JPH08202116A - Electrifying roller member - Google Patents

Abstract

PURPOSE: To correct the nonuniformity of the shaving of a carrier transfer layer(CTL) caused by variation in an axial direction in the film thickness of the CTL of a photoreceptor drum and to prolong the life of the drum by making the outside diameter of an electrifying roller larger in a part where the film thickness of the CTL of the drum is small. CONSTITUTION: One side or one end part of the electrifying roller 18 has the outside diameter larger than that in the other part, that is, the range of B, in the range of A (when respective outside diameters are defined as C and D, C>D is established). The range of A corresponds to the part where the film thickness of the CTL of the drum is small. In the range of A where the outside diameter is larger than that in the range of B, the collapsing of the elastic layer of the roller becomes great, so that on both ends of a nip, an angle formed by the outer periphery of the electrifying roller and the drum is made large. In other words, when the electrifying roller 18 is separated from its contact part with the drum 1, reduction in the strength of an electric field which is rapider than that in the range of B is attained in the range of A. Thus, in the part where the film thickness of the CTL is small, the AC current of primary electrification is reduced up to one-third, to prevent the shaving of the CTL.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a charging roller member for charging an image carrier of an image forming apparatus.

[0002]

2. Description of the Related Art FIG. 6 shows a structure around a charging device of a conventional image forming apparatus.

Reference numeral 1 shown in FIG. 6 is a photoconductor drum, which has an aluminum cylinder having an organic photoconductor (OPC) layer as a surface layer, and is used for A3 printing (printing width 297 m).
In the example of the device for performing m), the length is 380 mm and the outer diameter is 3
It is 0 mm.

The charging roller 2 is provided in pressure contact with the photosensitive drum 1. The charging roller 2 is formed by winding a rubber material around a core metal 5 having a diameter of 8 mm, and the rubber material has an outer diameter of 14 mm and a length of 310 mm. The contact pressure of the photosensitive drum 1 is 700 gf on one side.

The charging of the photosensitive drum 1 is performed by the power source 3 between the aluminum cylinder portion of the photosensitive drum and the charging roller core metal.
It is carried out by applying an AC bias on which DC is superimposed.

The bias to be applied is AC 1000 Hz,
The voltage is about 2200 V _PP at a constant current bias of 1400 μA, and the DC bias is a constant voltage of −700 V. As a result, the potential on the photosensitive drum 1 is dark potential (VD) -680.
It can be converged to V and a stable potential can be obtained.

The photosensitive drum 1 uniformly charged by the charging roller 2 is exposed by the exposure light 16 which is scanned in the axial direction of the photosensitive drum 1. At this time, the exposure light 16 blinks according to the image signal, and an electrostatic latent image is formed on the photosensitive drum 1. The potential of the exposed portion is bright potential (VL) -20.
It becomes 0V.

The electrostatic latent image is visualized by the developing roller 15. A thin layer of developer is coated on the developing roller 15 by a developer regulating means (not shown). Developing roller 15
The upper developer is negatively charged by rubbing against the developing roller and the control means.

A bias of -500V is applied to the developing roller 15 by a bias means (not shown).
Therefore, the toner on the developing roller 15 is transferred to the bright potential (V _L ) portion on the photosensitive drum 1, and the latent image is visualized.

The developer image on the photosensitive drum 1 is transferred by the transfer roller 13 onto the paper 17, which is a transfer material.

When the paper 17 is fed by a paper feeding device (not shown) according to the image on the photosensitive drum 1, the paper 17 is nipped by the transfer roller 13 and the photosensitive drum 1 which are pressed against the photosensitive drum 1. While carrying. At this time, the transfer roller 13
Is applied with a bias of +3 kV by a bias means (not shown), and the toner image on the photosensitive drum is transferred onto the paper.

Thereafter, the developer image on the paper 13 is fixed by a fixing means (not shown) to form a fixed image. The developer remaining on the photosensitive drum 1 without being transferred is removed by the cleaning blade 14 contacted in the counter direction.
After being scraped off, the photosensitive drum 1 is cleaned.
Then, the photosensitive drum 1 is again subjected to the charging process.

Further, in this cleaning step, a foreign substance attached to the drum, for example, paper dust or talc discharged from the paper (which causes fusion of the drum where the developer adheres to the drum)
At the same time, it is scraped to prevent drum fusion.

The layer structure of the photosensitive drum 1 and the charging roller will be described in detail as shown in FIG.

