JP2003098761A - Electrostatic latent image developing carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developer which prevents color contamination caused by the wear of the carrier during development and with time and which can give an image having excellent color reproducibility, excellent reproducibility of a highlight part and high resolution. SOLUTION: The electrostatic latent image developing carrier is obtained by forming a coating film on the surfaces of magnetic particles. The coating film contains conductive inorganic fine particles and a constant k defined by k[nm<-1> ]=(m<2> +1)/r2×d×(m<2> -1), wherein m=r1/r2, with respect to the refractive index r1 and the particle size d of the inorganic fine particles and to the refractive index r2 of the coating film, is >=0.015 nm<-1> .

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a carrier for developing an electrostatic charge image.

[0002]

2. Description of the Related Art In general, a full-color image is produced by a digital electrophotographic method by converting a full-color image signal into three primary colors (yellow, magenta, cyan: hereinafter Y, M, C respectively) and black (hereinafter BK) of a subtractive color mixture. , Or electrically separated into four color dot images, which are printed on paper,
Alternatively, it is generally performed by superposing it on an intermediate transfer member and finally fixing and fixing it on a transfer paper.
In recent years, the full-color image quality of electrophotography has improved dramatically compared to the past, but the problems with images unique to electrophotography are:
There is still room for improvement.

The developing method using a two-component developer consisting of a magnetic carrier and toner particles is widely used because it is relatively easy to form a color image, increase the printing speed, and stabilize the chargeability of the toner. ing. In the two-component development, optimizing the electric resistance of the carrier is important for making the development characteristics suitable. For adjusting the electric resistance of the carrier, it is easy to provide a film having a suitable electric resistance on the surface of the carrier, and it is widely used. In order to adjust the electric resistance of the film and improve the strength of the film, various kinds of films are used. Additives are included.

However, in the case of a developer for a full-color image, if the coating film of the carrier is colored, color stains may be generated due to abrasion powder of the coating film after use. Conventionally, carbon black used as an electric resistance adjusting agent, not to mention color stains when it is contained in a carrier film, even if the conductive material is white, turbidity of an image during use over time or It increased dullness and was one of the causes of the change in color reproducibility. Further, in recent years, in order to cope with the increase in resolution and the improvement in highlight reproducibility, the minimum unit (1 dot) diameter of the latent image has been reduced and the density has been increased. Therefore, more faithful development is required.

In the two-component developer, it is effective to reduce the carrier diameter in order to more uniformly supply the toner due to the latent image, but since the carrier surface area is increased thereby, the transparency of the coating film is further improved. High is desirable.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a developing system that solves the above problems. That is,
Prevents color stains due to carrier wear over development,
An object of the present invention is to provide a developer that is excellent in color reproducibility and highlight reproducibility and that can obtain an image with high resolution.

[0007]

According to the results of intensive studies by the present inventors, the above problems can be achieved by the invention having the following constitution. That is, the present invention provides (1) "a carrier having a coating formed on the surface of magnetic particles, containing conductive inorganic fine particles in the coating, and having a refractive index r1, a particle diameter d of the inorganic fine particles,
A carrier for developing an electrostatic latent image, wherein the k value represented by the following general formula is 0.015 nm ⁻¹ or more, where r 2 is the refractive index of the coating,

[Equation 2] (However, r1 / r2 = m) ”, (2)“ the carrier has a weight average particle size of 25 μm to 45 μm, and
70% by weight or more of particles smaller than 4 μm and 7% by weight or less of particles smaller than 22 μm, and the ratio of the weight average particle diameter Dv to the number average particle diameter Dp is 1 ≦ (Dv / Dp)
The carrier for developing an electrostatic latent image according to item (1), characterized in that a coating is provided on the surface of a core material satisfying ≦ 1.30 ”and (3)“ inorganic particles are titanium oxide. The carrier for developing an electrostatic latent image according to item (2) above, (4) "wherein the surface of the titanium oxide used is coated with a silane coupling agent. The carrier for developing an electrostatic latent image according to item (2), (5) "the coating film is a silicone compound containing Si-O as a main repeating unit, and the above-mentioned (2).
The carrier for developing an electrostatic latent image according to item 1.

