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
  • G03G5/005—Materials for treating the recording members, e.g. for cleaning, reactivating, polishing
• • 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
  • G03G21/00—Arrangements not provided for by groups G03G13/00 - G03G19/00, e.g. cleaning, elimination of residual charge
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S430/00—Radiation imagery chemistry: process, composition, or product thereof
  • Y10S430/001—Electric or magnetic imagery, e.g., xerography, electrography, magnetography, etc. Process, composition, or product
  • Y10S430/102—Electrically charging radiation-conductive surface

Definitions

• a sheet of white or light gray electrophotographic paper having sensitivity over almost the entire visible region is evenly charged by corona discharge in the dark and is exposed to a color image through a green filter, thereby forming an electrostatic latent image thereon.
• This latent image can be developed into a visible magenta image with a magenta toner.
• the electrophotographic paper is evenly charged with electricity in the dark and is exposed to the same color image through a red filter in registration with the said magenta image, thereby forming a latent image thereon.
• This latent image is then developed with a cyan toner.
• the electrophotographic paper is then charged once again in the dark and is exposed to the same color image through a blue filter to form a latent image.
• This latent image is developed with a yellow toner, to reproduce the color image.
• This overall method of reproducing a color image is known as registration development type electrophotography.
• More intense charging in connection with the practical charging mode involving corona discharge, comprises bringing the electrophotographic paper closer to the corona discharge electrode than when it was charged for the first time.
• an increased voltage can be applied to the color discharge electrode, or else the color discharge electrode can be passed over the surface of the electrophotographic paper an increased number of times.
• Such intensified electric charging has various harmful effects. For instance, it causes dielectric breakdown at the surface of electrophotographic paper to such an extent that pin holes in the form of dots more readily occur thereon. These pin holes are not electrically charged, and result in blank spots in the toner image.
• the toner image of the first color is subjected to an unnecessary over electrical charging. Such charge in the toner image is diflicult to discharge completely even by the second exposure, causing an undesirable color mixture or impure color when the toner image of the second color is developed.
• the present invention essentially comprises a color electrophotographic technique characterized by exposing an electrophotographic paper surface bearing a toner-developed image to a polar solvent vapor for a comparatively short period of time in the aforementioned registration development type color electrophotography be tween development and subsequent charging processes.
• the inventors have found that by the exposure of electrophotographic paper surfaces bearing a toner-developed image to a polar solvent vapor in the dark, light fatigue thereof can be avoided to thereby facilitate subsequent electric charging. It has further been found that the unused static charge left in the toner image can be eliminated completely.
• One object of the present invention is to overcome the problem of electrophotographic paper light fatigue caused by rapid exposure in the registration development type color electrophotography.
• Another object is to eliminate the residual charge left in the electrophotographic paper under the toner image after development.
• polar organic solvent 80 long as a polar organic solvent meets the above criteria it may be used in the present invention.
• Acceptable polar organic solvents can easily be determined by one skilled in the art with a preliminary process run.
• the preferred polar organic solvents have a maximum dielectric constant at 20 C. of about 35, though polar organic solvents having a dielectric constant above this value can, of course, be used.
• Solvents having a boiling point above 100 C. are difficult to vaporize and are of low vapor pressure at normal temperature. These may therefore be retained in the photoconductive sheet for rather long periods of time after treatment, which is undesirable.
• Organic solvents having such properties include alcohols, such as methanol and ethanol, ketones, such as acetone and methylethyl ketone, and esters, such as methyl acetate, ethyl formate and propyl formate.
• the electrophotographic paper used in the process of the present invention is provided with a photosensitive layer composed of mixture of photoconductive powder and a resin binder on the surface thereof.
• a thermosetting binder resin is preferred, as electrophotographic papers using a thermosetting resin binder are well suited to liquid development processing, and a thermosetting binder has the advantage of not being affected by the polar solvent vapors.
• Thermoplastic resins are not preferred as binders for the photosensitive layer, as they tend to swell or soften to such a degree when used with the polar solvents of this invention that further treatments become difilcult, or special care has to be taken during further treatments.
• the photoconductive material used in the present invention includes those well known in the art, and no special novelty is attached to the photoconductive material per se. Such materials may comprise the essential photoconductive material per se or such material may be modified with the many special sensitizing agents, additive materials, etc., known to the art. Many patents are available describing such materials, e.g., US. Pat. 3,121,006, etc.
• the preferred photoconductive materials employed in the present invention are photoconductive zinc oxide, titanium oxide, cadmium sulfide, zine sulfide, etc.
