Patent Publication Number: US-3878120-A

Title: Process for preparing liquid developer for electrostatic images

Description:
Nagashima et al.  
 Filed: Sept. 17, 1973 Appl. No.: 397,804  
 Related US. Application Data Continuation of Ser. No. 144,285, May 17, 1971, which is a continuation of Ser. No. 864,647, Jan. 28, 1968, abandoned.  
 Foreign Application Priority Data Nov. 28, 1966 Japan 41-77879 Apr. 23, 1967 Japan 42-25704 US. Cl. 252/62.1 L; 252/62.l Int. Cl. G03g 9/00 Field of Search 252/621 L References Cited UNITED STATES PATENTS 6/1964 York 252/621 Apr. 15, 1975 3,241,957 3/1966 Fauser et al. 252/621 3,241,998 3/1966 Oliphant 252/621 3,251,687 5/1966 Fohl et al 252/621 3,256,197 6/1966 Fauser et al. 252/621 3,293,183 12/1966 Matkan et al. 252/621 L 3,334,047 8/1967 Matkan 252/621 3,576,744 4/1971 Sharrock et al.... 252/621 L 3,682,825 8/1972 Tamai et al. 252/621 L Primary ExaminerMaynard R. Wilbur Assistant Examiner-T. M. Blum Attorney, Agent, or Firm-Fitzpatrick, Cella, Harper &amp; Scinto developer material, and comprises the steps of adding such solvating agent to at least one of the carrier liquid and the developer material, and mixing both of them to disperse-suspend fine particles of the developer material in the carrier liquid.  
 4 Claims, No Drawings PROCESS FOR PREPARING LIQUID DEVELOPER FOR ELECTROSTATIC IMAGES This is a continuation, of application Ser. No. 144,285, filed May 17, 1971, which in turn, is a continuation of Ser. No. 684,647, filed Jan. 28, 1968 now abandoned.  
  This invention relates to a new process for preparing liquid developer for electrostatic images in electrophotography, electrorecording and electrostatic printing, etc.  
  As the conventional process for preparing liquid developer for electrostatic images, such a process that controlling agent or fixing agent and pigment are dispersed, and the pigment is crushed to a required granularity, and then the resulting paste is dispersed into a carrier liquid, and the liquid developer is obtained, has been known, but in order to produce a liquid developer of excellent resolving power in accordance with said conventional method, the pigment of the secondary coagulation must be dissociated into the constituting unit size, and the surface thereof must be uniformly coated with a controlling agent or fixing agent, and therefore a large energy is required, and therefore the pigment must be passed through a rolling mill of large type several times, or an expensive dispersing machine such as an ultrasonic dispersing machine must be employed, and the pigment must be subjected to crush-dispersing operation by using a ball mill for a long time, and high cost is required for the equipment or long time is required for the operations, and the conventional method is remarkably inconvenient from an industrial point of view.  
  On the other hand, there has been known a liquid developer obtained by dispersing a liquid into another liquid, but when the two liquids cannot be mutually dissolved, the two liquids are vigorously stirred by using a homogenizer or the like to prepare emulsion liquid developer. In general, itis difficult to produce a liquid developer. ln general, it is difficult to produce a liquid developer of excellent resolution and stability only by using mechanical stirring operation.  
  Thus, according to the conventional processes, special equipment are required for carrying out the dispersing operation, and moreover, highly skilled technique and considerably longer time are required to attain excellent dispersion.  
  ln addition, when the liquid-liquid developer of emulsion type is employed, the durability of the produced emulsion is short according to the conventional method in which developer phase liquid and carrier are mechanically and vigorously stirred, and the durability is 2 or 3 days at most, and therefore the emulsion is decomposed before the emulsion developer is handed over to a user even if emulsion developer is prepared in a factory, and it does not work as a developer.  
  It was also proposed that an emulsuion should be prepared by vigorously stirring right before it is applied and used immediately. However, it is not possible to insert a high speed homogenizer or a ultrasonic disperser in a business copier in view of the cost of production, operation ability, or the form.  
  From these reasons, the emulsion developer is not at all practically used inspite of the fact that the emulsion developer posses excellent electric charging property or fixing property.  
  This invention is a novel method for producing a liquid developer having more excellent resolution and faithfulness of development by simpler method within shorter time than the liquid developers obtained in accordance with the conventional methods.  
