Patent ID: 6139963
Filing Date: 2000-10-31
Classification: C02F,C08F,C08J,Y02W,Y10T

Abstract:
A polyvinyl alcohol hydrogel having a surface layer comprising a net-like structure formed by entanglement of fiber-like articles having a diameter of 0.1 to 50 .mu.m, and obtained by one of the following process (1)-(4);(1) adding to a mixed polymer solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels on contact with a cation, a substance (substance C) capable of causing phase separation of said polymer solution, to prepare a phase-separated liquid,contacting said phase-separated liquid with a cation-containing liquid, to solidify the polymer B present at least on the surface of said phase-separated liquid; andcontacting the obtained solid with a coagulating liquid having coagulating function for said polymer A, to effect gelation; or(2) adding to a mixed polymer solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels on contact with a cation, a substance (substance C) capable of causing phase separation of said polymer solution, to prepare a phase-separated liquid,contacting said phase-separated liquid with a cation-containing liquid, to solidify the polymer B present at least on the surface of said phase-separated liquid;contacting the obtained solid with a coagulating liquid having coagulating function for said polymer A, to effect gelation; andremoving from the obtained gel said polymer B partially or entirely; or(3) adding to a mixed polymer solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels on contact with a cation, a substance (substance C) capable of causing phase separation of said polymer solution, to prepare a phase-separated liquid,contacting said phase-separated liquid with a cation-containing liquid, to solidify the polymer B present at least on the surface of said phase-separated liquid;contacting the obtained solid with a coagulating liquid having coagulating function for said polymer A, to effect gelation; andeffecting acetalization simultaneously with or after the above gelation; or(4) adding to a mixed polymer solution containing a vinyl alcohol polymer (polymer A) and a polymer (polymer B) that gels on contact with a cation, a substance (substance C) capable of causing phase separation of said polymer solution, to prepare a phase-separated liquid,contacting said phase-separated liquid with a cation-containing liquid, to solidify the polymer B present at least on the surface of said phase-separated liquid;contacting the obtained solid with a coagulating liquid having coagulating function for said polymer A, to effect gelation,effecting acetalization simultaneously with or after the above gelation; andremoving from the gel obtained in the above step said polymer B partially or entirely.