JPH0580541A - Image forming device - Google Patents

Abstract

PURPOSE:To attain the extension of the service life of a carrier, the stabilization of image quality for a long period, and the improvement of the reliability of a process by reducing stress applied to the carrier and a photosensitive body. CONSTITUTION:In this image forming device supplying a developer 71 to the side of the sensitive layer 27 of the photosensitive body 21, to form a developer puddle 73, and exposing an image from the side of the light transmissive conductive layer 25 of the photosensitive body 21, as the carrier of the developer, a conductive magnetic carrier having the formation of a conductive layer on the surface of a base grain incorporating a magnetic material grain in binder resin, in used, and when the surface roughness of the photosensitive body 21 is defined as (r), the average grain diameter of the carrier is defined as (Rc), and the average grain diameter of the magnetic material grain is defined as (Rm), (r)<=Rc, preferably, (r)<=Rm is set.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus used in printers, digital copying machines, facsimiles, copying machines and the like.

[0002]

2. Description of the Related Art An electrophotographic system represented by the Carlson system is widely used at present, in which uniform charging of a photoconductor is carried out → latent image formation by selective exposure → toner image formation by a developer →
The basic process is transfer → fixing.

On the other hand, various reports have recently been made on a non-Carlson image forming method which employs the backside exposure recording method, and it is said that the apparatus can be downsized and the process can be simplified. Journal, 16, (5),
306, (1987), JP-A-61-149968, JP-A-63-10071, and JP-A-63-214781.
Publication).

The backside exposure recording system is one in which a developer is supplied to the surface side of a photoreceptor to form a developer pool, and cleaning and rear image exposure-simultaneous development are carried out by this developer pool. (Signal) exposure and development can be performed simultaneously.

However, since it is necessary to inject an electric charge through the developer, the toner is required to be conductive in the one-component developer, and the conductive magnetic toner is used. Therefore, plain paper transfer cannot be performed using an electrostatic transfer method such as a corona transfer method or a bias roller transfer method.
Use of high resistance paper is required.

On the other hand, as a method using an insulating toner, a two-component developer consisting of an iron powder carrier of 10 ⁴ to 10 ⁸ Ω · cm and an insulating magnetic toner is used, and a charging bias electrode and a developing bias electrode are used. It is reported that two counter electrodes of No. 2 are provided and the image is formed by performing rear surface image exposure-simultaneous development (Electrophotographic Society, Vol. 27, No. 27).
3, p442, 1988, JP-A-61-46961).

However, when this system is mounted on an actual machine, it is difficult to control in practice, stable and clear images cannot be obtained, and the structure of the apparatus is complicated.

Therefore, the present applicant has previously used a two-component developer comprising a conductive magnetic carrier having a conductive layer formed on the surface of mother particles in which magnetic particles are contained in a binder resin, and an insulating toner. , Proposed to form an image by rear image signal exposure-simultaneous development (Japanese Patent Application No. 3-207).
554).

The present inventor diligently studied this image forming process and found that the surface roughness of the photosensitive member is a major factor that greatly affects the life of the carrier.

As a prior art relating to the surface roughness of the photosensitive member and the size of the developer in the back exposure recording system, there is JP-A-59-228256. Here, the maximum surface roughness of the image bearing member is set to 20 μm, and the average surface roughness r thereof is set to satisfy the relationship of r ≦ 2d with respect to the average particle diameter d of the toner. It is stated that the residual toner particles on the (photoconductor surface) can be completely recovered to prevent the accumulation of contamination on the surface of the image carrier.

However, this technique effectively cleans the toner by reducing the contact area between the surface of the photosensitive member and the toner, and prevents the stain on the photosensitive member due to the adhesion of the toner itself. This is from the viewpoint of use for displaying images. As described above, JP-A-59-228256
The publication does not consider the durability of the developer, especially the carrier, or the image quality maintenance of the recorded image obtained by transferring the formed toner image, and it is completely different in technical idea from the invention of the present application. is there.

[0012]

SUMMARY OF THE INVENTION The present invention provides an image forming apparatus capable of extending the life of a carrier and forming a stable image for a long period of time.

