JPH09230665A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize and reduce manufacturing cost of a color image forming device by conveying a transfer paper so as to pass through the area where a photosensitive body and an intermediate transfer belt come into contact with each other. SOLUTION: When making multicolor copies, a toner image on a photosensitive body drum 414 is once transferred to an intermediate transfer belt 415 and, after superposing one on top of another, it is transferred to a transfer paper P by a multicolor copying transfer machine 417 which transfers the toner image on the photosensitive body to the intermediate belt 415 by impressing AC+DC or DC elements through corona discharge system. Transfer papers P are supplied and conveyed from a storage cassette for paper sheets of a size specified by a transfer paper cassette 482 inside a paper supply bank to the resist roller direction by a paper supplying roller 483. The transfer papers P are supplied through either paper supply opening and await at the nip part of a resist roller pair 418 at the time image forming starts. The transfer papers P are conveyed so that they pass through the area where the photosensitive body drum 414 and the intermediate transfer belt 415 come into contact with each other.

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 such as a copying machine, a printer, a facsimile machine, etc., and particularly in a multicolor image forming apparatus using an intermediate transfer belt system, the size and cost of the apparatus are reduced. The present invention relates to an image forming apparatus which is designed to be downsized, improve a blurred image when a single color image is formed using this apparatus, and increase a print speed.

[0002]

2. Description of the Related Art As in a color copying machine, a toner image is formed on a photosensitive member for each different color component, and these toner images are sequentially transferred onto an intermediate recording medium and then transferred. Examples of the image forming apparatus capable of collectively transferring images onto a transfer sheet include the techniques described in JP-A-59-125765 and JP-A-59-75266. Further, there is an image forming unit of a color copying machine manufactured by the applicant of the present invention, which has a configuration as shown in FIG. This image forming unit is provided on the outer periphery of the photoconductor 1.
A charger 2, a developing device 3, an intermediate transfer belt 4, a cleaning unit 5 and the like are sequentially arranged, and a paper transfer unit 6 is attached to the intermediate transfer belt 4.

[0003]

In the image forming apparatus equipped with the intermediate transfer belt shown in this figure, a blurred image is easily generated particularly when the toner image is transferred from the photoconductor 1 to the intermediate transfer belt 4. In particular, this blur image tends to stand out in a monochromatic character image, which is a problem. In the case of a character image, the characters appear to be blurred and are very difficult to see. When a material having a low resistance is used as the material of the intermediate transfer belt, a blurred image is likely to be generated particularly when transferring from the photoconductor to the intermediate transfer belt. In the case of a low resistance material, the electric charge applied to the intermediate transfer belt is easy to move, so the toner holding force becomes weak. For this reason, the toner is scattered in areas other than the dot portion, often resulting in a blurred image. On the contrary, when the material having high resistance is used, the electric charge applied to the belt is hard to move, the toner holding force becomes strong, and the blurred image is hard to occur. However, when a material having a high resistance is used, charges are accumulated on the belt, and the charges applied before remain on the belt during continuous copying, and as a result, the optimum transfer bias for the image is changed. , The image cannot be stabilized. In addition, since the amount of electric charge accumulated in the area where toner is present is different from that where toner is present, it becomes difficult to transfer the area where toner was present in the previous image formation during continuous copying, and it appears as a negative afterimage overlapping the next image. Sometimes it becomes a problem. To deal with this, static elimination means such as corona discharge is required, but it is difficult to eliminate static electricity at the same time because a high resistance material easily holds electric charges, which is considerably more difficult than exposure static elimination of the photoconductor. .
Further, the transfer method by applying a voltage to the roller cannot be adopted because a current does not flow between the rollers. Generation of ozone due to static elimination corona discharge is also a problem.

