JPH11231667A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence, on an intermediate transfer belt having a high resistance layer, of an abnormal image such as transfer irregularity occurring at the time of a 2nd transfer and pre-transfer dust occurring at the time of a primary transfer. SOLUTION: When a color mode is selected on a color copying machine, the frequency of primary transfers to an intermediate transfer belt 51 is determined, while charged, potentials of the intermediate transfer belt 51 are different for each transfer. The potential becomes about -200 V after the 1st transfer of the primary transfer, about -400 V after the 2nd transfer, about -600 V after the 3rd transfer, and about -800 V after the 4th transfer. Thus, to discharge the intermediate transfer belt 51 before the secondary transfer, a DC output condition is set for each color mode. When a charged potential before the secondary transfer of the intermediate transfer belt 51 is made to -400 V or lower by operating a PTC(pre-transfer charge) 52, the charged potential of the intermediate transfer belt 51 becomes negative (-) after discharge even if the intermediate transfer belt 51 is charged to the positive (+) side after the secondary transfer.

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 copying machine, a printer and a facsimile, and more particularly to an image forming apparatus using an intermediate transfer member.

[0002]

2. Description of the Related Art As an image forming apparatus of this type, improvement of abnormal image "transfer unevenness" at the time of secondary transfer when an intermediate transfer belt having a high resistance layer is used as an intermediate transfer belt is improved before the secondary transfer. A method using a pre-transfer charger (PTC) has been proposed. The PTC is controlled by applying a (−) grid voltage to a DC voltage with the same (−) polarity as the toner. In addition, there has been proposed a method in which the neutralization of the intermediate transfer belt after the secondary transfer is performed by superimposing a DC bias component on the AC voltage (+ DC bias).

[0003]

In the former case of the above prior art, the abnormal image of two-color dust is improved by the high resistance layer of the intermediate transfer belt, but the intermediate transfer after the primary transfer is improved by the high resistance layer. Since the charged potential of the belt is maintained, good transfer is performed in the case of a high toner adhesion amount such as in the case of forming a color image in which toners of the respective colors are superimposed, but the first transfer (the first color) of the transfer process is performed. ), Transfer unevenness occurs on the toner in the second transfer (second color) as an abnormal image during the secondary transfer. Note that transfer unevenness refers to a state where transfer of toner in a halftone portion and a solid portion is non-uniform.

In the case of the latter of the above prior arts, 2
Since the potential after neutralization of the intermediate transfer belt after the next transfer is the DC bias voltage of the belt neutralization of the (+) polarity, if the intermediate transfer belt is charged to the (+) polarity after the neutralization, it is exposed during the primary transfer. A phenomenon in which toner on the body is transferred to the intermediate transfer belt before the transfer area, that is, pre-transfer occurs, and an abnormal image called pre-transfer dust in which toner is scattered around characters and the like of the image occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve such a conventional problem, and it is an object of the present invention to prevent the occurrence of an abnormal image such as transfer unevenness which occurs during secondary transfer in an intermediate transfer belt having a high resistance layer. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

Another object of the present invention is to provide an image forming apparatus capable of preventing occurrence of an abnormal image called pre-transfer dust which occurs during primary transfer in an intermediate transfer belt having a high resistance layer.

[0007]

According to a first aspect of the present invention, there is provided an image forming apparatus comprising: an intermediate transfer member for carrying a toner image transferred from an image carrier; Primary transfer charge applying means for applying, to the intermediate transfer member, a charge for transferring a toner image from the image carrier to the intermediate transfer member; and a charge for transferring a toner image from the intermediate transfer member to a transfer material. An image forming apparatus comprising: a secondary transfer charge applying means for applying the toner image to the transfer material or the transfer material carrier; and an intermediate transfer body static elimination means for neutralizing the surface of the intermediate transfer body having transferred the toner image onto the transfer material. An intermediate transfer body charge applying means for applying an electric charge to the intermediate transfer body before the secondary transfer, wherein an output condition of the intermediate transfer body charge applying means is switched according to the number of times of the primary transfer of the intermediate transfer body. Characterized by

According to a second aspect of the present invention, the number of operations of the means for applying a charge to the intermediate transfer member before the secondary transfer is at least one before the secondary transfer and at most not more than the number of times of the primary transfer. It is characterized by the following.