[0013]

An image forming apparatus of the present invention comprises a photoconductor having a photoconductive layer on a translucent conductive support, and a photoconductive layer disposed on the photoconductive layer side of the photoconductor. In a image forming apparatus having a developing means for supplying to the surface of a photoconductor and an exposing means arranged on the side of a light-transmitting conductive support of the photoconductor so as to face the developing means, a binder is used as a carrier of the developer. When a conductive magnetic carrier in which a conductive layer is formed on the surface of mother particles containing magnetic particles in a resin is used, and the average particle diameter of the carrier is Rc and the surface roughness of the photoreceptor is r, It is characterized in that r ≦ Rc.

Further, when the average particle diameter of the magnetic particles is Rm, by setting r ≦ Rm, the performance can be further improved.

[0015]

1 is an explanatory view showing an embodiment of an image forming apparatus of the present invention. A transparent conductive layer 25 and an amorphous silicon (a-Si) -based photosensitive layer 27 are formed on a light-transmitting hollow-cylindrical translucent support 23 such as glass, and the drum-shaped photosensitive body 21 is formed. It is configured. Also,
Instead of the drum-shaped photoconductor 21, a belt (sheet) photoconductor may be used. As the photosensitive layer 27, in addition to an a-Si photosensitive layer, any of an a-C type, an a-Se type, and various organic photosensitive layers can be adopted, but it has high photosensitivity, high hardness, and high durability. The a-Si photosensitive layer is desirable in that it is excellent, and it provides a stable image for a long period of time.

FIG. 2 shows such an a-Si type photosensitive member 2.
2 is an explanatory cross-sectional view showing details of the layer structure of No. 1, in which a carrier-side carrier injection blocking layer 26, an a-Si based photoconductive layer 29, and a carrier injection blocking surface layer 28 are laminated to form a photosensitive layer 27. The layer 27 is formed on the transparent conductive layer 25 to form the photoconductor 21.

The carrier-side carrier injection blocking layer 26 is a carrier from the light-transmissive conductive layer 25 to the a-Si based photoconductive layer 29 when the surface of the photosensitive member 21 contacts the developer 71 while applying a bias voltage. The image noise is removed by increasing the electrostatic charge contrast between the exposed portion and the non-exposed portion to improve the image quality and reduce the background fog during development.

An insulating layer, a high resistance layer, or an a-Si-based p-type or n-type semiconductive layer can be used as the carrier-side carrier injection blocking layer 26. Here, the insulating layer is
It has a very high volume resistivity and has the property of blocking the transfer of both positive and negative polar charges inside the layer. The high resistance layer means a layer having a volume resistivity smaller than that of the insulating layer but larger than that of the photoconductive layer. In particular, a material having a property of blocking the transfer of charges of one polarity but permitting the transfer of charges of the other polarity inside the layer is preferable for the photoreceptor.

The carrier-side carrier injection blocking layer 26 has an electrical characteristic of blocking the injection of carriers from the transparent conductive layer 25 and does not absorb image exposure light from the transparent support 23 side. Has a high light-transmitting property (a large optical band gap or a high light transmittance), and further has good adhesion to the light-transmitting conductive layer 25 and the a-Si-based photoconductive layer 29.
It is necessary to have a characteristic that the quality of the a-Si-based photoconductive layer 29 does not significantly change even when it is heated.

The insulating layer used for the carrier-side carrier injection blocking layer 26 is an insulating amorphous silicon carbide (a-SiCx), amorphous silicon oxide (a-SiOx), amorphous silicon nitride (a-SiNx), a-. SiC / O, a-SiC /
A-Si such as N, a-SiO / N, a-SiC / O / N
System insulation layer, polyethylene terephthalate, parylene,
It is preferable to use polytetrafluoroethylene, polyimide, polyfluoroethylenepropylene, urethane resin, epoxy resin, polyester resin, polycarbonate resin, cellulose acetate resin, or other organic insulating layer. In forming the a-Si-based insulating layer, it is possible to use a material in which the contents of C, N, O, etc. are changed in the layer thickness direction.

As the high resistance layer used for the carrier-side carrier injection blocking layer 26, a-SiCx and a-Si are particularly preferable.
Ox, a-SiNx, a-SiO.N, a-SiC.O
A preferable high resistance layer of a-Si system such as N is
Compared to the i insulating layer, the content of carbon (C), oxygen (O), and nitrogen (N) is reduced, or the film forming conditions are adjusted appropriately.

