TECHNICAL FIELD

The present invention relates to an aqueous hair cleansing agent.

BACKGROUND ART

A principal purpose of a hair cleansing agent resides in removing dirt on hair and scalp, and keeping the hair and scalp clean. In view of obtaining a hair cleansing agent having a high cleansing performance, it is preferable to use, as a main cleansing component, an anionic surfactant charged at the equivalent level with the hair and scalp. It is more preferable to use a strong-acid-based anionic surfactant having a sulfuric acid group or sulfonic acid group in the anionic portion thereof, in view of preventing re-adsorption of dirt. Among others, an alkyl sulfate and alkyl ether sulfate are most generally used as the main component of a hair cleansing agent, by virtue of their rich foaming property and excellent cleansing performance.

The alkylsulfate and alkyl ether sulfate, however, still have problems in terms of mildness to the scalp. Horny layer cells which form 10 to 20 layers in the surficial portion of the skin has important roles of keeping moisture within the skin, and protection from an external stimulation. The above-described alkyl sulfate and alkyl ether sulfate, however, permeate into the horny layer, strongly swell the cells, and elutes natural moisturizing components, such as an amino acid or lipid inherent to the cells, out from the cells. Accordingly, repetitive use of such hair cleansing agent, containing these surfactants as the main component, may tend to dry the skin due to the lowered moisture content of the scalp, and to induce itchiness of the scalp because the surfactant and some external stimulating substance may more readily permeate into the skin.

A known strategy for adding mildness to the scalp, typically by suppressing swelling of the horny layer, relates to a method of formulating a hair cleansing agent using an amino acid-based anionic surfactant as the main component, in place of the alkyl ether sulfate. The amino acid-based surfactant is generally believed to be less likely to swell the horny layer, and is therefore mild to the skin. The anionic portion thereof is, however, often weakly acidic such as carboxylic acid, so that the hair cleansing agent has been limited in the foamability and cleansing performance, only to prove that it has been insufficient to fulfill the basic performances as a hair cleansing agent. Aiming at solving the problem, a cleansing composition proposed in Patent Document 1 uses, as the main component, an anionic surfactant in the form of alkyloylalkyl taurine salt, having a sulfonic acid group in the anionic portion thereof. The composition, however, still has limited foamability and richness of foam as compared with the alkylsulfate and alkyl ether sulfate, and it has remained difficult to fulfill the basic performance requirements of a hair cleansing agent.

Another challenge to achieve both of mildness and foamability may be found in a cleansing agent composition proposed in Patent Document 2, characterized by using an anionic surfactant such as alkyl ether sulfate, in combination with a nonionic surfactant such as polyethoxylated alcohol, which has an alkyl group having 8 to 16 carbon atoms in the alcohol portion thereof, having 10 to 45 ethoxy groups per molecule, and having a pH value of 6.0 to 8.0. A similar challenge may be found in a shampoo composition proposed in Patent Document 3, characterized by using an anionic surfactant such as alkyl ether sulfate, in combination with a nonionic surfactant having an HLB value of at least 8.

The nonionic surfactant is generally known to show small swellability of the horny layer, and to be mild to the skin, but is difficult to obtain rich foam favored for a hair cleansing agent. The nonionic surfactant is used in an amount of at least 38% by weight in the composition according to the above-described Patent Document 2, and in an amount of at least 29% by weight in the composition according to Patent Document 3. Use of such relatively large amounts of nonionic surfactants has, however, failed in obtaining rich foam favored for a hair cleansing agent, and has prevented mildness and foamability from being attained at the same time.

RELATED DOCUMENTPatent Document

[Patent Document 1] Japanese Patent Publication No. JP-A-S61-272295
[Patent Document 2] Japanese Patent Publication No. JP-A-S49-099104
[Patent Document 3] Japanese Patent Publication No. JP-A-H04-225909
[Patent Document 4] Japanese Patent Publication No. JP-A-2001-131592

SUMMARY OF THE INVENTIONProblems to be Solved by the Invention

The present invention provides an aqueous hair cleansing agent which is excellent in foamability, smoothness of foam, finger combability during rinsing, mildness to the scalp, and less causative of itchiness.

