JPH0582575B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field: The present invention provides a novel resin dispersion useful for electrophotographic liquid developers, and the electrophotographic liquid developer using the resin dispersion of the present invention has excellent dispersion stability. Since there is no tackiness of the image and there is no blurring of the image, it is extremely suitable for offset mastering, color electronic copying, etc. Conventional technology: Conventionally, resin dispersions for electrophotographic liquid developers have been prepared by adding a polymer insoluble in the medium to a polymer in an organic solvent (hereinafter referred to as "medium") that has a low dielectric constant and high electrical insulation properties. Resin dispersions obtained by graft polymerization of the monomers produced have been proposed (e.g., JP-A-53-54029), but the method for producing such resin dispersions is complicated and When used as a developer, gels often form, making it difficult to obtain a stable dispersion as a developer. In recent years, attempts have been made to improve the above-mentioned drawbacks of resin dispersions of graft copolymers.
It consists of a polymer soluble in the medium and a polymer insoluble in the medium, and both of these polymers contain -COOH, -.
By incorporating polar functional groups such as SO ₃ H or -OCOCH ₃ , the stability of the resin dispersion can be improved by utilizing the adsorption ability between the polar functional groups of the soluble polymer and the polar functional groups of the insoluble polymer. Techniques for improving this have been disclosed (for example, Japanese Patent Application Laid-open No. 83174/1983). Problems to be Solved by the Invention: However, as a result of research by the present inventors, the stability of resin dispersions in which soluble polymers and insoluble polymers are simply provided with polar functional groups as described above is limited to a certain extent. It has been found that although this method improves image toughness and image smearing, it still poses a practical problem when used in an electrophotographic liquid developer. The present invention provides a novel resin dispersion for electrophotographic liquid developers that simultaneously solves all of the problems of the prior art, such as stability, image toughness, and image smearing. Therefore, the electrophotographic liquid developer using the resin dispersion of the present invention is simultaneously excellent in various aspects such as stability, image toughness, image bleeding, and image density, and is particularly suitable for color electrophotography. It is something. Means for solving the problem: According to the invention, in a highly insulating hydrocarbon medium, the formula (A)

[C] [Here, X represents hydrogen or methyl,
Y represents -COOR, -OCOR or -OR,
R represents _C4-20 alkyl] Monomer 95-15% by weight and formula

[Here, Z represents _C3-8 cycloalkyl or C1-3 aralkyl in the alkyl moiety, and X has the above meaning] 5-85% by weight of the monomer [However, ()as well as()
The total amount of monomers is 100% by weight] and an organic mercaptan having at least one thiol group with a sulfur content of 0 to 2% by weight (however, the sulfur content per soluble copolymer below). (B) a copolymer substantially soluble in the medium; and (B) a polymer substantially insoluble in the medium. be done. Formula () contained in the soluble copolymer of (A) above
As the monomer, n-butyl methacrylate,
Isobutyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-dodecyl methacrylate, n-octadecyl methacrylate,
Methacrylates such as lauryl methacrylate, stearyl methacrylate, isodecyl methacrylate, isononyl methacrylate, n-butyl acrylate, isobutyl acrylate, n-hexyl acrylate, n-octyl acrylate,
2-ethylhexyl acrylate, n-dodecyl acrylate, n-ocdadecyl acrylate,
Acrylates such as lauryl acrylate, stearyl acrylate, isodecyl acrylate, and isononyl acrylate; fatty acid vinyl and vinyl n such as vinyl butyrate and vinyl versatate;
Butyl ether, vinyl isobutyl ether,
Examples include vinyl ethers such as vinyl n-hexyl ether, vinyl n-octyl ether, and vinyl 2-ethylhexyl ether. A preferred monomer of formula () is

