JP2703917B2 - Two-component developer and image forming method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a two-component developer useful for electrophotography for forming a color image and an image forming method.

(Background technology)

Conventionally, for electrophotography, U.S. Pat.
No. 691, JP-B-42-23910, JP-B-43-24748, etc., a uniform electrostatic charge is applied to the photoconductive layer by corona discharge, and an The latent image is formed by exposing the exposed portion to eliminate the electric charge in the exposed portion. The development is carried out by attaching a fine powder electroconductive substance, a so-called toner, on the obtained electrostatic latent image.
The toner is attracted to the electrostatic latent image according to the amount of charge on the photoconductive layer, and forms a toner image having a density. This toner image is transferred to a support surface such as paper or cloth as necessary, and is permanently fixed to the support surface by using appropriate fixing means such as heating, pressing, solvent treatment, or overcoating. If it is desired to omit the toner image transfer step, the toner image can be fixed on the photoconductive layer.

In the development of the electrostatic latent image, the toner is mixed with a carrier having relatively large particles and used as an electrophotographic developer. The compositions of both the toner and the carrier are chosen such that the toner has a polarity opposite to the charge on the photoconductive layer due to mutual contact friction. As a result of the contact friction between the two, the carrier electrostatically attaches the toner to the surface, transports the toner as a developer in the developing device, and supplies the toner onto the photoconductive layer.

There are many known methods for developing a developer. Cascade developing method described in U.S. Pat.No. 2,618,552, magnetic brush method described in U.S. Pat.No. 2,874,063, U.S. Pat.
JP-A-62-63970 discloses a touchdown method described in JP-A-47-63970, and a developing method in which a bias electric field comprising an AC component and a DC component is applied between a developer carrier (developing sleeve) and a photoconductive layer. . There is a so-called J / B development method.

A typical method is a magnetic brush method. That is, magnetic particles such as steel and ferrite are used as the carrier, and the developer including the toner and the magnetic carrier is held by a magnet, and the developer is arranged in a brush shape by the magnetic field of the magnet. When the magnetic brush comes into contact with the electrostatic latent image surface on the photoconductive layer, only the toner is attracted from the brush to the electrostatic latent image to perform development.

When a large number of continuous copies are made with an electronic copying machine using a two-component developer, a clear image with good image quality can be obtained at the initial stage, but after tens of thousands of copies, the fogging edge effect is remarkable, and The resulting image is poor in tonality and sharpness.

In color copying using a chromatic toner, continuous tone is an important factor affecting image quality. Is greatly impaired. For example, a pseudo contour due to the edge effect is formed near the actual contour, thereby deteriorating copy reproducibility including color reproducibility in color copying. Also, the image area used in conventional black-and-white copying is 10% or less, and the image is almost a line image part such as a letter, a document, a report, etc., whereas in the case of color copying, the image area is at least 20% or more, and solid images having gradation such as photographs, catalogs, maps, and paintings occupy a considerable frequency or area.

When continuous copying is performed using such a document having a large image area, a copy having a high image density is usually obtained in the initial stage, but the toner supply to the two-component developer cannot be completed in time, and the density decreases. In some cases, the replenishment toner and the carrier are mixed in an insufficiently charged state, causing fogging, and a partial increase or decrease in the toner density (indicating the mixture ratio of the toner and the carrier) on the developing sleeve. There is a tendency that blurring of the image and uniformity of the density in the image cannot be obtained.

This is because the amount of toner included in the developer (that is, the toner concentration) is too low, or the rapid rise of triboelectric charging between the replenishment toner and the carrier in the two-component developer is poor, and the uncontrollability is insufficient. It is considered that such insufficient development causes fogging due to the fact that the toner having the charge amount participates in the development. As a color developer, the ability to always output a high-quality image even in continuous copying of a document having a large image area is essential. Conventionally, in order to cope with an original having a large image area and a very large amount of toner consumption, improvement of the developing device rather than improvement of the developer itself has been dealt with more. That is,
To increase the chance of the developing sleeve contacting the electrostatic latent image,
The peripheral speed of the developing sleeve is increased, or the size of the developing sleeve is increased.

