Patent GB-1011545-A (GB)
Title: Producing polyolefin by compression rolling of polyolefin sheets
IPC: B29C48/08
Filed: 1962-07-24
Abstract: 1,011,545. Producing polyolefine film. EASTMAN KODAK CO. July 24, 1962 [July 24, 1961], No. 28418/62. Heading B5B. Transparent crystalline polyolefine film is produced by passing two or more translucent polyolefine sheets each 2 to 10 times the desired thickness of the final film between rollers at the same time under sufficient pressure and with the aid of a lubricant to reduce the thickness of each sheet to the desired final thickness. As shown in Fig. 1, two polyolefine sheets 3 are run past the lubricating nozzles 15 associated with pipe 16 communicating with a source of lubricant and then pass between the pressure rollers 8 and 9, at which point the sheets 3 are reduced in thickness to ¢ to 1/10 of the thickness of the sheets as extruded. Next the sheets or films pass round the idler rollers 10 to take-up rollers 14. The two sheets may be in the form of lay-flat tubing which is preferably made by dry extruding seamless polypropylene tubing 3 (Fig. 2) from the extruder 17 through the annular die orifice 18 into an aqueous quench bath 19 and drawing the tubing around guide roll 20 between pinch rolls 21 to take-up roll 22. The tubing is distended in the bath by filling it with a liquid denser than water and maintained at a predetermined level within the tubing. The lay-flat tubing is then passed between compression rollers. It may be slit before being passed through these rollers so that both the inside and the outside surfaces of the tubing may be lubricated during the compression rolling operation. When compression rolling two or more sheets the lubricant must cover the surface of the sheets as they contact the compression rollers and both the sheets consist of the same olefine lubricant must also cover the surfaces of the sheets which contact one another as they are pressed together at the nip of the rolls. When the sheets consist of two different olefines, such as polyethylene and polypropylene, no lubricant is required between the sheets. The lubricant may be a liquid, a grease, or a solid such as powdered sodium stearate or powdered graphite. If water is used as a lubricant, it is desirable to dissolve in it a wetting agent such as sodium dioctyl sulphosuccinate. In the case of polyolefine sheet the sheet is preferably made by extruding a clear melt of the polyolefine and quenching the extruded sheet by passing it through cold water or else to a roll cooled with water at 60 F. so that the sheet is solidified and cooled during contact with the roll to a temperature of at least 100 F. below its frostline temperature within at most 60 seconds from the time it leaves the extruder. Preferably no appreciably drawdown occurs during the passage of the sheet from the extruder to the chilling means. The frost line temperature is defined as the temperature at which a melt cast polyolefine film becomes suddenly hazy or shows a significant loss in transparency on cooling. The compression rolled sheet may be heat treated under sufficient tension to impart to it dimensional stability preferably at a temperature greater than 10 F. less than the " creep temperature " of the polyolefine, and must be lower than the " fatigue temperature " of the polyolefine. The " creep temperature" is defined as the temperature at which the length of a test specimen has changed 2% of its original length when the specimen is supporting a load of 10 grams per square metre and the temperature is being increased at the rate of 10 C. per minute. The " fatigue temperature" is defined as the temperature at which the tensile strength of the sheet is between 14 and 20 p.s.i. Specifications 904,321, 980,260 and 982,912 are referred to.