Patent GB-1204349-A (GB)
Title: Porous coated film production
IPC: C23C14/20
Filed: 1967-11-01
Abstract: 1,204,349. Coated porous films. CELANESE CORP. 1 Nov., 1967 [16 Nov., 1966], No. 49613/67. Heading B5B. [Also in Divisions C3 and C7] Porous coated film is produced from a polymer film made by an extrusion, stretching and annealing process as claimed in Specification 1,143,474, Specification 1,180,066, or Specification 1,198,695, and in which the polymer crystallinity is at least 40%, by forming on the film a solid coating less elastic than the polymer film of a substance different from the polymer and then stretching the coated film and heating it while held against shrinkage for a sufficient time to reduce or eliminate the tendency of the coated film to contract on release from tension. The film may be coated with a metal coating, preferably by vacuum metallizing. Alternatively, the metal coating may be applied by chemical reduction of a metal compound, cathode sputtering, spraying or electrodeposition. The metal coating may be of aluminium, antimony, beryllium, cadmium, chromium, cobalt, copper, germanium, gold, magnesium, molybdenum, nickel, palladium, platinum, selenium, silver, tin or zinc. The electrical properties of the film may be enhanced by coating it with a layer of poly-para-xylylene formed on the film by polymerizing on it a monomeric para-xylylene from its vapour generated by heating the polymer to, e.g., 550‹ C. In producing the film to be coated it is preferred to use a draw-down during extrusion of from 75: 1 to 125: 1 and a melt temperature between 10‹ and 40‹ C. above the polymer melting point and to stretch the coated film at a draw ratio of from 1À10: 1 to 4: 1, and preferably 1À25: 1 to 2: 1 before annealing it under tension. In an example, crystalline polypropylene of melt index 4À0 and density 0À905 g./c.c. is melt extruded through a slot die at 380‹ F. and contacted with a rotating casting roll maintained at 185‹ F. and positioned “-inch from the lip of the die. During its passage from the die to the casting roll the extrudate is drawn down very rapidly to a draw-down ratio of 90 : 1. The film is annealed in a tensionless state in an oven at 130‹ C. for 15 minutes, removed from the oven and allowed to cool. The film is porous and has an elastic recovery from 100% strain of more than 70%. The film is then coated with aluminium by vacuum metallizing, stretched by 100% of its original length and annealed for one hour at 125‹ C. The process of Specification 1,143,474 comprises extruding a liquid consisting of or containing an organic polymer exhibiting crystallinity, andsubjecting the extrudate during or after solidfication to conventional treatment ensuring that the polymer crystallinity of the solidified extrudate is at least 50% and then stretching-and heating the solidified extrudate, while holding it against shrinkage for a sufficient-time to reduce or eliminate its tendency to contract on release from tension. The process of Specification 1,180,066 comprises the process of Specification 1,143,474 modified in that the solidified extrudate is drawn down at a ratio of at least 20: 1 and annealed and is thereafter stretched to increase its length by not more than 150%, followed by heating while restraining it against any greater shrinkage than 15% of its length for a sufficient time to reduce its tendency to contract on release from tension. The process of Specification 1,198,695 comprises the production of a film having an elastic recovery on its first extension of at least 70% from a 50% strain at 25‹ C. by extruding molten polyethylene, polypropylene or an oxymethylene polymer at a temperature no higher than 100‹ C. above its crystalline melting point, cooling the extrudate within two inches of the extrusion orifice by contact with a cooling roll or cooling air stream, stretching the solidifying extrudate at a high rate of draw-down and a draw-down ratio of between 20: 1 and 1000: 1 and annealing the stretched product by maintaining it at a temperature from 5‹ to 100‹ C. below the crystalline melting point for at least 5 seconds. Films made by this process are porous.