US3692523A

US3692523A - Process for developing electrostatic latent image and liquid developer used therefor

Info

Publication number: US3692523A
Application number: US8955A
Authority: US
Inventors: Yasuo Tamai; Satoru Honjo
Original assignee: Fuji Photo Film Co Ltd
Current assignee: Fujifilm Holdings Corp
Priority date: 1969-02-05
Filing date: 1970-02-05
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19
Also published as: DE2005268A1; DE2005268C3; NL7001561A; DE2005268B2; BE745533A; CA924167A; FR2032324B1; GB1255445A; FR2032324A1

Abstract

A PROCESS FOR CONVERTING AN ELECTROSTATIC LATENT IMAGE ON AN INSULATING RECORDING LAYER TO A MATERIAL IMAGE AND FIXING THE MATERIAL IMAGE, THE PROCESS COMPRISING THE STEPS OF DEVELOPING WITH A LIQUID DEVELOPER COMPRISING A NONPOLAR CARRIER LIQUID HAVING A SPECIFIC VOLUME RESISTIVITY NOT LESS THAN 10**10OHMS-CM., THE LIQUID CONTAINING (1) FINELYDIVIDED GELATIN PARTICLES HAVING A MEAN PARTICLE DIAMETER BETWEEN 0.01 AND 20 MICRONS WHERE THE AMOUNT OF THE GELATIN PARTICLES IS FROM 0.001 TO 5% BY WEIGHT OF THE CARRIER LIQUID AND (2) A SYNTHETIC RESIN SOLUBLE IN THE CARRIER LIQUID BUT INSOLUBLE IN AT LEAST ONE OF AN ISOPARAFFINIC SOLVENT AND A FLUOROCHLORINATED HYDROCARBON SOLVENT WHERE THE CONCENTRATION OF THE RESIN IS NOT LOWER THAN THAT OF THE GELATIN PARTICLES AND NOT MORE THAN 30% BY WEIGHT OF THE CARRIER LIQUID TO FORM AN IMAGE OF GELATIN, AND THEN RINSING THE GELATIN IMAGE WITH AT LEAST ONE OF THE ISOPARAFFINIC SOLVENT AND THE FLUOROCHLORINATED HYDROCARBON SOLVET TO THEREBY INSOLUBILIZE THE RESIN TO FIX THE GELETIN IMAGE ON THE INSULATING IMAGE RECORDING LAYER, BRINGING THE FIXED GELATIN IMAGE INTO CONTACT WITH AN AQUEOUS SOLUTION OF A WATER SOLUBLE DYE THEREBY IMBIBING THE DYE INTO THE FIXED GELATIN IMAGE, AND PLACING A DYE-RECEIVING SHEET COMPRISING A SURFACE COATING WHICH EASILY ABSORBS WATER-SOLUBLE DYES SO THAT THE DYED GELATIN IMAGE CONTACTS THE SURFACE LAYER, WHEREBY THE DYE IN THE GELATIN IMAGE IS TRANSFERRED ONTO THE SHEET, FORMING A FINAL DYE PRINT.

Description

Sept. 19, 1972 YASUO TAMAl ETAL 3,692,523

PROCESS FOR DEVELOPING ELECTROSTATIC LATENT IMAGE AND LIQUID DEVELOPER USED THEREFOR Filed Feb. 5, 1970 2 Sheets-Sheet 1 2 u n n Z j? 1 9 (50cm 0 amer-mam O ,2

P /j o o INVENTORS )6451/@ 4 2 /1441 $147090 Hon/J0 Sept. 19, 1972 YASUO'TAMM ETAL 3,692,523