Therefore, regarding the material of the intermediate transfer belt,
It is very difficult to set the electric resistance value so that there is no problem of blur image generation and no charge elimination means is required.
In the conventional device, the belt of medium resistance is unavoidably used,
Some blurry images are divided, and this is one of the main causes of image quality deterioration. Also, recent colors
As a development trend of image forming apparatuses, there is an increasing tendency to open up the small and medium-sized general office market by using a color machine as a monochrome machine. However, in a color machine that adopts the conventional intermediate transfer method, even a black-and-white image is transferred through the intermediate transfer belt once, so that the speed of the black-and-white image is delayed. To do. Further, the blurred image in the character portion described above is often unacceptable for a user who mainly uses a monochrome image. Further, in the small and medium-sized general office market, the space saving of the apparatus is important, but the color image forming apparatus is larger than the single color image forming apparatus, and it is difficult to secure a space for installing machines. Therefore, there is a need for smaller color image forming devices.
The present invention has been made in view of the above, and an object of the present invention is to reduce the size and cost of a color image forming apparatus. The second aspect of the present invention is, in addition to the first aspect, an object of the present invention to improve a blurred image at the time of forming a monochromatic image and to increase the print speed. The invention of claim 3 is, in addition to the object of claim 1, an object of increasing the print speed at the time of forming an image on both surfaces of the transfer paper.

[0005]

In order to achieve the above object, the invention of claim 1 is characterized in that a toner image on a photoconductor as an image carrier is transferred onto an intermediate transfer belt and then transferred onto the intermediate transfer belt. In a multicolor image forming apparatus using an intermediate transfer belt system for transferring the toner image of No. 1 to a transfer paper, the transfer paper is conveyed so as to pass through a contact portion between the photoconductor and the intermediate transfer belt. To do. According to a second aspect of the invention, in the image forming apparatus according to the first aspect, the toner image on the photoconductor is directly transferred onto the transfer paper from the photoconductor during the monochrome copy, and the toner image is transferred during the multicolor copy. It is characterized in that the toner image on the body is once transferred to the intermediate transfer belt, the toner images of respective colors are superposed on the intermediate transfer belt, and then the superposed toner image is transferred onto the transfer paper. According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, after a toner image of at least one color is transferred from the photoreceptor to the intermediate transfer belt, a toner image formed on the photoreceptor next. Is directly transferred onto the transfer paper, and the toner image on the intermediate transfer belt is transferred onto the back surface of the transfer paper.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The configuration and operation of the present invention will be described below with reference to an embodiment. FIG. 1 shows a color according to the present invention.
FIG. 1 is a schematic configuration diagram of an image forming apparatus. This color image forming apparatus is composed of a color image reading device, a color image recording device, a paper feeding bank, and the like. A color image reading device (hereinafter referred to as a color scanner) 200 connects an image of an original 180 on a contact glass 202 to a color sensor 207 via an illumination lamp 205, a mirror group 204, and a lens 206. An image is read, and color image information of the document is read for each color separation light of, for example, Blue, Green, and Red, and converted into an electric image signal. Color
In this example, the sensor 207 is composed of B, G, and R color separation means and a photoelectric conversion element such as a CCD, and simultaneously reads three colors. An image processing unit (not shown) performs color conversion processing on the B, G, and R color-separated image signals obtained by the color scanner 200, based on the intensity level.
Black (hereinafter, described as Bk), Cyan (the same,
C), Magenta (same, M), Yellow (same,
The color image data of Y) is obtained. This is a color image recording device (hereinafter referred to as a color printer) 4 described below.
00, Bk, C, M, and Y are visualized to obtain a final color copy. The operation method of the color scanner 200 for obtaining the image data of Bk, C, M, and Y is as follows, in response to the operation of the color printer 400 and a scanner start signal in timing. In FIG.
The illumination / mirror optical system scans the document in the direction of the left arrow to obtain image data of one color for each scanning. By repeating this operation four times in total, sequential four-color image data is obtained.
Then, each time it is visualized by the color printer 400, they are superposed to form a four-color full-color image.

