JPH06313978A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a contact electrostatic charging device from directly coming in contact with a pin hole, to prevent a belt-like electrostatic charging faulty area from being formed and to make the voltage of a power source lower by coating the outer peripheral surface of a body to be electrostatically charged with a surface protective layer. CONSTITUTION:A photosensitive drum 1 is constituted of a base substance 1a made of aluminum and an organic photosensitive layer 1b formed on the outer peripheral surface of the base substance 1a, and further the surface of the drum 1 is coated with the surface protective layer 4, and the drum is driven to be rotated at specified circumferential speed in a direction shown by an arrow A. An electrostatic charging roller 2 is constituted of a conductive core bar 2a made of SUS and a conductive elastic layer 2b made of EPDM containing carbon, which is formed on the outer peripheral surface of the core bar 2a, and the roller 2 is allowed to press-contact with the surface of the drum 1 by a spring member at both ends in the longitudinal direction of the core bar 2a and rotated with the drum 1. By impressing specified voltage on the roller 2 by a high voltage power source 3, the surface of the drum 1 is electrostatically charged to be at specified potential.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus equipped with a contact charging device for charging a surface of a member to be charged to a predetermined potential by bringing a conductive member to which a voltage is applied into contact with the surface of the member to be charged. And a conductive member to which a predetermined bias is applied is brought into contact with the surface of the image carrier, and the transfer material is passed through the contact portion, whereby the image previously formed on the surface of the image carrier is transferred onto the transfer material. The present invention relates to an image forming apparatus equipped with a contact transfer device for transferring to a sheet.

[0002]

2. Description of the Related Art Next, a conventional example will be described.

<Prior Art Example 1> As a charging device used in an image forming apparatus such as an electrophotographic apparatus, a corona discharge device has been generally used conventionally. However, in recent years, a contact charging device using a roller-type or blade-type conductive member has been adopted because it has advantages such as a low power supply voltage and a very small amount even if ozone is generated. It's starting.

FIG. 5 is a schematic configuration diagram showing an example of a contact charging device using a roller type conductive member, that is, a so-called charging roller.

In FIG. 5, reference numeral 21 denotes a member to be charged, which is a photosensitive drum as an image carrier which is rotationally driven in the direction of arrow B at a predetermined peripheral speed (process speed). The photosensitive drum 21 includes a base 21a made of aluminum,
Organic photosensitive layer 21b formed on the outer peripheral surface of the base 21a
It consists of and. Further, 22 is a charging roller as a contact charging device which is brought into contact with the surface of the photosensitive drum 21 and is driven to rotate, and 23 is a high voltage power source for applying a voltage to the charging roller 22.

The charging roller 22 comprises a conductive cored bar 22a made of iron, SUS or the like, and an outer peripheral surface thereof covered with a conductive elastic layer 22b made of carbon-containing EPDM or the like. Both ends of the cored bar 22a in the longitudinal direction are pressed against the surface of the photosensitive drum 21 by spring members (not shown).

An oscillating voltage obtained by superimposing an AC voltage having a peak-to-peak voltage which is more than twice the charging start voltage on the surface of the photosensitive drum 21 is applied to the charging roller 22 by a high voltage power source 23, and the oscillating voltage is applied. The surface of the drum 21 is charged to a predetermined potential.

<Prior Art Example 2> As a transfer device used in an image forming apparatus such as an electrophotographic apparatus, a corona discharge device has been generally used in the past. However, in recent years, it has been possible to reduce the power supply voltage, generate an extremely small amount of ozone, excel in transportability of transfer materials, and simplify the device.
A contact transfer device using a conductive member such as a roller type is being adopted because it has advantages such as downsizing.

FIG. 9 is a schematic structural view showing an example of a contact transfer device using a roller type conductive member, that is, a so-called transfer roller.

In FIG. 9, reference numeral 51 is a photosensitive drum as an image bearing member, which is rotationally driven in the direction of arrow C at a predetermined peripheral speed (process speed). This photosensitive drum 51
Is a base 51a made of aluminum and the base 51a.
and an organic photosensitive layer 51b formed on the outer peripheral surface of a.
Further, reference numeral 52 denotes a transfer roller as a contact transfer device that is driven to rotate by being brought into contact with the surface of the photosensitive drum 51, and 53 denotes a high voltage power source for applying a predetermined bias to the transfer roller 52.

The transfer roller 52 has a foamed EPD containing zinc oxide on the outer peripheral surface of a conductive cored bar 52a such as iron or SUS.
The transfer roller 52 is covered with a conductive elastic layer 52b such as M. The transfer roller 52 is pressed against the surface of the photosensitive drum 51 by spring members (not shown) at both ends in the longitudinal direction of the conductive cored bar 52a.

