Nanofiber, additive for dermatological preparation, dermatological preparation, and method for producing nanofiber

Abstract

This nanofiber comprises anion group-modified paramylon. The anion group-modified paramylon has an anion group substitution degree of 0.016-0.040 per glucose unit.

Description

Nanofiber, additive for topical skin preparation, topical skin preparation, and method for producing nanofiber

[0001] The present invention relates to a nanofiber, an additive for an external skin preparation, an external skin preparation, and a method for producing the nanofiber.

[0002] In recent years, the development of nanofibers has been actively pursued. Known raw materials for nanofibers include carbon, thermoplastic resins, and polysaccharides. Nanofibers made from polysaccharides as starting materials have been developed, including cellulose nanofibers made from cellulose, a β-1,4-glucan, and paramylon nanofibers made from paramylon, a β-1,3-glucan (see Patent Documents 1 and 2).

[0003] Nanofibers made from these polysaccharides are being considered for use in the health food industry and as thickeners.

[0004] JP 2011-184816 A JP 2014-095159 A

[0005] However, conventional nanofibers made from polysaccharides have room for improvement in viscosity and transparency.

[0006] Therefore, an object of the present invention is to provide nanofibers that have excellent viscosity-increasing properties and transparency when used as a thickener.

[0007] The present invention provides the following [1] to

[13] . [1] A nanofiber made of anionic group-modified paramylon, wherein the degree of anionic group substitution per glucose unit of the anionic group-modified paramylon is 0.016 to 0.040. [2] The nanofiber according to [1], wherein the anionic group of the anionic group-modified paramylon is a carboxyalkyl group. [3] The nanofiber according to [1] or [2], wherein the crystallinity of the anionic group-modified paramylon is 10% to 43%. [4] The nanofiber according to any one of [1] to [3], wherein a 1% by mass aqueous dispersion of the nanofiber has a light transmittance at a wavelength of 660 nm of 10% or more. [5] The nanofiber according to any one of [1] to [4], wherein the average fiber diameter is 1 nm to 50 nm. [6] An additive for a topical skin preparation comprising the nanofiber according to any one of [1] to [5]. [7] A topical skin preparation containing the additive for a topical skin preparation according to [6]. [8] The topical skin preparation according to [7], which is for use in cosmetics or quasi-drugs. [9] A method for producing the nanofiber according to any one of [1] to [5], comprising a step of contacting paramylon with a basic aqueous solution and substituting anionic groups with an anionic modifier, wherein the molar ratio of the anionic modifier to the paramylon is 0.1 to 1.

[10] The production method according to [9], wherein the molar ratio of the base in the basic aqueous solution to the paramylon is 1 to 3.

[11] Use of the nanofiber according to any one of [1] to [5] for addition to a topical skin preparation (application).

[12] Use of the nanofiber according to any one of [1] to [5] as an additive for a topical skin preparation (application).

[13] Use of a composition containing the nanofiber according to any one of [1] to [5] as a topical skin preparation (application).

[0008] According to the present invention, nanofibers are provided that, when used as a thickener, have excellent thickening properties and transparency.

[0009] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0010] The nanofiber according to the embodiment is a nanofiber made of anionic group-modified paramylon, and the degree of anionic group substitution per glucose unit of the anionic group-modified paramylon is 0.016 or more and 0.040 or less.

[0011] Paramylon is a polysaccharide (β-1,3-glucan) produced as an intracellular storage substance unique to Euglena (Euglena gracilis). Within Euglena cells, it exists as paramylon granules, which are aggregates of multiple glucan molecules (three chain-like β-1,3-glucans forming a right-handed triple helix structure) (see, for example, Food Sci Nutr. 2023;11:953-962).

[0012] β-1,3-glucan refers to a polysaccharide structure in which glucose is linked by β1,3 bonds, and paramylon is said to have approximately 2,000 glucose bonds.

[0013] The weight-average molecular weight of the paramylon that constitutes the nanofiber is 1 x 10 ４ ~2 x 10 ７ , 1 x 10 ５ ~2 x 10 ７ or 5 x 10 ５ ~2 x 10 ７ This weight-average molecular weight is the value for the entire trimeric β-1,3-glucan that forms the triple helix structure of paramylon. The weight-average molecular weight of paramylon can be measured by size exclusion chromatography.

[0014] When the weight average molecular weight of paramylon is within the above range, the viscosity of the nanofiber can be improved.

[0015] Nanofibers made of paramylon can be obtained, for example, by the following method. Specifically, by contacting paramylon isolated and purified from Euglena with a basic aqueous solution, the molecules that form the triple helix structure of paramylon are dissociated, yielding single-stranded β-1,3-glucan. By mixing this single-stranded β-1,3-glucan with neutral water, the β-1,3-glucan reforms the triple helix structure to form a single fiber, and multiple single fibers then associate to obtain nanofibers made of multiple single fibers.

