Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
  • G03G5/02—Charge-receiving layers
  • G03G5/04—Photoconductive layers; Charge-generation layers or charge-transporting layers; Additives therefor; Binders therefor
  • G03G5/09—Sensitisors or activators, e.g. dyestuffs
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G13/00—Electrographic processes using a charge pattern
  • G03G13/01—Electrographic processes using a charge pattern for multicoloured copies
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G13/00—Electrographic processes using a charge pattern
  • G03G13/26—Electrographic processes using a charge pattern for the production of printing plates for non-xerographic printing processes
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G5/00—Recording members for original recording by exposure, e.g. to light, to heat, to electrons; Manufacture thereof; Selection of materials therefor
  • G03G5/12—Recording members for multicolour processes

Definitions

• This invention relates to a process for the production of multi-colored prints by electrophotographic methods in which a set of at least two electrophotographic materials, each of which comprises a photoconductive layer containing a sensitizer which causes the layer to be lightsensitive only in a selected portion of the spectrum of visible light, are electrostatically charged, separately exposed to the same light image of a colored original to be reproduced, developed, fixed, and converted into printing plates, and the latter are printed over each other on a print-receiving material using printing inks, the colors of which are determined by the selected portions of the spectrum.
• a notable disadvantage of the foregoing process is that relatively complicated-optical devices, such as color filters, must be used. Apart from the additional work and equipment involved, the ever-present source of error of the optical devices have a notably unfavorable effect through deviations with regard to image sharpness.
• the present invention provides a process for the preparation, from colored originals using uncomplicated electrophotographic materials or sets of material without the use of optical color filters, of a set of printing plates which permits the inexpensive preparation of color prints according to the known color printing processes.
• the invention more specifically, provides a process for the preparation of colored prints by means of electrophotographic methods in which at least two electrophotographic materials suitable for printing purposes, whose photoconductive coatings are in each case through addition of sensitizers light-sensitive in only one part of the visible light spectrum, are exposed, after charging, with the colored original to be reproduced and then, in conventional manner, developed, fixed, and converted into printing plates. These plates are then printed over one another with the colors corresponding to the selected ranges of the spectrum.
• the invention also provides a material for use in the process of the invention, comprising a set of at least two electrophotographic materials suitable for printing purposes, whose photoconductive coatings are in each case light-sensitive, due to the presence of at least one sensitizer, in only one part of the visible light spectrum.
• the invention renders it possible, in an advantageous manner, to dispense with the use of interposed optical color filters. This simplifies the printing process substantially.
• electrophotographic materials which are suitable for printing purposes is meant materials which comprise, in conventional manner, a support suitable for printing purposes, such as an aluminum foil or a corresponding printing plate on a paper base, and a photoconductive coating containing one or more organic or inorganic photoconductors applied to the support, which photoconductive coating also contains additives controlling the lightsensitivity, i.e., so-called sensitizers.
• photoconductors is meant inorganic and organic substances usable for electrophotographic purposes, in particular oxazoles, oxadiazoles, thiodiazoles, quinazolines, triazines or polymeric compounds, such as polyvinylcarbazoles, or polyacrylates, or inorganic substances, especially zinc oxide.
• sensitizing dyes one or several dyes may be used in each case. The choice of the sensitizing dyes, which are added to the photoconductive coatings, is explained below.
• the reflectance range of these printing inks should be in close relationship with the range of the spectral sensitivity in the electrophotographic material caused by the sensitizing.
• the reflectance curve should lie with its maximum or with the largest part outside the range of spectral sensitivity of the sensitizer and the sensitivity curve of the sensitizer should if possible encompass the entire range of the visible spectrum except the reflectance range, i.e., the valuesof the spectral light-sensitivity should for each wavelength be inversely proportional to the reflectance values of the corresponding printing ink.
