raw material, or the fine fiber raw material may be defibrated and then the modifying group may be introduced. The fine fibers 3 may be defibrated in a hydrophobic solvent 5, or may be defibrated in a hydrophilic solvent and then dispersed in the hydrophobic solvent 5 by a known method such as solvent substitution.

(Second step)
The second step is a step of coating the surfaces of the droplets 4 containing the core particle precursors in the dispersion of the fine fibers 3 with the fine fibers 3, and stabilizing the resulting emulsion.
Specifically, this is a process in which a core precursor-containing liquid containing a core particle precursor is added to the hydrophobic solvent dispersion of the fine fibers 3 obtained in the first process, the core precursor is dispersed as droplets 4 in the hydrophobic solvent dispersion of the fine fibers 3, the surfaces of the droplets 4 are covered with the fine fibers 3, and a W/O type emulsion stabilized by the fine fibers 3 is prepared. The W/O type emulsion stabilized by the fine fibers 3 is called an emulsion liquid.

The method for producing a W/O type emulsion is not particularly limited, but general emulsification treatments, such as various homogenizer treatments and mechanical stirring treatments, can be used. Specific examples of such mechanical treatments include high-pressure homogenizers, ultra-high-pressure homogenizers, universal homogenizers, ball mills, roll mills, cutter mills, planetary mills, jet mills, attritors, grinders, juicer mixers, homomixers, ultrasonic homogenizers, nanogenizers, underwater counter-impingement, and paint shakers. A combination of multiple mechanical treatments may also be used.

For example, when an ultrasonic homogenizer is used, a core particle precursor-containing liquid is added to a dispersion liquid of the fine fibers 3 to prepare a mixed solvent, and the tip of the ultrasonic homogenizer is inserted into the mixed solvent to perform ultrasonic treatment. The treatment conditions of the ultrasonic homogenizer are not particularly limited, but for example, the frequency is generally 20 kHz or more, and the output is generally 10 W/ ^cm2 or more. The treatment time is also not particularly limited, but is usually about 10 seconds to 1 hour.

The above ultrasonic treatment causes droplets 4 containing the core particle precursor to disperse in the dispersion of fine fibers 3, and emulsification proceeds. Furthermore, the fine fibers 3 are selectively adsorbed to the liquid/liquid interface between the droplets 4 and the fine fiber dispersion, and the droplets 4 are covered with the fine fibers 3 to form a stable structure as a W/O type emulsion. In this way, emulsions stabilized by adsorption of solid matter to the liquid/liquid interface are academically called "Pickering emulsions." As mentioned above, the mechanism by which Pickering emulsions are formed by fine fibers 3 is unclear, but cellulose exhibits amphiphilicity due to its molecular structure having hydrophilic sites derived from hydroxyl groups and hydrophobic sites derived from hydrocarbon groups, and is therefore thought to be adsorbed to the liquid/liquid interface between the core precursor-containing liquid and the solvent 5 due to its amphiphilicity.

The W/O type emulsion structure can be confirmed by observation with an optical microscope. The particle size of the W/O type emulsion is not particularly limited, but the average particle size is preferably 0.1 μm or more and 1000 μm or less. The average particle size can be calculated by measuring the diameter of 100 emulsions at random and taking the average value.
In the W/O type emulsion structure, the thickness of the coating layer (fine fiber layer) formed on the surface of the droplets 4 is not particularly limited, but is preferably 3 nm or more and 1000 nm or less. Although not particularly limited, the particle size in the emulsion structure is approximately the same as the particle size of the composite particle 1 obtained in the third step. The thickness of the coating layer can be measured, for example, using a cryo-TEM.

The mass ratio of the fine fiber dispersion and the core particle precursor that can be used in the second step is not particularly limited, but it is preferable that the core particle precursor is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of the fine fibers 3. If the core particle precursor is 1 part by mass or less, the yield of the composite particle 1 decreases, which is not preferable, and if it exceeds 50 parts by mass, it becomes difficult to uniformly coat the droplets 4 with the fine fibers 3, which is also not preferable.

The core particle precursor-containing liquid is required to contain the core particle precursor and to be able to form a W/O type emulsion, and is preferably hydrophilic in order to stably form the W/O type emulsion. The core particle precursor is a precursor that solidifies through a chemical or physicochemical change to form the core particle 2. The core particle precursor is not particularly limited, but may be any precursor that can stably form the droplets 4. Examples of the core particle precursor that can be used include polymerizable monomers (monomers), polymerizable oligomers (oligomers), curable polymers, molten polymers, and dissolved polymers.

The type of polymerizable monomer and/or polymerizable oligomer (polymerizable monomer/oligomer) that can be used in the second step is not particularly limited as long as it is a polymer monomer, has a polymerizable functional group in its structure, is liquid at room temperature, is compatible with water, and can form a hydrophilic polymer (high molecular weight polymer or polymer material) by a polymerization reaction. The polymerizable monomer has at least one polymerizable functional group. A polymerizable monomer/oligomer having one polymerizable functional group is also called a monofunctional monomer/oligomer. A polymerizable monomer/oligomer having two or more polymerizable functional groups is also called a polyfunctional monomer/oligomer. A polymerizable monomer/oligomer is a substance that hardens through a crosslinking reaction when exposed to active energy rays such as ultraviolet rays or electron beams.

The type of polymerizable monomer is not particularly limited, but examples include amide monomers, urethane (meth)acrylates, (meth)acrylic monomers, and vinyl monomers. It is also possible to use polymerizable monomers having a cyclic ether structure such as an epoxy group or an oxetane structure (e.g., ε-caprolactone, etc.). The term "(meth)acrylate" includes both "acrylate" and "methacrylate."

As the amide monomer, it is particularly preferable to select from (meth)acrylamides. Examples include dimethylacrylamide, acryloylmorpholine, isopropylacrylamide, diethylacrylamide, dimethylaminopropylacrylamide, dimethylaminopropylacrylamide methyl chloride quaternary salt, hydroxyethylacrylamide (HEAA), dimethylaminoethyl acrylate benzyl chloride quaternary salt (manufactured by KJ Chemicals), etc., and among these, HEAA is preferable. HEAA has a hydroxyl group at the end, and the texture of the obtained composite particle 1 is good. Note that one or more of the above monomers may be mixed and used.

The urethane (meth)acrylate is a monomer/oligomer having a urethane skeleton in one molecule and containing one or more acryloyl groups or methacryloyl groups.
The urethane (meth)acrylate is preferably water-soluble or water-dispersible, and examples thereof include UA-W2A and UA-7100 (manufactured by Shin-Nakamura Chemical Co., Ltd.), and Beamset AQ-17 (manufactured by Arakawa Chemical Co., Ltd.) Note that urethane (meth)acrylate resins in which a part of the resin skeleton is substituted with an alkyl group ε-caprolactone can also be used, and the material is not particularly limited.

Examples of monofunctional (meth)acrylic monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, isodecyl (meth)acrylate, and lauryl (Meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphate (meth)acrylate, ethylene oxide modified phosphate (meth)acrylate, phenoxy (meth)acrylate, ethylene oxide modified phenoxy (meth)acrylate, propylene oxide modified phenoxy (meth)acrylate, nonylphenol (meth)acrylate, ethylene oxide modified nonylphenol Nonylphenol (meth)acrylate, propylene oxide modified nonylphenol (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, methoxypropylene glycol (meth)acrylate, 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, 2-(meth)acryloyloxyethyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hydrogen phthalate, 2-(meth)acryloyloxypropyl hexa Examples of the mono(meth)acrylate include hydrohydrogen phthalate, 2-(meth)acryloyloxypropyl tetrahydrohydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, and adamantane derivative mono(meth)acrylates such as adamantyl acrylate having a monovalent mono(meth)acrylate derived from 2-adamantane and adamantanediol.

