JPH1172992A - Contact charging type image forming apparatus and image forming method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a contact electrifying member from being soiled with toner sticking to an image carrier with the result that an electrification irregularity occurs and ends up degrading image quality, in the image forming device of the contact electrification system which brings the contact electrifying member, an electrifying blade or the like into contact with the surface of the image carrier, a photoreceptor or the like, and applies a specific voltage to the contact electrifying member, thereby electrifying the image carrier. SOLUTION: When an image is not formed, a voltage switch 33 is switched right after the transmission of a stop signal for stopping a photoreceptor 17, and the conductive blade 12 of a cleaning device 11 is grounded. Under the condition, the photoreceptor 17 is rotated in a direction opposite to that used for image formation, thereby transferring toner sticking to the blade 12 onto the photoreceptor 17. Then, the transferred toner is removed with the blade 12 again during the subsequent image-formation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium such as paper by transferring an image formed on an image carrier by an electrophotographic method, such as a copying machine, a facsimile, a printer, and a multifunction machine using a laser. The present invention can be applied to an image forming apparatus that performs recording on a paper. More specifically, the present invention relates to a contact charging type image forming apparatus and an image forming method in which a contact charging member is brought into contact with the surface of a rotating image carrier and a predetermined charging voltage is applied to the contact charging member to charge the image carrier. .

[0002]

2. Description of the Related Art Heretofore, in this type of contact charging type image forming apparatus, there is a type using a conductive blade as a contact charging member, and the conductive blade is further provided with a photosensitive member as an image carrier. There is a device which can be used as a cleaning member for cleaning the surface of the device and removing the toner.

For example, Japanese Unexamined Patent Publication No. Sho 60-147756 discloses a charging device that contacts a surface of a photosensitive member having an amorphous silicon surface layer with a conductive plate member to charge the photosensitive member and perform cleaning. It has been disclosed.

[0004] Also, Japanese Patent Application Laid-Open No. 7-92769 discloses that
In order for the same blade to have a cleaning function and a charging function for the photoconductor, the electric resistance range of the blade is set to 1
0 ⁵ ~10 ⁹ Ω, technique the contact pressure against the photosensitive member was 1.5 g / mm or more is disclosed.

[0005]

In these prior arts, toner on a photoreceptor is scraped off by a blade, and charging is performed on the downstream side in the rotation direction of the photoreceptor. However, generally, 100% of the toner on the photoconductor cannot be removed even by cleaning with a blade, and about 2 to 10 post-transfer toners remain on the photoconductor after the blade slides. In addition, the post-transfer toner has both “+” and “−” polarities, and the toner passing through the blade has both “+” and “−” polarities.

Therefore, in the case of N / P (negative / positive) transfer, when the "+" polarity toner passes through the blade, a "-" polarity voltage is applied to the blade, so that the toner is When the toner adheres to the surface and the amount of the toner having the “+” polarity adheres to the blade, the amount of the toner gradually increases. There was a problem that.

[0007]

Accordingly, the invention described in claim 1 is applied to the surface of an image carrier such as a photoconductor 17 which is driven to rotate, as in an embodiment described with reference to the following drawings. In a contact charging type image forming apparatus that contacts a contact charging member such as a blade 12 and applies a predetermined charging voltage to the contact charging member to charge the image carrier,
Image carrier reverse rotation means for rotating the image carrier in a direction opposite to that during image formation during non-image formation, and applying a voltage to the contact charging member during image formation during reverse rotation of the image carrier during image formation. Is characterized by including a voltage switching means such as a voltage switch 33 for switching to a different voltage.

According to a second aspect of the present invention, a blade 12 is provided on a surface of an image carrier such as a photosensitive member 17 which is driven to rotate, as in an embodiment described with reference to the following drawings.
In a contact charging type image forming apparatus in which a contact charging member is contacted and a predetermined charging voltage is applied to the contact charging member to charge the image carrier, the image carrier is not formed during image formation, By switching the voltage applied to the contact charging member to a voltage different from that for image formation while rotating in the opposite direction to the above, the toner 32 adhered to the contact charging member was transferred to the image carrier side. Thereafter, the transferred toner 32 is removed from the image carrier at the time of the next image formation.

According to a third aspect of the present invention, in the contact charging type image forming apparatus according to the first aspect, for example, as in an embodiment described with reference to the following drawings, the contact charging member is connected to the image carrier. It is also used as a cleaning member for cleaning the surface of the device.

According to a fourth aspect of the present invention, in the contact charging type image forming apparatus of the first aspect, the contact charging member is a blade as in an embodiment described with reference to the following drawings. It is characterized by.

According to a fifth aspect of the present invention, in the contact charging type image forming apparatus according to the first aspect, for example, as in an embodiment described with reference to the following drawings, the voltage switching means includes the image carrier. By grounding the contact charging member during the reverse rotation of the body, the voltage applied to the contact charging member is switched to a voltage different from that used during image formation.

According to a sixth aspect of the present invention, in the contact charging type image forming apparatus according to the first aspect, as in an embodiment described with reference to the following drawings, for example, the voltage switching means includes the image carrier. The present invention is characterized in that the voltage applied to the contact charging member is switched to a voltage different from that used during image formation by superimposing an AC component on a DC voltage during the reverse rotation of the body.

According to a seventh aspect of the present invention, in the contact charging type image forming apparatus according to the first aspect, as in an embodiment which will be described with reference to the following drawings, for example, the voltage switching means includes the image carrier. Immediately after sending a stop signal for stopping the body, the voltage applied to the contact charging member is switched to a voltage different from that used during image formation.

According to an eighth aspect of the present invention, in the contact charging type image forming apparatus according to the first aspect, for example, as in an embodiment described with reference to the following drawings, the image carrier reverse rotation means comprises: When the image carrier is rotated in a direction opposite to the direction of image formation, a position where a transferred portion of the toner transferred from the contact charging member to the image carrier passes through a cleaning member for cleaning the surface of the image carrier. Up to this point, the image carrier is reversely rotated.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

First, a series of processes of image formation will be described with reference to FIG. When a print button of an operation unit (not shown) is pressed, a static elimination lamp 10, a conductive blade (“contact charging member” in the present invention) 12 of a cleaning device 11, a developing roller 14 of a developing device 13, a transfer roller 15, A predetermined voltage or current is sequentially applied to the separation electrode 16 at a predetermined timing. At substantially the same time, a drum-shaped photosensitive member 17 serving as an image carrier, a developing roller 14, a left screw 18 of a developing device 13, and a right Screw 1
9, the transfer roller 15, and the toner discharge screw 20 of the cleaning device 11 start to rotate in a predetermined direction.

The photosensitive member 17 is neutralized by the neutralization lamp 10 with the rotation in the positive direction indicated by the solid line arrow in the drawing, and the conductive blade is in contact with the surface of the photosensitive member at a position away from the neutralization part. At 12, the image is uniformly negatively charged (for example, −850 V), and a latent image is formed by a laser beam L from an unillustrated exposure device (the black solid potential is, for example, −150
V) is performed. The latent image is developed by a magnetic brush formed by the developing roller 14 (the applied voltage is, for example, -65).
0V) to form a toner image. Reference numeral 21 denotes a doctor of the developing device 13, 22 denotes an upper lid, and 23 denotes a lower case.

On the other hand, the transfer paper fed by a paper feed mechanism (not shown) is synchronized with the leading edge of the image by the upper registration roller 24 and the lower registration roller 25, and the upper and lower guide plates 2
Guided by 6.27, it is fed between the photoreceptor 17 and the transfer roller 15. Then, the transfer paper is transferred to the photosensitive member 17.
After the upper toner image is transferred (for example, +10 μA), the toner image is separated from the photoreceptor 17 by the separation electrode 16, guided by the transport guide plate 28, and sent to a fixing device (not shown).
After the toner image is fixed, the toner image is discharged to the outside.

The toner remaining on the photoreceptor 17 by the above-described transfer is transferred to the cleaning device 11 by the forward rotation of the photoreceptor 17, removed from the photoreceptor 17 by the blade 12, and removed from the cleaning case 29 of the cleaning device 11. The toner is discharged from inside by the toner discharge screw 20.

The photosensitive member 17 is provided with the cleaning device 1.
Before the cleaning by 1, the charge is removed by the charge removing lamp 10. Since the charge removal is performed by irradiating the irregularly reflected light from above the toner, the charge is removed almost uniformly.

The blade 12 is held in a cleaning case 29 by a blade holder 30. Since the blade 12 is conductive and a voltage of “−” polarity is applied by the charging power supply 31, the photosensitive member 17 is charged at the same time as cleaning after the charge removing lamp 10 is removed.

By the way, 100% of the toner on the photoreceptor cannot be scraped off even by cleaning with a general blade, and about 2 to 10 toners remain on the photoreceptor after cleaning. The toner after transfer is “+”
And "-" are mixed.

Therefore, as shown in FIG.
7, when the toner 32 having the “+” polarity has passed through the blade 12 due to the rotation in the positive direction indicated by the solid line arrow in the figure, the toner 32 having the “+” polarity is charged by the charging power source 31.
Blade 12 to which a voltage having a “−” polarity is applied
And is attached to the surface. If a long time elapses in such a state, the surface of the blade 12 gradually becomes dirty, uneven charging occurs on the photoreceptor 17, and eventually appears as a background stain on an image.

Therefore, in the present invention, the charging power supply 31 is provided with the voltage switch 33, and the control unit (not shown) rotates the photosensitive member 17 in a direction opposite to the image forming direction during non-image forming. There is provided reverse rotation means (for example, control means for reversely rotating the motor of the photoconductor 17). Then, immediately after the stop signal for stopping the photoreceptor 17 is transmitted after the image is formed, the voltage switch (the "voltage switching means" in the present invention) 33 is switched as shown in FIG. While the blade 12 to which the polarity voltage was applied was grounded and the time required for the photosensitive member 17 to completely stop and the amount of inertial rotation were measured, the photosensitive member 17 was moved in the reverse direction by a required amount as shown in FIG. (In the direction indicated by).

That is, even if a stop signal for the photosensitive member 17 is issued, the motor for rotating the photosensitive member 17 stops by inertial rotation unless a forced stopping means is separately provided. For example, if a stop signal is issued when the point A on the photoconductor 17 comes into contact with the blade 12, the blade 12 is grounded, so that the photoconductor 17 is not charged during the subsequent inertial rotation. No, the photosensitive member 17 stops completely when a new point B comes into contact with the blade 12 as shown in FIG.

Therefore, on the photosensitive member 17, from point A to B
Although no charging is performed up to the point, the upstream side of the point A (the positive rotation direction side of the photoconductor 17 as shown by a broken line) is “−”.
By the blade 12 to which the polarity voltage was applied,
It is charged to a predetermined potential of “−” polarity.

Then, the toner 32 of "+" polarity attached to the blade 12 is removed from the grounded blade 12.
4 to the “−” charged portion of the photosensitive member 17, the photosensitive member 17 passes through the state shown in FIG. 4 until the point A exceeds the contact portion with the blade 12 by a required amount in the opposite direction.
Is rotated in the opposite direction (the direction of the dashed arrow in FIG. 4). Due to the reverse rotation, the toner 32 attached to the blade 12 is transferred to the “−” charged portion of the photoconductor 17.
At this time, since the blade 12 comes into contact with the photoconductor 17 in the trailing direction (forward direction), there is almost no force for scraping off the toner 32, and the toner 32 of “+” polarity transferred to the photoconductor 17. During the reverse rotation of the photoreceptor 17
Without easily re-adhering to the grounded blade 12, it easily passes through the contact with the blade 12 and its front side (FIG. 4).
To the left).

The toner moved to the front side of the blade 12 is cleaned again by the blade 12 when the photosensitive member 17 rotates in the forward direction by the next image forming operation. At this time, since the voltage changeover switch 33 is switched to the original state, the voltage “−” is applied again from the charging power supply 31 to the blade 12, and the photosensitive member 17 is charged again.

Therefore, after a long time has passed since the image forming apparatus was turned off, when the image is formed again, the toner 32
Does not occur even if the Q / M (unit charge amount) of the toner drops.

The switching of the voltage of the blade 12 to the ground side and the reverse rotation of the photosensitive member 17 as described above may be performed for each transfer of a fixed number of sheets or for each job (for example, for each copy operation). In the above example, the blade 12
Although the voltage switching is performed by grounding, the toner can be transferred from the blade 12 to the photoconductor 17 by superimposing an AC component on the DC voltage.

In the above-described image forming apparatus, the blade 12 which also functions as a cleaning member for cleaning the surface of the photoreceptor 17 is used as a contact charging member. However, the present invention can also be applied to an image forming apparatus that separately includes, for example, a contact charging member dedicated to charging and a cleaning member dedicated to cleaning provided upstream thereof. In this case, when the image carrier rotates in the direction opposite to the direction of image formation, the image carrier is rotated in the reverse direction until the toner transfer portion where the toner has transferred from the contact charging member to the image carrier passes through the cleaning member. Then, at the time of the next image formation, when the image carrier is rotated forward, the toner at the toner transfer portion is removed by the cleaning member.

[0032]

The effects of the present invention are as follows. According to the first to fourth aspects of the present invention, a voltage different from that during image formation is applied to a contact charging member such as a blade while rotating the image carrier in a direction opposite to that during image formation during non-image formation. In order to transfer the toner adhering to the contact charging member to the image carrier side and remove the transferred toner from the image carrier at the time of the next image formation, contact charging is performed with the toner adhered as in the conventional art. It is possible to prevent the member from becoming dirty and causing charging unevenness on the image carrier, thereby preventing the image quality from deteriorating.

According to the fifth and sixth aspects of the present invention,
Voltage switching for temporarily transferring the toner adhered to the contact charging member to the image carrier and removing it again can be easily performed.

According to the seventh aspect of the present invention, the voltage switching for the contact charging member is performed immediately after the stop signal for stopping the image carrier is transmitted, so that the image carrier is reversely rotated immediately thereafter. In addition, the toner can be transferred from the contact charging member to the image carrier side, and the time disadvantage caused by reversing the image carrier side can be minimized.

According to the eighth aspect of the invention, all the toner once transferred from the contact charging member to the image carrier can be removed by the cleaning member, so that the toner is reattached at the time of the next image formation. And scattering of toner can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a contact charging type image forming apparatus to which the present invention is applied.

FIG. 2 is an operation explanatory view showing the rotation of the photosensitive member and the state of voltage application to a blade during image formation.

FIG. 3 is an explanatory diagram of the operation when the charging power supply for the blade is switched to the ground side immediately after the stop signal is sent to the photosensitive member.

FIG. 4 is an explanatory diagram of an operation when toner is transferred from the blade to the photosensitive member while rotating the photosensitive member in the reverse direction.

[Explanation of symbols]

 Reference Signs List 12 blade (contact charging member) 17 photoconductor (image carrier) 32 toner 33 voltage switch (voltage switch)

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kei Yasutomi Ricoh Co., Ltd. 1-3-6 Nakamagome, Ota-ku, Tokyo

Claims (8)

[Claims] In a contact charging type image forming apparatus, a contact charging member is brought into contact with a surface of an image carrier which is driven to rotate and a predetermined charging voltage is applied to the contact charging member to charge the image carrier. Image carrier reverse rotation means for rotating the image carrier in the opposite direction to the image formation at the time of image formation, and applying a voltage applied to the contact charging member during the reverse rotation of the image carrier at the time of image formation. A contact charging type image forming apparatus, comprising: voltage switching means for switching to a different voltage. 2. A contact charging type image forming apparatus, wherein a contact charging member is brought into contact with the surface of a rotating image carrier and a predetermined charging voltage is applied to the contact charging member to charge the image carrier. The image carrier is attached to the contact charging member by switching the voltage applied to the contact charging member to a voltage different from that during image formation while rotating the image carrier in the opposite direction to that during image formation. After transferring the toner to the image carrier side, the transferred toner is removed from the image carrier at the time of the next image formation. 3. The image forming apparatus according to claim 1, wherein the contact charging member is also used as a cleaning member for cleaning a surface of the image carrier. 4. The image forming apparatus according to claim 1, wherein said contact charging member is a blade. 5. The voltage switching means switches the voltage applied to the contact charging member to a voltage different from that used during image formation by grounding the contact charging member during the reverse rotation of the image carrier. The contact charging type image forming apparatus according to claim 1, wherein: 6. The voltage switching unit switches a voltage applied to the contact charging member to a voltage different from that used during image formation by superimposing an AC component on a DC voltage during the reverse rotation of the image carrier. The contact charging type image forming apparatus according to claim 1, wherein: 7. The voltage switching means switches a voltage applied to the contact charging member to a voltage different from that used during image formation immediately after sending a stop signal for stopping the image carrier. The contact-charging type image forming apparatus according to claim 1. 8. The image carrier reverse rotation means, when the image carrier is rotated in a direction opposite to the direction of image formation, a transfer portion of the toner transferred from the contact charging member to the image carrier, 2. The contact-charging type image forming apparatus according to claim 1, wherein the image carrier is reversely rotated to a position where the image carrier passes a cleaning member for cleaning a surface of the image carrier.