embedded image wherein R represents a C _4-12 alkyl monomer, and n-octyl methacrylate or 2-ethylhexyl methacrylate is particularly preferably used. Formula () contained in the soluble copolymer of (A) above
Examples of monomers include cycloalkyl methacrylates such as cyclopropyl methacrylate, cycloheptyl methacrylate, cyclohexyl methacrylate, cyclopentyl methacrylate, and cyclooctyl methacrylate; Alkyl acrylate, γ-phenylpropyl methacrylate, β-phenylethyl methacrylate,
Examples include aralkyl methacrylates such as benzyl methacrylate, and aralkyl acrylates such as γ-phenylpropyl acrylate, β-phenylethyl acrylate, and benzyl acrylate. Preferred monomers of formula () are C _3-8 cycloalkyl methacrylates or C _3-8 cycloalkyl acrylates, and cyclohexyl methacrylate or cyclohexyl acrylate is particularly preferably used. The soluble copolymer of (A) is a monomer of formula () 95 to 15
% by weight, preferably 80-40% by weight, most preferably
70-50% by weight and 5-85% by weight of monomers of formula (), preferably 20-60% by weight, most preferably 30-50% by weight
% by weight [however, the total of monomers () and () is 100% by weight]. If the amount of the monomer of the formula () is too small, such as less than 5% by weight, it is not preferable because the image will become tough and the image will bleed. In particular, when used in an electrophotographic liquid developer for color electrophotography, the monomer of formula () should be 20 to 60% in consideration of image toughness and image smearing.
A weight percentage in the range from 30 to 50 weight percent is particularly advantageous. The soluble copolymer (A) also contains an organic mercaptan having at least one thiol group in a sulfur content of 0 to 2% by weight per copolymer. Organic mercaptans having at least one thiol group have from 1 to about 4 thiol groups per molecule and contain from 1 to about 12 carbon atoms, preferably from 2 to 8 carbon atoms per thiol group. These organic mercaptans can contain other substituents in addition to hydrocarbon groups, such as carboxylic acid groups, hydroxyl groups, ether groups, ester groups, sulfide groups, amine groups and amide groups. included. Examples of useful mercaptans include methyl mercaptan, ethyl mercaptan, butyl mercaptan, octyl mercaptan, lauryl mercaptan, mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid, mercaptopropionic acid, thiomalic acid, benzyl mercaptan, phenyl mercaptan, and cyclohexyl mercaptan. , 1-thioglycerol, 2,2'-dimercapto diethyl ether,
2,2'-dimercaptodipropyl ether, 2,
2'-dimercapto diisopropyl ether, 3,
3′-dimercaptodipropyl ether, 2,2′-
Dimercapto diethyl sulfide, 3,3'-dimercapto dipropyl sulfide, 1,11-dimercapto-3,9-dioxa-6-thiaundecane, bis(β-mercaptoethoxy)methane, bis(β-mercapto ethylthio)methane, ethanedithio-1,2, propanedithiol-1,2,
Butanediol 1,4,3,4-dimercaptobutanol-1, trimethylolethane tri(3-
mercaptopropionate), pentaerythritol tetra(3-mercaptopropionate),
Includes trimethylolpropane trithioglycolate and pentaerythritol tetrathioglycolate. Suitable organic mercaptans include butyl mercaptan, octyl mercaptan, lauryl mercaptan, mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid,
Mercaptopropionic acid, benzylmercaptan, phenylmercaptan, and laurylmercaptan, mercaptoethanol, mercaptopropanol, mercaptobutanol, mercaptoacetic acid, and mercaptopropionic acid are particularly preferred. The soluble copolymer (A) contains an organic mercaptan in a sulfur content of 0 to 2% by weight, preferably 0.03 to 2% by weight, more preferably 0.1 to 0.7% by weight per copolymer. If the amount of organic mercaptan is too low (less than 0.1% by weight), it is unfavorable in terms of sedimentation stability and contamination of non-image areas (scumming) when used as a developer, while if it is too large (more than 2% by weight), it is not stable. This is not preferable because it makes it impossible to obtain a resin dispersion liquid. In addition, the soluble copolymer (A) contains components other than the monomer of formula (), the monomer of formula (), and organic mercaptan, which have an adverse effect on various properties such as stability, image toughness, and image smearing. It may be