Examples of bifunctional (meth)acrylic monomers include di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and hydroxypivalic acid neopentyl glycol di(meth)acrylate.

Examples of trifunctional or higher (meth)acrylic monomers include tri(meth)acrylates such as trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, and glycerin tri(meth)acrylate, as well as trifunctional (meth)acrylate compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate. Examples of such compounds include trifunctional or higher polyfunctional (meth)acrylate compounds such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate, as well as polyfunctional (meth)acrylate compounds in which part of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.

Examples of monofunctional vinyl monomers include vinyl ethers, vinyl esters, aromatic vinyls, and in particular styrene and styrene monomers.
Examples of the (meth)acrylate among the monofunctional vinyl monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, alkyl (meth)acrylate, tridecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, diethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, heptafluorodecyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and tricyclodecanyl (meth)acrylate.

Examples of monofunctional aromatic vinyl monomers include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ethylstyrene, isopropenyltoluene, isobutyltoluene, tert-butylstyrene, vinylnaphthalene, vinylbiphenyl, and 1,1-diphenylethylene.
The polyfunctional vinyl monomer includes a polyfunctional group having an unsaturated bond, such as divinylbenzene.

For example, specific examples of polyfunctional vinyl monomers include: (1) divinyls such as divinylbenzene, 1,2,4-trivinylbenzene, and 1,3,5-trivinylbenzene; (2) dimethacrylates such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-propylene glycol dimethacrylate, 1,4-butylene glycol dimethacrylate, 1,6-hexamethylene glycol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, and 2,2-bis(4-methacryloxydiethoxyphenyl)propane; (3) trimethacrylates such as trimethylolpropane trimethacrylate and triethylolethane trimethacrylate; (4) ethylene glycol diacrylate, diethylene glycol dimethacrylate, and dimethacrylates such as diethylolpropane trimethacrylate and diethylolethane trimethacrylate; diacrylates such as aryl diacrylate, triethylene glycol diacrylate, polyethylene glycol diacrylate, 1,3-dipropylene glycol diacrylate, 1,4-dibutylene glycol diacrylate, 1,6-hexylene glycol diacrylate, neopentyl glycol diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, 2,2-bis(4-acryloxypropoxyphenyl)propane, 2,2-bis(4-acryloxydiethoxyphenyl)propane, (5) triacrylates such as trimethylolpropane triacrylate, triethylolethane triacrylate, (6) tetraacrylates such as tetramethylolmethane tetraacrylate, and (7) others, such as tetramethylene bis(ethyl fumarate), hexamethylene bis(acrylamide), triallyl cyanurate, and triallyl isocyanurate.

Specific examples of polyfunctional styrene monomers include divinylbenzene, trivinylbenzene, divinyltoluene, divinylnaphthalene, divinylxylene, divinylbiphenyl, bis(vinylphenyl)methane, bis(vinylphenyl)ethane, bis(vinylphenyl)propane, and bis(vinylphenyl)butane.

The curable polymer (resin) is preferably a resin composition containing an unsaturated polyester resin or an epoxy resin as a main component, more specifically, an unsaturated polyester resin, a reactive diluent having a hydroxyl group and a carbon-carbon double bond, and a polymerization initiator as essential components, or a resin composition containing a liquid bisphenol-type epoxy resin, a phenolic resin curing agent having a hydroxyl group and a carbon-carbon double bond, and a curing accelerator as essential components.
Polyether resins, polyester resins, polyurethane resins, epoxy resins, alkyd resins, spiroacetal resins, polybutadiene resins, polythiolpolyene resins, and the like, each of which has at least one polymerizable functional group, can be used, and the material is not particularly limited.
The above polymerizable monomers/oligomers and curable polymers may be used alone or in combination of two or more kinds.

It is preferable to add a crosslinking agent to the core precursor-containing liquid according to the embodiment. When crosslinked by the crosslinking agent, the core particles 2 are likely to maintain a spherical shape while having water absorption. As the crosslinking agent, a compound having two or more polymerizable functional groups can be used, and specific examples thereof include ethylene glycol, propylene glycol, trimethylolpropane, glycerin, polyoxyethylene glycol, polyoxypropylene glycol, polyglycerin, N,N'-methylenebisacrylamide, N,N-methylene-bis-N-vinylacetamide, N,N-butylene-bis-N-vinylacetamide, tolylene diisocyanate, hexamethylene diisocyanate, allylated starch, allylated cellulose, diallyl phthalate, tetraallyloxyethane, pentaerythritol triallyl ether, trimethylolpropane triallyl ether, diethylene glycol diallyl ether, and triallyl trimellitate.

A polymerization initiator may be added to the polymerizable monomer. Examples of common polymerization initiators include radical initiators such as hydrogen peroxide, persulfates, organic peroxides, and azo polymerization initiators. Hydrogen peroxide, persulfates, and organic peroxides can also be used as redox initiators in combination with reducing substances such as sulfites and L-ascorbic acid, or amine salts.
Examples of persulfates include potassium persulfate, sodium persulfate, and ammonium persulfate.
Examples of the organic peroxide include peroxyketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxycarbonates, and peroxyesters.

Examples of azo polymerization initiators include 2,2-azobis(isobutyronitrile) (AIBN), 2,2-azobis(2-methylbutyronitrile) (AMBN), 2,2-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1-azobis(1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2-azobisisobutyrate (MAIB), 4,4-azobis(4-cyanovaleric acid) (ACVA), 1,1-azobis(1-acetoxy-1-phenylethane), 2,2-azobis(2-methylbutyramide ... These include 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2-azobis(2-methylamidinopropane) dihydrochloride, 2,2-azobis[2-(2-imidazolin-2-yl)propane], 2,2-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2-azobis(2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2-azobis(N-butyl-2-methylpropionamide), 2,2-azobis(N-cyclohexyl-2-methylpropionamide), etc.

In particular, from the viewpoint of ease of preparation of the composite particle 1 and safety, it is preferable to use water-soluble azo-based polymerization initiators such as 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis[2-(-imidazolin-2-yl)propane] disulfate dihydrate, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] n-hydrate, 2,2'-azobis[2-(2-imidazolin-2-yl)propane], 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], and 4,4'-azobis(4-cyanovaleric acid).

The core particle precursor-containing liquid preferably contains a solvent. The solvent of the core particle precursor-containing liquid is preferably a solvent having low solubility in the hydrophobic solvent 5, which is the solvent of the dispersion liquid of the fine fibers 3. If the solubility in the hydrophobic solvent 5 is high, the solvent of the dispersed phase (droplets 4) easily dissolves in the continuous phase (hydrophobic solvent 5), making it difficult to form a stable emulsion.
Specifically, water; alcohols such as methanol, ethanol, isopropanol, and the like; and cyclic ethers such as tetrahydrofuran, and the like are preferred. In particular, it is preferred that the suspension contains 50% by mass or more of water. If the proportion of water in the suspension is less than 50% by mass, the stability of the W/O type emulsion is deteriorated. In addition, the above-mentioned hydrophilic solvent is preferred as the solvent contained other than water.

