Cellulose-microfiber-containing additive for antipollution dermatological agent for external use

Abstract

Provided is a material having an antipollution effect. Cellulose microfibers are used as an additive for an antipollution dermatological agent for external use, the additive having an antipollution effect. Also provided is an antipollution dermatological agent for external use, the agent including this additive. Preferably the cellulose microfibers are chemically modified cellulose microfibers.

Description

Additives for anti-pollution topical skin preparations containing cellulose microfibers

[0001] The present invention relates to an additive for anti-pollution topical skin preparations containing cellulose fine fibers, and also to an anti-pollution topical skin preparation containing this additive.

[0002] In recent years, there has been an increasing need for anti-pollution cosmetics that prevent the adhesion of pollutants (pollutants) that irritate the skin, such as pollen and yellow sand, and research into materials with anti-pollution effects has been progressing. For example, Patent Document 1 discloses an anti-pollution skin topical preparation containing lysozyme chloride as an active ingredient. Patent Document 2 discloses a skin care cosmetic with anti-pollution effects that contains magnesium aluminometasilicate and an ultraviolet protection agent as active ingredients. Patent Document 3 discloses an agent for inhibiting the adhesion of air hazardous substances, which contains composite particles formed by coating at least a portion of the surface of organic core particles with inorganic fine particles. Patent Document 4 discloses an anti-pollution agent containing hyaluronic acid and / or a salt thereof as an active ingredient.

[0003] JP 2022-98734 A JP 2017-105825 A JP 2020-200250 A JP 2017-186276 A

[0004] Research into materials with anti-pollution effects is ongoing, but the variety of such materials is still limited. Providing new materials with anti-pollution effects would be desirable, as it would broaden the formulation options available when developing anti-pollution cosmetics. The object of the present invention is to provide a material with anti-pollution effects (the effect of inhibiting the adhesion of pollutants).

[0005] As a result of extensive research, the present inventors have discovered that cellulose fine fibers have the effect of inhibiting the adhesion of particulate contaminants, leading to the completion of the present invention. The present invention includes the following: (1) An additive for antipollution topical skin preparations containing cellulose fine fibers. (2) An additive for antipollution topical skin preparations according to (1), in which the cellulose fine fibers have an average fiber diameter of 3 to 500 nm and an aspect ratio of 10 to 1,000. (3) An additive for antipollution topical skin preparations according to (1) or (2), in which the cellulose fine fibers are chemically modified cellulose fine fibers. (4) An additive for antipollution topical skin preparations according to (3), in which the chemically modified cellulose fine fibers are carboxymethylated cellulose fine fibers. (5) An additive for antipollution topical skin preparations according to (4), in which the carboxymethylated cellulose fine fibers have a degree of carboxymethyl substitution within the range of 0.01 to 0.50 and a degree of crystallinity of cellulose type I of 50% or more. (6) The additive for an anti-pollution topical skin preparation according to (3), wherein the chemically modified cellulose fine fibers are oxidized cellulose fine fibers. (7) The additive for an anti-pollution topical skin preparation according to any one of (1) to (6), wherein the average roughness Ra of the surface of a coating of the cellulose fine fibers obtained by the following method is 1.0 nm or more and 4.0 nm or less: A water dispersion of the cellulose fine fibers at a concentration of 0.5% by mass is applied to a smooth mica plate at a concentration of 10 mg / cm using a micropipette. ２ The coating is then dried at 50°C for 20 minutes to form a film, and the line roughness at 500 nm is measured at five locations using an atomic force microscope, and the arithmetic mean value of the measured values ​​is taken as the average roughness Ra of the coating surface. (8) An anti-pollution topical skin preparation comprising the additive for an anti-pollution topical skin preparation according to any one of (1) to (7).

[0006] By applying cellulose microfibers to a solid surface such as skin, it becomes possible to inhibit the adhesion of particulate contaminants to the solid surface. Therefore, cellulose microfibers can be added to topical skin preparations as an active ingredient exhibiting anti-pollution effects. The mechanism by which cellulose microfibers exhibit the effect of inhibiting the adhesion of contaminants is unclear, but the inventors speculate as follows: When cellulose microfibers are applied to a solid surface such as skin and dried, a thin film is formed on the solid surface. This thin film has very fine irregularities corresponding to the diameter and surface shape of the cellulose microfibers, which is thought to reduce the contact area between the particulate contaminants and the film and also reduce the van der Waals forces acting between the contaminant particles and the film, making it difficult for the contaminants to adhere to the film.

[0007] 1 is an image of the surface shape of a coating observed by an atomic force microscope.

[0008] The present invention relates to an additive for anti-pollution topical skin preparations containing cellulose fine fibers. (Cellulose Fine Fibers) The cellulose fine fibers used in the present invention are fine fibers made from cellulose and can be obtained by defibrating the cellulose raw material to reduce its fiber diameter. The average fiber diameter of the cellulose fine fibers is not particularly limited, but is approximately 3 nm to 10 μm. The average fiber diameter is preferably 3 nm to 1 μm, more preferably 3 nm to 500 nm, even more preferably 3 nm to 100 nm, and even more preferably 3 nm to 50 nm. This range is preferred because it results in finer surface irregularities when formed into a coating film, thereby enhancing the effect of inhibiting the adhesion of contaminants. The average fiber diameter and average fiber length of the cellulose fine fibers can be determined by averaging the fiber diameters and fiber lengths obtained from observations of each fiber using an ABB Fiber Tester, a Valmet Fractionator, a scanning electron microscope (SEM), an atomic force microscope (AFM), or a transmission electron microscope (TEM), appropriately selected depending on the fiber diameter. When measuring nanoscale fiber diameters, it is preferable to measure the cross-sectional height of a fiber shape image observed using an atomic force microscope (AFM). The average fiber diameter can be determined by measuring the fiber diameters of 50 randomly selected fibers using the method described above and calculating the length-weighted average fiber diameter. Furthermore, when measuring the fiber length of nanoscale fibers, it is preferable to use an atomic force microscope (AFM). The average fiber length can be determined by measuring the fiber lengths of 200 randomly selected fibers using the method described above and calculating the length-weighted average fiber length.

