US3558342A

US3558342A - Development process for permanently fixing an image on an electrophotographic copying material

Info

Publication number: US3558342A
Application number: US780901A
Authority: US
Inventors: Takayoshi Tanno; Itsuo Ikeda
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 1967-12-12
Filing date: 1968-12-03
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26
Also published as: DE1814044A1; BE725328A

Abstract

A PROCESS FOR DEVELOPING AN ELECTROPHOTOGRAPHIC COPYING MATERIAL COMPRISING THE STEPS OF: DIPPING AN ELECTROPHOTOGRAPHIC COPYING MATERIAL IN A LIQUID DEVELOPER CONSISTING OF A CARRIER LIQUID AND A TONER DISPERSED THEREIN, SAID COPYING MATERIAL HAVING AN ELECTROSTATIC LATENT IMAGE ON A PHOTOCONDUCTIVE LAYER FORMED ON ONE SURFACE OF A SUPPORT WITH A BINDER, SAID DEVELOPER BEING PREPARED BY DISPERSING, IN SAID CARRIER LIQUID, A KNEADED MIXTURE CONSISTING OF PIGMENT PARTICLES, A RESINOUS POLARITY REGULATING AGENT AND A DYE INSOLUBLE IN SAID CARRIER LIQUID, WETTING A SURFACE OF A VISIBLE TONER IMAGE FORMED ON SAID PHOTOCONDUCTIVE LAYER WITH A SOLVENT CAPABLE OF DISSOLVING SAID DYE, AND THEN DRYING THE RESULTANT WETTED COPYING MATERIAL TO FIX A VISIBLE IMAGE CONSISTING OF SAID DYE IN SAID PHOTOCONDUCTIVE LAYER AND SAID SUPPORT SHEET.

Description

United States Patent G F US. Cl. 117-37 6 Claims ABSTRACT OF THE DISCLOSURE A process for developing an electrophotographic copying material comprising the steps of:

dipping an electrophotographic copying material in a liquid developer consisting of a carrier liquid and a toner dispersed therein, said copying material having an electrostatic latent image on a photoconductive layer formed on one surface of a support with a binder, said developer being prepared by dispersing, in said carrier liquid, a kneaded mixture consisting of pigment particles, a resinous polarity regulating agent and a dye insoluble in said carrier liquid,

wetting a surface of a visible toner image formed on said photoconductive layer with a solvent capable of dissolving said dye,

and then drying the resultant wetted copying material to fix a visible image consisting of said dye in said photoconductive layer and said support sheet.

BACKGROUND OF THE INVENTION (a) Field of invention This invention relates to a process of developing electrophotographic copying materials, and more particularly to a process of forming a lasting electrophotographic print image which is not easily erasable when it is rubbed with a rubber eraser.

(b) Description of the prior art In the conventional electrophotographic copying process using a liquid developer, the print image is normally no more than a mere adsorption of developer particles (toner) consisting of a pigment (normally carbon black is used) and resins to the surface of a photoconductive layer of the copying material, or more precisely, to an electrostatic latent image area formed on such photoconductive layer. Hence, the print image is easily erasable in most cases by rubbing it strongly with a finger tip or a rubber eraser. The image quality of electrophotographic prints deteriorates with repeated usage of the prints. The same phenomenon is observed in an office Where the papers are circulated to many people.

SUMMARY OF THE INVENTION This invention provides a developing process for forming a visible image not only on the surface of a photo- 3,558,342 Patented Jan. 26, 1971 conductive layer of an electrophotographic copying material, but also within the photoconductive layer as well as on the support sheet thereof. In other words, the invention provides an improved electrophotographic developing process whereby the aforesaid drawback of the conventional developing process can be eliminated.

