TWI905091B - External components and methods to inhibit viscosity reduction - Google Patents

Abstract

The purpose of this invention is to provide a topical composition containing urea and a thickener, wherein viscosity reduction is inhibited. The topical composition containing (A) urea, (B) a thickener, and (C) a solid oil exhibits good inhibition of viscosity reduction after high-temperature storage. Preferably, component (B) is a (meth)acrylic acid polymer, and component (C) is petrolatum.

Description

External ingredients and methods to inhibit viscosity reduction

This invention relates to a topical formulation containing urea and a thickener, wherein viscosity reduction is inhibited.

Urea possesses the ability to retain moisture in the skin's stratum corneum and also has keratolytic properties. Therefore, urea has long been used as an active ingredient in topical cosmetics, pharmaceuticals, and quasi-pharmaceuticals for the treatment of skin conditions such as atopic dermatitis, xeroderma senilis, and ichthyosis, and to improve dry, itchy, and chapped skin.

Generally, thickeners are used in urea-containing topical formulations to improve user experience. However, a problem exists where viscosity cannot be maintained when urea and thickeners coexist, depending on their type or amount, resulting in insufficient formulation stability. As a formulation solution to this viscosity reduction problem, Patent 1 discloses a transparent gel cosmetic characterized by: containing urea, a urea stabilizer comprising a combination of amino acids and their salts, and a carboxyvinyl polymer, wherein the carboxyvinyl polymer comprises 0.65% to 2% by mass of the total cosmetic amount.

[Existing technical literature] [Patent Documents]

[Patent Document 1] Japanese Patent Application Publication No. 2009-190986

However, the formulations described above have limitations due to restrictions such as the relatively high content of carboxyvinyl polymers or the use of irritating hydroxy acids as urea stabilizers, making them unsuitable for the increasingly diverse formulations of topical ingredients in recent years. Therefore, there is a need to develop a new formulation technology to suppress viscosity reduction in topical ingredients containing urea and thickeners.

The purpose of this invention is to provide a topical composition containing urea and a thickener, wherein viscosity reduction is inhibited.

Through diligent research, the inventors discovered that excellent viscosity-reducing and inhibitory effects can be achieved by blending solid hydrocarbons into topical formulations containing urea and thickeners. Based on these findings and further repeated research, this invention was completed.

That is, this invention provides inventions in the form disclosed below.

Item 1. A topical composition comprising (A) urea, (B) a thickener, and (C) a solid oil.

Item 2. The topical composition as described in Item 1, wherein component (C) is petrolatum.

Item 3. The topical composition as described in Item 1, wherein component (B) is a (meth)acrylic acid polymer.

Item 4. The topical composition as described in any one of items 1 to 3, wherein the content of component (A) is 5% to 40% by weight.

Item 5. The topical composition as described in any one of items 1 to 4, wherein the content of component (C) is 0.01% to 20% by weight.

Item 6. The topical composition as described in any one of items 1 to 5, wherein the content of component (C) is 0.01 parts by weight to 1 part by weight relative to 1 part by weight of component (A).

Item 7. The topical composition as described in Item 1, which is an emulsified composition.

Item 8. A method for inhibiting viscosity reduction, wherein the viscosity reduction of a topical composition containing (A) urea and (B) a thickener is inhibited, and wherein, in said method, a solid oil (C) is formulated together with said (A) and (B) components into the topical composition.

The topical formulation of this invention contains urea and a thickener, and exhibits excellent viscosity-reducing and inhibitory effects.

1. External application components

The topical composition of this invention is characterized by containing (A) urea (hereinafter also referred to as "(A) component"), (B) a thickener (hereinafter also referred to as "(B) component"), and (C) a solid hydrocarbon oil (hereinafter also referred to as "(C) component"). The topical composition of this invention will now be described in detail.

(A)Ingredients

The topical formulation of this invention contains urea as component (A). Urea is a known component that possesses the functions of retaining moisture in the skin's keratinocytes by utilizing hydrogen bonds and the keratolytic function of removing unwanted keratinocytes through protein modification.