[0009] The aspect ratio of the cellulose fine fibers is preferably 10 to 1000, more preferably 10 to 500, and even more preferably 10 to 200. The aspect ratio can be calculated by the following formula: Aspect ratio = average fiber length (nm) / average fiber diameter (nm).

[0010] The cellulose raw material from which the cellulose fine fibers are made is not particularly limited as long as it contains cellulose, and examples thereof include those derived from plants, animals (e.g., ascidians), algae, and microorganisms (e.g., acetic acid bacteria (Acetobacter)). Examples of plant-derived materials include wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, and pulp (softwood unbleached kraft pulp (NUKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), hardwood bleached kraft pulp (LBKP), softwood unbleached sulfite pulp (NUSP), softwood bleached sulfite pulp (NBSP), thermomechanical pulp (TMP), softwood dissolving pulp, hardwood dissolving pulp, recycled pulp, waste paper, etc.). Cellulose powder obtained by pulverizing the above-mentioned cellulose raw materials may also be used. Any one or a combination of these may be used as the cellulose raw material, but cellulose fibers derived from plants or microorganisms are preferred, cellulose fibers derived from plants are more preferred, and wood pulp is even more preferred.

[0011] (Chemically modified cellulose fine fibers) Cellulose has three hydroxyl groups per glucose unit and can be chemically modified in various ways. As an example of the cellulose fine fibers, it is preferable to use chemically modified cellulose fine fibers obtained by defibrating a cellulose raw material (chemically modified cellulose fibers) obtained by chemical modification, from the viewpoint of promoting the progress of defibration.

[0012] A preferred chemical modification is anionic modification, which introduces anionic groups into cellulose. Specifically, anionic modification refers to the introduction of anionic groups into the pyranose rings of cellulose by substitution or oxidation. Examples of types of anionic modification include, but are not limited to, carboxyalkylation, which ether-links a carboxyalkyl group such as a carboxymethyl group (hereinafter, "carboxymethyl" will be referred to as "CM") to the cellulose chain; oxidation (also referred to as carboxylation), which introduces carboxy groups into the cellulose chain; and phosphate esterification, which introduces phosphate groups into the cellulose chain. Among these, carboxyalkylation is preferred, and CM modification is most preferred.

[0013] Examples of chemically modified cellulose microfibers include carboxymethyl cellulose microfibers, carboxyalkylated cellulose microfibers, TEMPO-oxidized cellulose microfibers, ozone-oxidized cellulose microfibers, phosphate-esterified cellulose microfibers, phosphite-esterified cellulose microfibers, cationized cellulose microfibers, sulfonated cellulose microfibers, and xanthated cellulose microfibers, with carboxymethyl cellulose microfibers and oxidized cellulose microfibers being particularly preferred.

[0014] Chemically modified cellulose fine fibers such as anion-modified cellulose fine fibers may have an anionic group such as a carboxyl group, a CM group, or a phosphate group having a metal ion such as a sodium ion or a potassium ion as a counter ion (this form is called a "salt form"), or may have an anionic group having a proton as a counter ion (this form is called a "hydrogen form").

[0015] Chemically modified cellulose fibers, which are the raw material for chemically modified cellulose microfibers, maintain at least a portion of the fibrous shape of cellulose even when dispersed in water. That is, when an aqueous dispersion of chemically modified cellulose fibers is observed with an electron microscope or the like, a fibrous substance can be observed, and when measured by X-ray diffraction, a peak of cellulose type I crystals can be observed. The crystallinity of cellulose in chemically modified cellulose fibers or chemically modified cellulose microfibers is preferably 50% or more, more preferably 60% or more, of cellulose type I crystals. The crystallinity of cellulose can be controlled by the degree of chemical modification. There is no particular upper limit to the crystallinity of cellulose type I. In practice, the upper limit is thought to be around 90%. The crystallinity of cellulose type I is measured as follows: A sample is placed in a glass cell and measured using an X-ray diffraction measurement device (product name: LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity is calculated using the method of Segal et al., and is calculated using the diffraction intensity of the 002 plane at 2θ = 22.6° and the diffraction intensity of the amorphous portion at 2θ = 18.5°, with the diffraction intensity at 2θ = 10° to 30° in the X-ray diffraction pattern as the baseline, according to the following formula: X ｃ= (I ００２ｃ -I ａ ) / I ００２ｃ x100 x ｃ = Crystallinity of cellulose type I (%) ００２ｃ : 2θ = 22.6°, diffraction intensity of 002 plane I ａ : 2θ=18.5°, diffraction intensity of the amorphous part.

