JP2006220765A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove residues such as toner and external additives adhering to a charging means, particularly external additives, to prevent a charging ability of the charging means from being lowered and to achieve a long life of the charging means. I will provide a.
SOLUTION: A photosensitive member 2 that carries an electrostatic latent image, a charging unit 3 that uniformly charges the photosensitive member 2, an exposure unit 4 that forms an electrostatic latent image on the photosensitive member 2, and a photosensitive member 2. A toner is supplied to the formed electrostatic latent image to form a toner image, and at the same time, a developing unit 5 including a developing roller 5 b that collects toner remaining on the photosensitive member 2, and a photosensitive member formed by the developing unit 5. 2 and the transfer means 6 for transferring the toner image on the recording material 11, using the developing means 5 and the photosensitive member 2, and further changing the voltage applied to the charging means 3 to adhere to the charging means 3. An image forming apparatus 1 that performs a cleaning operation for removing and collecting residues is provided.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus.

  An image forming apparatus using an electrophotographic method is generally configured to include a charging unit, an exposure unit, a developing unit, a transfer unit, a fixing unit, a cleaning unit, and a charge eliminating unit arranged around a photoconductor as an image carrier. The The charging unit uniformly charges the surface of the image carrier. The exposure means exposes light according to image information to the charged image carrier surface to form an electrostatic latent image. The developing means stirs the toner and frictionally charges it, and forms the visible image by attaching the frictionally charged toner to the electrostatic latent image formed on the surface of the image carrier. The transfer means transfers a toner image, which is a visible image, to the recording material by applying a charge having a polarity opposite to that of the toner to the recording material. The fixing unit fixes the toner image transferred by means such as heating and pressing on the recording material. The cleaning unit collects toner remaining on the surface of the image carrier without being transferred to the recording material. The neutralizing unit neutralizes the image carrier after the toner image is transferred. A desired image is formed on the recording material by the image forming apparatus using the electrophotographic system configured as described above.

  Recently, a cleanerless system is known in which toner remaining on the surface of an image carrier without being transferred to a recording material is collected simultaneously with the visualization of an electrostatic latent image by a developing unit. The image forming apparatus using the cleanerless system can be miniaturized because a cleaning unit that collects toner on the surface of the image carrier is unnecessary. Further, by collecting the toner in the developing means, the toner can be reused and waste toner can be eliminated.

  By the way, when image formation is performed by electrophotography, it is desirable from the viewpoint of image stability and reliability that the toner can obtain a stable charge amount that is the same as the initial use stage even when used for a long time. The charge amount of the toner is determined by friction generated by stirring with the developing unit. In addition, the particle size distribution of toner may change with long-term use. When the particle size distribution changes, the fluidity and frictional state of the toner also change, and the charge amount of the toner changes greatly between the initial use stage and after long-term use. When the charge amount of the toner changes in this way, it becomes difficult to obtain a stable image over a long period of time.

  Therefore, conventionally, an external additive such as silica or titanium oxide is added to the toner particles for the purpose of improving fluidity and charging stability. By adding such an external additive to the toner particles, the fluidity of the toner does not change even if the particle size distribution changes, and the toner can be stably charged even after long-term use.

  However, when such a toner containing an external additive is used, there arises a problem that the toner and the external additive adhere as a residue to a charging unit used in direct contact with an image carrier such as a charging roller. If such dirt is attached to the charging means, the charging ability of the charging means is reduced, and the image carrier cannot be uniformly charged, and the image quality of the formed image is lowered.

  As means for solving such a problem, a cleaning means for removing the residue of the contact-type charging means has been proposed (see, for example, Patent Document 1). In the cleaning unit disclosed in Patent Document 1, it is assumed that the residue of the charging unit can be removed by bringing a cleaning brush into contact with the charging unit.

  When such a cleaning unit is used, toner particles having a particle size of several μm among the deposits attached to the charging unit can be removed. However, the external additives such as silica and titanium oxide contained in the toner have a particle size as small as about 10 nm, and the adhesive force when the external additive is attached alone is the adhesive force when the toner is attached together with the toner. It has a property that it is larger than the size and difficult to remove once attached. The cleaning unit disclosed in Patent Document 1 can remove the toner particles adhering to the charging unit, but it is very difficult to remove the external additive contained in the toner.

  In view of this, an image forming apparatus that can remove such an external additive that has a small particle size and is difficult to remove has been proposed (see, for example, Patent Document 2). In the image forming apparatus disclosed in Patent Document 2, a developer having a low content of external additive in the toner is used, and the external additive is removed by bringing a sponge-like cleaning member into contact with the charging unit. Take the configuration.

  However, in the image forming apparatus disclosed in Patent Document 2, the amount of the external additive attached to the charging means is reduced by reducing the content of the external additive, and once the external additive remains. If an object adheres to the charging means, it is difficult to remove external additives such as silica and titanium oxide having a small particle diameter even if a sponge-like cleaning member is used. Further, in such a method in which the cleaning unit is brought into contact with the charging unit to scrape off the adhered matter, the surface of the charging unit may be worn out or scratched, so that the life of the charging unit may be shortened.

JP 2002-108069 A JP 2002-169327 A

  The purpose of the present invention is to efficiently remove the toner, external additives and other residues adhering to the charging means, in particular, external additives to prevent the charging ability of the charging means from being lowered, and to extend the life of the charging means. A cleaning device and an image forming apparatus are provided.

The present invention relates to an image carrier that carries an electrostatic latent image, a charging unit that uniformly charges the image carrier, a latent image forming unit that forms an electrostatic latent image on the image carrier, and the image carrier. A toner is supplied to an electrostatic latent image formed on the body to form a toner image, and at the same time, a developing means having a developer carrier for collecting the toner remaining on the image carrier, and the developing means An image forming apparatus including a transfer unit that transfers the toner image on the image carrier onto the transfer material.
An image forming apparatus characterized in that a cleaning operation for collecting a residue adhering to a charging unit is performed using a developing unit and an image carrier.