If a core particle precursor-containing liquid containing a polymerizable monomer/oligomer and a polymerization initiator is used in the second step, the polymerization initiator will be contained in the W/O type emulsion droplets 4 in the third step described below, and this will facilitate the polymerization reaction when polymerizing the monomer/oligomer inside the emulsion droplets 4 in the third step described below.
The mass ratio of the polymerizable monomer or oligomer to the polymerization initiator that can be used in the second step is not particularly limited, but in general, it is preferable that the amount of the polymerization initiator is 0.1 part by mass or more per 100 parts by mass of the polymerizable monomer/oligomer. If the amount of the polymerizable monomer/oligomer is less than 0.1 part by mass, the polymerization reaction does not proceed sufficiently, and the yield of the composite particle 1 decreases, which is not preferable.

The polymer for obtaining the dissolved polymer is not particularly limited, but it is preferable that the polymer is difficult to dissolve in the hydrophobic solvent 5. If the polymer dissolves in the hydrophobic solvent 5, a stable W/O type emulsion cannot be formed.
As the polymer for obtaining the dissolved polymer, a water-soluble polymer can be used. The water-soluble polymer is a compound having a molecular weight of 1000 or more, which dissolves at 85° C. in an amount of 1 part by mass or more in 100 parts by mass of a solvent containing at least one of an aqueous alcohol solution containing 50% by mass of any one of methanol, ethanol, propanol, and isopropyl alcohol, and water, at least one part by mass.
Examples of the water-soluble polymer include proteins, vinyl resins, acrylic resins, polyethylene resins, urethane resins, and epoxy resins.

Examples of proteins include gelatin, casein, sodium chondroitin sulfate, and the like.
Examples of the vinyl resin include polyvinyl alcohol, polyvinylpyrrolidone, and polyvinylpyrrolidone-vinyl acetate copolymer.
Examples of the acrylic resin include sodium polyacrylate, carboxyvinyl polymer, polyacrylamide, and acrylamide-acrylate copolymer.
Examples of the polyethylene resin include polyethyleneimine, polyethylene oxide, and polyethylene glycol.
The water-soluble polymer may be used alone or in combination of two or more kinds.

The water-soluble polymer can be dissolved in water or a hydrophilic solvent to obtain a dissolved polymer. As the solvent for dissolving the polymer, it is preferable to use a solvent that has low solubility in the hydrophobic solvent 5, which is the solvent for the dispersion of the fine fibers 3. If the solubility in the hydrophobic solvent 5 is high, the solvent of the dispersed phase (droplets 4) will easily dissolve in the continuous phase (hydrophobic solvent 5), making it difficult to form a stable emulsion. In addition, it is preferable that the solvent for dissolving the polymer has a boiling point equal to or lower than the boiling point of the hydrophobic solvent 5 of the continuous phase. If the boiling point of the solvent for dissolving the polymer is higher than the boiling point of the solvent 5 of the continuous phase, the hydrophobic solvent 5 of the dispersion of the fine fibers 3 will evaporate before the solvent for dissolving the polymer, making it difficult to obtain the composite particle 1.

Specifically, the solvent that can be used as the solvent for dissolving the dissolved polymer is preferably water; alcohols such as methanol, ethanol, isopropanol, and cyclic ethers such as tetrahydrofuran. In particular, it is preferable that the suspension contains 50% by mass or more of water. If the proportion of water in the suspension is less than 50% by mass, the stability of the W/O type emulsion may deteriorate. In addition, the above-mentioned hydrophilic solvent is preferable as the solvent contained other than water.
The mass ratio of the polymer to be dissolved and the solvent is not particularly limited as long as the polymer can be dissolved. Preferably, the mass ratio of the solvent is 0.005 parts by mass or more and 100 parts by mass or less, more preferably 0.1 parts by mass or more and 80 parts by mass or less, relative to 100 parts by mass of the polymer.

A method for obtaining a molten polymer by melting a polymer is, for example, to melt a polymer that is solid at room temperature to make it liquid. It is preferable to stabilize the molten polymer droplets in the dispersion as a W/O type emulsion by adding the molten polymer to a dispersion of fine fibers 3 that has been heated to a temperature at which the polymer can be maintained in a molten state while subjecting the molten polymer to mechanical processing such as with an ultrasonic homogenizer as described above.

The molten polymer is preferably one that has low solubility in the hydrophobic solvent 5 of the fine fibers 3. If the solubility in the hydrophobic solvent 5 is high, the polymer will easily dissolve from the dispersed phase (droplets 4) into the continuous phase (hydrophilic solvent 7), making emulsification difficult. In addition, the melting point of the molten polymer is preferably equal to or lower than the boiling point of the solvent 5. If the melting point is higher than the boiling point of the solvent 5, the solvent 5 in the dispersion of the fine fibers 3 will evaporate, making emulsification difficult.
The polymer used for the molten polymer may be the water-soluble polymer described above.

It is preferable to use a core forming agent in the core particle precursor-containing liquid in order to obtain pore-containing core particles 2. As the pore forming agent, a known pore forming agent can be used as described above, and the pore forming agent can contain an organic solvent similar to the water-incompatible solvent 5.
In addition, the droplets 4 may contain other components such as functional components in advance in addition to the polymerization initiator. The above-mentioned functional components can be used as the other components. For example, they are substances that affect and function on living organisms such as animals, plants, and fungi. Although not particularly limited, examples of the functional components include anti-mold agents, fragrances, fertilizers (biofertilizers, chemical fertilizers, organic fertilizers, etc.), pH adjusters, pesticides (insecticides, fungicides, herbicides, etc.), plant revitalizers, plant life-extending agents, pest and animal repellents, soil penetrants, nutritional components (minerals, etc.), plant hormones, inorganic particles (titanium oxide, silica, clay, etc.), and antibacterial components.

In particular, it is preferable to include functional components that exert their functions in personal care products. For example, oil-based raw materials such as oils and waxes, colorants, oil absorbents, light shielding agents (UV absorbents, UV scattering agents, etc.), antibacterial agents, antioxidants, antiperspirants, peeling agents, sebum suppressants, blood circulation promoting agents, whitening agents, anti-aging care agents, anti-inflammatory agents, cooling agents, warming agents, deodorizing agents, defoaming agents, antistatic agents, binders, bleaching agents, chelating agents, fragrances, perfumes, anti-dandruff active substances, skin softeners, insect repellents, preservatives, vitamins, amino acids, hormones, natural extracts, etc. Among them, it is preferable to include at least any of UV absorbents, UV scattering agents, perfumes, deodorizing agents, peeling agents, anti-aging care agents, whitening agents, anti-inflammatory agents, and colorants.
When the core particle precursor already contains components other than the polymerization initiator, the above-mentioned components can be contained inside the core particle 2 when it is formed into the composite particle 1, making it possible to express functions according to the application.

It is preferable that the other component is easily dissolved or dispersed in the droplets 4 and is difficult to dissolve or disperse in the hydrophobic solvent 5. By dissolving or dispersing the other component in the droplets 4, the other component such as a functional component can be easily encapsulated in the droplets 4 of the emulsion when a W/O type emulsion is formed, and composite particles 1 encapsulating the other component can be efficiently obtained. In addition, the amount of the encapsulated other component can be increased.
Furthermore, it is also possible to use a combination of a polymerizable monomer and a dissolved polymer or a molten polymer as the core particle precursor to form droplets 4 and emulsify them. When a biodegradable polymer is selected as the polymer (resin) type of the core particle 2 of the composite particle 1, the obtained composite particle 1 is composed of the core particle 2 and the fine fibers 3 made of a biodegradable polymer, and therefore it is also possible to provide the composite particle 1 containing a biodegradable material and being highly environmentally friendly.

