JP2990631B2 - Black toner for color digital copier - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a black toner for a color digital copying machine, and more particularly, to a black toner for a color digital copying machine having good reproducibility for halftones.

[0002]

2. Description of the Related Art In a digital system, an area ratio of a halftone dot for each pixel is changed by using a halftone dot by a digital copying machine to form an electrostatic latent image corresponding to the area ratio, and the electrostatic latent image is formed. A toner image is formed by attaching toner particles to the toner. In this case, the amount of the toner particles adhered to the electrostatic latent image is determined according to the area ratio of the halftone dots. Gradation recording can be performed. However, the mainstream of conventional copiers uses an analog system, and the development of toners is also directed to toners suitable for analog copiers, and the current situation is that the development of black toner for digital copiers is delayed.

[0003]

When a conventional black toner for an analog copying machine is used in a digital copying machine, when the development amount of the black toner is changed in accordance with the area ratio of the halftone dots, the amount of toner adhesion is constant. , There is a problem that the optical density of the toner image does not change any more, that is, the phenomenon that the optical density of the reproduced toner image does not change linearly with the change in the development amount of the toner occurs. . The reason is that black toner for analog copying machines, which has been conventionally used, increases the optical density for the purpose of improving the moist feeling, the soft feeling and the character reproduction of the toner image. Since a large amount of carbon black is used, in a region where the amount of toner adhered is small, the concealment rate of the base by carbon black is quickly saturated, and as a result, the image density of the obtained toner image is saturated. It is thought that there is.

Therefore, when the above problem is improved by reducing the content of carbon black in the toner particles, the following new problem arises. That is, conventionally, carbon black having a relatively small particle size manufactured by the furnace method has been used. In toner particles using such a relatively small particle size carbon black particle, carbon black is used. When the content is reduced,
Since the area where carbon black does not exist in the toner particles increases, a difference occurs between the transmittance of long-wavelength light and the transmittance of short-wavelength light. As a result, the developed black image has a brown-red color. There is a problem that a color tone is developed and black cannot be reproduced well.

[0005] The present invention has been made in view of the above-described circumstances of the prior art. That is, the object of the present invention is to provide a good area gradation even when the content of carbon black is low, to reduce the change in color tone even when the light source is changed, and to provide a digital copying machine that exhibits faithful black reproducibility. It is to provide a black toner. Another object of the present invention is to provide a black toner for a digital copying machine having good tone reproducibility.

[0006]

The present inventors have conducted various studies on a black toner for a digital copying machine, and as a result,
It has been found that the above problems can be solved by setting the average primary particle size and the content of carbon black in the toner particles in certain ranges, and the present invention has been completed. That is, in the black toner for a color digital copying machine of the present invention (hereinafter simply referred to as the toner of the present invention), the toner particles contain carbon black having an average primary particle diameter of 35 mμm to less than 50 mμm as a colorant in a binder resin. -6% by weight. The carbon black in the toner of the present invention has an average primary particle size and content between the image density (ID) and the development amount (TMA) when the toner particles are developed using the following inequalities (1) and (2). ) Is satisfied, and the image density (ID) preferably falls within the range of the following inequality (3). ID ≦ 8/3 (TMA) +4/5 (1) ID ≧ 5/3 (TMA) +1/2 (2) 1.2 ≦ ID ≦ 1.7 (3) Here, the development amount is a solid image. This is the number of milligrams of toner supplied per unit square centimeter of the photoconductor when developing the corresponding electrostatic latent image. The image density is a value measured by a Macbeth densitometer.

