JPH04369662A - Multcolor image forming device - Google Patents

Abstract

PURPOSE:To easily obtain a multicolor image which does not have irregularity and whose quality is excellent even when the large-sized multicolor image is formed after the small-sized multicolor image is continuously formed in a multicolor image forming device which forms the multicolor image by using one image carrier and one latent image forming means. CONSTITUTION:When the small-sized multicolor image is continuously formed, the images of the number of sheets as many as possible are formed on a photosensitive drum 1 continuously and at one time, and the part of the drum 1 which is not used for forming the image is extremely made small. Therefore, the image characteristic of a photosensitive layer on the surface of the drum 1 can be easily fixed. Besides, the multicolor image which does not have the irregularity and whose quality is excellent can be easily obtained even when the large-sized multicolor image is continuously formed, not to mention the small-sized multicolor image. Moreover, an image forming speed with respect to the small-sized multicolor image can be also improved.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a multicolor image forming apparatus such as a multicolor image copying machine, and in particular, the present invention relates to a multicolor image forming apparatus such as a multicolor image copying machine. The present invention relates to a multicolor image forming apparatus that forms toner images of different colors in a superimposed manner on a body and transfers them all at once onto a recording material.

0002

2. Description of the Related Art Conventional multicolor image forming apparatuses generally use an image forming method such as that described in Japanese Patent Laid-Open No. 56-144452.

The image forming method described in JP-A-56-144452 described above charges an image carrier with a primary charger and exposes it with a first exposure means to form an electrostatic latent image of a first color. The electrostatic latent image of the first color is developed by the first developing means to form a toner image of the first color on the image carrier, and then the electrostatic latent image of the second color is developed by the second exposing means. An electrostatic latent image is formed, a toner image of a second color is formed by a second developing means, an electrostatic latent image of a third color is formed by a third exposure means, and a toner image of a third color is formed by a third developing means. This is a method of forming a multicolor image in which toner images of the first to third colors are superimposed on an image carrier.

[0004] In this image forming method, when forming an electrostatic latent image of each color on the image carrier, a separate exposure means for each color is required, which increases the size and cost of the image forming apparatus itself. Moreover, it is difficult to synchronize the electrostatic latent images by the exposure means of each color, and there is a problem in that color misregistration is likely to occur between the toner images of each color obtained by development.

Furthermore, in Japanese Patent Application Laid-Open No. 60-76766, when forming electrostatic latent images of each color on an image carrier, one common electrostatic latent image forming means is used instead of separate ones for each color, That is, an image forming method is disclosed in which one primary charger and one exposure means are used to repeatedly form one electrostatic latent image of each color for each rotation of an image carrier.

[0006] According to such an image forming method, a separate exposure means is not required, and since the electrostatic latent images of each color are exposed by one exposure means, synchronization control of the electrostatic latent images can be easily performed. , has the advantage of being advantageous in preventing color misregistration between toner images of each color obtained by development.

[0007]

However, according to research by the present inventor, the method disclosed in Japanese Patent Laid-Open No. 60-76766 does not work well in an image forming apparatus that can use recording materials of multiple sizes. Naturally, it is necessary to provide an image carrier having a circumference longer than the length of the maximum size recording material, and for this reason, in particular, a continuous image forming operation of small size images corresponding to a small size recording material is performed. It has been found that when successive copying operations of large-sized images corresponding to large-sized recording materials are performed, there is a drawback that good image formation cannot be achieved.

According to the results of research and experiments on this point, the surface of the image carrier during the formation of the above-mentioned small-sized image is susceptible to the formation of an electrostatic latent image, the formation of a toner image, the contact of a recording material, and the like.
There are parts where operations associated with a series of image forming steps, such as application of a transfer electric field and contact with a blade of a cleaning member to remove residual toner after transfer, are performed and other parts where operations are not. The areas where operations associated with the image forming process are performed and the areas where operations are not performed are determined by whether or not the photosensitive layer on the surface of the image carrier has, for example, optical memory due to exposure, electrical memory due to transfer electric field, paper, etc. Differences in characteristics occur depending on the presence or absence of deposits such as paper dust due to the contact of the recording material, and the presence or absence of cleaning. When an image forming operation for a large-sized image is subsequently performed, unevenness occurs in the resulting image due to the differences in characteristics left in the photosensitive layer, making it difficult to obtain a good quality image. I found out that it is not possible.

[0009] Such a problem is particularly solved when a toner image is formed by a so-called reversal development method using toner of the same polarity as the electrostatic latent image formed on the image carrier, and a toner image is formed using a toner of the opposite polarity to that of the toner. This occurs significantly when transferring by applying an electric field. This is because the transfer electric field applied in the transfer process has a polarity opposite to that of the electrostatic latent image on the image carrier, so a memory effect occurs on the photosensitive layer of the image carrier due to charges of opposite polarity, and as a result, the transfer electric field This is due to the fact that the next image characteristics will change greatly depending on whether the image is received or not.

