JP7496305B2 - Method for evaluating cleansing cosmetics - Google Patents

Description

The present invention relates to a method for evaluating cleansing cosmetics.

Conventionally, the cleaning power of a cleansing cosmetic has been evaluated by applying a certain amount of an indicator substance such as an ultraviolet absorber onto actual skin or artificial skin, applying and blending the cleansing cosmetic, rinsing with water, and measuring the amount of the indicator substance remaining on the skin or artificial skin. However, with this method, uneven application of the indicator substance and cleansing cosmetic occurs due to the manual application of the indicator substance and cleansing cosmetic, and there is a possibility that errors may occur in the blending action depending on the amount of force used. Furthermore, since a spatula is used for application, the indicator substance and cleansing cosmetic may adhere to the spatula, and indicator substances such as ultraviolet absorbers may seep into the artificial skin, and even if the remaining indicator substance is extracted with ethanol to measure it, there is a possibility that not all of it may be recovered. Therefore, it is necessary to perform the same action multiple times and take the average, which is a very cumbersome task.

On the other hand, a method is known for evaluating the ease of rinsing a cleansing cosmetic after washing and the refreshing feeling on the skin after washing off by adding water to the cleansing cosmetic and measuring the particle size of the O/W type emulsion particles formed (Patent Documents 1 and 2). In general, it is said that the smaller the average particle size of the emulsion particles, the easier it is to rinse after washing and the more refreshing the skin feels after washing off, and the larger the average particle size, the more sticky and slimy the skin becomes, and the more oily the skin feels. Patent Document 2 reports that if the average emulsion particle size is 0.3 μm or less, the cleansing cosmetic can be washed off quickly and cleanly.

JP 2009-029758 A JP 2018-070481 A

Conventional methods for evaluating the detergency of cleansing cosmetics cannot eliminate the influence of manual technique, and evaluations using such methods do not necessarily coincide with evaluations of the intrinsic detergency of the cleansing cosmetic itself.
Therefore, an object of the present invention is to provide a method for evaluating cleansing cosmetics in which the influence of manual technique is suppressed.

After much investigation, the inventors discovered that by adding a cleansing cosmetic to a filter medium to which an indicator substance had been added, removing the cleansing cosmetic from the filter medium by adding a solvent and filtering, and then measuring the amount of the indicator substance remaining in the filter medium or contained in the filtrate, it is possible to evaluate the cleaning power of the cleansing cosmetic while suppressing errors due to manual techniques, and by measuring the emulsion particle size of the cleansing cosmetic contained in the filtrate, it is possible to evaluate the feel of the cleansing cosmetic when in use, thus completing the present invention.

That is, the present invention provides the following [1] to [7].
[1] A method for evaluating a cleansing cosmetic, comprising:
(1) adding an indicator substance to a filter medium;
(2) adding a cleansing cosmetic to the filter medium obtained in the step (1) to bring the indicator substance into contact with the cleansing cosmetic; and (3) adding a solvent for removing the cleansing cosmetic to the filter medium obtained in the step (2) and filtering the mixture.
A method comprising:
[2] The method according to [1], further comprising, after the step (3), a step (4) of measuring the indicator substance remaining in the filter medium obtained in the step (3).
[3] The method according to [1], further comprising, after the step (3), a step (4') of measuring the indicator substance contained in the filtrate obtained in the step (3).
[4] The method according to any one of [1] to [3], further comprising, after the step (3), (4) or (4'), a step (5) of measuring the emulsion particle size of the cleansing cosmetic contained in the filtrate obtained in the step (3).
[5] Any of the methods according to [1] to [4], wherein the filter material is filter paper.
[6] Any of the methods according to [1] to [5], wherein the retention particle size of the filter medium is 0.1 to 30 μm.
[7] The method according to any one of [1] to [6], which is used for the relative evaluation of at least two types of cleansing cosmetic preparations.

The method of the present invention makes it possible to evaluate the essential cleansing power of a cleansing cosmetic while suppressing errors due to manual techniques. It also makes it possible to evaluate the feel of the cleansing cosmetic when used.