Means for Solving the Problems

The present inventor have found that swelling of the horny layer may be suppressed, and mildness to the scalp and excellent foamability may be attainable at the same time, with respect to an aqueous hair cleansing agent having an alkylsulfate or alkyl ether sulfate contained as a main cleansing component, by mixing a small amount of polyoxyethylene alkyl ether-type nonionic surfactant having an alkyl group of a specific chain length.

According to the present invention, there is provided an aqueous hair cleansing agent which includes the following components (A), (B):

(A) a sulfate-type anionic surfactant represented by the following general formula (1):

R¹O(CH₂CH₂O)_nSO₃Mâ€ƒâ€ƒ(1)

wherein, in the general formula (1), R¹represents an alkyl group or alkenyl group having 10 to 18 carbon atoms, M represents a cation originated from an alkali metal, alkali earth metal, ammonium, alkanolamine or basic amino acid, and n represents a number of 0 to 5 estimated based on weight average; and

(B) polyoxyethylene alkyl ether-type nonionic surfactant represented by the following general formula (2):

R²O(CH₂CH₂O)_mHâ€ƒâ€ƒ(2)

wherein, in the general formula (2), R²represents a straight-chain or branched alkyl group or alkenyl group having 18 carbon atoms, and m represents n number of 6 to 10 estimated based on weight average,

and further comprising water,

wherein the ratio of the component (B), relative to the total of the components (A) and (B) is from 1 to 25% based on the weight ratio.

Advantageous Effect of the Invention

The aqueous hair cleansing agent of the present invention is excellent in foamability, smoothness of foam, finger combability during rinsing, mildness to the scalp, and less causative of itchiness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating a configuration of an apparatus used for evaluating quickness of foaming.

DESCRIPTION OF THE EMBODIMENTS

The aqueous hair cleansing agent of the present invention contains the above-described components (A), (B), and water. The individual components will be explained below in detail.

First, the component (A) will be explained.

In the aqueous hair cleansing agent of the present invention, the component (A) is a sulfate-type anionic surfactant, which is exemplified by alkylsulfate or alkyl ether sulfate, represented by the general formula (1).

(A) Sulfate-Type Anionic Surfactant Represented by the Following General Formula (1):

R¹O(CH₂CH₂O)_nSO₃Mâ€ƒâ€ƒ(1)

(in the general formula (1), R¹represents an alkyl group or alkenyl group having 10 to 18 carbon atoms, M represents an alkali metal, alkali earth metal, ammonium, alkanolamine or basic amino acid, and n represents a number of 0 to 5 estimated based on weight average.)

Among these, in view of ensuring quick foamability and excellent cleansing performance, polyoxyethylene alkyl ether sulfate having an alkyl group of 12 to 14 carbon atoms for R¹, 1 to 2 for n estimated based on weight average, and ammonium or sodium for M in the general formula (1), is preferable.

The component (A) may be a single species, or may be a combination of two or more species, wherein the content of which is preferably 1 to 25% by weight, more preferably 5 to 23% by weight, and even more preferably 8 to 20% by weight of the aqueous hair cleansing agent of the present invention, in view of foamability, pH under condition of use, and finger combability during rinsing.

Next, the component (B) will be explained.

In the aqueous hair cleansing agent of the present invention, the component (B) is a polyoxyethylene alkyl ether-type nonionic surfactant represented by the general formula (2).

(B) Polyoxyethylene Alkyl Ether-Type Nonionic Surfactant Represented by the Following General Formula (2):

R²O(CH₂CH₂O)_mHâ€ƒâ€ƒ(2)

(in the general formula (2), R²represents a straight-chain or branched alkyl group or alkenyl group having 18 carbon atoms, and m represents a number of 6 to 10 estimated based on weight average.)

Representative products commercially available as the component (B) may be exemplified by polyoxyethylene alkyl ether-type surfactants such as EMALEX 606 (polyoxyethylene (6) stearyl ether, with a molecular weight of 518, from Nihon Emulsion Co., Ltd.), Emalgen 306P (polyoxyethylene (6) stearyl ether, with a molecular weight of 518, from Kao Corporation), and Emalgen 409P (polyoxyethylene (9) oleyl ether, with a molecular weight of 648, from Kao Corporation).