The a-Si-based p-type or n-type semiconductor layer used for the carrier-side carrier injection blocking layer 26 is a.
In order to make the optical bandgap larger than that of the —Si-based photoconductive layer 29, or to further improve the adhesiveness, an element such as C, O, or N is contained, and the light-transmitting conductive layer 25 is added. An impurity element is contained to prevent carrier injection. That is, in order to prevent the injection of negatively charged carriers, 1 to 1 elements of the Group IIIa element of the periodic table (hereinafter, the Group IIIa element of the periodic table is abbreviated as the IIIa element) are used.
0000 ppm, preferably 100-5,000 ppm
On the other hand, in order to prevent the injection of positive charge carriers, on the other hand, in order to prevent the injection of positive charge carriers, a group Va element of the periodic table (hereinafter, a group Va element of the periodic table is abbreviated as a group Va element) is added at 5,000 pp.
m or less, preferably 300 to 3,000 ppm. Then, these elements may be provided with a gradient in the layer thickness direction, in which case the average content of the entire layer may be within the above range.

Thus, the carrier injection blocking layer 2 on the support side
When III contains a Group IIIa element, a positive development bias is used, while when it contains a Va group element, a negative development bias is used.

Here, as the group IIIa element and the group Va element, the element B and the element P, respectively, have excellent covalent bond properties and can sensitively change the semiconductor characteristics, and in addition, an excellent injection blocking ability can be obtained. Desirable in terms.

The thickness of the support carrier injection blocking layer 26 is
The range is preferably 0.01 to 5 μm, and more preferably 0.1 to 3 μm, whereby it is easy to secure a good injection blocking ability, and unnecessary absorption of exposure in the support carrier injection blocking layer 26 is suppressed. As a result, photocarriers can be effectively generated in the a-Si-based photoconductive layer 29, and an increase in residual potential can be suppressed.

The a-Si-based photoconductive layer 29 is formed by, for example, glow discharge decomposition method, sputtering method, ECR method, vapor deposition method or the like, and hydrogen (H) or a halogen element for the termination of the dangling bond is used in the formation thereof. -40% by atom. Further, in order to obtain desired characteristics with respect to electrical characteristics such as dark conductivity and photoconductivity of the a-Si-based photoconductive layer 29 and optical bandgap, IIIa group element and V
It is advisable to include an a-group element or an element such as C, N or O. Above all, when a-SiC is used for the photoconductive layer 29,

[0027]

[Chemical 1] X value of 0 <x ≦ 0.5, preferably 0.05 <x ≦ 0.
It is good to set it in the range of 45, and in this range, a-
It is desirable in that the resistance becomes higher than that of the Si layer and good carrier travel can be ensured. IIIa group elements and V
As the a-group element, B element and P element are desirable because they have excellent covalent bond properties and can sensitively change semiconductor characteristics, and in addition, excellent photosensitivity characteristics can be obtained.

Further, in the a-Si photoconductive layer 29,
When a layer region having a function of generating photocarriers and a layer region having a function of carrier transport are stacked, photosensitivity, electrostatic contrast, withstand voltage and the like can be increased.

At this time, in the photoexcitation layer region, in order to enhance the generation of photocarriers, under the conditions of film formation, (1) film formation is performed at a low film formation rate, and (2) dilution ratio with H ₂ or He is set. It is preferable to increase, (3) contain more doping element than the transport layer.

The carrier transport area is mainly used for the photoconductor 2.
In addition to increasing the withstand voltage of No. 1, the carrier injected from the excitation layer region smoothly travels to the surface of the photoconductor 21. In this layer region as well, carriers are generated from the light transmitted through the photoexcitation layer region. , Contribute to the photosensitivity of the photoconductor 21.

When the a-Si photoconductive layer 29 is formed by laminating the photoexcitation layer region and the transport layer region, the thickness of the photoexcitation layer region is approximately equal to the thickness of the light absorption layer. Good to set.

An insulating layer or a high resistance layer can be used as the carrier injection blocking surface layer 28, and can be formed of either an organic material or an inorganic material. The meanings of the insulating layer and the high resistance layer are the same as in the case of the carrier-side carrier injection blocking layer 26 described above.