A predetermined transfer bias is applied to the transfer roller 52 by a high voltage power source 53, and
By passing the transfer paper P as a transfer material through the contact portion between the surface of the photosensitive drum 51 and the transfer roller 52, for example, a toner image previously formed on the surface of the photosensitive drum 51 is transferred onto the transfer paper. The predetermined transfer bias value is set as follows. That is, as is well known, a transfer roller in which conductive particles are dispersed in rubber or the like and the volume resistance value thereof is appropriately adjusted, or a transfer paper generally used as a transfer material has a resistance value depending on surrounding environmental conditions. Changes drastically. In such a state, if the transfer bias is controlled to a constant voltage so that good transfer can be performed in a normal temperature and normal humidity environment, the resistance of the transfer roller and the transfer paper will become high in a low temperature and low humidity environment. In addition, so-called transfer failure occurs, and in a high-temperature and high-humidity environment, the transfer roller and the transfer paper have low resistance, so that so-called transfer omission and transfer memory occur. Therefore, if the transfer bias is subjected to constant current control, the inconvenience due to the change in the resistance value as described above is solved, but the following inconvenience occurs. That is, generally, the image forming apparatus can use transfer sheets of various sizes, and when a transfer sheet of a small size is used, it goes without saying that the photosensitive drum and the transfer roller are directly connected to each other. Since there is a contact area, most of the current flows in this area, and transfer defects occur especially in a low temperature and low humidity environment.

In order to comprehensively avoid the inconveniences described above, a predetermined bias controlled by a constant current is set to a predetermined value when there is no transfer sheet at the contact portion between the photosensitive drum and the transfer roller. For a period of time, the output voltage value at this time is monitored and held, and at the time of sheet passing, a bias whose constant voltage is controlled to this voltage value is applied as a transfer bias to the transfer roller (hereinafter referred to as ATV).
The transfer bias is set by C).

[0014]

However, in the contact charging device as shown in the prior art example 1, when a pinhole exists on the surface of the photosensitive drum, a leak occurs between the charging roller and the pinhole. As a result, there is a problem that a rapid voltage drop occurs in the power feeding portion, and so-called charging failure occurs in the entire area where the charging roller is in contact with the photosensitive drum. When this charging failure occurs, in the actual image, a black band-shaped image unevenness appears in the so-called reversal development system, and a white band-shaped image unevenness appears in the regular development system at each rotation cycle of the photosensitive drum. It was supposed to significantly reduce the image quality.

In order to solve the above problems, a contact charging device using a charging roller having a structure in which the outer peripheral surface of the conductive elastic layer is covered with a resistance layer made of resin or the like has been proposed. The required resistance value is 10 ⁵
Limited to a very narrow range of Ω to 10 ⁷ Ω,
It was difficult to control the resistance value in this manufacturing process.

Further, in the contact transfer device as shown in the above-mentioned conventional example 2, particularly in the transfer device adopting ATVC, A
In performing the TVC, first, a predetermined bias controlled by a constant current is applied to the transfer roller for a predetermined time when the paper is not passed. At this time, if a pinhole exists on the surface of the photosensitive drum, A leak occurs between the transfer roller and the pinhole, causing a sudden voltage drop in the power supply section, which causes a voltage value different from the true output voltage value to be originally monitored and held to be detected. Along with this, there has been a problem that it is difficult to apply a transfer bias to the transfer roller, which enables good transfer during paper passing.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems. According to the solving means of Conventional Example 1, a conductive member is brought into contact with the surface of the member to be charged, and the conductive member is brought into contact with the surface. In an image forming apparatus equipped with a contact charging device for charging the surface of the body to be charged to a predetermined potential by applying a voltage to the outer surface of the body to be charged with a surface protective layer, Even when there is a pinhole on the surface of the photosensitive drum as a charging body, the surface protection layer covers the pinhole, so that the charging roller as a contact charging device does not directly contact the pinhole,
It is possible to prevent the occurrence of a strip-shaped poor charging region.

Furthermore, it is not necessary to provide a resistance layer on the outer peripheral surface of the charging roller as the contact charging device, and the manufacturing thereof can be facilitated.

Further, according to the solving means of the second conventional example, the conductive member is brought into contact with the surface of the image carrier, the transfer material is passed through the contact portion, and a predetermined bias is applied to the conductive member. In the image forming apparatus provided with a contact transfer device for transferring the image previously formed on the surface of the image carrier onto the transfer material, by coating the outer peripheral surface of the image carrier with a surface protective layer, Even when there is a pinhole on the surface of the photosensitive drum as the image carrier, the surface protection layer covers the pinhole, so that the transfer roller as the contact transfer device does not directly contact the pinhole. , ATV to enable good transfer
It becomes possible to operate C normally.