Regarding the urea used in this invention, there are no particular restrictions on its raw materials, manufacturing methods, or refining methods. It can be chemically synthesized, or it can be a commercially available product. Examples of commercially available urea products include those manufactured or sold by companies such as Takasugi Pharmaceutical Co., Ltd., Showa Chemical Co., Ltd., and Kanto Chemical Co., Ltd.

The urea content in the topical composition of this invention can be appropriately set according to the desired medicinal effect, and is not particularly limited; for example, it can be 5% to 40% by weight. The topical composition of this invention has excellent viscosity reduction inhibition effect; therefore, even when containing a relatively large amount of urea, which would otherwise significantly reduce viscosity, viscosity reduction can be effectively inhibited. In view of this effect of the invention, preferred examples of the urea content in the topical composition of this invention include: preferably 10% to 40% by weight, more preferably 15% to 30% by weight, and even more preferably 20% to 25% by weight.

(B) Thickeners

The topical formulation of this invention contains a thickener as component (B). The thickener may be a type commonly used in cosmetics or topical pharmaceuticals. Preferred examples of the thickener used in this invention include water-soluble thickeners. Examples of water-soluble thickeners include: (meth)acrylic acid polymers, cellulose ether polymers, vinyl polymers, polysaccharides, etc.

As (meth)acrylic acid polymers, examples include: carboxyl vinyl polymers, (meth)acrylic acid alkyl ester copolymers, acrylic acid/methacrylic acid alkyl ester copolymers; acrylate/methacrylic acid polyoxyethylene (20) calamari ether copolymers, acrylate/methacrylic acid polyoxyethylene (20) stearyl ether copolymers, acrylate/methacrylic acid polyoxyethylene (25) benzyl ether copolymers, etc.; acrylate/itaconic acid polyoxyethylene (20) calamari ether copolymers, acrylate/itaconic acid polyoxyethylene (20) stearyl ether copolymers, etc.; acrylate/methacrylic acid alkyl ester/itaconic acid polyoxyethylene (20) stearyl ether crosspolymers, etc.; acrylate/methacrylic acid alkyl ester/methacrylic acid polyoxyethylene (20) stearyl ether crosspolymers, etc.; acrylate/neodecaic acid vinyl ester crosspolymers, etc. Furthermore, the values in parentheses indicate the molar number of ethylene oxide addition. These (meth)acrylic acid polymers can be used alone, or in combination of two or more.

Examples of cellulose ether polymers include: methylcellulose, ethylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, and hydroxypropylmethylcellulose. These cellulose ether polymers can be used individually or in combination of two or more.

Examples of vinyl-based polymers include polyvinyl alcohol and polyvinylpyrrolidone. These vinyl-based polymers can be used individually or in combination of two or more.

Examples of polysaccharides include: xanthan gum, guar gum, locust bean gum, carrageenan, dextran, alginate or its salts, etc. These polysaccharides can be used alone, or in combination of two or more.

In the topical composition of this invention, component (B) may be selected from (meth)acrylic acid polymers, cellulose ether polymers, vinyl polymers, and polysaccharides, or may be used in combination of two or more.

Among these (B) components, those that, from the viewpoint of achieving further enhanced viscosity-reducing inhibition, include: preferably (meth)acrylic acid polymers, and more preferably carboxyl vinyl polymers.

Carboxyvinyl polymers are hydrophilic polymers with acrylic acid as the main structural unit. There are no particular restrictions as long as they can dissolve in water and produce a thickening effect; partial crosslinking is possible. Furthermore, they can also be copolymers containing other structural units. Examples of carboxyvinyl polymers with an average molecular weight (measured using gel permeation chromatography (GPC) as the mass average molecular weight converted from polystyrene) ranging from 300,000 to 5,000,000 can be listed. Specific examples of carboxyvinyl polymers with this molecular weight include: Carbopol 980 and Carbopol 981 (all from Noveon Inc.), which are mainly composed of polyacrylic acid; Hiviswako 103, Hiviswako 104, and Hiviswako 105 (all from Wasoku Junki); Hispagel (Hispano Quimica), an aqueous solution of a carboxyvinyl polymer; and Jelly CP (Showa Denko), an aqueous solution of a similar polymer. Carboxyvinyl polymers can be used alone or in combination of two or more.

