Liquid developer and method of preparing the same

Abstract

 A liquid developer comprises a nonaqueous dispersion medium and coloring resin particles, containing a pigment and/or a dye, dispersed in the nonaqueous dispersion medium and microcapsularized by resin which is insoluble in the dispersion medium.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to a liquid developer for developing an electrostatic latent image in an electrophotographic process or the like and a method of preparing the same.

Description of the Background Art

[0002] In relation to an electrophotographic process, methods of developing electrostatic latent images are roughly classified into dry development and wet development. The dry development, which is adapted to distribute and bond colorant powder on and to an electrostatic latent image, is excellent in handling quality and preservation of a toner. In recent years, however, a high-definition image having high resolution is required in application to a video printer or the like, and it is necessary to further refine particle diameter of the developer in order to attain such high resolution. In the dry development, however, refinement of the particle diameter leads to problems such as aggregation of the toner, spreading of charging quantity distribution, imperfect cleanability and the like. Thus, improvement of the resolution is limited.

[0003] On the other hand, the wet development employs a liquid developer which is prepared by dispersing a dye or a pigment serving as a colorant in an insulating medium and the particle diameter of this developer can be further reduced as compared with that employed in the dry development, whereby high resolution and gradient can be attained. Thus, study and development of such liquid developers are increasingly made in recent years.

[0004] For example, liquid developers which are disclosed in Japanese Patent Laying-Open Nos. 3-196154 (1991) and 3-223770 (1991) are known in the art. These liquid developers are prepared by dispersing pigments in hydrocarbon nonaqueous dispersion media containing resin components.

[0005] Further, Japanese Patent Laying-Open Nos. 63-151868 (1988), 3-211565 (1991) and 3-225353 (1991) disclose liquid developers which are obtained by mixing and dispersing nonaqueous dispersion polymerization particles and pigments in nonaqueous dispersion media.

[0006] In each of such conventional liquid developers, however, the resin and the pigment which are mixed into the nonaqueous dispersion medium are prepared independently of each other and hence the same are at different mobility levels in the nonaqueous dispersion medium. Thus, the resin and the pigment are bonded to a surface of a photosensitive drum at such different degrees that the composition of the liquid developer is disadvantageously changed over time, to change the image density.

[0007] Further, such a conventional liquid developer tends to cause fogging and toner sediment resulting from aggregation of the pigment since the resin component and the resin particles are merely adsorbed by the pigment, leading to contamination of an apparatus due to adhesion of the pigment.

[0008] A liquid developer which is obtained by mixing a pigment in melted resin for preparing resin particles containing the pigment and dispersing the same in a nonaqueous dispersion medium is known as means for solving such problems. Examples of such a liquid developer are disclosed in Japanese Patent Laying-Open Nos. 63-301966 to 301969 (1988), 63-5351 (1988) and 2-883 (1990), for example. In such a liquid developer, the pigment and the resin particles are so integrated with each other that the same integrally behave to cause no change with time in composition resulting from difference between mobility levels, and hence no change is caused in image density. Further, a developing apparatus is hardly contaminated since the pigment is contained in the resin.

[0009] However, the resin particles which are kneaded with the pigment in a melted state have large particle diameters of about 1 to 10 µm, and contain a large amount of coarse particles due to wide particle diameter distribution.

[0010] Therefore, coloring particles are easy to sediment in the liquid developer, and hence an image of high resolution cannot be obtained.

SUMMARY OF THE INVENTION

[0011] An object of the present invention is to provide a liquid developer which can solve the aforementioned problems of the prior art, reduce change with time of image density, reduce contamination in a developing apparatus, and develop a clearer image, and a method of preparing the same.

[0012] The liquid developer according to the present invention comprises a nonaqueous dispersion medium and coloring resin particles, containing a pigment and/or a dye (hereinafter simply referred to as "pigment or the like"), which are microcapsularized by resin insoluble in the dispersion medium.

[Coloring Resin Particles]

[0013] According to the present invention, the coloring resin particles contain a pigment or the like, with a pigment dispersant for dispersing the pigment or the like at need.

[0014] The pigment or the like and the pigment dispersant which are contained in the coloring resin particles, and a microcapsule wall material are now described.

Pigment or the Like

[0015] The pigment or the like which is employed in the present invention is not particularly restricted, but a well-known inorganic or organic pigment, a well-known dye or a mixture thereof can be employed, for example.

[0016] Examples of the pigment are as follows:
   Magenta Pigments: azolake, monoazo and quinacridone pigments such as C.I. Pigments Nos. Red-57-1, Red-31 and Red-122
   Cyan Pigments: phthalocyanine pigments such as C.I. Pigments Nos. Blue-60, Blue-15-6, Blue-15, Blue-15-2, Blue-15-3 and Blue-15-4
   Yellow Pigments: disazo and benzoimidazoline pigments such as C.I. Pigments Nos. Yellow-12, -13, -14, -17, -55, - 83 and -154
   Black Pigments: carbon black, copper oxide, manganese dioxide, aniline black, active carbon, magnetite, magnetic ferrite and non-magnetic ferrite
   Examples of the dye are as follows:
   C.I. Direct Black 19, 22 and 154
   C.I. Direct Yellow 12, 16 and 88
   C.I. Direct Red 9, 13 and 17
   C.I. Direct Blue 78 and 90
   C.I. Acid Black 8, 31 and 52
   C.I. Acid Yellow 23 and 25
   C.I. Acid Red 37, 52, 92 and 94
   C.I. Acid Blue 9 and 22
   C.I. Food Black 2

Pigment Dispersant

[0017] The pigment dispersant must be capable of dispersing the pigment or the like in the nonaqueous dispersion medium or a monomer of a microcapsule wall material described later. Such a pigment dispersant can be prepared from a commercially available material such as Solsper 27000 (product by ZENEKA Co., Ltd.), or a general material such as acrylic resins, melamine resins, styrene-maleic acid copolymers, polyester resins, epoxy modified resins, butadiene modified resins or urethane resins. In consideration of the degree of freedom in design, the acrylic resins are particularly preferable.

Microcapsule Wall Material

[0018] The microcapsule wall material for the coloring resin particles according to the present invention is prepared from resins which are insoluble in the nonaqueous dispersion medium. Such resins are preferably prepared from polyurethane resins and/or polyurea resins.

Particle Diameter of Coloring Resin Particles

[0019] The number average particle diameter of the coloring resin particles according to the present invention is preferably 0.05 to 1 µm. In the present invention, the number average particle diameter of the coloring resin particles is preferably minimized so far as the particles can be stably dispersed, while a generally obtained number average particle diameter is at least 0.05 µm. If the number average particle diameter is too large, the coloring resin particles are easily sedimented to provide a faint image and to reduce the image density. If the particle diameters are increased, high resolution cannot be attained. The mean particle diameter of the coloring resin particles can be measured with a particle diameter measurer utilizing light scattering or laser diffraction.

[Nonaqueous Dispersion Medium]

[0020] The nonaqueous dispersion medium for forming the liquid developer according to the present invention is not particularly restricted so far as the same is generally employed as a dispersion medium for a liquid developer, while its volume specific resistance value is at least 10¹⁰ Ω ·cm in general, and its dielectric constant is at least 3.5 in general. Examples of such a nonaqueous dispersion medium are aliphatic hydrocarbon, alicyclic hydrocarbon, aromatic hydrocarbon, halogenated hydrocarbon and polysiloxane, while an isoparaffin petroleum solvent is suitable in consideration of volatility, safety, toxicity and odor. Examples of such an isoparaffin petroleum solvent are ISOPAR M, ISOPAR G, ISOPAR H, ISOPAR L and ISOPAR K (products by Esso Sekiyu K. K.) and SHELLSOL (product by Shell Sekiyu K. K.).

[0021] The liquid developer according to the present invention can be obtained by interfacially polymerizing monomers A and B with each other in the aforementioned nonaqueous dispersion medium thereby preparing coloring resin particles which are microcapsularized containing the pigment or the like.

[0022] It is possible to microcapsularize the coloring resin particles by dispersing/emulsifying one of the monomers A and B which is insoluble in the nonaqueous dispersion medium with the pigment or the like in the presence of a protective colloid and adding the other monomer to the dispersion/emulsion liquid for carrying out interfacial polymerization.

[0023] In general, the monomer A is insoluble in the nonaqueous dispersion medium, and hence the same is dispersed/emulsified in the nonaqueous dispersion medium with the pigment or the like so that the monomer B is dropped in the dispersion/emulsion liquid for carrying out polymerization reaction, thereby forming microcapsule walls.

[Ratio of Coloring Resin Particles to Nonaqueous Dispersion Medium]

[0024] The ratio of the coloring resin particles to the nonaqueous dispersion medium is not particularly restricted in the liquid developer according to the present invention, while a blending ratio for a general liquid developer can be applied so that the concentration of the coloring resin particles is 1 to 45 percent by weight, for example. It may be impossible to obtain a clear image if the concentration of the coloring resin particles is too small, while interparticle aggregation may be easily caused if the concentration of the coloring resin particles is too high.

[0025] If the coloring resin particles are highly concentrated in synthesis and storage, the same can be properly diluted with a solvent before supply to a developing apparatus.

[Electrification of Coloring Resin Particles]

[0026] The coloring resin particles contained in the liquid developer, which are adapted to adhere to a surface of a photosensitive drum or the like for forming an electrostatic latent image by electrophoresis through the nonaqueous dispersion medium, must be electrified in the nonaqueous dispersion medium. Charges for such electrification can be applied by introducing a polar group into the coloring resin particles, or adding a charge adjuster, as described later.

[Method of Preparing Liquid Developer]

[0027] The liquid developer according to the present invention can be prepared by microcapsularizing the pigment or the like by interfacial polymerization, for example.

Microcapsulation by Interfacial Polymerization

[0028] With employment of interfacial polymerization, the inventive liquid developer can be prepared by reacting a compound having at least two active hydrogens and another compound having at least two functional groups which are reactive with the active hydrogens, for example. These compounds are now described.

(1) Compound Having at least Two Active Hydrogens (hereinafter referred to as "monomer A")

[0029] The active hydrogens are preferably prepared from those of a primary amino group and a hydroxyl group, in consideration of reactivity. Examples of the compound having at least two such active hydrogens are polyamines and polyol compounds. Examples of the polyamine compound are hexamethylenediamine, m-xylylenediamine, iminobispropylamine, α,ω-bis-(3-aminopropyl)-propylene glycol ether, and 2-methylpentadiamine. Examples of the polyol compound are ethylene glycol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,9-nonanediol, glycerol, and pentaerythritol.

[0030] The monomer A is preferably insoluble in the nonaqueous dispersion medium.

(2) Compound Having at least Two Functional Groups Reactive with Active Hydrogens (hereinafter referred to as "monomer B")

[0031] The functional groups which are reactive with the aforementioned active hydrogens are preferably prepared from isocyanate groups in consideration of reactivity. An example of the compound having at least two functional groups which are reactive with the active hydrogens is a polyisocyanate compound. Examples of the polyisocyanate compound are hexamethylenediisocyanate, toluenediisocyanate, isophoronediisocyanate, xylenediisocyanate, tetramethylxylenediisocyanate, trimers of such diisocyanates, and addition products of such diisocyanates and polyhydric alcohols.

(3) Blending Ratio of Monomer B to Monomer A

[0032] The equivalent ratio of the monomer B to the monomer A is preferably 0.4 to 2, and more preferably 0.6 to 1.2. If the equivalent ratio is out of this range, it may not be possible to obtain target microcapsules.

Pigment Dispersant

[0033] The aforementioned pigment dispersant is preferably employed in order to allow stable presence of the pigment or the like in the nonaqueous dispersion medium in interfacial polymerization.

Protective Colloid

[0034] The protective colloid is preferably employed for stablizing emulsified states of the pigment or the like and the monomer A (or the monomer B, as the case may be) in the nonaqueous dispersion medium. Such a protective colloid can be prepared from that having hydrophobic and hydrophilic parts in molecules, which is generally employed in interfacial polymerization.

[0035] Examples of the hydrophobic parts are long-chain hydrocarbon groups and polyorganosiloxane units. Examples of the hydrophilic parts are polyalkylene oxide units. Examples of the protective colloid having such hydrophobic and hydrophilic parts are a block polymer having polyorganosiloxane units and polyalkylene oxide units, a copolymer of an acrylic monomer (MA-50, 100 or 150 (trade name) by Nippon Nyukazai Co., Ltd.) and an acrylic monomer having long-chain hydrocarbon groups such as lauryl methacrylate or cetyl methacrylate, polyethylene glycol long-chain alkylether and sorbitan fatty acid ester.

Phase Inversion

[0036] In one of preferred embodiments of the method according to the present invention, the pigment or the like and the monomers are dispersed by phase inversion, and microcapsularized by interfacial polymerization. The interfacial polymerization by phase inversion can be carried out through the following three steps:
   First Step: When the pigment dispersant is employed, the same is mixed with the pigment or the like, for preparing pigment dispersed paste. This pigment dispersed paste is added to the monomer A and dispersed, to prepare a dispersion liquid. Alternatively, the pigment dispersant, the pigment or the like, and the monomer A are mixed to prepare the dispersion liquid.

[0037] Second Step: The dispersion liquid obtained in the first step is added to the nonaqueous dispersion medium in the presence of the protective colloid and dispersed and emulsified, to prepare an emulsion liquid.

[0038] Third Step: The monomer B is dropped into the emulsion liquid obtained in the second step, so that the liquid is microcapsularized by interfacial polymerization of the monomers A and B.

[0039] While the emulsion is carried out through phase inversion in the preferred embodiment as described above, the inventive method is not restricted to this but the monomers A and B may alternatively be directly dispersed/emulsified in the nonaqueous dispersion medium in the presence of the protective colloid, to be interfacially polymerized.

[Blending Ratio]

Pigment or the Like

[0040] The weight of the pigment or the like is preferably 5 to 25 percent by weight with respect to the total weight of the pigment or the like, the monomers A and B and the pigment dispersant. It may be impossible to obtain a clear image if the rate of the pigment or the like is too small, while stability of the liquid developer may be deteriorated if the rate is too large.

Pigment Dispersant

[0041] The rate of the pigment dispersant with respect to the pigment or the like is preferably 5 to 30 percent by weight as a solids content. Dispersion stability is deteriorated if the rate of the pigment dispersant is too small, while it may be impossible to obtain particles of target particle sizes if the rate is too large.

Protective Colloid

[0042] The rate of the protective colloid is preferably 5 to 30 percent by weight with respect to the weight of the monomer A, the pigment dispersant and the pigment or the like. If the rate is out of this range, it may be impossible to obtain particles of target particle sizes.

Nonaqueous Dispersion Medium

[0043] The rate of the nonaqueous dispersion medium is preferably 1 to 5 times, more preferably 2 to 4 times with respect to the total weight of the monomers A and B, the pigment dispersant and the pigment or the like. It is difficult to prepare the liquid developer if the amount of the nonaqueous dispersion medium is too small, while the developer is economically disadvantageous if the amount of the nonaqueous dispersion medium is too large.

[Electrification of Coloring Resin Particles]

[0044] According to the present invention, it is preferable to introduce a polar group into any one of the microcapsule wall material for the coloring resin particles, the protective colloid employed for the interfacial polymerization, and the pigment dispersant contained in the coloring resin particles, in order to electrify the coloring resin particles. Examples of such a polar group are anion groups such as a carboxylic acid group and its metal salt, a sulfonic acid group and its metal salt, and metal chelate groups, and cation groups such as an amino group, and quaternary ammonium groups.

Introduction of Polar Group into Pigment Dispersant and Protective Colloid

[0045] Such a polar group can be introduced by copolymerizing the following reactive emulsifier, for example:

(1) Reactive Emulsifier having Anionic Group

[0046] 


   wherein

and


   trade name: Antox-MS-60 by Nippon Nyukazai Co., Ltd.


   wherein X:H or SO₃NH₄
   trade name: ADEKASOAP SE-10N by Asahi Denka Kogyo K.K.


   wherein R:C₉H₁₉ and m = 10
   trade name: AQUARON HS-10 by Daiichi Seiyaku Co., Ltd.


   wherein R:C₁₈H₃₆F₁ and M:NH₄
   trade name: LATEMUL S-180A by Kao Corporation


   wherein


   prepared by ring-opening trimellitic anhydride with a compound having a hydroxyl group on its end obtained by adding ε-caprolactone to 2-hydroxyethyl methacrylate by 5 moles on the average and reacting one of carboxyl groups with long-chain epoxy (KARJULAR E)
   A compound prepared by ring-opening phthalic anhydride with 2-hydroxyethyl methacrylate such as ACRYLESTER PA (trade name) by Mitsubishi Rayon Co., Ltd., for example

(2) Reactive Emulsifier having Cationic Group

[0047] N,N-dimethylaminopropyl acrylamide (DMAPAA (trade name) by Koujin Co., Ltd.) and a compound prepared by making the same quaternary (DMAPAA-Q (trade name) by Koujin Co., Ltd.)

[0048] It is possible to prepare the pigment dispersant and the protective colloid by copolymerizing the aforementioned reactive emulsifier having anionic or cationic groups and an acrylic monomer (MA-50, 100 or 150 (trade name) by Nippon Nyukazai Co., Ltd.) having a polyethylene oxide part, for example.

[0049] As to the rate of copolymerization, 5 to 25 percent by weight of the reactive emulsifier having the anionic or cationic groups may be employed with respect to at least 40 percent by weight of the acrylic monomer having a polyethylene oxide part, and the rest may be prepared from the following (meth)acrylates, polymerizable aromatic compounds and hydroxyl group monomers:
   (Meth)acrylate: methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate, 2-ethylhexyl acrylate, lauryl methacrylate, phenyl acrylate or the like
   Polymerizable Aromatic Compound: styrene, α-methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinyl naphthalene or the like
   Hydroxyl Group Monomer: 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, allyl alcohol, methallyl alcohol or the like

Introduction of Polar Group into Capsule Wall Material

[0050] When an anionic group is introduced into the capsule wall material, 2,5-dihydroxy-1,4-benzenediacetic acid, for example, can be added.

[0051] When a cationic group is introduced into the capsule wall material, on the other hand, diamine (EDR-148 (trade name) by Mitsui Texco Co., Ltd.), for example, may be added to isocyanato by about 1.2 to 1.4 equivalents.

Addition of Charge Adjuster

[0052] The following charge adjuster may be added during or after the interfacial polymerization, to supply the coloring resin particles with charges, preferably in an amount of 0.05 to 5 percent by weight with respect to the coloring resin particles:
   Charge Controller Providing Positive Charges
   sulfosuccinate dioctyl sodium, zirconium octoate, copper oleate, metal salt of naphthenic acid, metal complex salt of ethylenediaminetetraacetic acid, and quaternary ammonium compounds
   Charge Controller Providing Negative Charges
   lecithin, barium petronate, alkyl succinimide, Oil Black BY or the like
   The liquid developer according to the present invention comprises the nonaqueous dispersion medium and the coloring resin particles, containing the pigment or the like, which are microcapsularized and dispersed in the nonaqueous dispersion medium. According to the present invention, the pigment or the like and the resin particles are so integrated with each other by microcapsulation to integrally move in the nonaqueous dispersion medium and adhere to the surface of the photosensitive drum or the like. Thus, no composition change with time is caused and hence it is possible to prevent reduction of image density with time and fogging of characteristics or the like.

[0053] Further, the coloring resin particles are formed by microcapsulation, whereby the particle diameters thereof can be reduced as compared with conventional coloring resin particles which are integrated by melting or kneading. Thus, sedimentation of the coloring particles is suppressed in the nonaqueous dispersion medium, to cause no defect in picture quality.

[0054] According to the inventive method, the coloring resin particles containing the pigment or the like are prepared by interfacial polymerization in the nonaqueous dispersion medium which is employed for the liquid developer. According to the present invention, as-prepared coloring resin particles may be employed as the liquid developer, or may be employed after dilution with the nonaqueous dispersion medium. Thus, it is not necessary to disperse in a nonaqueous dispersion medium coloring resin particles which is separately prepared, dissimilarly to the prior art, and the inventive liquid developer can be prepared through simpler steps.

[0055] The liquid developer according to the present invention is widely useful in the field of a wet copying machine, electrophotography or the like.

[0056] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] Samples of polymers for dispersing pigments in coloring resin particles (hereinafter referred to as "pigment dispersants") were prepared as follows:

〈Synthetic Example 1 (Pigment Dispersant)〉

[0058] 300 g of polyethylene glycol (PEG-200 by Kishida Chemical Co., Ltd.) was introduced into a reaction vessel comprising a stirring heater, a cooling tube, a nitrogen introducing tube and a temperature controller, stirred with introduction of nitrogen and heated to 80°C, while a mixed solution of 60 g of polyethylene glycol (15) monomethacrylate (MA-150 by Nippon Nyukazai Co., Ltd.), 40 g of a reactive emulsifier (Antox-MS-60 by Nippon Nyukazai Co., Ltd.) and 2 g of dimethyl 2,2'-azobis(2-methylpropionate) (V-601 by Wako Pure Chemical Industries, Ltd.) was dropped therein over 2 hours, and thereafter reaction was continued for 5 hours. The obtained polymer exhibited a number average molecular weight of 41,000 by GPC.

〈Synthetic Example 2 (Pigment Dispersant)〉

[0059] 300 g of ethylene glycol was introduced into a reaction vessel, and polymerization reaction was caused similarly to Synthetic Example 1 except that a mixed solution of 60 g of polyethylene glycol monomethacrylate (MA-150 by Nippon Nyukazai Co., Ltd.), 40 g of a reactive emulsifier which was prepared by ring-opening trimellitic anhydride with a compound having a hydroxyl group on its end obtained by adding ε-caprolactone to 2-hydroxyethyl methacrylate by 5 moles on the average and reacting one of carboxyl groups with long-chain epoxy (KARJULAR E) and 1 g of dimethyl 2,2'-azobis(2-methyl propionate) (V-601 by Wako Pure Chemical Industries, Ltd.) was dropped. The obtained polymer exhibited a number average molecular weight of 39,000.

〈Synthetic Example 3 (Pigment Dispersant)〉

[0060] 300 g of ethylene glycol was introduced into a reaction vessel, and polymerization reaction was caused similarly to Synthetic Example 1 except that a mixed solution of 60 g of polyethylene glycol (50) monomethacrylate (MA-50 by Nippon Nyukazai Co., Ltd.), 40 g of N,N-dimethylaminopropyl methacrylamide (DMAPMA by Koujin Co., Ltd.) and 1 g of dimethyl 2,2'-azobis(2-methyl propionate) (V-601 by Wako Pure Chemical Industries, Ltd.) was dropped. The obtained polymer exhibited a number average molecular weight of 38,000.

[0061] Samples of protective colloids employed for microcapsulation by interfacial polymerization were prepared as follows:

〈Synthetic Example 4 (Protective Colloid)〉

[0062] 476.5 g of polydimethylsiloxane (FM-0421 by Chisso Corporation) of 5000 in molecular weight having an OH group on one end, 23.5 g of isophoronediisocyanate and 0.06 g of dibutyltin laurate were mixed in a reaction vessel comprising a stirring heater, a thermometer and a cooling tube, and reaction was continued while maintaining the temperature at 75°C. After a lapse of 8 hours, the isocyanate equivalent was measured to confirm disappearance of the isocyanate group in a theoretical amount. The temperature was reduced to the room temperature, thereafter 191.5 g of polyethylene glycol (JEFARMINE M2070 by Mitsui Texco Co., Ltd.) of 2000 in molecular weight having an amino group on one end was added to the mixture, which in turn was stirred at the room temperature for 2 hours, and reaction was further continued at 40°C for 2 hours. Only a small amount of isocyanate was detected by IR. The number average molecular weight and the weight average molecular weight measured by GPC were 7160 and 9240 respectively.

〈Synthetic Example 5 (Protective Colloid)〉

[0063] 230 g of methyl ethyl ketone was introduced into a reaction vessel comprising a stirring heater, a thermometer, a nitrogen introducing tube and a cooling tube, stirred in a nitrogen atomosphere, and heated to 80°C. Further, a mixed solution of 65 g of cetyl methacrylate (CMA by Nippon Oil and Fats Co., Ltd.), 15 g of polyethylene glycol (15) monomethacrylate (MA-150 by Nippon Nyukazai Co., Ltd.), 10 g of methyl methacrylate, 10 g of acrylic acid and 1 g of 2,2'-azobis(cyanovaleric acid) (ACVA) was dropped for 2 hours, and thereafter reaction was continued for 5 hours. After the reaction, desolvention was made by an evaporator. The obtained resin contained 90 % of non-volatile components, and exhibited a number average molecular weight of 12,000 through measurement by GPC.

〈Synthetic Example 6 (Protective Colloid)〉

[0064] Polymerization reaction was made similarly to Synthetic Example 5, except that a mixed solution of 65 g of lauryl methacrylate, 15 g of polyethylene glycol (10) monomethacrylate (MA-100 by Nippon Nyukazai Co., Ltd.), 10 g of methyl methacrylate, 10 g of N,N-dimethylaminopropyl methacrylamide (DMAPMA by Koujin Co., Ltd.) and 1 g of dimethyl 2,2'-azobis(2-methyl propionate) (Wako Pure Chemical Industries, Ltd.) was dropped. The obtained resin contained 92 % of non-volatile components, and exhibited a number average molecular weight of 11,000 through measurement by GPC.

[0065] The samples of the pigment dispersants and the protective colloids obtained in the aforementioned manner were employed to prepare the following liquid developers of Examples 1 to 8 and comparative examples 1 to 6:

Example 1

[0066] 20 g of phthalocyanine blue (Blue 4938 by Dainichiseika Colour & Chemicals Mfg. Co., Ltd.), 80 g of polyethylene glycol having a molecular weight of 200, 5 g of resin commercially available as a pigment dispersant (Solspers 17000 by ZENEKA Co., Ltd.) and 125 g of glass beads (GB503M by Toshiba Barotiene Co., Ltd.) were introduced into a sand grinder, and dispersed at 200 rpm for 3 hours. 70 g of the obtained pigment paste and 30 g of the protective colloid obtained in Synthetic Example 4 were blended with each other in POLYTRON at 4000 r.p.m. and continuously stirred, while 200 g of ISOPAR M was gradually dropped to emulsify the mixture. This mixture was transferred to a reaction vessel, thereafter 0.05 g of dibutyltin laurate was added thereto, and a 15 % ISOPAR M solution of toluene diisocyanate (TD180 by Mitsubishi Chemical Industries Ltd.) was dropped at the room temperature for 1 hour, to be equivalent with respect to the aforementioned polyethylene glycol. After a lapse of 2 hours from completion of the dropping, the temperature was increased to 45°C, to make further polymerization for 2 hours. 20 g of the obtained polymer and 5.4 g of zirconium octoate were introduced into 500 g of ISOPAR M and stirred, to prepare a developing solution.

[0067] The particle diameters of the obtained particles, which were measured by a particle diameter measurer SALAD 2000A (by Shimadzu Corporation), were 0.58 µm. Further, the particles were observed with a transmission electron microscope, whereby it was found that the pigment was capsularized and present in the particles. It was confirmed that the liquid developer was positively charged.

Examples 2 to 8

[0068] Developing solutions were prepared similarly to Example 1 at blending ratios shown in Tables 1 and 2. In each of Examples 7 and 8, 0.7 equivalent of isocyanate was added to polyamine.

[Table 1]

[Table 2]

[0069] In each of Examples 2 to 8 prepared in the aforementioned manner, an acidic group or a basic group was introduced into any of the pigment dispersant, the protective colloid and the capsule wall material as a polar group, thereby positively or negatively charging surfaces of the coloring resin particles. Table 3 shows types and introduced portions of the polar groups and charging properties of the resin particles.

[Table 3]

Comparative Example 1 (Developer by Pigment Dispersion)

[0070] 5 g of a phthalocyanine pigment (Blue 4938 by Dainichiseika Colour & Chemicals Mfg. Co., Ltd.), 50 g of the protective colloid according to Synthetic Example 5 and 200 g of ISOPAR M were mixed with each other in SG mill at 2000 rpm for 3 hours, to prepare a concentrated toner. 20 g of this concentrated toner was added into 700 g of ISOPAR M and diluted, to obtain a negatively charged developing solution. The obtained particles were 0.23 µm in particle diameter. The structures of the particles were observed with a transmission electron microscope, whereby it was found that the pigment and the resin were partially heterogeneously present.

Comparative Example 2 (Developer by Pigment Dispersion)

[0071] 5 g of an azo pigment (Red 10 by Dainichiseika Colour & Chemicals Mfg. Co., Ltd.), 50 g of the protective colloid according to Synthetic Example 6, and 200 g of ISOPAR M were mixed with each other in SG mill at 2000 rpm for 3 hours, to prepare a concentrated toner. 20 g of this concentrated toner was added into 700 g of ISOPAR M and diluted, to obtain a positively charged developing solution. The obtained particles were 0.25 µm in particle diameter. The structures of the particles were observed with a transmission electron microscope, whereby it was found that the pigment and the resin were partially heterogeneously present.

Comparative Example 3 (Developer by Mixture of Protective Colloid and Pigment)

[0072] Negatively charged particles were synthesized in a similar manner to Example 1, except that the pigment was not contained and the protective colloid was replaced by 20 g of the protective colloid according to Synthetic Example 5. The obtained particles exhibited particle diameters of 0.53 µm. 100 g of these particles, 5 g of Blue 4938, 50 g of the protective colloid according to Synthetic Example 5 and 200 g of ISOPAR M were mixed with each other in SG mill at 2000 rpm for 3 hours, to prepare a concentrated toner. 20 g of this concentrated toner was added into 700 g of ISOPAR M and diluted, to obtain a negatively charged developing solution. Through observation with a transmission electron microscope, the pigment and the resin particles were partially heterogeneously present.

Comparative Example 4 (Developer by Mixture of Protective Colloid and Pigment)

[0073] Positively charged particles were synthesized in a similar manner to Example 1, except that the pigment was not contained and the protective colloid was replaced by 20 g of the protective colloid according to Synthetic Example 6.
The obtained particles exhibited particle diameters of 0.49 µm. 100 g of these particles, 5 g of Phthalocyanine Blue, 50 g of the protective colloid according to Synthetic Example 6 and 200 g of ISOPAR M were mixed with each other in SG mill at 2000 rpm for 3 hours, to prepare a concentrated toner. 20 g of this concentrated toner was added into 700 g of ISOPAR M and diluted, to obtain a positively charged developing solution. Through observation with a transmission electron microscope, the pigment and the resin particles were partially heterogeneously present.

Comparative Example 5 (Developer by Kneading → Emulsification)

[0074] Sorbitan tristearate employed as a protective colloid and the pigment dispersant according to Synthetic Example 1 were emulsified in a similar manner to Example 1, with no interfacial polymerization of a later step. The obtained particles were 5.7 µm in particle diameter. 20 g of these particles were added into 700 g of ISOPAR M and diluted, to obtain a negatively charged developing solution. The developing solution was observed with a transmission electron microscope, whereby it was found that the pigment was substantially present in the particles.

Comparative Example 6 (Developer by Kneading → Emulsification)

[0075] Sorbitan tristearate employed as a protective colloid and the pigment dispersant according to Synthetic Example 3 were emulsified in a similar manner to Example 1, with no interfacial polymerization of a later step. The obtained particles were 6.3 µm in particle diameter. 20 g of these particles were added into 700 g of ISOPAR M and diluted, to obtain a positively charged developing solution. Through observation with a transmission electron microscope, the pigment was substantially present in the particles.

〈Evaluation Example 1 (Developer for Wet Copying Machine)〉

[0076] The negatively charged liquid developers according to Examples 2, 3 and 5 and comparative examples 1, 3 and 5 were introduced into a commercially available copying machine (CT5085 by Ricoh Co., Ltd.), to make a printing test. Table 4 shows the results.

[Table 4]

〈Evaluation Example 2 (Developer for Electrophotography)〉

[0077] A scan exposure type prepress machine (1440 EZ Plate Setter by Printaware Co., Ltd., U.S.A.) having a semiconductor laser of 780 nm in wavelength as a light source and the positively charged liquid developers according to Examples 4, 6, 7 and 8 and comparative examples 2, 4 and 6 were employed for electrophotographic printing original plates, to form images by operations of electrification, exposure, liquid development and fixation. Thereafter photosensitive layers of non-image portions having no adhesion of toners were dissolved and removed with an alkaline developer (1440 EZ developer by Printaware Co., Ltd., U.S.A.), and protection with gum solution was carried out to prepare planographic printing plates while leaving toner images as scanning portions.

[0078] The respective printing plates were mounted on a miniature offset printer (HAMADASTER 7000CDX by Hamada Printing Machine Manufacturing Co., Ltd.), to print images on high quality papers with commercially available ink. Table 5 shows the results.

[Table 5]

[0079] As clearly understood from the results shown in Tables 3 and 4, the liquid developers according to inventive Examples hardly cause sedimentation of the toners, and can develop clear images. It is also understood that the developing apparatus is hardly contaminated.

[0080] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.

Claims

1. A liquid developer comprising:
   a nonaqueous dispersion medium; and
   coloring resin particles, containing a pigment and/or a dye, being dispersed in said nonaqueous dispersion medium and microcapsularized by resin being insoluble in said nonaqueous dispersion medium.

2. The liquid developer in accordance with claim 1, wherein said insoluble resin forming said coloring resin particles is polyurethane resin and/or polyurea resin.

3. The liquid developer in accordance with claim 1, wherein the number average particle diameter of said coloring resin particles is 0.05 to 1 µm.

4. The liquid developer in accordance with claim 1, wherein said pigment and/or said dye is contained in a state being dispersed or dissolved by a pigment dispersant.

5. A method of preparing a liquid developer by interfacially polymerizing a compound having at least two active hydrogens and another compound having at least two functional groups being reactive with said active hydrogens in the presence of a pigment and/or a dye in a nonaqueous dispersion medium, thereby preparing coloring resin particles being microcapsularized containing said pigment and/or said dye.

6. The method of preparing a liquid developer in accordance with claim 5, comprising the steps of:
   dispersing or dissolving said pigment and/or said dye to be contained in said microcapsules and a pigment dispersant in that of said compounds, to be interfacially polymerized with each other, being insoluble in said nonaqueous dispersion medium,
   adding said nonaqueous dispersion medium to said dispersion liquid or said dissolution liquid in the presence of a protective colloid, and dispersing or emulsifying the same, and
   adding the other said compound to be interfacially polymerized to said dispersion or emulsion liquid for carrying out said interfacial polymerization.

7. The method of preparing a liquid developer in accordance with claim 5, wherein said compound having at least two active hydrogens is a compound having at least two amino groups and/or hydroxyl groups, and said compound having at least two functional groups being reactive with said active hydrogens is a compound having at least two isocyanate groups.

8. The method of preparing a liquid developer in accordance with claim 6, wherein a protective colloid in which a polar group for supplying charges to said coloring resin particles is introduced is employed as said protective colloid.

9. The method of preparing a liquid developer in accordance with claim 6, wherein a pigment dispersant in which a polar group for supplying charges to said coloring resin particles is introduced is employed as said pigment dispersant contained in said microcapsules.