JP2007065235A - Liquid electrostatic developer and method for manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative charging liquid electrostatic developer which can disperse pigment particles in a high concentration into a low dielectric carrier liquid of low dielectric property, such as vegetable oil, can enhance the image density and can simultaneously provide storage stability and desired charge holding characteristic over a long period of time, and a method for manufacturing the same. <P>SOLUTION: The liquid electrostatic developer contains microencapsulated pigment particles which have a coating layer composed of a polymerization polymer having at least a repeating unit derived from an ionic polymerizable surfactant having an opposite charge, a repeating unit derived from a hydrophilic macromonomer, and a repeating unit derived from an anionic polymerizable surfactant and/or a hydrophilic monomer having an anionic group on the pigment particle surface having ionic groups on the surface in a low dielectric carrier liquid; and in which the anionic groups are arrayed on the coating layer surface and the self-negative charging property is exhibited. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid electrostatic developer used in an electrophotographic image forming apparatus used for a copying machine, a printer, and the like, and a method for manufacturing the same.

  In electrophotography, a wet development method is known as a method for developing an electrostatic latent image, and an electrostatic latent image is formed on a photoreceptor by charging and image exposure, and a resin and a colorant are the main components. An electrostatic latent image is developed using a liquid electrostatic developer in which toner particles are usually dispersed in an aliphatic hydrocarbon such as Isopar, and the resulting toner image is transferred and fixed on a transfer paper. To be formed. In such a wet development method, toner particles of submicron to several μm are dispersed in a highly insulating carrier such as an aliphatic hydrocarbon to form a liquid electrostatic developer. Since the particle size can be made smaller than that of the dry development method, it is possible to obtain high resolution and gradation.

  However, in a liquid electrostatic developer, colored particles tend to settle, and when a charge control agent (CCA) is added to impart charge, the storage stability becomes unstable, the viscosity increases during long-term storage, and the liquid electrostatic developer It may be difficult to fulfill the function as a developer. In addition, the addition of CCA has a problem that the resistance of the carrier liquid is lowered and the dot reproducibility and fine line reproducibility during development is lowered. To solve this problem, pigment particles are coated by melt-kneading with resin, or microencapsulated by interfacial polymerization of polar monomers in the presence of pigment particles to give colored resin particles with polarity. It is known (Patent Documents 1 to 6), however, since the polymer to be coated is not removed at all, the content of the pigment is limited from the viewpoint of dispersion stability, and the pigment particles are highly concentrated in the carrier. In other words, the image density cannot be increased, and it is difficult to simultaneously obtain storage stability over a long period of time and desired charge retention.

  In addition, a liquid containing an aqueous medium and a coloring material component by adding a non-aqueous solvent to the coloring material that covalently bonds the polymer component or an aqueous medium in which the monomer and the coloring material forming the polymer are emulsified and dispersed. It is known that a liquid electrostatic developer having excellent dispersibility can be obtained by forming droplets and interfacial polymerization or by removing aqueous solvent to form colored resin particles (Patent Documents 7 and 8). The charge stability is due to the addition of a charge control agent, and the above-described problems due to the addition of CCA still remain.

  In Patent Documents 1 to 8, volatile aliphatic hydrocarbons are used as the carrier liquid, and when the toner image is fixed, the carrier liquid contained in the toner is volatilized or evaporated by means such as heating. Although it is necessary, there is a problem of deteriorating the use environment. Further, even if a means for collecting the aliphatic hydrocarbons volatilized in the vicinity of the fixing device is provided in consideration of the use environment, it is disadvantageous for downsizing the image forming apparatus.

  Attempts have been made to respond to the demands for consideration for the use environment and miniaturization by using non-volatile silicone oil or liquid paraffin instead of volatile aliphatic hydrocarbons as the carrier liquid. Because of its excellent chemical stability, it will continue to exist on the transfer paper for a long time, resulting in problems such as a decrease in the print quality texture, a decrease in the stamping ability, and a decrease in the writing performance using water-based ink. is there.

  Further, it is known that the use of vegetable oil as a carrier does not cause environmental pollution as compared with volatile aliphatic hydrocarbons, and can reduce the risk of fire (Patent Document 9). It is also known that a modified product (unsaturated higher fatty acid ester) is used as a carrier liquid (Patent Document 10), and it is particularly required to use vegetable oil as a carrier as an environmentally friendly liquid electrostatic developer. According to the study by the present inventors, it has been found that the vegetable oil itself may be negatively charged, and the pigment may exhibit both positive and negative polarities.

Therefore, when vegetable oil is used as the carrier liquid, it is indispensable to use CCA to obtain the desired polarity. However, the addition of CCA basically lowers the resistance of the carrier liquid, and dot reproducibility and fine line reproduction during development. In addition, the storage stability of the dispersion becomes unstable, and the viscosity increases when stored for a long period of time, making it difficult to function as a liquid electrostatic developer.
JP-A-8-30040 Japanese Patent Laid-Open No. 9-218540 JP-A-9-311506 JP 2005-10528 A Japanese Patent Laid-Open No. 2004-2501 JP 2001-31900 A JP 2002-212302 A Japanese Patent Laid-Open No. 2002-226591 JP 2000-19787 A JP 2001-98197 A

  The present invention can disperse pigment particles in a high concentration in a low dielectric carrier to increase the image density, and at the same time, can provide long-term storage stability and desired charge retention at the same time. It is an object to provide a liquid electrostatic developer and a method for producing the same, and in particular, to provide a negatively chargeable liquid electrostatic developer using vegetable oil as a carrier and a method for producing the same.

  The liquid electrostatic developer of the present invention is a liquid developer in which microencapsulated pigment particles are dispersed in a low dielectric carrier liquid, and the microencapsulated pigment particles are formed on the surface of pigment particles having ionic groups on the surface. An ionic polymerizable surfactant having an ionic group, a hydrophobic group, and a radically polymerizable group is ionically bonded in one molecule having an opposite charge to the pigment particles having an ionic group on the surface, and the ion A repeating unit derived from a polymerizable polymerizable surfactant, a repeating unit derived from a hydrophilic macromonomer having a hydrophilic group, a long-chain hydrophilic part, and a radically polymerizable group in one molecule; The number of repeating units derived from an anionic polymerizable surfactant having an anionic group, a hydrophobic group and a radically polymerizable group and / or a hydrophilic monomer having an anionic group is small. A coating layer comprising at least a radically polymerized polymer, and at least an anionic group derived from an anionic polymerizable surfactant is arranged on the surface of the coating layer toward the low dielectric carrier liquid dispersion medium side, and is self-negatively charged. It is characterized by exhibiting sex.

  The radical polymerization polymer in the microencapsulated pigment particles further has a repeating unit derived from at least one comonomer of a hydrophobic monomer and a crosslinking monomer.

  The pigment particles in the microencapsulated pigment particles are pigment particles having an anionic group on the surface, and the ionic polymerizable surfactant is a cationic polymerizable surfactant.

Cationic polymerizable surfactant
General formula R _{[4- (l + m + n)]} R ¹ _l R ² _m R ³ _n N ⁺ · X ⁻
Wherein R is a radical polymerizable group, R ¹ , R ² and R ³ are selected from hydrogen, alkyl group, aryl group, aralkyl group and alkylaryl group, at least one of which is a hydrophobic group , X is Cl, Br or I, l, m and n are 1 or 0 and are not 0 at the same time.)
It is a compound represented by these.

  The anionic polymerizable surfactant is a compound represented by the following general formula (1).

(In the formula, p is an integer of 9 or 11, q is an integer of 2 to 20, A is an anionic group, and the counter ion is an alkali metal ion, an ammonium ion, or an alkanolamine ion.)
The volume primary average particle diameter of the microencapsulated pigment particles is 0.2 μm to 1 μm.

  It is characterized by containing 2 mass% to 50 mass% of microencapsulated pigment particles.

The low dielectric carrier liquid contains a vegetable oil containing an unsaturated group or an unsaturated fatty acid ester, and has a volume resistance of 10 ⁹ Ω · cm or more and a dielectric constant of 3.6 or less.

  The vegetable oil containing an unsaturated group is selected from safflower oil containing at least 50% linoleic acid component, sunflower oil, soybean oil, corn oil, cottonseed oil, or linseed oil containing at least 50% linolenic acid component It is characterized by being a vegetable oil.

The method for producing the liquid electrostatic developer of the present invention comprises:
(1) Step of dispersing pigment particles having an ionic group on the surface in an aqueous dispersion medium (2) In the dispersion, ionicity in one molecule having an opposite charge to the pigment particles having an ionic group on the surface A step of adding an ionic polymerizable surfactant having a group, a hydrophobic group and a radical polymerizable group, followed by a dispersion treatment;
(3) In the dispersion, a hydrophilic macromonomer having a hydrophilic group, a long-chain hydrophilic part and a radical polymerizable group in one molecule, an anionic group, a hydrophobic group and radical polymerizable in one molecule. A step of adding at least an anionic polymerizable surfactant having a group and / or a hydrophilic monomer having an anionic group, and a dispersion treatment;
After carrying out sequentially,
(4) The dispersion treatment liquid is heated and a polymerization initiator is added, emulsion polymerized, and ionic in one molecule having a charge opposite to that of the pigment particle having an ionic group on the surface of the pigment particle. Hydrophilic group having a repeating unit derived from an ionic polymerizable surfactant having a group, a hydrophobic group and a radically polymerizable group, and a hydrophilic group, a long-chain hydrophilic part and a radically polymerizable group in one molecule Derived from a repeating unit derived from a macromonomer, an anionic polymerizable surfactant having an anionic group, a hydrophobic group and a radical polymerizable group in one molecule and / or a hydrophilic monomer having an anionic group. Forming a microencapsulated pigment particle by forming a coating layer made of a radically polymerized polymer having at least a repeating unit.
(5) The aqueous medium is removed from the dispersion treatment liquid, and the resulting microencapsulated pigment particles are dispersed in a low dielectric carrier liquid, and the low dielectric carrier liquid dispersion medium side on the surface of the coating layer of the microencapsulated pigment particles A liquid electrostatic developer exhibiting self-negative charging property by anionic groups derived from a hydrophilic monomer having at least an anionic polymerizable surfactant and / or an anionic group.

  The microencapsulated pigment particles in the above production method are dispersed in a low dielectric carrier liquid by a wet method selected from a ball mill, a bead mill, and an attritor, and a volume primary average particle diameter is 0.2 μm to 1 μm. It is characterized by.

When the pigment particles have an anionic group on the surface, the process of forming the coating layer will be described with reference to the schematic diagrams shown in FIGS.
FIG. 1 shows a cationic polymerizable property in which pigment particles 1 having an anionic group 14 as an ionic group are dispersed in an aqueous medium and have a cationic group 11, a hydrophobic group 12, and a radical polymerizable group 13. It is a figure which shows the state coexisting with respect to the surfactant 2, the hydrophilic macromonomer 3 which has the hydrophilic group 15, the long-chain hydrophilic part 17, and the radically polymerizable group 16. FIG. It is considered that the cationic polymerizable surfactant 2 is arranged so that the cationic group 11 faces the anionic group 14 of the pigment particle 1 and is adsorbed with a strong ionic bond.

  In this state, when the hydrophilic macromonomer, the anionic polymerizable surfactant 4 and / or the hydrophilic monomer 5 having an anionic group are added and dispersed, the hydrophilic macromonomer 3 becomes a radical polymerizable group 16 side, an anion. The cationic polymerizable surfactant is a radical polymerizable group 13 'and a hydrophobic group 12' side, and the hydrophilic monomer having an anionic group is cationic polymerized from the polymerizable group 13 "side by the affinity of the hydrophobic groups. The surfactant 2 is oriented toward the hydrophobic group 12 or radical polymerizable group 13 side, while the hydrophilic group 15 and anionic groups 14 'and 14 "sides are in the direction in which the aqueous medium exists, that is, the pigment particle 1 It is considered that an admicelle state oriented in a direction away from the surface is formed. And it is thought that the microencapsulated pigment particle 100 in which the pigment particle 1 is covered with the polymer layer 60 is produced by adding a polymerization initiator in this state and emulsion polymerization as shown in FIG. .

