JPH0713768B2 - Image forming method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an electrophotographic image forming method, and in particular, two or three or more monochromatic colors,
The present invention relates to an image forming method in an image forming apparatus such as a so-called multi-color electrophotographic copying apparatus and full-color electrophotographic copying apparatus or a color recording apparatus of a computer output section. In the following description, a copying machine will be described, but the present invention is not limited to this.

2. Description of the Related Art Recently, the demand for color copying has rapidly increased not only in the special field but also in the field of general office work, and there is a demand for an improved quality of color copied images and a low-priced copying apparatus.

One of the important problems to be solved in order to meet such a demand is a development for developing an electrostatic latent image of each color formed on a developing object, that is, a photoconductor in a full-color and multi-color color copying apparatus. It depends on how to configure the device.

Particularly, in full-color and multi-color color copying machines, there is an increasing demand for two-color or three-color or more single-color copying, so-called multi-color copying. Further, in a color copying apparatus having a multi-mode capable of storing the copied transfer material in an intermediate tray in the machine and performing the copying again, multicolor composite copying can be easily performed, and there are many such applications.

Several methods have been proposed as a developing method for obtaining such a monocolor copy. One of them is a method of preparing a plurality of developing units containing different color developers, that is, a plurality of developing units, and sequentially mounting desired developing units in the developing unit of the copying machine main body.

The second method is to arrange a plurality of developing units having developers of respective colors in parallel along the surface of the photoconductor and select one developing unit to perform development.

Problems to be Solved by the Invention The operation of the first method is extremely complicated. According to the second method, when the developed image developed by the selected developing unit passes in front of the unselected developing unit, the toner on the developing roller of the unselected developing unit is mixed with the developed image. However, there was a problem that the image becomes a mixed color.

Conventionally, in order to solve such a problem, for example, a means has been proposed such as providing a shutter between the developing roll and the photoconductor, or keeping an unselected developing unit away from the surface of the photoconductor. It becomes complicated, it is difficult to downsize the developing device and the copying device, and there is a disadvantage when the price of the copying machine becomes high.

OBJECTS OF THE INVENTION Accordingly, a main object of the present invention is that of a so-called mixed color development in which toner on a developing roller of an unselected developing unit is mixed with a developed image on a photoreceptor surface without requiring a special device. An object of the present invention is to provide an image forming method capable of achieving prevention.

Means for Solving the Problems The above objects are completely achieved by the present invention. Image formation for developing an electrostatic latent image on a latent image carrier by applying a bias voltage to the developing rollers of a plurality of developing units arranged along the periphery of a moving latent image carrier and containing toners of different colors. In the method, before the start of the developing process, a bias voltage is applied to the developing roller of the unselected developing device in a non-rotating state to adhere toner to the non-image portion of the latent image carrier, and the developing device of the unselected developing device is developed. An image forming method, characterized in that the roller is held in a non-rotating state, and the developed image developed on the latent image carrier by the selected developing device passes through the developing roller of the unselected developing device. Is.

FIG. 1 is a schematic view partially showing the latent image carrier 1 and the developing roller 4a of the developing unit 4 for explaining the principle of the present invention.

An electrostatic latent image is formed on the surface of the latent image carrier 1 by a normal image forming process. On the other hand, a developer, that is, toner T is formed in a thin layer on the surface of the developing roller 4a, and during the developing process, the toner T on the developing roller 4a flies to the electrostatic latent image of the latent image carrier 1 to develop. Eggplant However, as described above, the toner t of another color scattered from the other developing unit adheres to the surface of the developing roller 4a before the developing work, and if the toner is directly developed, a color mixture occurs.

According to the present invention, the developing roller 4a applies a bias voltage to the developing roller 4a as shown in FIG. Part or all of the toner T located at the position is made to fly to the latent image carrier 1, and part or all of the toner T is removed from the surface of the developing roller 4a, and the toner t part mixed at the same time is also developed from the developing roller 4a. It is removed before the working process. As a result, the mixed toner portion is removed from the surface of the developing roller 4a, and the mixed color development does not occur during the subsequent developing operation.