Hereinafter, the present invention will be described in detail. It is necessary that the carbon black used in the present invention has an average primary particle diameter determined by observation with an electron microscope in the range of 35 mμm to less than 50 mμm. Average primary particle diameter is 35m
If it is less than μm, the color rendering properties will be poor. That is, when the light source is changed, the color tone changes, and an image with good black reproducibility cannot be obtained. In addition, the average primary particle diameter is 50 μm
In the case described above, there is a problem that the charge retention of the toner becomes unstable, and also a problem occurs in the production of carbon black. That is, carbon black is usually produced by a furnace method.
In order to produce a product having the above particle size, the heating temperature must be lowered. In the furnace method, if the heating temperature is lowered, there is a problem that impurities, for example, carcinogens having a problem in safety such as PAH (polycyclic aromatic hydrocarbon) and nitropyrene are likely to remain. If the heating temperature is increased to avoid this, only carbon black having a small average primary particle diameter can be obtained. Also,
The carcinogen is decomposed by heat treatment (800 ° C.)
Although it can be reduced, in this case, there is a problem that the cost becomes considerably high and it is not practical.

In the present invention, the content of carbon black in the toner particles must be in the range of 2 to 6% by weight. When the content is lower than the above range, a region where the carbon black is not present in the toner particles increases, so that a difference occurs between the transmittance of the long wavelength light and the transmittance of the short wavelength light. As a result, a brown-red color tone is developed in the developed black image, and good black reproducibility cannot be obtained. If it is higher than the above range, the optical density of the toner image does not change in a linear relationship, and good tone reproducibility cannot be obtained.

[0009] The carbon black has a pH
However, those having a range of 7.0 to 9.0 are preferably used. When the pH deviates from the above range, the environmental stability of charging of the toner when the toner is formed tends to decrease, and
There is a problem that the fixing roll deteriorates quickly.

In controlling the development amount of the toner particles of the present invention as described below, the absolute value of the average charge amount is in the range of 10 to 50 μC / g, particularly 20 to 40 μC / g.
It is preferably in the range of g.

In the toner of the present invention, when the average primary particle diameter and the content of carbon black are in the above ranges, the development amount of the toner image and the image density change linearly,
The black reproducibility (color rendering) is also good, and good gradation recording can be performed. However, as a result of experiments, it was found that the primary particle diameter and the content of carbon black in the toner particles and the development amount latitude were different. Has the following relationship. That is, the image density ID = 1.2, which is the area where the visual perception is most likely to change the density as the reproduction density area of the halftone image.
In the range of ~ 1.7, the latitude of the development amount required to obtain an image density in the range becomes smaller as the average primary particle diameter of carbon black becomes smaller and as the content thereof becomes larger, and on the other hand, the carbon content becomes smaller. The larger the average primary particle size of the black is, and the smaller the content is, the wider the black becomes. In other words, the smaller the inclination of the straight line, the larger the latitude required for the development amount. The larger this latitude is, the easier it is to reproduce the gradation. That is, the tolerance for other factors for controlling the development amount is increased. In the toner of the present invention, in order to further ensure the reproducibility of halftones and perform good gradation recording, the average primary particle diameter and content of carbon black are determined when the toner particles are developed using toner particles. Image density (I
It is preferable that the inequalities (1) and (2) be satisfied between D) and the development amount (TMA), and that the image density (ID) be adjusted so as to be in the range of the inequality (3). found.

The case will be described with reference to the drawings.
FIG. 1 is a graph showing the relationship between the image density and the development amount.
In the figure, a straight line 1 represents an image density (ID) and a development amount (TMA).
Shows a case where ID = 8/3 (TMA) +4/5, specifically, the average primary particle diameter is 35 mμ.
This corresponds to the case where the toner particles containing 6% by weight of carbon black (m) are used (the toner of Example 1). The straight line 2 has an ID = 5/3 (TMA) +1/2
Specifically, the case where toner particles containing 2% by weight of carbon black having an average primary particle diameter of 47 m μm are used (the toner of Example 2) corresponds to this case. That is, in the present invention, in order to further ensure the reproduction of good tone recording, the relationship between the image density and the development amount must be within the masked area of FIG.
And the straight line 2 and the amount of carbon black to be contained in the toner particles and the average primary particle diameter are adjusted so as to fall within the range of 1.2 to 1.7, which is the image density most easily perceived visually. There is a need to.