The method for evaluating a cleansing cosmetic of the present invention comprises:
(1) adding an indicator substance to a filter medium;
(2) adding a cleansing cosmetic to the filter medium obtained in the step (1) to bring the indicator substance into contact with the cleansing cosmetic; and (3) adding a solvent for removing the cleansing cosmetic to the filter medium obtained in the step (2) and filtering the mixture.
The method includes:

In the present invention, the term "cleansing cosmetic" refers to a cosmetic for cleansing the skin that has the effect of removing oily dirt from the skin, such as makeup cosmetics. The cleansing cosmetic is not particularly limited, and examples thereof include cleansing oil, cleansing cream, cleansing foam, cleansing gel, cleansing lotion, and the like. The method of the present invention is particularly suitable for liquid or cream cleansing cosmetics, and the viscosity of the cleansing cosmetic is preferably less than 100,000 cP, more preferably less than 10,000 cP, and even more preferably less than 1,000 cP, in view of ease of addition to the filter medium and ease of contact with the indicator substance. Here, the viscosity may be measured by a known method, and can be measured, for example, at 20°C using a rotational viscometer (for example, a rotational viscometer <BM type, manufactured by Tokyo Keiki Co., Ltd.>).

In the present invention, "evaluation of a cleansing cosmetic" means evaluation of the performance of the cleansing cosmetic, and includes evaluation of the compatibility of the cleansing cosmetic with the skin, the cleaning power of the cleansing cosmetic (ease of removing makeup), ease of rinsing off the cleansing cosmetic, and the refreshing feeling on the skin after rinsing off the cleansing cosmetic.

Step (1) of the method for evaluating cleansing cosmetics of the present invention is a step of adding an indicator substance to a filter medium.

The term "filter material" used in the present invention means a porous material used for filtration. The filter material is not particularly limited as long as it can retain the cleansing cosmetic and the indicator substance, and examples thereof include filter paper, nonwoven fabric, woven fabric, membrane filter, particles, etc. Examples of the material of the filter material include organic materials such as cellulose, cellulose acetate, cellulose mixed ester, polyethylene, polypropylene, polyolefin, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), nylon, activated carbon, cotton, etc., and inorganic materials such as glass, silica gel, alumina, stainless steel, and sand. The filter material may be appropriately selected in consideration of the retention of the indicator substance and cleansing cosmetic to be added, the permeability of the solvent, etc., and is preferably filter paper or cotton, more preferably filter paper, and even more preferably cellulose filter paper. These filter materials may be used alone or in combination of two or more types.

The retention particle size of the filter medium is preferably 0.1 μm or more, more preferably 0.5 μm or more, and preferably 30 μm or less, more preferably 20 μm or less. Also, 0.1 to 30 μm is preferable, 0.1 to 20 μm is more preferable, and 0.5 to 20 μm is even more preferable. If the retention particle size is less than 0.1 μm, the filter medium may become clogged, and if it exceeds 30 μm, the indicator substance is likely to not remain on the filter medium and to drip. Here, the retention particle size refers to the particle size that can retain 90% or more when a seven-type powder dispersion water specified in JIS Z 8901 is naturally filtered.

The thickness of the filter medium is not particularly limited as long as the indicator substance and cleansing cosmetic to be added do not drip, and can be appropriately selected according to the type and material of the filter medium. The thickness is preferably 0.05 mm or more, more preferably 0.1 mm or more, and preferably 10 cm or less, more preferably 5 cm or less, even more preferably 1 cm or less, even more preferably 3 mm or less, and even more preferably 2.5 mm or less. Also, 0.05 mm to 10 cm is preferable, 0.05 mm to 5 cm is more preferable, 0.05 mm to 1 cm is more preferable, 0.05 to 3 mm is more preferable, 0.05 to 2.5 mm is more preferable, and 0.1 to 2.5 mm is even more preferable. For example, when using a flat filter medium such as filter paper, the thickness is preferably 0.05 to 3 mm, more preferably 0.05 to 2.5 mm, and even more preferably 0.1 to 2.5 mm, and when using a filter medium to be filled into a container such as cotton or sand, the thickness is preferably 0.05 mm to 10 cm, more preferably 0.05 mm to 5 cm, and even more preferably 0.1 mm to 1 cm. Two or more types of filter medium may be stacked together as long as the total thickness is within the above range.

The water absorbency of the filter medium is not particularly limited, but is preferably 0.5 cm or more, more preferably 1 cm or more, and preferably 25 cm or less, more preferably 20 cm or less. Also, 0.5 to 25 cm is preferable, 0.5 to 20 cm is more preferable, and 1 to 20 cm is even more preferable. Here, water absorbency refers to the height of water that rises in 10 minutes when a long and thin filter medium (for example, a filter medium with a width of about 1.5 cm and a length of about 20 cm) is placed in water at 20°C.

There are no particular limitations on the size or shape of the filter medium, but for example, if it is circular, the diameter is preferably 10 mm or more, more preferably 25 mm or more, and preferably 600 mm or less, more preferably 300 mm or less. Also, 10 to 600 mm is preferable, 25 to 300 mm is more preferable, and 50 to 150 mm is even more preferable.

