JPH08106176A - Electrophotographic developer - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an electrophotographic developer that prevents aggregation of toner causing white spots, is less likely to cause toner scattering, has good color developability, and reduces fogging. To do. [Structure] A developer containing a binder resin and a colorant. The colorant has a DBP oil absorption of 300 to 500.
a first carbon black having a BET surface area of 500 to 1500 m ² / g, which is ml / 100 g;
A second carbon black having a DBP oil absorption of 50 to 200 ml / 100 g and a BET method surface area of 100 to 200 m ² / g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developer used for image formation by visualizing an electrostatic latent image.

[0002]

2. Description of the Related Art In an electrophotographic apparatus or an electrostatic recording apparatus, it has conventionally been necessary to visualize an electrostatic latent image formed on an electrostatic latent image holding member made of a photoconductor or a dielectric. 2 using a two-component toner containing a toner and a carrier
A component developing method, a one-component developing method using a toner having a carrier function, and the like are widely used.

These electrophotographic methods are disclosed, for example, in US Pat. No. 2,297,691, JP-B-42-23910.
U.S. Pat. No. 3,666,363, U.S. Pat. No. 4,324,728, U.S. Pat. No. 4,071,361, U.S. Pat. No. 3,909,258, U.S. Pat. 4,121,931 and 2,895,84
No. 7, No. 3,152,012, Japanese Patent Publication No. 41-9475, No. 45-2877, No. 5
Many are disclosed in, for example, Japanese Patent Publication No. 4-3624.

In these electrophotographic methods, an image is generally formed by the following steps. That is, first,
An electrostatic latent image is formed on the surface of the photoconductor using a photoconductive material by various means. Next, the toner charged by friction is attached to the latent image formed on the surface of the photoconductor to develop the latent image. Further, after the toner image is transferred onto a transfer material such as paper, if necessary, it is fixed by heat, pressure or solvent vapor.

The toner used in such an electrophotographic developing method is generally colored fine particles containing a thermoplastic resin and a colorant, and these raw materials are mixed with other additives (external additives). And then uniformly dispersed, and the solidified product is pulverized and then classified. Hydrophobic silica is added to the obtained colored fine particles as an external additive in order to prevent filming of the toner on the photosensitive member and to improve the fluidity (Japanese Patent Publication No. 54-16219, etc.). ) Is proposed.

[0006]

However, since the toner used in the electrophotographic method is easily charged,
May exhibit undesired behavior. That is, in the toner replenishing cartridge, the toner is stressed by the rotation of the auger at the replenishing port, and aggregates are formed. The toner agglomerate is supplied into the developing unit together with the normal toner, and then adheres to the latent image on the surface of the photoconductor.
Of the toner adhered to the surface of the photoconductor, the normal toner near the agglomerates remains on the photoconductor without being transferred to a transfer material such as paper during the transfer process. As a result, so-called white spots occur, in which the image in that portion appears white.

Such a phenomenon has been a particular problem in the case of a toner using carbon black as a colorant. In order to prevent the occurrence of white spots, it is necessary to avoid toner aggregation, but even when the type and amount of carbon black were adjusted, white spots could not be sufficiently prevented.

Therefore, the present invention prevents toner aggregation that causes white spots and prevents toner scattering.
It is an object of the present invention to provide a developer for electrophotography, which has good color developability and has reduced fogging.

[0009]

In order to solve the above problems, the present invention contains a binder resin and a colorant, and the colorant has a DBP oil absorption of 300 to 500 ml / 100.
and has a BET surface area of 500 to 1500 m
^{A second} carbon black having a DBP oil absorption of 50 to 200 ml / 100 g and a BET surface area of 100 to 200 m ² / g is contained. A developer for electrophotography is provided.

[0010]

The present inventors pay attention to the DBP oil absorption amount and the BET method surface area as the properties of carbon black, and when two kinds of carbon blacks having different values are mixed and used, toner aggregates are generated. It has been found that a toner which is difficult to produce, has good color developability, and has no fog problem can be obtained. The present invention was made based on such knowledge.

That is, the DBP oil absorption is 300 to 500.
ml / 100g, BET surface area is 500 to 1
The carbon black having a good conductivity of 500 m ² / g has an advantage of lowering the toner resistance value and suppressing the aggregation of the toner, but the dispersibility in the resin is poor and the color developability is also deteriorated. Therefore, when only this carbon black is used as the colorant, toner scattering is likely to occur and fogging may increase on the obtained image.

