JP2024061241A - Cosmetic composition - Google Patents

Abstract

[Problem] To provide a cosmetic composition that has excellent dispersion stability and is capable of imparting a smooth appearance and improving gloss when applied to the skin. [Solution] The composition contains anion-modified cellulose nanofibers, a plate-like pigment, and water. [Selected Figure] None

Description

The present invention relates to a cosmetic composition containing anionically modified cellulose nanofibers.

Water-based cosmetic compositions provide a refreshing feeling when applied to the skin, and compared to oil-based cosmetic compositions, they are not sticky after use and have a smooth feel, so they are being developed for use in various types of cosmetics.

In makeup cosmetics, pigments such as natural mica or synthetic mica, pearl pigments, etc. are blended to create a glossy look, but when added to water-based cosmetic compositions, the added pigments may separate and settle if left to stand for a long period of time.

In aqueous cosmetic compositions, specific lipid peptide-type compounds are used as dispersants to prevent separation and sedimentation of pigments over time (for example, Patent Document 1).

Recently, cellulose nanofibers, which are cellulose fibers defibrated into nano-sized fibers, have been attracting attention. Cellulose fibers are a biomass made from pulp such as wood, and their effective use is expected to reduce the environmental impact.

Patent Document 2 discloses a technique for producing a solid powder cosmetic by obtaining a slurry composition containing a powder of mica or the like, an oil and/or a polyhydric alcohol, and cellulose nanofibers, and then removing water from this composition.

International Publication No. 2018/190383 JP 2019-43854 A

There has been a demand for liquid cosmetic compositions that are less likely to cause pigment sedimentation, even when they contain pigments such as mica. There is also a demand for them to contribute to reducing environmental impact. Because Patent Document 2 is a technology related to solid powder cosmetics, it is difficult to apply it directly to liquid cosmetic compositions.

The object of the present invention is to provide a cosmetic composition that has excellent dispersion stability and is capable of imparting a smooth appearance and improving gloss when applied to the skin.

As a result of extensive research into solving the above problems, the inventors discovered that the above objectives could be achieved by using anion-modified cellulose nanofibers, and thus completed the present invention.

That is, the present invention provides the following.
(1) A cosmetic composition comprising anion-modified cellulose nanofibers, a plate-like pigment, and water.
(2) The cosmetic composition according to (1), wherein the anion-modified cellulose nanofiber is a cellulose nanofiber having a carboxyl group or a cellulose nanofiber having a carboxyalkyl group.
(3) The cosmetic composition according to (2), wherein the anion-modified cellulose nanofiber has a carboxymethyl group as the carboxyalkyl group, and is a carboxymethylated cellulose nanofiber having a degree of carboxymethyl substitution of 0.01 to 0.50.
(4) The cosmetic composition according to (1) or (2), further comprising carboxymethyl cellulose.
(5) The cosmetic composition according to (1) or (2), wherein the plate-like pigment is mica.

The present invention provides a cosmetic composition that has excellent dispersion stability and, when applied to the skin, can provide a smooth appearance and improve gloss.

1 is a graph showing the results of measuring glossiness of the measurement samples of Example 1, Example 2, Comparative Example 1, and Comparative Example 2. 1 shows SEM observation results for the measurement samples of Example 1, Example 2, Comparative Example 1, and Comparative Example 2: (a) surface observation results (secondary electron mode); (b) surface observation results (reflected electron mode); (c) cross-sectional observation results (reflected electron mode). This graph shows the measurement results of shear viscosity of 0.5 mass% aqueous solutions (dispersions) of CMC-containing carboxylated CNF, CMC, and xanthan gum used in Examples 1, 2, Comparative Example 1, and Comparative Example 2.

The present invention will be described in detail below. In the present invention, "~" includes the end values. In other words, "X~Y" includes the values X and Y at both ends.

The cosmetic composition of the present invention contains anion-modified cellulose nanofibers, a plate-like pigment, and water.

(Cellulose nanofiber)
In the present invention, cellulose nanofibers (CNF) are fine fibers with a fiber diameter of about 3 to 500 nm, which are made by pulp, a cellulose raw material, being refined to the nanometer level. The average fiber diameter and average fiber length of cellulose nanofibers can be obtained by averaging the fiber diameters and fiber lengths obtained from the results of observing each fiber using an atomic force microscope (AFM) or a transmission electron microscope (TEM). Cellulose nanofibers can be obtained by applying a mechanical force to pulp to refine it, or by defibrating modified cellulose obtained by chemical modification, such as carboxylated cellulose (also called oxidized cellulose), carboxymethylated cellulose, cellulose into which a phosphate ester group has been introduced, or cationized cellulose. The average fiber length and average fiber diameter of fine fibers can be adjusted by chemical modification treatment or defibration treatment.

The average aspect ratio of the cellulose nanofibers used in the present invention is preferably 10 or more, and more preferably 20 or more. There is no particular upper limit, but it is usually 1000 or less. The average aspect ratio can be calculated by the following formula:
Aspect ratio = average fiber length/average fiber diameter

(Cellulose raw material)
Known cellulose raw materials are derived from plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, 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), recycled pulp, waste paper, etc.), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc.), and any of these can be used in the present invention. Cellulose fibers derived from plants or microorganisms are preferred, and cellulose fibers derived from plants are more preferred.

