JP2002278214A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device by which color mixture at a next transfer process due to electrified toner having a reverse polarity at a previous transfer process and defective transfer at the next transfer process due to the large electrified amount of a toner image at the previous transfer process are prevented. SOLUTION: This color image forming device is provided with a toner image electrifying means by which a transferred toner image has the same polarity as that of toner to be developed and has low electrified amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus using an intermediate transfer member used for image formation such as a copying machine, a printer, and a facsimile, and more particularly to a color image forming apparatus having a plurality of image forming units arranged on the intermediate transfer member. The present invention relates to a color image forming apparatus that forms a superposed color toner image.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a multi-color image, an image carrier having the same number of images as required and a charging means, an image writing means and a developing means provided around the image carrier are provided. A device in which a single-color toner image formed on each image carrier is superimposed to form a color image, or charging, image exposure (image writing), and development for each color are repeated by rotating one image forming body a plurality of times. A device for forming a color image superimposed on an image carrier, or repeating charging, image exposure (image writing), and development for each color on one image carrier during one rotation of the image carrier. 2. Description of the Related Art An apparatus for forming a superimposed color image on an image carrier is known.

[0003] In particular, an image carrier having the same number of images as necessary and an image forming process means (toner image forming means) such as a charging means, an image writing means and a developing means are provided around the image carrier. Each of a color image forming apparatus and a plurality of image forming process units (toner image forming units) that superimpose a single color toner image formed on each image carrier on a belt-shaped intermediate transfer body to form a color image A color image forming apparatus or the like that forms a color image by superimposing a single-color toner image formed on an image carrier on a transfer material conveyed on a belt-shaped intermediate transfer body to form a good color image It has been used recently.

[0004]

SUMMARY OF THE INVENTION However,
By a plurality of image forming process units (toner image forming units) such as an image carrier, a charging unit, an image writing unit, and a developing unit,
In a color image forming apparatus that forms a superimposed color toner image on a belt-shaped intermediate transfer body or a transfer material, a toner used for development by corona discharge in a previous transfer step of a toner image on an image carrier. There is a problem that the toner is charged to the opposite polarity to the polarity (the opposite polarity charged toner is generated), and the opposite polarity charged toner adheres to the image carrier at the next transfer to cause color mixing. Further, in the transfer step of the toner image on the image carrier, the charge amount (Q / M) of the previous toner image is high due to corona discharge, and the transfer rate of the toner image in the next transfer step is reduced. The problem of poor transfer occurs.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and provides a color image forming apparatus for forming a color toner image to be superimposed on a belt-like intermediate transfer member or a transfer material by a plurality of image forming process means. Provided is a color image forming apparatus that prevents color mixing in a next transfer step using a toner of the opposite polarity charged in a transfer step and transfer failure in the next transfer step due to a high charge amount of a toner image in a previous transfer step. With the goal.

[0006]

An object of the present invention is to provide an image forming apparatus, comprising: a plurality of image forming units for forming a toner image on an image bearing member arranged on an intermediate transfer member; The toner images formed on the image carrier are sequentially transferred to an intermediate transfer body to form a superimposed color toner image on the intermediate transfer body, and then the color toner image on the intermediate transfer body is transferred. In a color image forming apparatus which collectively transfers images onto a transfer material and fixes the color toner image on the transfer material by a fixing device, the transferred toner image has the same polarity as the toner to be developed and has a low charge amount. The present invention is achieved by a color image forming apparatus (first invention) in which a toner image charging means is provided.

Another object of the present invention is to arrange a plurality of image forming units for forming a toner image on an image bearing member on an intermediate transfer member, and to use the image bearing member with a different color for each image forming unit. The toner image formed on the transfer material is sequentially transferred to a transfer material conveyed on an intermediate transfer body, and a color toner image is formed on the transfer material, and then the color toner image on the transfer material is fixed. A color image forming apparatus which fixes the transferred toner image by using a toner image charging unit which has the same polarity as the toner to be developed and performs low charging on the transferred toner image. Invention).

[0008]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. In the following description of each image forming apparatus in the embodiment, members having the same functions and structures are given the same numbers or the same symbols.

