JPH0944002A - Image forming device - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: Even if a transfer target having a size equal to or smaller than the maximum sheet-passing size is passed, unevenness of the resistance value is reduced due to the reduction of the resistance value of the intermediate transfer belt in the non-sheet passing area. It is an object of the present invention to prevent the occurrence of abnormal images such as white spots on the edges (uneven density). SOLUTION: An endless intermediate transfer belt composed of a medium resistance material and stretched between a plurality of rollers is superposed with an image of a single color or a plurality of colors formed on a photoconductor, and then a paper is formed. In an image forming apparatus that collectively transfers the image to a transfer target by applying a bias from a transfer roller, a solid toner portion as an insulating layer is formed on the non-sheet passing portion of the intermediate transfer belt according to the size of the transfer target. I decided to do it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and in particular, in an image forming section using an intermediate transfer belt, even after passing a transfer target having a size which is equal to or smaller than the maximum sheet transferable size, The present invention relates to an image forming apparatus that prevents the occurrence of unevenness in the resistance value of an intermediate transfer belt and prevents the occurrence of abnormal images such as blank areas at the edges.

[0002]

2. Description of the Related Art As an image forming apparatus using an electrophotographic process such as a copying machine, a printer, a facsimile machine, there is one using an intermediate transfer belt.
No. 0 publication discloses that on an intermediate transfer belt made of a medium resistance material,
A method is disclosed in which an image of a single color or a plurality of colors formed on an image carrier (photoreceptor) is primarily transferred, and then secondarily transferred to a transfer paper by a contact transfer method using a paper transfer roller.

[0003]

By the primary transfer of a single-color or multi-color image formed on an image bearing member (photoreceptor) onto an intermediate transfer belt, a contact transfer method using a paper transfer roller is used. In the method of performing secondary transfer on a transfer paper, there is a problem that the resistance value of the intermediate transfer belt decreases. When the resistance value of the intermediate transfer belt decreases, the transfer bias easily flows to the intermediate transfer belt with the decreased resistance,
The transfer condition is far from the optimum transfer bias value,
The image corresponding to the portion where the resistance has decreased becomes an abnormal image.
As shown in FIG. 3A, the decrease in the resistance value of the intermediate transfer belt 100 is caused by the transfer paper 102 in the area where the intermediate transfer belt and the paper transfer roller 101 of the contact transfer system contact each other.
Is likely to occur in the areas (the areas where the intermediate transfer belt and the paper transfer roller are in direct contact) A1 and A3 in which the paper is not passed.
This is because the bias applied to the paper transfer roller 101 is more likely to flow to the portion in direct contact than the portion in contact with the transfer paper 102 having high resistance. Fig. 3 (a)
The resistance value measurement results shown in are the results of actual measurement of the resistance values of the belt in the paper passing area A2 and the non-paper passing areas A1 and A3 for one image forming apparatus.
There is a difference in the resistance value between 1 and A3, which is considered to be due to the variation in the contact thickness of the paper transfer roller. Different machines are expected to produce different results.
In any case, it can be seen that the resistance value in the non-sheet passing area is likely to decrease.

There is no problem as long as the resistance value of the intermediate transfer belt 100 is uniform throughout. However, for the reason described above, if the transfer paper having a size smaller than the maximum paper-passable size in the drum axis direction is passed. , As shown in Fig. 3 (b), the resistance value becomes uneven between the non-sheet passing area A1 and the sheet passing area A2 of the transfer sheet. It becomes difficult to apply the bias uniformly, and a blank image is formed in a portion having a low resistance value, resulting in an abnormal image (density unevenness).

The present invention has been made in view of the above problems, and the resistance value of the intermediate transfer belt in the non-paper passing area is obtained even after the paper to be transferred having a size equal to or smaller than the maximum paper passing size is passed. The purpose of the present invention is to prevent the occurrence of unevenness in the decrease in the resistance value caused by the decrease in the resistance value, and as a result, to prevent the occurrence of abnormal images such as white spots on the edge (uneven density).

[0006]

In order to achieve the above object, the present invention according to claim 1 provides an endless intermediate transfer belt made of a medium resistance material and stretched between a plurality of rollers, and a photosensitive member. In an image forming apparatus that superimposes the single-color or multi-color images configured above and then collectively transfers the images to a transfer target by applying a bias from a paper transfer roller, depending on the size of the transfer target. Thus, a solid toner portion is formed on the non-sheet passing portion of the intermediate transfer belt.

