Patent GB-1139892-A (GB)
Title: Method and material for thermorecording
Inventor: VRANCKEN MARCEL NICOLAS
IPC: B41C1/055
Filed: 1965-02-11
Abstract: 1,139,892. Printing processes. GEVAERTAGFA N.V. 11 Feb., 1966 [11 Feb., 1965], No. 6047/65. Heading B6C. [Also in Division G2] A thermographic process comprises imagewise heating a material consisting of or containing a water-permeable layer which comprises polyvinyl alcohol of which at least 95% is vinyl alcohol units and thus rendering the material water-impermeable or less permeable in the heated areas. The exposed material may be developed by (1) treatment with an aqueous solution of a dye, a catalyst for initiating a colour reaction between components present in the material, a colour-forming component with the other component present in the material, a bleaching agent for a dye or silver present in the layer, or an etching agent for etching a metal support, the aqueous solution permeating the still water-permeable areas, (2) diffusion of a water-soluble dye, catalyst, colour forming component or a complexed silver salt from the water-permeable areas on to a receptor sheet which, if necessary, contains the requisite reactants, (3) removing the water-permeable areas by washing them out to produce a waterpermeable membrane which may be used in electrolytic printing or produce a printing plate after etching the support, or if the support is electrically conductive charging the remaining water-impermeable areas and powder developing these areas or transferring the charge to a receptor and developing; or if the support is a screen, producing a screen printing master and (4) transferring the water-permeable areas to a receptor sheet or by transferring portions of a dye sheet to the water-permeable areas to prodyce a dye master. The material may be exposed to infra-red radiation or to light intensity flash for 0.0001 to 0.01 second if the material contains light-absorbing, heat generating materials such as carbon black, heavy metals or their sulphides and oxides and certain dyes as in Specification 1,076,799. The material may also contain hydrophobic, thermoplastic polymer particles such as polyethylene dispersed in the polyvinyl alcohol layer as disclosed in Specification 1,139,891. In Example I, polyvinyl alcohol is coated on a paper support, image-wise exposed to infra-red radiation and developed by applying an aqueous dye solution to give a positive dye image. The material is now molten and pressed into contact with a carbon paper so that the dye layer of the carbon paper is transferred on to the dye image to produce a hectographic master. In Example 2, the polyvinyl alcohol layer contains carbon black and is exposed as above and the unexposed areas are transferred to a wetted receptor sheet to give a negative image thereon. In Example 3, the support is coated with a gelatine layer containing colloidal silver and over-coated with a polyvinyl alcohol so that after exposure, the silver is bleached out by a bleach solution which permeates the water-permeable areas of the polyvinyl alcohol. In Example 4, a stencil is produced by using Japan paper as support and washing out the unexposed areas of polyvinyl alcohol after exposure. In Example 5, a printing plate was made by dispersing polyethylene particles in the polyvinyl alcohol layer and hardening the layer after exposure. In Example 6 the layer contains carbon black and is image-wise exposed to a xenon discharge lamp for 2 x 10<SP>-4</SP> seconds and the non-exposed areas washed out.