Oil-in-Water Emulsion and Emulsifying or Solubilizing Agent Composition Useful Therein

1. Field of the Invention

The present invention relates to an emulsifying or solubilizing composition which is capable of emulsifying or solubilizing liquid vegetable oils and highly polar synthetic ester oils which have heretofore been considered to be very difficult to emulsify or solubilize. The composition possesses excellent color and smell and excellent stability against photo-discoloration and decomposition.

2. Description of the Prior Art

As emulsifiers for cosmetics, there have heretofore been used non-ionic surface active agents such as polyoxyethylene sorbitan fatty acid esters, sorbitan fatty acid esters, glycerol fatty acid esters, polyethylene glycol fatty acid esters and polyoxyethylene alkyl ethers, and in addition, a great number of other non-ionic, anionic, cationic and amphoteric surface active agents. These emulsifiers, in general, have a good emulsifying power to mineral oils composed of hydrocarbons and the like and animal oils such as squalane and they provide stable emulsions of these oils. However, they scarcely emulsify liquid vegetable oils (hereinafter referred to as "vegetable oils") composed of triglycerides rich in alkyl groups having an unsaturated bond, such as camellia oil and olive oil, and esters (hereinafter referred to "synthetic esters") having at least one branched alkyl group, which are derived from branched or linear higher fatty acids and branched or linear higher alcohols, and stable emulsions of these oils cannot be obtained.

We previously discovered an emulsifying or solubilizing agent composition having a high emulsifying or solubilizing property to vegetable oils and synthetic ester oils. That composition was formed by mixing in specific weight ratios, an alkali metal salt of a fatty acid, a fatty acid and a polyethylene glycol unsaturated fatty acid ester-type surface active agent into a polyoxyethylene sorbitol unsaturated fatty acid ester-type surface active agent, (see the specification of Japanese patent application No. 91086/74, corresponding to U.S. Pat. No. 3,954,658).

That composition is satisfactory in its emulsifying and solubilizing properties, but it is defective in that it becomes colored or generates unwanted odors under some storage conditions and it is readily discolored when it is exposed to sun-light. This defect is serious when the composition is used for emulsifying cosmetics and the like.

We have discovered an improved emulsifying or solubilizing composition which possesses excellent emulsifying and solubilizing properties and which possesses, surprisingly, reduced tendency toward coloration and generation of bad odors.

More specifically, in accordance with the present invention, there is provided an emulsifying or solubilizing composition comprising

I. from 58 to 95% by weight of a surface active agent of the polyoxyethylene sorbitol branched saturated fatty acid ester-type (hereinafter referred to as "component (I)") having the formula (A): ##STR1## wherein the value of n.sub.1 + n.sub.2 + n.sub.3 + n.sub.4 + n.sub.5 + n.sub.6 is in the range of 10 to 100, and wherein from 3 to 6 of the total number of X's (i.e., 6) on the average of the mixture are branched saturated acyl (RCO-) groups having 11 to 21 carbon atoms (R is branched alkyl having 10 to 20 carbon atoms), the rest of the X's being hydrogen,

Ii. from 0.5 to 2.5% by weight of an alkali metal salt of a linear or branched fatty acid having 11 to 21 carbon atoms (hereinafter referred to as "component (II)"),

Iii. from 2.5 to 6.0% by weight of a linear or branched fatty acid having 11 to 23 carbon atoms (hereinafter referred to as "component (III)"), and

Iv. from 2 to 35% by weight of a branched saturated fatty acid ester of a polyethylene glycol having an average molecular weight of 150 to 2000 wherein the branched saturated fatty acid moiety has from 11 to 21 carbon atoms (hereinafter referred to as "component (IV)").

When the above composition is used as an emulsifying or solubilizing agent, vegetable oils and highly polar oils synthesized as emollient oils, which have heretofore been considered difficult to emulsify, can easily be emulsified or solubilized, and ideal emulsions having a good color with a reduced odor can be obtained.

