GB1230599A - - Google Patents

Abstract

1,230,599. Biaxially stretching polyamide films. NIPPON RAYON K.K. 25 July, 1968 [25 July, 1967], No. 35590/68. Heading B5B. A process for drawing a substantially amorphous polyamide film comprises treating the film with water whereby from 1 to 6% of water by weight (based upon the weight of the film) is absorbed by the film, passing the film through a preheating zone, the temperature of the preheating zone and the period of residence of the film in the preheating zone being such that the water content in the surface layer of the film is substantially lower than the water content of the interior of the film and thereafter drawing the film simultaneously in the longitudinal and transverse direction at a temperature of at least 5‹ C. above the temperature of the preheated film and at least 30‹ C. below the melting point of the film. The film may consist of poly-#-caproamide, polyhexamethylene adipamide or sebacamide, poly-11-aminoundecanamide, polylaurinamide, or a polyamide copolymer. If the film consists of polyhexamethylene sebacamide the treating of the film with water may be effected in such a manner that the average water content of the film is 1 to 5% by weight. The film may be preheated to a temperature of from 60‹ to 30‹ C. below the melting point of the film. The film may be drawn at a speed of from 6000 to 100,000% per minute. The ratio of the longitudinal and transverse draw speeds may range from 2 : 1 to 0À5 : 1. The draw ratio at which the film is drawn simultaneously in the longitudinal and transverse directions may range from 16 : 1 to 4 : 1. The drawn film may be heat-set at a temperature not higher than 10‹ C. below the melting point of the film with the film maintained under tension such that its width remains constant. The temperature of the preheating zone and the period of residence of the film in this zone may be such as to provide a steep downward gradient in water content in a traverse from the interior of the film to its surface as shown by a curve obtained when the water content of successive layers of the film from the central layer to one or other of the surfaces of the film is plotted against the distance of the layer from the film surface. The expressions " draw speed ", "ratio of draw speeds " and " draw ratio " have the meanings specified in Specification 1,111,305.