JP4664789B2 - Electrophotographic image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus applied to a copying machine, a facsimile, a printer, and the like, and in particular, an electrophotography that maintains the image quality even after printing a large number of sheets by polishing the surface of a photoreceptor when no image is formed. The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus, a corona charger has been generally used as a charging means for charging an electrophotographic photosensitive member as a member to be charged to a predetermined polarity and potential. In this method, a corona charger is disposed in a non-contact manner on the photoconductor to charge the photoconductor to a predetermined polarity and potential. Also, in recent years, compared to the non-contact type corona charging method, there is an advantage such as low ozone generation, so that a charging member (contact charging member) to which a charging bias is applied is brought into contact with a photosensitive member as a member to be charged. Many contact charging methods for charging the surface of the photoreceptor to a predetermined polarity and potential have been put into practical use. Examples of the contact charging member include a roller type (charging roller), a fur brush type, a magnetic brush type, and a blade type (charging blade). Among these, from the viewpoint of uniform charging, a roller charging method using a conductive roller is preferable from the viewpoint of charging stability and is widely used. In particular, Patent Document 1 discloses a contact charging member used in a cleaner-less image forming apparatus that does not have a photosensitive member cleaning unit such as a cleaning blade. Specifically, a conductive fine powder (conductive zinc oxide or the like) is supplied to the surface of the contact charging member (conductive), a voltage is applied to the contact charging member, and the surface of the photoconductor is passed through the conductive fine powder. It is to be charged. The conductive fine powder is also a toner charge control agent, and the conductive fine powder is supplied to the contact charging member via the photosensitive member by a non-contact jumping developing device. The charging roller as the conductive roller is manufactured using a conductive or medium resistance rubber material or foam. Further, there are some which are laminated to obtain desired characteristics. The charging roller has elasticity in order to obtain a certain contact state with the photosensitive member. When the charging roller is brought into pressure contact, the surface potential of the photosensitive member begins to rise if a threshold voltage of a certain level or more is applied. Thereafter, the surface potential of the photoreceptor increases linearly with the applied voltage. The threshold voltage Vth is a charging start voltage determined based on Paschen's discharge law.

In order to obtain the photoreceptor surface potential V0 necessary for the electrophotographic image forming process, it is necessary to apply a DC voltage of (V0 + Vth) to the charging roller, and this charging method is called a DC charging method.
In order to obtain charging uniformity, an AC charging method in which an AC voltage having a peak-to-peak voltage of 2 × Vth or higher is superimposed on a DC voltage of (V0 + Vth) is also used. This utilizes the smoothing effect due to alternating current, and the potential of the photosensitive member converges to V0 which is the median value of the peak of the alternating voltage, and the influence of the resistance value fluctuation caused by the environment of the rubber roller can be suppressed.

  The surface of the photosensitive member is uniformly charged to a predetermined polarity with such a contact charging member, then image exposure is performed by light irradiation based on predetermined document information to form an electrostatic charge image, and this charge image is developed. Thus, a toner image is formed. Subsequently, the toner image is transferred onto a recording material such as paper. From the advantages of low ozone generation and paper transportability as in the above charging method, an elastic body, rubber, and foam that rotate in contact with the photoconductor In general, the toner image is transferred to a recording material such as paper by applying a predetermined voltage to the roller. Finally, the toner image is fixed on the recording material by heating and pressurizing with a fixing roller in the fixing step, thereby forming an image. Further, after the toner image is transferred, the surface of the photoconductor is cleaned by a cleaning blade to remove the remaining toner, and if necessary, the charge is removed by light irradiation or the like, and the next image forming process is performed.

  In addition, since the charging method in the image forming apparatus is a contact method, in addition to the reduction of ozone generated at the time of discharge compared to the conventional discharge type such as scorocolon, charging that causes charging failure and image flow phenomenon. Products etc. will also decrease. As a result, there is no need for a cleaning roller or a polishing roller for the photoconductor, and the pressure contact force can be reduced to reduce the rotational load of the photoconductor.