Examples of the organic material used as the insulating layer in the carrier injection blocking surface layer 28 include Mylar, polycarbonate, polyester, polyparaxylylene, etc., which are formed by a method such as coating or vapor deposition.

As the inorganic material used as the insulating layer or the high resistance layer in the carrier injection blocking surface layer 28, for example, a-SiC is suitable, and a-SiC is also suitable.
There are N, a-SiO, a-SiC.O, a-SiN.O, etc., which are formed by a thin film forming means. When an a-SiC layer is used as the carrier injection blocking surface layer 28,
Chemical 2

[0035]

[Chemical 2] X value of 0.3 <x <1.0, preferably 0.5 ≦ x ≦
A range of 0.95 is good.

The thickness of the carrier injection blocking surface layer 28 is 0.
05-5 μm, preferably 0.1-3 μm,
When the thickness is less than 0.05 μm, the surface layer 28 cannot sufficiently improve the image density and the withstand voltage, and when it is repeatedly used, the life is deteriorated due to abrasion. If the thickness exceeds 5 μm, an electric field (lines of electric force) spreads in the film surface direction in the surface layer 28 in forming a fine charge pattern, whereby the resolution is lowered and sufficient resolution cannot be obtained. Moreover, since the amount of electric charges remaining on the surface increases and the residual potential increases, problems such as a decrease in image density, fogging of the background, and a change in image density during repeated use occur.

The total thickness of the photosensitive layer 27 thus obtained depends on the settings of the above-mentioned layers, but an LED as an exposure light source is used.
When EL or EL is used, the thickness is preferably about 1 to 15 μm, and preferably 1 to 5 μm. By setting the film thickness within this range, the exposure is sufficiently absorbed to exhibit good photosensitivity, the withstand voltage of the photoconductor can be secured, and a good image can be obtained even with a low bias voltage.

An LED array 41 as an exposing means (image signal exposing device) is arranged inside the translucent support 23, that is, on the back side of the photoconductor 21 so as to face the developing unit 31. Back exposure is performed via the condensing element 43 (selfoc lens). Further, as the exposure means, instead of the LED array, an EL light emitting element array,
It is also possible to use a plasma light emitting element array, a phosphor dot array, a shutter array in which a light source is combined with a liquid crystal or PLZT, an optical fiber array, or the like.

A developing unit 31 is provided around the photoconductor 21.
A transfer unit 51 and a fixing unit 61 are provided. FIG. 3 is a partial view showing the vicinity of the facing portion of the photoconductor 21 and the developing unit 31, and for convenience of illustration, a part is shown in detail and a part is simplified with respect to FIG.

The developing unit 31 is disposed on the light-transmissive conductive layer 25 side of the photoconductor 21 and supplies the developer 71 to the surface of the photoconductor 21. Conductive sleeve 35 of developing unit 31
Include the transparent conductive layer 25 of the photoconductor 21 and the developing unit 3
A developing bias power source 39 for applying a voltage is connected between the first and second terminals. The developing unit 31 includes a magnet roller 33 having several magnetic poles (N and S poles) and a conductive sleeve 35, and a doctor blade 37 for controlling the layer thickness of the developer 71. In this example,
The photoconductor 21 and the sleeve 35 are rotated in the directions of arrows P and S, respectively, to convey and supply the developer 71 to the surface of the photoconductor 21. The mag roller 33 may be fixed or may be rotated.

In this way, when the developer 71 is rotated in the direction opposite to the photoconductor 21, the developing unit 31 (sleeve 3
5) and the photoconductor 21 at the closest position (portion A in FIG. 3), a developer pool 73 is formed on the downstream side (the side away from the developer 71) in the rotation direction of the photoconductor 21. A portion of the developer 71 protruding beyond the original height is the developer pool 73,
Transport speed of developer 71, height of developer 71, sleeve 3
The gap and the like between 5 and the surface of the photoconductor 21 are appropriately set according to the rotation speed of the photoconductor 21 and the required size of the developer pool 73.