The "indicator substance" used in the present invention is not particularly limited as long as it is a substance that can be a target for cleaning in cleansing, particularly a substance that can be incorporated into cosmetics. Examples of indicator substances include ultraviolet absorbers such as ethylhexyl methoxycinnamate (310 nm, hereinafter, the wavelength measured by the spectrophotometer for each substance is shown in parentheses), oxybenzone (288 nm), and t-butyl methoxydibenzoylmethane (358 nm); preservatives such as paraoxybenzoic acid esters (e.g., methylparaben (254 nm)) and phenoxyethanol (254 nm); water-soluble bases such as ascorbic acid glucoside (254 nm) and dipotassium glycyrrhizinate (254 nm); and oil-soluble bases such as tetra 2-hexyldecanoate ascorbyl (254 nm), stearyl glycyrrhetinate (254 nm), and tocopherol acetate (284 nm). Of these, ultraviolet absorbers, preservatives, and oil-soluble bases are preferred.

The indicator substance may be added to the filter material as it is, as a solution or suspension dissolved or suspended in a suitable solvent, or as a semi-solid preparation (e.g., ointment, cream, etc.) uniformly kneaded in a suitable base. The solvent can be appropriately selected according to the type of indicator substance, and may be, for example, water; alcohols such as methanol, ethanol, propyl alcohol, isopropyl alcohol, butanol, etc.; polyhydric alcohols such as ethylene glycol, propylene glycol, 1,3-butylene glycol, glycerin, etc.; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate; ethers such as diethyl ether, tetrahydrofuran, dioxane, etc.; halogenated hydrocarbons such as chloroform and dichloromethane; hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, etc.; amides such as dimethylformamide; nitriles such as acetonitrile; glyceryl trioctanoate, isopropyl alcohol, etc. Examples of the solvent include ester oils such as pyrimyristate, pentaerythritol tetra-2-ethylhexanoate, myristic acid esters, palmitic acid esters, stearic acid esters, lauric acid esters, linoleic acid esters, octanoic acid esters, oleic acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbit fatty acid esters, lactate esters, malic acid esters, adipic acid esters, sebacic acid esters, succinic acid esters, citrate esters, polyhydric alcohol esters, and lanolin; hydrocarbon oils such as paraffin, liquid paraffin, and squalane; and silicone oils such as methylphenyl silicone, dimethyl silicone, and cyclic silicone. These solvents may be used alone or in combination of two or more. Examples of the base of the semi-solid preparation include oleaginous bases such as petrolatum, liquid paraffin, plastibase, silicone, simple ointment, white ointment, vegetable oil, and wax; emulsion bases such as hydrophilic petrolatum, purified lanolin, eucerin, neocerin, water-absorbent ointment, hydrous lanolin, hydrophilic plastibase, and cold cream; water-soluble bases such as macrogols, sorbase, and macrogol ointment; and suspension bases such as hydrogel and lyogel. These bases may be used alone or in combination of two or more. The concentration of the indicator substance in the solution, suspension, or semi-solid preparation is preferably 0.01% by mass or more, more preferably 0.5% by mass or more, and more preferably 20% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less. Also, 0.01 to 20% by mass is preferable, 0.01 to 5% by mass is preferable, and 0.5 to 3% by mass is more preferable. In addition, the viscosity of the semi-solid agent is preferably less than 100,000 cP, more preferably less than 10,000 cP, and even more preferably less than 1,000 cP. Here, the viscosity can be measured by a known method, as in the case of the above-mentioned cleansing cosmetic preparation.

As another example of the indicator substance, a cosmetic containing the above-mentioned indicator substance can be used as is. When a cosmetic is used as the indicator substance, from the viewpoint of permeability into the filter medium and contact with the cleansing cosmetic, the cosmetic is preferably in the form of a liquid, emulsion, or cream, and the viscosity of the cosmetic is preferably less than 100,000 cP, more preferably less than 10,000 cP, and even more preferably less than 1,000 cP. Here, the viscosity can be measured by a known method, as in the case of the above-mentioned cleansing cosmetic.