The carrier in the present invention is formed by forming a film having a resistance adjusting function on the surface of the magnetic powder. When the coating contains conductive inorganic fine particles as a resistance adjusting agent, and the refractive index r1 of the inorganic fine particles, the particle size d, and the refractive index r2 of the coating, the k value represented by the following general formula is 0. It is preferably 015 or more.

[0009]

[Equation 3] (However, r1 / r2 = m) It is preferable that this value is larger than 0.015. The decrease in the transmittance of the coating is due to light scattering at the particle interface in the coating. This scattering intensity depends on the relative refractive index between the coating and the particles and the particle size. By properly controlling the refractive index and the particle size, the transparency of the coating can be secured even when a white conductive material is used, and the color stain of the image can be prevented. If this value is smaller than 0.015, the light scattering due to the additives in the coating film becomes strong, and the transparency of the coating film deteriorates. 0.0
When it is 15 or more, the transparency can be improved.

The refractive index of the coating material can be measured with a commercially available refractometer when the material is obtained as a liquid or a homogeneous pellet, but when the value is unknown for powder such as conductive fine powder. , Can be measured as follows, for example. That is, an object to be measured is dispersed in a liquid having a known refractive index, and the intensity of scattered light is measured. In liquids with various refractive indices,
The scattered light is compared, and the refractive index of the liquid having the smallest intensity is taken as the refractive index of the measured object. The scattered light intensity is measured by DLS700 manufactured by Otsuka Electronics Co., Ltd. at a scattering angle of 90 °.

In the two-component developer, it is effective to reduce the carrier diameter in order to more uniformly supply the toner by the latent image. Especially like digital color images,
In an image forming system that uses a lot of halftones, uniform development is required for each pixel in order to obtain high image quality. Therefore, it is preferable that the carrier diameter is smaller. Conventionally, since the carrier surface area is increased by reducing the carrier diameter, color stains due to the carrier are likely to occur,
By setting the above k value range, a carrier having a smaller particle size can be used. Preferably, the weight average particle diameter of the carrier used is 25 μm to 45 μm, 70% by weight or more of particles smaller than 44 μm and 7% by weight or less of particles smaller than 22 μm, and the weight average particle diameter Dv and number. The ratio of the average particle diameter Dp is 1 ≦ (Dv / Dp) ≦ 1.30
Is. When developing an image having a high pixel density, if the carrier diameter is small, the toner supply density to the latent image is improved, so that the image can be developed more uniformly. As a result, like the highlight portion, the dot diameter can provide the image density and the uniformity of the image. In addition, in general, by reducing the carrier diameter,
Since the magnetic moment per carrier particle becomes small, the so-called carrier adhesion phenomenon, in which the carrier adheres to the image depending on the image pattern, easily occurs. Therefore, the carrier particle size distribution is required to be narrower for smaller particle size carriers. , The ratio of the weight average particle diameter Dv to the number average particle diameter Dp is 1
It is preferable that ≦ (Dv / Dp) ≦ 1.30.

The inorganic fine particles constituting the coating are white,
Particles having a relatively low electric resistance are used. For example,
Conductive metal powder such as ZnO and Al, made by various methods
SnO ₂And SnO doped with various elements₂Boring
Thing, eg TIB₂, ZnB₂, MoB₂Silicon carbide etc.
It In particular, titanium oxide can obtain finer particles at lower cost.
Therefore, it is preferable. Create as a carrier coating
If a coating material is formed in a volatile organic solvent,
It is possible to dissolve and disperse the material and coat it on the carrier core material.
It's easy. Since the surface of titanium oxide is generally hydrophilic,
When using the Uta method, use silane coupling
It is more preferable to use titanium oxide coated with a coating agent.
Yes.

Further, the surface of the carrier is preferably coated with a substance having a low surface energy in order to prevent adsorption and adhesion of the toner constituent material and reduce adsorption of moisture in the air.

Examples of the low surface energy coating material include the following conventionally known materials. Polytetrafluoroethylene (PTFE), perfluoroalkoxy / fluorine resin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer (FEP), ethylene / tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene Fluoroethylene (PCTF
E), vinylidene fluoride (PVDF), vinyl fluoride (PV
F), polyimide resin, polycarbonate resin, styrene resin, acrylic resin and the like. It can also be used as a mixture of two or more selected from these.

Particularly, a silicone polymer having Si-O as a repeating unit and a hydrophobized product thereof are preferably used. Examples of the silicone compound having Si-O as a basic repeating unit include a silicone resin containing a repeating unit represented by the following general formula.

