JPH1031321A - Image forming device - Google Patents

Abstract

(57) [Problem] To form a good image without image unevenness and fogging by suppressing charging unevenness of a photosensitive drum. A charging bias is applied to a charging magnetic brush arranged in contact with a photosensitive drum to uniformly charge the surface of the photosensitive drum. The photosensitive drum 1 has a drum substrate, a charge generation layer, a charge transport layer, a charge injection layer, and the like, and is charged by directly injecting charges from the charged magnetic brush into the charge injection layer. For example, the charge generation layer is formed of a phthalocyanine derivative having a strong spectral sensitivity in a wavelength region longer than around 400 nm, and the charge injection layer is formed by adding zinc oxide having a spectral sensitivity in a short wavelength region of 400 nm or less in a suitable binder resin. It is formed by including it. Immediately before or immediately after charging, by performing a leveling exposure by the leveling exposure device 8 that emits light of 400 nm or less, the apparent resistance of the charge injection layer is temporarily reduced, thereby preventing charging unevenness generated in the charging process. it can.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member used for a copying machine, a laser beam printer or the like, and an image forming apparatus provided with the same.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus such as a copying machine or a laser beam printer, a charging device using a contact charging member is used for a so-called medium-to-low speed machine in which the number of prints per unit time is relatively small. It is heavily used. In this method, a contact charging member such as a charging roller or a charging blade is brought into contact with the surface of an electrophotographic photoreceptor (hereinafter, simply referred to as a “photoreceptor”) (including a case where a minute gap of several hundred μm is provided). A voltage is applied to uniformly charge the surface of the photoreceptor. According to this contact charging member,
There are advantages such as lower ozone and lower power than when a non-contact charging member such as a corona charger using a discharge phenomenon is used. However, even in this case, charging is performed in principle by a discharge phenomenon through a minute gap between the photoconductor and the contact charging member, so that a small amount of ozone is generated and the charging start voltage of the photoconductor is reduced. It is necessary to apply a higher charging voltage.

In order to improve these problems, a charging system for directly injecting electric charge from a contact charging member to a photoreceptor (hereinafter referred to as "charge injection system") is disclosed in, for example, Japanese Patent Application Laid-Open No. 06-00392.
1.

In this charge injection method, a charge injection layer having a float electrode is provided on the surface of a photoreceptor, and a conductive contact charging member such as a charging roller, a charging brush, or a charging magnetic brush is brought into contact with the surface of the photoreceptor. At the same time, a charging voltage is applied to the contact charging member to inject charges directly into the float electrode. Specifically, as the charge injection layer, it is possible to apply and use a dispersion of SnO ₂ particles made conductive with antimony dope as a conductive filler in an acrylic resin on the surface of the photoreceptor. There is a description. The above-described charged magnetic brush is a charging member formed in a brush shape by magnetically constraining conductive magnetic particles by a magnet roll or the like, and performs charging by bringing the brush into contact with a photoconductor. In the injection charging method, since a discharge phenomenon is not used, a DC voltage substantially equal to a desired photoconductor surface potential may be applied to the contact charging member, and ozone is not generated. Further, by superimposing the minimum necessary AC voltage, more stable charging is possible.

FIG. 4 schematically shows the configuration of the entire image forming apparatus when the above-described charge injection type charging apparatus is used as a charger of an electrophotographic image forming apparatus.

The photosensitive member 101 is disposed so as to be rotatable in the direction of arrow R1. A magnetic brush charger 102 and an exposure device 10
3, developing device 104, transfer charger 105, cleaner member 1
06 is arranged. Further, a fixing device 107 is disposed downstream of the photoconductor 101 in the transport direction of the transfer material P.

The above-described charged magnetic brush 102 has an arrow R2
The charging sleeve includes a charging sleeve rotatable in the direction, a magnet roller fixedly disposed inside the charging sleeve, and conductive magnetic particles supported in a spike shape on the charging sleeve surface by the magnetic force.