[0016] In order to obtain chemically modified cellulose fibers having a peak of cellulose type I crystallinity, it is preferable to use a cellulose raw material having a high degree of crystallinity of cellulose type I. The degree of crystallinity of cellulose type I of the cellulose raw material is preferably 50% or more, more preferably 60% or more.

[0017] (Carboxyalkylation, carboxymethylation) Carboxyalkylated cellulose fine fibers, preferably carboxymethylated cellulose fine fibers, which are an example of chemically modified cellulose fine fibers, can be obtained by defibrating carboxyalkylated cellulose fibers, preferably carboxymethylated cellulose fibers, obtained by known methods. The degree of carboxyalkyl substitution per anhydroglucose unit of cellulose is preferably 0.01 to 0.50. The upper limit is preferably 0.40 or less. If the degree of carboxyalkyl substitution exceeds 0.50, the cellulose becomes more susceptible to dissolution in water, making it impossible to maintain a fibrous form in water. To obtain the effects of carboxyalkylation, a certain degree of substitution is necessary. For example, if the degree of substitution is less than 0.02, the benefits of introducing a carboxyalkyl group may not be obtained depending on the application. Therefore, the degree of carboxyalkyl substitution is preferably 0.02 or more, more preferably 0.05 or more, and even more preferably 0.10 or more. The degree of carboxyalkyl substitution can be adjusted by controlling the amount of carboxyalkylating agent added to the reaction, the amount of mercerizing agent, the composition ratio of water to organic solvent, etc.

[0018] In this specification, anhydroglucose unit refers to each anhydroglucose (glucose residue) constituting cellulose. The degree of carboxyalkyl substitution (also referred to as the degree of etherification) refers to the proportion of hydroxyl groups in the glucose residues constituting cellulose that are substituted with carboxyalkyl ethers (the number of carboxyalkyl ethers per glucose residue). The degree of carboxyalkyl substitution is sometimes abbreviated as DS.

[0019] The method for measuring the degree of carboxyalkyl substitution is as follows: Approximately 2.0 g of sample is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of nitric acid methanol (a solution of 1000 mL of methanol and 100 mL of special-grade concentrated nitric acid) is added and the mixture is shaken for 3 hours to convert the salt-type carboxyalkylated cellulose fiber to hydrogen-type carboxyalkylated cellulose fiber. 1.5 to 2.0 g of hydrogen-type carboxyalkylated cellulose fiber (bone dry) is weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. The mixture is moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH is added, and the mixture is shaken at room temperature for 3 hours. Phenolphthalein is used as an indicator, and the 0.1 N NaOH is added. ２ SO ４ The excess NaOH is back-titrated with 0.01% NaOH, and the degree of carboxyalkyl substitution (DS) is calculated by the following formula: A = [(100 × F' - 0.1N - H ２ SO ４ (mL) × F) × 0.1] / (bone dry mass (g) of hydrogen-type carboxyalkylated cellulose fiber) Degree of carboxyalkyl substitution (DS) = 0.162 × A / (1-0.058 × A) F': 0.1N-H ２ SO ４ F: Factor of 0.1N NaOH.

[0020] The DS of the carboxyalkylated cellulose fibers is usually the same as the DS of the carboxyalkylated cellulose fine fibers obtained by defibrating the carboxyalkylated cellulose.

[0021] As an example of a method for producing carboxyalkylated cellulose fibers, an example of the production of carboxymethylated cellulose fibers is described below. First, a cellulose raw material is mixed with a solvent and a mercerizing agent, and the cellulose raw material is mercerized at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Next, a carboxymethylation agent is added in an amount of 0.05 to 10.0 times the molar amount per glucose residue, and carboxymethylation is carried out at a reaction temperature of 30 to 90°C, preferably 40 to 80°C, for a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0022] The solvent can be 3 to 20 times by mass of water or an organic solvent, or a mixture thereof. Examples of organic solvents include, but are not limited to, alcohols such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol, and tertiary butanol; ketones such as acetone, diethyl ketone, and methyl ethyl ketone; and dioxane, diethyl ether, benzene, and dichloromethane. Among these, monohydric alcohols having 1 to 4 carbon atoms are preferred due to their excellent compatibility with water, and monohydric alcohols having 1 to 3 carbon atoms are more preferred. As the mercerizing agent, it is preferable to use an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, in an amount of 0.5 to 20 times the molar amount per anhydrous glucose residue of the cellulose raw material. Examples of mercerizing agents include monochloroacetic acid, sodium monochloroacetate, methyl monochloroacetate, ethyl monochloroacetate, and isopropyl monochloroacetate. Of these, monochloroacetic acid or sodium monochloroacetate is preferred due to the ease of raw material availability. The amount of carboxymethylation agent used is not particularly limited, but is preferably added in the range of 0.5 to 1.5 mol per anhydroglucose unit of cellulose. The lower limit of the above range is more preferably 0.6 mol or more, even more preferably 0.7 mol or more, and the upper limit is more preferably 1.3 mol or less, even more preferably 1.1 mol or less. The carboxymethylation agent may be added to the reactor as, for example, a 5 to 80 mass % aqueous solution, more preferably 30 to 60 mass %, but is not limited thereto, or may be added in powder form without being dissolved in a solvent such as water.