The timing for applying the bias voltage to the developing roller 4a in order to cause the mixed color toner portion to fly to the latent image carrier is, for example, immediately after the start of the latent image forming process operation and the image area on the latent image carrier is the developing roller. It may be suitable before passing through 4a or before the latent image carrying step is completed and the latent image carrier stops moving.

In order to efficiently fly the mixed color toner portion to the latent image carrier, an electrostatic latent image is formed in the non-image area preceding the image area of the latent image carrier, and the non-image latent image area is formed in the mixed color toner portion. T,
It is effective to develop at t.

Also, the bias voltage applied to the developing roller 4a will be the same polarity as the toner T or approximately 0V. Further details will be described later.

Next, the image forming method according to the present invention will be described in more detail with reference to Examples.

Embodiment 1 As described above, the image forming method according to the present invention can be suitably implemented in an image forming apparatus such as a multi-color or full-color electrophotographic copying apparatus or a color recording apparatus for a computer output section. However, in this embodiment, it is assumed that the method is applied to a color electrophotographic copying apparatus for obtaining a three-color image such as black, red, and blue. Further, such a color electrophotographic copying apparatus is a so-called NP process or primary charging monochromatic separation including various electrostatic latent image forming processes, for example, steps of primary charging-secondary charging / color separation exposure-overall exposure. Although a so-called Carlson process including various exposure steps can be used, this embodiment describes an electrophotographic copying apparatus to which the Carlson process is applied.

FIG. 3 is a schematic sectional view showing an embodiment of an image forming apparatus capable of carrying out the image forming method according to the present invention, for example, a color electrophotographic copying apparatus for obtaining black, red and blue three color images. Indicated. First, the overall structure of the color electrophotographic copying apparatus will be described. A photosensitive drum 1 having a photosensitive layer for electrophotography formed on the surface thereof in the approximate center of the copying apparatus.
Are placed. The photosensitive drum 1 is rotatably and detachably attached to a rotary support shaft (not shown) having a rotation center O in a known manner. In this embodiment, the photosensitive drum 1
Shall rotate in the direction of arrow X, that is, clockwise in FIG.

The primary charging device 2 is located substantially directly above the photosensitive drum 1, the multicolor developing device 3 is located on the right side of the photosensitive drum 1 in FIG. 3, and the transfer discharger 9 and the photosensitive drum 1 are located directly below the photosensitive drum 1.
The cleaning device 10 is arranged on the left side in FIG. Further, an optical system 11 is arranged above the electrophotographic copying apparatus, and the image of the original is transferred to the primary charger 2 and the multicolor developing device 3
It is configured to project on the photosensitive drum 1 at the exposure section E located between the and. The optical system 11 may utilize any optical system. In addition, a potential sensor S for measuring the surface potential of the photosensitive drum 1 is provided between the exposure position E and the developing device 3, and the photosensitive drum 1 is provided between the primary charger 2 and the cleaning device 10. A light source 12 is provided for erasing the residual charges of the.

Since the color copying machine described here is a color electrophotographic copying machine for obtaining black, red and blue three color images as described above, the multicolor developing device 3 has three developing units 4, 5 and 6. Although it has a developing unit, the present invention is not limited to this constitution, and it is also possible to have two or four or more developing units. Of course, an apparatus having one developing unit may be used.

The operation of the color electrophotographic copying machine configured as described above will be briefly described.

The photosensitive drum 1 starts rotating in the direction of arrow X when the operation is started, and is charged by the primary charger 2. The charged photosensitive drum 1 is further rotated, and an optical image is slit-exposed at the exposure section E by the action of the optical system 11 to form an electrostatic latent image of each color on the photosensitive drum 1. At this time, the surface potential of the photosensitive drum 1 is measured by the potential sensor S. Photosensitive drum 1
The upper latent image is then brought into rotation by the rotation of the photosensitive drum 1 to the development area D in which the multicolor developing device 3 is arranged. In the developing area D, the electrostatic latent image on the photosensitive drum 1 is visualized as a toner image in one selected developing unit in the multicolor developing device 3. Each developing unit 4, 5, 6 is a developing roll.
Although the developing units having 4a, 5a, and 6a may have various structures, in the present specification, the developing units 4, 5, and 6 have basically the same structure, and each of them has a mono structure. A developing unit of the jumping developing system as described in, for example, JP-B-58-32375 or JP-B-58-32377, which contains a color developer.