Also, the DBP oil absorption is 50 to 200 ml /
100 g, BET method surface area 100-200 m
Carbon black having a poor conductivity of ² / g has good dispersibility in a resin and excellent color development. However, the toner in which only carbon black is mixed as a colorant has a high resistance value, and therefore aggregation that causes white spots easily occurs.

In the present invention, the above-mentioned two kinds of carbon black are mixed and used as the colorant, so that the defects of both carbon blacks can be compensated. Therefore, it is possible to obtain an electrophotographic developer capable of forming an image with less fogging, less toner scattering, excellent color development, and less toner aggregation.

[0014]

EXAMPLES As the binder resin used in the present invention, a copolymer of styrene and a substitution product thereof which has been conventionally used as a binder resin for toner, or an acrylic resin can be used.

Examples of the copolymer of styrene and its substitution product include polystyrene homopolymer, hydrogenated styrene resin, styrene-isobutylene copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene terpolymer. Polymer, acrylonitrile-styrene-acrylic acid ester terpolymer, styrene-acrylonitrile copolymer, acrylonitrile-
Acrylic rubber-styrene terpolymer, acrylonitrile-chlorinated polystyrene-styrene terpolymer, acrylonitrile-EVA-styrene terpolymer, styrene-p-chlorostyrene copolymer, styrene-propylene copolymer , Styrene-butadiene rubber, styrene-maleic acid ester copolymer, styrene-isobutylene copolymer, styrene-maleic anhydride copolymer and the like.

Examples of the acrylic resin include polyacrylate, polymethylmethacrylate, polyethylmethacrylate, poly-n-butylmethacrylate, polyglycidylmethacrylate, polyfluorinated acrylate, styrene-methacrylate copolymer, styrene-butyl. Examples thereof include a methacrylate copolymer and a styrene-ethyl acrylate copolymer.

Other binder resins include polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene,
Polyester, polyurethane, polyamide, epoxy resin, phenol resin, urea resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin , Paraffin wax and the like can be used alone or as a mixture.

In the toner of the present invention, two kinds of carbon black having different DBP oil absorption and BET surface area are used as colorants. The first carbon black has a DBP oil absorption of 300 to 500 ml / 100 g,
The BET method surface area is 500 to 1500 m ² / g, and the second carbon black has a DBP oil absorption of 50 to 200.
ml / 100g, BET method surface area is 100-200m
² / g. These first and second carbon blacks have pH values of 7 or more and 10 or less, and 1 respectively.
It is preferably 5 or more and 5 or less.

Examples of the first and second carbon blacks that satisfy such conditions include, but are not limited to, Ketjen black and furnace black.

The mixing ratio of the first and second carbon blacks is preferably 1: 2 to 2: 1. If it is less than 1: 2, white spots due to toner aggregation tend to occur, and if it is more than 2: 1, toner scattering may occur and fogging may increase. The total amount of carbon black added is 100 parts by weight of the binder resin.
It is preferably 2 parts by weight or more and 6 parts by weight or less. If it is less than 2% by weight, a sufficient image density may not be obtained, and if it exceeds 6 parts by weight, toner scattering tends to occur and fogging tends to increase.

In the present invention, waxes for improving anti-offset characteristics, a charge control agent for controlling the amount of triboelectric charge, and the like may be blended, if necessary. Examples of the charge control agent include negative electrode polarity control agents such as metal chelates of alkylsalicylic acid, chlorinated polyesters, polyesters with excess acid groups, chlorinated polyolefins, aliphatic metal salts, and fatty acid soaps; dimethylaminoethyl methacrylate-styrene. Examples thereof include copolymers, fluorine-based surfactants, and positive polarity control agents such as hydrophobic silica.

The toner of the present invention can be manufactured, for example, as follows using a binder resin, a colorant, and an external additive. First, a binder resin, a colorant satisfying a predetermined condition, and if necessary, wax and the like are mixed and dispersed using a ball mill, a V-type mixer, or the like. Next, this mixture is heated and melted and kneaded by using a pressure kneader, a roll or the like. The obtained kneaded product is roughly pulverized using a hammer mill, a jet mill or the like. Furthermore, after finely pulverizing with a jet mill, etc., the particles are classified into a desired particle size by a wind classification method, etc., an external additive is added to this, and the mixture is mixed with a high-speed flow type mixer to obtain a desired toner. Obtainable.