(anion modification)
The cellulose nanofibers used in the present invention are preferably anionically modified cellulose nanofibers, which can be obtained by defibrating anionically modified cellulose raw material. Anion modification refers to the introduction of anionic groups to cellulose, specifically, the introduction of anionic groups to pyranose rings by oxidation or substitution reaction. In the present invention, the oxidation reaction refers to a reaction in which the hydroxyl groups of the pyranose rings are directly oxidized to carboxyl groups. In addition, in the present invention, the substitution reaction refers to a reaction in which anionic groups are introduced to the pyranose rings by a substitution reaction other than the oxidation.

The anion-modified cellulose used as the raw material for anion-modified cellulose nanofibers is one that maintains at least a part of its fibrous shape even when dispersed in water or a water-soluble organic solvent. If one that does not maintain its fibrous shape (i.e., one that dissolves in a dispersion medium) is used, nanofibers cannot be obtained. "At least a part of the fibrous shape is maintained when dispersed" means that when a dispersion of anion-modified cellulose is observed with an electron microscope, a fibrous substance can be observed. In addition, anion-modified cellulose that can observe a cellulose I type crystal peak when measured by X-ray diffraction is preferable.
The crystallinity of the cellulose in the raw material anionically modified cellulose is preferably 50% or more, more preferably 60% or more, for crystalline I type. By adjusting the crystallinity to the above range, it is possible to obtain sufficient crystalline cellulose fibers that do not dissolve even after the fibers are finely divided by defibration. The crystallinity of the cellulose I type of the anionically modified cellulose nanofiber is preferably 50 to 90%, more preferably 60 to 80%, and particularly preferably 65 to 75%. If the crystallinity is less than 50%, the dispersion effect decreases.
The crystallinity of cellulose can be controlled by the crystallinity of the raw cellulose and the degree of anion modification. The method for measuring the crystallinity of anion-modified cellulose and anion-modified CNF is as follows:
The sample is placed in a glass cell and measured using an X-ray diffraction measuring device (LabX XRD-6000, manufactured by Shimadzu Corporation). The degree of crystallinity is calculated using the method of Segal et al., and is calculated from the diffraction intensity of the 002 plane at 2θ = 22.6° and the diffraction intensity of the amorphous part at 2θ = 18.5° using the diffraction intensity of 2θ = 10° to 30° in the X-ray diffraction pattern as the baseline, according to the following formula.
Xc = (I002c - Ia) / I002c x 100
Xc: Crystallinity (%) of cellulose I type
I002c: 2θ=22.6°, diffraction intensity of the 002 plane. Ia: 2θ=18.5°, diffraction intensity of the amorphous portion.

(Carboxylation)
Carboxylated (oxidized) cellulose can be used as the anion-modified cellulose. The carboxyl group in the present invention refers to -COOH (acid type) or -COOM (salt type). Here, M is a metal ion, such as sodium or potassium. Carboxylated cellulose (also called "oxidized cellulose") can be obtained by carboxylating (oxidizing) the above-mentioned cellulose raw material by a known method. Although not particularly limited, the amount of carboxyl groups is preferably 0.6 to 3.0 mmol/g, more preferably 1.0 to 2.0 mmol/g, based on the bone dry mass of the anion-modified cellulose nanofiber. As an example of the carboxylation (oxidation) method, a method in which the 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 can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the cellulose surface is selectively oxidized, and cellulose fibers having aldehyde groups and carboxyl groups (-COOH) or carboxylate groups ( ^-COO- ) on the surface can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

An N-oxyl compound is a compound capable of generating nitroxy radicals. Any compound that promotes the desired oxidation reaction can be used as the N-oxyl compound. Examples include 2,2,6,6-tetramethylpiperidine-1-oxy 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 capable of oxidizing the cellulose raw material. For example, 0.01 to 10 mmol is preferable, 0.01 to 1 mmol is more preferable, and 0.01 to 0.5 mmol is even more preferable, for 1 g of bone-dry cellulose raw material. The amount of the N-oxyl compound used is about 0.1 to 4 mmol/L for the reaction system.

Bromides are compounds that contain bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Iodides are compounds that contain 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. The modification is due to an oxidation reaction.

As the oxidizing agent, a known oxidizing agent can be used, for example, a halogen, a hypohalous acid, a hypohalous acid, a perhalogen acid or a salt thereof, a halogen oxide, a peroxide, etc. can be used. Among them, sodium hypochlorite is preferable because it is inexpensive and has a low environmental impact. The appropriate amount of the oxidizing agent to be used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, and even more preferably 2.5 to 25 mmol, per 1 g of bone-dry cellulose raw material. Also, for example, 1 to 40 mol is preferable per 1 mol of the N-oxyl compound.

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 of about 15 to 30°C. As the reaction proceeds, carboxyl groups are generated in the cellulose, and the pH of the reaction solution decreases. In order to proceed efficiently with the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to the reaction system from time to time to maintain the pH of the reaction solution at about 9 to 12, preferably 10 to 11. The reaction medium is preferably water, because it is easy to handle and does not easily cause side reactions. The reaction time in the oxidation reaction can be set appropriately according to the degree of oxidation progress, and is usually about 0.5 to 6 hours, for example, about 0.5 to 4 hours.