[0016] Anionic group-modified paramylon can be obtained by modifying paramylon by introducing anionic groups using an anionic modifier. Examples of anionic modifiers include monochloroacetic acid and succinic anhydride. Examples of anionic groups include carboxyalkyl groups such as carboxymethyl and carboxyethyl groups, carboxy groups, phosphate ester groups, phosphite ester groups, and sulfate ester groups. When the anionic groups of the anionic group-modified paramylon are carboxyalkyl groups, the viscosity and transparency of the nanofibers can be improved.

[0017] The degree of anionic group substitution per glucose unit of anionic group-modified paramylon can be determined by conductometric titration. For example, the degree of carboxymethyl group substitution of carboxymethyl-modified paramylon nanofibers can be determined as follows. Approximately 0.5 g (w) of carboxymethyl-modified paramylon nanofibers is precisely weighed, added to 300 mL of ion-exchanged water, and thoroughly stirred. The pH is then adjusted with 0.1 mol / L aqueous hydrochloric acid to obtain a nanofiber dispersion with a pH of 3.2. This nanofiber dispersion is then subjected to conductometric titration using a conductivity meter (manufactured by Horiba, Ltd., model number: F-2000C), a low conductivity cell (manufactured by Horiba, Ltd., model number: 3551-10D, immersion type), and a 0.01 mol / L aqueous sodium hydroxide solution. As sodium hydroxide is added, the electrical conductivity decreases once, then becomes constant at a sodium hydroxide addition volume of V1 mL, and then increases from a sodium hydroxide addition volume of V2 mL. From the titration results, the degree of carboxymethyl group substitution of carboxymethyl-modified paramylon nanofiber can be calculated using the following formula: Degree of carboxymethyl group substitution = 162.16 x [(V2 - V1) x 0.01 x 0.001] / [w - 58 x (V2 - V1) x 0.01 x 0.001]

[0018] The degree of anionic group substitution per glucose unit of the anionic group-modified paramylon is 0.016 to 0.040. This degree of anionic group substitution may be 0.018 or more or 0.02 or more, and may be 0.036 or less, 0.032 or less, or 0.028 or less. Alternatively, it may be 0.016 to 0.036, 0.016 to 0.032, 0.016 to 0.028, 0.018 to 0.040, 0.018 to 0.036, 0.018 to 0.032, 0.016 to 0.028, 0.02 to 0.040, 0.02 to 0.036, 0.02 to 0.032, or 0.02 to 0.028.

[0019] When the degree of anionic group substitution per glucose unit of the anionic group-modified paramylon is within the above range, the viscosity and transparency of the nanofiber can be improved.

[0020] The crystallinity of the anionic group-modified paramylon may be 10% or more, 15% or more, or 20% or more, or 43% or less, 41% or less, or 39% or less, or 10% to 43%, 10% to 41%, 10% to 39%, 15% to 43%, 15% to 41%, 15% to 39%, 20% to 43%, 20% to 41%, or 20% to 39%.

[0021] When the crystallinity of the anionic group-modified paramylon is within the above-mentioned range, the resulting coating has high mechanical strength and excellent chemical resistance when used as a thickener, while also exhibiting excellent transparency and thickening properties.

[0022] The degree of crystallinity can be calculated from an X-ray diffraction spectrum measured with an X-ray diffractometer. For example, the degree of crystallinity of carboxymethyl-modified paramylon nanofibers can be calculated by the following procedure. An X-ray diffraction spectrum of the nanofibers is obtained using an X-ray diffractometer (e.g., Smart Lab, manufactured by Rigaku Corporation) with CuKα as the X-ray source. Then, using the diffraction intensity at 2θ = 10° to 40° in the X-ray diffraction spectrum as the baseline, the diffraction integrated intensity of the amorphous portion at 2θ = 22° [I (amorphous)] and the diffraction integrated intensity of the other crystalline portions [I (crystal)] are determined, and the degree of crystallinity can be calculated using the following formula: Crystallinity (%) = I (crystal) / [I (amorphous) + I (crystal)] × 100

[0023] The light transmittance at a wavelength of 660 nm of a 1% by mass aqueous dispersion of the nanofibers may be 10% or more. This light transmittance may be 15% or more, 20% or more, 25% or more, or 30% or more, and may be 100% or less or 99% or less. Alternatively, it may be 10% to 100%, 10% to 99%, 15% to 100%, 15% to 99%, 20% to 100%, 20% to 99%, 25% to 100%, 25% to 99%, 30% to 100%, or 30% to 99%.