Next, the outline of the color printer 400 will be described. The writing optical unit converts the color image data from the color scanner into an optical signal, performs optical writing corresponding to the original image, and forms an electrostatic latent image on the photosensitive drum 414. The writing optical unit includes a laser light emitting means 441 and its light emission drive control section (not shown).
Polygon mirror-443 and its rotation motor 444, f /
The θ lens 442 and the reflection mirror-446 are included. The photoconductor drum 414 rotates clockwise as indicated by the arrow, but around the photoconductor drum 414, the photoconductor cleaning unit 42 is rotated.
1, static elimination lamp 414M, charger 419, potential sensor-
414D, a selected developing device of the revolver developing device 420, a developing density pattern detector 414P, an intermediate transfer belt 415, and the like are arranged. Revolver developing device 42
Reference numeral 0 denotes a Bk developing device 420K, a C developing device 420C, an M developing device 420M, a Y developing device 420Y, and a revolver rotation driving unit (not shown) that rotates each developing device counterclockwise as indicated by an arrow. Each developing device has a developing sleeve that rotates by bringing the ears of the developer into contact with the surface of the photoconductor 414 to develop the electrostatic latent image, a developing paddle that rotates to scoop and agitate the developer, and the like. It is composed of.

In the standby state, the revolver developing device is set to the position Bk, and when the copying operation is started, the color scanner 200 starts reading the Bk image data from a predetermined timing. -This image data
Optical writing / latent image formation by laser light starts based on the data (hereinafter, an electrostatic latent image by Bk image data is referred to as a Bk latent image. The same applies to C, M, and Y). Before the latent image front end reaches the developing position of the Bk developing device so that the front end of the Bk latent image can be developed, the developing sleeve is started to rotate and the Bk latent image is developed by the Bk toner. . And after that, B
Although the developing operation of the k latent image area is continued, the revolver developing device is rapidly rotated from the Bk developing unit developing position to the next color developing position when the trailing edge of the latent image passes the Bk developing position. This is completed at least before the leading edge of the latent image by the next image data reaches the developing position.

Image formation for each color is performed as follows. The charger 419 uses the corona discharge for the photoconductor drum 4
Negatively charge 14 to approximately -700V. Then, the laser diode 441 performs raster exposure based on the image signal. When the raster image is exposed in this way, in the exposed portion of the photosensitive drum 414 that is initially uniformly charged, the charge proportional to the amount of exposure light disappears and an electrostatic latent image is formed. The toner in the developing device 420 is negatively charged by stirring with the ferrite carrier, and the developing sleeve of each color of the developing device is negative with respect to the metal base layer of the photosensitive drum 414 by a power source means (not shown). It is biased to a potential in which a direct current potential and an alternating current are superposed. As a result, the toner does not adhere to the portion of the photoconductor 414 where the electric charge remains, and the toner of each color is adsorbed to the non-charged portion, that is, the exposed portion, and a visible image similar to the latent image is formed. Will be done.

Next, the transfer operation by the multicolor image forming apparatus of the present invention having the above structure will be described separately for multicolor copying, single color copying, and double-sided copying. During multicolor copying In the case of multicolor copying, the toner image on the photoconductor is temporarily transferred onto the intermediate transfer belt 415, and after overlapping, the multicolor transfer C
It is transferred to the transfer paper by H417. When the image forming cycle is started, first, the photosensitive drum 414 is rotated clockwise as indicated by an arrow and the intermediate transfer belt 415 is rotated counterclockwise by a drive motor (not shown). As the intermediate transfer belt 415 rotates, Bk toner image formation and C toner
Image formation, M toner image formation, and Y toner image formation are performed, and finally a toner image is formed by superimposing them on the intermediate transfer belt 415 in the order of Bk, C, M, and Y. Intermediate transfer belt 415
Is stretched around a driving roller 415D, an ascending roller 415T, a cleaning counter roller 415C and a driven roller group, and is driven and controlled by a driving motor (not shown). Now, the Bk toner image formed on the photoconductor 414 is transferred onto the surface of the intermediate transfer belt 415 which is in constant contact with the photoconductor and is driven at a constant speed. This is performed by applying a predetermined bias voltage to the corona discharge transfer device 417 to generate corona discharge when the photoconductor 414 and the intermediate transfer belt 415 are in contact with each other (hereinafter, the toner from the photoconductor to the intermediate transfer belt will be described). Image transfer is referred to as belt transfer).

