Patent GB-988228-A (GB)
Title: Electrothermographic image-recording processes
Inventor: CONIX ANDRE JAN
IPC: G03G5/028
Filed: 1959-12-04
Abstract: 988,228. Electrothermography. GEVAERT PHOTO-PRODUCTEN N.V. March 3,1961 [Dec. 4, 1959], No. 41351/59. Heading G2H. [Also in Division H1] A latent electrostatic image of a subject having a pattern of heat absorbing portions comprises applying to an electrothermographic layer as defined below, either after or simultaneously with an electrostatic charging step, a heat pattern reproducing the patter. of heat-absorbing portions of the object by exposing the subject while its heatabsorbing portions are in heat-conductive relationship with the electrothermographic layer to energy which is absorbed by said portions of the subject and causes heating, and allowing the charges in the heated portions of the layer to flow away. An "electrothermographic layer" is one in which its electrical volume resistivity shows a substantial decrease when the temperature of the layer is increased over an appropriate range. Suitable substances for such a layer are those which, when in a negatively charged layer of 5 to 10Á thickness which has been pressed against a metal plate along which the temperature varies uniformly from 50‹ to 250‹C. and thereafter developed with a magnetic brush loaded with developer powder, gives three distinct zones, viz a dense powder zone, a powderfree zone, and an intermediate zone. The temperature range corresponding to this intermediate zone is referred to as "the critical temperature interval" and preferably is not greater than 20‹C. in extent. The only substances disclosed as satisfying these conditions are polymeric, organic materials having a resistivity of at least 10<SP>9</SP> ohm. cm. such as (I) chlorinated rubber, pine resins, and cellulose derivatives such as cellulose diacetate; (II) vinyl polymers such as polymers and copolymers of acetals of polyvinyl alcohol, vinyl chloride, vinyl acetate,vinylidene chloride, vinyl carbazole, esters of acrylic and alkyl acrylic acids with or without the acids, and styrene, or polyalkylenes; or (III) linear polyesters formed from (i) aliphatic diols and aliphatic or aromatic dicarboxylic acids, (ii) aromatic dihydroxy compounds and aromatic or aliphatic unsaturated dicarboxylic acids or aromatic disulphonic acids, (iii) polycarbonates, (iv) polyphosphonates, or non-linear polyesters formed by using instead of difunctional starting materials polyfunctional starting materials such as pentaerythritol. Plasticizers may be added to the polymers used in amounts of 10 to 30% of the polymer weight, and any other additives such as pigments, stabilizers, coating aids, may be included providing that they do not impair the resistivity of the material. Preferably the electrothermographic layer is carried on a conductive plate preferably of resistivity less than 10<SP>5</SP> ohm. cm. and can be of insulating materials made conductive by coating with a transparent layer of silver, gold, or stannous oxide, a metal powder dispersed in a small amount of binder, a hygroscopic or antistatic compound in a hydrophilic binder, a metal plate, a polyamide film, or a paper sheet. Subbing layers may be provided between the hydrophilic coating layer and a hydrophobic support, and a paper sheet may bear a smooth surfacing layer of 2 to 10Á thickness of a synthetic organic polymer, cellulose derivatives, or a natural resin, with plasticizers if desired, providing such layer does not prevent escape of charge. The electrostatic images are formed typically by infra red contact printing exposure and formed may be developed and fixed or transferred by the techniques wellknown in electrophotography. Specifications 799,184, 819,592, 865,123, 883,312, 891,781, 898,354, 901,605, 910,308, 916,660, 947,479, 964,871, 964,872, 964,875, 964,877, 964,879,and 975,813 are referred to.