JP3058204B2 - Multicolor image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus such as a color copying machine or a plus one color copying machine, and more particularly to a multicolor image forming apparatus for forming an image with a plurality of colors including black. Regarding improvement.

[0002]

2. Description of the Related Art For example, in a color copier, a color image is reproduced by superimposing four color toner images of cyan, magenta, yellow, and black on a recording sheet. Is provided with four sets of developing devices for developing the electrostatic latent images formed on the carrier into the above-mentioned respective colors. Generally, developing devices in PPC can be broadly classified into two types of developing systems depending on whether a developer used is mainly composed of a magnetic toner or a non-magnetic toner as a main component. The development method using a magnetic toner is not suitable for forming a color image that requires sharpness of the image, since the magnetic powder contained in the toner impairs the color developing property of the toner image.

For this reason, in a conventional color copying machine, a single-component developing system using a non-magnetic toner or a two-component developing system is adopted in each color developing device for forming a cyan, magenta or yellow toner image. In addition, since the color development of black toner images does not pose a problem, the black developing device that forms this toner image may be a developing method that uses magnetic toner.However, parts are shared with developing devices of other colors. In this developing device, a one-component developing system using a non-magnetic toner or a two-component developing system is adopted from the viewpoint of cost reduction.

[0004]

The performance required of the developing device of the color copying machine is not only good in the quality of the toner image formed by developing the electrostatic latent image, but also the toner from the developing device. Is less generated in the form of a toner cloud that is released in the form of mist. This is because, when the toner cloud is generated, the toner floating in the atmosphere enters the developing device of another color to cause color mixing, thereby deteriorating the image quality of a color image. In particular, color mixing with black toner will significantly impair the color developability of color images even in very small amounts.
Generation of a toner cloud by the black developing device is a serious problem in a color copying machine.

In general, in a developing method using a non-magnetic toner, the frictionally charged toner is held on the developer carrier only by electrostatic attraction based on its own electric charge. However, there is a disadvantage that the toner is easily released from the developer carrier and a toner cloud is easily generated. Therefore, from the above viewpoint, the developing method using the non-magnetic toner is not suitable for at least the black developing device of the color copying machine, and in actual application, the black toner cloud enters another developing device to mix colors. In order to avoid this, it is necessary to take measures such as arranging the black developing unit at the bottom of the four sets of developing units, which severely restricts the freedom of apparatus layout.

[0006] Among the existing developing methods proposed and used in the related art, a one-component developing method using a magnetic toner (hereinafter, referred to as a "one-component developing method") is described as having a relatively small generation of toner cloud.
Magnetic one-component developing system). In this developing method, since the toner is held on the developer carrier by the interaction between the electrostatic attraction and the magnetic force, the toner is less likely to be released from the developer carrier, and the amount of toner cloud is reduced accordingly. Therefore, from the viewpoint of effectively preventing the black toner from mixing with other color toners, it is desirable to apply the magnetic one-component developing method to the black developing device of the color copying machine.

In addition, the magnetic one-component developing system can perform high development without contact between the photosensitive member carrying the electrostatic latent image and the developer carrier, so that high image quality can be expected. There is no need to periodically replace the developer, and the reliability in frequent use situations exceeds that of other developing methods.
Therefore, considering that the frequency of copying a black-and-white document is much higher than the frequency of copying a color document even in a color copying machine, it is desirable to apply the magnetic one-component developing method to the black developing device.

