Patent GB-980260-A (GB)
Title: Improvements in the preparation of polyolefin sheeting
IPC: B29C55/18
Filed: 1961-02-20
Abstract: 980,260. Producing polyolefine film. KODAK Ltd. Feb. 20, 1961 [Feb. 18, 1960; March 21, 1960], No. 6163/61. Drawings to Specification. Heading B5B. [Also in Divisions G2 and H1]  Polyolefine film is produced by heating the polyolefine to form a clear melt, forming a sheet therefrom 2 to 10 tissues the desired sheet therefrom 2 to 10 times the desired thickness of the final film, and obtaining the final film from the sheet by passing the sheet between rollers under sufficient pressure to reduce the thickness of the sheet to the desired final thickness, a lubricant covering the surface of the film at the line of pressure. The lubricant may be water (desirably containing a wetting agent), any conventional lubricating oil, lubricating grease or solid lubricant, or any other liquid, grease-like or solid organic substance which has no deleterious effect on the poly-olefines or the processing equipment at the rolling temperatures employed and which has the ability at the rolling temperature of reducing the friction between the rolls and the polyolefine sheet, as indicated by a marked increase in percentage elongation of the sheet at a given roll pressure as compared with rolling under the same conditions without a lubricant. In the examples the lubricants used for polypropylene are ethylene glycol, diethylene glycol, butyl acetate, n-butanol, 2-ethoxyethanol, ethylene glycol diethyl ether, methyl isobutyl ketone, VM and P naphtha, and xylene. The lubricants used for polyethylene are butyl acetate, hexane, xylene, butyl alcohol, water, methanol, isopropyl alcohol, methyl ethyl ketone, cyclohexane and tetralin. Typical lubricants which may be employed in the process are sodium stearate and graphite. The initial sheet may be formed by melt extrusion. It may be cooled to at least 100 F. below its frost-line temperature within 60 seconds from the time it leaves the extruder. The initial sheet may be formed without drawdown. The pressure rollers may have a temperature of at least 40 F. but below the fatigue temperature of the polyolefine employed. The sheet from the pressure rollers may be relaxed by heating under sufficient tension to prevent any dimensional change at a temperature from 10 C. less than the creep temperature up to the fatigue temperature. The sheet may be first formed of a thickness 4 to 60 times that desired in the final film, and may then be stretched 100-400% at 65 to 240 F. in a direction at right-angles to that in which the pressure rolling takes place before passing through the pressure rollers. The polyolefine used may be polyethylene having a density of 0.910 to 0.970 at 23 C. In an example, polypropylene film produced according to the invention is treated with chlorine gas in the presence of sunlight to improve its adhesion and subbed using a combination of butadieneacrylonitrile copolymer and a prepolymer of resorcinol and formaldehyde diluted with 10 parts of methylethyl ketone. The sub is dried and a dilute aqueous-alcoholic gelatine solution applied to the surface and redried. A cine-negative gelatino silver halide emulsion is then applied and dried. In another example, the above subbed polypropylene film is coated with a gamma-Fe 2 O 3  magnetic oxide having an approximate particle size of about 1 micron using a nitrocellulose binder and an organic solvent. U.S.A. Specification 2,694,656 is referred to.