[0020]

【Example】

<Embodiment 1> FIG. 1 is a view showing an embodiment of a photosensitive drum as a member to be charged and a charging roller as a contact charging device according to the present invention.

In FIG. 1, reference numeral 1 denotes a photosensitive drum, which comprises a base 1a made of aluminum and an organic photosensitive layer 1b formed on the outer peripheral surface of the base 1a. Further, the surface of the photosensitive drum 1 is a surface protective layer 4. And has an outer diameter of 30 mm and is rotationally driven in the direction of arrow A at a predetermined peripheral speed.

A charging roller 2 is composed of a conductive cored bar 2a made of SUS and a conductive elastic layer 2b made of carbon-containing EPDM formed on the outer peripheral surface thereof, and its outer diameter is 12 mm. At both ends in the longitudinal direction of the conductive core metal 2a, spring members (not shown) are pressed against the surface of the photosensitive drum 1 and driven to rotate.

The charging roller 2 is provided with a high voltage power source 3
By applying a predetermined voltage, the surface of the photosensitive drum 1 is charged to a predetermined potential. The voltage applied to the charging roller 2 is preferably an oscillating voltage obtained by superimposing an AC voltage on a DC voltage. The oscillating voltage here is a voltage whose voltage value periodically changes with time, and the AC voltage preferably has a peak-to-peak voltage that is at least twice the charging start voltage of the surface of the photosensitive drum 1. The waveform is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or a pulse wave. Needless to say, the voltage applied to the charging roller 2 is not limited to the oscillating voltage as described above and may be a DC voltage alone.

Now, the photosensitive drum 1 and the surface protective layer 4, which are the features of the present invention, will be described in detail with reference to FIG.

In FIG. 2, reference numeral 1 denotes a photosensitive drum, on which a base 1a made of aluminum and an organic photosensitive layer 1b composed of a charge generation layer 1c and a charge transport layer 1d in this order are formed on the outer peripheral surface of the base 1a. ing. The surface of the photosensitive drum 1 is covered with a surface protective layer 4. As an example of a method of manufacturing such a photosensitive drum 1, the charge generating layer 1c is first formed on the outer peripheral surface of the base body 1a by dipping to have a predetermined film thickness, and dried, and then the outer peripheral surface is similarly subjected to the same process. The charge transport layer 1d is formed to a predetermined thickness by dipping and dried. After that, the outer peripheral surface of the charge transport layer 1d is sprayed or the like onto the surface protective layer 4
Is formed into a predetermined film thickness.

As the material of the surface protective layer 4, polyester, acrylic, polyvinylcarbazole, phenoxy,
Resins such as polyvinyl butyral, polystyrene, polyvinyl acetate, polysulfone, polyarylate, vinylidene chloride / acrylonitrile copolymer, and polycarbonate having a light transmittance of 80% or more are preferable, and the film thickness thereof is the surface of the organic photosensitive layer 1b. 1μ in order to fully cover the pinholes existing in
It is preferably m to 20 μm. Furthermore, in order to maintain the photosensitivity of the photosensitive drum, a hydrazone-based compound, a pyrazoline-based compound, a triarylamine-based compound, a stilbene-based compound, an oxazole-based compound,
A charge transport material such as a thiazole compound and a triallylmethane compound may be dispersed. Since the surface protective layer 4 thus formed is not in direct contact with the charge generation layer 1c, by dispersing an additive therein, it is possible to give various functions without significantly impairing the photosensitive characteristics. It is possible.

Now, the surface of the photosensitive drum having pinholes is covered with a surface protective layer having a thickness of 3 μm in which a charge transport material is dispersed in a polycarbonate resin, and the peripheral speed is 40
The charging roller is rotated at a speed of mm / sec, and the charging roller is supplied with a DC voltage of -700V and a peak-to-peak voltage of 1800.
When an oscillating voltage in which an AC voltage of V and a frequency of 400 Hz is superposed is applied, the surface of the photosensitive drum is charged to about -700 V, and the outer peripheral surface of the conductive elastic layer is covered with a resistance layer made of resin or the like. Even without using, an image without the conventional black band-shaped or white band-shaped periodic image unevenness was obtained. It is also possible to use a charging roller having a structure in which the outer peripheral surface of the conductive elastic layer is covered with a resistance layer made of resin or the like.
The latitude of the resistance value of the resistance layer can be widened, and the manufacture thereof can be made easier than ever before.

In this embodiment, a photosensitive drum having a charge property of negative polarity having a charge transport layer formed on the charge generation layer was used, but the charge generation layer was formed on the charge transport layer. Needless to say, it may be applied to a photosensitive drum having a positive charging characteristic.

