Unsaturated polyester resin composition

#This invention relates to an unsaturated polyester resin composition which possesses excellent low shrinkage and also excellent mechanical strength.

#Sheet molding compounds (hereinafter referred to as SMCs), bulk molding compounds and the like, which are prepared by blending unsaturated polyester resins with fillers, pigments, thickeners, fiber reinforcing materials, hardening agents, stabilizers, mold releasing agents and the like, have recently been used in increasing amounts as new industrial materials. These compositions fulfill the requests for materials capable of reducing the labor cost and improving the productivity and the working environment in the reinforced plastic industry.

#However, molded products of unsaturated polyester resins tend to have cracks, distortions, warps, waviness and the like, since the resins show large shrinkage on hardening and the shrinkage causes embossings of reinforcing agents and peelings at the interface. In addition, it is difficult to produce molded products of high dimensional precision because of the shrinkage on hardening.

#ST solutions of BPAC-VAC random copolymers having a concentration thereof of 40%, were prepared by respectively dissolving BPAC-VAC random copolymers obtained in Reference Examples 1, 2, 3, and 4 into ST and each solution was blended with UPRs obtained in Reference Example 9 in ratios as shown in Table 3 to produce SMCs under the mixing conditions as shown in Table 3, which SMCs were the unsaturated polyester resin compositions.

#The resultant respective SMCs were aged to achieve thickening at 40.degree. C. for 24 hours.

#Immediately after the aging was over, the SMCs were pressed in a mold under the pressure of 100 kg/cm.sup.2 at a temperature of 140.degree. C. for 4 minutes, thereby obtaining moldings.