FIG. 1 shows an image forming process and each mechanism of an embodiment of a color image forming apparatus according to the present invention.
This will be described with reference to FIG. FIG. 1 is a sectional view showing an embodiment of a color image forming apparatus according to the present invention, FIG. 2 is an explanatory view of a toner image charging means in FIG. 1, and FIG. FIG. 4 is a diagram illustrating a state in which a carrier cleaning unit is omitted, and FIG. 4 is a schematic cross-sectional configuration diagram illustrating another example of a color image forming apparatus according to the present invention.

According to FIGS. 1 to 3, as shown in FIG. 1, an original plate made of a transparent glass plate or the like and an original D placed on the original plate are covered on the upper portion of the color image forming apparatus. There is a document placing portion 111 composed of a document cover or the like, and a first mirror unit 112, a second mirror unit 113, a main lens 12
0, an image reading unit A including a color CCD 123 and the like is provided. The first mirror unit 112 includes an exposure lamp 114 and a first mirror 115.
It is attached so as to be able to move linearly in the horizontal direction of the drawing, and optically scans the entire surface of the document D. The second mirror unit 113 integrally includes a second mirror 116 and a third mirror 117, and linearly moves in the same direction on the left and right at half the speed of the first mirror unit 112 so as to always maintain a predetermined optical path length. Of course, the movement of the second mirror unit 113 is the first movement.
Like the mirror unit 112, it is parallel to the platen. The image of the document D on the document table illuminated by the exposure lamp 114 is
Color CC through the second mirror 116 and the third mirror 117
The image is formed on D123. When the scanning is completed, the first mirror unit 112 and the second mirror unit 113 return to their original positions, and wait for the next copy.

The image data of each color obtained by the color CCD 123 is subjected to image processing in an image processing section, and image writing is performed in an image forming section E described below as an image signal.

The color image forming apparatus shown in FIG. 1 is a tandem type color image forming apparatus using a belt-shaped intermediate transfer member as an image forming portion E, and a transfer belt 14a which is an intermediate transfer member has a peripheral portion. Black (K), cyan (C),
A process unit 100, which is four sets of image forming process means (toner image forming means) including magenta (M) and yellow (Y), is provided in this order from the upstream side in the rotation direction of the transfer belt 14a. Unit 1
At 00, K, C, M, and Y toner images are formed, these toner images are superimposed and transferred on the transfer belt 14a, and the superimposed color toner image on the transfer belt 14a is transferred to a transfer material. Are collectively transferred onto the recording paper P, fixed, and discharged outside the apparatus.

Photosensitive drums 1 each serving as an image carrier
0, a scorotron charger 11 as a charging unit, an exposure optical system 12 as an image writing unit, and a developing unit 13 as a developing unit
The four process units 100 each including the photoconductor cleaning device 19 serving as an image carrier cleaning unit have a common structure, and only one of them will be described.

A photosensitive drum 10 as an image carrier has a conductive layer and an organic photosensitive layer (OPC) on the outer periphery of a cylindrical substrate.
Is formed.

The photosensitive drum 10 is rotated in a counterclockwise direction indicated by an arrow with the conductive layer grounded by power from a driving source (not shown) or by the transfer belt 14a.

Reference numeral 11 denotes a scorotron charger as charging means, which is attached to the photosensitive drum 10 in a direction orthogonal to the moving direction of the photosensitive drum 10 so as to face and be close to the photosensitive drum 10;
A uniform potential is applied to the photosensitive drum 10 by corona discharge having the same polarity (minus polarity in the present embodiment) as the toner at the time of development.

Reference numeral 12 denotes an exposure optical system as an image writing means for performing K, C, M, and Y image exposure (image writing) based on image data, and a rotating shaft of the photosensitive drum 10 by, for example, a polygon mirror. Is a scanning optical system that performs scanning in parallel with. Exposure optical system 1 on photoreceptor drum 10 uniformly charged
2 performs image exposure (image writing) to form a latent image.

A one-component developer using a negatively (negatively-polarized) conductive toner or a two-component developer including a conductive toner and a magnetic carrier is built in the periphery of the photosensitive drum 10. A developing unit 13 is provided, and performs reversal development by a developing roller 13a as a developer carrier that rotates while holding the developer.

