JP2000003064A - Image forming method using color toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a high-quality color image by an electrophotographic system. SOLUTION: In this color image forming method yellow, magenta, cyan and black electrostatic latent images are formed on a photoreceptor and developed with color toner such as yellow, magenta, cyan and black toner, and four colors of toner are superimposed on a body to be printed and transferred, so that the color toner on the body to be printed is fixed in the electrophotographic system color image forming device. In such a case, spherical toner whose volume average particle size is 2 to 6 μm, which has binding resin including colorant and whose average roundness is >=0.97 is used as the four colors of toner, thereby, a high-quality color image is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-quality color image forming method in a non-magnetic one-component development or two-component development type electrophotographic printer or copier.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus, full-color development for forming an image by superimposing yellow, magenta, cyan and black toners is performed. This full-color development is to expose a multi-color document after color separation processing, and then perform this process in yellow, magenta,
It is intended to obtain a multi-color image by repeating a plurality of times using cyan and black toners and superimposing the toner images.

The image quality of current electrophotographic copiers and printers is remarkably inferior to lithographic printing, silver halide photography, etc., especially when compared with color images. Various improvement efforts have been made.

[0004] From the viewpoint of toner, as a means for improving image quality such as resolution, it has recently become increasingly important to reduce the particle size, and various techniques have been developed. However,
Most of the commercially available powder toners for developing electrostatic images have a volume average particle diameter of about 7 to 13 μm (the particle diameter is measured by Coulter Multisizer (Nikkaki Kiki)) to improve image quality. Regarding the reduction of the particle size of the toner, which is extremely useful, it is only about 7 μm at present, and there is no practical application of the small particle size toner which greatly exceeds that. In fact, the formation equipment has not been developed much.

As a method for producing a powder toner, there is a pulverization method as a dry method, and a polymerization method as a wet method and described in JP-A-5-66600 and JP-A-09-311502. There is a so-called phase inversion emulsification method. In the case of the toner produced by the pulverization method, it is said that the limit of the particle size reduction is about 6 to 7 μm in the current industrial production using a pulverizer. Of course, it is possible to produce a toner having a small particle size of about 5 μm. However, it is not practical because there are problems such as an increase in cost and a deterioration in triboelectric chargeability and powder fluidity due to the decrease in the particle size of the toner. hard.

On the other hand, in a wet method such as a polymerization method or an emulsification method,
Although there is no difficulty in reducing the particle size of the powder toner, the main development and production target so far is to replace the pulverized toner having a particle size of about 7 to 13 μm, and the average particle diameter is about 6 μm. The image forming method using the electrostatic image developer composed of the following small particle size toner has not been studied so far, and its practical method and effect have not been clarified.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to specify a color toner for developing an electrostatic image in a copying machine or a printer of an electrophotographic full-color image forming apparatus, thereby improving the color image quality. An object of the present invention is to provide a significantly improved image forming method. Further, a method for producing such a color toner is provided.

[0008]

SUMMARY OF THE INVENTION In a color image forming apparatus in a non-magnetic one-component development or two-component development system, yellow, magenta, cyan and black electrostatic latent images are formed on a photoreceptor. After developing these with yellow, magenta, cyan, and black color toners, respectively, these four color toner images are superimposed and transferred on a printing medium, and the color toner on the printing medium is fixed. In the method, the color toners of these four colors have a volume average particle diameter of 2 to 6 μm, and a colorant is included in a binder resin. It has been found that the use of a spherical toner having an average circularity defined by (length) / (peripheral length of particle projected image)) of 0.97 or more as a developer significantly improves image quality.

[0009] As a color toner, a mixture containing a colorant and a binder resin as essential components and an aqueous medium are mixed and emulsified to form spherical colored resin particles, and then the particles dispersed in the liquid medium are dispersed. It has been found that it is preferable to use a spherical toner having a volume average particle diameter of from 2 to 6 μm, which is obtained by a method of taking out as a dry powder, and particularly when a polyester resin is used as a binder resin, a remarkable effect is exhibited.

Further, as a color toner, after polymerizing a polymerizable monomer in which a colorant is dispersed in a liquid medium to form spherical colored resin particles, the particles dispersed in the liquid medium are converted into a dry powder. It has been found that high image quality can be realized also by using a spherical toner having a volume average particle diameter of 2 to 6 μm obtained by a removal method.

The details of the invention and the circumstances leading to the present invention will be described below.

In general, electrophotographic printing is inferior to lithographic printing in image quality. This is due to the fact that the particle size of the image element of the ink layer on the printing medium in the lithographic printing method is submicron, Although the thickness of the layer is about 0.5 μm, the particle size of the image element of the toner layer on the printing object in electrophotographic printing using powder toner is about 10 μm, and the thickness of the toner layer is 10 to 10 μm. It is stated that it is about 20 microns. From such a point of view, the present inventors have found that if the toner particle diameter of the electrostatic image developer is made much smaller than before and the thickness of the toner layer is made much thinner than before, electrophotographic printing can be performed. We thought that we could improve the image quality and approach lithographic printing.

In order to reduce the particle size of the image element of the toner layer on the photoreceptor and the printing medium and to make the toner layer thinner, it is effective to reduce the particle size of the toner used. In order to ensure sufficient powder fluidity and chargeability even if the particle size is reduced, it is considered that the toner shape is preferably spherical, and the composition and manufacturing method of the spherical and small particle size powder color toner, and such A high quality color image forming method using toner has been found.

By using a toner having a high sphericity with an average circularity of 0.97 or more and a small particle diameter, a thin toner layer can be formed on the photosensitive member, and The toner layer also becomes thin. For this reason, the effect that the toner consumption per page is greatly reduced is also exhibited.

In the case of reducing the particle size of the powder toner by the pulverization method, not only does the average particle size of about 6 μm sharply increase the pulverization energy cost, but also the shape of the obtained toner particles is irregular. Further, since the colorant and the like are exposed on the surface of the toner particles, the uniformity of the triboelectric charging of the obtained toner is reduced, and the powder fluidity is deteriorated. This is a major problem in putting a small particle size toner of about 6 μm or less into practical use.

