JP2008003407A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus designed so as to stably retain satisfactory, high density image characteristics and prevent trailing even in the case where a printing operation is repeated over a long period of time. <P>SOLUTION: The image forming apparatus 10 includes image forming units 12A to 12D. The image forming units 12A to 12D include corresponding photoreceptors 14a to 14d. Disposed around the photoreceptors 14a to 14d are: corresponding electrifying rollers 16a to 16d, which electrify the corresponding photoreceptors 14a to 14d; corresponding exposure devices 18a to 18d, which form latent images on the corresponding photoreceptors 14a to 14d; and corresponding developing devices 20a to 20d, which develop the latent images into corresponding toner images. An intermediate transfer belt 24, to which the toner images are transferred, is disposed below the image forming units 12A to 12D. In this case, the intermediate transfer belt 24 is operated, except a period of the operation of transferring the toner images to the intermediate transfer belt 24 from the photoreceptors 14a to 14d, and a current is applied to the intermediate transfer belt 24 one or more times with the toner images held on the belt 24. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, a facsimile machine, or a composite machine thereof, and more particularly, an image forming apparatus that forms an image using an intermediate transfer member such as a full color electrophotographic system. About.

According to the conventional full-color electrophotographic system, good colors and hues can be reproduced initially in a room temperature environment. For example, in a usage environment that does not require a large amount of document processing in an office environment where humidity is stable, The problem did not occur.
However, in recent years, full-color electrophotographic systems have been required to have higher speeds and longer lifespans, and if the printing environment is in a high humidity environment or the environment in which printing is repeated over a long period of time, development is required. The developer in the apparatus is affected by humidity and stress, and the charge amount changes. That is, when the printing operation is repeated for a long time in an electrophotographic system having an intermediate transfer member, the toner charge amount in the developing device and the charging characteristics of the toner after development may be deteriorated.
For this reason, in the transfer process, there is a problem that the adhesion between the toner and the paper is lowered, and image defects such as density reduction and dropout due to transfer efficiency reduction occur. Also, in the fixing process, since the adhesion between the toner and the paper is low, there are mainly problems such as the occurrence of a so-called tail image in which characters and part of the line image in the optical main scanning direction are scattered and missing. It has occurred. The trailing image is presumed to be mainly due to the pressure of the vapor generated from the inside of the paper, and is due to toner scattering immediately before the fixing of the transfer toner on the paper.
On the other hand, in the fixing process, the volume resistance of the conductive layer of the fixing roll is kept constant, the surface resistance of the release layer is lowered, and a potential difference is provided between the conductive layer and the release layer. Has proposed an image forming apparatus aimed at preventing a fixing offset and a trailing image (see, for example, Patent Document 1).
In addition, by focusing on the triboelectric charge characteristics of the toner particles and specifying the amount of external additive added and the particle diameter within a certain range, in this case, by adjusting the external additive of the magnetic toner having a weak tribo charge imparting effect. An image forming method for improving the triboelectric charging characteristics of the toner itself and improving transferability and preventing tailing has been proposed (see, for example, Patent Document 2).

JP 2002-40856 A JP-A-9-297425

However, in the configuration shown in the image forming apparatus of Patent Document 1, when the printing speed is increased and printing is repeated for a long time, the toner charge amount on the transfer paper approaches zero, thereby preventing the fixing offset and the trailing image. There was a problem that the effect gradually became insufficient.
In addition, in the adjustment range of the external additive shown in the image forming method of Patent Document 2, in a full-color electrophotographic system that undergoes a transfer process twice before the fixing process, printing is performed at a high speed or for a long time. When it was repeated, the effect of improving transferability and preventing tailing was insufficient. In order to obtain a greater effect, when the particle size and amount of the external additive are adjusted to a large extent, adverse effects such as changes in the toner conveyance amount and image fogging occur, so that stable development durability performance is achieved. It was difficult to maintain.

  Therefore, a main object of the present invention is to provide an image forming apparatus that maintains stable and good high-density image characteristics and does not generate tailing even when the printing operation is repeated for a long period of time. .