The oxidation reaction may also be carried out in two stages. For example, the oxidized cellulose obtained by filtering after the first stage reaction is oxidized again under the same or different reaction conditions, allowing carboxyl groups to be efficiently introduced into the cellulose raw material without reaction inhibition by the salt by-product of the first stage reaction.

The amount of carboxyl groups in carboxylated cellulose can be adjusted by controlling the reaction conditions, such as the amount of oxidizing agent added and the reaction time. The amount of carboxyl groups in carboxylated cellulose is usually the same as the amount of carboxyl groups in carboxylated cellulose nanofibers obtained by defibrating the same carboxylated cellulose.

In the present invention, in the oxidized cellulose obtained in the above process, the carboxyl groups introduced into the cellulose raw material are usually in the form of a salt, and are alkali metal salts such as sodium salts. Prior to the defibration process, the alkali metal salts of the oxidized cellulose may be replaced with other cationic salts such as phosphonium salts, imidazolinium salts, ammonium salts, and sulfonium salts. The replacement can be carried out by a known method.

(Carboxyalkylation)
Preferred anionic groups include carboxyalkyl groups such as carboxymethyl groups. The carboxyalkyl group in the present invention refers to -RCOOH (acid type) or -RCOOM (salt type). Here, R is an alkylene group such as a methylene group or an ethylene group, and M is a metal ion. The carboxyalkylated cellulose may be obtained by a known method, or a commercially available product may be used. The degree of carboxyalkyl substitution per anhydrous glucose unit of cellulose is preferably 0.50 or less. Furthermore, when the anionic group is a carboxymethyl group, the degree of carboxymethyl substitution is preferably 0.50 or less. If the degree of substitution is greater than 0.50, the crystallinity decreases and the proportion of soluble components increases, resulting in the loss of function as nanofibers. The lower limit of the degree of carboxyalkyl substitution is preferably 0.01 or more. In consideration of operability, the degree of substitution is particularly preferably 0.02 to 0.50, and more preferably 0.10 to 0.40. One example of a method for producing such a carboxyalkylated cellulose includes a method including the following steps. The modification is a modification by a substitution reaction. The following will be described using carboxymethylated cellulose as an example.
i) mixing the raw material with a solvent and a mercerizing agent, and subjecting the mixture to a mercerization treatment 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;
ii) Next, a carboxymethylating agent is added in an amount of 0.05 to 10.0 times the moles per glucose residue, and an etherification reaction 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.

The above-mentioned cellulose raw material can be used as the bottom raw material. As the solvent, 3 to 20 times by mass of water or lower alcohol, specifically water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol, tertiary butanol, etc., can be used alone or in combination of two or more. When lower alcohol is mixed, the mixing ratio is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 times by mole of an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, can be used per anhydrous glucose residue of the bottom raw material.

As mentioned above, the degree of carboxymethyl substitution per glucose unit of cellulose is preferably 0.01 to 0.50, more preferably 0.02 to 0.50, and even more preferably 0.10 to 0.40. By introducing carboxymethyl substituents into cellulose, the celluloses are electrically repelled from each other. Therefore, cellulose into which carboxymethyl substituents have been introduced can be easily nanofibrillated. Note that if the carboxymethyl substituents per glucose unit are less than 0.02, nanofibrillation may not be sufficient. The degree of carboxymethyl substitution in carboxymethylated cellulose and the degree of carboxymethyl substitution in carboxymethylated cellulose nanofibers obtained by fibrillating the same carboxymethylated cellulose are usually the same.

In the present invention, in the carboxyalkylated cellulose obtained in the above process, the carboxyalkyl group introduced into the cellulose raw material is usually in the form of a salt, such as an alkali metal salt, such as a sodium salt. Before the defibration process, the alkali metal salt of the carboxyalkylated cellulose may be replaced with another cationic salt, such as a phosphonium salt, an imidazolinium salt, an ammonium salt, or a sulfonium salt. The replacement can be carried out by a known method.

In this specification, "carboxymethylated cellulose," a type of anion-modified cellulose used in the preparation of cellulose nanofibers, refers to cellulose that maintains at least a part of its fibrous shape even when dispersed in water. Therefore, it is distinguished from carboxymethyl cellulose, a type of water-soluble polymer. When an aqueous dispersion of "carboxymethylated cellulose" is observed with an electron microscope, a fibrous substance can be observed. On the other hand, when an aqueous dispersion of carboxymethyl cellulose, a type of water-soluble polymer, is observed, no fibrous substance is observed. Furthermore, when "carboxymethylated cellulose" is measured by X-ray diffraction, a peak of cellulose type I crystals can be observed, but cellulose type I crystals are not observed in the water-soluble polymer carboxymethyl cellulose.