Japanese Patent Laying-Open No. 2003-5521 (FIG. 1, paragraph 0022)

  However, when a toner whose toner charge adjusting agent is titanium dioxide is used in a normal image forming apparatus (an image apparatus having a cleaning blade or the like), that is, an image apparatus that is not a cleanerless system, it differs from Patent Document 1. Problems arise. This is because when the toner for image formation during normal operation is transported to the photoreceptor cleaning blade and cleaned by the cleaning blade, the metal oxide externally added to the toner particles is released from the toner particles. While acting as an abrasive for the photoconductor, the metal oxide having an outer diameter of about 1/10 or less slips off the cleaning blade while adhering to the surface of the photoconductor, and adheres to the contact charging member in contact with the photoconductor May end up.

  In particular, in drums such as amorphous silicon, the surface hardness is high compared to commonly used organic photoreceptors, and the durability against abrasion during actual use is much higher, but the surface cannot be scraped, so that deposits, Charging failure may occur due to surface accumulation of charged products, etc. Amorphous silicon photoconductor that retains titanium oxide or the like externally added as a charge control material in the toner generally used in one-component development systems etc. in the photoconductor cleaning part Used as a surface abrasive. However, titanium oxide or the like, which is an abrasive, may slip through the cleaning blade, reducing the effect as an abrasive.

  Therefore, the object of the present invention is to polish a photoconductor which has a high surface hardness and the surface cannot be scraped, and which may cause a charging failure due to surface accumulation of deposits, charged products, etc., and is durable even after printing many sheets. An electrophotographic image forming apparatus is provided.

Therefore, in the present invention, when image formation is not performed, an applied voltage output different from the normal image formation operation of the contact charging member is performed, and titanium dioxide which is an external additive attached to the surface of the contact charging member. Once the metal oxide is moved onto the photoconductor, a voltage capable of recovering the metal oxide is applied to the transfer roller that rotates at a predetermined linear velocity difference from the photoconductor, and the photoconductor is polished by the transfer roller. Increase the effect.
Here, the metal oxide as an external additive is physically and chemically very stable, does not change in quality, and is stable in conductivity. Titanium oxide is used because there is no adhesion to the photoreceptor and no effect on the image.

  Specifically, the first means for solving the above-described problems includes a contact charging member that uniformly charges the photosensitive member, a transfer roller that transfers the toner image on the photosensitive member onto the recording member, and contact charging. An electrophotographic image forming apparatus comprising: a control unit that controls a voltage applied to the member and the transfer roller, wherein the control unit applies toner to a contact charging member that uniformly charges the photosensitive member when image formation is not performed. A voltage having the same polarity as that of the externally added external additive is applied to transfer the external additive attached to the contact charging member to the photoconductor, and the transfer roller is in contact with the photoconductor. In other words, a voltage having a polarity opposite to the charging polarity of the external additive is applied, the photoconductor is rotated one or more times, and the photoconductor is polished with the external additive transferred onto the transfer roller.

  As a result, the contact charging roller contaminated with the external additive can be cleaned, and the photoconductor can be cleaned with the external additive peeled off from the contact charging roller.

  The second means is that, in the first means, the peripheral speed of the transfer roller is different from the peripheral speed of the photosensitive member.

  As a result, the external additive after the photoconductor polishing can be effectively collected on the transfer roller.

  A third means is that the external additive is titanium dioxide.

  Thus, the external additive is effectively used as an abrasive for controlling the charging of the toner and cleaning the photoreceptor.

  According to the present invention, there is provided a durable electrophotographic image forming apparatus that polishes a photosensitive member that has a high surface hardness and is difficult to be scraped, and that may cause a charging failure due to surface accumulation of adhered matter and charged product. Provided.

  Embodiments of the present invention will be described below with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only.

[Configuration of this embodiment]

  FIG. 1 is a component layout diagram of the electrophotographic image forming apparatus of the present invention. In this apparatus, a contact charging member, for example, a charging roller 13 (performs uniform charging of the surface of the photosensitive drum 11) is arranged around the photosensitive drum 11 rotating in the clockwise direction in the drawing, and then the exposure device 15 (currently the exposure unit 15). An image is exposed on the surface of the photosensitive drum 11 to form an electrostatic latent image), followed by a developing unit 17 (developing the electrostatic latent image with toner), and then a transfer roller 19 (toner image). Is transferred to a sheet or the like, followed by a cleaning blade 21 (to clean the toner remaining on the photosensitive drum 11), and finally a static elimination lamp 23 (uniform charging of the photosensitive drum 11 by the charging roller 13). Prior to this, the surface potential of the photosensitive drum 11 is uniformly reduced). The toner removed by the cleaning blade 21 is conveyed to a waste toner bottle.