The manner in which the indicator substance is added to the filter medium is not particularly limited, but for example, the indicator substance may be placed in the center of the filter medium using a tool such as a pipette. The amount of indicator substance added may be appropriately set in consideration of the type of indicator substance, the filter medium used, etc. For example, when the filter medium is a filter paper with a diameter of 55 mm, the amount added is preferably 5 to 100 μL, more preferably 10 to 50 μL. The filter medium to which the indicator substance has been added may be left to stand, and the added indicator substance remains on the filter medium or a part or all of it penetrates into the filter medium. The standing time is preferably 1 minute or more, more preferably 5 minutes or more, and preferably 96 hours or less, and more preferably 24 hours or less. Also, 1 minute to 96 hours are preferable, 1 minute to 24 hours are more preferable, and 5 minutes to 24 hours are even more preferable. In addition, when the indicator substance is a cosmetic material, in order to prevent deterioration of the cosmetic material on the filter medium, the standing time is preferably 1 minute or more, more preferably 5 minutes or more, and preferably 3 hours or less, and more preferably 1 hour or less. Additionally, 1 minute to 3 hours is preferable, 1 minute to 1 hour is more preferable, and 5 minutes to 1 hour is even more preferable.

Step (2) of the method of the present invention is a step of adding a cleansing cosmetic to the filter medium obtained in step (1) to bring the indicator substance into contact with the cleansing cosmetic.

The manner of adding the cleansing cosmetic to the filter medium is not particularly limited, but for example, it is preferable to place the cleansing cosmetic on the filter medium so as to cover the area on the filter medium to which the indicator substance was added in step (1) using a tool such as a pipette. The amount of the cleansing cosmetic added may be appropriately set in consideration of the type and amount of the indicator substance, the filter medium used, etc., and is preferably equal to or greater than the amount of the indicator substance added. For example, when the filter medium is a filter paper with a diameter of 55 mm, the amount added is preferably 5 to 100 μL, more preferably 10 to 50 μL. The filter medium to which the cleansing cosmetic is added may be left to stand, and the added cleansing cosmetic remains on the filter medium or a part or all of it penetrates into the filter medium. The standing time is preferably 1 minute or more, more preferably 5 minutes or more, and preferably 3 hours or less, more preferably 1 hour or less, in order to avoid deterioration of the cleansing cosmetic on the filter medium. Also, 1 minute to 3 hours is preferable, 1 minute to 1 hour is more preferable, and 5 minutes to 1 hour is even more preferable.
The step (2) allows the indicator substance and the cleansing cosmetic to come into contact on or in the filter medium. At this time, the compatibility of the indicator substance and the cleansing cosmetic can be visually observed to evaluate the skin compatibility of the cleansing cosmetic. The better the compatibility, the better the skin compatibility of the cleansing cosmetic can be judged to be.
In addition, if the added cleansing cosmetic or the indicator substance and cleansing cosmetic do not penetrate the filter medium and remain on the filter medium, a new filter medium may be layered on top of the filter medium after step (2) and before step (3) described below to increase the contact area between the indicator substance and the cleansing cosmetic.

Step (3) of the method of the present invention is a step of adding a solvent for removing the cleansing cosmetic to the filter medium obtained in step (2) and performing filtration.

The term "solvent for removing cleansing cosmetics" used in the present invention means a solvent that is added to a filter medium and filtered to separate the cleansing cosmetics from the filter medium. Considering the actual face washing method, such a solvent is preferably an aqueous medium, more preferably water or a wipe-off cosmetic, and even more preferably water. Here, the water that can be used is distilled water, purified water such as ion-exchanged water, tap water, etc., and from the viewpoint of evaluation accuracy, purified water is even more preferable.

The mode of adding the solvent for removing the cleansing cosmetic to the filter is not particularly limited. For example, the filter is placed in a filtration device, and the solvent for removing the cleansing cosmetic is added using a tool such as a pipette so that it spreads over the entire filter. The amount of solvent added may be an amount sufficient to remove the cleansing cosmetic from the filter, and may be appropriately set in consideration of the type and amount of the cleansing cosmetic, the filter used, the filtration method, etc., and is preferably about 1 to 100,000 times the amount of the cleansing cosmetic added, more preferably about 10 to 30,000 times, and particularly preferably about 5,000 to 25,000 times. For example, when the filter is a filter paper with a diameter of 55 mm, the amount of the cleansing cosmetic added is 10 to 50 μL, and suction filtration is performed, the amount added is preferably 100 to 300 mL, and more preferably 150 to 250 mL. As the filtration method, known methods such as natural filtration, suction filtration, pressure filtration, and centrifugal filtration can be used. Among these, suction filtration is preferred from the viewpoint of the high filtration speed. The filtration device may be any device commonly used depending on the filtration method, and the filtration conditions may be appropriately determined taking into consideration the performance of the filter medium and the filtration device.
By the step (3), the indicator substance that has not been washed away by the cleansing cosmetic remains on or in the filter medium, and the indicator substance that has been washed away is contained in the filtrate together with the cleansing cosmetic. Therefore, the cleaning power of the cleansing cosmetic can be evaluated by measuring the indicator substance remaining on the filter medium or the indicator substance contained in the filtrate.