<Embodiment 2> Another embodiment of the present invention will be described below. The basic structure of the photosensitive drum as the member to be charged and the charging roller as the contact charging device is as follows.
It is the same as that shown in the above-mentioned "Example 1", and therefore will be described with reference to FIG.

That is, in FIG. 1, reference numeral 1 denotes a photosensitive drum, which is a base 1a made of aluminum and the base 1a.
And an organic photosensitive layer 1b formed on the outer peripheral surface of the photosensitive drum 1 and the surface of the photosensitive drum 1 is covered with a surface protective layer 4 having an outer diameter of 30 mm and rotating at a predetermined peripheral speed in the direction of arrow A. Driven.

A charging roller 2 is composed of a conductive core metal 2a made of SUS and a conductive elastic layer 2b made of carbon-containing EPDM formed on the outer peripheral surface of the charging metal core 2a and having an outer diameter of 12 mm. At both ends in the longitudinal direction of the conductive core metal 2a, spring members (not shown) are pressed against the surface of the photosensitive drum 1 and driven to rotate.

The charging roller 2 is provided with a high voltage power source 3
By applying a predetermined voltage, the surface of the photosensitive drum 1 is charged to a predetermined potential.

As described above, in the system using the charging roller as the contact charging device, the frequency of the AC voltage applied to the charging roller must be increased as the peripheral speed of the photosensitive drum increases, but the frequency is about 300 Hz. If it exceeds the limit, there is a problem that the vibration of the photosensitive drum becomes large and the charging sound resulting from this becomes large. Therefore, in this embodiment, by dispersing silicone powder in the surface protective layer 4 formed on the upper layer of the photosensitive drum 1, the surface protective layer 4 has elasticity, absorbs vibration of the charging roller 2, and is exposed to light. It is characterized in that the vibration of the drum 1 is reduced.

In this example, 5% by weight of silicone powder having a particle size of 1 μm was further added to the surface protective layer 4 shown in the above-mentioned “Example 1”. The amount of silicone powder to be added is preferably 40% in weight ratio, in order to maintain the conventional photosensitivity.

Now, a photosensitive drum having a surface protection layer in which a charge transport material and a silicone powder are dispersed in a polycarbonate resin is coated on the surface of the photosensitive drum having pinholes in a thickness of 10 μm at a peripheral speed of 40 mm / sec. Rotate and charge the charging roller with a high voltage power supply, -700V DC voltage, peak-to-peak voltage 1800V, frequency 400Hz
When an oscillating voltage superposed with the AC voltage is applied, the surface of the photosensitive drum is charged to approximately -700 V, and the outer peripheral surface of the conductive elastic layer is covered with a resistance layer made of resin or the like without using a charging roller. An image was obtained without the conventional black band-shaped or white band-shaped periodic image unevenness. In addition, since the surface protection layer has elasticity, it is possible to reduce charging noise.

<Embodiment 3> FIG. 3 shows an embodiment in which a photosensitive drum as a member to be charged according to the present invention and a charging blade as a contact charging device are used. The same members as those shown are designated by the same reference numerals.

In FIG. 3, reference numeral 1 denotes a photosensitive drum, which is composed of a substrate 1a made of aluminum and an organic photosensitive layer 1b formed on the outer peripheral surface of the substrate 1a, and the surface of the photosensitive drum 1 is a surface protective layer 4. And has an outer shape of 30 mm and is rotationally driven in the direction of arrow A at a predetermined peripheral speed.

Numeral 5 is a charging blade, which is a holder 5a made of SUS, and a plate-like conductive elastic body 5 made of urethane rubber containing carbon, which is supported on this side surface by adhesion.
b, the thickness of which is 2 mm, and the photosensitive drum 1
It is arranged in a so-called counter direction so as to uniformly contact the surface in the direction of the rotation axis of the photosensitive drum 1. Then, a predetermined voltage is applied to the charging blade 5 by the high-voltage power supply 3, so that the surface of the photosensitive drum 1 is charged to a predetermined potential.

By the way, in such a system using the charging blade as the contact charging device, when the charging blade rubs the surface of the photosensitive drum, so-called "chatter" occurs, whereby the charging sound is amplified, There is a problem that it becomes larger than that when a charging roller is used. According to the experimental study by the applicant of the present invention, this is greatly improved by reducing the friction coefficient of the contact surface between the photosensitive drum and the charging blade.

Therefore, in this embodiment, the photosensitive drum 1
Teflon (trade name) on the surface protective layer 4 formed on the upper layer
It is characterized in that the friction coefficient of the surface of the surface protective layer 4 is lowered by dispersing the particles. In this example, Teflon particles having a particle size of 0.5 μm were further added to the surface protective layer 4 shown in “Example 1” in a weight ratio of 3%.
0% was added. When the contact angles of the surface protective layer used in "Example 1" and the Teflon-added surface protective layer shown in this Example were compared, the former was about 80 °, whereas the latter was about 95 °. It was °. In addition, as the amount of Teflon to be added, in order to maintain the conventional photosensitive characteristics,
The upper limit of the weight ratio is preferably 60%.

