JP2961441B2 - Color developer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is applied when an image is formed by using a photoconductor made of an organic semiconductor (OPC) (hereinafter, referred to as an “OPC photoconductor”) as an image carrier. Color developers, especially OP
The present invention relates to a color developer applied to an electrophotographic color copier or a printer using a C photosensitive member.

[Related Art] In recent years, many image forming apparatuses such as an electrophotographic color copying machine or a printer using an OPC photosensitive member as an image holding member have been manufactured. FIG. 1 shows an example of the configuration. Usually, such an image forming apparatus forms a latent image on the OPC photoreceptor 1 by a normal electrophotographic process, develops the latent image with a developing device to form a toner image, and transfers the image to a transfer material. Transferred to
A visible image is obtained. On the other hand, the residual image on the image carrier is cleaned by the cleaning means, and the image carrier is used repeatedly.

In addition, a blade cleaning unit having a configuration in which a cleaning blade 2 made of a rubber elastic material is pressed against the image holding member 1 in a counter direction is widely used, particularly from the viewpoint of downsizing and low cost.

In general, the OPC photoreceptor 1 has a configuration in which a charge generation layer composed of a binder in which a charge generation material is dispersed on a conductive support and a charge transport layer composed of a binder in which a charge transport material is dispersed are laminated in this order. ing. Here, as the charge generation material, phthalocyanine pigments, anthantrone pigments, azo pigments, pigments such as indigo pigments, dyes such as pyrylium dyes,
Or a dye such as a cyanine dye, and the charge transport material includes carbazoles such as pyrene and isopropylcarbazole, hydrazones, pyrazolines, oxasonyl compounds, thiazole compounds, triarylmethane compounds, and polyaryls. Alkanes are used,
Further, as a binder, polyarylate resin, polysulfone resin, polyamide resin, acrylic resin, acrylonitrile resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, phenol resin, epoxy resin, polyester resin, alkyd resin, polycarbonate, polyurethane Alternatively, copolymer resins containing two or more of the repeating units of these resins, for example, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer and the like are used.

When such an OPC photoreceptor is used as the image carrier 1, the friction coefficient of the image carrier 1 tends to increase as the temperature of the image carrier 1 increases, as shown in FIG.

It has been found that such a rise in the coefficient of friction is due to the temperature characteristics of the binder occupying most of the surface of the OPC photoreceptor.

Therefore, for the purpose of suppressing such an increase in the coefficient of friction, for example, Japanese Patent Application Laid-Open No. 63-311356 proposes a method in which a resin in which fluorine resin particles are dispersed is provided on the surface layer of a photoreceptor. Although such a means is certainly effective in lowering the coefficient of friction, improving cleaning properties, abrasion resistance, damage resistance, etc., it is difficult to control the surface roughness by the degree of dispersion. It was not always satisfactory enough to keep printing out.

Further, when an image is formed by combining negative developers having different surface properties, such as a magnetic toner and a non-magnetic toner, there is a difference in the slipperiness or scraping property of each toner with respect to the photoconductor, and the At present, it is difficult to always stably hold the pressure-bonded state between the body 1 and the cleaning blade 2.

[Problems to be Solved by the Invention] In view of the problems of the prior art as described above, the present invention improves the developer without modifying the photoreceptor.
To achieve the following objectives.

. That is, to provide a color developer which is hardly influenced by the environment such as temperature and humidity and can always form a color image having stable cleaning characteristics. An object of the present invention is to provide a color developer which has high-definition image characteristics excellent in highlight reproduction, fine line reproduction and the like and can form a color image with excellent durability stability.

[Means and Actions for Solving the Problems] The above object is achieved by the invention having the following constitutions: a developer is provided on the surface of a latent image holding member made of an organic photoreceptor having a surface containing a fluorine-based resin body in an amount of 5 to 40% by weight. To form a developed image, transfer the developed image to a transfer material, remove the residual developed image on the latent image holding member with a cleaning blade, and form a color image by repeatedly using the latent image holding member. In the color developer used in the image forming method, the color developer comprises at least a colorant-containing resin particle and an external additive, and the external additive has at least a polarity opposite to that of the flow improver and the colorant-containing resin particle. This is achieved by a color developer containing organic resin particles that are electrically charged and spherical fine particles having a weight average particle size of 0.2 to 2.5 μm.