[0016]

[Chemical 1] In the formula, R represents a hydrogen atom, a halogen atom, a hydroxy group, a methoxy group, a C ₁ -C ₄ lower alkyl group, or a phenyl group.

As a straight silicone resin, KR
271, KR272, KR282, KR252, KR2
55, KR152 (Shin-Etsu Chemical Co., Ltd.), SR240
0, SR2406 (manufactured by Toray Dow Corning Silicone Co., Ltd.) and the like.

Examples of the modified silicone include epoxy-modified silicone, acryl-modified silicone, phenol-modified silicone, urethane-modified silicone, polyester-modified silicone and alkyd-modified silicone. Examples of modified silicone include epoxy-modified silicone: ES -1001N, acrylic modified silicone: KR-5208, polyester modified silicone: K
R-5203, alkyd modified silicone: KR-20
6, urethane-modified silicone: KR-305 (above, Shin-Etsu Chemical Co., Ltd.), epoxy-modified silicone: SR21
15. Alkyd-modified silicone: SR2110 (manufactured by Toray Dow Corning Silicone Co., Ltd.) and the like.

Further, the dispersibility of the silicone resin and the additive,
In order to improve the compatibility, a generally known silane coupling agent can be included. As a silane coupling agent,

[0020]

Embedded image X-Si (OR) n (where n is a positive number from 1 to 3), X is various functional groups having reactivity with organic substances and inorganic substances and adsorptivity,
And a saturated or unsaturated hydrocarbon chain having a functional group. OR means an alkoxy group. In particular, a so-called aminosilane coupling agent having an amino group in X is preferably used.

The aminosilane coupling agent that can be used in the present invention has the following general formula.

[0022]

Embedded image H ₂ N (CH ₂ ) ₃ Si (OCH ₃ ) ₃ MW 179.3

[0023]

Embedded image H ₂ N (CH ₂ ) ₃ Si (OC ₂ H ₅ ) ₃ MW 221.4

[0024]

[Chemical 5]

[0025]

[Chemical 6]

[0026]

[Chemical 7]

[0027]

[Chemical 8]

[0028]

[Chemical 9]

[0029]

[Chemical 10]

[0030]

[Chemical 11]

As the carrier core material that can be used in the present invention, conventionally known ones can be used. For example,
Ferromagnetic materials such as iron and cobalt, magnetite, hematite, Li-based ferrite, Mn-Zn-based ferrite, Cu
-Zn type ferrite, Ni-Zn ferrite, Ba ferrite, etc. are mentioned. As the carrier core material, the above-mentioned magnetic particles are generally used, but a so-called resin-dispersed carrier having a form in which magnetic powder is dispersed in a known resin such as phenol resin, acrylic resin or polyester resin is also suitably used.

As a method for forming the coating resin of the present invention, a known method such as a spray drying method, a dipping method, or a powder coating method can be used.

The toner used in the present invention contains a thermoplastic resin as a binder resin as a main component, and contains a colorant, fine particles, a charge control agent, a release agent and the like. Then, a toner prepared by various toner manufacturing methods such as a generally known pulverization method, polymerization method, and granulation method can be used.

The following can be used as the binder resin. As the acrylic type, polystyrene, a homopolymer of styrene such as polyvinyltoluene or a substitution product thereof, a styrene-p-chlorostyrene copolymer, a styrene-propylene copolymer, a styrene-vinyltoluene copolymer,
Styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-methyl methacrylic acid copolymer, styrene-ethyl methacrylic acid copolymer, styrene-meth Butyl acrylate copolymer, styrene-α-chloromethacrylic acid methyl copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer Copolymers, styrene-isoprene copolymers, styrene-maleic acid copolymers, styrene-based copolymers such as styrene-maleic acid ester copolymers, polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene , Polypropylene, polyester , Polyurethane, epoxy resin,
Polyvinyl butyral, polyacrylic acid resin, rosin,
Modified rosin, terpene resin, phenol resin, aliphatic or aliphatic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax and the like can be used alone or in combination.

