Patent GB-761494-A (GB)
Title: Process for producing graphic prints and light-sensitive sheets for that process
IPC: G03C5/10
Filed: 1954-06-29
Abstract: 761,494. Printing surfaces. CHEMISCHE FABRIEK L. VAN DER GRINTEN N. V. June 29, 1954 [June 30, 1953], No. 18994/54. Addition to 740,166 [Group, XX]. Class 100(2) Also in [Group XX] A printing plate is made by exposing, in the manner of screen reflectography, a light sensitive sheet comprising a light-pervious support, a reflectographic light screen composed of hydrophobic matter and a lightsensitive material in that order, the lightsensitive material being free from grains scattering actinic light and being such that exposure effects an alteration in its adhesive power, pressing the exposed surface of the sheet against the surface of a receiving printing plate, having wetted either or both the surfaces, separating the surfaces so that the more adhesive portions of the sheets are transferred imagewise to the printing plate and then finishing the plate to render it suitable for printing. In the light-sensitive sheet the screen may be applied directly to the support, the surface of which is preferably hydrophilic (such as a cellulose ester support) or an auxiliary. hydrophilic layer may first be applied such as a layer of polyvinyl alcohol, gum arabic, agar-agar, methyl cellulose, casein and tanned or hardened gelatin. The support may be embossed with cavities in the form of a screen, the screen parts being located in these cavities and superimposed thereon the light-sensitive layer. Suitable lightsensitive sheets are described in the parent Specification. The screen parts may be formed of pigments as described in the parent Specification and if the pigment is hydrophilic, a hydrophobic binder may be included as decribed in the parent Specification. The light-sensitive materials may be those described in the parent Specification, and include bichromates, a mixture of a ferric compound, tartaric acid and gum arabic, auramin, erythrosin, diazo-compounds (which may be treated after exposure to give an azo-dye or mixed with an auxiliary substance such as a chromate or a coupling component), azido-styryl-ketones, and azido-stryl aryl azides. The use of p ; p<SP>1</SP> - diazido - stilbene - o ; o<SP>1</SP> - disulphonic acid, anthraquinone 2 ; 7 disulphonic acid and Lippmann type emulsions also is referred to. The light-sensitive material may contain a lyophilic binder as described in the parent Specification. It is preferred that the support is dimensionally stable against wetting such as a support of glass plate, glass cloth or transparent artificial resin. Supports of transparent paper, cellulose hydrate, polyvinyl acetate or glass carrying a layer of cellulose acetate also may be used. The receiving printing plate may be a bi-metal plate, a lithographic stone, a grained aluminium, zinc or steel plate, paper specially prepared for planography, an aluminium plate with an ozide layer or a plastic sheet having a water-receptive surface such as a superficially deacylated cellulose ester sheet. Wetting of at least one of the transfer surfaces may be with pure water, or with aqueous solutions of salts, wetting agents or alcohol. Reference is made in the examples to the use of ethyl acetate, isopropyl acetate, benzene, 2 - nitro propane, trichloroethylene and propylene dichloride as transfer liquids. In certain cases an auxiliary adhesive may be added to the transfer liquid, suitable transfer liquids being gum arabic in water, polyvinyl alcohol in water or water and alcohol, and dextrin and fish glue in water. Alternatively the surface of the receiving plate may be treated with an adhesive such as gelatin, polyvinyl alcohol, casein and artificial resin emulsions. The transfer is assisted by pressure and the wetting and pressing together may be combined in one operation. Heat may also assist in the transfer which may be carried out with the apparatus described in the parent Specification. As in the parent Specification only part of the transferable matter may be transferred in the first transfer operation and then further transfers may be obtained under the same or different conditions. In a modification the first transfer need not be on to a printing plate. The printing plate may be finished by a treatment which improves the resistance of the transferred matter to printing operations. Such treatments include subjecting the plate to high pressure, covering the transferred matter with a substance resistant to water heating-preferably using a thermosetting resin (such as urea-formaldehyde, phenol-formaldehyde or melamine-formaldehyde resins) in the light-sensitive matter so that this is transferred to the printing plate, using a tannable substance in the matter transferred (e.g. gelatin) and tanning after transfer (e.g. with formaldehyde, aluminium or chrome alum), using a diazo compound as light-sensitive material and forming an azo-dyestuff after transfer by treatment with a buffered solution of an azo coupling component, transferring an azo coupling component with the diazo compound and treating the transferred image with ammonia, fumes or, in the case where the water-receptivity of the light-sensitive matter decreases on exposure to light, exposing the transferred image to light. Finishing of the printing plate may also comprise etching the open portions or making them more water-receptive before inking, e.g. by "fixing" zinc or aluminium plates in phosphoric acid and gum arabic or by removing the top metal layer of a bimetallic plate. Alternatively a layer of metal may be deposited in the open spaces, or the plate may be rubbed over or coated with an asphalt solution and dried and the transferred matter eliminated from the plate. Numerous examples are given in most of which the support is cellulose acetate having a screen impressed on one side and filled with a composition of carbon black, asphalt and xylene. The light-sensitive layer which in most of the examples contains " diazo-aldehyde " (see the parent Specification) is coated on top. Details of the finishing operation are given in the examples. Specification 678,599 [Group XX] also is referred to.