As means for mixing, kneading, and classifying the toner,
In addition to those described above, a high-speed dissolver, a wet dispersion method using a ball mill or the like, an internal mixer, a melt-kneading method using a screw type extruder, or the like can be used, and as a mixing means, a ball mill, A V-type mixer, a Forberg, a Henschel mixer, etc. can be used. Moreover, as a means for roughly pulverizing the mixture, for example, a cutter mill, a roller mill, a ball mill, or the like can be used. Further, as a means for finely pulverizing the coarsely pulverized product, a high speed rotary pulverizer or the like can be used. Further, as a means for classifying the finely pulverized product, an airflow classifier or the like can be used.

The amount of the external additive added before the toner is sieved is 100 parts by weight of the toner particles.
It is preferably 0.1 to 5.0 parts by weight, more preferably 0.3 to 0.5 parts by weight.

As the external additive, silica fine particles, metal oxide fine particles, a cleaning aid, and the like can be used. Examples of the silica fine particles include silicon dioxide, aluminum silicate, sodium silicate, potassium silicate, zinc silicate, and magnesium silicate. Examples of the metal oxide fine particles include zinc oxide, titanium oxide, aluminum oxide, zirconium oxide, strontium titanate, and barium titanate. Examples of the cleaning aid include resin fine powder such as polymethylmethacrylate, polyvinylidene fluoride, and polytetrafluoroethylene. These external additives may be subjected to surface treatment such as hydrophobization.

As a means for mixing the external additive, a known mixing device can be used, but it is preferable to use, for example, a high speed fluid type mixer. Examples of the high-speed fluid type mixer include a Henschel mixer, a super mixer, and a micro speed mixer.

The toner thus obtained has a resistance value of 1.0 × 10 ¹¹ Ω · cm or more and 4.0 × 10 ¹¹ Ω · cm or more.
The following is preferred. If it is less than 1.0 × 10 ¹¹ Ω · cm, the toner may scatter and fogging may increase, and if it exceeds 4.0 × 10 ¹¹ Ω · cm, the toner aggregates to cause white spots. May occur.

The toner of the present invention can be applied to all known developing methods. For example, a two-component developing method such as a cascade method, a magnetic brush method, and a microtoning method; a one-component developing method containing a magnetic material such as a conductive one-component developing method, an insulating one-component developing method, and a jumping developing method; The powder cloud method, the fur brush method, and the non-magnetic one-component developing method in which the latent image is developed by being carried to the developing unit by being electrostatically held on the toner carrier can be mentioned.

An example of an image forming apparatus to which the toner of the present invention can be applied will be described with reference to FIG. The copying machine shown in FIG. 1 is configured as follows. That is, the copying machine body 10
A drum-shaped photosensitive member 103 is provided as an image bearing member in a substantially central portion of 1 (hereinafter referred to as a main body 101) so as to be rotatable in a direction indicated by an arrow a. The photoconductor 103 has a photoconductive layer on its surface, and the following devices are fixed around the photoconductor 103 along the rotation direction thereof.

That is, the slit charger 107 is provided above the charging charger 105 and on the downstream side of the charging charger 105 in the rotation direction of the photosensitive member 103.
The charging charger 105 uniformly charges the surface of the photoconductor 103, and slit-exposes the surface of the photoconductor 103 with a document image as a light source through the slit glass 107. Further, on the downstream side of the slit glass 107, a developing device 109 for performing development by attaching toner to the electrostatic latent image on the photoconductor 103 is installed.
A toner 110 containing a carrier as a developer is provided therein.
Is housed.

Further, in the developing device 109, the stirring roller 2 which stirs the developer by the rotation of the roller and frictionally charges the developer.
01, and a supply roller 202 that supplies the developer stirred by the stirring roller 201 to the magnet roller 203.
Is provided. Further, in the developing device 109, a magnet roller 203 is provided rotatably in a direction indicated by an arrow 1 in the drawing in a state where the magnet roller 203 is close to the photoconductor 103. Inside the magnet roller 203, along the rotation direction of the roller. S poles and N poles are arranged alternately.

