JPH05265333A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain an image forming device where the life of a photosensitive body is prolonged without an adverse effect on a user's health by reducing an amount of ozone generated during image formation. CONSTITUTION:The image forming device carries out image formation on an image carrier 10 a number of times (four times) and carries out transfer and fixing on a recording sheet after the formation of a multicolor toner image on the image carrier 10. After forming the final toner image on the image carrier 10, the image forming device carries out transfer when it comes to a transfer area 35 at the second time. Also, after the formation of the final toner image, it turns off an electrifying means 12 so as not to electrify at least an image area where transfer is not finished.

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 capable of obtaining a color image by an electrophotographic method, and in particular, after forming a multicolor toner image by forming an image a plurality of times on an image carrier. The present invention relates to an image forming apparatus that transfers and fixes on a recording paper.

[0002]

BACKGROUND OF THE INVENTION As one of apparatuses for obtaining a color image by an electrophotographic method, latent image formation according to the number of separated colors of an original image is formed on a photosensitive drum or a photosensitive belt which is an image carrier.
There is a method in which color toner images are obtained by repeating development with color toners, superposing the color toner images on a photosensitive drum or belt, and then transferring them. The basic process for forming this multicolor image is described in Japanese Patent Application Laid-Open Nos. 60-75850 and 60-76766 by the present applicant.
No. 60-95456, No. 60-95458, No. 60-158475 and the like.

In a multicolor image forming apparatus which obtains a color image by such superposition, a plurality of developing devices accommodating color toners of different colors are arranged on the periphery of a photoconductor, Generally, the photosensitive drum is rotated plural times to develop the latent image on the photosensitive drum to obtain a color toner image.

The toner image formed on the peripheral surface of the photoconductor drum is transferred by a physical means onto a recording paper fed at a timing, and the recording paper having the toner image transferred thereto is separated from the photoconductor drum. The toner image is conveyed to a fixing unit, and the toner image is fixed on the recording paper and then discharged to the outside of the apparatus.

The toner image adhering to the peripheral surface of the photosensitive drum is transferred to the recording paper by being charged with a polarity opposite to that of the toner by a transfer device which discharges from the back of the recording paper. After the transfer, the separator is separated from the photoconductor drum by applying a high AC voltage to remove the charge. However, it is difficult to reliably maintain transferability and separability, and it is difficult to separate, especially when the drum diameter of the photoconductor drum is large, and the recording paper on which the toner image has been transferred adheres to the photoconductor drum without being separated. It has the drawback that it tends to cause paper jams. A transfer belt device is used as a technique for improving this drawback.

The transfer belt device rotates the transfer belt stretched by a plurality of holding rollers at the same speed as the photosensitive drum. The transfer belt device is provided with a charge applying unit that applies an electric charge to the recording paper and attracts the recording paper to the transfer belt by an electrostatic force. Then, a high voltage having a polarity opposite to that of the toner charge is applied under constant current control at the transfer portion to transfer the toner image.
In such a transfer belt device, excellent transfer efficiency and separation effect can be obtained in the transfer section.

Such a transfer belt device is used as a particularly preferable device in a color image forming apparatus in which a toner image is formed on a photosensitive drum in an overlapping manner and transferred to a recording sheet at once. In such a color image forming apparatus, since a plurality of developing devices are provided on the peripheral portion of the photosensitive drum in order to superimpose toner images on the photosensitive member, the drum diameter becomes large, and sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation method. Therefore, more reliable separation performance is required, and in the method of superposing toner images, a large amount of transfer charge is required because the toner adhesion amount is large, and thus it is necessary to have a large transfer charge holding ability. This is because the transfer belt device is excellent in two respects.

[0008]

Objects of the Invention Transferring using such a transfer belt device is not without problems. At the time of transfer, the recording paper is pressed against the photosensitive drum by the transfer belt and is transferred at the transfer portion.At this time, the peripheral speed of the photosensitive drum and the linear speed of the recording paper are completely matched. If a cleaning device operates during the transfer operation and the cleaning blade comes into contact with the photosensitive drum during the transfer operation, an image shift occurs due to load variation.
As a means for avoiding such image misregistration, it is possible to rotate the photoconductor drum one extra rotation to perform transfer in a manner that avoids load fluctuation, but conventionally, the toner image formed at the final time is formed. It was supposed to be recharged. However, although this recharging is effective in bringing the toner deposited on the photoconductor drum the last time and the toner deposited before it into an electrostatically similar state, according to the experimental study by the present inventors. For example, the transfer process using the transfer belt device was not always necessary.

