Process for producing chopped strands

Abstract

It is to provide a process for producing chopped strands capable of giving a molded product of which the mechanical strength and the water resistance are not impaired and of which the color tone is not deteriorated, capable of providing favorable dispersibility of glass fibers in molding material pellets, and being excellent in the releasability at the time of molding, and a fiber-reinforced polyamide resin molding material using the chopped strands. Glass fiber strands consisting of glass filaments spun from a bushing are subjected to a surface treatment with a sizing agent comprising, in terms of solid content, 100 parts by mass of an unsaturated copolymer of maleic anhydride with an unsaturated monomer, from 10 to 90 parts by mass of a polyurethane resin and from 5 to 100 parts by mass of a silane coupling agent, and then the obtained strands are chopped.

1 . A process for producing chopped strands, which comprises subjecting glass fiber strands consisting of glass filaments spun from a bushing to a surface treatment with a sizing agent comprising, in terms of solid content, 100 parts by mass of an unsaturated copolymer of maleic anhydride with an unsaturated monomer, from 10 to 90 parts by mass of a polyurethane resin and from 5 to 100 parts by mass of a silane coupling agent, and then chopping the obtained strands.  
   
   
       2 . The process for producing chopped strands according to  claim 1 , wherein the sizing agent further contains an acrylic acid polymer or a copolymer of acrylic acid with at least one monomer in an amount of from 5 to 100 parts by mass in terms of solid content per 100 parts by mass of the unsaturated copolymer of maleic anhydride with an unsaturated monomer.  
   
   
       3 . The process for producing chopped strands according to  claim 1 , wherein the sizing agent further contains a fluorescent brightening agent.  
   
   
       4 . The process for producing chopped strands according to  claim 1 , wherein the number average molecular weight of the unsaturated copolymer of maleic anhydride with an unsaturated monomer is at least 5,000 and at most 100,000.  
   
   
       5 . The process for producing chopped strands according to  claim 1 , wherein the content of maleic anhydride in the unsaturated copolymer of maleic anhydride with an unsaturated monomer is from 30 to 75 mol %.  
   
   
       6 . The process for producing chopped strands according to  claim 1 , wherein the unsaturated copolymer of maleic anhydride with an unsaturated monomer is soluble in an alkaline aqueous medium.  
   
   
       7 . The process for producing chopped strands according to  claim 1 , wherein the polyol component constituting the polyurethane resin is an aliphatic ether.  
   
   
       8 . The process for producing chopped strands according to  claim 1 , wherein the amount of the sizing agent attached is from 0.1 to 2 mass % in terms of solid content based on the glass fiber strands having the sizing agent attached thereto.  
   
   
       9 . The process for producing chopped strands according to  claim 1 , wherein the glass fiber strands have an average filament diameter of from 6 to 23 μm, and each fiber strand contains from 100 to 4,000 glass filaments.  
   
   
       10 . A fiber-reinforced polyamide molding material which is obtained by kneading chopped strands obtained by the process as defined in  claim 1  and a polyamide resin, and which has a glass content of from 5 to 70 mass %.