The nonionic surfactant which configures the component (B) in the present invention is supposed to form a protective film over the surface of the horny layer, to thereby suppress the anionic surfactant, composing the component (A), from permeating into the horny layer. In order to allow expression of this sort of effect, it is preferable that the nonionic surfactant which configures the component (B) effectively adsorb onto the surface of the horny layer, but does not permeate thereinto.

In view of allowing the component (B) to efficiently adsorb onto the surface of the horny layer, the component (B) preferably has a critical micelle concentration (CMC) of approximately 1Ã—10^âˆ’6M or smaller. The CMC value decreases as the length of alkyl chain elongates. In view of achieving both of adsorptivity onto the horny layer and foamability of the hair cleansing agent at the same time, R²in the above-described formula (2) is preferably a polyoxyethylene stearyl ether having 18 carbon atoms.

In order to avoid permeation of the component (B) into the horny layer, the component (B) preferably has a molecular weight of 500 or larger. In the above-described formula (2), m is preferably 6 to 10. In particular, m is preferably 6. More specifically, polyoxyethylene (6) stearyl ether may be exemplified.

The component (B) may be a single species, or may be a combination of two or more species, wherein the content of which is preferably 0.1 to 10% by weight, more preferably 0.5 to 7% by weight, and even more preferably 1 to 5% by weight of the aqueous hair cleansing agent of the present invention, in view of mildness to the scalp, foamability, shortening of rinsing time, and finger combability during rinsing.

In view of achieving both mildness to the scalp and good foamability, the components (A), (B) preferably give the weight ratio of the component (B) relative to the total of the components (A) and (B) (i.e. (B)/((A)+(B))), of from 1/100 to 25/100 (1 to 25%), more preferably 3/100 to 23/100 (3 to 23%), and even more preferably 5/100 to 20/100 (5 to 20%).

In order to further improve the effect of suppressing dandruff, itchiness, rash and cracking of the scalp, the aqueous hair cleansing agent of the present invention may further contain an organic carboxylic acid and anti-inflammatory agent.

The organic carboxylic acid preferably has 2 to 6 carbon atoms, and is more preferably dicarboxylic acid (which may have a hydroxy group) and hydroxymonocarboxylic acid. More specifically, the dicarboxylic acid may be exemplified by malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, phthalic acid, and oxalic acid. The dicarboxylic acid having a hydroxy group may be exemplified by malic acid and tartaric acid. The hydroxymonocarboxylic acid may be exemplified by glycolic acid, lactic acid, hydroxyacrylic acid, oxybutyric acid, glyceric acid, and gluconic acid.

Among these organic carboxylic acids, preferable examples include glycolic acid, lactic acid, malonic acid, maleic acid, and malic acid. Salts of these organic carboxylic acids may be exemplified by those formed with alkali metal, alkali earth metal, ammonia, and organic amine compound.

The organic carboxylic acid or salt thereof may be a single species, or may be a combination of two or more species, wherein the content of which is preferably 0.1 to 5% by weight, more preferably 0.2 to 3% by weight, and even more preferably 0.5 to 2% by weight of the aqueous hair cleansing agent, in view of ensuring a sufficient level of scalp improvement.

In view of maximizing the effect of improving scalp conditions by the organic carboxylic acid, the aqueous hair cleansing agent of the present invention preferably has a pH value of 1 to 5, preferably 2 to 4.5, and even more preferably 3 to 4.5, at 25Â° C. when diluted 20-fold by weight with water.

For the purpose of adjusting the pH of the composition within such desirable range, an organic or inorganic acid, or an alkali agent may be used while being appropriately combined and quantified. The organic acid may be exemplified by citric acid and glutamic acid, besides the above-described organic carboxylic acid. The inorganic acid may be exemplified by hydrochloric acid, sulfuric acid, and phosphoric acid. The alkali may be exemplified by sodium hydroxide, and potassium hydroxide.

The aqueous hair cleansing agent of the present invention is excellent in foamability, smoothness of foam, and smooth rinsability, and expresses an effect of suppressing swelling of the horny layer, and itchiness, irrespective of the pH value. The cleansing agent may also successfully obtain an additional anti-dandruff effect which could not be obtained under a neutral condition, if the cleansing agent contains the organic carboxylic acid or salt thereof so as to adjust the pH to 1 to 5 at 25Â° C. when diluted 20-fold by weight with water.