As described above, according to the first aspect of the invention, the toner solid portion is provided on the non-sheet passing portion of the intermediate transfer belt to form the insulating layer, so that the transfer bias is applied to the sheet passing portion and the non-sheet passing portion. It is possible to eliminate the difference between the two, thereby preventing unevenness in resistance reduction of the intermediate transfer belt, and preventing occurrence of abnormal images such as white spots on the edge (uneven density).

According to a second aspect of the present invention, a solid portion is formed in the non-sheet passing portion of the intermediate transfer belt in a mode in which the bias from the paper transfer roller is applied at a certain value or more. .

As described above, according to the second aspect of the present invention, the lowering of the resistance of the intermediate transfer belt is more remarkable as the bias of the paper transfer roller is higher. Therefore, the solid toner portion is provided only when the bias of the transfer roller exceeds a certain value. Therefore, it is possible to prevent wasteful consumption of toner and effectively prevent a decrease in resistance of the intermediate transfer belt.

According to a third aspect of the invention, a yellow toner is used as a toner used when forming the solid toner portion of the non-sheet passing portion of the intermediate transfer belt.

As described above, according to the third aspect of the present invention, even if the toner forming the solid portion provided to prevent the resistance of the intermediate transfer belt from decreasing is adhered to the transfer-receiving member, it should be yellow toner. If it is not noticeable, the influence on the image can be reduced.

According to a fourth aspect of the present invention, as the toner used when forming the solid toner portion of the non-sheet passing portion of the intermediate transfer belt, the toner of the color least used by the user is used. . As described above, according to the fourth aspect of the invention, since the solid portion is formed by using the toner that the user rarely uses, the toner consumption amount is well balanced, and the toner in the toner hopper is fixed for a long time without being used. It is possible to eliminate the problem of being lost.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic configuration explanatory view of an example of a color copying apparatus to which the present invention is applied, and FIG. 2 is an enlarged view around a photoconductor and an intermediate transfer belt. A color image reading device (hereinafter, referred to as a color scanner) 1 forms an image of an original 3 on a color sensor 7 via an illumination lamp 4, a mirror group 5, and a lens 6 to obtain color image information of the original. For example, it is read for each color-separated light of blue, green, and red and converted into an electric image signal. In this example, the color sensor 7 is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD, and simultaneously reads three colors. Based on the B, G, and R color-separated image signal intensity levels obtained by the color scanner 1, color conversion processing is performed by an image processing unit (not shown), and Black (hereinafter, Bk), Cyan (hereinafter, Bk) , C), Magenta (hereinafter M), Yellow
Color image data (hereinafter referred to as Y) is obtained.

The Bk, C, M and Y color image data thus obtained are visualized by a color image recording device (hereinafter referred to as a color printer) 2 described below to form a final color copy. The operation method of the color scanner 1 for obtaining the Bk, C, M, and Y image data is that the illumination / mirror optical system in FIG. 1 receives the scanner start signal in timing with the operation of the color printer 2. The original is scanned in the left direction, and image data of one color is obtained for each scanning. By repeating this operation a total of four times, sequential four-color image data is obtained. Then, each time, the image is sequentially visualized by the color printer 2, and the images are superposed to form a four-color full-color image.

Next, the outline of the color printer 2 will be described. The writing optical unit 8 converts the color image data from the color scanner 1 into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 9. The unit 8 includes a laser 8-1, a light emission drive control unit (not shown), a polygon mirror 8-2, a rotation motor 8-3 for the polygon mirror 8-2, an f / θ lens 8-4, a reflection mirror 8-5, and the like. It is composed of. The photoconductor drum 9 rotates counterclockwise as indicated by the arrow, but around the photoconductor drum 9, a photoconductor cleaning unit 10, a charge eliminating lamp 11, a charger 12, a potential sensor 13, a Bk developing device 14, and a C developing device 1 are provided.
5, an M developing device 16, a Y developing device 17, a developing density pattern detector 18, an intermediate transfer belt 19 and the like are arranged. Each developing device rotates a developing sleeve (14-) which rotates by bringing the brush of the developer into contact with the surface of the photoconductor 9 in order to develop the electrostatic latent image.
1, 15-1, 16-1, 17-1) and a developing paddle (14-2, 14-2, which rotates to draw up and agitate the developer).
15-2, 16-2, 17-2) and the toner concentration detection sensor (14-3, 15-3, 16-3, 17) of the developer.
-3) etc.