First, the background to the present invention will be described. As a result of intensive studies by the present inventors, regardless of the surface properties of the toner and the surface properties (surface roughness) of the photoconductor, the relationship between the photoconductor 1 and the cleaning blade 2 is not significant. It has been found that a good image and stable cleaning characteristics can be obtained when a minute gap of 0.2 to 2.5 μm exists in the pressure-bonded portion.

As a means for generating the above-mentioned gap in the pressure-bonded portion between the photosensitive member 1 and the cleaning blade 2, it is possible to control the surface roughness of the photosensitive member, or if the surface roughness of the photosensitive member is larger than 2.0 μm, the image quality is reduced. In particular, when the surface roughness is small, it becomes difficult to control the roughness. In addition, depending on the degree of the surface shaving, the gap is 0.2 μm. When the diameter is smaller, the pressure of the cleaning blade becomes too strong, and cleaning failure due to the turning over of the blade occurs, and sufficient cleaning characteristics are not necessarily achieved only by the means for controlling the surface roughness of the photoreceptor.

Therefore, as a result of further studies by the present inventors, the latent image holding member 1 was coated with a fluororesin powder on the surface thereof for 5 to 5 minutes.
In color image formation using an organic photoreceptor containing 40% by weight, as an external additive, at least a weight average particle diameter of 0.1% is used.
It has been found that a developer containing spherical particles of 2 to 2.5 μm is extremely excellent in cleaning and high image quality under various environments and provides a good image.

Here, the reason why the cleaning property is stabilized is that excessive pressure contact between the surface of the organic photoreceptor and the cleaning blade is mitigated by the above-mentioned spherical fine particles serving as spacers, and excessive friction characteristics can be obtained.

Hereinafter, the components of the present invention will be described in detail. The spherical fine particles as the external additive according to the present invention are not particularly limited as long as they have a weight average particle diameter of 0.2 to 2.5 μm. In addition, the starting materials and the production method are not limited at all. When the spherical fine particles are smaller than 0.2 μm, the cleaning blade cannot follow the surface of the photoconductor when the surface roughness of the photoconductor is rough, so that the cleaning blade often passes through the cleaning blade, causing uneven charging when a latent image is formed. Deterioration is likely to occur. On the other hand, if it is larger than 2.5 μm, cleaning is performed more than necessary by the cleaning blade, and it is difficult for the cleaning blade to collect at the blade edge portion, so that the spacer function is reduced and efficiency is deteriorated.

Examples of the material of the spherical fine particles that can be used in the present invention include inorganic oxides such as silicic acid fine powder, alumina fine powder, titanium oxide fine powder, zirconium oxide fine powder, and magnesium oxide fine powder, boron nitride fine powder, and titanium oxide fine powder. Examples include nitrides such as aluminum nitride fine powder and carbon nitride fine powder, and inorganic resin particles such as silicone resin particles.

Among these, silicone resin particles having a siloxane structure having one alkyl group on a silicon atom are particularly preferable because they can sharpen the particle size distribution.

Further, as for the particle size distribution, it is desirable that 80% or more of the volume distribution is within ± 30% of the average particle size, and a surface treatment may be performed as necessary. The amount of the additive is 0.05 to 3% by weight, preferably 0.1 to 2% by weight.

The measurement of the particle size distribution of the spherical fine particles according to the present invention,
Performed with a particle analyzer CAPA500.

Next, as the binder used in the colorant-containing resin particles according to the present invention, various material resins conventionally known as electrophotographic toner binder resins are used.

For example, styrene-based copolymers such as polystyrene, styrene-butadiene copolymer, styrene-acrylic copolymer, and ethylene-based copolymers such as polyethylene, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer Phenolic resin, epoxy resin, acrylic phthalate resin, polyamide resin, polyester resin, maleic acid resin and the like. In addition, the production method of any resin is not particularly limited.

Among these resins, when a polyester-based resin is used, the effect of the present invention is remarkable. That is, the polyester resin has excellent fixability and is suitable for a color developer.

