JPH077216B2 - Liquid developer for electrophotography - Google Patents

Description

The present invention relates to a developer used for liquid development for converting an electrostatic latent image into a visible image in electrophotography or the like.

[Conventional technology]

Generally, a liquid developer for electrophotography includes a coloring agent such as carbon black or phthalocyanine blue, and a coating agent or a carrier that is adsorbed on or coated with the coloring agent to promote charge control or dispersion of toner particles and further, fixability of an image after development. A dispersant that dissolves or swells in a liquid and imparts dispersion stability to toner particles,
It comprises a charge control agent for controlling the charge amount of toner particles and a carrier liquid having high electric resistance (10 ⁹ to 10 ¹⁵ Ω · cm). As a method for producing such a liquid developer, there are generally the following methods. First, a colorant and a resin as a coating material are mixed and melt-kneaded at a softening temperature of the coating material or higher using a kneader such as a three-roll mill to obtain a mixture. Alternatively, the colorant and the coating agent are dispersed and kneaded in the hydrophilic solvent by a dispersing machine such as a ball mill or an attritor, and the kneaded product is dried or added to the non-solvent to obtain a mixture. The mixture thus obtained is dry pulverized by various pulverizers, and then wet-dispersed with a dispersant by a disperser such as a ball mill, a paint shaker or a sand mill to obtain a toner concentrated liquid. A charge control agent and a carrier liquid are added to this toner concentrated liquid to obtain a liquid developer for electrophotography. The important problems in such a liquid developer are, firstly, that the particles dispersed in the carrier liquid are uniformly charged and stably held, and the dispersion stability of the particles,
Second is the fixability and sharpness of the image generated by development.

However, the conventional liquid developers of this type have serious drawbacks in terms of stability of charged particles, dispersion stability, fixing property, and the like. That is, the developer immediately after the particles are dispersed is in a very good dispersed state and gives a clear image, but the resin coated with the colorant is desorbed with continued use or with the passage of time, causing aggregation of the particles and sedimentation. However, there is a drawback in that the amount of charge is increased and the amount of charge is changed to deteriorate the image forming property.
Further, in most of the liquid developers obtained in this way, tail tails on the downstream side of the formed image (downstream side in the direction in which the developer flows), that is, so-called image deletion occurs. As a result, the finished image becomes extremely unclear, and such a developer cannot be used.

Desorption of the coating resin from the colorant is an essential problem in the developer prepared in this way, and cannot be solved by additives such as charge control agents. The image flow can be reduced to some extent by adjusting the developing conditions such as decreasing the flow rate of the developer, but this is not necessarily preferable because it causes an increase in developing time and a decrease in image density.
Therefore, it has been desired to solve the problem by the characteristics of the toner particles.

Furthermore, in order to improve the color reproducibility of a black-and-white copy image or a color copy image, the blackness of the black pigment has a great influence. As the black pigment, carbon black, activated carbon, nigrosine pigment, aniline black pigment, etc. are used, but the color tone of the pigment is originally reddish black or a dark brownish black when the image density becomes low. There was a tendency that the color tone of the black color was deteriorated.

In recent years, in order to solve the above drawbacks, Japanese Examined Patent Publication Nos. 40-40347 and 5
1-9614, 51-28233, 51-28234, etc., the use of a salt formed by the reaction of a nigrosine pigment or an aniline black pigment with a saturated or unsaturated fatty acid, and JP-B-47 -38824, 48-24901, 49-2615
No. 0, No. 51-40806, No. 51-47046, etc., the use of a derivative formed by the reaction of a nigrosine pigment or an aniline black pigment and a carboxylic acid chloride having an alkyl or alkenyl group, As described in JP-B-51-1981, it has been proposed to use a dihydroabietic acid modified product of an azine dye such as nigrosine and spirit black in combination with a methacrylic acid ester dispersant resin. However, among these pigments, the carboxylic acid amidated nigrosines have improved black color tone, but other than that, the reddish black color does not change and there is a problem in reproducing the black color tone. On the other hand, a known developer has excellent dispersibility at the time of preparation and has clear image forming ability, but still has problems in satisfying the dispersibility at storage, image quality, and charge stability (temporal stability). In particular, there is a drawback that the stability with time is insufficient and the charge characteristics gradually change during long-term storage to lower the image density, cause image deletion, and cause fog.

