JP7773308B2 - Emulsified cosmetics - Google Patents

Description

The present invention relates to an emulsion cosmetic.

There are two types of emulsions: oil-in-water (O/W) and water-in-oil (W/O). Oil-in-water emulsion cosmetics emulsified as O/W emulsions are preferred in the cosmetics industry due to their pleasant texture. In particular, fine emulsions, in which the oil droplets are refined to nano-size, are highly valued in the market because they offer a beautiful, transparent appearance, an excellent texture with reduced stickiness of oils, and a sense of deep penetration into the skin.
Emulsification methods for producing fine emulsions include (1) a method of reducing the size of oil droplets by high shear force (high-pressure emulsification method) and (2) a method of reducing the size of oil droplets by utilizing the properties of surfactants.

When high-pressure emulsification (1) is used as the emulsification method, it is possible to design a lower amount of surfactant than with conventional emulsification (such as homomixers or propeller stirring). This results in an emulsified cosmetic that is highly safe for the skin. High-pressure emulsification requires special equipment such as a high-pressure homogenizer, and the amount that can be processed at one time is small, resulting in high production costs. Furthermore, precise control of shear force is required to homogenize the oil droplets, making management of the production process complicated. Refining emulsions using high-pressure emulsification is not necessarily a modern technology from the perspective of energy conservation, given the recent rise in environmental awareness.

On the other hand, if the emulsification method (2) that utilizes the properties of surfactants to refine oil droplets is adopted, special emulsification equipment is not required and emulsification can be performed with low energy, so it can be said to be a modern technology from the viewpoint of energy conservation. Examples of emulsification methods that utilize the properties of surfactants to refine oil droplets include phase inversion emulsification, liquid crystal emulsification, D-phase emulsification, and phase inversion temperature emulsification.
The inventors of the present application believe that the technology of adjusting the emulsion particle size depending on the characteristics of the surfactant (2) makes it easier to predict the characteristics of the resulting composition (emulsion particle size, skin safety, feel during use, appearance) by focusing on the value calculated by dividing the total content of oils by the total content of surfactants (hereinafter, this may be referred to as the oil/surfactant ratio), and have utilized this technology in formula development.
In a typical composition, a small oil/surfactant ratio results in a small emulsion particle size, while a large oil/surfactant ratio results in a large emulsion particle size. When the oil/surfactant ratio is small, the amount of surfactant is relatively high, which reduces skin safety. When the oil/surfactant ratio is large, the amount of surfactant is relatively low, which increases skin safety. The smaller the emulsion particle size, the better the feel in use and the transparency of the appearance.
The inventors of the present application, through their extensive experience in formula development, have realized that the numerical value of the oil/surfactant ratio is significant, and have classified the prior art into three categories, based on the idea that if the value calculated by dividing the amount of oil by the amount of surfactant is set at "2.5," it is possible to distinguish whether the emulsification technology is ordinary or excellent.
(a) A technique for reducing the emulsion particle size by setting the oil/surfactant ratio to less than 2.5. (b) A technique for increasing the emulsion particle size by setting the oil/surfactant ratio to 2.5 or more. (c) A technique for reducing the emulsion particle size by setting the oil/surfactant ratio to 2.5 or more and adding a third component.

An example of technology classified as (a), where the "oil/surfactant ratio is less than 2.5," is Patent Document 1. The emulsion particle size is reduced to 100 nm or less. In these conventional technologies, the amount of surfactant is relatively large compared to the amount of oil, which can lead to stickiness caused by the surfactant and reduce usability. Furthermore, using a large amount of surfactant can reduce skin safety.

An example of the technology classified as (b), in which the "oil/surfactant ratio is 2.5 or more", is disclosed in Patent Document 2.
In these conventional technologies, the amount of surfactant relative to the amount of oil is relatively small, so that skin safety is high. The emulsion particle size exceeds 100 nm. If the emulsion particle size is large, the transparency of the appearance decreases, and depending on the purpose of the product, it is judged to lack aesthetics. Furthermore, if the emulsion particle size is large, the "sticky feeling" caused by the oil is easily felt.

As for the technology classified as (c), which sets the oil/surfactant ratio at 2.5 or more and reduces the emulsion particle size by adding a third component, many companies have proposed it. The emulsion particle size has been reduced to 100 nm or less.
Representative third components are listed below.