In particular, (Wherein R is an ethylene or propylene group, x and y are each an integer of 1 or more, and the average value of x + y is 2
~ 10. A) a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, fumaric acid, maleic acid, maleic anhydride, phthalic acid) Acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.) are more preferable because they have sharp melting properties.

As the coloring agent, known dyes and pigments, for example, phthalocyanine blue, induslen blue, peacock blue, permanent red, lake red, rhodamine lake, Hanza yellow, permanent yellow, benzidine yellow and the like can be widely used. The content thereof is 12 parts by weight or less, preferably 0.5 to 9 parts by weight, based on 100 parts by weight of the binder resin so as to be sensitive to the light transmittance of the OHP film.

Furthermore, in the present invention, in addition to the spherical fine particles,
It is necessary to contain a flow improver for stabilizing the fluidity and an organic resin particle for stabilizing the charge. Such organic resin particles are determined by the above-described binder resin, and are preferably organic resin particles having a polarity opposite to that of the toner for charging stability and having a weight-average particle size having at least a peak at 20 to 200 mμ. . Here, the reason why the charging is stabilized is that the charge-up due to excessive rubbing between the settlement resin and the developer carrier used in the present invention,
This is because it is neutralized by the aforementioned organic resin particles.

Further, by adding the organic resin particles, the rise of the charge of the toner is promoted, and a very stable charge characteristic is achieved from the beginning.

The reason for this is not yet clear, but is presumed as follows. That is, the organic resin particles are strongly attracted and charged toward the developer carrier rather than the colorant-containing resin particles at the beginning of the rubbing between the developer carrier and the toner. Therefore, the rising of the charge of the colorant-containing resin particles having the opposite polarity is promoted. On the other hand, once started up, on the other hand, it is more strongly attracted to the colorant-containing resin particles than the developer carrier,
The function of neutralizing excessive charging works. Therefore, the toner having the constitution of the present invention can maintain the rising charge and the saturated charge level in a good and stable manner in various environments.

Further, the monomer constituting the reverse polarity resin particles used in the present invention is not particularly limited, but needs to be selected in consideration of the charge amount of the toner and the like. Specific examples of the addition-polymerizable monomer that can be used in the present invention include the following monomers.

That is, styrene and its derivatives, for example, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene, alkyl styrene such as octyl styrene, fluorostyrene, chlorostyrene , Bromostyrene, dibromostyrene, halogenated styrene such as iodostyrene, further nitrostyrene, acetylstyrene,
Methoxystyrene and the like.

Further, addition polymerization such as addition-polyunsaturated unsaturated carboxylic acids, that is, acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, α-methylcrotonic acid, α-ethylcrotonic acid, isocrotonic acid, tiglic acid, ungeric acid, etc. And addition-polymerizable unsaturated aliphatic dicarboxylic acids such as unsaturated unsaturated aliphatic monocarboxylic acids, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, glutaconic acid and dihydromuconic acid.

Further, those obtained by metal salification of these carboxylic acids can be used, and the metal salification can be performed after the polymerization is completed.

In addition, esterified products of the above-mentioned addition polysynthetic unsaturated carboxylic acid with alcohols such as alkyl alcohols, halogenated alkyl alcohols, alkoxyalkyl alcohols, aralkyl alcohols and alkenyl alcohols may be mentioned. And, as specific examples of the alcohol, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, amyl alcohol, hexyl alcohol, heptyl alcohol, octyl alcohol,
Alkyl alcohols such as nonyl alcohol, dodecyl alcohol, tetradecyl alcohol, hexadecyl alcohol, halogenated alkyl alcohols obtained by partially halogenating these alkyl alcohols, methoxyethyl alcohol, ethoxyethyl alcohol, ethoxyethoxyethyl alcohol, methoxypropyl alcohol, ethoxypropyl alcohol Examples include alkoxyalkyl alcohols such as propyl alcohol, aralkyl alcohols such as benzyl alcohol, phenylethyl alcohol and phenylpropyl alcohol, alkenyl alcohols such as allyl alcohol and crotonyl alcohol.