The indicator substance remaining in the filter medium, specifically the indicator substance remaining on and in the filter medium, may be measured, for example, by adding a suitable extraction solvent to the filter medium itself to obtain an extract containing the indicator substance, and using the extract to measure the indicator substance by a known measurement method. The extraction solvent may be appropriately selected depending on the type of indicator substance, and may be, for example, water; alcohols such as methanol, ethanol, propyl alcohol, isopropyl alcohol, butanol, etc.; polyhydric alcohols such as ethylene glycol, propylene glycol, 1,3-butylene glycol, glycerin, etc.; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate; ethers such as diethyl ether, tetrahydrofuran, and dioxane; halogenated hydrocarbons such as chloroform and dichloromethane; hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, and xylene; amides such as dimethylformamide; nitriles such as acetonitrile; glyceryl trioctanoate, isopropyl alcohol, etc. Examples of suitable extracting solvents include ester oils such as ethylhexanoate, pentaerythritol tetra-2-ethylhexanoate, myristic acid esters, palmitic acid esters, stearic acid esters, lauric acid esters, linoleic acid esters, octanoic acid esters, oleic acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, lactate esters, malic acid esters, adipic acid esters, sebacic acid esters, succinic acid esters, citrate esters, polyhydric alcohol esters, and lanolin esters; hydrocarbon oils such as paraffin, liquid paraffin, and squalane; and silicone oils such as methylphenyl silicone, dimethyl silicone, and cyclic silicone. Of these, it is preferable to use the same solvent as the solvent in which the indicator substance is dissolved or suspended. These solvents may be used alone or in combination of two or more. The amount of the extraction solvent used is not particularly limited as long as the filter material is completely immersed in the extraction solvent, but is preferably 3 to 30 mL, and more preferably 5 to 15 mL. The extraction time is not particularly limited, but is preferably 1 minute to 1 hour, more preferably 10 minutes to 1 hour, and even more preferably 10 to 30 minutes. The method for measuring the amount of the indicator substance may be appropriately selected from known methods depending on the type of indicator substance, and an example of such a method is to measure the absorbance at a specified wavelength using a spectrophotometer.

More specifically, the cleaning power of a cleansing cosmetic can be expressed as the removal rate of the indicator substance from the filter medium. The removal rate can be calculated, for example, by the following formula (1).

The amount of indicator substance in the control refers to the amount of indicator substance remaining in the filter medium after performing only steps (1) and (3) above, i.e., the amount of indicator substance remaining in the filter medium when no cleansing cosmetic is added, and the amount of indicator substance in the test refers to the amount of indicator substance remaining in the filter medium after performing steps (1), (2), and (3) above. The higher the removal rate of the indicator substance, the higher the cleaning power of the cleansing cosmetic can be evaluated.

The indicator substance contained in the filtrate may be measured by a known measurement method using the filtrate. Examples of the measurement method include the same method as the method for measuring the amount of indicator substance remaining in the filter medium. If necessary, the filtrate may be further diluted with a solvent used to remove the cleansing cosmetic and then measured.

More specifically, the cleaning power of a cleansing cosmetic can be expressed as the removal rate of the indicator substance from the filter medium. The removal rate can be calculated, for example, by the following formula (2).

The amount of indicator substance in the test refers to the amount of indicator substance contained in the filtrate after carrying out the above steps (1), (2), and (3). The amount of indicator substance in the control refers to the amount of indicator substance contained in the filtrate after carrying out only the above steps (1) and (3). The higher the removal rate of the indicator substance, the higher the cleaning power of the cleansing cosmetic can be evaluated.

When evaluating the cleaning power of a cleansing cosmetic product, it is preferable to measure the amount of indicator substance remaining on or in the filter medium in order to reduce the influence of substances other than the indicator substance on the measurement system.

In addition, if a cleansing cosmetic to which a certain amount of water has been added in advance is used as the cleansing cosmetic to be added in step (2), the cleansing power of the cleansing cosmetic can be evaluated when the face is wet with water or when the cleansing cosmetic is applied with wet hands. The amount of water added is preferably 3 to 30% by mass, more preferably 5 to 20% by mass, of the cleansing cosmetic.