In this invention, when using a carboxyl vinyl polymer, the polymer can be dispersed or dissolved in water for direct use or neutralized with an alkali. In this case, examples of inorganic alkalis used as neutralizing agents include sodium hydroxide, potassium hydroxide, and ammonia; and organic alkalis include triethanolamine, diethanolamine, diisopropanolamine, triisopropanolamine, and arginine. Organic alkalis are preferred, and triethanolamine is even more preferred.

In the topical composition of this invention, the content of component (B) is not particularly limited and can be appropriately determined according to the type of thickener. For example, it can be listed as: 0.05 wt% to 2 wt%, preferably 0.1 wt% to 1 wt%, more preferably 0.3 wt% to 0.8 wt%, and even more preferably 0.3 wt% to 0.55 wt%.

(C) Solid hydrocarbon oil

The topical formulation of this invention contains a solid hydrocarbon oil as component (C). By blending the solid hydrocarbon oil into a topical formulation containing urea and a thickener, excellent viscosity-reducing and inhibitory effects are achieved.

Solid hydrocarbons are hydrocarbons that maintain a solid state at 25°C. The solid hydrocarbons used in this invention can be those commonly used in cosmetics or topical pharmaceuticals, such as: petrolatum, ozokerite, ceresin, paraffin wax, polyethylene wax, microcrystalline wax, and gelled hydrocarbons.

These solid hydrocarbons can be used alone, or in combination of two or more.

Among these (C) components, from the viewpoint of achieving further improved viscosity inhibition, petrolatum, ceresin, mineral wax, paraffin wax, polyethylene wax, and microcrystalline wax are preferable, with petrolatum being the most preferred. Furthermore, as petrolatum, a highly refined petrolatum, such as white petrolatum, is preferred.

In the topical composition of the present invention, the content of component (C) is not particularly limited, and for example, it can be 0.1% to 20% by weight. From the viewpoint of obtaining further improved viscosity inhibition, the content of component (C) can be: preferably 0.5% to 15% by weight, more preferably 1% to 10% by weight, and even more preferably 5% to 8% by weight.

In the topical composition of this invention, the ratio of component (A) to component (C) is not particularly limited and can be determined based on the content of each of component (A) and component (C). From the viewpoint of obtaining further improved viscosity inhibition, the content of component (C) relative to 1 part by weight of component (A) can be listed as: 0.01 parts by weight to 1 part by weight, preferably 0.05 parts by weight to 0.8 parts by weight, and more preferably 0.25 parts by weight to 0.5 parts by weight.

In the case where the external application composition of the present invention includes component (E) described below, the content of component (C) relative to 100 parts by weight of components (C) and (E) is not particularly limited, and can be determined according to the content of each of components (C) and (E). From the viewpoint of obtaining further improved viscosity inhibition, the content of component (C) relative to 100 parts by weight of components (C) and (E) can be listed as: 3 parts by weight to 50 parts by weight, preferably 10 parts by weight to 40 parts by weight, and more preferably 15 parts by weight to 30 parts by weight.

(D) Water

The topical composition of this invention may contain water (hereinafter also referred to as "(D) component"). Topical compositions containing urea and thickeners exhibit significant viscosity reduction in the presence of water; however, according to the topical composition of this invention, even when containing water, viscosity reduction can be effectively inhibited.

In the case where the topical composition of the present invention contains component (D), its content can be appropriately set according to the formulation, for example, 30% to 70% by weight. From the viewpoint of obtaining further superior viscosity reduction inhibition, the content of component (D) can be: preferably 35% to 55% by weight, more preferably 40% to 50% by weight, and even more preferably 40% to 46% by weight.

(E) Oil content

The topical formulation of this invention may further contain an oil component other than component (C) (hereinafter also referred to as "component (E)"). Component (E) may be used as appropriate depending on the formulation form, for example, it may be used as the oil phase when the topical formulation of this invention is an emulsion.

Regarding the oils used in this invention, there are no particular restrictions, limited to those pharmaceutically or cosmetically permissible, and at least one selected from liquid oils and solid oils other than hydrocarbons may be used.