[0024] A 1% by mass aqueous dispersion of nanofibers is a liquid in which nanofibers are dispersed in water so that the amount of nanofibers is 1% by mass. When the 1% by mass aqueous dispersion of nanofibers has a light transmittance at a wavelength of 660 nm of the above-mentioned value, the transparency of the nanofibers can be made even better.

[0025] The light transmittance at a wavelength of 660 nm can be measured using a spectrophotometer (for example, UV-3600 manufactured by Shimadzu Corporation) with a cell optical path length of 1 cm and a measurement temperature of 25°C.

[0026] The average fiber diameter of the nanofibers may be 1 nm or more, 1.2 nm or more, or 1.5 nm or more, or 50 nm or less, 40 nm or less, or 30 nm or less, or 1 nm to 50 nm, 1 nm to 40 nm, 1 nm to 30 nm, 1.2 nm to 50 nm, 1.2 nm to 40 nm, 1.2 nm to 30 nm, 1.5 nm to 50 nm, 1.5 nm to 40 nm, or 1.5 nm to 30 nm.

[0027] When the average fiber diameter of the nanofibers is within the above range, the viscosity increasing property and transparency of the nanofibers can be improved.

[0028] The average fiber diameter of the nanofibers can be determined by small-angle X-ray scattering measurement. For example, the average fiber diameter of the carboxymethyl-modified paramylon nanofibers can be calculated from the scattering profile of the nanofibers obtained by performing small-angle X-ray scattering measurement of the carboxymethyl-modified paramylon nanofibers in the region of 2θ = 0.018° to 5.000° (q = 0.013 to 0.356) using an X-ray diffractometer (e.g., Smart Lab, manufactured by Rigaku Corporation) and subtracting the scattering profile of water as the background.

[0029] The viscosity of a 2 mass% aqueous dispersion of the nanofibers may be 35,000 mPa·s or more, 45,000 mPa·s or more, 55,000 mPa·s or more, or 60,000 mPa·s or more, and may be 100,000 mPa·s or less, 95,000 mPa·s or 90,000 mPa·s or less. Alternatively, the viscosity may be 35,000 mPa·s to 100,000 mPa·s, 35,000 mPa·s to 95,000 mPa·s, 35,000 mPa·s to 90,000 mPa·s, 45,000 mPa·s to 100,000 mPa·s, 45,000 mPa·s to 95,000 mPa·s, 45,000 mPa·s to 90,000 mPa·s, 55 The viscosity may be 50,000 mPa·s to 100,000 mPa·s, 55,000 mPa·s to 95,000 mPa·s, 55,000 mPa·s to 90,000 mPa·s, 60,000 mPa·s to 100,000 mPa·s, 60,000 mPa·s to 95,000 mPa·s, or 60,000 mPa·s to 90,000 mPa·s. The viscosity is measured using a Brookfield viscometer at 25°C with a No. 4 rotor at a rotation speed of 6 rpm.

[0030] When the viscosity of a 2 mass % aqueous dispersion of nanofibers is within the above range, the thickening properties of the nanofibers when used as a thickener can be made even better.

[0031] The above-described nanofibers can be added to topical skin preparations. That is, the nanofibers can be used as additives for topical skin preparations. Examples of additives for topical skin preparations include thickeners. When used as a thickener, the nanofibers according to this embodiment exhibit excellent viscosity and transparency. Note that topical skin preparations refer to compositions that are applied to the skin, and include cosmetics, fragrances, pharmaceuticals, and quasi-drugs. As topical skin preparations, cosmetics or quasi-drugs are preferred. As cosmetics, sunscreens are included.

[0032] The topical skin preparation contains ingredients that topical skin preparations typically contain depending on the type of topical skin preparation, and in addition to these ingredients, it will contain nanofibers.

[0033] Examples of ingredients typically contained in topical skin preparations include aqueous components, oily components, surfactants, moisturizers, thickeners, powder components, preservatives, antioxidants, chelating agents, fragrances, and solvents.

[0034] Examples of aqueous media include water (distilled water, purified water, hot spring water, deep sea water, etc.), water-soluble solvents, and mixtures thereof.