[0010] Through such investigation of the cause, the present inventor has
In the case of a multicolor image forming device that repeatedly forms and develops an electrostatic latent image on one image carrier, and forms a multicolor image by superimposing toner images of each color on the image carrier, small size When continuously forming multicolor images, as many multicolor images as possible are formed on the image carrier at one time,
By minimizing the portions of the image carrier where operations associated with the series of image forming steps described above are not performed,
We have found that the above problem can be solved.

[0011] Therefore, an object of the present invention is to continuously form small-sized multicolor images equivalent to a small-sized recording material using one image-bearing member, and to print as many images as possible on the image-bearing member. By continuously forming multicolor images at once,
Easily keep the image characteristics of the photosensitive layer on the surface of the image carrier constant,
Not only a small-sized multicolor image, but also a large-sized multicolor image equivalent to a large-sized recording material can be formed with ease, without image unevenness and with good quality. However, it is an object of the present invention to provide a multicolor image forming apparatus that can also improve the image forming speed of small-sized multicolor images.

0012

Means for Solving the Problems The above objects are achieved by a multicolor image forming apparatus according to the present invention. To summarize, the present invention sequentially forms latent images of each color corresponding to a multicolor image on an image carrier by one latent image forming means, and each time the latent image of each color is formed, the latent image is transferred to the latent image. Multicolor image formation in which a multicolor image is formed by overlapping toner images of each color on the image carrier by sequentially developing with developers of corresponding colors, and the multicolor image is transferred onto a recording material. In the apparatus, a discriminator is provided for determining whether or not a plurality of successive multicolor images that are successively formed can be formed on the image carrier at once when the multicolor images are continuously formed. and a mode setting device for setting the mode of the image forming sequence of the multicolor image;
When the discriminator determines that it is possible, the plurality of consecutive multicolor images are caused to be formed on the image carrier at once, and the plurality of multicolor images obtained thereby This multicolor image forming apparatus is characterized in that a mode is set in which images are transferred one by one onto corresponding recording materials.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing an embodiment of a multicolor image forming apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier, and the photosensitive drum 1 includes a photoconductive photosensitive layer having a charge transfer layer on its surface, such as so-called OPC containing an organic polymer. The outer diameter of the photosensitive drum 1 is such that a large-sized image corresponding to an A3 size or B4 size recording material is placed on at least one side of the photosensitive drum 1 with the longitudinal direction of the photosensitive drum 1 in the circumferential direction. Or, in the case of a small-sized image corresponding to A4 size or B5 size, the diameter is such that at least two sides of the small-sized image can be formed with the width direction of the small-sized image being the circumferential direction of the photosensitive drum 1. In this embodiment, in consideration of the margin between images, the photosensitive drum 1
The outer diameter of the photosensitive drum 1 was set to 160 mm, but the outer diameter of the photosensitive drum 1 was
It is only necessary that small-sized images corresponding to A4 size or B5 size recording material can be formed on at least two sides, and if the photosensitive drum 1 has such an outer diameter condition, the present invention can be applied. It becomes possible.

Around the photosensitive drum 1, a primary charger 2 and four developing devices 4M, 4C, 4Y, 4 are arranged in the direction of rotation.
B, a recording material P passing through an image transfer section in which a cleaning device 7 having a transfer charger 5 and a cleaning blade 8 is disposed, and the photosensitive drum 1 and the transfer charger 5 face each other;
A fixing device 6 is disposed downstream in the moving direction.

The image forming apparatus with the above configuration first uniformly charges the photosensitive drum 1 with the primary charger 2;
A negative charge is uniformly applied to the photosensitive drum 1. As the primary charger 2, we use a scorotron type device that can stably and uniformly charge the entire surface of the photosensitive drum 1 when it is superimposed on the already charged photosensitive drum 1, that is, when it is recharged. It is preferable to do this, and this example was also used as shown in the figure. After charging by the primary charger 2, an exposure means (not shown) such as a laser beam exposure device irradiates the photosensitive drum 1 with a light image 3 corresponding to a magenta image among the image information, so that a magenta image is formed on the photosensitive drum 1. form an electrostatic latent image corresponding to

Next, this electrostatic latent image is developed by a reversal development method by a developing device 4M containing negatively charged magenta toner, and is visualized as a magenta toner image. When a laser beam exposure device or the like is used as an exposure means to obtain a clear image, it is preferable to use a reversal development method, which has good reproducibility of thin lines, as described above. This development is carried out using a non-contact jumping development method for the second and subsequent colors so as not to disturb the toner image formed on the photosensitive drum 1 before one rotation of the photosensitive drum 1 or to prevent color mixing. It is preferable to use Although it is not necessarily necessary to use a non-contact jumping development method in the development of the first color, in this case, a configuration that allows the developer to be in both contact and non-contact states with respect to the photosensitive drum 1, For example, it is preferable that a mechanism for moving the developing device is provided.