Although these measures increase the developing ability, they cause contamination inside the apparatus due to toner scattering from the developing device, and significantly limit the life of the device due to overload on the driving of the developing device. Further, in some cases, a large amount of developer is charged into the developing device in order to compensate for the lack of developing ability of the developer. As in the case described above, this results in an overload on the driving of the developing device, which is not very preferable.

As an indication of the average particle size and particle size distribution of the carrier, JP-A-51-3238, JP-A-58-144839,
There is JP-A-61-204646. JP-A-51-3238 refers to a rough particle size distribution. However, it does not specifically disclose the magnetic properties closely related to the developability of the developer and the transportability in the developing device. Further, all of the carriers in the examples have about 250% by weight or more of about 80% by weight or more, and have an average particle size of 60 μm or more.

Further, JP-A-58-144839 discloses only the average particle size, and mentions the amount of fine powder affecting carrier adhesion to a photoreceptor and the amount of coarse powder affecting image sharpness. The distribution is not described in detail in consideration of the characteristics of color copying. Further, Japanese Patent Application Laid-Open No. 61-204646 discloses a combination of a copying machine and an appropriate developer as the gist of the invention, and does not specifically describe the particle size distribution and magnetic properties of the carrier. Furthermore, it does not even disclose why the developer is effective in the copying machine.

Japanese Patent Application Laid-Open No. 49-70630 describes the magnetic force of the carrier, but these are iron materials having a higher specific gravity than ferrite as a carrier material, and have a high saturation magnetism. . These iron powder carriers have been widely used in the past, but because of their large specific gravities, the copying apparatus is liable to increase in weight and overload of the driving torque, and is greatly dependent on the environment.

Further, the ferrite carrier described in JP-A-58-23032 is for a material having a large number of porous holes, and such a carrier is liable to have an edge effect and has poor durability. It has been found to be unsuitable as a color carrier.

Until now, there has been a demand for a developer capable of continuously copying an image having a large image area with a small amount of developer and satisfying the characteristic characteristic of color copying in which an edge effect does not occur even after durability. Although studies have been made on developers and carriers, most of them have been proposed in consideration of black-and-white copying, and very few have been proposed for full-color copying. In addition, a carrier that has the ability to continue copying an image with an image area of 20% or more, which is almost a solid image, to reduce the edge effect, and to maintain the uniformity of image density in one copy. Long awaited.

The present inventors have intensively studied a carrier most suitable for color copying, and as a result, have reached the present invention.

[Object of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a two-component developer and an image forming method which do not cause a decrease in image density and no blurring even when a color original having a large image area is continuously copied.

SUMMARY OF THE INVENTION An object of the present invention is to provide a two-component developer and an image forming method capable of obtaining a color copy having a suppressed edge effect even after durability by repeated copying.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a two-component developer and an image forming method capable of obtaining a rapid rise in triboelectric charging between a toner and a carrier.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a two-component developer and an image forming method which have less environmental dependency of triboelectric charging.

An object of the present invention is to provide a two-component developer having good transportability in a developing device.

[Summary of the Invention]

Specifically, the present invention relates to a two-component developer used in an image forming apparatus having at least a photosensitive drum and a rotary developing unit having a plurality of developing devices, wherein the two-component developer is A chromatic toner containing at least a coloring resin and a colorant; a fluidity improver; an average particle size of 20 to 60 μm; a fine powder content of 350 mesh or less being 30% by weight or less; The amount of fine powder is 20% by weight or less, and the amount of coarse powder of 250 mesh or more is 10%.
% Or less, the saturation magnetization is 55 to 75 emu / g with respect to an applied magnetic field of 3000 Oe, and the residual magnetization is 10 emu.
/ g or less, and a resin-coated magnetic carrier having a coercive force of 10e or less.