[0023] When monochloroacetic acid or sodium monochloroacetate is used as the carboxymethylating agent, the molar ratio of the mercerizing agent to the carboxymethylating agent (mercerizing agent / carboxymethylating agent) is generally set to 0.90 to 2.45. The reason for this is that if the ratio is less than 0.90, the carboxymethylating reaction may be insufficient, resulting in unreacted monochloroacetic acid or sodium monochloroacetate remaining and causing waste, and if the ratio exceeds 2.45, a side reaction between the excess mercerizing agent and monochloroacetic acid or sodium monochloroacetate may proceed, resulting in the production of an alkali metal glycolate, which may be uneconomical.

[0024] When mercerizing a cellulose raw material, there are generally two methods for carrying out both mercerization and CM formation in a solvent primarily composed of water (aqueous medium method), and two methods for carrying out both mercerization and CM formation in a mixed solvent of water and an organic solvent (solvent method), either of which may be used. Alternatively, a solvent primarily composed of water may be used for mercerization, and a mixed solvent of an organic solvent and water may be used for CM formation. By doing so, mercerized cellulose in which CM groups have been introduced uniformly, rather than locally, can be economically obtained even when the crystallinity of the cellulose is maintained at 50% or higher.

[0025] A solvent primarily containing water (a water-based solvent) refers to a solvent containing water at a ratio of more than 50% by mass. The water content in the water-based solvent is preferably 55% by mass or more, more preferably 60% by mass or more, more preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more. A particularly preferred water-based solvent is 100% by mass (i.e., water). The higher the water content during mercerization, the more advantageously CM groups are introduced more uniformly into cellulose. The solvent other than water in the water-based solvent (used in a mixture with water) can be the organic solvent described above. The amount of organic solvent in the water-based solvent is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, even more preferably 20% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and more preferably 0% by mass.

[0026] It is preferable to add an organic solvent or an aqueous solution of an organic solvent to the reactor simultaneously with the addition of the carboxylation agent, or before or immediately after the addition of the carboxylation agent, or to appropriately reduce the organic solvents other than water used in the mercerization treatment by reducing the pressure, etc., to form a mixed solvent of water and an organic solvent, and then to allow the carboxylation reaction to proceed in this mixed solvent of water and an organic solvent. The timing of adding or reducing the organic solvent is not particularly limited as long as it is between the end of the mercerization reaction and immediately after the addition of the carboxylation agent, but is preferably within 30 minutes before or after the addition of the carboxylation agent, for example.

[0027] The proportion of organic solvent in the mixed solvent during carboxymethylation is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more, relative to the total of water and organic solvent. The higher the proportion of organic solvent, the more likely it is that uniform CM group substitution will occur, thereby stabilizing the quality of the resulting carboxymethyl cellulose. The upper limit of the proportion of organic solvent is not limited and may be, for example, 99% by mass or less. Considering the cost of the organic solvent to be added, the proportion is preferably 90% by mass or less, more preferably 85% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0028] The reaction medium for carboxymerization (a cellulose-free mixed solvent of water, organic solvent, etc.) preferably has a lower proportion of water (in other words, a higher proportion of organic solvent) than the reaction medium for mercerization. By satisfying this range, it becomes easier to maintain the crystallinity of the resulting carboxymerized cellulose. Furthermore, when the reaction medium for carboxymerization has a lower proportion of water (a higher proportion of organic solvent) than the reaction medium for mercerization, there is also the advantage that, when transitioning from the mercerization reaction to the carboxymerization reaction, a mixed solvent for the carboxymerization reaction can be formed by the simple means of adding a desired amount of organic solvent to the reaction system after the mercerization reaction is completed.

[0029] (Oxidation) Oxidized cellulose fine fibers (also called "carboxylated cellulose fine fibers"), which are an example of chemically modified cellulose fine fibers, can be obtained by defibrating oxidized cellulose fibers obtained by oxidizing (carboxylating) the above-mentioned cellulose raw material using a known method. The amount of carboxy groups is preferably 0.1 to 2.5 mmol / g, more preferably 0.6 mmol / g to 2.5 mmol / g, and even more preferably 1.0 mmol / g to 2.0 mmol / g, based on the bone dry mass of the oxidized cellulose. The amount of carboxy groups in oxidized cellulose fiber can be measured by the following method: 60 mL of a 0.5 mass% slurry (aqueous dispersion) of oxidized cellulose fiber is prepared, and 0.1 M aqueous hydrochloric acid is added to adjust the pH to 2.5. After that, 0.05 N aqueous sodium hydroxide is added dropwise and the electrical conductivity is measured until the pH reaches 11. The amount of carboxy groups is calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid, where the change in electrical conductivity is gradual: Amount of carboxy groups [mmol / g oxidized cellulose fiber] = a [mL] × 0.05 / mass of oxidized cellulose fiber [g].

[0030] The amount of carboxyl groups in oxidized cellulose fibers is usually the same as the amount of carboxyl groups in oxidized cellulose fine fibers obtained by defibrating the oxidized cellulose fibers. One example of an oxidation method is a method in which a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides, and mixtures thereof. This oxidation reaction selectively oxidizes the primary hydroxyl group at C6 of the glucopyranose ring on the cellulose surface, yielding a cellulose raw material (oxidized cellulose fibers) bearing aldehyde groups and carboxyl groups (—COOH) or carboxylate groups (—COO—) on the surface. The concentration of the cellulose raw material during the reaction is not particularly limited, but is preferably 5% by mass or less.

