JPH09311542A - Developing device, and color image forming device mounting the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate irregular density and to hardly cause image staining or color mixture by respectively applying bias voltage to a developing sleeve functioning as a developer carrier, an electrode part and an elastic member. SOLUTION: The bias voltage capable of superposing AC on DC is impressed on the developer carrier 41 by a DC bias power source E1 and an AC bias power source E2 through a protective resistance R1. Then, at least the DC bias is impressed on the elastic member 50 on which DC bias and AC bias can be superposed by a DC bias power source E5 and an AC bias power source E6 through a protective resistance R3. A plate-like member 45a having the electrode part 45b is laminated on the elastic member 50 and supported. In such a case, it is preferable to form the member 45a on the lower layer of the elastic member 50 in order to make the member 45a press-contact with the carrier 41 in the ease of laminating the member 45a on the elastic member 50.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device such as an electrophotographic copying / recording device, and more particularly to a plate on the upstream side in the moving direction of the developer carrier in the space where the image carrier and the developer carrier face each other. The present invention relates to a developing device in which a cylindrical member is installed, a two-component developer is supplied to the developer transporting body, and toner is ejected under an oscillating electric field to perform reversal development, and a color image forming apparatus equipped with the developing device.

[0002]

2. Description of the Related Art Various methods have been disclosed for forming a color image in a conventional electrophotographic copying / recording apparatus or the like.

For example, Japanese Patent Laid-Open No. 60-76766 discloses a color image recording method in which toner images are superposed on an image carrier by using a two-component developer in which toner and an insulating carrier are mixed. This method is very useful because it has features such that the recording apparatus is compact and low-cost, and that the toner charge control is easy because a two-component developer is used. However, the toner particle size conventionally used in this method is relatively coarse, that is, 10 μm or more, and it is not possible to reproduce the density that is faithful to a fine line or a document, and it is incomplete for obtaining a high-quality image. there were.
In order to solve this problem, atomization of the toner is indispensable, but it is known that various problems occur when using a fine particle toner of 10 μm or less. As a cause, the van der Waals force becomes relatively larger than the Coulomb force due to atomization, and it becomes difficult to prevent fogging by applying a DC bias voltage to the developer transport body.
The atomization makes it difficult to uniformly charge the toner, and the toner may be fogged by a poorly charged toner. Various methods have been proposed to overcome such problems.

For example, in Japanese Unexamined Patent Publication No. 1-94368, a leveling member is set between the central portion of the developing area and a member for controlling the layer thickness of the developer, and the leveling member is set to have a charging polarity of toner particles. Discloses that a DC voltage of opposite polarity is applied as a bias voltage. In this method, since a bias having a polarity opposite to the charging polarity of the toner particles is applied to the leveling member, the toner adheres to the leveling member, which adheres to the image carrier to cause image stains or leveling. When the toner is fused to the member, vertical streaks occur in the image.

For example, in Japanese Unexamined Patent Publication No. 4-115264, developers of different colors are sequentially applied to the image carrier by a plurality of developing devices to form a visible image of the developers of a plurality of colors, and then the images are transferred. In an image forming apparatus, an oscillating electric field is formed between an electrode body arranged close to and in contact with the developer of the developer carrier and having a tip portion located in the developing area and the developer carrier. Then, a method is disclosed in which the developer is dispersedly ejected from the tip of the electrode body and supplied to the image carrier. In this method, the electrode body for dispersing and flying the developer is
Since it also exists in the upstream portion of the contact portion with the developer transport body, a fluctuating electric field similar to that in the developing area is formed during transport of the developer, and the developer is returned to the upstream side. As a result, the amount of the developer that passes through the electrode body and is carried to the developing region is reduced, and the developability is poor, and the developer returned to the upstream side causes
Toner easily adheres to the back surface of the electrode body, and toner fusion easily occurs.

For example, in Japanese Unexamined Patent Publication No. 6-236106, a plate-shaped member having an electrode in the upstream portion of the developing area is brought into contact with a developer carrying body so that the developer carrying body and the image carrying body and the developer carrying body are in contact with each other. A toner is attached to the electrostatic latent image on the image carrier by forming an oscillating electric field of the same phase between the electrode and the tip electrode of the plate-shaped member, and a portion having a portion upstream of the tip electrode is formed. A method of holding two electrodes and forming an electric field that applies an electric force from the second electrode to the tip electrode side is disclosed. In this method, since the absolute value of the DC bias voltage applied to the second electrode is larger than that of the tip electrode, it is good for the developer stain on the electrode.

However, when undulation or warpage occurs when setting the plate-like member having the electrodes as described above, the positional relationship of the electrodes in the developing space is changed. As a result, the developability is lowered, and in particular, uneven density occurs.

[0008]

As described above, in order to cope with small particle size toner, an electrode is installed in the developing space in which the image carrier and the developer carrier are opposed to each other, and reversal development is performed by an oscillating electric field. However, there is a problem in that the developability is lowered depending on the position of the electrode, and in particular, image unevenness due to uneven density and stains on the control electrode plate and color mixing during color image formation occur.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a developing device and a color image forming apparatus equipped with the developing device which can obtain a clear recorded image without density unevenness or color mixture and without image stain. And

[0010]

This object is achieved by any one of the following technical means (1) to (17).

(1) A plate-shaped member having an electrode portion supported by being laminated on a free end of an elastic member is installed in a space where the developer carrier and the image carrier are opposed to each other, and the electrode of the plate-shaped member is installed. At least a DC voltage is applied to the portion, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer transport body to fly the toner on the developer transport body to form a latent image on the image carrier. In the developing device for developing, a bias can be applied to the elastic member.

(2) The developing device according to item (1), wherein the bias applied to the elastic member is a DC voltage having the same polarity as that of the toner.

(3) The developing device as described in the item (1), wherein the bias applied to the elastic member is a superimposed voltage of a DC voltage and an AC voltage.

(4) The developing device according to any one of items (1) to (3), wherein a latent image is formed before or after image formation.