On the intermediate transfer belt 415, the toner images of Bk, C, M, and Y which are sequentially formed on the photoconductor 414,
By sequentially aligning on the same surface, a belt transfer image of four colors is formed, and then a corona discharge transfer device 418 collectively transfers the transfer image onto the transfer paper. By the way, Bk on the side of the photoconductor 414
After the step C, the C image data reading by the color scanner starts at a predetermined timing, and the C latent image is formed by laser light writing by the image data. The C developing device rotates the revolver developing device with respect to the developing position after the trailing edge of the previous Bk latent image passes and before the leading edge of the C latent image reaches to develop the C latent image. C
Develop with toner. After that, the development of the C latent image area is continued, but when the trailing edge of the latent image passes, the rotation operation of the C developing unit is performed as in the case of the previous Bk developing device. This is also completed before the leading end of the next M latent image arrives. Regarding the steps of M and Y, the respective image data
The operations of reading the data, forming the latent image, and developing are the same as the steps Bk and C described above, and thus the description thereof will be omitted.

The belt cleaning device 415e includes an inlet seal, a rubber blade, a discharge coil, and an inlet seal.
It is composed of a contacting / separating mechanism for the blades and blades. While the second, third, and fourth colors are belt-transferred after the first color Bk image is transferred by the belt, the blade contacting / separating mechanism is used. Separate the entrance seal and blade from the belt surface. Multicolor copy transfer device 417 is AC + D by corona discharge method.
By applying the C or DC component, the toner image on the photoconductor is transferred onto the intermediate transfer belt. Transfer papers of various sizes are stored in the transfer paper cassette 482 in the paper supply bank, and the papers are fed and conveyed in the registration roller direction by the paper feed rollers 483 from the storage cassette of the designated size paper. At the time when the image formation is started, the transfer sheet P is fed from any one of the sheet feeding ports and stands by at the nip portion of the registration roller pair 418R. When the front end of the toner image on the intermediate transfer belt 415 reaches the paper transfer unit 418, the registration roller pair 418R is driven so that the front end of the transfer paper P coincides with the front end of the image, and the registration of the paper and the image is performed. Done. In this way, the transfer paper P is superposed on the toner image on the intermediate transfer belt and passes under the paper transfer device 418 connected to the bias applying means of positive potential. At this time, the transfer paper is positively charged by the corona discharge current,
Most of the toner image on the belt is transferred onto the transfer paper.

The transfer paper on which the four-color superimposed toner images are collectively transferred from the surface of the intermediate transfer belt is conveyed to a fixing device 423 and is fixed at a predetermined temperature by a fixing roller 423A.
The toner image is melted and fixed at the nip portion of the pressure roller 423B, sent out of the main body by the discharge roll pair 424, and is stacked face up on a copy tray (not shown) to obtain a full color copy. . The photosensitive member 414 after the belt transfer
Is a photoconductor cleaning unit 421 (brush roll).
La, rubber blade) is used to clean the surface,
The static elimination lamp 414M uniformly eliminates static electricity. The intermediate transfer belt 415 after transferring the toner image on the transfer paper cleans the surface by pressing the blade of the cleaning unit 415e again by the blade contact / separation mechanism. In the case of repeat copy, the operation of the color scanner and the image formation on the photoconductor are performed in the second (first color) image process at a predetermined timing after the first (fourth color) image process. move on.
For the intermediate transfer belt, following the batch transfer process of the first four-color superimposed image onto the transfer paper, the surface is cleaned by the belt cleaning device and the Bk toner for the second sheet is used. – Allow the image to be belt transferred. After that, the operation is the same as that of the first sheet. The above is the description of the copy mode for obtaining the full color of four colors. In the case of the three-color copy mode and the two-color copy mode, the designated color and the number of times are as follows. The same operation as above is performed.

In the case of the single color copy mode, until the predetermined number of sheets is completed, only the developing device of the predetermined color of the revolver developing device 420 is in the developing operation (developing position of the predetermined color) state, and the photosensitive member. A toner image is formed on the toner image, and the toner image is transferred to a monochrome image transfer device 417 (corona discharge method, AC + DC or D
According to C), the image is directly transferred onto the transfer paper. As a result, in the case of a monochrome copy mode, a mirror-reversed image of the original image must be formed on the photoconductor. Multicolor copy mode
In the case of the image, in order to make an image that does not reverse on the photoconductor,
In the case of single color and multicolor, it is necessary to switch the signal sent from the image processing unit to the writing unit and perform mirror inversion.

