JPH05297681A - Electrostatic charging member and electrostatic charging device as well as image forming device having the device and process unit attachable and detachable to and from the image forming device - Google Patents

Abstract

PURPOSE:To decrease partial friction and to prevent the fusion of a toner to an image carrying member by setting the thickness of the coating layer of an electrostatic charging member at the thickness larger the furtherer from the pressing position of a pressing means for pressing the electrostatic charging member and a body to be electrostatically charged. CONSTITUTION:The electrostatic charging roller 2 as the contact electrostatic charging member consists of, for example, a conductive arbor 2a consisting of iron or the like which is a base material (core material), a conductive rubber roller part 2b of EPDM (ternary copolymer of ethylene, propylene and diene) which is an elastic layer integrally formed on the outer periphery of the arbor and a resistance layer 2c which is formed on the outer periphery of the roller part and is a coating layer consisting essentially epichlorohydrin rubber. Namely, the electrostatic charging member 2 has the base material 2a, the elastic material 2b and the resistance layer 2c nearer the photosensitive drum. The thickness of the coating layer (resistance layer) 2c of the electrostatic charging member 2 is set larger nearer the central part in the longitudinal direction of the electrostatic charging member 2. Bearings 3 on both end sides of the roller are energized movably toward the photosensitive drum by respectively conductive pressurizing springs 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type charging device for charging a surface of an object to be charged (including static elimination processing) by bringing a charging member into contact with an object to be charged such as a photoconductor, and an image provided with the same. The present invention relates to a forming apparatus and a process unit that can be attached to and detached from the image forming apparatus.

[0002]

BACKGROUND ART For example, in an image forming apparatus such as an electrophotographic apparatus (copying machine, laser beam printer, etc.), electrostatic recording apparatus, etc., a surface of an image carrier as a charged body such as a photoconductor or a dielectric is charged. A corona discharge device (corona charger) provided with a wire electrode and a shield electrode has been widely used as a means for doing so.

The corona discharge device is effective as a means for uniformly charging the surface of an object to be charged such as an image carrier to a predetermined potential. However, it requires a high voltage power source, the charging efficiency is poor,
There are problems that the structure is large and complicated, the cost is high, a relatively large amount of unfavorable ozone is generated by corona discharge, and the discharge wire is contaminated or cut.

In such a corona discharge device, the contact charging means for charging the surface of the body to be charged by bringing the charging member to which a voltage is applied into contact with the body to be charged can reduce the power supply voltage.
Since the structure is simple, there is no cutting of wires, and even if ozone generation is observed, the amount is extremely small. For example, in an image forming apparatus, an image carrier such as a photoconductor or a dielectric, As another means for charging the surface of the body to be charged, which is an alternative to the corona discharge device, research on its practical use is underway (Japanese Patent Application Laid-Open No. 57-178267 / 56-104351).
・ 58-40566 ・ 58-139156 ・ 58-15
0975 publication).

7A and 7B show an example of a contact charging device using a rotating roller body (hereinafter referred to as a charging roller) as a charging member. (A) is a side view and (B) is a partially cutaway front view.

Reference numeral 101 denotes a member to be charged, which is, for example, a rotating drum type photosensitive member (hereinafter referred to as a photosensitive drum) of an electrophotographic apparatus. The photosensitive drum is rotationally driven in the clockwise direction indicated by the arrow at a predetermined process speed (peripheral speed).

The cored bar 102 is a charging roller, and is made of a conductive cored bar 102a which is a base material, and an elastic layer 10 which is integrally formed on the outer circumference of the cored bar 102 and is made of conductive rubber having a low deposition resistivity.
2b and a high resistance surface layer (high resistance layer) 102c formed on the outer circumference of the roller portion. That is, the cover layer of the base material includes the elastic layer 102b and the surface layer 102c.

The reason why the high resistance layer 102c is provided in the vicinity of the upper layer is as follows.

First, if the resistance of the charging roller is too low and pinholes are generated in the photoconductor even if they are minute, the charging current concentrates there and a voltage drop occurs. A desired charging potential cannot be obtained across (charging member contacting direction), and a white belt appears in regular development, and a black belt appears in a reversal development system which has become popular in laser beam printers in recent years. The image quality is degraded.

On the other hand, if the resistance of the charging roller is too high, on the contrary, the current required for charging cannot be sufficiently supplied,
It causes charging failure.

In order to satisfy the above two points, it is of course necessary to provide a certain resistance range. However, the resistance range in which these two points are compatible with each other in a single layer is very narrow, and the production is very stable. It's not worth it.

What has been devised there is a contact charging member having at least two layers.

