JPH04190274A - Image formation device - Google Patents

Abstract

PURPOSE:To have an image portion tip part copied distinctly and in addition, have transport conducted with sure separation from a photosensitive body, by making photosensitive potential of toner image tip position of an image carrier right before a transfer process, the middle of white ground potential and black ground potential on the image carrier. CONSTITUTION:At a photosensitive body drum 10 with multi-color toner images piled up, photosensitive body potential of its image tip part is lowered to a predetermined level by the de-electrification operation of a pre-transfer de- electrifier 61 positioned ahead of a transfer portion. For example, the separation probability of a recording paper sheet is secured 100% by making photosensitive body potential of toner image tip position of the photosensitive body right before a transfer process, the middle of white ground potential and black ground potential on the photosensitive body.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a transfer material for an image forming apparatus such as an electrophotographic copying machine,
The present invention relates to an image forming apparatus having a transfer belt device that electrostatically supports and transports a toner image on an image carrier, transfers it onto the transfer material by physical means, and then transports the toner image to a fixing means.

[Conventional technology]

FIG. 7 is a sectional view showing an embodiment of a conventional electrophotographic copying machine. In the figure, IO is a photosensitive drum which is a drum-shaped image carrier, 20 is a charger that charges the circumferential surface of the photosensitive drum 10, 30 is an exposure device, 13 is an image exposure section, 40 is a developing device, and 50 is a transfer device. A material supply device, P is a recording paper which is a transfer material, 16 is a transfer device which is a charger for transfer, 17 is a separator which is a static eliminator for separation, 80 is a fixing device, 90 is a cleaning device, 56 is a recording paper P This is a conveyor belt that is the means of conveyance.

To explain the operation of the copying machine, after the charger 20 uniformly charges the circumferential surface of the photoreceptor drum 10, the photoreceptor drum 1
The exposure device 30 performs exposure in the image exposure section 13 on the zero peripheral surface to form an electrostatic latent image. Thereafter, the latent image is developed and visualized by the developing device 40 to become a toner image. This toner image is transferred onto the recording paper P fed by the transfer material supply device 50 at the same timing. This transfer is performed by charging the recording paper P with a polarity opposite to that of the toner by a transfer device 16 from behind. After the transfer, a high AC voltage is applied to the recording paper P by the separator 17 to eliminate static electricity.
is separated from the photoreceptor drum 10. The separated recording paper P is conveyed to the fixing device 80 by the conveyance belt 56, and the toner image thereof is fixed and discharged from the apparatus.

On the other hand, the cleaning device 90 cleans the toner remaining on the circumferential surface of the photoreceptor drum IO onto which the toner image has been transferred.

However, in the above configuration, in order to ensure the transferability and separation of the toner image, the transfer device 16 and the separator 1 are
The discharge efficiency must be adjusted to find the point that works best, and this discharge efficiency is greatly affected by the environment, and the range of reliability is narrow. The transferability is influenced by the electric charge of the recording paper P and the mechanical properties of the recording paper P (sturdiness 2 surface smoothness, curl, etc.), and these are influenced by the storage condition of the recording paper P and the environment at the time of transfer ( It fluctuates greatly depending on factors such as temperature and humidity, making it difficult to maintain it in good condition at all times.

Furthermore, when the drum diameter of the photoreceptor drum 10 is large, the force with which the recording paper P wraps around the photoreceptor drum 10 and tries to return to its original flat state is smaller than when the drum diameter is small. After the image has been transferred, the recording paper P remains attached to the photoreceptor drum 1O, easily causing a paper jam.
This method has drawbacks such as a decrease in paper passing performance as a machine and a deterioration in reliability.

A belt-shaped transfer/conveying device shown in FIG. 8 is disclosed in US Pat. No. 3,357.325 and other publications as a technology that has overcome the above-mentioned drawbacks.

In FIG. 8, IO is a photosensitive drum which is a drum-shaped image carrier, 71 is a transfer belt consisting of a dielectric single-layer belt, and 72 and 73 are rollers for supporting, extending and rotating the transfer belt 71. , 79 is a roller for guiding the recording paper P;
60 is the electrostatic force number on the recording paper P (thereby the recording paper bell) 21
16 is a transfer device which is a charger for transferring the toner image from the photosensitive drum IO to the recording paper P, and 160 is a transfer section. With this configuration, the recording paper P can be firmly attached to the transfer belt 71 and transported reliably, and excellent transfer efficiency and separation efficiency can be obtained.

