GB858154A - Method and apparatus for simultaneously conditioning and conveying films of plastic material in a conditioning apparatus - Google Patents

Abstract

<PICT:0858154/IV(a)/1> Thin plastic film is simultaneously conditioned and conveyed in a conditioning apparatus by directing at an oblique angle to the plane of the film one or more streams of heated air against at least the undersurface of the film to raise the temperature thereof and remove any internal stresses existing in the film, and utilizing said air stream or streams to propel the film through the apparatus in such manner that, during the heating step, physical contact between the film and the apparatus is avoided, whereby the conditioned film is maintained in an unstressed state. By "conditioning" is meant applying to the film a constant temperature at which the molecular structure of the film is returned to and/or maintained in a state corresponding to that of unstressed film. Preferably, two air streams are directed against the film, one stream being arranged to impinge on the undersurface of the film and the other stream on the upper surface thereof. Suitable apparatus comprises a tunnel through which the film is conveyed and means for directing one or more heated air streams obliquely against at least the undersurface of the film. The apparatus shown includes a mechanically operated film supply roller 16 which causes the film on unwinding to form a free loop 18 extending between a source of light 19 and a photocell 20 controlling the roller speed. The tunnel 3 is provided with two oppositely positioned sheaths 1, 2, which are each provided with at least one air-blowing fan 5, 6 and at least one heating element 9,10, and have openings through which the air streams are fed on to the surfaces of the film. These openings may be provided with deflectors 7,8, The sidewalls of the tunnel may be made of yielding material, whereby the positions of the roof and floor of the tunnel may be adjusted relative to each other. The tunnel may be pivotally secured to a machine for applying a subsequent treatment to the film, e.g. a press 13, 14, the pivotal movement of the tunnel relative to said machine, e.g. about hinge 15, allowing the formation of a loop of film 28 at the entrance of the machine. Additional features of the apparatus may include yielding flaps 21, 22 at the input end of the tunnel, angularly disposed flaps 24, 25 which serve to maintain a constant air pressure along the length of the tunnel, and a turbine 29 having means operatively connected thereto for adjusting the speed of fans 5, 6.