When the photoconductor 21 and the developer 71 are rotated in the opposite directions, a developer pool 73 is generated on the downstream side of the closest position between the developing unit 31 and the photoconductor 21.
Is rotated in the same direction as the photoconductor 21 and the peripheral speed of the developer 71 is made higher than the peripheral speed of the photoconductor 21. Therefore, in order to obtain the developer reservoir 73 stably and with good reproducibility, it is preferable to rotate the photoconductor 21 and the developer 71 in opposite directions.

At the time of image formation, the sleeve 35 conveys the developer 71 to the developer reservoir 73, and the developing bias power source 39 applies a positive developing bias voltage to the conductive sleeve 35. In this embodiment, the toner having a positive charging property is used, but the charging property of the toner and the positive / negative of the bias voltage are determined by the characteristics of the photoconductor. Photosensitive layer 27
From the time when the toner comes into contact with the developer 71, charges are injected into the photoconductor 21 by the developing bias power source 39 via the magnetic brush composed of the carrier 11 of the developer 71, and erase and erasure of the residual charge at the time of the previous image formation. The body is charged. At the same time, the residual toner remaining on the photoreceptor 21 without being transferred by the transfer unit 51 is cleaned by the magnetic brush.

The LED array 4 arranged on the light-transmissive support 23 side of the photoconductor 21 so as to face the developing unit 31.
1 (exposure means), the developing unit 31 and the photoconductor 21.
The image signal is irradiated in the vicinity of the facing portion of the.

When the image signal is selectively exposed by the LED array 41, the potential of the photosensitive layer 27 in the exposed portion is rapidly lowered and a potential difference is created. At this time, the toner dissipates the magnetic force or electrostatic force from the magnetic brush due to this potential difference, and adheres to the photosensitive layer 27. Then, when the photosensitive layer 27 and the developer layer of the developer reservoir 73 are separated from each other, the developed toner remains on the photosensitive layer 27 without being disturbed, and a toner image 75 is formed on the surface of the photoconductor 21. In this developing step as well, since the stable magnetic brush is formed by the magnetic carrier 11 as in the above, the developer pool 7
3 is constant and a sharp and stable image is obtained.

The position where the image is exposed by the LED array 41 is not at the closest position A between the surface of the photoconductor 21 and the developing sleeve 35, but at the developer reservoir 73 formed on the downstream side in the rotation direction of the photoconductor 21. The position is preferable, and it is more preferable that the latter half of the downstream side of the developer pool 73, that is, the position B where the developer 71 and the photoconductor 21 separate from each other.

By performing the exposure at the position of the developer pool 73, the application of the developing bias voltage to the photoconductor 21 is sufficiently stabilized until the exposure, and uniform charging is performed so that the influence of the history of the photoconductor 21 is suppressed. At the same time, the residual toner on the surface of the photoconductor 21 and the toner on the image background portion are sufficiently collected. Furthermore, since the application of the developing bias voltage to the photoconductor 21 is sufficiently stable to perform the exposure to generate the photocarriers, a good toner image 75 is formed. After the toner image 75 is formed, the photoconductor 21 is quickly separated from the developer pool 73, so that the toner image 75 on the surface of the photoconductor 21 is mechanically affected by collision or friction with the developer 71. The toner image 75 having good resolution can be obtained without being disturbed.

At the position of the developer reservoir 73, the position A where the surface of the photosensitive member 21 and the developing sleeve 35 are closest to each other.
The distance between the surface of the photoconductor 21 and the mag roller 33 becomes larger than that. Therefore, the magnetic force for attracting the developer 71 to the mag roller 33 side becomes weak, and a part of the toner image 75 formed on the surface of the photoconductor 21 is magnetically attracted to the developing unit 3.
It is possible to prevent the image density from being reduced by being collected on the side of No. 1 and the resolution from being deteriorated by being disturbed by the magnetic force.

The toner image 75 on the photoconductor 21 is transferred to the paper 81 (transferred member) by the transfer roller 51 to which a negative bias voltage is applied by the transfer bias power source 55 in the transfer unit 51. In the present invention, since the toner is insulating, it is possible to perform stable transfer with high transfer efficiency even when plain paper is used. Next, the transfer toner is transferred to the paper 81 by the fixing roller 63 (heating roller) in the fixing unit 61.
Is fixed in. Reference numeral 65 indicates a pressure roller. The residual toner on the photoconductor 21 after the transfer is transferred to the carrier 1 when the photoconductor 21 comes into contact with the developer 71 at a position facing the developing unit 31.
It is removed by the magnetic brush No. 1 and there is no need to provide a separate cleaning member. Of course, a cleaning unit may be separately provided in front of the developing unit 31.