The belt-shaped transfer/transport device is particularly suitable for the photosensitive drum l.
This is a preferred color image forming apparatus in which toner images are formed on O and transferred to recording paper P at once. In the image forming apparatus, since toner images are superimposed on the photoreceptor drum IO, the drum diameter becomes large;
Conventional electrostatic transfer separation methods do not provide sufficient separation performance, so more reliable separation performance is required, and when toner images are overlapped, the amount of toner adhesion increases, so a large amount of transfer charge is required. This is because the belt-type transfer/transport device is superior in two respects: it needs to have a large transfer charge retention capacity.

[Problem to be solved by the invention]

The image forming apparatus equipped with the transfer/conveyance device (transfer belt device) shown in FIG. 8 has good separation characteristics of the recording paper, and has good conveyance performance of the transfer belt 71 and clear copy image quality. In order to achieve this, it is preferable to apply a high voltage for transfer to the transfer device 16 immediately after the leading edge of the recording paper P passes through the transfer unit 160 to provide a non-transfer area at the leading edge of the recording paper.

By providing a non-transfer area at the leading edge of the recording paper P and applying a necessary charging potential to the transfer unit 160 while the leading edge of the recording paper P passes through the non-transfer area, a However, such measures alone are not sufficient, and in rare cases, the drum may wind around the drum and cause a jam.

The present invention solves the above-mentioned problems and provides an image forming apparatus in which a non-transfer part is provided at the leading edge of the recording paper, the leading edge of the image area is clearly copied, and the leading edge of the recording paper is conveyed while being reliably separated from the photoreceptor. This is the purpose.

[Means to solve the problem]

The above purpose is to apply a transfer voltage to transfer the toner image formed on the image carrier by reversal development to the transfer paper that is attached to the transfer belt rotating in synchronization with the image carrier by charging the paper, and then separate and fix the image. In an image forming apparatus, the transfer voltage is not applied to the leading edge of the transfer paper, but the potential of the photoreceptor at the leading edge of the toner image on the image bearing member immediately before the transfer process is set to the white background potential on the image bearing member. This is achieved by an image forming apparatus characterized in that the potential is intermediate between the black background potential and the black background potential.

〔Example〕

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

In the drawings, parts that are the same as those of the conventional image forming apparatus and transfer belt device shown in FIGS. 7 and 8 are designated by the same reference numerals.

In the figure, IO is a drum-shaped image carrier, that is, a photosensitive drum, which is coated with an oPC photosensitive member, and is grounded and rotated clockwise.

Reference numeral 20 denotes a scorotron charger that applies an electric charge to the photoreceptor on the surface of the photoreceptor drum 10; 13, an exposure optical system (not shown) causes image exposure light or a laser beam to be focused on the circumferential surface of the photoreceptor drum 10; This is the image exposure section where the image is projected.

For example, a laser writing system unit is used as the exposure optical system. When a color signal output from an image reading device separate from the image forming device is input to the laser writing system unit, the laser beam (wavelength 78
0 nm) is rotated and scanned by a polygon mirror, the optical path is bent by a reflection mirror via an fθ lens, and the photosensitive drum 10 is uniformly charged in advance by the charger 20.
Projected onto the surrounding surface.

On the other hand, when scanning is started, the laser beam is detected by the index sensor, modulation of the laser beam by the first color signal is started, and the modulated laser beam scans the circumferential surface of the photoreceptor drum 10. Therefore, a latent image for the first color is formed in the image area on the photoreceptor drum IO by main scanning by the laser beam and sub-scanning by the rotation of the photoreceptor drum IO. This latent image is reversely developed by a developing means containing toner of, for example, yellow (Y) as a first color, and a yellow toner image is formed on the circumferential surface of the photoreceptor drum 10. The obtained toner image in the image area is held on the circumferential surface of the photoreceptor drum 10 and then transferred to the photoreceptor drum l.
It passes under the transfer means and cleaning means which are separated from the surface of O, and enters the next copy cycle.

That is, the photosensitive drum 10 is charged again by the charger 2°, and then the second photoreceptor drum 10 is charged by the charger 2°.
The color signal is input to the writing system unit, and the second color signal is written on the circumferential surface of the photoreceptor drum 10 to form a latent image in the same manner as in the case of the first color signal described above. This latent image is subjected to reversal development by a developing means containing toner of magenta (M) as a second color, for example,
A magenta toner image is formed. This magenta toner image is formed over the previously formed yellow toner image.

The toner image in the image area thus obtained passes under the transfer means and cleaning means which are separated from the circumferential surface of the photoreceptor drum 10 while being held on the surface of the photoreceptor drum 10, and is transferred to the next copy cycle. enter.

Similarly, writing is performed on the photosensitive drum 10 using the third color signal to form a latent image. This latent image is subjected to reversal development by a developing means containing toner of a third color, for example, cyan (c).

A color image is obtained by forming this cyan toner image on top of the yellow and magenta toner images described above. Furthermore, a developing means containing black toner is provided, and a high-quality color image is obtained by further superimposing black toner images in the same manner as described above.

41 and 44 are yellow and yellow, respectively, which perform the above-mentioned development.
All of them have similar structures, with developing devices serving as developing means containing magenta, cyan, and black toners.

FIG. 2 shows the structure of the developing device 41.
Inside, there are a developing sleeve 411 and a magnet roller 4.
12, stirring screws 413, 414, scraping plate 415
etc. are provided. The gap between the developing sleeve 411 and the photosensitive drum 10 is determined by a roller (coaxially provided with the developing sleeve 411) that abuts outside the image area of the circumferential surface of the photosensitive drum 10.
1! (not shown), the gap is always maintained at a constant gap of around 0-5 mm.

The toner supplied from the toner storage device (not shown) is
The magnetic carrier is sufficiently stirred and mixed by the stirring screw 414 and the stirring screw 413, which rotate in opposite directions. This two-component developer consisting of magnetic carrier and toner is stirred and mixed and then supplied to the developing sleeve 411. A magnet roller 412 having a fixed magnetic pole is disposed inside the developing sleeve 411, and the above-described thin layer of developer is formed between the developing sleeve 411 and the magnet roller 412.

For example, a cylinder made of a magnetic material is provided facing the magnetic pole of the magnet roller 412 so that the thickness of the thin layer of developer on the surface of the developing sleeve 411 is thinner than the gap between the developing sleeve 411 and the photosensitive drum 1o. By pressing the developer thin layer forming means 416 of the rod against the developing sleeve 411, the developer layer is shaped into an even thin layer of about 300 μm. A developing bias is applied to the developing sleeve 411,
The latent image in the image area on the photosensitive drum 10 is developed. After the development has been completed, the thin layer of developer on the developing sleeve 411 is once scraped off by the scraping plate 415, and a new thin layer of developer is formed by the method described above.

Charging by the charger 20 provided on the photosensitive drum IO and its periphery, exposure by the laser writing system unit for each color printing, and development processing by the developing devices 41 to 44 are performed four times for each color, and the photosensitive drum IO is A color toner image is formed on the image area on the circumferential surface of the body drum 10 by overlapping.

Reference numerals 51 and 52 refer to a path for recording paper, which is a transfer material according to size, which is fed one by one from a transfer material supply device, and 53 a transfer section 160 in synchronization with the movement of the color toner image on the photoreceptor drum 10. This is a registration roller for conveying the recording paper to.

70 is a transfer belt device, 71 is a transfer belt which is a belt portion, 72 and 73 are rollers made of conductive metal material,
The upstream roller 72 is a roller that has a rotatable shaft that is at a predetermined potential that is grounded or close to the grounded state, and the downstream roller 73 is a roller that drives the transfer belt 71 and has a fixed shaft. Reference numeral 74 denotes a belt support member, one end of which has the axis of the roller 73 as a fixed shaft, and the other end connected to the movable shaft of the roller 72, and is connected to the roller 72 by an elastic member (not shown).
is biased so that it is positioned downward. Therefore, the transfer belt 71 is normally retracted from the surface of the photoreceptor drum 10, and during transfer, the eccentric cam 77, which is operated under the control of the device control section, is attached to the belt support member 74 via the leaf spring 78.
is pressed upward in the figure and rotated counterclockwise about the roller 73 as the center of rotation, and the rollers 76 provided at both ends of the belt support member C move the side edges of the circumferential surface of the photoreceptor drum 10 outside the image area. The transfer bell) 71 is brought into contact with the transfer 5160 of the photosensitive drum IO.

Reference numeral 79 is a cleaning blade that scrapes off toner adhered to the transfer belt 71 for cleaning, and 95 is a toner transport pipe having a flexible transport screw inside, and the toner scraped by the cleaning blade 79 is sent to a toner collection box (not shown). transport.

Reference numeral 16 denotes a transfer device, which is a charger for transfer, provided at a position facing the transfer unit 160, and 60, a transfer device located at a position opposite to the roller 72 in the horizontal cross-sectional space between the transfer bell l-71 and the photosensitive drum IO. It is a paper charger installed.

After the development by the developer 44 containing the fourth color toner on the photoreceptor drum 10 is started as described above, the registration roller 53 is activated, the transfer belt device 70 is pressed, and the paper charger 60 is applied with a high voltage. The applications occur approximately simultaneously.

As a result, the paper charger 60 charges the recording paper fed one by one from the transfer material supply device to the same polarity as the toner on the photosensitive drum IO. The paper charger 60 efficiently and reliably charges the roller 72, which is close to the ground, as a counter electrode, and since it is provided very close to the transfer section 160, the charge decreases little during conveyance, and the recording paper can be firmly adsorbed and held on the transfer belt 71 and conveyed to the transfer section 160.

When the leading edge of the recording paper reaches the transfer section 160, the transfer belt 7
1, the recording paper is brought into pressure contact with the photosensitive drum IO. Then, the transfer device 16 charges the toner with a polarity opposite to that of the toner on the photoreceptor drum 10, and transfers the toner image onto the recording paper (the timing at which the transfer voltage is applied by the transfer device 16 will be described in detail later). The recording paper onto which the image has been transferred is transferred to the transfer belt 7
1, the sheet is further conveyed to a fixing section (not shown), where it is fixed by heat welding, and then discharged onto an external sheet discharge tray.

Reference numeral 55 denotes a separation claw for preventing the recording paper from accidentally entering upwards.

The structure of the transfer belt 71 used as the transfer means is, for example, composed of two layers, and the main body is made of an endless material of silicone rubber, polyurethane rubber, butyl rubber, etc. with a thickness of about 0.5 to 1 mm, and has a volume resistance of about 1OIoΩ・Cl11. It is a high-resistance sheet, and the frictional resistance is lowered by spraying, for example, fluorocarbon resin on the upper layer of the sheet.

On the other hand, the photosensitive drum 10 after the transfer is cleaned by a cleaning device 90 as a cleaning means. The cleaning blade 91 is equipped with a toner collecting roller 92 and the like which acts as an electrostatic counter to convey residual toner.
is in the retracted state, and when the transfer is completed, the photoreceptor drum 1
0 to perform cleaning. Further, a static eliminating lamp 93 is located on the upstream side of the cleaning device 90, and a static eliminating lamp 94 is located on the downstream side. The static elimination lamp 94 indicates the photosensitive drum 1 that has been cleaned.
To uniformly remove static electricity from the 0 circumferential surface so that uniform charging is performed. Further, a toner conveying pipe 95 having a toner conveying screw made of a flexible material is provided at the bottom of the cleaning device 90, and conveys the waste toner collected by cleaning to a toner collecting box (not shown). The photosensitive drum IO that has been cleaned is subjected to the next image forming process.

The image forming apparatus has the above-mentioned image forming means arranged at the peripheral edge of the photosensitive drum 10 in the positional relationship shown in FIG. A pre-transfer static eliminator (hereinafter referred to as PTL) 61 for lamp irradiation is used as an exposure means for removing potential.
has been established.

The image forming process in the image forming apparatus is performed according to the time chart shown in FIG. 4, and the photosensitive drum 10 on which multicolor toner images are superimposed is subjected to the static eliminating action of the PTL 61 located before the transfer section. As a result, the potential of the photoreceptor at the leading edge of the image is lowered to a predetermined level. For example, by using such means, the potential of the photoconductor at the leading edge of the toner image on the photoconductor immediately before the transfer process is set to be intermediate between the white background potential and the black background potential on the photoconductor.
The separation probability of the recording paper was ensured at 100%.

Hereinafter, the static neutralization effect of the photoreceptor by the PTL 61 and its effect of improving the separation of the recording paper from the photoreceptor drum IO will be explained using the results of experiments conducted separately.

FIG. 5(a) shows a recording paper being conveyed in the direction of the arrow, and the non-image area at the front end (3 mm from the leading edge of the recording paper in the case of a multicolor image due to transferability).