(Third process)
This is a process in which the core particle precursors inside the droplets 4 are solidified by polymerization, crosslinking, coagulation, solvent diffusion, or the like to obtain a dispersion of composite particles 1 coated with fine fibers 3, in which the surfaces of core particles 2 are coated with fine fibers 3. Note that gel is also a type of solid.
The method for solidifying the core particle precursor is not particularly limited. When a polymerizable monomer is used as the core particle precursor, the core particle precursor can be solidified by polymerizing the polymerizable monomer. When a dissolved polymer is used as the core particle precursor, the solvent inside the droplet 4 can be removed by diffusing the solvent into a hydrophobic solvent 5 or evaporating the solvent, and the polymer can be solidified. When a molten polymer is used as the core particle precursor, the molten polymer can be solidified by cooling and solidifying it.

In the production method of the present invention, the core particle precursor is solidified in the second step to become the core particle 2, so that the composite particle 1 coated with the fine fiber 3 can be obtained.
For example, the W/O type emulsion in which droplets 4 containing a polymerizable monomer and a polymerization initiator as a core particle precursor prepared in the second step are coated with fine fibers 3 and stabilized is heated while being stirred to polymerize the polymerizable monomer and solidify the core particle precursor. The stirring method is not particularly limited, and a known method can be used, and specifically, a disperser or a stirrer can be used. Alternatively, only the heat treatment can be performed without stirring.

The temperature conditions during heating can be set appropriately depending on the type of polymerizable monomer and the type of polymerization initiator, but is preferably 20°C or higher and 150°C or lower. Temperatures below 20°C are undesirable because the polymerization reaction rate decreases, and temperatures above 150°C are undesirable because the fine fibers 3 may be denatured. The time allowed for the polymerization reaction can be set appropriately depending on the type of polymerizable monomer and the type of polymerization initiator, but is usually about 1 to 24 hours. The polymerization reaction may be carried out by irradiation with ultraviolet light, which is a type of electromagnetic wave. In addition to electromagnetic waves, particle beams such as electron beams may also be used.

Specific methods for evaporating the solvent of the dissolved polymer include evaporating and removing the solvent by heating and/or drying under reduced pressure. If the boiling point of the solvent that dissolves the dissolved polymer is lower than that of the solvent 5 of the continuous phase, it is possible to selectively remove the solvent that dissolved the dissolved polymer. Although not particularly limited, the solvent can be efficiently removed by heating under reduced pressure conditions. The heating temperature is preferably 20°C or higher and 100°C or lower, and the pressure is preferably 600 mmHg or higher and 750 mmHg or lower.

Specifically, the method for diffusing the solvent of the dissolved polymer is to add an additive to the W/O type emulsion liquid to diffuse the solvent inside the droplets 4. The solvent dissolving the dissolved polymer diffuses into the continuous phase over time, causing the polymer to precipitate and solidify as particles. Note that the solvent does not need to be completely diffused, and it is sufficient that the solvent is diffused to the extent that it becomes solid.
As a method for solidifying the molten polymer, the W/O type emulsion liquid is cooled to solidify the molten polymer.

(Fourth step)
The fourth step is a step of purifying the composite particles 1 from the dispersion of the composite particles 1 in which the core particles 2 are covered with the fine fibers 3 obtained through the above steps. Specifically, this is a step of purifying the composite particles 1 from the free fine fibers 3 and the solvent 5 by centrifugation.
Immediately after the production of the composite particles 1, the solvent 5 and free fine fibers 3 that do not contribute to the formation of a coating layer are mixed in the dispersion liquid of the composite particles 1. Therefore, the composite particles 1 need to be recovered and purified, and the preferred recovery and purification method is washing by centrifugation or washing by filtration.

A known method can be used for the cleaning method by centrifugation. Specifically, the composite particles 1 are precipitated by centrifugation, the supernatant is removed, and the composite particles 1 are redispersed in a hydrophilic solvent such as water or methanol, and the procedure is repeated. Finally, the residual solvent is removed from the precipitate obtained by centrifugation to recover the composite particles 1. A known method can also be used for filtration and cleaning. For example, suction filtration with water and methanol is repeated using a PTFE membrane filter with a pore size of 0.1 μm, and finally, the residual solvent is further removed from the paste remaining on the membrane filter to recover the composite particles 1.

If necessary, it is possible to dry the mixture at room temperature or by heating under normal pressure or reduced pressure. The dried solid material containing the composite particles 1 thus obtained is not in the form of a film or aggregate as described above, but is obtained as a finely textured powder.
If necessary, the composite particles 1 may be dispersed in a solvent, and the functional material may be supported on the fine fibers 3 on the surfaces of the composite particles 1 in the dispersion of the composite particles 1 .

There is no particular limitation on the method for supporting the functional material on the composite particle 1, and any known method can be used. For example, a method can be used in which the composite particle 1 is redispersed in a solvent to prepare a dispersion of the composite particle 1, and the functional material is added to, mixed with, and adhered to the dispersion of the composite particle 1. Alternatively, the functional material can be synthesized in the dispersion of the composite particle 1 and supported thereon.
Pores can be formed in the composite particle 1, and the pores can be impregnated with or encapsulated with the above-mentioned functional component. By including the functional component, the function of the functional component can be exerted.

The composite particle 1 of the present embodiment can be used as a home care product or a personal care product either in the form of a dry powder or as a swollen gel after absorbing water. It is particularly preferable to use the composite particle 1 as a personal care particle for personal care purposes.
Personal care products are cosmetics, toiletries, and other products that keep people's skin clean and groom them, as well as products related to hair care, oral care, scent care, nail care, body care, skin care, and makeup, such as toothpaste, perfume, nail lacquer, skin lotion, milky lotion, cleansing agent, eye shadow, eyeliner, foundation, blush, hair gel, hair spray, shampoo, rinse, hair growth agent, lotion, cream, and soap.

The composite particles 1 can be mixed or dispersed as a swollen gel in other cosmetic raw materials and used in personal care products such as skin care products. The composite particles 1 can also be dispersed in a solvent containing cosmetic raw materials and used as a personal care composition. The composite particles 1 can form a stable W/O type emulsion due to the fine fibers 3, so a swollen gel that is spherical and has a narrow particle size distribution can be obtained. In addition, the coating of the fine fibers 3 makes it difficult for the particles to aggregate and provides good dispersibility. Therefore, when used in personal care products, a smooth and very good texture can be obtained.

Cosmetic raw materials include solvents such as water and ethanol, aqueous components such as butylene glycol, dipropylene glycol, water-soluble collagen, and hyaluronic acid, oil-based components such as higher alcohols, higher fatty acids, fats and oils, wax, ester oils, and silicones, surfactants such as anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants, functional components such as whitening components, anti-inflammatory components, anti-aging components, deodorant components, skin quality improving components, and UV protection agents, and other components such as pH adjusters, preservatives, antioxidants, thickeners, chelating agents, fragrance components, and colorants.

(Effect of Composite Particle 1)
According to the first aspect of the composite particle 1 of the present invention, the problem of excess solvent in fine fibers 3 such as cellulose nanofibers or chitin nanofibers is solved, and a composite particle 1 having a new type of fine fibers 3 that can be produced by a simple method can be provided.
It is possible to provide, by a simple method, composite particles 1 which not only have excellent water absorbency and the like, but also have a high restoration rate without disintegrating due to external forces such as transport, have good dispersibility and dispersion stability in various solvents such as water and oil, have good compatibility with the skin, and have good moisturizing properties. Another object of the present invention is to provide a personal care product using the composite particles 1.
The fine fibers 3, such as cellulose nanofibers and chitin nanofibers, are made of biodegradable polymers such as cellulose and chitin/chitosan. Therefore, by making the core particles 2 out of a material containing a biodegradable polymer, it is possible to provide composite particles 1 that can reduce the burden on the environment.