[0035] Examples of oily components include fats and oils, waxes, hydrocarbon oils, vegetable oils, ester oils, higher alcohols, higher fatty acids, silicone oils, and oil-soluble ultraviolet absorbers. Examples of oil-based components other than oil-soluble UV absorbers include liquid oils and fats such as linseed oil, camellia oil, macadamia nut oil, corn oil, olive oil, avocado oil, camellia oil, castor oil, safflower oil, apricot kernel oil, cinnamon oil, jojoba oil, grape oil, almond oil, rapeseed oil, sesame oil, sunflower oil, wheat germ oil, rice germ oil, rice bran oil, cottonseed oil, soybean oil, peanut oil, tea seed oil, evening primrose oil, egg yolk oil, cod liver oil, triglycerin, glyceryl trioctanoate, and glyceryl triisopalmitate; octanoic acid esters such as cetyl octanoate, isooctanoic acid esters such as glyceryl tri-2-ethylhexanoate and pentaerythritol tetra-2-ethylhexanoate, lauric acid esters such as hexyl laurate, and myristates such as isopropyl myristate and octyldodecyl myristate. acid esters, palmitic acid esters such as octyl palmitate, stearic acid esters such as isocetyl stearate, isostearic acid esters such as isopropyl isostearate, isopalmitic acid esters such as octyl isopalmitate, oleic acid esters such as isodecyl oleate, adipic acid diesters such as diisopropyl adipate, sebacate diesters such as diethyl sebacate, ester oils such as diisostearyl malate and macadamia nut fatty acid phytosteryl; hydrocarbon oils such as liquid paraffin, isododecane, and squalane; silicone oils such as methylpolysiloxane (e.g., dimethicone), methylphenylpolysiloxane, methylhydrogenpolysiloxane, and methylcyclopolysiloxane (e.g., cyclopentasiloxane).The oil-soluble UV absorber is not particularly limited, but specific examples include organic UV absorbers such as ethylhexyl methoxycinnamate, octocrylene, dimethicodiethyl benzalmalonate, polysilicon-15, t-butyl methoxydibenzoylmethane, ethylhexyl triazone, diethylamino hydroxybenzoyl hexyl benzoate, bisethylhexyloxyphenol methoxyphenyl triazine, oxybenzone-3, methylene bisbenzotriazolyl tetramethylbutylphenol, phenylbenzimidazole sulfonic acid, homosalate, and ethylhexyl salicylate. The oil component can be used alone or in combination of two or more.

[0036] Examples of surfactants include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, and silicone surfactants. Surfactants can be used singly or in combination of two or more. Examples of nonionic surfactants include polyglyceryl-5 stearate and polyglyceryl stearate. Examples of silicone surfactants include polyoxyalkylene-modified silicone, polyoxyalkylene / alkyl-co-modified silicone, polyglycerin-modified silicone, and polyglycerin / alkyl-co-modified silicone.

[0037] Examples of moisturizing agents include saturated monohydric alcohols having from 1 to 3 carbon atoms, such as ethanol and isopropyl alcohol, polyhydric alcohols, such as 1,3-butylene glycol, dipropylene glycol, glycerin, 1,2-pentanediol, 1,2-propanediol, 1,3-propanediol, isoprene glycol, polyglycerin, sorbitol, and mannitol, and sodium hyaluronate. These moisturizing agents can be used alone or in combination of two or more.

[0038] Examples of thickeners that can be used include polysaccharide thickeners, organic clay minerals, acrylic acid amide copolymers, polyacrylic acid-based water-soluble polymers, cellulose-based thickeners, and other thickeners. The water-soluble thickeners can be used alone or in combination of two or more. Examples of polysaccharide thickeners include pectin, guar gum, xanthan gum, carrageenan, gellan gum, gum arabic, and locust bean gum. Examples of clay minerals include magnesium aluminum silicate, magnesium sodium silicate, bentonite, aluminum silicate, and sodium silicate. Examples of organic clay minerals include dimethyl distearammonium hectorite, dimethyl alkyl ammonium hectorite, benzyl dimethyl stearyl ammonium hectorite, and magnesium aluminum silicate treated with distearyl dimethyl ammonium chloride. Examples of acrylic acid amide copolymers include polyacrylamide, (hydroxyethyl acrylate / sodium acryloyldimethyltaurate) copolymer, (sodium acrylate / sodium acryloyldimethyltaurate) copolymer, (ammonium acryloyldimethyltaurate / VP) copolymer, (ammonium acryloyldimethyltaurate / beheneth-25 methacrylate) crosspolymer, polyacrylate crosspolymer-11, and sodium polyacryloyldimethyltaurate. Examples of polyacrylic acid-based water-soluble polymers include acrylic acid-based polymers such as polyacrylic acid, carboxyvinyl polymer, alkyl-modified carboxyvinyl polymer, polyacrylic acid amide, and acrylamide / acrylic acid copolymer. These acrylic acid-based polymers are typically neutralized with sodium hydroxide, potassium hydroxide, triethanolamine, triethylamine, basic amino acids such as lysine and arginine, or the like. Examples of cellulose-based thickeners include methylcellulose, ethylcellulose, carboxymethylcellulose, cellulose gum (sodium carboxymethylcellulose), hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethylcellulose, crystalline cellulose, and cellulose nanofiber. Other thickeners include chitin nanofiber and paramylon nanofiber.