A suitable electrophotographic material for use in the developing process according to this invention will comprise a support sheet such as paper, a plastic film or a metal sheet with powdered photoconductive material such as zinc oxide, titanium oxide, cadmium sulphide, lead sulphide and zinc sulphide, bound by a resinous binder to the surface of said support sheet to form a photoconductive layer thereon. The present invention provides a process for forming, on a commercially available electrophotographic copying material, a copy image both on the surface of the photoconductive layer and also within said photoconductive layer. The process immediately preceding the formation of a copy image, namely, the process for providing an electrostatic latent image on the surface of a photoconductive layer, can be any of the known processes. The generally known process for providing an electrostatic latent image first provides the copying material with electrostatic photosensitivity by applying an electrostatic charge through corona discharge to the surface of the photoconductive layer of said copying material, then overlaying same on an original form having the desired image to be reproduced on the copying material and then exposing same to white light.

The developer to be used for this invention comprises a carrier liquid and a toner dispersed therein, said toner consisting of a kneaded mixture of a dye insoluble in said carrier liquid, a carbon black and a polarity regulating resin or oil fat generally used for conventional toners. According to this invention, the steps of making the copy image on the surface of a photoconductive layer of a copying material using the above-mentioned developer are not different from the conventionally known steps. Then, however, the surface of the copy image is wetted with a solvent which is capable of dissolving the aforesaid dye contained in the toner. By this treatment, the dye dissolves out of the toner which has been adsorbed to the surface of the photoconductive layer and it penetrates into the photoconductive layer, thereby forming, (within said layer, an image identical to the one formed on the surface by the adsorption of the toner. It has been observed that the image further penetrates down to the support sheet when the latter is made of paper. Thus, inasmuch as the copy image is formed not only on the surface of the photoconductive layer of the copying material, but also within the layer, the copy image within the layer remains unerased while the image on the surface may be erasable.

Generally, zinc oxide powder used in a photoconductive layer makes the latter relatively porous, and together with the paper base, the copy image may be formed in threefold when development is made according to this invention; namely, the image formed by the toner adsorption to the photoconductive layer, the image formed by the dye penetration into said layer, and the image formed within the support sheet by said dye which has penetrated through the photoconductive layer.

The materials usable for a developer according to this invention are described hereinbelow in further detail.

Materials for toner (a) Pigment particles:

Carbon black, indigo blue, rouge, phthalocyanine blue, (b) Dye:

Spirit black, aniline black, oil brown BB, oil blue G,

extra, oil red B, (c) Resinous polarity regulating agent:

Natural rosin, asphalt, alkyd resin compound, laurylmethacrylate dimethylaminoethylmethacrylate copolymer, and other synthetic resins.

Naturally, the resins usable for this invention are not limited to the above-mentioned resins, but any resins known as polarity regulating agents for liquid developing electrophotography can be used.

A developer according to this invention may be obtainable by making a concentrated toner by kneading one of each of the aforesaid materials (a), (b) and (c) (preferably at the ratio of 1 part by weight of pigment against 0.1-1 part by weight of dye and 0.5 parts by weight of resin(s)) with a small amount of a kneading medium (normally, the same kind as the carrier liquid is desirable) and then dispersing the resultant concentrated toner in one of the following carrier liquids.

((1) Carrier liquid:

Isoparafl'inic hydrocarbons having an electric resistance of not less than 10 9 cm. and a dielectric constant of a maximum 3, normal paraffinic hydrocarbons and various petroleum hydrocarbons having the same characteristics.

These hydrocarbons are sold by Esso Standard Oil Co.

under the trade names of Isopar-H and or Isopar-G.

A suitable solution for wetting the image surface after the image is formed by the aforementioned developer on the photoconductive layer surface will include: various kinds of alcohols (such as mono-valent alcohol: methylalcohol, ethylalcohol, propylalcohol, butylalcohol, polyvalent alcohol: ethyleneglycol, propyleneglycol, diethyleneglycol), various kinds of ketones (such as acetone, methylethylketone, methylisobutylketone, diethylketone), various kinds of ethers (such as ethylether, isopropylether, 1,4-dioxane) and fatty acids (such as oleic acid, linolic acid, linolenic acid, elaeostearic acid).