The charging roller 2 includes a cored bar 5 made of an iron round bar having a diameter of 8 mm and plated with nickel from the center part, and an upper layer of the cored bar 5 made of hydrin rubber, EPDM, urethane rubber or the like and a metal oxide (TiO ₂ or the like). The elastic layer 6 in which carbon black or the like is dispersed, foamed, vulcanized and shaped has a function of lowering the overall hardness of the charging roller. Resistance value is 10 ^6-8 Ωc
m, hardness 30-35 ° (Asuka C hardness meter 1000 gf
When loaded), the thickness is approximately 3 mm. The upper layer thereof has a function of converging the resistance unevenness of the elastic layer 6 in the electrode layer 7, and is obtained by dispersing conductive carbon black in water-soluble nylon and having a resistance value of 10 ⁴ Ωcm and coating it in a thickness of 5 μm. .. The upper layer functions to give the charging roller a withstand voltage by the resistance layer 8, and a filler such as an organic metal salt, carbon black or metal oxide is dispersed in hydrin rubber or NBR to adjust the resistance value to 10 ⁸ Ωcm, It is applied with a film thickness of 150 μm. The surface layer is a protective layer 9, which has a function of covering the surface of the charging roller so that foreign matter from the charging roller does not adhere to the surface of the photosensitive drum 1. The material is water-soluble nylon with metal oxide, carbon black, etc. dispersed, and the resistance value is 10
It is coated with a film thickness of ⁸ Ωcm and a thickness of 10 μm.

Alternatively, instead of the three layers above the elastic layer, a film thickness of 1
It is replaced with one layer of urethane rubber (including elastomer) whose resistance value is adjusted with an organic metal salt or filler of 60 μm.

The charging roller 2 configured as described above has a hardness of 40 ° (when an Asuka C hardness meter of 1000 gf is loaded). The resistance value was brought into contact with a metal cylinder having a diameter of 30 mm, and AC: 300 was applied between the charging roller core metal 5 and the metal cylinder.
Hz 500V _PP , DC: AC current 500 to 700 μA, DC current 50 when bias of -200V is applied
It has an electric resistance of 0 to 700 μA.

The photosensitive drum 1 comprises a carrier generating layer (CGL) 11 having a thickness of several μm and a carrier moving layer (CTL) 12 having a thickness of 30 μm on an aluminum cylinder 10.
Both 1 and CTL 12 are coated by the dipping coating method.
Styrene resin and polycarbonate resin are used as the binder for CTL12.

The CTL 12 is gradually abraded by the cleaning blade 14 due to durable use.
This is about 1 μm per 1,000 sheets, and the film thickness at which image defects (fogging due to poor charging) occur is about 5 μm, so 25,000 sheets can be used for this drum.

Further, one of the factors causing the scraping of the drum is the charging roller.

Discharge occurs near the nip of the charging roller. This discharge makes the resin of the CTL 12 gradually decompose and becomes brittle, and is easily peeled off by the cleaning blade 14, that is, it is easily scraped.

For this reason, when the current value of the charging roller, especially the AC current value, increases, the discharge increases, so that the abrasion amount tends to increase.

Next, charging of the photosensitive drum by the charging roller will be described.

FIG. 9 is a diagram showing the vicinity of the contact nip between the photosensitive drum 1 and the charging roller.

The charging of the photosensitive drum 1 by the charging roller 2 is performed by the contact nip S between the photosensitive drum 1 and the charging roller 2 shown in FIG.
Is performed in the discharge region H formed outside the.

Here, the width of the charging nip (width of both ends of the discharge area) N by the charging roller 2 is 2 mm, and the contact nip S is
Is about 0.5 mm and the discharge area H is about 0.6 mm.

Since the width of the discharge region H depends on the electric field strength of the space, it becomes large when the diameter of the charging roller 2 or the photosensitive drum becomes large, and becomes small when it becomes small.

[0028]

However, in the above-mentioned conventional example, since the drum is dip-coated, as shown in FIG.
As shown in (3), there is a problem that the film thickness on the drum coating start side becomes small, the abrasion amount on the side where the film thickness is small becomes large, and the life of the photosensitive drum becomes short.

The reason why the amount of abrasion on the side where the film thickness is small is large is that when the film thickness is small, the electrostatic capacity becomes large and the AC current easily flows.

Since the amount of abrasion on the side where the film thickness is small is large, the difference in the film thickness from other portions becomes large, and the abrasion at this portion is further accelerated, and the life of the photosensitive drum is increased. Was shortened.

An object of the first invention according to the present application is that the CTL is caused by the axial variation of the CTL film thickness of the photosensitive drum.
It is to correct the unevenness of abrasion and to secure the life of the photosensitive drum.

A second object of the present invention is to correct the unevenness of CTL abrasion caused by a biased member other than the charging roller contacting the photosensitive drum, and ensure the life of the photosensitive drum. Especially.