In the topical formulation of this invention, as component (E), either a liquid oil or a solid oil other than a hydrocarbon may be used, or a combination of both may be used.

When the topical composition of the present invention contains component (E), its content is not particularly limited and can be appropriately set according to the emulsion type, form, and application when the topical composition of the present invention is an emulsion composition. For example, it can be listed as: 0.1 wt% to 40 wt%, preferably 1 wt% to 30 wt%, and more preferably 10 wt% to 27 wt%.

(Liquid oil)

The term "liquid oil" refers to oil that maintains a liquid state at 25°C. The liquid oil used in this invention can be any liquid oil commonly used in cosmetics or topical pharmaceuticals, such as: avocado oil, camellia oil, macadamia nut oil, olive oil, jojoba oil, and other plant oils; fatty acids such as oleic acid and isostearic acid; cerebrolysin ethylhexanoate, ethylhexyl palmitate, octyl dodecyl myristate, neopentyl glycol diethylhexanoate, etc. Ester oils such as glyceryl 2-ethylhexanoate, octyl dodecyl oleate, isopropyl myristate, glyceryl triisostearate, and di-p-methoxycinnamic acid-monoethylhexanoate; silicone oils such as dimethyl polysiloxane, methyl hydrogen polysiloxane, methyl phenyl polysiloxane, and octamethylcyclotetrasiloxane; liquid hydrocarbons such as fluidized paraffin, squalene, and squalane; and higher alcohols such as lauryl alcohol.

Among these liquid oils are: preferably ester oils and liquid hydrocarbon oils; more preferably isopropyl myristate and fluidized paraffin.

These liquid oils can be used alone, or in combination of two or more.

When the topical composition of the present invention contains liquid oil, its content is not particularly limited. It can be appropriately set according to the emulsion type, form, and application when the topical composition of the present invention is an emulsion composition. For example, it can be listed as: 0.1% to 30% by weight, preferably 1% to 25% by weight, and even more preferably 10% to 20% by weight.

(Solid oils other than hydrocarbons)

The term "non-hydrocarbon solid oil" refers to oils other than hydrocarbons that maintain a solid state at 25°C. The non-hydrocarbon solid oils used in this invention can be those commonly used in cosmetics or topical pharmaceuticals, such as: candelilla wax, rice bran wax, beeswax, cotton wax, carnauba wax, lanolin, and shellac wax. Waxes such as lauric acid, myristic acid, palmitic acid, stearic acid, benzyl acid, 12-hydroxystearic acid, undecenoic acid, and other higher fatty acids; myristate, myristate cetyl ester, stearate, cetyl stearate, cetyl palmitate, cholesterol stearate, cholesterol oleate, palmitate dextrin, inulin stearate, hydrogenated jojoba oil, and other esters; cetyl alcohol, stearyl alcohol, benzyl alcohol, myristic alcohol, cetyl stearyl alcohol, oleyl alcohol, batyl alcohol, and other straight-chain or branched higher alcohols; silicone waxes, etc.

Among these solid oils other than hydrocarbons, straight-chain or branched higher alcohols are preferred, straight-chain higher alcohols are more preferred, and cetearyl alcohol and stearyl alcohol are even more preferred.

These solid oils, other than hydrocarbons, can be used alone or in combination of two or more.

When the topical composition of the present invention contains solid oil, its content is not particularly limited. It can be appropriately set according to the emulsion type, form, and application when the topical composition of the present invention is an emulsion composition. For example, it can be listed as: 0.1% to 30% by weight, preferably 1% to 20% by weight, and even more preferably 5% to 10% by weight.

(F) Surfactants

The topical formulation of this invention further includes a surfactant (hereinafter also referred to as "(F) ingredient"). The (F) ingredient may be used appropriately depending on the formulation form, for example, to create an emulsion state in the case where the topical formulation of this invention is an emulsion. As a surfactant, it is limited to pharmaceutical or fragrance-permissible methods and is not particularly restricted; examples include nonionic surfactants, anionic surfactants, cationic surfactants, amphoteric surfactants, etc., with nonionic surfactants being preferred.

