JP2000275979A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To hardly cause defective transfer even by making an interval between a primary transfer part and a secondary transfer part narrow in an image forming device in which an intermediate transfer body system is adopted. SOLUTION: After a toner image electrified so as to be negative on the surface of a photoreceptive drum 21K is primarily transferred to a transfer belt 11 by applying positive voltage to a primary transfer roller 31K by a constant voltage power source 32K, negative voltage is applied to a secondary transfer roller 41 by a constant voltage power source 42, so that an image is formed by secondarily transferring the toner image on the transfer belt 11 to transfer paper S. In this case, the image is formed by applying the positive voltage having the same polarity as that applied to the primary transfer roller 31K, also to an opposed roller 43 arranged opposed to the roller 41. Here, the level of voltage applied to the opposed roller 43 is nearly equal to the level of the voltage applied to the primary transfer roller 31K.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer and a copying machine, and more particularly to an improvement in a transfer technique in an image forming apparatus employing an intermediate transfer system.

[0002]

2. Description of the Related Art In a tandem-type color image forming apparatus employing an intermediate transfer member system, for example, a toner image formed on a plurality of photosensitive drums arranged in a running direction of a transfer belt is previously formed. An image is formed by superimposing and transferring the image on the transfer belt as an intermediate transfer body, and then transferring the image onto a transfer sheet as a transfer material. That is, the transfer from the photosensitive drum to the transfer belt (hereinafter referred to as “1
Next transfer. ) And transfer from the transfer belt to transfer paper (hereinafter, referred to as “secondary transfer”), so that an image can be obtained by a total of two transfers.

FIG. 3 shows one of a plurality of photosensitive drums at the end.
FIG. 5 is a diagram illustrating an image forming unit 200K including a photosensitive drum 210K on which a next transfer is performed and a secondary transfer unit 400. The primary and secondary transfer will be described with reference to FIG. The primary transfer is performed by a primary transfer roller 310K provided opposite to the photosensitive drum 210K via the transfer belt 110.
Is performed by generating an electric field between the primary transfer roller 310K and the photosensitive drum 210K so that the primary transfer roller 310K side has the opposite polarity to the charged toner.

In the secondary transfer, a voltage is applied to the secondary transfer roller 410, and the secondary transfer roller 410 and the transfer belt 11
This is performed by generating an electric field between the secondary transfer roller 410 and the opposing roller 430 which is grounded and opposed to the secondary transfer roller 410 so that the secondary transfer roller 410 side has the opposite polarity to the charged toner.

[0005]

However, with the recent miniaturization of the image forming apparatus, the interval between the elements constituting the apparatus tends to be reduced. Spacing between departments is no exception. In particular, in a tandem-type machine in which a plurality of image forming units are arranged in one direction, the length tends to be long in the direction, and more severe reduction is required.

[0006] However, if the primary transfer portion and the secondary transfer portion are too close to each other, a transfer failure occurs. That is,
If the primary transfer portion and the secondary transfer portion are too close to each other, the potential difference between the primary transfer roller and the opposing roller cannot be ignored. Current (transfer current) to flow to the opposite roller via the inner peripheral surface of the transfer belt due to the potential difference (hereinafter, the current flowing on the surface of the transfer belt is referred to as “leakage current”). And, uneven transfer due to insufficient transfer current occurs.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide an image forming apparatus in which transfer failure is unlikely to occur even when the distance between the primary transfer section and the secondary transfer section is reduced.

[0008]

In order to achieve the above-mentioned object, an image forming apparatus according to the present invention is configured such that a toner image formed on an image carrier is primarily transferred onto an outer peripheral surface of an endless transfer belt. An image forming apparatus for performing secondary transfer to a transfer material to form an image, wherein the image forming apparatus is disposed at a position facing the image carrier on the inner peripheral surface side of the transfer belt via a transfer belt, and a voltage is applied. Thereby, a primary electrode for generating an electric field for primary transfer with the image carrier, a secondary electrode disposed on the outer peripheral surface side of the transfer belt, and the second electrode on the inner peripheral surface side of the transfer belt. A counter electrode disposed at a position facing the next electrode,
When a voltage is applied to the secondary electrode, the secondary
A counter electrode for generating an electric field for secondary transfer with the next electrode, wherein a voltage applied to the counter electrode is a voltage of the same polarity as that applied to the primary electrode. I do.