With regard to pinholes, if there is sufficient resistance in the vicinity of the surface layer of the charging member, excessive current will not concentrate there, and therefore sufficient charging ability can be satisfied. Regarding charging failure, total resistance (product resistance) from the voltage supply source (= core metal) of the charging roller to the surface
Since it can be sufficiently prevented if
By providing a low-resistivity layer with sufficient elasticity in the lower layer part (the part away from the photoconductor) on the core metal, and by providing a relatively high resistance thin layer in the upper part (the part close to the photoconductor), the vicinity of the surface layer Is to keep the total resistance relatively high while keeping the total resistance relatively low.

As a result, a good image can be stably obtained.

Further, as an apparatus, both ends of 102a are rotatably held by conductive bearings 103 so that the longitudinal direction of the roller is substantially parallel to the generatrix direction of the photoconductor drum 101 and brought into contact with the photoconductor drum surface. Bearing 103 at both ends
The charging roller 102 is brought into contact with the photosensitive drum 101 with a predetermined pressing force by urging each of them by a conductive pressure spring 104 so as to be movable toward the photosensitive drum.

Reference numeral 105 denotes a power source for applying a bias voltage to the charging roller 102. The power source 105 applies to the charging roller 102 via a conductive pressure spring 104, a conductive bearing 103, and a conductive cored bar 102a. , For example 1
A current voltage V _{DC of} about 2 KV or a bias voltage of a superimposed voltage V _DC + V _AC of a DC voltage and an AC voltage V _AC is applied.

As a result, the peripheral surface of the photosensitive drum 101, which is rotationally driven, is contact-charged with a predetermined polarity and potential.

A indicates an effective charging width (for example, about 300 mm).

[0019]

The contact charging device using the charging roller 102 as the charging member as described above has the following problems.

That is, the charging roller 102 is pressed against the photosensitive drum 101, which is the member to be charged, at the pressing positions at both ends of the roller core metal 102a, and is in pressure contact with the surface of the photosensitive drum. 7 (C), the charging roller 10
The contact nip portion N between the photosensitive drum 101 and the photosensitive drum 101 becomes larger and smaller in the longitudinal direction, the width is large on both end sides close to the pressing position, and small at the central portion distant from the pressing position. Then, although stable charging is performed in the vicinity of both ends, defective charging is likely to occur in the vicinity of the central portion. The above charging is a discharge phenomenon in a minute gap between the drum 101 and the roller 102, and the minute gap becomes too large in the vicinity of the central portion, so that defective charging occurs.

For this reason, the nip width on both end sides is increased in order to increase the pressing force F · F so that the width at the longitudinal center of the contact nip N is sufficient as compared with the width at the center, for example. It will be about 2 to 4 times too large.

Therefore, the charging roller 102 and the photoconductor drum 101 are easily worn near both ends, and the photosensitive layer is scraped off in the photoconductor drum portion near the ends, for example, as a result of long-term use, and leakage due to charging occurs. It tends to occur.

Further, if the pressing force F · F is made too large as described above, there is a possibility that the layers may be separated during the contact rotation process with the photosensitive drum 101, particularly in the charging roller having a laminated structure of a plurality of layers.

Further, as described above, particularly when an oscillating voltage such as a superimposed voltage of a DC voltage and an AC voltage (a voltage value periodically changes with time) is applied to the charging roller 102, the charging roller 102 is charged. Vibration occurs at the frequency 102 of the vibration voltage. The toner that has slipped out of the cleaning device for the photoconductor drum is charged by the charging roller 10.
The minute vibration 2 causes the surface of the charging roller 102 to be pressed onto the surface of the photosensitive drum 101. In a high-temperature and high-humidity environment (H / H environment, for example, 32.5 ° C., 85% RH), the toner fusion phenomenon easily occurs on the surface of the photoconductor drum 101, and the photoconductor drum 101 in which the toner fusion has occurred occurs. Since the exposure light is blocked in the area of, the image defect occurs. As described above, when the pressing force F · F is large,
The frictional force between the charging roller 102 and the photosensitive drum 101 increases, and the toner fusion phenomenon tends to occur particularly prominently in the vicinity of both ends of the charging roller.

In order to prevent the toner fusion in the H / H environment, if the pressing force F · F at both ends of the charging roller 102 is lowered, the straight type charging roller is already in the conventional non-pressurized state. As described above, the charging failure is likely to occur at the longitudinal center of the contact nip portion N.

When the roller shape is not straight without being pressed due to the variation in the manufacturing process but is slightly curved, the surface of the photosensitive drum and the charging roller are rotated at the center of the roller where the end pressing force is not applied by rotation. There was a portion separated from the surface, which made charging impossible, which sometimes appeared as an output image defect.