(Esterification)
As the anion-modified cellulose, esterified cellulose can also be used. Examples of the method include a method of mixing a powder or an aqueous solution of a phosphoric acid compound A with a cellulose raw material, and a method of adding an aqueous solution of a phosphoric acid compound A to a slurry of a cellulose raw material. Examples of the phosphoric acid compound A include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of a salt. Among the above, a compound having a phosphoric acid group is preferred because it is low cost, easy to handle, and can be introduced into the cellulose of the pulp fiber to improve the defibration efficiency. Examples of the compound having a phosphoric acid group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, 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. These can be used alone or in combination to introduce a phosphoric acid group. Among these, 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 introduction of phosphate groups, ease of defibration in the defibration step described below, and ease of industrial application. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. In addition, it is desirable to use the phosphoric acid compound A as an aqueous solution, since the reaction can proceed uniformly and the efficiency of introduction of phosphate groups is high. The pH of the aqueous solution of phosphoric acid compound A is preferably 7 or less, since the efficiency of introduction of phosphate groups is high, but a pH of 3 to 7 is preferred from the viewpoint of suppressing hydrolysis of pulp fibers.

The following method can be given as an example of a method for producing cellulose phosphate. Phosphate compound A is added to a suspension of cellulose raw material having a solid content 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 phosphorus compound A added is preferably 0.2 to 500 parts by mass, and more preferably 1 to 400 parts by mass, in terms of the amount of phosphorus element. If the proportion of phosphorus compound A is equal to or greater than the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the proportion exceeds the upper limit, the effect of improving the yield reaches a plateau, which is not preferable from a cost perspective.

In addition to the phosphoric acid-based compound A, a powder or an aqueous solution of compound B may be mixed. Compound B is not particularly limited, but a nitrogen-containing compound exhibiting basicity is preferable. "Basicity" here is defined as an aqueous solution exhibiting a pink to red color in the presence of a phenolphthalein indicator, or an aqueous solution having a pH of greater than 7. The nitrogen-containing compound exhibiting basicity used in the present invention is not particularly limited as long as it exhibits the effects of the present invention, but a compound having an amino group is preferable. Examples include urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among them, urea, which is low-cost and easy to handle, is preferable. The amount of compound B added is preferably 2 to 1,000 parts by mass, more preferably 100 to 700 parts by mass, relative to 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. The reaction time is not particularly limited, but is about 1 to 600 minutes, more preferably 30 to 480 minutes. When the esterification reaction conditions are within these ranges, it is possible to prevent cellulose from being excessively esterified and becoming easily soluble, resulting in a good yield of phosphated cellulose. After the resulting phosphated cellulose suspension is dehydrated, it is preferable to heat treat it at 100 to 170°C in order to suppress hydrolysis of cellulose. Furthermore, it is preferable to heat it at 130°C or less, preferably 110°C or less, while it contains water during the heat treatment, and then heat treat it at 100 to 170°C after removing the water.

The degree of phosphate substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 or more and less than 0.40. By introducing a phosphoric acid group substituent into cellulose, the cellulose particles are electrically repelled from each other. Therefore, cellulose with phosphoric acid groups introduced therein can be easily nanofibrillated. If the degree of phosphate substitution per glucose unit is less than 0.001, nanofibrillation cannot be performed sufficiently. On the other hand, if the degree of phosphate substitution per glucose unit is more than 0.40, the cellulose may swell or dissolve, and may not be obtained as nanofibers. In order to perform defibration efficiently, it is preferable to boil the phosphoric acid esterified cellulose raw material obtained above and then wash it with cold water. The modification by these esterifications is a modification by substitution reaction. The degree of phosphate substitution in phosphoric acid esterified cellulose and the degree of phosphate substitution in phosphoric acid esterified cellulose nanofibers obtained by defibrating the same phosphoric acid esterified cellulose are usually the same.

In the present invention, in the cellulose phosphate obtained in the above process, the phosphate group introduced into the cellulose raw material is usually in the form of a salt, and is an alkali metal salt such as a sodium salt. Before the defibration process, the alkali metal salt of the cellulose phosphate may be replaced with another cationic salt such as a phosphonium salt, an imidazolinium salt, an ammonium salt, or a sulfonium salt. The replacement can be performed by a known method.

(Defibrilization)
In the present invention, the device for defibrating anion-modified cellulose is not particularly limited, but it is preferable to apply a strong shear force to the aqueous dispersion of anion-modified cellulose using a device such as a high-speed rotation type, a colloid mill type, a high-pressure type, a roll mill type, or an ultrasonic type. In particular, in order to defibrate efficiently, it is preferable to use a wet-type high-pressure or ultra-high-pressure homogenizer that can apply a pressure of 50 MPa or more to the aqueous dispersion and a strong shear force. The pressure is more preferably 100 MPa or more, and even more preferably 140 MPa or more. In addition, prior to the defibration and dispersion treatment with the high-pressure homogenizer, it is also possible to subject the above-mentioned CNF to a preliminary treatment using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer, as necessary. The number of treatments (passes) in the defibration device may be one or two or more, and two or more are preferable.

In the dispersion process, anionically modified cellulose is usually dispersed in a solvent. The solvent is not particularly limited as long as it can disperse anionically modified cellulose, but examples include water, organic solvents (e.g., hydrophilic organic solvents such as methanol), and mixtures thereof. Since the cellulose raw material is hydrophilic, it is preferable that the solvent is water.

The solids concentration of the anionically modified cellulose in the dispersion is usually 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. This ensures that the amount of liquid relative to the amount of cellulose fiber raw material is appropriate and efficient. The upper limit is usually 10% by mass or less, and preferably 6% by mass or less. This allows fluidity to be maintained.

Prior to the defibration or dispersion process, a preliminary treatment may be carried out as necessary. The preliminary treatment may be carried out using a mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer.