According to a first aspect of the present invention, there is provided an image carrier, a charging unit that charges the image carrier, a latent image forming unit that forms a latent image on the image carrier, and a latent image formed on the image carrier. An image forming apparatus including a developing unit that develops an image and an intermediate transfer member to which a toner image is transferred, and operates the intermediate transfer member other than the transfer operation of the toner image from the image carrier to the intermediate transfer member. An image forming apparatus comprising an applying unit that applies a current once or a plurality of times while a toner image is placed on an intermediate transfer member.
The present invention according to claim 2 is an invention dependent on the invention according to claim 1, and when the application means is implemented, the surface potential of the image carrier is zero or the applied current of the application means The image forming apparatus is characterized in that the potential has a polarity opposite to that of the image forming apparatus.
The present invention according to claim 3 is an invention subordinate to the invention according to claim 1 or claim 2, and the applied current when the applying means is applied is that of the toner image from the image carrier to the intermediate transfer member. An image forming apparatus, wherein the voltage is changed from a transfer application voltage during a transfer operation.
The present invention according to claim 4 is an invention dependent on any one of claims 1 to 3, wherein the intermediate transfer member is an image forming apparatus including a drum shape or a sheet shape. .
In the present invention according to claims 1 to 4, the intermediate transfer member is operated other than the transfer operation of the toner image from the image carrier to the intermediate transfer member, and the toner image is placed on the intermediate transfer member once or The toner charge amount on the intermediate transfer member can be increased by the application means for applying the current multiple times, so that the toner transfer property onto a recording medium such as paper is improved, and the occurrence of tailing occurs. Is suppressed.

  According to the present invention, it is possible to obtain an image forming apparatus that stably maintains good high-density image characteristics and does not generate tailing even when the printing operation is repeated for a long period of time.

  The above-described object, other objects, features, and advantages of the present invention will become more apparent from the following description of the best mode for carrying out the invention with reference to the drawings.

FIG. 1 is an illustrative view showing one example of an embodiment according to the present invention. In this embodiment, as an example of an image forming apparatus, an image forming apparatus such as a so-called tandem type color printer of an intermediate transfer method capable of color printing will be described below.
The image forming apparatus 10 includes, for example, four image forming units 12A, 12B, 12C, and 12D that form toner images of, for example, yellow, magenta, cyan, and black color components by electrophotography. Each of the four image forming units 12A, 12B, 12C, and 12D includes, for example, drum-shaped photoconductors 14a, 14b, 14c, and 14d as image carriers for the respective colors.

  Around the photoreceptors 14a, 14b, 14c and 14d, for example, charging rollers 16a, 16b, 16c and 16d as charging means for charging the photoreceptors 14a, 14b, 14c and 14d, and the photoreceptors 14a, 14a, 14d, respectively. For example, exposure devices 18a, 18b, 18c and 18d as latent image forming means for forming latent images of the respective colors on 14b, 14c and 14d, and the latent images formed on the photoreceptors 14a, 14b, 14c and 14d are used as toners. Developing devices 20a, 20b, 20c and 20d as developing means for developing an image, and photosensitive member cleaning devices 22a, 22b as image carrier cleaning means for cleaning the toner on the photosensitive members 14a, 14b, 14c and 14d, 22c and 22d are arranged.

  Under the photoreceptors 14a, 14b, 14c, and 14d, for example, a sheet-like endless belt is formed as an intermediate transfer member to which toner images of the respective colors developed by the developing devices 20a, 20b, 20c, and 20d are transferred. An intermediate transfer belt 24 is provided. Inside the intermediate transfer belt 24, for example, primary transfer rollers 26a, 26b, 26c, and 26d as first transfer means, a driving roller 28, a driven roller 30, and a secondary transfer roller as second transfer means, for example. A secondary transfer counter roller 34 and a tension roller (not shown) arranged opposite to the roller 32 are arranged, and the intermediate transfer belt 24 is provided on these roller members while maintaining a constant tension.

The intermediate transfer belt 24 is driven to rotate at a predetermined rotation speed when the driving roller 28 is driven by a driving motor (not shown).
The primary transfer rollers 26a, 26b, 26c, and 26d are disposed to face the photoconductors 14a, 14b, 14c, and 14d, respectively. , 14c and 14d are electrostatically attracted to the intermediate transfer belt 24 and transferred. An intermediate transfer belt cleaning device 36 is disposed in the vicinity of the driven roller 30 as an intermediate transfer member cleaning unit that cleans residual toner on the intermediate transfer belt 24.