According to a third aspect of the present invention, the intermediate transfer member static elimination means superimposes a DC bias component on an AC voltage (-D
C deviating means).

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Hereinafter, an example in which the image forming apparatus according to the present invention is applied to an electrophotographic color copying machine (hereinafter, referred to as a color copying machine) will be described.

FIG. 1 is a schematic configuration diagram of an image forming section which is a main part of a color copying machine. This color copier is shown in FIG.
, A color image reading unit (hereinafter, referred to as a color scanner) (not shown), a paper feeding unit, a control unit, and the like. The color scanner reads color image information of a document for each color separation light of, for example, RED, GREEN, and BLUE (hereinafter, referred to as R, G, and B, respectively) and converts it into an electrical image signal. Based on the R, G, and B color separation image signal intensity levels obtained by the color scanner, a color conversion process is performed by an image processing unit (not shown),
ck (hereinafter, Bk) Cyan (hereinafter, C), Magen
The color image data of ta (hereinafter, M) and Yellow (hereinafter, Y) is obtained.

The image forming unit shown in FIG. 1 includes a photosensitive drum 1 as an image carrier, a charging charger 2 as a charging unit, a photosensitive member cleaning device 3 including a cleaning blade and a fur brush, and a writing unit (not shown) as an exposure unit. It comprises an optical unit, a revolver developing unit 4 as a developing means, an intermediate transfer unit 5, a paper transfer unit 6, a fixing unit 7 using a pair of fixing rollers, and the like.

The photosensitive drum 1 rotates in a counterclockwise direction in the drawing, and any one of the charging units 2, the photosensitive member cleaning device 3, and the selected one of the developing units 41 to 44 of the revolver developing unit 4 is disposed around the photosensitive drum. An intermediate transfer belt 51 and the like as an intermediate transfer body of the transfer unit 5 are arranged.

In the drawing, reference numeral 52 denotes a pre-transfer charger (P
TC), 53 is a belt neutralization charger, 54 is a belt cleaning blade, 55 is a primary transfer bias roller,
56 is a belt driving roller, 57 is a belt tension roller, 58 is a secondary transfer opposing roller, 59 is a belt neutralizing opposing member, 511 is a cleaning opposing roller, 512 is an earth roller, 61 is a secondary transfer belt, and 62 is secondary transfer. A bias roller, 81 is a primary transfer power supply, 82 is a secondary transfer power supply, 83 is a PTC power supply, and 84 is a power supply for static elimination.

In the full-color mode of such a color copying machine, a Bk toner image is visualized on the photosensitive drum 1 by a revolver developing unit Bk41, and is then transferred to a primary transfer bias roller 55 of the intermediate transfer unit 5. The image is transferred onto the intermediate transfer belt 51 by the applied primary transfer bias. The C toner image, the M toner image, and the Y toner image are sequentially superimposedly transferred onto the intermediate transfer belt 51 in the following order. The order of forming the toner is an example, and the present invention is not limited to the above order. The intermediate transfer belt 51 includes
For example, the surface layer is formed of an insulating layer of about 1 μm, and the intermediate layer is formed of P
75 μm thick made of VDF (polyvinylidene fluoride)
And a base layer formed of a medium resistance layer (volume resistivity: E8 to E11 Ωcm) of PVDF (polyvinylidene fluoride) and titanium oxide having a thickness of about 75 μm. Things are used.

The toner image of each color transferred onto the intermediate transfer belt 51 is subjected to corona discharge consisting of an AC component and a DC component by the pre-transfer charger 52 after the fourth transfer in the primary transfer process is completed, and then the paper is printed. The image is transferred to the transfer material by the secondary transfer bias roller 62 of the transfer unit 6. The pre-transfer charger 52 includes a corona charger member and a PTC power supply 83 which is a DC superimposed AC power supply, and an AC voltage of 5.8 KV is applied. Here, the DC component DC
Since the voltage is such that the charging polarity of the toner is (-) polarity, the primary transfer bias is a bias of (+) polarity, and thus the charging potential of the toner surface of the intermediate transfer belt 51 is charged to (-) polarity. Therefore, the DC voltage has a (+) polarity.

