JPH08305129A - Image forming device - Google Patents

Abstract

PURPOSE: To make an image smooth and to maintain high image quality by specifying the surface roughness of the surface of an electrifying roller formed with grinding. CONSTITUTION: The electrifying roller 2 as an electrifying member is arranged on the surface to be electrified of a photoreceptor 1, in a contact state. The electrifying roller 2 is of a conductive roller made of properly charged urethane rubber, for instance and the outer periphery of the roller 2 is used as an electrifying surface. At this time, the electrifying roller 2 is provided with the electrifying surface finished to obtain surface roughness RZ of <=8μm by the grinding, the electrifying surface is brought into contact with the surface to be electrified of the photoreceptor 1, to form an electrifying nip part N and a DC voltage is applied by a power source. The electrifying surface of the electrifying roller 2 is finished at this value by the grinding, so that when only the DC voltage is applied or a superimposed voltage that the DC voltage is superimposed on an AC voltage, the smoothness of the image quality is secured and the melt- sticking of a developer can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a charging device for charging an image bearing member by a charging member brought into contact with the image bearing member.

[0002]

2. Description of the Related Art A contact charging device is used as a means for charging an image carrier, such as a photoconductor or a dielectric, used in an electrophotographic system (copier, laser beam printer, etc.) or electrostatic recording system image forming apparatus. Is used. This is for charging by a charging member that is brought into contact with the surface to be charged of the image carrier, and unlike a corona discharge device which is a non-contact charging device, for example, it is possible to reduce the voltage of the power supply,
It has the advantage that the amount of ozone generated can be reduced.

Examples of the charging member of such a contact charging device include a charging roller, a charging blade, a charging brush, etc., each of which uses a conductive roller, blade, brush or the like. These charging members are arranged in contact with the contacted surface of the image bearing member surface, and a charging voltage is applied to the charging member by a power source to charge the charged surface to a predetermined potential. Among the above three charging members,
At present, it is said that the charging roller is most suitable because it can withstand long-term use.

[0004]

By the way, as described above, when the charging roller is used as the charging member, the shape of the outer peripheral surface of the charging roller, which is the charging surface, and the charging surface of the charged surface of the image carrier are compared. It was found that the moving direction greatly affects the final image quality and the cleaning property of the surface to be charged. For example, in a system in which only a DC voltage is applied as a power source, when the surface roughness of the charging surface of the charging roller is rough,
There is a problem that the smoothness of the image quality is lost. On the other hand, in the method of applying a so-called superimposed voltage in which an AC voltage and a DC voltage are superimposed as a power source, when the surface roughness of the charging roller is made too small, there is a problem that the developer is fused to the surface to be charged. To do.

In particular, when the charging surface of the charging roller is finished by grinding, the above-mentioned problem is greatly influenced by the relationship between the direction of the eyes during grinding and the moving direction of the surface to be charged with respect to the eyes. become.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an image forming apparatus that smoothes an image and prevents fusion of a developer to a surface to be charged.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is an image carrier having a surface to be charged, and a conductive charging member arranged in contact with the surface to be charged. In an image forming apparatus provided with a roller and a power source for applying a charging voltage to the charging roller to charge the surface to be charged of the image carrier, the charging roller has a surface roughness R by grinding.
z has a charging surface finished to Rz ≦ 8 μm, the charging surface is brought into contact with the surface to be charged of the image carrier to form a charging nip portion, and a DC voltage is applied by the power source. Is characterized by.

Further, an image carrier having a surface to be charged, a conductive charging roller disposed in contact with the surface to be charged, and a charging voltage applied to the charging roller to charge the image carrier. In the image forming apparatus provided with a power source for charging the surface, the conductive roller has: x = (moving speed of charged surface / moving speed of charged surface) × 10
When the surface roughness Rz is 0, x ≦ 100, 0.02x + 8 ≦ Rz ≦ 16, and x ≧ 100, the surface roughness Rz has a charged surface finished to satisfy −0.02x + 12 ≦ Rz ≦ 16. Then, the charging surface is brought into contact with the surface to be charged of the image carrier to form a charging nip portion, and the power source applies a superimposed voltage obtained by superimposing a DC voltage on an AC voltage. To do.

In these cases, cleaning means for cleaning the charging surface of the charging roller may be provided.