In the present invention, the residue adhering to the charging means is
It is characterized by being silica or titanium oxide mixed with the toner as an external additive.

In the present invention, the developing means includes
A developing bias applying means for applying a developing bias to the developing means;
The cleaning operation
The toner in the developing tank of the developing means is attached to the image carrier, and the residue on the charging means is attached to the toner attached to the image carrier by rotation of the image carrier, and the residue is collected on the image carrier. It is implemented by doing.

In the present invention, the charging means is
Charging voltage application means for applying a voltage to the charging means,
The cleaning operation
The toner supplied from the developing unit to the image carrier is transferred from the image carrier to the charging unit by contact between the charging unit and the image carrier, and after the residue on the charging unit is adhered to the toner, the charging unit Applying a voltage having a small absolute value of the discharge starting voltage for charging the body to the charging means, and transferring the toner adhering to the residue from the charging means to the image carrier, the residue on the image carrier It is characterized by being carried out by collecting.

In the present invention, the charging means is
Charging voltage application means for applying a voltage to the charging means,
The cleaning operation
A voltage having the opposite polarity to the toner is applied to transfer the toner from the image carrier to the charging unit, and the residue on the charging unit is attached to the toner. The present invention is characterized in that it is carried out by collecting the residual toner on the image carrier by transferring the adhering toner from the charging means to the image carrier.

In the present invention, the absolute value of the voltage applied to the charging means to recover the residue is
The charging means is smaller than the absolute value of the discharge starting voltage for charging the image carrier.

In the present invention, the transfer means includes
Including a transfer voltage applying means for applying a voltage to the transfer means,
When the residue is collected on the image carrier, a voltage having the same polarity as the toner is applied to the transfer means.

In the present invention, the cleaning operation
It is performed at a timing other than the time of image formation after completion of the image forming operation.

The present invention also provides a print number detecting means for detecting the number of printed sheets, which is the number of printed sheets on a transfer material in the image forming apparatus,
A print number storage means for storing a detection result by the print number detection means,
A cleaning operation is performed in accordance with the detection result of the number of printed sheets stored in the number-of-printed-sheet storage means.

  According to the present invention, an image carrier that carries an electrostatic latent image, a charging unit that uniformly charges the image carrier, a latent image forming unit that forms an electrostatic latent image on the image carrier, A developing means comprising a developer carrier for supplying toner to an electrostatic latent image formed on the image carrier to form a toner image and simultaneously collecting the toner remaining on the image carrier, and the developing means In the image forming apparatus including a transfer unit that transfers the toner image formed on the image carrier onto the transfer material, cleaning that collects the residue attached to the charging unit using the developing unit and the image carrier An image forming apparatus that performs the operation is provided. According to this image forming apparatus, residues such as toner and external additives adhering to the charging unit can be removed, so that the charging unit can be prevented from being deteriorated and the life of the charging unit can be extended. be able to.

  According to the present invention, the residue adhering to the charging means is silica or titanium oxide mixed with the toner as an external additive. According to the image forming apparatus of the present invention, residues such as external additives that are difficult to remove when attached to such charging means can be suitably removed by the cleaning means.

  According to the invention, the developing means includes a developing bias applying means for applying a developing bias to the developing means, and the cleaning operation causes the toner in the developing tank of the developing means to adhere to the image carrier, The rotation is carried out by attaching the residue on the charging means to the toner adhering to the image carrier by rotation and collecting the residue on the image carrier. In such an image forming apparatus, first, toner is forcibly adhered to the surface of the image carrier by application of a development bias from the development bias application unit, and the toner is conveyed to the charging unit side by rotation of the image carrier. The toner to be transported adheres to the surface of the charging means, and residues such as external additives attached to the surface of the charging means adhere so as to enter the dents of the toner particles attached. After the residue is attached to the toner particles in this way, the toner attached to the surface of the charging unit is attached to the image carrier together with the residue and removed from the charging unit. When the cleaning operation of the charging unit is performed in this way, the charging unit surface is not deteriorated and the member is not deteriorated such as generation of scratches, and the life of the charging unit can be extended.

  According to the invention, the charging means includes a charging voltage applying means for applying a voltage to the charging means, and the cleaning operation is performed by contacting the toner supplied from the developing means to the image carrier with the charging means and the image carrier. After transferring from the image carrier to the charging unit and attaching the residue on the charging unit to the toner, the charging unit charges a voltage whose absolute value is smaller than the absolute value of the discharge start voltage for charging the image carrier. It is carried out by collecting the residue on the image carrier by transferring the toner to which the residue adheres to the image carrier from the charging means to the image carrier. In this way, cleaning is performed by switching the voltage applied to the charging means between a voltage larger than the absolute value of the discharge start voltage applied when charging the image carrier and a voltage smaller than the absolute value of the discharge start voltage. Since the operation can be performed, it is not necessary to provide a special cleaning means.

  According to the invention, the charging unit includes a charging voltage applying unit that applies a voltage to the charging unit, and the cleaning operation applies a voltage having a polarity opposite to that of the toner to transfer the toner from the image carrier to the charging unit. Then, after the residue on the charging unit is attached to the toner, the toner is transferred from the charging unit to the image carrier by applying a voltage having the same polarity as the toner to transfer the residue to the image carrier. It is carried out by collecting on the top. Thus, the cleaning operation can be performed by switching the voltage applied to the charging means between the voltage having the same polarity as the toner applied when charging the image carrier and the voltage having the opposite polarity to the toner. There is no need to provide special cleaning means.