Regarding the color mode of the color copying machine,
In the case of one-color single-color mode (first transfer is performed once), and two-color (BK + (any one of Y, M, and C)) primary transfer is performed in two colors.
In the full color mode (BK + C + M + Y), primary transfer is performed four times. That is, when the color mode is selected, the number of times of the primary transfer is determined, and the charging potential of the intermediate transfer belt 51 is different for each number of times of the transfer. For example, the voltage is about -200 V after the first transfer of the primary transfer, at -400 V after the second transfer, at -600 V after the third transfer, and at -800 V after the fourth transfer. Therefore, for the neutralization of the intermediate transfer belt 51 before the secondary transfer, the DC output condition may be set for each color mode. FIG. 2 shows D for each transfer mode.
The C output condition is shown.

In the case of the full-color mode, the number of times of the primary transfer is four as described above, but the charging potential of the intermediate transfer belt 51 is set to -400 V or less before the secondary transfer. As shown in FIG. 3, when the charging potential of the intermediate transfer belt 51 is set to −400 V or less, an image without transfer unevenness can be obtained with a transfer rate of 90% or more.
DC voltage). So Figure 4
The operation mode and the number of operations of the PTC power supply 83 can be set. In either case, adjust the DC output. However, as for the number of operations, one operation after the fourth transfer of the primary transfer is the least energy-saving because both ozone generation and power consumption are small.

When the charging potential of the intermediate transfer belt 51 before the secondary transfer is reduced to (−) 400 V or less by operating the PTC 52, the intermediate transfer is performed after the secondary transfer due to the (+) polarity of the secondary transfer bias of the secondary transfer unit. Even if the charging potential of the belt 51 is charged to the (+) polarity side, the DC output of the discharging power supply 84 to the discharging charger 53 of the intermediate transfer belt 51 has the (-) polarity. Later, it becomes (-) polarity.

[0020]

Since the image forming apparatus according to the first and second aspects is as described above, it is possible to prevent the occurrence of an abnormal image such as transfer unevenness occurring at the time of secondary transfer in an intermediate transfer belt having a high resistance layer. This has the effect.

Since the image forming apparatus according to the third aspect is as described above, it is possible to prevent the occurrence of an abnormal image such as pre-transfer dust generated at the time of primary transfer in an intermediate transfer belt having a high resistance layer. is there.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming unit that is a main part of a color copying machine.

FIG. 2 is a diagram showing DC output conditions set for each color mode.

FIG. 3 is a diagram showing a charging potential of an intermediate transfer belt versus a secondary transfer rate.

FIG. 4 is a diagram showing an operation mode and the number of operations of a PTC power supply.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor drum 2 Charger 3 Photoconductor cleaning device 4 Revolver developing unit 5 Intermediate transfer unit 6 Paper transfer unit 7 Fixing unit 41-44 Developing device 51 Intermediate transfer belt 52 Pre-transfer charger (PTC) 53 Belt discharging charger 54 Belt cleaning Blade 55 Primary transfer bias roller 56 Belt drive roller 57 Belt tension roller 58 Secondary transfer opposing roller 59 Belt neutralizing opposing member 61 Secondary transfer belt 62 Secondary transfer bias roller 81 Primary transfer power supply 82 Secondary transfer power supply 83 PTC power supply 84 Power supply for static elimination

Claims (3)

[Claims] An intermediate transfer member for carrying a toner image transferred from an image carrier, and a primary member for applying a charge to the intermediate transfer member for transferring a toner image from the image carrier to the intermediate transfer member. Transfer charge applying means, secondary transfer charge applying means for applying a charge for transferring a toner image from the intermediate transfer member to the transfer material to the transfer material or the transfer material carrier, and transferring the toner image to the transfer material An image forming apparatus comprising: an intermediate transfer body static elimination unit configured to neutralize the surface of the intermediate transfer body.
An intermediate transfer body charge applying means for applying an electric charge to the intermediate transfer body before the secondary transfer, wherein an output condition of the intermediate transfer body charge applying means is switched according to the number of times of the primary transfer of the intermediate transfer body. An image forming apparatus comprising: 2. The method according to claim 1, wherein the number of operations of the means for applying a charge to the intermediate transfer member before the secondary transfer is at least one before the secondary transfer.
2. The image forming apparatus according to claim 1, wherein the number of times of transfer is less than or equal to the number of times of primary transfer. 3. The image forming apparatus according to claim 1, wherein said intermediate transfer member static elimination means includes means for superimposing a DC bias component on the AC voltage (−DC bias).