(5) A plate-shaped member having an electrode portion supported by being laminated on the free end of an elastic member is installed in a space where the developer carrier and the image carrier are opposed to each other, and the electrode of the plate-shaped member is installed. At least a DC voltage is applied to the portion, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer transport body to fly the toner on the developer transport body to form a latent image on the image carrier. In a color image forming apparatus that has a plurality of developing devices for developing and collectively transfers images superposed on a drum, a voltage can be applied to the elastic member, and the elastic member is provided with another color during development. When developing toner, a DC voltage of the same polarity as that of electrically floating toner is applied,
A color image forming apparatus characterized in that a DC voltage having at least the same polarity as that of toner is applied during non-development.

(6) The color image forming apparatus according to item (5), wherein an AC voltage is superimposed on the DC voltage during non-development according to item (5).

(7) The color image forming apparatus according to item (5) or (6), wherein latent image formation is performed during non-development according to item (5) or (6).

(8) In the color image forming apparatus, a plurality of sets of charging means, image exposing means and developing means are arranged on the image carrier, and charging, image exposure and development are performed during one rotation of the image carrier. Item 5. The method according to any one of items (5) to (7), characterized in that the toner images are repeatedly formed on the image carrier so as to be superposed, and then the toner images are collectively transferred to a transfer material. Color image forming apparatus.

(9) A plate-shaped member having an electrode portion supported by being laminated on the free end of an elastic member is installed in the space where the developer carrier and the image carrier are opposed to each other, and the electrode of the plate-shaped member is installed. At least a DC voltage is applied to the portion, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer transport body to fly the toner on the developer transport body to form a latent image on the image carrier. In a developing device for developing, a piezoelectric vibrator is installed, and a vibration from the piezoelectric vibrator acts on the elastic member or the plate-shaped member.

(10) The developing device according to item (9), wherein the installation angle α of the plate-shaped member with respect to the horizontal line is larger than 45 ° and smaller than 270 °.

(11) Item (9) or (1), wherein the latent image formation is performed before or after image formation.
The developing device according to item 0).

(12) The developing device according to any one of items (9) to (11), wherein the elastic member is formed with a mesh.

(13) A plate member having an electrode portion supported by being laminated on the free end of an elastic member is installed in a space where the developer carrier and the image carrier face each other, and the electrode of the plate member is placed. At least a DC voltage is applied to the part, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer transport body,
In a color image forming apparatus that has a plurality of developing devices that fly the toner on the developer transport body to develop the latent image on the image carrier, A color image forming apparatus, wherein a vibrator is installed, and vibration from the piezoelectric vibrator is applied to the elastic member or the plate-shaped member in a non-image portion.

(14) The color image forming apparatus as described in the item (13), wherein the installation angle α of the plate member with respect to the horizontal line is larger than 45 ° and smaller than 270 °.

(15) The latent image formation is performed before image formation or during non-development after image formation (13).
An image forming apparatus according to item (14).

(16) The color image forming apparatus described in any one of (13) to (15), wherein the elastic member is formed with a mesh.

(17) In the color image forming apparatus, a plurality of sets of charging means, image exposing means and developing means are arranged on the image carrier, and charging, image exposure and development are performed during one rotation of the image carrier. The toner image is repeatedly formed on the image carrier to form the toner image, and then the toner images are collectively transferred onto a transfer material. (13) to (16) Color image forming apparatus.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a partial sectional view of an example of a developing device having a plate-shaped member of the present application. In the figure, 4
1 is JIS 10 point average roughness indication by sand blasting of aluminum alloy, stainless steel, etc. (J
IS-B0610) is used to perform a rough surface treatment of 1 to 2 μm, and the developer carrier is rotatably supported, 43 is a stirrer for stirring the developer 42 to make the components uniform, 44 is the developer 4
Supply roller for supplying 2 to the developer transport body 41,
Is a developer transport regulating rod that regulates the thickness of the developer layer on the developer transport body 41, and 47 is a scraper that scrapes off the consumed developer 42 on the developer transport body 41. 45
Is a plate-shaped member having an electrode portion, is supported by the elastic member 50, and includes a plate-shaped member 45a and an electrode portion 45b. The details of the plate member 45 having the electrode portion will be described later.

The developer carrier 41 has a DC bias power source E.
A bias voltage capable of superimposing an alternating current on a direct current is applied through the protection resistor R1 by the AC bias power source 1 and the AC bias power source E2. A bias voltage capable of superimposing an alternating current on a direct current is applied to the electrode portion 45b by a direct current bias power source E3 and an alternating current bias power source E4 via a protective resistor R2, and at least a direct current bias can be applied.

Further, a DC bias power source E5 and an AC bias power source E6 can also superimpose a DC bias and an AC bias on the elastic member 50 through the protective resistor R3, and at least a DC bias can be applied.

FIG. 2 shows the plate member 4 which can be used in the present invention.
5A and 5B are schematic diagrams showing the configuration and arrangement of a plate-shaped member 45 having an electrode portion 45b and an elastic member 50.

As shown in FIG. 2A, the plate member 45a having the electrode portion 45b is supported by being laminated on the elastic member 50. At this time, the plate member 45a and the elastic member 5
The region where 0 and 0 are stacked is d1, and the distance from the tip of the elastic member 50 to the tip of the plate member 45a is d2. When the plate-shaped member 45a and the elastic member 50 are stacked, the plate-shaped member 45
In order to press a onto the developer transport body 41, the plate-shaped member 45
It is preferable to form a in the lower layer of the elastic member 50. In addition, the plate-shaped member 45a is formed of an elastic member 50 through an adhesive or the like.
It is a usual use method to support. The width of the electrode portion 45b is L. Further, the closest distance h1 between the electrode portion 45b and the developer transport body 41 is set. Further, the electrode portion 45b is configured so as to be located on the downstream side in the rotation direction of the developer transport body 41 from the closest contact point P of the plate-shaped member 45a and the developer transport body 41. With this configuration, the toner cloud does not occur on the upstream side of the closest contact point P, and the toner concentration of the developer on the downstream side can be kept uniform.

FIG. 2B shows a plurality of electrode portions 45b and 45c.
Are formed on the plate member 45a. At this time, it is preferable to reduce the distance between the upstream electrode portion 45b and the downstream electrode portion 45c because the toner can be pushed out to the developing area.

In FIG. 2C, a canopy portion 45d is provided in front of the electrode portion 45b on the upstream side. This is preferable because fogging at the time of developing another color toner can be suppressed. 2 (A), (B),
As shown in (C), it is desirable that the exposed portions of the electrode portions 45b and 45c be coated with an insulating layer of about 10 to 100 μm in order to prevent current leakage.

