Polyvinyl alcohol-based fiber, fiber structure, and method for producing same

Abstract

[Problem to be solved] a polyvinyl alcohol fiber that have sufficient shrinkage rate and shrinkage stress when absorbing moisture at a temperature equal to room temperature or higher, especially around 35° C. is provided. [Solution] the present invention relates to a polyvinyl alcohol fiber containing modified polyvinyl alcohol containing 1 mol % or more of a carboxyl group and having a birefringence index of 0.040 or more, a fiber structure using the polyvinyl alcohol fiber, and a method for producing the polyvinyl alcohol fiber.

1 . A polyvinyl alcohol fiber comprising modified polyvinyl alcohol containing 1 mole or more of a carboxy group and having a birefringence index of 0.040 or more. 
     
     
         2 . The polyvinyl alcohol fiber as claimed in  claim 1 , wherein the carboxy group is contained in at least one functional group selected from the group consisting of an acrylic acid group, a methacrylic acid group and an itaconic acid group. 
     
     
         3 . The polyvinyl alcohol fiber as claimed in  claim 1 or 2 , which has a crystallinity of 30 to 60%. 
     
     
         4 . A fiber structure containing at least a portion of the polyvinyl alcohol fiber as claimed in any one of  claims 1 to 3 . 
     
     
         5 . The fiber structure as claimed in  claim 4 , wherein the fiber structure is a nonwoven fabric or a spun yarn. 
     
     
         6 . A method for producing a polyvinyl alcohol fiber comprising:
 wet or dry-wet spinning a spinning stock solution containing 5 to 30% by mass of modified polyvinyl alcohol containing 1 mol % or more of a carboxy group into a solidifying bath mainly composed of an organic solvent that has a solidifying ability for polyvinyl alcohol,   wherein in any one step of wet drawing, drying, dry drawing or heat treatment, a total drawing ratio in all steps is set to 7 times or more at 180° C. or higher.   
     
     
         7 . The method for producing the polyvinyl alcohol fiber as claimed in  claim 6 , wherein a drawing tension is set to 0.40 cN/dtex or more when the total drawing ratio in all steps is set to 7 times or more. 
     
     
         8 . The method for producing the polyvinyl alcohol fiber as claimed in  claim 6 or 7 , wherein the drawing temperature in the dry drawing step is 180° C. or higher.