Now, in the standby state, all four developing devices are
Although the agent on the developing sleeve is in the state of cutting off (development inoperative), the order of developing operation (color image forming order) is B.
The case of k, C, M, and Y will be described. However, the image forming order of the present invention is not limited to this. When the copy operation is started, the color scanner 1 starts reading the Bk image data at a predetermined timing, and the optical writing by the laser beam is performed based on the image data.
Latent image formation begins. In order to enable development from the tip of the Bk latent image, the developing sleeve 14-1 is started to rotate and the agent is raised before the latent image tip reaches the developing position of the Bk developing device 14. The Bk latent image is developed with Bk toner. After that, the developing operation of the Bk latent image area is continued, but when the trailing edge of the latent image passes the Bk developing position, the agent spike on the Bk developing sleeve 14-1 is promptly cut off, and the developing operation is disabled. To do. This is completed at least before the leading end of the C latent image based on the next C image data arrives. It should be noted that the brush cutting is performed by switching the rotation direction of the developing sleeve 14-1 to the opposite direction to that during the developing operation.

The Bk toner image formed on the photoconductor 9 is transferred onto the surface of the intermediate transfer belt 19 which is driven at the same speed as the photoconductor. The belt transfer is performed by the photoconductor 9 and the intermediate transfer belt 1.
This is done by applying a predetermined bias voltage to the transfer bias roller 20 in the contact state 9. For the intermediate transfer belt 19, Bk, which is sequentially formed on the photoconductor 9,
The toner images of C, M, and Y are sequentially aligned on the same surface to form a belt transfer image of four-color superimposition, and then they are collectively transferred to a transfer paper. The structure of this intermediate transfer belt unit,
The operation will be described later.

On the side of the photosensitive member 9, the Bk process is followed by the C process. Here, the C image data is read by the color scanner 1 at a predetermined timing, and the C image is formed by writing the laser beam with the image data. I do. In the C developing device 15, the B position
After the trailing edge of the k latent image has passed and before the leading edge of the C latent image arrives, the developing sleeve 15-1 is started to rotate so that the agent is spiked and the C latent image is developed with the C toner. After that, the development of the C latent image area is continued, but when the trailing edge of the latent image passes,
As in the case of the Bk developing device, the C developing sleeve 15-1
Cut the top of the agent. This is also completed before the leading end of the next M latent image arrives. Note that the steps of M and Y are the same as the steps of Bk and C in the operations of reading image data, forming a latent image, and developing, respectively, and therefore description thereof will be omitted.

Next, the transfer belt unit will be described. The intermediate transfer belt 19 is stretched around a drive roller 21, a belt transfer bias roller 20, and a driven roller group, and is driven and controlled by a drive motor (not shown) as described later. The belt cleaning unit 22 includes a brush roller 22-1, a rubber blade 22-2, a belt contact / separation mechanism 22-3, and the like.
While the second, third, and fourth colors are transferred on the belt after the image is transferred on the belt, they are separated from the belt surface by the contact / separation mechanism 22-3. The paper transfer unit 23 includes a paper transfer bias roller 23-1, a roller cleaning blade 23-
2 and a belt contact / separation mechanism 23-3 and the like. The bias roller 23-1 is normally the belt 19
Although separated from the surface, the four-color superimposed image formed on the surface of the intermediate transfer belt 19 is pressed by the contacting / separating mechanism 23-3 at a timing when collectively transferring to the transfer paper, and the roller 23-1 A predetermined bias voltage is applied to the paper to transfer the paper.

The transfer paper 24 is fed by the paper feed roller 25 and the registration roller 26 at the timing when the leading edge of the four-color superimposed image on the intermediate transfer belt surface reaches the paper transfer position. The movement of the intermediate transfer belt 19 is
As the operation method after the belt transfer of the Bk toner image of the first color is completed up to the rear end portion, a constant speed forward movement method, a skip forward movement method, and a reciprocating movement (quick return) method can be considered. Or a combination of efficient methods depending on the copy size (eg, in terms of copy speed). The transfer paper 24 to which the four-color superimposed toner images have been collectively transferred from the surface of the intermediate transfer belt is conveyed to the fixing device 28 by the paper conveying unit 27, and the fixing roller 28-1 and the pressure roller 28-2 controlled at a predetermined temperature. Then, the toner image is fused and fixed, and is carried out to the copy tray 29 to obtain a full-color copy.

At the time of repeat copying, the color scanner 1
The operation of and the image formation on the photoconductor 9 are performed on the first Y (4
Subsequent to the (color) image process, the process proceeds to a second Bk (first color) image process at a predetermined timing. Further, the intermediate transfer belt 19 has its surface cleaned by a cleaning unit 22 following the batch transfer process of the first four-color superimposed image onto the transfer paper.
The second Bk toner image is belt-transferred to the area cleaned in step. After that, the same operation as the first sheet is performed. In the above, the copy mode for obtaining four full colors has been described, but the three color copy mode,
In the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Also, in the case of single color copy mode,
With only the developing device for that color in the developing operation (agent standing) state, the intermediate transfer belt 19 is driven in the forward direction at a constant speed while being in contact with the surface of the photoconductor 9, and the belt cleaner 22 is also in contact with the belt 19. The copy operation is performed as it is.
The transfer paper ejected from the fixing device 28 is ejected to a paper ejection tray 29 mounted outside the printer.

The characteristic constitution of the present invention is that in the above constitution, the size of the transfer paper (transfer target) used in the axial direction of the photosensitive drum is the maximum size (when there is no non-image area). Other than the above, toner is supplied from the developing device onto the electrostatic latent image obtained by irradiating the photoconductor 9 with laser light at a predetermined timing from the writing optical unit 8 to form a developed image. Is transferred onto the intermediate transfer belt 19 to form a solid portion with toner in the non-image area corresponding to the non-sheet passing portion on the intermediate transfer belt.

In the present invention, by forming a solid toner portion as an insulating layer on the non-sheet passing portion where the resistance of the intermediate transfer belt 19 is apt to decrease, unevenness in the decrease of the resistance of the intermediate transfer belt is prevented, and white spots on the edges are eliminated. It is possible to prevent the occurrence of such an abnormal image. Whether or not to form a solid toner portion is determined according to the size and direction of the transfer paper used, except for the case where the transfer paper covers the axial length of the photoconductor drum. A control unit (not shown) controls the image forming unit so that the toner is attached in a solid state so as to cover the whole. Specifically, the control unit creates write data so that a latent image for adhering toner to the non-image area is previously formed by the laser light from the writing optical unit 8, and the original image forming area is formed. The control is performed so that a solid image can be formed in other non-image areas of the above image data.

In the above embodiment, the toner solid portion is uniformly formed in the non-image area in forming any image. However, it is truly necessary to form the toner solid portion serving as the insulating layer. This should not be the case during the formation, but only when the resistance of the intermediate transfer belt is significantly reduced. Therefore, in the second embodiment of the present invention, a method is adopted in which a solid toner portion is provided in the non-passage area of the transfer paper of the intermediate transfer belt only when the paper transfer roller bias becomes higher than a certain value. . That is, the higher the bias applied from the paper transfer roller 23-1, the higher the bias applied to the intermediate transfer belt, so that the resistance of the intermediate transfer belt is apt to decrease. By controlling so that the solid toner portion is formed only in the above modes, wasteful consumption of toner is prevented,
It is possible to effectively prevent the occurrence of unevenness in the decrease in resistance of the intermediate transfer belt and prevent the occurrence of an abnormal image with white spots at the edges.

The degree of resistance decrease of the intermediate transfer belt is different in the single color mode, the two-color mode, the three-color mode, and the four-color mode. As the number of colors increases and the toner layer becomes thicker, the paper transfer roller 23-1. Since it is necessary to increase the bias applied from, the resistance of the intermediate transfer belt is likely to decrease. Therefore, it is effective to form a solid portion on the non-sheet passing portion of the intermediate transfer belt in the mode in which the number of toner layers is large. That is, in the case of the three-color mode and the four-color mode, the paper transfer roller bias becomes particularly high. Therefore, by forming the toner solid portion in the non-image area, it is possible to effectively prevent the occurrence of uneven resistance lowering of the intermediate transfer belt. It is possible to prevent the occurrence of an abnormal image with blank areas at the edges.

Next, when the image forming apparatus is used in a low temperature and low humidity environment, the transfer rate deteriorates. Therefore, there is known a technique for compensating for the decrease in the transfer rate by increasing the bias value of the paper transfer roller. Therefore, the temperature and humidity inside the machine are detected by a temperature and humidity sensor (not shown), and when the temperature is low and the humidity is low, the bias value of the paper transfer roller is increased to increase the transfer rate, and at the same time, the toner solid is not printed on the non-sheet passing portion (non-image area) of the intermediate transfer belt. It is effective to configure the control unit so as to provide the control unit. As a result, it is possible to effectively prevent the occurrence of unevenness in resistance reduction of the intermediate transfer belt and prevent the occurrence of an abnormal image with blank areas at the edges.

Next, in the case of OHP or thick paper having a high resistance value of the transfer paper, it is known that the paper transfer roller bias value is set high in order to obtain the same transfer efficiency as the plain paper. Therefore, when the user selects OHP or thick paper as the transfer paper, the paper transfer roller bias value is increased to improve the transfer efficiency, and at the same time, the solid transfer portion is formed on the non-sheet passing portion of the intermediate transfer belt. Is effective. When a solid toner portion is formed on the non-sheet passing portion of the intermediate transfer belt, it is preferable to use yellow toner. this is,
Even if the solid toner in the non-sheet passing portion adheres to the transfer paper, the yellow toner is not conspicuous and has little adverse effect on the image.

It is also effective to use a toner of a color that the user does not use most as the toner used when forming the solid toner portion on the non-sheet passing portion of the intermediate transfer belt.
As a method of selecting such a color that is rarely used,
For example, a color having the smallest data amount may be selected from the write data obtained by color-separating R, G, and B into Bk, C, M, and Y for each copying operation. The toner having the smallest frequency may be stored in the memory and selected. By forming the solid toner portion by using the toner that is least frequently used by the user, the toner consumption balance is improved for each color, and the toner of a specific color in the toner hopper is solidified without being used for a long time. Can be prevented.

[0029]

As described above, according to the first aspect of the invention, the toner solid portion is provided on the non-sheet passing portion of the intermediate transfer belt to form the insulating layer, so that the transfer bias of the sheet passing portion and the non-sheet passing portion can be improved. Eliminates the difference in the applied voltage, prevents uneven resistance drop of the intermediate transfer belt, and eliminates white spots on the edge (uneven density)
It is possible to prevent the occurrence of abnormal images such as. Claim 2
In the invention described above, the resistance decrease of the intermediate transfer belt is more remarkable as the bias of the paper transfer roller is higher, so by providing the toner solid portion only when the bias of the transfer roller exceeds a certain value, wasteful consumption of toner is prevented, It is possible to effectively prevent a decrease in resistance of the intermediate transfer belt.

According to the third aspect of the invention, even if the toner forming the solid portion provided to prevent the resistance of the intermediate transfer belt from decreasing is adhered to the transfer target, it is conspicuous if it is a yellow toner. And the influence on the image can be reduced. According to the fourth aspect of the present invention, since the solid portion is formed by using the toner that the user does not use most, the toner consumption amount is well balanced, and the toner in the toner hopper is fixed for a long time without being used. It is possible to eliminate defects.

[Brief description of drawings]

FIG. 1 is an overall configuration explanatory diagram of an image forming apparatus to which the present invention is applied.

FIG. 2 is an explanatory diagram of a main part configuration of the apparatus of FIG.

3 (a) and 3 (b) are views for explaining the defects of the conventional example.

[Explanation of symbols]

1 color image reading device (color scanner, 3 originals, 4 illumination lamps, 5 mirror groups, 6 lenses, 7 color sensor, 8 writing optical unit, 9 photoconductor drum (image carrier), 10 photoconductor cleaning unit, 11 charge removal Lamp, 12 charger, 13 potential sensor, 14 k developing device, 15 C developing device, 16 M developing device, 17 Y developing device, 18 development density pattern detector, 19 intermediate transfer belt (intermediate transfer member = image carrier) ,
20 belt transfer bias roller, 21 belt drive roller, 22 belt cleaning unit, 23 paper transfer unit.

Claims (4)

[Claims] 1. A single-color or multi-color image formed on a photoconductor is superposed on an endless intermediate transfer belt made of a medium resistance material and stretched between a plurality of rollers. In an image forming apparatus that collectively transfers the image to a transfer target by applying a bias from a paper transfer roller, a toner solid as an insulating layer is formed on the non-sheet passing portion of the intermediate transfer belt according to the size of the transfer target. An image forming apparatus, characterized in that a portion is formed. 2. The image according to claim 1, wherein a toner solid portion is formed on a non-sheet passing portion of the intermediate transfer belt in a mode in which a bias from the paper transfer roller is applied at a certain value or more. Forming equipment. 3. The image forming apparatus according to claim 1, wherein a yellow toner is used as a toner used when forming a solid toner portion of a non-sheet passing portion of the intermediate transfer belt. 4. The toner of a color that is least frequently used by a user is used as the toner used when forming the solid toner portion of the non-sheet passing portion of the intermediate transfer belt. Image forming device.