KR19990088169A - Image forming apparatus having improved charging roller - Google Patents

Abstract

A novel image forming apparatus of the present invention includes a rotatable photosensitive member, a charging roller that contacts the surface of the photosensitive member so as to be rotated by a rotation operation of the photosensitive member, and charges the surface of the photosensitive member with an applied voltage, And a cleaning member which contacts the surface and cleans the surface of the charging roller by sliding contact with the surface of the charging roller. The surface of the charging roller is provided with a predetermined surface roughness having directivity, and the direction of the surface roughness of the charging roller is set to the rear with respect to the rotational direction of the photosensitive member and to the front of the surface of the cleaning member. .

Description

IMAGE FORMING APPARATUS HAVING IMPROVED CHARGING ROLLER}

The present invention relates to an image forming apparatus, and more particularly, is rotated by contact with a photosensitive element and by rotation of the photosensitive element to charge a surface of the photosensitive element by a charging roller, and a cleaning member is formed on the surface of the charging roller. The present invention relates to an image forming apparatus which always cleans its surface in contact with.

Recently, for example, in a copying machine, a facsimile apparatus, or a similar kind of image forming apparatus, a large number of apparatuses integrate a photosensitive element, a developing apparatus, a charging apparatus, and the like into one body and receive it in one case. By adopting an image forming unit, it is made compact.

Many charging devices provided in the image forming unit employ a roller-type charging member and uniformly charge the surface of the photosensitive element by applying a voltage to the charging roller in contact with the photosensitive element. When the charging roller is in contact with the photosensitive element and driven for rotation, toner and paper powder tend to move from the photosensitive element to the surface of the charging roller and adhere to the surface.

Typically, in such a charging roller, for example, a cleaning member made of a sponge and similar material cleans the surface of the charging roller by sliding contact with the rotating charging roller at an appropriate pressure, and thus the toner and paper powder Are removed from the surface of the charging roller.

Two types of sweeping members are disclosed. One type is always in contact with the surface of the charging roller, which is called "cleaning member of the always-contact method", and the other type is in contact with the surface of the charging roller only when necessary, which is called "contact / separation method". Cleaning member ".

The cleaning / detachment cleaning member has an advantageous point, because vibration of the charging roller due to sliding contact with the cleaning member is not generated during the image forming operation, because the cleaning member is used during the image forming operation. This is because it is separated from the charging roller, so that the stability of the rotational speed of the photosensitive element is not disturbed by the charging roller during the image forming operation. Therefore, jittering of the image due to variation in the rotational speed of the photosensitive element can be prevented.

However, since the contact / separation type sweep member requires a mechanism for contacting or separating from the surface of the charging roller, the contact / separation type sweep member tends to increase in size. Therefore, the contact / separation cleaning member is not suitable when the size of the image forming apparatus is required to be small.

On the other hand, since the sweeping member of the always contacting manner always contacts the surface of the rotating charging roller, a load is always applied from the cleaning member to the rotating charging roller. As a result, when the charging roller is always in contact with the photosensitive element, and is rotated by the rotation of the photosensitive element, unnecessary vibration of the cleaning member is transmitted to the photosensitive element via the charging roller during the image forming operation. This is because the cleaning member is in contact with the charging roller even when the image forming operation is performed. As a result, the photosensitive element changes its rotational speed by unnecessary vibration, thereby causing hunting of the image.

Therefore, this always-contact cleaning element is undesirable in practical applications, and although the cleaning element can be made compact, it is not often applied in practice.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to solve these problems.

1 is a schematic diagram showing the directivity of the surface of the photosensitive element and the rough surface of the charging roller relative to the roller cleaning member;

2 is an enlarged view showing that the shape of the rough surface of the charging roller on which the rough surface is formed has directivity;

3 is an enlarged view showing the rough surface shape of the charging roller in which the rough surface of the charging roller is formed without direction;

4 is a sectional view showing a configuration of an image forming unit of the image forming apparatus according to the present invention;

FIG. 5 is a graph showing an experimental result of performing image formation using various kinds of charging rollers having different surface roughness and directionality.

Explanation of symbols on the main parts of the drawings

1 ..... photosensitive elements 2 ..... charging device

3 ..... Exposure device 4 ..... Developer

5 ..... transfer belt 6 ..... cleaning material

7 ..... Antistatic Lamp 9 ..... Daejeon Roller

13 .... conductive rubber 22 .... roller cleaning material

According to a preferred embodiment of the present invention, a new image forming apparatus is a rotatable photosensitive member, a charging roller which is brought into contact with the surface of the photosensitive member so as to be rotated by a rotation operation of the photosensitive member, and charges the surface of the photosensitive member as the applied voltage And a cleaning member which contacts the surface of the charging roller and cleans the surface of the charging roller by sliding contact with the surface of the charging roller.

The surface of the charging roller is provided with a predetermined surface roughness having directivity, the directionality of the surface roughness of the charging roller in a backward direction with respect to the rotational direction of the photosensitive member, and with respect to the surface of the cleaning member. It is set in the forward direction.