As nonionic surfactants, examples include: polyoxyethylene-cured castor oil; sorbitan fatty acid esters (e.g., sorbitan monooleate, sorbitan monoisostearate, sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan sesquioleate, sorbitan trioleate, sorbitan pent-2-ethylhexanoate diglyceride, sorbitan tetra-2-ethylhexanoate diglyceride, etc.); and glycerol fatty acid esters (e.g., cottonseed oil fatty acid glycerides, glycerol monosinic acid, glycerol sesquioleate, glycerol monostearate, glycerol α,α'-oleic acid pyroglutamic acid glycerides, glycerol monostearate, etc.). Fruit acids, etc.; propylene glycol fatty acid esters (e.g., propylene glycol monostearate, etc.); glyceryl alkyl ethers; stearyl alcohol polyether (steareth)-2; polyoxyethylene sorbitan fatty acid esters (e.g., polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tetraoleate, etc.); polyoxyethylene sorbitol fatty acid esters (e.g., polyoxyethylene sorbitol monolaurate, polyoxyethylene sorbitol monooleate, polyoxyethylene sorbitol pentaoleate, polyoxyethylene sorbitol monostearate, etc.); polyoxyethylene glycerol fatty acid esters (e.g., polyoxyethylene glycerol monostearate, polyoxyethylene glycerol monoisostearate, poly... Polyoxyethylene triisostearate, etc.; polyoxyethylene fatty acid esters (e.g., polyoxyethylene monooleate, polyoxyethylene monostearate, polyoxyethylene distearate, polyoxyethylene dioleate, polyethylene distearate, etc.); polyoxyethylene alkyl ethers (e.g., polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene benzyl ether, polyoxyethylene 2-octyl dodecyl ether, polyoxyethylene cholesterol alcohol ether, etc.); pluronic type ethers (e.g., pluronic, etc.); polyoxyethylene/polyoxypropylene alkyl ethers (e.g., polyoxyethylene-whale wax ether, polyoxyethylene/polyoxypropylene-2-decyl ether). Tetradecyl ether, polyoxyethylene/polyoxypropylene monobutyl ether, polyoxyethylene/polyoxypropylene hydrogenated lanolin, polyoxyethylene/polyoxypropylene glycerol ether, etc.; polyglycerol fatty acid esters (e.g., polyglycerol stearate-2, polyglycerol oleate-2, polyglycerol isostearate-2, polyglycerol triisostearate-2, polyglycerol stearate-4, polyglycerol oleate-4, polyglycerol tristearate-6, polyglycerol stearate-10, polyglycerol pentastearate-10, polyglycerol pentahydroxystearate-10, polyglycerol pentaisostearate-10, polyglycerol pentaolelate-10, polyglycerol ricinoleate-6, polyglycerol ricinoleate-10, etc.), stearyl alcohol polyether-21, etc.

Among these nonionic surfactants, polyoxyethylene-cured castor oil and polyoxyethylene sorbitan fatty acid esters are preferred examples; more preferably, polyoxyethylene-cured castor oil, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monostearate, and polyoxyethylene sorbitan tetraoleate are preferred examples; and even more preferably, polyoxyethylene-cured castor oil and polyoxyethylene sorbitan monostearate are preferred examples.

These surfactants can be used alone, or in combination of two or more.

In the topical formulation of this invention, when component (F) is present, its content can be appropriately set according to the formulation form and the type of surfactant used, for example: 0.5% to 7% by weight, preferably 1% to 5% by weight, and even more preferably 2% to 5% by weight.

Other ingredients

In addition to the ingredients described above, the topical formulation of this invention may, as needed, contain other commonly used additives. Examples of such additives include: pH adjusters, polyols, buffers, solubilizers, chelating agents, preservatives, antioxidants, stabilizers, fragrances, and colorants.

Furthermore, in the topical formulation of this invention, other additives are preferably free of hydroxy acids such as citric acid, malic acid, tartaric acid, lactic acid, and mevalonic acid, from the viewpoint of avoiding skin irritation.