At this time, the preferable range of the width L is determined by the condition of giving an oscillating electric field to fly from the developer transport body 41 to the image carrier 1. That is, it depends on the moving speed V _S (mm / sec) of the developer transport body 41 and the frequency f _AC (Hz) of the AC bias voltage applied to the developer transport body 41.
If the moving speed V _S (mm / sec) of the developer transport body 41 is high, the developer transport amount increases, which is effective in improving the developability. However, if it is too fast, the image density becomes uneven.
0 to 500 (mm / sec) is preferable. Frequency f
_{If the AC} is low, it is advantageous for the developability and gradation, but if it is too low, the toner previously developed on the photosensitive drum 1 is pulled back to the developing device, resulting in color mixture. Therefore, the frequency f _AC is preferably in the range of 500 Hz to 20 kHz.
However, considering the number of vibrations due to the balance between both electrode plates, 5 ≦ L · f _AC / V _S ≦ 20 is preferable, and L (mm) is preferably 0.05 ≦ L ≦ 1.0.

The plate-like member 45a is made of an insulating material having a thickness of about 50 μm to 400 μm. For example, polyethylene terephthalate, polystyrene, polypropylene,
Polycarbonate, polybutylene terephthalate, phenol resin, polyimide resin, polyamide-imide resin,
Epoxy resins, polyether resins, etc. are preferable, and it is more preferable to use glass fibers, carbon fibers, or the like in which the insulator is reinforced. Further, it is not possible to use a ceramic such as alumina, aluminum nitride, single crystal sapphire, silicon carbide, silicon nitride, zirconia, mullite, cordierite, steatite, wollastonite, etc., or a mixture of these ceramics with a resin. Since the dielectric constant in the space is increased, the substantial development gap is narrowed, which is preferable. The electrode portion 45b is made of copper foil or Ag having a width of about 100 μm to 2000 μm in the developer conveying direction.
/ Pd paste, gold foil, etc. are used, and the plate-shaped member 45a
Supported by

The elastic member 50 is preferably a plate having a thickness of about 50 μm to 2 mm, and a stainless plate, a phosphor bronze plate, a polyimide resin or an epoxy resin reinforced by glass fiber or carbon fiber, etc. can be used. , Is attached to the external image of the developing device 4 via the insulating plate 51.

As a method of supporting the plate-like member 45a on the elastic member 50, bonding with a thermosetting resin or an ultraviolet curable resin in addition to an epoxy adhesive,
It is preferable to bond them with a double-sided tape.

The configuration and arrangement of the plate-like member 45a having the plate-like member 45a and the electrode portion 45b and the elastic member 50 used in the developing device 4 of the image forming apparatus of the present application are described in FIG. As described above, it goes without saying that those having a configuration derived from this can be similarly used in the developing device of the present invention.

FIG. 3 is an overall block diagram of an example of an image forming apparatus I using the developing device of the present invention (DC 9028 modified machine manufactured by Konica Corporation). Reference numeral 1 denotes a photosensitive drum, which is an image carrier having an aluminum tube coated with a photoconductor, and is configured to rotate clockwise.

2 is a scorotron charger which is a charging means, and 3
Is an image writing device using a laser beam as an image exposing means, 4A, 4B, 4C and 4D are developing devices each containing a developer of a specific color, 5 is a transfer device, 6 is a cleaning device, and 8 is an image reading device. is there.

Each of the developing devices 4A, 4B, 4C, 4D
Is yellow (Y), magenta (M), cyan (C),
A developer containing black (K) developer is provided, and each developer transport body 41 having a predetermined gap from the photoconductor drum 1 is provided, and a latent image on the photoconductor drum 1 is visualized by non-contact reversal development. It has a mechanism to change. The developer transport body 41 is configured to rotate counterclockwise.

The transfer belt 5b of the transfer device 5 includes a transfer pole 5a and is kept at a position separated from the surface of the photosensitive drum 1 during image formation, and is transferred after the image formation on the photosensitive drum 1 is completed. Only when transferring to a material, the surface of the photosensitive drum 1 is contacted as shown in the figure.

The cleaning blade 6a and the toner carrying roller 6b of the cleaning device 6 are kept at a position separated from the surface of the photoconductor drum 1 during image formation, and as shown in the figure only during cleaning after image transfer. 1
Is pressed against the surface of A color image is formed by the image forming apparatus as follows.

First, the formation of a multicolor toner image according to this embodiment starts by reading an image. That is, the halogen lamp 80 of the image reading device 8 irradiates the original document placed on the document table 7, and the reflected light is reflected by the first mirror 81,
The lens 8 is reflected by the second mirror 82 and the third mirror 83.
4. The color is separated into blue, red and green through the dichroic prism 85. Blue is a CCD 86 for blue and red is a CCD 8 for red.
7. Green is read by the CCD 88 for green. An analog signal from the CCD is converted into a digital signal by an A / D conversion board (not shown) and image processed.

When the image-processed first color digital signal is input to the image writing device 3, the semiconductor laser which is a writing light source (not shown) passes through a collimator lens and a cylindrical lens (not shown) and is driven. It is rotationally scanned by the rotary polygon mirror 34 rotated by the motor 31, and the fθ lens 32 and the cylindrical lens 3
After passing through 3, the optical path is bent by the mirror 35 and is projected onto the peripheral surface of the photoconductor drum 1 to which uniform charge is applied in advance by the scorotron charger 2 which is a charging means, and main scanning is performed to form a bright line. To form. Therefore, by the main scanning by the laser beam and the sub-scanning by the rotation of the photosensitive drum 1, the first surface is formed on the peripheral surface of the photosensitive drum 1.
An electrostatic latent image corresponding to the color of is formed.

This electrostatic latent image is reversely developed by the developing device 4A loaded with a two-component developer consisting of yellow (Y) toner and a magnetic carrier, and a toner image is formed on the photosensitive drum 1. The obtained toner image is the photosensitive drum 1.
After passing through the transfer device 5 and the cleaning device 6 which are separated from the photoconductor drum 1 while being held on the surface thereof, the next image forming cycle is started.