Furthermore, the present invention forms an electrostatic latent image on a photosensitive drum, and uses a two-component developer magnetic brush provided in a rotary developing unit having a plurality of developing devices to convert the electrostatic latent image by a reversal developing method. An image forming method for forming a color toner image by developing, respectively, wherein the two-component developer has a chromatic toner containing at least a binder resin and a colorant, a fluidity improver, and an average particle diameter. 20-60μ, the amount of fine powder of 350 mesh or less is 30% by weight or less, the amount of ultrafine powder of 400 mesh or less is 20% by weight or less, and the amount of coarse powder of 250 mesh or more is 10%.
% Or less, the saturation magnetization is 55 to 75 emu / g with respect to an applied magnetic field of 3000 Oe, and the residual magnetization is 10 emu.
/ g or less, and a resin-coated magnetic carrier having a coercive force of 10e or less.

The resin-coated magnetic carrier used in the present invention is different from a conventionally known carrier in that the average particle size is small, the particle size distribution is narrow, and the carrier is magnetically cut. It is a uniform small-diameter carrier with a uniform diameter. Therefore, the rise of the triboelectric charging property with the toner is also preferably improved. Further, since the carrier is small and homogeneous, the amount of toner having good chargeability that can be included in the developer is much larger than that of a carrier having a broad particle diameter. When a broad carrier having a particle size is used, the toner mixed with the fine carrier is
Sufficient charging is difficult to obtain, and the phenomenon that the carrier adheres to the photoreceptor together with the fine powder carrier and the toner during development is caused. Further, the toner mixed with the coarse powder carrier often has a charge amount that is too high in terms of charge, and is often difficult to develop.

The ultrafine powder of 400 mesh or less is 20% by weight or less, preferably 16% by weight or less. If it exceeds 20% by weight, it tends to hinder carrier adhesion and smooth triboelectric charging with the toner, thereby promoting the edge effect. When the amount is 20% by weight or less, the frictional charge between the carrier and the toner is hardly affected.

It has been found that the amount of fine powder of 350 mesh or less is a factor defining the rise of triboelectric charging with the toner. If the content exceeds 30% by weight, the amount of ultrafine powder of 400 mesh or less will inevitably increase, resulting in a broad particle size distribution.
The rise of the charge of the toner is remarkably deteriorated, and the edge effect is increased. In the present invention, it is preferably at most 25% by weight, more preferably at most 20% by weight.

In addition, the amount of coarse powder having a carrier amount of 250 mesh or more is closely correlated with the sharpness of the image. If it exceeds 10% by weight, the scattering of toner to non-images increases, and the resolution of the image decreases. In addition, it becomes easier for the roughness to become apparent. Therefore, the content of 250 mesh or more is 10% by weight or less, preferably 7% or less.
%, More preferably 5% by weight or less. The average particle size of the carrier is preferably from 20 to 60μ, more preferably from 30 to 56μ. When the average particle diameter is less than 20 μm, the image density is reduced due to the toner gap and the carrier adheres to the photoreceptor, and the carrier having the average particle diameter exceeding 60 μ deteriorates the fine line reproducibility of color copying.

The magnetic properties of the carrier greatly affect the developing properties and transport of the developer. Especially in color copying, as mentioned above, the uniformity and gradation of the image are emphasized, so if the saturation magnetization exceeds 75 emu / g (for an applied magnetic field of 3000 ersted), the photoreceptor during development The brush-like spikes of the magnetic brush composed of the toner and the magnetic carrier on the developing sleeve that contains the magnet facing the electrostatic latent image above are tightly tightened, reproducing the gradation and halftone Gets worse. On the other hand, if it is less than 55 emu / g, it becomes difficult to hold the toner and the carrier on the developing sleeve satisfactorily, and the problem that the fog and the toner scattering become worse easily occurs. Further, if the remanent magnetization and the coercive force of the magnetic carrier are too high, good transportability of the developer in the developing device is hindered, and image defects such as blurring and uneven density in a solid image are liable to occur. Will be reduced. Therefore, unlike ordinary black-and-white copying, in order to maintain developability in color copying, the residual magnetization is 10 emu / g or less, preferably 5 emu / g or less, and the coercive force is 10 e or less (3000 ersted, applied magnetic field). It is important that it is preferably 6.0e or less.