contained as necessary to the extent that it does not affect. As the monomer that provides the insoluble polymer described in (B) of the present invention, a monomer that is soluble in the medium as a monomer but has the property of decreasing its solubility and precipitating when it becomes a polymer is used. Ru. Such monomers include styrene and its derivatives, acrylic acid alkyl esters, methacrylic acid alkyl esters, maleic anhydride, N-vinylpyrrolidone, maleic acid mono- or di-alkyl esters, fumaric acid mono- or di-alkyl esters, Alkyl esters, itaconic acid mono- or di-alkyl esters, acrylonitrile, methacrylnitrile, vinyl acetate, vinyl propionate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate,
Vinylpyridine, vinylimidazole, ethoxyethyl (meth)acrylate, methoxyethyl (meth)acrylate, vinylsulfonic acid, p-
Vinylbenzenesulfonic acid, vinylamine, p-
Examples include vinylnitrobenzene and other monomers. As the insoluble polymer of the present invention, single or copolymers of the above monomers can be used. Preferred insoluble polymers for use in the present invention are (i)
20-100% by weight of vinyl acetate and (ii) C _1-20 alkyl methacrylate, C _1-20 alkyl acrylate,
and/or a polymer consisting of 80-0% by weight of _C3-8 cycloalkyl (meth)acrylate. If the amount of vinyl acetate is too small, such as less than 20% by weight, the image density tends to decrease, which is not preferable. Particularly preferred insoluble polymers for use in the present invention are (i) 60-95% by weight vinyl acetate and (ii) C _1-8 alkyl acrylate, C _1-8 alkyl methacrylate,
At least one selected from C _3-8 cycloalkyl acrylate and C _3-8 cycloalkyl methacrylate
More than one species of acrylate and/or methacrylate
A copolymer consisting of 40-5% by weight, the most preferred insoluble polymer being (i) 70-90% by weight of vinyl acetate and (ii)
C _1-8 alkyl acrylate, C _1-8 alkyl methacrylate, C _3-8 cycloalkyl acrylate,
It is a copolymer consisting of 30 to 10% by weight of at least one acrylate and/or methacrylate selected from _C3-8 cycloalkyl methacrylates. When the above-mentioned particularly preferred to most preferred copolymers are used in an electrophotographic liquid developer for color electrophotography, they have excellent developer stability and are particularly excellent in terms of image toughness, image bleeding, and image density. achieved. The above-mentioned insoluble polymer may be copolymerized with monomers other than the above-mentioned exemplified monomers, if necessary, within a range that does not adversely affect various performances as a liquid developer. The molecular weight (weight average) of the soluble copolymer used in the present invention is preferably 3,000 or more, especially considering obtaining a stable dispersion, obtaining an image without toughness, and preventing sediment from forming in the developer. Preferably it is 5,000 to 500,000. The ratio of the soluble copolymer (A) to the insoluble polymer (B) in the resin dispersion of the present invention is not particularly limited, but the soluble copolymer is 20 to 50% by weight, preferably 30% by weight. A proportion of ~40% by weight and 80-50%, preferably 70-60% by weight of insoluble polymer is used. If the soluble copolymer is too small (less than 20% by weight), the stability of the dispersion resin liquid will decrease, which is undesirable, and if it is too large (more than 50% by weight), the image density will decrease when used as a developer. Undesirable. The highly insulating hydrocarbon medium used in the present invention is an organic solvent with a low dielectric constant and high electrical insulation properties, and examples of such organic solvents include nornull paraffinic hydrocarbons, isoparaffinic hydrocarbons, and alicyclic hydrocarbons. Hydrocarbons, halogenated aliphatic hydrocarbons, etc. can be exemplified, and paraffinic or alicyclic hydrocarbons having a boiling point of 150 to 200°C are particularly preferred from the viewpoint of odor, safety, and drying properties. For example, Isobar G, H,
K and L (manufactured by Exxon Chemical), Ivy Albento (manufactured by Idemitsu Oil), Ciel Sol 71 (manufactured by Ciel Sekiyu)