  Thus, oneof the objects of this invention is to provide a new method for producing liquid developer of excellent dispersion without using no special equipment at all.  
  Another object of this invention is to provide a new method for producing the liquid developer of excellent dispersion without requiring any skill at all.  
  Another object of this invention is to provide a new method for producing excellent finely dispersed liquid developer only in a short time, furthermore in a amount.  
  Another object of this invention is to provide a new method for practically producing emulsion liquid developer of extremely fine particle in a moment within a duplicator.  
  Another object of this invention is to provide a new method for producing the liquid developer having improved reproductivity concentration.  
  The feature of this invention resides in the employment of solvating agent having solubility into both carrier liquid and developer material in order to attain these objects of this invention.  
  Other objects and features of this invention will be clarified from the following detailed explanation of this invention.  
  This invention is a method for preparing liquid developer for electrostatic image which is characterized in that in a liquid developer for electrostatic image composed of carrier liquid and developer material which are not mutually dissolved at a room temperature or at a developing temperature, a solvating agent which can be dissolved into both the carrier liquid and developer material, is added to at least either one of the carrier liquid and developer material, and thereafter the two are mixed, and the fine particles of developer material are dispersed into the carrier liquid and suspending the same.  
  The developer material of this invention convertes electrostatic image into a visible image, and is colorless or colored solid or liquid, and is not dissolved into carrier liquid at a room temperature or developing temperature, but can be well dissolved into the solvating agents. Representives of the developer materials are, for example, natural materials such as rosin, copal, gilsonite, bitumen, pitch, pine-tar, wax, rubber, gelatine,  
 &#39; cellulose derivatives; the synthetic resins such as vinyl resin, acryl resin, styrol resin, alkyd resin, polyester resin, xylene resin, epoxy resin, urethane resin, amino resin, etc.; liquid solvents such as water, alcohol, ester, ketone, ether, hydrocarbon, alcohol ester, ketone alcohol, ether alcohol, ketone ether, ketone ester, ester ether, etc,; aliphatic acids such as oleic acid, linoleic acid, isostearic acid, napthenic acid, etc,; oils such as soy-bean oil, linseed oil, tung oil, etc.  
  Generally, one or more than one kind of the above given substances can be used. When a developing material is composed of more than one kind of the substances, not only solid and solid, or liquid and liquid substances can be used, but also the combination of solid and liquid can be used. Moreover, a developer material may contain, if desired, one or more of various kinds of pigments or dyes. As the examples of the pigments or dyes, besides the conventional pigments or dyes, recently developed polymer bonded coloring matters or macromolecular coloring matters can also be used. Said polymer bonded coloring matters and macromolecular coloring matters may become developer materials by themselves. Polymer bonded coloring matters are described in detail in the Japanese Patent No. 429,096 (the Japanese Patent application Publication No. 3980/1964), the Japanese Patent application Publication No. 14433/1966, and the Japanese Patent application Publication No. 14434/1966, and also in lnsatsu Jyoho, August Issue, pages 12 to 21 (1966). This is a single material obtained by chemically bonding pigment or dye to a polymer, and has the properties of coloring matter and the properties ofa polymer. The Japanese Patent application No. 36219/1966 discloses in detail the application of such polymer bonded coloring matter as a toner. Said macromolecular coloring matters are the single materials obtianed by chemically bonding coloring matter and non-polymer electric charge controlling agent and are described in the Japanese Patent application No. 57371/1967.  
  The carrier liquids of this invention are the substances having comparatively high electric resistance of such a degree that the conventional electrostatic images are not destroyed, i.e., petroleum solvents such as ligroine, naphtha, kerosene; hydrocarbons such as npentane, n-heptane, cyclohexane, etc.; oils such as dimethyl polysiloxane, diphenyl pentachloride, polybutene, etc.; chlorinated fluorinated hydrocarbons known as Fleon, Daiflon&#34; or such like trade names.  
  The solvating agent of this invention is a liquid or solid which can be dissolved into both developer materials and carrier liquids. One or more materials similar to the developer materials are selected as the solvating agent taking the relation of developing materials and carrier liquids into consideration. As the solvating agents of this invention, those which can be substantially more easily dissolved into carrier liquids than the developing materials, are preferable, and any materials having such properties as above can be used regardless of solid or liquid.  