Amides and nitriles derived from the above addition-polymerizable unsaturated carboxylic acids, aliphatic monoolefins such as ethylene, propylene, butene, and isobutylene, vinyl chloride, vinyl bromide, vinyl iodide, and 1,2-dichloroethylene. , Halogenated aliphatic olefins such as 1,2-dibromoethylene, 1,2-diiodoethylene, isopropenyl chloride, isopropenyl bromide, allyl chloride, allyl bromide, vinylidene chloride, vinyl fluoride and vinylidene fluoride , 1,
3-butadiene, 1,3-pentadiene, 2-methyl-1,3
-Butadiene, 2,3-dimethyl-1,3-butadiene, 2,4
Conjugated diene-based aliphatic diolefins such as -hexadiene and 3-methyl-2,4-hexadiene.

Further, nitrogen-containing vinyl compounds such as vinyl acetates, vinyl ethers, vinyl carbazole, vinyl pyridine, vinyl pyrrolidone and the like can be mentioned.

As the fine powder according to the present invention, one obtained by polymerizing one or more of these monomers can be used.

The reverse polarity resin particles used in the present invention are not limited to using only one kind, and a plurality of kinds can be used in combination.

The method for producing the opposite polarity resin particles used in the present invention includes a method capable of producing spherical fine particles, such as a spray drying method, a suspension polymerization method, an emulsion polymerization method, a soap-free polymerization method, a seed polymerization method, and a mechanical pulverization method. Any method can be used. Among the most suitable of these are:
Since there is no residual emulsifier, there is a soap-free polymerization method which does not hinder the chargeability of the toner and causes little environmental fluctuation of the specific electric resistance, but is not particularly limited.

Further, the opposite polarity resin particles may be subjected to a particle surface treatment as necessary. As a method of surface treatment, a method of subjecting a metal such as iron, nickel, cobalt, copper, zinc, gold, silver, or the like to a surface treatment by a vapor deposition method, plating, or the like; An organic compound capable of being triboelectrically charged, such as a method of fixing an object by ion adsorption or external addition, or a pigment or dye, or a polymer resin, may be supported by coating or external addition.

The molecular weight distribution of the opposite polarity resin particles used in the present invention needs to have a peak molecular weight in the range of 10,000 to 5,000,000, and preferably in the range of 20,000 to 1,000,000.
When the peak molecular weight is larger than 5,000,000, the fixability of the color toner is adversely affected, and when the peak molecular weight is smaller than 10,000,
It contaminates the magnetic particles and has poor blocking resistance.

Next, the flow improver used in the present invention will be described. Such a flow improver is not particularly limited as long as it imparts flowability. Examples of such a flow improver include silica, alumina, titanium oxide, zirconium oxide and the like, and those having a BET specific surface area of 50 m ² / g or more are preferable in terms of imparting fluidity. The flow improver may be subjected to a surface treatment as needed.

Examples of the flow improver suitably used in the present invention include low tribo aluminum oxide and titanium oxide so as not to impair the charge stabilizing function of the organic resin particles. Of these, titanium oxide having the same polarity as that of the toner is particularly preferable because of its excellent stability under high humidity. The titanium oxide or alumina may be subjected to a surface treatment as long as the charging stability is not impaired. Furthermore, this addition amount is 0.3
~ 2% by weight is good.

Further, a charge control agent may be added to the toner according to the present invention in order to stabilize the charge characteristics. At that time, a colorless or light-colored charge control agent that does not affect the color tone of the toner is preferable. In the present invention, it becomes more effective when a negatively charged developer is used. In this case, examples of the negatively charged charge control agent include metal complexes of alkyl-substituted salicylic acid (for example, chromium complex or zinc complex of di-tert-butyl salicylic acid). And organometallic complexes such as When the negative charge control agent is added to the toner, it is added in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the binder resin.

When the toner according to the present invention is used as a two-component developer, the magnetic particles used in the present invention include, for example, surface-oxidized or unoxidized iron, nickel, copper, zinc, cobalt, manganese, chromium, and the like. Metals such as rare earths and their alloys or oxides and ferrites can be used. In addition, there is no particular limitation on the manufacturing method.