According to the production method of the second aspect of the present invention, the composite particle 1 of the first aspect of the present invention can be produced.
The composite particle 1 can be used for personal care applications, and a personal care product or composition for personal care can be provided that includes the composite particle 1. For example, the composite particle 1 can be used in hair care, oral care, odor care, body care, skin care, and makeup-related products. Specifically, the composite particle 1 can be used in toothpaste, perfume, nail lacquer, beauty serum, skin lotion, milky lotion, cleansing agent, eye shadow, eyeliner, foundation, blush, hair gel, hair spray, shampoo, rinse, hair growth agent, lotion, cream, soap, and the like.

Although the embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like that do not deviate from the gist of the present invention are also included. In addition, the components shown in the above-mentioned embodiment can be appropriately combined to form a configuration. For example, the core particle 2 may contain other components in addition to the polymer and functional component.

The present invention will be described in detail below based on examples, but the technical scope of the present invention is not limited to these examples. In each of the following examples, "%" indicates mass % (w/w%) unless otherwise specified.

Example 1
(First step: Step of obtaining cellulose nanofiber dispersion)
(TEMPO oxidation of wood cellulose)
70 g of softwood kraft pulp was suspended in 3500 g of distilled water, and a solution of 0.7 g of TEMPO and 7 g of sodium bromide dissolved in 350 g of distilled water was added and cooled to 20 ° C. 450 g of sodium hypochlorite aqueous solution with a concentration of 2 mol / L and a density of 1.15 g / mL was added dropwise to start the oxidation reaction. The temperature in the system was always kept at 20 ° C., and the pH drop during the reaction was maintained at pH 10 by adding a 0.5 N aqueous sodium hydroxide solution. When the total amount of sodium hydroxide added reached 3.0 mmol / g relative to the mass of cellulose, about 100 mL of ethanol was added to stop the reaction.

The introduced carboxyl groups formed salts with sodium ions derived from the reaction reagent remaining in the reaction medium as counter ions. Then, 0.5 N hydrochloric acid was added dropwise to lower the pH to 2. The cellulose was filtered using a glass filter and further washed three times with 0.05 N hydrochloric acid to convert the carboxyl groups to carboxylic acids, followed by washing five times with pure water to obtain oxidized cellulose in a wet state with a solids concentration of 20%.
The amount of carboxyl groups in the obtained oxidized cellulose was calculated to be 1.44 mmol per dry mass of cellulose by neutralization titration with sodium hydroxide.

(Washing of oxidized cellulose)
The oxidized cellulose prepared above was suspended in water to a solids concentration of 5%, and 1.0 equivalent of sodium hydroxide was added as an alkali relative to the amount of carboxyl groups in the oxidized cellulose. After stirring for 2 hours, the oxidized cellulose was filtered out using a glass filter and washed.
(Defibrillation treatment of oxidized cellulose)
0.5 g of the above oxidized cellulose was dispersed in 99.5 g of water and subjected to a micronization treatment in a juicer mixer for 30 minutes to obtain a cellulose nanofiber dispersion with a concentration of 0.5%.
(Evaluation of cellulose nanofibers)
For the obtained oxidized cellulose and cellulose nanofibers, the amount of carboxyl groups, degree of crystallinity, number average axis diameter of the major axis, light transmittance, and rheology were measured and calculated as follows.

(Measurement of Carboxy Group Amount)
For the oxidized cellulose before dispersion treatment, the amount of carboxy groups was calculated by the following method.
0.2 g of oxidized cellulose in terms of dry mass was placed in a beaker, and 80 mL of ion-exchanged water was added. 5 mL of 0.01 mol/L aqueous sodium chloride solution was added thereto, and 0.1 mol/L hydrochloric acid was added while stirring to adjust the overall pH to 2.8. Using an automatic titrator (product name: AUT-701, manufactured by DKK-TOA Corporation), 0.1 mol/L aqueous sodium hydroxide solution was injected at 0.05 mL/30 seconds, and the conductivity and pH value were measured every 30 seconds, and measurements were continued up to pH 11. The titration amount of sodium hydroxide was determined from the obtained conductivity curve, and the carboxyl group content was calculated.

(Calculation of Crystallinity)
The crystallinity of the TEMPO oxidized cellulose was calculated.
For TEMPO-oxidized cellulose, the X-ray diffraction pattern was measured in the range of 5°≦2θ≦35° using a horizontal sample multipurpose X-ray diffractometer (product name: Ultima III, manufactured by Rigaku Corporation) under conditions of X-ray output: (40 kv, 40 mA). Since the obtained X-ray diffraction pattern is derived from the cellulose type I crystal structure, the crystallinity of TEMPO-oxidized cellulose was calculated using the following formula (2) by the method shown below.
Crystallinity (%) = [(I22.6-I18.5)/I22.6] x 100... (2)
Here, I22.6 indicates the diffraction intensity of the lattice plane (002 plane) (diffraction angle 2θ=22.6°) in X-ray diffraction, and I18.5 indicates the diffraction intensity of the amorphous portion (diffraction angle 2θ=18.5°).

(Calculation of number average axis diameter of the long axis of cellulose nanofibers)
The number-average axis diameter of the long axis of the cellulose nanofibers was calculated using an atomic force microscope.
First, the cellulose nanofiber dispersion was diluted to 0.001%, and then 20 μL of each was cast onto a mica plate and air-dried. After drying, the shape of the cellulose nanofiber was observed in DFM mode using an atomic force microscope (product name: AFM5400L, manufactured by Hitachi High-Technologies Corporation). The number-average axis diameter of the long axis of the cellulose nanofiber was calculated by measuring the long axis diameter (maximum diameter) of 100 fibers from the image observed by the atomic force microscope and averaging the results.

(Measurement of light transmittance of cellulose nanofiber aqueous dispersion)
The light transmittance was measured for an aqueous dispersion containing 0.5% by mass of cellulose nanofiber.
Water was placed in one of the quartz sample cells as a reference, and the cellulose nanofiber aqueous dispersion was placed in the other cell without allowing air bubbles to get mixed in. The light transmittance at a wavelength of 220 nm to 800 nm at an optical path length of 1 cm was measured using a spectrophotometer (product name: NRS-1000, manufactured by JASCO Corporation). The results are shown in Figure 3.

(Rheological measurements)
The rheology of a 0.5% by mass dispersion of cellulose nanofibers was measured using a rheometer (product name: AR2000ex, manufactured by TA Instruments) with a cone plate at an inclination angle of 1°. The temperature of the measurement section was adjusted to 25°C, and the shear viscosity was continuously measured at shear rates from 0.01 s ^-1 to 1000 s ^-1 . The results are shown in Figure 4. As is clear from Figure 4, the cellulose nanofiber dispersion exhibited thixotropy. The shear viscosities at shear rates of 10 s ^-1 and 100 s ^-1 are shown in Table 1.

As is clear from Figure 3, the cellulose nanofiber aqueous dispersion exhibited high transparency. Furthermore, the number average minor axis diameter of the cellulose nanofibers (TEMPO oxidized CNF) contained in the cellulose nanofiber aqueous dispersion was 3 nm, and the number average major axis diameter was 831 nm. Figure 4 shows the results of steady-state viscoelasticity measurements performed using a rheometer, and the cellulose nanofiber dispersion exhibited thixotropic properties.