Further, the magnitude of the voltage applied to the counter electrode is substantially equal to the magnitude of the voltage applied to the primary electrode.

[0010]

Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming unit of the tandem-type printer according to the embodiment. Although a printer is taken as an example here, it goes without saying that the present invention can be applied to an image forming apparatus such as a copying machine or a facsimile.

As shown in FIG. 1, the image forming units are mainly provided horizontally in a printer housing and run in the direction of arrow a, and are arranged in the running direction of the transfer belt 11. Four image forming units 20C, 20M, 20
Y, 20K, primary transfer units 30C, 30M, 30Y, 30K and secondary transfer units 40 provided corresponding to the respective image forming units, and each color formed by each of the image forming units 20C to 20K. After the toner image of the component is once superimposed on the transfer belt 11 and transferred,
This is a so-called intermediate transfer body type image forming unit that forms a color image by transferring to a transfer sheet S as a transfer material.

The image forming units 20C to 20K are arranged around a photosensitive drum 21C to 21K serving as an image carrier, around which a charger, a developing device and the like are arranged. This is a unit structure for forming an image by a so-called electrophotographic method in which an electrostatic latent image formed by exposure is exposed as toner by a developing device while exposing a photosensitive drum that rotates. The developing device of each unit applies a C (cyan), M (magenta), Y (yellow), and K (black) toner as a developer to the photosensitive drum in accordance with the light modulation color component of the laser beam. Supply.

The transfer belt 11 as an intermediate transfer member is an endless belt made of a semiconductive (medium resistance) material having a volume resistivity of about 10 ⁶ to 10 ¹² Ω · cm.
2. Tension roller 13 and opposing roller 43 described later
It is stretched by. When the drive roller 12 is driven to rotate by a motor (not shown), the transfer belt 11 travels in the direction of arrow a.

The primary transfer units 30C to 30K include primary transfer rollers 31 serving as electrodes for generating a transfer electric field.
C to 31K and constant voltage power supplies 32C to 32K. 1
Each of the next transfer rollers 31C to 31K is disposed directly below the corresponding photosensitive drum via the transfer belt 11. Each of the constant voltage power supplies 32C to 32K
A voltage is applied to the next transfer roller. By the application of the voltage, an electric field is generated between the primary transfer rollers 31C to 31K and the corresponding photoconductor drum, and the electric field causes a negatively charged toner image on the surface of the photoconductor drums 21C to 21K to be formed.
The images are sequentially transferred to the outer peripheral surface of the transfer belt 11. That is, in each of the constant voltage power supplies 32C to 32K, the polarity of the electric field on the primary transfer roller side is opposite to the polarity of the charged toner (negative in this example) (positive in this example). Such a voltage is applied to the corresponding primary transfer roller.

The secondary transfer unit 40 includes a secondary transfer roller 41 serving as an electrode for generating a transfer electric field, a constant voltage power supply 42 for applying a voltage to the secondary transfer roller, and a transfer belt 1.
1, an opposing roller (opposing electrode) 43 provided to oppose the secondary transfer roller 41 through the first transfer roller 1 and a constant voltage power supply 44 for applying a voltage to the opposing roller 43. The secondary transfer unit 40 transfers the toner image superimposed on the transfer belt 11 onto the transfer paper S fed by the timing roller 14 as described later.

The transfer paper S on which the toner image has been transferred is discharged to a discharge tray (not shown) after the toner image is fixed by a fixing unit (not shown). FIG. 2 is a diagram showing the image forming unit 20K where the primary transfer is performed last and the vicinity of the secondary transfer unit 40 among the above four image forming units. The cyan, magenta, and yellow toner images formed on the photoconductor drums 21C to 21Y are sequentially transferred to the corresponding primary transfer units 30C to 30Y so as to be superimposed on the outer peripheral surface of the transfer belt 11, respectively.
Finally, the black toner image formed on the photosensitive drum 21Y is transferred by the primary transfer unit 30K, and the primary transfer ends. Of course, when a monochrome image is formed, a toner image is not formed on the photoconductor drums 21C to 21Y, a toner image is formed only on the photoconductor drum 21K, and the primary transfer to the transfer belt 11 is also performed by one. This is performed only by the next transfer unit 30K.

