Method of Thickening Cosmetic Composition

Abstract

A method of thickening cosmetics containing a crosslinked water-swellable polymer, or a microgel obtained by pulverizing a hydrophilic compound having gelation ability. The method comprises adding a linear polyacrylic acid or a salt thereof, or a linear poly(2-acrylamido-2-methylpropanesulfonic acid) or a salt thereof, having a weight-average molecular weight of 500,000 to 8,000,000, which has a thread length of 10 mm or less at room temperature when formed into a 1% by mass solution. The method provides cosmetics having an improved viscoelastic ratio, with a rich and full-bodied feeling upon application.

We claim: 
     
         1 . A method of increasing the viscoelastic ratio of a cosmetic, the cosmetic comprising
 (a) one or more crosslinked water-swellable polymers having a crosslinking density of 0.01 to 1% by mole, or   (b) a microgel obtained by pulverizing a gel consisting of a hydrophilic compound having gelating ability;   
       which comprises adding to said cosmetic a linear polymer comprising
 (c) a linear polyacrylic acid or a salt thereof, or 
 (d) a linear poly(2-acrylamido-2-methylpropanesulfonic acid) or a salt thereof; 
 
       having a weight-average molecular weight of 500,000 to 8,000,000 and a thread length of 10 mm or less at room temperature when formed into a 1% by mass solution; 
       wherein the thread length is a distance determined by putting a round disk having a diameter of about 1 cm uniformly and lightly into contact with a surface of the solution, lowering a container that contains the solution at a velocity of 5 mm/sec, and measuring the distance that the container descended until a thread of the solution is cut. 
     
     
         2 . The method according to  claim 1 , wherein the one or more crosslinked water-swellable polymers are one or more selected from the group consisting of carboxyvinyl polymer, acrylamidealkylsulfonic acid/beheneth-25 crosslinked copolymer, acrylamidealkyl sulfonic acid/vinylpyrrolidone crosslinked copolymer, and acrylamidealkylsulfonic acid/alkylacrylamide crosslinked copolymer. 
     
     
         3 . The method according to  claim 1 , wherein the one or more crosslinked water-swellable polymers further comprise an (acrylates/alkyl (C10-30) acrylate) crosspolymer. 
     
     
         4 . The method according to  claim 1 , wherein the fraction of the linear polymer having a molecular weight of 10,000,000 or more in is 10% by mass or less. 
     
     
         5 . The method according to  claim 2 , wherein the fraction of the linear polymer having a molecular weight of 10,000,000 or more is 10% by mass or less. 
     
     
         6 . The method according to  claim 3 , wherein the fraction of the linear polymer having a molecular weight of 10,000,000 or more in is 10% by mass or less.