Patent GB-1245456-A (GB)
Title: Planographic printing plate and process for the production thereof
IPC: G03G13/28
Filed: 1968-10-10
Abstract: 1,245,456. Photoconductive recording element. ITEK CORP. 10 Oct., 1968 [17 Oct., 1967], No. 48009/68. Heading H1K. [Also in Division G2] A recording element suitable for the production of a planographic printing plate comprises a photoconductor which becomes reversibly activated and capable of being made heat producing in developed image areas corresponding to the reversibly activated areas of the element upon exposure to activating radiation and a heatsensitive composition comprising a high melting-point continuous phase and a low melting point disperse phase which forms an oleophilichydrophilic image pattern upon selective imagewise application of heat. The element is exposed imagewise to produce a latent image, contacted with image-forming materials to develop the image and uniformly exposed to heat-producing activating radiation which causes selective heating in the image areas thereby producing an oleophilic-hydrophilic image pattern. The heat-sensitive composition may form a separate layer to the photo-conductor or be mixed therewith. Alternatively the composition may be provided as two layers one hydrophilic the other oleophilic. Either of the phases may be respectively oleophilic and hydrophilic. The hydrophilic phase may comprise polyvinyl alcohol, ethylcellulose, carboxymethylcellulose, casein, gelatin, sodium alginate, guar gum (a water soluble vegetable gum), sodium or ammonium polyacrylate. These may be insolubilized to improve their durability by treatment with formaldehyde, dimethylolurea or zinc chloride. Hydrophilic fillers such as clay, CaCO 3 , SiO 2 , infusorial earth, chalk, BaSO 4  or satin white may be added to the hydrophilic phase. The oleophilic material may comprise polyethylene, polystyrene, polymethylmethacrylate, polyvinyl chloride, polyacrylonitrile or poly N-vinylcarbazole preferably used as a latex containing wetting or dispersing agents. Synthetic or natural waxes may be added to the oleophilic phase. The photoconductor may be ZnO, TiO 2 , ZrO 2 , GeO 2 , In 2 O 3 , CdS, SnS 2 , ZnS, CdSe, Ag activated ZnS or Zn activated ZnO and may be mixed with Crystal Violet, Basic Fuschin, Auroamine O or Rhodamine B and copoly butadiene-styrene, polymethyl methacrylate, polyvinyl acetate, polyvinyl alcohol, polyvinyl pyrrolidone or a polyamide and coated on a support of aluminium, paper, cloth, glass, polyethylene terephthalate or cellulose acetate. Elements sensitive to an image pattern of X or γ rays or an electron beam may be produced. In use the element is exposed to an actinic image pattern, treated with an oxidizing agent e.g. AgNO 3 , a developer e.g. p-methylaminophenyl sulphate and fixed in sodium thiosulphate. The element is then irradiated with IR radiation whereupon the image areas are heated and converted from a hydrophilic to an oleophilic hydrophobic surface. In another example a saturated solution of AgNO 3  in methanol is used followed by a solution of citric acid and phenidone in methanol. A further example describes an element incorporating AgNO 3  and 2 - p - dimethylamino styryl - 4 - methylthiazole methochloride which is imagewise exposed to activating radiation, developed and then fixed in an aqueous solution of K 2 SO 3 , Na 2 S 2 O 3  and acetic acid. The radiation suitable to heat the element includes visible light. Many suitable oxidizing and reducing agents are specified.