[0008] Based on the above facts, it is ideal that the black developing device in a color copying machine is a magnetic one-component developing system, while the other developing devices are a non-magnetic developing system. Forming an image by mixing with a magnetic toner has the following problems. That is, since the magnetic toner contains the magnetic powder, the temperature-viscosity characteristics are greatly different from those of the non-magnetic toner, and the optimum fixing temperature does not match that of the non-magnetic toner. Therefore, if a toner image in which a magnetic toner and a non-magnetic toner are mixed is to be fixed on a recording sheet in one process, a problem arises in that the fixability of one of the toners is sacrificed. Further, since the magnetic toner has a lower glossiness of the image after fixing than that of the non-magnetic toner, an image formed by mixing the magnetic toner and the non-magnetic toner has uneven gloss and deteriorates the image quality. It also has problems.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems. It is an object of the present invention to improve a black developing device in a multicolor image forming apparatus so that there is no mixing of colors. It is an object of the present invention to provide a multicolor image forming apparatus capable of forming an image having good properties and gloss.

[0010]

Means for Solving the Problems In order to achieve the above object, the present inventors have solved how to solve the problems relating to the fixability and gloss of a toner image when a magnetic one-component developing system is applied to a black developing device. We studied repeatedly. As a result, by fixing the content of the magnetic powder contained in the magnetic toner as compared with that of a normal magnetic toner, the fixing property and the glossiness of the magnetic toner are made close to those of the non-magnetic toner. However, when the content of the magnetic powder is reduced, the magnetic force acting on the toner from the developer carrying member is weakened, which has an adverse effect on suppressing the generation of the toner cloud.
For this reason, the present inventors employ a configuration in which the toner is pressed against the developer carrier by the developer regulating member to improve the charge amount in order to improve the electrostatic attraction force acting on the toner from the developer carrier. I decided that.

That is, the multicolor image forming apparatus of the present invention comprises:
A plurality of developing units including a black developing unit are provided, and the electrostatic latent image formed on the electrostatic latent image carrier is developed by a corresponding developing unit according to image information to form a toner image. In a multicolor image forming apparatus that forms a recorded image by transferring
Only the above black developing unit uses a magnetic one-component developer.
The other developing devices use non-magnetic developer
The black developing device includes a developer carrier that faces the electrostatic latent image carrier while maintaining a predetermined gap, and that rotates by attracting the developer around by magnetic force. A developer regulating member for pressing the body to make the developer thinner, wherein a magnetic toner having a magnetic powder content of 30 to 50% by weight is used as the developer.

[0012]

According to the above technical means, the magnetic toner is used in the black developing device, and the multicolor toner image formed on the recording sheet corresponds to the magnetic toner corresponding to the black color and the other colors. However, since the content of the magnetic powder in the magnetic toner is kept low, the fixing temperature of the mixed magnetic toner and the fixing temperature of the non-magnetic toner are substantially similar. Thus, the multicolor toner image transferred onto the recording sheet can be satisfactorily fixed in one fixing step. Further, the glossiness of the fixed toner image does not differ between the black portion made of the magnetic toner and the multicolor portion made of the non-magnetic toner, and it is possible to obtain good gloss without unevenness in the recorded image. Further, in the black developing device, the developer is thinned by pressing the developer regulating member against the developer carrier, thereby increasing the charge amount of the magnetic toner. Even if the magnetic toner has a small amount of toner, the toner can be reliably held on the developer carrying member and generation of a toner cloud can be suppressed.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A multicolor image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 shows a schematic configuration of a color laser printer to which the present invention is applied. This printer is an electrostatic latent image carrier 1 having a photoconductive layer (hereinafter, referred to as
A full-color recorded image is obtained by transferring a single-color toner image formed for each rotation of the photosensitive drum onto a recording sheet 3 carried on a transfer drum 2 and repeating this for each of yellow, magenta, cyan, and black. It is configured as follows.

