JPH06172673A - Ultraviolet-absorbing pigment - Google Patents

Abstract

PURPOSE:To obtain an ultraviolet-absorbing pigment having high safety and stability by adsorbing and bonding melanin exhibiting ultraviolet absorbing action to a metal oxide such as alumina or powder surface coated with the metal oxide. CONSTITUTION:3,4-Dihydroxyphenylalanine (dopa) is used as a starting raw material and subjected to oxidative polymerization on the surface of a metal oxide having basic surface such as alumina to obtain the objective pigment coated with synthetic melanin. The melanin can be adsorbed to other inorganic powder or organic powder by treating the surface of the powder with the metal oxide. Ultraviolet-absorbing pigments having various colors such as milky white, gray, yellowish brown and brown in addition to black can be produced by carrying out the oxidative polymerization of dopa in the presence of a reducing agent such as cysteine to form a copolymer. The above process is also effective for shifting the ultraviolet absorption spectrum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a UV-absorbing pigment having a high UV-absorbing effect and safety and useful for skin cosmetics, makeup cosmetics and the like.

[0002]

2. Description of the Related Art Conventionally, body cosmetics, white pigments and pearl pigments have been generally used in various cosmetics such as skin cosmetics and makeup cosmetics for the purpose of coloring and toning, imparting lubricity and gloss. It is used for. Especially in the field of makeup cosmetics, the frequency of use of these pigments is high.

Further, in recent years, as the adverse effects of ultraviolet rays on the skin have become clear, the development of cosmetics for preventing erythema and sunburn due to ultraviolet rays has been advanced. In such cosmetics, it is common to blend a metal oxide such as titanium oxide having an ultraviolet scattering effect, or an ultraviolet absorber.

Further, recently, attention has been paid to melanin, which is a black pigment of hair or skin, and it is used as a black pigment or an ultraviolet absorbing pigment by holding it on the surface or inside of powder ( JP-A-1-92273, JP-A-2-
111715, JP-A-2-232264).

[0005]

Although the above-mentioned extender pigments and the like used conventionally have a slight effect of suppressing the transmission of ultraviolet rays by coating the skin surface, almost none of them also have ultraviolet absorptivity. Further, the use of a metal oxide having an ultraviolet scattering effect has problems such as difficulty in color matching and occurrence of powder floating.

On the other hand, the use of the ultraviolet absorber has various safety problems such as the occurrence of contact dermatitis and photocontact dermatitis and the appearance of sensitization. In addition, since most UV absorbers are water-soluble or oil-soluble, they have poor water resistance or oil resistance, and have drawbacks due to their physical properties such that they are easily removed by water, sweat or sebum.

[0007] Conventionally, black pigments which hold melanin on the surface or inside are suitable for mascara, eyeliner, hair dye, etc., but are generally difficult to use for makeup cosmetics such as foundations due to their color matching Even if it is used for the purpose of absorption, it is only deposited or held on the surface of the powder or inside, and there is a problem in stability such as chemical resistance.

An object of the present invention is to solve the above-mentioned problems and to provide an ultraviolet absorbing pigment which is physically and chemically stable and is highly safe to the skin.

[0009] In achieving the above object, the present inventors have also found that the in-vivo component contained in human skin is
We focused on the melanin pigment, which has the function of protecting against damage caused by ultraviolet rays. Then, in order to solve the above-mentioned drawbacks of the conventional melanin composite pigment, and to obtain a melanin-binding pigment that is more stable, has a color tone other than black, and is easy to tone when applied to cosmetics and external preparations for skin. I went.

[0010]

Means for Solving the Problems Melanin is synthesized in vivo from tyrosine by an enzymatic reaction such as tyrosinase, and can be obtained by oxidative polymerization of dopa, which is an intermediate thereof, as a starting material. . At that time, since the oxidative polymerization proceeds under an alkali catalyst, when the reaction is carried out on a metal oxide whose surface is basic such as alumina, the surface is polymerized, and the polymer is strongly bonded to the metal oxide surface. Adsorb. If a metal oxide with high surface activity is used,
It is also possible to covalently attach melanin to the metal oxide surface.

When oxidatively polymerizing dopa,
When a melanin copolymer was produced on the metal oxide surface in the coexistence of a reducing agent such as cysteine, the color tone of the resulting pigment was changed, and a shift in absorption wavelength was also observed.

Therefore, it is possible to oxidatively polymerize dopa on a metal oxide whose surface is basic to obtain a black pigment having an ultraviolet absorbing property. Further, by performing oxidative polymerization in the presence of a reducing agent, it is possible to obtain an ultraviolet absorbing pigment having various tones such as gray to yellow and brown.

Furthermore, when inorganic powders such as talc and mica and organic powders such as nylon powder are coated with metal oxides such as alumina by a mechanochemical method or the like, the surface of them is also treated with melanin as described above. Alternatively, the melanin copolymer can be adsorbed or bound.

The ultraviolet absorbing pigment according to the present invention is prepared as follows.

First, silver oxide is added to an aqueous solution of dopa to form dopachrome and then filtered, and a metal oxide- or metal oxide-treated powder is added to the filtrate and stirred at room temperature. Then, the powder is collected by filtration. When a reducing agent coexists, it is added together with the metal oxide or the metal oxide-treated powder. Suitable reducing agents for the purpose of the present invention include cysteine, glutathione, resorcin, pyrogallol, p-aminophenol, m-aminophenol, L-ascorbic acid, kojic acid, hydroquinone and pyrocatechol.

[0016]

All the ultraviolet absorbing pigments according to the present invention have an absorption maximum in the ultraviolet region, and particularly show effective absorption in the UVB region. Further, in the pigment bound with the copolymer of pyrogallol and dopa, absorption in the UVA region was also recognized.