[0039] The powder component may be a known powder used in cosmetics, such as an extender powder or a color pigment. The powder component may be used alone or in combination of two or more. Examples of the powder component include ultraviolet scattering agents such as fine particle titanium oxide and fine particle zinc oxide. While both untreated and hydrophobically treated ultraviolet scattering agents can be used as the ultraviolet scattering agent, ultraviolet scattering agents that have been hydrophobically treated with a surface treatment agent are preferred. Examples of surface treatment agents that can be used include those commonly used in the cosmetic field, such as dimethicone, silicones such as alkyl-modified silicone, alkoxysilanes such as octyltriethoxysilane, dextrin fatty acid esters such as dextrin palmitate, fatty acids such as stearic acid, metal soaps such as aluminum stearate, and amino acids such as N-acylglutamic acid.

[0040] Examples of color pigments, which are powder components, include red iron oxide, yellow iron oxide, black iron oxide, cobalt oxide, chromium oxide, ultramarine, Prussian blue, titanium oxide, zinc oxide, pearl pigments, organic pigments, natural dyes (carmine, safflower, etc.), etc. The color pigments can be used alone or in combination of two or more.

[0041] As the preservative, known preservatives used in cosmetics such as caprylyl glycol and phenoxyethanol can be used. The preservatives can be used alone or in combination of two or more. Examples of the preservative include phenoxyethanol.

[0042] Examples of the solvent include 1,2-hexanediol, 1,2-pentanediol, 1,3-butylene glycol, 2-octyldodecanol, PEG-6, PEG-8, and diethylhexyl sebacate.

[0043] In addition to the above-mentioned ingredients, the topical skin preparation may contain, as needed, ingredients commonly used in quasi-drugs and cosmetics, such as whitening agents, alcohols, powder ingredients, aqueous surfactants, film-forming agents, etc. The topical skin preparation can be produced by a conventional method.

[0044] The quasi-drugs may be in the form of liquid, cream, spray, etc., and the cosmetics may be in the form of lotion, serum, cream, emulsion, etc.

[0045] Application to the skin can be carried out by methods commonly used for quasi-drugs or cosmetics, such as applying or spraying the product as a liquid onto the skin, or contacting the product with the skin in a state where it is impregnated into a nonwoven fabric or the like.

[0046] The nanofibers of this embodiment can be produced by a production method that includes a step of contacting paramylon with a basic aqueous solution and then substituting anionic groups with an anionic modifier, in which the molar ratio of the anionic modifier to the paramylon is 0.1 to 1.

[0047] Examples of basic aqueous solutions include aqueous solutions of alkali metal or alkaline earth metal hydroxides such as sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, and calcium hydroxide, or alkali metal or alkaline earth metal carbonates such as sodium carbonate, potassium carbonate, potassium bicarbonate, and sodium bicarbonate. The concentration of the basic aqueous solution may be 0.1 mol / L to 5 mol / L, 0.1 mol / L to 2 mol / L, 0.5 mol / L to 5 mol / L, or 0.5 mol / L to 2 mol / L. The pH of the basic aqueous solution may be 12 to 14, 12 to 13, or 13 to 14.

[0048] By contacting the above-mentioned basic aqueous solution with paramylon, the molecules that form the triple helix structure of paramylon dissociate, and single-stranded β-1,3-glucan can be obtained.

[0049] In the manufacturing method according to this embodiment, the paramylon that has been brought into contact with the basic aqueous solution may be prepared by the process described above, or it may be prepared by purchasing paramylon that has been brought into contact with the basic aqueous solution in advance to become single-stranded β-1,3-glucan.

[0050] An anion group-modified paramylon can be obtained by adding an anion modifier to a mixture of the single-stranded β-1,3-glucan paramylon and a basic aqueous solution, followed by heating to perform anion group substitution on the paramylon. The heating temperature may be 40°C to 70°C or 45°C to 65°C.

[0051] The amount of anionic modifier used may be adjusted as appropriate depending on the nanofiber production conditions, such as the type of anionic modifier. By producing nanofibers with a molar ratio of the anionic modifier to paramylon of 0.1 to 1, it is possible to achieve higher viscosity. The molar ratio of the anionic modifier to paramylon may also be 0.1 to 0.5, 0.1 to 0.3, 0.15 to 1, 0.15 to 0.5, or 0.15 to 0.3.

[0052] The amount of base in the basic aqueous solution may be adjusted as appropriate depending on the nanofiber production conditions, such as the type of base. The molar ratio of the amount of base in the basic aqueous solution to paramylon may be set to 1 to 3, 1 to 2, 1 to 1.8, 1.2 to 3, 1.2 to 2, or 1.2 to 1.8. By setting the amount of base in the basic aqueous solution to the paramylon at the above-mentioned value, anionic modification can be performed while preventing a decrease in the molecular weight of paramylon.