A third object of the present invention is to correct non-uniformity of axial abrasion of CTL due to a member sliding on the photosensitive drum, and to secure the life of the photosensitive drum.

[0034]

In order to achieve the above object, the first invention of the present application is characterized in that the outer diameter of the charging roller is large in the portion where the CTL film thickness of the photosensitive drum is small.

In the above structure, in the portion where the outer diameter of the charging roller is large, the discharge current between the charging roller and the photosensitive drum is smaller than that in the other portions, and the portion where the CTL film thickness of the photosensitive drum is thin and the current easily flows. In other words, it works so as to suppress the abrasion even in the easily eroded part. In order to achieve the above object, the second invention of the present application is characterized in that the outer diameter of the charging roller is large at the portion where a member other than the charging roller to which a bias is applied comes into contact with the photoconductor during sheet feeding.

In the above structure, the portion of the charging roller having a large outer diameter is caused by a member other than the charging roller to which a bias is applied because the discharge current between the charging roller and the photosensitive drum is smaller than that of the other portions. Even if CTL is scraped,
The CTL abrasion due to the charging roller at that portion is reduced so that the CTL abrasion amount in the axial direction of the photosensitive drum becomes uniform.

In order to achieve the above object, a third invention of the present application is to provide a charging roller at a portion where there is a member that slides on a photosensitive drum or a portion where the contact pressure of the member that slides is large. Is characterized by having a large outer diameter.

In the above-mentioned structure, the discharging current between the charging roller and the photosensitive drum in the portion where the outer diameter of the charging roller is large is smaller than that in the other portions, so that the sliding member or the sliding member for the photosensitive drum is used. Even when the CTL abrasion in the photosensitive drum axial direction becomes non-uniform due to the non-uniform contact pressure, the CTL abrasion in the photosensitive drum axial direction due to the charging roller is reduced to reduce the CTL abrasion in the photosensitive drum axial direction. It works to make the quantity uniform.

[0039]

【Example】

(First Embodiment) FIG. 1 shows a charging roller 18 embodying the present invention. The charging roller 18 has one side or one end as shown in FIG.
The outer diameter is larger in the range A than in the other areas and in the range B as shown in FIG. (C> D when the outer diameters are C and D.) The range of A is C of the photosensitive drum.
It corresponds to the part where the TL film thickness is small.

FIG. 2 shows a discharge area when the charging roller 18 is brought into contact with the photosensitive drum 1.

In the range A where the outer diameter is larger than the range B, the amount of collapse of the elastic layer of the roller is large, so that the angle between the outer peripheral surface of the charging roller and the photosensitive drum is large at both ends of the nip.

That is, in the range of A, the electric field strength decreases more rapidly than that of the area B when the distance from the contact portion between the charging roller 18 and the photosensitive drum 1 is increased.

That is, the discharge region J is smaller in the range A having a larger outer diameter than in the range B. In the experiment, by setting the outer diameter of the range B to 14 mm and the outer diameter of the range A to 14.5 mm, the respective discharge regions are H = 0.6 mm and J =
It could be 0.2 mm.

As a result, the primary charging AC current in the small portion of the CTL film of the photosensitive drum 1 can be reduced to a maximum of 1/3, and it is possible to prevent the extreme CTL abrasion in this portion. .

That is, by making the outer diameter of the charging roller larger in correspondence with the portion of the photosensitive drum where the CTL film thickness is small, extreme abrasion at that portion can be prevented, and the image forming process near the center of the photosensitive drum can be prevented. It becomes possible to determine the life of the drum by the CTL film thickness of the part concerned.

(Second Embodiment) In this embodiment, a case where the amount of CTL scraping of the photosensitive drum by the transfer roller is large will be described.

FIG. 3 shows a second embodiment of the present invention.

A transfer roller 13 shown in FIG.
The toner image on the photosensitive drum 1 is transferred to the transfer material 17 while being rotated by a driving device (not shown) while being applied with a voltage from the power source 20, and the transfer material 17 is conveyed.

In an apparatus having a process speed of 90 mm or more, the length of the transfer roller 13 may be longer than that of the transfer material 17 in order to stabilize the conveyance of the transfer material 17.

However, in this case, since the photosensitive drum 1 and the transfer roller are in direct contact with each other in the non-paper passing area E, a larger amount of transfer current flows than in the paper passing area.

It has been confirmed that even when a DC bias is applied, a discharge is generated in the vicinity of the contact nip with the photosensitive drum 1, which causes the CTL to be scraped.

The scraping amount due to the transfer bias is about 1/3 of the charging bias, and cannot be ignored when the life of the photoconductor is intended to be extended.

