Process for production of polypropylene sheets or films

A process for producing a polypropylene sheet or film which comprises:

• (a) providing two opposing cooling rolls which are maintained at a temperature of 10.degree. to 50.degree. C.;
• (b) passing a metallic endless belt having a surface roughness of not more than 1.5 .mu.m under tension, between said opposing cooling rolls;
• (c) producing a molten sheet or film of a polypropylene composition, the composition comprising polypropylene and at least one additive selected from the group consisting of
• (i) a nucleating agent being at least one member selected from the group consisting of talc, organic carboxylic acid salts;
• organic phosphoric acid metal salts;
• polyvinyl cycloalkane and at least one dibenzylidene sorbitol compound of the formula ##STR2## wherein R is an alkyl group having 1 to 8 carbon atoms, a halogen atom or an alkoxy group having 1 to 4 carbon atoms, and m and n are each 0 to 3,
• (ii) a finely powdered high melting point polymer having a melting point of more than 200.degree. C.,
• (iii) a petroleum resin,
• (iv) a terpene resin,
• (v) an organic peroxide, and
• (vi) a crystalline propylene-based copolymer, and
• (d) subjecting the produced sheet or film to a specular finishing treatment by passing the sheet or film between said metallic endless belt and one of said cooling rolls and conveying the sheet or film on said metallic endless belt over a surface portion of at least one of said cooling rolls;
• and
• (e) separating said sheet or film from said metallic endless belt after said specular finishing treatment.