[0031] An N-oxyl compound refers to a compound capable of generating a nitroxy radical. Any compound that promotes the target oxidation reaction can be used as the N-oxyl compound. Examples include 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO). The amount of the N-oxyl compound used is not particularly limited, as long as it is a catalytic amount that can oxidize the cellulose raw material. For example, 0.01 to 10 mmol is preferred, 0.01 to 1 mmol is more preferred, and 0.05 to 0.5 mmol is even more preferred, per 1 g of bone-dry cellulose raw material. The concentration of the N-oxyl compound in the reaction system is preferably about 0.1 to 4 mmol / L.

[0032] Bromides are compounds containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Iodides are compounds containing iodine, examples of which include alkali metal iodides. The amount of bromide or iodide used can be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol, per 1 g of bone-dry cellulose raw material.

[0033] Known oxidizing agents can be used, such as halogens, hypohalous acids, halous acids, perhalogen acids or their salts, halogen oxides, and peroxides. Among these, sodium hypochlorite is preferred because it is inexpensive and has a low environmental impact. The appropriate amount of oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, per 1 g of bone-dry cellulose raw material. Furthermore, for example, 1 to 40 mol is preferred per 1 mol of the N-oxyl compound.

[0034] The oxidation process of cellulose raw materials can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, or may be room temperature, about 15 to 30°C. As the reaction proceeds, carboxyl groups are generated in the cellulose chains, resulting in a decrease in the pH of the reaction solution. To efficiently proceed with the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. Water is preferred as the reaction medium because of its ease of handling and the low occurrence of side reactions. The reaction time in the oxidation reaction can be appropriately set depending on the degree of oxidation progress, and is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours.

[0035] The oxidation reaction may also be carried out in two stages. For example, the oxidized cellulose obtained by filtration after the completion of the first-stage reaction can be oxidized again under the same or different reaction conditions, thereby enabling efficient oxidation without reaction inhibition by sodium chloride produced as a by-product in the first-stage reaction.

[0036] Another example of an oxidation method is a method in which the cellulose raw material is oxidized by contacting an ozone-containing gas with the raw material. This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring, and decomposes the cellulose chain. The ozone concentration in the ozone-containing gas is 50 to 250 g / m. ３ It is preferable that the density is 50 to 220 g / m ３It is more preferable that the ozone addition amount relative to the cellulose raw material is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass, based on 100 parts by mass of the solids content of the cellulose raw material. The ozone treatment temperature is preferably 0 to 50°C, and more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is approximately 1 to 360 minutes, and preferably approximately 30 to 360 minutes. When the ozone treatment conditions are within these ranges, excessive oxidation and decomposition of the cellulose raw material can be prevented, resulting in a good yield of oxidized cellulose fiber. After the ozone treatment, a further oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the further oxidation treatment is not particularly limited, but examples include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the further oxidation treatment can be performed by dissolving these oxidizing agents in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and then immersing the cellulose raw material in the solution.

[0037] The amount of carboxyl groups in the oxidized cellulose fibers can be adjusted by controlling the reaction conditions, such as the amount of oxidizing agent added and the reaction time. (Phosphate Esterification) Phosphate-esterified cellulose fine fibers, which are an example of chemically modified cellulose fine fibers, can be obtained by defibrating phosphate-esterified cellulose fibers. As the phosphate-esterified cellulose fibers, commercially available fibers may be used, or they may be produced by phosphate-esterifying the above-mentioned cellulose raw material using a known method. The degree of phosphate substitution per glucose unit of the phosphate-esterified cellulose fibers is preferably 0.001 or more and less than 0.40. The degree of phosphate substitution in the phosphate-esterified cellulose fibers and the degree of phosphate substitution in the phosphate-esterified cellulose fine fibers obtained by defibrating the phosphate-esterified cellulose fibers are usually the same.

[0038] Examples of methods for phosphate esterification include mixing a powder or aqueous solution of a compound having a phosphate group with a cellulose raw material, or adding an aqueous solution of a compound having a phosphate group to a slurry of the cellulose raw material. Examples of compounds having a phosphate group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium phosphite, potassium phosphite, sodium hypophosphite, potassium hypophosphite, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. Phosphate groups can be introduced into the cellulose raw material by using one or more of these compounds in combination. Among these compounds, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are preferred from the viewpoints of high efficiency of phosphate group introduction and ease of industrial application. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. Furthermore, it is desirable to use the compound having a phosphate group in the form of an aqueous solution, as this allows the reaction to proceed uniformly and increases the efficiency of phosphate group introduction. The pH of the aqueous solution of the compound having a phosphate group is preferably 7 or less because this increases the efficiency of introducing the phosphate group, but from the viewpoint of suppressing hydrolysis of the fiber, a pH of 3 to 7 is preferred. When reacting the compound having a phosphate group, a basic compound (for example, a compound having an amino group that exhibits basicity, such as urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, or hexamethylenediamine) may be further added to the reaction system.

[0039] The following method can be given as a specific example of a method for producing phosphated cellulose fibers. A compound having a phosphate group is added to a suspension of a cellulose raw material having a solids concentration of 0.1 to 10% by mass while stirring, to introduce phosphate groups into the cellulose. When the cellulose raw material is taken as 100 parts by mass, the amount of the compound having a phosphate group added is preferably 0.2 to 500 parts by mass, more preferably 1 to 400 parts by mass, in terms of elemental phosphorus.

[0040] After the resulting suspension of phosphated cellulose fibers is dehydrated, from the viewpoint of suppressing hydrolysis of cellulose, it is preferably heat-treated at 100 to 170° C. Furthermore, it is preferable that the suspension be heated at 130° C. or lower, preferably 110° C. or lower, while water is contained during the heat treatment, and then be heat-treated at 100 to 170° C. after the water has been removed.