As the vegetable oil to be emulsified or solubilized, there can be mentioned liquid vegetable oils composed of triglycerides rich in unsaturated alkyl groups, such as camellia oil, olive oil, safflower oil, rapeseed oil, palm oil and cotton seed oil, and as the synthetic ester oil, there can be mentioned esters having at least one branched alkyl group, which are derived from branched or linear higher fatty acids and branched or linear higher alcohols, such as 2-heptylundecyl isostearate, glycerol tri-2-ethylhexanoate, hexadecyl 2-ethyl-hexanoate, hexadecyl isostearate and hexadecyl isotridecanoate. These vegetable oils and synthetic ester oils are widely used in cosmetics. By using the composition of the present invention, it is possible for the first time to employ these oils, in the emulsified or solubilized state, in cosmetics. Namely, it is possible to incorporate these vegetable oils or synthetic ester oils into various cosmetic creams such as sun creams and hair creams and other cosmetics such as lotions. By incorporation of these oils, emulsified or solubilized by the composition of the present invention, it is possible to obtain milder cosmetics having a higher emollient effect than conventional cosmetics composed mainly of mineral oils. Of course, the composition of the present invention also has an excellent emulsifying power for mineral oils and animal oils, that can also be emulsified by conventional emulsifiers, as well as the above-mentioned vegetable oils and synthetic ester oils.

The polyoxyethylene sorbitol branched saturated fatty acid ester (I) that is used in the present invention is, as is seen from the formula (A), an ester formed by esterifying an ethylene oxide adduct of sorbitol with a branched saturated fatty acid having 11 to 21 carbon atoms, such as isostearic acid or isotridecanoic acid. It is necessary that among the total of the 6 hydroxyl groups of sorbitol, from 3 to 6 of them, on the average, of the mixture should be esterified. More specifically, in the general formula (A), 3 to 6 of the 6 X's are acyl groups, the rest being hydrogen. (In the description given hereinafter, the number of such acyl groups will be called "the degree of esterification"). If the degree of esterification is lower than in the above range i.e. from 3 to 6, the emulsifying property is diminished and a good and stable emulsion cannot be obtained.

As the fatty acid employed for the above esterification, there are preferably employed branched saturated fatty acids having 11 to 21 carbon atoms, such as isostearic acid, isotridecanoic acid and isoundecanoic acid. When a linear saturated fatty acid such as stearic acid or palmitic acid is used instead of the specified branched acids, the emulsifying property is diminished, and the resulting ester is solid at room temperature and hence, good results cannot be obtained. When a linear unsaturated fatty acid such as oleic acid or linoleic acid is used, a sufficient emulsifying or solubilizing property can be attained, but the resulting ester is inferior to an ester derived from a liquid branched saturated fatty acid, according to the invention, with respect to its chemical stability (the resistance to changes with the passage of time), smell, color and resistance to discoloration.

The above ester is prepared by conventional procedures by adding sorbitol to a solvent such as xylene, adding ethylene oxide to sorbitol in the presence of a basic catalyst to effect the addition reaction, adding a branched saturated fatty acid in an amount of 3 to 6 moles per mole of the ethylene oxide adduct of sorbitol, heating the mixture at 180.degree. to 240.degree. C. to effect the esterification reaction, and then decolorizing and purifying the resulting ester.

It is necessary that the composition of the present invention comprises 58 to 95% by weight of the component (I), 0.2 to 2.5% by weight of the component (II), 2.5 to 6.0% by weight of the component (III) and 2 to 35% by weight of the component (IV). If this requirement is not satisfied, the emulsifying property to vegetable oils and synthetic ester oils is diminished and the resulting emulsion is so poor in the stability that when it is allowed to stand, the emulsion is destroyed in a short time and phase separation takes place.

In view of the properties of the oils which are to be emulsified or solubilized by the emulsifying or solubilizing composition of the present invention, the composition of the invention is utilized most effectively in the field of cosmetics. Of course, the composition of the present invention can also be used as an emulsifying or solubilizing agent in any fields where the foregoing oils are used, for example, in the fields of foods, fiber oiling agents, detergents, metal processing oils and the like.

The features of the present invention will now be described in greater detail by reference to the following illustrative Examples: In the Examples all references to "%" are by weight unless otherwise indicated.

Emulsifying agent compositions containing the ingredients indicated below were prepared and emulsifying tests were made on various oils by using these compositions.

A mixture of 20 parts (by weight; the same shall apply hereinafter) of an oil component, 5 parts of the emulsifying composition and 75 parts of deionized water were emulsified at a temperature of 70.degree. C., using an agitation vane rotating at 600 rpm, according to the phase inversion emulsification method. The emulsifiability and stability of the resulting emulsion were evaluated according to the following standards:

The state of the as-emulsified emulsion was observed with the naked eye and by a microscope and the emulsifiability was evaluated according to the following standards:

A: bluish white emulsion of fine particles having an average particle size smaller than 1.mu. as measured under a microscope

B: milky white emulsion of particles having an average particle size of 1 to 5.mu. as measured under a microscope

C: opaque emulsion of crude particles having an average particle size larger than 5.mu. as measured under a microscope

The emulsion formed was allowed to stand still at 25.degree. C. for 7 days, and the state of the emulsion was examined. The stability was evaluated according to the following standards:

(-): homogeneous, no phase separation found

(+): slight formation of an oil phase by coalescence or an aqueous phase by separation of water was observed

(++): oil phase formed by coalescence or aqueous phase formed by separation of water was clearly observed

(+++): both oil phase formed by coalescence and aqueous phase formed by separation of water were clearly observed

The test results are shown in Table 1.

