Patent GB-647821-A (GB)
Title: A method and apparatus for printing by the action of heat on heat-sensitive materials
IPC: H01J29/86
Filed: 1946-09-23
Abstract: 647,821. Copying telegraphy. GROAK, J. Sept. 23, 1946, No. 28469. [Class 40 (iii)] [Also in Groups XX and XL (a)] A method of making images consists in bring- ing into contact two surfaces, one of which contains, consists of, or is coated with a substance adapted to be softened by heat, and scanning said substance with a controlled radiant energy beam consisting either of an electrically-charged corpuscular beam or a radiant heat beam to soften parts thereof so that material is transferred from one surface to the other in correspondence with the softened parts of the substance on contacting the two surfaces. The transfer of material may be only temporary, e.g. if the reproduction is produced on a transparent or translucent surface, the heat-softened material on a second strip may be brought into engagement with the non-opaque strip to produce an image which may be viewed through the non-opaque strip but which is destroyed by parting the two surfaces. The controlled radiant energy beam may be either the electronic beam of a cathode-ray tube modulated by signals derived from objectscanning means such as an iconoscope, or a beam of infra-red radiation modulated by means ot a movable concave reflector or infrared transparent lens which is controlled in its movements by signals from an iconoscope or other scanning means. For this purpose apparatus is provided comprising a cathoderay tube, means for feeding two strips (one of which is coated with a heat-softenable material) through a liquid seal between the atmosphere and the tube vacuum, and means for guiding said strips and contacting one with the other inside the tube. Preferably the uncoated strip passes from the atmosphere through a mechanical seal to a partial-vacuum before passing through the liquid seal. As shown, an iconoscope 11 with associated line and frame time bases 12, 12<SP>1</SP> scans a stationary object (not shown) and the picture signals produced are passed through an amplifier 19 to the grid of a cathode-ray tube 13 having a line time base 20 synchronized with line time base 12 by a unit 21. The frame time base for the tube is provided by the rate of movement of the material 34 scanned across the direction of movement by the tube 13, the material being driven by rollers 35, 50 in turn driven from a motor 52 controlled through a unit 53 by the frame time base 12<SP>1</SP>. The power pack is shown at 18. An endless band 34 arranged round rollers 35 to 44 is continuously coated with a heat-softenable composition coloured as required, by a roller 50 which dips into a bath 45 of melted composition fed from a reservoir 47, where it is heated by a surrounding steam pipe 48, either by a pump or by atmospheric pressure, the coating chamber 16<SP>11</SP> being maintained at less than atmospheric pressure. The thickness of the coating on the strip is determined by a doctor blade 51 and the coated band passes through a mercury seal 28 to a high vacuum chamber 16<SP>1</SP> housing the cathoderay tube 13. A paper or like strip 54 from a supply reel 55 also passes first into a subatmospheric chamber 16<SP>111</SP> through a mechanical seal formed by resilient rollers 67... 69 and then into the vacuum chamber 161 via a mercury seal 29 and finally out to a take-up reel 56, the strip being supported by rollers 57 ... 66 and driven by roller 70 in turn driven by the motor 52. The two bands 34, 54 are pressed into close contact as they pass round rollers 40, 61 and just prior to this the coating on the band 34 is softened by the heating action of the modulated scanning electron beam 22 of the tube 13 so that on contacting the band 54 transfer of material occurs imagewise between them. If the image formed by the electron beam on the receiving material would be a negative of the original, an electrical signal inverter may be included in the grid circuit of the tube 13 to ensure positive reproductions. Preferably the tube 13 has its envelope coated with colloidal graphite to form an anode (insulated from the envelope when this is metal) and the roller 40, which is either a rubber-covered metal roller or a rubber roller impregnated with graphite, is connected thereto. The chambers 16<SP>1</SP>, 16<SP>11</SP>, 16<SP>111</SP> are continuously evacuated through ducts 17, 32, 33. Instead of separate contacting rollers 40, 61 both sheets may pass around a single roller with the electron beam aligned on the contacting portions of the strip and passing first through the uncoated strip to the heat softenable composition. If desired, two registered subtractive colour picture components may be formed on opposite sides of a transparent strip 54 by passing it between two rollers 40 supporting coated strips 34 softened by separate cathode-ray tubes controlled by separate iconoscopes working behind appropriate colour filters. Further coloured component reproductions may be