JPH05273837A - Electrostatic charging device - Google Patents

Abstract

PURPOSE:To obtain an electrostatic charging device suppressing a change (a recess) in the shape of an electrostatic charging member and hardly causing fluctuations in a void by specifying the hardness of an elastic rubber as the electrostatic charging member. CONSTITUTION:The elastic rubber layer of an electrostatic charging roller 2 is made of the elastic rubber of the rubber hardness of JISA 50 deg. or above, and even if the electrostatic charging roller 2 is strongly pressed in contact with a photosensitive drum 1 by the pressing force of a spring 6, these is no fear of causing a recess at the position where the electrostatic charging roller 2 is brought into contact with an insulating tape 3. Therefore, correction corresponding to dispersion in a member by a spring, is more effectively executed, and the fluctuations in the void (ts) are extremely suppressed. On the other hand, the insulating tape 3 is not an annular member as in the conventional manner, so that variation in the outer diameter of the annular member and deflection itself are excluded from the factor of the fluctuations in the void (ts). Consequently, a charge is uniformly imparted to the photoconductive layer of the photosensitive drum 1, and an excellent copied image can be always obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoconductive layer of a photoreceptor in which an electrostatic latent image is formed by a charging member such as a charging roller to which a high voltage is applied in an electrophotographic apparatus such as a copying machine. The present invention relates to a charging device for charging.

[0002]

2. Description of the Related Art A conventional general electrophotographic apparatus such as a copying machine is provided with a photoconductor drum having a photoconductive layer on its surface, and a charger for uniformly charging the surface of the photoconductor drum. ing. As a charger, a corona discharger that applies a high voltage to a charger wire to generate a corona discharge has been widely used, but there is a problem that ozone secondary to corona discharge deteriorates the components. It was

Therefore, a charging roller to which a high voltage is applied is brought into contact with the photosensitive drum, or it is disclosed in JP-A-63-63.
As disclosed in Japanese Unexamined Patent Application Publication No. 186282 and Japanese Unexamined Patent Publication No. 2-148059, a minute air gap of about 50 to 100 μm is formed and held between a charging roller and a photoconductor drum, and the charging roller and the photoconductor drum are respectively provided with a shaft. A charging device having a supporting structure is known.

As shown in FIG. 4, the charging device configured to hold the above-mentioned minute gap has a charging roller 32 on both end sides (outer end regions of the charging roller 32) of the support shaft 34 of the charging roller 32. By mounting the collars 33, 33 having a radius slightly larger than the radius, and pressing these collars 33, 33 to both ends of the photoconductor drum 31, the gap between the surface of the charging roller 32 and the surface of the photoconductor drum 31 is fixed. To
A gap tg corresponding to the difference between the radius of the collar 33 and the radius of the charging roller 32 is formed.

However, in such a configuration, variations in dimensional accuracy of each component constituting the charging mechanism, that is, variations in the tolerance range of the diameter of the support shaft 34, the outer diameter of the collar 33 and the charging roller 32, and the color. The gap tg fluctuates due to the deflection of the charging roller 32 and the charging roller 32, and the space resistance of the gap tg greatly fluctuates accordingly. Therefore, even if the voltage applied to the charging roller 32 is constant, the photosensitive drum 31 The surface potential of the element fluctuates according to the fluctuation of the void tg. As a result, the surface potential of the photosensitive drum 31 fluctuates, the surface potential after charging is not uniform, and the image quality of the copied image is deteriorated.

In order to solve these problems, the inventor of the present application inserts an insulating tape between the surface of the charging member and the surface of the photosensitive member, as disclosed in Japanese Patent Application No. 3-272420. , We proposed a structure in which a minute gap is formed by pressing the charging member against the surface of the photoconductor by the urging force of a spring that supports the bearing of the charging member via the insulating tape. As a result, even if the dimensional accuracy of the thickness or outer diameter of the charging member varies, the spring changes its displacement amount according to the variation, so the surface of the charging member is the surface of the photoconductor through the insulating tape. Therefore, the gap formed between the surface of the photoconductor and the surface of the charging member is maintained at a constant value corresponding to the thickness of the insulating tape. Therefore, the space resistance of the void is maintained at a constant value, and the surface potential of the photoconductor after charging can be maintained uniform. In this case, as the charging member,
EPDM (ethylene-propylene-diene around the metal core
terpolymer) or polyurethane, etc., a charging roller provided with an elastic rubber layer, or a protective layer made of resin such as nylon on the outer peripheral surface of the charging roller, or a metal body for discharge around the metal mandrel. The provided charging roller or the like is used.

