Patent GB-647831-A (GB)
Title: A method and apparatus for printing by the action of heat on heat-sensitive materials
IPC: B41M5/26
Filed: 1946-09-23
Abstract: 647,831. Copying telegraphy. GROAK, J. Sept. 23, 1948, No. 647831. Divided out of 647,821.. [Class 40 (iii)] [Also in Groups XX and XL (a)] A method of making images consists in scanning with a radiant energy beam consisting either of an electrically-charged corpuscular beam or a radiant heat beam, the surface of a material consisting of, containing, or being coated with a heat-sensitive substance which can change its nature under the influence of heat generated therein or applied thereto by the scanning beam so as either to produce direct colour change of said substance to render visible the colour of said substance, to initiate colour change in or render visible the colour of another substance associated with said heatsensitive substance, or to render the heatsensitive substance capable of retaining, combining with, or reacting with a further substance subsequently applied to the heat-sensitive substance to produce an image. The radiant energy beam may be either the modulated electronic beam of a cathode-ray tube or an infra-red beam modulated by movement of a reflector or an optical system transparent to infra-red and controlled by signals generated by an iconoscope. An apparatus for carrying out the electronic beam scanning method comprises a cathode-ray tube, liquid sealing columns between the interior and exterior of the tube, guide means for moving a heatsensitive strip through the liquid seals and the interior of the tube, and mechanical sealing means, e.g. rollers, which are adapted to be traversed by the strip and are disposed between the atmosphere and the liquid sealing columns. As shown, an iconoscope 5 with associated line and frame time bases 6, 7 scans a stationary object (not shown) and the picture signals produced are passed through an amplifier 44 to the grid 43 of a cathode-ray tube 8 having a line time base 45 synchronized with the time base 6 by a unit 46. The frame time base for the tube is provided by the rate of movement of the material 9 scanned across its direction of movement by the tube 8, the material being driven by a roller 34 driven from a motor 35 controlled through a unit 37 by the frame time base 7. The power pack is shown at 39. A strip 9 pre-coated with a heatsensitive material passes from a supply reel 10, which may be positively driven, through a resilient roller seal to a sub-atmospheric chamber 12, through a mercury seal 15 to a modified cathode-ray tube 8 where it is line scanned across its direction of movement as it moves over guide rollers 26, 27. The heatexposed strip is then passed out of the tube through the seal 15 and finally to the exterior by way of a second resilient roller seal. An electrical signal inverter may be included in the grid circuit of the tube if the image produced without it would be a negative of the original. The tube envelope, of glass as shown, may be coated with an electricallyconducting layer 38 forming an anode and the tube and fore- and after-chambers 12, 13 are continuously evacuated. Threading of the strip is accomplished by releasing the wing nuts securing the tube proper to a lower chamber in which a frame 24 carrying the rollers 26, 27 is removably mounted. If desired the strip 9 may be fed intermittently and line- and frame-scanned by the tube during the stationary period. Subtractive three-colour pictures may be produced by coating contiguous areas of the strip with materials yielding different colours on heating, viz. yellow, red and blue and sequentially exposing them with violet, green and orange filters in front of the iconoscope. The strip is then cut up and the three colour components are cemented together in register. Alternatively three units of the kind shown in Fig. 1, with separate iconoscopes scanning behind violet, green and orange filters respectively and means at each stage for coating the strip 9 with materials yielding respectively yellow, red and blue, each stage being followed by a mercury vapour lamp which destroys the unexposed colour-producing material in the strip. Instead of scanning a coloured object through colour filters, the object may be illuminated with light of the appropriate colour. Suitable materials contain thiourea, thiosinamine, boric acid, water and sodium diazosulphonates prepared from 1-diethylamino 4 amino 3-methoxy- or 3- ethoxy-benzene to which are added so as to produce on heating dark violet blue, dark red, and yellow colours respectively phloroglucinol and sodium bisulphate ; 3-methyl 5-pyrazolone and sodium bisulphite; and acetoacetic acid anilide. To produce black silver stearate, silver palmitate, silver anthranilate or lead thiobenzoate may be used. Alternative red, yellow and blue colour-yielding materials are gelatin and water solutions containing respectively an oxidizing agent (nickel or sodium nitrates) and phenolphthalein ; potassium nitrate and aniline hydrochloride ; and sodium thiosulphate, sodium nitrate and nickel nitrate. Coloured image formation may also be achieved by using a material having two or more layers and either melting an inner layer which is either coloured and is absorbed by the outermost layer or dissolves dye out of the outermost layer which is coloured, or melting an obscuring white layer from a coloured inner layer. Alternatively the strip may be coated with albumin, hardened imagewise by scanning and treated with printing ink, so that on wash-off development with water a black-and-white record is produced so that the method may be employed for the production of letter-press blocks and offset printing plates. For coloured images the albumin may be pigmented, exposed to heat, and wash-off developed. To assist the production of the coloured image the heatsensitive substance may be pre-heated uniformly either by an unmodulated scanning electron beam or by heating the liquid seal through which the strip passes to the exposure position. Three-colour films for kinematograph projection may be produced by making the separate colour components on separate strips, or making two components on one strip, one on each side, and the third component on a second strip and subsequently uniting the strips in register. For producing small numbers of three-coloured still pictures paper sheets bearing appropriate colour image yielding substances may be attached to a belt secured at one end to a spring-blind type of take-up roller within the exposure chamber when the belt is pulled out against the spring roller and the separate colour components subsequently united in register. Applications. In addition to the production of colour still pictures and kinematograph films, the letter-press blocks and offset printing plates as described above, composite pictures can be produced either by disposing a screen between the heat-sensitive material and the scanning beam or on either side of the heatsensitive material and in contact with it a screen of heat conducting material. In the production of records of oscillatory phenomena such as oscillograms cardiograms or radar signals, the oscillatory signals may be applied directly to the " printing " cathode-ray tube. The Provisional Specification contains references to heat-softenable transferable materials and to Specification 647,821 which is concerned with methods employing such materials.