The photosensitive drum 1 is recharged by the scorotron charger 2, and then a digital signal corresponding to the second color is input to the image writing device 3.
Writing on the surface of the photosensitive drum 1 is performed in the same manner as in the case of the first color signal described above, and an electrostatic latent image is formed. The electrostatic latent image is a developing device 4B loaded with a two-component developer including a magenta (M) toner and a magnetic carrier as a second color.
Reverse development is performed by. This magenta (M) toner image is also formed on the previously formed yellow (Y) toner image.

4C is a developing device having a two-component developer composed of cyan (C) toner and a magnetic carrier, and a cyan (C) toner image is formed on the surface of the photosensitive drum 1 in the same manner as the first and second colors. To form. Further, 4D is a developing device having a two-component developer composed of black toner and a magnetic carrier, and forms a black toner image on the surface of the photosensitive drum 1 by the same processing as the above-mentioned color.

The multicolor toner image thus formed on the peripheral surface of the photosensitive drum 1 is sent from the paper feeding device 9 by applying a high voltage having a polarity opposite to that of the toner to the transfer pole 5a of the transfer device 5. It is configured to be transferred to a transfer material.

That is, the transfer material accommodated in the paper feeding device 9 is fed to the transfer device 5 at the same timing as the image formation on the photosensitive drum 1 by carrying out the uppermost one sheet by the rotation of the paper feeding roller 10. To be done.

The transfer material thus transferred with the image is separated from the photosensitive drum 1 along the transfer belt 5b of the transfer device 5. The transfer material separated from the transfer belt 5b by a paper removing electrode (not shown) is conveyed to the fixing device 12 by the conveying belt 11, the image is fused by the fixing roller 12a of the fixing device 12, and then the paper discharge roller 12b.
Then, the sheet is discharged to the sheet discharge tray 13.

On the other hand, the photosensitive drum 1 which has been transferred to the transfer material is further rotated to bring the blade 6a of the cleaning device 6 and the toner carrying roller 6b into a pressure contact state,
After the remaining toner is removed, the blade 6a is separated after the removal, and a little later, the toner supply roller 6b is removed.
To start a new image forming process.

The overall configuration diagram of FIG. 4 and the sectional view of FIG. 5 show the configuration of a color image forming apparatus II having a system different from that of the color image forming apparatus I. The developing device of the present invention is effective even when mounted on the color image forming device II, so the color image forming device II will be described below.

Reference numeral 110 denotes a drum-shaped image forming body, that is, a photosensitive drum, and a transparent conductive layer and an organic photosensitive layer (OPC) are applied to the outer periphery of a cylindrical substrate formed of a transparent member such as optical glass or transparent acrylic resin. It was done.

In the present invention, in the photoconductor layer of the photoconductor drum, which is the image formation point of the exposure beam for image exposure, a proper contrast is given to the light attenuation characteristic (photocarrier generation) of the photoconductor layer. It suffices that the exposure light amount has a wavelength that can be used. Therefore, the light transmittance of the transparent substrate of the photoconductor drum in the present invention does not have to be 100%, and may have a characteristic that some light is absorbed when the exposure beam is transmitted. As the material of the translucent substrate, various translucent resins such as soda glass, Pyrex glass, borosilicate glass and fluorine, polyester, polycarbonate and polyethylene terephthalate used for general optical members can be used. Further, as the translucent conductive layer,
Indium, tin oxide (ITO), tin oxide, lead oxide, indium oxide, copper iodide, Au, Ag, Ni, A
A thin metal film that maintains translucency, such as l, is used.
As the film forming method, a vacuum vapor deposition method, an active reaction vapor deposition method, various sputtering methods, various CVD methods, dip coating methods, spray coating methods and the like are used. Also, as the photoconductor layer,
An amorphous silicon (a-Si) photosensitive layer, an amorphous selenium photosensitive layer, and various organic photosensitive layers (OPC) can be used.

A flange 110A at one end of the photosensitive drum 110 is bearing-supported by a guide pin 130P provided in a cartridge 130 described later, and a flange 110B at the other end is a plurality of guide rollers provided on a substrate 140 of the apparatus main body. 140R externally fitted to the outer gear 110
G is engaged with the drive gear 140G, and the power thereof is rotated clockwise with the transparent conductive layer being grounded.

Reference numeral 111 denotes a scorotron charger, which performs a charging operation on the above-described organic photoconductor layer of the photoconductor drum 110 by a grid held at a predetermined potential and a corona discharge by a discharge wire, and charges the photoconductor drum 110 with one. Such a potential is applied.

Reference numeral 112 designates FL, EL, in which light emitting elements arranged in the axial direction of the photosensitive drum 110 are arranged in a line in an array.
An exposure optical system composed of PL, LED, LISA, PLZT, LCS in which light emitting elements and elements having an optical shutter function are lined up in one row, and a SELFOC lens as an equal-magnification imaging element, and a separate image reading The image signals of the respective colors read by the apparatus are sequentially taken out from the memory and input to the exposure optical systems 112 as electric signals.

Each of the exposure optical systems 112 is mounted on a cylindrical support member 120 which is fixed to the substrate 140 of the apparatus main body with guide pins 140P1 as guides, and is housed inside the base of the photosensitive drum 110. .

Reference numerals 4Y to 4K denote developing units for accommodating yellow (Y), magenta (M), cyan (C), and K (black) developers, respectively, and a predetermined gap with respect to the peripheral surface of the photosensitive drum 110. A developing sleeve serving as a developer transporting body 41 that rotates in the same direction while maintaining the above state is provided.

Each of the above-mentioned developing devices corresponds to the above-mentioned charging device 111.
The electrostatic latent image formed on the photoconductor drum 110 by the charging by the charging and the image exposure by the exposure optical system 112 is reversely developed in a non-contact state by applying a developing bias voltage.

Next, the process of the color image forming apparatus in this apparatus will be described.

The image of the original is read by an image reading apparatus separate from this apparatus, and the image read by the image pickup device or the image edited by the computer is once used as an image signal for each color of Y, M, C and K. Stored and stored in memory.

By the start of the image recording, the drive gear 140G is rotated by the start of the photoconductor drive motor to rotate the photoconductor drum 110 clockwise, and at the same time, the charger 1
The charging action of 11 (Y) starts applying the potential to the photoconductor drum 110.

