Patent GB-1278325-A (GB)
Title: Color copying method and apparatus
IPC: G03B27/30
Filed: 1969-05-09
Abstract: 1278325 Multi-colour processes and apparatus therefor MINNESOTA MINING & MFG CO 9 May 1969 [10 May 1968 (2)] 23798/69 Headings G2A, G2C and G2H A multi-colour process comprises (i) exposing a multi-coloured original to produce a colour separation infrared absorptive image on a photosensitive intermediate, (ii) holding this intermediate in heat-conductive contact with a layer containing a heat-transferable dye or reactant which reacts on heating to produce a colour with a co-reactant in a receptor sheet, and with the receptor sheet, (iii) exposing the assembly to infrared radiation to produce a coloured image on the receptor and then conducting the following steps at least once, (iv) exposing the original to a different area of the intermediate or to a different intermediate to produce a different colour separation infrared absorptive image, (v) holding this image in heat-conductive contact with a layer containing a different dye or reactant and with the receptor and (vi) exposing the assembly to infrared radiation to produce a differently coloured image on the receptor. The invention also relates to apparatus for carrying out the process which comprises means to maintain the original and receptor in first and second fixed positions, means to form a light-path between the fixed positions, positioning means adjacent the second fixed position to hold the intermediate against the receptor, a light source for exposing the original to the intermediate, developing means for developing the intermediate and an infrared radiation source to irradiate the developed image and produce an image on the receptor. As shown, multi-coloured original 12 is placed on transparent area 10 of a light-tight box and held by pressure cover 11. It is reflex exposed and the light passes through primary colour filter to form a colour separation image on the photo-sensitive or photo-conductive surface of intermediate sheet 18 which is held in contact with receptor sheet 26 by vacuum platen 31. If a photo-conductive material is used, it is developed by station 35 which is moved in front of the latent image. The station contains developer roller 38 maintained at 1000 volts which applies infrared radiation absorptive powder which is selectively deposited on the unexposed areas. When station 35 is retracted infrared lamp 40 is switched on and the radiation absorbed by the image is transmitted through the sheet to the band 53 of heat transferable material containing a dye complementary to that of the filter, see Fig.6, so that this band is imagewise transferred to the receptor sheet. The vacuum is switched off and separator bar 42 is moved downwards to separate intermediate and receptor sheets. The intermediate sheet is now advanced so band 54 of a heat-transferable but differently coloured dye material is placed in the path of the image beam. Disc 14 is rotated to place a differently coloured filter in the image path and the above exposure, development and transfer steps are repeated. The same steps are repeated to produce the third coloured image on the receptor sheet which is then advanced and cut off by knife 33. Preferably the receptor sheet is paper coated with a vinyl chloride/vinyl acetate copolymer containing silica to absorb and stabilize the dyes transferred. The photo-conductive material may be developed by toner without using a potential to give a toner in the exposed areas or a print-out silver halide material may be used which requires no development. Photo-conductive materials which are electrolytically developed or silver halide materials which are wet processed have the heattransferable dye coatings applied after development. Alternatively, three sheets containing 1-hydroxy-4-methacynaphthalic and a dye which sensitizes the sheet to a primary colour may be exposed without filters to the multi-coloured original and then heated in contact with a receptor sheet containing silver behenate to produce three infrared absorbing colour separation negative. Instead of using heat-transferable dye coatings, each intermediate sheet may be coated with a heattransferable colour reactant and the receptor sheet coated with the other colour reactants; two different reactants being coated on side and the third coated on the opposite side. Alternatively, two transferable dye coatings and one pair of reactants may be used. Specified pairs are leuco dyes with oxidants such as quinones and N-n-butyl-N- [bis(4-dimethylaminophenyl)-methylene] urea with an acid. Alternatively, the receptor sheet may contain heat-sensitive reactants to produce the first image (e.g. an indole and a guadinium salt) and the second and third images being produced by transferring by heat colour reactants (e.g. an acid and an oxidant respectively) from intermediate sheets on to the receptor sheet coated with the other reactants; the heat used for transfer being insufficient to affect the first image. Infrared absorptive colour separation images need not be used if a sheet of indium oxide or silver carbonate is exposed to a colour separation image using light as this renders the exposed areas of the sheet infrared absorptive. This sheet may now be exposed to infrared in contact with an intermediate sheet containing the heat-transferable dye coatings and with a receptor sheet to produce the multi-coloured image.