The toner image formed on the outer peripheral surface of the transfer belt 11 by transfer is transferred to a position where the secondary transfer roller 41 and the opposing roller 43 face each other (hereinafter, “secondary transfer position”) as the transfer belt 11 travels. Is transported to On the other hand, the transfer paper S is fed from the timing roller 14 in synchronization with the toner image transfer timing (the timing of forming the electrostatic latent image in the image forming unit), and is transferred to the secondary transfer position.

Here, a positive voltage is applied to the secondary transfer roller 41 by a constant voltage power supply 42, and accordingly,
An electric field (transfer electric field) having a positive polarity on the secondary transfer side is generated between the opposing roller 43 and the secondary transfer roller 41. As a result, at the secondary transfer position, the negatively charged toner image is electrostatically attracted to the transfer paper S and the transfer is performed. That is, in order to generate a transfer electric field for secondary transfer, the constant voltage power supply 42 applies a voltage having a polarity opposite to the polarity of the toner charged on the secondary transfer roller 41 to the secondary transfer roller 41. .

In this embodiment, the opposing roller 4
3 is also applied with a voltage. The application of the voltage is performed by the constant voltage power supply 44, and the polarity is opposite to the polarity of the toner. That is, the voltage applied to the opposing roller 43 has the same polarity as that applied to the primary transfer roller 31K. By applying a voltage having the same polarity as that applied to the primary transfer roller 31K to the opposing roller 43, the opposing roller 4
The potential gradient on the inner peripheral surface of the transfer belt 11 between the primary transfer roller 31K and the opposing roller 43 becomes gentler than when the ground 3 is grounded. As a result, the leakage current flowing from the primary transfer roller 31K to the opposing roller 43 is reduced, and the transfer failure in the primary transfer roller 31K is prevented.

That is, the magnitude of the voltage applied to the opposing roller 43 may be at least smaller than twice the magnitude of the voltage applied to the primary transfer roller 31K. By setting the magnitude of the voltage applied to the opposing roller 43 in such a range, the inner circumference of the transfer belt 11 between the primary transfer roller 31K and the opposing roller 43 can be compared with the case where the opposing roller 43 is grounded. This is because the potential gradient on the surface becomes gentle.

In the above range, the opposing roller 43
Is preferably substantially equal to the voltage applied to the primary transfer roller 31K. By making them equal, the potential difference between the primary transfer roller 31K and the opposing roller 43 is eliminated, and almost no leakage current is generated. The voltage is applied to the opposing roller 43 not only during the secondary transfer but also at least during the time when the primary transfer is performed by the primary transfer roller 31K.

Next, a voltage value V1 for the primary transfer rollers 31C to 31K and a voltage value V for the secondary transfer roller 41
2. The magnitude relationship of the voltage value V3 with respect to the opposing roller 43 will be described. Note that the magnitude relationship here is that the polarity of the voltage applied to each roller is, as described above, FIGS.
This is established under the polarity shown in FIG.

First, as described above, it is preferable that the magnitudes of V1 and V3 are substantially equal. That is, V1 ≒ V3. V2 is set higher than V1. Figure 3
Assuming that the opposite roller 43 is grounded as in the case of the prior art shown in FIG. 1, the value of the voltage applied to the secondary transfer roller 41 is generally set to about 1.2 to 5 times V1. . This is because the toner layer to be transferred is thicker in the secondary transfer than in the primary transfer (although it is almost the same in the case of a monochrome image), and the transfer belt 1
This is because the transfer is performed in a state where the transfer paper S is interposed in addition to the transfer sheet 1, and therefore, it is necessary to generate an electric field (transfer electric field) stronger in the secondary transfer than in the primary transfer.