The cleansing cosmetic forms O/W type emulsion particles by adding a solvent for removing the cleansing cosmetic, and disperses oily dirt such as makeup cosmetics in water to remove the dirt. Therefore, the filtrate obtained in step (3) contains emulsion particles of the cleansing cosmetic. As described above, the particle size of the emulsion particles of the cleansing cosmetic can be an index for evaluating the usability of the cleansing cosmetic, such as the ease of rinsing after washing and the refreshing feeling of the skin after washing (Patent Documents 1 and 2). Therefore, the usability of the cleansing cosmetic can be evaluated by measuring the particle size of the emulsion particles of the cleansing cosmetic in the filtrate. The emulsion particle size can be measured using a particle size distribution measuring device (e.g., LA-350, manufactured by Horiba, Ltd.) as shown in the examples below. It can be evaluated that the smaller the average emulsion particle size, the better the ease of rinsing after washing and the refreshing feeling after washing, and the larger the average emulsion particle size, the more sticky and slimy the skin becomes, and the more oily the skin remains. In addition to the average emulsion particle size, the mode diameter or median diameter of the emulsion particles may also be used as an index, and in this case, the smaller the diameter, the easier it is to rinse after washing and the more refreshing the feeling after washing. The mode diameter and median diameter can be measured using a particle size distribution measuring device (for example, LA-350, manufactured by Horiba, Ltd.).

As shown in the Examples below, the method for evaluating a cleansing cosmetic of the present invention can suppress the influence of variability in the manual technique and can evaluate the essential cleansing power of the cleansing cosmetic itself. It can also evaluate the feel of the cleansing cosmetic when used.
As shown in the Examples below, the results of evaluation of cleansing cosmetics using the method of the present invention are consistent with the results of sensory evaluation of cleansing cosmetics by humans, making the method of the present invention extremely useful as an evaluation system for cleansing cosmetics.

The method for evaluating cleansing cosmetics of the present invention can be suitably used for the relative evaluation of the detergency and/or usability of at least two types of cleansing cosmetics.
Alternatively, the method of the present invention can be suitably used to evaluate the detergency of a cleansing cosmetic against at least two kinds of indicator components. For example, by using an indicator component to be removed by the cleansing cosmetic and an indicator component to be left behind, it is possible to evaluate whether only the indicator component to be removed can be selectively cleaned.

In the method of the present invention, a washing agent that removes aqueous dirt is further added to the filter medium obtained in step (3), and then a solvent for removing the washing agent is added and filtration is performed, so that the effect of double face washing can be evaluated in addition to the evaluation of the cleansing cosmetic. The details of the addition of the washing agent, the solvent for removing the washing agent, and the filtration are the same as those of the addition of the cleansing cosmetic, the solvent for removing the cleansing cosmetic, and the filtration described above. The effect of double face washing can be evaluated by measuring the indicator substance remaining in the filter medium or the indicator substance contained in the filtrate, in the same way as the evaluation of the cleaning power of the cleansing cosmetic.

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

Example 1 Cleansing Cosmetic Evaluation System An ethanol solution of ethylhexyl methoxycinnamate (1% methoxycinnamate concentration) as an indicator substance was added to the center of a filter paper (qualitative filter paper No. 1, retention particle size 6 μm, diameter 55 mm, thickness 0.2 mm, water absorption 9.0 cm, manufactured by ADVANTEC Co., Ltd.) in an amount of 10 μL using a pipette, and allowed to stand for 15 hours. Thereafter, 10, 20, 30, or 40 μL of the cleansing cosmetic product 1 (cleansing oil, viscosity: 330 cP (measurement conditions: B-type viscometer, 20° C., No. 2, 60 rpm, 1 minute)) was added to the filter paper from above the addition point of the indicator substance, and allowed to stand for 10 minutes. The aforementioned filter paper was placed in a suction filtration device, 200 mL of purified water was poured in, and suction filtration was performed. Suction filtration was performed by placing an aspirator and opening the water faucet at a certain angle for each test. The obtained filter paper was immersed in 10 mL of ethanol to extract the ethylhexyl methoxycinnamate remaining in the filter paper, and the absorbance (310 nm) of the extract was measured using a spectrophotometer (U-5100, Hitachi High-Tech Science Co., Ltd.). As a control, 10 μL of an ethanol solution of ethylhexyl methoxycinnamate (ethylhexyl methoxycinnamate concentration 1%) was added with a pipette, and the filter paper was left to stand for 15 hours. The filter paper was then placed in a suction filtration device, and the same filtration and extraction processes were performed, and the absorbance (310 nm) was measured. The removal rate of the indicator substance was calculated using the following formula (3). Each operation was performed three times. The average removal rate of the indicator substance is shown in Table 1.

