Process for forming sheets from molten film-forming materials

摘要

In the production of a film or sheet from an organic film-forming polymer, which is capable of being drawn when in the solid state, both sides of the sheet are formed by chilling the polymer rapidly from the molten to the solid state by means of cold surfaces. A reservoir of molten polymer may be maintained in the wedge-shaped cavity formed by two parallel and horizontally disposed rolls rotating in opposite directions with their adjacent surfaces moving in a downward direction and separated at their nip by a distance equal to that of the sheet desired. The rolls are cooled so that a film of the polymer solidifies on the surface of each roll before reaching the nip of the rolls, and the two films are united into a single sheet as they pass through the nip of the rolls. The initially solidified component films may each have a thickness greater than one-tenth, but less than one-half of the thickness of the sheet desired. The depth of the reservoir of molten polymer in the nip of the rolls may be maintained more nearly uniform over its whole length by providing small electrically-heated dams. The polymer may be a polyamide, e.g. of the amino-acid, diamine-dibasic acid, or amino-alcohol-dibasic acid type, or it may be a polymerization product of ethylene. As shown in Fig. 2, molten polymer 5 is forced from the slot 4 of the hopper 1 into the space between the cooled rolls 6, 7. To prevent the stream of polymer from necking-in, the ends of the hopper lips may be provided with edge guides. As the molten polymer is cooled it solidifies on the surface of each roll and film layers 14, 15 are formed. On passing the nip of the rolls, the two films unite to form a single sheet 16 with a thin layer of molten polymer between the outer solidified parts. Upon further cooling the sheet becomes solid throughout its thickness. The sheet may be further cooled by passing round one of the rollers to a stripping roller or it may be immediately removed from both rollers and guided vertically downwards. Polyhexamethylene adipamide or an interpolymer from hexamethylene diammonium adipate and hexamethylene diammonium sebacate may be used. The polymer may be one of high or low viscosity properties and the fluidity may be increased by the presence of a small proportion of moisture. The casting zone may be surrounded with carbon dioxide, nitrogen or other inert gas. The surfaces of the rolls may be prepared by applying a very thin layer of a contact agent such as kerosene, tricresyl phosphate, chlorinated diphenyl, xylene, or a long chain alcohol. Other polymers which may be used are polyesters, polyethers, polyurethanes, polythioureas, and ester-amide interpolymers. The polymers may contain plasticizers, pigments, dyes, resins, antioxidants and other additions. The sheets may be used for safety glass interlayers, artificial leather, coatings for cloth and paper, floor coatings, automobile tops, wall coverings, window shades, playing cards, battery plate separators, strips for making hats and furniture seats and aircraft windshields. Specification 471,590 is referred to.