The image carrier is formed in a cylindrical shape, and the rotation direction of the charging surface and the charging surface in the charging nip portion is the rotation direction of the charging surface. When the same time is the forward rotation and the different time is the counter rotation, the charged surface is in contact with the charged surface with (1) the direction of the eyes of grinding as the forward direction, and with respect to the charged surface. Forward rotation,
(2) The direction of the grinding eyes is changed to the opposite direction and the surface to be charged is contacted, and the forward rotation is performed on the charged surface. (3) The direction of the eyes to be ground is changed to the opposite direction. While making contact with the surface to be charged, counter rotation with respect to the surface to be charged, (4) the direction of the eyes of the grinding is in the forward direction to contact the surface to be charged, and to the surface to be charged Counter rotation can be performed.

[0011]

According to the above construction, the charging surface of the charging roller is finished to the above-mentioned value by grinding, so that only the DC voltage is applied as the charging voltage to the charging roller arranged in contact with the image carrier, or the AC voltage is converted into the DC voltage. When the superposed voltage in which the voltages are superposed is applied, the smoothness of the image quality can be ensured and the fusion of the developer can be prevented.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 shows a schematic configuration of an image forming apparatus according to the present invention.

This image forming apparatus has an image carrier 1 as a member to be charged. The image carrier 1 is a drum-shaped OPC photoreceptor having an outer diameter of 30 mm (hereinafter, simply referred to as “photoreceptor 1”), and the charged surface on the surface is driven by an arrow mark at a peripheral speed of 100 mm / sec by a driving unit (not shown). It is rotationally driven (moved) in the R1 direction.

A charging roller 2 as a charging member is arranged in contact with the surface to be charged of the photoreceptor 1. Charging roller 2
Is, for example, a conductive roller having an outer diameter of 16 mm made of appropriately charged urethane rubber, and its outer peripheral surface serves as a charging surface. Regarding the resistance value of the charging roller 2, the charging surface was brought into contact with a metal plate at a total pressure of 1000 g so that the value of current flowing when DC-200 V was applied was about -200 μA. The charging roller 2 has its charging surface abutted against the surface to be charged of the photoconductor 1 at a total pressure of about 1000 g, and forms a strip-shaped charging nip portion N between the charging roller 2 and the surface to be charged.

The charging roller 2 charges the surface of the photosensitive member to -700V. Thereafter, the charged surface to be charged is subjected to image exposure 3 to form an electrostatic latent image.

The above-mentioned electrostatic latent image is visualized (developed) as a toner image with a developer (toner) attached by the developing device 4. In this embodiment, the developer has a styrene-acrylic resin as a binder and an average particle size of 7 μm.
m one-component magnetic developer was used.

The toner image on the surface 1a to be charged of the photosensitive member 1 is transferred at a transfer position T by a transfer roller (transfer means) 5 to a transfer material (not shown) such as paper. The transfer material P is transported in the direction of arrow K1 by a transport device (not shown) and supplied to the transfer position T. The transfer material P after the toner image transfer is separated from the charging surface 1a of the photoconductor 1 with the help of a charge removing member (charge removing means) 6, and is transported to a fixing unit (not shown) by a transport belt 7. The toner image on the surface of the transfer material P is fixed here, and then the transfer material P is discharged to the outside of the apparatus main body. On the other hand, in the photoreceptor 1 after the transfer of the toner image, the developer remaining on the surface to be charged 1a is removed by the cleaning device 8 and the residual charge is removed by the pre-exposure device 9, and then the next image starting from charging is generated. Used for formation.

In the image forming apparatus as described above, in relation to the surface roughness of the charging surface 2a of the charging roller 2, the smoothness of the halftone image and the cleaning property due to the durability, especially the developer on the photoreceptor are The adhesion, so-called fusion, was evaluated.

The durability is high temperature and high humidity (temperature 33 ° C., humidity 90
%), A4 size copying (image formation) was continuously performed on 50,000 sheets and evaluated. This is because under high temperature and high humidity, the worst condition for fusion is the condition. The smoothness of the halftone image was evaluated at a temperature of 23 ° C. and a low humidity of 10%. This is because the lower the humidity is, the more easily the difference in discharge characteristics appears in the image.

As shown in FIG. 2, the charging surface 2a of the charging roller 2 is brought into contact with the surface to be charged 1a on the surface of the photosensitive member 1 with a total load (total pressure) of 1000 g to form a charging nip portion N. A DC voltage of −1400V was applied to the core metal 2b of the charging roller 2 by the power source 21.