PROCESS FOR DEVELOPING ELECTROSTATIC LATENT IMAGE AND LIQUID DEVELOPER USED THEREFOR Filed Feb. 5, 1970 .2 Sheets-Sheet 2 F I 6 INVENTORS PZsuo Z'QMA/ 95197020 ffo/vj United States Patent Ofilce US. Cl. 961.4 4 Claims ABSTRACT OF THE DISCLOSURE A process for converting an electrostatic latent image on an insulating recording layer to a material image and fixing the material image, the process comprising the steps of developing with a liquid developer comprising a nonpolar carrier liquid having a specific volume resistivity not less than 10 ohms-0111., the liquid containing (1) finelydivided gelatin particles having a mean particle diameter between 0.01 and 20 microns where the amount of the gelatin particles is from 0.001 to 5% by weight of the carrier liquid and (2) a synthetic resin soluble in the carrier liquid but insoluble in at least one of an isoparaffinic solvent and a fluorochlorinated hydrocarbon solvent where the concentration of the resin is not lower than that of the gelatin particles and not more than 30% by weight of the carrier liquid to form an image of gelatin, and then rinsing the gelatin image with at least one of the isoparafiinic solvent and the lluorochlorinated hydrocarbon solvent to thereby insolubilize the resin to fix the gelatin image on the insulating image recording layer, bringing the fixed gelatin image into contact with an aqueous solution of a water soluble dye thereby imbibing the dye into the fixed gelatin image, and placing a dye-receiving sheet comprising a surface coating which easily absorbs water-soluble dyes so that the dyed gelatin image contacts the surface layer, whereby the dye in the gelatin image is transferred onto the sheet, forming a final dye print.

This invention relates to a process for developing an electrostatic latent image and also to a liquid developer to be employed in the process.

The most prevailing method of producing a multi-colored print of a high quality comprises color-forming development of silver halide emulsion coatings. As another method based on silver halide emulsion, dye transfer or dye imbibition process, which makes use of tanning development to form gelatin relief images, is also under practical use, for example, in technicolor process.

The former method is suitable for mass production, having a wide range of various applications, but, generally speaking, the resulting color image lacks in fastness to light and other effects. On the contrary, the dye transfer process can provide an image having a better stability, but this process may be referred to as printing rather than photography, since it needs a time-consuming, skilled operation for producing gelatin reliefs. Thus, the cost of the resulting prints becomes reasonable only for a large number of runs.

We invented a simplified color printing process overcoming the above noted deficiencies, which is disclosed in Belgian Pat. No. 724,581.

This process comprises the following steps:

(i) An electrostatic latent image formation on an insulating coating of an electrostatic recording or electrophotographic material.

(ii) Development of said latent image into a material image employing a toner comprising a finely-divided pow- 3,692,523 Patented Sept. 19, 1972 der which can easily absorb an aqueous solution of a water-soluble dyestuff.

(iii) Fixation of the developed image by a suitable means.

(iv) Dye imbibition in said fixed image by bringing into contact with an aqueous solution of a water-soluble dyestutf.

(v) Transfer of the absorbed dyestulf to a dye-receiving sheet which is made to contact with the dyed image.

The principal object of the present invention is to provide a development method of an electrostatic latent image as well as a liquid developer of new composition for use in practicing the above-cited color printing process. In other words, the object is to provide a development method and a liquid developer for use in producing electrographically a gelatin relief image for dye imbibition process.

The process for developing electrostatic latent images of this invention comprises developing with a liquid developer containing in a carrier liquid having a specific volume resistivity not less than 10 0 cm., a finely-divided gelatin powder having a mean particle diameter between 0.01 and 20 microns, and a resin soluble in said carrier liquid but insoluble in at least one of isoparafiinic solvent and fluorochlorinated hydrocarbon solvent, and then rinsing with at least one of an isoparafiinic solvent and fluorochlorinated hydrocarbon solvent both insoluble to said resin.

Gelatin toner may be prepared by any of the following procedures;

(i) Mechanical pulverization of gelatin granules. Pulverization may be carried out by dry or wet process, by means of ball mill, colloid mill, mechanical mortar, jet stream mill, or Attriter (a wet blender marketed by Mitsui-Miike Seisakusho Co.).