The decrease in powder fluidity due to the reduction in toner particle size can be greatly improved by making the toner particle shape spherical, and the average circularity of the toner having a small particle size of 2 to 6 μm, which is the object of the present invention, is considered. 0.97 or more is required. In the present invention, this degree of circularity is referred to as a spherical shape. The average circularity can also be obtained by taking an SEM (scanning electron microscope) photograph of the toner particles, measuring and calculating the same, and a flow-type particle image analyzer FPIP- manufactured by Toa Medical Electronics Co., Ltd. Use of 1000 allows easy measurement.

Regarding the deterioration of the chargeability due to the reduction in particle size,
The main cause is that a part of the contained coloring agent and other additives (usually wax and charge controlling agent) is exposed on the surface of the toner particles. That is, the content of the colorant and the like (% by weight)
Are the same, the surface area of the toner particles increases due to the reduction in the particle size, the ratio of the colorant or the like exposed on the surface of the toner particles increases, and as a result, the composition of the surface of the toner particles greatly changes, The triboelectric charging performance changes greatly, making the control difficult.

In order to maintain good triboelectric charging performance even when the particle size of the toner is reduced, the colorant and the like must not be exposed on the surface of the toner particles, that is, the toner structure in which the colorant and the like are included in the toner particles. It is effective to Further, a toner in which a colorant or the like is included in the toner particles exhibits the same chargeability even when the type of the colorant is changed, so that it is very convenient when used as a full-color toner. That is, the charging properties of the yellow, magenta, cyan, and black toners are inevitably the same, which is very effective for stable and good color image formation.

A coloring agent or a charge controlling agent (C
CA), whether the wax or the like is not exposed can be easily determined, for example, by observing the cross section of the particles with a TEM (transmission electron microscope). More specifically, a section obtained by embedding the toner particles in a resin and cutting with a microtome is stained with ruthenium oxide or the like if necessary, and observed with a TEM.
It can be clearly seen whether a colorant or the like is included in the particles.

The above-mentioned spherical toner of 2 to 6 μm in which the colorant or the like is included in the toner particles is theoretically formed into a spherical shape by, for example, treating the irregular particles produced by a pulverization method with a resin surface. Although it is possible to obtain it by carrying out the method, it is practical and preferable to produce it by a wet method such as a polymerization method or an emulsification method in view of easiness of production and cost. In particular, the emulsification method is capable of forming spherical colored resin particles having a good particle size distribution even when the kind of the binder resin is widely changed, and the pigment concentration is easily increased. It is particularly suitable as

Further, when such a method is used, a sharp particle size distribution of the small particle size toner as described below can be easily obtained, so that the effect of improving the image quality is further enhanced.

The particle size distribution of the toner particles also has an effect on the charging performance.
It is preferable to have a sharper particle size distribution than the commercially available toner of about 7 to 13 μm. In the spherical toner having a volume average particle diameter of 2 to 6 μm used in the present invention,
When measured by a Coulter Multisizer, the 50% volume particle size / 50% number particle size is 1.25 or less, particularly preferably 1.
It is particularly preferable that the particles have a particle size distribution of 20 or less and a square root of 84% volume particle size / 16% volume particle size of 1.25 or less, since a better image without fog can be obtained.

The use of such a spherical toner having a narrow particle size distribution and a small particle size not only improves the image quality, but also leads to a drastic reduction in the toner consumption per printed sheet. Is exhibited. By reducing the toner consumption per print, there are advantages such as reduction in printing / copying cost and reduction in toner box capacity.

The preferred composition and manufacturing method of the spherical color toner used in the image forming method of the present invention will be described in detail below.

The colorant used in the present color toner is not particularly limited, and a colorant conventionally used in an electrophotographic toner or the like can be used, and a pigment is preferable. Can be illustrated.

Examples of the yellow pigment that can be used in the yellow toner include, for example, yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, loess, titanium yellow, naphthol yellow S, Hansa yellow 10G, Hansa yellow 5G, and Hansa yellow G. , Hanza Yellow GR, Hanza Yellow A, Hanza Yellow RN, Hanza Yellow R, Pigment Yellow L, Benzidine Yellow, Benzidine Yellow G, Benzidine Yellow GR, Permanent Yellow NCG, Vulcan First Yellow 5G, Vulcan First Yellow R, Quinoline Yellow Lake, Anslagen Yellow 6GL, Permanent Yellow FGL,
Permanent yellow H10G, permanent yellow HR, anthrapyrimidine yellow, other isoindolinone yellow, chromophthal yellow, novo palm yellow H2G, condensed azo yellow, nickel azo yellow, copper azomethine yellow, and the like.

Examples of red pigments that can be used in magenta toner include red graphite, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, induslen brilliant orange RK, induslen brilliant orange GK, benzidine orange G, Permanent Red 4R, Permanent Red BL, Permanent Red F5RK, Risor Red, Pyrazolone Red, Watching Red, Lake Red C, Lake Red D, Brilliant Carmine 6B, Brilliant Carmine 3B, Rhodamine Lake B, Alizarin Lake, Permanent Carmine FB
B, verinone orange, isoindolinone orange, anthranthrone orange, pyranthrone orange, quinacridone red, quinacridone magenta, quinacridone scarlet, perylene red and the like.

Examples of the blue pigment that can be used for the cyan toner include cobalt blue, cerulean blue, alkali blue lake, peacock blue lake,
Fanatone Blue 6G, Victoria Blue Lake, metal-free phthalocyanine blue, copper phthalocyanine blue,
Fast Sky Blue, Indazulene Blue RS, Indazulene Blue BC, Indiko, and the like.

Examples of the black pigment that can be used in the black toner include carbon black, cyanine black, aniline black, ferrite, and magnetite. Alternatively, the above-mentioned chromatic pigment prepared so as to be black can be used, but carbon black is more preferable.

Since the toner used in the present invention has a small particle size of 2 to 6 μm and a true spherical shape, the printing medium (paper or O 2) is compared with a toner using a normal toner of about 10 μm.
The thickness of the toner layer on the HP sheet, etc.) is greatly reduced. Therefore, the content of the colorant (% by weight of the colorant based on the total weight of the binder resin and the colorant) of the color toner used in the present invention is 3 to 15 in the cyan, magenta and yellow toners. %, Particularly preferably 4 to 10%
In carbon black toner, it is 6-20%,
Particularly preferably, it is 8 to 15%. If the pigment concentration is lower than this, a sufficient image density cannot be obtained, and if the pigment concentration is too high, the transparency of each color is unfavorably deteriorated.

