Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/12—Developers with toner particles in liquid developer mixtures
  • G03G9/13—Developers with toner particles in liquid developer mixtures characterised by polymer components
  • G03G9/132—Developers with toner particles in liquid developer mixtures characterised by polymer components obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/12—Developers with toner particles in liquid developer mixtures
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G9/00—Developers
  • G03G9/08—Developers with toner particles
  • G03G9/093—Encapsulated toner particles

Definitions

• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• the resin particles which are kneaded with the pigment in a melted state have large particle diameters of about 1 to 10 ⁇ m, and contain a large amount of coarse particles due to wide particle diameter distribution.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• resins are preferably prepared from polyurethane resins and/or polyurea resins.
• the number average particle diameter of the coloring resin particles according to the present invention is preferably 0.05 to 1 ⁇ m.
• 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 ⁇ m. 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.
• 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 ⁇ ⁇ 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.).
• 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.
• 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.
• 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.
• 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.
• 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.
• the liquid developer according to the present invention can be prepared by microcapsularizing the pigment or the like by interfacial polymerization, for example.
• 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.
• the active hydrogens are preferably prepared from those of a primary amino group and a hydroxyl group, in consideration of reactivity.
• the compound having at least two such active hydrogens are polyamines and polyol compounds.
• the polyamine compound are hexamethylenediamine, m-xylylenediamine, iminobispropylamine, ⁇ , ⁇ -bis-(3-aminopropyl)-propylene glycol ether, and 2-methylpentadiamine.
• the polyol compound are ethylene glycol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,9-nonanediol, glycerol, and pentaerythritol.
• the monomer A is preferably insoluble in the nonaqueous dispersion medium.
• 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.
• the polyisocyanate compound are hexamethylenediisocyanate, toluenediisocyanate, isophoronediisocyanate, xylenediisocyanate, tetramethylxylenediisocyanate, trimers of such diisocyanates, and addition products of such diisocyanates and polyhydric alcohols.
• 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.
• 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.
• 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.
• a protective colloid can be prepared from that having hydrophobic and hydrophilic parts in molecules, which is generally employed in interfacial polymerization.
• hydrophobic parts are long-chain hydrocarbon groups and polyorganosiloxane units.
• hydrophilic parts are polyalkylene oxide units.
• 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.
• acrylic monomer MA-50, 100 or 150 (trade name) by Nippon Nyukazai Co., Ltd.
• acrylic monomer having long-chain hydrocarbon groups such as lauryl methacrylate or cetyl methacrylate, polyethylene glycol long-chain alkylether and sorbitan fatty acid ester.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• Such a polar group can be introduced by copolymerizing the following reactive emulsifier, for example:
• 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
• DMAPAA N,N-dimethylaminopropyl acrylamide
• DMAPAA-Q a compound prepared by making the same quaternary
• 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.
• 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, ⁇ -methylstyrene, vinyl ketone, t-butylstyrene, parachlorostyrene, vinyl naphthalene or the like Hydroxyl Group Mono
• 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.
• 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.
• 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.
• 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.
• sedimentation of the coloring particles is suppressed in the nonaqueous dispersion medium, to cause no defect in picture quality.
• 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.
• as-prepared coloring resin particles may be employed as the liquid developer, or may be employed after dilution with the nonaqueous dispersion medium.
• the inventive liquid developer can be prepared through simpler steps.
• the liquid developer according to the present invention is widely useful in the field of a wet copying machine, electrophotography or the like.
• pigment dispersants Samples of polymers for dispersing pigments in coloring resin particles (hereinafter referred to as "pigment dispersants”) were prepared as follows:
• polyethylene glycol PEG-200 by Kishida Chemical Co., Ltd.
• 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.
• ethylene glycol 300 g 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.
• 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.
• polyethylene glycol JEFARMINE M2070 by Mitsui Texco Co., Ltd.
• 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.
• CMA cetyl methacrylate
• MA-150 polyethylene glycol (15) monomethacrylate
• ACVA 2,2'-
• the particle diameters of the obtained particles which were measured by a particle diameter measurer SALAD 2000A (by Shimadzu Corporation), were 0.58 ⁇ m. 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.
• 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 ⁇ m.
• 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.
• 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 ⁇ m.
• 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.
• the pigment and the resin particles were partially heterogeneously present.
• 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 ⁇ m 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.
• 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 ⁇ m 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.
• the pigment was substantially present in the particles.
• 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.
• 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.
• an alkaline developer (1440 EZ developer by Printaware Co., Ltd., U.S.A.
• 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.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Liquid Developers In Electrophotography (AREA)
• Manufacturing Of Micro-Capsules (AREA)
• Pigments, Carbon Blacks, Or Wood Stains (AREA)

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Citations (14)

• 1994
  • 1994-07-18 JP JP6165548A patent/JPH0830040A/ja active Pending
• 1995
  • 1995-07-17 EP EP95111185A patent/EP0695974A1/fr not_active Withdrawn

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