Thickener, cosmetic preparation containing the same, and process for producing the same
The present invention is a thickener consisting of a microgel obtained by radical polymerization of water soluble ethylene-type unsaturated monomers dissolved in the dispersion phase in a composition having an organic solvent or an oil component as the dispersion medium and water as the dispersion phase, as well as a cosmetic containing said thickener. Also, the present invention is a method of manufacturing a water-swelling polymer in a radical polymerization system consisting of a composition having an organic solvent or oil component as the dispersion medium and an aqueous solution of a water soluble ethylene type unsaturated monomer as the dispersion phase wherein said system contains a surfactant chosen in such a way that the aforementioned composition forms a single phase W/O microemulsion or fine W/O emulsion at a thermal radical polymerization temperature and said thermal radical polymerization is carried out at a temperature equal to or higher than the phase transition temperature of the radical polymerization system, yet not higher than the phase transition temperature by 20° C. or more.
1. A method of thickening a cosmetic comprising adding thereto a microgel, said microgel being produced via radical reverse phase emulsion polymerization of a mixture of water soluble monomers of a dialkylacrylamide represented by general formula (1) and an anionic acrylamide derivative represented by general formula (2) as follows:
wherein R1 denotes a H or methyl group; R2 and R3, independent of each other, denote a methyl, ethyl, propyl, or isopropyl group;
wherein R4 and R5, independent of each other, denote a H or methyl group, R6 denotes a straight chain or branched alkyl group having 1-6 carbon atoms, and X denotes a metal ion or NH3;
dissolved in a dispersion phase in a polymerization system composition having an organic solvent or an oil component as the dispersion medium and water as the dispersion phase, wherein said polymerization system composition contains a surfactant and forms a single phase microemulsion or fine W/O emulsion said polymerization being carried out in a thermodynamically stable single microemulsion region or a metastable fine W/O emulsion region of a phase diagram for the polymerization system composition,
wherein said microgel has:
(a) an apparent viscosity of a microgel aqueous dispersion (0.5% mass percentage of the microgel at 25° C.) of 10,000 mPa·s or higher at a shear rate of 1.0 s −1 ;
(b) an apparent viscosity of a microgel ethanol dispersion (0.5% mass percentage of the microgel at 25° C.) of 5,000 mPa·s or higher at a shear rate of 1.0 s −1 ; and
(c) a dynamic elastic modulus of a microgel aqueous or ethanol dispersion having 0.5% (mass percentage) at 25° C. satisfying a relationship G′ (stored elastic modulus) greater than G″ (loss elastic modulus) at a strain of 1% or less and a frequency range of 0.01-10 Hz.
2. The method of thickening a cosmetic of claim 1 , wherein the microgel is in powder form.
3. The method of thickening cosmetics of claim 1 , wherein the powder microgel is first dispersed in water, ethanol, or a water/ethanol mixed solvent to form a thickener, and the thickener is then added to the cosmetic.
4. The method of thickening a cosmetic of claim 1 , wherein 0.1-10 mass % of the microgel is added to the cosmetic.
5. The method of thickening a cosmetic of claim 1 , wherein said microgel exhibits a stable thickening effect over a pH range of about 2 to about 11.
6. The method of thickening a cosmetic of claim 1 , wherein an organic solvent and surfactant in the polymerization system composition are selected so a single phase microemulsion for fine W/O emulsion region in the phase diagram corresponds to an optimum polymerization temperature for a polymerization initiator for a thermal polymerization or redox polymerization.
7. The method of thickening a cosmetic of claim 1 , wherein the polymerization system composition contains a surfactant chosen so that the polymerization system composition has a clouding point at a temperature used for thermal radical polymerization.
8. The method of thickening a cosmetic of claim 1 , comprising radical polymerization of water soluble ethylene-type unsaturated monomers dissolved in the dispersion phase in a composition having an organic solvent or an oil component as the dispersion medium and water as the dispersion phase.
9. A method of thickening a cosmetic comprising adding thereto a microgel, said microgel being produced via radical polymerization of a mixture of water soluble monomers of:
a dialkylacrylamide represented by general formula (1),
an anionic acrylamide derivative represented by general formula (2) and
a cross-linking monomer represented by general formula (4) as follows:
(R 1 denotes a H or methyl group; R 2 and R 3 , independent of each other, denote a methyl, ethyl, propyl, or isopropyl group);
(R 4 and R 5 , independent of each other, denote a H or methyl group, R 6 denotes a straight chain or branched alkyl group having 1-6 carbon atoms, and X denotes a metal ion or NH 3 );
dissolved in a dispersion phase in a polymerization system composition having an organic solvent or an oil component as the dispersion medium and water as the dispersion phase, wherein said polymerization system composition contains a surfactant and forms a single phase microemulsion or fine W/O emulsion said polymerization being carried out in a thermodynamically stable single microemulsion region or a metastable fine W/O emulsion region of a phase diagram for the polymerization system composition, and
wherein said microgel has (a) an apparent viscosity of a microgel aqueous dispersion (0.5% mass percentage of the microgel at 25° C.) of 10,000 mPa·s or higher at a shear rate of 1.0 s−1; (b) an apparent viscosity of a microgel ethanol dispersion (0.5% mass percentage of the microgel at 25° C.) of 5,000 mPa·s or higher at a shear rate of 1.0 s−1; and (c) a dynamic elastic modulus of a microgel aqueous or ethanol dispersion having 0.5% (mass percentage) at 25° C. satisfying a relationship G′ (stored elastic modulus) greater than G″ (loss elastic modulus) at a strain of 1% or less and a frequency range of 0.01-10 Hz.
10. The method of thickening a cosmetic of claim 9 , wherein the microgel is in powder form.
11. The method of thickening cosmetics of claim 9 , wherein the powder microgel is first dispersed in water, ethanol, or a water/ethanol mixed solvent to form a thickener, and the thickener is then added to the cosmetic.
12. The method of thickening a cosmetic of claim 9 , wherein 0.1-10 mass % of the microgel is added to the cosmetic.
13. The method of thickening a cosmetic of claim 9 , wherein said microgel exhibits a stable thickening effect over a pH range of about 2 to about 11.
14. The method of thickening a cosmetic of claim 9 , wherein an organic solvent and surfactant in the polymerization system composition are selected so a single phase microemulsion for fine W/O emulsion region in the phase diagram corresponds to an optimum polymerization temperature for a polymerization initiator for a thermal polymerization or redox polymerization.
15. The method of thickening a cosmetic of claim 9 , wherein the polymerization system composition contains a surfactant chosen so that the polymerization system composition has a clouding point at a temperature used for thermal radical polymerization.
16. The method of thickening a cosmetic of claim 9 , comprising radical polymerization of water soluble ethylene-type unsaturated monomers dissolved in the dispersion phase in a composition having an organic solvent or an oil component as the dispersion medium and water as the dispersion phase.