JP2704278B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial Application Field) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer, and in particular, a photoconductor and a nip portion. The present invention relates to an image forming apparatus having a transfer member to be formed.

(Problems to be Solved with the Prior Art) An image carrier and a transfer unit that comes into contact with the image carrier are provided, and a transfer material is passed between the two. At this time, a transfer bias is applied to the transfer unit, and an image is transferred in advance. An image forming apparatus configured to transfer a toner image formed on the surface of a carrier to a transfer material has already been proposed.

FIG. 8 is a schematic side view of a main part showing a typical example of such an image forming apparatus. The toner is uniformly charged by the charging roller 3 connected to the power supply 4, and the charged surface is provided with an image signal 5 by an image-modulated laser beam, slit exposure, or the like, thereby forming an electrostatic latent image. The toner is supplied from the developing device 6 to the latent image to form a toner image and arrives at a transfer portion.

The transfer portion includes a nip portion between the photosensitive member 1 and a conductive transfer roller that comes into contact with the photoreceptor 1. When the transfer material arrives at the transfer portion, the transfer material P is supplied by the transport path 7 at the same time as the transfer material. At this time, the toner passes through the nip portion. At this time, a transfer bias is applied to the transfer roller 2 by the power supply 4, and the toner image on the photoconductor is transferred to the transfer material P.

After that, the transfer material carrying the toner image leaves the transfer portion and is transported to a fixing portion (not shown).

In such an image forming apparatus, the bias applied to the transfer roller 2 as a transfer unit is generally controlled at a constant voltage or a constant current.

However, since the resistance value of the transfer roller 2 in contact with the photoreceptor 1 changes greatly depending on the environment, the following problems are unavoidable with the above-described control means. That is, in the case of constant voltage control, normal temperature and normal humidity (23 ° C, 60% RH, N /
In the case of low temperature and low humidity (15 ° C., 10% RH, L / L), the resistance value of the transfer means becomes large, resulting in poor transfer. Conversely, when the temperature is high and high humidity (referred to as 32 ° C., 60% RH, H / H), the resistance value of the transfer unit becomes small, so that an excessive bias is applied and the image quality is deteriorated.

In the case of constant current control, it is possible to secure the amount of charge necessary for transfer, but since the capacity of the photoconductor is larger than that of the transfer material, it is used in the image forming apparatus. If there is a non-paper passing portion where the photoconductor 1 and the transfer roller 2 are in direct contact with each other using a postcard smaller than the maximum possible size as a transfer material, most of the non-paper passing portion is used. Current flows, especially L / L
Under the environment, there is a possibility that the charge is insufficient and transfer failure occurs.

The present invention has been made in order to cope with such a situation. By controlling the transfer unit at a constant current in the non-sheet passing portion and controlling the constant voltage in the sheet passing portion, the transfer unit can be used in all environments. It is another object of the present invention to provide an image forming apparatus capable of always obtaining good transferability to a transfer material of any size.

(2) Configuration of the Invention (Technical Means for Solving the Problems and the Function thereof) In order to achieve the above object, the present invention provides a movable photoconductor, an exposure unit for exposing the photoconductor to an image, and the photoconductor. A transfer member that transfers an image from a transfer material to a transfer material at a transfer position, and a transfer member that contacts a surface of the transfer material that is sent to the transfer position on a side opposite to a surface on a photoconductor side; and a voltage is applied to the transfer member. Voltage applying means for applying, the exposure means,
In the image forming apparatus that exposes an area other than the image area of the photoconductor when performing light amount adjustment, the voltage applying unit performs constant current control on the transfer member, and a voltage generated on the transfer member during the constant current control. Performing the constant voltage control on the image transfer to the transfer material at the time, when performing the light amount adjustment, the area exposed by the exposure unit is different from the area of the photoconductor at the transfer position during the constant current control. It is a feature.

With this configuration, it is possible to always obtain good transferability stably regardless of the environment and the size of the transfer material.

(Description of Embodiment) FIG. 1 is a schematic side view of an image forming apparatus showing an embodiment of the present invention, which includes a photosensitive layer made of an organic photoconductor (OPC) and rotates in the direction of an arrow. 1 is contacted during the rotation process and is uniformly charged by the charging roller 3 connected to a power supply 4 capable of constant current control and constant voltage control.

Then, in the illustrated apparatus, an image-modulated laser beam 5 is projected on the charged surface to form an electrostatic latent image on the charged surface, and the latent image is developed by the developing device 6 with the rotation of the photoconductor 1. , The toner is supplied from this point, and the latent image is visualized to become a toner image.

When the photoreceptor 1 and the elastic transfer roller 2 formed of a conductive member come into contact with each other and reach a transfer portion formed as a nip portion, the toner image is transferred from the transfer path 7 in time with the toner image. P is brought to the transcription site,
At the same time, a transfer bias is applied from the power supply 4 to the transfer roller 2, and the toner image on the photosensitive member is transferred to the transfer material.