  The representative examples of the solvating agents are the natural materials such as copal, rosin, hydrogenated rosin, hydrogenated rosin ester, various kinds of asphalt products, waxes, rubber, cellulose derivatives, etc,; solid or liquid resins such as vinyl type resin, acryl resin, styrol resin, alkyd resin, polyester resin, xylene resin, epoxy resin, urethane resin, silicon resin, amino resin, etc,; aliphatic acids such as caproic acid, caprylic acid, myristic acid, oleic acid, linolic acid, isostearic acid, stearic acid, etc,; and oils such as soybean oil, linseed oil, tug oil, etc.  
  In addition to the oleoresinous materials as mentioned above, organic solvents such as alcohol, ester, ketone, ether, hydrocarbon, ether alcohol, etc, are particularly effective.  
  There are various kinds of methods for using the solvating agents in this invention. These methods are generally classified into the following groups.  
  1. Method according to which solvating agent and developer materials are melt-mixed in advance, and the mixture is added into a carrier liquid.  
  2. Method according to which a part of a solvating agent is dissolved into a carrier liquid in advance, and then the mixture solution of the solvating agent and the developer material are mixed along with the above prepared solution.  
  3. Method according to which a solvating agent is dissolved into carrier liquid in advance and a developer material is added thereto.  
  The following are the typical examples of the methods.  
  The most generally employed method is that a liquid form solvating agent such as an organic solvent is used. According to this method, a developer material is first dissolved into the solvating agent, and then the resulting solution is added to a carrier liquid or a carrier liquid in which a part of the solvating agent is dissolved in advance to obtain a liquid developer. When the solvating agent is a thermoplastic material such as wax which is solid at a room temperature, but easily becomes liquid by heating, the developer material is first dissolved into the thermoplastic solvating agent by heating, and then it is added to a carrier liquid or a carrier liquid in which a part of the solvating agent is previously dissolved, or the developer material is crushed after cooling the same to solidify and then it is added into a carrier liquid or a carrier liquid in which a part of the solvating agent is dissovled. When a solid such as petroleum resin, which can be easily dissolved in a carrier liquid, is used as a solvating agent, the developer material is first dissolved into the petroleum resin by heating, and is directly added to a carrier liquid, or into a carrier liquid in which a part of the solvating agent is dissolved in advance, or after cool-solidifying the same, it is crushed, and then the obtained crushed matter is added into a carrier liquid or into the carrier liquid in which a part of the solvating agent is dissolved. When the mixture ofa solid and a liquid, or the mixture ofa liquid and a liquid is used as a solvating agent, first the respective components are uniformly mixed to form a liquid form substance, and then a liquid developer is prepared in accordance with the same procedure as in the case where an organic solvent is used as a solvating agent.  
  When the mixture of a solid and a solid is used as a solvating agent, a liquid developer is prepared by the same procedure as in the case that said petroleum resin is used as a solvating agent.  
  Thus, when a solvating agent is prepared from the mixture of the two or more than two kinds of substances, as is described hereinafter, there is an advantage that the granularity, stability, fixation of the ob-- tained developer can be more delicately controlled than when the solvating agent is composed of a singlesolvating agent as is described hereinafter. The factors which affects the properties of the final developer in carrying out this invention are, for example, the amount of the solvating agent against a developer material, the quantitative relation between the solvating agent, the carrier liquid and th developer materials, the method for adding the solvating solution of the developer material to the carrier liquid, the speed of the addition, stirring operation, or heating etc.  
  These factors are preferably determined by experiment by taking into consideration the various properties required for the produced liquid developer, and the combination of the materials to be used. The amount of the solvating agent against the developer material and carrier liquid is determined by the solubility of the solvating agent into the two. Namely, a solvating agent of high solubility presents sufficient effect with a little amount thereof and a solvating agent of less solubility must be used in larger amount. The solvating agent may be used in large amount to such an extent that it does not dissolve the surface material on which electrostatic image is supported and the electrostaic image is not be destroyed.  
  In selecting solvating agents, the amount of the solvating agent must be carefully selected so that the electric resistivity after the solvating agent has been dissolved into the carrier liquid is so high that said resistivity does not destroy the electrostatic image, particularly when a solvating agent of lower electric resisitivity is used. However, when the solvating agent is removed later, such consideration is not necessary.  
  Such method of removing the solvating agent later is particularly useful when a solvating agent is a material of low boiling point or high volatility having low electric resisitivity.  