When the anion-modified cellulose nanofiber obtained through the defibration process is in the salt form, it may be used as is, or it may be converted to the acid form by acid treatment using a mineral acid or a method using a cation exchange resin. It may also be used after being made hydrophobic by a method using a cationic additive.

The cellulose nanofibers used in the present invention may be an aqueous dispersion of anion-modified cellulose nanofibers obtained through the above-mentioned defibration treatment, or may be a powder obtained by drying and pulverization, or may be redispersed in an aqueous solvent such as water.

The cellulose nanofiber used in the present invention preferably has a B-type viscosity of 100 to 8,400 mPa·s, more preferably 300 to 7,000 mPa·s, at a solids concentration of 1%, at 60 rpm, and at 25°C.

The anion-modified cellulose nanofiber used in the present invention preferably has a viscosity at 25°C and 6 rpm when dispersed in water with a solid content of 1% (w/v) divided by the viscosity at 25°C and 60 rpm when dispersed in water with a solid content of 1% (w/v) (also simply referred to as "the viscosity at 6 rpm divided by the viscosity at 60 rpm") of 6.0 or more. The higher this value, the greater the change in viscosity due to the difference in shear stress, indicating high thixotropy. Cellulose nanofibers with high thixotropy are suitable for use as viscosity modifiers and pigment dispersants. There is no upper limit to the value obtained by dividing the viscosity at 6 rpm by the viscosity at 60 rpm, but in practice it is thought that the upper limit is about 15.0.
The viscosity of the anion-modified cellulose nanofiber at 6 rpm (aqueous dispersion with 1% (w/v) solid content, 25°C) is preferably 2000 mPa·s or more, and more preferably 3000 mPa·s or more. The higher the viscosity at a low shear rate (6 rpm), the higher the possibility of thixotropy. There is no particular upper limit to the viscosity at 6 rpm, but in reality it is thought to be around 30,000 mPa·s.
The viscosity of the anion-modified cellulose nanofiber at 60 rpm (aqueous dispersion with a solid content of 1% (w/v), 25°C) is preferably about 100 to 8,400 mPa·s, more preferably about 200 to 7,000 mPa·s, even more preferably about 250 to 7,000 mPa·s, and even more preferably about 300 to 7,000 mPa·s.

(Plate-shaped pigment)
Examples of plate-like pigments that can be used in the present invention include pigments having a plate-like shape, such as mica, mica titanium, talc, sericite, glass, plate-like silica, plate-like cerium, plate-like alumina, plate-like barium sulfate, etc. The plate-like pigment can be selected according to the cosmetic composition to which it is applied, and can be used alone or in combination of two or more types.
From the viewpoint of obtaining sufficient gloss, the average particle size of the plate-like pigment is preferably 10 to 1000 μm, more preferably 10 to 500 μm. The average particle size referred to here means the volume average particle size, and can be measured by a laser diffraction type particle size distribution measuring device.

(Cosmetic composition)
The cosmetic composition of the present invention is obtained by dispersing anion-modified cellulose nanofibers, a plate-like pigment, and water as essential components in an aqueous solvent containing the water. The aqueous solvent used in the present invention is preferably water, a water-soluble organic solvent, or a mixed solvent thereof. Considering the dispersibility of the chemically modified pulp and CNF, the aqueous solvent is preferably water or a mixed solvent of water and a water-soluble organic solvent. Furthermore, from the viewpoints of cost, environment, and safety, it is more preferable to use water as the aqueous solvent.

A water-soluble organic solvent is an organic solvent that dissolves in water. Examples include methanol, ethanol, 2-propanol, butanol, glycerin, acetone, methyl ethyl ketone, 1,4-dioxane, N-methyl-2-pyrrolidone, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, acetonitrile, and combinations thereof. Among them, lower alcohols having 1 to 4 carbon atoms such as methanol, ethanol, and 2-propanol are preferred, and from the viewpoints of safety and availability, methanol and ethanol are more preferred, and ethanol is even more preferred. The amount of the water-soluble organic solvent in the mixed solvent is preferably 10% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. There is no upper limit to the amount, but it is preferably 95% by mass or less, and more preferably 90% by mass or less. In addition, the aqueous solvent may contain a non-water-soluble organic solvent to the extent that the effect of the invention is not impaired.

In the cosmetic composition of the present invention, the blending ratio of each component is not particularly limited, but the content of the plate-like pigment in the cosmetic composition is preferably 0.01 to 30% by mass, more preferably 0.05 to 25% by mass, and even more preferably 0.1 to 20% by mass, from the viewpoint of providing a moderate gloss. The solid content concentration of the cellulose nanofiber in the cosmetic composition is preferably 0.01 to 3% by mass, more preferably 0.1 to 2% by mass, and even more preferably 0.2 to 1% by mass, from the viewpoint of dispersion stability and workability. In addition, from the viewpoint of uniformly dispersing the pigment, it is preferable to blend 0.01 to 2000 parts by mass of the solid content of CNF with respect to 100 parts by mass of the plate-like pigment, and more preferably 0.1 to 1000 parts by mass. In addition, the content of the aqueous solvent in the cosmetic composition is preferably 50 to 99% by mass, and more preferably 60 to 95% by mass, from the viewpoint of obtaining a moderate feeling of freshness and moisturizing properties.