Examples of the anti-inflammatory agent includes glycyrrhetinic acid, glycyrrhizic acid and derivatives thereof; and also include components having anti-inflammatory function, such as Îµ-aminocaproic acid, allantoin, sodium guaiazulene sulfonate, d-camphor, l-menthol, urea, pyridoxine dipalmitate, glycyrrhetinyl stearate, tranexamic acid, vitamin A oil, hydrocortisone, prednisolone, pyridoxine hydrochloride, Kankohso (photosensitizer) 301, zinc oxide, and hydrocortisone acetate. The derivatives of glycyrrhetinic acid or glycyrrhizic acid include salts which include alkali metal salts represented by sodium salt and potassium salt, and ammonium salt; and esters such as glycerin ester and stearyl ester. More specifically, dipotassium glycyrrhizinate, disodium glycyrrhizinate, trisodium glycyrrhizinate, monoammonium glycyrrhizinate, glycerin glycyrrhetinate, and stearyl glycyrrhetinate may be exemplified.

The anti-inflammatory agent may be a single species, or may be a combination of two or more species, wherein the content of which is preferably 0.001 to 10% by weight, more preferably 0.005 to 5% by weight, and even more preferably 0.01 to 1% by weight of the aqueous hair cleansing agent.

From another aspect, the hair cleansing agent may occasionally be required to more effectively suppress dandruff and itchiness of the scalp. It is also generally known that killing of resident bacteria is one effective means for suppressing dandruff. The hair cleansing agent is often added also with antibacterial agent.

An exemplary hair cleansing agent which contains alkyl ether sulfate as a main cleansing component, together with the antibacterial agent, may be found in Patent Document 4. While the cleansing performance and anti-dandruff performance are reportedly good by virtue of the combination of the anionic surfactant and the antibacterial agent, the hair cleansing agent still has room for improvement as for suppression of itchiness.

From this point of view, the present invention provides an aqueous hair cleansing agent containing an alkylsulfate or alkyl ether sulfate as a main cleansing component, which is excellent in mildness to the scalp and foamability, and strongly effective in suppressing dandruff and itchiness of the scalp, by virtue of the combination of a specific polyoxyethylene alkyl ether-type nonionic surfactant with the antibacterial agent.

This sort of antibacterial agent (referred to as â€œcomponent (C)â€ , hereinafter) may be exemplified by triclosan, triclocarban, pirocton olamine, zinc pyrithione, selenium disulfide, 3-methyl-4-(1-methylethyl)phenol, benzalkonium salt or benzethonium salt represented by the general formula (3), and pyridinium salt represented by the general formula (5).

[Image Omitted]

(In the formula, R⁵represents an alkyl group having 8 to 18 carbon atoms or a group represented by formula (4), and Z^âˆ’ represents a halogen ion.)

[Image Omitted]

(In the formula, R⁶represents a straight-chain or branched alkyl group having 6 to 18 carbon atoms, and Z^âˆ’ represents a halogen ion.)

In view of obtaining a sufficient level of antibacterial performance, the component (C) is preferably mixed into the hair cleansing agent in an amount of from 0.1 to 4% by weight, particularly 0.4 to 3% by weight.

The component (C) is preferably zinc pyrithione, pirocton olamine, or benzalkonium salt having an alkyl group of 12 to 16 carbons for R⁵in the general formula (3). Zinc pyrithione and pirocton olamine are more preferable.

While the aqueous hair cleansing agent of the present invention is excellent in foamability, smoothness of foam and smooth rinsability, suppresses swelling of the horny layer, and suppresses itchiness irrespective of the pH value, the pH value when applied to hair (diluted 20-fold with water at 25Â° C.) is preferably 5 to 8, in view of stability of the antibacterial agent such as zinc pyrithione. The pH may be adjustable by using any pH adjusting agents (acid, alkali) generally adopted.

The aqueous hair cleansing agent of the present invention may contain an anionic surfactant other than the component (A), and a nonionic surfactant or amphoteric surfactant other than the component (B), for the purpose of further improving the cleansing performance.