The predetermined surface roughness of the charging roller may be between about 5 μm and about 40 μm.

The cleaning member may be made of a sponge.

Hereinafter, the present invention will be described in more detail with reference to the drawings. Like reference numerals denote like or identical parts throughout the drawings.

1 is a schematic diagram showing the directivity of the rough surface of the charging roller with respect to the surface of the photosensitive element and the roller cleaning member, Figure 2 is a shape of the rough surface of the charging roller having the rough surface is formed and directed 3 is an enlarged view showing that the rough surface of the charging roller is formed without directivity, and FIG. 4 is a cross-sectional view showing an image forming unit of the image forming apparatus according to the present invention.

As shown in Fig. 4, the image forming apparatus is provided with a drum type photosensitive element (image supporting member) 1 which can be rotated in the direction shown by arrow A. Figs. The charging device 2 including the charging roller 9 is provided around the photosensitive element 1 to uniformly charge the surface of the photosensitive element 1 by applying a voltage supplied from a power source (not shown). The charging roller 9 is kept in contact with the surface of the photosensitive element 1 and is driven to rotate by its rotational operation. An exposure apparatus 3 for forming an electrostatic latent image on the photosensitive element 1 by illuminating the laser light L and a developing apparatus 4 for developing the electrostatic latent image into a visible toner image are also provided around the photosensitive element.

A transfer belt 5 for transferring the toner image formed by the developing apparatus 4 to the transfer sheet, a cleaning device 6 for removing residual toner remaining on the photosensitive element 1 after the toner image is transferred to the transfer sheet; An antistatic lamp 7 for removing residual charge on the photosensitive element 1 is also provided around the photosensitive element. Toner is supplied from the inlet of the developing apparatus 4 by a toner supply device (not shown).

When the image forming operation starts, the image forming apparatus starts the rotation of the photosensitive element 1. Accordingly, the surface of the photosensitive element 1 is static-discharged as the antistatic light emitted by the antistatic lamp 7, and the surface potential of the electrostatic portion of the photosensitive element 1 is averaged to a reference voltage of 0V to -150V. Then, the photosensitive element 1 is charged by applying a voltage to the charging roller 9 which is driven to rotate by contacting the surface of the rotating photosensitive element 1, and the surface potential of the photosensitive element 1 becomes a voltage of approximately -1000V.

The laser light L is emitted from the exposure apparatus 3 to the charged surface of the photosensitive element 1, and by the irradiation of the laser light L, the surface potential of the image portion of the surface of the photosensitive element 1 becomes a voltage of 0V to -200V. Thus, the toner on the developing sleeve 10 of the developing apparatus 4 is attracted to the image portion on the photosensitive element 1. The toner image formed on the photosensitive element 1 moves to the transfer station, where the photosensitive element 1 contacts the transfer belt 5 by rotation of the photosensitive element 1 in the direction shown by arrow A. FIG.

The transfer sheet is supplied from a sheet supply unit (not shown), and is transferred by a registration roller pair 8. The leading edge of the transfer sheet is provided to the transfer station at a timing coinciding with the leading edge of the toner image formed on the photosensitive element 1. Will be reached. Then, the transfer sheet is transferred to a fixing unit (not shown), the toner image is melted by heating and pressurization and fixed thereon, and then discharged to a paper discharge tray (not shown).

Residual toner remaining on the photosensitive element 1 after the transfer operation is scraped off from the surface of the photosensitive element 1 by the sweep blade 11 of the cleaning device 6, and the surface of the photosensitive element 1 is discharged by the antistatic lamp 7.

Thereafter, the image forming process is repeated.

Next, the charging device 2 will be described.

The charging roller 9 of the charging device 2 is made of a conductive rubber 13 having low moisture absorbency and a stable resistance. The conductive phase rubber 13 is formed around the circumferential surface of the metal shaft 12 except for both ends. The surface layer may additionally be formed on the surface of the conductive rubber 13. In addition, the surface of the conductive rubber 13 is always in contact with the surface of the photosensitive element 1 at a constant pressure so that the charging roller 9 can be rotated in accordance with the rotation operation of the photosensitive element 1. The surface of the photoconductive element 1 is uniformly charged when a high voltage is applied to the axis 12 of the charging roller 9.

The roller cleaning member 22, which is a cleaning member, is always in pressure contact with the surface of the charging roller 9. The roller charging member is formed, for example, as a foam such as a sponge or the like, and is attached to a cleaning pad support member (not shown), for example, as a double-sided adhesive tape or the like. The surface of the charging roller 9 is contaminated as toner moved from the photosensitive element 1 because it is always in pressure contact with the rotating photosensitive element 1. The surface of the charging roller contaminated by the toner tends to cause charging unevenness. Thus, the roller cleaning member 22 removes the toner adhered to the surface of the charging roller 9, so that the charging nonuniformity caused by the contamination of the charging roller 9 can be prevented.

The charging roller 9 is formed in a roller shape as a rubber molding, and is formed to have a desired linearity in a final step after rubber molding, a surface roughness set in advance and a polishing process by a polishing process. And, in this embodiment of the present invention, the surface of the charging roller 9 is formed to have a predetermined surface roughness provided with a predetermined direction as shown in Figure 2, which is provided with a direction as shown in FIG. Contrast with poor surface finish.