  The microencapsulated pigment particle in the present invention has a cationic polymerizable surfactant, an anionic polymerizable surfactant and / or an anionic group present around the pigment particle before the polymerization reaction shown in FIG. The arrangement state of each of the hydrophilic monomer and the hydrophilic macromonomer can be controlled to a very high degree, and in the outermost case, it becomes an admicelle state in which anionic groups are oriented and arranged toward the aqueous medium phase side. Then, by the emulsion polymerization reaction, the cationic polymerizable surfactant, the anionic polymerizable surfactant, and the hydrophilic macromonomer are converted into a polymer in this highly controlled state, and a coating layer can be formed. Therefore, it is considered that microencapsulated pigment particles coated with an encapsulating resin whose structure is controlled with extremely high accuracy can be obtained.

  Although the above explanation is inferred, the liquid electrostatic developer of the present invention clearly shows a self-negative charging property as described in Examples described later. This indicates that the anionic group oriented and arranged on the surface of the coating layer of the microencapsulated pigment particles exhibits self-negative chargeability, and is considered to support the formation mechanism of the coating layer.

  As described above, the pigment particle having an anionic group on the surface has been described as an example. However, in the present invention, the ionic group on the surface of the pigment particle is not limited to the anionic group. An anionic polymerizable surfactant having a cationic group and having an opposite charge may be used as an anionic polymerizable surfactant, and can be similarly adsorbed with a strong ionic bond. When a macromonomer or an anionic polymerizable surfactant is added, an admicelle state can be similarly formed by the mutual affinity action of the polymerizable group and the hydrophobic group, and the negatively charged microencapsulated pigment particles can be formed by an emulsion polymerization reaction. can do.

  The liquid electrostatic developer of the present invention is obtained by dispersing self-negatively charged microencapsulated pigment particles in a low dielectric carrier liquid, and in the low dielectric carrier liquid, the self negatively charged microencapsulated pigment particles Does not aggregate due to mutual repulsion of anionic groups arranged on the surface of the coating layer, can be excellent in dispersibility, and can be dispersed at a high concentration. Further, since the pigment concentration in the microencapsulated pigment particles can be controlled, the toner image concentration can be increased.

  In addition, since it is self-negatively charged, it is not necessary to add CCA, so that long-term storage stability and desired charge retention can be obtained simultaneously, and hydrophilic macromolecules can be added without adding a fixing resin. It can be fixed on plain paper by an encapsulating resin layer derived from monomers.

  In addition, even when vegetable oil is used as a carrier liquid, long-term storage stability and desired charge retention as a liquid electrostatic developer can be obtained at the same time regardless of the polarity of the vegetable oil itself. The liquid electrostatic developer does not cause the VOC) problem.

  In addition, according to the method for producing a liquid electrostatic developer of the present invention, microencapsulated pigment particles in which anionic groups are arranged and oriented on the surface of the coating layer can be easily produced. Due to the excellent dispersibility of the encapsulated pigment particles, a long-term storage stability can be obtained, and a negatively chargeable liquid electrostatic developer that simultaneously satisfies the desired charge retention can be easily produced.

  The microencapsulated pigment particles in the liquid electrostatic developer of the present invention will be described focusing on the case where the pigment particles have an anionic group on the surface thereof.

  The pigment particles having an anionic group on the surface are derived from an inorganic pigment or an organic pigment, and can be suitably produced by surface treatment with an anionic (hydrophilic) group imparting agent. The pigment needs to be a pigment that does not dissolve in the anionic (hydrophilic) group-providing agent described later, and examples thereof include the following pigments.

  Examples of the inorganic pigment include carbon blacks such as furnace black, lamb black, acetylene black, and channel black (C.I. Pigment Black 7), iron oxide pigments, and the like. Organic pigments include azo pigments (including azo lakes, insoluble azo pigments, condensed azo pigments, and chelate azo pigments), and polycyclic pigments (eg, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxane pigments). Thioindigo pigments, isoindolinone pigments, or quinofuranone pigments), dye chelates (such as basic dye-type chelates or acidic dye-type chelates), nitro pigments, nitroso pigments, or aniline black.

  Examples of carbon black include No. manufactured by Mitsubishi Chemical. 2300, no. 900, MCF88, No. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, or No2200B, etc .; Columbia-made Raven5750, Raven5250, Raven5000, Raven3500, Raven1255, Raven700, etc .; 800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300, Monarch 1400, etc .; or Color Black FW1, Color Black FW2, Bck, Col Black FW2, Cck W200, Color Black S150, Color Black S160, Color Black S170, Printex 35, Printex U, Printex V, can be used Printex 140U, Special Black 6, Special Black 5, Special Black 4A, or Special Black 4 and the like. Further, as the organic pigment for black, a black organic pigment such as aniline black (C.I. Pigment Black 1) can be used.

  Further, as organic pigments for yellow, C.I. l. Pigment Yellow 1 (Hansa Yellow), 2, 3 (Hansa Yellow 10G), 4, 5 (Hansa Yellow 5G), 6, 7, 10, 11, 12, 13, 14, 16, 17, 24 (Flavantron Yellow) , 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108 (anthrapyrimidine yellow), 109, 110, 113, 117 ( Copper complex pigment), 120, 124, 128, 129, 133 (quinophthalone), 138, 139 (isoindolinone), 147, 151, 153 (nickel complex pigment), 154, 167, 172, 180, etc. it can.

  Further, organic pigments for magenta include C.I. l. Pigment Red 1 (Para Red), 2, 3 (Toluidine Red), 4, 5 (lTRRed), 6, 7, 8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38 (pyrazolone red), 40, 41, 42, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 88 (thioindigo), 112 ( Naphthol AS system), 114 (naphthol AS system), 122 (dimethylquinacridone), 123, 144, 146, 149, 150, 166, 168 (antanthrone orange), 170 (naphthol AS system), 171, 175, 176, 177, 178, 179 (berylene maroon), 184, 185, 187, 202, 209 (dichloroquinacridone), 219, 224 (vector) Ren-based), 245 (Naphthol AS-based), or, C. I. Pigment violet 19 (quinacridone), 23 (dioxazine violet), 32, 33, 36, 38, 43, 50, and the like.

  Further, as an organic pigment for cyan, C.I. l. Pigment Blue 1, 2, 3, 15, 15: 1, 15: 2, 15: 3, 15:34, 15: 4, 16 (metal-free phthalocyanine), 18 (alkali blue toner), 22, 25, 60 ( Slen Blue), 65 (Biolantron), 66 (Indigo), C.I. l. Vat blue 4, 60 etc. can be mentioned.

  Examples of organic pigments used in color developers other than magenta, cyan or yellow include C.I. I. Pigment green 7 (phthalocyanine green), 10 (green gold), 36, 37; C.I. I. Pigment brown 3, 5, 25, 26; I. Pigment orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, and the like.

  In the macroencapsulated pigment according to the present invention, the above pigments can be used alone or in combination of two or more.

  Inorganic pigments or organic pigments may be produced from the synthesis stage, and after synthesis, a known wet method such as a pole mill, a bead mill, a sand mill, or an attritor is used, and an anionic dispersion is used depending on the structure and polarity of the pigment. Agent, cationic dispersant or nonionic dispersant is added at a ratio of 0.1% by mass with respect to the pigment, and the primary average particle size is pulverized to a primary average particle size of 10 nm to 1000 nm, preferably 20 nm to 900 nm. It is good to keep.

  Examples of the anionic (hydrophilic) group imparting agent that introduces an anionic group into the pigment particles include sulfur-containing treatment agents and carboxylating agents.

Examples of the treatment agent containing sulfur include sulfuric acid, fuming sulfuric acid, sulfur trioxide, chlorosulfuric acid, fluorosulfuric acid, amidosulfuric acid, sulfonated pyridine salt, sulfamic acid, etc. Among them, sulfur trioxide, sulfonated pyridine salt or sulfamine. Sulfonating agents such as acids are suitable, and these can be used alone or in admixture of two or more. The sulfonating agent means at least one anionic (hydrophilic) group of a sulfonic acid group (—SO ₃ H) or a sulfinic acid group (—RSO ₂ H) (hereinafter simply referred to as a sulfonic acid group (hydrophilic group). )) Is applied to the pigment particle surface. In addition, R in a sulfinic acid group is a C1-C12 alkyl group or a phenyl group, and may have a substituent.

  Further, a solvent capable of forming a complex with sulfur trioxide, for example, a basic solvent such as N, N-dimethylformamide, dioxane, pyridine, triethylamine, trimethylamine, a solvent described later with nitromethane, acetonitrile or the like. It is also useful to complex with one or more mixed solvents.

  In particular, when sulfur trioxide itself is highly reactive and the pigment itself is decomposed or altered, or if it is difficult to control the reaction with a strong acid, a complex of sulfur trioxide and a tertiary amine as described above. It is preferable to sulfonate the pigment particles using In addition, if sulfuric acid, fuming sulfuric acid, chlorosulfuric acid, fluorosulfuric acid, etc. are used alone, the pigment particles may dissolve, so it is necessary to suppress the reaction against strong acids that react per molecule. There is a need to pay attention to the type of solvent and the amount to be used.

  The solvent used in the reaction is selected from those which do not react with the treatment agent containing sulfur and in which the above-mentioned pigment becomes insoluble or hardly soluble. For example, sulfolane, N-methyl-2-pyrrolidone, Examples include dimethylacetamide, quinoline, hexamethylphosphoric triamide, chloroform, dichloroethane, tetrachloroethane, tetrachloroethylene, dichloromethane, nitromethane, nitrobenzene, liquid sulfur dioxide, carbon disulfide, and trichlorofluoromethane.

  The treatment with the treatment agent containing sulfur is preferably performed by adding a treatment agent containing sulfur to a dispersion obtained by dispersing pigment particles in a solvent, heating to 60 to 200 ° C., and stirring for 3 to 10 hours. Specifically, a method of carrying out high-speed shearing with a high-speed mixer or the like in advance, or impact-dispersing with a bead mill or a jet mill to form a slurry (dispersion) is preferable. Then, after moving to gentle stirring, a treatment agent containing sulfur is added to introduce hydrophilic groups onto the pigment particle surface. At this time, the introduction amount of the hydrophilic group is greatly affected by the reaction conditions and the kind of the treatment agent containing sulfur. After the reaction, in order to remove the treatment agent containing the solvent and residual sulfur from the slurry of pigment particles, repeated heat treatment, water washing, ultrafiltration, reverse osmosis, etc., centrifugation, filtration, etc. It may be dried and pulverized.

The sulfonic acid group (—SO ₃ H) and / or the sulfinic acid group (—RSO ₂ H) may be treated with an alkali compound, and a sulfonic acid anion group (—SO ₃ ⁻ ) and / or a hydrophilic group may be used. Pigment particles having a sulfinic acid group (—RSO ₂ ⁻ ) on the surface are preferred. As the alkali compound, the cation is an alkali metal ion or chemical formula (R ₁ R ₂ R ₃ R ₄ N) ⁺ (R ₁ , R ₂ , R ₃ and R ₄ may be the same or different, and may be a hydrogen atom, an alkyl group, An alkaline compound that is a monovalent ion represented by (showing a hydroxyalkyl group or an alkyl halide group) is selected. Preferably, the cation is an alkali compound that becomes an alkanolamine cation such as lithium ion (Li ⁺ ), potassium ion (K ⁺ ), sodium ion (Na ⁺ ), ammonium ion (NH ₄ ⁺ ), or triethanolamine cation. As an anion of an alkali compound for treating a sulfonic acid group and / or a sulfinic acid group, a hydroxide anion is preferably used. Specific examples thereof include monovalent alkali metal hydroxides (LiOH, NaOH, KOH). In addition, ammonia, alkanolamine (monoethanolamine, diethanolamine, N, N-butylethanolamine, triethanolamine, propanolamine, aminomethylpropanol, 2-aminoisopropanol and the like are exemplified.

  The addition amount of the alkali compound is preferably not less than the neutralization equivalent of the sulfonic acid group and / or sulfinic acid group of the pigment particles. When a volatile additive such as ammonia or alkanolamine is used as the alkali compound, the addition amount is approximately 1.5 times or more of the neutralization equivalent.

  The neutralization operation may be performed by introducing pigment particles having sulfonic acid groups and / or sulfinic acid groups chemically bonded to the surface into an alkali compound, and shaking with a paint shaker or the like.

  The amount of sulfonic acid groups (hydrophilic groups) introduced was such that pigment particles having sulfonic acid groups (hydrophilic groups) introduced on the surface were treated by an oxygen flask combustion method and absorbed in a 0.3% aqueous hydrogen peroxide solution. Thereafter, the content of sulfate ion (divalent) is quantified by ion chromatography (Dionesque, 2000i), and this value may be converted to the amount of sulfonic acid group, in millimolar amount (mmol / g) per gram of pigment. Indicated.

  The amount of sulfonic acid group (hydrophilic group) introduced is preferably 0.01 mmol / g or more. When the introduction amount of the sulfonic acid group is less than 0.01 mmol / g, in the microencapsulation step of the pigment particles in the aqueous solvent, the aggregation of the pigment particles is likely to occur, and the average particle size of the microencapsulated pigment particles The diameter tends to increase, the dispersibility of the pigment particles is low, the microencapsulation of the pigment particles becomes insufficient, and resin particles containing no pigment are easily produced as a by-product, which is not preferable. Moreover, even if it exceeds 0.15 mmol / g, the effect accompanying the increase in the amount of introduced sulfonic acid groups is not observed.

  Next, the carboxylating agent is a treatment agent for imparting a carboxylic acid group (—COOH) to the pigment surface. Examples of the carboxylating agent include hypohalites such as sodium hypochlorite and potassium hypochlorite. Hypohalite breaks a part of the bond (C = C, C—C) on the pigment particle surface and oxidizes it to introduce a carboxylic acid group (—COOH) onto the pigment particle surface. Further, a carboxylic acid group (hydrophilic group) may be introduced by physical oxidation such as plasma treatment.

  An example of treatment with a carboxylating agent is effective after high-speed shear dispersion of pigment particles in an aqueous medium with a high-speed mixer or the like, or impact dispersion with a bead mill or jet mill to make a slurry dispersion. Hypohalite having a halogen concentration of 10 to 30% is added, and the mixture is reacted at 60 to 80 ° C. for 5 to 10 hours, preferably 10 hours or more with appropriate stirring. After the reaction, heat treatment is performed to remove the solvent and the remaining carboxylating agent from the slurry, and after being subjected to treatment such as washing with water, ultrafiltration, reverse osmosis, centrifugation, filtration, etc., if necessary, Dry and pulverize.

  Since it is difficult to measure the amount of carboxylic acid group (—COOH) introduced, the amount of active hydrogen on the pigment surface is measured, and the measured amount is taken as the amount of carboxylic acid group (—COOH) introduced. The amount of active hydrogen on the pigment surface can be measured using the Zeisel method. That is, after all active hydrogen on the surface of the pigment particles is exchanged with methyl groups using a diazomethane solution, hydroiodic acid having a specific gravity of 1.7 is added and heated to vaporize the methyl groups as methyl iodide. Subsequently, methyl iodide is trapped with a silver nitrate solution to precipitate as methyl silver iodide, and the amount of the original methyl group, that is, the amount of active hydrogen is measured by the weight of the obtained methyl silver iodide. The amount of active hydrogen is indicated by the amount of millimoles per gram of pigment (mmol / g).

  The active hydrogen content in the pigment is preferably 1.0 mmol / g or more, and more preferably 1.5 mmol / g or more. If it is less than 1.0 mmol / g, the dispersibility in an aqueous solvent is low, the microencapsulation of pigment particles becomes insufficient, resin particles containing no pigment are by-produced, and aggregates of pigment particles are easily generated. It is not preferable. The active hydrogen content is at most 6.0 mmol / g.

  The average particle diameter of the pigment particles having an anionic group (hydrophilic group) on the surface is preferably 1000 nm or less, and preferably 50 nm to 800 nm. In order to make the average particle diameter of pigment particles having an ionic group (hydrophilic group) within this range, the primary particle diameter of the pigment, the kind of hydrophilic group imparting agent, the anionic group (hydrophilic group) of An introduction amount or the like may be appropriately selected. By making the average particle size 1000 nm or less, it is possible to obtain microencapsulated pigment particles that have excellent dispersion stability in an aqueous medium and can increase the image density. The pigment particle size is measured using a laser Doppler type particle size distribution analyzer “Microtrac UPA150” manufactured by Leeds & Northrop.

  Next, the cationic polymerizable surfactant contains a hydrophilic group composed of a radical polymerizable group, a hydrophobic group, and a cationic group in one molecule at the same time by covalent bonding, and polymerization by a radical polymerizable group is performed. It has a function and a function as a surfactant by a hydrophilic group and a hydrophobic group made of a cationic group.

Cationic polymerizable surfactants are, for example,
General formula R _{[4- (l + m + n)]} R ¹ _l R ² _m R ³ _n N ⁺ · X ⁻
Wherein R is a radical polymerizable group, R ¹ , R ² and R ³ are selected from hydrogen, alkyl group, aryl group, aralkyl group and alkylaryl group, at least one of which is a hydrophobic group , X is Cl, Br or I, l, m and n are 1 or 0 and are not 0 at the same time.)
The compound represented by these is illustrated.

  In the formula, R is a radical polymerizable group, and is selected from the group consisting of unsaturated hydrocarbon groups such as vinyl group, allyl group, acryloyl group, methacryloyl group, propenyl group, vinylidene group, vinylene group, acryloyl group, A methacryloyl group is preferred.

R ¹ , R ² and R ³ are hydrogen, an alkyl group, an aryl group, an aralkyl group, and an alkylaryl group. The aralkyl group is an alkyl group substituted with an aromatic hydrocarbon, and the alkylaryl group is an alkyl group substituted. Aromatic hydrocarbon groups are exemplified.

Specific examples include dimethylaminoethyl methyl chloride {(methacryloyloxyethyltrimethylammonium chloride) [CH ₂ ═C (CH ₃ ) COOCH ₂ CH ₂ N (CH ₃ ) ₃ ] ⁺ Cl ⁻ }, dimethylamino methacrylate Examples thereof include ethyl benzyl chloride, diallyl dimethyl ammonium chloride, 2-hydroxy-3-methacryloxypropyl trimethyl ammonium chloride and the like. Commercially available products include Acryester DMC (Mitsubishi Rayon Co., Ltd.), Acryester DML60 (Mitsubishi Rayon Co., Ltd.), C-1615 (Daiichi Kogyo Seiyaku Co., Ltd.), etc., alone or in combination. May be used.

Moreover, the general formula X is described in Japanese Patent Kokoku ^{_{4-65824 - · (R 1 R 2}} R 3) N + CH 2 CH (OH) CH 2 OCH 2 C (R 4) = CH 2
(Wherein R ₁ represents a hydrocarbon group having 8 to 22 carbon atoms, R ₂ and R ₃ represent an alkyl group having 1 to ₃ carbon atoms, R ₄ represents a hydrogen atom or a methyl group, and X ⁻ represents a monovalent group. Represents the negative ion.)
A cationic polymerizable surfactant represented by the formula is also preferably exemplified.

  The cationic polymerizable surfactant is not limited to the above examples, and any cationic polymerizable surfactant may be used as long as it has the following cationic group, hydrophobic group, and polymerizable group in one molecule and has surface activity.

As the cationic group, a cationic group selected from a primary amine cation, a secondary amine cation, a tertiary amine cation, and a quaternary ammonium cation is preferable. The primary amine cation is a monoalkyl ammonium cation (RNH ₃ ⁺ ), the secondary amine cation is a dialkyl ammonium cation (R ₂ NH ₂ ⁺ ), and the tertiary amine cation is a trialkyl ammonium cation (R ₃ NH ⁺ ) and the like, and examples of the quaternary amine cation include (R ₄ N ⁺ ) and the like. Here, R is a hydrophobic group or a polymerizable group, and examples thereof include those represented by R, R ¹ , R ² and R ³ described above. Examples of the counter anion of the cationic group include chlorine ion, bromine ion and iodine ion. In addition, examples of the hydrophobic group include those selected from an alkyl group, an aryl group, and a group in which these are combined. Examples of the polymerizable group include unsaturated hydrocarbon groups such as vinyl group, allyl group, acryloyl group, methacryloyl group, propenyl group, vinylidene group, vinylene group, preferably acryloyl group, methacryloyl group. Is mentioned.

  The cationic polymerizable surfactant can be used alone or as a mixture of two or more.

  The addition amount of the cationic polymerizable surfactant is 0. 0 with respect to the total number of moles of anionic groups in the pigment (= weight of the pigment used (g) × anionic group on the pigment surface (mol / g)). The range is 5 to 2 times mol, preferably 0.8 to 1.2 times mol. By setting the addition amount to 0.5 times mol or more, the pigment particles having an anionic group as a hydrophilic group are strongly ionically bound and can be easily encapsulated. By setting the addition amount to 2 times or less, it is possible to reduce the generation of a cationic polymerizable surfactant that is not adsorbed on the pigment particles, and polymer particles that do not have pigment particles as a core substance (particles made only of a polymer). ) Can be suppressed.

  Next, in the present invention, after introducing a cationic polymerizable surfactant on the surface of the pigment particles, the hydrophilic dispersion is added with a hydrophilic macromonomer, an anionic polymerizable surfactant and / or an anionic group. The hydrophilic monomer is mixed and dispersed.

  The hydrophilic macromonomer has a hydrophilic group, a long-chain hydrophilic part, and a radical polymerizable group in one molecule, and preferably has a weight average molecular weight in the range of 100 to 5000. Examples of the hydrophilic group include sulfonic acid. , Sulfinic acid, carboxyl group, carbonyl group, hydroxyl group, alkylene oxide group, amide group, amino group and the like. As the polymerizable group, those described above for the cationic polymerizable surfactant can be similarly applied. In addition, examples of the long-chain hydrophilic portion include polyalkylene oxide, polymethacrylic acid, and polyacrylic acid.

  Examples of the hydrophilic macromonomer include hydroxyl group-terminated polyalkylene glycol mono (meth) acrylate. Specific examples include polyethylene glycol monomethacrylate, polyethylene glycol monoacrylate, hydroxypropyl methacrylate, polypropylene glycol monomethacrylate, polypropylene glycol monoacrylate. , Poly (ethylene glycol-propylene glycol) monomethacrylate, polyethylene glycol-polypropylene glycol monomethacrylate, poly (ethylene glycol-tetramethylene glycol) monomethacrylate, poly (ethylene glycol-tetramethylene glycol) monoacrylate, poly (propylene glycol-tetra Methylene glycol) monometac , Poly (propylene glycol - tetramethylene glycol) monoacrylate, polypropylene glycol - polybutylene glycol monomethacrylate, polypropylene glycol - polybutylene glycol monoacrylate, and the like. Examples of the alkyl group-terminated polyalkylene glycol mono (meth) acrylate include methoxy polyethylene glycol monomethacrylate, octoxy polyethylene glycol polypropylene glycol monomethacrylate, lauroxy polyethylene glycol monomethacrylate, stearoxy polyethylene glycol monomethacrylate. Etc. are exemplified. Moreover, an allyl terminal polymethacrylic acid macromonomer, an allyl terminal polyacrylic acid macromonomer, etc. are mentioned.

  The hydrophilic group of the hydrophilic macromonomer is considered to be present on the capsule surface after being microencapsulated and oriented to the aqueous medium side, and has excellent dispersibility and dispersion stability in the aqueous phase of the encapsulated particles. It becomes. In addition, when the liquid electrostatic developer is used, the hydrophilic group and the long-chain hydrophilic part are various metal ions such as magnesium, calcium, and aluminum usually contained in plain paper, cationic starch, cationic polymer, Further, the toner image has a high image density with affinity for cellulose fibers and no bleeding.

  Next, an anionic polymerizable surfactant contains a radical polymerizable group, a hydrophobic group, and a hydrophilic group composed of an anionic group in one molecule as a substituent at the same time by a covalent bond. It has both a polymerizability by a group and a function as a surfactant by an anionic group (hydrophilic group) and a hydrophobic group.

  Preferred examples of the anionic polymerizable surfactant include compounds represented by the following general formula (1).

(In the formula, p is an integer of 9 or 11, q is an integer of 2 to 20, A is an anionic group, and the counter ion is an alkali metal ion, an ammonium ion, or an alkanolamine ion.)
Examples of the anionic group A include a sulfonate ion (—SO ₃ ⁻ ) and a sulfinate ion (—RSO ₂ ⁻ ), and R in the sulfinate group is an alkyl group having 1 to 12 carbon atoms or a phenyl group. It may have a substituent.

  As the compound represented by the general formula (1),

(Wherein r is 9 or 11, s is 5 or 10)
Are preferable, and examples thereof include Aqualon KH series (Aqualon KH-5, Aqualon KH-10) from Daiichi Kogyo Seiyaku Co., Ltd. “Aqualon KH-5” is a mixture of a compound of r = 9 and s = 5 and a compound of r = 11, s = 5 in the general formula (1). “AQUALON KH-10” is a mixture of a compound with r = 9 and s = 10 and r = 11 and s = 10 in the general formula (1).