With respect to this problem, in particular, when the surface of the photosensitive drum and the charging roller are separated from each other by about 50 μm or more, defective charging is partially caused at that time, resulting in defective output image. Accordingly, it was confirmed by the applicant of the present application that an image defect is caused. This is because, for example, if the gap is about 20 μm, sufficient charging can be performed initially by applying a voltage of _VDC + _VAC , but as the apparatus is used, it may be changed by the toner (or a component in the toner such as silica). The charging roller gradually becomes dirty and causes a slight uneven charging in a portion where the dirt is large and a portion where the dirt is small. In such a state, there is almost no effect on a solid black or solid white image, but in a halftone image, light and shade unevenness occurs, and the image quality deteriorates remarkably. Even in a laser beam printer, this appears in the image by dithering or the like. In order to prevent such an image defect, the gap between the photosensitive drum and the charging roller is at least 10 μm or less, preferably over the entire area, although it may vary depending on the electrophotographic process.
The applicant of the present application has determined that uniform contact is necessary.

As described above, due to the problem of toner fusion, it is difficult to obtain proper roller pressure at both ends and the center of the charging roller.

The above problems are shown in FIGS. 8 (A) and 8 (B).
As shown in FIG. 7, a non-rotating rod-shaped or horizontally-long pad-shaped member 102A is used as a charging member, and both ends of the cored bar 102a are pressed by the pressing springs 104 toward the photosensitive drum 101 as the charged body. The same applies to the structure in which the charging member is brought into contact with the photosensitive drum 101 with a predetermined pressing force as an urging force.

[0030]

[Means (and Action) for Solving the Problems]
The present invention has been made in view of the above problems, and an object thereof is to provide a charging member, a charging device, a process unit, and an image forming apparatus which perform uniform charging in a generatrix direction of an object to be charged such as an image carrier. Is.

Another object of the present invention is to provide a charging device and a process unit in which abrasion between the charged body and the charging member is reduced by appropriately pressing the charged body such as an image carrier and the charging member. And an image forming apparatus.

Another object of the present invention is to provide a process unit and an image forming apparatus which prevent the toner from being fused to the image carrier by the charging member and form a good image.

Further, an object of the present invention is to provide a charging device in which, when a member to be charged and a charging member are pressed, regardless of the distance from the pressing position, each part along the nip part of both is substantially uniform in width and pressure contact force. And a process unit and an image forming apparatus.

Further, an object of the present invention is to provide a charging member, a charging device, a process unit and an image forming apparatus which are excellent in accuracy and manufacturability and have a merit in cost.

Further objects and features of the present invention will become more apparent by reading the following detailed description with reference to the drawings.

[Structure of the Invention] In order to achieve the above object, according to the present invention, there is provided a charging member for charging a body to be charged, which comprises at least a base material and a coating layer as the body approaches the body to be charged. In the charging member provided, the thickness of the coating layer of the charging member is larger toward the central portion in the longitudinal direction of the charging member.

According to the present invention, there is provided a charging member which is provided so as to be in contact with a charged body and charges the charged body,
In a charging device having a charging member including at least a base material and a coating layer as it approaches an object to be charged, and a pressing unit pressing the charging member and the object to be charged, the charging member and the object to be charged There is provided a charging device characterized in that the thickness of the coating layer of the charging member increases as the distance from the pressing position by the pressing means in a state where is not pressed.

According to the present invention, the image carrier, the image forming means for forming an image on the image carrier, the charging member provided so as to be in contact with the image carrier and charging the image carrier. And an image forming apparatus comprising: a charging member including at least a base material and a coating layer as approaching the image carrier, and a pressing unit that presses the charging member and the image carrier, Provided is an image forming apparatus characterized in that the thickness of the coating layer of the charging member increases as the distance from the pressing position by the pressing means in a state where the charging member and the image carrier are not pressed.

Further, according to the present invention, a process unit detachable from the image forming apparatus, comprising an image carrier,
A charging member which is provided so as to be contactable with the image carrier and charges the image carrier, the charging member including at least a base material as it approaches the image carrier, and a coating layer,
In a process unit having a pressing unit that presses the charging member and the image carrier, the thickness of the coating layer of the charging member depends on the pressing unit when the charging member and the image carrier are not pressed. Provided is a process unit which is characterized in that it is larger as it is farther from a pressing position.

[0040]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an image forming apparatus using a contact type charging device according to the present invention as a primary charging means of an electrophotographic photosensitive drum (hereinafter referred to as a photosensitive drum) as an image bearing member which is a member to be charged. The schematic block diagram of an example is shown.
The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process.

The photosensitive drum 1 is a photosensitive drum layer 1b (thickness, for example, 20) formed of an organic photoconductive layer (OPC) on the outer peripheral surface of a drum base 1a made of a grounded conductive material such as aluminum.
The diameter is 30 mm and the predetermined process speed (peripheral speed) is, for example, 5
It is driven to rotate at 0 mm / sec. Selenium, amorphous silicon, ZnO, or the like can be used as the photoreceptor layer.