The formation of a color image in this printer is specifically performed as follows. First, the image information of a color image read by an optical scanning system (not shown) such as a scanner is extracted only by image processing means (not shown), only image information on one of the four color components, It is supplied to a laser writing means 4 having a semiconductor laser, a polygon mirror, a lens and the like. The laser writing means 4 exposes the photosensitive drum 1 based on the supplied image information, but the surface of the photosensitive drum 1 is charged to -450 V in advance by the charger 5 and is exposed by the laser writing means 4. An electrostatic latent image is formed by increasing the potential of the region to -150V. Around the photosensitive drum 1, a black developing device 6k, a cyan developing device 6c, a magenta developing device
6m, a yellow developing unit 6y is arranged in order along the rotation direction of the photosensitive drum 1, and the electrostatic latent image formed on the photosensitive drum 1 is one of the ones corresponding to the color components of the image information. The toner image is developed by the developing device. That is, if the image information supplied to the laser writing means 4 is black image information, the electrostatic latent image is
It is developed by 6k to form a black toner image. The detailed configuration of each developing device will be described later.

On the other hand, after the recording sheet 3 is fed to the transfer drum 2 at a predetermined timing in synchronization with the formation of the toner image by the registration roller 7, the electrostatic attraction generated by the discharge of the suction corotron 8. By transfer drum 2
It is adsorbed on the dielectric sheet that wraps around. The recording sheet 3 held on the transfer drum 2 in this manner is sent to a position facing the photosensitive drum 1, that is, to a transfer section, and a black toner image is transferred from the photosensitive drum 1 with the discharge of the transfer corotron 9. Is done.

Next, the photosensitive drum 1 has a recording sheet 3
After the residual toner not transferred to the photosensitive drum 1 is removed by the cleaning device 10 and then uniformly charged again by the charger 5, a cyan toner image is formed on the photosensitive drum 1 through the same process as the black toner image. You. At this time, transfer drum 2
Is rotating while holding the recording sheet 3 on which the black toner image has been transferred, and the cyan toner image is transferred onto the recording sheet 3 sent again to the transfer portion so as to overlap the black toner image. By repeating the same process for magenta and yellow, a color image in which the above-described four color toner images are multiplex-transferred on the recording sheet 3 is completed.

The recording sheet 3 on which the transfer of the yellow toner image has been completed is eliminated by the peeling corotron 11 from the electrostatic attraction acting on the transfer drum 2, and is released from the transfer drum 2 by the peeling claw 12. On the transfer drum 2 from which the recording sheet 3 has been peeled off, the charge of the dielectric sheet is removed by the charge removing corotron 13, and the paper dust and the like are cleaned by the brush cleaner 14, and the next recording sheet is prepared for adsorption. . Further, the released recording sheet 3 is subjected to fixing of the toner image by the fixing device 15, and is discharged by the discharge tray 17 by the discharge roller 16.
Is discharged on top. This completes a series of recording operations for forming a color image.

Next, the configuration of each developing device for developing an electrostatic latent image will be described. In the black developing device 6k, a magnetic one-component developing method is employed from the viewpoint of positively preventing the generation of a toner cloud. The specific configuration is as shown in FIG. 2, in which a developer carrier 18 (hereinafter referred to as a developing roll) opposed to the photosensitive drum 1 and a front end portion of the developing roll 18 are provided.
And a developer regulating member 19 disposed so as to be in pressure contact with the toner cartridge T, and these are disposed in a hopper 20 that stores the magnetic toner T. Further, an AC high voltage power supply 21 and a DC power supply 22 for applying a developing bias voltage are connected to the developing roll 18.

The developing roller 18 has a plurality of magnetic poles (N, S,...) Having different polarities and magnetic forces, and is magnetized and fixedly supported by a casing (not shown). The sleeve 18b rotates around the circumference, and the suction, conveyance, and release from the sleeve 18b of the magnetic toner T are performed according to the magnetic pattern of the magnet roll 18a with the rotation of the sleeve 18b. ing. In this example, the sleeve 18b was formed by molding a phenol resin having a non-resistance value of 4.2 × 10 ⁷ Ωcm into a cylindrical shape having a thickness of 1.0 mm, and the surface thereof was R _Z = 10 points average roughness of JIS. Four.
A semiconductive sleeve polished in the longitudinal direction to 3 μm was used.