A one-component developer consisting only of toner or a two-component developer obtained by mixing a toner with a carrier having ferrite as a core and an insulating resin coated around the core is coated on a developing roller 13a with 0.1 to 0.1. It is regulated to a layer thickness of 6 mm and transported to the development zone.

Developing roller 13a and photosensitive member in developing area
The gap with the drum 10 is larger than the layer thickness of the developer by 0.2
Developing roller 13a and photosensitive drum
In the present embodiment, there is a negative polarity
DC voltage V_DCAC voltage V_ACSuperimposed on the developing bias
Apply. DC voltage V_DCAnd the same polarity (My
Negative voltage), the AC voltage V_ACBy carrier
The toner that has been triggered to leave the
V_DCV with a higher absolute value of potential_HDoes not adhere to the part of
V with low potential absolute value_LIn the area corresponding to the potential difference
The toner amount adheres and the image is visualized. Further, the developing roller 13a and
DC voltage V between the photosensitive drum 10 _DCOnly apply
You may. The development may be contact development.
No.

A photoconductor cleaning device 19, which is an image carrier cleaning means, is provided downstream of a primary transfer position, which will be described later, in the rotation direction of the photoconductor drum 10. The upper transfer residual toner is cleaned.

The transfer belt 14a, which is an intermediate transfer member, in which four color process units 100 composed of K, C, M and Y face in parallel, has a volume resistivity of 10 ¹⁰ to 10 ¹⁵ Ω · c.
m, an endless belt having a surface resistivity of 10 ¹⁰ to 10 ¹⁵ Ω / □. A conductive material is dispersed in engineering plastics such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy. This is a seamless belt having a two-layer structure in which a 0.1 to 1.0 mm thick semiconductive film substrate is coated with a fluorine coating having a thickness of preferably 5 to 50 μm as a toner filming preventing layer. In addition to the above, the base of the transfer belt 14a has a thickness of 0.1 mm in which a conductive material is dispersed in silicon rubber or urethane rubber.
A 5 to 2.0 mm semi-conductive rubber belt can also be used. The transfer belt 14a is stretched around a drive roller 14d, a driven roller 14e, a backup roller 14j, and a tension roller 14i.
The drive roller 14 is driven by a drive motor (not shown).
d, the transfer belt 14a is pressed against the photosensitive drum 10 by the primary transfer roller 14c as a first transfer unit at the transfer position for each color, and the transfer belt 14a is rotated in the direction indicated by the arrow in the figure. .

A primary transfer roller 14c, which is a first transfer unit for each color, is provided to face the photosensitive drum 10 for each color with the transfer belt 14a interposed therebetween, and the transfer belt 14a and the photosensitive drum for each color are provided. 10, a transfer area (no sign) for each color is formed. A primary transfer bias VTa composed of a DC voltage having a polarity opposite to that of the toner (positive polarity in the present embodiment) is applied to the primary transfer roller 14c for each color, and a transfer electric field is formed in a transfer area. The toner image on the photosensitive drum 10 is transferred onto the transfer belt 14a.

Toner image charger 2 as toner image charging means
00 is a ground roller 14k with the transfer belt 14a interposed therebetween.
As described in detail below, an AC voltage having an AC component (AC component) and a DC voltage having a DC component (DC component) having the same polarity (minus polarity in the present embodiment) as the toner. A toner image charging bias VTb (see FIG. 2, not shown in FIG. 1) including a voltage is applied to the toner image charger 200 to charge the toner image transferred onto the transfer belt 14 a and perform the primary transfer. The polarity of the oppositely charged toner (toner of positive polarity in the present embodiment) in the toner image on the transfer belt 14a generated at this time is converted to negative polarity to prevent color mixing at the time of the next primary transfer, and The charge amount (Q / M) of the toner of the toner image transferred onto the transfer belt 14a is reduced to prevent a decrease in the transfer rate in the next primary transfer. As the toner image charging bias VTb, an AC voltage may be applied to the corona discharge wire, and a DC voltage may be applied to the seal member (no symbol).

The process unit 1 of black (K) is started by starting a photoconductor drive motor (not shown) by starting image recording.
The photoconductor drum 10 is rotated in the direction indicated by the arrow in the figure, and at the same time, the application of a potential to the K photoconductor drum 10 is started by the charging action of the K scorotron charger 11.