Next, a method for producing spherical toner particles suitable for use in the present invention will be described. First, the method of producing toner particles by the emulsification method is as follows. A mixture containing a colorant and a binder resin as essential components and an aqueous medium (water or a liquid medium containing water as a main component) are mixed, emulsified to form spherical colored resin particles, and then dispersed in the liquid medium. The obtained particles are taken out as a dry powder, and if necessary, classified to adjust the particle size distribution, thereby producing a spherical color toner. In this case, a water-insoluble binder resin is used as the binder resin.

In this case, the mixture of the colorant and the binder resin is
As described in JP-A-5-66600, it may be prepared by using an organic solvent.
As described in 1502, it may be made by a method of melting by heating without using an organic solvent.

When an organic solvent is used, examples of suitable organic solvents include hydrocarbons such as pentane, hexane, heptane, benzene, toluene, xylene, cyclohexane and petroleum ether; methylene chloride, chloroform,
Halogenated hydrocarbons such as dichloroethane, dichloroethylene, trichloroethane, trichloroethylene and carbon tetrachloride; alcohols such as methanol, ethanol, isopropyl alcohol, n-propyl alcohol and butanol; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; acetic acid Examples thereof include esters such as ethyl and butyl acetate, and two or more of these may be used as a mixture.

The binder resin is not particularly limited as long as it is soluble in the above-mentioned organic solvent or can be melted by heating. The binder resin itself is not dispersed in an aqueous medium, but is used only when an emulsifier or a dispersion stabilizer is used. There are a water-insoluble resin dispersible in water and a water-insoluble resin having self-water dispersibility that can be dispersed in an aqueous medium by itself.

Examples of such non-water-soluble resins for toner include styrene resins, (meth) acrylic resins,
Examples include a polyester resin, a polyurethane resin, and an epoxy resin. Among them, a polyester resin is most preferable as the color toner used in the present invention from the viewpoints of color development and gloss.

Among the binder resins, a self-water-dispersible resin is a resin containing a functional group which can be converted into an anionic form by neutralization. A resin that can form a stable aqueous dispersion under the action of an aqueous medium without using an emulsifier or a dispersion stabilizer. Examples of the functional group that can become a hydrophilic group upon neutralization include a so-called acidic group such as a carboxyl group, a phosphoric acid group, and a sulfonic acid group.

Such a polyester resin which can become self-water dispersible by neutralization can be obtained by subjecting the starting polybasic acid and polyhydric alcohol to dehydration polycondensation in the presence or absence of a solvent in the presence of a catalyst. Can be manufactured. Some of the polybasic acids are one of their ester-forming derivatives,
Demethylation polycondensation may be performed using the methyl ester.

More specifically, an aromatic polyester-based resin obtained by reacting an aromatic dicarboxylic acid such as phthalic acid or an ester-forming derivative thereof as an essential component is preferable. In the emulsification method, a binder resin soluble in a solvent used for the emulsification method is used.

Examples of the polybasic acid used include aromatic carboxylic acids such as terephthalic acid, isophthalic acid, phthalic anhydride, trimellitic anhydride, pyromellitic acid, naphthalenedicarboxylic acid, maleic anhydride, fumaric acid, and the like. Examples thereof include aliphatic carboxylic acids such as succinic acid, alkenyl succinic anhydride and adipic acid, and alicyclic carboxylic acids such as cyclohexanedicarboxylic acid. One or more of these polybasic acids can be used.

Examples of the polyhydric alcohol to be used include aliphatic diols such as ethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol and glycerin, cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A and the like. Alicyclic diols, bisphenol A
And aromatic diols such as ethylene oxide adduct of bisphenol A and propylene oxide adduct of bisphenol A. One or more of these polyhydric alcohols can be used.

The glass transition point of the polyester resin is 50 to
The temperature is preferably 75 ° C, more preferably 55 to 70 ° C.
° C. If the glass transition point is less than 50 ° C., the heat cohesion of the toner becomes poor, and if it exceeds 75 ° C., the fixability becomes poor, which is not preferable.

The content of the acid group in the polyester resin is determined by the mixing ratio of the polybasic acid and the polyhydric alcohol and the reaction rate.
It can be adjusted by controlling the terminal carboxyl group of the polyester. Alternatively, a polyester having a carboxyl group in the main chain can be obtained by using trimellitic anhydride as the polybasic acid component. The content of the acid group in the polyester resin is preferably 1 to 30 mg · KOH / g as the acid value.

As the polyester resin, those containing a skeleton based on an alkylene oxide adduct of bisphenols have excellent hardness and moderate hardness even at a relatively low molecular weight.
This is preferable in that a fixed image having both toughness and blocking resistance can be obtained. Further, as a polyester resin used to obtain a toner used in a full-color image developing method,
The superimposed toner of each color is evenly mixed at a fine level, and the intended color can be reliably reproduced on the printing medium.
Straight-chain non-crosslinked polyester resins are more preferred than crosslinked ones. This means that
For example, when a light-transmissive printing medium such as an OHP sheet is selected and used, the difference in color developing property and transparency of the image is remarkably exhibited.

The anionic styrene (meth) acrylic resin which can become self-water dispersible by neutralization includes (meth) acrylic polymerizable vinyl monomers containing a styrene monomer as an essential component and containing an acid group. Those obtained by radically polymerizing a polymerizable vinyl monomer represented by a (meth) acrylate ester other than an acid group-containing polymerizable vinyl monomer in the presence of a radical initiator can be used. The polymerization reaction for obtaining it can be suitably used in solution polymerization, suspension and emulsion polymerization.

Such acid group-containing (meth) acrylic polymerizable monomers include, for example, acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid,
Monobutyl itaconate, monobutyl maleate and the like can be mentioned.

Examples of the polymerizable monomers other than the acid group-containing polymerizable monomers include styrene-based monomers (aromatic vinyl monomers) such as styrene, vinyltoluene,
There are 2-methylstyrene, t-butylstyrene or chlorostyrene.

Examples of the acrylates include methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, acryl 2-ethylhexyl acrylate, n-octyl acrylate, decyl acrylate or dodecyl acrylate, 2-chloroethyl acrylate,
Examples include phenyl acrylate and methyl alpha-chloroacrylate.

Examples of the methacrylate include methyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and n-methacrylate. Octyl, decyl methacrylate, dodecyl methacrylate, 2-chloroethyl methacrylate, phenyl methacrylate, and alpha-methyl methacrylate.