The hopper 20 is disposed so as to cover the side from below the developing roll 18, and the contained magnetic toner T accumulates on the rear side of the developing roll 18, and after passing through the developing area. The structure is such that the magnetic toner T can be continuously supplied to the surface of the sleeve 18b.

On the other hand, the developer regulating member 19 has a thickness of 0.1 m.
A soft elastic member 19b made of silicon rubber having a rubber hardness of 50 ° and a thickness of 1 mm is flow-bonded to the tip of a spring plate member 19a made of non-magnetic stainless steel (SUS304 3 / 4H material). The restricting member 19 is supported by the holder 23 such that the direction of the free end faces the rotational direction of the sleeve 18b, and the soft elastic member 19b abuts on the sleeve 18b at a linear pressure of 100 g / cm. ing.

The magnetic toner T used in the black developing device 6k has an apparent viscosity of 10 ⁵ poise at a temperature of 100 ° C.
Is a low-melting toner containing 40% by weight of magnetic powder in a polyester-based binder, and is frictionally charged to a negative charge by rubbing with the developer regulating member 19. Therefore, in view of the relationship with the photosensitive drum 1 charged to a negative potential, a black toner image is formed by reversal development.

The black developing device 6k configured as described above is provided with a spacing roller abutting on the photosensitive drum 1.
(Not shown) allows the developing roll 18 to move the photosensitive drum 1
And at a distance of 300 μm, and at the time of development of the electrostatic latent image 24, a developing bias voltage whose waveform is shown in FIG. 3, that is, a frequency f = 2.4 kHz, a peak-to-peak voltage V _PP = 2 kV, a DC component -250 V, by the time t _a from the maximum voltage to vary the minimum voltage applies a voltage that is set to 1/6 with respect to the period T to the sleeve 18b, it is held on the developing roll 18 The toner T flies toward the photosensitive drum 1 and the electrostatic latent image 24 is developed. Also, a black developer
When 6k is not used, the developing roll 18 is not rotated and the application of the developing bias voltage is stopped, and the developing roll 18 is in the same state as the high resistance ground.

On the other hand, in each of the cyan, magenta and yellow developing units 6c, 6m and 6y, a two-component magnetic brush developing system using a developer in which a non-magnetic toner and a carrier are mixed is applied. Regarding the magnetic brush developing method and a developing device for carrying out this method, for example, JP-A-57-177171, JP-A-58-140766, JP-A-53-106052 or JP-A-59-105605 Since it is described in Japanese Patent No. 170013, detailed description of the configuration of these developing devices is omitted here.

A retract mechanism (not shown) is provided at the back of each of the three color developing units 6c, 6m, and 6y. Have been. Therefore, these developing devices advance to a position close to the photosensitive drum 1 only when developing the electrostatic latent image of the corresponding color,
At the time of development by the developing device of another color, it is in a state separated from the photosensitive drum 1.

The inventors of the present invention actually form a color image with the color laser printer of the present embodiment configured as described above and check the amount of toner cloud generated from the black developing device 6k. The presence or absence of color mixture on 6c, 6m, 6y was observed. Further, in order to confirm the effectiveness of the present embodiment, a color laser printer similar to the present embodiment was constructed using a black developing device using a developing method other than that used in the present embodiment, and the And the occurrence of color mixing were examined. There are the following three types of black developing devices using other developing methods. As shown in FIG. 4, a one-component developer in which a thin layer of the magnetic toner T is formed on the developing roll 18 by a magnetic trimmer bar 25 arranged at a predetermined distance from the developing roll 18 (hereinafter, Comparative Example 1) . A two-component magnetic brush developing device (hereinafter, comparative example 2) using a developer composed of a non-magnetic toner and a carrier similarly to other developing devices 6c, 6m, and 6y other than black. A one-component developing device using a non-magnetic toner disclosed in JP-A-60-233669 (hereinafter, Comparative Example 3).