• Zinc oxide produced by the French process (firing zinc in air to produce ZnO) is most preferred.
• Thermosetting binder resins which are typically employed in the process of this invention include polyisocyanate-cured alkyd resins, epoxy ester resins and copolymers of a vinyl monomer having a primary OH group (hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl methacrylate, etc.) and styrene, acrylic and methacrylic esters or the like, alkyd resins cured with melamine formaldehyde resins, alkyd resins cured with benzoguanamine formaldehyde resins, drying oil modified alkyd resins, epoxy ester resins cured with a catalyst e.g., salts of organic acids, such as cobalt, lead and manganese salts thereof, etc.
• a catalyst e.g., salts of organic acids, such as cobalt, lead and manganese salts thereof, etc.
• electrophotographic development techniques may be used in the present invention, of which liquid development methods are preferred, most preferably wherein a liquid developer containing a toner composed primarily of pigment is used.
• suitable development techniques include, for example, aerosol development, cascade development or magnetic development (cf. U.S. Pats. 2,725,304, 2,786,441, 2,618,551 etc.).
• liquid developers comprising a dispersion of a pigment and an alkyd resin, expoxy ester, acrylic ester, polystyrene, etc., in a carrier liquid may be suitably employed in the present invention, e.g., see, for example, US. Pats, 3,053,688, 3,076,722, 2,907,674, etc.
• the exposure of the electrophotographic paper with the toner image of the first color thereon to a polar solvent vapor can be accomplished by any desired technique, e.g., by blowing air containing the vapor onto the photosensitive layer side of the electrophotographic paper or by placing the electrophotographic paper in a container filled with the vapor.
• exposure to the vapor for about one second to about one minute is preferred.
• the treatment with the polar solvent vapor is repeated twice for a three-color imaging process (magenta, cyan and yellow, for example), three times for a four-color imaging process (magenta, cyan, yellow and black, for example).
• the difference in number between exposures to the vapor and the colors formed is due to the fact that vapor treatment is not necessary when the final color image has been obtained.
• the process of the present invention is effective for quickly eliminating residual charge and the hysteresis effect results which result from previous exposures.
• a photoconductive layer may be brought into the dark where it is exposed to polar solvent vapors, e.g., acetone or metha- 1101, according to the process of the present invention, whereby it quickly recovers from fatigue and is restored to its dark-acclimatized state.
• EXAMPLE 1 (INCLUDING A COMPARATIVE EXAMPLE) Five weight parts of photoconductive zinc oxide powder having added thereto tartrazine for sensitization of the blue region (430-500 mg), erythorosine for the sensitization of the green region (520-580 mg) and Brilliant Milling Green B (0.1. Acid Green 9) for the sensitization of the red region (630-680 mg), at a ratio of mg. to 10 g.
• a composition of a styrenated alkyd resin (the styrenated alkyd resin was a commercial product named Styresol 4250 by Japan Reichhold Chemical Co.,) and a polyisocyanate compound curing agent (the polyisocyanate was a condensation product of 3 moles of tolylene diisocyanate and 1 mole of trimethylol propane) to cure the styrenated alkyd resin (mixed at ratio of 0610.4).
• the dispersion was applied to a sheet of paper made electrically conductive (Surface resistivity of the paper was about 2X10 ohm per square cm. at 55% RH) by the immersion in a solution of a hygroscopic substance.
• the dried thickness of the photosensitive layer was 10 microns.
• the hygroscopic substance was poly(vinyl benzyl trimethyl ammonium chloride) incorporated into the paper in an amount of 2 g. per m?.
• the photosensitive paper thus prepared was stored in the dark for a period of time sufficient to have the photosensitive layer thereof acclimatized to the darkness.
• Two corona discharge electrodes (impressed with 6 kv.) were then passed 3 cm. above the photosensitive paper to charge the photosensitive layer surface.
• the photosensitive layer was charged to a surface potential of 270 v.
• the photosensitive layer surface was then exposed to imaging light projected thereon through a color slide color positive original and a red filter.
• the resulting electrostatic latent image was developed by the use of a cyan developer prepared as explained hereinafter containing a toner with positive charge.
• the development lasted for seconds under the influence of the development electrode, which was maintained at ground potential.
• the photosensitive layer was washed with pure isooctane and dried, whereupon the surface potential thereof was (residual potential) -15 v. in the cyan toner-deposited area (a subsequent optical density measurement showed that this area had an image density of 1.90).
• the photosensitive layer was exposed to methanol vapor in a container, which eliminated the residual potential in four seconds. After a further eleven seconds retention in the container, the photosensitive layer was subjected to the repeated charging process in the heretofore described manner. Charging with three sweeps of the corona discharge electrodes resulted in a toner-free area electrically charged to a surface potential of -261 v. The toner-deposited area showed a potential of 265 v.
• the photosensitive layer electrically charged to 26 v. in accordance with the present invention was exposed to imaging light through a green filter.
• the resulting electrostatic latent image was developed for fifteen seconds by the use of magenta developer prepared as described hereinafter containing a toner with a positive charge. It was then washed with pure isooctane and dried. In the area wherein magenta toner deposited there was found a potential of v. (a subsequent optical density measurement showed that this was an area having an image density of 1.86).