[0053] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0054] The following materials were prepared: Paramylon (manufactured by Eugleed Co., Ltd.) Purified water 1,3-butylene glycol (manufactured by Daicel Corporation) Phenoxyethanol (manufactured by Yokkaichi Chemical Industry Co., Ltd., product name: Phenoxyethanol-S) Aqueous dispersion of titanium oxide microparticles (manufactured by Sakai Chemical Industry Co., Ltd., product name: DIS-AB-10W, average particle size of titanium oxide: 15 nm, powder concentration: 50%) Aqueous dispersion of zinc oxide microparticles (manufactured by Sakai Chemical Industry Co., Ltd., product name: DIF-AB-33W, average particle size of zinc oxide: 35 nm, powder concentration: 60%)

[0055] The paramylon used in the examples was obtained from a resistant strain of Euglena (Euglena gracilis Z strain NIES48). The resistant strain has acquired tolerance to a culture medium with a high glucose concentration through the acclimation step. Therefore, even if Euglena is cultured in a culture medium with a high glucose concentration of more than 2% and not more than 8% during the growth step, the growth rate is not reduced or inhibited, and Euglena can be grown stably and efficiently. Therefore, paramylon can also be produced stably and efficiently.

[0056] [Preparation of Paramylon Nanofibers] (Example 1) 10 g of paramylon was added to 35.4 g of ion-exchanged water, and 7.6 g of 50% aqueous sodium hydroxide solution was added little by little while thoroughly stirring to obtain a paramylon nanofiber dispersion. 5.9 g of 20% aqueous monochloroacetic acid solution was added to the paramylon nanofiber dispersion, and the mixture was allowed to react at 60 °C for 1 hour and then cooled. 200 g of water was then added for dilution, and the pH was adjusted to 3 using sulfuric acid. Paramylon nanofibers were precipitated, and the mixture was centrifuged using a centrifuge (Beckman Coulter, Model: Avanti J-26S XPI), and the supernatant was removed. Ion-exchanged water was added to the obtained solid to make a volume of 800 mL, and the solid was then redispersed. This centrifugation and redispersion in water were repeated three times, and the slurry obtained by centrifugation was then freeze-dried to obtain a paramylon nanofiber powder. The amount (molar ratio) of monochloroacetic acid relative to paramylon and the amount (molar ratio) of sodium hydroxide relative to paramylon were as shown in Table 1.

[0057] (Example 2 and Comparative Example 1) Carboxymethyl-modified paramylon nanofibers were obtained in the same manner as in Example 1, except that the molar ratio of sodium hydroxide to paramylon and the molar ratio of monochloroacetic acid to paramylon were changed to the values ​​shown in Table 1 and the reaction temperature was changed to 50°C.

[0058] The degree of carboxymethyl group substitution per glucose unit of the obtained nanofibers was calculated using the following procedure. The results are shown in Table 1. <Method for calculating the degree of carboxymethyl group substitution> Approximately 0.5 g (w) of the obtained nanofiber powder was precisely weighed, added to 300 mL of ion-exchanged water, and thoroughly stirred. The pH was then adjusted with 0.1 mol / L aqueous hydrochloric acid to obtain a nanofiber dispersion with a pH of 3.2. This nanofiber dispersion was subjected to conductometric titration using an electrical conductivity meter (manufactured by HORIBA, Ltd., model number: F-2000C), a low electrical conductivity cell (manufactured by HORIBA, Ltd., model number: 3551-10D, immersion type), and 0.01 mol / L aqueous sodium hydroxide solution. As sodium hydroxide was added, the electrical conductivity decreased once, then reached a constant value when V1 mL of sodium hydroxide was added, and then increased when V2 mL of sodium hydroxide was added. From the titration results, the degree of carboxymethyl group substitution was calculated using the following formula. Degree of carboxymethyl group substitution = 162.16 × [(V2 - V1) × 0.01 × 0.001] / [w - 58 × (V2 - V1) × 0.01 × 0.001]

[0059] Comparative Raw Material Example 1 Carboxymethyl-modified cellulose nanofiber (manufactured by Nippon Paper Industries Co., Ltd., trade name: Cellenpia CS-01C) was prepared.