Then, each of the comparative example and the color laser printer of the present embodiment collects 1000 copies,
For each example, the amount of toner cloud and the occurrence of color mixing were relatively evaluated. The toner cloud was evaluated from the amount of toner adhering around the black developing device after collecting 1000 copies, and the color mixture was evaluated by visual observation of a developing roll of a cyan developing device disposed below the black developing device. Table 1 below shows the evaluation of the toner cloud, and Table 2 shows the evaluation of the color mixture.

[0028]

[Table 1]

[0029]

[Table 2]

According to the above results, it is confirmed that both the amount of toner cloud and the occurrence of color mixture are smaller in each of the present examples than in each of the comparative examples, and it is expected that a good color image can be formed.

As described above, in order to prevent the toner cloud, it is necessary that the toner other than the toner adhering to the surface of the photosensitive drum 1 is securely held on the developing roll 18. Factors that greatly affect the holding power include the amount of charge per toner, and in the case of magnetic toner, the content of magnetic powder in the toner also has a large effect.
The larger the charge amount per toner and the content of the magnetic powder in the toner, the more the generation of toner cloud can be suppressed. Table 3 below summarizes the magnetic powder content and the amount of charge per toner for the toners of this example and each comparative example.

[0032]

[Table 3]

In Comparative Examples 2 and 3, the toner does not contain magnetic powder, and the toner is held on the developing roll only by electrostatic attraction according to its own charge. It is considered that a toner cloud is likely to be generated as compared with the present embodiment and the comparative example 1 in which the toner is held on the developing roll by interaction with the attraction. In addition, this example and Comparative Example 1
In this example, the charge amount of the toner was
It can be said that a larger electrostatic attraction force acts on the toner by an amount greater than 1 to make it difficult to generate a toner cloud.

The reason why the charge amount of the toner T becomes large in the black developing device 6k of the present embodiment is as follows.
This is because the frictional charging of the toner T is more effectively performed by the developer regulating member 19 pressed against the toner. Incidentally, as a developer regulating member capable of effectively performing triboelectric charging,
As shown in the present embodiment, the present invention is not limited to the one that obtains the pressure contact force with the developing roll 18 by the spring plate member 19a, and the one that urges the end of the rigid blade toward the developing roll by a coil spring or the like.

Next, the present inventors examined how the content of the magnetic powder in the black developing device 6k affects the fixability and glossiness of a color image in the color printer of the present embodiment. FIG. 5 shows the fixing property, and FIG. 6 shows the glossiness.Each of the black developing units 6k has a magnetic powder content of 20 to 70% by weight in which the magnetic powder content is changed by 10% for each color. An image is formed, and the fixing temperature of a color image is changed in several steps with respect to each magnetic powder content. For reference, the fixability and glossiness of the non-magnetic toner with the change in the fixing temperature are also shown in the same figure.

As is apparent from FIGS. 5 and 6, when the magnetic powder content of the black toner is within 50%, the color image has almost the same fixability and gloss as the non-magnetic toner image at any fixing temperature. However, if the content of the magnetic powder exceeds 50% by weight, depending on the fixing temperature, the fixing property and the glossiness greatly differ from those of the non-magnetic toner. According to this result, in the present embodiment, if the magnetic powder content of the magnetic toner T in the black developing device 6k is within 50% by weight, a color image in which the non-magnetic toner and the magnetic toner are mixed in one fixing step can be obtained. It can be said that the toner can be fixed with a uniform fixing property, and a glossiness without unevenness can be obtained.

FIG. 7 shows a black developing device 6k of this embodiment.
In this example, the amount of toner cloud generated due to the change in the magnetic powder content of the magnetic toner T was evaluated. As is apparent from this figure, when the content of the magnetic powder is less than 20% by weight, the amount of toner cloud generated increases, and there is a concern that color mixing with the other developing devices 6c, 6m, and 6y may occur.

