US3428453A

US3428453A - Image forming process utilizing xerography

Info

Publication number: US3428453A
Application number: US439764A
Authority: US
Inventors: Satoru Honjo
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1964-03-19
Filing date: 1965-03-15
Publication date: 1969-02-18
Anticipated expiration: 1986-02-18
Also published as: DE1497199C3; GB1085151A; DE1497199A1; DE1497199B2

Description

Feb. 18, 1969 SATORU} HONJO 3,428 453 IMAGE FORMING PROCESS UTILIZING XEROGRAPHY Filed March 15; 1965 F 6. I F/ 6. 2

INVENTOR. SATORU HONJO A T TORNEYS United States Patent 3,428,453 IMAGE FORMING PROCESS UTILIZING XEROGRAPHY Satoru Honjo, Odawarashi, Kanagawa-ken, Japan, as-

signor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Mar. 15, 1965, Ser. No. 439,764 Claims priority, application Japan, Mar. 19, 1964,

39/ 14,988 US. Cl. 96-1.8 7 Claims Int. Cl. G03g 7/00 ABSTRACT OF THE DISCLOSURE This invention relates to a new process of obtaining a relief image and more particularly to a process for obtaining a relief image through the use of xerography.

There are several known processes for obtaining relief images utilizing xerography. One process uses a photosensitive xerographic layer which can be dissolved into suitable organic solvents and this layer is deposited upon a photopolymerizable substrate layer as described in Japanese Patent 35 4,172. Another known process employs a xerographic toner which can change the solubility in an organic solvent of the resinous binder used in a bindertype xerographic plate layer, as described in Japanese Patent 38/13,410.

There are several disadvantages to these prior processes. A xerographic binder layer comprising finely divided, photoconductive particles dispersed in a resinous binder generally utilizes a hydrophobic resin as the binder so that the completed layer will have a high resistivity in the dark. Such hydrophobic insulating resins are not soluble in water or polar solvents but only in some of the more volatile non-polar, organic, liquid solvents. Therefore, in order to dissolve the binder layer according to the prior art techniques, one must employ volatile organic liquids. The use of these volatile organic liquid solvents is not only injurious to the health because of the toxicity of their vapors but, in addition, is expensive and is also dangerous because of the fire hazard which they create. These disadvantages would, of course, be avoided if the layer could be treated with water or an aqueous solution of acids, alkalis, or salts.

Xerographic layers utilizing organic photoconductive materials and alkali-soluble film-forming materials are known. However, these materials have much lower sensitivity to light than those containing zinc oxide and, accordingly, have very limited application.

Solubility modulation with toner materials can only be applied to those xerographic binder layers which utilize chemically reactive resins such as thermosetting resins.

Now, in accordance with the present invention, there has been developed a new proress of obtaining a relief divided, photoconductive particles dissolved in a resinous binder. After the imaging process with this photoconductive layer has been carried out, it may be treated with either water, volatile organic liquids or mixtures of these. Furthermore, there is no restriction imposed on the composition of the xerographic binder layer provided that the structure of the layer is such that it permits water or other non-solvents for the layer to penetrate easily through it. The present invention utilizes a xerographic plate in cluding a substrate, a suitable undercoating and a xero graphic binder layer thereon. It also utilizes a special image-forming material which acts on the undercoating substance to decrease its solubility in water or non-polar organic liquids. The solubility of this underlayer is varied through the use of a toner material which penetrates the xerographic binder layer according to the treatment de scribed hereinafter to change the solubility of that underlayer.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings wherein:

FIG. 1 is a side sectional view of the xerographic plate utilized in the present invention.

FIG. 2 is a side sectional view of the same xerographic plate as shown in FIG. 1 with a xerographic toner image thereon.

FIG. 3 is a side sectional view of the same xerographic plate shown in FIGS. 1 and 2 after the toner has been caused to penetrate through the binder layer to insolublize the undercoating.

FIG. 4 is a side sectional view of the same xerographic plate as shown in FIGS. l-3 after the xerographic layer and undercoating have been removed in non-image areas.

FIG. 5 is a side sectional view of a laminating process by which the plate of FIG. 1 may be prepared.