Further, the transfer unit 53 and the developing unit 3
It is also possible to provide a charge eliminating means (for example, a charge eliminating light source) in order to eliminate the electric charge remaining in the photosensitive layer 27 during the period 1.
FIG. 4 is a partial explanatory view corresponding to FIG. 3, showing another embodiment of the image forming apparatus of the present invention. This embodiment is the same as the embodiment shown in FIGS. 1 to 3 except that the developing unit 31 is provided with a control electrode 32 and a member associated therewith.

The control electrode 32, which can be controlled separately from the developing bias power source 39, is provided in the vicinity of the opposing portion of the photoconductor 21 and the developing unit 31, but as shown in the figure, the photoconductor 21 is located more than the exposure position of the LED light. It is preferably provided on the upstream side, and in FIG. 6, it is provided on the sleeve 35 at the closest portion A to the photoconductor 21. The control electrode 32 is the insulator 3
4 is insulated from the sleeve 35 by the control electrode power source 36 (voltage applying means), and the developing bias power source 3
Voltage is applied independently of 9. The control electrode 32 and the insulator 34 are not attached to the sleeve 35 but are fixed, and are always located at the closest position A regardless of the rotation of the sleeve 35 and the photoconductor 21. Further, the control electrode 32 has a strip shape along the length direction (axial direction) of the sleeve 35 so that a uniform magnetic field can be applied to the photoconductor 21 and the developer 71.

The potential of the control electrode 32 is set to the control electrode power source 3
6, the potential is adjusted to a predetermined potential independently of the potential of the sleeve 35. For example, the control electrode 32 is grounded to have a common potential with the translucent conductive layer 25. Alternatively, the potential of the sleeve 35 is set to be low or high.

As described above, by providing the control electrode 32 to which the potential can be applied independently of the sleeve 35, the potential on the surface can be made uniform and the influence of the history of the photoconductor 21 due to the previous image forming process can be canceled. As a result, when repeatedly used, for example, when the photoconductor 21 is rotated several times to obtain one image, a stable development state and a recorded image can be obtained.

Here, when the potential of the control electrode 32 is adjusted,
Optimal image forming conditions for image density, background fog, etc. can be adjusted. In addition, although the mechanism is not clear at present, in the image evaluation experiment of the present inventors, by increasing the potential of the control electrode 32 and decreasing the potential of the sleeve 35, the toner adheres to the non-exposed portion. However, so-called reversal development, in which toner does not adhere to the exposed portion, is also possible.

As the developer 71, a two-component developer composed of a conductive and magnetic carrier and an insulating toner is used. As the carrier, a binder type carrier in which magnetic particles are dispersed and contained in a binder resin and the surface of mother particles is subjected to a conductive treatment in order to obtain magnetic properties, conductivity and toner concentration necessary for image formation is used. .. Such binder type carrier particles are more likely to crack the carrier particles due to the impact force applied to the carrier and shorten the life of the carrier, as compared with the iron powder carrier or the magnetic powder carrier used in a normal two-component developer. .. In particular, FIG.
In the back side exposure recording method as shown in FIG. 3, since the magnetic brush is formed and the carrier conveyed to the developer reservoir 73 by the sleeve 35 is rubbed against the surface of the photoconductor while being pressed, the pressure, Receives rubbing force and collision force at the same time. At this time, if the surface roughness of the photoconductor is large, a strong impact force is applied to the carrier by being caught by the irregularities on the surface of the photoconductor.

Therefore, in the present invention, the average surface roughness r of the photosensitive member is made smaller than the average particle size Rc of the binder type carrier (r≤Rc) to reduce the stress applied to the carrier.
Reduces the occurrence of carrier cracks and chips. Further, this also makes it possible to smoothly and effectively clean the surface of the photoconductor with the developer, so that the photoconductor can be prevented from being contaminated, and the life of the carrier and the developer can be extended. A recorded image is obtained.