After a potential is applied to the K photosensitive drum 10, image writing is started by an electric signal output from the control unit by the K exposure optical system 12, and the control unit is placed on the surface of the K photosensitive drum 10. An electrostatic latent image corresponding to the output image from is formed.

The K latent image is subjected to reversal development in a contact or non-contact state by a K developing unit 13, and a K toner image is formed in accordance with the rotation of the K photosensitive drum 10. Formed on top.

The K toner image formed on the K photoreceptor drum 10 serving as an image carrier by the above-described image forming process is transferred by the K primary transfer roller 14c in the K transfer area (no symbol). The image is transferred onto the transfer belt 14a.

The K toner image on the transfer belt 14a is charged by the toner image charger 200. At this time, as shown in FIG. 2, for example, an AC component (AC component) having a frequency of about 1 to 5 kHz and a peak-to-peak voltage of about 8 to 10 kV _PP.
And a DC bias E1 (DC voltage) having the same polarity as the toner (negative polarity in the present embodiment) and having a DC component (DC component) of, for example, about -250 to -750 V. Is applied to the toner image charger 200 to charge the toner image at the time of the previous primary transfer transferred onto the transfer belt 14a, and the toner image is charged on the transfer belt 14a generated at the time of the previous primary transfer. The polarity of the opposite polarity charged toner (the positive polarity toner in the present embodiment) in the toner image is converted into the negative polarity, and the previous toner image is converted into the negative polarity.
Adhesion to the photosensitive drum 10 at the time of the next transfer is prevented, and color mixing is prevented. Further, the charge amount (Q / Q) of the toner image of the toner image at the time of the primary transfer previously transferred onto the transfer belt 14a by the AC component (AC component) of the toner image charging bias VTb.
M), for example, from about -20 to -40 μC / g,
Lower to about -15μC / g (about 1/3 to 2/3)
This prevents a decrease in transfer rate during the next primary transfer that occurs when the charge amount (Q / M) of the previous toner image is high. At the time of the primary transfer of the next toner image by the primary transfer roller 14c to which the primary transfer bias VTa having the same polarity as the toner (in this embodiment, a negative polarity) is applied (in this case, cyan (C ), When the toner image is transferred from the photosensitive drum 10 to the transfer belt 14a), the oppositely charged toner (positive polarity toner in this embodiment) is generated again. Thereafter, charging by the toner image charger 200 is performed, and the polarity of the opposite polarity charged toner (positive polarity toner in the present embodiment) in the toner image on the transfer belt 14a generated at the time of the primary transfer is changed. The polarity of the toner image is converted to a negative polarity (the charged polarity of the transferred toner image is aligned).
In addition to preventing color mixing during the next transfer, the transfer belt 14a
The charge amount (Q / M) of the toner of the toner image transferred above is reduced to prevent a decrease in the transfer rate in the next primary transfer.

By charging by the toner image charger 200,
The polarity of the toner image at the time of the previous primary transfer is made uniform (in this embodiment, the polarity is made negative), and the charge amount (Q / M) is reduced. 3, the photoreceptor cleaning device 19 (see FIG. 2 and not shown in FIG. 3) for cleaning the transfer residual toner on the photoreceptor drum 10 as shown in FIG. (Not shown), it is also possible to form a toner image. Photoconductor cleaning device 19 for transfer residual toner on M and Y photoconductor drums 10
Is also unnecessary (cleaner-less). Further, since there is no risk of color mixing for the black (K) toner, the K photoconductor cleaning device 19 is not required. For cleanerless,
The transfer residual toner is collected by each developing device 13.

Slightly after the operation of the K process unit 100, the photosensitive drum 10 of the cyan (C) process unit 100 is rotated in the direction shown by the arrow in the figure, and at the same time, the charging action of the C scorotron charger 11 is performed. As a result, the application of the potential to the C photoconductor drum 10 is started.

After the potential is applied to the photosensitive drum 10 of C, image writing by an electric signal corresponding to the image data of C is started by the exposure optical system 12 of C in synchronization with the toner image of K. An electrostatic latent image corresponding to the image C of the original image is formed on the surface of the photosensitive drum 10.