  Further, according to the present invention, the absolute value of the voltage applied to the charging unit to collect the residue is smaller than the absolute value of the discharge start voltage for the charging unit to charge the image carrier. In the reversal development method, the charging of the image carrier by the charging unit is performed by applying a voltage having the same polarity as the toner. When the charging unit is cleaned as described above, when the residue together with the toner adheres to the image carrier and is removed from the charging unit, the voltage has the same polarity as that of the toner and is applied to the image carrier by the charging unit. When a voltage having an absolute value larger than the absolute value of the discharge start voltage is applied to the charging means, the image carrier is charged and the surface potential is the same as that of the toner, so that the toner may not adhere to the image carrier. There is. When a voltage having an absolute value smaller than the absolute value of the discharge start voltage is applied to the charging means, the image carrier is not charged and the surface potential of the image carrier hardly changes from the exposed state. Therefore, the difference in surface potential between the charging means and the image carrier can be increased, and the toner can be surely adhered to the surface of the image carrier, so that residues such as toner external additives are sufficiently removed from the charging means. can do.

  According to the invention, the transfer means includes a transfer voltage applying means for applying a voltage to the transfer means, and when the residue is collected on the image carrier, a voltage having the same polarity as the toner is applied to the transfer means. . In this manner, the toner applied to the transfer unit is prevented by switching the voltage applied to the transfer unit between the voltage having the opposite polarity to the toner applied when the toner image is transferred and the voltage having the same polarity as the toner. Therefore, the toner can be reliably conveyed to the charging unit and the charging unit can be suitably cleaned.

  According to the invention, the cleaning operation is performed at a timing other than the time of image formation after the end of the image formation operation. As described above, when the cleaning operation is performed at a timing other than the time of image formation after the end of the image forming operation, a good image can be obtained at the next image formation.

  According to the invention, the number of printed sheets includes a number of printed sheets detecting means for detecting the number of printed sheets, which is the number of sheets printed on the transfer material in the image forming apparatus, and a number of printed sheets storing means for storing a detection result by the number of printed sheet detecting means. Since the cleaning operation is performed according to the detection result of the number of printed sheets stored in the storage unit, the charging unit is cleaned before the number of printed sheets is increased and the charging performance of the charging unit is deteriorated to deteriorate the image quality. be able to.

  FIG. 1 is a cross-sectional view showing a simplified configuration of the image forming apparatus 1 according to the first embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the image forming apparatus 1 shown in FIG. FIG. 2 is an external perspective view of the image forming apparatus 1 shown in FIG. 1. The image forming apparatus 1 includes a photoconductor 2 as an image carrier, a charging unit 3, an exposure unit 4 as a latent image forming unit, a developing unit 5, a transfer unit 6, a fixing unit 7, and a charge removing unit 8. It is comprised including. The image forming apparatus 1 of the present embodiment is characterized in that the charging unit 3 is cleaned using the developing unit 5 and the photoreceptor 2.

  The image forming apparatus 1 according to the present embodiment forms an image by a reversal development method using negatively charged toner. The image forming apparatus 1 of the present embodiment is a cleanerless electrophotographic image forming apparatus that does not include a photosensitive member cleaning unit that removes toner remaining on the surface of the photosensitive member 2. In the present invention, the removal of the toner adhering to the surface of the charging unit 3 and the residue such as the external additive mixed with the toner, particularly the external additive, is called cleaning of the charging unit 3.

  The photosensitive member 2 is an image carrier that carries an electrostatic latent image, and is supported by a driving unit (not shown) so as to be rotatable around an axis, and is provided on a cylindrical conductive substrate (not shown) and the surface of the conductive substrate. And a photosensitive layer to be formed. As the photoconductor 2, those commonly used in this field can be used. For example, a photoconductor having a diameter of 30 mm including an aluminum base tube which is a conductive substrate and an organic photosensitive layer formed on the surface of the aluminum base tube. A drum is used. The organic photosensitive layer is formed by laminating a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. The organic photosensitive layer may include a charge generation material and a charge transport material in one layer.

  The charging unit 3 uniformly charges the surface of the photoreceptor 2 to a potential having a predetermined polarity. Although the charging unit 3 is a charging roller, a contact charging unit such as a charging brush may be used instead of the charging roller. The charging unit 3 includes a metal shaft 3a that supports the charging unit 3 so as to be rotationally driven, a cored bar 3b that covers the periphery of the metal shaft 3a, and a resistance layer 3c that covers the periphery of the cored bar 3b. The charging unit 3 contacts the photoreceptor 2 to form a nip N, and the photoreceptor 2 is charged from the nip N.

  The charging unit 3 is electrically connected to a charging voltage applying unit 9 that applies a voltage having the same polarity as the toner to the charging unit 3. The charging voltage application unit 9 is controlled by a control unit provided in a CPU (not shown). During normal image formation, the charging unit 3 is a voltage larger than the absolute value of the discharge start voltage for charging the photoreceptor 2. For example, a voltage of −1.3 kV is applied to the charging unit 3 to charge the surface of the photoreceptor 2 to −650V. Further, when performing the cleaning operation of the charging unit 3, a voltage having an absolute value smaller than the absolute value of the discharge starting voltage for the charging unit 3 to charge the photoconductor 2, for example, a voltage of −550 V is applied to the charging unit 3. To do.

  Here, if the absolute value of the voltage applied from the charging voltage applying means 9 to the charging means 3 is smaller than the absolute value of the voltage, the surface of the photoconductor 2 is not charged. The discharge start voltage for charging the photosensitive member 2 by the charging unit 3 is a voltage applied to the charging unit 3 when the charging of the surface of the photosensitive member 2 is started.