After a potential is applied to the photosensitive drum 110, the exposure optical system 112 (Y) starts exposure by an electric signal corresponding to the first color signal, that is, the image signal of yellow (Y), and the exposure of the drum is started. By rotating and scanning, an electrostatic latent image corresponding to the yellow (Y) image of the original image is formed on the photosensitive layer on the surface thereof.

The latent image is reversal-developed by the developing device 4 (Y) while the developer on the developing sleeve 41 serving as the developer transporting body 41 is in a non-contact state, and yellow (Y) is generated according to the rotation of the photosensitive drum 110. Toner image is formed.

Next, the photoconductor drum 110 is further given a potential on the yellow (Y) toner image by the charging action of the charger 111 (M), and the exposure optical system 112 (M).
Of the second color signal, that is, an electric signal corresponding to a magenta (M) image signal, is exposed, and non-contact reversal development is performed by the developing device 4 (M) to form an image on the yellow (Y) toner image. Toner images of magenta (M) are sequentially superposed and formed.

By the same process, the charger 111
(C), exposure optical system 112 (C) and developing device 4 (C)
In addition, a cyan (C) toner image corresponding to the third color signal is generated by the charger 111 (K) and the exposure optical system 11.
The black (K) toner image corresponding to the fourth color signal is sequentially formed by 2 (K) and the developing device 4 (K), and the color image is formed on the peripheral surface of the photosensitive drum 110 within one rotation. Toner image is formed.

Photoreceptor drum 1 by each of these exposure optical systems
The exposure of the organic photosensitive layer 10 is performed from the inside of the drum through the transparent substrate. Therefore, the exposure of the images corresponding to the second, third, and fourth color signals is performed without any influence of the toner image previously formed,
It is possible to form an electrostatic latent image equivalent to the image corresponding to the first color signal. In order to stabilize the temperature inside the photoconductor drum 110 and prevent the temperature from rising due to the heat generated by each exposure optical system 112, a material having good thermal conductivity is used for the support member 120, and a heater 201 is used when the temperature is low. When the temperature is high, it can be suppressed to a level without any trouble by taking measures such as radiating heat to the outside through the heat pipe 202.

The color toner image thus formed on the peripheral surface of the photoconductor drum 110 is conveyed from the paper feed cassette 115 in the transfer unit 114A and is transferred to the timing roller 116.
Is transferred to the transfer paper which is fed in synchronism with the driving of.

The transfer sheet on which the toner image has been transferred is separated from the peripheral surface of the drum by removing the charge in the static eliminator 114B, and the toner is fused by the fixing device 117, and then the upper part of the device is passed through the paper discharge roller 118. Will be ejected onto the tray.

On the other hand, the photosensitive drum 11 from which the transfer paper is separated
In the case of 0, the cleaning device 119 removes and cleans the residual toner to continue forming the toner image of the original image, or temporarily stops and forms a toner image of a new original image.

The above-mentioned photosensitive drum 110 and each charger 11
1. Each developing device 4 and further the cleaning device 119 are housed in the cartridge 130 and integrated into the main body of the apparatus, leaving the supporting member 120 having the optical system 112, without giving a load or a shock to the image exposing means. It is configured to be removable. The structure in which the supporting member 120 is left when attaching / detaching is achieved by fixing the heater 201, the heat pipe 202, the lead wire 203 for operating the LED, and the optical system 112 to the supporting member 120 despite the rotation of the photoconductor and the attachment / detachment of the photoconductor. It has a feature that can be set. In addition, photosensitive drum 1
It can also be used to determine the 10 axis.

The color image forming apparatus II has been described above. Although the two color image forming apparatuses I and II have different systems, the same developing apparatus (developing device) of the present invention is mounted and the same. Although it has such an effect, this will be described in detail later.

FIG. 6 shows an enlarged sectional view of the developing area. At the time of development, an AC bias voltage with a DC bias superimposed is applied to the developer transport body 41, and at least a voltage of the DC bias power source E3 is applied to the electrode portion 45b provided on the plate member 45a.
Then, the voltage of the AC bias power source E6 is applied to the elastic member 50 via the protection resistor R3 so as to be superimposed on the DC bias power source E5. As a result, a first oscillating electric field 48 that causes the toner to fly is formed between the electrode portion 45b including the elastic member 50 and the developer transport body 41, and between the image carrier 1 and the developer transport body 41. A second oscillating electric field 49 that is weaker than the first oscillating electric field is formed. The toner cloud generated by the first oscillating electric field 48 is guided to the second oscillating electric field side and further guided to the image carrier 1 to promote toner adhesion on the image carrier 1.

When the plate-like member 45 having the electrode portion is set in the developing space A, the angle θ formed by the tip of the electrode portion and the position where the developer carrier 41 and the image carrier 1 face each other is considered in terms of developability. It is preferable that θ is large, but if it is too large, the electrode portion 45
Since the effect of installing b in the development space A is lost, θ is preferably an angle of 0 to 20 °. If the gap between the photoconductor drum 1 and the developer transport body 41 is small, the applied bias voltage can be reduced, but if it is too small, it becomes difficult to install the plate-like electrode 45 having the electrode portion. To 1.0 mm is preferable. The distance between the developer transport body 41 and the developer transport body downstream electrode portion 45c is preferably 0.2 to 0.6 times the gap between the developer transport body 41 and the image carrier 1. Developer carrier 41
If the ratio of the moving speed V _S (mm / sec) of the image carrier to the moving speed V _P (mm / sec) of the image carrier 1 is large, the developability is improved, but if it is too large, the edge effect at the trailing edge of the image becomes remarkable. Therefore, the range of V _S / V _P = 0.5 to 4.0 is preferable. If the amount of the developer transported by the developer transport body 41 is large, the developability is improved, but if it is too large, the carrier adheres to the photosensitive drum 1 due to the spikes, so that the amount is 5 mg / cm ² to 40 mg / cm ^2. It is preferably included in the range of ² .