The C latent image is subjected to reversal development in a contact or non-contact state by a C developing unit 13, and a C toner image is formed on the C photosensitive drum 10 in accordance with the rotation of the C photosensitive drum 10. Formed.

The C toner image formed on the C photoreceptor drum 10 as an image carrier by the above-described image forming process is transferred by the C primary transfer roller 14c in the C transfer area (no symbol). The image is superimposed and transferred on the K toner image on the transfer belt 14a.

The K and C superposed toner images on the transfer belt 14a are charged by the toner image charger 200.

Next, the transfer belt 14a is synchronized with the M toner image, and the magenta (M) process unit 1
00, the M toner image corresponding to the M image data formed on the M photosensitive drum 10 is transferred by the M primary transfer roller 14c in the M transfer area (no sign).
The toner images are superimposed and formed on the superposed toner images of K and C.

The superposed toner image of K, C and M on the transfer belt 14a is charged by the toner image charger 200.

By the same process, the image is synchronized with the superposed toner image of K, C, and M, and is formed on the Y photosensitive drum 10 by the process unit 100 using the yellow (Y) toner. In the Y transfer area (no sign), the Y toner image corresponding to the Y image data
Is formed by superimposing on the toner image of the superimposition of K, C, and M by the primary transfer roller 14c.
A superposed color toner image of K, C, M and Y is formed on the transfer belt 14a.

The K, C, M and Y superposed toner images on the transfer belt 14a are charged by the toner image charger 200.

The untransferred toner remaining on the peripheral surface of the photosensitive drum 10 for each color after the transfer is cleaned by a photosensitive member cleaning device 19 as an image carrier cleaning unit for each color.

In synchronization with the formation of the superposed color toner images on the transfer belt 14a, the recording paper P is transferred from the paper feed cassette 15 as the transfer material storage means via the timing roller 16 as the transfer material supply means. Is transferred to a transfer area (no symbol) of a secondary transfer unit 14g, which is a transfer unit, and is transferred by a secondary transfer unit 14g to which a DC voltage having a polarity opposite to that of the toner (positive polarity in this embodiment) is applied. The superimposed color toner images on the belt 14a are collectively transferred onto the recording paper P. On the recording paper P, K, C, M
And Y are present as superimposed color toner images.

The recording paper P on which the superimposed color toner image has been transferred is neutralized by the neutralizing electrode 16b which is a separating means composed of a sawtooth electrode plate, and is conveyed to the fixing device 17.

The fixing device 17 is a fixing roller member for fixing a superposed color toner image.
7a and a pressure roller 17b, which is a pressure roller member provided to face the fixing roller 17a.
A halogen lamp HLa, which is a heating unit having a heating filament (no symbol) as a heat source, is provided in the center of the inside of the fixing roller 17a.

After heat and pressure are applied between the fixing roller 17a and the pressure roller 17b, the superposed color toner image on the recording paper P is fixed, and then sent by the discharge roller 18 to be transferred to the upper portion of the apparatus. It is discharged to the tray.

The untransferred toner remaining on the peripheral surface of the transfer belt 14a after the transfer is transferred by an intermediate transfer member cleaning device 19a as an intermediate transfer member cleaning means provided opposite the driven roller 14e with the transfer belt 14a interposed therebetween. Will be cleaned.

As described above, after forming a superimposed color toner image on the belt-shaped intermediate transfer member by a plurality of image forming process means, the superimposed color toner image on the intermediate transfer member is transferred to the transfer material. Image formation in a color image forming apparatus that transfers color to a toner image in the previous transfer step, preventing color mixing with the oppositely charged toner and transfer failure in the next transfer step due to the high charge amount (Q / M) of the previous toner image. The device can be provided.