  The exposure unit 4 is a latent image forming unit that forms an electrostatic latent image on the photosensitive member 2 and forms an electrostatic latent image by irradiating the charged surface of the photosensitive member 2 with laser light corresponding to image information. Since the image forming apparatus 1 according to this embodiment forms an image by the reversal development method, the exposure unit 4 irradiates a portion where an image is formed (a portion where toner is attached and developed) with laser light. A semiconductor laser or the like is used as a laser light source.

  The developing means 5 is electrically connected to a toner storage container 5a for storing toner, a developing roller 5b that faces the photosensitive member 2 and is rotatably provided by a rotating shaft 5c, and a rotating shaft 5c of the developing roller 5b. And a developing bias applying means 10 for applying a developing bias to the roller 5b. The developing means 5 is controlled by the control means (not shown).

  The toner storage container 5a is a container for storing toner made of, for example, hard synthetic resin. The toner container 5a has an opening facing the photoreceptor 2, and the developing roller 5b faces the photoreceptor 2 in a state where a part of the toner container 5a is exposed outwardly from the opening, and the developing roller 5b is slightly separated. Provided. A toner stirring roller (not shown) is provided in the toner container 5a, and the toner is frictionally charged by the stirring of the toner stirring roller and supplied to the developing roller 5b.

  The developing roller 5b is a developer carrying member that supplies toner to the electrostatic latent image formed on the photoreceptor 2 to form a toner image, and at the same time collects toner remaining on the photoreceptor 2; A cylindrical member having a diameter of 25 mm. The developing roller 5b is rotatably supported by the toner storage container 5a via the rotation shaft 5c and is driven to rotate by a motor (not shown).

  In the non-contact development method in which the photosensitive member 2 and the developing roller 5b are provided apart from each other, the toner is applied to the surface of the photosensitive member 2 by causing the charged toner supplied on the developing roller 5b to fly and sit on the surface of the photosensitive member with electric field force. Supply a toner image.

  The developing bias applying means 10 included in the developing means 5 is controlled by a control means (not shown). At the time of image formation, the developing bias applying means 10 has a developing bias having the same polarity as the toner predetermined for the developing roller 5b, for example, Apply a bias of -400V.

  The transfer unit 6 transfers the toner image formed on the photoreceptor 2 formed by the developing unit 5 onto a recording material 11 that is a transfer material such as paper. In the present embodiment, the transfer means 6 is formed in a roller shape, is in contact with the photosensitive member 2 and is provided so as to be rotatable around its axis. The transfer unit 6 presses the recording material 11 against the photosensitive member 2 from the surface opposite to the contact surface of the recording material 11 with the photosensitive member 2, and presses the photosensitive member 2 and the recording material 11 in pressure contact. Provided. The transfer unit 6 includes a transfer voltage application unit 12 that applies a voltage to the transfer unit 6.

  The transfer voltage applying unit 12 is a power source that applies a voltage having the same or opposite polarity to the toner to the transfer unit 6. Which bias is applied to the transfer unit 6 is selected by a transfer voltage switching unit 13 included in the transfer voltage application unit 12. At the time of image formation, the transfer voltage applying unit 12 applies a voltage having a polarity opposite to that of the toner, for example, +3 kV, to the transfer unit 6 and synchronizes with the exposure of the exposure unit 4 by a recording material transport unit (not shown). Thus, the recording material 11 supplied to the transfer means 6 is charged with a polarity opposite to that of the toner, and the toner image formed on the surface of the photoreceptor 2 is transferred onto the recording material 11. On the other hand, during the cleaning operation, a voltage having the same polarity as the toner, for example, a voltage of −0.5 to −2 kV is applied to the transfer unit 6.

  The transfer unit 6 is not limited to the configuration using the transfer roller as described above. For example, the transfer unit 6 may include a transfer belt formed in a belt shape instead of the transfer roller. The transfer unit 6 is not limited to a transfer unit that uses a contact transfer system that directly transfers the toner image to the recording material 11. The transfer unit 6 transfers the toner image to the transfer belt, and the toner image is transferred onto the transfer belt. It may be a transfer means using an intermediate transfer method such as transferring a toner image to a recording material.

  The fixing unit 7 is a thermocompression fixing unit including a heating roller 14 and a pressure roller 15. The heating roller 14 includes heating means (not shown) and is heated to a predetermined temperature. In the present embodiment, the heating roller 14 is provided so as to contact the surface of the recording material 11 on which the toner image is transferred. The fixing unit 7 sequentially receives the recording material 11 onto which the toner image is transferred by the transfer unit 6 and is conveyed by a recording material conveying unit (not shown), passes through the contact portion between the heating roller 14 and the pressure roller 15, and is heated. The toner image is fixed on the recording material 11 by heating and pressing with the roller 14 and the pressure roller 15. The recording material 11 is held between the heating roller 14 and the pressure roller 15 and is conveyed by the rotation of the heating roller 14 and the pressure roller 15.

  The fixing unit 7 is not limited to the one having the heating roller 14 and the pressure roller 15 as described above, and may have a configuration including, for example, a belt-shaped heating member and a pressure member.

  The neutralization unit 8 is configured by a neutralization lamp or the like, and removes the charge on the surface of the photoreceptor 2 after the toner image is transferred to the recording material 11.

  Hereinafter, an image forming operation of the image forming apparatus 1 of the present embodiment will be described. As described above, the image forming apparatus 1 uses negatively charged toner and forms an image by a reversal development method. Further, as described above, the image forming apparatus 1 according to the present embodiment employs a cleanerless system in which the developing unit 5 collects residual toner on the surface of the photoconductor 2 and does not include a cleaning unit for cleaning the photoconductor. Yes.