The waveform of the AC voltage component applied to the developer carrier 41 is not limited to a rectangular wave, and may be a sine wave or a triangular wave. The higher the voltage value, the more the toner vibrates and the developability improves. However, if the voltage value is too high, the lightning strike phenomenon on the photosensitive drum 1 due to the dielectric breakdown and the fogging on the non-image area become remarkable. Therefore the applied AC bias voltage (V _AC p-p)
Is preferably in the range of 200V to 2kV. If the frequency is low, it is advantageous for the developability and gradation, but if it is too low, the toner previously developed on the image carrier 1 is returned to the developing device to cause color mixing. Therefore, the frequency is 500Hz
To 20 kHz is preferred. The fogging is prevented by controlling the DC voltage component applied to the developer transport body 41, and the dielectric breakdown is provided with an insulating or semi-insulating coating on the surface of the developer transport body 41. The carrier can be prevented by providing an insulating coating.

As the developer used in the developing device of the present invention, preferable toner is styrene resin, vinyl resin,
Acrylic resin, polyamide resin, silicone resin, polyester resin, fluororesin, epoxy resin, and other resins are mixed with a coloring component such as a color pigment or color dye and a charge control agent, etc. It can be made by any method. This is obtained by selecting particles having an average particle size of 20 μm or less, preferably 5 to 10 μm, by a conventionally known particle size selecting method. The charge amount of the toner depends on the particle size, but is preferably 3 to 300 μC / g, and more preferably 10 to 50 μC / g.

The carrier may be a metal such as iron, chromium, nickel, cobalt, zinc or copper, or a compound or alloy thereof such as γ-ferric oxide, chromium dioxide, manganese oxide, or a ferromagnetic material such as ferrite. Or spherical particles of paramagnetic material, or the surfaces of these magnetic material particles are spherically coated with a resin such as styrene resin, vinyl resin, ethylene resin, acrylic resin, polyamide resin, polyester, or magnetic material. Particles obtained by forming spherical particles of a resin or fatty acid wax containing fine particles dispersed therein are used. An average particle size of 100 μm or less, preferably about 30 to 60 μm, is suitably used. If the average particle diameter is larger than this, unevenness appears in the toner image and the toner density becomes low, so that problems such as high-density development occur. If it is smaller than this, the photosensitive drum 1 together with the toner occurs. It causes a problem of flying above. Further, it is more preferable that the carrier is spherical because the stirring property and the transport property of the toner and the carrier are improved and the charge controllability of the toner is also improved. Coating the carrier particles with a resin or the like has the effect of increasing the bias voltage applied to the developer transport body 41. Therefore, even if a high bias voltage is applied to the developer transport body, the photosensitive drum 1 is not discharged and the image is not disturbed. Further, the carrier having a resistivity of 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm or more, is preferable. This resistivity was measured by placing the particles in a container having a cross section of 0.5 cm ² and tapping them, and then putting 1 on the packed particles.
A load of kg / cm ² is applied, and 1 is applied between the load and the bottom electrode.
It is a value obtained by reading the current value when a voltage that generates an electric field of 000 V / cm is applied. When this resistance value is low, when a bias voltage is applied to the developer transport body 41, electric charges are injected into the carrier, carrier particles adhere to the photosensitive drum, and a bias voltage breakdown easily occurs.

In the developing device of the present invention, a two-component developer in which a spherical carrier and a toner are mixed as described above is preferably used, and a fluidizing agent for increasing the fluidity of particles as necessary. Also, a cleaning agent for cleaning the surface of the image forming body can be mixed with the toner. As the fluidizing agent, colloidal silica, silicon varnish, metal soap, nonionic surface active agent and the like can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicon, fluorine and other surface active agents can be used. You can

Concretely, the demonstration of the embodiments of claims 1 to 8 was performed as follows, and the results of Experiment 1, Experiment 2 and Experiment 3 were obtained.

Experiment 1 Experimental machine used: Color image forming apparatus A as shown in FIG. That is, a modified 9028 (manufactured by Konica Corporation) was used.

Developer (42) used: A spherical magnetic carrier obtained by resin-coating ferrite particles having an apparent density of 2.45 g / cm ³ , a volume average particle size of 45 μm, and a saturation magnetization of 60 emu / g was used as the carrier. ,
Manufactured by kneading 100 parts by weight of styrene-acrylic resin and 10 parts by weight of pigment with the required amount of charge control agent,
The non-magnetic toner having a weight average particle size of 7 μm obtained by the pulverization and granulation method has a toner ratio of 10 wt% with respect to the carrier,
600 g of a black developer was prepared so that the average toner charge amount (measured by the development separation method) measured by the development separation method was −20 μC / g.

Photoconductor (1): OPC photoconductor drum (φ1
80) Peripheral speed is 140 mm / sec Developer carrier (41): Stainless steel is roughened by sandblasting, diameter φ20 mm, rotation speed is 300
rpm plate electrode member (45) having an electrode part: an electrode having a width of 0.5 mm was formed by etching a copper foil on an epoxy resin (thickness 0.16 mm) reinforced by glass fiber, and a dielectric constant at 1 MHz was 4.5 at 25 ° C. Elastic member (50): Stainless steel plate (thickness 0.1 mm) Method of supporting plate-shaped member on elastic member: Supported by adhesion with an ultraviolet curable resin. (Structure of FIG. 2 (A)) d1 is 5 m
m and d2 were 5 mm.

Gap between the developer transport body 41 and the image carrier 1: 0.5 mm Closest distance between the developer transport body 41 and the electrode portion 45b: 0.25 mm V _S / V _P = 2.24 Developer transport amount : 10 mg / cm ² Maximum potential of the electrostatic latent image on the image carrier 1 at the black developing position: -800 V Bias voltage applied to the electrode part 45 b: DC bias voltage: -700 V Bias voltage applied to the developer transport body 41: DC bias voltage component: -700V AC bias voltage component: 8kHz, 800V With such an experimental configuration, a latent image is formed in a non-image area as in the following Comparative Examples and Examples, and only K is developed, Each 1000 sheets were copied and the result was obtained.

Comparative Example 1: No bias was applied to the elastic member 50. Result: toner adhered to the elastic member 50, and image was stained. Example 1: -1000 V was applied to the elastic member 50 (during development and non-development). Result: No toner adhered to the elastic member and no image stains Example 2: -1000V applied to elastic member 50 (during development) -1000V + 800Vp-p applied (non-developed) Result: on elastic member No toner adhered and no image smear Example 3: Floating elastic member 50 (during development) -1000 V (no development) Result: No toner adhered to elastic member, no image smear Example 4 : Elastic member 50 Floating (during development) -1000V + 800Vp-p applied (during non-development) Result: No toner adhered to the elastic member and no image smear Experiment 2 Experiment 1 In addition to such an experimental configuration, a latent image is formed in a non-image area as in the following comparative examples and examples, and not only K but also Y,
Full color development is performed using the M and C developers, each 1
000 sheets were copied and the result was obtained.