Reference numeral 2 denotes a charging roller as a contact charging member. For example, a conductive core metal 2a made of iron or the like as a base material (core material) as a material is an elastic layer EPDM (which is integrally formed on the outer periphery thereof. A terpolymer of ethylene propylene diene) conductive rubber roller portion 2b, and a resistance layer 2c which is a coating layer mainly composed of epichlorohydrin rubber formed on the outer periphery thereof. That is, the charging member includes a base material, an elastic layer, and a resistance layer as the charging member approaches the photosensitive drum.

A power source 10 is connected to the core metal 2a of the charging roller 2.
Thus, an oscillating voltage, which is a superimposed voltage of the negative DC voltage and the AC voltage, is applied. At this time, on the surface of the rotary photosensitive drum 1 that has been negatively charged by the charging roller 2, at a constant print density Ddpi corresponding to the time series electric digital pixel signal of the target image information output from the laser scanner 12. By scanning exposure with the image-modulated laser beam 5, the potential of the exposed portion is attenuated and an electrostatic latent image is formed on the surface of the photosensitive drum 1. To the latent image surface, the negatively charged toner is supplied from the developing sleeve 4 of the developing device 6 to reversely develop the latent image.

On the other hand, the transfer material P is fed from a sheet feeding section (not shown) through the guide 7 to the contact nip section (transfer section) between the photosensitive drum 1 and the transfer roller 8 as a transfer member.
The toner image on the surface of the photoconductor drum 1 is transferred to the transfer material P by the transfer bias having the polarity opposite to the charging polarity of the toner applied from the power source 10 to the transfer roller 8 at the same timing as the toner image on the surface. Are sequentially transferred (transcribed) to.

The transfer material P that has passed through the transfer portion is the photosensitive drum 1
The image is separated from the surface and introduced into a fixing unit (not shown) to undergo image fixing, and is output as an image formed product (print).

After the transfer material is separated, the surface of the photosensitive drum 1 is cleaned by a cleaning device 9 to remove adhering contaminants such as toner remaining after transfer, and is repeatedly used for image formation.

Reference numeral 11 denotes a control unit (CPU) for automatically setting the bias applying power source 10 for the charging roller 2 and the transfer roller 8 to a predetermined application timing and a predetermined potential.

The charging roller 2, the developing device 6, the cleaning device 9, and the photosensitive drum 1 as an image carrier are supported by the process unit 13. The process unit 13 is attachable to and detachable from a laser beam printer which is an image forming apparatus.
Is slid along the guide 14, that is, moved in the direction perpendicular to the plane of FIG. However, the process unit 13 may include at least the charging roller 4 and the photoconductor drum 1.

As shown in FIG. 2, the charging roller 2 is rotatably supported by the conductive bearings 3 at both ends of the core metal 1a so that the roller longitudinal direction is substantially parallel to the generatrix direction of the photosensitive drum 1. Contacting the surface of the photoconductor drum, the bearings 3 on both ends of the roller are biased by conductive pressure springs 4 so as to be movable in the direction of the photoconductor drum. Abutted. In this example, the spring constant of the pressure spring 4 is 0.08 Kg / mm on one side. In addition, the applied pressure is 1 Kg in total pressure with the spring on one side being 500 g. If the total pressure exceeds 1.5 kg, the friction of the roller 2 and the drum 1 becomes severe, so 1.5 k
It is preferably g or less. In the case of this example, the charging roller 2 is driven to rotate in accordance with the rotational driving of the photosensitive drum 1.

As described above, a predetermined bias voltage is applied to the charging roller 2 from the bias power source 10 through the conductive pressure spring 4 and the conductive cored bar 2a to rotate the photosensitive drum. The peripheral surface of No. 1 is charged with a predetermined polarity and potential. Here, the charging is performed by the discharge generated in the minute gap between the photosensitive drum and the charging roller.
In the case of this example, it is negatively charged. The charging roller 2 has a DC voltage of -600V and a peak-to-peak voltage of 140 from the bias power source 10.
Oscillating voltage is applied is 0V _PP ~2000V superposed voltage of a sine wave AC voltage of _PP. Here, if the peak-to-peak voltage of the oscillating voltage is less than twice the charging start voltage value of the photoconductor drum 1 that is the member to be charged, spot-like uneven charging occurs on the photoconductor drum 1. It is desirable that the charging start voltage value is twice or more. This charging start voltage is defined as follows.

That is, when only a direct current voltage is applied to the contact charging member with respect to an object to be charged having a potential of 0 and gradually increased, the photosensitive drum, which is the object to be charged, responds to the applied current voltage. Write a graph of surface potential. At this time,
DC voltage is taken every 100V, but the first point is 100V when the surface potential appears when the surface potential is 0.
Take 10 points for each. From these 10 points, minimum 2 in statistics
A straight line is drawn by the multiplication method, and when the surface potential is 0 on this straight line, the value of the applied DC voltage is the charging start voltage.