etc. can be suitably used. As the resin dispersion of the present invention, one in which the particle size distribution of dispersed particles is 70% or more, preferably 90% or more of 0.5μ or less is suitably used. The resin dispersion of the present invention can generally be easily produced by polymerizing an insoluble polymer in a solution of a soluble copolymer in a medium; It can also be suitably produced by a method such as separately producing a combination, dissolving both polymers in a common solvent for both polymers, and then dropping the mixture dropwise into a hydrocarbon medium with stirring. The particle size distribution of the resin dispersion can be adjusted by changing the ratio of the soluble copolymer to the insoluble polymer, and by changing the blending ratio of the methacrylate or acrylate described in (ii) above in the insoluble polymer. It can be adjusted even if it twists. In order to produce an electrophotographic liquid developer from the resin dispersion of the present invention, the dispersed particles may be colored and charged. To color the dispersed particles, a coloring agent generally used in electrophotographic liquid developers is used. Examples of such dyes include basic azo dyes such as Oil Black, Oil Red, and Bismarck Brown; acidic azo dyes such as Wool Black, Amid Black Green, and Blue Black HF; direct dyes such as Direct D Black E and Congo Stain; The following pigments include anthraquinone dyes such as violet and acid blue, carbonium dyes such as auramine, malachite green, crystal violet, and Victoria blue, rhodamine dyes such as rhodamine B, and quinone imine dyes such as saphnin, nigrosine, and methylene blue. can be mentioned. Examples of pigments include carbon black, phthalocyanine blue, benzine yellow, and washing red. Pigments surface-treated by dyeing with nigrosine or rhodamine B can also be used. As a method for coloring the resin dispersion, a method can generally be used in which a dye solution is prepared and added dropwise to the resin dispersion while stirring. The solvent for the dye is preferably a solvent that is miscible with the medium, has relatively insulating properties, and has a high boiling point. A charge control agent is used to charge the resin dispersion of the present invention, and such charge control agents include:
Examples include zinc naphthenate, manganese naphthenate, copper oleate, cobalt octylate, lecithin, sodium dioctyl sulfosuccinate, and aluminum salt of steverytrozin. Effects of the invention: Liquid developers for electrophotography are usually used as dilute solutions of 5% or less, so dispersion stability is required in such diluted states, and furthermore, the obtained images have high density and are free from bleeding. Contamination of non-image areas (background stains)
A lack of toughness and toughness is required. In order to maintain dispersion stability, conventional techniques have proposed a method using a graft copolymer consisting of soluble polymer chains and insoluble polymer chains in an organic solvent as a medium, but this production method is extremely complicated. In addition, unreacted substances in the functional group used for graft bonding react with the formulation used in developer manufacturing, resulting in gelation or coloring during the graft bonding reaction, which poses a problem, especially for color electrophotography. Ta. In addition, methods that do not use graft copolymers require a large amount of soluble component to maintain dispersion stability, but the soluble component, an alkyl ester of acrylic acid or methacrylic acid with a C ₈ or higher, has a glass transition point. Since the (Tg) is low, there is a problem that using a large amount of this will cause toughness in the image. Therefore, acrylic acid or methacrylic acid, which has a relatively high Tg and can easily obtain dispersion stability in small amounts, is used.
When an alkyl ester of C ₁₆ or higher is used, the charge control of the developer becomes unstable, resulting in the problem of blurring of images. In order to solve these problems, there is a method of copolymerizing styrene or its derivatives as a soluble component (Japanese Unexamined Patent Application Publication No. 1986-1999).
127939, 58-139155, etc.) In this case, the polymerization reaction is slow, and the production method is severely restricted, especially when a polyvinyl acetate copolymer is used as a component that is insoluble in the medium. According to the present invention, the above-mentioned problems do not occur even if the amount of soluble components is increased, and furthermore, since a polyvinyl acetate copolymer can be used as a component that is insoluble in the medium, the resin dispersion of the present invention can be used as a dispersion itself. Not only can it be used as an electrophotographic liquid developer, but it also has excellent stability after dilution, and when used as an offset master or color electrophotograph, there is no smearing of the image (the outline of the image is sharp) and the image remains sharp. It exhibits excellent performance due to its high concentration. In particular, in color electrophotography, when a large number of photographs (copy paper) are stacked, the prior art had the disadvantage that blocking between photographs was likely to occur due to the toughness of the images, but with the resin dispersion of the present invention, Even when I stacked 1,000 photos for about a month in the summer and left them alone, no blocking occurred. Examples Parts used in the following Examples and Comparative Examples refer to parts by weight. Example 1 After stirring, 35 parts of n-heptane and n-octyl methacrylate were placed in a reactor equipped with a reflux device and a dropping device.
After adding 120 parts of cyclohexyl methacrylate, 80 parts of cyclohexyl methacrylate, and 0.15 parts of azobisisobutyronitrile and heating at 90°C for 1 hour, a solution of 0.8 parts of azobisisobutyronitrile dissolved in 40 parts of toluene was added dropwise over 2 hours. During the course of the reaction, reflux started due to foaming and polymerization heat, so the reflux state was continued. Further, as the viscosity increased as the polymerization progressed, 125 parts of n-heptane was added to adjust the viscosity, and stirring was continued. After the addition of azobisbutyronitrile was completed, the mixture was allowed to react under reflux for 1 hour. Next, a solution of 3 parts of benzoyl peroxide dissolved in 300 parts of vinyl acetate was added dropwise over 2 hours.
After reacting for 1 hour under reflux, n-heptane 400
Add 3 parts of benzoyl peroxide to 1 part, stir, disperse, divide into 4 parts, add every 10 minutes, further age under reflux for 2 hours, and add Isopar G (manufactured by Exxon Chemical).
400 parts were added and cooled. The product liquid is a slightly transparent milky white emulsion with an average particle size of 0.25μ.
0.5μ or less accounted for more than 90%. Add 0.55 nigrosine dye to 10 parts of the resulting resin dispersion.
and 24.5 parts of Isopar G in a ball mill.
The mixture was kneaded for 18 hours to obtain a concentrated developer. Further, 0.4 parts of zinc naphthenate and 330 parts of Isopar G were added to this to prepare a developer. Example 2 Vinyl Versatinate 15 was added to the reactor of Example 1.
After adding 40 parts of 2-ethylhexyl methacrylate, 5 parts of stearyl methacrylate, 40 parts of cyclohexyl methacrylate, 40 parts of n-hexane and 0.1 part of azobisisobutyronitrile and heating to reflux for 30 minutes, azobisisobutyronitrile of the same monomer composition was added. A solution containing 0.2 parts of nitrile was added dropwise over 1 hour, and the mixture was allowed to react under reflux for 1 hour, and then a solution of 0.6 parts of azobisisobutyronitrile dissolved in 30 parts of toluene was added dropwise over 1 hour. During the course of the reaction, the viscosity increased, so to adjust it, 130 parts of n-heptane was added dropwise, and the reaction was allowed to continue under reflux for an additional hour. Next, while maintaining a refluxing state, a mixture of 250 parts of vinyl acetate, 92 parts of ethyl acrylate, 8 parts of 2-hydroxyethyl acrylate, and 3.5 parts of Perbutyl IB (manufactured by NOF Corporation) was added dropwise over 2 hours and reacted for 1 hour. - A mixed solution of 400 parts of heptane and 3.5 g of Perbutyl IB was added dropwise over 1 hour, and after aging for 8 hours, 500 parts of Isopar G was added and cooled. The resulting liquid was a slightly transparent milky white emulsion. A solution prepared by dissolving 1.5 parts of oil yellow in 6 parts of toluene was added dropwise to 100 parts of the resulting resin dispersion while stirring, and 0.3 g of aluminum myristate was added thereto to obtain a concentrated developer. Furthermore, isopar
The developer was diluted with 2500 parts of G. Example 3 In the reactor of Example 1, 130 parts of n-octyl methacrylate, 70 parts of cyclohexyl methacrylate,
Add 4 parts of mercaptopropionic acid and react at 80°C for 6 hours while introducing a small amount of air to the surface.
-20 parts of heptane and 0.5 parts of Perloil L (manufactured by NOF)
A mixed solution of 50% was added twice every 30 minutes for reaction to obtain a solution consisting of a polymer having a non-volatile content of 80% and a molecular weight of about 8,000. Next, 50 parts of n-heptane was added to this, and while maintaining the reflux state, a mixture of 270 parts of vinyl acetate, 30 parts of n-octyl acrylate, 3 parts of Perloyl L, and 50 parts of n-heptane was added dropwise over 8 hours, and after 2 hours of reaction, n-heptane was added.
- 1 part of a mixture of 40 parts of heptane and 1.5 parts of Perloyl L
After dripping for 2 hours and aging for another 2 hours, isopar
160 parts of G was added and cooled. Add 100g of Isopar G to 100 parts of the obtained resin dispersion.
A solution of 3 parts of Crystal Violet Victoria Blue dissolved in 15 parts of dichloroethylene was added dropwise with stirring, heated to 80°C, kept for 2 hours, cooled, and 0.6 parts of aluminum myristate was added to develop a concentrated solution. I got the liquid. Furthermore, isopar G
4,800 parts of the solution was added to obtain a blue developer with excellent dispersion stability. Example 4 In the reaction vessel of Example 1, 140 parts of 2-ethylhexyl methacrylate, 60 parts of benzyl methacrylate,
40 parts of n-hexane, 1 part of mercaptoethanol,
Add 0.1 part of azobisisobutyronitrile, heat to reflux, continue the reaction for 2 hours, and then add toluene.
A mixture of 40 parts of azobisisobutyronitrile and 0.8 parts of azobisisobutyronitrile was added dropwise over 1 hour, and the mixture was reacted under reflux for 4 hours.
To this was added 50 parts of n-heptane, and while maintaining the reflux state, 125 parts of vinyl acetate, 35 parts of 2-ethylhexyl methacrylate, 15 parts of benzyl methacrylate, and
- 40 parts of heptane and Perbutyl O (manufactured by NOF)
2 parts of the mixture was added dropwise over 1 hour. After 2 hours of reaction, 125 parts of vinyl acetate, 10 parts of n-heptane, and 1 part of perbutyl O were added.
of the mixture was added dropwise over 1 hour, and after further reaction for 1 hour, n-
1 mixture of 40 parts heptane and 1.5 parts perbutyl O
After the reaction was continued for 2 hours, 120 parts of Isopar G was added and the mixture was cooled. The resulting dispersion was a slightly transparent milky white emulsion with an average particle size of 0.2μ. 100 parts of this resin dispersion, 6 parts of Lionogen Magenta R (manufactured by Toyo Ink) whose surface was treated with aluminum hydroxide, and 1.2 parts of aluminum stearate.
After kneading in a ball mill for 10 hours, 4500 parts of Isopar G was added to dilute the mixture to obtain a developer. Example 5 In the reaction vessel of Example 1, 30 parts of n-butyl methacrylate and 120 parts of 2-ethylhexyl methacrylate were added.
50 parts of cyclohexyl methacrylate, 40 parts of n-hexane, 0.5 parts of mercaptoethanol, 0.5 parts of lauryl mercaptan, and 0.1 part of azobisisobutyronitrile were heated to reflux, reacted for 2 hours, and then mixed with 40 parts of toluene. 0.8 part of azobisisobutyronitrile was added dropwise over 1 hour, and the reaction was continued for an additional 4 hours to obtain a solution consisting of a polymer with a non-volatile content of 70% and a molecular weight of about 12,000. Next, 50 parts of n-heptane was added to this, and while maintaining the reflux state, 300 parts of vinyl acetate, 100 parts of isononyl acrylate, 70 parts of n-heptane, and perloyl were added.