These solvents can be directly sprayed or applied on the copy image, or sprayed with other solvents or mixed with emulsion. The desired result can be obtained so long as the surface of the copy image is wetted with these solvents.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 Parts by wt. Carbon black 0.5 Spirit black 1.0 High diesel HD 1 A concentrated toner was made by kneading the above mixture for hours in a ball mill, of which 4 parts by weight were then dispersed in 1000 parts by weight of a carrier liquid of isoparaffinic hydrocarbon (Isopar-H) to make a developer for electrophotographic use. In this developer was dipped, in order to produce a print image, a sheet of commercially available electrophotographic copying sheet (Electronic Ricopy paper BS 1 made by Kabushiki Kaisha Ricoh) carrying an electrostatic latent image processed by a normal electrophotographic method. The image surface was then wetted with diethyleneglycol and the copying sheet was dried thereafter.

By rubbing the print image thus obtained with a rubber eraser, the image portion formed by the toner adsorbed to the photoconductive layer surface disappeared, but the print image formed within the photoconductive layer and the base material remained unerased.

Furthermore, the same results Were obtained when diethyleneglycol, or a 50% solution thereof in water or in ethanol, was directly distributed on, or applied to an absorbent cotton for wetting the surface of the print image processed in a developer comprising 1 part by weight of carbon black and 0.5 part by weight of spirit black but otherwise the same composition as the previously mentioned developer.

Example 2 By applying acetic acid independently, or a solution thereof in water, onto the surface of a print image processed in the normal electrophotographic method and developed with the same developer as described in Example 1, and then drying the resultant sample, an unerasable print image was obtained.

Example 3 An unerasable print image was also obtained when the same process as described in Example 1 was repeated using a mixture of diethyleneglycol and acetone mixed at the ratio of 3 parts by weight to 1 part by weight.

Example 4 The same result was also obtainable by repeating the same process as described in Example 1 using a mixture of diethyleneglycol and Inspregnol A Z (a wax emulsion made by Dainippon Ink and Chemicals Inc.) mixed at a ratio of 1 part by weight to 3 parts by weight.

What is claimed is:

1. A development process for permanently fixing an image on an electrophotographic copying material having on one surface of a support a photoconductive layer comprised of a resinous binder containing dispersed therein a powdered photoconductive material, said process comprising the steps of:

(a) applying a liquid developer on said electrophotographic copying material having an electrostatic latent image on the surface of the photoconductive layer thereof to form on said surface of said photoconductive layer a visible image corresponding to said latent image, said developer consisting essentially of a carrier liquid and a toner uniformly dispersed therein, said toner being a uniform mixture consisting essentially of pigment particles, a dye insoluble in said carrier liquid but soluble in the followingnamed solvents and a resinous polarity regulating agent selected from the group consisting of rosin, asphalt, alkyd resin and laurylmethacrylate-dimethylaminoethylmethacrylate copolymer;

(b) then applying on the surface of said photoconductive layer carrying said visible image at least one liquid solvent for said dye, said solvent being selected from the group consisting of alcohols, ketones, ethers and oliphatic carboxylic acids, to form a liquid solution of said dye so that said dye solution penetrates into and through the photoconductive layer; and then (c) drying the thus treated copying material whereby the dye forms within said photoconductive layer a visible image corresponding to the visible image formed on the surface of said photoconductive layer.

2. A development process according to claim 1, wherein said toner is a mixture consisting of carbon black, spirit black and said resinous polarity regulating agent, and said solvent is diethyleneglycol.

3. A development process according to claim 1, wherein said toner is a mixture consisting of 1 part by weight of said pigment particles, 0.1 to 1 part by weight of said dye and 0.5 to 10 parts by weight of said resinous polarity regulating agent.

4. A development process according to claim 1, wherein said pigment is selected from the group consisting of carbon black, indigo blue, rouge and phthalocyanine blue, and said dye is selected from the group consisting of spirit black, aniline black, oil brown BB, oil blue G. extra and oil red B.

References Cited UNITED STATES PATENTS Metcalfe et a1 117-33 Dessaver et a1 96-1 Walkup 101-1492 Carlson 34-77 6 Carlson 34-155 Carlson 117-21X Okishima 95-1.7 Brynko 96-1.4 Fauser 117-37 WILLIAM D. MARTIN, Primary Examiner E. J. CABIC, Assistant Examiner US. Cl. X.R.