(Substitution into Carboxylic Acid Type)
Next, 1M hydrochloric acid was added to 100mL of the cellulose nanofiber aqueous dispersion to adjust the pH to 1, and 1mL was added while stirring, and stirring was continued for 60 minutes. The gelled cellulose nanofibers were then collected by centrifugation (12000g), and the collected cellulose nanofiber gel was washed with 1M hydrochloric acid and then with distilled water. Through the above process, 90% or more of the carboxyl groups on the cellulose surface were replaced with carboxylic acid types.

(Solvent Replacement)
Ethanol was added to the recovered cellulose nanofiber gel to make a gel dispersion (concentration approximately 0.2% by mass), and then the process of recovering the cellulose nanofiber by centrifugation (12,000 g) was repeated five times to replace the solvent in the cellulose nanofiber with ethanol.
Next, toluene was added to the cellulose nanofiber gel that had been solvent-substituted with ethanol to form a gel dispersion (concentration of approximately 0.2% by mass), and then the process of recovering the gel by centrifugation (12,000 g) was repeated five times to solvent-substitute the cellulose nanofiber with toluene (Step 1D).
Next, polyethylene glycol amine (molecular weight 2000) was added in an amount equimolar to the carboxyl groups of the cellulose nanofibers to prepare a toluene dispersion of the cellulose nanofibers (0.2% by mass). The mixture was then subjected to ultrasonic treatment for 3 minutes to prepare a toluene dispersion of the cellulose nanofibers.

(Second step: Preparation of W/O type emulsion)
Next, as a core precursor-containing liquid, 5 g of hydroxyethylacrylamide (hereinafter also referred to as HEAA) as a polymerizable monomer and 0.5 g of VA-044 (2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride) as a polymerization initiator were dissolved in 5 g of pure water.
When the entire amount of the polymerizable monomer mixture was added to 40 g of the cellulose nanofiber dispersion, the polymerizable monomer mixture and the cellulose nanofiber dispersion each separated into two phases.

Next, the shaft of an ultrasonic homogenizer was inserted from the liquid surface of the upper phase of the mixture in the two-phase separated state, and ultrasonic homogenization was performed for 3 minutes at a frequency of 24 kHz and an output of 400 W. The appearance of the mixture after ultrasonic homogenization was a cloudy emulsion. When a drop of the mixture was placed on a slide glass, sealed with a cover glass, and observed under an optical microscope, countless emulsion droplets of about several μm were generated, and it was confirmed that the W/O type emulsion, in which the cellulose nanofiber dispersion was the continuous phase and the polymerizable monomer mixture was the dispersed phase, was dispersed and stabilized.

(Third step: solidifying the core particle precursor)
The W/O type emulsion dispersion was placed in a water bath at 70° C. and treated for 8 hours while stirring with a stirrer to carry out a polymerization reaction. After 8 hours of treatment, the dispersion was cooled to room temperature. There was no change in the appearance of the dispersion before and after the polymerization reaction.

(Fourth step: purification and drying step)
The resulting dispersion was centrifuged at 75,000 g for 5 minutes to obtain a precipitate. The supernatant was removed by decantation to recover the precipitate, which was then washed twice with methanol and twice with pure water using a PTFE membrane filter with a pore size of 0.1 μm.
The purified and recovered material thus obtained was redispersed at a concentration of 1%, and the particle size was evaluated using a particle size analyzer (SALD-200VER). The purified and recovered material was then air-dried, and further subjected to a vacuum drying process at room temperature of 25°C for 24 hours, yielding a dry powder with a fine texture.

(Shape observation using a scanning electron microscope)
The obtained dry powder was observed with a scanning electron microscope (SEM). It was confirmed that the polymerization reaction was carried out using the W/O type emulsion droplets as a template, resulting in the formation of countless spherical particles derived from the shape of the emulsion droplets, and further confirmed that the surfaces were uniformly covered with cellulose nanofibers with a width of several nm. Despite repeated washing by filtration and washing, the surfaces of the particles were equally and uniformly covered with cellulose nanofibers, and the core particles and cellulose nanofibers were bonded, indicating that composite particles 1 in an inseparable state were obtained.
Furthermore, when the dry powder was embedded in resin and the cross section was observed under SEM, the cellulose nanofiber layer was found to be approximately 10 nm thick.

(Preparation of Wet Gel)
500 g of 0.9% by mass saline (physiological saline) was placed in a beaker and stirred while 5.0 g of dry powder was added while taking care not to cause lumps. The mixture was left to stand for 30 minutes with stirring until the dry powder was fully swollen, giving a swollen gel. The mixture was poured into a cotton bag, the top was tied with a rubber band, and the bag was dehydrated for 1 minute using a dehydrator to collect the wet gel. The particle size of the resulting wet gel was measured using a particle size analyzer (SALD-200VER), and was found to be similar to that before drying.

(Evaluation of water absorption)
500 g of 0.9% by mass saline (physiological saline) was placed in a beaker and stirred, while 5.0 g of the dry powder was added while taking care not to cause lumps. The mixture was left to stand for 30 minutes while stirring, and the dry powder was allowed to fully swell to obtain a swollen gel.
The mixture was poured into a cotton bag, the top of which was tied with a rubber band, and the bag was dehydrated for 1 minute using a dehydrator. The mass of the cotton bag containing the swollen gel after dehydration was measured. The same procedure was repeated without adding dry powder, and the mass of the cotton bag after wetting was measured. The mass of the swollen gel was calculated using the following formula, and the amount of water absorbed per gram of dry powder was calculated.
Water absorption amount = (mass of cotton bag containing swollen gel - mass of cotton bag without swollen gel) / mass of dry powder

(Evaluation of restoration rate)
A 20 μm flat compression terminal was used in the micro compression tester MCT-510, the swollen gel was spread on the sample stage, and a load-unloading test was performed in the load-unloading test mode under conditions of a minimum test force of 0.01 mN to a maximum test force of 0.5 mN, a load speed of 0.045 mN/s, and a holding time of 0 seconds. N=10 was used to calculate the average recovery rate, which was high at 20% or more.

(Evaluation of Water Dispersibility)
When the wet gel was added to pure water at a concentration of 10% by mass and redispersed by stirring with a stirrer for 24 hours, it was easily redispersed and no aggregation was observed with the naked eye. When the particle size was evaluated using a particle size distribution meter, there was no signal indicating aggregation in the data from the particle size distribution meter.

(Evaluation of Oil Dispersibility)
The swollen gel obtained by absorbing water into the dry powder in the same manner as in the evaluation of water absorption capacity was added to mineral oil at a concentration of 10% by mass and dispersed by stirring with a stirrer for 24 hours. The gel was easily redispersed and no aggregation was observed visually. In addition, when the particle size was evaluated using a particle size distribution meter, the average particle size was about the same as before drying, and there was no signal indicating aggregation in the particle size distribution meter data. From the above, it was shown that the composite particle 1 was obtained as a powder without forming a film by drying, even though its surface was covered with cellulose nanofibers, and that it also had good redispersibility.

(Evaluation of Usability)
The swollen gel was added to mineral oil at a concentration of 10% by mass and stirred with a stirrer for 24 hours to form a dispersion, which when applied to the skin, had good affinity with the skin and a smooth feel when used.
(Evaluation of Moisture Retention)
The swollen gel was added to mineral oil at a concentration of 10% by mass and stirred with a stirrer for 24 hours to form a dispersion, which was then applied to the inside of the lower arm of a subject (a woman in her 30s) in a room with an air temperature of 20°C and a humidity of 40% RH. Specifically, 0.2 g of the dispersion was spread with the fingers in a circle with a diameter of about 5 cm. 30 minutes after application, the moisture content of the skin at the site of application of the dry powder was measured using a moisture checker MY-707S (Scalar Corporation), and the moisture content was maintained at a high level of 60% or more.