The surface of the photosensitive drum having pinholes is covered with a surface protective layer in which a charge transport material and a Teflon particle are dispersed in a polycarbonate resin at a thickness of 3 μm, and the peripheral speed is 40 mm / sec. By rotating and applying an oscillating voltage in which a peak voltage 1800V and an AC voltage having a frequency of 400Hz are superposed on a charging blade with a DC voltage of -700V by a high-voltage power supply, the surface of the photosensitive drum is charged to about -700V, and the conductive property Even without using a charging blade having a structure in which the outer surface of the elastic body is covered with a resistance layer made of resin or the like, an image without the conventional black band-shaped or white band-shaped periodic image unevenness was obtained. . Further, by reducing the friction coefficient of the surface protective layer, it becomes possible to reduce the charging noise. Furthermore, the amount of wear of the surface protective layer is reduced, and the life of the surface protective layer can be extended.

<Embodiment 4> FIG. 4 shows an embodiment of a process cartridge provided with a photosensitive drum as a member to be charged and a charging roller as a contact charging device according to the present invention. The same members as the members shown in FIG.

In FIG. 4, reference numeral 6 denotes a process cartridge, which comprises a photosensitive drum 1, a charging roller 2, a developing device 7, a cleaning device 8 and a protective cover 9.
Such a process cartridge 6 is inserted into a predetermined portion in an image forming apparatus main body (not shown) in a predetermined manner, and a mechanical drive system and an electric circuit system between the process cartridge 6 and the image forming apparatus main body are provided. Combined, mechanical,
And electrically integrated.

The photosensitive drum 1 is composed of a base 1a made of aluminum and an organic photosensitive layer 1b formed on the outer peripheral surface of the base 1a, and the surface of the photosensitive drum 1 is covered with a surface protective layer 4. There is. The charging roller 2 is
A conductive cored bar 2a made of SUS and a conductive elastic layer 2 made of carbon-containing EPDM formed on the outer peripheral surface thereof.
b and.

The protective cover 9 is the process cartridge 6
When it is mounted in the main body of the image forming apparatus, the transfer device of the main body of the image forming apparatus faces the surface of the photosensitive drum 1 exposed from the opening of the process cartridge 6 to the outside. Further, the process cartridge 6 is closed when it is taken out from the image forming apparatus main body and stored, and the surface of the photosensitive drum 1 facing the outside from the opening of the process cartridge 6 collides with another object. It has a function of protecting from damage due to damage, contamination due to adhesion of dust, and deterioration due to exposure to external light.

However, in spite of the provision of the protective cover 9 as described above, in the process in which the process cartridge 6 is repeatedly put in and taken out from the image forming apparatus main body due to a defective conveyance of the transfer sheet in the image forming process, For example, the surface of the photosensitive drum 1 is abutted against and damaged by a protrusion or the like in the main body of the image forming apparatus, and when the charging roller 2 comes into contact with this portion in the next image forming process, a leak occurs and the charging failure as described above occurs. There was a case that occurred.

However, as shown in this embodiment, by covering the surface of the photosensitive drum 1 with the surface protective layer 4, it becomes possible to prevent the large scratches that would cause the above-mentioned leakage from occurring.

<Embodiment 5> FIG. 6 is a view showing an embodiment of a photosensitive drum as an image carrier and a transfer roller as a contact transfer device according to the present invention.

In FIG. 6, 31 is a photosensitive drum,
It is composed of a base 31a made of aluminum and an organic photosensitive layer 31b formed on the outer peripheral surface of the base 31a, and the surface of the photosensitive drum 31 is covered with a surface protective layer 34 having an outer diameter of 30 mm and an arrow mark. It is rotationally driven in the direction A at a predetermined peripheral speed.

A transfer roller 32 is composed of a conductive cored bar 32a made of SUS and a conductive elastic layer 32b made of zinc oxide-containing EPDM formed on the outer peripheral surface of the transfer roller. At both ends in the longitudinal direction of the conductive cored bar 32a, they are pressed against the surface of the photosensitive drum 31 by spring members (not shown) to be driven and rotated. The material of the transfer roller is not limited to the above materials. For example, rubber such as urethane, silicone or NBR, or sponge material, conductive filler such as carbon black or metal powder, tin oxide, or oxide may be used. It goes without saying that a metal oxide such as titanium may be dispersed and the volume resistance value thereof may be appropriately adjusted.