As is clear from Table 1, the removal rate of the indicator substance increased depending on the amount of the cleansing cosmetic, and the variation in the removal rate between operations was small. Therefore, it was demonstrated that the evaluation system for the cleansing cosmetic of this example is capable of evaluating the cleaning power of the cleansing cosmetic, and that the variation between operations is small.

Reference Example 1 Comparison of evaluation systems for cleansing cosmetics As a reference example, 10 μL of an ethanol solution of ethylhexyl methoxycinnamate (1% ethylhexyl methoxycinnamate concentration) as an indicator substance was added to the center of filter paper (Qualitative filter paper No. 1, retention particle size 6 μm, diameter 55 mm, thickness 0.2 mm, water absorbency 9.0 cm, manufactured by ADVANTEC Co., Ltd.) with a pipette and left to stand for 15 hours. The obtained filter paper was then immersed in 10 mL of ethanol to extract the ethylhexyl methoxycinnamate remaining in the filter paper, and the absorbance (310 nm) of the extract was measured using a spectrophotometer (U-5100, manufactured by Hitachi High-Tech Science Co., Ltd.). As a comparative example (conventional method), 15 μL of a commercially available cream foundation containing 2.5% ethylhexyl methoxycinnamate was added to 4 cm x 5 cm artificial leather (urethane) with a pipette and manually spread using a spatula. Then, the artificial leather was divided into 4 equal sections, each section was immersed in 10 mL of ethanol to extract the ethylhexyl methoxycinnamate remaining in the artificial leather, and the absorbance (310 nm) of the extract for each section was measured using a spectrophotometer. Each operation was performed three times. The results of the absorbance measurement for the reference example are shown in Table 2, and the results of the absorbance measurement for the comparative example are shown in Table 3.

In the comparative example (conventional method), large uneven application of the indicator substance was observed between sections. In the evaluation of cleansing cosmetics, there is a concern that not only uneven application of the indicator substance but also similar uneven application occurs at the stage of applying the cleansing cosmetic, and that these may have a synergistic effect on the evaluation results. It has become clear that the conventional method is unable to eliminate the influence of variability in technique on the evaluation, and is therefore insufficient for evaluating the performance of the cleansing cosmetic itself. On the other hand, in the reference example corresponding to step (1) of the method of the present invention, the variability between operations was very small.

Example 2 Evaluation of the cleaning power of the cleansing cosmetic An ethanol solution of ethylhexyl methoxycinnamate (1% methoxycinnamate concentration) as the indicator substance was added to the center of a filter paper (Qualitative filter paper No. 1, retention particle size 6 μm, diameter 55 mm, thickness 0.2 mm, water absorption 9.0 cm, manufactured by ADVANTEC Co., Ltd.) in an amount of 10 μL using a pipette, and allowed to stand for 1 hour. Thereafter, 20 μL of the cleansing cosmetic of test product 1 or the cleansing cosmetic of test product 2 used in Example 1 (cleansing oil, viscosity: 32.5 cP (measurement conditions are the same as in Example 1)) (both cleansing cosmetics before adding water) was added to the filter paper from above the addition point of the indicator substance using a pipette, and allowed to stand for 10 minutes. The aforementioned filter paper was placed in a suction filtration device, 200 mL of purified water was poured in, and suction filtration was performed. Suction filtration was performed by installing an aspirator and opening the water faucet at a certain angle for each test. The obtained filter paper was immersed in 10 mL of ethanol to extract the ethylhexyl methoxycinnamate remaining in the filter paper, and the absorbance (310 nm) of the extract was measured using a spectrophotometer (U-5100, Hitachi High-Tech Science Co., Ltd.). In addition, instead of the cleansing cosmetic before water addition, a sample (cleansing cosmetic after water addition) in which 10% by mass of water was added to the cleansing cosmetic was used and treated in the same manner as above. As a control, a filter paper to which 10 μL of an ethanol solution of ethylhexyl methoxycinnamate (ethylhexyl methoxycinnamate concentration 1%) was added by pipette and left to stand for 1 hour was placed in a suction filtration device, and the same filtration and extraction treatments were performed, and the absorbance (310 nm) was measured. Thereafter, the removal rate of the indicator substance was calculated using formula (3) in the same manner as in Example 1. In the test using the cleansing cosmetic before water addition, each operation was performed five times, and in the test using the cleansing cosmetic after water addition, each operation was performed three times. The average removal rates of the indicator substances are shown in Table 4.