  Further, the intermediate transfer belt 24 is sandwiched between the secondary transfer roller 32 and the secondary transfer counter roller 34, and the intermediate transfer belt 24 passes between the secondary transfer roller 32 and the secondary transfer counter roller 34. In synchronization with this, the recording paper P is supplied to the toner image carrying surface side of the intermediate transfer belt 24 from a paper feed cassette (not shown) via a timing roller (not shown). In this case, when a voltage having the same polarity as the charging polarity of the toner is applied to the secondary transfer roller 32, the contact surface of the recording paper P that is in contact with the toner image carrying surface side of the intermediate transfer belt 24 is The toner image is secondarily transferred.

  Further, the recording paper P onto which the toner image has been secondarily transferred is separated from the intermediate transfer belt 24 by an appropriate separating unit (not shown), and is conveyed by the conveying belt 38 to, for example, a heat fixing device 40 as a fixing unit. Is done. The unfixed toner image on the recording paper P conveyed to the thermal fixing device 40 is subjected to a fixing process of the toner image by heating and then discharged toward a predetermined paper discharge tray (not shown).

  In the image forming apparatus 10 of the present embodiment, in order to increase the toner charge amount on the intermediate transfer belt 24 and improve the transferability of the toner onto the recording paper P even when the printing operation is repeated for a long time, In the printing process, the intermediate transfer belt 24 is operated so as to rotate, for example, by one rotation other than the transfer operation of the toner image from the photoconductors 14 a, 14 b, 14 c and 14 d to the intermediate transfer belt 24. The image forming apparatus includes an applying unit that applies current to the toner image once or a plurality of times while the image is placed on the toner image.

  That is, without supplying the recording paper P to the image forming apparatus 10, the electrophotographic operation for forming toner images on the photoconductors 14a, 14b, 14c and 14d is not performed, and the photoconductors 14a, 14b, 14c and 14d are performed. Is brought into contact with the intermediate transfer belt 24 to rotate the intermediate transfer belt 24, for example, by one rotation. At this time, the primary transfer rollers 26a, 26b, 26c and 26d are applied by a power supply device (not shown) as an application means. In addition, the current is applied once or a plurality of times.

  In this case, the photoconductor 14a, 14b, 14c and 14d located on the opposite side of the intermediate transfer belt 24 from the primary transfer rollers 26a, 26b, 26c and 26d has a polarity opposite to the applied voltage of the intermediate transfer belt 24 (in other words, , The same polarity as the toner) is injected and applied to the toner on the intermediate transfer belt 24. Therefore, in this image forming apparatus 10, the toner charge amount on the intermediate transfer belt 24 can be increased, and the transfer efficiency of the toner image onto the recording paper P can be improved. Furthermore, the occurrence of problems such as tailing can be suppressed.

  Therefore, in this image forming apparatus 10, even when the printing operation is repeated for a long period of time, it is possible to maintain stable and good high density image characteristics and to prevent the occurrence of tailing.

  In the image forming apparatus 10, the intermediate transfer belt 24 is operated to rotate, for example, one rotation other than the transfer operation of the toner image from the photoreceptors 14 a, 14 b, 14 c and 14 d to the intermediate transfer belt 24. When a current is applied to the toner image once or a plurality of times while the toner image is placed on the surface, the surface charge of the photoconductors 14a, 14b, 14c, and 14d is zero. In addition, the applied current to the toner image is appropriately changed, for example, to be larger than the transfer applied voltage during the transfer operation of the toner image from the photoreceptors 14a, 14b, 14c and 14d to the intermediate transfer belt 24. You may do it.

  Further, the intermediate transfer belt 24 is operated so as to make, for example, one rotation other than the transfer operation of the toner image from the photoconductors 14a, 14b, 14c and 14d to the intermediate transfer belt 24, and the toner image is placed on the intermediate transfer belt 24. The application means for applying the current to the toner image once or a plurality of times is preferably performed before the start of the printing operation by the image forming apparatus 10 and / or after the end of the printing operation. You may make it implement during work.