Example 2
Composite particles 1 were obtained under the same conditions as in Example 1, except that in the second step of Example 1, dimethylacrylamide (DMAA) was used instead of HEAA, which is a polymerizable monomer.
Example 3
Composite particles 1 were obtained under the same conditions as in Example 1, except that in the second step of Example 1, acryloylmorpholine (ACMO) was used instead of HEAA, which is a polymerizable monomer.

Example 4
Composite particles 1 were obtained under the same conditions as in Example 1, except that in the second step of Example 1, a neutralized product of acrylic acid (AA) was used instead of HEAA, which is a polymerizable monomer, and further, ethylene glycol diglycidyl ether was used as a crosslinking agent.
Example 5
Composite particles 1 were obtained under the same conditions as in Example 1, except that in the second step of Example 1, PVA (PVA-117 manufactured by Kuraray Co., Ltd., average polymerization degree 1,700, saponification degree 99.0 mol%) was used instead of HEAA as a polymerizable monomer, and a methyl vinyl ether-maleic anhydride copolymer (GANTREZ AN119 manufactured by International Specialty Products, average molecular weight 130,000) was used as a crosslinking agent instead of VA-044 as a polymerization initiator.

Example 6
Composite particle 1 was prepared under the same conditions as in Example 1, except that in Example 1, a carboxymethylated CNF dispersion obtained by performing a carboxymethylation (hereinafter also referred to as CM) treatment according to Patent Document 2, which is cited as a prior art document, was used instead of TEMPO oxidation.
Example 7
Composite particle 1 was prepared under the same conditions as in Example 1, except that in Example 1, a phosphated CNF dispersion obtained by performing a phosphate esterification treatment according to Non-Patent Document 1, which is listed as a prior art document, was used instead of TEMPO oxidation.

Example 8
Composite particle 1 was produced under the same conditions as in Example 1, except that trihexyltetradecylphosphonium chloride (Hex3TDP+Cl-) was used instead of polyethylene glycol amine as a compound for introducing a modifying group, and butyl acetate was used instead of toluene as a solvent.

<Example 9>
In Example 1, instead of TEMPO-oxidized CNF, fine fibers 3 were prepared by the following method. N,N-dimethylformamide (DMF) and dimethylacetamide (DMA) were added to the dried pulp and mixed uniformly, then 1,2-epoxydecane was added, and the mixture was sealed and left to react at 90°C for 24 hours. After the reaction, the mixture was neutralized with acetic acid, thoroughly washed with a mixed solvent of DMF and water/isopropyl alcohol to remove impurities, and further vacuum dried overnight at 50°C to obtain cellulose with a modified group introduced therein. 0.2 g of the obtained modified cellulose was dispersed in 99.8 g of water and subjected to a micronization treatment in a juicer mixer for 30 minutes to obtain a dispersion of cellulose nanofibers with a concentration of 0.2% by mass. Composite particles 1 were prepared in the same manner as in Example 1 except for the above.

Example 10
Composite particles 1 were obtained in the same manner as in Example 9, except that stearyl glycidyl ether was used instead of 1,2-epoxydecane.
Example 11
Composite particles 1 were obtained under the same conditions as in Example 9, except that a purified chitin/chitosan raw material was used instead of pulp in Example 9, and a dispersion of fine fibers 3 was obtained in the same manner as in Example 9.

<Comparative Example 1>
The same procedure as in Example 1 was repeated, except that the second and third steps were not carried out and the particles were produced by spray drying.
<Comparative Example 2>
The same procedure as in Example 1 was repeated except that sorbitan monostearate, an oil-soluble surfactant, was used instead of the TEMPO-oxidized CNF dispersion.

<Comparative Example 3>
The same procedures as in Example 1 were carried out except that polyoxyethylene sorbitan tristearate, an oil-soluble surfactant, was used instead of the TEMPO-oxidized CNF dispersion.
<Comparative Example 4>
The same procedure as in Example 5 was repeated except that, in place of the TEMPO-oxidized CNF dispersion, sorbitan monostearate, an oil-soluble surfactant, was used.

<Comparative Example 5>
Various evaluations were carried out in the same manner as in Example 1 for a mixed dry powder (conventional polymer particles) of commercially available styrene-divinylbenzene copolymer microbeads (particle diameter 4.5 μm, Techno Chemical) and spherical silver particles (particle diameter 10 nm, Sigma-Aldrich).
<Comparative Example 6>
The same conditions as in Example 1 were used except that divinylbenzene (DVB) was used instead of HEAA.
<Comparative Example 7>
The same conditions as in Example 1 were used except that the conversion of TEMPO-oxidized CNF to a carboxylic acid type and the solvent replacement were not performed, an aqueous dispersion of TEMPO-oxidized CNF was used, and divinylbenzene (DVB) was used instead of HEAA.

<Evaluation method>
(Evaluation of water absorption)
500 g of 0.9% by mass saline (physiological saline) was put into a beaker and stirred, while adding 5.0 g of dry powder while preventing the formation of lumps. The mixture was left for 24 hours with stirring to allow the dry powder to swell sufficiently to obtain a swollen gel. The mixture was poured into a cotton bag, the top was tied with a rubber band, and the mixture was dehydrated for 1 minute using a dehydrator, and the mass of the cotton bag containing the swollen gel after dehydration was measured. The same operation was performed without adding the dry powder, and the mass of the cotton bag after wetting was measured, and the mass of the swollen gel was obtained by the following calculation, and the water absorption per 1 g of dry powder was calculated.
Water absorption amount=(mass of cotton bag containing swollen gel−mass of cotton bag without swollen gel−mass of dry powder)/mass of dry powder. ◯: Water absorption amount was 30 g or more.
Δ: The amount of water absorbed was 20 g or more and less than 30 g.
×: The amount of water absorbed was less than 20 g.
It was judged as such.

(Evaluation of restoration rate)
A 20 μm flat compression terminal was used in the micro compression tester MCT-510, the swollen gel was spread on the sample stage, and a load-unloading test was performed in the load-unloading test mode under the conditions of a minimum test force of 0.01 mN to a maximum test force of 0.5 mN, a load speed of 0.045 mN/s, and a holding time of 0 seconds. N=10 was performed, and the average value of the recovery rate was calculated.
A: The recovery rate was 20% or more.
×: The recovery rate was less than 20%.

(Evaluation of Water Dispersibility)
The dry powder was added to pure water at a concentration of 10% by mass, and redispersed by stirring with a stirrer for 24 hours, and the presence or absence of aggregation was confirmed visually.
A: No aggregates were observed by visual inspection.
x: Aggregates were visually observed.
It was judged as such.

(Evaluation of Oil Dispersibility)
A swollen gel obtained by absorbing water into a dry powder in the same manner as in the evaluation of water absorption capacity was added to mineral oil at a concentration of 10% by mass, and the mixture was dispersed by stirring with a stirrer for 24 hours, and the presence of aggregation was visually confirmed.
◯: No aggregates were observed by visual inspection.
x: Aggregates were visually observed.
It was judged as such.

(Evaluation of skin compatibility)
The swollen gel was added to mineral oil at a concentration of 10% by mass and stirred with a stirrer for 24 hours to obtain a dispersion. In a room with a temperature of 20°C and a humidity of 40% RH, the dispersion in oil was applied to the inside of the lower arm of a subject (a woman in her 30s). Specifically, 0.2 g of each dispersion was spread with a finger in a circle with a diameter of about 5 cm. The feeling of use when applied to the skin was evaluated as follows.
Good: Good compatibility with skin and little irritation to skin.
×: Not compatible with the skin, causing skin irritation.
It was judged as such.