4A and 4B are diagrams for explaining the change in the surface potential of the photoreceptor 2 and the movement of the toner provided in the image forming apparatus 1 using the cleanerless system. Incidentally, shown Vr, residual potential Vb and V ₀ are respectively the surface of the photoreceptor 2, the surface potential of the photosensitive member 2 is charged by the values and the charging means 3 of the developing bias at the time of image formation.

  FIG. 4A (a) is a diagram illustrating a static elimination process. In the charge eliminating step, the surface of the photoreceptor 2 after the transfer is neutralized by the charge eliminating means 8 so that the potential on the surface of the photoreceptor 2 is made uniform. The potential on the surface of the photoreceptor 2 when uniformed becomes the residual potential Vr. At this time, toners 31 and 32 (hereinafter referred to as residual toners 31 and 32) that remain without being transferred adhere to the surface of the photosensitive member 2. Such residual toners 31 and 32 generally do not have a constant charging polarity, and there are positively charged particles and negatively charged particles.

FIG. 4A (b) is a diagram illustrating a charging process. In the charging step, for example, a voltage of −1.3 kV is applied to the charging unit 3 by the charging voltage applying unit 9, and the surface of the photoreceptor 2 is uniformly negatively charged. At this time, the surface potential of the photosensitive member 2 is the charging potential V ₀ , and V ₀ is, for example, −650V. At this time, the residual toners 31 and 32 are also charged at the same time, and are made to have a negative polarity having the same polarity as that of the toner used for development stored in the toner storage container 5a of the developing unit 5. This phenomenon is peculiar to the reversal development method. In the normal development method, the residual toner is charged with a polarity opposite to that of the toner used for the development.

  FIG. 4A (c) is a diagram showing an exposure process. In the exposure process, the surface of the photosensitive member 2 is exposed by the exposure unit 4 to form an electrostatic latent image corresponding to the image information. At this time, even if a small amount of residual toner 32 exists on the surface of the photoreceptor 2, the spot diameter of the light beam from the exposure unit 4 is sufficiently larger than the particle diameter of the residual toner 32. The resulting exposure unevenness is practically not a problem.

  FIG. 4B (d) is a diagram illustrating a development simultaneous cleaning process. The cleaning in the development simultaneous cleaning step is not cleaning of the charging unit 3 which is a cleaning operation which is a feature of the present invention but cleaning of the photosensitive member 2 performed to remove the toner remaining on the photosensitive member 2. In the development simultaneous cleaning step, toner 33 (hereinafter referred to as development toner 33) used for development is supplied from the developing unit 5 to the surface of the photoreceptor 2. Since all the negatively charged developing toner 33 tends to move to the high potential side (the upper side of the drawing showing the surface potential of the photosensitive member 2), the developing toner 33 has a higher potential than the developing bias Vb (for example, −400 V). The dislocation is transferred to the exposed portion and the exposed portion is developed. At the same time, the residual toner 31 adhering to an unexposed portion (for example, −650 V) having a potential lower than the developing bias Vb is transferred to the developing roller 5 b of the developing unit 5 and collected, and remains from the surface of the photoreceptor 2. The toner 31 is removed. In the reversal development method, the residual toners 31 and 32 are aligned with the same polarity as the toner used for development in the charging step shown in FIG. 4A (b), so that such simultaneous cleaning of development is possible.

  FIG. 4B (e) is a diagram showing a transfer process. In the transfer step, a toner image formed on the surface of the photosensitive member 2 by charging the recording material 11 with a polarity opposite to that of the toner by applying a voltage of, for example, +3 kV to the transfer device 6 by the transfer voltage applying device 12. Transfer on top. At this time, the residual toner 32 is also transferred to the recording material 11 similarly to the developing toner 33.

  As described above, even if toner that remains without being transferred to the recording material 11 is present on the photosensitive member 2, the toner remaining in the portion where the image is not formed (unexposed portion) is collected by the developing unit 5 and is stored in the image. Since fog does not occur, it is not necessary to clean the photoreceptor 2 after the transfer of the toner image onto the recording material. Even if the toner remains in the portion where the image is formed (exposed portion), the light shielding effect by the residual toner at the time of exposure does not cause a problem, and no image defect occurs.

  In the image forming apparatus 1 using such a cleanerless system, it is not necessary to clean the photoconductor 2 after the toner image is transferred to the recording material 11, and therefore photoconductor cleaning means such as a blade for cleaning the photoconductor 2. In addition, a space such as a toner collection box collected by the photosensitive member cleaning unit can be reduced, and the image forming apparatus can be miniaturized. Further, it is possible to prevent the surface of the photosensitive member 2 from being worn and scratched by contact of the photosensitive member cleaning means such as a blade with the photosensitive member 2, and the life of the photosensitive member 2 can be extended.

  Next, the cleaning operation of the charging unit 3 in the image forming apparatus 1 of the present embodiment will be described. FIG. 5 is a view for explaining the cleaning operation of the charging means 3.

  In the cleaning operation of the charging unit 3, the toner is supplied to the photosensitive member 2 by the developing unit 5, the charging unit 3 is cleaned with the toner supplied to the photosensitive member 2, and the external additive 41 is generated by cleaning the charging unit 3. Each step of collecting the toner 42 containing a large amount by the developing means 5 is included. The cleaning operation of the charging unit 3 is started when a control signal is sent to the charging unit 3 and the developing unit 5 from a control unit (not shown) that controls the entire operation of the image forming apparatus 1.

