Resin coated foundry sand using crystalline unsaturated polyester as binder

A process of preparing a resin coated sand for forming molds and cores for use in a sand molding process, the process comprising the step of:

• mixing a major amount of a foundry sand with a minor amount of a binder composition which comprises a crystalline unsaturated polyester which is solid at room temperature as a principal component thereof and diallyl phthalate, the weight ratio of said diallyl phthalate to said unsaturated polyester being in the range from 5:100 to 30:100, at an elevated temperature at which said binder composition is in a fluidized state in the presence of an organic peroxide which serves as a curing catalyst for said unsaturated polyester, the weight ratio of said organic peroxide to said unsaturated polyester being in the range from 0.1:100 to 10:100, said binder composition being a scarcely tacky solid at room temperature, the viscosity of said binder composition at a temperature about 30.degree. C. above the softening temperature thereof being below about 500 poises.