After the first color magenta toner image is thus formed on the photosensitive drum 1, the next second color image is formed without performing a transfer process or a cleaning process on this magenta toner image. Let's move on to the process. In the second color image forming step, the photosensitive drum 1 on which the first color magenta toner image has been formed is again uniformly charged by the primary charger 2, and then the exposure means is used to charge the image information of cyan A light image 3 corresponding to the image is irradiated onto the photosensitive drum 1, and an electrostatic latent image corresponding to the cyan image is formed on the photosensitive drum 1, overlapping the magenta toner image. Next, this electrostatic latent image is developed by a developing device 4C having cyan toner to make it visible as a cyan toner image, and the cyan toner image is formed over the magenta toner image. Thereafter, without performing a transfer step or a cleaning step, the process moves to an image forming step of a third color yellow image and then a fourth color black image.

The image forming steps for the third color and the fourth color are performed in the same manner, and a yellow toner image and a black toner image are respectively formed. As a result, a multicolor image is formed on the photosensitive drum 1 by superimposing a magenta toner image, a cyan toner image, a yellow toner image, and a black toner image in this order. Next, in the transfer process, the recording material P, which is fed through a paper feed cassette and a paper feed device (not shown) in synchronization with the rotation of the photosensitive drum 1, is transferred to the photosensitive drum 1 at an image transfer section equipped with a transfer charger 5. The recording material P is brought into contact with the photosensitive drum 1, and a transfer charger 5 charges the recording material P from the back side to give a positive charge to the recording material P, and the multicolor image on the photosensitive drum 1 is formed at once with the four color toner images superimposed. Transfer onto recording material P. After the transfer, the recording material P is continuously sent to the fixing device 6, where the four-color toner image is heated and fixed onto the transfer material P, and the colors are mixed to form a permanent color image. It is ejected from the aircraft.

Meanwhile, the photosensitive drum 1 proceeds to a cleaning process. Cleaning blade 8 of cleaning device 7
is brought into contact with the photosensitive drum 1 to clean residual toner on the portion of the photosensitive drum 1 where the toner image has been formed. After the photosensitive drum 1 is cleaned by the cleaning device 7, it is again subjected to the image forming process. Further, when cleaning is completed, the cleaning blade 8 is separated from the photosensitive drum 1 in preparation for the next cleaning process.

Now, in the image forming apparatus of the present invention, when continuously forming multicolor images, it is difficult to determine whether or not a plurality of successive multicolor images can be formed on the photosensitive drum 1 at once. If it is determined that it is possible, the mode of a mode setting device (not shown) of the image forming sequence is changed, thereby causing a plurality of successive multicolor images to be formed on the photosensitive drum 1. , it is possible to transfer a plurality of obtained multicolor images onto corresponding recording materials one by one.

[0021] To this end, a discriminator is required to determine whether two or more screens of images can be formed on the photosensitive drum 1, but this can normally be determined when an image reading section (not shown) reads the original image. Therefore, in this embodiment, the above discriminator is replaced by an image reading section.

According to the outer diameter conditions of the photosensitive drum 1 of this embodiment, it is possible to form two small-sized multicolor images corresponding to A4 size or B5 size recording material.
As an example, a case where a plurality of images corresponding to A4 size are successively formed will be described in detail with reference to the timing chart of the image forming sequence shown in FIG. As mentioned above, when the image reading unit reads a multicolor image document equivalent to A4 size, the mode of the mode setting device is automatically switched as a result of determining whether two screens can be formed on the photosensitive drum 1. , a mode for forming images on two screens is set, and the image forming sequence shown in FIG. 2 is executed.

As can be seen from the timing chart in FIG. 2, after uniformly charging the photosensitive drum 1, image exposure M1 corresponding to the first magenta image is performed, and then after an appropriate distance between images, the first magenta image is exposed. Image exposure M2 corresponding to the second magenta image is performed. The distance between images was determined as follows.

[0024] Inter-image distance = (peripheral length of photosensitive drum - circumferential length of A4 size x 2)/2 Next, the latent images formed by exposure M1 and M2 are sequentially developed by magenta developing device 4M, and then First and second magenta toner images are formed. In the next rotation of the photosensitive drum 1, after uniform charging, image exposure C1 corresponding to the first cyan image is performed in synchronization with the previous magenta toner image.
Image exposure C2 corresponding to the second cyan image is performed, and the formed latent image is developed by the cyan developing device 4C.
First and second cyan toner images are formed on top of the second and second magenta toner images, respectively. The same process is performed for the yellow image and the black image, thereby forming a magenta toner image, a cyan toner image, and a cyan toner image on the photosensitive drum 1.
Two multicolor images are formed by overlapping four color toner images, a yellow toner image and a black toner image.

