JPH01273074A - Image forming method - Google Patents

Abstract

PURPOSE:To achieve multiple transfer free of image disorder by employing an intermediate transfer body forming dielectric layers on a conductive base material, electrostatically charging the dielectric layers one time and thereby repeatedly bringing into contact with a photosensitive body. CONSTITUTION:The intermediate transfer belt 10 is composed by laminating the dielectric layers on the surface of the conductive base material. In synchronization with a photosensitive drum 6, the belt 10 is driven at speed the same as the drum 6, and is negatively charged from the surface of the dielectric layer only in first transfer when the belt 10 passes by the charger 22. The negative potential of the belt 10 at that time is set higher than the negative potential of the drum 6 in the final transfer of multiple transfer process. As a result, when the electrified part of the belt 10 comes to a primary transfer position, an image of positive toner is transferred onto the belt 10. Thus, each transfer in multiple transfer can be surely performed without its pretransfer part being adversely affected by image disorder or the occurrence of ozone.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention electrostatically transfers images of each color multiple times from a photoreceptor onto an intermediate transfer member to form a multicolor image, and transfers this at one time. It relates to an image forming method that can be transferred onto a material, and is used, for example, in copying machines and laser beam printers.

(Prior Art) For example, Japanese Patent Publication No. 49-209 (Prior Art Example 1) describes a device that applies electrophotography to print multicolor images on flexible materials such as cloth, and uses an intermediate transfer body to print each color image on a flexible material such as cloth. A multi-color image formed on the intermediate transfer member is transferred to a flexible material under pressure under an electrostatic voltage.

In addition, after sequentially multiple-transferring each color image formed on a photoconductor to an intermediate transfer body to form a multicolor image on the intermediate transfer body, the image is electrostatically re-transferred all at once to transfer paper to prevent image misalignment. There are also apparatuses for forming multi-color images, such as those disclosed in Japanese Patent Publication No. 54-28740 (Conventional Example 2) and Japanese Patent Application Laid-Open No. 56-147166 (Conventional Example 2).
Conventional example 3) is already known. This device uses an insulating bell I as an intermediate transfer member. At a transfer portion where this insulated heald contacts the photoreceptor, a transfer charger operated from the back side of the insulated heald transfers the developed image on the photoreceptor onto the intermediate transfer member. Further, the intermediate transfer member is charged each time the primary transfer is performed.

(Problem to be Solved by the Invention) However, according to the transfer method of Conventional Example 2.3, the action of the transfer charger operated from the back side of the insulating belt is strong, but concentrated at the transfer position where the photoreceptor and the insulated heald are in contact. do not. Therefore, the action of the transfer charger extends to the pre-transfer portion of the surface of the photoreceptor near the transfer position, causing transfer. In this pre-transfer portion, the photoreceptor and the insulating belt are not yet in contact with each other and there is a gap. Therefore, the transfer here (hereinafter referred to as pre-transfer) is not performed normally and the transferred image is disturbed.

Conventional Example 1 does not specifically mention transfer. Neither the above-mentioned problems are raised nor solutions are disclosed.

Furthermore, if the transfer member is charged during primary transfer or each time the primary transfer is performed, in the case of multiple transfers, the number of times of charging increases, and the amount of ozone generated by the charger operation increases, which does not adversely affect image formation.

The present invention provides an image forming method in which a stable charged intermediate transfer member is charged only once and repeatedly comes into contact with a photoreceptor, thereby obtaining a high-quality image free from the effects of previous transfer and without any adverse effects caused by repeated charging. The purpose is to provide the following.

(Means for Solving the Problems) In order to achieve the above objects, the present invention develops an electrostatic latent image on a photoreceptor, and transfers the developed image to an intermediate transfer member. An image forming method that electrostatically transfers and then electrostatically retransfers a developed image on an intermediate transfer member onto a transfer material, the intermediate transfer member having a dielectric layer formed on a conductive base material. By charging the dielectric layer of this intermediate transfer member once and repeatedly contacting it with the photoreceptor, the developed image from the photoreceptor is electrostatically transferred to the surface of the photoreceptor a necessary number of times to perform multiple transfer. This is a characteristic feature.

(Function) The present invention has the above structure, and in order to transfer the developed image formed on the photoreceptor onto the intermediate transfer member, the dielectric layer of the intermediate transfer member is charged. The state is stabilized by the conductive layer on the back side of the dielectric layer, making it less susceptible to environmental influences and capable of maintaining a predetermined charge for a relatively long time. Therefore, the dielectric layer is charged only once prior to transfer, and by repeatedly bringing the charged dielectric layer into contact with the photoreceptor, transfer can be performed as many times as necessary for multiple transfer.