The photosensitive member 1 in the transfer nip portion N is
Rotation direction (movement direction) of the surface to be charged 1a, rotation direction (movement direction) of the charging surface 2a of the charging roller 2, and charging surface 2a.
3 to 6 are enlarged views of the transfer nip portion N showing the relationship with the direction of the eye (hereinafter referred to as "grinding eye") 2c during grinding. In these figures, the charged surface 1a of the photoconductor 1 is
It always rotates in the direction of arrow R1. Charging surface 2 of charging roller 2
The rotation of a is the forward rotation of the rotation in the same direction as arrow R1 (direction of arrow R2a) as shown in FIGS. 3 and 4, and the reverse direction of arrow R1 (direction of arrow R2b) as shown in FIGS. The rotation is called counter rotation. Regarding the ground surface 2a of the charging surface 2a, the states shown in FIGS. 3 and 6 are sequentially abutted, and the states shown in FIGS. 4 and 5 are oppositely abutted because of the relationship with the rotation direction of the charging surface 2a. And

When determined in this way, FIG. 3 shows the forward contact forward rotation, FIG. 4 shows the reverse contact forward rotation, FIG. 5 shows the reverse contact counter rotation, and FIG. 6 shows the forward contact counter rotation. It turns out that.

The surface roughness Rz of the charging surface 2a of the charging roller 2 according to the present invention is determined by rotating the charging roller 2 in the arrow direction with respect to the stylus 22a of the surface roughness meter 22, as shown in FIG. It is the value when the ground stitch 2c is in abutting contact. When the charging roller 2 was rotated in the opposite direction, that is, in the case of contact with the opposite eye, the measurement was about 2 μm larger than this.

The unit of the surface roughness Rz is μm,
The numbers after the decimal point are truncated.

8 and 9 show the results when a DC voltage was applied to the charging roller 2.

FIG. 8 shows results corresponding to the forward contact forward rotation of FIG. 3 and the forward contact counter rotation of FIG. The vertical axis of the figure shows the surface roughness Rz of the charging surface 2a of the charging roller 2, and the horizontal axis shows the charging roller 2 with respect to the surface 1a to be charged of the photoconductor 1 in the charging nip portion N.
The peripheral speed ratio of the charging surface 2a is shown in%. Here, the peripheral speed ratio will be described. The peripheral speed ratio x of the charging roller 2 is x = (moving speed of charging surface / moving speed of charged surface) × 10
Decide as 0. However, the moving speed of the charged surface 1a is positive in the arrow R1 direction in FIG. 3, and the moving speed of the charging surface 2a is positive in the arrow R2a direction in FIG. 3 and negative in the arrow R2b direction in FIG.

When determined as described above, for example, the peripheral speed ratio x
Indicates that the charged surface 1a and the charged surface 2a move in the same direction,
When the sizes are the same, that is, when the charged surface 2a rotates following the charged surface 1a, x = 100. Further, the peripheral speed ratio x = 0 means that the charging surface 2a of the charging roller 2 is stopped.

In this embodiment, (1) driven rotation (peripheral speed ratio 100%, peripheral speed 100 mm / sec)
) (2) Forward rotation (peripheral speed ratio 0-200%, peripheral speed 0-200
mm / sec) (3) Counter rotation (peripheral speed ratio 0-200%, peripheral speed 0-
The measurement was carried out in the range of 200 mm / sec) and the examination was added. In FIG. 8, the peripheral speed ratios are -200, -100, 0, 100, 20 among them.
The case of 0% is illustrated. Regarding the halftone image quality, in the figure, ◯ indicates good, Δ indicates slightly bad, and x indicates bad.

From the figure, the surface roughness Rz for realizing a smooth halftone image is Rz ≦ 8 μm in all the ranges of the above-mentioned embodiments, and the smaller Rz, the better. I understood.

The influence on the halftone image quality has a surface roughness Rz of the charging surface 2a of the charging roller 2 within the range of the above examination.
The result depends only on.

This means that the charging mechanism by the charging roller 2 is the discharge in the minute gap formed by the photoconductor 1 and the charging roller 2, and the difference in the above-mentioned examination conditions does not affect the discharge characteristics. It indicates that there is. <Second Embodiment> FIG. 9 shows a second embodiment. This embodiment corresponds to the above-described FIGS. 4 and 5, and the charging surface 2a of the charging roller 2 is brought into contact with the charged surface 1a of the photoconductor 1 in the opposite direction. The procedure is the same as that of the first embodiment corresponding to FIGS. As for the results, almost the same results as in Example 1 were obtained. That is, the charging roller 2
Regardless of the peripheral speed ratio of, when Rz ≦ 8 μm, good halftone image quality was obtained. <Third Embodiment> In the first and second embodiments described above, only the DC voltage is applied to the charging roller 2.
In the third embodiment, instead of this, a superimposed voltage obtained by superimposing a DC voltage on an AC voltage is applied.