On the other hand, the first sheet of the transfer material P is placed on the photosensitive drum 1 at the image transfer section facing the transfer charger 5 of the photosensitive drum 1.
The image is fed in synchronization with the upper image, and then the second image is fed with the distance between the images mentioned above. Then, by applying a transfer electric field with the transfer charger 5 in the image transfer section, the first
The first and second multicolor images on the photosensitive drum 1 are sequentially transferred onto the first and second recording materials P, respectively. After the transfer process, the photosensitive drum 1 is cleaned in a cleaning process.
The cleaning blade 8 is brought into contact with the surface for a time corresponding to approximately one revolution for cleaning, and is then used for the next image formation.

As described above, multicolor images equivalent to A4 size are successively formed two at a time. When continuously forming multicolor images of a size that allows three or more images to be formed at once, the image formation may be performed according to the same sequence as described above after the photosensitive drum 1 has rotated once necessary for the cleaning process.

When continuously forming images of a small size equivalent to a small recording material such as A4 size, conventionally, approximately half or more of the photosensitive drum 1 is not used for image formation, and the image forming process is not performed. However, in this embodiment, as described above, two images are formed on the photosensitive drum 1 at a time, and the portions of the photosensitive drum 1 that are not used for image formation and are not subjected to a series of image forming steps are I'm trying to minimize it as much as possible. Therefore, in this embodiment, even if a large-sized image corresponding to a large-sized recording material such as A3 is subsequently formed, image unevenness due to differences in residual characteristics on the surface of the photosensitive drum 1 can be significantly reduced, resulting in a good result. It is now possible to obtain high-quality images. Furthermore, when forming an image corresponding to a small-sized recording material, it has become possible to increase the copying speed to twice that of the conventional method.

Furthermore, from this, when continuously forming a multicolor image equivalent to a small-sized recording material, the contact time of the cleaning blade 8 can be reduced to about half of the conventional one, so that the cleaning blade 8 can be It has also become possible to reduce the deterioration of the photosensitive layer on the surface of the photosensitive drum 1, which had occurred due to the scraping by 8.

In the above embodiments, the drum-shaped photosensitive drum 1 was used as the image carrier, but the present invention is not limited to this, and the image carrier may have a belt shape or the like. Needless to say, it may be used and similar effects can be obtained. Furthermore, although the electrostatic transfer method using the transfer charger 5 has been shown to transfer the multicolor image onto the recording material P, it goes without saying that a pressure transfer method or a transfer method using an intermediate transfer member may be used. Although the fixing device 6 using a heat roller fixing method is shown as the fixing device, it is needless to say that the present invention is not limited to this.

[0030]

As explained above, in the image forming apparatus of the present invention, when a single image carrier is used to continuously form small-sized multicolor images equivalent to a small-sized recording material, Since the maximum possible number of multicolor images are continuously formed on the image carrier at one time, the image characteristics of the photosensitive layer on the surface of the image carrier can be easily maintained constant, making it possible to form multicolor images in a small size. Not only images, but also large-sized multi-color images equivalent to large-sized recording materials can be formed with ease. In the case of multicolor images, the image formation speed can also be increased.

[Brief explanation of the drawing]

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

2 is a sequence diagram showing an image forming sequence in a continuous image forming mode for small-sized multicolor images in the image forming apparatus of FIG. 1; FIG.

[Explanation of symbols]

1 Photosensitive drum 2 Primary charger 3 Optical images 4M to 4B Developing device 5 Transfer charger 6 Fixing device 7 Cleaning device P
recording material

Claims (1)

[Claims] Claim 1: One latent image forming means sequentially forms latent images of each color corresponding to a multicolor image on an image carrier, and each time the latent image of each color is formed, the latent image is changed to correspond to the latent image. In a multicolor image forming apparatus that sequentially develops with color developers to form a multicolor image in which toner images of each color are superimposed on the image carrier, and transfers the multicolor image onto a recording material. , providing a discriminator for determining whether or not a plurality of successive multicolor images that are successively formed can be formed on the image carrier at the same time when the multicolor images are continuously formed; A mode setting device that sets a mode of an image forming sequence of the multicolor images is configured to sequentially form the plurality of consecutive multicolor images on the image carrier when the discriminator determines that it is possible. A multicolor image forming apparatus characterized in that a mode is set in which a plurality of multicolor images obtained thereby are transferred one by one onto corresponding recording materials.