Accordingly, taking into account the above results, in order to obtain good fixability and glossiness of a color image in this embodiment, the content of the magnetic powder of the toner T in the black developing device 6k should be 20 to 50% by weight. Control is required. Conventionally, considering that the magnetic powder content of the magnetic toner used in a copying machine or the like is about 55% by weight, it is doubtful whether this value is sufficient to hold the toner on the developing roll 18 by magnetic force. However, in the present embodiment, as described above, the amount of charge per toner is large due to the action of the developer regulating member 19, so that the toner
T can be reliably held on the developing roll 18, and toner cloud can be effectively prevented from being generated even with the above magnetic powder content.

As means for making the fixability and glossiness of the magnetic toner and the non-magnetic toner at the same fixing temperature more approximate, not only the content of the magnetic powder in the magnetic toner is reduced but also a resin binder containing the magnetic powder. Modification. The inventors of the present application confirmed that the temperature was 100 ° C.
When a resin binder having an apparent viscosity of 10 ⁵ poise or less was used, the fixability and glossiness of the magnetic toner could be made closer to those of the nonmagnetic toner.

As described above, in the multicolor image forming apparatus to which the present invention is applied, since the generation of the toner cloud from the black developing device 6k is extremely small, the layout of the plurality of developing devices around the photosensitive drum 1 is not limited, and the layout is not limited. A multicolor image forming apparatus as shown in FIGS. 8 to 10 can also be configured.

FIG. 8 shows a rotary developing unit 6 in which developing units 6k, 6c, 6m, and 6y of four colors are radially arranged.
2 shows a main part of the color image forming apparatus arranged adjacent to FIG. In this image forming apparatus, the rotary developing unit
6 rotates, and the electrostatic latent image is developed into a predetermined single color by one of the developing devices facing the photoconductor tram 1.

FIG. 9 shows a black developing device 6k and a rotary developing unit 6 'in which developing devices 6c, 6m, and 6y for the other three colors are radially arranged. This shows a multicolor image forming apparatus in which a container 6k is arranged above a rotary developing unit 6 '. In this image forming apparatus, a color image can be formed by multi-transferring four color toner images onto a recording sheet in the same manner as in FIG. 8, but a second exposure unit is provided to provide a black developing device 6k and a rotary developing unit. 6 'again with photosensitive drum 1
Is exposed, a black toner image and a toner image of another color can be formed on the photosensitive drum at one time.

FIG. 10 shows a second embodiment in which a black developing unit 6k and a developing unit 6r for another color such as red are arranged adjacent to the photosensitive drum 1, and the black developing unit 6k is arranged above the red developing unit 6r. 1 shows a color image forming apparatus. In this apparatus, if the second exposure unit is provided to expose the photosensitive drum 1 again between the black developing device 6k and the red developing device 6r,
A black toner image and a toner image of another color can be formed on the photosensitive drum 1 at a time.

Generally, when a plurality of developing devices are arranged around the photosensitive drum, the lower the developing position, the lower the surface potential of the photosensitive drum due to dark attenuation becomes. The potential needs to be set higher. However, in long-term use, this tends to cause electrical deficiency of the photosensitive drum, causing black spots on the copy,
This causes image quality defects such as white spots to appear. Therefore, a developing device that is expected to be used more frequently than a developing device of another color, such as a black developing device, should be placed in the first color, and the potential of the initial charging of the photosensitive drum should be kept low to reduce the load. Is desirable. In this regard, in the multicolor image forming apparatuses of the above-described embodiments, the black developing device 6k can be used as the first color by using the magnetic one-component developing system, so that the electric power for the photosensitive drum 1 can be changed. This has the advantage that the environmental load can be reduced and the occurrence of image quality defects during long-term use can be prevented.