In the binder type carrier of the present invention, for example, magnetic particles having an average particle diameter of 0.1 to 10 μm are dispersed in a binder resin to form mother particles having an average particle diameter of 10 to 100 μm, and the surface thereof is averaged. It is manufactured by fixing conductive fine particles having a particle size of several tens to several hundreds of nm and making them conductive. It is desirable that magnetic particles such as magnetite, ferrite, and iron powder are contained in a relatively large amount, for example, 70 to 90% by weight, in the carrier mother particles to enhance the magnetic force of the carrier. When the surface of this carrier is viewed microscopically, the magnetic particles are larger than the conductive fine particles, so the magnetic particles are exposed and protrude on the carrier surface, and the carrier particles due to the collision between the carrier and the photosensitive member surface. Stress is applied to the magnetic particles as the center.

Therefore, in the present invention, the average surface roughness r of the photoconductor is made smaller than the average particle size Rm of the magnetic substance particles (r≤Rm) so that the magnetic substance particles are caught on the irregularities on the surface of the photoconductor. The stress received by the carrier is reduced, and the magnetic particles are prevented from falling out of the carrier and the carrier itself is prevented from cracking. Further, since the impact force applied to the carrier is weakened, the conductive fine particles are also prevented from falling off. With these,
The life of the carrier is extended and the durability of the developer is enhanced.

In the above description, the method of conducting the conductive treatment by forming the conductive layer by fixing the conductive fine particles to the surface of the carrier mother particles in which the magnetic substance particles are dispersed in the binder resin is formed. Although described, the present invention is not limited to this, and a conductive thin film may be formed on the surface of the mother particle by, for example, CVD, sputtering, or vacuum deposition to form a conductive layer.

[0060]

According to the present invention, the following operational effects can be obtained. (1) Stress applied to a binder type carrier in which magnetic particles are dispersed in a binder resin is reduced, the life of the carrier is extended, and the image quality is stabilized for a long period of time.

(2) The carrier is prevented from being destroyed, and the magnetic particles and the conductive layer (conductive fine particles, etc.) are prevented from being lost from the carrier, whereby the contamination of the photoreceptor is reduced, the life of the photoreceptor and the reliability of the process are improved. Is improved.

(3) Since the frictional force between the developer and the photoconductor is reduced, the load on the developing machine and the photoconductor is reduced, the driving force is reduced, and the mechanical reliability is improved. (4) Since the impact force between the developer and the photoreceptor is reduced,
The occurrence of fogging and the deterioration of resolution are prevented, and stable and good image quality can be obtained.

Test Example 1 Styrene / n-butyl acrylate copolymer (copolymerization ratio 80/20) 25 parts by weight Magnetite (average particle size 0.2 μm) 75 parts by weight After kneading the above mixture, it was pulverized with a jet mill. The particles were classified to obtain carrier mother particles having an average particle size of 20 μm.

With respect to 100 parts by weight of the carrier mother particles, 2 parts by weight of conductive carbon black (conductive fine particles, average particle size 20 to 30 nm) were sufficiently mixed with a Henschel mixer to make the surface of the carrier mother particles uniform. Attached. Then, using a surface treatment device (Hybridizer, manufactured by Nara Machinery Co., Ltd.), these fine particles were fixed to the surface layer of carrier mother particles by a mechanical impact force to obtain a carrier.

70 parts by weight of this carrier and 30 parts by weight of a conventional magnetic insulating toner were uniformly mixed to prepare a developer. The volume resistivity of this developer was 3 × 10 ³ Ω · cm. On the other hand, an ITO layer having a thickness of 0.1 μm was vapor-deposited as a translucent conductive layer on the peripheral surface of a transparent cylindrical glass substrate having an outer diameter of 30 mm, and then a capacitively coupled glow discharge decomposition device was used thereon. , A p-type a-Si injection blocking layer, an a-Si photoconductive layer, and an a-SiC surface layer are sequentially stacked to form a 3 μm thick a layer.
A Si-based photoconductor was produced.

When the surface roughness of this photoreceptor was measured,
It was 0.12 μm. By using these, an image forming apparatus of the rear exposure recording system shown in FIG.
When an image was formed at 50 V and transferred to a commercially available plain paper to obtain a recorded image, an image having an image density of 1.2 and good resolution and fogging was obtained.