A transfer bias controlled by ATVC by a high voltage power supply 33 is applied to the charging roller 32, and the surface of the photosensitive drum 31 and the transfer roller 3 are also applied.
By passing the transfer material P through the contact portion with 2, the toner image previously formed on the surface of the photosensitive drum 31 is transferred onto the transfer material.

Now, the photosensitive drum 31 and the surface protective layer 4, which are the features of the present invention, will be described in detail with reference to FIG.

In FIG. 7, 31 is a photosensitive drum,
A base 31a made of aluminum and an organic photosensitive layer 31b composed of a charge generation layer 1c and a charge transport layer 31d in this order are formed on the outer peripheral surface of the base 31a. Further, the surface of the photosensitive drum 31 is covered with a surface protective layer 34. As an example of a method of manufacturing such a photosensitive drum 31, the charge generation layer 31c is first formed on the outer peripheral surface of the substrate 31a by dipping to have a predetermined film thickness and dried, and then the outer peripheral surface of the substrate 31a is similarly formed. The charge transport layer 31d is formed to a predetermined thickness by dipping and dried. After that, the surface protection layer 34 is formed to a predetermined thickness by spraying on the outer peripheral surface of the charge transport layer 31d.

The material of the surface protective layer 34 is a resin such as polyester, acrylic, polyvinylcarbazole, phenoxy, polyvinylbutyral, polystyrene, polyvinylacetate, polysulfone, polyarylate, vinylidene chloride / acrylonitrile copolymer, and polycarbonate. The rate is preferably 80% or more,
The film thickness is preferably 1 μm to 20 μm in order to sufficiently cover the pinholes existing on the surface of the organic photosensitive layer 31b and obtain a sufficient withstand voltage.

Further, in order to maintain the photosensitive characteristics of the photosensitive drum, the above-mentioned resin is used as a hydrazone compound, a pyrazoline compound, a triarylamine compound, a stilbene compound, an oxazole compound, a thiazole compound, a triallylmethane compound. A charge transport material such as a compound may be dispersed.

The surface protective layer 3 formed in this way
Since No. 4 is not in direct contact with the charge generation layer 31c, by dispersing an additive therein, various functions can be provided without significantly impairing the photosensitive characteristics.

The surface of the photosensitive drum having pinholes is covered with a surface protective layer having a thickness of 5 μm in which a charge transport material is dispersed in a polycarbonate resin, and this is coated with an ATVC laser beam printer "LBP-A404". "
When mounted on (Canon Co., Ltd.), erroneous control of ATVC due to pinholes does not occur, and transfer defects, transfer omissions, transfer memory, etc. do not occur from low temperature low humidity environment to high temperature high humidity environment , A good image was obtained.

In this embodiment, a photosensitive drum having a charge property of negative polarity having a charge transport layer formed on the charge generation layer was used, but the charge generation layer was formed on the charge transport layer. The transfer roller may be used as the contact transfer device in the present embodiment, but it is needless to say that a transfer belt or the like may be used.

<Embodiment 6> Another embodiment of the present invention will be described below. The basic structure of a photosensitive drum as an image carrier and a transfer roller as a contact transfer device is as follows.
It is similar to that shown in the above-mentioned "Fifth Embodiment", and therefore will be described with reference to FIG.

That is, in FIG. 6, reference numeral 31 denotes a photosensitive drum, which comprises a base 31a made of aluminum and an organic photosensitive layer 31b formed on the outer peripheral surface of the base 31a. Further, the surface of the photosensitive drum 31 is a surface protective layer. It is covered with 34, has an outer diameter of 30 mm, and is rotationally driven in the direction of arrow A at a predetermined peripheral speed.

A transfer roller 32 is composed of a conductive cored bar 32a made of SUS and a conductive elastic layer 32b made of foamed EPDM containing zinc oxide, which is formed on the outer peripheral surface thereof, and has an outer diameter of 20 mm. And conductive core metal 32a
At both ends in the longitudinal direction of the photosensitive drum 31, they are pressed against the surface of the photosensitive drum 31 by spring members (not shown) and are driven and rotated.

A transfer bias controlled by an ATVC is applied to the transfer roller 32 by a high-voltage power supply 33, and the surface of the photosensitive drum 31 and the transfer roller 3 are transferred.
By passing the transfer material P through the contact portion with 2, the toner image previously formed on the surface of the photosensitive drum 31 is transferred onto the transfer material.

As described above, in the system using the transfer roller as the contact transfer device, in order to secure sufficient transportability of the transfer paper, the transfer roller is set to several tens to several hundreds g / g on the surface of the photosensitive drum. Since the pressure roller is pressed and rotated at a pressure of cm ^2, the surface of the photosensitive drum is rubbed by the friction between the transfer roller and the photosensitive drum when the sheet is not passed and by the transfer sheet and the photosensitive drum when the sheet is passed. It ’s worn out a lot,
Compared to the case of using a conventional corona discharge transfer device,
There is a problem that the life of the photosensitive drum is significantly shortened.

