JPH03126977A - Cleaning device for image forming device - Google Patents

Abstract

PURPOSE:To obtain an excellent image by forming a charged image having opposite polarity to the electrifying polarity of a cleaning blade and cleaning roller in the cleaning area of a photosensitive body, where the cleaning blade and the cleaning roller are present thereon, just before a device is shut off, and shutting off the device with the cleaning blade and the cleaning roller by facing each other. CONSTITUTION:The residual toner remaining on the photosensitive body 1 is removed by the cleaning roller 9 and the cleaning blade 11 in a position opposed to a cleaning device 6. Just before the device is shut off, the charged image having opposite polarity of the electrifying polarity of the cleaning members 9 and 11 is formed on the surface of the photosensitive body. When the charged image is arrived at the position of the cleaning members 9 and 11, the device is shut off, so that the charges having polarity opposite from the cleaning roller 9 and the blade 11 are present on the surface of the photosensitive body 1. Thus, highly reliable cleaning function is maintained to obtain an excellent image.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus that utilizes an electrostatic transfer process, such as an electrostatic copying machine and a printer, and particularly to a cleaning device therefor. It is.

(Prior Art and Issues to be Solved) In a well-known image forming apparatus that repeats the process of transferring a toner image electrostatically formed on the surface of an image carrier onto a transfer material mainly made of paper, residual toner that remains on the image carrier without contributing to Sufficient removal of foreign matter adhering to the image carrier is an essential requirement for obtaining high-quality images.

Conventionally, as a cleaning means for this purpose, a cleaning blade made of an elastic material such as rubber is mainly used as a means to remove residual toner, and an elastic cleaning blade made of urethane rubber or the like is particularly used to remove various foreign substances as mentioned above. A structure in which a roller rubs against an image carrier has already been proposed.

FIG. 2 shows a typical example of such a cleaning device, in which a cleaning device 6 is arranged parallel to and close to an image carrier l that extends perpendicularly to the plane of the paper and rotates in the direction of the arrow hole. , l of the other free edge of the cleaning blade 11 with one edge attached to the cleaning device.
The edge is pressed against the surface of the image carrier to remove residual toner remaining on the image carrier without being transferred to the transfer material at a transfer site (not shown).

When viewed in the running direction of the image carrier l, the cleaning blade 1
An elastic cleaning roller 9 is disposed upstream of the image carrier 1 and is in pressure contact with the surface of the image carrier. During operation, the roller moves at a relative speed of 50 to 300% of the running speed of the image carrier. It is configured to run.

In practice, such a configuration does not have sufficient foreign matter removal function. Therefore, for example, at least the surface of the cleaning roller is made of an insulating material, and the cleaning roller 9 is charged by friction with the scraper 8 that comes into contact with the cleaning roller 9. It has been proposed to charge the toner to a high potential with a polarity opposite to that of the toner, and it has been found that this can sufficiently perform the function of removing not only the toner but also foreign matter as described above.

For example, in an image forming apparatus that uses an organic semiconductor as an image carrier and positively charged toner, foreign matter can be effectively removed by changing the surface potential of the cleaning roller from 1.0 KV to a negative number. function can be obtained.

However, when such a leaning device is used, when the device is operated again after a short pause after continuous operation, the image position corresponding to the portion where the cleaning blade and cleaning roller were in pressure contact with the image bearing member during the pause is removed. For example, when an OPc photoreceptor is used as the image carrier and polyurethane rubber is used on the surface of the cleaning blade and cleaning roller, it has been found that white spots occur in low density areas and in severe cases. , A4 size transfer paper 500
After passing the sheet, it is paused for 20 minutes, and then printing is performed at an image density of about 0.3. When printing is performed with an image density of about 0.3, white spots (about 1 to 6 mm+) appear in the image area corresponding to the pressure contact area between the image carrier, cleaning blade, and cleaning roller. (referred to as blade or roller marks).

The above phenomenon can be prevented by forcibly removing static electricity from the cleaning roller at all times, or by constructing the cleaning blade and cleaning roller with conductive materials.Conversely, the above-mentioned rollers, etc. can be prevented by using rubber mixed with fluororesin. Judging from the fact that the image defects are noticeable when the surface of the image bearing member is formed, it is assumed that the defects are caused by the cleaning roller, blade, etc. being in contact with the image carrier for a long time while being kept at a high potential.

In order to avoid such drawbacks, it is possible to make blades, rollers, etc. conductive so that they do not become charged, but in the case of blades, adding a conductive material to them may affect their physical properties. This can lead to a decrease in abrasion resistance, strength, and residual flexure, leading to a decline in cleaning function.In addition, preventing the cleaning roller from being charged with electricity can improve its cleaning function due to charging. Of course, such a thing is impossible because it contradicts the original purpose.

The reason why the white spots mentioned above occur is not necessarily clear, but in the case of the above example, the potential on the surface of the urethane rubber was charged to -2KV or more during operation, and after stopping, this potential gradually decreased. However, since it is still in contact with the image carrier while maintaining a minus several hundred volts, a potential close to this is also applied to the photosensitive layer of the image carrier, and positive charges are injected from the image carrier base to form a trap. This is considered to be because the electric potential of the rollers and blades cannot be sufficiently increased during operation after a pause.

The present invention has been made to deal with such a situation, and while maintaining the function of charging the cleaning roller and blade, it solves the above-mentioned problems when the cleaning roller and blade are stopped, thereby achieving high reliability. It is an object of the present invention to provide a cleaning device that maintains its cleaning function and helps obtain high-quality images.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention provides an image bearing member, a means for forming a charge image on the surface thereof, and a means for removing residual toner, etc. In an image forming apparatus including at least one cleaning member that presses against the image carrier, when the image forming apparatus stops, a charge polarity of the cleaning member is applied to the surface of the image carrier immediately before stopping. is a cleaning device characterized by forming a charge image of opposite polarity and stopping the charge image when it reaches the position of the cleaning member.

With this configuration, it is possible to maintain good linning properties and to avoid the occurrence of roller marks even when the roller is stopped, thereby causing deterioration in image quality.

(Description of Embodiments) FIG. 1 is a schematic side view showing the main parts of an image forming apparatus suitable for applying the present invention.

After the surface of a cylindrical OPC photoreceptor having an axis perpendicular to the plane of the paper and rotating in six directions of arrows is uniformly negatively charged by a primary charger 2, an optical image signal 7 is irradiated onto the charged surface. An electrostatic latent image is formed, and when this latent image arrives at the development area where the developing device 3 and the photoreceptor 1 face each other, positively charged toner is supplied from the developing device and adheres to the latent image to form a toner. An image is formed.

Then, as the photoreceptor 1 rotates, this toner image becomes
When the transfer charge 5a and the photoreceptor l reach the opposing transfer site, the transfer material 4 is supplied to the transfer site in synchronization with the toner image, and at the same time, the transfer charger 5a causes a negative transfer in this case. A bias is applied and the toner image on the photoreceptor side is transferred to the transfer material 4.

Thereafter, the transfer material carrying the toner image is transferred to the separation charger 5b.
The toner is separated from the photoconductor 1 by the alternating current bias shifted to the positive voltage side, and is further conveyed to a fixing site (not shown), and the residual toner remaining on the photoconductor 1 without contributing to transfer is directed toward the cleaning device 6. The cleaning roller 9 and the cleaning blade 11 remove the cleaning roller 9 and the cleaning blade 11 to prepare for the next process.

FIG. 2 is an enlarged sectional view of the cleaning device 6, and its structure and operation are basically the same as those of the known cleaning device described above, so the explanation will be omitted unless necessary. , a blade 1 made of polyurethane
1, and an insulating elastic cleaning roller 9 disposed upstream thereof and having a surface layer 9a made of polyurethane rubber and an inner layer 9b made of silicone sponge.

FIG. 3 shows a part of the operation sequence of the apparatus shown in FIG. 1. When the operator turns on the copy button,
The photoreceptor 1 rotates, and then the negative charger 2, the developing bias of the developer 3, the transfer charger 5a, and the separation charger 5b are turned on.

Thereafter, image exposure 7 is performed a predetermined number of times to execute the image forming operation.

After the work is completed, the developing device and each charger are turned off in sequence, but the photoreceptor 1 continues to rotate for a while for post-rotation. At this point, after each member has stopped, the charger 5b, which substantially applies a positive charge, is turned on for t2 seconds.

The operating time t1 seconds at this time is defined as the distance in the circumferential direction of the area of the photoreceptor 1 where the cleaning blade 11 and the cleaning roller 9 face the photoreceptor l, which is indicated by the symbol C1 in FIG. Value divided by V (t+ = 12+ /v)
shall be.

After tl seconds (tz>t+) after the charging 5b is turned on, the photoreceptor I stops, and the apparatus enters a stopped state.

Here, tl seconds is the value (t
a=42□/V).

With this configuration, the cleaning device can be moved from the position of the cleaning blade 11 to the cleaning roller 9.
Up to the position of the photoreceptor (on the surface of the cleaning roller, there is a charge of opposite polarity to that of the blade, in this case positive polarity. In other words, since 5b is positively biased, A positive charge exists on the photoreceptor.

FIG. 4 is an enlarged side view showing the state of the cleaning roller 9 and cleaning blade 11 and their vicinity after the end of the sequence.

As shown in the figure, while the apparatus is in rest, positive charges exist on the surface of the photoreceptor 1 opposite to the negatively charged roller 9 and blade 11, so that both are neutralized.
Roller 9. The electric charge remaining on the blade 11 side becomes substantially very small, and even if the apparatus is started again after stopping, the above-mentioned blade and roller marks will not be generated in the image.

In addition, the charge on the photoreceptor side described above is formed only immediately before stopping, and the conventional sequence is not changed during image formation, and the negative charge on the cleaning roller does not impede cleaning performance. It will never occur.

FIG. 5 is a sequence showing another embodiment of the present invention.

The apparatus used in this case may be the same as that in the sixth embodiment.

After the image forming operation is completed, the chargers 2, 5a and 5b are turned off, and while the photoreceptor is rotating, a bias having the same polarity as that of the toner is applied for t1 seconds by the developer 3. A positively charged toner image is formed in the Q+ portion similar to the example.

Then, after t1 seconds, all operations of the device are stopped.

Here, t1 seconds is a value obtained by dividing the distance from the developing device 3 to the blade 11 (as viewed in the traveling direction of the photoreceptor) by the circumferential speed of the photoreceptor (ta = is /v).

As a result, a positive charge exists on the surface of the photoreceptor in the range from the blade 11 to the roller 9 when the photoreceptor is stopped, and image defects can be prevented from occurring as in the case described above.

FIG. 6 shows a sequence according to yet another embodiment of the present invention.

Naturally, the degree of white spots may vary depending on the material of the cleaning roller and blade in the cleaning device, the portion in contact with the roller, and the portion away from the roller.

This embodiment deals with such a situation,
In this case, a higher charge and a larger amount of toner are applied to material and areas with significant white spots.

The figure shows the cleaning roller portion. Assume that the white spot is more noticeable than the blade part, and tz2 is set in the same manner as in the above embodiment, and furthermore, when the charger 5b is turned on during tl, the voltage applied to the charger is switched to two stages. , a time t 4 (t 4 = Q s / v ) corresponding to the length of the pressure nip between the cleaning roller 9 and the photoreceptor 1 (as viewed in the traveling direction of the photoreceptor)
The charge shall be particularly high.

By doing this, while the cleaning roller is stopped, the contact area of the cleaning roller faces a high positive charge to prevent roller marks, and the other parts face a low positive charge to sufficiently prevent white spots. It becomes possible.

(3) As described in the detailed description of the invention, according to the present invention, in a cleaning device equipped with a cleaning blade and a cleaning roller that are in pressure contact with a photoreceptor, the charge polarity of these blades and rollers is By forming a charge image with a polarity opposite to that of the blade and roller, by stopping the blade and roller in a state where they are facing each other, the cleaning function of the blade and roller is not impaired at all, and when the blade and roller are restarted.
This greatly contributes to preventing the occurrence of roller marks and stably obtaining high-quality images.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of an image forming apparatus suitable for applying the present invention; FIG. 2 is a sectional side view showing the configuration of a cleaning device of the same apparatus; FIG. 3 is a diagram showing the operation sequence of the same; FIG. 4 is an enlarged side view of essential parts of the cleaning device, FIG. 5 is a sequence diagram showing another embodiment of the present invention, and FIG. 6 is a sequence diagram showing still another embodiment. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 5a... Transfer charger, 5b... Separation charger, 6... Cleaning device, 7... Scraper, 9... Cleaning roller, 1... Cleaning blade. Figure Figure Figure 4 Figure C = C `` ``:'' C:l: C:o□oo
ooooo. ,ΩU)

Claims (2)

[Claims] (1) An image forming apparatus comprising an image carrier, a means for forming a charge image on the surface of the image carrier, and at least one cleaning member that presses against the image carrier to remove residual toner, etc. When this image forming apparatus stops, a charge image having a polarity opposite to that of the cleaning member is formed on the surface of the image carrier immediately before stopping, and the image forming apparatus stops when the charge image reaches a position facing the cleaning member. A cleaning device characterized by: (2) The cleaning device according to claim 1, wherein the cleaning member is a cleaning blade and/or a cleaning roller.