  The toner supply to the photoreceptor 2 by the developing unit 5 is performed in the same manner as in normal image formation, and a developing bias having the same polarity as the toner is applied to the developing roller 5b to remove the negatively charged toner. This is performed by forcibly adhering to the surface of the photoreceptor 2 to be neutralized by 8. When a developing bias having the same polarity as that of the toner 42 is applied to the developing roller 5b, the toner 42 having a negative charge is forcibly attached to the surface of the photoreceptor 2 to be neutralized by the neutralizing means 8. The developing bias Vb at this time is, for example, −400 V, which is the same as that during image formation.

  The photoreceptor 2 to which the toner 42 is attached reaches the contact portion with the transfer means 6 by its own rotation. Here, as described above, a control signal is also sent to the transfer means 6 in synchronization with the control means (not shown) issuing a control signal to the charging means 3 and the developing means 5. The transfer means 6 has a voltage (−) having the same polarity as that of the toner 42, which is a voltage different from the case where the toner 42 is transferred to the recording material 11 by the transfer voltage switching means 13 provided in the transfer voltage applying means 12, for example, −0. Switch to apply 5 to -2 kV to transfer means 6. In this way, by changing the polarity of the voltage applied to the transfer unit 6 to the same polarity (−) as that of the toner, it is possible to prevent the toner 42 from adhering to the transfer unit 6, and the charging unit 3 and the photoreceptor 2. Thus, the toner 42 can be reliably fed to the abutting portion, and the charging unit 3 can be suitably cleaned. The photoconductor 2 that has passed through the contact portion with the transfer means 6 further rotates to reach the contact portion with the charging means 3.

  In the cleaning of the charging unit 3 with the toner supplied to the photosensitive member 2, first, the toner 42 fed to the contact portion with the charging unit 3 by the rotation of the photosensitive member 2 is transferred between the charging unit 3 and the photosensitive member 2. The photosensitive member 2 is transferred to the charging means 3 by contact. Next, the external additive 41 on the charging unit is attached to the toner 42 thus transferred to the charging unit 3.

  The external additive 41 such as silica or titanium oxide has a property of easily adhering to the toner 42. Therefore, when the toner 42 adheres to the charging unit 3, the external additive 41 is separated from the charging unit 3 and adheres to the toner 42 so as to enter the recess of the toner particles contained in the toner 42.

  Thereafter, a voltage having an absolute value smaller than the absolute value of the discharge starting voltage for charging the photoreceptor 2 by the charging unit 3, for example, a voltage of −550 V, is applied to the charging unit 3, and the toner to which the external additive 41 adheres is applied. 42 is transferred to the photoreceptor 2 by electrostatic force acting from the charging means 3. In this way, the external additive 41 can be removed from the charging means 3.

  The toner 42 containing a large amount of the external additive 41 generated by the cleaning of the charging unit 3 is collected by the developing unit 5 by a control unit (not shown) by applying a voltage applied from the developing bias applying unit 10 to a voltage applied during image formation. The developing bias applying unit 10 is controlled so that a voltage having an absolute value smaller than the absolute value is applied to the developing unit 5, and a potential difference is formed between the photosensitive member 2 and the developing unit 5. The toner 42 to which the external additive 41 transferred to 2 adheres is transferred from the photoreceptor 2 to the developing means 5 by electrostatic force and collected.

  In the present embodiment, in order to increase the recovery efficiency of the toner 42, the developing roller 5b is grounded without applying a developing bias. That is, a voltage of 0 V is applied to the developing roller 5b.

  When a two-component developer is used as the developer, the toner is negatively charged, but the carrier that carries the toner and adheres to the developing roller 5b is positively charged. Therefore, when a two-component developer is used as the developer, an electrostatic force acts on the toner from the carrier, so that it can be recovered in the developing means 5 without changing the applied bias.

  Such a cleaning operation of the charging unit 3 is preferably performed at a timing other than the time of image formation after the end of the image formation operation. By cleaning the charging unit 3 at such timing, a good image can be obtained at the next image formation.

  Note that the cleaning operation of the charging unit 3 is not limited to being performed every time image formation is completed, and for example, the user may select whether to clean the charging unit 3 or not.

  The cleaning operation of the charging unit 3 may be performed when a predetermined number of sheets is reached by a CPU control unit (not shown). In such a case, the CPU (not shown) includes a print number detection unit that detects the number of prints that is the number of sheets printed on the transfer material in the image forming apparatus, and a print number storage unit that stores a detection result by the print number detection unit. And a control signal is issued so that the control means performs a cleaning operation in accordance with the detection result of the number of printed sheets stored in the printed number storage means.

  When the cleaning operation of the charging unit 3 is performed at such timing, the charging unit 3 can be cleaned when the predetermined number of sheets is reached, the number of printed sheets is increased, and the charging performance of the charging unit 3 is improved. The charging unit 3 can be cleaned before the image quality of the formed image deteriorates.

  The image forming apparatus 1 of the present embodiment uses a cleaner-less method and is not provided with a photosensitive member cleaning unit such as a blade. Therefore, the toner 42 adhering to the surface of the photosensitive member 2 is cleaned before reaching the charging unit 3. Not removed by means. For this reason, since the toner 42 can be adhered to the charging means 3, the external additive 41 can be suitably removed from the charging means 3.

  Further, the image forming apparatus 1 according to the present embodiment is configured such that the voltage applied to the charging unit 3 as described above is a voltage whose absolute value is smaller than the absolute value of the discharge start voltage for the charging unit 3 to charge the photosensitive member 2. And the charging means 3 by controlling and changing the voltage having a larger absolute value than the absolute value of the discharge starting voltage for charging the photosensitive member 2, the external additive 41 and the toner 42 adhered to the charging means 3. Can be efficiently removed. Further, the cleaning of the charging unit 3 is performed by changing the magnitude of the voltage. Therefore, the deterioration of the member such as the surface of the charging unit 3 and the generation of scratches can be prevented, and the long life of the charging unit 3 can be prevented. Can be achieved.