[0007]

However, in the above-mentioned structure, when the elastic member is made of elastic rubber, if the elastic rubber has a low hardness, a dent is formed in the portion of the charging member that comes into contact with the insulating tape. Due to this depression, the gap between the surface of the photoconductor and the surface of the charging member fluctuates, and as a result, the effect of correcting the variation in the dimensional accuracy of the parts due to the spring cannot be effectively obtained, and the surface potential of the photoconductor remains. However, there is a problem in that the image quality of the copied image is not stable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a charging device using elastic rubber, which suppresses the shape change (concave) of the charging member and causes almost no variation in the gap.

[0009]

The charging device of the present invention is a biasing means provided on the charging member via a gap holding member for holding a minute gap between the surface of the charging member and the surface of the photosensitive member. Is a charging device that suppresses the variation of the voids by urging the charging member toward the surface of the photoconductor and uniformly charges the surface of the photoconductor by the discharge in the voids, wherein the charging member has a JISA of 50 ° or more. It is characterized by being formed from a rubber having a rubber hardness of.

[0010]

According to the above structure, the charging member is the JIS A5 type.
Since it is made of rubber having a hardness of 0 ° or more,
When the charging member is urged to the surface of the photoconductor by the urging means provided in the charging member, the generation of the dent at the surface of the charging member contacting the space holding member is suppressed. Therefore, the void formed between the surface of the photoconductor and the surface of the charging member is reliably held at a constant value corresponding to the thickness of the void holding means, and the space resistance of the void is maintained at a constant value.
The surface potential of the photoreceptor after charging becomes uniform.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following will describe one embodiment of the present invention with reference to FIGS.

As shown in FIG. 1, a gear 7 is integrally attached to a photoconductor drum 1 which is a photoconductor on which an electrostatic latent image is formed. The gear 7 meshes with a transmission gear 8 which transmits a driving force. is doing. In the pre-exposure step, the charging roller 2 that is a charging member that uniformly charges the photoconductor drum 1 by minute air gap discharge is attached to the photoconductor drum 1 via the insulating tape 3 that is a space holding member arranged near both ends. They are placed close together. As a result, a gap ts corresponding to the thickness of the insulating tape 3 is formed between the surface of the photosensitive drum 1 and the surface of the charging roller 2 described later. The thickness of the insulating tape 3 is 0.1 mm, for example.

The insulating tape 3 has a width of several mm and a length of 1 to 2 cm.
It is made of polyethylene resin, polyester resin, or the like. Each end of these insulating tapes 3 is sandwiched by a fixture 3a, and one end of a spring 4 is attached to each fixture 3a. As shown in FIG. 2, the other end of each spring 4 is fixed to each end of a fixed frame 9 that is bifurcated with respect to the photosensitive drum 1. As a result, the above-mentioned two insulations are fixed. The tape 3 is stretched in an arch shape on both edges of the photosensitive drum 1. The spring 4 may be any elastic material that gives the insulating tape 3 tension.

The photoconductive (OPC) layer of the photosensitive drum 1 is
As indicated by a range L _OPC in FIG. 1, the insulating tape 3 is provided inside the surface portion of the photosensitive drum 1 with which it comes into contact. This is because the photoconductive layer is apt to wear, and therefore, when the photoconductive drum 1 and the insulating tape 3 rub with the rotation of the photoconductive drum 1, the photoconductive layer is worn away and the voids ts are formed over time. This is to prevent changes.

As shown in FIG. 3 (a), the charging roller 2 has an EPDM (ethylene-propyle) around the metal core 2a.
neon diene terpolymer) or polyurethane provided with an elastic rubber layer 2b, or as shown in FIG. 3B, the outer peripheral surface of the roller shown in FIG. It has a structure in which a protective layer 2c made of resin or the like is provided. As the elastic rubber layer 2b, JI
A rubber having a rubber hardness of SA 50 ° or more is used. The reason for setting the rubber hardness will be described later.