Also, acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; vinyl methyl ketone, vinyl hexyl ketone and methyl isopropenyl ketone. Examples thereof include vinyl ketones, N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, N-vinyl compounds such as N-vinylpyrrolidone, and the like.

For obtaining a resin which can become self-water dispersible by neutralization, a general-purpose organic solvent can be used in the case of solution polymerization. Specifically, for example, various aromatic hydrocarbons such as toluene, xylene or benzene; various alcohols such as methanol, ethanol, propanol or butanol; various ether alcohols such as cellosolve or carbitol; acetone And so-called inert solvents such as various ketones, such as methyl ethyl ketone or methyl isobutyl ketone; various esters, such as ethyl acetate or butyl acetate; or various ether esters, such as butyl cellosolve acetate.

As the polymerization initiator to be used, various commonly used organic peroxide-based initiators and azo-based initiators can be used. Specifically, for example, peroxides such as benzoyl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, sodium persulfate and ammonium persulfate, and azo-based compounds such as azobisisobutyronitrile and azobisisovaleronitrile Compounds.

The content of the carboxyl group of the carboxy group-containing anionic resin which can be converted into a hydrophilic group by neutralization is not particularly limited, but may be a styrene resin, a (meth) acrylic resin and a suitable styrene (meth) In the acrylic resin, the acid value (the number of mg of KOH required to neutralize 1 g of the resin) is preferably 30 to 150.

Such a styrene (meth) acrylic resin has a molecular weight of a level necessary to exhibit sufficient mechanical strength, usually 3000 to 300 as a weight average molecular weight.
000 and a glass transition temperature (Tg) of 50 to 100 ° C. are preferred.

The basic neutralizing agent used for causing these resins to exhibit self-water dispersibility is not particularly limited. Examples thereof include sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, Examples include inorganic alkalis such as sodium carbonate and ammonia, and organic bases such as diethylamine, triethylamine and isopropylamine.

When a water-insoluble resin having no self-water dispersibility is used as the water-insoluble resin as a binder resin, an emulsifier and / or a dispersion stabilizer are added to an aqueous medium mixed with the resin solution. It is necessary to use.

As the dispersion stabilizer, a water-soluble polymer compound is preferable, and examples thereof include polyvinyl alcohol, polyvinyl pyrrolidone, hydroxyethyl cellulose and carboxymethyl cellulose. Examples of the emulsifier include various nonionic surfactants such as polyoxyethylene alkylphenol ether, and various anionic or cationic surfactants such as sodium alkylbenzenesulfonate. Of course, two or more kinds of emulsifiers may be used in combination, two or more kinds of dispersion stabilizers may be used in combination, or an emulsifier and a dispersion stabilizer may be used in combination. It is common to use an emulsifier in combination.

In this case, when an emulsifier or a dispersion stabilizer is used, its concentration in the aqueous medium is suitably adjusted to about 0.5 to 3% by weight.

Further, even when a resin which can be made self-water dispersible by neutralization as described above is used, if necessary, the emulsifier and / or the dispersion stability may be used as long as the effects of the present invention are not impaired. Agents may be used.

The spherical colored resin particles targeted by the present invention may include, if necessary, a charge control agent (CCA) such as a metal-containing azo compound or a salicylic acid-based metal complex, or a polyethylene wax, a polypropylene wax, a paraffin wax or the like. Additives such as waxes (release agents) and silicone oil may be added in an amount of about 0.1 to 10% by weight based on the binder resin.

In the case where an organic solvent is used, these additives and the coloring agent are added to an organic solvent solution of the binder resin, and then mixed with a general mixture such as a ball mill or a continuous bead mill. A method such as sufficient pulverization and mixing using a disperser may be used, and when an organic solvent is not used, the binder resin, the colorant, and the additives are sufficiently kneaded with a kneader, a two-roll, twin-screw extruder, or the like. Just knead it.

When the dispersion of spherical colored resin particles obtained by emulsification in this manner is used with an organic solvent, the organic solvent is first removed by means such as distillation, and then the aqueous dispersion is filtered. The raw material particles are obtained by filtering and drying the particles. The colored resin fine particles obtained by using the emulsifier and the dispersion stabilizer are preferably used after being sufficiently washed.

Of course, as a binder resin, a self-water-dispersible resin obtained by neutralizing a water-insoluble resin having an acidic group, which becomes an anionic hydrophilic group by neutralization, with a basic neutralizing agent is used. When the resin fine particles are obtained by using the present invention, after removing the organic solvent in advance, for example, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid,
Reverse neutralization treatment to return the hydrophilic group obtained by neutralization with a basic compound on the surface of the fine particles with an acidic neutralizing agent such as oxalic acid to the original functional group, to enhance the hydrophilicity of the fine particles themselves It is preferable to adopt a method of removing water, filtering and drying after further lowering.

The drying can be carried out by any known and commonly used method. For example, drying may be carried out under normal pressure or reduced pressure at a temperature at which the toner particles do not fuse or agglomerate, or freeze drying. No. There is also a method of simultaneously separating and drying toner particles from an aqueous medium using a spray dryer or the like. A method in which the powder is agitated and dried under reduced pressure while heating at a temperature at which the toner particles are not thermally fused (eg, a mixing and drying machine of Tanabe Wiltech),
A drying method using a high-temperature air stream (eg, a flash jet dryer from Seishin Enterprise) is efficient and preferred.

When classification for removing coarse particles and fine particles is necessary in order to adjust the particle size distribution of the toner particles, a common dry classifier commercially available for toners or the like is used to carry out the classification. Or a method in which a water slurry of spherical colored resin particles is classified using a centrifugal separator by utilizing the difference in sedimentability depending on the particle size. Among the commercially available dry classifiers, those that can remove coarse particles and fine powder simultaneously by wind power (eg, an elbow jet classifier manufactured by Nippon Steel Mining) are efficient and preferable. The removal of coarse particles can also be performed by filtering a water slurry of spherical colored resin particles using a filter.

Next, a method of producing a color toner by a polymerization method is as follows. After the polymerizable monomer in which the colorant is dispersed is polymerized in a liquid medium to form spherical colored resin particles,
The particles dispersed in the liquid medium are taken out as a dry powder, and if necessary, classified to adjust the particle size distribution, thereby producing a spherical color toner.

