Patent GB-565752-A (GB)
Title: Improvements relating to the formation of designs in printing and other surfaces
IPC: B41N1/14
Filed: 1943-03-22
Abstract: <PICT:0565752/IV/1> A method of forming a design in a sheet for printing or other purposes comprises removing areas of a surface that has been uniformly hydrolysed or converting them to a different chemical composition while protecting the other areas by means of a stencil of the design superposed on the hydrolysed surface, and then removing the stencil to expose the protected hydrolysed areas.  Such a sheet may be used to produce a coloured design by dyeing, the design areas and the hydrolysed areas having a different affinity for dyes, but the sheet is primarily for use as a printing surface, in which case, the design areas must be ink receptive.  The stencil employed may be a preformed stencil applied to the sheet or may be formed in situ photographically and the hydrolysation may be effected before, during, or after the formation of the stencil.  In one form, Fig. 3, a sheet 2 of cellulose acetate having an ink-receptive surface is hydrolysed to a certain depth as indicated at 1, by treatment with an aqueous solution of sodium hydroxide.  The sheet is then coated with a sensitized gelatin emulsion, exposed through a positive of the design and developed by a tanning developer.  The unhardened parts are removed in the usual way forming a stencil 4. The exposed portions of the hydrolysed layer 1 are then removed by vigorous rubbing with a solution of zinc chloride, lactic acid, copper ammonium hydroxide or other solvent of cellulose hydrate.  The addition of ethyl lactate to the zinc chloride facilitates the removal.  Instead of partially hydrolysing the sheet, the sheet may be secured to an under layer of ink-receptive material, such as cellulose nitrate, and hydrolysed throughout.  Instead of removing the parts of the layer 1 exposed through the stencil, they may be converted into a different chemical composition, e.g. by only lightly rubbing with a mixture of zinc chloride and ethyl lactate, or, such exposed parts may be rubbed with a solution of a phenol-aldehyde ink-receptive resin to form a coating of resin thereon.  In another form, the photographic stencil is formed before the hydrolysation of the surface of the sheet which is mounted on a base of cellulose nitrate or of metal.  After the formation of the stencil the whole is immersed in a solution containing sodium hydroxide, commercial alcohol and acetone until the whole of the acetate sheet is hydrolysed.  The subsequent treatment is as above described in connection with Fig. 3.  The hydrolysis may be effected during the formation of the stencil by using a tanning developer containing the hydrolysing agent, e.g. a solution consisting of equal parts of a 2.5 per cent solution of pyrocatechol and a solution containing 500 c.c. of 2 per cent sodium hydroxide, 450 c.c. of commercial alcohol, and 50 c.c. of acetone.  The tanning action may be interrupted while allowing the hydrolysation to proceed, by the addition after a suitable interval of strong sodium sulphuric solution.  Specification 368,083, [Group XX], and German Specification 509,010 are referred to.