Referring to FIG. 1 more specifically,
If the average primary particle diameter of the carbon black is smaller than 35 m μm and the content exceeds 6% by weight, development for reproducing the image density of 1.2 to 1.7 after fixing necessary for gradation recording is performed. The amount of latitude is reduced. Further, even when the content of carbon black is within the range of 2 to 6% by weight, if the average primary particle size is smaller than 35 mμm, a reddish brown color is developed. On the other hand, when the average primary particle diameter of the carbon black is larger than 50 μm and the content is smaller than 2% by weight, the image density after fixing required for gradation recording is 1.2 to 1.7. Therefore, there is a problem that the image thickness after fixing becomes large and the transfer paper curls.

The factors that control the development amount of toner particles include, when viewed from the copying machine side, the latent image potential of a halftone dot, the developing bias value of the developing device, the distance between the developing device and the latent image potential, and the like. The factors seen from the developer side include the average charge amount of the toner particles, the toner density expressed by toner weight / (toner + carrier) weight in the case of a two-component developer composed of toner and carrier, In the case of a one-component developer,
For example, the amount of toner transported. Therefore, the development amount cannot be controlled simply by controlling only the toner particles, but as shown in FIG. 1, when the toner particles of the present invention are used, the development amount is approximately 0.15 to 0.72. Good tone reproducibility can be obtained within the range of values and when the image density by the Macbeth densitometer when the developed toner image is transferred and fixed is in the range of 1.2 to 1.7.

As the binder resin in which the carbon black is dispersed, any known resin can be used. For example, styrene, chlorostyrene,
Styrenes such as vinyl styrene; monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate; methyl acrylate, ethyl acrylate, and butyl acrylate Esters of α-methylene aliphatic monocarboxylic acids such as dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate; vinyl methyl ether, vinyl ethyl ether, Examples include vinyl ethers such as vinyl butyl ether; and homopolymers or copolymers of vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and vinyl isopropenyl ketone. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, and wax can be used.

In the present invention, a charge controlling agent such as a metal salt of salicylic acid, a metal-containing azo compound, nigrosine and a quaternary ammonium salt, an anti-offset agent such as a low-molecular-weight propylene, a low-molecular-weight polyethylene, and a wax are contained in the binder resin. Other known components such as a fixing aid can be added. In addition, external additives such as a fluidizing agent such as silica, titania, and alumina, a cleaning aid such as polystyrene fine particles, polymethyl methacrylate fine particles, and polyvinylidene fluoride fine particles or a transfer aid can be used.
In particular, hydrophobic silica having a primary particle size of 5 nm to 30 nm is preferably used. The black toner of the present invention is obtained by melting and kneading the above-described carbon black with a binder resin, and additives added as necessary, using a Banbury mixer, a kneader, a continuous mixer, a roll mill, an extruder, and the like. It can be manufactured by crushing and classifying with a means such as a mill. At this time, the average particle diameter of the black toner is 4 to 12 μm
It is necessary to classify so as to be within the range. Preferably 5
10 to 10 μm. When the average particle size of the black toner is out of the above range, the granularity is deteriorated, and the image tends to be grainy and the image quality tends to be reduced.

[0017]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, "part" represents "part by weight".

Example 1 Bisphenol A type polyester resin 94 parts (Tg = 65 ° C., Tm = 105 ° C., Mn = 3000, Mw = 10000) Carbon black (Asahi # 60HMAF, manufactured by Asahi Carbon Co., Ltd.) 6 parts Primary particle diameter 35 mμm Specific surface area 49 m ^{2 /} g, pH 7.0) The above components were melt-kneaded with an extruder, cooled, and then pulverized with a jet type pulverizer (PJM) to a particle size of about 4.0 to 12.0 μm. Machine (TC-25
Using a mold (manufactured by Nisshin Flour Milling Co., Ltd.) so as to obtain a particle size distribution d90 / d10 of 3.2 or less (measured by Microtrac, manufactured by Nikkiso Co., Ltd.) to obtain a black toner having a particle diameter of 7 μm. A silica fine powder (R8
12, manufactured by Nippon Aerosil Co., Ltd.) and 1.5 parts with respect to 100 parts of the toner, and mixed with a Henschel mixer. 6 parts of this toner was mixed with 100 parts of a silicon-coated carrier having an average particle diameter of 50 μm in a V blender for 20 minutes to obtain a developer. The charge amount at this time is −30 μC / g
Met. Using the above developer, a digital copier (FX5
800 remodeled machine, manufactured by Fuji Xerox Co., Ltd.), the development amount of the solid image was adjusted to be 0.15 and 0.34 mg / cm ² , and the unfixed image was formed using a single-side coated paper as copy paper Created. The unfixed image on the copy paper was heated by a heat roll-type heat fixing machine wound with silicone rubber at a heat roll temperature of 160 ° C., a pressure roll temperature of 160 ° C., and a fixing speed of 160 mm / sec. And the image density was 1.2 and 1.7, respectively.
(RD914 Macbeth densitometer) to obtain a fixed image.