Furthermore, when the toner image previously formed on the surface of the photosensitive drum is transferred onto the transfer paper by the transfer roller, the toner is strongly pressed against the surface of the photosensitive drum, so that the toner is attached to the surface of the photosensitive drum. The adhesion force becomes large, and a part of the toner image originally transferred from the surface of the photosensitive drum to the transfer paper remains on the surface of the photosensitive drum, and as a result, a part of the image on the transfer paper is lost. There is also a problem that a hollow hole is likely to occur.
Therefore, in the prior art, as a means for preventing the hollow portion, the peripheral speed of the photosensitive drum and the peripheral speed of the transfer roller are made different based on the idea of scraping the toner image from the surface of the photosensitive drum. Has proposed a means for conveying the transfer paper at a speed slightly higher than the peripheral speed of the photosensitive drum. However, even with the above means, the transfer paper conveyance speed is easily influenced by, for example, the thickness of the transfer paper, the outer diameter of the transfer roller, the pressure contact force of the transfer roller against the photosensitive drum, and the transfer paper is always conveyed at the optimum speed. It is difficult to get it done.

Therefore, in this embodiment, the photosensitive drum 3
By dispersing Teflon (registered trademark) particles in the surface protective layer 34 formed as the upper layer of No. 1, the friction coefficient of the surface of the surface protective layer 34 is reduced and the releasability is improved. . In this example, 30% by weight of Teflon particles having a particle size of 0.5 μm was added to the surface protective layer 34 described in “Example 5”. When the contact angles of the surface protective layer shown in "Example 5" and the Teflon-added surface protective layer shown in this Example were compared, the former was about 80 °, while the latter was about 95. It was °. The amount of Teflon added is preferably up to 60% by weight in order to maintain the conventional photosensitivity.

Here, an experimental example showing the effect of the Teflon-added surface protective layer will be shown.

First, regarding the reduction of the abrasion amount of the surface of the photosensitive drum by the Teflon-added surface protective layer, the conventional photosensitive drum not having the surface protective layer and the film thickness of 5 μm in which Teflon is added by 30% by weight ratio. A photosensitive drum having a surface protective layer is used as a contact transfer device and has an outer diameter of 2
It was mounted on a laser beam printer "LBP-A404" equipped with a 0 mm transfer roller, and an actual print durability test of 5,000 sheets was performed. After the test, the amount of abrasion on the surface of the photosensitive drum was measured and compared. The wear amount was about 6 μm in the drum, whereas the wear amount was about 2 μm in the latter photosensitive drum having the Teflon-added surface protective layer, which is about 1/3 of the conventional amount. Was confirmed. Furthermore, the amount of wear of the transfer roller was also reduced.

Next, regarding the effect of hollowing out the Teflon-added surface protective layer, the laser beam printer "LB"
Table 1 below shows the results obtained by sequentially mounting several types of photosensitive drums having different amounts of Teflon added to the surface protective layer having a film thickness of 5 μm on P-A404 ”and evaluating the level of the hollow portion of each. At this time, the peripheral speed difference between the photosensitive drum and the transfer roller was set to 0, and an OHP sheet was used as the transfer paper.

[0069]

[Table 1]

By the way, on the surface of the photosensitive drum having pinholes, a charge transport material of polycarbonate resin and 30% by weight of the above Teflon particles were added and dispersed to cover a surface protective layer having a thickness of 5 μm. When this was attached to a laser beam printer "LBP-A404" equipped with an ATVC, a good image without transfer defects, transfer omissions, transfer memories, etc. was obtained from a low temperature and low humidity environment to a high temperature and high humidity environment. At the same time, by reducing the amount of wear on the surface of the photosensitive drum, it is possible to extend the life of the photosensitive drum and prevent the hollow portion.

<Embodiment 7> FIG. 8 shows a seventh embodiment according to the present invention. In this embodiment, a photosensitive belt is used as an image carrier, and in addition to the above-mentioned "Embodiment 5", The same members as those shown in "Example 6" are designated by the same reference numerals.

In FIG. 8, reference numeral 35 is a photosensitive belt,
The substrate 35a is formed by depositing aluminum on a polyester sheet film, and the organic photosensitive layer 35b is formed on the outer peripheral surface of the substrate 35a.
The surface is covered with a surface protection layer 34, the total length of which is 200 mm, and three support rollers 36a, 36b, 3 are provided.
While being stretched by 6c, it is rotationally driven in the direction of arrow B at a predetermined speed.