The toner image on the photosensitive drum is transferred from the paper feeding device (not shown) in the transfer area Tr in which the transfer discharger 9 is arranged, and is transferred by the registration roller 8 to the transfer material 7 which is timely supplied. . The transfer material 7 carrying the toner image is then conveyed to a fixing device (not shown) and fixed.

The photosensitive drum 1 is subjected to the actions of the cleaning device 10 and the light source 12 and then performs the next image forming process again.

Next, the operation of the multicolor developing device 3, that is, the developing units 4, 5, and 6 will be described.

Referring to FIG. 4, the developing units 4, 5 and 6 have a developer supply container 20 which is open on the side. Developing rolls 4a, 5a, 6a are arranged in the openings. The developing rolls 4a, 5a
Is a fixed magnet 24, and a developing sleeve that surrounds the magnet 24 and is rotatably attached to the developing container 20.
26 and. The developing sleeve 26 is made of a non-magnetic material such as aluminum or stainless steel, and rotates as shown by an arrow 28 in the figure.

A black, red or blue toner 30 containing magnetite is stored in the developing container 20. The color toner 30 is attracted to the surface of the developing sleeve 26 by the magnetic field of the magnet 24 fixed in the developing sleeve 26, and is conveyed from the inside of the developing container to the outside of the developing container toward the photosensitive drum 1 by the rotation of the developing sleeve 26. However, the toner 30 is prevented from moving to the outside of the developing container by the blade 32 provided at the opening of the developing container, is thinned on the developing sleeve 26, and is charged in the opposite polarity to the electrostatic latent image. The magnetic toner 30 in this state is transferred to the outside of the developing container.

Now, it is assumed that the developing unit 5 on the upstream side in the rotation direction of the photosensitive drum 1 is selected in the developing units 4, 5 and 6 and the above-mentioned copying process is started.

The developing rolls 4a, 5 of the developing units 4, 5, 6 having the above-mentioned configuration
A and 6a are held in a stopped state before the development of the electrostatic latent image on the surface of the photosensitive drum is started. According to the present invention, the developing roll 5a in the rotation stop state before starting the development of the electrostatic latent image on the photoreceptor surface, and the developing roll 5a also in the rotation stop state, located on the upstream side and the downstream side. A bias voltage of several hundred volts to several kilovolts having the same polarity as the toner contained in each developing unit is applied to the developing rollers 4a and 6a. The bias voltage will be variously adjusted depending on the charge amount of the latent image on the photosensitive drum 1. An example is as follows. If the surface potential of the non-image area on the photoconductor drum is about + 50V in the light portion potential, about -500V, and if it is about + 500V in the dark portion potential, a bias of about 0V is enough.

Such bias voltage of the same polarity is applied to the developing roll 5a with respect to the developing roll 4a until the latent image in the image area of the photosensitive drum passes near the developing unit 4 as the photosensitive drum 1 rotates. Before the developing roll 5a starts to rotate, and for the developing roll 6a, the powder image on the surface of the photosensitive drum developed by the developing roll 5a is developed as the photosensitive drum 1 rotates. It is applied continuously or in pulses (intermittently) until it passes near the unit 6.

A bias voltage of the same polarity as that of the toner of several hundred volts to several kilovolts is sequentially applied from the upstream side. Therefore, the non-image area on the surface of the photoconductor drum is set to
It is forcibly developed by a and 6a.

By such forced development, the color-mixed toner on the selected developing roll 5a is transferred to the non-image area of the photoconductor before the electrostatic latent image on the surface of the photoconductor reaches the position of the developing roll. The development with mixed color toner is prevented.