This can prevent the action of the charger that charges the dielectric layer from reaching the transfer area and causing pre-transfer. Developed images that are repeatedly formed multiple times can be successively transferred onto the intermediate transfer member without any disturbance.

During multiple transfer, the charge on the intermediate transfer body is 1 in the untransferred state.
Since charging is performed only once, much less ozone is generated than when charging is repeated, and the influence of ozone can be significantly reduced.

(Embodiment) An embodiment in which the present invention is applied to a color copying apparatus will be described below with reference to FIGS. 1 to 4.

In FIG. 1, an optical system consisting of an exposure lamp 2, first to fifth mirrors 3a to 3e, a lens 4, and a color separation filter unit 1-5 is arranged below a document table glass 1 on which a document is placed. ing. As shown in FIG. 2, the color separation filter Unino I-5 includes a blue filter plate 5B, a green filter plate 5G, and a red filter plate 5R supported in parallel by a frame 51, and a drive motor 52. and filter plates 5B and 5G at position sensors 53a and 53b.
, 5R can be selectively positioned in the exposure optical path.

A photosensitive drum 6 is provided beneath the fifth mirror 3e. An erase lamp 7 is provided around the photoconductor tram 6.
A charger 8 , a developing section 9 , an intermediate transfer belt 10 , and a drum cleaner 11 are sequentially arranged in the rotational direction of the photosensitive drum 6 .

The developing section 9 includes a yellow developing device 9Y and a magenta developing device 9Y.
M and a cyan developer 9C are installed. Further, each developing device is equipped with a developing sleeve, a tip shank, a toner concentration detector, a toner replenishing device, and the like.

The intermediate transfer heald 10 has a conductive base material 1 as shown in FIG.
Urethane rubber as 0a (103~104Ω・cm)
It is composed of a flexible endless bell 1 on which a polytetrafluoroethylene layer (10'4 Ω·can or more) is formed as a dielectric layer 10b. According to experiments, when the dielectric constant of the dielectric layer 10b is 2 or less and the volume resistivity is 10'6 Ω·cm or less, the ability to retain electric charge decreases, and even if it is charged, the electric charge decreases quickly. It ends up. Also, the relative dielectric constant is 4 or more, and the volume resistivity is 1017Ω・cm.
If it is more than that, the charging and static elimination efficiency will be poor, and it will be difficult to charge and eliminate static electricity. Next, the resistance value of the conductive base material 10a is 10
If it exceeds 10Ω·cm, the conductivity becomes poor, charging becomes uneven and unstable, and problems such as a large potential drop during toner image transfer occur.

From the above, the dielectric layer should have a relative dielectric constant of 2 to 4, a volume resistivity of 1016 to 10"7 (Ωcm), and a conductive base material should have a volume resistivity of 105 (Ωcm) or less. in,
It is effective as an intermediate transfer member because it has good charging and neutralizing efficiency, and the charge generated by charging can be stably maintained for a relatively long time without being affected by the environment.

Around the intermediate transfer heald 10, there is a bell I/charger 12 for primary transfer which transfers the image from the photosensitive drum 6 to the intermediate transfer heald 10, and a charger 12 which transfers the image from the intermediate transfer heald 0 to the transfer paper S. Secondary transfer charger 13, separation charger 13a, heald static elimination charger 15, bell [
A cleaner 16 and the like are provided.

Further, as shown in detail in FIG. 3, the intermediate transfer heald 10 includes a heald charging roller 17 facing the belt charging charger 12, a pressure roller 18 facing the photoreceptor drum 6, and a secondary transfer roller 18 facing the photosensitive drum 6. It is stretched by five straight rollers including a roller 19, a heald cleaner roller 20, and a tension roller 14, and the dielectric layer 10b on the surface faces the photosensitive drum 6. The pressure roller 18 is moved by the solenoid 21 so that the intermediate transfer heald IO can be moved between a first position where the intermediate transfer heald IO is pressed against the photoreceptor drum 6 at the primary transfer position and a second position where it is separated from the photoreceptor drum 6. It is configured to switch between. Reference numeral 22 denotes a solenoid that presses and separates the belt cleaner 16 from the intermediate transfer belt 10 .

A paper feed cassette 23 is provided on the left side of the secondary transfer section, and is configured to feed the transfer paper S sent out by a paper feed roller 23a to the secondary transfer section via a timing roller 24. A transfer paper conveyance heald 25 is provided on the right side of the secondary transfer section, and sends the transfer paper S after the secondary transfer to a fixing device 26.

Next, to explain the operation, an original placed on the original table glass 1 is sequentially scanned in the horizontal direction, and the reflected light is transmitted to the first to third mirrors 3a to 3c, the color separation filter unit 5, and the lens. The image is formed on the photosensitive surface of the photosensitive drum 6 via the fourth and fifth mirrors 3d and 3e. After being exposed and neutralized by the photoconductor tram 6 and erase lamp 7, it is charged to, for example, a constant negative potential by a charger 8, and is rotated and exposed in synchronization with the above scanning. When the photosensitive surface is irradiated with reflected light from the original, the surface potential changes depending on the intensity of the light, and an electrostatic latent image is formed.