A mixture of 10 parts of L L was added dropwise over 4 hours, and after reacting for 1 hour, a mixture of 40 parts of n-heptane and 2 parts of Perloyl L was added, and the reaction was continued for another 3 hours to produce 160
1 part was added and cooled. A developer was obtained in the same manner as in Example 4 using 90 parts of the obtained resin dispersion. Example 6 120 parts of n-octyl methacrylate of Example 1,
A soluble copolymer solution was obtained in the same manner as in Example 1 except that 95 parts of isononyl methacrylate, 10 parts of stearyl methacrylate, and 95 parts of cyclohexyl methacrylate were used instead of 80 parts of cyclohexyl methacrylate. Next, under reflux, a mixture of 200 parts of vinyl acetate and 2 parts of benzoyl peroxide was added dropwise over 2 hours, and after reacting for 1 hour, n-heptane was added.
A mixture of 300 parts of Perloil L and 2 parts of Perloil L was added dropwise over 1 hour, reacted for an additional 2 hours, and then added to Isopar G300.
part was added and cooled. A developer was prepared in the same manner as in Example 1 using 10 g of the obtained resin dispersion. Example 7 The mixture of 300 g of vinyl acetate and 3 g of benzoyl peroxide in Example 1 was made into a mixture of 900 g of vinyl acetate, 9 g of benzoyl peroxide, and 200 g of n-heptane,
Next, the amounts of n-heptane and benzoyl peroxide added were changed to 900 g and 9 g, respectively, and the amount of Isopar G added during cooling was changed to 900 g.
A developing solution was obtained by performing all the same operations as in Example 1. Comparative Example 1 120 parts of n-octyl methacrylate of Example 1,
A developer was obtained in the same manner as in Example 1 except that 80 parts of cyclohexyl methacrylate was replaced with 108 parts of n-octyl methacrylate and 92 parts of stearyl methacrylate. Comparative Example 2 A developer was obtained by carrying out the same operations as in Example 2, except that vinyl versatate, stearyl methacrylate, and cyclohexyl methacrylate in Example 2 were all replaced with 2-ethylhexyl methacrylate. The main composition fractions of the soluble copolymers in Examples 1 to 7 and Comparative Examples 1 to 2 are summarized in Table 1. Further, Table 2 shows the results of forming images on zinc oxide coated electrostatic photographic paper using the developing solutions of Examples 1 to 7 and Comparative Examples 1 to 2. In order to make the image density the same in each example, a developer was prepared in the same manner as in Example 1 using a resin dispersion adjusted with Isopar G so that the dispersion concentration was the same as in Example 1. and compared.

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Claims (1)

[Claims] 1. In a highly insulating hydrocarbon medium, (A) formula [Formula] [where X represents hydrogen or methyl,
Y represents -COOR, -OCOR or -OR,
R represents a _C4-20 alkyl] 95-15% by weight of _the monomer and the formula 5 to 85% by weight of the monomer [wherein () and ()]
The sum of the monomers is 100% by weight] and an organic mercaptan having at least one thiol group with a sulfur content of 0 to 2% by weight (however, the sulfur content per soluble copolymer shown below) (B) a copolymer substantially soluble in the medium; and (B) a polymer substantially insoluble in the medium. 2. The resin dispersion according to claim 1, wherein the monomer of formula () is cyclohexyl methacrylate, benzyl methacrylate, cyclohexyl acrylate, or benzyl acrylate. 3. The resin dispersion according to claim 1 or 2, wherein R represents _C4-12 alkyl. 4. The resin dispersion according to any one of claims 1 to 3, wherein the insoluble polymer contains 20 to 100% by weight of vinyl acetate. 5. The resin dispersion according to any one of claims 1 to 4, wherein the soluble copolymer contains the organic mercaptan in a sulfur content of 0.03 to 2% by weight.