Furthermore, in addition to the aforementioned ingredients, the topical formulation of this invention may, as needed, contain pharmacologically or cosmetically effective ingredients. Examples of such pharmacologically effective ingredients include: steroids (dexamethasone, dexamethasone hydrochloride, dexamethasone acetate, hydrocortisone hydrochloride, prednisolone hydrochloride, prednisolone acetate, etc.), and antihistamines (diphenhydramine, chlorpheniramine maleate, etc.). Maleate, etc.), local anesthetics (lidocaine, dibucaine, procaine, tetracaine, bupivacaine, mepivacaine, chloroprocaine, proparacaine, meprylcaine or their salts), alkyl benzoates (e.g., ethyl aminobenzoate, diethylaminobenzoate hydrochloride), orthocaine, oxethazaine, oxy-polyethoxydecane, scopolia extract, percamin, etc. Pase, polyoxyethylene lauryl ether, etc.), anti-inflammatory agents (allantoin, salicylic acid, ethylene glycol salicylate, methyl salicylate, indomethacin, felbinac, diclofenac sodium, loxoprofen sodium, etc.), bactericides (ammonium benzyl chloride, dequalinium chloride, benzethonium chloride, cetylpyridinium chloride, isopropyl methylphenol, chlorhexidine hydrochloride, chlorhexidine gluconate). The active ingredients include gluconate, ammonia, sulfadiazine, lactic acid, phenol, etc.; itch suppressants (diphenhydramine, crotamiton, thianthol, etc.); skin protectants (collodion, castor oil, etc.); blood circulation promoters (vanillyl nonanoate, benzyl nicotinate, capsaicin, capsicum extract, etc.); vitamins (vitamin A, vitamin B, vitamin C, vitamin D, etc.); and mucopolysaccharides (chondroitin sulfate, sodium sulfate, hyaluronic acid, etc.). These active ingredients can be used individually or in combination. Furthermore, in the topical formulation of this invention, the content of these active ingredients can be appropriately set according to the type of active ingredient used and the desired effect.

Formulation/Uses

Regarding the formulation form of the topical composition of the present invention, there are no particular limitations as long as it possesses a certain degree of viscosity; for example, oily gel-like compositions and emulsion compositions can be listed. Topical compositions containing urea and thickeners show a significant decrease in viscosity in the presence of water, but according to the topical composition of the present invention, even when containing water, the decrease in viscosity can be effectively suppressed. In view of this effect of the present invention, emulsion compositions are a preferred formulation form for the topical composition of the present invention. Regarding the emulsion type when the topical composition of the present invention is an emulsion composition, it can be either an oil-in-water type or an oil-in-water type; however, in view of the aforementioned effect of the present invention, an oil-in-water type with a relatively high water content is a preferred emulsion type.

The viscosity of the external component of this invention is not particularly limited, but from the viewpoint of obtaining good coatability, the following values can be listed: preferably 1000 mPa·s to 50000 mPa·s, more preferably 3000 mPa·s to 30000 mPa·s, and even more preferably 7000 mPa·s to 15000 mPa·s. Here, the viscosity is a value measured at 25°C using an E-type viscometer (spindle No. RC3-50-1, 1 rpm).

The topical formulation of this invention can be used as a cosmetic, a topical quasi-pharmaceutical, or a topical pharmaceutical preparation. This topical formulation exhibits excellent viscosity reduction inhibition effects; therefore, even when containing a relatively large amount of urea, which would otherwise significantly reduce viscosity, viscosity reduction can be effectively inhibited. In view of this effect, the topical formulation of this invention is preferably used as a topical pharmaceutical preparation with a high urea content.

The external application composition of this invention is not particularly limited in its product form, and examples include: creams, ointments, lotions, gels, oils, lotions, liniments, aerosols, etc. Among these, creams, ointments, lotions, and lotions are preferred examples, creams, lotions, and lotions are more preferred examples, and creams and lotions are even more preferred examples.

Manufacturing method

The topical composition of this invention can be manufactured according to a formulation form and a known formulation method. For example, as a method for manufacturing the topical composition of this invention, it can be prepared by mixing the required amounts of components (A) to (C), and components (D) to (F) as needed, other active ingredients, additives, etc. When the topical composition of this invention is an emulsion composition, it can be manufactured according to the type of emulsion and a known formulation method for emulsion preparations. For example, regarding the method for manufacturing the topical composition of this invention when it is an emulsion composition, the following method can be listed: separating the contained components into water-soluble components and oil-soluble components, preparing an aqueous phase containing the water-soluble components and an oil phase containing the oil-soluble components, and emulsifying them according to a known method.