Example 1 of the addition of a third component is the inclusion of an anionic surfactant. This is described, for example, in Patent Document 3, Patent Document 4, and Patent Document 5. Anionic surfactants have a large curvature and are therefore effective in reducing the size of emulsion particles, but when incorporated into leave-on skin care products, they may cause skin irritation.

Example 2 of the addition of a third component is to include a high content of polyhydric alcohol as a hydrotrope. This is described, for example, in Patent Documents 6 and 7. The inclusion of a high content of polyhydric alcohol may cause a sticky feeling and reduce usability.

An example 3 of adding the third component is a technique of adding a large amount of ethanol to the aqueous phase during emulsification.
For example, Patent Document 8 describes in its working examples a composition in which the oil/surfactant ratio is 10 or more and the emulsion particle size is 100 nm or less. Although the emulsion particle size is fine, the technology requires ethanol, which can irritate skin that is sensitive to alcohol and may lead to dryness of the skin.

An example 4 of the third component is the inclusion of an emulsifier. This is a technology that reduces the emulsion particle size by combining an emulsifier with a high oil/surfactant ratio while ensuring skin safety. However, depending on the type of emulsifier, there is a risk that the feel and safety of the product may be impaired.
As seen above, conventional techniques have not yet achieved an emulsion cosmetic with fine emulsion particles that is excellent in all aspects of safety to the skin, ease of use, and stability. There is a demand for an oil-in-water emulsion cosmetic that satisfies all of the above.

Japanese Patent Application Laid-Open No. 2020-105077 Patent No. 5053557 Patent No. 4185081 Patent No. 4116020 Patent No. 5134197 JP 2010-6739 A JP 2008-100937 A

The objective of this project is to provide a translucent oil-in-water emulsion cosmetic that is safe for the skin, easy to use, and stable over time, without using special emulsifying equipment such as a high-pressure homogenizer.

The present invention is configured as follows.
(1) An oil-in-water emulsion cosmetic comprising (A) to (D), and containing (D) water in an amount of 50 to 98% by mass per cosmetic.
(A) a surfactant which is a diester of a fatty acid having 14 to 22 carbon atoms and polyglycerol; (B) a surfactant which is an ester of a linear fatty acid having 6 to 10 carbon atoms and polyglycerol; (C) an oil; (D) water; (2) the mass ratio of the surfactant containing (A) and (B) to the oil (C) is 2.5 or more.
(3) The oil-in-water emulsion cosmetic according to (1) or (2), wherein the volume-based average particle size of the emulsion particles is 100 nm or less.
(4) The oil-in-water emulsion cosmetic according to any one of (1) to (3), which has a transmittance (wavelength 600 nm, optical path length 1 cm) of 0.1% or more.

By adopting the configuration of the present invention, an oil-in-water emulsion cosmetic was obtained that exhibited excellent skin safety, ease of use, and stability over time. In particular, even in a composition in which the mass ratio of surfactants (A) and (B) to oil (C) was 2.5 or greater, i.e., a composition in which the amount of surfactant was relatively small relative to the oil, a fine emulsion was obtained in which the emulsion particles had a volume-based average particle size of 100 nm or less. This oil-in-water emulsion cosmetic was stable and showed no change in appearance across all temperature ranges (-5°C, 0°C, 25°C, 40°C, and 50°C). In particular, it remained stable without creaming even after one month of storage under the harsh conditions of 50°C. Furthermore, it exhibited excellent skin safety, ease of use, and stability. Its beautiful translucent (blue-white translucent) appearance made it ideal for a luxurious lotion. By adopting the configuration of the present invention, complicated process management during production was eliminated, enabling the production of an oil-in-water emulsion cosmetic with low energy consumption.

The present invention relates to an oil-in-water emulsion cosmetic comprising: (A) a surfactant that is a diester of a fatty acid having 14 to 22 carbon atoms and a polyglycerol; (B) a surfactant that is an ester of a linear fatty acid having 6 to 10 carbon atoms and a polyglycerol; (C) an oil; and (D) 50 to 98% by mass of water.
The components of the present invention are described below.

Component (A): Diester of a fatty acid having 14 to 22 carbon atoms and polyglycerol The oil-in-water emulsion cosmetic of the present invention uses a diester of a fatty acid having 14 to 22 carbon atoms and polyglycerol as Component A. Examples of the diester of a fatty acid having 14 to 22 carbon atoms and polyglycerol that constitutes Component A include polyglyceryl-10 diisostearate, polyglyceryl-10 distearate, and polyglyceryl-10 dioleate. The content of the diester of a fatty acid and polyglycerol as Component A is preferably 0.05 to 4.9% by mass, more preferably 0.1 to 3% by mass, and even more preferably 0.1 to 2% by mass, based on the total amount of the cosmetic. The polyglycerin in the polyglycerol fatty acid ester preferably has an average degree of polymerization of 5 to 15.