Further, the polyester resin is preferable, as compared with the acrylic resin, because it is possible to further reduce the melt viscosity while ensuring the stability during storage of the toner. The polyester resin is obtained by polycondensation reaction of alcohol and acid. For example, the alcohol is polyethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3.
-Propylene glycol, 1,4-propylene glycol, neopentyl glycol, diols such as 1,4-butenediol, 1,4-bis (hydroxymethyl)
Etherified bisphenols such as cyclohexane, bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropyleneized bisphenol A, etc., which are substituted with a saturated or unsaturated hydrocarbon group having 3 to 22 carbon atoms 2 Polyhydric alcohol units, other dihydric alcohol units, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaethritol dipentaethritol,
Tripentaethritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-
Examples thereof include high alcohol monomers having a valence of 3 or more, such as 1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

Examples of the carboxylic acid used for obtaining the polyester resin include palmitic acid, stearic acid, oleic acid and other monocarboxylic acids, maleic acid, fumaric acid, mesaconic acid, citraconic acid, terephthalic acid and cyclohexanedicarboxylic acid. Acid, succinic acid, adipic acid, sebacic acid, malonic acid, these have 3 to 22 carbon atoms
Divalent organic acid monomers substituted with saturated or unsaturated hydrocarbon groups, anhydrides of these acids, dimers of lower alkyl esters and linoleic acid, 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,
4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid,
1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid embol trimer acid, anhydrides of these acids, etc. Examples thereof include trivalent or higher polyvalent carboxylic acid monomers.

Further, as the epoxy resin, there is a polycondensation product of bisphenol A and epochlorhydrin, and the like, for example, Epomic R362, R364, R365, R3.
66, R367, R369 (above, manufactured by Mitsui Petrochemical Co., Ltd.), Epotote YD-011, YD-012
YD-014, YD-904, YD-017 (all manufactured by Tohto Kasei Co., Ltd.), Epocote 1002, 1004, 1
There are commercially available products such as 007 (all manufactured by Shell Chemical Co., Ltd.).

As the colorant, carbon black, lamp black, iron black, ultramarine blue, nigrosine dye, aniline blue, phthalocyanine blue, Hansa yellow G, rhodamine 6G, lake, chalco oil blue, chrome yellow, quinacridone, benzidine yellow, rose Any conventionally known dyes and pigments such as bengal, triallylmethane dyes, monoazo dyes, disazo dyes and dyes may be used alone or in combination.

There is no inconvenience even if the toner contains a drug to be contained for the purpose of controlling the triboelectrification like the toner which is usually used. As such a so-called polarity control agent, for example, a metal complex salt of a monoazo dye,
Examples include nitrohumic acid and its salts, salicylic acid, naphthoic acid salts, metal complex amino compounds such as Co, Cr, and Fe of dicarboxylic acids, quaternary ammonium compounds, and organic dyes.

Furthermore, a releasing agent may be added to the toner of the present invention, if necessary. As the release material, low molecular weight polypropylene, low molecular weight polyethylene, carnauba wax, microcrystalline wax, jojoba wax, rice wax, montanic acid wax and the like can be used alone or in combination, but are not limited thereto. is not.

As an additive, it is important that the toner imparts sufficient fluidity to obtain a good image and obtains a good image without abnormalities such as transfer omission. It is generally known that externally added fine particles of hydrophobized metal oxide as a fluidity improver, or fine particles such as a lubricant,
The following materials such as metal oxides, organic resin fine particles and metal soaps can be used. For example, polytetrafluoroethylene-based fluororesin, lubricant such as zinc stearate,
Alternatively, abrasives such as acid value cerium and silicon carbide, or fluidity-imparting agents such as inorganic oxides such as SiO ₂ and TiO ₂ whose surfaces are hydrophobized, those known as anti-caking agents, and their surfaces For example, processed products. Particularly, conventionally, hydrophobic silica is preferably used for the effect of improving fluidity.

The shape of the toner particles can be obtained by appropriately selecting the toner temperature at the time of pulverization by an ordinary pulverization method, but the toner prepared by the polymerization method can easily obtain a toner having a high sphericity. preferable. For example, a desired pigment, a charge control agent, a release agent, a polymerization initiator, a chain transfer agent, etc. are dissolved in the monomer of the polymer to be the binder resin shown above,
It is possible to granulate by dispersing, dispersing the dispersion in water together with a dispersant so as to have a desired particle size, and polymerizing the dispersion.