The cosmetic composition of the present invention may contain a dispersant other than CNF, as long as the effect of the present invention is not impaired. Examples of dispersants other than CNF include water-soluble polymers, acrylic dispersants, polycarboxylic acid dispersants, polyoxyethylene-type nonionic surfactants, silicone-based materials, and silane coupling agents.

Water-soluble polymers include cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, ethylcellulose), xanthan gum, xyloglucan, dextrin, dextran, carrageenan, locust bean gum, alginic acid, alginates, pullulan, starch, potato starch, kudzu starch, cationic starch, phosphorylated starch, corn starch, gum arabic, gellan gum, polydextrose, pectin, chitin, water-soluble chitin, chitosan, casein, albumin, soy protein lysate, peptone, polyvinyl alcohol, poly Examples of suitable materials include acrylamide, sodium polyacrylate, polyvinylpyrrolidone, polyvinyl acetate, polyamino acids, polylactic acid, polymalic acid, polyglycerin, latex, rosin-based sizing agents, petroleum resin-based sizing agents, urea resins, melamine resins, epoxy resins, polyamide resins, polyamide-polyamine resins, polyethyleneimine, polyamines, vegetable gums, polyethylene oxides, hydrophilic crosslinked polymers, polyacrylates, starch-polyacrylic acid copolymers, tamarind gum, guar gum, and colloidal silica, as well as mixtures of one or more of these. Among these, carboxymethylcellulose is preferably used from the viewpoint of improving dispersibility.

(Method for producing cosmetic composition)
The method for producing the cosmetic composition of the present invention is not particularly limited, and any method may be used as long as the anion-modified cellulose nanofiber and the plate-like pigment can be dispersed in an aqueous solvent containing water. For example, a method of adding an aqueous dispersion of anion-modified cellulose nanofiber to the plate-like pigment while stirring it in water and further stirring it, a method of mixing an aqueous dispersion of anion-modified cellulose nanofiber with a plate-like pigment and stirring it, and a method of mixing a dispersion of anion-modified cellulose nanofiber with a dispersion of a plate-like pigment in an aqueous solvent little by little and stirring it. The cosmetic composition of the present invention can be obtained by stirring and mixing using a conventional device and means, and the temperature conditions, etc. are not particularly limited.

The cosmetic composition of the present invention contains anion-modified cellulose nanofibers, so that plate-like pigments such as mica are stably dispersed and are less likely to settle. As a result, when this cosmetic composition is applied to the skin, a smooth appearance can be obtained, and further, the effect of improving gloss can be obtained. Therefore, this cosmetic composition can be suitably used in makeup cosmetics (eye shadow, lip, foundation, concealer, primer, etc.).

In addition to the dispersants exemplified above, the cosmetic composition of the present invention may contain ultraviolet absorbers, oils, surfactants, preservatives, fragrances, moisturizers, salts, antioxidants, chelating agents, neutralizing agents, pH adjusters, etc., within the scope of not impairing the effects of the present invention.

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

(Production Example 1)
(Production of carboxymethylated cellulose nanofibers)
In a 5L twin-shaft kneader with the rotation speed adjusted to 100 rpm, 1089 parts of isopropanol (IPA) and 31 parts of sodium hydroxide dissolved in 121 parts of water were added, and 200 parts of hardwood pulp (LBKP, manufactured by Nippon Paper Industries Co., Ltd.) was added in terms of dry mass when dried at 100 ° C. for 60 minutes. The mixture was stirred and mixed at 30 ° C. for 60 minutes to prepare mercerized cellulose. Further, 117 parts of sodium monochloroacetate was added while stirring, and after stirring at 30 ° C. for 30 minutes, the mixture was heated to 70 ° C. over 30 minutes, and a carboxymethylation reaction was carried out at 70 ° C. for 60 minutes. The proportion of water in the reaction medium during the mercerization reaction and the carboxymethylation reaction was 10% by mass. After the reaction was completed, the mixture was neutralized, washed with 65% water-containing methanol, deliquored, dried, and pulverized to obtain a sodium salt of carboxymethylated cellulose with a carboxymethyl substitution degree of 0.27 and a crystallinity of cellulose I type of 64%. The method for measuring the crystallinity of cellulose type I is as described above.
The obtained sodium salt of carboxymethyl cellulose was dispersed in water to obtain a 1% (w/v) aqueous dispersion. This was treated three times with a high-pressure homogenizer at 150 MPa to obtain a dispersion of carboxymethyl cellulose nanofibers. The obtained carboxymethyl cellulose nanofibers had an average fiber diameter of 3.2 nm and an aspect ratio of 40.

The obtained carboxymethylated cellulose nanofiber was dispersed in water to a solid content of 0.7% by mass, and carboxymethyl cellulose (hereinafter sometimes referred to as "CMC") (manufactured by Nippon Paper Industries Co., Ltd., product name: FS350HC-4, viscosity (1% by mass, 25°C, 60 rpm) approximately 3000 mPa·s, degree of carboxymethyl substitution approximately 0.90) was added at 40% by mass relative to the carboxymethyl cellulose nanofiber (i.e., so that the solid content of carboxymethyl cellulose was 40 parts by mass when the solid content of the carboxymethyl cellulose nanofiber was 100 parts by mass), and the mixture was stirred for 60 minutes with a TK homomixer (12,000 rpm). The obtained aqueous dispersion of CMC-containing carboxymethylated (CM-modified) cellulose nanofiber was added with an aqueous sodium hydroxide solution to adjust the pH to 9, and then dehydrated and dried in a drum dryer to obtain a dry solid, which was then pulverized, and the pulverized product was classified using a 30 mesh to obtain a powder of CMC-containing CM-modified cellulose nanofiber.