[0041] (Fibration) The above-mentioned cellulose raw material or chemically modified cellulose raw material (chemically modified cellulose fiber) can be defibrated to obtain cellulose fine fibers or chemically modified cellulose fine fibers. The device used for defibration is not particularly limited, and devices that can apply strong shear force, such as high-pressure, high-speed rotation, colloid mill, roll mill, ultrasonic, and cavitation types, as well as devices such as disk-type, conical-type, and cylinder-type refiners, high-pressure homogenizers, colloid mills, high-pressure jet dispersers, beaters, PFI mills, kneaders, and dispersers, can be used.

[0042] Defibration is preferably performed in a wet manner (i.e., in the form of a dispersion in which water or the like is used as a dispersion medium). When performing wet defibration, first, a dispersion of cellulose raw material or chemically modified cellulose fibers is prepared. The solids concentration in the dispersion to be subjected to defibration is preferably 0.1% by mass or more, more preferably 0.5% by mass or more. The upper limit of the concentration is preferably 40% by mass or less, more preferably 30% by mass or less, even more preferably 10% by mass or less, and even more preferably 8% by mass or less. The dispersion medium is preferably water.

[0043] (Additive for anti-pollution topical skin preparations) When the above-mentioned cellulose fine fibers are applied to a solid surface to form a film, they exhibit the effect of inhibiting the adhesion of particulate matter to the solid surface. Therefore, the cellulose fine fibers can be used as an additive to an anti-pollution topical skin preparation to inhibit the adhesion of particulate matter to the skin. The cellulose fine fibers can also be used as an agent for inhibiting the adhesion of particulate matter to a solid surface. In this specification, anti-pollution refers to preventing the adhesion of pollutants (pollution). Examples of pollutants include, but are not limited to, particulate matter of about 1 to 1000 μm in size that can irritate the skin, such as pollen, yellow sand, and dust that can float in the air.

[0044] The cellulose fine fibers contained in the additive for anti-pollution topical skin preparations may be in the form of a dispersion in which they are dispersed in a dispersion medium such as water, or may be in the form of a dried product obtained by removing the dispersion medium. Considering the stability of the cellulose fine fibers and ease of addition to topical skin preparations, the dispersion form is preferred.

[0045] The additive for anti-pollution topical skin preparations is preferably in the form of a dispersion of cellulose fine fibers, although this is not limited thereto. The dispersion is preferably an aqueous dispersion using water as the main dispersion medium. The solids concentration of the cellulose fine fibers in the dispersion is not particularly limited, but considering the stability of the cellulose fine fibers and ease of addition to the topical skin preparation, it is preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, and even more preferably 0.5 to 10% by mass.

[0046] The cellulose microfibers contained in the anti-pollution skin topical preparation additive preferably form a film with nanoscale micro-irregularities on the surface when applied to a solid surface and dried. This is thought to make it difficult for contaminants to adhere to the film. The arithmetic mean roughness of the film surface is preferably somewhat large. For example, when a film is formed on a mica surface using an aqueous dispersion of cellulose microfibers at a concentration of 0.5% by mass and measured with an atomic force microscope, the arithmetic mean roughness (average roughness Ra of the coating surface) is preferably 1.0 nm or more. The upper limit is not particularly limited, but is preferably about 4.0 nm or less. The average roughness Ra can be specifically measured by the method described in the Examples.

[0047] (Anti-pollution topical skin preparation) An anti-pollution topical skin preparation can be produced using the additive for an anti-pollution topical skin preparation containing the cellulose fine fibers of the present invention. The anti-pollution topical skin preparation is an agent that prevents adhesion of pollutants (pollution) to the skin by applying it to the surface of the skin. Examples of areas to which the anti-pollution topical skin preparation can be applied include the face (e.g., forehead, cheeks, mouth, around the nose, around the eyes, etc.), chest, neck, shoulders, arms, hands, feet, and head (scalp, hair).

[0048] The dosage form of the anti-pollution topical skin preparation is not particularly limited as long as it can be applied to the skin. Examples include liquids, gels, lotions, emulsions, creams, ointments, sprays, and sticks. The agent of the present invention may be impregnated into a sheet-like substrate, or may be packed in a roll-on container.

[0049] The solids concentration of the cellulose fine fibers in the anti-pollution topical skin preparation is not particularly limited as long as it is a concentration at which a film is formed when applied to the skin, but for example, it is preferably 0.1 to 30% by mass, more preferably 0.1 to 20% by mass, even more preferably 0.1 to 10% by mass, even more preferably 0.1 to 5.0% by mass, and may be about 0.1 to 1.0% by mass.

[0050] The anti-pollution topical skin preparation may contain, in addition to the cellulose microfibers, other components that can be used in topical skin preparations. Examples of other components include, but are not limited to, water, oil, surfactants, thickeners, excipients, disinfectants, preservatives, antioxidants, chelating agents, pH adjusters, moisturizers, deodorants, cooling agents, anti-inflammatory agents, plant extracts, coloring materials, and fragrances. Furthermore, the anti-pollution topical skin preparation may contain other components that have anti-pollution effects in addition to the cellulose microfibers.

[0051] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these. Unless otherwise specified, parts and % represent parts by mass and % by mass.