2. Methods to Inhibit Viscosity Reduction

As described above, by blending solid hydrocarbon oil into a topical composition containing urea and a thickener, excellent viscosity reduction inhibition effects are achieved. Therefore, this invention further provides a viscosity reduction inhibition method that inhibits the viscosity reduction of a topical composition containing (A) urea and (B) a thickener, wherein solid hydrocarbon oil (C) is blended together with components (A) and (B) in the topical composition. In the viscosity reduction inhibition method of this invention, "inhibition of viscosity reduction" means that, compared to the case without solid hydrocarbon oil, the viscosity reduction rate after high-temperature storage is smaller in the topical composition containing urea and a thickener. Viscosity reduction inhibition can be measured, for example, by storing the topical composition at 50°C for 2 weeks, and then suppressing the viscosity reduction rate to less than 15%, preferably less than 5%, when the initial viscosity is set to 100%.

In the viscosity reduction suppression method of this invention, the types or contents of components (A) to (C), the types or contents of other formulated components, and the formulation form of the topical composition are the same as those described in "1. Topical Composition".

[Implementation Example]

The following examples illustrate the invention in further detail, but the invention is not limited to these examples.

Experimental Example 1

Prepare a topical formulation with the composition shown in Table 1. Specifically, mix component (I) of Table 1 and stir at 80°C until homogeneous to obtain an oily preform. Then, after mixing component (II), slowly add the carboxyvinyl polymer and stir until homogeneous to obtain an aqueous preform. Add the aqueous preform to the oily preform and mix until homogeneous. Next, add triethanolamine and stir until homogeneous to obtain a creamy, emulsified topical formulation.

(Evaluation of viscosity reduction inhibition)

The initial viscosity of the prepared topical composition was measured. Specifically, a Brookfield E-type viscometer (R/S-CPS PLUS RHEOMETER) was used, with spindle No. RC3-50-1, to measure the viscosity (initial viscosity). The measurement conditions were set at a temperature of 25°C and a rotation speed of 1 rpm, and the viscosity was measured one minute after the start of the measurement. For example, in Example 3, the initial viscosity was 10150 mPa·s. The topical composition was stored at 50°C for two weeks, and the viscosity of the topical composition after storage was measured again. The viscosity reduction rate after storage was derived when the initial viscosity was set to 100%. Based on the following criteria, the viscosity reduction rate was classified, and the inhibition of viscosity reduction was evaluated. The results are shown in Table 1.

◎: Less than 5%

○: 5% or more but less than 15%

△: 15% or more but less than 25%

×：More than 25%

As shown in Table 1, no viscosity reduction after high-temperature storage was observed in the topical formulation containing a thickener but without urea (Comparative Example 1). However, a significant viscosity reduction after high-temperature storage was observed in the topical formulation containing urea (Comparative Example 1). In contrast, the topical formulation containing white petrolatum in addition to urea and a thickener (Examples 1-4) exhibited excellent viscosity reduction inhibition effects after high-temperature storage.

Claims (5)

A topical formulation comprising (A) urea, (B) a thickener, and (C) a solid oil, wherein the content of component (A) is 20% to 25% by weight, the content of component (B) comprises only a carboxyvinyl polymer is 0.50% to 0.55% by weight, and the content of component (C) is 0.25% to 0.35% by weight relative to 1 part by weight of component (A). The topical composition as described in claim 1, wherein component (C) is petrolatum. The topical composition as described in claim 1 or claim 2, wherein the content of component (C) is 5% to 8% by weight. The topical composition as described in claim 1 is an emulsified composition. A method for inhibiting viscosity reduction in a topical composition containing (A) urea and (B) a thickener, wherein a (C) solid oil is formulated together with components (A) and (B) in the topical composition, wherein the content of component (A) is 20% to 25% by weight, the content of component (B) is 0.50% to 0.55% by weight, the content of component (B) is 0.25% to 0.35% by weight relative to 1 part by weight of component (A).