From the results shown in Table 1, it will be understood that the compositions of the present invention, in which the average degree of esterification (the number of acyl groups as X in the general formula (A)) in the component (I) is in the range of from 3 to 6, have an excellent emulsifying property and form emulsions, having good stability, whereas when a component (I) having a degree of esterification not higher than 2 is employed, the emulsifying property is bad, and the stability of the resulting emulsion is low and phase separation takes place.

An emulsifying test for olive oil was carried out using various emulsifying compositions as listed in Table 2. In each run, an emulsion was prepared from 20 parts of olive oil, 5 parts of the emulsifier composition and 75 parts of deionized water. The test and evaluation methods were the same as described in Example 1. The results obtained are shown in Table 2.

A mixture of 20 parts of a synthetic ester oil obtained by esterification of 2-heptylundecanol with isostearic acid, 5 parts of an emulsifier composition and 75 parts of deionized water was emulsified and tested in the same manner as described in Example 2. The results obtained are shown in Table 3.

A mixture of 20 parts of a synthetic ester oil (glycerol tri-2-ethylhexanoate), 5 parts of an emulsifier composition and 75 parts of deionized water were emulsified and tested in the same manner as described in Example 2. The results obtained are shown in Table 4.

As will be apparent from the results shown in Tables 2 to 4, when known emulsifiers are used, vegetable oils or synthetic ester oils cannot be emulsified at all or they can be emulsified only insufficiently. In contrast, when the emulsifying composition of the present invention is used, such oils can easily be emulsified and good emulsions of excellent stability can be obtained. Even when the same components as used in the present invention are employed, if the weight ratio of the components is outside the ranges specified in the present invention, both the emulsifiability and the stability of the emulsions are diminished.

The emulsifier agent compositions set forth in Table 5 were subjected to a photo-discoloration test. Each sample was exposed to artificial sunlight for 24 hours by using a sun-shine weather-meter, and the hue of each sample according to the Gardner color scale was measured before and after the exposure. The results are shown in Table 5.

As will be apparent from the results shown in Table 5, the polyoxyethylene sorbitol branched saturated fatty acid ester which is the main component (I) of the emulsifying composition of the present invention is superior to that of the polyoxyethylene sorbitol linear unsaturated fatty acid ester with respect to the resistance or stability to photo-discoloration.

A product (A) of the present invention and a comparative product (B), each having a composition as described below, were subjected to the sensory odor test by a panel of 30 persons according to the pair-comparison method of Scheffe. The results obtained are shown in Table 6.

When the above data were subjected to t inspection, the result of t (.alpha.) = 3.514 > t (n-1.0.01) = 2.756 (n = 30) was obtained. Thus, it was found that the odor of A was more pleasant than the odor of B with a significance level of 1%.

Thus, it is apparent that with respect to the odor, a branched saturated fatty acid moiety is superior to a linear unsaturated fatty acid moiety for the fatty acid moiety of the polyoxyethylene sorbitol fatty acid which is the main component (I) of the composition of the present invention.

An emulsifying composition comprising the following ingredients was prepared:

The composition was a yellowish brown liquid having a specific gravity (d.sub.4.sup.20) of 0.981, a viscosity of 256 cps as measured at 20.degree. C., a saponification value of 116.8 and an HLB value of 7.2.

An o/w type cream having the following composition was prepared by using the thus prepared emulsifying composition:

The ingredients of group (1) and of (2) were heated and melted at 80.degree. C. separately, and the melts were mixed vigorously to effect emulsification. While the resulting emulsion was being cooled, the ingredients of group (3) were added thereto and dispersed therein. The resulting cream had a very good emulsion state.

The thus prepared emulsifying composition was a yellowish brown liquid having a specific gravity (d.sub.4.sup.20) of 1.012, a viscosity of 390 cps as measured at 20.degree. C., a saponification value of 94.2 and an HLB value of 10.4.

In the same manner as described in Example 7, a milky lotion comprising the following ingredients was prepared by using the thus obtained emulsifying composition:

The resulting milky lotion had a very good emulsion state, and the emulsion system was stable even after it had been allowed to stand for a long time.