In the case of a monochrome image, a length of about 5 m+n from the leading edge of the recording paper) is charged potential group; the corresponding high potential (
On the other hand, the potential of the circumferential surface of the photoreceptor drum 10 corresponding to the image transfer area is maintained at the highest potential (white background potential) as shown in FIG. 5(b) depending on the image configuration. VH, the lowest low potential (black background potential) VL, or an intermediate potential VM between them.

The above-mentioned high potential VH and low potential VL are each -80
When a latent image is formed by laser recording on the surface of the photoreceptor by holding potentials equivalent to 0 V and -50 V, the former is called the white ground potential and the latter is called the black ground potential because they are made white and black, respectively, by reversal development.

On the other hand, the present inventor conducted an experiment to determine the correlation between the charging potential of the photoreceptor at the leading edge of the recording paper and the separability of the recording paper from the circumferential surface of the photoreceptor drum 10 after transfer.
We were able to obtain the results shown in Figure 6.

That is, the photoreceptor potential corresponding to the non-image area at the leading edge of the recording paper is always a high potential VH, and the photoreceptor potential in the following image area is a high potential VH, an intermediate potential VM, or a low potential VL depending on the configuration of the image. Therefore, the photoreceptor potential near the leading edge of the recording paper is VH
-VH, VH-VM.

It is either VH-VL. (Figure 5(b) shows this) Now VH-VH (indicated by O), vH-VL
FIG. 6 shows the separation probability for the two states (indicated by Δ) when the potential of VH is under the conditions shown on the horizontal axis.

What is clear from Figure 6 is that VH is -200v to -60v.
This means that if it is between 0v, there is a 100% probability of separation.

From this, if the photoreceptor potential corresponding to the non-image area at the leading edge of the recording paper is between -200V and -600V, which corresponds to the middle of the white background potential (-800V) and the black background potential (-50V),
Regardless of the potential of the image area, the separation is almost certain.

Therefore, due to the static eliminating action of the pre-transfer static eliminator 61, the photoreceptor potential (
V) corresponds to the middle of the above-mentioned white background potential and black background potential.
It has been confirmed that by lowering the absolute value to a range of 00v to -200v, it is possible to separate and transport the recording paper after the transfer from the circumferential surface of the photoreceptor drum IO with almost 100% probability.

Note that the charge removal of the photoreceptor potential for the above purpose may be performed using a pre-transfer charge remover other than the lamp irradiation type shown in this embodiment. Photoreceptor potential that is neutralized by an electric device (
Experimental results have shown that V) is preferably within the range of .

〔Effect of the invention〕

According to the present invention, almost 100% separation performance of the leading edge of the recording paper from the photoreceptor surface after image transfer can be ensured, and as a result, the recording paper can be securely placed on a predetermined transport path without deteriorating the image transferability. I believe that an image forming apparatus capable of feeding images will be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of the image forming apparatus of the present invention, FIG. 2 is a sectional view of the developing device, FIG. 3 is a layout diagram of each image forming means, and FIG.
The figure is a time chart showing the process of image formation, Figure 5 is an explanatory diagram showing the potential of the photoreceptor, Figure 6 is a graph showing the separability of the photoreceptor potential and recording paper, and Figures vg7 and 8 are conventional graphs. FIG. 3 is a cross-sectional configuration diagram of an electrophotographic copying machine and a transfer belt device. lO...Photosensitive drum 13...Image exposure section 16.
・Transfer device 20 ・Charger 41 to 44 ・・
Developing device 53... Registration roller 55... Separator 60... Paper charger 61... Pre-transfer static eliminator 70... Transfer belt device 71... Transfer belt 90... Cleaning device 93 .94...
Static elimination lamp

Claims (2)

[Claims] (1) The toner image formed on the image carrier by reversal development is transferred by applying a transfer voltage to the transfer paper attached to the transfer belt rotating synchronously with the image carrier by paper charging, and then separated. In an image forming apparatus for fixing, the transfer voltage is not applied to the leading edge of the transfer paper, but the photoreceptor potential at the leading edge position of the toner image on the image bearing member immediately before the transfer process is applied to the white background on the image bearing member. An image forming apparatus characterized in that the potential is intermediate between the potential and the black background potential. (2) The image forming apparatus according to claim 1, wherein the intermediate photoreceptor potential is achieved by exposing the surface of the image carrier to light using an exposure means provided before the transfer area.