[0045]

As described above, according to the multicolor forming apparatus of the present invention, the content of the magnetic powder contained in the magnetic toner of the black developing device is suppressed to 20 to 50% by weight, so that the color image can be formed. The fixing temperature of the magnetic toner mixed therein and the fixing temperature of the non-magnetic toner are approximately similar, and the multicolor toner image transferred on the recording sheet can be satisfactorily fixed in one fixing step. In addition, the glossiness of the fixed toner image does not differ between the magnetic toner portion and the non-magnetic toner portion, and a good gloss without unevenness in the recorded image can be obtained.

In the black developing device, a large amount of charge can be given to the magnetic toner by the action of the developer regulating member, and even if the magnetic toner has a small content of magnetic powder, it can be reliably transferred to the developer carrier. Can be held,
It is possible to effectively suppress the occurrence of toner cloud and prevent the occurrence of color mixture.

Further, in the present invention, since the black developing device can be arranged in the first color, there is no need to set the potential of the initial charge of the electrostatic latent image carrier higher, and the electrostatic latent image carrier is not required to be set. Electric load is reduced, and high image quality can be maintained for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of a multicolor image forming apparatus of the present invention.

FIG. 2 is a sectional view showing a black developing device according to the first embodiment.

FIG. 3 is a graph showing a waveform of a developing bias voltage applied to a black developing device.

FIG. 4 is a sectional view showing a magnetic one-component developing device according to Comparative Example 1.

FIG. 5 is a graph showing the fixability of a toner image with a change in the content of magnetic powder in the toner.

FIG. 6 is a graph showing the glossiness of a toner image with a change in the content of magnetic powder in the toner.

FIG. 7 is a graph showing the amount of toner cloud generated with a change in the magnetic powder content in the toner.

FIG. 8 is a schematic view showing another embodiment of the multicolor forming apparatus of the present invention.

FIG. 9 is a schematic view showing another embodiment of the multicolor forming apparatus of the present invention.

FIG. 10 is a schematic view showing another embodiment of the multicolor forming apparatus of the present invention.

[Explanation of symbols]

1 ... Electrostatic latent image carrier (photosensitive drum), 2 ... Transfer drum, 6k
... Black developing device, 6c: Cyan developing device, 6m: Magenta developing device, 6y: Yellow developing device, 18: Developer carrier (developing roll), 19: Developer regulating member, T: Magnetic toner

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaaki Fukuhara 2274 Hongo, Ebina-shi, Kanagawa Prefecture, inside Ebina Business of Fuji Xerox Co., Ltd. (72) Inventor Makoto Hirota 2274 Hongo, Ebina-shi, Kanagawa Prefecture, Fuji Xerox Co., Ltd. Ebina Works (72) Inventor Tetsuya Fujita 2274 Hongo, Ebina City, Kanagawa Prefecture, Ebina Works of Fuji Xerox Co., Ltd. (56) References JP-A-58-87558 (JP, A) JP-A-2-173674 (JP) JP-A-61-203478 (JP, A) JP-A-1-94357 (JP, A) JP-A-3-127082 (JP, A) JP-A-58-75159 (JP, A) 61-201264 (JP, A)

Claims (2)

(57) [Claims] A plurality of developing units including a black developing unit;
A multicolor image forming a toner image by developing the electrostatic latent image formed on the electrostatic latent image carrier in accordance with the image information with a corresponding developing device and transferring the toner image to a recording sheet to form a recorded image In the image forming apparatus, only the black developing device described above uses a magnetic one-component developer.
The other developing devices use non-magnetic developer
The black developing device includes a developer carrier that faces the electrostatic latent image carrier while maintaining a predetermined gap, and that rotates by attracting the developer around by magnetic force. A multi-color image forming apparatus, comprising: a developer regulating member that presses against a body to reduce the thickness of the developer; and uses a magnetic toner having a magnetic powder content of 30 to 50% by weight as a developer. . 2. The black developing device according to claim 1, wherein said black developing device is arranged in a first color.
2. A multicolor image forming apparatus according to claim 1, wherein
apparatus.