When carrying out this batch transfer, in the present invention, the conveying path is constituted so that the transfer paper passes through the contact portion between the intermediate transfer belt and the photosensitive member.

In the conventional apparatus shown in FIG. 2, the conveyor belt unit 7 is installed in front of the transfer section 6 for transferring the toner image on the intermediate transfer belt 4 onto the transfer paper. The transport belt unit 7 is installed because it is necessary to secure a certain distance between the transfer sheet transfer section and the fixing section. That is, when the distance between the transfer paper transfer unit and the fixing unit is short, when the transfer paper enters the fixing unit, a shock is applied to the transfer paper, and the transfer paper shakes at the transfer unit. The distance must be lengthened to a certain extent to create a bend that can be absorbed even when a shock is applied to the transfer paper. Therefore, the distance is
At least 100 mm or more is necessary. In the first aspect, unlike the conventional example shown in FIG. 2, since the transfer sheet is passed through the contact portion between the intermediate transfer belt 415 and the photoconductor 414, the transfer sheet is fixed by the intermediate transfer belt 415. Can be transported up to. This allows
There is no need to install a conveyor belt unit, which leads to cost reduction and machine downsizing.

Single Color Copying In the second aspect of the present invention, the toner image on the photoconductor is directly transferred onto the transfer paper at the time of single color copying.
The toner image formed on the photoconductor 414 is directly transferred by the transfer device 417 to the transfer paper fed by the registration roller 418R at substantially the same speed as the photoconductor. In the conventional color image forming apparatus using the intermediate transfer system, the toner image on the photoconductor is temporarily transferred to the intermediary transfer medium even in the case of single-color copying, and further transferred to the transfer paper. There is a problem that a transfer dust is generated at the time of transferring each of the intermediate transfer member and the transfer paper from the intermediate transfer member to create a blurred image. Further, there is a drawback that the image forming speed becomes slow. According to the second aspect of the present invention, the toner image on the photoconductor is directly transferred onto the transfer paper at the contact portion between the photoconductor and the intermediate transfer belt during the single color copy, and the toner image is intermediate during the multicolor copy. Once transferred to the transfer belt, the images of each color are overlaid on the intermediate transfer belt, and then the toner on the intermediate transfer belt is transferred.
The image is transferred onto a transfer paper. According to this mode example, it is possible to prevent the occurrence of a blurred image due to transfer dust during a single-color copy.

In double-sided copying In claim 3, after the toner image of at least one color is transferred from the photosensitive member to the intermediate transfer belt, the toner image formed on the photosensitive member is intermediately transferred to the photosensitive member. Transfer is directly performed on the surface of the transfer paper at the contact portion with the transfer belt (transfer device 417
Is used). When the toner image on the photoconductor is transferred to the surface of the transfer paper, the image on the intermediate transfer belt is in alignment with the back surface of the transfer paper. Then, after that, the toner image on the intermediate transfer belt 415 is transferred to the transfer device 418.
Then, double-sided copying is performed by transferring the image onto the transfer paper P. In this embodiment, when performing the double-sided copy, the front surface transfer and the back surface transfer are sequentially performed on the same conveyance path, and the fixing is performed simultaneously. However, it is limited to the case where the front side is monochrome and the back side is monochrome or multicolored. The transfer operation in this embodiment is described in detail. As in the case of the multicolor copy described above, color superimposition is performed on the intermediate transfer belt, and this color superposed toner image (the image for the back side of the transfer paper) is intermediately transferred. The belt is moved in the direction of the arrow to move out of the transfer position. Next, a toner image to be transferred to the front side of the transfer paper is formed on the photosensitive member 414, and first, at the nip portion between the photosensitive member 414 and the intermediate transfer belt 415, the toner image on the photosensitive member is transferred by the transfer device 417. Is directly transferred onto a transfer paper. This transfer is performed at a timing such that the superposed image already formed on the intermediate transfer belt makes a round and is just positioned on the back side of the transfer paper. Further, when the transfer paper having undergone the surface transfer reaches the transfer device 418, the transfer device 418 transfers the superimposed image on the intermediate transfer belt 415 to the back surface of the transfer paper,
The fixing unit 423 fixes the front and back sides at the same time. At the time of double-sided copying in a conventional image forming apparatus, a method is adopted in which transfer is performed once on the transfer sheet surface, then the transfer sheet is reversed, and then the sheet is passed again, which slows down the copying speed. In this case, the transfer paper needs to be conveyed only once, and the copy speed can be clearly improved.

