JPH1039536A - Electrophotographic toner, developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a toner having electrostatic chargeability almost independent of the environment, less liable to the variation of the performance at the time of continuous use and hardly varying image quality when it is allowed to stand at high humidity by incorporating a specified inorg. additive and fine polymer particles having a specified volume average particle diameter as org. fine particles. SOLUTION: This toner contains at least a resin, a colorant, an inorg. additive and org. fine particles. The inorg. additive is obtd. by treating fine silica particles with a titanate coupling agent. The org. fine particles are fine polymer particles having 0.03-2.0μm volume average particle diameter. The fine silica particles preferably have <=100m<2> /g BET specific surface area and <=0.2wt.% Al2 O3 content. The titanate coupling agent is stuck to the silica particles preferably by about 0.01-15wt.%. The org. fine particles are contained preferably by 0.1-5wt.% of the total amt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner, a developer and an image forming method using the developer, which have less fatigue deterioration upon repeated use, high durability and excellent moisture resistance. .

[0002]

2. Description of the Related Art It has been widely known that silica fine particles are added to improve the fluidity of an electrophotographic toner (hereinafter, also simply referred to as toner). The change is large, and the toner to which the silica fine particles are added has a drawback that the charge amount greatly varies depending on the environmental humidity, and as a result, the stability of the image is easily lowered.

[0003] In order to improve this, means for treating the surface of the silica fine particles with a silane coupling agent or silicone oil are known. However, the silica fine particles treated by these means become excessively charged under low humidity. This tends to cause image densities and reduce the reproducibility of characters.

[0004] In order to compensate for such a disadvantage, there is known a technique in which titania fine particles or alumina fine particles treated with a silane coupling agent or silicone oil are used instead of silica fine particles. Since the specific gravity is large, it is difficult to hold the toner on the surface of the toner. In particular, alumina fine particles have the disadvantage that the surface treatment tends to be non-uniform, and the chargeability tends to be non-uniform.

In order to improve such disadvantages, there has been proposed a technique using silica fine particles treated with a titanate-based coupling agent as disclosed in JP-A-59-123850.

[0006]

However, when such fine particles are used for a negatively charged toner, particularly when the fine particles have a BET specific surface area of more than 100 m ² / g, the fine particles may be left under a high humidity condition. The toner has a drawback that the amount of charge of the toner is greatly reduced and the reproducibility of characters such as dust, fine lines, and halftone dots is poor.

Further, conventionally known fine particles of silica, titania, alumina and the like have a large BET specific surface area,
Since it has a small particle size, it has a disadvantage that it is easily buried in the toner surface during continuous use, and the toner performance tends to change with a change in state.

In recent years, various image forming methods have been proposed in accordance with an increase in applications for reproducing a color image. However, in view of miniaturization of an apparatus and printing speed, a toner image of a plurality of colors is formed on a photoreceptor. An image forming method has been proposed in which the image is formed and then transferred collectively onto a transfer material.

In this method, since the change in the state of the additive on the toner surface greatly affects the transfer performance, it has been difficult to secure sufficiently stable performance with the conventional additive having a small particle diameter. .

On the other hand, carriers having a particle size of 80 to 200 μm have conventionally been used as carriers for use as a two-component developer, but these carriers have a small specific surface area.
There is a tendency that the charged charge with the toner cannot be held effectively,
There is a problem that the above-mentioned additives are liable to be buried because the poor charge tends to occur during continuous use, the weight of one carrier is large, and the stress applied to the toner is large.

The present invention has been proposed in view of the above-mentioned circumstances, and it is an object of the present invention to provide a toner which is less likely to be affected by the environment, is always uniform, and has a sufficiently high image density, characters and fine lines. High reproducibility, low contamination, high durability, small fluctuations in performance during continuous use, little change in image quality when left under high humidity conditions, and excellent transferability And a developer.

Another object of the present invention is to provide a stable color image forming method capable of reducing the size of the apparatus and performing high-speed printing.