[0052] <Production of carboxymethylated cellulose fine fibers 1> 1,089 parts of isopropanol (IPA) and a solution of 242 parts of sodium hydroxide dissolved in 121 parts of water were added to a 5 L twin-screw kneader with the rotation speed adjusted to 100 rpm, and 200 parts of hardwood pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added (dry mass) after drying at 100°C for 60 minutes. The mixture was stirred and mixed at 30°C for 60 minutes to prepare mercerized cellulose. 484 parts of sodium monochloroacetate was further added with stirring, and the mixture was stirred at 30°C for 30 minutes. The mixture was then heated to 70°C over 30 minutes and subjected to a carboxymethylated cellulose reaction at 70°C for 60 minutes. The proportion of water in the reaction medium during the mercerization reaction and carboxymethylated cellulose reaction was 10% by mass. After the reaction was completed, the mixture was neutralized, washed with 65% aqueous methanol, deliquored, dried and pulverized to obtain carboxymethyl cellulose fibers (sodium salt type) with a carboxymethyl substitution degree of 0.17 and a crystallinity of cellulose I type of 64%.

[0053] The obtained carboxymethyl cellulose fibers were dispersed in water to prepare a 1% (w / v) aqueous dispersion, which was then treated three times with a high-pressure homogenizer at 150 MPa to obtain an aqueous dispersion of carboxymethyl cellulose fine fibers 1. The obtained carboxymethyl cellulose fine fibers 1 had an average fiber diameter of 15 nm and an aspect ratio of 41.

[0054] <Production of carboxymethylated cellulose fine fibers 2> 130 parts of water and a solution of 20 parts of sodium hydroxide dissolved in 100 parts of water were added to a twin-screw kneader adjusted to a rotation speed of 100 rpm, and 100 parts of hardwood pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added (dry mass: 100 parts after drying at 100°C for 60 minutes). The mixture was stirred and mixed at 30°C for 90 minutes to prepare mercerized cellulose. 230 parts of IPA and 60 parts of sodium monochloroacetate were further added with stirring, and after stirring for 30 minutes, the mixture was heated to 70°C and subjected to a carboxymethylated cellulose reaction for 90 minutes. The concentration of IPA in the reaction medium during the carboxymethylated cellulose reaction was 50%. After completion of the reaction, the mixture was neutralized, deliquored, dried, and pulverized to obtain carboxymethylated cellulose fibers (sodium salt type) with a carboxymethylated cellulose substitution degree of 0.31 and a crystallinity of cellulose type I of 67%.

[0055] The resulting sodium salt of carboxymethyl cellulose was dispersed in water to prepare a 1% (w / v) aqueous dispersion, which was then treated five times with a high-pressure homogenizer at 150 MPa to obtain an aqueous dispersion of carboxymethyl cellulose fine fibers 2. The resulting carboxymethyl cellulose fine fibers 2 had an average fiber diameter of 3 nm and an aspect ratio of 40.

[0056] <Production of Oxidized Cellulose Fine Fibers 1> 500 g (bone-dry) of bleached, unbeaten kraft pulp (brightness 85%) derived from coniferous trees was used as the cellulose raw material. 500 g of the cellulose raw material, TEMPO (Sigma-Aldrich) (0.025 mmol relative to the cellulose raw material), and sodium bromide (1.0 mmol / g relative to the cellulose raw material) were added to 20 L of aqueous solution and stirred until the pulp was uniformly dispersed. A commercially available low-salt aqueous sodium hypochlorite solution (effective chlorine concentration 12% by mass, sodium chloride content 4% by mass or less) was added to the reaction system to achieve an effective chlorine concentration of 5.2 mmol / g relative to the cellulose raw material, initiating the oxidation reaction. As the reaction progressed, the pH of the system decreased, so 3 M aqueous sodium hydroxide solution was gradually added to adjust the pH to 10. The reaction was terminated when the pH no longer decreased. Hydrochloric acid was added to the reaction mixture to a pH of 2.4 or less, and the pulp was separated by filtration through a glass filter. The pulp was dispersed again in ion-exchanged water, and then hydrochloric acid was added to adjust the pH to 2.5 or less. The pulp was then separated by filtration through a glass filter, and this procedure was repeated to remove excess salts and impurities. The pulp was then thoroughly washed with water to remove excess hydrochloric acid, yielding carboxylated pulp (oxidized cellulose fiber). The carboxyl group content of the oxidized cellulose was 1.38 mmol / g.

[0057] The obtained oxidized cellulose fibers were dispersed in water to prepare a 1% (w / v) aqueous dispersion, which was then treated three times with a high-pressure homogenizer at 150 MPa to obtain an aqueous dispersion of oxidized cellulose fine fibers 1. The obtained oxidized cellulose fine fibers 1 had an average fiber diameter of 3 nm and an aspect ratio of 250.

[0058] <Verification of adhesion suppression effect> Using the carboxylated cellulose fine fibers 1 and 2 and oxidized cellulose fiber 1 produced in the above manufacturing examples and the comparative coating-forming components below, the ease with which particulate contaminants adhere to the films obtained from each was investigated using the following procedure.