Specifically, for example, in the presence of a dispersion stabilizer or an emulsifier, a colorant and a reactive monomer capable of forming a binder resin are suspended or emulsified and dispersed in a liquid medium to form a polymerization initiator. Polymerization reaction by radical polymerization is carried out with stirring in the presence of a toner, whereby a spherical aqueous dispersion of toner particles containing a colorant in a binder resin can be obtained.

The above radical polymerizable monomers include:
Specifically, for example, styrenes, α-methylstyrene, chlorostyrene, styrenes such as vinylstyrene, ethylene, propylene, butylene, monoolefins such as isobutylene, vinyl acetate, propion vinyl, vinyl butyrate, vinyl benzoate and the like Α-methylene aliphatic monocarboxylic acids such as vinyl esters, methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, dodecyl acrylate phenyl, methyl methacrylate, ethyl methacrylate, ethyl butyl methacrylate, dodecyl methacrylate Acid esters, glycol mono (meth) acrylates such as ethylene glycol monoacrylate, propylene glycol monoacrylate, tetramethylene ether glycol monoacrylate, vinyl methyl ether, vinyl acetate Acrylic monomers such as vinyl ethers such as ethyl ether and vinyl butyl ether, and vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl propenyl ketone, and the like, each of which is used alone or in combination of two or more. be able to.

The monomer composition of the binder resin is adjusted so that the glass transition temperature (Tg) of the polymer is 50 to 80 ° C.

If necessary, a small amount of a reactive monomer having two or more ethylenically unsaturated double bonds may be used in combination therewith. Examples of the reactive monomer having two or more ethylenically unsaturated double bonds include conjugated dienes such as butadiene and isoprene, divinylbenzene, di (meth) acrylate of bisphenol A alkylene oxide adduct, and trimethylolpropanetri (meta). A) acrylate, pentaerythritol tetra (meth) acrylate, and the like.

As the polymerization initiator used for obtaining such a polymer resin, of course, a usual oil-soluble or water-soluble one can be used.
Various peroxides such as di-t-butyl peroxide, cumene hydroperoxide, t-butyl peroxide or 2-ethylhexanoate; or various azos such as azobisisobutyronitrile or azobisisovaleronitrile. Compounds and the like can be mentioned.

In the case of suspension polymerization, a polymerization initiator which is insoluble in the liquid medium used for the polymerization and which is soluble in the monomer is selected and used as an essential component. In the case of emulsion polymerization, a water-soluble polymerization initiator is selected and used as an essential component. used. The amount of the polymerization initiator used is not particularly limited, but is 0.01 to 5 parts by weight per 100 parts by weight of the total reactive monomers (total monomers).

The binder resin formed by polymerization can be arbitrarily prepared according to polymerization conditions and the like, but is preferably adjusted to have a weight average molecular weight of 10,000 to 500,000.

As the colorant, charge control agent, wax and the like in the present toner particles, those known and used as described above can be used.

As the dispersion stabilizer that can be used during suspension polymerization, a water-soluble polymer compound is generally used, and examples thereof include polyvinyl alcohol, polyvinyl pyrrolidone, hydroxyethyl cellulose, carboxymethyl cellulose, cellulose gum, and ramzan gum. No.

Further, it is insoluble in water and has a particle size of 0.01 to 5 μm.
m inorganic fine powder can also be used as a suspension dispersion stabilizer, for example, tricalcium phosphate, talc, bentonite, kaolin, titanium oxide, alumina, zinc white, aluminum hydroxide, magnesium hydroxide, basic magnesium silicate, Examples include titanium hydroxide, ferric hydroxide, barium sulfate, silica, magnesium carbonate, calcium carbonate, and the like.

These dispersion stabilizers may be used alone or in combination of two or more. The amount used is usually 0.1 to 10 parts by weight per 100 parts by weight of all reactive monomers.

Examples of the emulsifier that can be used in the emulsion polymerization include anionic surfactants such as sodium dodecylbenzenesulfonate, sodium lauryl sulfate and sodium dodecyldiphenyloxide disulfonate; polyoxyethylene lauryl ether; And the like. These may be used alone or in combination of two or more. The amount used is usually 0.01 to 5 parts by weight per 100 parts by weight of the total reactive monomers.

In suspension polymerization, an emulsifier may be used in combination with a dispersion stabilizer, or in emulsion polymerization, an emulsifier may be used in part with a dispersion stabilizer. Further, a self-emulsifiable epoxy resin or a self-emulsifiable polyurethane resin can be used in place of the dispersion stabilizer or the emulsifier.

A polymerizable monomer, a colorant, a dispersion stabilizer, a liquid medium insoluble in the monomer, and a polymerization initiator insoluble in the liquid medium and soluble in the monomer are simultaneously added and stirred. Although monomer droplets may be polymerized, a polymerizable monomer and a colorant may be used.
For example, in a ball mill or a colloid mill, etc., previously sufficiently mixed, then added to the polymerization medium, the liquid medium containing a dispersion stabilizer, for example, a homogenizer, a rotor-stator mixer, static stirring, etc., It is preferable to suspend monomer droplets containing a polymerizable monomer in a liquid medium and carry out polymerization while stirring to form toner particles having a predetermined particle size.

Examples of the liquid medium that can be used in carrying out such polymerization include water such as distilled water and ion-exchanged water,
Various aromatic hydrocarbons such as toluene, xylene or benzene; various alcohols such as methanol, ethanol, propanol or butanol; various ether alcohols such as cellosolve or carbitol; acetone, methyl ethyl ketone or methyl isobutyl Examples include various ketones such as ketones; various esters such as ethyl acetate or butyl acetate; and various ether esters such as butyl cellosolve acetate.

In each of the polymerization methods, the core
By employing a shell polymerization formulation, a power feed polymerization formulation, or a graft polymerization formulation, the chemical structure and layer structure of the particles can be varied. The reaction conditions in each of the suspension polymerization method and the emulsion polymerization method of the above inventions are not particularly limited, and in each case, the reaction temperature is usually from room temperature to 80 ° C. for 15 minutes to 24 hours.

The dispersion of spherical colored resin particles thus obtained can be easily dried to obtain powder of spherical colored resin particles by removing the liquid medium and drying. In addition, in order to remove the dispersion stabilizer and the emulsifier in the dispersion, it is preferable to repeat the washing. In carrying out the liquid medium removing / drying step, the spherical colored resin particles may be separated by filtration, and then the particles may be dried in the same manner as in the case of the emulsified toner.