Further, the toner on the developing rolls 4a and 6a is forcibly developed in the non-image area before the developed toner powder image reaches the positions of the developing rolls 4a and 6a, thereby selecting the developing roll 5a.
Rolls not selected for the developed image developed by
The toner on 4a and 6a does not mix.

Further, as a bias for the image areas of the developing units 4 and 6 which are not selected, a bias having the same polarity as that of the float or the toner or a bias having a different polarity may be applied. For example, the bias voltage of the same polarity may be arbitrarily selected within the range of 0 to 500V, and the bias voltage of the opposite polarity may be selected within the range of 0 to 1000V. At this time, a bias voltage of several hundreds of volts having a polarity different from that of the toner contained in the developing units is applied to the developing units 4 and 6 which are not selected, forcibly causing color mixing on these developing rolls and causing a color mixture on the photosensitive drum. If a method that does not allow mixed color development is used, the toner on the mixed color developing rolls should be of the same polarity or approximately 0 V before being used.
It is necessary to remove the bias by applying.

Further, as described above, in the non-image area, a bias having the same polarity as the stored toner is applied to each developing roll in order to forcibly perform the development from the upstream side in order to remove the mixed color toner on the developing roll, Next, the developing roll not selected for the image area is switched so as to apply a bias having a polarity different from that of the stored toner so as to prevent development of the electrostatic latent image (or visible image) on the surface of the photosensitive drum. Then, the applied bias voltage can be lowered. In some cases, it can be floated.

Example 2 In the same constitution as in Example 1, the selected developing unit
A bias voltage of several hundred to several thousand volts, which has a polarity different from that of the toner contained in the developing unit 4 is applied to the developing roll 4a of the developing unit 4 located upstream of 5a, unlike the first embodiment. . In this case, the toner on the developing roll 4a is not removed to the photosensitive drum 1,
The latent image in the image area of the latent image carrier is prevented from being developed with mixed toner.

At this time, it would be more preferable if the unselected developing rolls could be moved a little further away from the photoreceptor.

The image forming method according to the present invention configured as described above is
Before the start of the developing process, a bias voltage is applied to the developing roller of the unselected developing device in a non-rotating state to adhere toner to the non-image portion of the latent image carrier, and the developing roller of the unselected developing device is not rotated. The development image on the latent image carrier developed by the selected development device passes through the development roller of the non-selected development device while being held in rotation, and the development of the non-selected development device is performed. It is possible to prevent so-called mixed color development in which toner on the roller is mixed with the developed image on the surface of the photoconductor, and it is possible to obtain a high quality copy.

[Brief description of drawings]

1 and 2 are partial schematic sectional views of a latent image carrier and a developing roller for explaining the principle of color mixing prevention in the image forming apparatus according to the present invention. FIG. 3 is a schematic sectional view of a color copying machine showing an embodiment of the multicolor developing device according to the present invention. FIG. 4 is a schematic sectional view showing an embodiment of a developing unit that can be used in the image forming apparatus according to the present invention. 2: Latent image carrier 3: Multicolor developing device 4, 5, 6: Developing unit 4a, 5a, 6a: Developing roll

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Nobutoshi Yoshida 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Atsushi Takagi 3-30-2 Shimomaruko, Ota-ku, Tokyo Kya Non-Incorporated (72) Inventor Kei Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (56) Reference JP-A-61-77872 (JP, A)

Claims (1)

[Claims] 1. An electrostatic latent image on a latent image carrier by applying a bias voltage to the developing rollers of a plurality of developing units arranged along the periphery of a moving latent image carrier and containing toners of different colors. In the image forming method of developing the toner image, a bias voltage is applied to the non-image portion of the latent image bearing member by applying a bias voltage in a non-rotating state of the developing roller of the developing device that is not selected before the development process is started. The developing roller of a non-developing device is kept in a non-rotating state, and the developed image on the latent image carrier developed by the selected developing device passes through the developing roller of the non-selected developing device. Image forming method.