On the other hand, with respect to the color tone of the ultraviolet absorbing pigment according to the present invention, it shows a black gray color when polymerized with only dopa, and can be changed from gray to milky white to yellow brown to brown by a reducing agent to be copolymerized.

Further, in the ultraviolet absorbing pigment according to the present invention, melanin having an ultraviolet absorbing action is a polymer and has a large molecular weight, and is strongly adsorbed or bonded to the surface of the pigment, and water, organic solvent, acid It does not elute into alkalis and other chemicals, is stable in products such as cosmetics and external preparations for the skin, and does not cause problems such as irritation or sensitization to the skin.

Therefore, the ultraviolet-absorbing pigment according to the present invention can be applied to sunscreen cosmetics such as sunscreen foundations and sunscreen powders and can exert an effective ultraviolet protection effect. Furthermore, as a cosmetic for hair, it is possible to protect the hair from the adverse effects of ultraviolet rays while dyeing the hair in black, brown or the like.

[0020]

EXAMPLES The features of the present invention will be described in more detail with reference to examples.

Examples of the present invention are shown in Table 1. Example 1
The melanin-binding pigment of was prepared as follows.

First, silver oxide is added to a 0.2 wt% dopa aqueous solution, and 1 minute after the solution turns red, it is filtered. Alumina was added to this filtrate so as to be 1% by weight, and the mixture was stirred at room temperature for 6 hours and filtered to recover a powder.

The ultraviolet absorbing pigments according to Examples 2 to 11 of the present invention were prepared by adding an aqueous solution of each reducing agent together with alumina so as to be 0.2% by weight.

The color tone and absorption maximum of each example are shown in Table 1. The ultraviolet absorption spectrum measured using an integrating sphere is shown in FIGS. 1 and 2. At this time, the black iron oxide powder was designated as Comparative Example 1 and the yellow iron oxide powder was designated as Comparative Example 2.

[Table 1]

As is clear from Table 1 and FIGS. 1 and 2, all of the examples of the present invention showed the maximum absorption in the ultraviolet region, and the absorption in the UVB region was particularly observed. In the pyrogallol-dopa copolymer-bonded pigment of Example 5, 3
Absorption was observed even in the region of 20 to 370 nm, and U
VA can be protected at the same time. On the other hand, no absorption at such a specific wavelength was observed in any of the comparative examples.

The color tones of the examples of the present invention are as shown in Table 1, but by selecting the type and amount of the reducing agent to be copolymerized, white gray to black gray, milky white, yellow brown to brown to green brown. Etc. could be changed widely. Therefore,
Sunscreen foundation, sunscreen powder, etc.
It was easy to apply to sunscreen skin cosmetics, makeup cosmetics, and external skin preparations in terms of toning.

[0027]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a melanin dye can be more strongly adsorbed on and bound to the surface of a pigment than conventional ones, and an ultraviolet-absorbing pigment having higher safety and stability can be obtained. It was Further, as in the conventional case, not only black or black gray but also pigments of various color tones that can be easily adjusted can be obtained.

On the other hand, the powder to which the melanin pigment or the melanin copolymer is adsorbed or bonded is not limited to metal oxides, but may be adsorbed to various inorganic or organic powders by coating these or the like. Thus, it is possible to provide an ultraviolet absorbing pigment having various shapes such as spherical shape, plate shape and porosity and having various usability.

[Brief description of drawings]

FIG. 1 is a diagram showing an ultraviolet absorption spectrum of Example 1, Example 2, Example 4, Example 5 and Comparative Example 1 of the present invention.

FIG. 2 is a diagram showing ultraviolet absorption spectra of Example 7, Example 9, Example 11 and Comparative Example 2 of the present invention.

[Explanation of symbols]

 1 Example 1 2 Example 2 3 Example 4 4 Example 5 5 Comparative Example 1 6 Example 7 7 Example 9 8 Example 11 9 Comparative Example 2

Claims (8)

[Claims] 1. An ultraviolet absorbing pigment comprising a metal oxide surface coated with melanin synthesized by oxidative polymerization of 3,4-dihydroxyphenylalanine (dopa). 2. A UV absorption obtained by coating the surface of a metal oxide with a melanin copolymer synthesized by copolymerizing dopachrome obtained by oxidizing 3,4-dihydroxyphenylalanine (dopa) and a reducing substance. Sex pigment. 3. The ultraviolet absorbing pigment according to claim 1, wherein the metal oxide is alumina. 4. The reducing substance is cysteine, glutathione, resorcin, pyrogallol, p-aminophenol,
The ultraviolet absorbing pigment according to claim 2 or 3, which is one or more selected from m-aminophenol, L-ascorbic acid, kojic acid, hydroquinone and pyrocatechol. 5. An ultraviolet absorbing pigment, which is obtained by treating a powder with a metal oxide and then coating the powder with melanin synthesized by oxidative polymerization of 3,4-dihydroxyphenylalanine (dopa). 6. A melanin copolymer synthesized by copolymerizing dopachrome obtained by oxidizing 3,4-dihydroxyphenylalanine (dopa) with a reducing substance after treating the powder with a metal oxide. Consisting of a UV absorbing pigment. 7. The ultraviolet absorbing pigment according to claim 5, wherein the metal oxide is alumina. 8. The reducing substance is cysteine, glutathione, resorcin, pyrogallol, p-aminophenol,
The ultraviolet absorbing pigment according to claim 6 or 7, which is one or more selected from m-aminophenol, L-ascorbic acid, kojic acid, hydroquinone and pyrocatechol.