Below this concentration expulsion takes place.The crosslinkable unsaturated polyester is preferably is preferably composed of three types of components, namely units derived from a polyhydric alcohol, such as glycerol, pentaerytritol, manitol or sorbitol, units derived from a phthalic acid,preferably isophthalic acid, and units derived from an unsaturated aliphatic acid, most preferably linoleic