A transfer device 111 and a peeling device 113 are provided on the downstream side of the developing device 109. The toner image formed by the developing device 109 is transferred to the transfer device 11
The sheet transferred onto the copy sheet (hereinafter, referred to as sheet) by 1 and attached to the surface of the photoconductor 103 is removed by the peeling device 11
3 peels from the surface of the photoconductor 103.

A cleaning device 115 is provided on the downstream side of the peeling device 113 to remove the toner 110 remaining on the photoconductor 103 after the transfer. Cleaning device 115 and charging charger 105
A static eliminator 117 for lowering the potential of the photoconductor 103 is fixedly installed between and.

Further, the main body 101 has an original glass 119 on which an original is placed and an original glass 119.
It has an optical system 121 that irradiates the upper document with light and guides the reflected light to the surface of the photoconductor 103. The optical system 121 includes a lamp 123 serving as a light source and mirrors 124, 125, 127, 129 for reflecting light emitted from the light source.
131, 133 and a lens unit 135 for forming an image of reflected light.

The lamp 123 and the mirror 124 are constructed so as to be movable under the original glass 119, and in order to keep the optical path length constant, the mirror 125 and the mirror 1 are kept.
27 is configured to move at half the speed of ramp 123. The reflected light from the mirror 133 is configured to pass through the slit glass 107 and be guided to the surface of the photoconductor 103.

A manual feed tray 141 for accommodating sheets is detachably provided in the middle of the right side of the main body 101, and the main body 101 is accommodated in the manual feed tray above the tip of the manual feed tray 141. A pickup roller 143 for pulling out the paper is provided.

On the left side of the main body 101, there is provided a paper discharge tray 171 for discharging the copied paper.
A paper transport path, that is, a transport path 142 is formed between the manual feed tray 141 and the paper discharge tray 171, and the transport path 142 is indicated by a dotted line in FIG. 1.

Upstream of the transport path 142, the first and second
The roller pair is attached to the main body 101. First
The pair of rollers is composed of two rollers, a paper feed roller 145 and a separation roller 147, which are adjacent to the manual feed tray 141. The paper feed roller 145 is rotatable in the direction of the arrow b in the figure, and feeds the paper pulled out by the pickup roller 143 to the second roller pair. Separation roller 14
7 is provided below the paper feed roller 415 so as to be in contact therewith, and rotates in a direction opposite to the rotation direction of the paper feed roller 145 when there are two or more sheets sent from the pickup roller 143. Then, the excess paper is pulled back to the manual feed tray 141. When the number of sheets sent from the pickup roller 143 is one, the separation roller 147 rotates according to the rotation of the sheet feeding roller 145.

The second roller pair is a registration roller 149 composed of an upper roller and a lower roller. The registration roller 149 aligns the sheet by hitting the leading edge of the sheet sent from the sheet feeding roller 145, and then aligns the sheet.
1 and 1 so that the toner image on the photoconductor 103 overlaps.

The transfer device 111 is provided in the middle of the conveying path 142.
And a peeling device 113 is arranged, and beyond that,
A belt-shaped belt for conveying paper, that is, a conveyor belt 1
51 is provided. Further, a fixing device 153 that heats and presses the toner 110 to fix the toner 110 on a sheet is installed downstream of the transport path 142. The fixing device 153 has a heat roller 157 and a pressure roller 159 that are rotatable in the directions of arrows c and d, respectively. The heat roller 157 has a built-in heat lamp 155, which is a heating body, and includes the pressure roller 1
59 is partially crimped. The surface of the heat roller 157 is made of a metal member having good thermal conductivity, and the pressure roller 1
The surface of 59 is made of an elastic rubber member so as to be easily pressed against the heat roller 157.

Further, downstream of the conveying path 142, a paper discharge roller 161 for discharging the paper on which the copy image is formed to the paper discharge tray 171 is provided. The copying process by the above-mentioned copying machine is as follows.

First, the surface of the photoconductor 103 is uniformly charged by the corona discharge of the charging charger 105. Next, the lamp 123 in the optical system 121 scans below the original glass 119 on which the original is placed, and the original is irradiated with light. When scanning is performed by the lamp 123, the lamp 1
The light emitted from 23 is reflected and then guided to the lens unit 135. The reflected light is reflected by the lens unit 135.
And is exposed on the charged photoconductor 103 via the slit glass 107. When the light is exposed,
The charge on the surface of the photoconductor 103 is lost and an electrostatic image is formed.