At the time of image formation, the photosensitive member 101 is moved by an arrow R1
It is driven to rotate in the direction. The charging sleeve of the charging magnetic brush 102 is rotated in the direction of arrow R2 to rub the conductive magnetic particles on the surface against the surface of the photoreceptor 101, and by applying a charging bias to the charging sleeve, the conductive magnetic particles are interposed through the conductive magnetic particles. To uniformly charge the surface of the photoreceptor. As the charging bias at this time, a DC voltage enough to obtain a potential required as a photoconductor surface potential or a superimposed voltage of DC and AC is applied. As a result, the photoconductor surface is charged to a predetermined charging potential. Thereafter, the image is exposed through image exposure by an exposure device 103, toner adhesion by a developing roller 104a of a development device 104, transfer of a toner image onto a transfer material P by a transfer charger 105, fixing of a toner image by a fixing device 107, and the like. The formation is completed.

In the above-described charge injection type charging, since the charge is directly injected from the contact charging member to the photosensitive member to perform charging, the photosensitive member is charged linearly with respect to the bias applied to the contact charging member. can do.

[0010]

However, in the above-described charge injection method, there are gaps in the ears of the charging magnetic brush 102 as a contact charging member, and an AC voltage is applied to the contact charging member. Photoconductor 1 after electrification
01, charging unevenness occurs on the surface, and the charging unevenness causes fogging during development, thereby deteriorating the image quality on the transfer material. here,
Fogging refers to an image defect in which a part which should be a non-image part (blank paper part) is slightly developed and loses optical contrast with the image part.

That is, the photosensitive member reacts sensitively to the contact state between the contact charging member and the photosensitive member and the potential cycle of the AC voltage, and fine charging unevenness occurs on the photosensitive member surface, which causes image unevenness and AC fogging during development. Will be.

On the other hand, if the charging device is configured so as not to cause image unevenness and AC fogging, then the charging potential is reduced due to the reduced charge injection capability, and fog and ghost images appear. This degrades the image quality.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing charging unevenness and charging potential from lowering, and preventing image quality deterioration due to image unevenness and AC fogging. is there.

[0014]

According to a first aspect of the present invention, there is provided an image carrier having a charge generation layer and a charge injection layer, wherein the image carrier is arranged in contact with the image carrier and a charging voltage is applied thereto. A charging unit having a contact charging member for uniformly charging the image carrier, an exposure unit for exposing the charged image carrier surface to form an electrostatic latent image, and a toner adhering to the electrostatic latent image. And a developing means for forming a toner image, wherein the charge injection layer of the image carrier is made of a conductive material whose resistance value can be changed reversibly.

The present invention according to claim 2 is characterized in that the conductive material of the charge injection layer is a photoresponsive conductive material.

The present invention according to claim 3 is characterized in that the conductive material of the charge injection layer is a thermo-responsive conductive material.

According to a fourth aspect of the present invention, the conductive material of the charge injection layer is a conductive material having a different spectral sensitivity from the conductive material of the charge generation layer.

The present invention according to claim 5 is characterized in that the conductive material of the charge injection layer is irradiated with light to cause a reversible change in the resistance value.

The present invention according to claim 6 is characterized in that the conductive material of the charge injection layer is heated to cause a reversible change in resistance.

According to a seventh aspect of the present invention, the reversible change of the resistance value of the conductive material of the charge injection layer is performed by using light having a wavelength inconsistent with the spectral sensitivity of the conductive material of the charge generation layer. Wake up.

According to the present invention, a color for suppressing light of an unnecessary wavelength when performing a leveling exposure for increasing the conductivity of the charge injection layer and an image exposure for forming an electrostatic latent image. It has a cut filter.

According to a ninth aspect of the present invention, the resistance value of the charge injection layer of the image carrier is reversibly changed before charging the image carrier or after charging the image carrier.

According to a tenth aspect of the present invention, the image bearing member has a charge transporting layer, and the charge transporting layer absorbs light for performing a leveling exposure to increase conductivity of the charge injection layer; Further, it is characterized by comprising a substance that transmits light for performing image exposure at the time of forming an electrostatic latent image.