In order to adjust the particle size distribution of the toner particles, if necessary, the same classification operation as in the case of the emulsified toner can be performed.

As for the binder resin for forming the toner particles used in the present invention, if only the final toner performance is taken, compared with styrene resin or (meth) acrylic resin, A polyester resin is more preferable, but in a resin system such as a styrene resin or a (meth) acrylic resin, which can produce a toner by either a polymerization method or an emulsification method, the resin is obtained by employing the emulsification method. It is preferable to use a toner, and in particular, a toner produced by an emulsification method using only a self-water dispersible resin is particularly preferable in that it does not require sufficient washing of an emulsifier or a dispersion stabilizer. In the image forming method of the present invention, the one manufactured by an emulsification method using a polyester resin having self-water dispersibility is optimal in both the toner manufacturing process and the finally obtained toner performance.

The toner of the present invention can be prepared with either a positive charge or a negative charge. The toner of the present invention may contain a charge control agent, but is preferably a negatively chargeable toner not containing it. In consideration of environmental pollution and safety, those containing no charge control agent are preferable.

The emulsion obtained by the above-mentioned emulsification method or polymerization method,
It is preferable that inorganic fine particles and / or organic fine particles are externally added to the surface of the spherical toner particles having a volume average particle diameter of 2 to 6 μm used in the present invention before use as a developer.

By appropriately selecting the type and amount of the inorganic oxide fine particles to be used by adding to the toner surface, the triboelectric chargeability and powder fluidity of the small particle size toner can be improved. Examples of the inorganic oxide fine particles that can be used in the present invention include silica (silicon oxide), titanium oxide, aluminum oxide, and zinc oxide having a primary particle diameter of 5 to 100 nm.
Examples include tin oxide, antimony oxide, and magnesium oxide. These may be used alone or in combination of two or more. It is also preferable for the toner used in the present invention to use, as the metal oxide fine particles, titanium oxide or silicon oxide which has been subjected to surface treatment with tin oxide / antimony and imparted conductivity.

It is also preferable to use hydrophobically treated silica or titanium oxide having a primary particle diameter of about 5 to 50 nm in view of excellent powder fluidity, environmental stability of charging, and rising property of charging. It is. Many hydrophobic silicas for toner are commercially available, and it is practically convenient to select and use them according to the purpose from them.

Among them, the hydrophobic titanium oxide that has been surface-treated with an organic compound containing a trifluoromethyl group has the environmental stability of charge and the rising property (the speed at which the charge reaches a saturated charge amount and the uniformity of charge). From the viewpoint of (3), it is particularly suitable when used for a negative polarity toner.

The organic compound containing a trifluoromethyl group is an organic compound (including a polymer) having at least a —CF 3 group in the molecular structure, and is a perfluoroalkyl acrylate resin, a perfluoroalkyl group-containing alkoxysilane, or an alkylsilane. Alternatively, a chlorosilane compound is suitable. As a specific example, Vasteras guard NH-15 (manufactured by Dainippon Ink and Chemicals of CF _3- (CF _{2) 7} - toluene dispersion of group-containing acrylate _{resin) CF 3 - (CH 2)} 9 -Si (OCH _{3) 3 CF 3 - (CH} 2) 2 -Si (OCH 3) 3 CF 3 - (CF 2) 7 - (CH 2) 2 -Si (OCH 3) 3 CF 3 - (CF 2) 7 - (CH _{2) 2 -Si (CH 3)} (OC
_{H 3) 2 CF 3 - (} CF 2) 7 - (CH 2) 2 -Si (CH 3) 3 CF 3 - (CF 2) 7 - (CH 2) 2 -SiCl 3 CF 3 - (CF 2) 7 —SO ₂ NH (CH ₂ ) ₃ NH _{2 and the} like.

The surface treatment of the titanium oxide fine particles with the organic compound containing a trifluoromethyl group is performed by dissolving the organic compound in an organic solvent such as toluene or an alcohol and thoroughly mixing the organic compound with the titanium oxide fine particles. After removing the solvent by a method such as distillation, it can be performed by a method such as heat treatment and crushing.

The surface treatment amount of the trifluoromethyl group-containing organic compound on the metal oxide fine particles is preferably about 5 to 30% by weight based on the metal oxide fine particles. If the external addition amount is the same, as the surface treatment amount of the organic compound to the metal oxide fine particles increases, the charge amount of the toner tends to increase. Therefore, the surface treatment amount is adjusted according to the application. Is preferred.

These trifluoromethyl group-containing organic compounds exhibit strong water repellency because the surface energy of the trifluoromethyl group is extremely low, and have the property of being highly negative due to friction. It has the effect of significantly increasing the properties. For this reason, the toner to which the titanium oxide fine particles surface-treated with the organic compound containing a trifluoromethyl group is externally added has remarkably improved environmental stability and charge rising property.

The amount of the inorganic oxide fine particles to be added varies depending on the purpose of use of the powder toner, but generally, the smaller the toner particle size, the larger the added amount. In the 2 to 6 μm toner particles of the present invention, it is preferable to externally add 0.3 to 5% by weight to the toner particles.

The external addition may be carried out by a known and conventional method using a Henschel mixer or a hybridizer, and is not particularly limited.

When the toner thus obtained is used as a two-component developer, the volume average particle diameter is 20 to 15%.
It is mixed with a 0 μm resin-coated carrier to form an electrostatic image developer.

As such a carrier, any of iron powder, ferrite, magnetite, and those coated with various resins, or a composite carrier of a resin and a magnetic powder may be used. In a developer using a small particle size toner, 20 to 150 μm,
More preferably, a resin-coated small particle size carrier having a particle size of 20 to 80 μm is used, so that a good image can be obtained.

As the coating resin for the carrier, acrylic resin, acrylic styrene resin, silicone resin, fluorine-containing resin, a combination of these resins, and a combination thereof with a silane coupling agent are commercially available. In the present invention, it is preferable to select from these depending on the use of the developer.

A developer comprising a spherical color toner having a volume average particle diameter of 2 to 6 μm to which hydrophobic silica and hydrophobic titanium oxide are externally added, and a substantially spherical carrier having a volume average particle diameter of 20 to 150 μm coated with a resin is used. It is particularly suitable for the present invention.