"Before adding water" is a model in which the cleansing cosmetic is used with dry hands, and "after adding water" is a model in which the cleansing cosmetic is used with a wet face or with wet hands.
In the cleansing cosmetic of test product 1, the removal rate of the indicator substance was the same both before and after the addition of water. This indicates that the cleansing power of test product 1 does not decrease even when the face is wet with water or when the hands are wet. On the other hand, in the cleansing cosmetic of test product 2, the removal rate of the indicator substance was about 10% lower before the addition of water and 50% lower after the addition of water compared to the cleansing cosmetic of test product 1, and the removal rate of the indicator substance was about 40% lower after the addition of water compared to before the addition of water. This indicates that the cleansing power of test product 2 is lower than that of test product 1, and the cleansing power is greatly reduced when the face is wet with water or when the hands are wet.

Example 3 Evaluation of Usability of Cleansing Cosmetic Preparation The particle size of the emulsified particles in the filtrate obtained by the filtration treatment in Example 2 was measured using a particle size distribution measuring device (LA-350, manufactured by Horiba, Ltd.).
As a result, the average particle size was 0.1 μm when the cleansing cosmetic test product 1 was used, whereas the average particle size was 7.8 μm when the cleansing cosmetic test product 2 was used. It is known that a cleansing cosmetic with a smaller particle size is easier to wash off and leaves the skin feeling refreshed after washing off, so the above results show that test product 1 has a better feel when used than test product 2.

Reference Example 2: Human Evaluation of Cleansing Cosmetics The cleansing cosmetics of test products 1 and 2 used in Examples 2 and 3 were subjected to a sensory evaluation by 29 panelists. Test product 1 or 2 was evenly spread and blended with dry hands on the skin (whole face) to which a commercially available makeup cosmetic had been applied, and then rinsed with water or lukewarm water until the stickiness disappeared, and evaluation was performed on "ease of makeup removal,""ease of rinsing off the cleansing cosmetic (test product)," and "refreshing feeling after rinsing." The evaluation score was determined after three days of use. In addition, the same operation was performed with wet hands to evaluate "ease of makeup removal." The evaluation items and evaluation scores are as follows. The evaluation scores and average scores of the 29 panelists are shown in Tables 5 and 6.

"Easy removal of makeup"
Very easy to remove: 2 points Somewhat easy to remove: 1 point Unknown: 0 points Somewhat difficult to remove: -1 point Very difficult to remove: -2 points

"Easy washing off of cleansing cosmetics"
Very easy to flush: 2 points Somewhat easy to flush: 1 point Don't know: 0 points Somewhat difficult to flush: -1 point Very difficult to flush: -2 points

"A refreshing feeling after rinsing"
Very refreshing: 2 points Somewhat refreshing: 1 point Unknown: 0 points Somewhat not refreshing: -1 point Very not refreshing: -2 points

In the panel's evaluation, Test Product 1 received higher scores than Test Product 2 in all evaluation items. With regard to ease of makeup removal, Test Product 1 received the same evaluation whether it was used with dry hands or wet hands. On the other hand, Test Product 2 received a much lower evaluation when used with wet hands than when it was used with dry hands. These human evaluation results were consistent with the results of the evaluation of the cleansing power of the cleansing cosmetic (Example 2) and the evaluation of the usability (Example 3) using the method for evaluating cleansing cosmetics of the present invention. Therefore, it was confirmed that the method of the present invention is useful as a method for evaluating cleansing cosmetics.

Claims (7)

A method for evaluating a cleansing cosmetic, comprising:
(1) adding an indicator substance to a filter medium;
(2) adding a cleansing cosmetic to the filter medium obtained in the step (1) to bring the indicator substance into contact with the cleansing cosmetic; and (3) adding a solvent for removing the cleansing cosmetic to the filter medium obtained in the step (2) and filtering the mixture.
A method comprising: The method according to claim 1, further comprising, after step (3), a step (4) of measuring the indicator substance remaining in the filter medium obtained in step (3). The method according to claim 1, further comprising, after step (3), a step (4') of measuring the indicator substance contained in the filtrate obtained in step (3). The method according to any one of claims 1 to 3, further comprising, after step (3), (4) or (4'), a step (5) of measuring the emulsion particle size of the cleansing cosmetic contained in the filtrate obtained in step (3). The method according to any one of claims 1 to 4, wherein the filter medium is filter paper. The method according to any one of claims 1 to 5, wherein the retention particle size of the filter medium is 0.1 to 30 μm. The method according to any one of claims 1 to 6, which is used for the relative evaluation of at least two types of cleansing cosmetic products.