According to the present invention, the multicolor toner image formed on the photosensitive drum is transferred onto the recording paper in a good condition, and the amount of ozone generated from the charger in the process of image formation is reduced. An object of the present invention is to provide an image forming apparatus capable of extending the life of a photoconductor.

[0010]

SUMMARY OF THE INVENTION The present invention achieves the above object. The present invention forms an image on an image carrier a plurality of times, forms a multicolor toner image on the image carrier, and then forms the image on recording paper. In the image forming apparatus for transferring and fixing, after the final toner image formation on the image carrier, when the image portion reaches the transfer area for the second time, the transfer is performed on the recording paper and the final toner image is transferred. After the image formation, the charging means is OF'd so as not to charge at least the image area where the transfer is not completed.
The present invention provides an image forming apparatus characterized by performing F control. Here, the above-mentioned transfer is preferably performed by a transfer belt device including a transfer belt and a belt electrode provided on the back surface thereof.

[0011]

FIG. 1 is a sectional view showing the construction of a color image forming apparatus as an embodiment of the image forming apparatus of the present invention.
First, the configuration and operation will be described.

In the figure, reference numeral 10 denotes a photosensitive drum which is an image bearing member, which is formed by coating an OPC photosensitive member on the drum and is grounded and driven and rotated clockwise. Reference numeral 12 is a scorotron charger, which is _VH (-600 to -900V) with respect to the peripheral surface of the photosensitive drum 10.
Is uniformly charged by a corona discharge by a grid and a corona discharge wire whose potential is held at V _G (-600 to -900 V). Prior to the charging by the scorotron charger 12, the peripheral surface of the photoconductor is neutralized by exposure by the PCL 11 using a light emitting diode or the like in order to eliminate the history of the photoconductor until the previous printing.

After uniformly charging the photoconductor, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 via a polygon mirror 131 that rotates using a laser diode (not shown) as a light emitting source, an fθ lens, and the like.
The optical path is bent by 32 and scanning is performed, and a latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10.
In the present embodiment, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L (0 to -100V).

Yellow (Y) on the periphery of the photosensitive drum 10,
Developers each containing a developer composed of toner such as magenta (M), cyan (C), black (K), and a carrier.
14 is provided, and first, the development of the first color is performed by the developing sleeve 141 which contains a magnet and holds the developer and rotates. The developer is a carrier in which ferrite is used as a core and an insulating resin is coated around the core, polyester is used as a main material, and a pigment and a charge control agent are used according to the color.
It consists of toner to which silica, titanium oxide, etc. have been added.
The layer is regulated to a layer thickness (developer) of up to 600 μm and conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.4 to larger than the layer thickness (developer).
As 0.7mm, D of AC Baaisu and V _DC of V _AC during this time
C bias (-500 to -700V) is applied in a superimposed manner. V
_{Since DC} and V _H and the toner are charged with the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion having a higher potential than V _{DC and} has a potential higher than V _DC . It adheres to the low V _L portion and is visualized (reverse development).

After the visualization of the first color is completed, the process proceeds to the image forming process of the second color, the uniform charging is performed again by the scorotron charger 12, and a latent image based on the image data of the second color is formed by the image exposing means 13. To be done. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the sudden decrease in the potential around the image.

Again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and no image of the first color is developed, but the portion of the photoreceptor having the first color image is developed again. In the portion to be performed, the latent image of V _M ′ is formed by the light shielding by the toner attached to the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M ′ and V _M ′. At the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
When the latent image of is formed, the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M > V
_It may be an intermediate potential that becomes _L.

An image forming process similar to that for the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10. In the image forming apparatus according to the present invention, when the toner image of the fourth color is formed on the peripheral surface of the photoconductor drum 10 and then the image portion comes to the transfer area for the second time, the paper feed cassette.
The recording paper P fed by the paper feed mechanism 22 from the paper 21 is fed to the transfer area by the transfer belt device 30 in which the transfer belt 31 is stretched, and a multicolor image on the peripheral surface of the photoconductor drum 10 is collected. And is transferred onto the recording paper P. The charging by the charger 12 is turned off when the fourth color image is formed, and at least the image area where the transfer is not completed after the final image formation is not charged.

FIG. 2 shows the transfer belt device section taken out, and FIG. 2 (b) shows a state in which an image is being formed on the photosensitive drum 10 and the transfer belt 31 is separated from the photosensitive drum 10. 2A shows a state in which transfer is performed on the recording paper P.

The transfer belt 31 has a thickness of 0.4 having a resistance of 10 ⁶ to 10 ¹⁴ Ω · cm formed by forming an outer FLC layer of a urethane rubber base.
An endless rubber belt of ~ 1.0mm, ribs may be provided at the ends to prevent deviation during rotation.