In the present invention, the surface of the magnetic particles is coated with a resin or the like.A method of dissolving or suspending a coating material such as a resin in a solvent and applying the coating material to adhere to the magnetic particles, or simply a powder method Any of the conventionally known methods, such as a method of mixing with, can be applied. For the safety of the coating layer, it is preferable that the coating material be dissolved in a solvent.

The coating material on the surface of the magnetic particles varies depending on the toner material, for example, amino acrylate resin,
Acrylic resins or copolymers of those resins and styrene resins are preferred. As the negatively charged resin, silicone resin, polyester resin, polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride and the like are preferably located on the negative side in the charging series, but are not necessarily limited thereto.

Most suitable for the present invention are acrylic resins or copolymers of those resins with styrene resins.

The most suitable material for the magnetic particles used in the present invention is 98% or more of Cu—Zn—Fe (composition ratio (5 to 20): (5 to 20%).
20): Ferrite particles having a composition of (30 to 80)), which are easy to smoothen the surface and have a stable charging ability,
In addition, the coating can be stabilized.

The coating amount of the above-mentioned compound may be appropriately determined so that the charge imparting property of the magnetic particles satisfies the above-mentioned condition, but is generally 0.1 to 30% by weight (preferably 0.3 to 20% by weight) based on the magnetic particles of the present invention. % By weight).

These magnetic particles preferably have a weight average particle size of 35 to 65 μm, preferably 40 to 60 μm. Furthermore, the weight distribution is 26 μm or less of 2 to 6%, and the weight distribution is 35 to 43%.
A good image can be maintained when the interval between μm is 5 to 25% and the interval between 74 μm and more is 2% or less.

In the present invention, when the mixing ratio between the magnetic particles and the toner particles is 2.0 to 9% by weight, preferably 3 to 8% by weight, as the toner concentration in the developer, generally good results can be obtained. If the toner density is less than 2.0%, the image density is low, making it impractical. If the toner density is more than 9%, fog and scattering inside the machine are increased, and the useful life of the developer is shortened.

Furthermore, in order to prepare the colorant-containing resin particles according to the present invention, a thermoplastic resin, if necessary, a pigment or dye as a colorant, a charge control agent, and other additives are sufficiently mixed by a mixer such as a ball mill. After mixing, heat roll, kneader, melt using a hot kneader such as extruder,
Pigments or dyes may be dispersed or dissolved in the resin after kneading and kneading to make the resins compatible with each other, and after cooling and solidification, pulverization and strict classification may be performed.

EXAMPLES Hereinafter, examples of the present invention will be described in detail.

Example 1 The mixture was sufficiently premixed by a Henschel mixer, melt-kneaded by a twin-screw extruder, cooled, coarsely pulverized to about 1 to 2 mm using a hammer mill, and then finely pulverized by an air jet pulverizer. Further, the obtained finely pulverized product was classified by a multi-segment classification device, and 2 to 10 μm was selected so as to have the particle size distribution of the present invention, thereby obtaining colorant-containing resin particles.

A hydrophilic titanium oxide (BET7
0 m ² / g) 0.7 parts by weight and methyl methacrylate / styrene / butyl acrylate with a weight average diameter of 60 mμ (87: 10: 3)
A cyan toner was obtained by combining 0.3 parts by weight of resin particles (charge amount with iron powder + 80 μc / g) and 0.5 parts by weight of spherical silicone resin particles having a methyl group and a weight average particle diameter of 0.8 μm.

To this toner, Cu-Zn-Fe-based ferrite particles whose surface was coated with a styrene-methyl methacrylate copolymer were added to prepare a developer at a toner concentration of 5%.

Using this developer, a commercially available color copier (CLC500,
(Canon) photoreceptor to an organic photoreceptor (surface roughness of about 1.6 μm) having a surface layer of polycarbonate containing 10 parts by weight of polytetrafluoroethylene powder (Rublon L-2, manufactured by Daikin Industries, Ltd.). Change the development contrast to 350V constant, and use the original document with an image area ratio of 25%,
Under the conditions of a temperature and humidity of 23 ° C./65%, 20 ° C./10%, and 30 ° C./80%, 20,000 images were respectively output.

As a result, no cleaning failure occurred, the image density was extremely stable at 1.4 to 1.55, and a very clear image without roughness was obtained.