Comparative Example 2: No bias was applied to the elastic member 50. Result: toner adhered to the elastic member 50, image smeared, large color mixture Example 5: elastic member 50-1000V (during development) floating (others) Color toner development) -1000V + 800Vp-p application (non-development) Result: No toner adhered to the elastic member, no image stain (small color mixture) Example 6: Elastic member 50-1000V (during development) -1000V ( Other color toner development) -1000V + 800Vp-p application (non-development) Result: No toner adhered to elastic member, no image stain (small color mixture) Example 7: Elastic member 50-1000V (always) Result: elasticity No toner adhered to the member and no stain on the image (small color mixture) Example 8: Elastic member 50 Floating (during development) Floating (other color toner development) ) -1000V + 800Vp-p applied (at the time of non-development) Result: No toner adhered to the elastic member, no image stain (small color mixture) Experiment 3 Next, as described in FIG. 4 and FIG. A plurality of sets of charging means, image exposing means and developing means are arranged, charging, image exposure and development are repeated during one rotation of the image carrier to form toner images on the image carrier, and Using a color image forming apparatus B of the type in which a toner image is collectively transferred to a transfer material, the same experimental configuration as in Experiment 1 and Experiment 2 was used, and the latent image was formed in the non-image area as in the following Comparative Examples and Examples. An image was formed and full-color development was performed using not only K but also Y, M, and C developers, and 1000 copies were made, and the following results were obtained.

Comparative Example 3: No bias was applied to the elastic member 50 Result: toner adhered to the elastic member 50, image smearing and large color mixing Example 9: elastic member 50 floating (during development) -1000V + 800Vp-p Application (at the time of non-development) Result: No toner adhered on elastic member, no image stain (small color mixture) Example 10: Elastic member 50-1000 V (always) Result: No toner adhered on elastic member, image No stain (small color mixture) Example 11: Elastic member 50-1000V (during development) -1000V + 800Vp-p application (non-development) Result: No toner adhered on the elastic member, no image stain (small color mixture) Example 12: Elastic member 50 floating (during development) -1000 V applied (non-developed) Result: No toner adhered to the elastic member, no image stain (small color mixture) Above is the embodiment of the preceding claims.

Next, the piezoelectric vibrator is provided, and the elastic member is vibrated instead of applying the bias to the elastic member. 5 and Experiment 6 will be described with reference to Comparative Examples and Examples.

As shown in the partial sectional view of FIG. 7, the electrode portion 4 is provided with the above-mentioned piezoelectric vibrator to give vibration to the elastic member.
The piezoelectric vibrator 55 is mounted on the elastic member 50 to which the plate-shaped member 45a having the tip 5b attached is laminated and attached. The vibration causes the toner that tends to accumulate on the elastic member 50 to be filtered out, so that the risk of image contamination and color mixing is eliminated by setting the timing of energization for applying vibration.

The mounting angle α of the elastic member 50 with respect to the horizontal plane is shown in the side view of the developing device in FIG. 8, and any of the plurality of developing devices 4 is larger than 45 ° and larger than 270 °. The range is small.

Experiments 4, 5 and 6 were carried out with the same experimental configuration except that the above Experiments 1 to 3 were different only in the above conditions.

Experiment 4 With α = 60 ° in the above experimental configuration, a latent image was formed in a non-image area and K was developed as in the following Comparative Examples and Examples, and 1000 copies were made for each. The following results were obtained.

Comparative Example 4: No Piezoelectric Vibrator Set Result: Large Toner Adhesion, Image Staining Example 13: Piezoelectric Vibrator Installed on Elastic Member, Vibrated in Non-Image Area Result: Large Toner Adhesion, Image No Contamination Example 14: Piezoelectric vibrator installed on plate member and vibrated in non-image area Result: Large amount of toner adhesion, no image contamination Experiment 5 In addition to the experimental configuration of Experiment 4, color image forming apparatus A was used.
Using α, Y is 135 °, M is 110 °, and C is 85
.Degree. And K are set to 60.degree., A latent image is formed in a non-image area as in the following comparative examples and examples, and not only K but also Y, M,
Full color development is performed using the C developer and 100
0 copies were made and the following results were obtained.

Comparative Example 5: No Piezoelectric Vibrator Set Result: Large Toner Adhesion, Image Contamination (Large Color Mixing) Example 15: Piezoelectric Vibrator Installed on Elastic Member, Vibrated in Non-Image Area Result: Toner Large adhesion, no image stain (small color mixture) Example 16: Piezoelectric vibrator installed on plate member and vibrated in non-image area Result: Large toner adhesion, no image stain (small color mixture) Experiment 6 Experiment 4 In addition to various experimental configurations, color image forming apparatus B
Using α, Y is 270 °, M is 210 °, and C is 150.
.Degree. And K are set to 90.degree., A latent image is formed in a non-image area as in the following comparative examples and examples, and not only K but Y, M,
Full color development is performed using the C developer and 100
0 copies were made and the following results were obtained.

Comparative Example 6: No Piezoelectric Vibrator Set Result: Large Toner Adhesion, Image Stain (Large Color Mixing) Example 17: Piezoelectric Vibrator Installed on Elastic Member and Vibrated in Non-Image Area Result: Toner Large adhesion, no image stain (small color mixture) Example 18: Piezoelectric vibrator installed on plate member and vibrated in non-image area Result: Large toner adhesion, no image stain (small color mixture)

[0099]

As described above, according to the present invention, it is possible to provide a developing device and a color image forming apparatus capable of obtaining a clear recorded image without density unevenness, image stain and color mixture.