(Method for measuring the degree of carboxymethyl substitution per glucose unit)
Approximately 2.0 g of carboxymethylated cellulose fiber (bone dry) was weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. 100 mL of a solution prepared by adding 10 mL of concentrated nitric acid to 90 mL of methanol was added and shaken for 3 hours to convert the carboxymethylated cellulose salt (carboxymethylated cellulose) into hydrogenated carboxymethylated cellulose. 1.5 to 2.0 g of hydrogenated carboxymethylated cellulose (bone dry) was weighed out and placed in a 300 mL Erlenmeyer flask with a stopper. The hydrogenated carboxymethylated cellulose was moistened with 15 mL of 80% methanol, 100 mL of 0.1 N NaOH was added, and the mixture was shaken at room temperature for 3 hours. Excess NaOH was back-titrated with 0.1 N H ₂ SO ₄ using phenolphthalein as an indicator. The degree of carboxymethyl substitution (DS) was calculated by the following formula:
A = [(100 x F' - (0.1 _{N H2SO4} ) (mL) x F) x 0.1] / (bone dry mass (g) of hydrogenated carboxymethyl cellulose)
DS=0.162×A/(1−0.058×A)
A: The amount of 1N NaOH required to neutralize 1 g of hydrogenated carboxymethyl cellulose (mL)
F: Factor of _{0.1N H2SO4} F': Factor of 0.1N NaOH

(Production Example 2)
(Production of carboxylated cellulose nanofibers)
500 g (bone dry) of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees was added to 500 mL of an aqueous solution in which 780 mg of TEMPO (Sigma Aldrich) and 75.5 g of sodium bromide were dissolved, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system to a concentration of 6.0 mmol/g to initiate the oxidation reaction. The pH of the system decreased during the reaction, but 3M aqueous sodium hydroxide was added successively to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH of the system did not change. The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain a pulp (carboxylated cellulose) into which a carboxyl group had been introduced. The amount of carboxyl groups in this carboxylated cellulose was 1.42 mmol/g.
The carboxylated pulp was diluted with water to a solids concentration of 1% by mass, and then defibrated three times using an ultra-high pressure homogenizer at 150 MPa to obtain carboxylated cellulose nanofibers with an average fiber diameter of 3 nm and an aspect ratio of 250.

(Measurement of Carboxyl Group Amount)
60 mL of a 0.5% by mass slurry (aqueous dispersion) of a carboxylated cellulose sample was prepared, and a 0.1 M aqueous hydrochloric acid solution was added to adjust the pH to 2.5. A 0.05 N aqueous sodium hydroxide solution was then added dropwise to measure the electrical conductivity until the pH reached 11. The electrical conductivity was calculated using the following formula from the amount (a) of sodium hydroxide consumed in the neutralization stage of the weak acid, where the change in electrical conductivity was gradual:
Amount of carboxyl groups [mmol/g carboxylated cellulose] = a [mL] × 0.05 / mass of carboxylated cellulose [g].

Example 1
(Production of cosmetic composition)
0.5 g of the powder of CMC-containing carboxymethylated cellulose nanofiber obtained in Production Example 1 was added to 94.5 g of water at 25°C and stirred with a homodisper at 3000 rpm for 60 minutes to obtain a slurry. 5 g of mica powder (manufactured by Yamaguchi Mica Co., Ltd., product name: A-21S, average particle size: 23 μm, shape: plate-like (flake-like) powder, bulk density: 0.13 g/mL, aspect ratio (reference value): 70) was added, and the resulting mixture was stirred with a homodisper at 3000 rpm for 10 minutes to obtain a uniformly dispersed suspension (cosmetic composition). A portion of the resulting suspension was used to produce a dried film as a measurement sample shown below. The remaining suspension was left to stand for 24 hours and then visually inspected for its dispersed state, and no sedimentation of mica was observed, showing that the dispersed state was maintained.

(Production of measurement samples)
Immediately after stirring with the homodisper, 1 g of the suspension (cosmetic composition) was poured into a silicon frame (2 cm x 2 cm) placed on a PET film and left to stand for 1 day at 40°C to obtain a dry film. The obtained dry film was subjected to measurement of gloss and observation using a scanning electron microscope (SEM).

Example 2
A uniformly dispersed suspension (cosmetic composition) was obtained in the same manner as in Example 1, except that a 1% by mass aqueous dispersion of carboxylated cellulose nanofibers obtained in Production Example 2 was used so that the CNF solid content was 0.5% by mass of the entire composition obtained, instead of the CMC-containing carboxylated cellulose nanofiber powder obtained in Production Example 1. This suspension maintained a dispersed state even after being left to stand for 24 hours, with no sedimentation of mica being observed.