superimposed on the first by subsequent scans with other modulated electron beams to produce say four-colour pictures. Subtractive three-colour pictures may be made by, in effect, repeating the apparatus of Fig. 1 for each component (Fig. 3, not shown). The object is scanned by separate iconoscopes through orange, green and violet filters and images in blue, red and yellow are transferred on to a single strip 54 by successively engaging the strip with separate strips coated with blue, yellow or red softenable compositions fed from separate reservoirs and softened by separate scanning tubes mounted within a single high vacuum chamber. A fourth tube scanning a black composition and controlled by an unfiltered iconoscope may be used to provide a grey " correction " component image. The melting points of the successively employed coloured compositions are arranged to be progressively lower so that by adjustment of the tube currents softening of the second and third layers does not affect previous layers. Threecolour films for kinematograph projection may be produced by making the separate colour components on separate strips or making two colour components on one strip, one on each side and the third component on a second strip and subsequently uniting the strips in register. In a further alternative, for producing small numbers of still pictures, a strip bearing successive areas of yellow, red and blue softenable compositions is carried between two spools in a vacuum chamber, and a paper sheet which is attached to a carrier belt secured at one end to a spring blind type of take-up roller when the belt is drawn off the spool to present its exposure frame to the exterior, is fed through a mercury seal to a position where it is retained stationary and stretched in contact with one of the coloured areas-yellowby two pairs of gripping rollers released by solenoids when the whole picture area has been scanned by a cathode-ray tube connected to an iconoscope fitted with a violet filter. The contacting coloured area and the iconoscope filter are then changed to red and green respectively, the tube current adjusted and the red image transferred, a similar process occurring for the blue image, whereupon a fresh sheet of paper is fed into the apparatus. Suitable colourless softenable compositions, which may include thermosetting materials held in a state to permit one or more softenings of the whole composition, to which pigments and/or dyes may be added, are combinations of an esterified phenolic resin " Crestavin resin 282 " (Registered Trade Mark), a high melting point paraffin wax and petroleum jelly ; ester gum, palm wax and a low-melting point paraffin wax ; and an esterified gum " Laculose B " (Registered Trade Mark) and petroleum jelly. The rate of scanning is usually lower than in television apparatus and, although it may be reduced to increase the temperature induced in the softenable material by the scanning spot, it is usually kept constant. Initially the unmodulated tube current is adjusted so that the " spot temperature " is close to that required to soften the heatsensitive material so that modulation of the electron beam causes proportional softening of the material. An oscilloscope may be provided to assist in the initial adjustment of the scanning beam and the iconoscope may control separated distant " printing " units by radio links. The final image may be formed either by transferring softened material from the strip 34 to the strip 54 or by removing material from the strip 54 which sticks to the softened parts of the strip 34 ; or, providing one strip is transparent or translucent, by causing the two strips to adhere intimately where softening occurs so that the' image is viewed through the non-opaque strip. The strip 54 on which the reproduction is made may include a thermoplastic substance such as abietic acid, a solid fatty acid, or a mixture of wax and a fatty acid, and the material transferring strip 34 may include an undissolved basic dye dispersion held in casein. Alternatively the strip 34 may also include in its coating, or be overcoated with, a white pigment and the reproduction may be made on either or both of the strips. The strip receiving the transferred material may be caused to react with the transferred material, e.g. the receiving strip may contain a mordant and the transferred material a dye reacting therewith. To assist transfer the strip 54 may be provided with a material having an affinity for the softenable material on strip 34 and either of the strips may be pre-heated to near its softening point by an unmodulated scanning electron beam prior to or in synchronism with the iconoscope modulated beam or with a second synchronized modulated beam. Alternatively the liquid traps through which the materials enter the chamber housing the cathode-ray tube may be heated to near the softening point of the materials. With high melting point materials the iconoscopes signals may be recorded optically and the records subsequently reproduced at