  Examples of the solvating agents are methyl alcohol, ethyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, ethyl ether, methyl acetate, ethyl acetate, chloroform, etc. As the method for removing these, naturally evaporating method, thermally evaporating method, vacuum evaporating method, bubbling method, or such like conventional methods may be employed.  
  When these methods are employed, the effect of the solvating agent given to the developer liquid can be decreased or eliminated in the resulting developer since a part or whole of the solvating agent is removed.  
  The present inventors have found in the research of the method for removing the solvating agents the fact that when these solvating agent removing methodsare carried out, the density of the developed image can be remarkably improved as compared with the case where said methods are not carried out, and also the fact that this is a phenomenon common to both the case when the solvating agent is a material of low resistivity and the case when it is a material of high resistivity. As a result of the microscopic investigation of the form and the size of the particle of the produced developer, it has been found that the improvement of the image density is due to the fact that the particles of the developer are granulated and the size of particles can be stabilized when the solvating agent is removed.  
  The details of the mechanism are not yet clear, but this phenomenon is an additional effect of the method for removing the solvating agent. As the mechanism which enables the method of this invention to attain the dispersion of fine particles more simply and easily than the conventional mechanical dispersing method, the inventors consider as follows, but the following observation of the inventors do never restrict the effect of this invention. Namely, a developer material is uniformly dissolved, in advance, by means of a solvating agent, and is dissolved into such an extremely finess such as molecule or micell or the like, and then when marged with a carrier liquid, the solvating agent is dissolved into the carrier liquid, and therefore it is dispersed into the carrier liquid from the developer material. As a result, the developer material is finely split, and the density of the developer material is increased micro-locally, and at last it is supersaturated, and the separation gradually starts. The size of the separated developer material is of such a remarkably minute sizes as in the case of the crystallization.  
  An effective means for size-controlling, is, for example, employment of a solvating agent composed of two or more than two components. Namely, when two or more than two components are used, by slightly changing the solubility of the respective components of the solvating agent in the developer material and the carrier liquid, two or three stage disperse separating effect can be resulted. For example, when xylol and hydrogenated rosin ester are used as the solvating agent, and the liquid form xylene-formaldehyde condensation product whose average molecular weight is 400, is used as the developer material, and isoparaffin petroleum solvent is used as the carrier liquid, xylene (the solubility parameter thereof being 8.8) can be easily dissolved into isoparaffin (the solubility parameter thereof being 7.1). The hydrogenated rosin ester (the solubility parameter thereof being 9.4) has somewhat poorer solubility than xylene. On the other hand, xylene has almost the same solubility as the hydrogenated rosin ester to xylene-formaldehyde condensation product (the solubility parameter thereof being 8.8 to 9.5).  
  Xylene and hydrogenated rosin ester are mutually dissolved first, and the resulting solution is added as the solvating agent to a xylene-formaldehyde condensation product. The whole solution is made into a uniform solution, and then the resulting mixture solution is slowly added to isoparaffm xylene is first dissolved into isoparaffin quickly from the mixture of xylene, hydrogenated rosin ester and xylene-formaldehyde condensation product. The solvating agent solution is split by the shock of the quick dissolution of xylene into isoparaffin, and turned into small spherical particles. The dissolving process of xylene is practically effected in two or three steps, and at every step, spherical particles containing less amount of xylene are split. Finally they are turned into small spherical particles of hydrogenated rosin ester and xylene-formaldehyde condensation product having poorer solubility.  
  Next, hydrogenated rosin ester begins to dissolve into isoparaffin. And the small spherical particles are further split, and every time they are split, the small spherical particles containing less amount of hydrogenated rosin ester are produced, and finally remarkably fine emulsion composed of xylene-formaldehyde condensation product alone can be obtained. All the solvating agent is dissolve-mixed into isoparaffin.  
  The above are the explanations about the mechanism of this invention, and the above explanations will serve to understand this invention more clearly, and they do not restrict the effects and the mechanism of this invention.  
  On the other hand, according to the conventional mechanical dispersing method in which first mechanical external force is given to coarse particles and said coarse particles are crushed into as fine particles as possible, and in order to produce fine particles, energy overcoming the surface tension and the bonding force of the surface of the substance is required.  