The obtained sample having a fixed image was evaluated for color characteristics at a wavelength of 380 nm to 700 nm using a spectrophotometer (color pack system, manufactured by Shimadzu Corporation). The color characteristics are measured using a C light source (sunlight), an A light source (incandescent lamp), and a D65 light source (standard light) as light sources, and evaluated by the following formula based on color measurement values (L ^* a ^* b ^* ). did. X = | A light source a ^* -C light source a ^* | Y = | A light source b ^* -C light source b ^* | where X is the absolute value of the difference between the a ^* value of the A light source and the a ^* value of the C light source. are shown, Y denotes the absolute value of the difference between b ^* values and b ^* values of C light source a source. a ^* and b ^* indicate chromaticity coordinate values.
L ^* indicates saturation. Note that, as a result of the calculation, if X = 1.3 or less and Y = 0.5 or less, it means that the color tone does not change due to the change of the light source, and that the gray balance is good. As a result, X and Y are 1.0 or less and 0.
5 or less.

Example 2 98 parts of bisphenol A type polyester resin (Tg = 65 ° C., Tm = 105 ° C., Mn = 3000, Mw = 10000) Carbon black (# 25, manufactured by Mitsubishi Kasei Corporation, 2 parts, primary particle diameter 47 mμm, (Specific surface area: 40 m ^{2 /} g, pH 8.0) A black toner having a particle diameter of 7 μm was obtained in the same manner as in Example 1, and a fixed image was obtained in the same manner as in Example 1. The development amounts of the solid image were 0.42 and 0.72 mg / cm ² , and the image densities were 1.2 and 1.7, respectively. The color characteristics were evaluated as in Example 1. As a result, X and Y were 0.5 or less and 0.3 or less, respectively. The charge amount was −33 μC / g.

Example 3 100 parts of styrene-butyl acrylate copolymer (80/20) (Tg = 65 ° C., Mn = 15000, Mw = 35000) Carbon black (produced by Asahi Carbon Co., 2 parts Asahi # 60HMAF) (primary) Particle size 35 mμm Specific surface area 49 m ^{2 /} g, pH 7.0 (hereinafter referred to as carbon black A) Charge control agent (Bontron-E-88, 1.0 part Orient, manufactured by Kagaku) The above components are melt-kneaded with a Banbury mixer. After cooling, the mixture was pulverized with a jet pulverizer (PJM) to a particle size of about 4.0 to 12.0 μm, and then classified using a classifier (TC-25).
Using a mold (manufactured by Nisshin Flour Milling Co., Ltd.) so that the particle size distribution d90 / d10 becomes 3.2 or less (measured by Microtrac, manufactured by Nikkiso Co., Ltd.) to obtain a black toner having a particle diameter of 9 μm.