[0024] The present invention according to claim 11 is to use a short-wavelength light for the normalizing exposure for increasing the conductivity of the charge injection layer and to provide a long-wavelength light for the image exposure at the time of forming the electrostatic latent image. Using light.

According to a twelfth aspect of the present invention, the contact charging member includes a charging sleeve, a magnet disposed inside the charging sleeve, and conductive magnetic particles magnetically constrained on the surface of the charging sleeve by the magnet. A charged magnetic brush constituted by:
The method is characterized in that the conductive magnetic particles are arranged in contact with the surface of the image carrier, and a charging voltage is applied to charge the image carrier via the conductive magnetic particles.

According to a thirteenth aspect of the present invention, in the image carrier, the charge injection layer has a resistance of 1 × 10 ⁹ to 1 × 10 ^14.
(Ω · cm).

[Operation] The main operation based on the above constitution (operation corresponding to claim 1) is that the charge injection layer of the image carrier is made of a conductive material whose resistance value can be reversibly changed. Above, low resistance during charging and high resistance during latent image formation, a uniform image with no potential unevenness during charging, and good image without flow during latent image formation Can be output.

[0028]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 schematically shows a schematic configuration of an image forming apparatus according to the present invention.

The image forming apparatus shown in FIG. 1 includes, for example, a drum type electrophotographic photosensitive member (hereinafter, referred to as "photosensitive drum") 1 as an image carrier. The photosensitive drum 1 is rotatably supported by an image forming apparatus main body (not shown), and is driven to rotate in a direction of an arrow R1 by a driving unit (not shown).

Around the photosensitive drum 1, a contact charging member (charging means) 2 for uniformly charging the surface of the photosensitive drum 1, and the surface of the photosensitive drum 1 are exposed in substantially the order along the rotation direction (the direction of the arrow R 1). Exposure means 3 for forming an electrostatic latent image by
A developing unit 4 having a developing roller 4a for applying toner to the electrostatic latent image to develop the toner image; a transfer unit 5 for transferring the toner image on the photosensitive drum 1 to a transfer material P; A cleaning means 6 for removing transfer residual toner remaining on the surface of the drum 1 and a leveling exposure device (or heater) 8 are provided. Further, a transfer unit 7 having a fixing roller 7a and a pressure roller 7b is provided downstream of the photosensitive drum 1 in the transport direction of the transfer material P, and a toner image on the transfer material P is formed here. Be established.

FIG. 2 is an enlarged sectional view showing the layer structure of the photosensitive drum 1 described above. FIG. 1 is a part of a vertical sectional view in a direction intersecting the axis of the drum type photosensitive drum 1.

The photosensitive drum 1 shown in the figure is configured as a drum type as a whole, and is arranged in order from the inside (below the figure).
It is composed of a conductive drum substrate 11 made of aluminum or the like, a charge generation layer 12, a charge transport layer 13, and a charge injection layer 14.

In this embodiment, a photoconductive substance having a spectral sensitivity different from that of the charge generation layer 12 is used for the charge injection layer 14. For example, when a phthalocyanine derivative, cadmium sulfide, amorphous silicon, or the like having strong spectral sensitivity in a wavelength region longer than around 400 nm is used for the charge generation layer 12, the charge injection layer 14 has a spectral sensitivity in a short wavelength region of 400 nm or less. Of a suitable binder resin containing zinc oxide or polyvinyl carbazole having

As the contact charging member 2, for example,
Use a charged magnetic brush. This charged magnetic brush 2
Place a magnet inside the rotatable charging sleeve,
The magnetic force of this magnet causes the conductive magnetic particles to be carried on the surface of the charging sleeve. The conductive magnetic particles are spike-shaped on the surface of the charging sleeve, and the photosensitive drum 1 is moved in the direction of arrow R1
The spike-shaped conductive magnetic particles rub on the surface of the photosensitive drum 1 by rotating the charging sleeve in the direction of arrow R2 while rotating the charging sleeve in the direction of arrow R2. At this time, the surface of the photosensitive drum 1 is uniformly charged, for example, by applying a superimposed voltage in which an AC voltage is superimposed on a DC voltage to the charging sleeve.
This charging is not performed by utilizing a discharge phenomenon, but is performed by, for example, directly injecting a charge into a float electrode (not shown) of the charge injection layer 14.

