Backing material

A material especially adapted for use as a backing for the wearing parts of machines consisting essentially of:

• a phthallic polyester resin consisting essentially of about 36-38 wt. % orthophthallic anhydride, about 21-26 wt. % maleic anhydride, and about 43-36% propylene glycol and a flexibilizing agent consisting essentially of about 30 wt. % styrene monomer and about 70 wt. % of a prepolymer consisting essentially of about 15-35 wt. % phthalic acid, about 15-5 wt. % adipic acid, about 20-30 wt. % other dibasic acid, and about 50-30 wt. % of a member from the group consisting of bis-phenol A, prodendro bis-phenol A, and mixtures thereof selected from the group consisting of bis-phenol A polyester resins and prodendro bis-phenol A polyester resins, the weight ratio of phthallic polyester resin to flexibilizing agent being between 1.65 and 5.0,
• an expansion agent present in an amount to compensate for the shrinkage of the polyester resin and flexibilizing agent during curing, and
• a filler present in an amount which can be wetted by the resin and flexibilizing agent.