According to FIG. 4 and FIG. 2 described above, FIG.
FIG. 1 shows another example of a color image forming apparatus. In this example, a color image forming apparatus includes a process unit 100 as an image forming unit similar to that described with reference to FIG. 1 on a transfer belt 14a as an intermediate transfer body. A plurality of sets (four sets in the embodiment of the present embodiment) are arranged, and the toner images formed on the photosensitive drum 10 serving as an image carrier using the toner whose color has been changed for each process unit 100 are transferred to each photosensitive unit. The sheet is fed from a timing roller 16 as a transfer material feeding means in synchronization with the formation of a toner image on the body drum 10, is attracted to a transfer belt 14 a by a paper charger 150 as a transfer material charging means, and is transferred onto the transfer belt 14 a. Are sequentially transferred by a primary transfer roller 14c to a recording paper P, which is a transfer material to be conveyed, to form a superimposed color toner image on the recording paper P.
The recording paper P is separated from the transfer belt 14a by a separation electrode 14m as a separating unit, and heat and pressure are applied between a fixing roller 17a having a halogen lamp HLa as a heating unit and a pressing roller 17b therein. With the recording paper P
The upper color toner image is fixed, and the recording paper P is discharged to the outside of the apparatus by the discharge roller 18.

Four sets of process units 10 in this example
Reference numeral 0 denotes a photosensitive drum 10 serving as an image carrier, a scorotron charger 11 serving as a charging unit, an exposure optical system 12 serving as an image writing unit, and a developing unit serving as a developing unit, as described above with reference to FIG. 13 and a photoreceptor cleaning device 19 serving as an image carrier cleaning means, both of which have a common structure. However, a toner image formed on the photoreceptor drum 10 is transferred to a recording paper conveyed on a transfer belt 14a. P
Since the transfer is performed by directly superimposing the image on the recording paper P, the color toner image of K, C, M, and Y is formed on the recording paper P from the upper side in the rotation direction of the transfer belt 14a. Each process unit 100 in the order of yellow (Y), magenta (M), cyan (C), and black (K)
Is disposed around the transfer belt 14a. Also, a member having the same structure and function as described above with reference to FIG.
The driving roller 14d, the driven roller 14e, the backup roller 14j, and the tension roller 14i are stretched around and rotated.

The toner image on the recording paper P transferred from the photosensitive drum 10 by the primary transfer roller 14c is transferred by a toner image charger 200 provided opposite the ground roller 14k with the transfer belt 14a interposed therebetween. Be charged. At this time, as described above with reference to FIG.
An AC bias AC1 (AC voltage) having an AC component (AC component) having a peak-to-peak voltage of about 8 to 10 kV _{PP at} about kHz and the same polarity as the toner (minus polarity in the present embodiment), for example, -250 to A toner image charging bias VTb including a DC bias E1 (DC voltage) having a DC component (DC component) of about −750 V is applied to the toner image charger 200, and the primary transfer is performed on the transfer belt 14a. The toner image at that time is charged, and the polarity of the oppositely charged toner (toner having a positive polarity in the present embodiment) in the toner image on the recording paper P generated at the time of the primary transfer is converted into a negative polarity. The previous toner image has a negative polarity to prevent the toner image from adhering to the photosensitive drum 10 at the time of the next primary transfer, thereby preventing color mixing. Further, the charge amount (Q) of the toner of the toner image at the time of the primary transfer previously transferred onto the recording paper P by the AC component (AC component) of the toner image charging bias VTb.
/ M), for example, about -20 to -40 μC / g,
To about -15 [mu] C / g (about 1/3 to 2/3) to reduce the transfer rate during the next primary transfer which occurs when the charge amount (Q / M) of the previous toner image is high. To prevent. During the primary transfer of the next toner image by the primary transfer roller 14c to which the primary transfer bias VTa composed of a DC voltage of the same polarity as the toner (in this embodiment, a negative polarity) is applied, the toner of the opposite polarity is again charged. Although a positive polarity toner is generated in the present embodiment, the polarity of the oppositely charged toner (a positive polarity toner in the present embodiment) in the toner image on the recording paper P generated at the time of the primary transfer is minus. The toner image is transferred to the recording paper P while converting the polarity into a uniform polarity (aligning the charged polarity of the transferred toner image) to prevent color mixing during the next primary transfer. To reduce the transfer rate in the next primary transfer.

As described above, the toner images formed by the plurality of image forming process means are sequentially transferred onto a transfer material conveyed on a belt-like intermediate transfer member, and a superimposed color toner image is transferred. In a color image forming apparatus for forming on a material, a color that prevents color mixing with the oppositely charged toner in the previous transfer step and transfer failure in the next transfer step due to a high charge amount (Q / M) of the previous toner image. An image forming apparatus can be provided.