[0060] The obtained paramylon nanofibers and the prepared cellulose nanofibers were subjected to small-angle X-ray scattering measurements in the 2θ = 0.018° to 5.000° (q = 0.013 to 0.356) range using an X-ray diffractometer (e.g., Smart Lab, manufactured by Rigaku Corporation). The average fiber diameter of the nanofibers was calculated from the scattering profile of the nanofibers, with the scattering profile of water subtracted as the background. The results are shown in Table 1. <Measuring conditions for average fiber diameter> Measurement device: Smart Lab (manufactured by Rigaku Corporation) X-ray source: CuKα (X-ray wavelength: 1.5405 Å) Tube voltage: 45 kV Tube current: 200 mA Start angle: 2θ = 0.018° (q = 0.013) End angle: 2θ = 5.000° (q = 0.356) Sampling width: 0.005° Scan rate: 0.05° / min

[0061] X-ray diffraction was measured for the obtained paramylon nanofibers under the following measurement conditions, and the diffraction intensity at 2θ = 10° to 40° of the obtained X-ray diffraction spectrum was used as the baseline. The diffraction integrated intensity of the amorphous portion at 2θ = 22° [I (amorphous)] and the diffraction integrated intensity of the other crystalline portions [I (crystalline)] were determined, and the crystallinity was calculated using the following formula. The results are shown in Table 1. Crystallinity (%) = I (crystal) / [I (amorphous) + I (crystal)] × 100 <Conditions for measuring crystallinity> Measurement device: Smart Lab (manufactured by Rigaku Corporation) Operation axis: 2θ / θ X-ray source: CuKα (X-ray wavelength: 1.5405 Å) Measurement method: continuous Tube voltage: 45 kV Tube current: 200 mA Start angle: 2θ = 10° End angle: 2θ = 40° Sampling width: 0.020° Scan speed: 5.0° / min

[0062] A 2% by mass aqueous dispersion of each of the obtained paramylon nanofibers and the prepared cellulose nanofibers was prepared and filled into a glass container. The viscosity of each 2% by mass aqueous dispersion was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., model: BMII) under the following conditions: rotor: No. 4, rotation speed: 6 rpm, measurement time: 60 seconds, temperature: 25°C. The results are shown in Table 1.

[0063] Aqueous dispersions of 1% by mass of the resulting paramylon nanofibers and the prepared cellulose nanofibers were prepared, and the light transmittance (%) of these aqueous dispersions at a wavelength of 660 nm was measured under the following conditions. The results are shown in Table 1. <Conditions for measuring light transmittance> Measuring device: UV-3600 (Shimadzu Corporation) Optical path length of cell: 1 cm Measurement temperature: 25°C

[0064]

[0065] [Preparation of Thickeners] The thickeners of Example 3 and Comparative Example 2 were prepared according to the following procedure. The amounts of components in each thickener are shown in Table 2. The amount of purified water in Table 2 indicates the total amount of purified water used in preparing each thickener.

[0066] (Example 3) 0.8 g of the nanofiber powder obtained in Example 1 was mixed with 97.9 g of purified water, and then the mixture was stirred at 8,000 rpm for 10 minutes using a homomixer to obtain a nanofiber dispersion. 1.0 g of 1,3-butylene glycol and 0.3 g of phenoxyethanol were added to the obtained nanofiber dispersion, and the mixture was mixed uniformly to prepare a thickener.

[0067] Comparative Example 2 A thickener was prepared in the same manner as in Example 3, except that the types and amounts of the components used were changed as shown in Table 2.

[0068] [Evaluation Test] (pH Measurement) Using a pH meter (manufactured by Horiba Ltd., Model: F-72), the pH of each of the thickeners prepared in Example 3 and Comparative Example 2 was measured at 25° C. The results are shown in Table 2.

[0069] (Viscosity Measurement) The viscosity (mPa s) of each of the thickeners prepared in Example 3 and Comparative Example 2 was measured using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd., model: BMII) under the conditions of rotor: No. 4, rotation speed: 6 rpm, measurement time: 60 seconds, and temperature: 25° C. The results are shown in Table 2.

[0070] (Storage stability) Each of the thickeners prepared in Example 3 and Comparative Example 2 was filled into a glass vial and stored in an incubator. Accelerated testing was performed under the following conditions: 5°C for 3 months, 25°C for 3 months, 40°C for 3 months, and 50°C for 1 month. The state of the thickener after the accelerated testing was observed, and changes in appearance and viscosity were evaluated according to the following evaluation criteria. The results are shown in Table 2. <Evaluation criteria> A: Very good (little change in state compared to before the test) B: Good (slight change in state compared to before the test) C: Poor (significant change in state compared to before the test)

[0071]

[0072] [Preparation of Sunscreen Agents] The sunscreen agents of Examples 4 to 7 and Comparative Examples 3 to 5 were prepared according to the following procedure. The amounts of components in each sunscreen agent are shown in Tables 3 and 4. The amount of purified water in Tables 3 and 4 indicates the total amount of purified water used in preparing each sunscreen agent.

[0073] Example 4: 0.8 g of the nanofiber powder obtained in Example 1 was mixed with 77.9 g of purified water, and then the mixture was stirred at 8,000 rpm for 10 minutes using a homomixer to obtain a nanofiber dispersion. 20.0 g of an aqueous dispersion of titanium dioxide fine particles, 1.0 g of 1,3-butylene glycol, and 0.3 g of phenoxyethanol were added to the obtained nanofiber dispersion, and the mixture was mixed uniformly to prepare a sunscreen.