Comparative Example 1 An image was formed in the same manner as in Example 1 except that the organic resin particles were not used.
%, The image density was initially 1.35, but dropped to 1.20 after 3000 copies.

Comparative Example 2 An image was formed in the same manner as in Example 1 except that hydrophilic titanium oxide was not used.
The evaluation was stopped because toner scattering occurred at 1000 sheets under / 80% and the image became rough.

Example 2 An image was formed in the same manner as in Example 1 except that the surface roughness of the photoreceptor was changed to 0.6 μm, and good results were obtained.

Comparative Example 3 In Example 1, a developer was produced in the same manner as in Example 1 except that spherical silicone resin particles were not used, and combined with a photoreceptor having a surface roughness of 2.6 μm to produce an image in the same manner as in Example 1. When cleaning was performed, cleaning failure occurred at 10,000 sheets at 30 ° C./80%.

Example 3 An image was formed in the same manner as in Example 1 except that hydrophilic aluminum oxide (BET 100 m ² / g) was used instead of hydrophilic titanium oxide.
Below, the image density was 1.5 to 1.7, which was higher than that of Example 1, but good results were obtained.

Example 4 In Example 1, the weight average particle diameter was used as the organic resin particles.
70mμ methyl methacrylate / styrene / methacrylate (75: 23: 2) resin (charge amount with iron powder + 45μc / g) 0.5
When image formation was performed in the same manner as in Example 1 except that parts by weight were used, good results were obtained.

Example 5 In Example 1, the developing device was modified so as to have the configuration shown in FIG. 1, and 3,000 images were produced by non-magnetic one-component development using the toner of Example 1. The result was obtained.

At this time, a sleeve (coat layer thickness: 10 μm) coated with a phenol resin in which 40 parts by weight of crystalline graphite was dispersed was used for the surface of the developer carrier 3, 4 was a urethane sponge roller, and 5 was a developer coating blade. Is in contact with the developer carrier 3 at a linear pressure of 50 g / mm (see FIG. 1).

The developing conditions are such that the gap between the developer carrier 3 and the latent image carrier 1 is
A developing bias in which an alternating electric field of 2.0 KHz and 1.8 KVpp was superimposed was applied.

[Effects of the Invention] As described above, according to the color developer of the present invention,
Stable image density can be obtained in various environments by incorporating specific spherical fine particles, organic resin particles, and flow improvers as external additives as a color developer used in an image forming apparatus having a specific latent image carrier. As a result, it is possible to form an image with excellent cleaning characteristics and high image quality.

[Brief description of the drawings]

FIG. 1 shows an example of a partial configuration of an image forming apparatus according to the present invention. FIG. 2 is a graph showing the relationship between the surface temperature of the latent image holding member and its friction coefficient. DESCRIPTION OF SYMBOLS 1 ... Image holding body, 2 ... Cleaning blade 3 ... Developer carrier, 4 ... Roller 5 ... Developer coating blade 6 ... Developer, 7 ... Power supply 8 ... Charger

Continuation of the front page (56) References JP-A-1-138573 (JP, A) JP-A-1-100563 (JP, A) JP-A-63-111356 (JP, A) JP-A-4-50859 (JP) , A) JP-A-4-142559 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/00-9/10 362

Claims (4)

(57) [Claims] 1. A developing image is formed on a surface of a latent image holding member comprising an organic photoreceptor containing 5 to 40% by weight of a fluororesin powder with a developer, and the developed image is transferred to a transfer material. Thereafter, a residual developing image on the latent image holding member is removed by a cleaning blade, and the latent image holding member is repeatedly used to form a color image. A colorant-containing resin particle and an external additive, and the external additive is at least a flow improver and a colorant-containing resin particle, the organic resin particles having the opposite polarity and a spherical shape having a weight average particle diameter of 0.2 to 2.5 μm. A color developer comprising fine particles. 2. The color developer according to claim 1, wherein said spherical fine particles are silicon-containing compounds such as fine silica powder and silicone resin particles. 3. The color developer according to claim 1, wherein said spherical fine particles are silicone resin particles having a siloxane structure having one alkyl group at a silicon atom. 4. The color developer according to claim 1, wherein said flow improver is titanium oxide or alumina.