A transfer roller 32 is composed of a conductive cored bar 32a made of SUS and a conductive elastic layer 32b made of foamed EPDM containing zinc oxide, which is formed on the outer peripheral surface thereof, and has an outer diameter of 20 mm. And conductive core metal 32a
At both ends in the longitudinal direction thereof, the surface of the photosensitive belt 35 is pressed against the surface of the photosensitive belt 35 by a spring member (not shown) and driven and rotated.

A transfer bias controlled by the ATVC is applied to the transfer roller 32 by the high-voltage power supply 33, and the surface of the photosensitive belt 35 and the transfer roller 3 are transferred.
An image previously formed on the surface of the photosensitive belt 35 is transferred onto the transfer material by allowing the transfer material P to pass through the contact portion with 2.

By the way, when a photosensitive belt having excellent flexibility is used as the image carrier and the surface of the photosensitive belt is covered with the surface protective layer, the surface protective layer can also follow the deformation of the photosensitive belt. Must be one.

Therefore, the present embodiment is characterized in that the surface protective layer formed on the upper surface of the photosensitive belt is made to have elasticity by dispersing silicone powder. In this Example, 10% by weight of silicone powder having a particle size of 1 μm was further added to the surface protective layer shown in “Example 5”.

The amount of silicone powder added was 4 in terms of weight ratio in order to maintain the conventional photosensitivity.
It is preferable that the upper limit is 0%.

Now, the film thickness of 5 μm having such a structure.
The photosensitive belt having the silicone powder-added surface protective layer of No. 1 was mounted on an idler composed of three supporting rollers, and the actual print was subjected to a durability test for 10,000 sheets. No cracks or fractures were found in the surface protective layer.

[0079]

As described above, according to the first aspect of the present invention, even when there are pinholes on the surface of the photosensitive drum, the surface protection layer covers the pinholes. The contact charging device such as a blade does not come into direct contact with the pinhole, and it is possible to prevent the occurrence of a strip-shaped charging failure area, which can reduce the power supply voltage and generate a small amount of ozone. It is possible to sufficiently operate the contact charging device included therein.

Furthermore, it is not necessary to provide a resistance layer on the outer surface of the charging roller or the like, and the manufacture thereof can be facilitated.

Further, according to the second aspect of the invention, even when there is a pinhole on the surface of the photosensitive drum, the surface transfer layer covers the pinhole, so that the contact transfer device such as the transfer roller has the pinhole. It is possible to operate the ATVC normally for good transfer without directly contacting with, and it is possible to reduce the power supply voltage, and the generation amount of ozone is extremely small. It is possible to sufficiently operate the contact transfer device, which has advantages such as excellent performance and simplification and downsizing of the device.

Furthermore, by dispersing an appropriate additive in the surface protective layer, it is possible to reduce the amount of abrasion on the surface of the photosensitive drum and prevent the hollow portion.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a diagram showing a photosensitive drum and a surface protective layer of the image forming apparatus according to the present invention.

FIG. 3 is a diagram showing a third embodiment of the image forming apparatus according to the present invention.

FIG. 4 is a diagram showing a fourth embodiment of the image forming apparatus according to the present invention.

FIG. 5 is a diagram showing a conventional example related to the present invention.

FIG. 6 is a diagram showing a first embodiment of the image forming apparatus according to the present invention.

FIG. 7 is a diagram showing a photosensitive drum and a surface protective layer of the image forming apparatus according to the present invention.

FIG. 8 is a diagram showing a third embodiment of the image forming apparatus according to the present invention.

FIG. 9 is a diagram showing a conventional example related to the present invention.

[Explanation of symbols]

1, 21 ... Photosensitive drum 2, 22 ... Charging roller 3, 23 ... High voltage power source 4 ... Surface protective layer 5 ... Charging blade 6 ... Process cartridge 7 ... Developing device 8 ... Cleaning device 9 ... Protective cover 31, 51 ... Photosensitive drum 32 , 52 ... Transfer rollers 33, 53 ... High-voltage power supply 34 ... Surface protective layer 35 ... Photosensitive belt

Claims (2)

[Claims] 1. An image forming apparatus comprising a contact charging device for charging a surface of a member to be charged with a conductive member and applying a voltage to the member to charge the surface of the member to a predetermined potential. An image forming apparatus, wherein an outer peripheral surface of the member to be charged is covered with a surface protective layer. 2. An image carrier is preliminarily formed on the surface of the image carrier by bringing the conductive member into contact with the surface of the image carrier, passing the transfer material through the contact portion, and applying a predetermined bias to the conductive member. An image forming apparatus comprising a contact transfer device for transferring the formed image onto the transfer material, wherein an outer peripheral surface of the image carrier is covered with a surface protective layer.