Patent GB-761493-A (GB)
Title: Process for producing planographic prints and light-sensitive sheets for that process
IPC: G03F7/016
Filed: 1954-06-29
Abstract: 761,493. Printing surfaces. CHEMISCHE FABRIEK L. VAN DER GRINTEN N. V. June 29, 1954 [June 30, 1953]. No. 18993/54. Drawings to Specification. Class 100(2). [Also in Group XX] A planographic printing plate is made by exposing a light-sensitive sheet comprising a support having a hydrophilic surface, porous hydrophobic matter, and light-sensitive matter containing a hydrophilic binder, in that order, the lightsensitive matter being such that exposure effects an alteration in the transferability after wetting with water of the porous hydrophobic matter, pressing the exposed surface of the light-sensitive sheet against the surface of a receiving printing plate having wetted at least one of the surfaces with water, separating the surfaces so that the porous hydrophobic matter is transferred imagewise from the sheet to the printing plate and then finishing the printing plate to render it suitable for planographic printing. In the light-sensitive sheet the hydrophobic matter may be applied directly to the support, or an auxiliary hydrophilic layer may first be applied, such as a layer of polyvinyl alcohol, gum arabic, agar-agar, methyl cellulose, casein, or tanned or hardened gelatine. It is preferred that the support is dimensionally stable against wetting, such as a support of metal, glass, artificial resin or ebonite. The support may have an intaglio relief, with elevations in the form of pyramids or cones, the porous hydrophobic matter being located in the relief, and superimposed thereon the light-sensitive layer. The porous hydrophobic matter may be a powder distributed in a binder. Powders such as baryte, titanium dioxide, and starch which are not themselves hydrophobic may be incorporated in a hydrophobic binder. Other powders such as soot, calcium stearate, aluminium and graphite may be used with hydrophobic or hydrophilic binders. Alternatively a hydrophobic film-forming material may be mixed with a water-soluble substance which can be washed out to leave a porous hydrophobic film, e.g. a mixture of collodion and glycerol. The hydrophobic matter may be a pigment which will contrast visually with the receiving plate, or such contrast may be obtained by including a pigment in the hydrophobic layer or in the light-sensitive layer. The lightsensitive material may be one whose receptivity for water alters on exposure to light, or by the action followed by some after-treatment. Suitable lightsensitive materials are bichromated colloids, a mixture of a ferric compound, tartaric acid and gum arabic, auramin, erythrosin, azido-styryl ketones, azidostyryl aryl azides, e.g. p ; p<SP>1</SP> - diazido - o ; o<SP>1</SP> - disulphonic acid stilbene, anthraquinone 2 : 7 disulphonic acid and diazo compounds. When using diazo compounds, exposure may be followed by an aftertreatment with chromate as described in Specification 296,008 [Class 98(ii)], or by treatment with a buffered solution of an azo coupling component. Alternatively, the chromate or azo coupler may be included with the light-sensitive diazo compound and in the latter case the exposed sheet is treated with ammonia fumes to induce coupling. The hydrophobic binding agent for the light-sensitive material may be gelatine, gum-arabic, proteins, fish glue, agar-agar, dextrin, gum tragacanth, methyl cellulose or polyvinyl alcohol. The light-sensitive matter may also contain a thermosetting resin such as ureaformaldehyde, phenol-formaldehyde or melamine-formaldehyde resins. The receiving printing plate may be a bimetallic plate, a lithographic stone, a grained aluminium, zinc or steel plate, paper specially prepared for planography, an aluminium plate with an oxide 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. The transfer is assisted by pressure and the wetting and pressing together may be combined in one operation. Heat may also assist the transfer and to this end the rollers between which the sheets are passed may be heated. Depending on the light-sensitive material and the conditions of transfer, a positive or negative transfer image may be obtained. Under certain conditions only part of the transferable matter may be transferred, and then further transfers may be obtained under the same or different transfer conditions. In modification the first transfer need not be onto a printing plate. It is preferred that the porous hydrophobic matter is transferable in the unexposed portions, i.e., that light causes a decrease in transferability of the light-sensitive matter. The printing plate may be finished by a treatment to improve the resistance of the transferred matter to printing operations. Suitable treatments are heating (which is particularly, useful when the light-sensitive material contains a thermosetting resin), including a tanning substance in the matter transferred and tanning it after transfer, using a diazo compound as lightsensitive material and forming an azodyestuff after transfer by treatment with a buffered solution of an azo coupling component, transferring an azo dyestuff coupling component with the diazo compound and treating the transferred image with ammonia fumes, or, in the case where the water receptivity of the lightsensitive 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 of the plate or the plate may be rubbed all over or coated with an asphalt solution and dried, and the transferred matter then eliminated from the plate. In many of the examples the light-sensitive material is "diazo-aldehyde" prepared according to Example I of Specification 418,011 [Group XX]. The porous hydrophobic matter may be a mixture of carbon black, asphalt and xylene or carbon black, cellulose acetate butyrate and ethyl acetate but numerous other compositions are given. In many examples the porous hydrophobic matter is placed in the cavities of the relief embossed on one side of a partially deacylated cellulose acetate support. The finishing operations are described in the examples. Specifications 401,898, 425,126, 510,233, 540,178, 614,155, 645,211, 655,274, 655,275, 678,599, 740,165, 740,166, [all in Group XX] 761,494, 761, 495 and U.S.A. Specification 1,618,505 also are referred to.