The anionic surfactant other than the component (A) adoptable herein includes sulfuric acid-based ones, sulfonic acid-based ones, and carboxylic acid-based ones. The examples include sulfosuccinic acid alkylene alkylphenyl ether sulfate, sulfosuccinic acid alkyl ester salt, polyoxyalkylene sulfosuccinic acid alkyl ester salt, alkane sulfonate, higher fatty acid salts, alkyl ether carboxylic acid and salt thereof. Among these, alkyl ether carboxylic acid or salt thereof is preferable.

The nonionic surfactant other than the component (B) adoptable herein may be exemplified by polyoxyalkylene solbitan fatty acid ester, polyoxyalkylene solbit fatty acid ester, polyoxyalkylene glycerin fatty acid ester, polyoxyalkylene fatty acid ester, polyoxyalkylene alkyl ether, polyoxyalkylene alkylphenyl ether, polyoxyalkylene (hydrogenated) castor oil, sucrose fatty acid ester, polyglycerin alkyl ether, polyglycerin fatty acid ester, fatty acid alkanolamide, alkylglycoside, mono alkyl and monoalkenyl glyceryl ether.

Among these, polyoxyalkylene solbitan fatty acid ester such as polyoxyethylene solbitan fatty acid ester, polyoxyalkylene fatty acid ester such as polyoxyalkylene (C₈to C₂₀) fatty acid ester, and polyoxyalkylene (hydrogenated) castor oil such as polyoxyethylene hydrogenated castor oil, and alkylglycoside are preferable.

Also fatty acid alkanolamide is preferable, allowing either of monoalkanolamide and dialkanolamide. Those having an acyl group of 8 to 18 carbon atoms, in particular 10 to 16 carbon atoms are preferable. Also those having a hydroxyalkyl group of 2 to 3 carbon atoms are preferable, which are exemplified by oleic acid diethanolamide, palm kernel oil fatty acid diethanolamide, coconut oil fatty acid diethanolamide, lauric acid diethanolamide, polyoxyethylene coconut oil fatty acid monoethanolamide, coconut oil fatty acid monoethanolamide, lauric acid isopropanolamide, and lauric acid monoethanolamide.

Also glyceryl monoalkyl ether or glyceryl monoalkenyl ether is preferable, where the alkyl group or alkenyl group is preferably a straight-chain or branched alkyl group having 4 to 10 carbon atoms, in particular 8 to 10 carbon atoms. The specific examples include n-butyl group, isobutyl group, n-pentyl group, 2-methylbutyl group, isopentyl group, n-hexyl group, isohexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-decyl group, and isodecyl group. In particular, 2-ethylhexyl group and isodecyl group are preferable.

The amphoteric surfactant may be exemplified by betaine-based surfactants. Among these, alkyl dimethyl aminoacetic acid betaine, fatty acid amidopropyl betaine, and alkyl hydroxy sulfobetaine are preferable, wherein fatty acid amidopropyl betaine is more preferable. The fatty acid amidopropyl betaine preferably has an acyl group of 8 to 18 carbon atoms, in particular 10 to 16 carbon atoms, wherein more preferable examples include lauric acid amidopropyl betaine, palm kernel oil fatty acid amidopropyl betaine, and coconut oil fatty acid amidopropyl betaine.

These surfactants may be a single species, or may be a combination of two or more species contained in the aqueous hair cleansing agent. In view of obtaining the aqueous hair cleansing agent of the present invention in the form of a water-based liquid cleaner, it is preferable to use fatty acid amidopropyl betaine, fatty acid alkanolamide, or mono alkylglyceryl ether, together with the components (A), (B), not only because the foamability is improved, but also because the appropriate level of pH may be obtained.

The content of these surfactants is preferably 0.1 to 15% by weight in the hair cleansing agent of the present invention, in view of obtaining a good effect of enhancing the foamability. From this point of view, the content is more preferably 0.5 to 8% by weight, and even more preferably 1 to 6% by weight.

The aqueous hair cleansing agent of the present invention may further be added with a cationic surfactant, a cationized polymer or silicones, for the purpose of improving the finger combability during rinsing, and of improving styling of hair after being dried.

The cationic surfactant may be exemplified by alkyltrimethyl ammonium salt, alkoxy trimethyl ammonium salt, dialkyldimethyl ammonium salt, alkyldimethylamine salt, alkoxy dimethylamine salt, and alkylamide dimethylamine salt.

(i) Alkyl Trimethylammonium Salt