When the photosensitive drum 1 having the organic photoconductive layer of this embodiment was used as the member to be charged, the charging start voltage value was 560V.

Next, the charging device equipped with the charging roller 2 will be described in detail.

(Embodiment 1) As the core metal 2a of the charging roller shown in FIG. 2, a metal rod having a diameter of 6 mm is used, and the diameter after completion of the charging roller is approximately 12 mm. Among them, the upper resistance layer 2c has a thickness of about 200 μm.

First, a thin layer of a conductive primer (not shown) is applied to the cored bar 2a, and then the conductive elastic layer 2b is integrally molded with the cored bar 2a in a mold. At this time, the resistance of the layer 2b is 10 ³ Ω or less between the core metal and the surface, and the outer diameter after molding the elastic layer 2b is about 11.6 mm. This elastic layer 2b
After vulcanization and drying, the resistance layer 2c as a coating layer is coated by dipping.

At this time, the thickness of the coating can be changed by changing the pulling speed of the dipping. Therefore, the thickness at the central portion is set to about 200 μm, and the thickness l near both ends is set to about 170 μm by slowly and gradually increasing at the coating start portion and gradually and gradually pulling up again from the central portion. After that, it is dried by heating and finished as a roll. By doing so, the outer diameter of the central portion is about 60 μm larger than the outer diameter near both ends. The resistance of the resistance layer 2d is controlled in advance so that the final resistance of the roller thus prepared is about 10 ⁵ to 10 ⁶ Ω between the surfaces of the core metal, and the final hardness in the roller state is 65 ° or less. The hardness of the layers 2b and 2c is controlled in advance so as to be (Asker c). According to such a method, it is possible to manufacture a roller which does not require a manufacturing process and does not cost much, and which has an extremely high accuracy because the film thickness is controlled and which is excellent in terms of function cost.

As the conductive elastic layer 2b, EPDM 100 parts by weight Ketjen Black 5 parts by weight Paraffin oil 10 parts by weight Zinc oxide 5 parts by weight Fatty acid 1 part by weight

The above materials are mixed on a two-roll roll cooled to 20 ° C. for 30 minutes to prepare a raw material compound.
2 parts by weight of dicumyl peroxide as a vulcanizing agent is added to 100 parts by weight of this raw material compound, and further mixed for 20 minutes on a roll. Φ6 using this compound
The elastic layer 2b was vulcanized and molded on the roller so that the outer diameter was φ12 around the stainless steel cored bar 2a.

As the paint for the resistance layer 2c,

[0061]

[Outer 1]

After the rubber compound was prepared, it was dissolved in an aromatic hydrocarbon solvent to prepare a 15% by weight solution to obtain an epichlorohydrin rubber paint.

(Comparative Example 1) The core bar to the elastic layer 2b were formed in the same manner as in Example 1, and the resistance layer 2c was formed by dipping to form a substantially uniform layer having a thickness of about 200 μm, dried by heating, and made into a roll. ..

According to this, although the hardness and resistance of the roller are the same as those in the first embodiment, the film thickness of the resistance layer 2c is different from that in the first embodiment, and as shown in FIG. It has a straight shape.

(Evaluation 1) In the image forming apparatus described in the section of Examples, each roller according to Example 1 and Comparative Example 1 was used for image evaluation, durability evaluation (5000 sheets), and pressure contact with the photosensitive drum. The condition was evaluated. The results are shown in Table 1.

[0066]

[Table 1]

Comparative Example 1-2 The elastic layer 2b is formed in the same manner as in Example 1, but thereafter the elastic layer 2b is made into a crown shape by polishing, and then the resistance layer 2c is coated.

Although the above problems should be solved by this, the proper amount of crown at this time is about 60 μm in outer diameter, and the above value can be stably obtained by polishing the elastic body. It is difficult.

(Evaluation 1-2) Durability evaluation was conducted on 50 pieces of each of Example 1 and Comparative Example 1-2.

[0070]

[Table 2]

It is apparent that the accuracy obtained by polishing the elastic body as described above is not sufficient for the present charging device including partial unevenness.

As is clear from the above results, this Example 1
The charging device, the image forming apparatus, and the process unit having the charging member according to the present invention have the effect of equalizing the contact state between the photosensitive drum and the charging roller without increasing the cost, and therefore, always obtain a good image. Can be provided. This is because in the present embodiment, the region of the minute gap (the range of the dischargeable gap is determined) in which the discharge is performed between the charging roller and the photosensitive drum in the longitudinal direction of the roller due to the uniform contact state. It is considered that this is because they are formed almost uniformly.

(Embodiment 2) Changing the film thickness of the resistance layer 2c as in Embodiment 1 means that the resistance can be distributed in the axial direction in the roll state. That is, the resistance is high where the film thickness is large and the resistance is low where the film thickness is thin.

The following table shows the results of image evaluation with respect to this, while changing the difference in the film thickness between the thick central portion and the thin end portions. In the table, "%" indicates that the thickness of the thick portion in the central portion is 100% and the thickness of the thin portion near both ends is expressed in%.

Here, the central film thickness was fixed at 200 μm.

The evaluation conditions (process speed, applied voltage, etc.) are the same as those shown in the above embodiment.

[0077]

[Table 3]

As can be seen from the above results, the thickness of the thin portion is preferably 20% or more of that of the thick portion.

This indicates that the resistance difference is good up to ⅕. In this roller, the total resistance is 10 ⁵ to 10 ⁶ Ω. That is, the central resistance is 5 ×
When a was the 10 ⁵ Omega, is near the ends is not is acceptable to 1 × 10 ⁵ Ω. That is, it can be said that the resistance is within the permissible range if the order of resistance does not change by one digit or more in one roller.

(Embodiment 3) FIG. 4 is a diagram showing a roller used in another embodiment, in which a low resistance elastic layer 2b is further formed on a core metal 2a, a resistance layer 2c is further formed on the elastic layer 2b, and a surface layer is used for preventing contamination. It consists of layer 2d.

In the first embodiment, since the resistance layer 2c is in direct contact with the photoconductor drum, materials and manufacturing conditions must be taken into consideration so as not to contaminate the photoconductor drum with viscous substances contained in the resistance layer 2c. In addition, it was a very big constraint in making the roller. Therefore, in the present embodiment, an example in which the pollution prevention layer 2d made of, for example, N-methoxymethylated nylon is provided on the resistance layer 2c is shown. According to this, the function of the pollution prevention layer and the function of the resistance layer are separated, so that the resistance layer has almost no restriction to consider the pollution and the degree of freedom increases, so that a very stable layer can be formed. become.

First, a thin layer of a conductive primer (not shown) is applied to the cored bar 2a, and then the conductive elastic layer 2b is integrally molded with the cored bar 2a in a mold. At this time, the outer diameter after molding the layer 2b is about 11.6 mm. The elastic layer 2b is vulcanized and dried, and then the resistance layer 2c as a coating layer is coated by dipping. At this time, by changing the pulling rate of the dipping, the film thickness in the central portion is about 200 μm and the film thickness in the vicinity of both ends is about 170 μm as in the first embodiment.
m. After that, it is dried by heating, the anti-contamination layer 2d is applied by dipping to about 10 μm, and dried by heating to form a roll.

The resistance of the resistance layer 2c is controlled in advance so that the final resistance of the roller thus prepared is about 10 ⁵ to 10 ⁶ Ω between the cored bar and the surface, and the final hardness in the roller state is set. The hardness of the layers 2b and 2c is controlled in advance so that the temperature becomes 65 ° or less (Asker c).

The outer diameter is larger by about 60 μm than the central portion or the vicinity of both ends.

COMPARATIVE EXAMPLE 3 As shown in FIG. 5, the core metal to the elastic layer 2b are formed in the same manner as in Example 2, and the resistance layer 2c is 200.
A substantially uniform layer having a thickness of about μm is formed. Further, the upper layer 2d is formed to have a thickness of 10 μm as in the second embodiment, and is a roll having a substantially straight shape.

(Evaluation 3) The rollers of Example 2 and Comparative Example 2 were evaluated in the same manner as in Evaluation 1.

[0087]

[Table 4] (Comparative Example 3-2) The elastic layer 2b is formed in the same manner as in Example 3, but thereafter the elastic layer 2b is made into a crown shape by polishing, and then the resistance layer 2c is formed in the longitudinal direction of the cored bar 2a which is the shaft. Coat evenly. Further, similarly to the third embodiment, the pollution prevention layer 2d is uniformly coated in the longitudinal direction of the cored bar 2a.

At this time, the crown amount has an appropriate value of about 60 μm in outer diameter, and it is difficult to stably obtain the above value by polishing the elastic body.

(Evaluation 3-2) Durability evaluation was performed on 50 pieces of each of Example 3 and Comparative Example 3-2.

[0090]

[Table 5]

It is apparent that the accuracy obtained by polishing the elastic body as described above is not sufficient for the present charging device including partial unevenness.

As described above, in Example 1, a good image can be obtained by controlling the film thickness of the outermost layer of the roller, but in this Example, the film thickness of the second layer is controlled from the roller surface. By doing so, the same effect is obtained. That is, the gist of the present invention is not limited to the surface layer, but by controlling the thickness of the layer in the vicinity of the surface layer, preferably about 50 to 500 μm, at low cost, the photosensitive drum and the charging roller can be formed. The contact state can be made uniform, and therefore a good image can always be provided.

Although the layer formation by dipping has been shown as an example of the present invention, the present invention is not limited to this, and it goes without saying that it can be achieved by roll coating or other methods. is there.

(Embodiment 4) In this embodiment, a non-rotating rod-shaped or horizontally long pad-shaped member 2A is used as a charging member.
Both ends of the cored bar 2a are pressed and urged toward the photosensitive drum 1 as a member to be charged by pressing springs 4 to press the charging member against the photosensitive drum 1.

FIG. 6 (A) is a partially cutaway front view of the charging member 2A in the unloaded state, FIG. 6 (B) is a side view thereof, and FIG. 6 (C) is a state of being pressed against the photosensitive drum 1. The partial cutaway front view is shown.

2b is a conductive elastic layer, 2c is a resistance layer, and 2d.
Are contamination prevention layers, which are members 2b and 2 of the third embodiment, respectively.
It is the same material as c and 2d.

This charging member 2A is shown in FIGS. 6 (A) and 6 (B).
As shown in FIG. 3, in the non-contact state with the photosensitive drum 1, the resistance layer 2c becomes smaller in thickness from the vicinity of the longitudinal center to the vicinity of both ends.

Since a force F is applied to both ends in the longitudinal direction of the photosensitive drum 1 against the surface of the photosensitive drum 1 as the member to be charged against pressure compression resistance, as described above, The pressure contact nip portion N between the charging member 2A and the photoconductor drum 1 has a substantially uniform nip width and pressure contact force as shown in FIG. 6D for each portion along the longitudinal direction.

The charging member can also be applied to the transfer roller 8 which is a member for contact-charging the back surface of the transfer material P.

(Embodiment 5) By dipping the conductive layer 2e on the conductive elastic layer 2b shown in Example 1 at the beginning of coating, gradually pulling it from the central portion again gradually. Coating is performed so that the thickness of the central portion is about 60 μm and the thickness of both ends is about 10 μm.

After drying at 100 ° C. for 20 minutes, the coating material for the resistance layer 2c shown in Example 1 was applied at a constant coating speed of 170 μm.

When the outer diameter of this product was measured, a difference of about 100 microns was recognized between the center and the end. Further, when the electric resistances at the central portion and the end portions were measured, the thickness of the resistance layer was constant, and therefore, a difference was not recognized at about 10 ⁶ ohms.

As a coating material for the conductive layer 2e, 100 parts by weight of alcohol-soluble nylon, 6 parts by weight of conductive carbon, and 400 parts by weight of methyl alcohol were sand mill dispersed together with glass beads to obtain a conductive layer coating material.

(Embodiment 6) In order to coat the resistance layer 2c on the conductive elastic layer 2b shown in Embodiment 1, it is put in the coating tank 29 shown in FIG.
Tank 29 with 00 micron nozzle tip 32 attached
The air pressure of 1 kgf / cm ² is applied to the air pipe 30 and the distance between the gun 25 and the object to be coated 2b held by the rotating shaft 22 is set to 20 mm, and the gun 2 is rotated at 100 rpm.
The feed speed of No. 5 was gradually decreased from 170 mm per minute at the end to 120 mm as it went to the center, and the feed speed was increased again from the center to coat with the coating liquid with the beam 24 and dried at 120 degrees for 2 hours. When the film thickness was measured, it was about 200 μm at the central portion and about 170 μm at the end portion. When the outer diameter was measured, a large center diameter of about 60 microns was obtained.

(Embodiment 7) In order to coat the resistance layer 2c on the conductive elastic layer 2b shown in Embodiment 1, the coating is put in the coating tank 29 shown in FIG.
Tank 29 with 00 micron nozzle tip 32 attached
Air pressure of 1 Kgf / cm ² is applied, the distance between the gun 25 and the object to be coated 2b is set to 20 mm, and the rotation speed is 100 rpm. The gun feed rate is constant from the end to the coating speed of 170 mm / min. The pressure of the tank 29 is 1 kg at the end.
f / cm ^2, and the pressure is increased toward the center so that the pressure becomes 1.4 Kgf / cm ² at the center, and the pressure is gradually increased to 1 Kgf / cm ² from the center to the end again. I worked.

After drying at 120 ° C. for 2 hours, the film thickness was measured and found to be about 200 microns at the center and about 170 microns at the edges. When the outer diameter was measured, a large center diameter of about 60 microns was obtained.

In order to realize uniform charging according to the present invention, it is necessary that the outer diameter of the charging member is larger toward the center and smaller toward the ends. As a concrete means, the coating method is dipping. Method, beam method, spray method, spin method, bead method, blade method, roller method, curtain method, and the like, but by devising each method, it is possible to obtain a film thickness distribution by coating.

For example, in the dipping method, it is known that the greater the difference in relative pulling speed, the thicker the coating film thickness. The coating speed is increased as it goes to the central portion, and the blade moves from the central portion to the blade again. It is possible to provide by gradually delaying.

Further, for example, the coating speed is gradually delayed by beam coating for discharging and coating the coating material while rotating the coating object, and if the speed is restored from the central part, both ends are thin and the central part It is possible to manufacture thick ones. Further, in the same method, by increasing the discharge amount toward the central portion, it is possible to obtain a film thickness distribution even if the coating speed is constant.

The distribution of the coating thickness as described above can be achieved by devising the coating method. However, in order to realize the distribution state more accurately, the coating viscosity, the solid content, and the solvent vapor pressure are required. By optimizing the coating temperature, ventilation air volume, etc., it is possible to create a film thickness distribution that is faithful to the coating conditions.

Furthermore, in manufacturing such a film thickness distribution by the coating means, if the coating material of the charging member is directly distributed in the film thickness, the charging characteristics will have some distribution, and the film thickness It is necessary to keep the difference below a certain value.

Further, by devising the above-mentioned various coating conditions, it is possible to give a film thickness distribution to a certain extent to most of the products, but the material is limited due to the restriction of the characteristics on the electric resistance. In some cases, it may be difficult to provide a film thickness distribution.

For such a thing, it is not a necessary condition to give the resistor a film thickness distribution. If a conductive paint is applied to the film thickness distribution, there is almost no unevenness in the root electric resistance, and a charging member with a film thickness distribution is possible. If the material is not a resistor but electrical conductivity, it is advantageous in that the restrictions on material design are relaxed, and a paint (paint viscosity, solid content, solvent type) that allows easy distribution of film thickness can be used.

[0114]

As described above, according to the present invention,
Since the thickness of the coating layer of the charging member increases as the distance from the pressing position of the pressing unit that presses the charging member and the body to be charged is increased, the minute gap between the charging member and the body to be charged can be achieved very accurately and inexpensively. Can be uniform in its longitudinal direction.

Therefore, partial abrasion between the charging member and the member to be charged can be reduced, and when the member to be charged is a toner image carrier, fusion of the toner to the image carrier can be prevented.

[Brief description of drawings]

FIG. 1 is a side view in which a charging member of the present invention is applied to a process unit that can be attached to and detached from an image forming apparatus.

FIG. 2 is a side view of the first embodiment of the charging member of the present invention.

FIG. 3 is a side view of a comparative example of a charging member.

FIG. 4 is a side view of a third embodiment of the charging member of the present invention.

FIG. 5 is a side view of a comparative example of the charging member.

FIG. 6 is an explanatory view of a fourth embodiment of the charging member of the present invention.

FIG. 7 is an explanatory diagram of a conventional charging member.

FIG. 8 is an explanatory diagram of a conventional charging member.

FIG. 9 is a side view of a charging member according to a fifth embodiment of the present invention.

FIG. 10 is an explanatory diagram of a method of manufacturing the charging member.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Charged member (image bearing member) 2 Charging member 2a Core metal 2b Conductive elastic layer 2c Resistive layer (coating layer) 2d Contamination prevention layer 4 Pressing means 13 Process unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Fumihiro Arahira 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeshi Watanabe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Incorporated (72) Inventor Takao Honda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (5)

[Claims] 1. A charging member for charging an object to be charged, comprising:
In a charging member including at least a base material and a coating layer as it approaches an object to be charged, the thickness of the coating layer of the charging member is larger toward the central portion in the longitudinal direction of the charging member. .. 2. A charging member, which is provided so as to be capable of contacting a charged body and charges the charged body, the charging member comprising at least a base material and a coating layer as the charged body is approached. In a charging device having a pressing unit that presses a member and a member to be charged, in a state where the charging member and the member to be charged are not pressed, the thickness of the coating layer of the charging member departs from the position pressed by the pressing unit. Charging device characterized by being about the same size. 3. An image carrier, an image forming means for forming an image on the image carrier, and a contactable member provided on the image carrier.
A charging member for charging the image carrier, the charging member including at least a base material and a coating layer as approaching the image carrier, and a pressing unit for pressing the charging member and the image carrier. In the image forming apparatus including the image forming apparatus, the thickness of the coating layer of the charging member increases as the distance from the pressing position by the pressing unit increases in a state where the charging member and the image carrier are not pressed. .. 4. The image forming apparatus according to claim 2, wherein the apparatus has a process unit including the image carrier and the charging member, and the process unit is detachable from the apparatus. 5. A process unit detachable from an image forming apparatus, comprising: an image carrier and a charging member that is provided so as to be in contact with the image carrier and charges the image carrier. In a process unit having a charging member including at least a base material and a coating layer as approaching the image carrier, and a pressing unit for pressing the charging member and the image carrier, the charging member and the image carrier A process unit characterized in that the thickness of the coating layer of the charging member increases as the distance from the pressing position by the pressing means in the state where and are not pressed.