• This residual potential was completely eliminated by exposure to methanol vapor for five seconds. A subsequent ten second exposure to the methanol vapor was followed by charging once again in the aforementioned manner.
• the toner-free area of the photosensitive layer was electrically charged to -258 v.
• a comparative photosensitive layer was electrically charged by the same corona discharge electrode sweeping five times immediately after development with the cyan developer.
• the toner-free area was charged to -250 v. and the tonerdeposited area was chraged to -290 v.
• This photosensitive layer (not treated with methanol vapor) was developed after being to imaging light in the same manner as the methanol vapor treated element to find that the magenta toner-deposited area (having an optical density of 1.80) showed a residual potential of 18 v.
• This photosensitive layer was charged after being left in the air for fifteen seconds, and the toner-free area was charged to only 35 v. with three sweeps. Charging with five sweeps charged it to a potential of 225 v.
• the surface potential at each step is approximately the same using the same charging operation. However, in the comparative example, stronger charging is necessary at the second and the third charging steps to obtain a sufficient surface potential. This illustrates that the photosensitive layer is fatigued by light, and that treatment with a polar solvent vapor, e.g., methanol vapor, is effective to revive the photosensitive layer.
• a polar solvent vapor e.g., methanol vapor
• a comparison of the final color images obtained showed that the photosensitive layer subjected to two methanol vapor treatments provided a color image of better quality with little color mixture, whereas a pinholed image with many blank spots and impure tone resulted on the photosensitive layer not treated with methanol vapor.
• the blank spots and pinholes can be attributed to dielectric breakdown of the photosensitive layer caused by charging with an increased number of corona discharge electrode sweeps.
• the color mixture is due to the residual charge left on the toner deposited area after development.
• Methanol with a boiling point of 641 C. and a dielectric constant of 33.2 was employed.
• Phthalocyanine Blue 1 Long-oil type safilower oil modified alkyd resin 3 Kerosene 500 (II)
• a mixture containing 1.2 weight parts of Brilliant Carmin Blue 6B in place of the Phthalocyanine Blue contained in the cyan developer was utilized.
• the long-oil type safflower oil modified alkyd resin used in this example whose oil length was 72%, is soluble in isooctane, but not in methanol. It is thus clear that solvent vapor fixing does not accrue by treating with methanol vapor.
• Example 2 The procedure of Example 1 was duplicated using methyl acetate vapor instead of the methanol vapor utilized in Example 1. It was found that methyl acetate was slightly inferior to methanol in its ability to recover the photosensitive layer from light fatigue. Methyl acetate with a boiling point of 57.5 C. and a specific dielectric constant of 6.68 was used.
• Example 3 The procedure of Example 1 was duplicated utilizing acetone vapor instead of methanol vapor, to find that acetone vapor was almost equal in effect to methanol vapor.
• the acetone used had a 56.5 C. boiling point and a specific dielectric constant of 21.4.
• Example 1 was duplicated except for using trichloroethylene instead of methanol. Trichloroethylene failed to show the intended effect of the present invention at all, and gave results the same as the case where the photosensitive paper was left in air.
• the trichloroethylene used had a 89 C. boiling point and a specific dielectric constant of 3.42.
• EXAMPLE 4 A photosensitive layer was prepared exactly as in Ex ample 1 using a methanol modified benzoguanamine resin. (The resin was BB-601 a trade name of the Nippon Shokubai Kagaku Co.) instead of the polyisocyanate compound curing agent. Results similar to those obtained in Examples 1, 2 and 3 involving methanol vapor, methyl acetate vapor and acetone vapor, respectively, were obtained.
• EXAMPLE 5 The photosensitive layer used in Example 1 was left in the light. Immediately thereafter, this photosensitive layer was transferred into the dark where it was electrically charged by sweeping two corona discharge electrodes impressed with 6 kv. 3 cm. thereabove three times in the same manner as in Example 1.
• a color electrophotographic process comprising contacting a photoconductive layer comprising a thermosetting resin binder and a photoconductive material with a polar organic solvent vapor having a specific dielectric constant of at least 5 at 20 C. after the development and before the charging processes on said photoconductive layer in a registration development type color photograph where the process of developing the electrostatic latent image formed on the photoconductive sensitive layer surface with the toner is repeated.

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• General Physics & Mathematics (AREA)
• Photoreceptors In Electrophotography (AREA)

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Cited By (5)

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• 1970
  • 1970-10-31 JP JP45096219A patent/JPS4923905B1/ja active Pending
• 1971
  • 1971-10-28 GB GB5028371A patent/GB1322847A/en not_active Expired
  • 1971-10-29 CA CA126,405A patent/CA946671A/en not_active Expired
  • 1971-10-29 US US00193919A patent/US3806340A/en not_active Expired - Lifetime
  • 1971-10-29 DE DE19712154145 patent/DE2154145A1/de active Pending
  • 1971-11-02 FR FR7139198A patent/FR2113457A5/fr not_active Expired
  • 1971-11-03 BE BE774878A patent/BE774878A/xx unknown

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