As the image forming apparatus 10 according to this embodiment, after performing 100,000 durable printings using the following machines, sample printing is performed under the following conditions, and the intermediate transfer toner is charged before the secondary transfer. Amount, secondary transfer efficiency [(toner amount on paper after secondary transfer / toner amount on intermediate transfer body after primary transfer) × 100 (%)], solid image density, and presence / absence of tail image defects Investigated and evaluated. The printing environment was a normal temperature / normal humidity environment (23 ° C./65%) and a high temperature high humidity environment (32 ° C./80%).
[Used machine]
Product name: LS-C8026N (Kyocera Mita Co., Ltd. color printer) modified machine

[Example 1]
In the printing process using the above-described machine, the exposure devices 18a to 18d use the primary transfer rollers 26a to 26d after the primary transfer process for placing toner on the intermediate transfer belt 24 and before the secondary transfer process. The application unit for operating the intermediate transfer belt 24 once again and applying the current to the primary transfer rollers 26a to 26d without performing the latent image forming process and the developing process by the developing devices 20a to 20d is changed. When this application means was implemented, it was evaluated after the surface charge of the photoconductors 14a to 14d was zero, and then evaluated.

[Example 2]
The surface potentials of the photoconductors 14a to 14d were reversed to the primary transfer applied voltage (same polarity as the toner), and the other conditions were evaluated after the same conditions as in Example 1 were evaluated.

[Example 3]
The applied current in the case where the above-described applying means is implemented is the same as that in Example 1 except that the applied current is increased by, for example, 1.5 times the transfer applied voltage during the transfer operation of the toner image from the photoconductors 14a to 14d to the intermediate transfer belt 24. Evaluation was carried out after carrying out under the same conditions.

[Comparative example]
Evaluation was carried out after carrying out a normal printing process without changing the printing process.

The evaluation results of [Example 1], [Example 2], [Example 3] and [Comparative Example] are shown in [Table 1]. In this case, the evaluation criteria are as follows, and the determination is indicated by ◯, Δ, and ×.

<Criteria>
Secondary transfer efficiency 95% or more: ○ (Good)
90 to less than 95%: △ (somewhat good)
90% or less: × (Poor)
Solid image density (hereinafter referred to as image density: “ID”)
ID ≧ 1.3: ○ (good)
1.3> ID ≧ 1.1: Δ (slightly good)
1.1> ID: x (bad)
Presence / absence of image tailing Not occurred: ○ (Good)
Occurrence: × (bad)

As shown in [Table 1], the toner charge amount can be increased in [Example 1], [Example 2] and [Example 3] compared to [Comparative Example], and the recording paper. It is clear that the transfer efficiency of the toner image to P can be improved and the occurrence of tailing is prevented. That is, [Example 1], [Example 2], and [Example 3] have stable and good high-density image characteristics even when the printing operation is repeated for a long time as compared with [Comparative Example]. It is clear that it maintains and prevents the occurrence of tailing.
As for the toner charge amount, [Embodiment 2] in which the surface potential of the photoconductors 14a to 14d has a polarity opposite to that of the primary transfer printing voltage (same polarity as that of the toner) has been described. It turned out to be more than [2]. Also, regarding the secondary transfer efficiency, it was found that [Example 2] and [Example 3] were higher than [Example 1].

It is an illustration figure which shows an example of embodiment concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12A, 12B, 12C, 12D Image forming unit 14a, 14b, 14c, 14d Photoconductor 16a, 16b, 16c, 16d Charge roller 18a, 18b, 18c, 18d Exposure apparatus 20a, 20b, 20c, 20d Developing apparatus 22a, 22b, 22c, 22d Photoconductor cleaning device 24 Intermediate transfer belt 26a, 26b, 26c, 26d Primary transfer roller 28 Drive roller 30 Driven roller 32 Secondary transfer roller 34 Secondary transfer counter roller 36 Intermediate transfer belt cleaning device 38 Conveyor belt 40 Thermal fixing device P Recording paper

Claims (4)

Image carrier,
Charging means for charging the image carrier,
A latent image forming means for forming a latent image on the image carrier;
Developing means for developing the latent image formed on the image carrier into a toner image;
An image forming apparatus including an intermediate transfer body to which the toner image is transferred,
The intermediate transfer member is operated other than the transfer operation of the toner image from the image carrier to the intermediate transfer member, and a current is applied once or a plurality of times while the toner image is placed on the intermediate transfer member. An image forming apparatus comprising an applying unit.   2. The image according to claim 1, wherein when the application unit is implemented, the surface potential of the image carrier is zero or a potential having a polarity opposite to the applied current of the application unit. Forming equipment.   The applied current in the case of performing the application means is changed from a transfer application voltage during a transfer operation of the toner image from the image carrier to the intermediate transfer member. The image forming apparatus according to claim 2.   The image forming apparatus according to claim 1, wherein the intermediate transfer member includes a drum shape or a sheet shape.

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