[Problems to be solved by the invention]

The present invention solves the conventional drawbacks and provides a novel liquid developer which is extremely practical. In particular, it is an object of the present invention to provide a black electrophotographic liquid developer capable of forming a clear image having excellent temporal stability and fixability.

Another object of the present invention is to provide a black electrophotographic liquid developer having excellent dispersion stability.

Still another object of the present invention is to provide a black electrophotographic liquid developer which retains a stable positive charge.

[Means for solving problems]

As a result of intensive studies by the present inventors, a highly insulating carrier liquid containing a sulfonamidated compound obtained by a reaction of a nigrosine or aniline black pigment and a compound represented by the following general formula (I) as a colorant component It was found that a liquid developer for electrophotography having a black plus charge, which is excellent in storage stability during storage, dispersion stability, image fixability, and image clarity, can be obtained by dispersing it in the medium.

During R-SO ₂ -X (I) formula, R represents a hydrocarbon group, preferably having 1 to 22 carbon atoms,
A linear or branched alkyl group which may be substituted (eg, methyl group, ethyl group, propyl group, butyl group, heptyl group, hexyl group, octyl group, decyl group, dodecyl group, tetradecyl group, hexadecyl group, Octadecyl group, docosanyl group, eicosanyl group, undecyl group, 2
-Acetamidoethyl group, 2-methoxyethyl group, 3-
Ethoxypropyl group, 3-methoxycarbonylpropyl group, 2- (N, N-diethyl) ethyl group, hydroxyethyl group, etc., alkenyl group having 2 to 22 carbon atoms which may be substituted (eg vinyl group, allyl group) , An isopropenyl group,
1-propenyl group, 2-butenyl group, 1,3-butadienyl group, 2-pentenyl group, hexenyl group, decenyl group,
Dodecenyl group, octadecenyl group, docosenyl group,
Etc.), an alicyclic group having 5 to 7 carbon atoms which may be substituted (for example, cyclopentyl group, cyclohexyl group, 2-cyclopenten-1-yl group, 2,4-cyclopentadiene-1)
-Yl group, etc.), an aralkyl group having 7 to 12 carbon atoms and which may be substituted (eg, benzyl group, 4-butylbenzyl group, 4-octylbenzyl group, phenethyl group, 4-butoxybenzyl group, 3-phenyl group) An enylpropyl group, a chlorobenzyl group, etc., and an optionally substituted aryl group having 6 to 12 carbon atoms (for example, a phenyl group, a tolyl group, a xylyl group, a mesityl group, a naphthyl group, a chlorophenyl group, a cumenyl group, 4
-Butylphenyl group, 4-octylphenyl group, 4-decylphenyl group, 4-dodecylphenyl group, 4-methoxyphenyl group, 4-butoxyphenyl group, etc.) and the like. X is a halogen atom, preferably a chlorine atom, a bromine atom or the like.

The sulfonamidated nigrosine derivative or aniline black derivative of the present invention can be produced by reacting a sulfonyl halide compound represented by the general formula (I) with a nigrosine or aniline black pigment. For example, edited by The Chemical Society of Japan, New Experimental Chemistry Course, Volume 14, Synthesis and Reaction of Organic Compounds [II], 1142, Maruzen Co., Ltd. (197
It can be produced by a method similar to the carboxylic acid amide synthesis described in 7) and the like.

Specifically, as a solvent for the sulfonamidation reaction, a solvent which does not react with the sulfonyl halide compound and which appropriately dissolves the sulfonyl halide compound and the pigment can be used. For example, polar solvents such as tetrahydrofuran, acetonitrile, dioxane, dimethyl sulfoxide, N, N-dimethylformamide, methylene chloride, chloroform, methylchloroform, dichloroethane, trichloroethane, trichloroethylene, perchlorethylene, and other chlorinated hydrocarbons. It is preferable to use a solvent or the like alone or as a mixture.

A basic compound is allowed to coexist in order to remove hydrogen halide produced as a by-product during the reaction. Preferably a tertiary amine (eg
Triethylamine, tripropylamine, triethanolamine, N, N-dimethylaniline, etc.), pyridine,
Morpholine, piperidine, 1,4-diazabicyclo (2,2,
2] Organic bases such as octane and 1,8-diazabicyclo [5,4,0] undec-7-ene.

The amount of the organic base used is appropriately an equimolar amount to 2 times the molar amount of the amount of the sulfonyl halide used.

The reaction temperature is suitably in the range of 0 ° C to 120 ° C, and the reaction time is suitably 3 hours to 24 hours.

Specific examples of the nigrosine pigment and the aniline black pigment used in the present invention are as follows. However, the color index numbers are shown in [].

Nigrosine [CI Solvent Black 5 (50415)] Nigrosine Base [CI Solvent Black 7 (50415)
B)] Aniline Black [CI Pigment Black 1 (5044
0)] The reaction ratio between the pigment and the sulfonamidating agent represented by the general formula (I) is 5 × 10 ⁻⁴ to 1 × 10 ⁻² mol of the compound represented by the general formula (I) per 1 g of the pigment. , Preferably 1 × 10 ^-3
~ 8 x 10 ^-3 mol.

The electric resistance used in the present invention is 10 ⁹ Ω · cm or more, and the dielectric constant is 3.5.
As the following non-aqueous solvent, linear or branched aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons or halogenated hydrocarbons can be preferably used.
From the viewpoint of volatility, stability, toxicity, odor, etc., more preferably octane, isooctane, decane, isodecane, nonane, dodecane, isododecane, decalin, isoparain-based petroleum solvent, Isopar E, Isopar G, Isopar H, Isopar L (manufactured by Exxon), Cielsol-71 (manufactured by Ciel), Amsco O, M, S (manufactured by Spirits) and the like are used alone or in combination.

The black pigment of the present invention is provided by being dispersed in the above-mentioned carrier, and specifically, the pigment is coated with a resin insoluble in the carrier liquid and a soluble resin for dispersing in the carrier liquid is adsorbed. It is carried out by a method of coating, a method of coating and dispersing with the same resin, a method of dispersing a pigment with a soluble resin and a method of mixing a pigment dispersion with insoluble resin particles, or a method of a combination thereof.

The insoluble resin used in the present invention may be any conventionally known resin, for example, Yuji Harasaki, The Electrophotographic Society of Japan, 16 (No. 2), p. 44 (1977), supervised by Koichi Nakamura, "Comprehensive Technical Data". , Recent Developments and Practical Uses of Electrophotographic Development Systems and Toner Materials, "Chapters 3 and 4, published by Japan Science Information Co., Ltd. (1984).

Specifically, polyisoprene, polyolefins such as polybutadiene, styrene-butadiene resin, cyclized rubber,
Terpene-based petroleum resin, coumarone-indene resin, natural rubber, resin obtained from styrene or its derivative, acrylate resin, methacrylate resin, polyester resin, polycarbonate resin, nitrile resin,
There are vinyl ether-based resins, maleic anhydride-based copolymers, vinyl alkanoate-based resins, rosin-based resins, alkyd-based resins including modified alkyds, and the like.For example, polyolefins are disclosed in Japanese Examined Patent Publication No. 60-39228, U.S. Pat. For cyclized rubbers, Japanese Patent Publication No. 47-41930 and Japanese Patent Publication No. 50-24105.
Japanese Patent Publication No. 50-24623, Japanese Patent Publication No. 51-13021, Japanese Patent Laid-Open No. 48
-71237, etc., styrene resin is Japanese Patent Publication No. Sho 48-24905,
JP-B-47-10199, JP-A-48-95842, JP-A-49-30
No. 040, U.S. Pat. No. 3417019, and the like, polyester resins include Japanese Patent Publication No. 51-10106, JP-A-51-89428, and JP-A-53-
80234, JP-A-60-76755, etc., alkyd resins are disclosed in Japanese Patent Publication No. 51-1431, Japanese Patent Publication No. 52-147443, U.S. Pat.
Polymers containing acrylic acid ester and / or methacrylic acid ester are disclosed in JP-B-48-43154.
Japanese Patent Publication No. 47-9317, Japanese Patent Laid-Open No. 50-147723, Japanese Patent Laid-Open No. 50
-1737, JP-A-50-1738, JP-A-52-91438, etc., vinyl alkalate resins are disclosed in JP-B-60-15063,
JP-B-60-18985, JP-A-60-164757, JP-A-60-1
No. 79751 etc.

The soluble resin used in the present invention is necessary for stabilizing the dispersion of the black pigment particles of the present invention or the particles coated with the insoluble resin and / or the insoluble resin particles. These soluble resins may be adsorbed on or chemically bound to the particles.

A conventionally known resin is used as the soluble resin, and examples thereof include any of various resins described above for the insoluble resin, as long as the resin dissolves or swells in the carrier liquid. Specific soluble resins are exemplified in the aforementioned patents and the like.

Further, a graft polymer is also known as a method of imparting each function of an insoluble resin and a soluble resin to one resin. For example, JP-B-47-4439, JP-B-48-5062,
Japanese Patent Publication No. 48-29071, Japanese Patent Publication No. 51-37789, U.S. Patent 3,90
0,412, JP-A-60-185962, JP-A-60-185963 and the like.

If desired, various additives may be added to the liquid developer of the present invention in order to enhance charge characteristics or improve image quality. For example, Yuji Harazaki, “Electrophotography”, Vol. 16, Vol.
No., p. 44.

For example, dialkyl sulfosuccinic acid metal salt, alkylbenzene sulfonate, naphthenic acid metal salt, stearic acid metal salt, higher fatty acid metal salt such as behenic acid metal salt, lecithin, polycarboxylic acid, poly (vinylpyrrolidone), and JP-B-49. -26594, a dialkyl butyric acid derivative of a diisobutylene-maleic acid copolymer described in JP-A-60-179750.
A copolymer of maleic anhydride and an amino compound, wherein the copolymer has a half-maleic acid amide component and a maleinimide component as repeating units. A metal salt of a compound containing a dialkyl-substituted amino group described in -162059 and a carboxyl group or a sulfone group in the same molecule can be used for controlling the charge characteristics.

A known method can be used for producing the liquid developer of the present invention. For example, a pigment derivative, polymer particles and a charge control agent are mixed to produce a petroleum-based aliphatic hydrocarbon, aromatic hydrocarbon or halogenated aliphatic. A method of using a paint shaker, an attritor, a ball mill, or the like to disperse the concentrated toner in a carrier liquid such as hydrocarbon, and diluting the obtained concentrated toner with a highly insulating carrier liquid, pigment derivative, polymer particles and a charge control agent There is a method of dropping the concentrate into the above carrier liquid to obtain toner particles, a method of polymerizing a monomer in a highly insulating carrier liquid to obtain polymer particles, and then adding a pigment derivative and a charge control agent. .

The amount of each main component of the liquid developer of the present invention will be described below.

Toner particles composed mainly of pigment derivatives are carrier liquids.
It is preferably 10 to 30 parts by weight with respect to parts by weight. If it is less than 10 parts by weight, the image density will be insufficient, and if it exceeds 50 parts by weight, fog will easily occur in the non-image area. The above-mentioned resin soluble and insoluble in the carrier liquid can be added in an amount of about 5 to 20 parts by weight per 100 parts by weight of the carrier liquid. The amount of charge control agent added depends on the amount of developer 1 used in the final use form.
It is desirable to adjust so that 0.001 g to 10 g is included. The range is more preferably 0.01 g to 1 g.

The upper limit of the total amount of the liquid developer as described above is regulated by the electric resistance of the developer. That is, if the electric resistance of the liquid developer with the toner particles removed is less than 10 ⁹ Ωcm, it becomes difficult to obtain a continuous tone image of good quality, so it is possible to control the addition amount of each additive within this limit. is necessary.

The particle size of the obtained dispersed particles is other than 3 microns, especially 1
It is desirable to have a micro or less to obtain a continuous tone image.

〔Example〕

The present invention will be described in more detail with reference to the following examples, but these examples are given to give an understanding of the content of the present invention, and the content of the present invention is limited by the examples. There is no.