  The value of the energy is surprisingly large and this is well known to those skilled in the art. In other words, the conventional methods are mechanical or physical dispersing methods while the method of this invention is a chemically dispersing method in which the solubility of chemicals are skillfully utilized.  
  In the method of this invention, when the combination and the-quantitative relation of developer material, solvating agent and carrier liquid are carefully selected,  
 it is possible to carry out effectively the method of this invention in such a manner that solid can be swollen with solvating agent when solid is separated, when it is used as a liquid developer, fixation of the image can be further improved. Further, when it is also a solvating agent of the resinous portion of the photoconductive layer, better fixation can be obtained. A number of such like modifications and variations can be effected.  
  According to the method of this invention, liquid developer in which extremely fine dispersed particles are suspended by delicate control of solubility can be easily produced. Therefore, such a vigorous mechanical crushing or stirring operation is not required as in the conventional methods, and any special equipment for producing the same is not required. Further, the time required for the production is short, and any special skill is not necessary. In addition, the developer liquid having more excellent resolution than that of the conventional methods is obtained and therefore the remarkable practical effects are attained by this inven tion.  
  The scope of this invention apparently covers such auxiliary means for effecting this invention as operations for heating or cooling the liquids or mechanical stirring operation.  
  The details of this invention are further explained in accordance with the following examples.  
 EXAMPLE 1 10 g. ofNikanol LL&#34; (trade mark) which is lOO percent liquid xylene resin of low viscosity was dissolved into l g. of benzole, and l g. of macromolecular coloring matter composed of tetra (4) amino copper phthalocyanine and acrylic acid ethyl was added thereto while stirring the same, and the whole mixture was made into a uniform blue solution, and then 500 g. of petroleum type hydrocarbon lsoper&#34; (trade mark) was quickly added thereto and a blue emulsion developer liquid was obtained. The negative electrostatic image on a zinc oxide coated electrophotographic paper was developed by using the above prepared developer liquid, and a clear positive blue image was obtained. The halftone reproductivity of the obtained image was excellent, and fog was little, and the image was perfectly fixed.  
  Benzole was dissolved into either of xylene resin as the developer material, coloring matter, and lsoper as the carrier liquid, and it worked as the solvating agent of this invention. Xylene resin was not dissolved into lsoper at a room temperature.  
  As a control, an emulsion developer liquid was prepared by using the same combination as above except for the point that benzole was not added, and the granularity of the emulsion particle was large, and only such a solution which was easily separated into two layers was obtained, and the quality of the developed image was remarkably poor, and no practicability was observed.  
 EXAMPLE 2 g. of polyester resin Rigolac 2004 (trade mark) -was used as the developer material, and this was added a uniform transparent liquid, and then it was added to 500 g. of kerosene, and a milk colored stable fine emulsion was obtained. An electrostatic image on a zinc oxide coated electrophotographic paper was developed, and the positive polyester resin image was obtained.  
  The obtained image was used as the master for an offset printing machine, and an excellent result was obtained.  
  In this example, polyester resin was not soluble in kerosene. Cyclohexanone can be dissolved into both polyester resin and kerosene.  
 EXAMPLE 3 5 g. of bitumen was dissolved into 20 g. of xylol, and the obtained brown colored solution was added into 500 g. of lsoper, and a developer liquid wherein the fine particles of bitumen were disperse-suspended in lsoper was prepared.  
  Thus obtained developer developed the negative electrostatic image into the positive brown image. On the other hand, when bitumen was directly mixed into Isoper, only the dispersed suspended matter of coarse particles was obtained inspite of 24 hours crushing operation by using a ball mill, and only an image of poor resolution was obtained. Xylol is a solvating agent which can be dissolved into both bitumen and lsoper&#34;, and the bitumen of the developer material was not soluble in the carrier liquid lsoper&#34;.  
 EXAMPLE 4 5 g. of polybutylene rubber was dissolved into 500 g. of the carrier liquid Isoper&#34;.  
  On the other hand, 5 g. of polyester resin was dissolved into 20 g. of cyclohexanone and the obtained solution was mixed with the above prepared carrier liquid, and an emulsion developer liquid of polyester resin was prepared.  
 Cyclohexanone and polybutylene rubber are solvating agents which can be mutually dissolved in polyester resin and lsoper.  
  Polybutylene rubber is effective for increasing the viscosity of the carrier liquid and for stabilizing the dispersion thereof.  
 EXAMPLE 5 500 g. of the carrier liquid lsoper and g. of xylene were dissolved and 15 g. of liquid xylene resin was added thereto. The resulting mixture was made into an emulsion by stirring the mixture. The xylene is a solvat-.  
 ing agent which can be dissolved in both lsoper and xylene resin.  
 EXAMPLE 6 Sudan Black&#34; dye (trade mark) was added to 3 g. of liquid form xylene resin and 0.4 g. of linseed oil was added thereto, and the whole mixture was heated to about C.  
  On the other hand, 0.2 g. of linseed oil was dissolved into g. of carrier liquid kerosene, and the solution was quietly dissolved into the above hot solution, and as a result the liquid developer liquid composed of black spherical particles was obtained.  
  Thus obtained developer liquid changed the negative electrostatic image into a positive black image.  
  The linseed oil is a solvating agent which can be dissolved into both xylene resin, kerosene and dye-stuff.  
 EXAMPLE 7 2 g. of macromolecular pigment obtained by graftcopolymerizing carbon black along with the copolymer of xylene resin and styrol resin at the ratio of 4:6, was dissolved into g. of trichloroethylene, and the obtained solution was added to 200 g. of ligroine, and the mixture was stir-dispersed, and then the obtained dispersed solution was heated at 80C to 90C to distil out trichloroethylene, and the liquid developer composed of said macromolecular pigment finely dispersed into ligroine, was obtained. The dispersed particles are remarkably fine, and an image of high resolution was obtained.  
  Trichloroethylene is a solvating agent which can dissolve both developer material macromolecular pigment and carrier liquid ligroine, but if trichloroethylene is excessively present in the carrier liquid, the resin adhered on the electrophotographic paper is dissolved, and the developing property becomes poor. Such a drawback as this can be removed in the developer obtained by distilling out trichloroethylene.  
 EXAMPLE 8 in Example 7, trichloroethylene was removed under a reduced pressure for about one hour in a desiccator sucked by an aspirator in place of removing trichloroethylene by evaporation, and thus obtained developer liquid presented the same excellent properties as above.  
 EXAMPLE 9 l g. of Nigrosine dye was dissolved into 10 g. of stearic acid by heating, and a uniform dark bluish purple solution was prepared at 90C, and the obtained solution was added little by little into one litre of lsoper while slowly stirring the mixture, and thus liquid developer wherein fine Nigrosine was dispersed, was obtained.  
 EXAMPLE 10 The uniform dark bluish solution obtained in Example 9 was cooled to a room temperature and allowed to stand to form black solid. The solid thus obtained was finely crushed by using a crusher, and then the ob tained powder was added into one litre of lsoper containing 100 g. of about 50C xylene, and a finely dispersed liquid developer was obtained. The negative electrostatic images on the zinc oxide coated electrophotographic papers were developed by using the liquid developers obtained in Example 9 and Example 10, and the liquid developer obtained by compulsively dispersing Nigrosine into lsoper&#34; merely by using a homogenizer, respectively. When the developer containing Nigrosine alone is used, such a crude image of no fixation was obtained, while images of high resolution and fixation were obtained in case of the developers of Example 9 and 10.  
 EXAMPLE 1 l 0.5 g. of non-polymer macromolecular coloring matter obtained by the chemical reaction of Nigrosine dye with oleic acid was dissolved into 50 g. of benzole, and the obtained solution was slowly added into one litre of lsoper and by finely dispersing the same, a finely dispersed liquid developer was obtained.  
  When a zinc oxide coated electrophotographic paper was developed with thus obtained developer, a developed image of poor image density and quality was obtained although the resolution thereof was very excellent. Thus, the obtained developer liquid was concentrated under reduced pressure by heating, and after removing benzole, it was used as the developer liquid, and an image of high resolution and excellent image density was obtained.  
  As a method for removing benzole, for example, fine air bubbles are pressed into the liquid, or the liquid is charged into a vessel of large opening area and air is blown into the liquid.  
 EXAMPLE 12 Victoria Blue dye was used as a developer material, and l g. thereof was uniformly dissolved into 50 g. of ethyl alcohol, and then 200 g. of perchloroethylene was added thereto. The blue solution thus obtained was added to one litre of kerosene to give an extremely fine liquid developer. Thus obtained developer looked a transparent solution. A negative electrostatic image on a zinc oxide electrophotographic paper was developed into a positive blue image by using said developer. When the quantitative relation of ethyl alcohol and perchloroethylene was changed, developers of various granularities were obtained. In this case, the developed images were perfectly fixed images, and Victoria Blue dye was found to be solvated by the solvating agents, ethyl alcohol and perchloroethylene.  
  On the other hand, the developer liquid obtained by compulsively dispersing Victoria Blue dye into kerosene by using a colloid-mill, presented quick precipitation, and proved to be not practical, and at the same time the resolution was poor, and only unfixed images could be obtained.  
 EXAMPLE l3 1 g. of polymer bonded coloring matter obtained from tetra-(4)-amino copper phthalocyanine and acryl type monomer, was used as the developer material, and 3 g. of piccopale resin and 3 g. of carnauba wax were added thereto, and the mixture was heat-melted at about C with stirring and then cooled to obtain blue solid resin. The solid resin thus obtained was finely pulverized and 2 g. of thus obtained powder was added into one litre of kerosene containing 10 vol. percent of Solvesso 150&#34;, and the whole mixture was stirred, and the liquid developer of fine granularity was obtained.  
 EXAMPLE 14 The solution composed of 10 g. ofliquid form xyleneformaldehyde resin whose average molecular weight is 350, Nikanol LL, and 30 g. of toluol was slowly added to 1,000 cc. of isoparaffin type petroleum solvent containing 5 g. of methyl ester of hydrogenated rosin, and the mixture was slowly stirred, and a uniform fine emulsion liquid developer was prepared.  
  Thus obtained developer was retained for 5 days, and the emulsified state still remained, but when methyl ester of hydrogenated rosin was not added thereto, it was separated into two layers by standing overnight.  
  A commercially available zinc oxide photosensitive paper for liquid developer was developed by the above prepared developer, and a positive image was obtained. The zinc oxide photosensitive layer was hydrophilized with the etching solution of off-set printing, and thus prepared master was used for printing on an business off-set machine, and excellent printings were obtained.  
 EXAMPLE 15 Xylene resin was dyed with 0.1 g. of Oil Black dye in advance in Example 1, and the negative electrostatic image was developed as the positive image of clear black color. The obtained image was proved to be fast fixed when subjected to strong abrasion.  
 EXAMPLE l6 10 g. of liquid form xylene-formaldehyde resin whose average molecular weight is 400, 0.1 g. of Oil Blue dye, and 8 g. of rosin containing 30 percent of abietic acid. were sufficiently dissolved into 20 g. of trichloroethylene and the obtained solution was slowly added into 1000 ml. of kerosene, to form an emulsion developer negative electrostatic image were developed into a blue fixed image by using the emulsion developer.  
  Thus obtained developer was allowed to stand for two weeks, but only a little amount of precipitation was obtained.  
 EXAMPLE l7 5 g. of Epikote 815, which is a liquid form epoxy resin having percent of non-volatile portion, the average molecular weight thereof being 350, the viscosity thereof being from 7 to l l poise, g. of hydrogenated rosin, 0.05 g. of Sudan Black dye, and g. of xylol were mixed to form a uniform black solution. 1,000 cc. of isoparaffin type petroleum solvent containing 10 g. of methyl ester of hydrogenated rosin, was quickly added thereto to prepare an emulsion developer.  
  Thus obtained developer was charged into a commercial liquid developing electronic duplicator to carry out a continuous copying and copies of excellent quality having sharp image could be obtained.  
  The obtained image was perfectly fixed, and the reproducibility of half-tone portions was especially excellent.  
  Thus obtained developer was used for two days, but only slight precipitation of the developer was observed, and on the other hand, when the emulsion developer containing no hydrogenated rosin and no methyl ester of hydrogenated rosin, was used for the development and the obtained image was remarkably deteriorated in about three hours. The developer was examined and it was found that the liquid was separated into two layers.  