Next, a running test of 30,000 sheets was conducted,
When a recorded image was obtained in the same manner, a good image equivalent to the initial one was obtained. On the other hand, when an a-Si photosensitive drum is manufactured, the deposition rate of the ITO layer is increased to obtain the same light transmittance and electric resistance as above, but the surface roughness of ITO is slightly larger.
A layer was vapor-deposited to a thickness of 0.1 μm, and a photoreceptor was prepared in the same manner as above.

The average surface roughness of this photosensitive member was measured and found to be 0.28 μm. Using this photoreceptor, a recorded image was obtained in the same manner as above, and it was found that the image density was 1.2 and the resolution and fog were good.

Next, a running test of 30,000 sheets was conducted,
When a recorded image was obtained in the same manner, the image density after printing 30,000 sheets was reduced to 0.7, and fog was also generated, and deterioration of the image quality was recognized. As a result of SEM observation of the developer at this time, it was confirmed that the magnetic powder and the conductive fine particles were dropped off and the carrier was cracked in many carriers.

Test Example 2 Photoreceptors having different surface roughnesses were prepared in the same manner as in Test Example 1. Using these photoreceptors, the same developer as in Test Example 1,
A recorded image was obtained by an image forming apparatus, and the initial image and the image after running 5,000 sheets were evaluated. The results are shown in Table 1.

[0071]

[Table 1]  Flat photoconductorBeginning After 5,000 sheets Uniform surface roughness Image density Cover Image density Cover 1 μm 1.2 ○ 1.2 ○ 10 μm 1.2 ○ 1.1 ○25 μm 1.2 ○ 0.7 ×

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram showing an example of a photoconductor used in the present invention.

FIG. 3 is a partial explanatory view showing a facing portion of a photosensitive member and a developing unit in an embodiment of the image forming apparatus of the present invention.

FIG. 4 is a partial explanatory view showing a facing portion of a photoconductor and a developing means in another embodiment of the image forming apparatus of the invention.

[Explanation of symbols]

 11 Carrier 13 Carrier Mother Particle 15 Magnetic Particle 17 Conductive Fine Particle 18 Conductive Thin Film 21 Photoconductor 23 Translucent Support 25 Transparent Conductive Layer 26 Support Side Carrier Injection Blocking Layer 27 Photosensitive Layer 28 Carrier Injection Blocking Surface Layer 29 a- Si-based photoconductive layer 31 Development unit 32 Control electrode 33 Mag roller 34 Insulator 35 Sleeve 36 Control electrode power supply 37 Doctor blade 39 Development bias power supply 41 LED array 43 Condensing element 51 Transfer unit 53 Transfer roller 55 Transfer bias power supply 61 Fixing unit 63 fixing roller 65 pressure roller 71 developer 73 developer pool 75 toner image 81 paper A closest position between the photoconductor 21 and the sleeve 35 B position where the developer 71 and the photoconductor 21 separate from each other

Claims (2)

[Claims] 1. A photoconductor having a photoconductive layer on a translucent conductive support, a developing means disposed on the photoconductive layer side of the photoconductor, and supplying a developer to the surface of the photoconductor, and the photoconductor. In the image forming apparatus having the exposing means arranged so as to face the developing means on the side of the translucent conductive support, a mother particle containing magnetic particles in a binder resin as a carrier of the developer. Using a conductive magnetic carrier having a conductive layer formed on its surface, where Rc is the average particle diameter of the carrier and r is the surface roughness of the photoreceptor, r ≦ Rc apparatus. 2. A photoconductor having a photoconductive layer on a translucent conductive support, a developing means disposed on the photoconductive layer side of the photoconductor, and supplying a developer to the surface of the photoconductor, and the photoconductor. In the image forming apparatus having the exposing means arranged so as to face the developing means on the side of the translucent conductive support, a mother particle containing magnetic particles in a binder resin as a carrier of the developer. Using a conductive magnetic carrier having a conductive layer formed on the surface thereof, r ≦ Rm, where Rm is the average particle size of the magnetic particles and r is the surface roughness of the photoconductor. Image forming apparatus.