Examples of the binder resin of the chromatic toner include styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, and styrene-acrylic acid. Styrene-acrylate resin such as phenyl copolymer and bisphenol-based polyester resin shown below are preferably used.

In particular, (Wherein R is an ethylene or propylene group, x, y
Is an integer of 1 or more, respectively, and the average value of x + y is 2 to 10. A) a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof, such as fumaric acid, maleic acid,
A polyester resin obtained by at least co-condensation polymerization of maleic anhydride, phthalic acid, terephthalic acid, trimellitic acid, pyrrolimetic acid, etc. is more preferable since it has a sharp melting property.

As a carrier used in the present invention, a resin ferrite is used in which a magnetic ferrite formed of an oxide of a metal such as iron, nickel copper, zinc, cobalt, manganese, chromium, or a rare earth is used as a carrier core, and the carrier core is coated with a resin. A magnetic ferrite carrier is used. Preferably, ferrite of an oxide of a metal selected from iron, zinc, copper, nickel, and cobalt is more preferable in terms of magnetic properties.

As a method of coating the carrier core with the resin, a method of dissolving or suspending the resin in a solvent, applying it, and attaching it to the carrier core particles, a method of simply mixing the resin powder and the carrier core particles, and the like are exemplified. Applicable.

Examples of the coating resin on the carrier core surface include polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin,
Polyester resin, styrene resin, acrylic resin,
It is appropriate to use one or more of polyamide, polyvinyl butyral, amino acrylate resin and the like.

The amount of the compound to be treated may be appropriately determined so that the carrier satisfies the above conditions, but is generally preferably 0.1 to 30% by weight (preferably 0.5 to 20% by weight) based on the carrier of the present invention.

In the present invention, a particularly preferred embodiment is a coated ferrite carrier whose surface is coated with two or more polymers including at least one fluorine-containing polymer. Such coating materials include, for example, polyvinylidene fluoride and styrene-methyl methacrylate resin; polytetrafluoroethylene and styrene-methyl methacrylate resin, fluorine-based copolymer and styrene-based copolymer; 10-20: 80, preferably 7
It is a mixture of 0:30 to 30:70 weight ratio, 0.01 to
Those coated with 5% by weight, preferably 0.1 to 1% by weight are mentioned. Particularly preferably, the fluorine-based copolymer is vinylidene fluoride-tetrafluoroethylene copolymer (10:90 to 90:10 (molar ratio)), and the styrene-based copolymer is styrene-acrylic acid 2 -Ethylhexyl-methyl methacrylate (20-60: 5-30: 10-50) combinations are exemplified.

As the ferrite, a ternary ferrite of Cu-Zn-Fe is particularly preferable.

When preparing a two-component developer by mixing with a color toner, the mixing ratio is 5.0% as the toner concentration in the developer.
Good results are usually obtained at weight percentages of from 15% to 15%, preferably from 6% to 13%. If the toner density is less than 5.0%, the image density is low and it becomes impractical. If the toner density is more than 15%, fog and scattering in the machine are increased, and the useful life of the developer is easily shortened.

As a colorant used when constituting a color developer together with the carrier of the present invention, as a dye, for example, CI Direct Red 1, CI Direct Red 4, CI
Acid Lead 1, CI Basic Credit 1, CI Modern Credit 30, CI Direct Blue 1, CI Direct Blue 2, CI Acid Blue 9, CI Acid Blue 15, C.
I. Basic Blue 3, CI Basic Blue 5, CI Modant Blue 7, and the like.