[0019]

The present invention has been made in view of the above, and the invention of claim 1 is to transfer the toner image on the photoconductor as an image carrier onto the intermediate transfer belt and then to perform the intermediate transfer. In a multicolor image forming apparatus using an intermediate transfer belt system for transferring a toner image on a belt to a transfer paper, the transfer paper is conveyed so as to pass through a contact portion between the photoconductor and the intermediate transfer belt. Therefore, the color image forming apparatus can be downsized and the cost can be reduced. That is, when the contact portion between the image carrier and the intermediate transfer belt is used as the primary transfer and the secondary transfer portion (paper transfer portion) is provided at another position of the intermediate transfer belt as in the conventional case, the number of parts is reduced. Although it causes problems such as an increase in size and an increase in size of the structure, according to the present invention, since the conventional primary transfer portion is also used as the secondary transfer portion, it is possible to reduce the size and cost.

According to a second aspect of the present invention, in the first aspect of the present invention, when the monochrome image is copied, the toner image on the photoconductor is directly transferred from the photoconductor to the transfer paper at the contact portion to obtain a multicolor copy. -When the toner image on the photoconductor is temporarily transferred onto the intermediate transfer belt at the contact portion, the toner images of respective colors are superposed on the intermediate transfer belt, and then the superposed toner image is transferred onto the transfer paper at the contact portion. By doing so, in addition to the effect of the first aspect, it is possible to improve the blurred image at the time of forming a monochromatic image and increase the printing speed.

According to the third aspect of the invention, after transferring the toner image of at least one color from the photosensitive member to the intermediate transfer belt, the toner image formed on the photosensitive member is directly transferred onto the transfer paper, and Since the toner image on the intermediate transfer belt is transferred to the back surface of the transfer paper, in addition to the effect of claim 1, the print speed at the time of forming an image on both surfaces of the transfer paper can be increased. You can

[Brief description of drawings]

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

FIG. 2 is a structural explanatory view of a conventional example.

[Explanation of reference numerals] 180 originals, 200 color image reading device (color scanner), 203 contact glass, 205 illumination lamp, 204 mirror group, 206 lens, 20
7 color sensor, 400 color image recording device (color printer), 414 photoconductor drum, 414D
Potential sensor, 414M static elimination lamp, 414P development density pattern detector, 415 intermediate transfer belt, 417
Multicolor copy transfer device, 418 paper transfer device, 419 charger, 420 revolver developing device, 421 photoconductor cleaning unit, 441 laser light emitting means, 44
2f / θ lens, 443 polygon mirror, 444 rotation motor, 446 reflection mirror,

Claims (3)

[Claims] 1. A multicolor system using an intermediate transfer belt system, in which a toner image on a photoconductor as an image carrier is transferred onto an intermediate transfer belt and then the toner image on the intermediate transfer belt is transferred onto a transfer paper. In the image forming apparatus, the transfer sheet is conveyed so as to pass through a contact portion between the photoconductor and the intermediate transfer belt. 2. The image forming apparatus according to claim 1, wherein the toner image on the photoconductor is transferred directly from the photoconductor onto the transfer paper when the single color copy is performed, and on the photoconductor when the multicolor copy is performed. Image forming apparatus, wherein the toner image of 1) is once transferred to an intermediate transfer belt, the toner images of respective colors are superposed on the intermediate transfer belt, and then the superposed toner image is transferred onto a transfer paper. 3. The image forming apparatus according to claim 1, wherein
After transferring the toner image of at least one color from the photosensitive member to the intermediate transfer belt, the toner image formed on the photosensitive member is directly transferred onto a transfer paper, and then the intermediate image is transferred to the back surface of the transfer paper. An image forming apparatus, which transfers the toner image on a transfer belt.