To the above toner, silica fine powder (R812, manufactured by Nippon Aerosil Co., Ltd.) as an external additive was added to the toner 100.
1.5 parts was added per part and mixed with a Henschel mixer. 6 parts of the toner was mixed with 100 parts of a silicon-coated carrier having a particle size of 50 μm in a V blender for 20 minutes to obtain a developer. Using this developer, a copier (F
X5800 remodeled machine, manufactured by Fuji Xerox Co., Ltd.) to increase the development amount of the solid image from 0.3 mg / cm ^{2 to} 1.4 mg / c.
The unfixed image was created by using the coated paper coated on one side as copy paper to adjust by shaking in the range of m ² . This copy paper is gross 60% or more (measured at 75-75 degrees) with an offline soft roll fixing machine (3GM-260).
TYPE, manufactured by Murakami Color Research Laboratory Co., Ltd.) and the image density was adjusted to 1.0 to 2.0 (RD914
(Macbeth densitometer). When the development amounts of the solid image were 0.41 and 0.65 mg / cm ² , the image densities were 1.2 and 1.7, respectively. In addition, in the sensory evaluation of the fixed image, good black coloring was exhibited, and it was confirmed that the fixed image was a good fixed image. The color characteristics of the obtained sample having a fixed image were evaluated in the same manner as in Example 1. As a result, X and Y were 1.3 or less and 0.5 or less, respectively.

Examples 4 and 5 Black toners were prepared in the same manner as in Example 3, except that the content of carbon black was changed to 3 parts (Example 4) and 6 parts (Example 5), respectively. Similarly, the image density and the color characteristics were evaluated. As a result, in Example 4, the development amount of the solid image was 0.35 and 0.55 m.
At g / cm ² , the image densities were 1.2 and 1.7, respectively. In Example 5, when the development amounts of the solid image were 0.23 and 0.36 mg / cm ² ,
The image densities were 1.2 and 1.7, respectively. Further, X and Y were 1.2 or less and 0.5 or less in Example 4, respectively, and were 1.0 or less and 0.5 or less in Example 5, and the gray balance was good.

Comparative Example 1 A toner was produced in the same manner as in Example 3 except that the amount of carbon black in Example 3 was changed to 10 parts, and image density and color characteristics were evaluated in the same manner as in Example 1. Was. As a result, when the development amount of the solid image was 0.30 mg / cm ² , the image density was 1.7, and when the image density was 1.2, no measurement was possible. X and Y are each set to 0.
It was 8 or less and 0.5 or less, indicating that the gray balance was good.

Comparative Examples 2 to 5 Instead of carbon black A in Example 3, carbon black (MA8, manufactured by Mitsubishi Kasei Co., Ltd., having a primary particle diameter of 24) was used.
Emumyuemu, except for using a specific surface area 138m ² /g,pH2.5), to produce a toner in the same manner as in Example 3, the image density in the same manner as in Example 1, the evaluation of color characteristics was performed.
As a result, the image density corresponding to the development amount of the solid image was as shown in Table 1, and X and Y were 3.0 or less and 1.0 or less in Comparative Example 2, respectively. In Comparative Example 2, the content of carbon black was 3
Parts (Comparative Example 3), 5 parts (Comparative Example 4), and 10 parts (Comparative Example 5), except that black toner was manufactured in the same manner.
The same evaluation was performed. As a result, in Comparative Example 3, 2.0 or less and 0.8 or less, and in Comparative Example 4, 1.0 or less and 0.5 or less.
Hereinafter, in Comparative Example 5, the values are 0.5 or less and 0.4 or less,
The gray balance was sometimes poor.

[Table 1]

Comparative Example 6 Bisphenol type polyester resin 100 parts (Tg = 65 ° C., Mn = 4000, Mw = 10000) Carbon black (REGAL330, 2 parts, manufactured by Cabot Corporation, primary particle diameter 25 mμm, specific surface area 94 m ² / g, pH 8) .0) The above components were melt-kneaded by a Banbury mixer, cooled, and then pulverized by a jet type pulverizer (PJM) to a particle size of about 4.0 μm to 12.0 μm.
5 type, manufactured by Nisshin Flour Milling Co., Ltd.) and the particle size distribution d90 / d10
Was 3.2 or less (measured by Microtrac, manufactured by Nikkiso Co., Ltd.) to obtain a black toner having a particle diameter of 9 μm. Image density and color characteristics were evaluated in the same manner as in Example 1. As a result, the image density with respect to the development amount of the solid image was as shown in Table 2, where X and Y were 3.0 or less and 0.9 or less, respectively, and there were cases where gray balance was poor.