This electrostatic latent image is formed by the yellow developing device 9Y of the developing section 9,
The image is developed with toner of each color in either the magenta developer 9M or the cyan developer 9c. For example, in the color separation filter unit 5, the blue filter plate 5B
is located in the optical path, the yellow developer 9Y, which is a complementary color to blue, is selected, and the other developers 9M and 9C scrape off the developer on the developing sleeve with the tip shank at the rear of each developing sleeve. After that, the yellow developing device 9Y is driven, and the electrostatic latent image is developed with yellow toner and made visible. Note that the toner is charged to, for example, a positive potential, which is opposite to that of the photoreceptor drum 6.

The intermediate transfer heald 10 is driven at the same speed as the photoconductor drum 6 in synchronization with the photoconductor drum 6, and as it passes through the heald charger 12 located in front of the next transfer section, as shown in FIG. Receives electrical charge. Held charger 12
A negative potential is applied to the dielectric layer 10b of the intermediate transfer heald 10, and the dielectric layer 10b of the intermediate transfer heald 10 is negatively charged even during multiple transfer for forming a multicolor image. This charging is performed with high efficiency by being directly performed from the material of the dielectric layer 10b and the surface of the dielectric layer 10b. This charging causes the surface of the dielectric layer 10b to -
A similar negative potential is formed. This state is dielectric layer 1
It is stabilized by the bank amplifier made of the conductive base material 10a on the back side of the 0b, is not easily affected by the environment, and can maintain the above state for a relatively long time, and the charge required for forming multiple images is achieved with just the one charging. A sufficient number of transfers can be performed.

On the other hand, at the primary transfer position, the pressure roller 18 presses the intermediate transfer heald 10 against the photosensitive drum 6 under the action of the solenoid 21 .

In this state, when the charged portion of the intermediate transfer heald 10 comes to the primary transfer position, the yellow I/toner image Tv at a positive potential on the photoreceptor tram 6 due to the negative potential on its surface.
is transferred onto the intermediate transfer heald 10 as shown in FIG. This transfer is not affected by the action of the heald charger 12 because it is far from the primary transfer position, and due to the stable and predetermined surface potential of the intermediate transfer bell 0, there is no disturbance caused by the previous transfer. definitely achieved. Also, since multiple transfer to form a multicolor image is achieved by charging the intermediate transfer heald 10 times,
Ozone generation due to charger operation and its influence on images can be suppressed by reducing the number of times of charging. Furthermore, if charging is simply performed each time a transfer is performed, the toner on the intermediate transfer belt 10 will also be charged to the same polarity as the intermediate transfer heald 10, and there is a concern that the toner may be reversely transferred from the intermediate transfer heald 10 to the photoreceptor 6 due to mutual repulsion. However,
In this embodiment, there is no such concern. Intermediate transfer heald 1
The charging potential in the one charging is set so that the negative potential of 0 is kept higher than the negative potential of the photosensitive drum 6 during the final transfer in multiple transfer. This makes it possible to successfully accomplish each round of transcription in the case of multiple transcription.

After that, the photosensitive surface of the photosensitive drum 6 is cleaned by a drum cleaner 11.
After cleaning, the exposure-development-next transfer process is completed.

In the case of full-color copying, when the first exposure-development-next transfer process for yellow is completed, the green filter plate 5G is selected in the color separation filter unit 5 and positioned on the optical path. The photosensitive surface of the photosensitive drum 6 is exposed to the reflected light from the original that has passed through the document, and an electrostatic latent image is formed. This electrostatic latent image is visualized using a magenta developer, which is a complementary color to green. At the same time, the intermediate transfer heald 10 is again brought into pressure contact with the photoreceptor 1 ram 6 with the yellow toner image Tv transferred thereon, and by maintaining a predetermined potential at this time, the yellow toner image Tv is transferred to the intermediate transfer heald 10, as shown in FIG. Magenta toner image T is superimposed on toner image 1 and 7.
, is transferred in substantially the same manner as the toner image T,.

When the second exposure-development and primary transfer process is completed,
For the third time, the red filter plate 5R is selected in the color separation filter unit 5 and placed on the optical path, and the light reflected from the original that passes through it exposes the photosensitive surface of the photosensitive drum 6, forming an electrostatic latent image. It is formed. This electrostatic latent image
' is visualized by the cyan developer 9C, which is the complementary color of '. Along with this, the intermediate transfer heald 10 has a yellow toner image Tv,
The transferred magenta toner image TM is again brought into pressure contact with the photosensitive drum 6, and at this time, by maintaining a predetermined potential, the yellow and magenta toner images T7, To' A cyan toner image TC is further superimposed and transferred in substantially the same manner as the toner images Tv and TH to form a full color toner image T of yellow, magenta and cyan.