Immediately before or immediately after the contact charging by the charging magnetic brush 2 on the photosensitive drum 1 having the above-described structure, the charge injection layer 14 is coated with a fluorescent material that emits light having a sensitivity of 400 nm or less. The entire surface is exposed by the fluorescent lamp 8. The exposure at this time is called "normalized exposure".
By this leveling exposure, the apparent resistance of the charge injection layer 14 is temporarily reduced, thereby suppressing the potential unevenness generated in the charging process and forming a uniform potential. Note that the apparent change in the resistance value of the charge injection layer 14 is reversible.

The above-mentioned switching of the wavelength of the exposure light during the normalizing exposure and the image exposure can be realized by using a color cut film that transmits the necessary light and cuts the unnecessary light. Can be.

The surface of the photosensitive drum 1 is uniformly charged by the charging after the above-mentioned exposure or the exposure after the charging. After that, the photosensitive drum 1 is subjected to image exposure by a semiconductor laser having a light emission wavelength in an infrared wavelength region by the exposure means 3 to form an electrostatic latent image. At this time, since light is not absorbed by the charge injection layer 14, it is possible to output a good image without fogging due to uneven charging without causing image deletion. <Embodiment 2> As the photosensitive drum 1 used in the image forming apparatus according to the present invention, a photosensitive drum 1A having a structure shown in FIG. 3 can be used instead of the structure shown in FIG. That is, a conductive drum base 11 made of aluminum or the like, a charge generation layer 12, and a charge injection layer 14 are provided in this order from the inside of the drum type photosensitive drum 1. In FIG. The charge transport layer 13 located between them is omitted. In such a configuration, the operation is almost the same as that of the photosensitive drum 1 of the first embodiment shown in FIG. <Third Embodiment> In a third embodiment, the charge injection layer of the photosensitive drum is replaced with the charge injection layer 14 of the first embodiment, and a heat-responsive conductive material whose conductivity (resistance) changes by heat is used. It is constituted by. That is, in the third embodiment, an ionic conductive substance whose conductivity is easily changed by increasing the temperature, such as polyvinyl carbazole and polyoxyethylene, is introduced into the charge injection layer.

Immediately before or immediately after contact charging by the charging magnetic brush, the entire surface of the photosensitive drum having such a layer structure is exposed to light having a wavelength at which the charge generating layer has no sensitivity, or directly heated by the heater 8. Then, the temperature of the charge injection layer is increased. By this treatment, the apparent resistance of the charge injection layer is temporarily reduced, and potential unevenness generated or generated during the charging process can be suppressed, and a uniform charging potential can be formed.

With the above operation, the charge injection layer is subjected to image exposure on the uniformly charged photosensitive drum with light having a wavelength at which the charge injection layer has no sensitivity, and a latent image is formed. Since it is not absorbed, it is possible to output a good image without fogging due to charging unevenness without causing image deletion. <Embodiment 4> In Embodiment 4, the charge transport layer of the photosensitive drum is replaced with the charge transport layer 13 of Embodiment 1, and a substance exhibiting absorption in the wavelength region of light used for leveling exposure is used. use. As a result, the charge generation layer does not react to the leveling exposure, so that a good image can be output without lowering the potential on the photosensitive drum.

It is necessary that the charge transport layer at this time has no absorption in the wavelength region of the light source used for the latent image forming exposure.

In any of the above-described first to fourth embodiments, the resistance value of the charge injection layer of the photosensitive drum is in the range of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm. Next, each charge injection layer is formed.