Comparative Examples 7 to 9 In the same manner as in Comparative Example 6, except that the content of carbon black was changed to 3 parts (Comparative Example 7), 6 parts (Comparative Example 8) and 10 parts (Comparative Example 9), respectively. To produce a black toner, and the image density and color characteristics were evaluated in the same manner. As a result, the image density corresponding to the development amount of the solid image is
As shown in Table 2, X and Y were 2.0 or less and 0.8 or less in Comparative Example 7, respectively.
The values were 1.0 or less and 0.5 or less, and in Comparative Example 9, the values were 0.5 or less and 0.4 or less.

[Table 2]

Examples 6-7 Bisphenol type polyester resin 110 parts (Tg = 65 ° C., Tm = 1.060178, Mn = 4000, Mw = 10000) Carbon black (# 25, manufactured by Mitsubishi Kasei Co., 3 or 6 parts primary) particle size 47Emumyuemu, melt-kneaded by an extruder a specific surface area 40m ² /g,pH8.0) above components, after cooling, a jet type pulverizer (PJM), ground to a particle size of about 4.0~12.0μm And a classifier (TC-25
Using a mold (manufactured by Nisshin Flour Milling Co., Ltd.) so that the particle size distribution d90 / d10 becomes 3.2 or less (measured by Microtrac, manufactured by Nikkiso Co., Ltd.) to obtain a black toner having a particle diameter of 9 μm. The content of carbon black was 3 parts in Example 6 and 6 parts in Example 7. Example 1
The image density and the color characteristics were evaluated in the same manner as described above. As a result, the image density corresponding to the development amount of the solid image is shown in Table 3.
X and Y are respectively the same as in Example 6.
Were 1.2 or less and 0.5 or less, and Example 7 was 1.0 or less and 0.5 or less, and the gray balance was good. In addition, in the sensory evaluation of the fixed image, good black coloring was exhibited, and it was confirmed that the fixed image was a good fixed image.

[Table 3]

Table 4 below summarizes the overall determination results of color rendering, density, gradation, and image for the above Examples 1 to 7 and Comparative Examples 1 to 9. The evaluation was based on the following criteria. 〇: good △: somewhat good ×: bad

[0030]

[Table 4]

Example 8 Bisphenol type polyester resin (Tg = 62 ° C., T
m = 110 ° C., Mn = 4000, Mw = 10000), using carbon black having a primary average particle diameter of 35 μm, and blending so that the concentration of carbon black becomes 3 parts. A black toner having an average particle size of 8 μm was obtained. The evaluation of the image density was performed in the same manner as in Example 1. As a result, the image density corresponding to the development amount of the solid image is as shown in Table 5.

Example 9 Bisphenol type polyester resin (Tg = 62 ° C., T
m = 110 ° C., Mn = 4000, Mw = 10000) and carbon black having a primary average particle size of 45 μm was blended so that the concentration of the carbon black was 3 parts. A black toner having an average particle size of 8 μm was obtained. The evaluation of the image density was performed in the same manner as in Example 1. As a result, the image density corresponding to the development amount of the solid image is as shown in Table 5.

Comparative Example 10 Bisphenol type polyester resin (Tg = 62 ° C., T
m = 110 ° C., Mn = 4000, Mw = 10000), using carbon black having a primary average particle size of 25 μm, and blending the carbon black so that the concentration becomes 3 parts. A black toner having an average particle size of 8 μm was obtained. The evaluation of the image density was performed in the same manner as in Example 1. As a result, the image density corresponding to the development amount of the solid image is as shown in Table 5.

Comparative Example 11 Bisphenol type polyester resin (Tg = 62 ° C., T
m = 110 ° C., Mn = 4000, Mw = 10000) with a primary average particle size of 50 μm, a specific surface area of 35 m ² / g, p
Using H8.0 carbon black, the carbon black was blended such that the concentration of the carbon black became 3 parts, and a black toner having an average particle diameter of 8 μm was obtained in the same manner as in Example 1. The image density and color characteristics were evaluated in the same manner as in Example 1. As a result, the image density corresponding to the development amount of the solid image is shown in Table 5
X was 0.8 or less and Y was 0.5 or less. The charge amount when an image defect occurred was measured to be -10 μC / g.