Component (B): Ester of a linear fatty acid having 6 to 10 carbon atoms and a polyglycerol The oil-in-water emulsion cosmetic of the present invention uses an ester of a linear fatty acid having 6 to 10 carbon atoms and a polyglycerol as component B. Examples of the ester of a linear fatty acid having 6 to 10 carbon atoms and a polyglycerol that is component (B) include triglyceryl caprylate, pentaglyceryl dicaprylate, eicosaglyceryl hexacaprylate, eicosaglyceryl hexacaprate, triglyceryl caprate, hexaglyceryl dicaprylate, and hexaglyceryl dicaprate. This component is an ester of a linear fatty acid having 6 to 10 carbon atoms and a polyglycerol, in which the ratio of the degree of polyglycerol polymerization to the number of fatty acid bond residues per molecule (degree of polyglycerol polymerization/number of fatty acid bond residues) is 2.5 to 3.5. The following are examples of the polyglycerol triglyceride (ratio of degree of polymerization of polyglycerin to the number of bound fatty acid residues is 3.0): pentaglyceryl dicaprylate (2.5), eicosaglyceryl hexacaprylate (3.3), eicosaglyceryl hexacaprate (3.3), triglyceryl caprate (3.0), hexaglyceryl dicaprylate (3.0), and hexaglyceryl dicaprate (3.0). Of these, eicosaglyceryl hexacaprylate (label name: Polyglyceryl-20 hexacaprylate) or hexaglyceryl dicaprate (label name: Polyglyceryl-6 dicaprate) are more preferred. The blending amount of component (B) is preferably 0.05 to 4.9% by mass, more preferably 0.1 to 3% by mass, and even more preferably 0.1 to 2% by mass, based on the total amount of the water-in-oil emulsion.

In the oil-in-water emulsion cosmetic of the present invention, the total content of the surfactant component (A) and the surfactant component (B) is preferably 0.1 to 9.8% by mass, more preferably 0.1 to 5% by mass, even more preferably 0.2 to 4% by mass, and even more preferably 0.2 to 3.5% by mass, based on the total amount of the cosmetic. This range is preferable because it reduces the risk of stickiness caused by the surfactants. Note that if the oil-in-water emulsion cosmetic of the present invention contains any surfactant other than (A) and (B), it is included in the total content of (A) and (B).