The present invention is also effective in preventing drum scraping in the non-sheet passing area E.

In this embodiment, the diameter of the charging roller 19 in the portion E corresponding to the non-sheet passing area at the transfer roller contact portion is made larger than the sheet passing area.

The diameter of the charging roller is 14 mm in the paper passing area, and the contact portion E of the transfer roller is 14.5 mm in the non-paper passing area.

As a result, the non-sheet passing area E of the charging roller 19
It is possible to reduce the amount of discharge at 1/3 of the sheet passing area, and even if the photosensitive drum 1 is scraped due to the transfer roller, it is possible to prevent the life of the photosensitive drum from being shortened due to partial scraping.

(Third Embodiment) In this embodiment, a case will be described in which a member sliding on the photosensitive drum abrades the photosensitive member.

FIGS. 4 and 5 show a third embodiment of the present invention.

In the figure, 14 is a cleaning blade, and 21 is an end seal attached to prevent toner leakage from the end of the cleaning blade. The material of the end seal is, for example, foamed urethane or EP.
DM, chloroprene rubber and the like.

The end seal 21 is attached so as to press the C blade against the photosensitive drum from the back side in order to secure the sealing property and to contact the photosensitive drum outside the cleaning blade 14. For this reason,
At the end of the cleaning blade 14, the contact pressure with the photosensitive drum 1 is high.

Since the abrasion of the photosensitive drum 1 increases when the contact pressure of the cleaning blade is large, the abrasion amount at the end portion of the cleaning blade 14 may increase in the case of the above-described configuration.

In the present embodiment, as shown in FIG. 5, the outer diameter of the charging roller 22 at the end portion of the cleaning blade and the portion F corresponding to the end seal is increased. Charging roller 2
The outer diameter of 2 is 14.5 mm in the F region and 14.0 mm in the other portions.

With the above-described structure, even if the amount of CTL scraping due to friction at the end of the cleaning blade increases, the amount of scraping by the charging roller is reduced to reduce the entire CTL of the photosensitive drum 1. It is possible to equalize the amount of abrasion and secure the life of the photosensitive drum.

The structure of this embodiment is not limited to the position corresponding to the end portion of the cleaning blade, but it is coaxial with the developing roller so as to maintain an accurate gap between the photosensitive drum and another contact member, for example, the developing roller. It is also an effective means when a roller or a roller type roller is brought into contact with the sensing drum.

[0065]

As described above, the first aspect of the present application
According to the invention, even if the photoconductor film thickness of the photoconductor drum is uneven at the contact portion of the charging roller, local abrasion is suppressed,
This has the effect of ensuring the life of the photosensitive drum.

Further, according to the second invention of the present application, even when the photoconductor is scraped due to a biased member other than the charging roller, the scraping due to the charging roller corresponding to the position is caused. By suppressing the effect, it is possible to secure the life of the photosensitive drum.

Further, according to the third invention of the present application, even when the photoconductor is abraded due to the sliding contact with the member abutting on the photoconductor, the charging roller is caused at the position where the member abuts the photoconductor. By suppressing abrasion of the photoconductor, the life of the photoconductor can be secured.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a charging roller according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a charging area of the charging roller according to the first exemplary embodiment of the present invention.

FIG. 3 is a diagram illustrating a charging roller and peripheral members according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a cleaning blade and an end seal.

FIG. 5 is a charging roller according to a third embodiment of the present invention,
It is a figure explaining a peripheral member.

FIG. 6 is a diagram illustrating an example of a conventional charging device.

FIG. 7 is a diagram illustrating a cross section of a main part of the conventional example of FIG.

FIG. 8 is a diagram illustrating a film thickness of a conventional charging device.

FIG. 9 is a diagram illustrating a charging mode of a conventional charging device.

[Explanation of symbols]

1 Photosensitive drum 2,18,19
Charging roller 13 Transfer roller 14 Cleaning blade

Claims (3)

[Claims] 1. A charging roller member for applying a bias to a cored bar to charge a photosensitive member, wherein an outer diameter in a range corresponding to a portion having a small thickness of the photosensitive member is larger than outer diameters of other portions. And a charging roller member. 2. A charging roller member for charging a photosensitive member by applying a bias to a core metal, wherein a member other than the charging roller, which is applied with a bias when the paper is passed, has a portion whose outer diameter is in contact with the photosensitive member. Charging roller member characterized by being larger than. 3. A charging roller member for charging a photosensitive member by applying a bias to a core metal, wherein a portion corresponding to a member sliding on the photosensitive member or a contact pressure of a contacting member is large. A charging roller member, wherein an outer diameter of the portion is larger than that of the other portion.