  Note that control means for controlling the voltage applied to the charging roller 13 and the transfer roller 19 is not shown.

  Next, each part of this apparatus will be described.

  FIG. 2 is a cross-sectional view of the photosensitive drum 11. The photosensitive drum 11 includes a carrier blocking layer 29, a photosensitive layer 31, and a surface protective layer 33 formed thereon on a conductive substrate 27. When the hardness of the surface protective layer 33 is high, the present embodiment can be applied regardless of the hardness of the photosensitive layer 31. Even when the surface protective layer 33 is not provided, the present embodiment can be applied even when the photosensitive layer 31 has a high hardness, for example, when amorphous silicon is employed.

The material is not particularly limited as long as it is amorphous silicon (a-Si), and preferred materials include inorganic materials such as a-Si, a-SiC, a-SiO, and a-SiON. Among these materials, a-SiC has a particularly high resistance, and is more suitable as a photosensitive layer material in the present embodiment because it can provide more excellent charging ability, abrasion resistance, and environmental resistance. Moreover, it is preferable to use a specific ratio of Si and C (carbon) in a-SiC. As such a-SiCc, a-Si _(1-x) C _x (X value is less than 0.3 to 1) is more preferable, and X value is more preferably 0.5 to 0.95. It is as follows. This is because such a-SiC has a particularly high resistance of 10 < ¹² > to 10 < ¹³ > [Omega] cm, there is little flow of the latent image in the surface direction of the photoreceptor, and the electrostatic latent image maintaining ability and moisture resistance are reduced. It is because it is also excellent.

  The charging roller 13 is formed, for example, by forming an epichlorohydrin rubber layer on the surface of a metal shaft.

  The developing system in the developing unit 17 is, for example, a method in which a magnetic brush of toner and carrier is formed on a magnetic roller, only the toner is transferred to the developing roll, and a voltage is applied to the developing roll to cause the toner to fly to the photoreceptor. A one-component jumping development system, that is, a hybrid development system. The toner is made of a resin and is used with an external additive applied and charge control. The toner and the carrier with the external additive are charged by friction, and only the toner with the external additive is transferred to the developing roller having a certain gap from the photoreceptor 11. The potential on the magnet roller superimposes alternating current on direct current. The developing system may be a two-component magnetic brush developing system that develops with toner and carrier on a magnetic brush.

  In addition to the function of developing the electrostatic latent image, the developing unit 17 discharges the toner forcibly developing a certain amount of toner depending on the number of printed sheets and the printing rate because the image density changes depending on the external additive state of the toner surface. A mode may be provided.

  The transfer roller 19 is made of a metallic shaft and an elastic member (sponge or rubber), and is pressed against the photoconductor by springs or the like from both ends of the metal shaft. The roller part is made of a conductive foam and rotates with the photosensitive drum 11 with a linear speed difference of 5%.

  Next, the operation of this embodiment will be described.

  The polishing of the photosensitive drum 11 is performed by controlling the voltage applied to the charging roller 13 and the transfer roller 19 by a control unit (not shown) when image formation is not performed. The exposure unit 15, the developing unit 17, and the charge removal lamp 23 are stopped. Further, the cleaning blade 21 remains in a predetermined position.

  First, a voltage having the same polarity as the charging polarity of the external additive is applied to the charging roller 13 to apply a repulsive force to the external additive attached to the charging roller and transfer it to the photoconductor. If the external additive is, for example, positively charged titanium dioxide, the voltage applied to the charging roller 13 is also a positive voltage.

  On the other hand, a voltage having a polarity opposite to the charging polarity of the external additive is applied to the transfer roller 19, and the photoconductor is polished by the transfer roller 19 while attracting the external additive to the photoconductor. If the external additive is, for example, positively charged titanium dioxide, the voltage applied to the transfer roller 19 is a negative voltage. In this way, the photoreceptor is rotated by one or more turns to polish the photoreceptor.