Component (C): Oil Examples of the oil (C) of the present invention include the following.
Examples of the oils and fats include natural animal and vegetable oils and semi-synthetic oils and fats, hydrocarbon oils, ester oils, glyceride oils, silicone oils, fat-soluble vitamins, higher fatty acids, and animal, vegetable, and synthetic essential oil components. Examples of the natural animal and vegetable oils and fats and semi-synthetic oils and fats include avocado oil, linseed oil, almond oil, olive oil (olive fruit oil), wheat germ oil, sesame oil, rice germ oil, rice bran oil, safflower oil, soybean oil, evening primrose oil, corn oil, rapeseed oil, horse fat, palm oil, palm kernel oil, castor oil, sunflower oil, jojoba oil, macadamia nut oil, coconut oil, hardened coconut oil, peanut oil, medusa oil, and lanolin. Examples of the hydrocarbon oils include squalane, squalene, liquid paraffin, and petrolatum. Ester oils include diisobutyl adipate, 2-hexyldecyl adipate, di-2-heptylundecyl adipate, isostearyl isostearate, trimethylolpropane triisostearate, cetyl ethylhexanoate, isotridecyl isononanoate, ethylhexyl palmitate, triethylhexanoin, neopentyl glycol di-2-ethylhexanoate, trimethylolpropane tri-2-ethylhexanoate, pentaerythritol tetra-2-ethylhexanoate, cetyl octanoate, oleyl oleate, octyldodecyl oleate, decyl oleate, neo dicaprate Examples of oils include pentyl glycol, 2-ethylhexyl succinate, isocetyl stearate, butyl stearate, diisopropyl sebacate, cetyl lactate, tetradecyl lactate, isopropyl myristate, octyl palmitate, 2-hexyldecyl palmitate, 2-heptylundecyl palmitate, cholesteryl 12-hydroxystearate, phytosteryl oleate, diisostearyl malate, para-methoxycinnamate, pentaerythrityl tetrarosinate, caprylyl caprylate/caprate, dicaprylyl ether, butylene glycol diisononanoate, and diethylhexyl succinate. Examples of glyceride oils include glyceryl triisostearate, glyceryl triisopalmitate, glyceryl tri-2-ethylhexanoate, glyceryl tritetradecanoate, and glyceryl di-para-methoxycinnamate monoisooctylate. Examples of silicone oils include higher alkoxy-modified silicones such as dimethylpolysiloxane, methylphenylpolysiloxane, methylhydrogenpolysiloxane, octamethylcyclopentasiloxane, decamethylcyclohexasiloxane, diphenylsiloxyphenyltrimethicone, and stearoxysilicone, alkyl-modified silicones, and higher fatty acid ester-modified silicones. Examples of fat-soluble vitamins include tocopherol, and examples of essential oils include orange peel oil and rosemary leaf oil.
Among these examples, cetyl ethylhexanoate, isotridecyl isononanoate, ethylhexyl palmitate, triethylhexanoin, caprylyl caprylate/caprate, dicaprylyl ether, butylene glycol diisononanoate, diethylhexyl succinate, mineral oil, avocado oil, medusa oil, olive fruit oil, tocopherol, orange peel oil, and rosemary leaf oil are preferred. Among these, cetyl ethylhexanoate, isotridecyl isononanoate, ethylhexyl palmitate, triethylhexanoin, caprylyl caprylate/caprate, dicaprylyl ether, butylene glycol diisononanoate, diethylhexyl succinate, and mineral oil are particularly preferred. The oils of component (C) may be formulated alone or in combination of two or more. The oil-in-water emulsion cosmetic of the present invention preferably contains an oil agent (component (C)) in an amount of 0.1 to 15% by mass, more preferably 0.5 to 12% by mass, and even more preferably 1 to 10% by mass, based on the total amount of the cosmetic.

Component (D): Water The oil-in-water emulsion cosmetic of the present invention contains 50 to 98% by mass of water as component (D). In the present invention, the blending amount of water as component (D) is preferably 50 to 98% by mass, more preferably 60 to 98% by mass, even more preferably 70 to 98% by mass, and even more preferably 73 to 98% by mass.

The oil-in-water emulsion cosmetic of the present invention may optionally contain the following components: The components exemplified below (E polyol, F antibacterial polyol) are components that the inventors have confirmed to exhibit favorable effects when included in the oil-in-water emulsion cosmetic having the configuration of the present invention.
(optional ingredient)
Component (E): Polyol The oil-in-water emulsion cosmetic of the present invention preferably optionally contains (E): a polyol. For example, the inclusion of one or more polyols selected from glycerin, diglycerin, polyglycerin-3, polyglycerin-4, polyglycerin-5, polyglycerin-6, polyglycerin-10, and methyl gluceth-10 is preferred because it acts as a solvent for the oil contained in the oil-in-water emulsion cosmetic and may contribute to the translucency of the oil-in-water emulsion cosmetic and its stability over time at high temperatures.
When the oil-in-water emulsion cosmetic of the present invention contains a polyol as an optional component (E), the content is preferably 0.01 to 15% by mass, and more preferably 0.1 to 13% by mass, based on the total amount of the cosmetic. This range is preferable because it may be possible to obtain an oil-in-water emulsion cosmetic that is more translucent and has excellent temperature stability without the stickiness that is typically associated with polyols.