Thereafter, the transfer material leaves the transfer portion and is transported to a fixing portion (not shown).

More specifically, the transfer roller 2 uses EPDM having an Asker C hardness of 25 mm and a volume resistance adjusted to about 10 ⁵ to 10 ⁶ Ωcm by dispersing carbon for imparting conductivity. did.

However, EPDM is highly environmentally dependent, and a roller with a 220 mm long EPDM layer formed on an aluminum drum,
When the resistance was measured by pressing against the photoreceptor 1 so that the nip width became 4 mm, a resistance of 10 ⁵ to 10 ⁶ Ωcm in an L / L environment was 10 ⁴ to 10 ⁴ Ωcm in an N / N environment. It decreased to 10 ⁵ Ωcm, and to 10 ³ to 10 ⁴ Ωcm under the H / H environment.

It is considered that the above-described inconvenience occurs because the transfer roller changes by orders of magnitude depending on the environment.

Therefore, in a non-sheet passing portion such as a pre-rotation of the image forming apparatus or a non-sheet passing portion such as between adjacent transfer materials, a constant current control is performed by passing a large current through the transfer roller so as not to generate a memory in the photoconductor. By holding the voltage of the ATVC “Active Trans.”
fer Voltage Control), which makes it possible to apply a transfer bias sufficient to obtain good transfer properties to the paper passing section under all circumstances.

However, as described above, in the image forming apparatus using a laser beam, since the light intensity correction (APC) is performed in the non-sheet passing portion between the transfer materials, the ATVC control is performed regardless of this operation. , The following problem occurs.

 This is outlined in FIGS. 6A to 6c.

If a constant current is supplied by executing the ATVC control at the same time as the APC is performed, the current flows into the potential level of the photoconductor as shown in FIG. 6A, and when the value is large, Vd (dark portion potential), Vl
Positive memory is formed on the photoreceptor irrespective of the (bright portion potential) level.

If the inflow current is small, as shown in FIG. 6B, no memory is generated in the Vd portion, but a memory is generated in the Vl portion.

When the current value is smaller, no memory occurs, but a sufficient current for ATVC control cannot be obtained, resulting in transfer failure.

Due to the primary charging, the memory mark on the surface of the photoconductor is slightly developed as shown in Fig. 6C, and is developed at the development site, and appears as fog on the next transfer material, resulting in deterioration of image quality. Depending on the above, it may cause transfer failure as described above, but the reality is that there is substantially no constant current value latitude for ATVC control that does not cause both of these inconveniences .

Therefore, in the present invention, as shown in the timing chart of FIG. 2, the ATVC control is executed immediately after the time when the Vl is formed by the APC.

Further, when the Vl portion formed by the APC comes into contact, the current does not flow into the Vl portion because the constant voltage application to the transfer roller 2 is cut in advance and grounded, so that a positive memory Does not occur.

Actually, APC and ATVC control were performed at the timings shown in FIG. 2, but no current flowed into the Vl portion to form a plus memory, and the AP was transferred to the next transfer material.
It was confirmed that it did not appear as a C mark.

FIG. 3 shows another embodiment of the control according to the present invention.

In this example, the non-sheet passing portion between the pre-rotation and the transfer material
At a time before the timing of executing C, constant current control of ATVC control is performed.

In the subsequent APC area, the voltage held by the ATVC is applied and held until the end of the transfer, and immediately after the end of the transfer, the constant current by the ATVC is again applied to the next APC area.
It flows into the Vd level on the photoconductor until just before the start.

FIG. 4 shows another control mode. Compared with the one shown in FIG. 1, from the rear end of the previous image area to immediately before the constant current control area by the next ATVC, including the APC area, The difference is that the constant voltage control is performed with the voltage held at the time of the previous image.

In the sequence shown in FIG. 2, the potential of the transfer roller is grounded from the rear end of the previous image in the non-sheet passing portion between the transfer materials to the end of the APC area. For this reason, the transfer power supply needs to control three modes: constant current, constant voltage, and ground potential.

By performing the control as shown in FIG. 4, the ground potential control is eliminated, and the control circuit is correspondingly simplified.

By the way, according to this control mode, the constant voltage is also applied to the Vl portion on the photoconductor formed by APC, but no memory is formed.

FIG. 7 shows an example of a voltage value obtained by a constant current when ATVC is performed. Open circles charges flowing into the V _D,
Black circles indicate charges flowing into _VL .

In the figure, the current at the time of performing ATVC is 0.1 μC / cm ²
Then, a voltage value of 530 V is obtained. The current flowing when this voltage is applied to the Vl portion is 0.04 μC / cm ² . This current value is the current limit value for generating the memory 0.06
It is well below μC / cm ² .

In this way, APs are arranged in a sequence as shown in FIG.
It can be seen that the same operation and effect as in the above embodiment can be obtained even when C and ATVC coexist.