(Evaluation of Moisture Retention)
The swollen gel was added to mineral oil at a concentration of 10% by mass and stirred with a stirrer for 24 hours to form a dispersion, which was then applied to the inside of the lower arm of a subject (a woman in her 30s) in a room with an air temperature of 20°C and a humidity of 40% RH. Specifically, 0.2 g of the dispersion was spread with the fingers in a circle with a diameter of about 5 cm. After 30 minutes had passed since application, the moisture content of the skin at the site where the dry powder was applied was measured using a moisture checker MY-707S (Scalar Corporation) and was judged as follows.
A: The moisture content was 60% or more.
×: The moisture content was less than 60%.
It was judged as such.

The evaluation results using the above examples and comparative examples are summarized in Table 2 below. The emulsion stabilizer in Table 2 is fine fiber 3 or an emulsion stabilizer used in place of fine fiber 3. Core particle 2 is shown. Composite particle 1 was produced using the manufacturing method shown in Figure 2.

When the dried powders obtained in Examples 1 to 11 were observed under an SEM and in cross section, it was found that regardless of the type of fine fiber (TEMPO-oxidized CNF, CM-modified CNF, phosphate-esterified CNF, chitin NF), spherical composite particles 1 coated with fine fibers 3 could be produced using polymers of various monomers and various polymers.
The water absorption amount of each of the samples from Example 1 to Example 11 was measured, and it was found that the samples had high water absorption and were able to obtain wet gels. The obtained wet gels were not destroyed in a compression test and showed a high recovery rate.
All of the composite particles 1 obtained in Examples 1 to 11 had good redispersibility when the dry powder obtained by drying was added to water to absorb the water and obtain a wet gel. Furthermore, the wet gel also had good dispersibility in oil. In addition, since the fine fibers 3 were coated, the composite particles 1 showed excellent compatibility with the skin and moisture retention.

On the other hand, in Comparative Example 1, no spherical particles were obtained and sufficient water absorbency was not exhibited. Redispersibility in water and oil were good, and moisturizing properties were also confirmed, but since the particles were not spherical, the feeling when used was not good.
In Comparative Examples 2 to 4, no coating of the fine fibers 3 was observed, and no spherical particles with a uniform particle size were obtained. Although high water absorption was observed, the strength of the wet gel was low and the recovery rate was low. Redispersibility in water was good, but dispersibility in oil was not good. In addition, the particle size distribution was wide and non-spherical particles were included, so the feeling of use was not very good, but moisturizing properties were confirmed.

In Comparative Example 5, even when wetted, water absorption was not exhibited and the recovery rate was low. Water dispersibility was not good, but oil dispersibility was good. Although it had a smooth feel when used, it did not exhibit moisturizing properties.
In Comparative Example 6, a stable emulsion was not formed, and spherical particles were not obtained. In addition, sufficient water absorption was not exhibited, and the water dispersibility and oil dispersibility were not good. The moisturizing property was also not good, and the feeling of use was not good.
In Comparative Example 7, spherical particles coated with fine fibers 3 were obtained, and the particles had excellent redispersibility in water, oil dispersibility, usability, and moisture retention, but did not exhibit water absorbency. In the load-unloading test, the particles were not easily compressed, and therefore the recovery rate was high.

The composite particle 1 according to the present invention is used in the fields of sanitary products, such as disposable diapers; in the fields of agriculture and horticulture, as soil water-retaining materials, seedling sheets, seed coatings, disintegration aids for pesticides, liquid seeding, and culture media for mushrooms; in the fields of food and distribution, as freshness-preserving materials, drip absorption materials, and food dehydration; in the fields of civil engineering and construction, as condensation prevention materials, water-retaining agents for spraying on slopes, as anti-lost circulation materials, and as sealing materials; and in the fields of personal care products and toiletry products, as gel air fresheners, sweat pads, disposable hand warmers, ice packs, and deodorants. It can be used in skin care products such as antiperspirants, portable toilets, cleansing agents, lotions, milky lotions, and packs; in the medical product field, wound protection dressings and poultices; in the electrical and electronic materials field, inkjet recording paper, water-stopping materials for communication cables, alkaline batteries, lead-acid batteries, etc.; in the paint and adhesive field, water-wet paints, water-swelling paints, anti-fouling paints for ship bottoms, emulsion paints, and other applications such as removing water from oil, water-swelling toys, gasket packing, and fire extinguishing water.

When the composite particle 1 according to the present invention is used in a personal care product, it can be used, for example, in hair care, oral care, odor care, body care, skin care, and makeup-related products. Specifically, it can be used in toothpaste, perfume, nail lacquer, beauty serum, skin lotion, milky lotion, cleansing agent, eye shadow, eyeliner, foundation, blush, hair gel, hair spray, shampoo, conditioner, hair growth agent, lotion, cream, soap, etc.

1 Composite particle 2 Core particle 3 Fine fiber 4 Droplet 5 Solvent

Claims (13)

A core particle having at least a hydrophilic polymer;
The core particles have fine fibers inseparably bonded thereto and covering the surfaces of the core particles,
The composite particle is characterized in that the fine fibers are made of chitin nanofibers . A core particle having at least a hydrophilic polymer;
The core particles have fine fibers inseparably bonded thereto and covering the surfaces of the core particles,
The composite particles are characterized in that the fine fibers contain both cellulose nanofibers and chitin nanofibers. A core particle having at least a hydrophilic polymer;
The core particles have fine fibers inseparably bonded thereto and covering the surfaces of the core particles,
The fine fibers are made of at least one of cellulose nanofibers and chitin nanofibers,
The composite particle , wherein the hydrophilic polymer is hydroxyethylacrylamide, dimethylacrylamide, acryloylmorpholine, acrylic acid, or polyvinyl alcohol . 3. The composite particle according to claim 1, wherein the hydrophilic polymer contains a polymer containing at least any one of a carboxyl group, an aldehyde group, a hydroxyl group, an amino group, an amide group, and a sulfone group. The composite particle according to claim 1 , wherein the composite particle has a water absorption per unit mass of a dry powder of 10 g/g or more. The composite particle according to any one of claims 1 to 5 , wherein the average recovery rate of the wet gel after unloading at a minimum test force of 0.01 mN to a maximum test force of 0.5 mN and a speed of 0.045 mN/s is 20% or more. 7. The composite particle according to claim 1, wherein the core particle contains at least one of an ultraviolet absorbing agent, an ultraviolet scattering agent, a fragrance, a deodorant component, a whitening component, an anti-inflammatory component, a peeling agent, and a colorant. The composite particle according to claim 1 , wherein the fine fibers have a modifying group. The composite particle according to claim 8 , wherein the modifying group is a hydrocarbon chain having at least one substituent. 10. The composite particle according to claim 8 , wherein the modifying group is introduced by an ionic bond, an amide bond, an ether bond, an ester bond or a urethane bond. A step of dispersing fine fibers, which are at least one of cellulose nanofibers and chitin nanofibers, in a hydrophobic solvent to obtain a hydrophobic solvent dispersion of the fine fibers;
a step of dispersing droplets containing core particle precursors in the hydrophobic solvent dispersion and coating surfaces of the droplets with the fine fibers;
a step of solidifying the core particle precursor inside the droplets to obtain a dispersion of composite particles in which the surfaces of the core particles are covered with the fine fibers;
purifying the composite particles;
A method for producing composite particles, comprising: The method for producing composite particles according to claim 11 , wherein at least one of a polymerizable monomer, a dissolved polymer, and a molten polymer is used as the core particle precursor. A personal care product comprising the composite particles according to any one of claims 1 to 10 .

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