A dry film was obtained in the same manner as in Example 1. The gloss of the obtained dry film was measured and observed using a scanning electron microscope (SEM).

(Comparative Example 1)
A uniformly dispersed suspension (cosmetic composition) was obtained in the same manner as in Example 1, except that a powder of CMC (manufactured by Nippon Paper Industries Co., Ltd., product name: FS350HC-4, viscosity (1 mass%, 25°C, 60 rpm) approximately 3000 mPa·s, degree of carboxymethyl substitution approximately 0.9) was used instead of the powder of CMC-containing carboxymethyl cellulose nanofiber obtained in Production Example 1. After leaving the suspension for 24 hours, sedimentation of mica was observed.

A dry film was obtained in the same manner as in Example 1. The gloss of the obtained dry film was measured and observed using a scanning electron microscope (SEM).

(Comparative Example 2)
A uniformly dispersed suspension (cosmetic composition) was obtained in the same manner as in Example 1, except that a powder of xanthan gum (manufactured by CP Kelco, product name: Keltrol CG-T) was used instead of the powder of CMC-containing carboxymethyl cellulose nanofiber obtained in Production Example 1. This suspension maintained a dispersed state, with no sedimentation of mica observed even after being left to stand for 24 hours.

A dry film was obtained in the same manner as in Example 1. The resulting dry film was subjected to measurement of gloss and observation using a scanning electron microscope (SEM).

(Measurement of Glossiness)
The glossiness of the dried films obtained in the Examples and Comparative Examples was measured under the following conditions. The glossiness was measured at four points for each sample, and the average value is shown in Figure 1. The higher the value, the higher the glossiness (the better the glossiness).
<Measurement conditions>
Apparatus: Gross Tester manufactured by Lorentzen & Wettre
Incident angle: 75°

(SEM Observation)
Before SEM observation of the dried films obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the state of the dried films was observed at a magnification of 100 times using an optical microscope (digital microscope VHX-6000, manufactured by Keyence Corporation). Next, the surface and cross section of the dried film were observed at a magnification of 700 times using a scanning electron microscope (JSM-IT100, manufactured by JEOL Ltd.). The surface observation was performed in secondary electron mode and reflected electron mode, respectively. The cross section observation was performed in reflected electron mode. The SEM observation results are shown in FIG. 2.

From the observation results of the optical microscope, it was found that the dried films of Example 1 and Example 2 had a smooth surface without color unevenness. On the other hand, it was found that the dried film of Comparative Example 1 had color unevenness and was dried unevenly. In addition, although the dried film of Comparative Example 2 did not have color unevenness, it was found to have unevenness in the center and had poor leveling properties.
2(a) and 2(b), it was found that plate-like mica was observed on the surfaces of the dried films of Examples 1 and 2 and Comparative Example 2. On the other hand, it was found that the dried film of Comparative Example 1 had agglomerated mica and had many irregularities.
From the cross-sectional observation results using an SEM shown in column (c) of Figure 2 (the upper side of the image shows the surface side of the sample), it was found that the mica was oriented relatively parallel to the surface in the cross sections of the dried films of Examples 1 and 2 and Comparative Example 2. On the other hand, in the cross section of the dried film of Comparative Example 1, it was confirmed that the mica was oriented vertically (perpendicular to the surface).

(Summary of evaluation results)
In Examples 1 and 2 in which CNF was added, and Comparative Example 2 in which xanthan gum was added, no sedimentation of mica was observed after the suspension was left to stand for 24 hours. On the other hand, in Comparative Example 1 in which only CMC was added, sedimentation of mica was observed after the suspension was left to stand for 24 hours. The reason for this is that the viscosity of CMC at a shear rate of 0.1 (1/s) or less when it is made into a 0.5% aqueous solution is lower than that of the other three types. For each of the CMC-containing CM-CNF, carboxylated CNF, CMC, and xanthan gum used in Examples 1 and 2 and Comparative Examples 1 and 2, 0.5% aqueous solutions (dispersions) were prepared, and the shear viscosity of these aqueous solutions (dispersions) was measured using a rheometer. A graph of the measurement results is shown in FIG. 3.

In addition, in Examples 1 and 2 where CNF was added, the mica was dispersed stably and uniformly, which allowed the mica to be fully exposed on the surface and made the surface smooth, which is believed to have led to an improvement in the glossiness of the dried film. On the other hand, in Comparative Example 1 where only CMC was added, the dispersion stability of the mica was low and it was unevenly dispersed, which led to an increase in unevenness due to uneven drying and the aggregation of the mica, which is believed to have led to a decrease in the glossiness of the dried film.

Claims (5)

A cosmetic composition comprising anionically modified cellulose nanofibers, a plate-like pigment, and water. The cosmetic composition according to claim 1, wherein the anion-modified cellulose nanofiber is a cellulose nanofiber having a carboxyl group or a cellulose nanofiber having a carboxyalkyl group. The cosmetic composition according to claim 2, wherein the anion-modified cellulose nanofiber has a carboxymethyl group as the carboxyalkyl group, and is a carboxymethylated cellulose nanofiber having a degree of carboxymethyl substitution of 0.01 to 0.50. The cosmetic composition according to claim 1 or 2, further comprising carboxymethylcellulose. The cosmetic composition according to claim 1 or 2, wherein the plate-like pigment is mica.