Furthermore, the oil-in-water emulsion cosmetic of the present invention may optionally contain a polyol with a high antibacterial effect in addition to the polyol described above. If the oil-in-water emulsion cosmetic of the present invention contains the following component (F), its content is not included in the polyol of component (E).
Component (F): Antibacterial Polyol. The water-in-oil emulsion cosmetic of the present invention preferably contains an antibacterial polyol as component (F). In order to prevent spoilage of a cosmetic composition containing water, it is important to incorporate an antibacterial component to enhance antibacterial properties in terms of quality design. Component (F) is not necessarily required when imparting antibacterial activity by incorporating a solid substance such as paraben. However, heating is required to dissolve paraben in water, and precipitation may occur depending on storage conditions. Furthermore, since oil-in-water emulsion cosmetics involve rubbing against the skin during use, precipitation of solid substances that may injure the skin significantly reduces quality. Furthermore, preservatives such as paraben are components that pose safety concerns for the eyes and skin. Therefore, it is even more preferable for the oil-in-water emulsion cosmetic of the present invention to further contain one or more antibacterial polyols (F) for the purpose of imparting antibacterial properties.
The antibacterial polyol for component (F) preferably contains one or more selected from BG (1,3-butylene glycol), DPG (dipropylene glycol), and pentylene glycol (1,2-pentanediol). In the present invention, the antibacterial polyol for component (F) is preferably incorporated in a total amount of 0.1 to 9 mass% based on the total amount of the cosmetic. For example, if BG or DPG is used alone, an appropriate amount is 5 to 9 mass%, and if pentylene glycol is used alone, an appropriate amount is 0.1 to 5 mass%. In the present invention, the antibacterial polyol for component (F) is preferably incorporated in a total amount of 0.1 to 9 mass% based on the total amount of the cosmetic, as this imparts antibacterial properties to the cosmetic. When the polyol for component (E) is incorporated into the oil-in-water emulsion cosmetic of the present invention, it is preferable to incorporate the polyol for component (E) and the antibacterial polyol for component (F) in a mass ratio of 10:9 to 100:1, as this facilitates achieving a translucent appearance.

(Regarding other optional ingredients)
The oil-in-water emulsion cosmetic of the present invention may also contain various ingredients commonly used in cosmetics, provided that the effects of the present invention are not impaired. For example, pH adjusters, neutralizing agents, antioxidants, fragrances, colorants (e.g., cyanocobalamin, chlorophyllin/copper complex), cosmetic ingredients (e.g., rosemary extract), etc. may be added.

The oil-in-water emulsion cosmetic of the present invention can be designed into a variety of formulations, taking into consideration ease of use and feel upon use. Specifically, it can be in liquid or gel form. The properties of the present invention are best exhibited in a lotion.

The present invention will be further explained below with reference to test examples (Examples and Comparative Examples). Oil-in-water emulsion cosmetics of Examples 1 to 6 and Comparative Examples 1 to 6 were prepared using the compositions shown in Table 1 by the following preparation method. The units of composition are % by mass.
<Preparation method>
The surfactant (Component A), the surfactant (Component B), the oil (Component C), and water (part of Component D) are heated and dissolved at 70-85°C to obtain a clear, single-phase composition (1). Next, the remaining water (Component D), which has been heated to 80-85°C for sterilization, is gradually added to composition (1) to obtain an oil-in-water emulsion cosmetic. The timing of addition of optional water-soluble components such as polyol is not important. That is, they may be added during the preparation of composition (1), after the preparation of the oil-in-water emulsion cosmetic, or in separate additions, such as adding a portion of the polyol during the preparation of composition (1) and adding the remaining polyol after the preparation of the oil-in-water emulsion cosmetic. In this test, the polyol was added separately.

[Testing and Evaluation]
For the test examples (Examples and Comparative Examples), the emulsion particle size and transmittance were measured, and appearance observation (the next day and one month later) and sensory evaluation were carried out to evaluate the stability and usability (usability).
<Emulsion particle size>
1 g of the prepared oil-in-water emulsion cosmetic was diluted with 99 g of ion-exchanged water to prepare a sample. The volume average particle size of the sample was measured by dynamic light scattering using a zeta potential/particle size measurement system (device name: ELSZ-1000ZS, manufactured by Otsuka Electronics Co., Ltd.).

Based on the extensive experience of formula development, the inventors are well aware that when the emulsion particle size of an oil agent is 100 nm or less, the oil agent is less likely to feel sticky. Therefore, in this test, the target emulsion particle size was set at 100 nm, and it was determined that the objective was achieved if the emulsion particle size was 100 nm or less.

<Transmittance>
The transmittance of the prepared oil-in-water emulsion cosmetic was measured using a spectrophotometer (device name: UV-visible spectrophotometer V-750DS, manufactured by JASCO Corporation). The measurement wavelength was 600 nm, the optical path length was 1 cm, and a quartz cell was used with ion-exchanged water as the standard.