Referring now to FIG. 1, there is shown a substrate layer 1 which may be either of electrically conductive materials such as paper, or metal, insulating materials with conductive surfaces or insulating materials with special undercoatings. Above substrate 1 there is provided an undercoating 2 which plays an important role in the process. This undercoating consists of a film-forming material which has higher electrical conductivity than the xerographic binder layer 3 above it. In addition, this layer is selected to be soluble in polar solvents such as water or certain organic solvents and can be made insoluble therein by the action of suitable chemical reagents as described hereinafter. Any suitable material having the aforementioned characteristics may be used for layer 2. Typical materials having these characteristics include gelatin, casein albumin, polyvinyl alcohol, arginic 'acid, carboxymethyl cellulose, polymethacrylic acid, polyacrylic acid, copolymers containing maleic acid or maleic anhydride, copolymers containing crotonic acid, partially esterified polyamide resins, and other amide converted polymers containing carboxyl radicals. Metal powders or other suitable colorants may also be compounded with these materials, When the underlying substrate l is an insulating material, the undercoating 2 is preferably formulated so as to have a high electrical conductivity which may be accomplished by mixing metal powders, carbon black particles, or graphite particles with the film-forming materials.

The photoconductive layer 3 must have a porous or other structure such that it permits the penetration of liquids which can dissolve non-converted portions of the undercoating layer 2. The xerographic plate shown in FIG. 1 can be prepared either by successive coatings or by a laminating process as shown in FIG. 5. In this latter process, a photoconductive binder layer is prepared by ordinary coating techniques on a temporary support layer 6 and then an adhesive layer 2 is coated thereon. This adhesive layer has the same composition as the undercoating described above. After the preparation of this laminate, it is pressed and bonded firmly upon a final substrate 1 through the adherence of layer 2 thereto and then the temporary support layer is stripped off.

As shown in FIG. 2, a xerographic image is formed on the plate with electroscopic developing powder 4 according to conventional xerographic imaging processes well known in the art. The particular powders employed are capable of converting the undereoating layer 2 into a form which is insoluble in water or suitable polar solvents in which the non-converted form of this layer is soluble. Any suitable material which will perform this function may be employed as the developing powder or as a component thereof. Chromium-containing compounds, for example, may be used with a number of water soluble film-forming materials in order to insolubilize them. Typical chromium compounds of this type include: chromium stearate, chromium naphthenate and other chromium salts of organic acids. Other polyvalent metal salts of organic acids may also be used. If these materials are solids, they may be made in the form of a powder and used by themselves as the image-forming material, If, on the other hand, they are liquid or crystalline at room temperature,

they may be blended with suitable resinous materials which are then crushed to form the fine developing particles thus required. Thus, for example, a polyamide resin which is soluble in a water/methanol solvent may be rendered insoluble in this solvent by the action of one of the aforementioned acids. These acid components may be used as the image-forming materials. Zinc chromate or lead chromate may, for example, be utilized as imageforming materials in combination with polyvinyl alcohol or gelatin layers. In this case, after development with the chromates, the sensitive layer and the image is treated with an acid solution to dissolve the chromates which liberates the chromium ion. This chromium ion participates in a reaction with the polyvinyl alcohol or gelatin layer to insolubilize it. In summary then, the image-forming material or powder must contain a chemical component that will give rise to or promote an insolubilizing reaction of the undercoating when this material reaches the undercoating, or it may also be a promoter or catalyst for such an insolubilizing reaction of the undercoat- As shown in FIG. 3, the image forming material penetrates the photoconductive layer 3 to reach the undercoating layer 2. This penetration is carried out by heating when the image is thermally fusible or by the application of a solvent liquid or vapor to the image. If the insolubilizing reaction rate of the undercoating with the imaging material is slow at room temperature, heating is effective in many instances to raise the reaction rate.

In FIG. 4, there is shown that stage in the process in which the photoconductive layer and the undercoating layer has been removed in non-image areas by the action of a solvent for the unconverted undercoating. This solvent is not a solvent for the photoconductive binder layer. Although the solvent for the unconverted undercoating could not generally dissolve the photoconductive layer, experimentation has shown that the upper photoconductive layer was easily removed by dissolving the unconverted underlayer beneath non-image areas. Among the solvents to be used, water is one of the most desirable but mixtures of water and water miscible polar organic liquids are also advantageous from the points of view of economy, and low toxicity in work areas.

The following examples of specific compositions, structures and process steps will serve more clearly to point out and explain preferred embodiments of the invention but it should be understood that these are not to be construed as a limitation thereof.