  Moreover, as an anionic polymerizable surfactant, following General formula (2)

Wherein R ²¹ and R ³¹ are each independently a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, Z ¹ is a carbon-carbon single bond or a linking group represented by —CH ₂ —O—CH _2. , M is an integer of 2 to 20, X is a group represented by the formula —SO ₃ M ¹ , and M ¹ is an alkali metal ion, an ammonium ion, or an alkanolamine ion.)
A compound represented by the formula is also preferably exemplified.

  The polymerizable surfactant represented by the general formula (2) is described in JP-A-5-320276 and JP-A-10-316909.

By appropriately adjusting the type of R ²¹ and the value of m in the general formula (2), it is possible to adjust the degree of hydrophilicity or hydrophobicity of the pigment particle surface. Examples of preferable polymerizable surfactants represented by the general formula (2) include compounds represented by the following general formula (3).

(In the formula, R ³¹ , m and M ¹ are the same as those in the general formula (2).)
Specifically, the following compounds can be mentioned.

  Such anionic polymerizable surfactants are available from Daiichi Kogyo Seiyaku Co., Ltd. “AQUALON HS series (AQUALON HS-05, HS-10, HS-20, HS-1025)”, or Asahi Denka Kogyo ( "Adekaria soap SE-10N, SE-20N" manufactured by the same company is exemplified.

“Adekalia Soap SE-10N” manufactured by Asahi Denka Kogyo Co., Ltd. is a compound represented by the general formula (3) in which M ¹ is NH ₄ , R ³¹ is C ₉ H ₁₉ , and m = 10. . “Adekalia Soap SE-20N” manufactured by Asahi Denka Kogyo Co., Ltd. is a compound represented by the general formula (3), wherein M ¹ is NH ₄ , R ³¹ is C ₉ H ₁₉ , and m = 20. .

  In addition, the following general formula (4)

(Wherein R ²² and R ³² are each independently a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, and D is a carbon-carbon single bond or a formula —CH ₂ —O—CH ₂ —. N is an integer of 2 to 20, Y is a group represented by the formula —SO ₃ M ² , and M ² is an alkali metal ion, an ammonium ion, or an alkanolamine ion. )
A compound represented by the formula is also preferably exemplified.

  In addition, as an anionic polymerizable surfactant

(Wherein R ⁴ is a hydrogen atom or a hydrocarbon group having 1 to 12 carbon atoms, l is an integer of 2 to 20, Z is an anionic group having an alkali metal ion, an ammonium ion or an alkanolamine ion as a counter ion) Represents.)
A compound represented by is also preferably exemplified.

  Also, an anionic allyl derivative described in JP-B-49-46291, JP-B-1-24142, or JP-A-62-104802, and an anionic derivative described in JP-A-62-221431. Propenyl derivatives, anionic acrylic acid derivatives described in JP-A-62-34947 or JP-A-55-11525, anions described in JP-B-46-34898 or JP-A-51-30284 Itaconic acid derivatives and the like can also be mentioned.

  The anionic polymerizable surfactants exemplified above can be used alone or as a mixture of two or more.

  The hydrophilic monomer having an anionic group that can be used in the present invention has at least an anionic group (hydrophilic group) and a radical polymerizable group in its structure, and the hydrophilic group is a sulfonic acid group. , A sulfinic acid group, a carboxy group, a carbonyl group, and a group selected from these groups. The polymerizable group is an unsaturated hydrocarbon group capable of radical polymerization, and is preferably selected from a vinyl group, an allyl group, an acryloyl group, a methacryloyl group, a propenyl group, a vinylidene group, and a vinylene group.

  Examples of the hydrophilic monomer having an anionic group include methacrylic acid, acrylic acid, phosphoric acid group-containing (meth) acrylate, sodium vinylsulfonate, 2-sulfoethyl (meth) acrylate, and 2- (meth) acrylamide-2-methyl. A propanesulfonic acid etc. can be illustrated.

  Similar to the anionic polymerizable surfactant, anionic groups such as sulfonic acid group, sulfinic acid group, carboxy group, carbonyl group and salts thereof are present on the surface of the coating layer so as to be oriented toward the aqueous phase. It is considered that the particles can be in an admicelle state with excellent dispersion stability in the aqueous phase. In addition, when the liquid electrostatic developer is used, the anionic group easily interacts with various metal ions, cationic starch, cationic polymers, and cellulose fibers contained in plain paper. In this case, it is easy to accumulate at the development position of plain paper, the occurrence of bleeding is suppressed, and a high image density can be obtained.

  The total amount of hydrophilic macromonomer, anionic polymerizable surfactant, and / or hydrophilic monomer having an anionic group is the cation used to adsorb ionically to pigment particles having an anionic group on the surface. The amount of the polymerizable polymerizable surfactant is 0.5 to 5 times mol, preferably 0.8 to 1.5 times mol. The addition ratio of the anionic polymerizable surfactant and / or the hydrophilic monomer having an anionic group to 1 mol of the hydrophilic macromonomer is in the range of 0.1 mol to 5 mol, more preferably 0.8 mol. It is good to set it as the range of -1.5 mol. By setting this range, the hydrophilic macromonomer forms a thick copolymer layer on the surface of the pigment particles, and the thick copolymer layer is entangled and fused in the fixing process as a liquid electrostatic developer. In addition, the anionic polymerizable surfactant and the hydrophilic monomer having an anionic group are on the surface of the coating layer so that the anionic group is oriented and the cellulose It can be excellent in affinity.

  In addition, the encapsulated resin in the present invention includes a hydrophobic monomer and a polyvalent monomer for the purpose of controlling fixability to a recorded matter, scratch resistance, storage stability and the like when a liquid electrostatic developer is used. It is preferable to have a repeating structural unit derived from a functional monomer, a monomer containing a bulky group represented by the following general formula (5), and a hydrophilic monomer other than the hydrophilic monomer having the anionic group. .

  The hydrophobic monomer has at least a hydrophobic group and a radical polymerizable group in one molecule. Hydrophobic groups include aliphatic hydrocarbon groups such as methyl, ethyl and propyl, alicyclic hydrocarbon groups such as cyclohexyl, dicyclopentenyl, dicyclopentanyl and isobornyl, benzyl and phenyl And aromatic hydrocarbon groups such as naphthyl group and the like. Examples of the radical polymerizable group include unsaturated hydrocarbon groups such as vinyl group, allyl group, acryloyl group, methacryloyl group, propenyl group, vinylidene group and vinylene group.

  Specifically, styrene derivatives such as styrene, methylstyrene, dimethylstyrene, chlorostyrene, dichlorostyrene, bromostyrene, p-chloromethylstyrene, divinylbenzene; methyl acrylate, ethyl acrylate, n-butyl acrylate, butoxy Simple substances such as ethyl acrylate, benzyl acrylate, phenyl acrylate, phenoxyethyl acrylate, cyclohexyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, dicyclopentenyloxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, etc. Functional acrylic acid esters; methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, butoxymethyl methacrylate Simple compounds such as benzoate, benzyl methacrylate, phenyl methacrylate, phenoxyethyl methacrylate, cyclohexyl methacrylate, dicyclopentanyl methacrylate, dicyclopentenyl methacrylate, dicyclopentenyloxyethyl methacrylate, tetrahydrofurfuryl methacrylate, isobornyl methacrylate, etc. Functional methacrylates; allyl compounds such as allylbenzene, allyl-3-cyclohexanepropionate, 1-allyl-3,4-dimethoxybenzene, allylphenoxyacetate, allylphenylacetate, allylcyclohexane, allyl polycarboxylate; Examples include acid, maleic acid, itaconic acid ester cheeks; monomers having radically polymerizable groups such as N-substituted maleimides and cyclic olefins.

  As the hydrophobic monomer, one satisfying the above required characteristics is appropriately selected, and the copolymerization ratio is arbitrarily determined.

  Next, by having a repeating structural unit derived from a crosslinkable monomer (polyfunctional monomer), a crosslinked structure is formed in the polymer, and the glass transition point (Tg) can be adjusted. The resistance to the sexual carrier liquid can be improved. When the low dielectric carrier liquid permeates into the encapsulating resin, the polymer may swell, deform, etc., disturb the orientation state of the anionic group, and decrease the dispersion stability of the microencapsulated pigment particles. Therefore, by forming a cross-linked structure in the polymer, the resistance can be improved, and microencapsulated pigment particles having excellent dispersion stability can be obtained.

The crosslinkable monomer has a compound having two or more unsaturated hydrocarbon groups selected from vinyl group, allyl group, acryloyl group, methacryloyl group, propenyl group, vinylidene group and vinylene group, and ethylene glycol. Diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, allyl acrylate, bis (acryloxyethyl) hydroxyethyl isocyanurate, bis (acryloxyneopentyl glycol) adipate, 1, 3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, propylene glycol diacrylate, Propylene glycol diacrylate, 2-hydroxy-1,3-diaacryloxypropane, 2,2-bis [4- (acryloxy) phenyl] propane, 2,2-bis [4- (acryloxyethoxy) phenyl] propane, 2,2-bis [4- (acryloxyethoxy diethoxy) phenyl] propane, 2,2-bis [4- (acryloxyethoxy polyethoxy) phenyl] propane, hydroxypentyl glycol neopentyl glycol diacrylate, 1, 4-butanediol diacrylate, dicyclopentanyl diacrylate, dipentaerythritol hexaacrylate, dipentaerythritol monohydroxypentaacrylate, ditrimethylolpropane tetraacrylate, pentaerythritol triacrylate, Labromobisphenol A diacrylate, triglycerol diacrylate, trimethylolpropane triacrylate, tris (acryloxyethyl) isocyanurate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol Dimethacrylate, propylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, 2-hydroxy -1,3-dimethacryloxypropane, 2,2-bis [4 Mono (methacryloxy) phenyl] propane, 2,2-bis [4- (methacryloxyethoxy) phenyl] propane, 2,2-bis [4- (methacryloxyethoxydiethoxy) phenyl] propane, 2,2-bis [ 4- (methacryloxyethoxypolyethoxy) phenyl] propane, tetrabromobisphenol A dimethacrylate, dicyclopentanyl dimethacrylate, dipentaerythritol hexamethacrylate, glycerol dimethacrylate, hydroxypentylglycol dipentaglycol dimethacrylate, dipentaerythritol Monohydroxypentamethacrylate, ditrimethylolpropane tetramethacrylate, pentaerythritol trimethacrylate, pentaerythritol tetramethacrylate, triglyceride Roll dimethacrylate, trimethylolpropane trimethacrylate, tris (methacryloxyethyl) isocyanurate, allyl methacrylate, divinylbenzene, diallyl phthalate, diallyl terephthalate, diallyl isophthalate, diethylene glycol bis allyl carbonate.
As the crosslinkable monomer, one satisfying the above required characteristics is appropriately selected, and the copolymerization ratio is arbitrarily determined.

  Further, the encapsulating resin may further have a repeating structural unit derived from a monomer represented by the following general formula (5).

(In the formula, R ¹ represents a hydrogen atom or a methyl group. R ² represents a bulky group, and represents a t-butyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group, m Represents 0 to 3, n represents an integer of 0 or 1, and when m is 0, n is also 0.)
The bulky group may be selected from a branched alkyl group, an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a heterocyclic group, and the mobility is increased when the bulky group is contained in the encapsulating resin. Is restrained, the mechanical strength, heat resistance and carrier liquid resistance can be improved, and microencapsulated pigment particles having excellent abrasion resistance and durability can be obtained.

  Examples of the branched alkyl group, alicyclic hydrocarbon group, and aromatic hydrocarbon group include a t-butyl group, a cycloalkyl group, a cycloalkenyl group, a benzyl group, a phenyl group, an isobornyl group, a dicyclopentanyl group, Examples include a dicyclopentenyl group, an adamantane group, a tetrahydrofuran group, and a naphthyl group.

  Specific examples of the monomer represented by the general formula (5) include the following.

  As the monomer represented by the general formula (5), those satisfying the above required characteristics are appropriately selected, and the copolymerization ratio thereof is arbitrarily determined.

  Polymers derived from crosslinkable monomers and polymers derived from monomers represented by general formula (5) have the advantages of high Tg and excellent mechanical strength, heat resistance and solvent resistance. As a result, the plasticity of the microcapsule pigment tends to be in a state where it is difficult to adhere to the recording medium, and as a result, the fixability and abrasion resistance of the microcapsule pigment to the recording medium may be reduced.

  On the other hand, a polymer composed of the above-mentioned hydrophobic monomer (for example, a hydrophobic monomer having a long-chain alkyl group as a hydrophobic group) gives a polymer having excellent flexibility. Therefore, a crosslinkable monomer or a monomer represented by the general formula (5) Thus, it is possible to obtain an encapsulating resin having mechanical strength and carrier liquid resistance to such an extent that the plasticity is not impaired, and it is easy to adhere to the recording medium and has excellent fixability. In addition, microencapsulated pigment particles having excellent carrier liquid resistance can be obtained.

  Next, a repeating unit derived from a hydrophilic monomer other than the hydrophilic monomer having an anionic group may be contained. Examples of the hydrophilic group in these hydrophilic monomers include those having a hydroxyl group, an ethylene oxide group, an amide group, an amino group, and the like. Like these sulfonic acid groups, these hydrophilic groups are thought to be oriented on the surface of the coating layer toward the aqueous medium or low dielectric carrier liquid side, and form hydrogen bonds with OH groups of cellulose fibers such as paper. Therefore, when these monomers having a hydrophilic group are used in combination, the fixability onto the cellulose fiber can be improved similarly to the anionic group such as the sulfonic acid group.

Specifically, hydroxyl group-containing 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, etc., ethyl diethylene glycol acrylate having an ethylene oxide group, polyethylene glycol monomethacrylate, methoxypolyethylene glycol methacrylate, etc., amide group Acrylamide, N, N-dimethylacrylamide, etc., such as N-methylaminoethyl methacrylate containing amino groups, N-methylaminoethyl acrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl methacrylate, diethylaminoethyl methacrylate, etc. Alkylamino esters of acid or methacrylic acid; N- (2-di- Acetylaminoethyl) acrylamide, N- (2-dimethylaminoethyl) methacrylamide, unsaturated amides having an alkylamino group such as N, N-dimethylaminopropylacrylamide, monovinylpyridines such as vinylpyridine, dimethylaminoethyl Examples include vinyl ethers having an alkylamino group such as vinyl ether; vinyl imidazole, N-vinyl-2-pyrrolidone, and the like.
As such a hydrophilic monomer, one satisfying the above-mentioned required characteristics is appropriately selected, and the copolymerization ratio is arbitrarily determined.

  When a toner image composed of microencapsulated pigment particles is formed on a recording medium such as plain paper, the low dielectric carrier liquid around the pigment particles penetrates into the recording medium and the pigment particles are close to each other. However, when the glass transition point (Tg) of the encapsulated resin is lower than the fixing temperature, the encapsulated resin is fused by the capillary pressure generated in the gap between the particles, and the toner image in which the pigment is encapsulated inside it can. In the liquid electrostatic developer of the present invention, when a vegetable oil having an unsaturated group is used as a low dielectric carrier liquid, it is possible to improve image fixability and scratch resistance in cooperation with its oxidative polymerization curability. . At the same time, the pigment particles have a small particle size, and the anionic groups are regularly and densely oriented toward the low dielectric carrier liquid side, so that the pigment particles are packed most closely on the recording medium. Since a good packing property is obtained, a glossy toner image can be obtained.

  In general, for polymer solids, especially amorphous polymer solids, when the temperature is raised from low temperature to high temperature, a state where a large amount of deformation is generated with a small force from a state where a small amount of deformation has a large force (glass state). The temperature at which this phenomenon occurs is called the glass transition point (Tg). In the differential heat curve obtained by measuring the temperature with a thermal scanning calorimeter (DSC), the endotherm The temperature at the intersection with the base line when a tangent line is drawn from the bottom molecular weight of the peak toward the end point of endotherm is defined as the glass transition point (Tg). In addition, since the physical properties such as elastic modulus, specific heat, refractive index and the like change suddenly at the glass transition point (Tg), it is known that the glass transition point (Tg) is also determined by measuring these physical properties. Yes. Moreover, the glass transition point (Tg) of the polymer obtained after the polymerization is predicted using the following formula from the glass transition point (Tg) of the homopolymer derived from the monomer used for the polymerization and the monomer composition used for the polymerization. However, the glass transition point (Tg) of the encapsulated resin may be measured using a thermal scanning calorimeter (differential operation calorimeter, DSC) DSC200 (manufactured by Seiko Denshi).

(Where Tg _(p) is the glass transition point of the polymer obtained, i is the number assigned to each of the different types of monomers, Tg _{(hp) i} is the glass transition point of the homopolymer of monomer i used for polymerization, and xi is This represents the weight fraction of monomer i with respect to the total weight of monomers to be polymerized.)
The glass transition point (Tg) of the encapsulated resin in the microencapsulated pigment particles of the present invention is -20 ° C to 90 ° C, preferably -10 ° C to 80 ° C. By setting the glass transition point (Tg) within this range, the toner image can be excellent in fixability and scratch resistance, but if Tg is lower than −20 ° C., the carrier liquid resistance is lowered. If the temperature is higher than 90 ° C., the burden on the fixing device is increased, and energy saving is not possible.

  Next, a method for producing a microencapsulated pigment will be described. The “aqueous solvent” used in the production method means a solvent containing water as a main component.

  Cationic polymerizable surfactant adsorbed on the surface of pigment particles, hydrophilic macromonomer, anionic polymerizable surfactant and / or hydrophilic monomer having an anionic group, in addition to these, hydrophobic property The copolymerization with a monomer, a polyfunctional monomer (crosslinkable monomer), or a monomer having the above-described bulky group is preferably initiated by adding a polymerization initiator.

  A method for producing a coating film of a microencapsulated pigment is obtained by adding a cationic polymerizable surfactant to an aqueous dispersion of pigment particles having an anionic group as a hydrophilic group on the surface, and water or water as necessary. After adding an aqueous solvent, mixing, and irradiating with ultrasonic waves for a predetermined time, a hydrophilic macromonomer, an anionic polymerizable surfactant and / or a hydrophilic monomer having an anionic group (in addition to the above hydrophobic properties) Monomers, crosslinkable monomers, monomers represented by general formula (5) can be added) and water is added if necessary, and then again irradiated with ultrasonic waves for a predetermined time to disperse, and subjected to ultrasonic irradiation and stirring However, it can be suitably carried out by raising the temperature to a predetermined temperature (temperature at which the polymerization initiator is activated), adding the polymerization initiator to activate the polymerization initiator, and emulsion polymerization.

  According to the emulsion polymerization method of the present invention, for example, a cationic polymerizable surfactant is ionically bonded to a hydrophilic group (for example, an anionic group) on the surface of a pigment particle having an anionic group on its surface, By adding a monomer and a hydrophobic monomer, and further adding an anionic polymerizable surfactant and / or a hydrophilic monomer having an anionic group and irradiating with ultrasonic waves, a polymerizable surfactant existing around the pigment particles, It can be controlled to a very high degree by the arrangement state of the monomer, and in the outermost shell, a state in which the anionic groups are oriented toward the aqueous phase is formed. Then, by emulsion polymerization, the monomer is converted into a polymer in this highly controlled form, and the microencapsulated pigment particles according to the embodiment of the present invention are obtained. According to the above method, since the generation of water-soluble oligomers and polymers as by-products can be reduced, the viscosity of the obtained dispersion liquid of the microencapsulated pigment particles can be reduced. Purification steps such as filtration can be facilitated. Further, when the dispersion medium is replaced with a solvent to obtain a liquid electrostatic developer, the dispersion stability is excellent, and a toner image with high color and high density can be obtained which is difficult to bleed even on plain paper.

  The emulsion polymerization reaction preferably uses a reaction vessel equipped with an ultrasonic generator, a stirrer, a reflux condenser, a dropping funnel and a temperature controller. The polymerization reaction is carried out by raising the temperature up to the cleavage temperature of the water-soluble polymerization initiator added to the reaction system to cleave the polymerization initiator to generate an initiator radical, whereby the initiator radical becomes a cationic polymerizable surfactant. Or by attacking the polymerizable group of the anionic polymerizable surfactant or the polymerizable group of the monomer. The addition of the polymerization initiator into the reaction system can be suitably carried out by dropping an aqueous solution obtained by dissolving a water-soluble polymerization initiator in pure water into the reaction vessel. Activation of the polymerization initiator in the reaction system can be suitably carried out by raising the temperature of the aqueous dispersion to a predetermined polymerization temperature.

  In producing the microencapsulated pigment particles, the pigment particles having an anionic group on the surface are dispersed in an aqueous medium in an amount of 10% by mass to 30% by mass, and then the polymerizable surfactant is used as described in each of the above production methods. The agent and each monomer are sequentially added and dispersed. As a dispersion method, an ultrasonic dispersion treatment, a homogenizer, or the like, preferably an ultrasonic dispersion treatment. As ultrasonic dispersion, ultrasonic waves of 1 MHz to 5 MHz are used, and processing conditions are preferably set to 5 minutes to 30 minutes. In addition, when the pigment particle which has an anionic group on the surface is not in an aqueous dispersion, it is preferable to carry out a dispersion treatment using a general disperser such as a ball mill, a roll mill, an Eiger mill, a jet mill or the like as a pretreatment.

  As the polymerization initiator, a water-soluble radical polymerization initiator is preferable, and potassium persulfate, ammonium persulfate, sodium persulfate, 2,2-azobis- (2-methylpropionamidine) dihydrochloride, or 4,4-azobis- ( 4-cyanovaleric acid) and the like, and a catalyst amount is added to the dispersion, and the polymerization temperature is preferably in the range of 60 ° C. to 90 ° C., and the polymerization time is 3 hours to 10 hours. Is preferred. After the polymerization is completed, the pH may be adjusted to 7.0 to 9.0, and then ultrafiltration may be performed.

  The microencapsulated pigment particles of the present invention are 40 mass parts to 900 mass parts, preferably 50 mass parts to 850 mass parts of encapsulated resin with respect to 100 mass parts of pigment particles having an anionic group on the surface. It should be coated.

  The primary volume average particle size of the microencapsulated pigment particles is 0.2 μm to 1 μm, preferably 0.2 μm to 0.8 μm. The particle size distribution is a value measured by a laser Doppler type particle size distribution measuring instrument “Microtrac UPA150” manufactured by Leeds & Northrop.

Next, the liquid electrostatic developer of the present invention will be described.
The liquid electrostatic developer is made into a liquid electrostatic developer by dispersing microencapsulated pigment particles in a low dielectric carrier liquid. The low dielectric carrier liquid can be a known carrier liquid such as an aliphatic hydrocarbon, silicone oil, vegetable oil or the like having a volume resistivity of 10 ⁹ Ω · cm or more and a dielectric constant of 3.6 or less. The microencapsulated pigment particles in the present invention are suitable for a liquid electrostatic developer using a vegetable oil or a fatty acid ester as a carrier liquid without causing the problem of environmental pollution (VOC).

  The vegetable oil is preferably selected from safflower oil, sunflower oil, soybean oil, corn oil, cottonseed oil containing at least 50% linoleic acid component, and linseed oil containing at least 50% linolenic acid component. The linoleic acid component contains two unsaturated bonds and the linolenic acid component contains three molecules. Such vegetable oils themselves have oxidative polymerization properties and are curable when fixed on transfer paper. Therefore, it is necessary to provide particularly positive fixing means after an image is formed on a recording medium. Therefore, the image can be fixed on the transfer paper, and the size and cost of the copying machine can be reduced. The vegetable oil may be purified by activated carbon treatment as a pretreatment for use. The amount (% by mass) of the acid component contained in the vegetable oil is shown in Table 1 below.

  Since the microencapsulated pigment particles in the present invention have a low Tg of the encapsulated resin, wet microparticles obtained in the preparation of the microencapsulated pigment particles are used at room temperature to be dispersed in a carrier liquid to form a liquid electrostatic developer. After drying, it may be dispersed in a carrier liquid (vegetable oil), and it can be a liquid electrostatic developer in which microencapsulated pigment particles are dispersed while maintaining the particle size of wet fine particles. The diameter is preferably at least 1 μm or less, more preferably 0.2 μm to 0.8 μm. If necessary, it may be produced by a wet method using a ball mill, a bead mill, an attritor or the like, and an anionic dispersing agent, a cationic dispersing agent or a nonionic dispersing agent is added to the pigment in accordance with the structure and polarity of the pigment. You may add about 1 mass% and grind | pulverize to the desired particle size.

  The microencapsulated pigment particles can be excellent in dispersibility even when contained up to 50% by mass with respect to the vegetable oil. However, the liquid electrostatic developer is 2% by mass to 45% by mass, preferably 3% by mass to 35%. It is good to contain by mass%.

  An antioxidant may be added for the purpose of preventing the carrier liquid from being oxidized. Examples of the antioxidant include t-butylhydroquinone, butylhydroxyanisole, isopropyl citrate and the like, and it is preferable to add 0.05% by mass to 2.0% by mass in the liquid electrostatic developer. If it is more than 2.0% by mass, it is not preferable because it affects the curing of the image during fixing.

  In addition, after the wet fine particles are dried at room temperature, they are dispersed in a carrier liquid (vegetable oil) to form a liquid electrostatic developer. When the liquid electrostatic developer is subjected to dehydration using a vacuum distillation, a desiccant or the like, The water content is preferably 0.5% by mass or less, preferably 0.1% by mass or less.

  The liquid electrostatic developer containing the microencapsulated pigment particles in the present invention in vegetable oil can function as a negatively chargeable liquid electrostatic developer.

  Further, in the microencapsulated pigment particles in the present invention, the anionic groups are regularly and densely oriented on the outermost contour of the pigment particles. Therefore, when the liquid electrostatic developer is used, the microencapsulated pigment particles are adjacent to each other. Effective electrostatic repulsive force is generated, and steric hindrance caused by the encapsulating resin can prevent aggregation of the microencapsulated pigment particles in the liquid electrostatic developer, and exhibits excellent dispersion stability. The microencapsulated pigment particles contain an encapsulated resin, and the encapsulated resin can be used as a fixing resin.

  In addition, the outermost surface of the microencapsulated pigment particles has an anionic group, a hydrophilic macromonomer, and a hydrophilic group derived from a hydrophilic polymer arranged in a state, and the plain paper is interacted with the cellulose fiber of the plain paper. It can be easily adsorbed on the cellulose fiber, a high image density can be obtained, and the occurrence of bleeding can be suppressed.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In Examples and the like, “part” means “part by mass”. In addition, the method for quantifying the amount of anionic group introduced in the present example is as follows.

(When an anionic group is introduced by a sulfonating agent)
Pigment particles whose surface has been treated with a sulfonating agent are treated by an oxygen flask combustion method and absorbed in a 0.3% aqueous hydrogen peroxide solution, and then sulfate ions (divalent) are obtained by an ion chromatography method (Dionex, 2000i). ) Is quantified, and this value is converted to a sulfonic acid group and expressed as a molar amount (mmol / g) per 1 g of pigment.

(When an anionic group is introduced by a carboxylating agent)
As a method, the Twizel method is used. Diazomethane is dissolved in a suitable solvent and added dropwise to exchange all active hydrogen on the surface of the pigment particles with methyl groups. To the pigment thus treated, hydroiodic acid having a specific gravity of 1.7 is added and heated to vaporize methyl groups as methyl iodide. The methyl iodide gas is trapped with a silver nitrate solution and precipitated as methyl iodide. The amount of the original methyl group, that is, the amount of active hydrogen, was measured from the weight of the silver iodide, and indicated as the molar amount (mol / g) per 1 g of pigment. That is, the amount of active hydrogen on the pigment particle surface corresponds to the amount of carboxylic acid groups.

The preparation method of the microencapsulated pigment particle in this invention is shown.
(Preparation of magenta pigment particles M1 having an anionic group on the surface)
20 parts of isoindolinone pigment (CI Pigment Red 122) is mixed with 500 parts of quinoline and 2 parts under conditions of Eiger Motor Mill M250 type (manufactured by Eiger Japan Co., Ltd.) with a bead filling rate of 70% and a rotational speed of 5000 rpm. The mixture of the pigment paste and the solvent dispersed in time is transferred to a rotary evaporator, heated to 120 ° C. while reducing the pressure to 30 mmHg or less, and the water contained in the system is distilled off as much as possible. Controlled. Next, 20 parts of a sulfonated pyridine complex was added and reacted for 8 hours. After completion of the reaction, the mixture was washed several times with excess quinoline, poured into water, and filtered to obtain magenta pigment particles M1 having an anionic group on the surface. It was. The amount of anionic groups introduced into the obtained magenta pigment particles M1 was 0.06 mmol / g.

(Preparation of black pigment particles Bk1 having an anionic group on the surface)
Carbon black (Mitsubishi Chemical Corporation MA-7) 15 parts is mixed in sulfolane 200 parts, Aiga Motor Mill M250 type (manufactured by Eiger Japan Co., Ltd.) for 2 hours under conditions of 70% bead filling and 5000 rpm. Disperse, disperse the mixture of pigment paste and solvent to a rotary evaporator, heat to 120 ° C while reducing the pressure to 30 mmHg or less, and distill off as much water as possible in the system, then control the temperature to 150 ° C. did. Next, 25 parts of sulfur trioxide was added and reacted for 6 hours. After completion of the reaction, after washing several times with excess sulfolane, the solution was poured into water and filtered to obtain a black having an anionic sulfonic acid group on the surface. Pigment Bk1 was obtained. The amount of sulfonic acid group introduced into the obtained black pigment particles Bk1 was 0.12 mmol / g.

(Preparation of cyan pigment particles C1 having an anionic group on the surface)
20 parts of a phthalocyanine pigment (CI Pigment Blue 15: 3) is mixed with 500 parts of quinoline and 2 parts under conditions of an Eiger motor mill M250 type (manufactured by Eiger Japan) with a bead filling rate of 70% and a rotation speed of 5000 rpm. The mixture of the pigment paste and the solvent dispersed in time is transferred to a rotary evaporator, heated to 120 ° C. while reducing the pressure to 30 mmHg or less, and the water contained in the system is distilled off as much as possible. Controlled. Next, 20 parts of a sulfonated pyridine complex was added and reacted for 8 hours. After completion of the reaction, the mixture was washed several times with excess quinoline, poured into water, and filtered to obtain cyan pigment particles C1 having an anionic group on the surface. It was. The amount of introduced anionic groups in the obtained cyan pigment particles C1 was 0.04 mmol / g.

(Preparation of microencapsulated pigment particles MCM1)
In an aqueous dispersion in which 100 g of magenta pigment particles M1 having an anionic group (sulfonic acid group) on the surface is dispersed in 500 g of ion-exchanged water, 1.25 g of dimethylaminoethyl chloride methacrylate is used as a cationic polymerizable surfactant. After adding and mixing, ultrasonic waves were irradiated for 15 minutes. Next, 12 g of benzyl methacrylate, 8 g of dodecyl methacrylate, 1.31 g of polyethylene glycol monomethacrylate (Blenmer PE-350, manufactured by NOF Corporation), an anionic polymerizable surfactant (Acron KH-10) having the following structural formula 2.34 g and ion-exchanged water 50 g were added and mixed, and ultrasonic waves were irradiated again for 30 minutes.

  This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After the temperature in the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.6 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 20 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 1 mol / l aqueous potassium hydroxide solution and filtered through a membrane filter having a pore size of 1 μm to remove coarse particles. This was then subjected to microfiltration to obtain the desired microencapsulated pigment wet fine particles MCM1. The volume average particle diameter of the obtained wet fine particles was measured using a “Laser Doppler type particle size distribution analyzer Microtrac UPA150” manufactured by Leeds & Northrop Co. As a result, it was 200 nm.

(Preparation of microencapsulated pigment particles MCM2)
In an aqueous dispersion in which 100 g of magenta pigment particles M1 having an anionic group (sulfonic acid group) on the surface is dispersed in 500 g of ion-exchanged water, 1.87 g of dimethylaminoethyl chloride methacrylate as a cationic polymerizable surfactant is used. After adding and mixing, ultrasonic waves were irradiated for 15 minutes. Next, 6 g of isobornyl methacrylate, 0.05 g of 1,6-hexanediol dimethacrylate and 1.21 g of polyethylene glycol polypropylene glycol monomethacrylate (Blenmer 70PEP-350B, manufactured by NOF Corporation), the anionic polymerizable surfactant 3.90 g of the agent (Acron KH-10), 0.207 g of 2-acrylamido-2-methylpropanesulfonic acid and 50 g of ion-exchanged water as hydrophilic monomers were added and mixed, and ultrasonic waves were irradiated again for 30 minutes.

  This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After the temperature in the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.6 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 20 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 1 mol / l aqueous potassium hydroxide solution and filtered through a membrane filter having a pore size of 1 μm to remove coarse particles. Next, this was microfiltered to obtain wet microparticles MCM2 of the desired microencapsulated pigment. The volume average particle diameter of the obtained wet fine particles was measured using a “Laser Doppler type particle size distribution analyzer Microtrac UPA150” manufactured by Leeds & Northrop Co. As a result, it was 215 nm.

(Preparation of microencapsulated pigment particles MCBk1)
4. An aqueous dispersion in which 100 g of black pigment particles Bk1 having an anionic group (sulfonic acid group) on the surface is dispersed in 500 g of ion-exchanged water, and dimethylaminoethylbenzyl chloride methacrylate as a cationic polymerizable surfactant are added. After adding 1 g and mixing, ultrasonic waves were irradiated for 15 minutes. Next, 12 g of benzyl methacrylate, 8 g of dodecyl methacrylate, 7.8 g of Lauroxy polyethylene glycol monomethacrylate (Blenmer PLE-200, manufactured by Nippon Oil & Fats Co., Ltd.), and 3. 3. anionic polymerizable surfactant (Acron KH-10) 5 g and 50 g of ion-exchanged water were added and mixed, and ultrasonic waves were irradiated again for 30 minutes.

  This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After the temperature in the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.7 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 30 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 2 mol / l potassium hydroxide aqueous solution and filtered through a membrane filter having a pore size of 1 μm to remove coarse particles. This was then subjected to microfiltration to obtain the desired microencapsulated pigment wet fine particles MCBk1. The volume average particle diameter of the obtained wet fine particles was measured using a “Laser Doppler type particle size distribution analyzer Microtrac UPA150” manufactured by Leeds & Northrop Co. As a result, it was 205 nm.

(Preparation of microencapsulated pigment particles MCC1)
In an aqueous dispersion in which 100 g of cyan pigment particles C1 having an anionic group (sulfonic acid group) on the surface are dispersed in 500 g of ion-exchanged water, dimethylaminoethyl benzyl methacrylate salt as a cationic polymerizable surfactant is 1. After adding 1 g and mixing, ultrasonic waves were irradiated for 15 minutes. Next, 12 g of benzyl methacrylate, 8 g of dodecyl methacrylate, 1.4 g of poly (propylene glycol tetramethylene glycol) monomethacrylate (Blenmer 50PPT-800, manufactured by NOF Corporation), the anionic polymerizable surfactant (Acron KH-10) ) And 2.9 g of ion exchanged water and 50 g of ion-exchanged water were added and mixed, and then ultrasonic waves were irradiated again for 30 minutes.

  This was put into a reaction vessel equipped with a stirrer, a reflux condenser, a dropping funnel, a temperature controller, a nitrogen introduction tube and an ultrasonic generator. After the temperature in the reaction vessel was raised to 80 ° C., an aqueous potassium persulfate solution in which 0.5 g of potassium persulfate was dissolved as a polymerization initiator was added dropwise to 20 g of ion-exchanged water. Polymerized for hours. After completion of the polymerization, the pH was adjusted to 8 with a 2 mol / l potassium hydroxide aqueous solution and filtered through a membrane filter having a pore size of 1 μm to remove coarse particles. This was then subjected to microfiltration to obtain the desired microencapsulated pigment wet fine particles MCBk1. The volume average particle diameter of the obtained wet fine particles was measured using a “Laser Doppler system particle size distribution analyzer Microtrac UPA150” manufactured by Leeds & Northrop Co. As a result, it was 210 nm.

(Preparation of Comparative Example M of Microencapsulated Pigment Particles of Comparative Example)
A flask was charged with 250 g of methyl ethyl ketone, heated to 75 ° C. with stirring under a nitrogen seal, and 170 g of n-butyl methacrylate, 58 g of n-butyl acrylate, 35 g of 2-hydroxyethyl methacrylate, 35 g of acrylic acid and a polymerization initiator perbutyl. A mixed solution composed of 20 g of O (Nippon Yushi Co., Ltd.) was added dropwise over 2 hours and further reacted for 15 hours to obtain a vinyl polymer solution.

  Add 15 g of the above polymer solution to a stainless steel beaker together with 0.8 g of dimethylethanolamine and 15 g of magenta pigment (CI Pigment Red 122), and then add ion-exchanged water so that the total amount becomes 75 g. 250 g of zirconia beads having a diameter of 0.5 mm was added, and kneading was performed for 4 hours using a sand mill. After completion of the kneading, the zirconia beads were separated by filtration to obtain a dispersion of a polymer having a carboxyl group neutralized with a base and a pigment dispersed in water. While stirring at room temperature, 1N hydrochloric acid was added until the resin was insolubilized and fixed to the pigment. The pH at this time was 3-5. The aqueous medium containing the pigment to which the polymer was fixed was filtered with suction and washed with water to obtain a water-containing cake.

(Production of Comparative Example Bk of Comparative Example Microencapsulated Pigment Particles)
A flask was charged with 250 g of methyl ethyl ketone, heated to 75 ° C. with stirring under a nitrogen seal, and 85 g of n-butyl methacrylate, 90 g of n-butyl acrylate, 40 g of 2-hydroxyethyl methacrylate, 25 g of methacrylic acid and a polymerization initiator perbutyl. A mixed solution composed of 20 g of O (Nippon Yushi Co., Ltd.) was added dropwise over 2 hours and further reacted for 15 hours to obtain a vinyl polymer solution.

  8 g of the above polymer solution is added to a stainless steel beaker together with 0.4 g of dimethylethanolamine and 8 g of black pigment (MA-100 manufactured by Mitsubishi Chemical), and ion exchange water is further added so that the total amount becomes 40 g. Was added with 250 g of 0.5 mm zirconia beads, and kneaded for 4 hours using a sand mill. After completion of the kneading, the zirconia beads were separated by filtration to obtain a dispersion in which a dispersion comprising a polymer having a carboxyl group neutralized with a base and a pigment was dispersed in water. While stirring at room temperature, 1N hydrochloric acid was added until the resin was insolubilized and fixed to the pigment. The pH at this time was 3-5. The aqueous medium containing the pigment to which the polymer was fixed was filtered with suction and washed with water to obtain a water-containing cake.

(Preparation of Comparative Example C of Microencapsulated Pigment Particles of Comparative Example)
The flask was charged with 250 g of methyl ethyl ketone, heated to 75 ° C. with stirring under a nitrogen seal, and 155 g of n-butyl methacrylate, 20 g of n-butyl acrylate, 35 g of 2-hydroxyethyl methacrylate, 40 g of methacrylic acid and a polymerization initiator perbutyl. A mixed solution composed of 5 g of O (manufactured by NOF Corporation) was added dropwise over 2 hours and further reacted for 15 hours to obtain a vinyl polymer solution.

  10 g of the above polymer solution, 7 g of cyan pigment (CI Pigment Blue 15: 3), 40 g of betyl ethyl ketone, and 150 g of ceramic beads having an average particle diameter of 0.5 mm are placed in a stainless steel beaker, and a bead mill disperser Then, the ceramic beads were separated by filtration to prepare a microencapsulated pigment paste.

  Next, 20 g of the microencapsulated pigment paste and 0.2 g of diethanolamine are mixed to form an organic solvent phase, and 25 g of ion-exchanged water is stirred for 20 minutes while the organic solvent phase is stirred while being irradiated with ultrasonic waves. And droplet-inversion emulsification was performed to obtain a microencapsulated pigment-containing aqueous dispersion. Further, the microencapsulated pigment-containing aqueous dispersion was distilled at 85 ° C. to distill off the solvent, thereby preparing wet encapsulated pigment particles.

Example 1
(Preparation of liquid developer using microencapsulated pigment particles MCM1)
170 g of sunflower oil containing 0.1% of TBHQ (t-butylhydroquinone) as an antioxidant in 13 g of the wet microparticles of the obtained microencapsulated pigment particles MCM1, 20 parts by weight of activated carbon in 200 parts by weight of commercially available sunflower oil In addition to stirring, the mixture was stirred for 1 hour and then used for filtration, and mixed by irradiation with ultrasonic waves. This mixed liquid was transferred to a rotary evaporator, and maintained at a temperature of 120 ° C. for 5 hours while reducing the pressure to 30 mmHg or less, thereby distilling off water contained in the system. Subsequently, it moved to the stainless steel beaker, and ultrasonic developer was irradiated for 10 minutes to produce a liquid developer MCML1 in which the microencapsulated magenta pigment was finely dispersed in sunflower oil.

(Comparative Example 1)
(Preparation of Liquid Developer (Comparative Example M1) Using Microencapsulated Pigment Particle M of Comparative Example)
In Example 1, 16 parts of the microencapsulated pigment particles M described above were used instead of the wet microparticles of the microencapsulated pigment particles MCM1, and a liquid developer of Comparative Example (Comparative Example M1) was prepared in the same manner.

(Evaluation of toner charge by electrophoresis)
The charging behavior of the liquid developer prepared using the electrophoresis experimental apparatus shown in FIG. 3 was examined. 3A and 3B are diagrams illustrating a measurement cell for charging characteristics of the liquid electrostatic developer, FIG. 3A is a perspective view illustrating the measurement cell, and FIG. 3B is a perspective view illustrating an electrode portion. .

  In the measuring cell 1, an anode side electrode portion 3 and a cathode side electrode portion 4 are installed in a container 2 made of an electrically insulating member such as glass or synthetic resin. The anode terminal 5 provided on the anode side electrode unit 3 is connected to a power supply anode side lead wire 6 coupled to a current supply device (not shown), and is provided on the cathode side electrode unit 4. A cathode-side lead wire 8 coupled to a current supply device (not shown) is connected to the cathode terminal 7. The anode side electrode part 3 and the cathode side electrode part 4 are provided with a holding member mounting groove 9 for holding both electrode parts at a predetermined interval on the upper part thereof. Is held at a predetermined interval. A flow groove 10 is provided below the anode electrode portion 3 and the cathode electrode portion 4 so that the liquid electrostatic developer is smoothly supplied.

  The anode electrode portion is shown and described in (B), but the cathode electrode portion is also formed of the same structure and members. The anode electrode portion 2 is formed of a molded body in which a protrusion 11 for anode engagement is provided on a resin having high oil resistance and solvent resistance, such as polyacetal resin (POM). An anode 12 is attached to the anode engaging projection 11 together with a spacer 13 made of an insulating member that maintains a constant distance from the counter electrode. The anode 12 is preferably formed on a transparent glass plate by forming a transparent conductive film 14 such as ITO that does not elute due to the applied current when a current is applied. By using a transparent conductive film formed on a transparent glass plate, it is easy to optically observe and measure the pigment deposited on the anode removed from the anode electrode after electrophoresis for a predetermined time. Can be performed. Alternatively, the pigment concentration may be measured with a reflection densitometer or the like after the anode removed from the anode electrode portion is pressed against a transfer material such as paper or a synthetic resin film to transfer the pigment. For each of the anode and the cathode, it is possible to determine whether it has a positive or negative charge characteristic by comparing the deposited pigment or its transferred image.

  The charging behavior of the liquid developer DCML1 produced using the electrophoresis experimental apparatus shown in FIG. 3 was examined. In the electrophoresis experimental apparatus, a 300V DC voltage was applied for 10 seconds to adhere the colored fine particles that had been electrophoresed to the ITO transparent electrode. Remove the transparent electrode from the measurement cell, press the colored fine particles attached on the electrode onto the transfer paper (J paper manufactured by Fuji Xerox Office Supply Co., Ltd.), and transfer the colored fine particles attached on each electrode onto the transfer paper. It was obtained as a colored solid image. The density of the obtained colored solid image was measured as the reflection density using a reflection densitometer (manufactured by X-Rite, model 520 type spectral densitometer) after being left for 1 day. Depending on the amount of adhesion to the electrode, that is, the reflection density value on the transfer paper, the colored dispersed fine particles are charged positively, negatively, or neutrally (in the ± display, the amount of adhesion is positive and negative, meaning the same amount). I was able to judge. The results are shown in Table 2.

  According to the results, the liquid developer composed of the microencapsulated magenta pigment fine particles of the present invention clearly showed negative chargeability, but the liquid developer composed of the microencapsulated magenta pigment fine particles of the comparative example was weak. It showed negative chargeability.

(Measurement of zeta potential of liquid developer)
Table 2 also shows the results of measuring the zeta potential of this liquid developer using a commercially available zeta electrometer (Zeta Sizer, manufactured by Sysmex Corporation). In measuring the zeta potential, the liquid developer was diluted 3000 times with methyl oleate and measured at room temperature of 25 ° C. and an applied voltage of DC 35V. The zeta potentials of the liquid developers of the present invention and the comparative liquid developers are determined by the above method and are shown in Table 2. The toner of the liquid developer of the present invention showed −93 mV, while the toner of the liquid developer of the comparative example showed a small value of −15 mV.

(Example 2)
(Preparation of liquid developer using microencapsulated pigment particles MCM2)
12 g of the wet microparticles of the microencapsulated pigment particles MCM2 thus obtained are mixed with 170 g of the sunflower oil containing 0.1% of the antioxidant TBHQ (t-butylhydroquinone) and irradiated with ultrasonic waves and mixed. did. This mixed liquid was transferred to a rotary evaporator, and maintained at a temperature of 120 ° C. for 5 hours while reducing the pressure to 30 mmHg or less, thereby distilling off water contained in the system. Subsequently, it moved to the stainless steel beaker, and ultrasonic developer was irradiated for 10 minutes to produce a liquid developer MCML2 in which the microencapsulated magenta pigment was finely dispersed in sunflower oil.

(Comparative Example 2)
(Preparation of Comparative Magenta Liquid Developer (Comparative Example M2))
Disperse by applying ultrasonic waves to 100 g of the sunflower oil containing 0.1% of TBHQ (t-butylhydroquinone), which is the above-mentioned antioxidant, and 6 parts of quinacridone pigment (C.I. Pigment Red 122). By mixing, a magenta toner liquid developer of Comparative Example (Comparative Example M2) was produced.

  Using the produced liquid developer of the present invention and the comparative developer, the evaluation of the toner charge by electrophoresis and the measurement of the zeta potential of the liquid developer described in Example 1 were performed. The results are shown in Table 2.

  According to the results, the liquid developer composed of the microencapsulated magenta pigment fine particles of the present invention clearly showed negative chargeability, but the liquid developer composed of the magenta pigment fine particles of the comparative example was both positive and negative. The developer was charged and was almost neutral. When the zeta potential was observed, the toner of the liquid developer of the present invention showed −98 mV, but the toner of the liquid developer of the comparative example was 5 mV.

(Example 3)
(Preparation of liquid developer using microencapsulated pigment particles MCBk1)
170 g of safflower oil containing 0.1% of TBHQ (t-butylhydroquinone) as an antioxidant in 14 g of the wet microparticles of the microencapsulated pigment particle MCBk1 thus obtained was added to 200 parts by weight of commercially available safflower oil and activated carbon. 20 parts by weight was added, and after stirring for 1 hour, the mixture was filtered and used) and mixed by irradiation with ultrasonic waves. This mixed liquid was transferred to a rotary evaporator, and maintained at a temperature of 120 ° C. for 5 hours while reducing the pressure to 30 mmHg or less, thereby distilling off water contained in the system. Subsequently, it moved to the stainless steel beaker, and ultrasonic developer was irradiated for 10 minutes to produce a liquid developer MCBk1 in which the microencapsulated magenta pigment was finely dispersed in safflower oil.

(Comparative Example 3)
(Production of Liquid Developer (Comparative Example Bk1) Using Microencapsulated Pigment Particles Bk of Comparative Example)
In Example 3, 15.5 g of the aforementioned microencapsulated pigment particle Bk was used in place of the wet fine particles of the microencapsulated pigment particle MCBk1, and a liquid developer of a comparative example (Comparative Example BkL1) was produced in the same manner.

  Using the produced liquid developer of the present invention and the comparative developer, the evaluation of the toner charge by electrophoresis and the measurement of the zeta potential of the liquid developer described in Example 1 were performed. The results are shown in Table 2.

  According to the results, the liquid developer comprising the microencapsulated carbon black pigment fine particles of the present invention clearly shows negative chargeability, and when the zeta potential is determined, the toner of the liquid developer of the present invention is -91 mV. However, the toner of the liquid developer of the comparative example was −20 mV.

Example 4
(Preparation of liquid developer using microencapsulated pigment particles MCC1)
170 g of corn oil containing 0.1% of TBHQ (t-butylhydroquinone) as an antioxidant in 13.5 g of the wet microparticles of the obtained microencapsulated pigment particles MCC1, and activated carbon in 200 parts by weight of commercially available corn oil 20 parts by weight was added, and after stirring for 1 hour, the mixture was filtered and used) and mixed by irradiation with ultrasonic waves. This mixed liquid was transferred to a rotary evaporator, and maintained at a temperature of 120 ° C. for 5 hours while reducing the pressure to 30 mmHg or less, thereby distilling off water contained in the system. Next, the developer was transferred to a stainless steel beaker, and ultrasonic developer was applied for 10 minutes to prepare a liquid developer MCCL1 in which a microcapsulated cyan pigment was finely dispersed in corn oil.

(Comparative Example 4)
(Preparation of Liquid Developer Using Microencapsulated Pigment Particle C of Comparative Example)
In Example 4, instead of the wet fine particles of the microencapsulated pigment particles MCC1, 17 parts of the aforementioned microencapsulated pigment particles C were used to prepare a liquid developer of a comparative example (Comparative Example CL1) in the same manner.

  Using the produced liquid developer of the present invention and the comparative developer, the evaluation of the toner charge by electrophoresis and the measurement of the zeta potential of the liquid developer described in Example 1 were performed. The results are shown in Table 2.

  According to the results, the liquid developer composed of the microencapsulated cyan pigment fine particles of the present invention clearly shows negative chargeability, and when the zeta potential is determined, the toner of the liquid developer of the present invention is −93 mV. As shown, the toner of the liquid developer of the comparative example showed a weak negative value and the zeta potential was -11 mV.

(Example 5)
(Preparation of liquid developer using microencapsulated pigment particles MCM2)
170 g of linseed oil containing 0.1% of TBHQ (t-butylhydroquinone) as an antioxidant, 12 g of the wet microparticles of the resulting microencapsulated pigment particle MCM2, 20 parts by weight of activated carbon in 200 parts by weight of commercially available linseed oil In addition to stirring, the mixture was stirred for 1 hour and then used for filtration, and mixed by irradiation with ultrasonic waves. This mixed liquid was transferred to a rotary evaporator, and maintained at a temperature of 120 ° C. for 5 hours while reducing the pressure to 30 mmHg or less, thereby distilling off water contained in the system. Subsequently, it moved to the stainless steel beaker, and ultrasonic developer was irradiated for 10 minutes to prepare a liquid developer MCML3 in which the microencapsulated magenta pigment was finely dispersed in linseed oil.

  Using the produced liquid developer of the present invention, the toner charge was evaluated by electrophoresis as described in Example 1 and the zeta potential of the liquid developer was measured. The results are shown in Table 2.

  According to the results, the liquid developer composed of the microencapsulated magenta pigment fine particles of the present invention clearly shows negative chargeability, and when the zeta potential is determined, the toner of the liquid developer of the present invention is −98 mV. Indicated.

Development, transfer, cleaning, and fixing were performed using a liquid developing type image forming apparatus shown in FIG.
A laminated negatively charged oil-repellent organic photoreceptor is used as the photoreceptor, and the developing roller is made of an elastic member. First, the surface of the photoreceptor is charged to −650 V with a scorotron, and a laser beam controlled by an image signal is irradiated to form a latent image. Next, development is performed by applying a developing bias of −600 V to the aforementioned elastic developing roller. A liquid developer whose layer thickness is regulated by a regulating blade is supplied to the developing roller while an anilox roller rotates in contact in the same direction. The anilox roller is supplied with liquid developer from a supply roller which is a sponge-like elastic roller.

  The transfer bias is +950 V, and the transfer paper is supplied in the left direction as indicated by the arrow while synchronizing the transfer timing with a pair of rollers from the lower right direction of the photoconductor. The transfer roller is an elastic roller, and the transfer bias described above is applied through a control system. After the transfer, the paper passes between heat fixing rollers made of an oil repellent material and is fixed. The fixing temperature is set to 90 ° C. Fixing is performed to such an extent that the toner image developed and transferred from the transfer paper does not transfer to another contact object (transfer paper, finger, device peripheral member, etc.) from the transfer paper at this temperature. The fixing temperature can be set to be optimal depending on the composition and viscosity of the vegetable oil used. Further, the process speed of this image forming jig is set to 200 mm / second.

  When the transfer residual toner is generated, the illustrated cleaning elastic roller is in contact with the photosensitive member, and is scraped off by a cleaning blade positioned above while moving the liquid developer slightly adhering from the photosensitive member. The cleaned photoreceptor can form a monochromatic image while repeating the cycle of charging, exposure, development, transfer, and cleaning again.

  Using the liquid developers of Examples 1 to 5 and Comparative Examples 1 to 4, 5% originals and solid images were printed out. Evaluation of the fixing property is performed by applying a mending tape (12 mm width) manufactured by Sumitomo 3M Co., Ltd. on the printed matter formed on the transfer paper (J paper manufactured by Fuji Xerox Office Supply Co., Ltd.) The density of the printed matter remaining on the transfer paper was expressed by the percentage presentation of the initial density. The results are shown in Table 3 together with the solid initial image density. Since the fog toner on the photosensitive member has a transfer bias of +950 V, it is not transferred on the transfer paper in principle. However, when the toner is shifted as a stain in some cases, it is evaluated as the print image quality. The reflection density of the printed matter was measured using the above-mentioned commercially available reflection densitometer (manufactured by X-Rite).

  Note that Comparative Example 2 did not have a fixing property and was not measured.

  According to the results, the liquid developer of the present invention has a high density in the image area, and no toner adheres to the non-image area, giving good print quality. In addition, these liquid developers were allowed to stand for one week and the dispersion stability was observed, and then the printed images were reproduced by placing them in the developing section of the image forming jig. However, the liquid developer of the present invention also showed sedimentation. However, although the printing quality was in the same state as the initial, the liquid developer of the comparative example was severely settled, and the reproduced printing quality was also worse than the initial, so it was difficult to interpret 5% original characters. .

In the production process of the microencapsulated pigment particles of the present invention, the pigment particles having an anionic group on the surface are dispersed in an aqueous medium and the cationic polymerizable surfactant and the anionic polymerization before polymerization of the first coating layer It is a figure for demonstrating the state coexisting with the hydrophilic surfactant, the hydrophilic macromonomer, and the hydrophilic monomer which has an anionic group. FIG. 2 is an explanatory diagram illustrating a state in which a cationic polymerizable surfactant, an anionic polymerizable surfactant, a hydrophilic macromonomer, and a hydrophilic monomer having an anionic group are polymerized in the dispersion state illustrated in FIG. 1. FIG. 3 is a diagram for explaining an electrophoresis experimental apparatus for measuring the charging behavior of the liquid electrostatic developer. FIG. 4 is a diagram for explaining a liquid developing type image forming apparatus.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Photoconductor, 22 ... Developing roller, 23 ... Scorotron, 24 ... Laser light controlled by image signal, 25 ... Anilox roller, 26 ... Restricting blade, 27 ... Supply roller, 28 ... transfer paper, 29 ... transfer roller, 30 ... thermal fixing roller, 31 ... cleaning elastic roller, 32 ... cleaning blade

Claims (11)

In a liquid developer in which microencapsulated pigment particles are dispersed in a low dielectric carrier liquid, the microencapsulated pigment particles are converted into pigment particles having an ionic group on the surface, and pigment particles having the ionic group on the surface. On the other hand, an ionic polymerizable surfactant having an ionic group, a hydrophobic group, and a radical polymerizable group in one molecule having an opposite charge is ionically bonded and derived from the ionic polymerizable surfactant. A repeating unit, a repeating unit derived from a hydrophilic macromonomer having a hydrophilic group, a long-chain hydrophilic part and a radical polymerizable group in one molecule; an anionic group, a hydrophobic group and a radical in one molecule; Radical polymerization having at least a repeating unit derived from an anionic polymerizable surfactant having a polymerizable group and / or a hydrophilic monomer having an anionic group It has a coating layer made of rimer, and anionic groups derived from at least an anionic polymerizable surfactant are arranged on the surface of the coating layer toward the low dielectric carrier liquid dispersion medium side to exhibit self-negative chargeability. A liquid electrostatic developer. 2. The liquid electrostatic developer according to claim 1, wherein the radical polymerization polymer in the microencapsulated pigment particles further has a repeating unit derived from at least one comonomer of a hydrophobic monomer and a crosslinking monomer. The pigment particles in the microencapsulated pigment particles are pigment particles having an anionic group on the surface, and the ionic polymerizable surfactant is a cationic polymerizable surfactant, or The liquid electrostatic developer according to claim 2. Cationic polymerizable surfactant
General formula R _{[4- (l + m + n)]} R ¹ _l R ² _m R ³ _n N ⁺ · X ⁻
Wherein R is a radical polymerizable group, R ¹ , R ² and R ³ are selected from hydrogen, alkyl group, aryl group, aralkyl group and alkylaryl group, at least one of which is a hydrophobic group , X is Cl, Br or I, l, m and n are 1 or 0 and are not 0 at the same time.)
The liquid electrostatic developer according to claim 3, wherein the liquid electrostatic developer is a compound represented by the formula: The liquid electrostatic developer according to claim 1, wherein the anionic polymerizable surfactant is a compound represented by the following general formula (1).

(In the formula, p is an integer of 9 or 11, q is an integer of 2 to 20, A is an anionic group, and the counter ion is an alkali metal ion, an ammonium ion, or an alkanolamine ion.) The liquid electrostatic developer according to claim 1, wherein the microencapsulated pigment particles have a volume primary average particle diameter of 0.2 μm to 1 μm. 2. The liquid electrostatic developer according to claim 1, wherein the microencapsulated pigment particles are contained in an amount of 2% by mass to 50% by mass. The low dielectric carrier liquid contains a vegetable oil containing an unsaturated group or an unsaturated fatty acid ester, and has a volume resistance of 10 ⁹ Ω · cm or more and a dielectric constant of 3.6 or less. The liquid electrostatic developer according to 1. The vegetable oil containing unsaturated groups is selected from safflower oil, sunflower oil, soybean oil, corn oil, cottonseed oil containing at least 50% or more linoleic acid component, or linseed oil containing at least 50% linoleic acid component. 9. The liquid electrostatic developer according to claim 8, which is a vegetable oil. (1) Step of dispersing pigment particles having an ionic group on the surface in an aqueous dispersion medium (2) In the dispersion, ionicity in one molecule having an opposite charge to the pigment particles having an ionic group on the surface A step of adding an ionic polymerizable surfactant having a group, a hydrophobic group and a radical polymerizable group, followed by a dispersion treatment;
(3) In the dispersion, a hydrophilic macromonomer having a hydrophilic group, a long-chain hydrophilic part and a radical polymerizable group in one molecule, an anionic group, a hydrophobic group and radical polymerizable in one molecule. A step of adding at least an anionic polymerizable surfactant having a group and / or a hydrophilic monomer having an anionic group, and a dispersion treatment;
After carrying out sequentially,
(4) The dispersion treatment liquid is heated and a polymerization initiator is added, emulsion polymerized, and ionic in one molecule having a charge opposite to that of the pigment particle having an ionic group on the surface of the pigment particle. Hydrophilic group having a repeating unit derived from an ionic polymerizable surfactant having a group, a hydrophobic group and a radically polymerizable group, and a hydrophilic group, a long-chain hydrophilic part and a radically polymerizable group in one molecule Derived from a repeating unit derived from a macromonomer, an anionic polymerizable surfactant having an anionic group, a hydrophobic group and a radical polymerizable group in one molecule and / or a hydrophilic monomer having an anionic group. Forming a microencapsulated pigment particle by forming a coating layer made of a radically polymerized polymer having at least a repeating unit.
(5) The aqueous medium is removed from the dispersion treatment liquid, and the resulting microencapsulated pigment particles are dispersed in a low dielectric carrier liquid, and the low dielectric carrier liquid dispersion medium side on the surface of the coating layer of the microencapsulated pigment particles A liquid electrostatic developer having a self-negative charging property in which at least an anionic polymerizable surfactant and / or an anionic group derived from a hydrophilic monomer having an anionic group are arranged A method for producing an electrostatic developer. The microencapsulated pigment particles are dispersed in a low dielectric carrier liquid by a wet method selected from a ball mill, a bead mill, and an attritor, and a volume primary average particle diameter is 0.2 μm to 1 μm. Item 11. A method for producing a liquid electrostatic developer according to Item 10.

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