In the course of research, the inventors have observed the appearance and measured the transmittance of various cosmetics. Cosmetics recognized as bluish-white translucent have a transmittance of 0.1% or more. Therefore, in the present invention, in order to obtain a bluish-white translucent cosmetic, the inventors set a goal of achieving a transmittance of 0.1% or more for the composition, and determined that the goal was achieved if the transmittance was 0.1% or more.
<Appearance observation>
The prepared oil-in-water emulsion cosmetic was filled into a 30 mm diameter transparent glass bottle with a screw cap, and after storing at room temperature (25°C) for one day, the appearance was visually observed from the side of the container. The observation results were recorded in the table as a direct representation of the appearance, with pale translucent being recorded as "pale translucent" and opaque being recorded as "opaque". No transparent cosmetic was found in this test.
<Stability over time/appearance observation after 1 month>
The prepared oil-in-water emulsion cosmetics were filled into transparent glass bottles with a diameter of 30 mm and equipped with screw caps, and stored for one month at each of the temperature ranges of -5°C, 0°C, 25°C, 40°C, and 50°C, after which the appearances of the containers were visually observed from the side. There was no change in appearance in the products stored at -5°C, 0°C, 25°C, and 40°C, and all were stable in both the Examples and Comparative Examples.
Only the test products stored at 50° C. showed a change in appearance (creaming). The table shows the results of the appearance observation after one month of storage at 50° C., and indicates whether creaming occurred or not.

Creamed: Yes Not creamed: No

<Sensory evaluation>
A professional sensory evaluator applied one drop of the obtained oil-in-water emulsion cosmetic to the inside of the forearm using a dropper, rubbed it into the skin, and then tapped it to evaluate the "stickiness."
○: No stickiness felt ×: Stickiness felt Note that in the sensory evaluation, there were cases where no stickiness was felt but the sliminess of the oil agent was felt. In this case, instead of being rated as "○", it was rated as "not sticky but sliminess felt" and the evaluation was rated as "△".

The present invention will be explained below focusing on the oil/surfactant ratio, focusing on the composition in which the oil/surfactant ratio is fixed at "3".
In this test, the oil/surfactant ratio was fixed at "3" because it is generally believed that an oil/surfactant ratio of 2.5 or more is a composition that is composed of a relatively small amount of surfactant, and it has been empirically proven that the resulting cosmetic is low in irritation to the skin.
This "system with an oil/surfactant ratio of 2.5 or more" that is guaranteed to be safe for the skin has achieved all of the following features that were difficult to achieve with conventional technology: a translucent (pale translucent) appearance, excellent usability (no stickiness or sliminess), and storage stability (no change in appearance after storage for one month at all temperature ranges (-5°C, 0°C, 25°C, 40°C, 50°C), and in particular no creaming after storage for one month at 50°C), which is the significance of the present invention. Test results are shown below for explanation. First, the compositions with different surfactant types and the test results are shown in Table 1.

(result)
In Examples 1 to 6, the oil/surfactant ratio was 3, exceeding 2.5. By adopting the configuration (A+B+C+D) of the present invention, an oil-in-water emulsion cosmetic was obtained with an emulsion particle size (volume-based mean diameter) of 100 nm or less, and the minimum transmittance at a wavelength of 600 nm was 0.86%, exceeding the target of 0.1%. The cosmetic exhibited a pale translucent appearance, was not sticky or slimy, and was excellent in usability. Furthermore, no creaming was observed after storage at 50°C for one month, demonstrating excellent stability. The compositions of Examples 1, 3, and 4 contained optional glycerin, while Examples 2 and 5 did not contain optional glycerin, but similar results were obtained.
In contrast, the oil-in-water emulsion cosmetic (A+C+D) of Comparative Example 1, which did not contain Component B but had an increased amount of Component A, had an emulsion particle size (volume-based average diameter) of 7506.3 nm, which did not achieve the target of 100 nm or less. The transmittance at a wavelength of 600 nm was 0.01%, which did not achieve the target of 0.1% or more. The cosmetic was cloudy in appearance, and in the sensory evaluation, it was rated Fair, as it did not feel sticky but had a slimy feeling due to the oil. Creaming was observed when stored at 50°C.
Comparative Examples 2 and 3 were compositions that did not contain Component A but had an increased amount of Component B. The resulting oil-in-water emulsion cosmetics (B+C+D) had emulsion particle sizes of 7545 nm (Comparative Example 2) and 267 nm (Comparative Example 3), which did not achieve the target of 100 nm or less. The transmittance at a wavelength of 600 nm was 0.01% (Comparative Example 2) and 0.01% (Comparative Example 3), which did not achieve the target of 0.1% or more. Both Comparative Examples 2 and 3 were cloudy in appearance, and in the sensory evaluation, a stickiness due to the oily agent was felt, resulting in a rating of Fair. Creaming was observed in both cases when stored at 50°C.
Comparative Example 4 did not contain Component A, but had a composition in which other surfactants were substituted (B + optional other surfactants + C + D). The resulting oil-in-water emulsion cosmetic had a wavelength of 691 nm (Comparative Example 4), which did not achieve the target of 100 nm or less. The transmittance at a wavelength of 600 nm was 0.0164% (Comparative Example 4), which did not achieve the target of 0.1% or more. Comparative Example 4 had a cloudy appearance, and in the sensory evaluation, a stickiness due to the oily agent was felt, resulting in a rating of △. Creaming was observed in all cases when stored at 50°C.
From the above, it was found that when either component A or component B is missing from the composition, the target emulsion particle size of 100 nm or less is not achieved, but is large, causing a sticky feeling and a problem with the feel when used, and the transmittance does not exceed 0.1%, resulting in a cloudy appearance. As component A, decaglyceryl diisostearate, decaglyceryl distearate, and decaglyceryl dioleate were effective. As component B, eicosaglyceryl hexacaprylate and hexaglyceryl dicaprate were effective.
The oil-in-water emulsion cosmetics shown in Table 2 below have a composition in which the oil/surfactant ratio is fixed at 3 and various oils are used.