As a color image forming apparatus such as an electrophotographic copying machine or a printer used in the present invention, a non-magnetic one-component developing method in which toner is frictionally charged in a gap between a developing sleeve and a blade, or an iron powder, Any of the two-component developing methods in which a carrier such as ferrite or magnetite and a toner are mixed and triboelectrically charged are suitable. As a method of developing a latent image formed on a photoreceptor with toner and transferring the latent image onto a printing medium such as paper or an OHP sheet, a tandem method (a photoreceptor and a developing device for each of four colors, one pass and one pass) is used. 4 colors are sequentially superimposed on the printing object).
Transfer drum method (transfers the toner image formed on the photoreceptor for each color onto the print-receiving body and superimposes four colors on the print-receiving body), and intermediate transfer method (four-color toner image on the intermediate transfer body) Are superimposed and then transferred onto a printing medium), and a multi-developing system (four colors are superimposed on a photoreceptor and then transferred to a printing medium) is known. However, the desired effect is exhibited.

As compared with the image forming apparatus using the two-component developing method, the color image forming method of the present invention is more compact when applied to the color image forming method using the non-magnetic one-component developing method. This is preferable in that the apparatus itself can be further simplified.

The thus-developed image formed of the color toner on the printing medium is fixed. By this fixing, the toner of each color of yellow, magenta, cyan, and black is fixed on the printing medium in a superimposed manner. Usually, the fixing is performed by heat-pressure fixing using, for example, a heat roll.

Since the toner used in the present invention has a small particle size of 2 to 6 μm and a spherical shape in which a colorant and the like are included in a binder resin, the uniformity of the surface of each toner particle is high. And uniformity of triboelectric charging is easily obtained. for that reason,
An image formed using such a toner is the current 7
Image quality such as resolution and gradation is improved as compared to an image formed using an amorphous toner having a colorant of about 13 μm exposed. Further, since the particle diameter is as small as 2 to 6 μm, the toner layer on the photoreceptor is much thinner than a normal toner layer having a particle diameter of about 10 μm.
In an apparatus for forming a color image by superimposing each color latent image which is the object of the present invention, the effect of the improvement is remarkably increased. In other words, the resolution and gradation of the obtained color image in the printed matter are greatly improved, and the toner layers of each color are thinned, so that the transparency is improved and a high quality color image is obtained. This is a synergistic effect that could not be expected by a person skilled in the art only from the result of developing and fixing with only one color toner.

In the color image forming apparatus of the present invention, in addition to the improvement of the image quality, the effect of reducing the toner consumption per page can be obtained.

[0105]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention includes the following embodiments. One. In an electrophotographic non-magnetic one-component development or two-component development color image forming apparatus, yellow, magenta, cyan, and black electrostatic latent images are formed on a photoreceptor, and these are respectively yellow, magenta, and magenta. After developing with cyan and black color toners, these four color toners are overlaid and transferred onto a printing medium such as paper or an OHP sheet, and the color toner on the printing medium is fixed. A color toner characterized by using a spherical toner having a volume average particle diameter of 2 to 6 μm, a colorant included in a binder resin, and an average circularity of 0.97 or more, as the four color toners. Image forming method.

2. A mixture containing a coloring agent and a binder resin as essential components and an aqueous medium (water or an aqueous solution containing water as a main component) are mixed, emulsified to form spherical colored resin particles, and then dispersed in a liquid medium. Using a spherical color toner obtained by removing the particles as a dry powder.
The color image forming method as described above.

3. 3. The color image forming method according to the above item 2, wherein the binder resin of the spherical color toner is a polyester resin.

4. After the polymerizable monomer in which the colorant is dispersed is polymerized in a liquid medium to form spherical colored resin particles,
2. The color image forming method according to the above item 1, wherein a spherical color toner obtained by a method of taking out the particles dispersed in a liquid medium as a dry powder is used.

5. The spherical toner has a 50% volume particle diameter / 50% number particle diameter of 1.25 or less, particularly preferably 1.20 or less, as measured by a Coulter Multisizer, and 8
2. The color image forming method according to the above 1, wherein the square root of 4% volume particle size / 16% volume particle size has a particle size distribution of 1.25 or less.

6. 2. The color image forming method according to the above item 1, wherein the spherical toner is a negatively chargeable toner containing no charge control agent.

7. The spherical toner has a primary particle diameter of 5 to 50.
2. The color image forming method according to the above item 1, comprising a hydrophobically treated silica and / or titanium oxide having a thickness of 10 nm.

8. 8. The color image forming method according to the above item 7, wherein the hydrophobically treated titanium oxide has been surface-treated with an organic compound having a trifluoromethyl group.

9. 4. The color image forming method according to the above item 3, wherein the polyester resin contains a skeleton based on an alkylene oxide adduct of a bisphenol.

10. 4. The color image forming method according to the above item 3, wherein the polyester resin is a linear non-crosslinked polyester resin.

11. 2. The color image forming method according to the above item 1, wherein the printing medium is an overhead projector (OHP) sheet.

12. 2. The color image forming method according to the above item 1, wherein the color image forming method is a non-magnetic one-component developing type color image forming method.

[0117]

Next, the present invention will be described in detail by reference examples, examples and comparative examples. All parts and percentages are by weight. All water is deionized water.

(Example of Toner Production) An acid value of 4 mg · K
OH / g, a linear non-crosslinked polyester resin having a weight average molecular weight of 12,000, a glass transition point of 61 ° C., and a melt viscosity of 40000 poise at 100 ° C. (bisphenol A propylene oxide 2.2 mol adduct, bisphenol A To a well-dissolved resin solution, 800 parts of methyl ethyl ketone was added to 1200 parts of a 2.2 mol adduct of ethylene oxide, a dehydrated condensate of terephthalic acid and isophthalic acid, and a phthalocyanine pigment “Ket Blue 12” was added.
7 "(manufactured by Dainippon Ink and Chemicals, Inc.) was added, and the mixture was stirred and mixed to sufficiently disperse. After the dispersion, the solid content was adjusted to 50% with methyl ethyl ketone.

Next, 50 parts of methyl ethyl ketone and 3.5 parts of 1N ammonia water were added to 200 parts of the mixture, and 225 parts of water were added at a time with stirring to effect phase inversion emulsification to form spherical blue resin particles. . Water 15 as dilution water
0 parts and 1N aqueous ammonia 4 to increase dispersion stability
Parts were added.