[Table 5]

Examples 8 and 9 and Comparative Examples 10 and 11
1.5 parts of hydrophobic silica fine powder (R812 manufactured by Nippon Aerosil Co., Ltd.) was added as an external additive to the black toner obtained in the above, and mixed with a Henschel mixer. Table 6 shows the environmental stability of charge, the charge retention, the color tone, and the overall determination result of this black toner. table
Among them, ○ means good and × means bad. The evaluation method of the color tone is the same as that of the first embodiment . The following methods were used to evaluate the environmental stability of charge and the charge retention.

(Environmental stability) Carrier diameter 40 μm to 5
Approximately 25 g of developer having a toner-to-carrier ratio of 6 to 94 using a ferrite carrier coated with 0 μm silicon.
The developer is placed in a 100 ml glass reagent bottle, the developer is mixed for 12 hours under high temperature and high humidity (30 ° C./85% RH), and the charge amount of the toner is measured at room temperature. Similarly, the toner is mixed under low temperature and low humidity (10 ° C./15% RH), and the charge amount of the toner is measured. At this time, the ratio between the charge amount under high temperature and high humidity and the charge amount under low temperature and low humidity was determined. In addition, a sample having a ratio of less than 1/2 and having a reverse polarity toner was evaluated as Δ.

(Charge Maintenance Property)
T / C (toner / carrier ratio) is 8% using a ferrite carrier coated with silicon of 0 μm to 50 μm.
FX50 manufactured by Fuji Xerox Co., Ltd.
Make a continuous copy with a 30M / C digital remodeling machine,
A running test under a 0 ° C./40% RH environment, that is, an image defect, that is, a case where fogging and image omission of a back were observed, was evaluated for charge retention. Here, the charge amount of Example 8 is −30 μC / g, and the charge amount of Example 9 is
−30 μC / g, and the charge amount of Comparative Example 10 was −31 μC / g.
g and Comparative Example 11 had a charge amount of −30 μC / g.
The evaluation was based on the following criteria. 〇: No image defect was observed even after 50,000 continuous copies. Δ: No image defect was observed after 30,000 continuous copies.

[0038]

[Table 6]

The above black toner was analyzed in terms of safety. That is, using a monocyclic aromatic organic solvent, Soxhlet was subjected to dry distillation for 12 hours and concentrated to analyze. As a result, carbon black having a particle size of 50 μm or more could not be used because of a high impurity concentration.

[0040]

The black toner for a color digital copying machine according to the present invention exhibits good area gradation, does not change the color tone even when the light source is changed, and is suitable for producing an image showing faithful black reproducibility. Useful.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the relationship between image density and development amount during development.

[Explanation of symbols]

1 ... ID = 8/3 (TMA) +4/5 straight line, 2 ... ID
= Straight line of 5/3 (TMA) + 1/2.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 9/09

Claims (4)

(57) [Claims] 1. A color digital copying machine characterized in that toner particles contain, as a colorant, 2 to 6% by weight of carbon black having an average primary particle diameter of 35 to less than 50 m.mu.m in a binder resin. Black toner. 2. The following inequalities (1) and (2) are set between the image density (ID) and the development amount (TMA) when the toner is developed using toner particles. 2. The black toner for a color digital copying machine according to claim 1, wherein the black toner is set so as to be satisfied and to have an image density (ID) in the range of the following inequality (3). ID ≦ 8/3 (TMA) +4/5 (1) ID ≧ 5/3 (TMA) +1/2 (2) 1.2 ≦ ID ≦ 1.7 (3) 3. The black toner for a color digital copying machine according to claim 1, wherein the absolute value of the average charge amount of the toner particles is in a range of 10 to 50 μC / g. 4. The black toner for a color digital copying machine according to claim 1, wherein the absolute value of the average charge amount of the toner particles is in a range of 20 to 40 μC / g.