(result)
The oil-in-water emulsion cosmetics of Example 1 (same composition as in Table 1) and Examples 7 to 11 contain one or more of the following oils: cetyl 2-ethylhexanoate, tri-2-ethylhexanoin, mineral oil, 2-ethylhexyl palmitate, isotridecyl isononanoate, and neopentyl glycol dicaprate. The oil/surfactant ratio is 3, exceeding 2.5. By adopting the configuration of the present invention, fine oil-in-water emulsion cosmetics with a volume-based average diameter of 100 nm or less were obtained. The obtained oil-in-water emulsion cosmetics exhibited a pale, translucent appearance, were free from stickiness and sliminess, and were excellent in usability. All of the cosmetics exhibited a transmittance of 0.1% or more at a wavelength of 600 nm. No creaming was observed in appearance observation after storage at 50°C for one month.
Examples 12 to 15 have compositions based on cetyl 2-ethylhexanoate as the oil agent, containing a combination of ascorbyl tetra-2-hexyldecanoate, di(octyldodecyl/phytosteryl) lauroyl glutamate, jojoba seed oil, and olive fruit oil. By adopting the composition of the present invention, a fine oil-in-water emulsion cosmetic was obtained with an emulsion particle size (volume-based average diameter) of 100 nm or less. The cosmetic exhibited a pale, translucent appearance, was neither sticky nor slimy, and was excellent in usability. No creaming was observed even after storage at 50°C for one month.
As described above, it has been found that excellent effects can be obtained by adopting the configuration of the present invention, even when the type of oil agent is changed or when a plurality of oil agents are combined.
The compositions shown in Table 3 below have an oil/surfactant ratio of 2.5 to 4.0.

The oil-in-water emulsion cosmetics of Example 1 (same composition as in Table 1) and Examples 16 to 18 had oil/surfactant ratios of 3.0, 2.5, 3.5, and 4.0, respectively, and the oil/surfactant ratio was in the range of 2.5 to 4.0. The compositions of Example 1 and Examples 16 to 18 resulted in fine oil-in-water emulsion cosmetics with a volume-based average particle diameter of 100 nm or less. These oil-in-water emulsion cosmetics had a pale, translucent appearance, were non-sticky, and were easy to use. All of the cosmetics exhibited a transmittance of 0.1% or more at a wavelength of 600 nm. No creaming was observed in appearance observations after storage at 50°C for one month.
Next, the oil content was increased and tested. The oil content of the test products was set to "1 to 10% by mass," which is the amount of oil contained in general lotions and emulsions. The test was conducted in the same manner as the above test. The results are shown in Table 4.

The oil-in-water emulsion cosmetics of Examples 19 to 22 had oil/surfactant ratios of 3.0, 3.0, 3.5, and 3.0, and the oil/surfactant ratio was in the range of 2.5 to 4. The compositions of Examples 19 to 22 yielded fine oil-in-water emulsion cosmetics with emulsion particle sizes (volume-based average diameter) of 100 nm or less. These oil-in-water emulsion cosmetics had a pale, translucent appearance, were not sticky or slimy, and were excellent in usability. All of the cosmetics exhibited the target transmittance of 0.1% or more at a wavelength of 600 nm. Even after storage at 50°C for one month, they did not cream and had excellent stability over time.
From the above results, it was confirmed that the excellent effects of the present invention are achieved when the amount of oil is in the range of "1 to 10% by mass", which is considered to be preferable when contained in emulsions and lotions from the viewpoint of usability.
Next, compositions containing other optional ingredients were tested in the same manner. The results are shown in Table 5.