Next, the organic solvent was removed by distillation under reduced pressure to obtain an aqueous dispersion. A 1N aqueous hydrochloric acid solution was added to the mixture to adjust the pH to 2.5, and the wet cake obtained by filtration and washing was dried by heating under reduced pressure while stirring.
A powder of spherical blue resin particles using a polyester resin as a binder resin was obtained.

This powder was classified using an elbow jet (manufactured by Nippon Steel Mining), and had a volume average particle diameter (measured with a Coulter Multisizer 2) of 5.2 μm and a volume particle diameter of 50% / 50% number of particles. 1.11,84% volume particle size /
Blue toner particles having a good particle size distribution with a square root of 16% volume particle size of 1.19 were obtained. The particles are subjected to a flow-type particle image analyzer FPIP-100 manufactured by Toa Medical Electronics Co., Ltd.
When measured at 0, the average circularity was a sphere of 0.990.
When observed with a (transmission electron microscope), the phthalocyanine pigment was uniformly encapsulated in the particles and dispersed.

To 100 parts of the spherical blue resin particles, 0.5 part of hydrophobic titanium oxide fine particles surface-treated with trifluoropropyltrimethoxysilane and 2.5 parts of hydrophobic silica (RY200 of Nippon Aerosil) were added to a Henschel mixer. Was used to prepare a spherical cyan toner having a particle size of 5.2 μm (pigment content: 6%).

The phthalocyanine pigment "Ket Blue"
123 ”instead of disazo pigment“ Ket Yel ”
low 403 "(manufactured by Dainippon Ink and Chemicals, Inc.), quinacridone pigment" Toner Magenta E-0 "
2 "(manufactured by Hoechst Industries) and carbon black pigment" Elfttex8 "(manufactured by Cabot) in the same manner as the above-mentioned spherical cyan toner, and a spherical yellow toner having a particle size of 5.1 μm (pigment content: 6%) ,
Spherical magenta toner having a particle size of 5.2 μm (pigment content 6
%) And a spherical black toner having a particle size of 5.1 μm (pigment content: 8%). Each color toner was negatively chargeable.

(Comparative Example of Toner Production) 960 parts of the polyester resin and 40 parts of a phthalocyanine pigment “Ket Blue 123” used in Examples of toner production were melt-kneaded, pulverized, and then classified using a dry classifier. And
Average circularity having a particle size distribution in which the volume average particle size is 8.3 μm, 50% volume particle size / 50% number particle size is 1.20, 84% volume particle size / 16% volume particle size, and the square root is 1.24. An amorphous blue resin powder of 0.943 was obtained, which was externally added with 0.5 parts of hydrophobic titanium oxide fine particles and 1.3 parts of hydrophobic silica same as those used in Examples of toner production. A non-spherical negatively chargeable cyan toner having a particle size of 8.3 μm (pigment content: 4%) was prepared.

The phthalocyanine pigment "Ket Blue"
123 ”instead of disazo pigment“ Ket Yel ”
low 403 ", quinacridone pigment" Toner
A non-spherical yellow toner having a particle size of 8.1 μm (pigment content: 4%) and a particle size of 8.2 μm by the same operation as the above non-spherical cyan toner using “Magenta E-02” and carbon black pigment “Elftex8”. A non-spherical magenta toner (pigment content: 4%) and a non-spherical black toner having a particle size of 8.1 μm (pigment content: 9%) were prepared. Each color toner was negatively chargeable.

(Formation and Evaluation of Color Image) Spherical color toner 4 having a particle size of about 5 μm, which was produced in the toner production example.
The color is filled into a toner cartridge of an electrophotographic non-magnetic one-component developing type color printer (a modified machine of "Color Page Pro PS" manufactured by Minolta) and a test pattern image test is performed.

Further, four colors of non-spherical color toner having a particle size of about 8 μm produced in the comparative example of toner production are filled in the color printer, and the surface of the photoreceptor is cleaned if necessary. Perform an image output test.

Comparing the color images printed on plain paper in the above-described image output test, both have the same good hue and gloss, but the resolution and gradation of the case using the toner of Example are remarkably high. And an excellent color image is formed as a whole. Further, comparing the color images printed on the OHP sheet in the above-described image output test, the use of the toner of the present example is superior in light transmittance, and a clearer projected image can be obtained.

Further, the toner adhesion weight on the printing paper when the test pattern image was printed on plain paper was measured.
In the case where the toner of the embodiment is used, it is about half as compared with the case where the toner of the comparative example is used, and the toner consumption per page is reduced by almost half.

[0130]

In an electrophotographic color image forming apparatus, electrostatic latent images of yellow, magenta, cyan, and black are formed on a photoreceptor, and these latent images are respectively formed in yellow, magenta, cyan, and black.
After developing with magenta, cyan, and black color toners, these four color toners are superimposed and transferred on a printing medium, and the color toner on the printing medium is fixed. A high quality color image can be obtained by using a spherical toner having a volume average particle diameter of 2 to 6 μm, a colorant included in a binder resin, and an average circularity of 0.97 or more. Can be
In addition, the amount of toner consumption per printing sheet can be significantly reduced.

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Claims (4)

[Claims] In an electrophotographic color image forming apparatus, an electrostatic latent image of yellow, magenta, cyan, and black is formed on a photoreceptor, and these latent images are respectively formed in yellow, magenta, cyan, and black. Developing using a toner, transferring the four color toner-developed images onto a print-receiving body, and fixing the color toner on the print-receiving body; The average circularity ((perimeter of a circle having the same area as the projected area of the particles) / (perimeter of the projected image of the particles) is as follows. (Average value of circularity defined by (1)) 0.97 or more spherical toner is used. 2. A mixture comprising a coloring agent and a binder resin as essential components and an aqueous medium are mixed and emulsified to form spherical colored resin particles, and then the particles dispersed in the liquid medium are dried. 2. The color image forming method according to claim 1, wherein a spherical color toner obtained by a method of taking out as a body is used. 3. The color image forming method according to claim 2, wherein the binder resin of the spherical color toner is a polyester resin. 4. A method in which a polymerizable monomer in which a colorant is dispersed is polymerized in a liquid medium to form spherical colored resin particles, and then the particles dispersed in the liquid medium are taken out as a dry powder. 2. A color image forming method according to claim 1, wherein a spherical color toner is used.