The directionality of the surface roughness of the charging roller 9 is greater sliding frictional resistance in the rearward direction, that is, between the surface of the charging roller 9 and the photosensitive element 1 with respect to the direction of rotation of the photosensitive element 1 (rotational direction shown by arrow A). The direction of the surface roughness of the charging roller 9 is set in the forward direction, that is, as shown schematically in FIG. 1 with respect to the roller cleaning member 22, rather than the rear contact direction. It is set in a direction that generates less sliding frictional resistance between the charging roller 9 and the roller cleaning member.

Then, the previously set ten-point mean surface roughness Rz described in JIS (Japanese Industrial Standard) of the charging roller 9 is set to, for example, approximately 5 µm to 40 µm.

(Example)

Several types of charging rollers whose surfaces were polished and whose surface roughness was set to approximately 2 μm to 50 μm at 10-point average surface roughness were used in the image reproduction test, and used for the results of sensory evaluation of image hunting. The correlation between the surface roughness of the charging roller is to be identified. Evaluation of the experiment is carried out in five steps by sensory evaluation of halftone image hunting. Stage 1 is the worst, stage 5 is the best. Step 4 or above is considered to be good. Then, the experiment is performed by setting the directionality of the surface roughness of the charging roller in the front direction (shown in FIG. 1) in one case, and setting all of the roller cleaning members in the rear direction in other cases. .

Next, the result of the said experiment is demonstrated.

5 is a graph showing the results of the experiment. In the graph, the solid line indicates the result of sensory evaluation when the directionality of the surface roughness of the charging roller is set to the forward direction, and the dotted line indicates the result of sensory evaluation when the directionality of the surface roughness of the charging roller is set to the rear, As described above, all of these are based on the roller cleaning member.

According to the results of the above experiment, when the 10-point average surface roughness Rz of the charging roller was in the range of about 2 μm to 5 μm, image hunting did not occur regardless of the direction of the surface roughness of the charging roller. This is because the vibration of the roller cleaning member in sliding contact with the surface of the charging roller is very small. However, when the charging roller is set in the rearward direction with a surface roughness of 10 μm or more at the 10-point average surface roughness Rz, the vibration of the roller cleaning member is relatively large and is transmitted to the photosensitive element. As a result, image hunting occurs.

On the other hand, when the charging roller is set in the forward direction and the charging roller has a surface roughness of approximately 2 μm to 40 μm at the 10-point average surface roughness Rz, the resulting sensory evaluation of image hunting is four or more steps. Is evaluated.

However, when the charging roller has a surface roughness of 45 µm or more, the vibration of the roller cleaning member becomes excessive, and waveform-shaped hunting occurs in the halftone image.

According to the experimental results as described above, even if the charging device is a contact type device that charges the surface of the photosensitive element by being rotated in contact with the surface of the photosensitive element, and always sliding contact with the cleaning member, the charging roller When the directionality of the surface roughness is formed forward with respect to the surface of the cleaning member, and the surface roughness of the charging roller is set as approximately 5 to 40 µm at the 10-point average surface roughness Rz, no image hunting is generated. It can be.

Many modifications and improvements of the present invention will be possible based on the above teaching. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

This application claims priority and describes by reference the topics related to Japanese Patent Application No. 10-139337, filed on May 5, 1998.

Therefore, the present invention solves the above conventional problems.

Claims (6)

Rotatable photosensitive member; A charging roller that contacts the surface of the photoconductor so as to be rotated by the rotation operation of the photoconductor, and charges the surface of the photoconductor with a voltage applied thereto; And And a cleaning member which contacts the surface of the charging roller and cleans the surface of the charging roller by sliding contact with the surface of the charging roller. The surface of the charging roller is provided with a predetermined surface roughness having directivity, and the direction of the surface roughness of the charging roller is set to the rear with respect to the rotational direction of the photosensitive member and to the front of the surface of the cleaning member. Image forming apparatus. An image forming apparatus according to claim 1, wherein a predetermined surface roughness of said charging roller is between about 5 m and 40 m. The image forming apparatus of claim 1, wherein the cleaning member is made of a sponge. Rotatable photosensitive means for supporting an image thereon; Charging means for contacting the surface of the photosensitive means so as to be rotated by the rotation operation of the photosensitive means, and charging the surface of the photosensitive means as an applied voltage to charge the photosensitive means; And A cleaning means for cleaning the surface of the charging means by contacting the surface of the charging means and cleaning the surface of the charging means in order to clean the surface of the charging means. The surface of the charging means is provided with a predetermined surface roughness having directivity, and the directionality of the surface roughness of the charging means is set to the rear with respect to the rotational direction of the photosensitive means and to the front of the cleaning member. Losing image forming apparatus. An image forming apparatus according to claim 4, wherein the predetermined surface roughness of said charging means is between about 5 micrometers and 40 micrometers. The image forming apparatus according to claim 4, wherein the cleaning means is made of a sponge.