FIG. 5 is a schematic side view of the image forming apparatus when the present invention is applied to an image forming apparatus using a transfer belt as a transfer unit.

The photoreceptor 1 is suspended by a support roller 55 and a driving roller 56 driven by driving means (not shown), and is in contact with the transfer belt 52 running in the direction of the arrow shown in FIG.
The photoconductor 1 passes through a transfer site formed when the transfer belt 52 comes into contact with the photoconductor 1 at the same timing as the toner image on the photoconductor surface.

In the transfer material P, a power supply for performing ATVC control to a roller electrode 53 disposed on the opposite side of the photoconductor 1 at the transfer site.
The toner image on the photoconductor 1 is transferred by the voltage supplied from 54.

After the transfer, the transfer belt is cleaned by the cleaning blade 57.

This device will be further described.
Are polyvinylidene fluoride, polyester-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyethylene-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, fluorine-based thermoplastic elastomer, ethylene-vinyl acetate-based thermoplastic elastomer It should be composed of a single-layer semiconductor selected from polyvinyl chloride thermoplastic elastomer, etc., and its volume resistance can be changed by changing the polymer structure to 10 ¹¹ to 10
^The configuration shall be adjusted to ¹⁵ Ωcm.

In the illustrated apparatus, the transfer belt is made of polyvinylidene fluoride, has a volume resistance of 10 ¹⁴ Ωcm and a thickness of 100 μm.
m.

EPDM is used as the roller electrode 53, and its volume resistance is
It was adjusted to 10 ⁵ to 10 ⁶ Ωcm and Asker C hardness 25 °.

Using this apparatus, ATVC control was performed at the timings shown in FIGS.

At this time, the current value at the time of constant current control differs depending on the material of the belt and the volume resistance value, but when the length of the transfer roller 53 is 220 mm and the nip width is 3 mm, about 0.15 μA /
cm ² .

When the transfer was performed with constant voltage control using the voltage obtained by the above current value, it was possible to obtain a high-quality image without causing the image to be fogged by the memory and without being affected by environmental changes. Was.

(3) Effects of the Invention As described above, according to the present invention, an image carrier, a photosensitive member in contact with the image carrier, and a transfer member forming a nip portion are formed, and an image is formed by a laser scanning optical system. At the same time, the transfer material is passed between the carrier and the transfer material, and at this time, constant current control is performed on the transfer material non-paper passing portion, and constant voltage control is performed on the paper passing portion with a voltage corresponding to the constant current. In the image forming apparatus configured to perform the above operation, the current is prevented from flowing into the bright portion potential portion of the APC region by performing constant current control while avoiding the APC region for performing luminous intensity correction by scanning the laser. Plus memory does not remain on the image carrier, preventing background fogging of the image due to this memory, and constantly maintaining good transferability irrespective of environment and transfer material size, stabilizing high quality images. Has the effect .

[Brief description of the drawings]

FIG. 1 is a schematic side view of an image forming apparatus to which the present invention is applied, FIG. 2 is a timing chart showing operation and control modes of the apparatus, and FIGS. 3 and 4 show other operation and control modes. FIG. 5 is a schematic side view of another image forming apparatus to which the present invention is applied, and FIGS. 6A to 6c show changes in the surface potential level of the image carrier during control between adjacent transfer materials. FIG. 7 is a VI characteristic of the roller electrode against the photoreceptor in a normal temperature and normal humidity environment. FIG. 8 is a schematic side view showing a configuration of an image forming apparatus using a known transfer roller. 1 photoconductor, 2 transfer roller, 3 charging roller,
4, 54: power supply, 6: developing device, 8: CPU, 52: transfer belt, 55, 56 (for suspending the transfer belt)
roller.

Continued on the front page (72) Inventor Yasushi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Toshio Miyamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Kimio Nakahata Canon Inc. 3- 30-2 Shimomaruko, Ota-ku, Tokyo

Claims (3)

(57) [Claims] A movable photosensitive member, an exposing means for exposing the photosensitive member to an image, and a transfer member for transferring an image from the photosensitive member to a transfer material at a transfer position, wherein the transfer member is sent to the transfer position. A transfer member that contacts a surface of the transfer material opposite to the photoconductor-side surface, and a voltage applying unit that applies a voltage to the transfer member;
In the image forming apparatus, wherein the exposure unit exposes an area other than the image area of the photoconductor when performing light amount adjustment, the voltage applying unit performs constant current control on the transfer member, The constant voltage control is performed on the image transfer to the transfer material with the voltage generated on the transfer member during the control, and the area exposed by the exposure unit when performing the light amount adjustment is moved to the transfer position during the constant current control. An image forming apparatus, which is different from an area of a certain photoconductor. 2. The image forming apparatus according to claim 1, wherein the constant current control is performed when a non-image area of the photoconductor is at the transfer position. 3. An image forming apparatus according to claim 1, wherein said transfer member is a rotating body.