In the developing device 109, the stirring roller 201
The toner 110 and the carrier that are agitated and frictionally charged by the supply roller 202 are supplied to the magnet roller 203.
Sent to The toner 110 and the carrier sent to the magnet roller 203 form a magnetic brush by the magnetic force lines formed between the S pole and the N pole inside the magnet roller 203. The carrier is always attracted to the magnet roller 203 by magnetism, and the toner 110 is electrically attracted to the carrier.

When the magnet roller 203 and the photoconductor 103 rotate and the magnetic brush and the electrostatic latent image on the photoconductor 103 come close to each other, the toner 110 has a stronger electrostatic attraction than the electrostatic latent image. It is attracted and adheres to the surface of the photoconductor 103 to form a toner image. Further, at the time of development, a developing bias is applied to the magnet roller 2 by a voltage device (not shown).
03 and the photoconductor 103 to prevent the toner 110 from adhering to the non-image portion on the surface of the photoconductor 103.

On the other hand, the paper stored in the paper feed cassette 141 is pulled out by the pickup roller 143, and only one paper is pulled out by the rotation of the paper feed roller 145 and the separation roller 147. It is sent to the registration roller 149. The registration roller 149 aligns the leading edge of the sheet and then sends the sheet between the photoconductor 103 and the transfer device 111 to superimpose it on the electrostatic latent image on the photoconductor 103. On the back side of this fed paper,
The toner image is transferred onto the paper by the action of the transfer device 111. In this way, the sheet on which the toner image is placed is peeled from the surface of the photoconductor 103 by the peeling device 113,
It is conveyed on the conveyor belt 151 and reaches the fixing device 153.

In the fixing device 153, the heat roller 157 heated by the built-in heat lamp 155 and the pressure roller 159 rotate in their respective rotation directions while partially pressure-bonding. Heat roller 157 and pressure roller 15
When 9 and 9 are rotated, the toner image is fixed on the paper by passing the paper through the pressure-bonded portions of these two rollers. The sheet is arranged so that the toner image is on the heat roller side. That is, the heat roller 1
The heat of 57 melts the toner 110, and the pressure of the pressure roller 159 increases the heat conduction efficiency, so that the toner permeates between the fibers of the paper.

Through the above process, the sheet on which the copy image is formed is ejected to the sheet ejection tray 171 via the sheet ejection roller 161. Hereinafter, the present invention will be described in more detail by showing specific examples of the present invention.

Styrene-acrylic resin (CPR-600
B, manufactured by Mitsui Toatsu Chemicals, Inc.) 100 parts by weight, Ketjen Black as the first carbon black (MA-100,
1.5 parts by weight, furnace black as a second carbon black (manufactured by EC Lion Corporation)
1.5 parts by weight and 1 part by weight of a low molecular weight polypropylene wax (Viscor 660P, manufactured by Sanyo Kasei Co., Ltd.) were heated and melted and kneaded, and the obtained kneaded product was cooled. Then, it is crushed by a supersonic jet air flow fine crusher and classified by a wind force classifier to obtain a volume average particle size of 9 μm and a particle size of 5 to 1
4 μm toner particles were obtained.

To 100 parts by weight of this toner, 0.5 parts by weight of hydrophobic silica (R-972, manufactured by Nippon Aerosil Co., Ltd.) was mixed with a Henschel mixer. The conditions of the mixer were such that the peripheral speed of the blade tip was 20 m / s and the blade rotation time was 3 minutes, and the obtained toner was used as Example 1.

Further, except that the proportions of the first and second carbon blacks are changed, respectively, the same steps as described above are carried out.
Toners of Examples 2 to 6 were obtained. Further, toners of Comparative Examples 1 and 2 were manufactured by the same process except that either the first carbon black or the second carbon black was not added. In the toner of Comparative Example, the amount of carbon black added was 3.0 parts by weight with respect to 100 parts by weight of the binder resin.

A developing agent was prepared by mixing 95 parts by weight of a ferrite carrier with 5 parts by weight of this toner. Using the toners obtained (Examples 1 to 6 and Comparative Examples 1 and 2), images were printed on a commercially available copying machine (Rheodry BD-5020, manufactured by Toshiba Corporation). For the obtained image, the presence or absence of white spots and the toner scattering state were observed. Further, the fog on the image, the ID, and the resistance value of the toner were measured and shown in Table 1 below together with the amount of carbon black added.