  FIG. 6 is a cross-sectional view showing a simplified configuration of the image forming apparatus 51 according to the second embodiment of the present invention. The image forming apparatus 51 of the present embodiment is similar to the image forming apparatus 1 of the first embodiment described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted.

  In the image forming apparatus 51 of the present embodiment, the charging voltage applying unit 53 included in the charging unit 52 can switch the voltage applied to the charging unit 52 between a voltage having the same polarity as the toner and a voltage having the opposite polarity to the toner. The development bias switching means 54 includes a voltage switching means 54, and a development bias application means 56 included in the development means 55 can switch the voltage applied to the development means 55 between a voltage having the same polarity as the toner and a voltage having a polarity opposite to that of the toner. Means 57 is provided.

  The charging unit 52 includes a charging voltage applying unit 53 that applies a voltage having the same or opposite polarity to the toner to the charging unit 52, and the polarity of the voltage applied to the charging unit 52 by the charging voltage applying unit 53 is the same as that of the toner. And voltage switching means 54 for selecting and switching from either of the reverse polarities.

  The voltage switching unit 54 operates so as to apply a voltage having the same polarity as the toner from the charging voltage applying unit 53 to the charging unit 3 when a normal image is formed. During normal image formation, the charging voltage applying unit 53 applies, for example, a voltage of −1.3 kV to the charging unit 52, thereby charging the photoreceptor to −650 V. When the cleaning of the charging unit 52 is performed, the voltage switching unit 54 issues a control signal from the control unit (not shown) so as to perform the cleaning operation on the charging unit 52, and the charging voltage applying unit 53 applies the charging unit 52 to the charging unit 52. Thus, it operates so as to apply a voltage having a polarity opposite to that of the toner.

  The developing unit 55 includes a developing bias applying unit 56 that applies a developing bias to the developing unit 55 and a developing bias switching unit 57. The developing bias applying unit 56 applies a developing bias having the same polarity or opposite polarity to the toner to the developing roller 5b. Which developing bias is applied to the developing roller 5b is selected by a developing bias switching means 57 provided in the developing bias applying means 56. In a normal image forming operation, the developing bias switching unit 57 operates so that a bias having the same polarity as the toner is applied to the developing roller 5b. At the time of image formation, the developing bias applying unit 10 applies a developing bias having the same polarity as the toner, for example, −400 V, to the developing roller 5b.

  On the other hand, when the cleaning operation is performed, a control signal is also sent to the developing means 55 in synchronization with a control means (not shown) sending a control signal to perform the cleaning operation on the charging means 3. . The developing means 55 from which the control signal has been issued applies a bias having the same polarity as the toner to the developing roller 5b so that the toner is forcibly attached to the surface of the photoreceptor 2 by the developing bias applying means 56, and then the charging means 52. In order to collect the toner adhering to the surface of the photoreceptor 2 after the cleaning, a bias having a polarity opposite to that of the toner is applied to the developing roller 5b.

  The cleaning operation of the charging unit 52 in the image forming apparatus 51 will be described. In the cleaning operation of the charging unit 52, as in the first embodiment, the toner is supplied to the photosensitive member 2 by the developing unit 55, the charging unit 52 is cleaned by the toner supplied to the photosensitive member 2, and the charging is performed. The recovery of the toner containing a large amount of the external additive generated by the cleaning of the means 52 by the developing means 55 is included.

  The toner supply to the photosensitive member 2 by the developing means 55 is performed by applying a developing bias having the same polarity as the toner to the developing roller 5b to remove the negatively charged toner, as in the first embodiment. This is performed by forcibly adhering to the surface of the photoreceptor 2 to be neutralized by 8.

  The photosensitive member 2 to which the toner is attached reaches the contact portion with the transfer means 6 by its own rotation. Similar to the first embodiment, a voltage having the same polarity as the toner is applied to the transfer unit 6 to prevent the toner from adhering to the transfer unit 6. The photoreceptor 2 that has passed through the contact portion with the transfer means 6 further rotates to reach the contact portion with the charging means 52.

  Cleaning of the charging unit 52 with the toner supplied to the photosensitive member 2 is performed by attaching the toner fed by the photosensitive member 2 to the charging unit 52, attaching an external additive to the toner, and then removing the external additive and the toner. It is carried out by removing from the charging means 52 and adhering it to the photosensitive member 2, specifically as follows.

  First, a voltage (+) having a polarity opposite to that of the toner, for example, a voltage of +200 V is applied to the charging unit 52 by the charging voltage applying unit 53, and the toner supplied from the developing unit 55 to the photoreceptor 2 is electrically charged. Adhere to. Here, to the toner adhering to the charging unit 52, the external additive adhering to the charging unit 52 adheres as in the first embodiment. Next, the voltage applied to the charging unit 52 is changed to a voltage (−) having the same polarity as that of the toner, and the toner to which the external additive adheres is removed from the charging unit 52 and transferred to the photoreceptor 2. In this way, the external additive can be removed from the charging means 52.

  Here, it is preferable that the absolute value of the voltage having the same polarity as that of the toner is smaller than the absolute value of the discharge start voltage to the photosensitive member 2 by the charging unit 52. When the toner to which the external additive adheres adheres to the surface of the photoreceptor 2 and is removed from the charging unit 52, the voltage (−) has the same polarity as the toner and is greater than the absolute value of the discharge start voltage of the charging unit 52. When a voltage having a large absolute value is applied to the charging unit 52, the photosensitive member 2 is negatively charged, and the surface potential is the same polarity (−) as that of the toner, so that the toner may not adhere to the photosensitive member 2.

  On the other hand, when a voltage having an absolute value smaller than the absolute value of the discharge start voltage is applied to the charging unit 52, the photoconductor 2 is not charged and the surface potential of the photoconductor 2 does not change from the neutralized state. As a result, the difference in surface potential between the charging means 52 and the photoconductor 2 can be increased, and the toner can be reliably adhered to the surface of the photoconductor 2.

  The recovery of toner containing a large amount of external additives generated by cleaning of the charging unit 52 by the developing unit 55 is performed by the developing bias switching unit 57 from the developing bias applying unit 56 to the developing roller 5b. For example, it is performed by operating so as to apply + 200V. By applying a bias having a polarity opposite to that of the toner to the developing roller 5b, the toner and the external additive adhering to the toner are collected in the developing unit 55 via the developing roller 5b.

  Here, the recovery of toner by applying a bias having a polarity opposite to that of the toner to the developing roller 5b is more efficient than the recovery of toner in which the bias described in the first embodiment is not applied to the developing roller 5b. Can be increased. However, in the collection of this embodiment in which a bias having a polarity opposite to that of the toner is applied to the developing roller 5b, the adhesion force of the toner to the developing roller 5b becomes too strong, and the toner may be fixed on the surface of the developing roller 5b. Therefore, the voltage applied to the developing roller 5b is preferably less than or equal to one half of the absolute value of the developing bias applied during image formation.

  As described above, the image forming apparatus 51 of the present embodiment can also remove residues such as external additives attached to the charging unit 52, and the same effect as the image forming apparatus 1 of the first embodiment. Can be played.

1 is a cross-sectional view showing a simplified configuration of an image forming apparatus 1 according to a first embodiment of the present invention. FIG. 2 is an enlarged view of a main part of the image forming apparatus 1 shown in FIG. 1. FIG. 2 is an external perspective view of the image forming apparatus 1 shown in FIG. 1. FIG. 3 is a diagram for explaining a change in surface potential of a photoconductor 2 provided in an image forming apparatus 1 using a cleanerless system and a toner movement. FIG. 3 is a diagram for explaining a change in surface potential of a photoconductor 2 provided in an image forming apparatus 1 using a cleanerless system and a toner movement. FIG. 4 is a diagram for explaining a cleaning operation of the charging unit 3. It is sectional drawing which simplifies and shows the structure of the image forming apparatus 51 which is 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,51 Image forming apparatus 2 Photoconductor 3,52 Charging means 4 Exposure means 5,55 Developing means 6 Transfer means 7 Fixing means 8 Static eliminating means 9,53 Charge voltage applying means 10,55 Developing bias applying means 11 Recording material 12 Transfer Voltage application means 13 Transfer voltage switching means 14 Heating roller 15 Pressure roller 54 Charging voltage switching means 57 Development bias switching means

Claims (9)

An image carrier that carries an electrostatic latent image, a charging unit that uniformly charges the image carrier, a latent image forming unit that forms an electrostatic latent image on the image carrier, and formed on the image carrier A toner is supplied to the electrostatic latent image to be formed to form a toner image, and at the same time, a developer having a developer carrier that collects the toner remaining on the image carrier, and the image formed by the developer In an image forming apparatus including a transfer unit that transfers a toner image on a carrier onto a transfer material,
An image forming apparatus, wherein a cleaning operation for collecting a residue adhering to a charging unit is performed using a developing unit and an image carrier. The residue adhering to the charging means is
2. The image forming apparatus according to claim 1, wherein the external additive is silica or titanium oxide mixed with the toner. Development means
A developing bias applying means for applying a developing bias to the developing means;
The cleaning operation
The toner in the developing tank of the developing means is attached to the image carrier, and the residue on the charging means is attached to the toner attached to the image carrier by rotation of the image carrier, and the residue is collected on the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is implemented. The charging means is
Charging voltage application means for applying a voltage to the charging means,
The cleaning operation
The toner supplied from the developing unit to the image carrier is transferred from the image carrier to the charging unit by contact between the charging unit and the image carrier, and after the residue on the charging unit is adhered to the toner, the charging unit Applying a voltage having an absolute value smaller than the absolute value of the discharge start voltage for charging the body to the charging means to transfer the toner to which the residue adheres from the charging means to the image carrier, thereby removing the residue from the image carrier. The image forming apparatus according to claim 3, wherein the image forming apparatus is implemented by collecting the image on the top. The charging means is
Charging voltage application means for applying a voltage to the charging means,
The cleaning operation
A voltage having the opposite polarity to the toner is applied to transfer the toner from the image carrier to the charging unit, and the residue on the charging unit is attached to the toner. 4. The image forming apparatus according to claim 3, wherein the toner is adhered to the image carrier by transferring the toner adhering to the image carrier to collect the residue on the image carrier. The absolute value of the voltage applied to the charging means to recover the residue is
6. The image forming apparatus according to claim 5, wherein the charging means is smaller than an absolute value of a discharge start voltage for charging the image carrier. The transfer means is
Including a transfer voltage applying means for applying a voltage to the transfer means,
The image forming apparatus according to claim 1, wherein when the residue is collected on the image carrier, a voltage having the same polarity as the toner is applied to the transfer unit. The cleaning operation
The image forming apparatus according to claim 1, wherein the image forming apparatus is performed at a timing other than the time of image formation after the end of the image forming operation. A number-of-printing-sheet detecting means for detecting the number of printed sheets that is the number of printed sheets on the transfer material in the image forming apparatus;
A print number storage means for storing a detection result by the print number detection means,
8. The image forming apparatus according to claim 1, wherein a cleaning operation is performed in accordance with a detection result of the number of printed sheets stored in the number of printed sheets storage unit.

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