• the reflectance curve of the dye lies approximately in the range between 400 to 550 mg.
• the sensitivity curve of the sensitizing dye should then lie approximately between 550 mp. and the limits of long-wave visible light. Dyes which encompass this range when e.g. oxadiazoles and Lytrons are used, are e.g.
• the reflectance range for the yellow color component of the printing ink lies approximately between 490 to 750 m one or several suitable sensitizing dyes must be chosen which render the coating light-sensitive in the range from approximately 500 m to the limit of short-wave visible light (about 400 m Sensitizers which cause light sensitivity in this range are e.g. Thioflavine TG, C.I. 49005, Acriflavine, C.I. 46000, Acridine Yellow G, CI. 46025 and trypaflavine. These dyes cause light-sensitivity in the stated range only.
• the pertinent sensitizing dye is chosen.
• sensitizing dye in this case a mixture of Rhodamine B extra, CI. 45170, Acridine Orange NO, CI. 46005 and Thioflavine TG, CI. 49005 may be used.
• concentrations of these dyes are chosen in accordance with their sensitizing action, according to the reflectance curve of the magenta print ing ink in the manner described above (inverse proportion w
• the dyes which correspond therewith in the manner stated can be chosen.
• dyes which sensitize in a certain range are known from US. Patents Nos. 3,052,540 and 3,060,019.
• a further method which permits good results for the choice of the sensitizers consists in matching the sensitivity range of the sensitizer as exactly as possible with the reflectance range of the printing inks to be used later.
• the methods of selection can be determined from what is stated above. This latter method naturally renders necessary the use of a reversal developer in the subsequent process steps.
• the concentrations of the sensitizers can be varied without affecting the image quality. By the use of greater additions of dye, shorter exposure times result and, by the use of smaller proportions of dye, correspondingly longer exposure times are required.
• An upper limit to the amount of dye is determined by dark discharge of the charged coating.
• a lower limit is determined by the sensitivity of the unsensitized coating.
• the sensitivity caused by selective sensitizing must naturally, and which is also practically always the case, lie above the sensitiv ity of the coating itself in order to achieve the effect of the invention.
• Photoconductive materials most advantageously can be used whose own sensitivity does not lie, or only a small part of which lies, in the visible spectrum. As is known, the dyes do not behave equally with regard to their sensitizing properties when dilferent photoconductors are used.
• the individual electrophotographic base materials are coated in each case with a photoconductor/sensitizer mixture which is different with regard to the sensitizer.
• the invention is further explained as follows, with reference to the process.
• the colored original to be reproduced is exposed to irradiation with light and thus a color photograph is produced.
• the first, previously charged, electrophotographic material sensitized e.g. in the range of approximately 550 to 750 Ill .4, is irradiated by means of contact or episcopic or diascopic methods.
• the electrostatic charge decays in the light-sensitive range, i.e. between 550 and 800 mg.
• There remains a latent electrostatic image which corresponds to the blue portions of the original.
• the subsequent electrophotographic materials sensitized for other spectral ranges are irradiated with the same photograph.
• the developing of the latent images is now effected in conventional manner by means of toners which settle on the areas carrying the charge.
• the color of the toner is immaterial here.
• the powder images thus obtained are fixed thermally or by solvent vapors and inked up with the colors which correspond to the originally non-lightsensitive ranges of the spectrum. Marginally sharp colored prints with accurate color reproduction can be obtained by conventional printing over one another of the individual colors on a print-receiving material.
• the developing itself can in each case be effected in the dry manner by means of toner powder, or in the wet manner by means of particles dispersed or dissolved in a liquid. Toners and developers of this kind are very well known in the electrophotographic field.
• the number of individual printing plates in the present set of printing plates is not critical, but it must be at least two. Normally, good color reproductions can be achieved with about 3-4 color separations.
• the present invention also encompasses color separations of 4 or 5, or more, printing plates.
• the quality of the colored image can be increased by preparing a black separation and thus increasing the contours and the so-called stability of the image.
• a panchromatic coating is naturally necessary for this purpose.
• Example 1 A set of electrophotographic material is prepared which is suitable for 3-color separations and thus for three-color printing:
• the electrophotographic material is charged, in conventional manner, under a corona device and exposed with the original in contact therewith or episcopically or diascopically, without interposing color filters and then the remaining charged areas of the latent electrostatic image are developed directly in conventional manner with a resin powder. After subsequent fixing, this image is converted into a printing plate. This can be effected by decoating, i.e. dissolving away of the areas which. are not intended to print. At the same time, these areas are rendered hydrophilic, i.e. water-accepting, by treatment e.g. with sodium metasilicate. The toner-bearing image areas are now inked up with blue printing ink.
• the sensitizer Brilliant Green, CI. 42040, as stated under (I), can be replaced by Malachite Green, CI. 42000, or Victoria Pure Blue B, CI. 44045, with equally good results.
• the sensitizer combination in (II) may be replaced by trypaflavine/Acridine Orange, 0.1. 46005.
• the dye thioflavine stated under (III) may be replaced by the dyes Acridine Yellow G, C.I. 46025, or trypaflavine.
• Example 2 The set of material of three electrophotographic plates stated in Example 1 is, for four-color printing, increased by one electrophotographic plate for the black separation.
• This plate is prepared as follows: 2 g. of 2,5-bis(-pdiethylamino-phenyl)-1,3,4-oxadiazole and 2 g. of Lytron are dissolved in 40 g. of methylglycol. To this is added a solution of 2 mg. of Acridine Yellow G, C.I. 46025, 2 mg. of Acridine Orange, CI. 46005, 1 mg. of Rhodamine B Extra, CI. 45170, and 1 mg. of Brilliant Green, CI. 42040, in 3 ml. of methanol.
• Example 3 For a blue-violet color separation inside a set of plate material, the following electrophotographic material may be used:
• a solution of 1.5 g. of 2,5-bis(-p-diethylaimino-phenyD- 1,3,4-oxadiazole and 1.5 g. of Lytron 820 in 30 g. of methylglycol is mixed with a solution of 3 mg. of Crystal Violet, C.I. 42555, in 1 ml. of methanol. This mixture is applied to an aluminum foil. After evaporation of the solvent, an electrophotographic coating is obtained whose light sensitivity lies between 500 and 650 m i.e. yellow color is not reproduced.
• Crystal Violet, C.I. 42555 can be replaced by the combinations Rhodamine B Extra/ Malachite Green or Rhodamine B Extra/ Brilliant Green with equally good results.
• Example 4 As a set of material for five-color printing, the 4 color separations of Example 2 can be used in combination with the following electrophotographic material, which yields a green separation:
• Example 5 A set of material for two-color printing consisting of:
• Lytron is a copolymer of styrene and maleic acid anhydride produced and marketed by Monsanto Chemicals Ltd., London.
• a process for the production of 'multi-colored prints by electrophotographic methods in which a set of at least two electrophotographic materials, each of which comprises a photoconductive layer containing a sensitizer which causes the layer to be light-sensitive only in a selected portion of the spectrum of visible light, are electrostatically charged, separately exposed to the same light image of a colored original to be reproduced, developed, fixed, and converted into printing plates, and the latter are printed over each other on a print-receiving material using printing inks, the colors of which are determined by the selected portions of the spectrum.
• each electrophotographic material is sensitized so that the values of the light-sensitivity for each wavelength of the visible spectrum are substantially inversely proportional to the reflectance values of the printing ink to be used.
• each electrophotographic material is sensitized so that the values of the light-sensitivity for each wavelength of the visible spectral region substantially correspond to the reflectance values of the printing ink to be used, and the material is developed with a reversal developer.
• each photoconductive layer contains an organic photoconductor.
• each photocondnctive layer contains an inorganic photoconductor.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Developing Agents For Electrophotography (AREA)
• Photoreceptors In Electrophotography (AREA)
• Color Electrophotography (AREA)
• Printing Plates And Materials Therefor (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=7226126

Family Applications (1)

Country Status (9)

Cited By (9)

Families Citing this family (2)

Citations (12)

• 1964
  • 1964-01-11 DE DE19641447907 patent/DE1447907A1/de active Pending
  • 1964-12-08 NL NL6415308A patent/NL6415308A/xx unknown
• 1965
  • 1965-01-08 US US424179A patent/US3458310A/en not_active Expired - Lifetime
  • 1965-01-08 SE SE00175/65A patent/SE331421B/xx unknown
  • 1965-01-08 BE BE658078A patent/BE658078A/xx unknown
  • 1965-01-08 CH CH26965A patent/CH450170A/de unknown
  • 1965-01-08 AT AT11665A patent/AT256628B/de active
  • 1965-01-08 GB GB1009/65A patent/GB1071433A/en not_active Expired
  • 1965-01-11 FR FR1448A patent/FR1420220A/fr not_active Expired

Patent Citations (12)

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