[0051]

According to the first, third or fourth aspect of the present invention, after a plurality of color forming images are formed on a belt-like intermediate transfer member by a plurality of image forming process means, the images are overlapped on the intermediate transfer member. In the color image forming apparatus for transferring the color toner image of the above to the transfer material, the color mixture by the opposite polarity charged toner in the previous transfer step and the high charge amount (Q
/ M), it is possible to provide a color image forming apparatus that prevents transfer failure in the next transfer step.

According to another aspect of the present invention, the toner images formed by the plurality of image forming process means are sequentially transferred onto a transfer material conveyed on a belt-like intermediate transfer member, and are superposed color toners. In a color image forming apparatus for forming an image on a transfer material, color mixing by the oppositely charged toner in the previous transfer step and a high charge amount (Q / M) of the previous toner image
, It is possible to provide a color image forming apparatus that prevents transfer failure in the next transfer step.

According to the fifth aspect, it is possible to provide a color image forming apparatus capable of cleaning the transfer residual toner on the image carrier without using the image carrier cleaning means and forming a toner image. Become.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram illustrating an embodiment of a color image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram of a toner image charging unit in FIG.

FIG. 3 is a view showing a state in which an image carrier cleaning unit in FIG. 2 is omitted.

FIG. 4 is a schematic cross-sectional configuration diagram illustrating another example of the color image forming apparatus according to the present invention.

[Explanation of symbols]

 Reference Signs List 10 photoconductor drum 11 scorotron charger 12 exposure optical system 13 developing device 14a transfer belt 14c primary transfer roller 14g secondary transfer device 15 paper feed cassette 16 timing roller 17 fixing device 100 process unit 200 toner image charger AC1 AC bias E1 DC bias P Recording paper VTa Primary transfer bias VTb Toner image charging bias

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H030 AB02 AD02 AD03 BB02 BB42 BB44 BB52 2H077 AA37 AC16 AD06 AD24 AD31 AE06 EA03 EA15 EA16 GA01 GA13 GA17 2H200 FA05 FA18 GA14 GA16 GA23 GA34 GA45 GA47 GA53 GA54 GA59 GB12 GB14 GB GB43 HA12 HB03 HB06 HB29 JA02 JA04 JA21 JB06 JB26 JB43 JB45 JB46 JB47 JC03 JC07 JC13 JC15 JC16 JC17 KA02 KA03 KA07 LA12 MA03 MA04 MA20 MB02 MB04 MC08

Claims (5)

[Claims] An image forming unit for forming a toner image on an image carrier is arranged on an intermediate transfer body, and a plurality of image forming units are formed on the image carrier by using toner of different colors for each image forming unit. Transferred to the intermediate transfer member in order,
After forming a superimposed color toner image on the intermediate transfer body, the color toner image on the intermediate transfer body is collectively transferred onto a transfer material, and the color toner image on the transfer material is fixed by a fixing device. 1. A color image forming apparatus for fixing, comprising: a toner image charging means for a transferred toner image having the same polarity as the toner to be developed and a low charge amount. 2. An image forming unit, which forms a toner image on an image carrier, is arranged on an intermediate transfer body. A plurality of image forming units are formed on the image carrier using toner of different colors for each image forming unit. The transferred toner images are sequentially transferred to a transfer material conveyed on the intermediate transfer body to form a superimposed color toner image on the transfer material, and then the color toner image on the transfer material is fixed by a fixing device. 1. A color image forming apparatus, comprising: a toner image charging means for charging a transferred toner image with the same polarity as the toner to be developed and performing low charging. 3. The toner image charging unit according to claim 1, wherein the toner image is charged by the toner image charging unit before the toner image is transferred to the intermediate transfer member or the transfer material. Color image forming apparatus. 4. The color image forming apparatus according to claim 1, wherein said toner image charging means has an AC component. 5. The image forming apparatus according to claim 1, wherein the toner image is formed without using an image carrier cleaning unit that cleans transfer residual toner on the image carrier. Item 10. A color image forming apparatus according to item 9.