Pigments include Naphthol Yellow S and Hansa Yellow
G, permanent yellow NCG, permanent orange GTR,
There are pyrazolone orange, benzidine orange G, permanent thread 4R, calcium phosphate calcium salt, brilliant carmine 3B, fast biolett B, methyl biolet lake, phthalocyanine blue, fast sky blue, indanthrene blue BC and the like.

Preferably, disazo yellow, insoluble azo, copper phthalocyanine are used as pigments, and basic dyes and oil-soluble dyes are suitable as dyes.

Particularly preferably, CI Pigment Yellow 17, CI Pigment Yellow 15, CI Pigment Yellow 13, CI Pigment Yellow 14, CI Pigment Yellow 12, CI Pigment Red 5, CI Pigment Red 3, CI Pigment Red 2, CI Pigment Red 6, CI Pigment Red
7, CI Pigment Blue 15, CI Pigment Blue 16, a copper phthalocyanine pigment having 2 to 3 carboxybenzamide methyl groups or a phthalocyanine skeleton having 2 to 3 carboxybenzamide methyl groups having a structural formula (1) shown below. And copper phthalocyanine pigments which are substituted Ba salts.

(Where X _{1 to} X ₄ are Or -H, and R and R 'represent an alkylene group having 1 to 5 carbon atoms. However, except in the case all of the X ₁ ~X ₄ is -H. Examples of dyes include CI Solvent Thread 49, CI Solvent Thread 52, CI Solvent Thread 109, CI Base Thread 12, CI Base Thread 1, and CI Base Thread 3b.

The method for measuring the particle size distribution in the present invention is as follows.

1. Measure about 100 g of the sample to the nearest 0.1 g.

2. Standard sieve of 100 Mesh to 400 Mesh (hereinafter referred to as sieve)
And stack them in order of size 100, 145, 200, 250, 350, 400 from the top, place a saucer on the bottom, put the sample in the top sieve and cover it.

3. This is shaken by a vibrator at 285 ± 6 horizontal revolutions per minute and 150 ± 10 impacts per minute for 15 minutes.

4. After sieving, measure the iron powder in each sieve and tray to the nearest 0.1 g.

5. Calculate to the second decimal place by weight percentage and round to the first decimal place according to JIS-Z8401.

However, the size of the sieve frame is 200 mm inside diameter above the sieve surface,
The depth from the top surface to the sieve surface is 45mm.

The sum of the weights of iron powder in each part shall not be less than 99% of the mass of the starting sample.

The average particle size is determined from the above measured particle size distribution according to the following equation.

As a measurement of the magnetic properties of the carrier, the device is a BHU-6.
A 0-type magnetization measurement device (manufactured by RIKEN) is used. About 1.0 g of a measurement sample is weighed, packed in a cell having an inner diameter of 7 mmφ and a height of 10 mm, and set in the above-mentioned apparatus.

The measurement is performed by gradually applying an applied magnetic field and changing the applied magnetic field to a maximum of 3000 Oersted. Next, the applied magnetic field is decreased, and finally a hysteresis curve of the sample is obtained on the recording paper. From this, the saturation magnetization, residual magnetization, and coercive force are obtained.

 Hereinafter, the present invention will be described in detail with reference to Examples.

Example 1 To 100 parts by weight of a polyester resin obtained by condensing propoxylated bisphenol and fumaric acid, a coloring agent and a charge control agent having the prescribed amounts shown in Table 1 were used, and yellow,
Magenta, cyan and black color toners were obtained.

The production method is that the above-mentioned formulation amounts are preliminarily mixed by a Hensiel mixer, melt-kneaded at least twice by a three-roll mill, cooled, roughly ground to about 1-2 mm using a hammer mill, and then cooled. It was pulverized to a particle size of 40 μm or less by a pulverizer using an air jet method. Furthermore, the obtained finely pulverized product is classified, 2 to 23 μm is selected so as to have the particle size distribution of the present invention, and a silica fine powder treated with hexamethyldisilazane as a fluidity improver is classified to 100.
0.5 parts by weight of an external additive was added to parts by weight to obtain a color toner.