[0059] The comparative film-forming components used were as follows: Carboxymethylcellulose: FS350HC-4, manufactured by Nippon Paper Industries Co., Ltd. Hydroxyethylcellulose: SE600, manufactured by Daicel Corporation Xanthan gum: CP Kelco, Keltrol (registered trademark) CG-T Carbomer: Carbopol (registered trademark) Ultrez 30, manufactured by Lubrizol Sodium hyaluronate: MW110 / 160, manufactured by BLOOMAGE BIOTECHNOLOGY Aqueous dispersions of the carboxymethyl cellulose fine fibers 1 and 2, the oxidized cellulose fine fibers 1, and the comparative film-forming components were prepared at the concentrations shown in Table 1. In addition, an artificial skin model, a Bioskin Plate (white) manufactured by Beaulux, was used as a skin substitute, and powdered charcoal (three types with average particle sizes of approximately 6 μm, 20 μm, and 190 μm) was used as the contaminant.

[0060] 0.25 g of each aqueous dispersion was dropped onto a 5 cm x 5 cm Bioskin plate, spread over the entire plate with a spatula, and dried at 50 °C for one day. The plate was then placed in an environment of 23 °C and 50% relative humidity for one day. A predetermined amount of powdered charcoal (three types: average particle size approximately 6 μm, 20 μm, and 190 μm) was sprinkled onto the plate, lightly rubbed with a finger, and excess charcoal was removed using an air duster. As a control, a blank plate was also prepared in which charcoal had been applied to a surface without the aqueous dispersion (blank). Microscope images (1 cm x 1 cm each) were taken of four locations on the plate. Using image processing software (ImageJ), the microscope images (RGB color) were converted to 8-bit images. The threshold was adjusted so that the contaminated areas appeared red, and binarization was performed. The area occupied by the contaminated areas was calculated. The same processing was performed on four observation images for each sample type, and the average value was calculated as the contaminant adhesion rate. The results are shown in Table 1.

[0061] <Measurement of average roughness Ra of coating surface> Aqueous dispersions of carboxylated cellulose fine fibers 1 and 2, oxidized cellulose fine fibers 1, and a comparative coating component were prepared at the concentrations shown in Table 1. The obtained aqueous dispersions were applied to a smooth mica plate at a concentration of 10 mg / cm using a micropipette. ２The solution was dropped onto the substrate so that the solution would become 100% by weight, and dried at 50°C for 20 minutes to form a coating. The surface shape of the resulting coating was measured using an atomic force microscope (SPM / AFM) (scanning probe microscope unit: Nanocute, scanning probe station: SPI3800N, manufactured by Hitachi High-Tech Science Corporation) under measurement conditions (cantilever: K-U001354500, DFM mode, scanning range: 3 μm × 3 μm) with n = 5 to determine the line roughness of 500 nm, and the arithmetic mean value was taken as the average roughness Ra of the coating surface. The results are shown in Table 1.

[0062]

[0063] The results in Table 1 show that applying cellulose microfibers significantly inhibits the adhesion of dirt to artificial skin compared to when other film-forming components are used. It can be said that cellulose microfibers are suitable for use as an active ingredient in anti-pollution topical skin preparations to inhibit the adhesion of pollutants. It can also be seen that cellulose microfibers have a good adhesion-inhibiting effect on particles of various particle sizes (e.g., 6 to 190 μm). It can also be seen that coatings made from cellulose microfibers tend to have a larger average surface roughness (Ra) than comparative coatings. Coatings made from cellulose microfibers have many nanoscale micro-irregularities on their surfaces, which is thought to make it more difficult for pollutants to adhere to the film.

[0064] <Observation of Coating Surface Shape> Each of the aqueous dispersions used in the above verification of adhesion suppression effect was dropped onto a mica surface and dried to form a coating. The surface shape of each coating was observed using an atomic force microscope (AFM). AFM observation images of each coating are shown in Figure 1. Figure 1 shows that the coating made of cellulose fine fibers has fine irregularities formed throughout the entire coating, unlike the coatings made of other comparative components.

Claims

1. An additive for anti-pollution topical skin preparations containing cellulose microfibers.

2. The anti-pollution additive for external skin preparations according to claim 1, wherein the cellulose fine fibers have an average fiber diameter of 3 to 500 nm and an aspect ratio of 10 to 1,000.

3. The additive for an anti-pollution skin preparation according to claim 1, wherein the cellulose fine fibers are chemically modified cellulose fine fibers.

4. The additive for an anti-pollution topical skin preparation according to claim 3, wherein the chemically modified cellulose fine fibers are carboxymethylated cellulose fine fibers.

5. The additive for an anti-pollution skin topical preparation according to claim 4, wherein the carboxymethylated cellulose fine fiber has a degree of carboxymethyl substitution within the range of 0.01 to 0.50 and a degree of crystallinity of cellulose I type of 50% or more.

6. The additive for an anti-pollution topical skin preparation according to claim 3, wherein the chemically modified cellulose fine fibers are oxidized cellulose fine fibers.

7. The anti-pollution additive for topical skin preparations according to claim 1, wherein the average roughness Ra of the surface of the coating of the cellulose fine fibers obtained by the following method is 1.0 nm or more and 4.0 nm or less: A water dispersion of the cellulose fine fibers having a concentration of 0.5% by mass is applied to a smooth mica plate at a thickness of 10 mg / cm using a micropipette. ２ The coating is then dried at 50° C. for 20 minutes to form a coating, and the line roughness of 500 nm is measured at five locations using an atomic force microscope, and the arithmetic mean value of the measured values ​​is taken as the average roughness Ra of the coating surface.

8. An anti-pollution topical skin preparation comprising the additive for anti-pollution topical skin preparations according to any one of claims 1 to 7.

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