That is, in the developing space where the developer carrier and the image carrier face each other, the electrode portion is installed on the plate member supported by the free end of the elastic member, and the developing sleeve as the developer carrier, An effective developing gap is reduced by the developing device or the color image forming apparatus according to claims 1 to 8 of the present invention in which a bias voltage is applied to the electrode portion and the elastic member, respectively.
Since the developing bias voltage can be set low and the plate-shaped member can be set accurately, a clear recorded image in which density unevenness does not occur and image stains and color mixing hardly occur can be obtained.

The developing device or the color image forming apparatus according to claims 9 to 17 of the present invention, which applies vibration by a piezoelectric vibrator instead of applying a bias to the elastic member or the plate-like member, causes an image without density unevenness. A clear recorded image similar to the above can be obtained in which stains and color mixing hardly occur.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an example of a developing device of the present invention.

FIG. 2 is a schematic diagram showing the configuration and arrangement of an electrode portion, a plate-shaped member, and an elastic member used in the developing device of the present invention.

FIG. 3 is an overall configuration diagram showing an embodiment of a color image forming apparatus A using a developing device of the present invention.

FIG. 4 is an overall configuration diagram showing an embodiment of a color image forming apparatus B using the developing device of the present invention.

FIG. 5 is a sectional view of a process cartridge of a color image forming apparatus B using the developing device of the present invention.

FIG. 6 is an enlarged cross-sectional view showing a developing area of the developing device of the present invention.

FIG. 7 is a partial cross-sectional view of a developing device to which a piezoelectric vibrator is attached.

FIG. 8 is a side view of the developing device showing the inclination angle α of the elastic member to which the piezoelectric vibrator is attached.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image bearing member) 4, 4A, 4B, 4C, 4D Developing device 41 Developer carrier 42 Developer 43 Stirrer 44 Supply roller 45 Plate member having an electrode part 45a Plate member 45b Electrode part 46 Developer conveyance regulation rod 47 Scraper 48 First oscillating electric field 49 Second oscillating electric field 50 Elastic member A Development space E1 DC bias power supply (developer transfer body side) E2 AC bias power supply (developer transfer body side) E3 DC bias power supply ( Electrode side) E5 AC bias power supply (electrode side) L Electrode width P Closest contact point between developer carrier and plate member R1 Protective resistance (developer carrier side) R2 Protective resistance (electrode side)

Claims (17)

[Claims] 1. A plate-shaped member having an electrode part supported by being laminated on a free end of an elastic member is installed in a space where a developer carrier and an image carrier are opposed to each other, and the electrode part of the plate-shaped member is provided. At least a DC voltage is applied to the developer carrier, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer carrier to fly toner on the developer carrier to develop a latent image on the image carrier. In the developing device described above, a bias can be applied to the elastic member. 2. The bias applied to the elastic member is a DC voltage having the same polarity as the toner.
The developing device according to 1. 3. The developing device according to claim 1, wherein the bias applied to the elastic member is a superimposed voltage of a DC voltage and an AC voltage. 4. The developing device according to claim 1, wherein a latent image is formed before or after image formation. 5. A plate-shaped member having an electrode part supported by being laminated on a free end of an elastic member is installed in a space where a developer carrier and an image carrier are opposed to each other, and the electrode part of the plate-shaped member is installed. At least a DC voltage is applied to the developer carrier, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer carrier to fly toner on the developer carrier to develop a latent image on the image carrier. In a color image forming apparatus having a plurality of developing devices for transferring images superposed on a drum at a time, a voltage can be applied to the elastic member, and another color toner is applied to the elastic member during development. A color image forming apparatus characterized in that a DC voltage of the same polarity as that of a toner is electrically applied during development, and a DC voltage of at least the same polarity as that of a toner is applied during non-development. 6. The color image forming apparatus according to claim 5, wherein an AC voltage is superimposed on the DC voltage during non-development according to claim 5. 7. The color image forming apparatus according to claim 5, wherein latent image formation is performed during non-development according to claim 5 or 6. 8. The color image forming apparatus comprises a plurality of sets of charging means, image exposing means and developing means arranged on an image carrier, and the charging, the image exposing and the developing are repeated during one rotation of the image carrier. 8. The color image forming apparatus according to claim 5, wherein a toner image is formed on the image carrier by superimposing the toner images, and then the toner images are collectively transferred to a transfer material. . 9. A plate-shaped member having an electrode part supported by being laminated on a free end of an elastic member is installed in a space where the developer carrier and the image carrier are opposed to each other, and the electrode part of the plate-shaped member is provided. At least a DC voltage is applied to the developer carrier, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer carrier to fly toner on the developer carrier to develop a latent image on the image carrier. In the developing device, a piezoelectric vibrator is installed, and the elastic member or the plate-shaped member is subjected to vibration from the piezoelectric vibrator. 10. The developing device according to claim 9, wherein an installation angle α of the plate member with respect to a horizontal line is larger than 45 ° and smaller than 270 °. 11. The developing device according to claim 9, wherein the latent image is formed before or after image formation. 12. The developing device according to claim 9, wherein the elastic member is formed with a mesh. 13. A plate-shaped member having an electrode part supported by being laminated on a free end of an elastic member is installed in a space where a developer carrier and an image carrier are opposed to each other, and the electrode part of the plate-shaped member is provided. At least a DC voltage is applied to the developer carrier, and a superimposed voltage of a DC voltage and an AC voltage is applied to the developer carrier to fly toner on the developer carrier to develop a latent image on the image carrier. In a color image forming apparatus having a plurality of developing devices that collectively transfer images superposed on a drum, a piezoelectric vibrator is installed, and the piezoelectric vibration is applied to the elastic member or the plate-shaped member in a non-image portion. A color image forming apparatus characterized by applying vibration from a child. 14. The color image forming apparatus according to claim 13, wherein an installation angle α of the plate member with respect to a horizontal line is larger than 45 ° and smaller than 270 °. 15. The color image forming apparatus according to claim 13, wherein the latent image is formed before image formation or during non-development after image formation. 16. The elastic member is formed with a mesh, as claimed in any one of claims 13 to 15.
Item 10. A color image forming apparatus according to item 9. 17. The color image forming apparatus comprises a plurality of sets of charging means, image exposing means and developing means arranged on the image carrier, and the charging, the image exposure and the development are repeated during one rotation of the image carrier. 17. The color image forming apparatus according to claim 13, wherein the toner images are formed on the image carrier by superimposing them, and then the toner images are collectively transferred to a transfer material. .