[0074] Examples 5 to 7 and Comparative Examples 3 to 5 Sunscreen agents were prepared in the same manner as in Example 4, except that the types and amounts of the components used were changed as shown in Tables 3 and 4.

[0075] [Evaluation Test] (pH Measurement) Using a pH meter (Model: F-72, manufactured by Horiba, Ltd.), the pH of each of the sunscreen agents prepared in Examples 4 to 7 and Comparative Examples 3 to 5 was measured at 25° C. The results are shown in Tables 3 and 4.

[0076] (Viscosity Measurement) The viscosity (mPa s) of each sunscreen agent prepared in Examples 4 to 7 and Comparative Examples 3 to 5 was measured using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd., model BMII) under the following conditions: rotor: No. 4, rotation speed: 6 rpm, measurement time: 60 seconds, and temperature: 25° C. The results are shown in Tables 3 and 4.

[0077] (Feeling of use (freshness)) Each of the sunscreens prepared in Examples 4 to 7 and Comparative Examples 3 to 5 was applied to the skin of 10 expert panels, and each expert panel evaluated the degree of freshness according to the following evaluation criteria. The results are shown in Tables 3 and 4. <Evaluation criteria> A: Very good (very excellent freshness), 9 or more panels rated it as good B: Good (excellent freshness), 3 to 8 panels rated it as good C: Poor (no freshness), 2 or fewer panels rated it as good

[0078] (Storage Stability) Each sunscreen prepared in Examples 4 to 7 and Comparative Examples 3 to 5 was filled into a glass vial and stored in an incubator. Accelerated testing was performed under the following conditions: 5°C for 3 months, 25°C for 3 months, 40°C for 3 months, and 50°C for 1 month. The condition of the sunscreen after the accelerated testing was observed, and changes in appearance and viscosity were evaluated according to the following evaluation criteria. The results are shown in Tables 3 and 4. <Evaluation Criteria> A: Very good (little change in condition compared to before the test) B: Good (slight change in condition compared to before the test) C: Poor (significant change in condition compared to before the test)

[0079] (UV Protection Performance) Each of the sunscreens prepared in Examples 4 to 7 and Comparative Examples 3 to 5 was applied to a PMMA plate (manufactured by Helio Screen, product name: SB6) at a concentration of 1.3 mg / cm ２ The coating was uniformly applied to a thickness of 100 μm, and then allowed to dry naturally for 15 minutes under light-shielded conditions to form a coating film, thereby preparing a measurement sample. The absorption spectrum (measurement wavelength: 290-450 nm) of the prepared measurement sample was measured using an SPF analyzer (manufactured by Labsphere, model: UV-2000S), and the in vitro SPF value and UVAPF value were calculated from the absorption spectrum value. The absorption spectrum was measured at nine points for each measurement sample, and the in vitro SPF value and in vitro UVAPF value were calculated from the respective absorption spectrum values, and the average values ​​of the in vitro SPF values ​​and UVAPF values ​​at the nine points were calculated. Three measurement samples were prepared and measured for each of the sunscreens prepared in Examples 4 to 7 and Comparative Examples 3 to 5, and the average values ​​were used as the SPF value and UVAPF value of the measurement sample. The results are shown in Tables 3 and 4.

[0080]

[0081]

Claims

1. A nanofiber made of anionic group-modified paramylon, A nanofiber in which the degree of anionic group substitution per glucose unit of the anionic group-modified paramylon is 0.016 or more and 0.040 or less.

2. The nanofiber according to claim 1, wherein the anionic group of the anionic group-modified paramylon is a carboxyalkyl group.

3. The nanofiber according to claim 1 or 2, wherein the crystallinity of the anionic group-modified paramylon is 10% or more and 43% or less.

4. The nanofiber according to claim 1 or 2, wherein a 1% by mass aqueous dispersion of the nanofiber has a light transmittance of 10% or more at a wavelength of 660 nm.

5. The nanofiber according to claim 1 or 2, having an average fiber diameter of 1 nm or more and 50 nm or less.

6. An additive for external skin preparations, comprising the nanofiber according to claim 1 or 2.

7. An external preparation for skin, comprising the additive for external preparations for skin according to claim 6.

8. The external skin preparation according to claim 7, which is for use as a cosmetic or quasi-drug.

9. A method for producing the nanofiber according to claim 1 or 2, The method includes a step of contacting the paramylon with a basic aqueous solution and then substituting an anionic group with an anionic modifier, A manufacturing method in which the molar ratio of the anionic modifier to the paramylon is 0.1 to 1.

10. The method according to claim 9, wherein the molar ratio of the base in the basic aqueous solution to the paramylon is 1 to 3.