Patent GB-909326-A (GB)
Title: Process and apparatus for producing non-blocking, oriented thermoplastic polymer film
Inventor: JONES WILLIAM CHARLES
IPC: B29C71/02
Filed: 1960-12-19
Abstract: Films of organic synthetic oriented thermoplastic <PICT:0909326/IV(a)/1> polymers are rendered non-blocking by passing the film at a constant rate around embossing rolls which are heated to a temperature below that at which the orientation of the film is destroyed, chilling and winding while a constant tension is maintained on the film from the initial step to the final wind-up. As shown, a film in the form of a flattened blown tubular film and consisting, for example, of 85/15% by weight vinylidene chloride/vinyl chloride copolymer plasticized with diisobutyl adipate, is fed by means of a pair of rubber covered pinch and feed rolls 11 over an idler roll 12 and then in a sinuous path over three driven hollow embossing rolls 13 maintained at a temperature appreciably below the melting point of the polymer by passing a heat transfer fluid such as steam through the rolls via rotary union couplings 14 and hollow trunnions 15.  The peripheral surface of each of the rolls 13 is roughened as by steel grit blasting to give a surface roughness of 1,000 to 1,300 root mean square centimetres, i.e. the average height of the protuberances in the rolls is 1,000 to 1,300 millionths of a centimetre.  The film is next passed over a hollow trimming roll 16 mounted at a higher level than the rolls 13 and chilled by passing a cooling fluid through the roll via rotary union coupling 17 and hollow trunnions 18.  The roll 16 is provided with circumferential guide grooves 19 in which ride the cutting blades 20 mounted on brackets 21.  From the roll 16 the trimmed webs of film pass under and over two driven unheated roughened cooling rolls 22, 23 the surface roughness of which serves the passive function of creating the least disturbance of the prior embossing. From the rolls 22, 23 the film sheets travel to two wind-up cores 24 which are driven independently of the other parts of the apparatus, but at a constant torque to provide a uniform tension on the film at all stages of the process and to ensure a smoothly wound roll of film. The feed rolls 11 are driven at a controllable rate, and if the process is incorporated as a sequential step in the production of the film, the peripheral speed of the feed rolls 11 is variable in order to adapt this speed to variations in the rate of feed of the film to the feed rolls.  The variable drive A may be a variable speed or constant torque electric motor.  Rolls 13, 16, 22 and 23 are driven at the same peripheral speed and the ratio of the speed of feed rolls 11 to the rolls 13, 16, 22 and 23 must be kept constant.  As shown, a variable drive electric motor B rotates a jack shaft 26 keyed to a drive gear (not shown) in gear-box 27 through which power is transmitted to each of the rolls 13, 16, 22 and 23.  A preferred method of maintaining constant the ratio of the peripheral speed of the feed rolls to that of the other rolls is to connect variable drives A and B in an electrical cascaded circuit.  The process creates a roughened surface on the film which minimizes the tendency of the film to adhere to itself without impairing the clarity of the film.