(ii) In solubilization of gelatin by adding an aqueous gelatin solution into an organic solvent miscible with water but being a non-solvent for gelatin. The precipitated gelatin is collected in the form of a finely-divided particle.

(iii) Grinding gelatin gel in an organic solvent miscible with water but incapable of dissolving gelatin, which results in a gelatin dispersion.

(iv) Spray drying of an aqueous gelatin solution in a dried air or in a vacuum.

(v) Preparation of gelatin dispersion by first preparing a gelatin solution comprising water and a water miscible organic solvent such as ethanol or methanol, the latter being present in the solution in such an amount that the phase separation of gelatin does not occur, then by adding this solution into an organic solvent system, whereby gelatin particles separate out of the liquid phase, resulting in a dispersion, and finally transferring the gelatin particles into an insulating carrier liquid required.

A liquid developer can be prepared by dispersing finelydivided gelatin made by any of these procedures in a carrier liquid. Among the above-listed procedures, those described in (i) and (iv) will provide toners having a rather large particle size, while those of (ii), (iii), and (v) are suitable to obtain toners of small particle diameter. Acceptable ranges for gelatin toner particle size may lie between 0.01 and 20 microns, since extremely fine toners are difficult to handle, and coarser ones will give images of poor quality. Deliberate control over electrophoretic property of gelatin toner is generally unnecessary to prepare a positively charged liquid developer, since gelatin itself has a strong tendency of assuming positive polarity in many insulating, nonpolar liquid. In order to impart a negative polarity of charge on gelatin toner, one may cover the surface of gelatin toner particles with a suitable resinous control agent, or may add a negatively charged,

second toner into the developer in which a positively charged gelatin toner is dispersed. By adjusting the amount of the second toner to be added, one can bring about a developer containing a negatively charged toner.

It should be noted that heat fixation of a gelatin toner image is impossible since gelatin is not thermoplastic. Therefore, a suitable fixing process is required.

The inventors have found that by developing electrostatic latent images with a liquid developer containing in a carrier liquid 21 finely-divided gelatin powder and a resin soluble in said carrier liquid but insoluble in at least one of isoparaflinic solvent and fluorochlorinated hydrocarbon solvent, and then rinsing with at least one of an isoparafiinic solvent and a fluorochlorinated hydrocarbon solvent, developed gelatin images are fixed. Suitable carrier liquids for such developer include any nonpolar ones having a volume resistivity not less than ohms-cm. which do not dissolve or attack photoconductive coating to be used, and ordinarily straight-chain, or cyclic saturated hydrocarbons and mixtures of these are used. Resins dissolved in these carrier liquids include rosin-modified phenolformaldehyde resins, vegetable oil modified alkyd resins having an oil length ranging from to 65%, styrenated alkyd resins, and varnishes made from these resins.

When an electrophotographic sheet is developed with a developer containing such resin dissolved in the carrier liquid, and taken out therefrom, the surface of the sheet is uniformly wetted with a thin film of the developer liquid. At the image area, the amount of the adhering liquid, and accordingly the amount of the resinous material, is larger than at the non-image area, since in the former area, the liquid is maintained at the interstices between the deposited toner particles, while at the latter area, only a thin uniform film of the developer is held by surface tension. When this liquid layer bearing sheet is immersed in or brought into contact with an isoparafiinic solvent or fluorochlorinated hydrocarbon solvent, the resin is forced to deposit out from the liquid phase around the deposited toner image, thus causing fixation of the image.

A self-fixing developer may be prepared in a practiced manner whereby a thermoplastic resinous material is incorporated as a surface coating agent for gelatin particles or as a finely-divided powder together with gelatin. However, preparation of such developer is sometimes ditficult, and also it provides a gelatin toner image which shows some drawbacks in the subsequent dye imbibition process.

Gelatin reliefs can be produced by the following steps upon employing the liquid developer disclosed in the present invention:

(i) Forming an electrostatic latent image on an insulating layer in an electrophotographic or electrostatic recording material.

(ii) Developing said electrostatic latent image with the liquid developer comprising a gelatin toner and a fixing resin disclosed in the present invention.

(iii) Fixing the developed gelatin image by immersing the material in an isoparaffinic or fluorochlorinated hydrocarbon liquid.

(iv) Bringing the gelatin image into contact with an aqueous solution of a water soluble dye, letting the dye imbibed into said gelatin image, and

(v) Placing a dye-receiving sheet comprising a surface coating which can easily absorb water-soluble dyes in such a manner that the dyed gelatin image contacts with said surface layer, whereby the dye in the gelatin image is completely transferred onto the sheet, forming a final dye rint. p 'Each step will be described more in detail referring to the accompanying drawings.

FIG. 1 shows a cross-sectional view of a recording material on the insulating layer of which is formed an electrostatic latent image 3; the recording material comprises a semi-conducting or conducting support 1 and an insulating layer 2.

Further explanation may be unnecessary as for such typical structure of recording sheet material, but it should be noted that it is advantageous to exclude any Watersoluble ingredient such as water-soluble resin or hydrophillic resin from the insulating layer, considering subsequent procedures with aqueous processing liquids. When paper support is used, a water-resistant paper is preferred. A special care must be taken with regard to conductivityincreasing subcoating ordinarily provided between the insulating layer and the paper support. Water-soluble subcoating, which is the general case, should not be used for the present method, since such coating will cause separation of the insulating layer from the support in the subsequent processing steps employing aqueous solutions. When a special device is used for such processing steps such as to permit the solutions to wet the surface of the recording layer only, water-soluble subcoating may be utilized.

In case where the insulating recording layer is photoconductive, it is desirable to impart it a panchromatic response, in which case three color separation images can easily be obtained from a multi-colored original by the use of color separation filter set. Examples of such panchromatic photoconductive coating are given in, for example, U.S.P. 3,241,959 to W. B. Kendall et al. Besides those which have a limited spectral sensitivity in the visible region or only in ultraviolet region may also be used for the preparation of relief images with a suitable combination originals.

An electrostatic latent image may be formed by any of various known methods such as typical xerographic one comprising image exposure on a uniformly charged photoconductive insulating layer, so called Kallman process characterized by charging after image exposure, those employing infrared light as energy source instead of visible rays, or electrostatic recording comprising imagewise charging by pattern electrodes.

FIG. 2 illustrates the recording material under development with a liquid development, which results in conversion of the electrostatic latent image into a gelatin image. In this figure the latent image having negative polarity which is the case for a zinc oxide/ resin electrophotographic coating, is developed with a gelatin toner 12 having positive polarity. Though not shown in the drawing, a development electrode is eifective to cause a faithful reproduction of a latent image of continuous tone; ll designates the carrier liquid of the developer, and 13 a developed image comprising gelatin powder.

Repulsive development may also be employed wherein a developer containing a toner of the same polarity as the latent image is used, or a half-tone may be used.

Any of known developing methods may be used for conversion of an electrostatic latent image into a material image comprising gelatin, but the best result can be obtained by liquid development.

The recording sheet, after processed with the liquid developer, is moved into a rinsing bath comprising isoparaflinic or iluorochlorinated hydrocarbon. Suitable isoparafiinic liquids include isooctane, isobutane, Isopar E, Esopar H, Esopar G marketed by Esso Standard Oil Co., etc. while fluorochlorinated hydrocarbons include Diflon S3 marked by 'Daikin Ind. Co. When the developed sheet is immersed in the rinse liquid, at fixing resin dissolved in the carrier liquid of the developer becomes insoluble and adheres on the sheet surface, thereby fixing the developed image.

FIG. 3 illustrates the sheet after fixation of the developed image by the insolubilized resin 14 protecting the gelatin particles. A very slight amount of deposited resin on the non-image area has been omitted in the figure.

The next step is dye imbibition into the gelatin. image, which is shown in FIG. -4, wherein the developed sheet is immersed in a dye solution, but dye imbibition may be accomplished by means of a moistening roller wetted with a dye solution pressed against the recording surface of the sheet. During this process the insulating layer accept substantially no dye solution since it ordinarily has strongly hydrophobic surface.

Suitable dyestuffs for use in dyeing gelatin nnages in clude primarily acid and mordant dyes, for example; as cyan dyestuffs, Acid Blue 45 (Color Index (Cl) 63010), Acid green 16 (CI. 44025), Acid green 1 (CI. 10020), Acid blue 1 (C.I. 42045), Acid blue 9 (CI. 42090), Acid blue 54 (Anthraquinoric); as magenta ones, Acid red 80 (CI. 68215), Acid red 34 (Cl. 17030), Acid red 1 CAI- 18050), Acid violet 19 (CI. 42685), Acid violet 7 (Cl. 18055), and as yellow ones, Acid yellow 23 (CI. 19140), Acid yellow 11 (0.1. 18820), Direct yellow 12 (C.-I. 24895), Acid yellow 34 (Cl. 18890).

These dyes are especially suitable for processes including superimposition of multiple dye images on a single dye receiving sheet because of their mordantability, thus excluding the possible deterioration of already transferred dye images due to diffusion or back transfer during subsequent dye transfer.

Many dyes other than acid or mordant groups may be utilized for producing a single color dye print.

In 'FIG. 4, the gelatin image 22 absorbed the dye solution 21.

The imbibed dye is then to be transferred onto a dyereceiving sheet, but before transfer operation it is recommended to wash off an excessive dye solution remaining on the surface of the sheet to improve the image quality of the final print. FIG. illustrates this washing step, wherein a weakly acid washing solution is desirable to minimize dissolving out of the imbibed dye.

'FIG. 6 illustrates the dye transfer step, a dye-receiving sheet comprising a support 31 and a dye-receiving surface coating 32 which is most preferably made of gelatin. The dye-receiving sheet is preferably moistened with an aqueous solution of mordanting agent prior to dye transfer. The dashed area 33 designates a dyed area after dye transfer.

The series of steps described above gives a monochromatic dye image on the dye-receiving sheet, and by repeating the similar operations with other reliefs together with other dyes on the same dye-receiving sheet, one may provide a multicolor image.

The image quality of the final dye print is excellent with faithfully reproduced hues and saturations as well as willciently high degree of light fastness. In comparison with multicolor print prepared by over-print technique of electrophotography, appearance of the print is far better with little surface reflection which is thought inherent to electrophotographic toner images, and with transparency of each color resulting in a complete mixing between primary colors.

A gelatin relief produced electrophotographically may be used repeatedly to provide a number of runs desired by supplying a dye solution.

Elementally processes have been described but auxiliary operations which will now be explained are also quite important to give good prints.

(1) Drying of a developed gelatin image after fixation, followed by hardening with a hardening agent for gelatin. These operations are efiFective to impart an improved mechanical strength to the gelatin image.

(II) Removal of zinc oxide photoconductor from the recording layer prior to dye imbibition. When an acid dyestuif is to be imbibed into a gelatin image, the image area should preferably be kept at a low value of pH, which is difiicult to realize on a photoconductive layer comprising zinc oxide because zinc oxide is basic material. If the pH is high at the gelatin image area, an incomplete dye absorption to gelatin occurs. Thus it is preferable to remove the zinc oxide from the layer prior to dye imbibition. Zinc oxide can easily be removed by dissolving off with an acid such as acetic acid. This additional operation ensures a sharper, and higher image quality to the final dye print.

Now there will be described the compositions of the electrophotographic liquid developer of the present invention.

The concentration of gelatin toner would practically be in the range between 0.001 to 5% by weight to a carrier liquid. A concentration less than the minimum as stated above will result in an insufiicient image density. Theoretically it is predicted that a developer with an extremely low toner concentration can develop an electrostatic latent image to give a high image density but it is not the case mainly due to degratation of the latent image in the developer. A concentration higher than the maximum will result in a high level of background, and at the same time, complete removal of such background by rinsing becomes diflicult. It should also be noted that dispersion stability becomes worse with toner concentration increase. The concentration of resin dissolved in carrier liquid, which is insoluble in isoparaffinic and/or fluorochlorinated hydrocarbons, should not be lower than that of the toner incorporated. Some resin may be incorporated up to 30% by weight for the carrier liquid, but generally a volume resistivity lowering due to the addition of resinous material determines the higher limit of its concentration. The liquid phase of the liquid developer should have a volume resistivity not less than 10 ohms-cm; this requirement permits many resinous materials to be incorporated up about to 8% by weight to a carrier liquid.

Presence of resin or vegetable oils in a carrier liquid improves dispersion stability of toner particles. When a resin which is insoluble in isoparaflinic or fluorochlorinated hydrocarbon solvents is incorporated at a high concentration, addition of vegetable oil is unnecessary. Generally speaking, it is preferable that the sum of the resinous material soluble in the carrier liquid but insoluble in the above-mentioned solvents and vegetable oil dissolved in the carrier liquid be not less than 0.3% by weight of the carrier liquid. Though many vegetable oils have a sufficiently high volume resistivity above 10 ohms-cm, which permits excessive amount of the oils in the carrier liquid, accompanying increase of viscosity tends to lower remarkable the depositing rate of the toner particles. Thus the practical maximum is about 30% by weight to the carrier liquid.

As for the combination of a resin for image fixation and a rinsing solvent, rinsing baths comprising isoparafiinic and/ or fluorochlorinated hydrocarbons are though best suitable. However, other rinse compositions will be possible so long as a carrier liquid the solubility property of which is clearly different from rinse solvents is combined.

When the toner particles in a liquid developer of the present invention are made solely of gelatin, the developed image therefrom will be translucent and not clearly discernible, making it difiicult to judge whether the image quality is acceptable. To avoid this difiiculty, it is advantageous to incorporate a colored toner comprising a pigment in an amount of from to M to the gelatin toner. One may also resort to a pigmented or dyed gelatin toner.

EXAMPLE I To 20 ml. of 5% by weight gelatin aqueous solution was added upon stirring 20 ml. of methanol. A dispersion of gelatin in acetone was prepared by adding this solution into 1 liter of acetone under ultrasonic stirring. The dispersed gelatin particles were separated centrifugally and the collected particles after washed with further acetone, while in a wetted state with acetone, were dispersed in a carrier liquid having the following composition in such a manner that 1000 parts by weight of the carrier liquid may contain 1 part by weight of gelatin.

Composition of the carrier liquid Parts by weight Cyclohexane 800 Kerosene 150 Soybean oil 45 Rosin-modified phenolformaldehyde resin 5 The rosin-modified phenolformaldehyde resin is soluble in this mixture of cyclohexane and kerosene but insoluble in an isoparaffinic solvent Isopar E" purchased from Esso Standard Oil Co. By the way, kerosene has a role to control the evaporation rate of the developer, while soybean oil works as dispersion stabilizer.

A photoconductive zinc oxide/resin coating was prepared in the following manner; a homogeneous mixture comprising 100 parts by weight of photoconductive zinc oxide, 20 parts of epoxyester of dehydrated caster oil fatty acid and a suitable amount of toluene was produced. To this mixture were added part of flnorescein, and 9 part of bromophenol blue dissolved in a small volume of ethylenglycol monomethylether to extend the photoconductive response of zinc oxide to almost whole range of the visible spectrum. After further dilution with toluene, the resulting mixture was coated on an aluminized surface of polyethylene terephthalate film hava thickness of 90 microns to give a dried thickness of about 8 microns. The electrophotographic recording sheet thus prepared proved to have acceptable properties after complete drying and dark adaptation. A piece of this sheet was negatively charged at darkness by means of corona, discharge, and subjected to image-wise exposure by an optical enlarger which was charged with a multicolor transparency superimposed with a red filter.

The exposed sheet was immersed in the developer described above, after wetted with pure kerosene, in such a manner that the photoconductive surface may face to the bottom of the developer tray which was made of stainless steel, whereby the tray worked as development electrode. After 90 seconds immersion, the sheet was taken out of the developer and rinsed in an isoparaffinic solvent Isopar E. Then the sheet was dipped in 1% methanol solution of formaldehyde briefly, and left at room temperature overnight so as to harden the developed gelatin image. The sheet then was immersed in 40% aqueous solution of acetic acid for 2 minutes whereby the zinc oxide particles contained in the photoconductive layer were completely dissolved away.

The above procedures provided a gelatin relief for cyan printer.

Similar procedures were carried out on another piece of the same electrophotographic recording member employing as the original the same transparency with a green filter, thus giving a relief for magenta printer. A relief for yellow printer was similarly obtained with a blue filter.

These three reliefs were immersed in three dye solutions containing Acid Blue 54 (Anthraquinoric dyestuff), Acid Violet 7 (CI. 18055) and Acid Yellow 23 (CI. 19140), respectively, for 2 minutes and then washed with a dilute acetic acid aqueous solution.

A dye-receiving sheet comprising a paper support and a gelatin surface coating after treated with aluminum sulfate aqueous solution, was brought into contact with the dye imbibed three gelatin reliefs in turn in register, whereby the imbibed dyes were transferred on the gelatin coating of the dye-receiving sheet, giving a multi-color print of excellent quality.

The reliefs proved to stand about 100 times runs.

EXAMPLE II (by weight) aqueous gelatin solution kept at 40 C. was ejected into a dry air stream kept at 80 C. by spraying to form a fine powder of gelatin, which was collected by a cyclon powder collector. The collected powder had a mean particle diameter of 8.5 microns.

1 part by weight of this gelatin powder was further ground in an attritor (a Wet blender marked by Mitsui- Miike Ind. Co.) together with the following liquid:

Parts by weight Toluene 6 Cyclohexane 2 Varnish obtained by cooking rosin-modified phenolformaldehyde resin with linseed oil 6 One part of the resulting paste was dispersed in the following carrier liquid:

Parts by weight Cycloh exane Kerosene 25 Cotton-seed oil 5 This dispersion worked well as liquid developer. This developer proved to give a similar satisfactory result as described in the first example.

EXAMPLE III Dried pellets of gelatin were pulverized by a jet stream mill; the resulting powder had a mean particle diameter of 13.5 microns.

1 part by weight of this powder was further ground in an attritor with the following liquid.

Parts by weight Cyclohexane 10 Linseed oil modified alkyd resin (oil length 51% 3 1 part of the resulting paste was dispersed in 100 parts by weight of a carrier liquid having the following composition.

Parts by weight Cyclohexane Kerosene l8 Linseed oil 2 A white opaque liquid developer resulted. The alkyd resin used was a soluble in cyclohexane but insoluble in isoparaffinic solvents.

EXAMPLE IV Parts by weight Cyclohexane 10 Styresol N-7l5 (Styrenated alkyd resin purchased from Japan Reichhold Co.) 4

1 part of the resulting paste was dispersed in parts of the same carrier liquid as in the third example. Styresol N-7l5 is used for fixing images since it is soluble in cyclohexane but not in isoparaffinic solvent such as Isopar H.

EXAMPLE V 5 grams of dry gelatin were ground in an agate mortar together with 20 ml. of toluol for 5 hours, during which toluene was replenished to make up for its evaporation loss. The finally obtained toluene dispersion of gelatin was added in the following solution:

Rosin-modified phenolformaldehyde resin g 10 Cyclohexane ml 50 Soybean oil ml 10 The mixture was further blended in a ball mill jar for 20 hours.

The resulting pale yellow dispersion was dispersed in 20 times of its weight of the same carrier liquid as in Example II. This liquid developer showed a fairly good dispersion stability.

What is claimed is:

1. A process for converting an electrostatic latent image on an insulating recording layer to a material image and fixing said material image, said process comprising the steps of developing with a liquid developer comprising a non-polar carrier liquid having a specific volume resistivity not less than 10 ohms-cm, said liquid containing (1) finely-divided gelatin particles having a mean particle diameter between 0.01 and 20 microns where the amount of said gelatin particles is from 0.001 to 5% by weight of said carrier liquid and (2) a synthetic resin soluble in said carrier liquid but insoluble in at least one of an isoparaffinic solvent and a fiuorochlorinated hydrocarbon solvent where the concentration of said resin is not lower than that of said gelatin particles and not more than 30% by weight of said carrier liquid to form an image of gelatin, and then rinsing said gelatin image with at least one of said isoparaffinic solvent and said fiuorochlorinated hydrocarbon solvent to thereby insolubilize said resin to fix said gelatin image on said insulating image recording layer, bringing the fixed gelatin image into contact with an aqueous solution of a water soluble dye thereby imbibing the dye into said fixed gelatin image, and placing a dyereceiving sheet comprising a surface coating which easily absorbs water-soluble dyes so that the dyed gelatin image contacts said surface layer, whereby the dye in the gelatin image is transferred onto the sheet, forming a final dye print.

2. The process for developing electrostatic latent images as claimed in claim 1, wherein said isoparafiinic solvent is selected from the group consisting of isooctane, and isobutane.

3. The process for developing electrostatic latent images as claimed in claim 1, wherein said resin is rosin-modified phenolformadehyde resin, vegetable oil modified alkyl resin having an oil length ranging from 35 to 65%, styrenated alkyd resin or varnish made therefrom.

4. An electrophotographic process comprising the following steps:

(i) forming an electrostatic latent image on an insulating recording layer;

(ii) contacting said electrostatic latent image with a liquid developer comprising a non-polar carrier liquid having a specific volume resistivity not less than 10 ohms-cm, said liquid containing 1) finely-divided gelatin particles having a mean particle diameter between 0.01 and 20 microns where the amount of said gelatin particles is from 0.001 to 5% by weight of said carrier liquid and (2) a synthetic resin soluble in said carrier liquid but insoluble in at least one of an isoparafiinic solvent and a fiuorochlorinated hydrocarbon solvent where the concentration of said resin is not lower than that of said gelatin particles and not more than 30%by weight of said carrier liquid to form an image of gelatin;

(iii) fixing the developed gelatin image by immersing the layer in at least one of an isoparafiinic or fluorochlorinated hydrocarbon solvent;

(iv) bringing the fixed gelatin image into contact with an aqueous solution of a water soluble dye thereby imbibing the dye into said fixed gelatin image; and

(v) placing a dye-receiving sheet comprising a surface coating which easily absorbs water-soluble dyes so that the dyed gelatin image contacts said surface layer, whereby the dye in the gelatin image is transferred onto the sheet, forming a final dye print.

References Cited UNITED STATES PATENTS 2,227,691 10/ 1942 Carlson 96-1 3,003,891 10/1961 Albrecht ll717.5 3,060,052 10/1962 Martin 1l7-l7.5 3,357,830 12/1962 Bixby 96-12 GEORGE F. LESMES, Primary Examiner I. P. BRAMMER, Assistant Examiner US. Cl. X.R.

1l737 LE; 25262.1; 96l LY