During this next transfer step, the heald cleaner 1G of the intermediate transfer heald 10 is separated from the intermediate transfer bell 1-10 by turning off the solenoid 22. -Force, -When the next transfer process is completed, the solenoid 21 is turned off and the pressure roller 18 is turned off.
is moved to separate the intermediate transfer bell number 0 from the photosensitive drum 6, and in this state, the intermediate transfer heald 10 is driven as it is.

In this way, the intermediate transfer heald 10 is brought into pressure contact with the photoreceptor drum 6 only in the next transfer step, and is kept apart at other times, so that the photoreceptor drum 6 is stopped when the next transfer is completed. Further, since the photoreceptor 6 and the intermediate transfer belt 10 are separated from each other, there is no possibility of damage or electrical fatigue due to repetition of frictional charging and peeling discharge during this time.

On the other hand, the transfer paper S is sent out from the paper feed cassette 23 by the paper feed roller 23a at a predetermined timing based on a signal from a position detection device (not shown) of the intermediate transfer heald 10, and is transferred to the secondary transfer via the timing roller 24 at a predetermined timing. Transfer paper is fed to the charger 14. Here, the transfer paper S is negatively charged by the secondary transfer charger 13 to which a negative potential is applied, as shown in FIG. and is transferred onto transfer paper S.

The transfer paper S on which the toner image TF has been transferred as shown in FIG. heated fuser 26
The image is sent to the printer, fixed, and then discharged.

On the other hand, the intermediate transfer belt 10 that has completed the secondary transfer is first neutralized by the operation of the heald static elimination charger 15, and cleaned by the action of the heald cleaner 16 when the solenoid 22 is turned on, in preparation for the next process.

In the above process, the photoreceptor tram 6, intermediate transfer bell I,
10, solenoids 21, 22, heald cleaner, and chargers 12, 13, 1.3a, and 15 are shown in FIG. 1I.

In the above explanation, the photoreceptor tram 6 and the intermediate transfer belt 1 are
Although an example has been described in which the toner is charged negatively and the toner is charged positively, the toner may be charged in the opposite manner.

In addition, in the above description, three primary transfers are performed on the intermediate transfer belt 10.
Although an example has been shown in which a full-color toner image is formed by rotating the toner image and transferred to a transfer paper, it goes without saying that a mode in which a monochromatic color image is formed and transferred may also be provided.

Further, in the above embodiment, the intermediate transfer heald 10 is used as an example of the intermediate transfer member, but an intermediate transfer drum may also be used.

(Effects of the Invention) According to the present invention, the developed image is electrostatically transferred from the photosensitive drum by charging the intermediate transfer member, which is not easily influenced by the environment and easily retains charge, so that the transfer is performed without image disturbance. Moreover, it can be carried out reliably and the image quality can be improved.Moreover, multiple transfers to form a multicolor image can be achieved by charging the intermediate transfer member once, so the number of times of charging can be reduced. Ozone generation due to charger operation and its influence on image quality can be suppressed.

[Brief explanation of the drawing]

1M to 4 show an embodiment in which the present invention is applied to a full-color copying apparatus, in which FIG. 1 is a general schematic diagram, FIG. 2 is a perspective view of a color selection filter unit, and FIG. 3 is an intermediate transfer held. FIG. 4 is an enlarged sectional view of the intermediate transfer heald, FIG. 5 is an enlarged sectional view showing the charging state of the intermediate transfer heald, and FIGS. 6 to 8M are views of toner images of each color in full-color copying. FIG. 9 is an enlarged cross-sectional view of the primary transfer section showing the state of primary transfer. FIG. 9 is an enlarged cross-sectional view of the secondary transfer section showing the state of secondary transfer of a full-color toner image. FIG. 10 is an enlarged view of the transfer paper after the secondary transfer. The cross-sectional view and FIG. 11 are diagrams showing the operation timing of each part.

Claims (1)

[Claims] (1) After developing the electrostatic latent image on the photoreceptor and electrostatically transferring the developed image to an intermediate transfer member, transfer the developed image on the intermediate transfer member onto a transfer material. This is an image forming method in which electrostatic retransfer is performed, using an intermediate transfer body in which a dielectric layer is formed on a conductive base material, and the dielectric layer of this intermediate transfer body is charged once to transfer it to a photoreceptor. An image forming method characterized by performing multiple transfers by electrostatically transferring a developed image from a photoreceptor onto the surface of the photoreceptor a necessary number of times by repeatedly contacting the surface of the photoreceptor.