[0052]

[Table 1]

The white spots in Table 1 were evaluated by the following method. White spots represent the number of elliptical white spots that occurred when a solid black image was printed on A3 paper.
10 or less were accepted.

The toner scattering was visually observed, and those having no influence on the image were regarded as acceptable. Fog is a color difference meter (CR-121, DP-100, manufactured by Minolta).
Was used to obtain the color difference between the white background portion of the image and the white paper. Fogging is preferably 1% or less.

The ID was evaluated by obtaining the density of a solid image using a Macbeth densitometer. ID is 1.0 ~
It is preferably within the range of 1.4. Toner resistance is
By pressing and compressing the toner, a disk-shaped molded sample having a thickness of 1 to 2 mm and a diameter of 50 mm is prepared, and measured with a dielectric loss measuring device (LCR meter manufactured by Ando Electric Co., Ltd.).

As shown in Table 1, when the toners of Examples 1 to 4 are used, white spots are not generated due to toner aggregation and toner scattering is small. Further, it was possible to form a good image having a proper ID with less fogging. The resistance values of these toners are all within the above-mentioned preferable range.

The image obtained using the toner of Example 5 does not cause toner scattering and fogging is small, but the resistance value is large, so there are many white spots due to toner aggregation and the ID is small. Further, the image obtained using the toner of Example 6 has a good ID, but toner scattering and fog often occur.

With the toner of Comparative Example 1 containing only furnace black, a large number of white spots were generated on the image because of the high toner resistance. In addition, the image formed using the toner of Comparative Example 2 containing only Ketjen Black has a low ID and large fog due to a large amount of toner scattering. Further, the toner of Comparative Example 2 was also inferior in color developability.

[0059]

As described in detail above, according to the present invention,
An electrophotographic developer that does not easily generate toner aggregates that cause white spots can be obtained. Further, since the developer of the present invention does not cause toner scattering and is excellent in color developability, when it is used, an image with less fogging can be formed.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross section of an image forming apparatus to which an electrophotographic toner of the present invention can be applied.

[Explanation of symbols]

101 ... Main body, 103 ... Photosensitive drum, 105 ... Charging charger 107 ... Slit glass, 109 ... Developing device, 110 ...
Toner 111 ... Transfer device, 113 ... Peeling device, 115 ... Cleaning device, 117 ... Eliminating device, 119 ... Original glass,
121 ... Optical system, 123 ... Lamp 124 ... Mirror, 125 ... Mirror, 127 ... Mirror, 1
29 ... Mirror 131 ... Mirror, 133 ... Mirror, 135 ... Lens unit 141 ... Manual feed tray, 142 ... Conveying path, 143 ... Pickup roller 145 ... Paper feeding roller, 147 ... Separation roller, 149 ... Registration roller 151 ... Conveying belt, 153 ... Fixing device, 155 ... Heat lamp 157 ... Heat roller, 159 ... Pressure roller, 161 ...
Paper discharge roller 171 ... Paper discharge roller, 201 ... Agitation roller, 202 ... Supply roller 203 ... Magnet roller.

Claims (4)

[Claims] 1. A binder resin and a colorant are contained, and the colorant has a DBP oil absorption of 300 to 500 ml / 100.
and has a BET surface area of 500 to 1500 m
^{A second} carbon black having a DBP oil absorption of 50 to 200 ml / 100 g and a BET surface area of 100 to 200 m ² / g is contained. Developer for electrophotography. 2. The pH of the first carbon black is 7
Is not less than 10 and not more than p of the second carbon black
The electrophotographic developer according to claim 1, wherein H is 1 or more and 5 or less. 3. The mixing ratio of the first carbon black and the second carbon black is 1: 2 to 2: 1, and the total amount of carbon black added is 2 with respect to 100 parts by weight of the binder resin. The developer for electrophotography according to claim 1, wherein the amount is 6 to 6 parts by weight. 4. The resistance value is 1.0 × 10 ¹¹ to 4.0.
The electrophotographic developer according to claim 1, wherein the developer is × 10 ¹¹ Ω · cm.