Example 1 7.0 g of triethylamine was added dropwise to a mixture of 5.0 g of nigrosine base (CI50415B), 7.0 g of n-octanesulfonyl chloride, 100 ml of methylene dichloride and 100 ml of distilling while maintaining the temperature at 30 to 35 ° C under stirring. The mixture was further stirred as it was for 2 hours and then at a temperature of 80 to 85 ° C. for 4 hours. The reaction mixture was concentrated under reduced pressure to about 1/3 of the total volume. Then, this mixture was added dropwise to 500 ml of water with stirring,
After stirring for 1 hour as it was, the precipitated black solid was collected in a furnace. The obtained solid was washed twice with 100 ml of ethyl acetate and then dried under reduced pressure at a temperature of 50 ° C. The yield of the obtained black substance (I) was 6.9 g.

Next, the above mixture was kneaded with a three-roll mill heated to 140 ° C., cooled and coarsely pulverized to obtain a resin mixture of pigments. To 1.0 part of this mixture, 2.0 parts of styrene-butadiene copolymer and 10 parts of toluene were added and dispersed by a paint shaker for 48 hours, and then 20 parts of this concentrate was added with 2 × 10 ^-4 mo of naphthenic acid Zr.
l /, 100 parts of Isopar H were added and diluted to prepare a liquid developer. A zinc oxide photosensitive paper having a negative electrostatic latent image was developed using this liquid developer to obtain a positive pure black image. The image quality of the obtained image, the fixability of the developer, the dispersibility,
The results of stability over time are shown in Table 1.

In order to prove that the developer of the present invention is superior to the conventional one, the developers shown in Comparative Examples 1-1 and 1-2 were prepared and their performances were compared.

Comparative Example 1-1 A black substance (I-1) was obtained by reacting nigrosine base (CI50415B) with nonanoyl chloride by the method disclosed in JP-B-51-40806. The black substance (I) shown in Example 1 was replaced with (I-1) and kneaded with the same formulation,
A liquid developer was prepared by diluting and dispersing. Using this liquid developer, a zinc oxide photosensitive paper having a negative electrostatic latent image was developed to obtain a positive black image. Table 1 shows the results of the image quality of the obtained image, the fixability of the developer, the dispersibility, and the stability over time.

Comparative Example 1-2 By the method disclosed in JP-B-50-40347, nigrosine base (CI50415B) was reacted with pelargonic acid to obtain a violet black substance (I-2). A liquid developer was prepared by replacing the black powder (I) shown in Example 1 with (I-2) and kneading and dispersing with the same formulation. Using this liquid developer, a zinc oxide photosensitive paper having a negative electrostatic latent image was developed to obtain a positive black image. Table 1 shows the results of the image quality of the obtained image, the fixability of the developer, the dispersibility, and the stability over time.

It can be seen from Table 1 that the developer according to the present invention (Example 1) has a pure black color tone and is excellent in image quality, fixability, dispersibility, and stability over time (immediately after preparation and after 1 month). However, in Comparative Example 1-1, the color tone was pure black as in Example 1, and the fixability and the image quality and dispersibility immediately after preparation were excellent, but both the image quality and the dispersibility deteriorated after 1 month of forced aging, and the stability with time was stable. The sex is also bad. Further, in Comparative Example 1-2, the color tone is purple black and the image quality and dispersibility immediately after preparation are excellent, but the fixability is poor, and the image quality and dispersibility are deteriorated after 1 month of forced storage, and the stability over time is also poor. .

Example 2 A mixture of 10.0 g of nigrosine base (CI50415B), 12.6 g of p-toluenesulfonyl chloride, 100 ml of dioxane and 200 ml of dimethylformamide was heated to a temperature of 35-40 ° C. 14 g of triethylamine was added dropwise with stirring at this temperature for 1 hour, and the mixture was further stirred for 1 hour. Then, the mixture was heated to 90 ° C. and stirred for 4 hours, and then concentrated under reduced pressure until the residual amount became about half. The reaction mixture was added dropwise to 1.0 of water with stirring, and the mixture was stirred as it was for 30 minutes. The deposited black matter is collected in a furnace,
After washing twice with 200 ml of ethyl acetate, the temperature was reduced to 50 ° C under reduced pressure.
Dried in. The yield of the obtained black substance (II) was 12.5 g.

