Patent GB-808344-A (GB)
Title: Method and apparatus for manufacturing sheeting, film or film base of organic high polymer material
Inventor: LANDUCCI ALFRED DOMINIQUE GERM
IPC: B29C48/08
Filed: 1955-03-10
Abstract: <FORM:0808344/IV (a)/1> Films of predetermined thickness are continuously made by depositing a film-forming composition containing a volatile solvent on a first casting wheel to form a film of a thickness (when partially cured) less than the predetermined thickness, this film-formation being effected at a greater speed than the speed which would be used in forming a film of the predetermined thickness directly, stripping the film from the casting wheel and partially curing it by evaporation of a portion of the volatile solvent, passing the partially cured film to at least one further casting wheel having the same dimensions as the first casting wheel, depositing further film-forming composition containing volatile solvent on the partially cured film as it passes over and in contact with the second casting wheel so as to bring the thickness of the film (when fully cured) to the predetermined thickness, and fully curing this film, the curing being effected by evaporation of substantially the whole of the remaining solvent from the film.  The apparatus used comprises a first casting wheel with associated feed hopper, at least one further casting wheel having the same dimensions as the first, a drying chamber interposed between each pair of wheels, a feed hopper associated with each of the further casting wheels, and a further drying chamber adapted to receive the film from the last wheel, the wheels being operated continuously and in series and means being provided for passing the film formed on one wheel through a drying chamber to the next wheel.  In the example, a solution of cellulose acetate and triphenyl phosphate in a mixture of methylene chloride and methyl alcohol is spread from the hopper 2 on to the rotating casting wheel 4 to a wet thickness of 0.012 inch to form a film 8, and the set film is stripped from the wheel at 9.  The film is drawn through the drying chamber 11 and festooned over rolls 12-14, some of which may be idler rolls and others positively driven, led under roll 16 and round and in contact with a second casting wheel 17 equal in dimensions to the first casting wheel 4.  More of the same dope as was spread on the first casting wheel is spread on the surface of the film that has been in contact with the first casting wheel as the film passes over the second casting wheel, the second layer of dope having a wet thickness of 0.023 inch, and the composite film 25 is then cured by passing it around rolls 27-29 and 31 in drying chamber 11 and around further rolls in drying chamber 35.  The finished film, now 0.0079 inch thick, is finally passed under terminal roller 41, withdrawn from the drying chamber 35 and collected on wind-up roll 42.  The thickness of the first-formed film may be less than, equal to or greater than the thickness of any one subsequent coating, or the total thickness of all subsequent coatings when more than one subsequent coating is applied.  The method of the invention enables production speeds to be increased.