Specifically, an examination was conducted by applying an AC voltage V _PP = 2200 V, a frequency f = 700 Hz, and a DC voltage −700 V to the charging roller 2.

The results are shown in FIGS. 10 and 11.

When the AC voltage is applied in addition to the DC voltage, even if the surface roughness Rz of the charging roller 2 is large to some extent as compared with the actual case of the DC voltage in Embodiments 1 and 2 described above. , The smoothness of the halftone image quality was not inferior because of the smoothing effect by the exchange.

However, unlike the above-described first and second embodiments, when the surface roughness Rz is too small, toner fusion occurs on the charged surface 1a of the photosensitive member 1. It is considered that this is because the charging surface 2a of the charging roller 2 vibrates due to the AC voltage and strikes the charging surface 2a of the photoconductor 2.

Approximately the same result was obtained for both the forward contact shown in FIG. 10 and the reverse contact shown in FIG. The shaded area in these figures is a good range for halftone image quality and toner fusion.

Regarding the halftone image quality, the surface roughness R
Good image quality was obtained when z was Rz ≦ 16 μm.

Similar to the difference between the results of Example 1 and Example 2 described above, there is no difference between the results of the forward contact shown in FIG. 10 and the reverse contact shown in FIG. It is shown that the difference in the order and the difference in the order has little influence on the discharge characteristics.

On the other hand, when the surface roughness Rz is small, fusion occurs as described above. The level was the worst when the peripheral speed ratio at which the charging roller 2 was driven to rotate was 100%, and the better the peripheral speed difference was, the better the result of the inspection was obtained.

The fact that there is no difference between the forward contact and the reverse contact indicates that the contact state is the same for both because of the small surface roughness Rz.

From the above results, as a preferable range of the surface roughness Rz, when the peripheral speed ratio x is 100% or less, 0.02X + 8 ≦ Rz ≦ 16 When the peripheral speed ratio x is 100% or more, −0 0.02X + 12 ≦ Rz ≦ 16 was obtained. <Embodiment 4> In Embodiment 4, as shown in FIGS. 12A and 12B, a cleaning means for cleaning the charging surface 2a of the charging roller 2 is provided. As the cleaning member of the cleaning means, a cleaning member 23a having a pad shape made of synthetic leather or sponge as shown in FIG. 12A or a bristle brush cleaning member 23b as shown in FIG. 12B is used. be able to. The cleaning members 23a and 23b are connected to the charging surface 2a of the charging roller 2.
Abut with an appropriate pressing force. The result is shown in FIG.

With respect to the DC voltage application systems of Examples 1 and 2, the toner fusion did not occur as described above, and the results were the same as those in FIGS. 8 and 9.

Regarding the AC + DC voltage system of the above-described third embodiment, the upper limit of the surface roughness Rz, that is, the halftone image quality is the same as in FIGS.

Further, as can be seen from FIG. 13, no toner fusion occurred. As a cause of the toner fusion, when the toner adhered to the charging surface 2a of the charging roller 2 with durability is vibrated by the AC voltage and the charging surface 2a of the charging roller 2 vibrates and strikes the charged surface 1a of the photoconductor 1, the toner is fused. It shows that you do.

As a preferable range of the surface roughness Rz in the AC + DC voltage system with the cleaning members 23a and 23b, Rz ≦ 16 μm was obtained.

[0046]

As described above, according to the present invention,
In an image forming apparatus that charges the surface to be charged by contacting the charging surface of the charging roller with the surface to be charged of the image carrier, when the voltage applied to the charging roller is only DC voltage, and when the DC voltage is superimposed on the AC voltage. The surface roughness of the charging roller surface formed by grinding is set as described above according to the case of different superimposed voltages, thereby smoothing the image and maintaining a high quality halftone image, for example. It is possible to prevent the fusion of the developer to the surface to be charged.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a state where a charging surface of a charging roller is brought into contact with a surface to be charged of a photoconductor.

FIG. 3 is a diagram showing a forward contact forward rotation of a charging roller with respect to an image carrier.

FIG. 4 is a diagram showing the rotation of the charging roller with respect to the image carrier in the forward direction in the reverse contact direction.

FIG. 5 is a diagram showing a reverse contact counter rotation of the charging roller with respect to the image carrier.

FIG. 6 is a diagram showing the rotation of a charging roller with respect to an image bearing member in the order contact counter.

FIG. 7 is a diagram showing how the surface roughness of a charging roller is measured.

