Patent GB-761495-A (GB)
Title: Process for producing transfer images and graphic prints and light-sensitive sheets therefor
IPC: G03F7/115
Filed: 1954-06-29
Abstract: 761,495. Printing surfaces. CHEMISCHE FABRIEK L. VAN DER GRINTEN N. V. June 29, 1954 [June 30, 1953], No. 18995/54. Drawings to Specification. Class 100(2) [Also in Group XX] A transfer image is formed on a receiving printing plate by exposing in the manner of screen reflectography a light-sensitive sheet comprising a light-pervious support, a.permanent screen consisting of portions substantially impervious to light alternating with areas substantially pervious to light there being no transition between the pervious and impervious portions, and light-sensitive material in that order, the light-sensitive material being free from grains scattering actinic light and being such that its transferability is altered by exposure to light; pressing the exposed surface of said sheet against the receiving surface of the printing plate, at least one of the surfaces being wetted, and separating the surfaces so that light-sensitive material is transferred imagewise from the sheet to the receiving surface, the entire screen being sufficiently strongly attached to its support to remain there during transfer. The light-sensitive sheet may have recesses in one side of its support in which the screen parts are located. The screen parts may fill the recesses and the light-sensitive layer be applied on top, or the screen parts may only partly fill the recesses and the light-sensitive layer which is applied on top will then be thicker in the impervious screen portions by filling the remainder of each recess, or the remainder of the recesses may be filled with porous hydrophobic matter as described below before the light-sensitive layer is applied. It is preferred that the surface of the screen remote from the support is hydrophilic, and carries together with the light-sensitive material porous hydrophobic matter for imagewise transfer. This porous hydrophobic matter may form an auxiliary layer between the screen and the light - sensitive layer. The examples illustrate the use of various pigments mixed with the light - sensitive material. The screen parts may take the form of circular islands of light - impervious matter surrounded by light-pervious areas, or of light-pervious areas in the form of circular islands surrounded by light-impervious matter. The light-sensitive material may be one whose receptivity for water alters on exposure to light or by the action of light followed by some after treatment. Suitable light-sensitive materials are Lippmann emulsions, chromates or bi-chromates, a mixture of a ferric compound, tartaric acid and gum-arabic, auramin, erythrosin, diazo-compounds, azido-styrye ketones and azido-styryl aryl azides, such as p : p<SP>1</SP> - diazo - o:o<SP>1</SP> - disulphonic acid stilbene. When the light-sensitive material is a diazo-compound, an auxiliary chemical may be included such as a chromate or an azo coupling component and in the latter case the imagewise exposed sheet may be treated with ammonia fumes to induce coupling. It is preferred that the light-sensitive layer contains a lyophilic binding agent such as gelatin, gum-arabic, proteins, fish glue, agar-agar, dextrin, gum tragacanth, methyl cellulose, shellac, colophony, synthetic resins and polyvinyl alcohol. The screen impervious parts may be deposits of metals, metal sulphides such as lead sulphide, or dyestuffs, or may be composed of pigment such as carbon black in a binder. The may be formed in or on the support by an imbibition process or photographically, e.g. by exposing a diazo layer under a screen and developing it to an azo dyestuff screen image. Where the screen surface carries hydrophobic porous matter this may be a powder distributed in a binder. Powders such as baryta, 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 copper may be used with hydrophobic or hydrophilic binders, or a hydrophobic filmforming material such as collodion may be mixed with a water soluble substance such as glycerol which is subsequently washed out to give a porous hydrophobic film. Where the screen surface carries an auxiliary layer this may be polyvinyl alcohol, gum-arabic, agar-agar, or methyl cellulose. The matter to be transferred may contain a pigment or dye or it may be almost invisible and may be developed on the receiving surface. Thus a diazo compound may be transferred and developed to an azo dye image on the receiving surface, or the matter transferred may contain also an azo dye coupling component and the receiving surface may be treated with ammonia fumes. The transferred image may contain a thermosetting resin such as a urea-formaldehyde, phenol-formaldehyde or melamine-formaldehyde resin. The support for the light-sensitive sheet may be tracing paper, cellulose hydrate, polyvinyl acetate or glass carrying a cellulose acetate layer. The receiving printing plate may be a bi-metallic 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 before transfer is preferably effected with water but aqueous solutions of salts, wetting agents or alcohol may also be used. In the examples reference is made to the use of acetone, 1 : 4 - dioxane, methyl acetate, methoxyethyl acetate or ethyl lactate as transfer liquids. The transfer is assisted by pressure and the wetting of one or both surfaces and the pressing together may be carried out in one operation. Heat also may assist in the transfer and to this end the rollers between which the sheets are passed may be heated. Depending on the light-sensitive material, the wetting, and 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 conditions. It is preferred that light-sensitive matter is transferable in the unexposed portions, i.e. light causes a decrease in transferability of the light-sensitive matter. The receiving printing plate may be finished by a treatment to improve the resistance of the transferred matter to printing operations. Such finishing treatments include the application of pressure, heating (which is particularly useful where the matter transferred contains a thermosetting resin), including a tanning substance in the light-sensitive matter and tanning after transfer, using a diazo compound and forming an azo dyestuff after transfer as described above, or in the case where the water receptivity of the light-sensitive matter decreases on exposure to light, exposing the transferred matter to light. Finishing may also comprise etching to give an intaglio plate using the transferred material as a resist, e.g. etching a copper plate with ferric chloride solution, or making the open portion of a planographic plate more waterreceptive before inking by etching, " fixing " zinc or aluminium plates in phosphoric acid and gum-arabic, or by removing the top metal layer of a bi-metallic 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 eliminated from the plate. In the examples the light sensitive material is generally " diazo aldehyde " which is the condensation product of p - diazo - diphenylamine and formaldehyde as described in Example I of Specification 418,011 [Group XX]. In many of the examples a cellulose acetate support is used having a relief pressed screen-wise in one side and partly filled with a suspension of carbon black, asphalt and xylene. The light sensitive layer is then applied on top. The finishing of the printing plate is described in the examples. Specifications 401,898, 425,126, 425,434, 510,233, 614,155, 626.501, 630,874, 645,211, 655,274, 655,275, 678,599, 740,165, 740,166 [all in Group XX] and U.S.A. Specification 1,618,505 also are referred to.