Next, the above mixture was kneaded with a three-roll mill heated to 140 ° C., cooled and coarsely pulverized to obtain a resin mixture of pigments. A liquid developer was prepared by diluting and dispersing with the same formulation as in Example 1 below. A zinc oxide photosensitive paper having a negative electrostatic latent image was developed using this liquid developer to obtain a positive pure black image. Table 2 shows the results of the image quality of the obtained image, the fixability of the developing solution, the dispersibility, and the stability with time.

The developers shown in Comparative Examples 2-1 and 2-2 were prepared and their performances were compared.

Comparative Example 2-1 A black substance (II-1) was obtained by reacting nigrosine base (CI50415B) with p-toluoyl chloride by the method disclosed in JP-B-51-40806. A liquid developer was prepared by replacing the black substance (II) shown in Example 2 with (II-1) and kneading, diluting and dispersing with the same formulation. Using this liquid developer, a zinc oxide photosensitive paper having a negative electrostatic latent image was developed to obtain a positive black image. Table 2 shows the results of the image quality of the obtained image, the fixability of the developing solution, the dispersibility, and the stability with time.

Comparative Example 2-2 A black substance (II-2) was obtained by reacting nigrosine base (CI50415B) with p-methylbenzoic acid by the method disclosed in JP-B-50-40347. A liquid developer was prepared by substituting (II-2) for the black substance (II) shown in Example 2 and kneading and dispersing with the same formulation. A zinc oxide photosensitive paper having a negative electrostatic latent image was developed using this liquid developer to obtain a positive black image. Table 2 shows the results of the image quality of the obtained image, the fixability of the developing solution, the dispersibility, and the stability with time.

From Table 2, it can be seen that the developer according to the present invention (Example 2) has a pure black color tone and is excellent in image quality, fixability, dispersibility, and stability over time (immediately after preparation and after 1 month). However, in Comparative Example 2-1, the color tone is the same as that of Example 2 and is pure black, and the fixing property and the image quality and dispersibility immediately after preparation are excellent, but both the image quality and the dispersibility are deteriorated after the forced aging for one month, Poor stability over time. Further, in Comparative Example 2-2, the color tone is purple black and the image quality and dispersibility immediately after preparation are excellent, but the fixability is poor, and the image quality and dispersibility deteriorate after a forced lapse of 1 month, and the stability over time is also poor. .

Example 3 A black substance (III) was obtained by sulfamidating aniline black under the same conditions except that the nigrosine base (CI50415B) in Example 1 was changed to aniline black (CI50440).

Next, the above mixture was kneaded with a three-roll mill heated to 140 ° C., cooled and coarsely pulverized to obtain a resin mixture of pigments. To 0.9 parts of this mixture, 2.0 parts of styrene-butadiene copolymer and 10 parts of toluene were added and dispersed for 48 hours with a paint shaker, and then 20 parts of this concentrate was added with 2 × 10 ^-1 mo of naphthenic acid Zr.
l /, 100 parts of Isopar G were added and diluted to disperse to prepare a liquid developer. A zinc oxide photosensitive paper having a negative electrostatic latent image was developed using this liquid developer to obtain a positive black image. The image quality of the obtained image, the fixability of the developer, the dispersibility,
The results of stability over time are shown in Table 3. In order to prove that the developer of the present invention is superior to the conventional one, the developers shown in Comparative Examples 3-1 and 3-2 were prepared and their performances were compared.

Comparative Example 3-1 A black substance (III-1) was obtained by reacting aniline black (CI50440) with nonanoyl chloride by the method disclosed in JP-B-48-24901. The black substance (III) shown in Example 3 was replaced with (III-1) and kneaded and dispersed in the same formulation to prepare a liquid developer. A zinc oxide photosensitive paper having a negative electrostatic latent image was developed using this liquid developer to obtain a positive black image. Table 3 shows the results of the image quality of the obtained image, the fixability of the developing solution, the dispersibility, and the stability with time.