To 8 to 12 parts by weight of these color toners, the carriers shown in Table 2 were mixed in a total amount of 100 parts by weight to prepare a developer. The carrier is a vinylidene fluoride-tetrafluoroethylene (PVDF-PTFE) copolymer (copolymer molar ratio).
8: 2) and styrene-2-ethylhexyl acrylate-
It was a coding ferrite carrier coated with a methyl methacrylate (st-2EHA-MMA) copolymer (copolymerization ratio 45:20:35) at a weight ratio of 1: 1 with a thickness of about 0.5 μm.

The developer concentration of each color toner is 9%, 8%, 1
0% and 10%.

A copy test was performed using a color electrophotographic apparatus having the OPC photosensitive drum shown in FIGS. 1 and 2 and a supply-development system.

The development and transfer of each color toner were performed in the order of magenta toner, cyan toner, yellow toner, and black toner.

An example of the replenishment-development system used in the present invention will be described. The replenishment toner sent by the supply screw 16 in the toner transport cable 4 is supplied to the developing device 2 through the toner replenishment port 15.
2 and supplied into the developing device.

When the developing device is rotated and comes to a position facing the opening drum 1, the replenishment toner is uniformly mixed with the developer within a very short time by the mixing-and-conveying screw 12, and the developer having a constant developer concentration is mixed with the developer. Become.

The developer has a constant developer amount by a developer regulating blade 14 on a developing sleeve 13 containing a magnet,
The negatively charged toner is transferred from the magnetic brush formed on the developing sleeve on the photosensitive drum by the reversal developing method at the opposite portion of the photosensitive drum 1 having the negatively charged electrostatic latent image.

In a full-color mode using this method, a full-color image faithfully reproducing the original color chart with little edge effect was obtained even after printing for 15,000 sheets using a manuscript having an image area of about 40%. Further, an image without blurring or density reduction was obtained even during continuous copying, and the conveyance in the copying machine and the detection of the developer density were good and stable. Further, a full-color image with excellent color was obtained even in an environment of low temperature and low humidity (15 ° C., 15% RH) and high temperature and high humidity (35 ° C., 85% RH). OH
Even when the P film was used, the transparency of the toner was very favorable.

Example 2 A magenta toner single color durability test was carried out using the carrier shown in the table, except that the colorant for magenta was changed to 12,0.8 parts by weight of CI base screed and 31,0.2 parts by weight of CI disperse violet. And a clear image was obtained.

Comparative Example 1 Using the carriers shown in Table 2, the colorant for cyan was changed to 6.0 parts by weight of CI Pigment Blue 15, the colorant for yellow was changed to 2.3 parts by weight of CI Disperse Yellow 54, and a document having an image area of 50% was prepared. The test was carried out in a high-temperature and high-humidity environment (32.5 ° C., 85% RH) in the same manner as in Example 1 except that it was used. As a result, an image with favorable color balance without fog was obtained. Was slightly inferior.

Example 3 Using the carriers shown in Table 2, the colorant for yellow was changed to 4.6 parts by weight of CI Pigment Yellow 13, and a durability test of a single yellow color was performed in the same manner as in Example 1. Thus, a performance having no problem in the developer mixing property was obtained.

Comparative Example 2 A test was conducted in the same manner as in Example 1 except that the carrier was changed to the carrier shown in Table 2. However, during continuous copying, the image density gradually decreased, and the gradation reproducibility was sharp.

In addition, the toner was spent on the carrier during the running, and the frictional charging ability was reduced. As a result, 80,000 sheets were scattered inside the machine, and the fiber for developer detection was contaminated, making detection impossible.

