Patent GB-770462-A (GB)
Title: Unitary, multi-coloured, plastic film, and a method for its production
IPC: B29C41/22
Filed: 1954-07-19
Abstract: <PICT:0770462/IV(a)/1> <PICT:0770462/IV(a)/2> A plastic film containing sharply defined zones of colour, e.g. coloured lettering, within and integral with the film is formed by depositing through a screen a layer of a fluid film-forming plastic material on a smooth surface, heating to partially cure it, similarly depositing successive layers thereon including the coloured design, each layer in turn being heated to partially cure it and bond it to the previous layer, the resulting composite film being heated to a higher temperature to fully cure it and peeled from its supporting surface. The preferred material is a vinyl chloride resin used as a suspension in a plasticizer, preferably a mixture of a low viscosity plasticizer and a high viscosity plasticizer compatible with the vinyl resin, together with a surface-active agent and a stabilizer for the vinyl resin. Suitable low viscosity plasticizers are dioctyl phthalate and dioctyl sebacate.  Suitable high viscosity plasticizers are chlorinated biphenyl, methyl abitate and hydrogenated methyl abietate.  Suitable surface active agents are organic silicone polymers such as dimethyl silicone polymer.  Suitable stabilizers for the vinyl resin are dibasic lead phosphite, tribasic lead sulphate and barium ricinoleate.  The coloured portions consist of the same material as the other layers together with a dye or pigment. Successive layers to build up a sign are deposited through silk screens, as used in the silk screen printing processes, portions of the screen through which the material is not to be deposited being coated with a shellac composition to close the mesh.  Figs. 2 and 3 illustrate how a sign having coloured letters and a different coloured border on a white background and having smooth top and bottom faces is built up. The white background 1 is formed from a composition containing polymerized polyvinyl chloride 40 parts, dioctyl phthlate 20 parts, alkyd resin plasticizer 30 parts, titanium dioxide 12 parts and 4 parts of a mixture containing dioctyl phthalate, triethylene glycol di-(2-ethyl butyrate), dimethyl silicone, white extender pigment and dibasic lead phosphite.  The composition is squeezed through a rectangular silk screen and deposited on a chromium-plated steel plate which is then heated to 300 DEG  F. to give a semi-cured resin.  This is repeated to form layer 2, the second layer fusing on to the first.  The letters are then formed by squeegeeing through an appropriate silk screen a similar composition but containing a blue pigment instead of the titanium dioxide the whole then being semi-cured at 300 DEG  F.  The border 4 is then formed by depositing a similar composition but containing a red pigment instead of the titanium dioxide and the whole heated to 350 DEG  F. to effect a full cure.  Finally, a transparent layer 5 is then formed by depositing through a rectangular silk screen a similar composition but without the titanium dioxide and curing at 325 DEG  F., it being found desirable to cure transparent layers at a temperature slightly lower than for the pigmented layers.  Finally, the composite film is stripped from its supporting plate.  A sign having a different lettering on each side may be built up in a similar manner but the two signs should be separated by a layer containing a metallic pigment such as metallic aluminium, to ensure complete opacity.  It is stated that composite films so produced have a surface sufficiently flat to be selfadherent to plane surfaces.