Patent GB-650786-A (GB)
Title: Improvements in or relating to the production of flexible film
IPC: C08L27/00
Filed: 1947-08-06
Abstract: <PICT:0650786/IV (a)/1> <PICT:0650786/IV (a)/2> <PICT:0650786/IV (a)/3> A flexible film having on one face an undulated area is obtained by applying a continuous layer of a film-forming substance to a carrier which is less absorbent in at least one area than in other areas, applying a swelling agent to the exposed surface of the continuous layer so that undulations therein occur, drying the layer, and stripping it from the carrier.  The absorbent nature of the carrier may be varied by applying a design of a relatively non-absorbent film substance to the absorbent carrier.  As shown in Fig. 11, an absorbent carrier 23 is taken from roll 24, passed through the design and film-forming devices, and is finally wound up on spool 48.  The carrier may consist of a web of heavy absorbent paper coated with one or more substances providing a smooth, flexible surface, e.g. nitrocellulose, casein, polyvinyl alcohol, or shellac. The coating should be porous and for this purpose may contain clay, chalk, activated carbon, or aluminium oxide.  The carrier 23 passes through tensioning rollers 25, and then over an engraved printing roller 26, fed with non-absorbent ink from container 28.  Roller 26 may have a single engraved channel in the form of a V, or each arm of the V may consist of several channels as in a line cut.  The ink or like non-absorbent composition may be a dispersion, emulsion, or solution of polyvinyl resins, cellulose derivatives, natural or synthetic rubbers, waxes, paraffins, or polyamides.  It may contain solvents such as methyl ethyl ketone, cyclohexanone, or acetone, and diluents such as xylol.  Plasticizers, pigments, dyes, fillers, luminescent materials, or metal flakes, may be included.  The non-absorbent composition may be such as to adhere more strongly to the subsequently-applied film-composition than to the carrier so that it becomes an integral part of the stripped film.  A suitable non-absorbent composition or ink comprises vinyl acetate-chloride copolymer, dioctyl phthalate, methyl ethyl ketone, and titanium dioxide.  The roller 26 is provided with a doctor blade which removes ink from all parts except the depressed or engraved regions.  The carrier 23 carrying the design passes round roller 31, which may be positively driven, and then over heated roller 32 which dries the ink, at least partially.  The carrier is then passed through a coating apparatus, and a continuous layer of film-forming substance is formed over the design.  The coating device consists of rubber-coated roller 33 for forwarding the carrier, a smooth metallic roller 34 rotating so that its surface is wiped across the surface of the coated carrier and design, a roller 35, and a trough 36 partly formed by rollers 34, 35.  The film-forming substance may be a dispersion or solution of a resin, e.g. a vinyl acetate chloride copolymer, a plasticizer, and a diluent.  The plasticizer may be dioctyl phthalate, and the diluent may be a mixture of a high with a lower-boiling liquid.  The carrier with the design coating and continuous film coating is then passed through a short oven 39 to remove part of the solvent and to solidify the film.  Owing to the absorbent nature of the carrier, those parts of the film over the areas of the carrier not covered by the non-absorbent ink contain substantially less residual solvent than those areas which are covered by the ink.  The carrier with the film is then passed under a spray 40 of swelling agent which may be acetone, methyl ethyl ketone, cyclohexanone, or other liquid or mixture of liquids having a pronounced swelling effect but little dissolving action. The swelling agent produces undulations or random designs in relief and intaglio in those regions on the upper surface of the film opposite the regions of non-absorbent ink.  In the other regions little or no undulations occur and the film becomes highly smooth and glossy.  The film on its carrier is then passed through an oven 41 having drying and fusing sections 41a, and 41b.  The film is then stripped and wound up on roll 49.  Fig. 3 shows the formation of undulations 22 on the upper surface of the film opposite the design coating 21.  The design roller 26 may bear designs of various kinds, e.g. lettering, fine lines imitating lacework, silhouettes, or pictures.  Provision may be made for obtaining undulations of varying degree.  Thus the roller may have a half-tone design and may apply dots of ink which are more closely grouped in some areas than in others.  This will produce more absorption of the film-solvent and consequently less undulation of the film in areas where the dots are spaced further apart.  Similarly if line-cut patterns are used on the design roller there will be less undulation of the film in regions where the lines are spaced further apart.  Fig. 10 shows a film in which the undulations vary with the spacing of the pattern lines. Similar variations in the undulations may be obtained by varying the depth of the channels or other engraved portions of the roller 26.  A series of rollers such as 26 using differently-coloured inks may be used, thereby producing a film having a multi-coloured embedded design. Specification 650,784 is referred to.