FIG. 8 is a diagram showing the relationship between the peripheral speed ratio of the charging roller and the surface roughness of the charging roller of Example 1.

FIG. 9 is a diagram showing the relationship between the peripheral speed ratio of the charging roller and the surface roughness of the charging roller of Example 2.

FIG. 10 is a diagram showing the relationship between the peripheral speed ratio of the charging roller and the surface roughness of the charging roller in the sequential contact according to the third embodiment.

FIG. 11 is a diagram showing the relationship between the peripheral speed ratio of the charging roller and the surface roughness of the charging roller in the reverse contact according to the third embodiment.

FIG. 12A is a diagram showing a state in which a pad-like cleaning member is brought into contact with the charging surface. FIG. 6B is a diagram showing a state in which a brush-like cleaning member is brought into contact with the charged surface.

FIG. 13 is a diagram illustrating the relationship between the peripheral speed ratio of the charging roller and the surface roughness of the charging roller when a cleaning member is provided in the fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier (photoreceptor) 1a Charged surface 2 Charging roller (charging member) 2a Charging surface 2b Core bar 2c Grinding eye (grinding eye) 3 Image exposure 4 Developing device 5 Transfer roller (transfer means) 6 Static eliminating member ( Charge removing means 7 Transport belt 8 Cleaning device 9 Pre-exposure device 23a Cleaning member 23b Cleaning member P Transfer material N Charging nip Rz Surface roughness x Peripheral speed ratio

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sorin Tana No. 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (7)

[Claims] 1. An image carrier having a surface to be charged, a conductive charging roller arranged in contact with the surface to be charged, and a charging voltage applied to the charging roller to charge the image carrier. In the image forming apparatus provided with a power source for charging the surface, the charging roller has a charging surface whose surface roughness Rz is finished by grinding to Rz ≦ 8 μm, and the charging surface is charged by the image carrier. An image forming apparatus comprising: a charging nip portion which is brought into contact with a surface, and a direct current voltage is applied by the power source. 2. An image carrier having a surface to be charged, a conductive charging roller disposed in contact with the surface to be charged, and a charging voltage applied to the charging roller to charge the image carrier. In the image forming apparatus provided with a power source for charging the surface, the conductive roller has: x = (moving speed of charged surface / moving speed of charged surface) × 10
When the surface roughness Rz is 0, x ≦ 100, 0.02x + 8 ≦ Rz ≦ 16, and x ≧ 100, the surface roughness Rz has a charged surface finished to satisfy −0.02x + 12 ≦ Rz ≦ 16. The charging surface is brought into contact with the surface to be charged of the image carrier to form a charging nip portion, and the power source applies a superimposed voltage obtained by superimposing a DC voltage on an AC voltage. Image forming apparatus. 3. The image forming apparatus according to claim 1, further comprising a cleaning unit that cleans a charging surface of the charging roller. 4. The image carrier is formed in a cylindrical shape, and the rotation direction of the charged surface is the rotation direction of the charged surface in the charging nip portion. When the direction is the same as the forward rotation and the different direction is the counter rotation, the charged surface is in contact with the charged surface with the direction of the eyes of grinding being the forward direction, and is forward with respect to the charged surface. The image forming apparatus according to claim 1, wherein the image forming apparatus rotates in a direction. 5. The image carrier is formed into a cylindrical shape, and the rotation direction of the charging surface and the charging surface in the charging nip portion is the rotation direction of the charging surface. When the direction is the same as the forward rotation and the different time is the counter rotation, the charged surface is in contact with the charged surface with the direction of the grinding eyes in the opposite direction, and is forward with respect to the charged surface. The image forming apparatus according to claim 1, wherein the image forming apparatus rotates in a direction. 6. The image carrier is configured in a cylindrical shape, and the rotation direction of the charged surface is the rotation direction of the charged surface in the charging nip portion. When the direction is the same as the forward rotation and the different time is the counter rotation, the charged surface contacts the charged surface with the direction of the grinding eyes in the opposite direction, and counters the charged surface. The image forming apparatus according to any one of claims 1 to 3, wherein the image forming apparatus rotates. 7. The image carrier is formed in a cylindrical shape, and the rotation direction of the charged surface and the charged surface in the charging nip portion is the rotation direction of the charged surface. When the direction is the same as the forward rotation, and when the direction is different from the counter rotation, the charged surface is in contact with the charged surface with the direction of the grinding eyes in the forward direction, and counters the charged surface. The image forming apparatus according to any one of claims 1 to 3, wherein the image forming apparatus rotates.