Patent GB-579023-A (GB)
Title: Improvements in or relating to the production of films consisting essentially of normally solid polymers of ethylene
IPC: B05D1/30
Filed: 1944-09-01
Abstract: A clear film is obtained by casting a solution of a polymer of ethylene on to a support, the temperature of which is below but not more than 15 DEG  C. below the melting point of the polymer, drying the film until substantially all the solvent is removed therefrom and bringing the film into contact with a non-solvent cooling liquid before crystallization and haze formation occur, but after the drying has continued beyond that stage at which contact of the <PICT:0579023/IV/1> non-solvent liquid with the film would yield a white opaque film. The melting-point is defined as the temperature at which haze disappears from a crystalline solid film of the polymer when it is subjected to gradually increasing temperature at the rate of 1 DEG  C. per minute.  A critical time interval exists within which the quenching may be applied to produce clear films.  This time interval is dependent on the conditions obtaining in any particular operation and may range from a few seconds to a few minutes.  It may be increased by incorporating in the ethylene polymer solution a small amount of a substance of the general formula X(R)a(OH)b in which X is hydrogen, the ammonium radical, an alkyl substituted ammonium radical, or a metal; R is a carboxylic or sulphonic acid radical containing 6-30 carbon atoms, a is an integer ranging from 1 to the valency of X, and b is an integer ranging from 0 to one less than the valency of X. Aluminium palmitate and stearate, magnesium stearate, titanium stearate, sodium oleate, ammonium stearate, potassium naphthenate, zinc stearate and palmitic acid are specified. The solvent used may be toluene or xylene or other aromatic or aliphatic hydrocarbon or chlorinated hydrocarbon of boiling point above 100 DEG  C.  The quenching liquid may be water at 0-70 DEG  C. Alcohols, esters, and ethers which are non-solvents for the ethylene polymer may be used.  The casting support may be a drum or endless belt.  The solution may be coated on to paper or cloth. The transparent films obtained are flexible, waterproof and resistant to tearing.  They may be used for wrapping food, tobacco, medicines and clothing.  They may be laminated with paper, cardboard or fabrics, by heat or pressure, or by means of an adhesive.  As shown in Fig. 1, polymer solution is cast as a film 3 from hopper 1 on to a casting drum 4.  The drum is heated internally by hot water or steam.  A nozzle 7 is placed to direct a spray of cold water against the film at the point B within the required period of time before crystallization and haze formation would occur.  The film is stripped from the drum and passes over roller 6 to a heated drying chamber or series of heated rollers. Instead of the spray of cold water, a bath of cold water may be used for quenching the film and the drum may dip below the surface of the water.  As shown in Fig. 3, the film of ethylene polymer solution is flowed on to a flat plate 11 which forms the upper side of a hollow steel box 12, and is heated by hot water passing through the box.  Warm air is passed through the casing 15. The film is quenched at the proper time by removing lid 17 and applying water to the film.  The ethylene polymer may be derived from ethylene alone or from ethylene and another polymerizable unsaturated organic compound.  It may have a melting point of 100-120 DEG  C. Specifications 471,590 and 497,643 are referred to.