Example I An aqueous solution of polyacrylic acid was coated on a steel plate and dried to produce a thickness of about 34 microns. The following composition was thoroughly mixed in a procelain ball mill until it was well blended, coated on the polyacrylic acid layer and dried to give a thickness of about microns. The composition con- Cir sisted of parts by weight of photoconductive zinc oxide, 40 parts by weight of a low viscosity silicone resin varnish and 40 parts by weight of toluene. One plate made according to this procedure was tested by applying water to its surface, and it was found that the surface photoconductive layer was porous enough so that water easily penetrated the layer, dissolved the sub-layer thereby removing the photoconductive coating. Testing with aqueous alkali solutions in place of the Water gave similar results. Another plate prepared according to the above procedure was tested by forming a latent electrostatic image thereon according to conventional xerographic techniques. 'This plate was then developed with a toner containing a mixture of chromium, naphthenate and rosin modified phenolformaldehyde resin. After development the image-bearing plate was heated to C. for about five minutes whereupon the toner particles melted and penetrated into the sub-layer. After cooling the plate was treated with a 50/50 water-methanol solvent. The sub-layer in non-image areas was dissolved by this treatment floating off the photoconductive layer above them While image areas remained unchanged.

Example II A photoconductive coating made according to the formulation of Example I was coated on a sheet of cellophane to give a dried thickness of 10 microns. After removal of the volatile solvent a methanol solution of polyacrylic acid was coated over the photoconductive layer to a dried thickness of 4 microns. This polyacrylic acid layer was then moistened with steam and the two layers were pressed onto a steel plate with the polyacrylic acid coating facing the steel. Subsequently, the cellophane was wet slightly and easily separated from the photoconductive layer leaving the tWo underlying layers on the steel plate. This plate was then treated according to the imaging procedure of Example I with essentially the same results.

What is claimed is:

1. An imaging member comprising a supporting substrate, a sub-layer on said substrate, said sub-layer being sufficiently soluble in a polar solvent so that said sublayer can be removed from said substrate by treatment therewith, said sub-layer comprising a material selected from the group consisting of gelatin casein albumin, polyvinyl alcohol, arginic acid, carboxmethyl cellulose, polymethylacrylic acid, polyacrylic acid, carboxy-group containing copolymers of organic acids or organic acid anhydrides, carboxyl-group containing polyamides, and mixtures thereof, an upper porous insulating layer on said sub-layer, said porous insulating layer comprising finely divided photoconductive particles dispersed throughout an insulating hydrophobic film-forming binder and being sufficiently porous to permit the successive penetration of insolubilizing material and solvent material for said sublayer through said insulating layer to said sub-layer.

2. The imaging member of claim 1 whereins said finely divided photoconductive particles comprise photoconductor zinc oxide.

3. An imaging member according to claim 1 in which said sub-layer comprises polyacrylic acid.

4. A method of forming a relief image comprising forming a latent electrostatic image on an imaging member made up of a supporting substrate, a sub-layer on said substrate, said sub-layer being at least partially soluble in a polar solvent and an upper porous insulating layer on said sub-layer, said insulating layer being insoluble in polar solvents, developing said latent electrostatic image with electroscopic developer including an insolubilizing agent for said sub-layer and then contacting said imaging member with a polar solvent whereby said insulating layer and said sub-layer are separated from said substrate in non-image areas.

5. A method according to claim 4 further including the step of causing said electroscopic developer to penetrate through said porous layer by applying heat thereto prior to contacting said imaging member with said polar solvent.

6. A method according to claim 4 further including the step of contacting said electroscopic developer with a solvent vapor so as to cause it to penetrate through said porous insulating layer and contact said sub-layer prior to contacting said imaging member with said polar solvent.

7. A method of forming a relief image comprising forming a latent electrostatic image on a photoconductive imaging member by exposing said member to a pattern of actinic electromagnetic radiation while applying an electrical field thereto, said imaging member being made up of a supporting substrate, a sub-layer on said substrate, said sub-layer being electrically conductive and at least partially soluble in a polar solvent and an upper porous photoconductive insulating layer on said layer, said photoconductive insulating layer being insoluble in said polar solvent, developing the latent electrostatic image formed on said imaging member with electroscopic References Cited UNITED STATES PATENTS 3,121,009 2/1964 Giaimo 96-1 3,226,227 12/1965 Wolfl 96-1-8 3,236,640 2/1966 Tomanek et al 96-1 3,291,738 12/1966 Sciambi 117-37 X 3,347,702 10/1967 Clancy 96-1 X I. TRAVIS BROWN, Primary Examiner. C. E. VAN HORN, Assistant Examiner.

US. Cl. X.R. 96-1; 101-401.1; 117-37