In the present embodiment, the opposing roller 43
Is applied, the value of the voltage applied to the secondary transfer roller 41 is raised accordingly. That is, if the voltage value required for the secondary transfer roller 41 is V0 when the opposing roller 43 is grounded as described above, the voltage value V2 required in the present embodiment is V0 To which V3 has been added. That is, V
2 = V0 + V3.

Here, the magnitude relation between V1, V2 and V3 is summarized as follows. V2> V1 ≒ V3 As described above, the present invention includes a plurality of photosensitive drums and a plurality of photosensitive drums.
Although a tandem type image forming apparatus for performing the next transfer has been described as an example, the present invention is not limited to this. For example, a developer for each color may be arranged around one photosensitive drum, and the photosensitive drum may be used. An image is formed by forming an image for each color on the surface, transferring the image on a transfer belt one after another, transferring all colors, and then transferring (secondary transfer) to transfer paper to form an image. It is also applicable to a forming apparatus.

Further, in the above-described embodiment, an example in which the toner of the toner image formed on the photosensitive drum is charged to the negative polarity is used. The invention is applicable. In this case, it goes without saying that it is necessary to change the polarity of the voltage applied to each transfer roller and the opposing roller.

[0027]

As described above, according to the image forming apparatus of the present invention, the counter electrode disposed on the inner peripheral surface side of the transfer belt and opposed to the secondary electrode also has the same structure as that of the transfer belt. Since a voltage having the same polarity as that applied to the primary electrode disposed on the peripheral surface is applied to form an image, the primary electrode and the secondary electrode are compared with a case where the opposite electrode is grounded. Since the potential gradient on the inner peripheral surface of the transfer belt between the electrodes becomes gentle, the leakage current flowing on the surface can be reduced. As a result, a transfer current to flow between the primary electrode and the image bearing member facing the primary electrode can be secured, and transfer failure of primary transfer hardly occurs.

Further, by making the magnitude of the voltage applied to the counter electrode substantially equal to the magnitude of the voltage applied to the primary electrode, the potential difference between the counter electrode and the primary electrode is substantially eliminated. In addition, since the leakage current hardly flows, occurrence of primary transfer failure can be further prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming section of a tandem-type color copying machine that is an application example of the present invention.

FIG. 2 is a schematic configuration diagram near a secondary transfer unit in the image forming unit.

FIG. 3 is a schematic configuration diagram of the vicinity of a secondary transfer unit of a conventional tandem-type copying machine.

[Explanation of symbols]

 Reference Signs List 11 transfer belt 20K imaging unit 21K photoreceptor drum 30K primary transfer unit 31K primary transfer roller 32K constant voltage power supply 40 secondary transfer unit 41 secondary transfer roller 42 constant voltage power supply 43 opposing roller 44 constant voltage power supply

Continuation of the front page (72) Inventor Futa Hamada 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Yasuyuki Inada 2-chome Azuchicho, Chuo-ku, Osaka-shi, Osaka No. 13 Osaka International Building Minolta Co., Ltd. F-term (reference) 2H032 AA05 AA15 BA09 BA19 BA23 BA26

Claims (2)

[Claims] 1. A toner image formed on an image carrier is primarily transferred onto an outer peripheral surface of an endless transfer belt.
An image forming apparatus that forms an image by performing a next transfer, wherein the image is arranged at a position facing the image carrier on the inner peripheral surface side of the transfer belt via a transfer belt, and the image is formed by applying a voltage. A primary electrode for generating an electric field for primary transfer with the carrier, a secondary electrode disposed on the outer peripheral surface of the transfer belt, and facing the secondary electrode on the inner peripheral surface of the transfer belt. A counter electrode disposed at the position, wherein a voltage is applied between the counter electrode and the secondary electrode, thereby generating an electric field for secondary transfer between the counter electrode and the secondary electrode; An image forming apparatus, wherein the voltage applied to the counter electrode is the same polarity as the voltage applied to the primary electrode. 2. The image forming apparatus according to claim 1, wherein the magnitude of the voltage applied to the counter electrode is substantially equal to the magnitude of the voltage applied to the primary electrode.