Comparative Example 3-2 A black substance (III-2) was obtained by reacting aniline black (CI50440) with pelargonic acid by the method disclosed in JP-B-50-40347. The black substance (II
I) was replaced with (III-2) and kneaded and dispersed in the same formulation to prepare a liquid developer. Using this liquid developer, a zinc oxide photosensitive paper having a negative electrostatic latent image was developed to obtain a positive black image. Table 3 shows the results of the image quality of the obtained image, the fixability of the developing solution, the dispersibility, and the stability with time.

It can be seen from Table 3 that the developer according to the present invention (Example 3) has a pure black color tone and is excellent in image quality, fixability, dispersibility, and stability over time (immediately after preparation and after 1 month). However, in Comparative Example 3-1, the color tone was pure black as in Example 3 and the image quality and dispersibility immediately after preparation were excellent, but both the image quality and dispersibility deteriorated after 1 month of forced storage, and the stability over time was improved. Is also bad. Further, in Comparative Example 3-2, the color tone is pure black and the image quality immediately after preparation is excellent, but the fixability and dispersibility are poor, and the image quality deteriorates after 1 month of forced elapse, and the dispersion further deteriorates. Poor stability over time.

Example 4 (1) Production of Resin Particle Dispersion A mixed solution of 14 g of polylauryl methacrylate (weight average molecular weight 3.8 × 10 ⁴ ) as a dispersion stabilizing resin, 100 g of vinyl acetate, 3 g of lauryl methacrylate and 383 g of isodecane was stirred under a nitrogen stream. While warming to a temperature of 75 ° C. 2.0 g of benzoyl peroxide was added and reacted for 4 hours. After 40 minutes from the addition of the initiator, the homogeneous solution became cloudy and the reaction temperature rose to 88 ° C. After cooling, pass a 200 mesh nylon cloth,
The white dispersion obtained had a polymerization rate of 95% and a latex having an average particle size of 0.21 μm.

(2) Production of Pigment Dispersion A pigment dispersion was prepared using the black substance (I) produced in Example 1 according to the following formulation.

Pigment dispersion Was dispersed in a ball mill for 48 hours. Using the above materials, the developer was prepared to have the following concentrations.

Developer The obtained liquid developer is used as a developer for Fuji ELP404V (manufactured by Fuji Photo Film Co., Ltd.), and ELP-II master (manufactured by Fuji Photo Film Co., Ltd.) as an electrophotographic photosensitive material for a printing master. An image was formed on a ELP-II master from a positive image original having continuous tone by using the to prepare a master plate. Table 4 shows the results of the color tone, image quality, fixability with a developing solution, dispersibility, and stability over time of the obtained image.

From Table 4, the developer according to the present invention has a pure black color tone and is excellent in image quality, fixability, dispersibility, and stability over time (immediately after preparation and after one month).

In addition, when 3000 sheets of ELP-II master were processed and the optical density of the image on the 3000th master plate was examined, there was no decrease in density compared to the one processed first, and both were very clear images. Atsuta

Next, the non-image areas of the first and 3000th master plates were desensitized to make offset printing plates, and 10,000 sheets were printed. In each of the plates printed, the printed matter on the 10,000th sheet was clear, there were no fine line breaks, and there was no fog.

As described above, when an electrophotographic lithographic printing original plate is prepared using the liquid developer in which the black pigment dispersion of the present invention and the insoluble resin particles are used in combination, the fixability of the image area is sufficiently maintained and the printing ink is It adheres sufficiently to the image area, and the good image quality of the printed matter is maintained even after printing a large number of sheets.

〔The invention's effect〕

The liquid developer according to the present invention gives a pure black color tone, has a positive charge, is excellent in storage stability, fixability and dispersibility, and is extremely excellent in charge stability over time.

Claims (1)

[Claims] 1. A liquid developer for electrophotography, comprising a carrier liquid having an electric resistance of 10 ⁹ Ω · cm or more and a dielectric constant of 3.5 or less, and at least a resin insoluble in the carrier liquid, a soluble resin and a black pigment. 2. The liquid developer for electrophotography, wherein the black pigment is a sulfonamide derivative obtained by reacting a nigrosine or aniline black pigment with a sulfonyl compound represented by the following general formula (I). R-SO ₂ -X (I) wherein, R represents a carbon hydrogen group, X represents a halogen atom.