It should be noted that a film such as PET or a high resistance belt such as a film coated with these may be provided by providing a charge removing mechanism or the like.

A holding roller 3 for stretching the transfer belt 31.
For the shaft 32a of the upstream side holding rollers 32 of 2, 33, the power source 38
Is applied with a voltage of V _PC (1.0 to 3.0 KV), and a conductive brush 34 is grounded as a means for applying a charge to the recording paper P at a position where the shaft 32a is installed via the transfer belt 31. There is. The fed recording paper P enters between the brush 34 and the transfer belt 31, and the brush 34 injects an electric charge into the recording paper P, so that an attraction force is exerted between the recording paper P and the transfer belt 31. Occurs. After that, the recording paper P enters the nip portion (transfer area) 35 formed by the photosensitive drum 10 and the transfer belt 31, and is applied to the corona discharger 36 applied by the constant current power source 39 from the back surface of the transfer belt 31 or the corona discharger 36. Instead, a transfer electric field is applied by the bias roller, and a multicolor image is transferred onto the recording paper P.

The recording paper P separated from the photosensitive drum 10 is
Shaft 33a of the holding roller 33 on the downstream side that stretches the transfer belt 31
Transfer belt 31 after receiving static electricity by AC corona discharge with the counter electrode as the counter electrode or while receiving AC corona discharge.
Separate from. A cleaning blade 37 removes the toner attached to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is separated from the photoconductor drum 10 about the shaft 33a of the holding roller 33 on the downstream side as a rotation center during the formation of the multicolor image.

The recording paper P holding the multicolor image separated from the transfer belt device 30 is conveyed to a fixing device 23 composed of two pressure bonding rollers having a heater inside at least one of the rollers or in the immediate vicinity thereof, and pressure bonded. The applied toner is melted by applying heat and pressure between the rollers, is fixed on the recording paper P, and is then discharged to the outside of the apparatus.

After the transfer, the residual toner remaining on the peripheral surface of the photoconductor drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, and then the rubber material contacted with the photoconductor is moved to the cleaning device 16. It is scraped off into the cleaning device 16 by the cleaning blade 16a and is discharged or stored by a screw or the like. The above static eliminator 15
Depending on the arrangement of the recording sheets, it is possible to also serve as static elimination of the recording paper as shown in FIG.

The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 16 is exposed by the PCL 11 and then uniformly charged by the scorotron charger 12.
Enter the next image forming cycle. The cleaning blade 16a is separated from the surface of the photoconductor during the formation of the multicolor image,
AC neutralization by 15 is kept in OFF state.

FIG. 3 shows a time chart of the above process. When a black (K) toner image, which is the final toner image, is formed on the photoconductor drum 10 and then the image portion comes to the transfer area for the second time (), the transfer onto the recording paper P is performed. For the image area where transfer is not completed, the charging by the scorotron charger 12 is turned off.
Was controlled so that recharging was not performed. Further, in this embodiment, the photosensitive drum of the cleaning blade 16a
The cleaning operation by pressure contact with 10 is performed after the transfer is completed, and the load is controlled so that the load does not change with respect to the rotation of the photosensitive drum 10 during the transfer.

[0028]

According to the present invention, the generation of ozone due to charging is reduced by controlling the pre-transfer image so that it is not recharged, and the user's health is not impaired. On the other hand, the damage is reduced and the life of the photoconductor is extended.

[Brief description of drawings]

FIG. 1 is a configuration sectional view showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a main part of the present invention.

FIG. 3 is a time chart diagram of the operation according to the present invention.

[Explanation of symbols]

 10 Photoconductor drum 11 PCL 12 Scorotron charger 13 Image exposure unit 14 Developer 15 Static eliminator 16 Cleaning device 21 Paper cassette 22 Paper feeding mechanism 23 Fixing device 30 Transfer belt device 31 Transfer belt 32, 33 Holding roller 34 Brush (charge) Application means) 35 Nip part (transfer area) 36 Corona discharger (for transfer) 37 Cleaning blade (transfer belt) 38 Power supply

Claims (2)

[Claims] 1. An image forming apparatus for performing image formation on an image carrier a plurality of times, forming multicolor toner images on the image carrier, and then transferring and fixing the image on a recording paper. After the final toner image formation, when the image area reaches the transfer area for the second time, the transfer onto the recording paper is performed, and
An image forming apparatus, characterized in that after the final toner image formation, the charging means is controlled to turn off so as not to charge at least an image area where transfer has not been completed. 2. The image forming apparatus according to claim 1, wherein the transfer is performed by a transfer belt device including a transfer belt and a belt electrode provided on a back surface of the transfer belt.