 What is claimed is:  
  l. A process for preparing an emulsion liquid developer for electrostatic images consisting essentially of a carrier liquid having a high electrical resistance such that the conventional electrostatic images are not destroyed and a developer phase liquid immiscible with said carrier liquid which comprises adding a solvating agent which is soluble in both the carrier liquid and the developer phase liquid to the carrier liquid and subsequently adding the developer phase liquid to the carrier liquid and solvating agent to disperse the developer phase liquid and to provide an emulsion liquid developer; wherein the carrier liquid is selected from the group consisting of petroleum solvents, aliphatic hydrocarbons, dimethyl polysiloxane and chlorinated fluorinated hydrocarbons; the developer phase liquid is a liquid resin selected from the group consisting of xylene-formaldehyde resin, polyester resin and epoxy resin; and the solvating agent is selected from the group consisting of aromatic hydrocarbons, aliphatic acids having 8 to 18 carbon atoms, cyclohexanone, rosin, hydrogenated rosin and hydrogenated rosin esters and is from 0.2 to 4 times the weight of the developer phase liquid.  
  2. A process for preparing an emulsion liquid developer for electrostatic images consisting essentially of a carrier liquid having a high electrical resistance such that the conventional electrostatic images are not destroyed and a developer phase liquid immiscible with said carrier liquid which comprises adding a solvating agent which is soluble in both the carrier liquid and the developer phase liquid to at least one of the carrier liquid and the developer phase liquid, and subsequently adding the developer phase liquid to the carrier liquid to disperse the developer phase liquid and to form a mixture, and thereafter, removing at least part of the solvating agent from the mixture by reducing pressure on the mixture or heating the mixture, to provide an emulsion liquid developer; wherein the carrier liquid is selected from the group consisting of petroleum solvents, aliphatic hydrocarbons, dimethyl polysiloxane and chlorinated fluorinated hydrocarbons; the developer phase liquid is a liquid resin selected from the group consisting of xylene-formaldehyde resin, polyester resin and epoxy resin; and the solvating agent is selected from the group consisting of aromatic hydrocarbons, aliphatic acids having 8 to 18 carbon atoms, cyclohexanone, rosin, hydrogenated rosin and hydrogenated rosin esters and is from 0.2 to 4 times the weight of the developer phase liquid.  
  3. A process for preparing an emulsion liquid developer for electrostatic images consisting essentially of a carrier liquid having a high electrical resistance such that the conventional electrostatic images are not destroyed and a developer phase liquid immiscible with said carrier liquid&#39;which comprises adding a solvating agent which is soluble in both the carrier liquid and the developer phase liquid to at least one of the carrier liquid and the developer phase liquid, and subsequently adding the developer phase liquid to the carrier liquid to disperse the developer phase liquid and to form a mixture, and thereafter, volatizing at least part of the solvating agent from said mixture to provide an emulsion liquid developer; wherein the carrier liquid is selected from the group consisting of petroleum solvents, aliphatic hydrocarbons, dimethyl polysiloxane and chlorinated fluorinated hydrocarbons; the developer phase liquid is a liquid re&#39;sin selected from the groupconsisting of xylene-formaldehyde resin, polyester resin and epoxy resin; and the solvating agent is selected from the group consisting of aromatic hydrocarbons, aliphatic acids having 8 to 18 carbon atoms; cyclohexanone, rosin, hydrogenated rosin and hydrogenated rosin esters and is from 0.2 to 4 times the weight of the developer phase liquid. 7  
 4. An emulsion liquid developer for electrophotography consisting essentially of:  
 a. a carrier liquid having a high electrical resistance such that conventional electrostatic images are not destroyed selected from the group consisting of petroleum solvents, aliphatic hydrocarbons, dimethyl polysiloxane and chlorinated, fluorinated hydrocarbons and mixtures thereof;  
 b. a liquid resin developer&#39;phase liquid immiscible with said carrier liquid and selected from the group a solvating agent soluble in both the carrier liquid 13 14 consisting of liquid xylene-formaldehyde resin, liqhydrogenated rosin, hydrogenated rosin esters, co- Polyester reslm liquid p y resim liquid acryl pal, soy bean oil, linseed oil, methyl alcohol, ethyl resin, liquid styrol resin and liquid alkyd resin and alcohol, isopropyl alcohol, acetone, methyl ethyl mixtures thereof; and  
 ketone, ethyl ether, methyl acetate, ethyl acetate,  
 and the developer phase liquid and selected from &#39;l&#34; and m.lxu lres thereof;  
 the group consisting of aromatic hydrocarbons said developer phase llqllld being chemically dispersed chloroethylene, perchloroethylene, aliphatic acids in fine emulsified Particles in Said carrier q having 8 to 18 carbon atoms, cyclohexanone, rosin,