Examples 23 to 25 are oil-in-water emulsion cosmetics (milky lotions/toners) containing optional polyols (E polyol, F antibacterial polyol) and preservatives (phenoxyethanol) to enhance moisturizing and preservative properties. Furthermore, Example 24 contains an optional viscosity modifier to impart viscosity (thickness). Furthermore, Example 25 contains an optional fragrance to impart fragrance. The oil-in-water emulsion cosmetics of Examples 23 to 25 have an oil/surfactant ratio of 3.0, falling within the range of 2.5 to 4.0. The compositions of Examples 23 to 25 produced fine oil-in-water emulsion cosmetics with emulsion particles of 100 nm or less (volume-based average diameter). Furthermore, the oil-in-water emulsion cosmetics had a pale, translucent appearance. They were neither sticky nor greasy, and were excellent in usability. All of these exhibited the target transmittance of 0.1% or more at a wavelength of 600 nm, and showed excellent storage stability with no creaming even after storage at 50°C for one month.

When the oil-in-water emulsion cosmetics (lotions) of Examples 1 to 25 were actually used, none of them caused skin irritation. As shown in Tables 1 to 5 (Examples 1 to 25), the oil-in-water emulsion cosmetics having the configuration of the present invention had a volume-based mean particle size of 49.6 to 93.7 nm, were free of the stickiness caused by oily agents, and achieved the target value of 100 nm or less, which is evaluated as providing a good feel in use. The transmittance (measured at a wavelength of 600 nm) of the oil-in-water emulsion cosmetics of Examples 1 to 25 was 0.29 to 29.12%, achieving 0.1% or more, which is evaluated as visually translucent, and was evaluated as bluish-white translucent by visual observation. The oil-in-water emulsion cosmetics of Examples 1 to 25 had a mass ratio of surfactants including (A) and (B) to oil (C) (oil/surfactant ratio) ranging from 2.5 to 4.0, with an oil/surfactant ratio of 2.5 or higher, but were not sticky or greasy and had an excellent feel when used. Furthermore, they remained stable with no change in appearance even after one month of storage at all temperature ranges (-5°C, 0°C, 25°C, 40°C, 50°C), demonstrating excellent storage stability.

By adopting the configuration of the present invention, an oil-in-water emulsion cosmetic was obtained that exhibited excellent skin safety, ease of use, and stability over time. In particular, even in a composition where the mass ratio of surfactants containing (A) and (B) to oil (C) was 2.5 or greater, i.e., a composition where the amount of surfactant was relatively small relative to the oil, a fine emulsion was obtained in which the emulsion particles had a volume-based average particle size of 100 nm or less. This oil-in-water emulsion cosmetic was stable and showed no change in appearance across all temperature ranges (-5°C, 0°C, 25°C, 40°C, and 50°C). In particular, it remained stable and did not cream even after one month of storage under the harsh conditions of 50°C. Furthermore, it exhibited excellent skin safety, ease of use, and stability. Its beautiful translucent (blue-white translucent) appearance made it ideal for a luxurious lotion. By adopting the configuration of the present invention, complicated process management during production was eliminated, enabling the production of an oil-in-water emulsion cosmetic with low energy consumption.

Claims (2)

An oil-in-water emulsion cosmetic comprising (A) to (D), wherein the mass ratio of the surfactant comprising (A) and (B) to the oil (C) [amount of oil ÷ amount of surfactant] is 2.5 to 4 , and the cosmetic contains 50 to 98 mass% of water (D).
(A) a surfactant which is a diester of a fatty acid having 14 to 22 carbon atoms and polyglycerin; (B) a surfactant which is an ester of a straight-chain fatty acid having 6 to 10 carbon atoms and polyglycerin; (C) an oily agent in an amount of 0.1 to 15% by mass based on the total amount of the cosmetic;
(D) Water The oil-in-water emulsion cosmetic according to claim 1, wherein the volume-based average particle size of the emulsion particles is 100 nm or less.