Further, by using an emulsion polymerization method or the like, resin particles having a particle diameter smaller than the toner particle diameter and a dispersion liquid of a pigment, a charge control agent, a release agent and the like are aggregated and united to obtain a toner having a desired particle diameter. It is also possible to obtain

In general, the styrene-acryl copolymer is generally selected as the binder resin of the polymerization toner because it is easy to polymerize by radical polymerization due to its production method.

Further, when polyester or polyol is selected as the binder resin in order to improve the fixing property, transparency and durability of the toner, another granulation method such as a binder resin and a pigment, a charge control agent is used. It is also possible to obtain toner particles by melting or dissolving a mixture of release agents in a solvent and dispersing and solidifying the mixture in an appropriate solvent.

[0046]

EXAMPLES The present invention will be described in more detail below with reference to examples. These examples are only one aspect of the present invention,
The invention is not bound by these examples. In addition, all the component amounts (parts) shown in the following examples are based on weight.

Example of Production of Carrier The carrier used for the developer was prepared as follows. Core material A Core material resistance: Log R = 10.3 Ω · cm Saturation magnetic moment: σs = 65 esu / g Weight average particle diameter = 49.2 μm, number average particle diameter = 42.6
μm 22-44 μm Particle weight = 90.5% Less than 22 μm particle weight = 0.8% Dv / Dp = 1.15

Core material B Core material resistance: Log R = 10.3 Ω · cm Saturation magnetic moment: σs = 65 esu / g Weight average particle diameter = 36.3 μm, number average particle diameter = 29.3
μm 22-44 μm Particle weight = 81.7% Particle weight less than 22 μm = 2.6% Dv / Dp = 1.24

Core material C Core material resistance: Log R = 10.3 Ω · cm Saturation magnetic moment: σs = 65 esu / g Weight average particle diameter = 35.6 μm, number average particle diameter = 28.4
μm 22-44 μm Particle weight = 89.2% Particle weight less than 22 μm = 2.0% Dv / Dp = 1.21 The core material resistance is obtained by filling the core material in a container having electrodes arranged in parallel at an interval of 2 mm. , DC resistance between both electrodes at 500V, Yokogawa Hewlett Packard Co. 4329A
It was measured with a High Resistance Meter. The saturation magnetic moment was measured with an applied magnetic field of 1000 Oe using a multi-sample rotary magnetization measuring device REM-1-10 manufactured by Toei Industry Co., Ltd. As the measured value of the particle size, the value measured by Microtrac was used. Table 1 shows the resistance adjusting material.

[0050]

[Table 1]

[Production Example A of Carrier] A carrier A was prepared by forming a silicone coating on the core material A. The silicone coating was performed as follows. Silicone resin (SR24
11: manufactured by Toray Dow Corning Silicone Co., Ltd.).
It was dispersed for 10 minutes using a ball mill, and this dispersion was diluted to a solid content of 5 wt% to obtain a dispersion. About 5 kg of each of the above core materials, the above dispersion liquid was used in a fluidized bed coating apparatus under an atmosphere of 100 ° C. for about 5
It was applied at a rate of 0 g / min and further heated at 250 ° C. for 2 hours to obtain a carrier A having a film thickness of 0.5 μm. The film thickness was adjusted by the amount of coating liquid. Further, the refractive index r2 of the cured product of only this silicone resin was 1.5 when measured.

[Production Example B of Carrier] A carrier B was obtained by forming a silicone coating on the core material A. The silicone film was formed in the same manner as in Carrier Production Example A. A carrier B having a film thickness of 0.5 μm was obtained.

[Manufacturing Example C of Carrier] A carrier C was obtained by forming a silicone coating on the core material C. The silicone coating was performed in the same manner as in Carrier Production Example A, except that Additive C was used in Carrier Production Example 1. A carrier C having a film thickness of 0.5 μm was obtained.

[Production Example D of Carrier] A carrier D was obtained by forming a silicone coating on the core material C. The silicone coating was performed in the same manner as in Carrier Production Example A, except that Additive B was used in Carrier Production Example 1. A carrier D having a film thickness of 0.5 μm was obtained.

[Production Example E of Carrier] A carrier E was obtained by forming a silicone coating on the core material C. The silicone coating was performed in the same manner as in Carrier Production Example A, except that Additive C was used in Carrier Production Example 1. A carrier E having a film thickness of 0.5 μm was obtained.

[Manufacturing Example F of Carrier] A carrier F was obtained by forming a silicone coating on the core material C. The silicone film was formed in the same manner as in Carrier Production Example A, except that Additive D was used in Carrier Production Example 1. A carrier F having a film thickness of 0.5 μm was obtained.

[Manufacturing Example G of Carrier] A carrier G was obtained by forming a silicone coating on the core material A. The silicone coating was performed in the same manner as in Carrier Production Example A, except that Additive E was used in Carrier Production Example 1. A carrier G having a film thickness of 0.5 μm was obtained. The DC resistance of the carrier was measured in the same manner as the core material resistance measurement method.

[Example 1] Images were printed using a Preter 600 (full color digital copying machine manufactured by Ricoh). As the developer, the developer consisting of the carriers A to G prepared in the above-mentioned carrier production example and the magenta toner was used, and evaluation was carried out by a magenta single color image. Image evaluation was performed as follows. While replenishing the toner, a running evaluation of 10,000 sheets was performed using a character image chart with an image area ratio of 6%. The images were evaluated as follows even after the running.

(Color turbidity) After copying 10,000 sheets, a magenta image was formed on OHP paper, and the color of the transmitted image was compared with the initial image for turbidity, and the turbidity of color was visually evaluated on a four-point scale. ◎: Very good, ○: Good, △: Slightly bad, ×: Bad (x
Is an unacceptable level)

(Fine line reproducibility) 600 dot / inch, 150 line / inc in both main scanning and sub scanning directions
A 1-dot lattice line image of h was output, and the line image was visually evaluated for breakage and blurring in four levels. ◎: Very good, ○: Good, △: Slightly bad, ×: Bad (x
Is an unacceptable level)

(Resolution) 6 in both main scanning and sub-scanning directions
00 dot / inch, 300 line / inch 1
A dot independent halftone dot image was output, and magnified 50 times with an optical microscope for observation, and dot omission and variation in dot diameter were visually evaluated in four levels. ◎: Very good, ○: Good, △: Slightly bad, ×: Bad (x
Is an unacceptable level)

(Granularity) Independent dot images of 600 dpi and 200 lpi are displayed with image area ratios of 0%, 25%, 50%,
Five types of 3 cm square images with 75% and 100% were formed. The graininess of the image of each area ratio was visually evaluated in four levels. ◎: Very good, ○: Good, △: Slightly bad, ×: Bad (x
Is an unacceptable level)

(Gradation) Using the same image as the evaluation of graininess, visual evaluation was carried out in four steps. ◎: Very good, ○: Good, △: Slightly bad, ×: Bad (x
Is the unacceptable level) Table 2 shows the evaluation results.

[0064]

[Table 2-1]

[0065]

[Table 2-2]

[0066]

As is apparent from the detailed and specific description above, according to the present invention, color stains due to carrier abrasion are prevented, color reproducibility is excellent, and highlight reproducibility is excellent. However, it has an extremely excellent effect that a developer capable of obtaining an image with high resolution can be provided.

Claims (5)

[Claims] 1. A carrier in which a coating is formed on the surface of magnetic particles, wherein conductive inorganic fine particles are contained in the coating, and when the inorganic fine particles have a refractive index r1, a particle diameter d, and a coating refractive index r2, A carrier for developing an electrostatic latent image, which has ak value represented by the general formula of 0.015 nm ^-1 or more. [Equation 1] (However, r1 / r2 = m) 2. The carrier has a weight average particle diameter of 25 μm.
To 45 μm and smaller than 44 μm,
70% by weight or more and 7% by weight or less of particles smaller than 22 μm, and the weight average particle diameter Dv and the number average particle diameter Dp
2. A core material having a ratio of 1 ≦ (Dv / Dp) ≦ 1.30 is provided with a coating on the surface of the core material.
The carrier for developing an electrostatic latent image according to item 1. 3. The electrostatic latent image developing carrier according to claim 2, wherein the inorganic fine particles are titanium oxide. 4. The carrier for developing an electrostatic latent image according to claim 2, wherein the surface of the titanium oxide used is coated with a silane coupling agent. 5. The carrier for developing an electrostatic latent image according to claim 2, wherein the coating film is a silicone compound containing Si—O as a main repeating unit.