Method for manufacturing heat-curable resin molded product

Abstract

A method of manufacturing a heat-curable resin molded product, such as an unsaturated polyester resin or the like, wherein concavities in the molded product generated as a result of the curing shrinkage of the resin are prevented. A central core member is first disposed within a mold, a heat-curable resin liquid is then injected into the mold and heated. The materials of the central core member and the heat-curable resin are selected such that the volume expansion of the central core member during heating of the mold corresponds to the volume shrinkage resulting from the curing of the heat-curable resin, and the expansion of the central core member is synchronized with the curing shrinkage of the heat-curable resin.

What is claimed is:  
     
         1 . A method of manufacturing a heat-curable resin molded product, the method comprising: 
 disposing a central core member within a mold, said central core member being formed from a material having a positive coefficient of thermal expansion that is not caused by water vapor;    injecting heat-curable resin around said central core member within said mold, said heat-curable resin having a negative coefficient of thermal expansion; and    heating said mold to cure said heat-curable resin so that said central core member expands and said heat-curable resin shrinks.    
     
     
         2 . The method of manufacturing a heat-curable resin molded product according to  claim 1 , wherein said central core member expands at a rate which is substantially the inverse of a rate at which said heat-curable resin shrinks.  
     
     
         3 . The method of manufacturing a heat-curable resin molded products according to  claim 1 , wherein: 
 said central core member is selected from the group consisting of epoxy resin foamed urethane resin, PPS (polyphenylene sulfide) resin, polycarbonate resin and ABS resin;    said heat-curable resin is selected from the group consisting of unsaturated polyester resin, urethane resin, epoxy resin and diallylphthalate resin, wherein one of a curing agent and a curing promoter is mixed with said heat-curable resin in an amount effective to adjust the curing rate and the curing temperature; and    said heating is conducted at a temperature in the range of 25 to 140° C.    
     
     
         4 . The method of manufacturing a heat-curable resin molded product according to  claim 1 , wherein a rate of volume expansion of said central core member is substantially equal to a rate of volume shrinkage of said heat-curable resin.  
     
     
         5 . A method of manufacturing a heat-curable resin molded product according to  claim 4 , wherein during the period that said mold is heated a total amount of said volume expansion of said central core member is equal to or slightly greater than a total amount of volume shrinkage of said heat-curable resin.  
     
     
         6 . A method of manufacturing heat-curable resin molded products, the method comprising: 
 disposing a central core member in a mold, said central core member being made of a resin which has a linear expansion coefficient of 4×10 −5 /° C. or less;    injecting heat-curable resin around said central core member in said mold, said heat-curable resin having a volume shrinkage ratio of 4.5% or greater; and    heating said mold to a maximum temperature of at least 80° C. to cure said heat-curable resin.    
     
     
         7 . The method of manufacturing heat-curable resin molded products according to  claim 6 , wherein said central core member is made of an epoxy resin or foamed urethane resin, said heat-curable resin is an unsaturated polyester resin or urethane resin and said maximum temperature is 100° C. or greater.  
     
     
         8 . The method of manufacturing heat-curable resin molded products according to  claim 6 , wherein said central core member is made of a foamed urethane resin, said heat-curable resin is an unsaturated polyester resin and said maximum temperature is 120° C. or greater.  
     
     
         9 . The method of manufacturing heat-curable resin molded products according to  claim 6 , wherein said central core member is made of an epoxy resin or foamed urethane resin and said heat-curable resin is an epoxy resin.  
     
     
         10 . The method of manufacturing heat-curable resin molded products according to  claim 6 , wherein said central core member is made of PPS, said heat-curable resin is selected from the group consisting of unsaturated polyester resin, urethane resin and epoxy resin, and said maximum temperature is 120° C. or greater.  
     
     
         11 . The method of manufacturing heat-curable resin molded products according to  claim 10 , wherein said heat-curable resin is unsaturated polyester resin or urethane resin and said maximum temperature is 140° C. or greater.  
     
     
         12 . A method of manufacturing a heat-curable resin molded product, the method comprising: 
 disposing a central core member within a mold, said central core member having a positive coefficient of thermal expansion;    injecting heat-curable resin around said central core member within said mold, said heat-curable resin having a negative coefficient of thermal expansion; and    heating said mold to cure said heat-curable resin so that said central core member expands at a rate which is substantially the inverse of a rate at which said heat-curable resin shrinks.    
     
     
         13 . A method of manufacturing a heat-curable resin molded product, the method comprising: 
 disposing a central core member within a mold, said central core member having a positive coefficient of thermal expansion;    injecting heat-curable resin around said central core member within said mold, said heat-curable resin having a negative coefficient of thermal expansion; and    heating said mold to cure said heat-curable resin so that a rate of volume expansion of said central core member is substantially equal to a rate of volume shrinkage of said heat-curable resin.    
     
     
         14 . A method of manufacturing a heat-curable resin molded product, the method comprising: 
 disposing a central core member within a mold, said central core member having a positive coefficient of thermal expansion;    injecting heat-curable resin around said central core member within said mold, said heat-curable resin having a negative coefficient of thermal expansion; and    heating said mold to cure said heat-curable resin so that during the period that said mold is heated, a total amount of said volume expansion of said central core member is equal to or slightly greater than a total amount of volume shrinkage of said heat-curable resin.