[0013]

The above object of the present invention is achieved by the following constitution.

(1) In an electrophotographic toner containing at least a resin, a colorant, an inorganic additive and organic fine particles, the inorganic additive is obtained by treating silica fine particles with a titanate coupling agent, and the organic fine particles have a volume An electrophotographic toner comprising polymer fine particles having an average particle size of 0.03 to 2.0 μm.

(2) The inorganic additive has a BET specific surface area of 1
00m ² / g or less, Al ₂ O ₃ The toner for electrophotography according to (1), wherein a content is obtained by treating the 0.2% by weight of silica fine particles titanate coupling agent.

(3) In a developer comprising at least an electrophotographic toner and a carrier, the electrophotographic toner contains at least a resin, a colorant, an inorganic additive and organic fine particles, and the inorganic additive comprises silica fine particles and a titanate-based cup. The organic fine particles are polymer fine particles having a volume average particle diameter of 0.03 to 2.0 μm, and the carrier is coated with a resin on the surface of a magnetic material having an average diameter of 20 to 60 μm and a specific gravity of 3 to 7 by a ring agent. A developer, comprising:

(4) The inorganic additive has a BET specific surface area of 1
00m ² / g or less, the electrophotographic developer according to Al ₂ O ₃ content is characterized by comprising processing the 0.2 wt% silica fine particles titanate coupling agent (3).

(5) The step of developing the electrostatic latent image formed on the photoreceptor with the developer described in (3) or (4) is repeated a plurality of times to form a plurality of toner images on the photoreceptor. An image forming method, comprising a step of forming a superposed toner image and transferring the superposed toner image to a transfer material at a time.

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

As the titanate-based coupling agent for treating and hydrophobizing the silica fine particles of the present invention, generally known ones can be used. For example, isopropyl triisostearoyl titanate, tetraisopropoxy titanium, Compounds such as butoxytitanium and tetrastearoxytitanium, and further, for example,
Compounds exemplified in JP-A-93353 and JP-A-57-93354 can be used.

As the treatment method for treating the silica fine particles using the titanate coupling agent, any of a dry treatment method and a wet treatment method can be applied. For example, a silica particle and an appropriate amount of a titanate coupling agent are mixed in a mixer. A dry processing method in which a ring agent and a mixing agent are charged and mixed may be used,
Further, a wet treatment method may be used in which silica fine particles are mixed in a solution in which a titanate-based coupling agent is dissolved in a solvent, and then the solvent is removed.

The amount of the titanate-based coupling agent attached to the silica fine particles (processing amount) is preferably about 0.01 to 15% by weight.

As the silica fine particles of the present invention, fumed silica fine particles obtained by a gas phase hydrolysis method are preferably used.

The inorganic additive of the present invention obtained by treating silica fine particles with a titanate-based coupling agent preferably has a BET specific surface area of 300 m ² / g or less, more preferably 1 m ² / g or less.
00m ² / g or less, still more preferably below 80 m ² / g, and 5 m ² / g or more.

The BET specific surface area of the inorganic additive is 300 m ²
When the ratio is larger than / g, the toner tends to have an excessive charge, and the chargeability of the toner tends to be unstable, and the particle diameter of the inorganic additive is too small. As a result, the performance of the toner, particularly, the transfer performance of the toner image becomes insufficient.

The BET specific surface area of the inorganic additive is 5
When it is smaller than m ² / g, the inorganic additive is easily separated from the toner, and the charge amount of the toner becomes unstable.

The BET specific surface area is measured by a one-point method of the nitrogen adsorption method, and a specific measuring device is Flow Soap 2300 (Shimadzu Corporation).

The content of Al ₂ O ₃ in the inorganic additive is as follows:
It is preferably at most 0.2% by weight. If the Al ₂ O ₃ content exceeds 0.2%, the treatment with the titanate-based coupling agent becomes non-uniform, adversely affecting the chargeability of the toner and its environmental characteristics.

The content of Al ₂ O ₃ can be measured by X-ray fluorescence analysis.

The inorganic additive obtained as described above is
It is preferable to add 0.1 to 10% by weight to the toner of the present invention. With smaller amounts, the fluidity of the toner,
Also, the effect of stability such as transferability of the toner image is poor. If the amount is larger than this, it is difficult to stably exist on the toner surface, and the stability of the toner charge is impaired.

The organic fine particles of the present invention are not particularly limited as long as they are polymer fine particles having a volume average particle size of 0.03 to 2.0 μm, but they may cause deformation of an addition polymer having a crosslinked structure, a polycondensate, or the like. Those having a difficult structure are preferred.

More specifically, examples of the addition polymer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, and p-methylstyrene. Phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene,
pt-butylstyrene, pn-hexylstyrene,
pn-octyl styrene, pn-nonyl styrene,
Styrene or styrene derivatives such as pn-decylstyrene, pn-dodecylstyrene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, methacryl Methacrylate derivatives such as n-octyl acid, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid Isopropyl, n-butyl acrylate, t-butyl acrylate,
Acrylic ester derivatives such as isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, phenyl acrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, and the like as constituent materials, Examples thereof include those crosslinked with a crosslinking agent such as divinylbenzene, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and triethylene glycol dimethacrylate.

As the polycondensate, melamine, formaldehyde condensate, polyester, polycarbonate,
Examples thereof include polyamide, polyurethane, and polyurea.

When the volume average particle diameter of the organic fine particles is smaller than the above range, the effect of preventing a decrease in the toner charge amount due to being left in a high humidity becomes poor. Defects such as letter dust occur.

The volume average particle size of the organic fine particles is measured by a particle size distribution analyzer "CAPA-700" (manufactured by Horiba, Ltd.).

The amount of the organic fine particles added to the toner is preferably 0.1 to 5% by weight. If the amount is less than this, the effect of preventing a decrease in the toner charge amount due to being left in a high humidity is poor. If the amount is more than this amount, the charge of the toner is hindered, and a defect such as letter dust occurs.

Next, the binder resin constituting the toner is not particularly limited, and various conventionally known resins are used. For example, a styrene resin, an acrylic resin, a styrene / acrylic resin, a polyester resin, and the like can be given.

The colorant constituting the toner is not particularly limited, and various conventionally known materials are used. Examples include carbon black, nigrosine dye, aniline blue, calcoil blue, chrome yellow, ultramarine blue, Dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, rose bengal, and the like.

Examples of other additives include charge control agents such as salicylic acid derivatives and azo metal complexes.

When a magnetic toner is obtained, magnetic particles are contained as an additive in the colored particles.
Preferably, particles such as ferrite and magnetite having an average primary particle diameter of 0.1 to 2.0 μm are used.

Examples of the release agent include low molecular weight polyolefins composed of polymers such as ethylene and propylene, and natural waxes such as carnauba wax and rice wax.
Higher fatty acid amides such as ethylenebisstearoylamide may be used.

The toner of the present invention preferably has a volume average particle diameter of 3 to 9 μm from the viewpoint of improving the reproducibility of characters and fine lines. The toner particle size can be measured in a standard manner by using a Coulter Counter TA-II.

Next, as a carrier used in the present invention, a ferromagnetic particle having a volume average particle diameter of 20 to 60 μm and a specific gravity of 3 to 7 is used as a core material, and a vinyl, styrene or acrylic material is formed on the surface thereof. A resin-coated carrier formed by coating a thermoplastic resin such as a resin or a thermosetting resin such as a phenol resin, a melamine resin, or an epoxy resin is used.

Examples of the ferromagnetic particles include iron oxides such as magnetite and maghemite, and metals other than iron (Mn, Z).
n, Mg, Cu, etc.), spinel type ferrite particles containing one or two types, magnetoplumbite type ferrite particles such as barium ferrite, or iron or iron alloy having an oxide film on the surface.

When the volume average particle size of the carrier (equivalent to the volume average particle size of the core material composed of ferromagnetic particles) is less than 20 μm, the carrier is liable to be scattered on the photoreceptor at the time of development and exceeds 60 μm. Has a small specific surface area of the carrier, and tends to be unable to effectively retain the charge generated due to the amount of frictional charge with the toner, and is likely to cause poor charging or the like during continuous use. Further, since the weight of one carrier is large and the stress applied to the toner is large, the above-mentioned burying of the inorganic additive in the toner is promoted.

Next, when the specific gravity of the carrier is less than 3, mixing with the toner becomes difficult and the charge of the toner becomes non-uniform. When it exceeds 7, the own weight of one carrier is large. Because the stress on the toner is large,
The above-mentioned inorganic additive is easily buried in the toner.

The average particle size of the magnetic material (carrier) represents a volume average particle size and is measured using a Microtrac particle size analyzer (manufactured by Nikkiso Co., Ltd.).

Next, the mixing ratio of the toner and the carrier in the developer of the present invention is 2 to 10 in terms of the toner concentration in the developer.
% By weight is preferred. As a method for mixing the toner and the carrier, it is preferable to use a dry mixer such as a V-type mixer or a W cone.

Hereinafter, the image forming method of the present invention will be described.

FIG. 1 is a sectional view of a main part of a color image forming apparatus for explaining an image forming method of the present invention. A charger 2, an image exposing unit 3, and a non-contact developing system are provided around an organic photosensitive drum 1. A yellow developing unit 4Y, a magenta developing unit 4M, a cyan developing unit 4C, and a black developing unit 4B are arranged, and four rotations of Y, M, C and B are performed by four rotations of the organic photosensitive drum 1.
The color toner images of the colors are formed in a superimposed manner, and these color toner images are collectively transferred on the transfer paper P supplied by the supply roll 5 by the action of the transfer pole 6 and subsequently separated and transported by the transport belt 7. The color image is formed by heating and fixing by a fixing device. The surface of the photosensitive drum 1 after the transfer is cleaned by the cleaning device 8 to be ready for the next image formation.

In the image forming apparatus shown in FIG. 1, a non-contact developing type developing device (4Y, 4M, 4C, 4B) filled with the four color developers of the present invention is used. A color image is formed by superimposing four color toner images on a transfer material and transferring and fixing the toner images collectively on a transfer material, so that the developer deteriorates in the process of repeated image formation over a long period of time. And stable high density, high resolution and clear color images can be obtained.

[0052]

EXAMPLES The present invention will be described below in more detail with reference to examples, but embodiments of the present invention are not limited thereto.

<Production Example of Inorganic Additive> Production Example 1: 100 g of silica fine particles “OX-50” (manufactured by Degussa) was added to a solution of 2 g of isopropyl triisostearoyl titanate dissolved in 100 ml of toluene. After heating and mixing for 3 hours, the mixture was dried to obtain the inorganic additive A of the present invention. The BET specific surface area of this inorganic additive A was 48 m ² / g, and the Al ₂ O ₃ content was 0.05%.

Production Example 2: Tetraisopropoxytitanium 1
g in 100 ml of toluene, 100 g of silica fine particles “Aerosil 50” (manufactured by Nippon Aerosil Co., Ltd.)
, And heat-mixed at 60 ° C. for 3 hours, and then dried.
An inorganic additive B of the present invention was obtained. BE of this inorganic additive B
The T specific surface area was 55 m ² / g, and the Al ₂ O ₃ content was 0%.

Production Example 3: 100 g of silica fine particles "Aerosil 130" (manufactured by Nippon Aerosil Co., Ltd.) was added to a solution of 5 g of isopropyl triisostearoyl titanate dissolved in 200 ml of toluene, and the mixture was heated and mixed at 60 ° C. for 3 hours and dried Thus, an inorganic additive C was obtained. The BET specific surface area of the inorganic additive C was 120 m ² / g, and the Al ₂ O ₃ content was 0.05%.

<Production Example of Organic Fine Particles> Production Example 1: 40 parts by weight of methyl methacrylate, 50 parts by weight of styrene, and 10 parts by weight of divinylbenzene were mixed with 1 part of distilled water.
00 parts by weight, 5 × 10 ⁻³ mol / L of potassium persulfate and sodium thiosulfate, and 2.5 × 10 ^{−5 of} copper sulfate.
mol / L, and after adding 0.2 parts by weight of sodium dodecylbenzenesulfonate, the mixture was reacted at 65 ° C. for 2 hours under a nitrogen stream. After cooling, the mixture was filtered and dried to obtain organic fine particles A. The volume average particle diameter of the organic fine particles A was 0.15 μm.

Production Example 2: Organic fine particles were prepared in the same manner as in Production Example 1, except that 40 parts by weight of methyl methacrylate, 50 parts by weight of styrene, and 10 parts by weight of divinylbenzene were changed to 50 parts by weight of styrene and 50 parts by weight of divinylbenzene. B was obtained. The volume average particle diameter of the organic fine particles B was 1.0 μm.

Production Example 3: Fine particles of melamine / formaldehyde condensate "Eposter S" (manufactured by Nippon Shokubai Co., Ltd.) were crushed by a jet mill to obtain organic fine particles C. The organic fine particles C
Was 0.22 μm.

<Production Example of Toner> Production Example 1: 100 parts by weight of a polyester resin (softening point 125 ° C., glass transition point 60 ° C.), 8 parts by weight of carbon black, and 3 parts by weight of polypropylene were mixed, kneaded, and pulverized. And classified to obtain particles having an average particle size of 8.5 μm. Further, 3 parts by weight of the inorganic additive A and 1 part by weight of the organic fine particles A were added to 100 parts by weight of the particles, and mixed with a Henschel mixer at a peripheral speed of a stirring spring of 30 m / sec for 5 minutes, and the toner A of the present invention was passed through a 300 mesh screen. Obtained.

Production Example 2: Styrene resin having a composition of styrene / methyl methacrylate / butyl acrylate = 70/15/15 (softening point: 120 ° C., glass transition point: 58 ° C.)
100 parts by weight, 3 parts by weight of a copper phthalocyanine pigment, and 3 parts by weight of polypropylene were mixed, kneaded, pulverized, and classified to obtain particles having an average particle size of 7.5 μm. Further, 3 parts by weight of the inorganic additive B and 1 part by weight of the organic fine particles B were added to 100 parts by weight of the particles, and the peripheral speed of the stirring spring was 30 m / s using a Henschel mixer.
After mixing at ec for 5 minutes, the toner B of the present invention was obtained through a 300 mesh screen.

Production Example 3: Polyester resin (softening point 12
100 parts by weight of 5 ° C., glass transition point of 60 ° C.), 6 parts by weight of a yellow pigment (CI Pigment Yellow 117), and 3 parts by weight of polypropylene were mixed, kneaded, pulverized and classified to obtain an average particle size of 8. A powder of 5 μm was obtained. Furthermore, this powder 1
1 part by weight of the inorganic additive C and 3 parts by weight of the organic fine particles C were added to 00 parts by weight, and the peripheral speed of the stirring spring was 30 using a Henschel mixer.
After mixing at m / sec for 5 minutes, the toner C of the present invention was obtained through a 300-mesh screen.

Production Example 4: Magenta pigment (CI Pigment Red 122) 8 with 3 parts by weight of copper phthalocyanine pigment
A toner D of the present invention was obtained in the same manner as in Production Example 2, except that the amount was changed to parts by weight and the organic fine particles B were changed to the organic fine particles A.

Production Example 5: Polyester resin (softening point 12
100 parts by weight of 5 ° C., glass transition point of 60 ° C.), 6 parts by weight of a yellow pigment (CI Pigment Yellow 117), and 3 parts by weight of polypropylene were mixed, kneaded, pulverized and classified to obtain an average particle size of 8. A powder of 5 μm was obtained. Furthermore, this powder 1
1 part by weight of the inorganic additive C was added to 00 parts by weight, and mixed with a Henschel mixer at a peripheral speed of a stirring spring of 30 m / sec for 5 minutes to obtain a comparative toner 1 through a 300-mesh screen.

Production Example 6: Silica fine powder obtained by treating 1 part by weight of inorganic additive C with dimethyldichlorosilane (BET specific surface area: 130 m ² / g, Al ₂ O ₃ content: 0.05%)
A comparative toner 2 was obtained in the same manner as in Production Example 5 except that the amount was changed to 1 part by weight.

Production Example 7 Titania fine powder (BE) obtained by treating 1 part by weight of an inorganic additive C with octyltrimethoxysilane
T specific surface area: 45 m ² / g) Other than changing to 2 parts by weight,
A comparative toner 3 was obtained in the same manner as in Production Example 5.

<Production Example of Carrier> Production Example 1: Magnetite particles having a particle diameter of 32 μm (specific gravity:
5.0) 1960 g and cyclohexyl methacrylate /
Methyl methacrylate = 5/5 copolymer fine particles 40 g
Was charged into a high-speed stirring type mixer and mixed at a product temperature of 30 ° C. for 15 minutes, then the product temperature was set at 105 ° C. and the mechanical impact force was 3
It was applied repeatedly for 0 minutes and cooled to prepare Carrier A of the present invention.

Production Example 2: Magnetite particles having a particle size of 45 μm
A carrier B of the present invention was prepared in the same manner as in Production Example 1, except that the m-Cu-Zn ferrite particles (specific gravity: 4.6) were used.

Production Example 3: Magnetite particles having a particle size of 70 μm
A carrier 1 for comparison was prepared in the same manner as in Production Example 1, except that the iron powder particles (specific gravity: 7.8) were used instead of m.

Production Example 4: Magnetite particles having a particle size of 13 μm
A carrier 2 for comparison was prepared in the same manner as in Production Example 1 except that the m was changed to magnetite particles (specific gravity: 5.0).

<Manufacture of Developer> The four types of carriers (carriers A and B of the present invention and carrier 1 for comparison,
2) and seven types of toners (toners A, B, C, and D
And the comparative toners 1, 2, and 3) were combined at a weight ratio of 95: 5 and mixed by a V-type mixer for 20 minutes, and the four types of developers of the present invention (developers A, B, and C) were mixed. And D) and four types of developers for comparison (developers 1, 2, 3 and 4).

<Evaluation 1> The above eight kinds of developers were filled in a color printer “KL-2010” (manufactured by Konica Corporation) in the order shown in Table 1, and each of them was charged at a temperature of 25 ° C. and 15% RH in an environment of 20%.
Eight types of image tests of Examples 1 to 4 and Comparative Examples 1 to 4 were performed for 000 sheets (20 KP) each.

In the image test, the charged potential of the photoconductor was 750 V, the exposed portion potential was -50 V, and the developing DC bias was
650 V, an AC bias of 2.0 kV (peak to peak), and an AC bias frequency of 8 kHz were set.

In the image test, developability, transferability, the number of adhered carriers, the state of occurrence of character dust, and the reproducibility of halftone images were evaluated based on the following evaluation criteria. The results are shown in Table 1. .

<Evaluation Criteria> Developability: The latent image having an exposed portion potential of −50 V was reversely developed, transferred to plain paper, and then stopped before fixing, and the amount of toner per unit area on transfer paper (mg) was measured. Is A, and the amount of toner per unit area remaining on the photoreceptor is B (mg).
+ B (mg) was defined as developability.

<< Transferability >> Similarly, ΔA / (A +
B) The transferability was defined as Δ × 100%, which was classified into the following four ranks and judged.

A: 90% or more B: 80% or more and less than 90% C: 60% or more and less than 80% D: less than 60%.

<< Number of Carriers Attached >> The number of carriers adhered per 1 cm × 1 cm on the surface of the photoreceptor after the developing operation was counted and classified into the following three ranks and judged.

A: 5 or less B: 6 to 20 C: 21 or more

<< Character dust >> At 200 μm intervals, width 200
A pattern in which five lines each having a length of 1 μm and having a length of 1 cm were arranged was printed, and the state of dust in the portion was visually and microscopically observed.

A: Dust around the line is not observed even with a microscope B: Dust is not observed visually but is observed around the microscope C: Dust around the line is visually observed D: D is too difficult to distinguish between lines Intense dusting occurs.

<Dot Reproducibility> A 120-line dot pattern having an area ratio of 20% was printed, and the reproducibility was classified into the following three ranks and judged.

A: Almost completely reproduced. B: Dots can be identified but shapes are not reproduced. C: Dots cannot be identified.

[0083]

[Table 1]

<Evaluation 2> The environmental conditions were 25 ° C. and 15% RH.
The image tests of Examples 5 to 8 and Comparative Examples 5 to 8 were conducted in the same manner as in Evaluation 1 except that the temperature was changed to 20 ° C. and 85% RH, and the results are shown in Table 2.

[0085]

[Table 2]

<Evaluation 3> 20 ° C. and 85% in Evaluation 2
After the image test of 20,000 sheets (20 KP) under the high humidity environment of RH, the printer is left under the high humidity environment of 20 ° C. and 85% RH for 50 hours and 100 hours, and the image test after the left is developed. The transferability, transferability, the number of adhered carriers, the occurrence of character dust, and the reproducibility of halftone images were evaluated. The results are shown in Table 3.

[0087]

[Table 3]

From Tables 1, 2 and 3, the developers used in Examples are excellent in developability, transferability, carrier adhesion, character dust, and halftone dot reproducibility. It can be seen that the developer has poor properties described above, and in particular, significantly deteriorates fatigue at high humidity in the process of repeatedly forming an image.

[0089]

As has been demonstrated in the examples, according to the electrophotographic toner, the developer and the image forming method of the present invention, the fatigue deterioration during repeated image formation even at high temperature and high humidity is suppressed. It has excellent effects such as high durability, high density and high resolution image formation, compactness of the apparatus and color image formation at high speed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a color image forming apparatus for explaining an image forming method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic photosensitive drum 2 Charging device 3 Image exposure device 4Y Yellow developing device 4M Magenta developing device 4C Cyan developing device 4B Black developing device 6 Transfer pole 8 Cleaning device

Claims (5)

[Claims] 1. An electrophotographic toner containing at least a resin, a colorant, an inorganic additive and organic fine particles, wherein the inorganic additive is obtained by treating silica fine particles with a titanate coupling agent, and the organic fine particles have a volume average Particle size 0.
An electrophotographic toner comprising polymer fine particles having a particle size of 03 to 2.0 μm. 2. The inorganic additive having a BET specific surface area of 100
^2. The electrophotographic toner according to claim 1, wherein silica fine particles having an m ² / g or less and an Al ₂ O ₃ content of 0.2 wt% or less are treated with a titanate coupling agent. 3. A developer comprising at least an electrophotographic toner and a carrier, wherein the electrophotographic toner contains at least a resin, a colorant, an inorganic additive and organic fine particles,
The inorganic additive is obtained by treating silica fine particles with a titanate coupling agent, the organic fine particles are polymer fine particles having a volume average particle diameter of 0.03 to 2.0 μm, and the carrier has an average diameter of 20 to 60 μm and a specific gravity of 3 7. The developer according to any one of items 1 to 7, wherein the magnetic material surface is coated with a resin. 4. An inorganic additive having a BET specific surface area of 100
The electrophotographic developer according to claim 3, wherein silica fine particles having an m ² / g or less and an Al ₂ O ₃ content of 0.2 wt% or less are treated with a titanate coupling agent. 5. A process for developing an electrostatic latent image formed on a photoreceptor with the developer according to claim 3 or 4 a plurality of times to form a plurality of toner images on the photoreceptor in a superimposed manner. And a step of batch-transferring the superposed toner images onto a transfer material.