[0042]

As described above, according to the present invention,
In an image forming apparatus in which the image carrier is uniformly charged by directly injecting charge into the charge injection layer of the image carrier through a contact charging member arranged in contact with the image carrier, the resistance of the charge injection layer is reduced. By using a reversibly changeable conductive material, for example, it is possible to suppress unevenness in charging, which is likely to be caused by an AC voltage superimposed as a gap between ears or a transfer bias when the contact charging member is a charged magnetic brush, and to reduce image unevenness and A good image without fog can be formed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged cross-sectional view illustrating a layer configuration of a photosensitive drum in the image forming apparatus according to the first embodiment.

FIG. 3 is an enlarged cross-sectional view illustrating a layer configuration of a photosensitive drum in the image forming apparatus according to the second embodiment.

FIG. 4 is a schematic diagram illustrating a schematic configuration of a conventional image forming apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging means (contact charging member, charged magnetic brush) 3 Exposure means 4 Developing means (developing device) 4a Developing roller 5 Transfer means 6 Cleaning means 7 Fixing means 8 Fixing exposure light (fluorescent lamp) ) Or heater 11 drum base 12 charge generation layer 13 charge transport layer 14 charge injection layer P transfer material

Claims (13)

[Claims] 1. An image carrier having a charge generation layer and a charge injection layer, and a contact charging member disposed in contact with the image carrier and applied with a charging voltage to uniformly charge the image carrier. Charging means, exposing means for exposing the charged image carrier surface to form an electrostatic latent image, and developing means for adhering toner to the electrostatic latent image to form a toner image, An image forming apparatus, wherein the charge injection layer of the image carrier is made of a conductive material whose resistance value can be reversibly changed. 2. The image forming apparatus according to claim 1, wherein the conductive material of the charge injection layer is a photo-responsive conductive material. 3. The image forming apparatus according to claim 1, wherein the conductive material of the charge injection layer is a thermo-responsive conductive material. 4. The image forming apparatus according to claim 1, wherein the conductive material of the charge injection layer is a conductive material having a different spectral sensitivity from the conductive material of the charge generation layer. . 5. The image forming apparatus according to claim 2, wherein the conductive material of the charge injection layer is irradiated with light to cause a reversible change in a resistance value. 6. The image forming apparatus according to claim 3, wherein the conductive material of the charge injection layer is heated to cause a reversible change in resistance. 7. The conductive material of the charge injection layer,
The image forming apparatus according to claim 4, wherein a reversible change in the resistance value is caused by using light having a wavelength that does not match the spectral sensitivity of the conductive substance of the charge generation layer. 8. A color cut filter for suppressing light of an unnecessary wavelength when performing a leveling exposure for increasing the conductivity of the charge injection layer and an image exposure for forming an electrostatic latent image. 8. One of claims 1 to 7, characterized in that
An image forming apparatus according to any one of the preceding claims. 9. The image forming apparatus according to claim 1, wherein the resistance of the charge injection layer of the image carrier is reversibly changed before charging the image carrier or after charging the image carrier. Any one
An image forming apparatus according to any one of the preceding claims. 10. The image carrier has a charge transport layer, the charge transport layer absorbs light for performing exposure to increase the conductivity of the charge injection layer, and forms an electrostatic latent image. 10. The image forming apparatus according to claim 1, comprising a material that transmits light for performing image exposure at the time.
An image forming apparatus according to any one of the preceding claims. 11. A process for increasing the conductivity of the charge injection layer, using short-wavelength light for exposure, and using long-wavelength light for image exposure when forming an electrostatic latent image. The image forming apparatus according to claim 10, wherein: 12. The contact charging member includes: a charging sleeve; a magnet disposed inside the charging sleeve;
And a conductive magnetic particle magnetically constrained to the surface of the charging sleeve by the magnet. The charging magnetic brush is arranged by bringing the conductive magnetic particles into contact with the surface of the image carrier. The image forming apparatus according to any one of claims 1 to 11, wherein a charging voltage is applied to charge the image carrier via the conductive magnetic particles. 13. The image carrier according to claim 1, wherein a resistance value of the charge injection layer is in a range of 1 × 10 ⁹ to 1 × 10 ¹⁴ (Ω · cm). 13. The image forming apparatus according to claim 12, wherein: