JPH07248667A - Contact electrifying member, contact electrifying device, and process cartridge - Google Patents

Abstract

PURPOSE:To provide a contact electrifying member, a contact electrifying device, and a process cartridge capable of preventing the occurrence of an abnormal discharge promoting the scraping of the surface of a charged body and improving the durability of the charged body. CONSTITUTION:An electrifying roller (contact electrifying member) 1 brought into contact with a charged body to electrify it is constituted of at least a conducting substrate 2, an electrification resistance layer 4 brought into contact with the charged body directly or via another layer, and a conducting layer (elastic layer) provided inside the electrification resistance layer 4. A difference in thickness is provided between both ends of the electrification resistance layer 4. The thicknesses M, N (M>N) at both ends of the electrification resistance layer 4 are set to 0.4:<=/M<=:0.9, M<=1000mum, 10mum<=N. When the thickness of the electrification resistance layer 4 of the electrifying roller 1 is made opposite to the thickness of the charged body, the occurrence of an abnormal discharge promoting the scraping of the charged body is suppressed, and the durability of the charged body can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact charging member, a contact charging device and a process cartridge used for image formation. The present invention relates to a contact charging member that uniformly charges a body, a contact charging device, and a process cartridge including these.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, a corona charging apparatus has hitherto been represented as a means for charging an object to be charged such as an electrophotographic photosensitive member or an electrostatic recording dielectric. The one using the non-contact charging method has been adopted.

By the way, the corona charging device having a built-in corona discharger is excellent in charging uniformity, but has been pointed out to be disadvantageous in terms of ecology such as high voltage consumption and ozone generation due to corona discharge.

Therefore, in recent years, a contact charging device for directly transferring (charging) electric charges to an object to be charged has been developed. This contact charging device applies a DC voltage or an oscillating voltage obtained by superimposing an AC voltage on a DC voltage to a charging member brought into contact with a member to be charged, and charges the member to be charged. , Ozone-less, low-voltage charging, cost reduction, etc. are realized.

In such a contact charging device, as disclosed in, for example, Japanese Patent Application Laid-Open No. 63-149669, when a DC voltage is applied to the contact charging member, the charging start voltage of the member to be charged is at least twice as high. By forming an oscillating electric field having a peak-to-peak voltage between the contact charging member and the member to be charged, the member to be charged can be uniformly charged.

Here, an example of the structure of the charging roller as the contact charging member will be shown.

FIG. 4 is a vertical cross-sectional view of the charging roller 1. The charging roller 1 is necessary for forming a uniform nip with the conductive substrate 2 as a supporting member (core metal) and the surface of the body to be charged. It is composed of a conductive layer 3 having elasticity and a medium resistance charging resistance layer 4 for controlling the resistance of the charging roller 1.
Even if a defect such as a pinhole occurs in a member to be charged (not shown), the charging failure does not occur in the image area.

FIG. 5 shows the configuration of a laser beam printer adopting a reversal development system as an example of an image forming apparatus equipped with the charging roller 1.

In FIG. 5, reference numeral 1 denotes a charging roller which is a contact charging member, which is formed by forming a roller-shaped conductive layer 3 and a charging resistance layer 4 on a conductive substrate 2 which is a supporting member as described above. As described above, an AC component having a peak-to-peak voltage that is at least twice the charging start voltage of the photosensitive drum 5 that is the member to be charged and a DC component that corresponds to the target charging potential are superimposed on the charging roller 1. The generated oscillating voltage is applied from the power supply 7.

As shown in FIG. 6, the charging roller 1 set in the contact charging device is disposed substantially parallel to the photosensitive drum 5 which is the member to be charged and has a constant contact nip width. Pressed against 5. The photosensitive drum 5 of this charging roller 1
The pressure roller 6 is pressed by the pressure springs 6 located at both ends of the conductive substrate 2 of the charging roller 1. In this state, the charging roller 1 is driven to rotate by the photosensitive drum 5 rotating at a predetermined process speed. The surface of the photosensitive drum 5 is sequentially charged to the target potential.

Next, the surface of the photosensitive drum 5 which has been charged as described above is scanned and exposed with the laser beam 12 to form an electrostatic latent image on the surface of the photosensitive drum 5. Then, the electrostatic latent image is developed (reverse development) as a toner image by the developing device 8, and the toner image is transferred to the transfer material 11 fed to the pressure contact portion between the transfer device 9 and the photosensitive drum 5. . still,
The transfer residual toner on the surface of the photosensitive drum 5 is removed by the cleaning device 10, and the photosensitive drum 5 is prepared for the next image formation.

Then, the transfer material 1 on which the toner image is transferred
The toner No. 1 is conveyed to the fixing device 13 and, after the toner image is fixed by the fixing device 13, it becomes an image-formed product and is discharged to the outside of the apparatus.

By the way, in the manufacture of the photosensitive drum 5 used in the electrophotographic process described above, in general, the drum substrate (the object to be coated) is dipped in the coating solution,
Then, by pulling up the drum base, the photosensitive material coating is applied to the surface of the drum base.

[0014]

As described above, the photosensitive drum is generally manufactured by the dipping method. In this manufacturing process, after the drum substrate (object to be coated) is pulled up, the coating film is dried and fixed. In addition, since the paint moves downward, the film thickness on the upper part of the drum base becomes thin, and the film pressure on the lower part becomes thicker, which causes a film thickness difference phenomenon.

Therefore, conventionally, the film thickness is corrected by improving the pulling rate and by vertically reversing the object to be coated and then reversing the film to dry and fix it as disclosed in JP-A-60-21052. Although the method has been put into practical use, it is difficult to completely suppress the occurrence of coating film unevenness (film thickness difference), and there is a slight film thickness difference at both ends of the photosensitive drum, which is the object to be coated. It is the current situation.

When the contact charging method is adopted as the charging method, unlike the non-contact charging method typified by a corona charging device, the contact charging member directly contacts the photosensitive drum. Wear tends to occur. In particular, the end portion of the photosensitive drum having a smaller film thickness is more likely to be deteriorated in performance due to wear than the end portion having a larger thickness.

When abrasion of the surface of the photoconductor drum causes abrasion of the photoconductor layer, the resistance of the photoconductor layer decreases, the uniform charging property of the contact charging member is lost, and discharge concentrates on the edge of the photoconductor drum having low resistance ( (Abnormal discharge), and abrasion of the photoconductor layer is promoted.

With the current low-speed machines and low-life cartridges (low-durability sheets), the above-mentioned tendency is hardly seen, but with high-speed machines and high-life cartridges (high-durability sheets), the above tendency becomes remarkable. Countermeasures against it will be essential for future speeding up of the main body and extension of cartridge life.

The present invention has been made in view of the above circumstances, and a purpose thereof is to prevent abnormal discharge which promotes abrasion of the surface of the charged body and to improve durability of the charged body. An object of the present invention is to provide a charging member, a contact charging device and a process cartridge.

[0020]

[Means for Solving the Problems] In order to achieve the above object,
The invention according to claim 1 is configured to include at least a conductive substrate, a charging resistance layer in contact with a body to be charged directly or through another layer, and an elastic body provided inside the charging resistance layer,
In the contact charging member for contacting and charging the body to be charged, a difference in film thickness is provided at both ends of the charging resistance layer.

According to a second aspect of the invention, in the invention of the first aspect, the film thicknesses M and N at both ends of the charging resistance layer are provided.
The ratio N / M of (M> N) is set to 0.4 ≦ N / M ≦ 0.9.

The invention according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the film thicknesses M and N at both ends of the charging resistance layer are set to M ≦ 1000 μm and 10 μm ≦ N, respectively. And

According to a fourth aspect of the present invention, there is provided an apparatus for charging a charged member by bringing the contact charging member into contact with the charged member, wherein the contact charging member includes at least a conductive substrate and a charged member. In a contact charging device comprising a charging resistance layer that is in direct contact with another layer via another layer, and an elastic body provided inside the charging resistance layer, a film thickness difference between both ends of the charging resistance layer of the contact charging member. Is provided.

According to a fifth aspect of the invention, in the invention of the fourth aspect, the ratio N / M of the film thicknesses M and N (M> N) at both ends of the charging resistance layer of the contact charging member is 0. 4 ≦ N / M
It is characterized by setting ≦ 0.9.

According to a sixth aspect of the invention, in the invention of the fourth or fifth aspect, the film thicknesses M and N at both ends of the charging resistance layer of the contact charging member are M ≦ 1000 μm and 1 respectively.
It is characterized in that 0 μm ≦ N is set.

According to a seventh aspect of the present invention, which is attachable to and detachable from the main body of the image forming apparatus and includes at least an object to be charged and charging means for the object to be charged, and the charging means uses the contact charging member as the object to be charged. Is a contact charging device for charging the body to be charged by bringing it into contact with a substrate, the contact charging member being at least a conductive substrate, a charging resistance layer in contact with the body to be charged directly or through another layer, and the charging resistance layer. In the process cartridge including the elastic body provided inside, the film thickness difference is provided at both ends of the charging resistance layer of the contact charging member.

[0027]

According to the present invention, if the film thickness of the charging resistance layer of the contact charging member is made to be opposite to the inclination of the film thickness of the member to be charged, the abnormal discharge that promotes the scraping of the surface of the member to be charged. Is suppressed, and the durability of the body to be charged is improved.

When the ratio N / M of the film thicknesses M and N (M> N) of the charging resistance layer of the contact charging member is set to 0.4 ≦ N / M, the film thickness is set to 0.4 ≦ N / M. A good image can be obtained because the resistance distribution near both ends of the contact charging member due to the difference becomes more uniform. In addition, under high humidity conditions, the current amount of the charging roller 1 tends to increase. Therefore, especially when N / M is set to N / M ≦ 0.9 during durable use, abnormal discharge becomes even more effective. It is prevented.

By the way, when the film thickness of the charging resistance layer of the contact charging member is increased and the resistance is increased, the current applied to the contact charging member is decreased. The partial potential becomes insufficient and image fog occurs. Therefore, the film thickness M of the charging resistance layer of the contact charging member as in the invention of claim 3 is M ≦ 10.
00 μm is desirable.

On the other hand, for the purpose of controlling the resistance of the charging resistance layer of the contact charging member so as to prevent charging failure even if defects such as pinholes are present in the member to be charged, the charging resistance layer according to claim 3 of the invention. Thus, the film thickness N of the charging resistance layer is preferably 10 μm ≦ N.

According to the fourth aspect of the present invention, in the contact charging device, the occurrence of abnormal discharge that promotes the abrasion of the surface of the member to be charged is suppressed by the same action as that of the first aspect of the invention.
It is possible to improve the durability of the body to be charged.

According to the fifth aspect of the invention, in the contact charging device, a good image can be obtained by the same operation as that of the second aspect of the invention, and abnormal discharge can be prevented more effectively, and the charged body can be further effectively prevented. The durability can be improved.

According to the sixth aspect of the invention, in the contact charging device, by the same operation as that of the third aspect of the invention, it is possible to prevent the occurrence of charging failure, image fog and the like and obtain a good image.

According to the seventh aspect of the present invention, in the process cartridge, by the same operation as the first aspect of the invention, the occurrence of abnormal discharge that promotes the abrasion of the surface of the charged body is suppressed, and the durability of the charged body is improved. It is possible to improve.

[0035]

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

FIG. 1 is a vertical cross-sectional view of a charging roller 1 which is a contact charging member according to the present invention. The charging roller 1 has a roller-shaped conductive member on a conductive base member 2 which is a supporting member as in the conventional case. A layer 3 and a charging resistance layer 4 are formed and configured.

Thus, in this embodiment, the charging roller 1 uniformly contacts the photosensitive drum (not shown), which is the member to be charged, to prevent local abnormal discharge at the end of the photosensitive drum. Then, the film thickness M of the charging resistance layer 4 of the charging roller 1 corresponding to the end portion (the left end in the illustrated example) of the photosensitive drum having the smaller film thickness is thicker than the film thickness N of the other end (M> N). ), The charging resistance layer 4 is provided with a film thickness difference.

The ratio N / M of the film thicknesses M and N on both ends of the charging resistance layer 4 is

[0039]

## EQU1 ## It is preferable that 0.4 ≦ N / M ≦ 0.9.

If the charging resistance layer 4 is provided with a thickness difference as described above, abnormal discharge at the scraped portion of the surface of the photosensitive drum, which is the original purpose, can be prevented. In particular, N / M is 0.4 or more. (0.
When 4 ≦ N / M), a favorable image can be obtained because the resistance distribution near both ends of the charging roller 1 due to the film thickness difference becomes more uniform. Further, since the current amount of the charging roller 1 tends to increase under high humidity conditions, abnormal discharge is caused especially when N / M is set to 0.9 or less (N / M ≦ 0.9) during durable use. Can be prevented even more effectively.

The charging resistance layer 4 of the charging roller 1 is generally formed by a dipping method. As a concrete means for providing a film thickness difference to this, a method of continuously adjusting the dipping speed, an arbitrary film thickness is used. Coated on the charging resistance layer 4
After forming the film, a method of polishing the film to process it into a desired film thickness and the like can be mentioned.

By the way, when the film thickness of the charging resistance layer 4 is increased and the resistance is increased, the roller current is decreased and, for example, in the image forming apparatus adopting the reversal developing system, the potential of the non-exposed portion becomes insufficient and the image fog is caused. Occurs. Therefore, the film thickness of the charging resistance layer 4 is preferably 1000 μm or less.

On the other hand, the charging resistance layer 4 has a film thickness of 10 μm or more for the purpose of controlling the resistance so as not to cause a charging failure even if defects such as pinholes exist in the body to be charged. preferable.

[Embodiment] In the manufacture of a charging roller as a contact charging member, EPDM in which conductive carbon was dispersed in a stainless steel metal core (conductive base) having a diameter of 6 mm was used.
Rubber was formed into a circular center (elastic layer), and its surface was polished to obtain a cylindrical base layer roller having a diameter of 12 mm. Then, a urethane resin solution in which conductive tin oxide was dispersed was applied on the surface of the base layer roller by a dipping method to form a charging resistance layer.

Here, the charging resistance layer was provided with a film thickness difference by coating while continuously changing the dipping speed. Edge film thicknesses M and N (see FIG. 1) are M = 20, respectively.
0 μm, N = 70 μm, and N / M = 0.35. This is designated as charging roller A-1.

A base layer roller is formed in the same manner as the charging roller A-1, and the viscosity and the dipping speed of the urethane resin solution in which the conductive tin oxide is dispersed are changed to change the charging roller A- having various thickness differences. 2, A-3, A-4, A-
6, A-7, A-9 were manufactured. The film thickness conditions are summarized in Table-1.

Further, a base layer roller is formed by the same method as the charging roller A-1, and two kinds of charging rollers having uniform film thicknesses of 1200 μm and 950 μm are manufactured at a constant dipping speed, and then the charging resistance layer is polished. And processed so that N / M was 0.37 and 0.55, respectively. These rollers are charging rollers A-5 and A-8. Here, the film thickness conditions are summarized in Table-1.

For comparison, after forming the base layer roller in the same manner as the charging roller A-1, the charging roller A-10, A-11 having a uniform film thickness of the charging resistance layer with a constant dipping speed. Was manufactured.

[0049]

[Table 1] In the manufacture of the charging roller A-1, the charging roller was manufactured in the same manner except that the elastic layer was changed from carbon-dispersed EPDM rubber to carbon-dispersed polystyrene foam (Asker C hardness 36 degrees). Here, the charging resistance layer film thickness is M = 200 μm, N = 60 μm, and N / M = 0.
The roller 3 is a charging roller B-1, M = 150 μm,
A roller having N = 100 μm and N / M = 0.67 is a charging roller B-2.

<Example 1> Charging roller 1 having different film thickness
(A-1 to A-4, B-1) were set in the process cartridge 14 shown in FIG. The process cartridge 14 is configured as a unit in which, in addition to the charging roller 1, the photosensitive drum 5, which is a member to be charged, the developing device 8 and the cleaning device 10 are housed in a common housing, and this is a unit for image formation. It can be attached to and detached from the device body.

The process cartridge 14 is replaced by a laser printer (Hewle) which is an image forming apparatus shown in FIG.
It was mounted on a Laserjet4 manufactured by tt Packerd (FIG. 6) and subjected to an image development durability test under the following conditions. A laser beam printer (Hewlett Packard) which is an image forming apparatus including at least an exposure device, a transfer device, and a fixing device.
It was mounted on a Laserjet 4 manufactured by rd Co., Ltd., and an image development durability test was performed under the following conditions.

Here, as shown in FIG. 6, the laser beam printer includes at least an exposure device, a transfer device 9 and a transfer device 13 which are not shown. In FIG. 5, 6 is a pressure spring, 7 is a power source,
Reference numeral 11 is a transfer material, and 12 is a laser beam.

Environmental conditions: high temperature and high humidity H / H (32.5 ° C,
85%), normal temperature and normal humidity N / N (23 ° C, 60%), low temperature and low humidity L / L (15 ° C, 10%).

Durability conditions: 1 second missing 6k sheets endurance.

Evaluation method: The image fog state due to the scraping of the edge of the photosensitive drum after the endurance of 6 k sheets was evaluated in four levels. The evaluation of the charging unevenness was made based on the charging unevenness caused by the non-uniform charging at the initial stage of durability. The evaluation results are summarized in Table 2.

[0056]

[Table 2] Generally, the photosensitive drum is scraped due to durability, but by providing the charging roller with a film thickness difference at the end portion, the discharge concentration from the charging roller is suppressed at the thin end portion of the photosensitive drum, which promotes the scraping of the photosensitive drum. As a result, charging failure due to image fog or leak could be prevented.

<Embodiment 2> Charging rollers A-6, A-7,
An image development durability test was conducted in the same manner as in Example 1 except that A-8, A-9 and B-2 were used. The evaluation results are summarized in Table 3.

[0058]

[Table 3] The ratio N / M of the film thicknesses M and N is 0.4 ≦ N / M ≦ 0.9, and the film thicknesses M and N are 10 μm ≦ M and N ≦ 1000 μ.
A charging roller having a charging resistance layer of m has an effect of preventing abrasion of the photosensitive drum, and when it is used, uniform charging property is improved and a good image is obtained.

<Comparison 1> Charging roller A having a uniform film thickness
Using -10 and A-11, an image development durability test was conducted in the same manner as in Example 1. The evaluation results are summarized in Table 4.

[0060]

[Table 4] A charging roller A-1 having a uniform film thickness that has been conventionally used
0 and A-11 had no problem with uneven charging,
The abrasion of the photosensitive drum progresses under H / H and N / N environment,
Abnormal discharge from the charging roller occurred at the scraped portion of the photosensitive drum, causing image fog and significantly deteriorating the image quality.

[0061]

As is apparent from the above description, according to the present invention as set forth in claim 1, the occurrence of abnormal discharge that promotes the abrasion of the surface of the member to be charged is suppressed, and the durability of the member to be charged is improved. The effect of being able to be obtained is obtained.

According to the second aspect of the invention, in addition to the effect of the first aspect of the invention, a good image can be obtained and abnormal discharge can be prevented more effectively. Is obtained.

According to the invention of claim 3, in addition to the effect of the invention of claim 1 or 2, there is an effect that a good image can be obtained by preventing the occurrence of charging failure, image fog and the like. can get.

According to the invention described in claim 4, in the contact charging device, occurrence of abnormal discharge which promotes abrasion of the surface of the body to be charged is suppressed by the same action as in the invention described in claim 1,
The effect that the durability of the member to be charged can be improved is obtained.

According to the invention of claim 5, in the contact charging device, in addition to the effect of the invention of claim 4, a good image can be obtained by the same operation as that of the invention of claim 2. The effect that the abnormal discharge can be more effectively prevented and the durability of the charged body can be improved is obtained.

According to the invention of claim 6, in the contact charging device, in addition to the effect of the invention of claim 4 or 5, in addition to the effect of the invention of claim 3, charging failure, image fog, etc. It is possible to obtain the effect that a good image can be obtained by preventing the occurrence of

According to the invention described in claim 7, in the process cartridge, by the same operation as in the invention described in claim 1, occurrence of abnormal discharge that promotes abrasion of the surface of the member to be charged is suppressed, and durability of the member to be charged is reduced. The effect that improvement can be aimed at is acquired.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a charging roller according to the present invention.

FIG. 2 is a cross-sectional view of a process cartridge including the contact charging device according to the present invention.

FIG. 3 is a configuration diagram of a main part of a laser beam printer including a process cartridge according to the present invention.

FIG. 4 is a vertical sectional view of a conventional charging roller.

FIG. 5 is a configuration diagram of a main part of a laser beam printer including a conventional contact charging device.

FIG. 6 is a front view of a conventional contact charging device.

[Explanation of symbols]

 1 Charging Roller (Contact Charging Member) 2 Conductive Substrate 3 Conductive Layer (Elastic Body) 4 Charging Resistance Layer 5 Photosensitive Drum (Chargeable Body) 14 Process Cartridge M, N Film Thickness at End of Charging Resistance Layer

Claims (7)

[Claims] 1. A structure comprising at least a conductive substrate, a charging resistance layer that is in contact with a member to be charged directly or via another layer, and an elastic body provided inside the charging resistance layer. In the contact charging member for contacting and charging the contact charging member, a thickness difference is provided at both ends of the charging resistance layer. 2. The film thicknesses M and N at both ends of the charging resistance layer
The contact charging member according to claim 1, wherein a ratio N / M of (M> N) is set to 0.4 ≦ N / M ≦ 0.9. 3. The contact charging member according to claim 1, wherein the film thicknesses M and N of the charging resistance layer are set to M ≦ 1000 μm and 10 μm ≦ N, respectively. 4. A device for charging a charged body by bringing the contact charging member into contact with the charged body, wherein the contact charging member is at least a conductive substrate and directly or through another layer to the charged body. In a contact charging device including a charging resistance layer in contact with the charging resistance layer and an elastic body provided inside the charging resistance layer, a film thickness difference is provided at both ends of the charging resistance layer of the contact charging member. And a contact charging device. 5. The ratio N / M of the film thicknesses M and N (M> N) of both ends of the charging resistance layer of the contact charging member is 0.4 ≦ N / M.
The contact charging device according to claim 4, wherein ≦ 0.9 is set. 6. The contact charging device according to claim 4, wherein the film thicknesses M and N of the charging resistance layer of the contact charging member are set to M ≦ 1000 μm and 10 μm ≦ N, respectively. 7. The apparatus is detachable from the main body of the image forming apparatus and includes at least a body to be charged and a charging means for the body to be charged, and the charging means brings the contact charging member into contact with the body to be charged. A contact charging device for charging an object to be charged, wherein the contact charging member is provided at least with a conductive substrate, a charging resistance layer in contact with the object to be charged directly or through another layer, and provided inside the charging resistance layer. A process cartridge including an elastic body, wherein a thickness difference is provided at both ends of the charging resistance layer of the contact charging member.