Under high temperature and high humidity, the frictional charge with the toner is remarkably reduced, and the image density of magenta becomes extremely high at 2.0 or more according to a Macbeth reflection densitometer, and fog, which is toner adhesion to non-image areas, is not practically preferable. Was something.

A full-color electronic copying machine used with reference to FIGS. 1 and 2 will be described.

The electrostatic latent image formed on the photosensitive drum 1 by an appropriate means is visualized by a developer in a developing device 2-1 attached to a rotary developing unit 2 rotating in the direction of the arrow. The developed toner is transferred by a transfer charger 8 to a transfer material held on a transfer drum 6 by a gripper 7.

Next, the rotary developing unit rotates as the second color, and the developing device 2-2 faces the photosensitive drum 1. And the developing device 2-2
The toner image is developed by the developer therein, and this toner image is also transferred onto the same transfer material as above.

Further, the third color and the fourth color are similarly performed. In this manner, the transfer drum 6 rotates a predetermined number of times while holding the transfer material, and an image of a predetermined number of colors is multiplex-transferred. The transfer material subjected to the multiple transfer is separated from the transfer drum 6 by a separation charger 9,
A full-color copy image is formed through the heating / pressing roller fixing device 10.

The replenishment toner supplied to the developing units 2-1 to 2-4 is supplied from a replenishing hopper 3 provided for each color by a predetermined amount based on a replenishment signal via a toner transport cable 4 to the center of the rotary developing unit 2. And is sent to each developing device. This replenishment toner is supplied to the second
By the mixing-conveying screw 12 shown in the drawing, the developer is uniformly mixed with the developer in the developing device in advance so as to have a predetermined developer concentration.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a color electrophotographic copying machine used in Examples and Comparative Examples, and FIG. 2 is an enlarged view of a replenishing system-developing system portion of the copying machine shown in FIG. FIG. DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 2-1,2-2,2-3,2-4 ... Developer 3 ... Replenishing hopper 4 ... Cable 6 ... Transfer drum 10 ... Heating pressure roller fixing device

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenji Okado 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-63-38961 (JP, A) JP-A-62 JP-A-297857 (JP, A) JP-A-62-284366 (JP, A) JP-A-62-238580 (JP, A) JP-A-62-31864 (JP, A) JP-A-49-70630 (JP, A) )

Claims (2)

(57) [Claims] 1. A two-component developer used in an image forming apparatus having at least a photosensitive drum and a rotary developing unit having a plurality of developing units, wherein the two-component developer is formed of a binder resin and a coloring agent. A toner having at least an average particle diameter of 20 to 60 μm, an amount of fine powder of 350 mesh or less is 30% by weight or less, and an amount of ultrafine powder of 400 mesh or less is 2%.
0% by weight or less, the amount of coarse powder of 250 mesh or more is 10% by weight or less, the saturation magnetization with respect to an applied magnetic field of 3000 Oe is 55 to 75 emu / g, and the residual magnetization is 10 emu / g or less, A two-component developer comprising a resin-coated magnetic carrier having a coercive force of 10 e or less. 2. An electrostatic latent image is formed on a photosensitive drum, and the electrostatic latent image is developed by a reversal developing method using a two-component developer magnetic brush provided in a rotary developing unit having a plurality of developing units. Wherein the two-component developer comprises: a chromatic toner containing at least a binder resin and a colorant; a fluidity improver; and an average particle diameter of 20. ~ 60μ, the amount of fine powder of 350 mesh or less is 30% by weight or less, and the amount of ultrafine powder of 400 mesh or less is 2%
0% by weight or less, the amount of coarse powder of 250 mesh or more is 10% by weight or less, the saturation magnetization with respect to an applied magnetic field of 3000 Oe is 55 to 75 emu / g, and the residual magnetization is 10 emu / g or less, An image forming method comprising: a resin-coated magnetic carrier having a coercive force of 10 e or less.