[Example]
In the electrophotographic image forming apparatus, the photosensitive member is polished automatically at a predetermined timing or manually. The external additive as an abrasive was titanium dioxide.

  The photosensitive drum 11 was rotated, a positive DC voltage of 800 V was applied to the charging roller 13, and the titanium dioxide was moved onto the photoreceptor. The voltage applied to the charging roller 13 is 1.0 kV for Vpp and 400 V for Vdc during image formation. Further, at the time of photoconductor rubbing polishing (at the time of photoconductor cleaning), as described above, Vpp is 0V and Vdc is 800V. Further, when the portion where the titanium dioxide had adhered to the photoconductor reached the transfer roller 19, a negative DC voltage of 1500V was applied to the transfer roller 19, and the photoconductor was polished with titanium dioxide. Further, the surface of the photosensitive member was polished by driving the transfer roller 19 for the time required for the photosensitive member to rotate one or more times. The voltage applied to the transfer roller 19 is 0 kV for Vpp and −1300 V to −2000 V for Vdc during image formation. As a result, the drum surface potential is 260V ± 15V. However, Vpp is 0V and Vdc is 1500 to 2200V at the time of photoconductor rubbing polishing (at the time of photoconductor cleaning). The reason is that if the applied voltage is set at the time of image formation, titanium oxide tends to remain on the photosensitive member, and therefore it is preferable to set the transfer bias higher during cleaning. The voltage applied to the developing roller of the hybrid developing device 17 is a rectangular wave, and Vpp is 1.5 kV, Vdc is 150 V, the frequency is 2.4 kHz, and the duty is 40% during image formation. However, since development is not performed at the time of photoconductor rubbing polishing (at the time of photoconductor cleaning), both Vpp and Vdc are 0V.

  Since the surface properties of the transfer roller 19 and the photosensitive drum 11 are completely different, titanium dioxide is collected by the transfer roller 19 if there is a peripheral speed difference. However, the peripheral speed difference is based on the premise that the peripheral speed difference between the sheet and the photosensitive drum 11 is within ± 1% so that transfer deviation or the like does not occur. Therefore, priority is given to transferability, and the peripheral speed difference between the transfer roller 19 and the photosensitive drum 11 is set within ± 6% so that the solid black image is not particularly omitted.

As a material of the transfer roller 19, for example, a sponge (elastic conductive foam having elasticity) such as carbon-based EPDM (10 ⁷ Ω) is preferable from the viewpoint of recovering titanium dioxide from the photoreceptor, and Asker C hardness. When the angle was in the range of 25 to 35 degrees, the photoconductor was rubbed and polished well.

FIG. 2 is a component layout diagram of an electrophotographic image forming apparatus. It is sectional drawing of a photoreceptor.

Explanation of symbols

11 Photosensitive drum 12 Charging cleaning roller 13 Charger (contact charging member)
15 Exposure unit 17 Development unit 19 Transfer roll 21 Cleaning blade 23 Static elimination lamp

Claims (3)

A contact charging member for uniformly charging the photoreceptor;
A transfer roller for transferring a toner image on the photosensitive member onto a recording member;
An electrophotographic image forming apparatus comprising a control means for controlling a voltage applied to the contact charging member and the transfer roller,
The control means includes
When image formation is not performed,
A voltage having the same polarity as the charging polarity of the external additive externally added to the toner is applied to the contact charging member for uniformly charging the photoconductor, and the external additive attached to the contact charging member is applied to the photoconductor. To
While the transfer roller is in contact with the photoconductor, a voltage having a polarity opposite to the charge polarity of the external additive is applied to the transfer roller, and the photoconductor is rotated one or more times, and the transfer roller is rotated. An electrophotographic image forming apparatus, wherein the photoconductor is polished with an external additive transferred to a surface.   2. The electrophotographic image forming apparatus according to claim 1, wherein a peripheral speed of the transfer roller is different from a peripheral speed of the photosensitive member.   2. The electrophotographic image forming apparatus according to claim 1, wherein the external additive is titanium oxide.

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