Both ends of the support shaft 5a of the charging roller 2 are fitted and inserted into the bearings 5b, and the bearings 5b are connected to the fixed frames 1 respectively.
It is hung vertically by means of each spring 6 which is a biasing means. The surface of the charging roller 2 has springs 6
The surface of the photosensitive drum 1 is pressed against the surface of the photosensitive drum 1 with a force of several 100 g through the insulating tape 3 by the urging force of. The charging roller 2 is preferably not rotated in order to prevent abrasion due to contact with the insulating tape 3. However, if the abrasion is negligible over time, a configuration may be adopted.

Now, the reason for setting the rubber hardness of the elastic rubber layer 2b of the charging roller 2 will be described. The set value of the rubber layer 2b changes the rubber hardness of the elastic rubber 2b constituting the charging roller 2 to charge the photosensitive drum 1, and the surface of the charging roller 2 contacting the insulating tape 3 at that time is charged. It is determined based on the experimental result of measuring the amount of depression and the surface potential of the photosensitive drum 1. The experimental results are shown in Table 1. The voltage applied to the charging roller 2 was 1.3 KV, and the depression amount of the charging roller 2 was an average value.

[0018]

[Table 1]

The rubber hardness of the elastic rubber 2b is JIS A 40 °.
In the case of the following, since the depression amount of the charging roller 2 is as large as 50 μ or more and the variation amount of the depression amount is large, the photosensitive drum 1
The change range of the surface potential in was 35 V or more. It is known that a surface potential change of 35 V or more on the photosensitive drum 1 affects a copied image. On the other hand, elastic rubber 2
When the rubber hardness of b was set to JIS A of 50 ° or more, the amount of depression of the charging roller 2 was 38 μ or less, and the variation range of the amount of depression was small. Therefore, the variation range of the surface potential on the photosensitive drum 1 was 30 V or less. It can be seen that a change in the surface potential of the photosensitive drum 1 of 30 V or less has almost no effect on the copy image, and thus a copy image with high image quality can be obtained.

From these results, the rubber hardness of the elastic rubber 2b constituting the charging roller 2 is set to JISA 50 ° or more.

In the above structure, the bearing 5b arranged on the charging roller 2 is constantly attracted toward the photosensitive drum 1 by the spring 6 fixed to the fixed frame 10, so that the supporting shaft of the charging roller 2 is supported. 5a and the outer diameter of the charging roller 2, or the support shaft 5 of the charging roller 2.
The void ts is kept constant by the thickness of the insulating tape 3 without being affected by the shake with respect to a.

For example, when the charging roller 2 whose outer diameter is slightly smaller than the average value is used, the displacement of the spring 6 becomes slightly smaller, so that the change of the outer diameter of the charging roller 2 is absorbed, and the void ts has an insulating tape. The thickness of 3 keeps it constant. On the other hand, even when the charging roller 2 having an outer diameter slightly larger than the average value is used, the displacement of the spring 6 is slightly increased, and the change in the outer diameter of the charging roller 2 is similarly absorbed.

The elastic rubber layer 2b of the charging roller 2 of this embodiment has a rubber hardness of JISA based on the above reason.
Since it is made of elastic rubber of 50 ° or more, even if the charging roller 2 is strongly pressed against the photosensitive drum 1 by the urging force of the spring 6, the charging roller 2 contacts the insulating tape 3 at a position where it contacts. Therefore, since there is no possibility of forming a dent, the correction of the variation of the member by the spring 6 is more effectively performed, and the variation of the gap ts is significantly suppressed. Further, since the insulating tape 3 is not a ring-shaped member as in the conventional case, variations in the outer diameter of the ring-shaped member and fluctuations thereof are excluded from the factors of fluctuation of the space ts.

As a result of the above, charges are uniformly applied to the photoconductive layer of the photosensitive drum 1, and a good copy image can always be obtained.

[0025]

As described above, the charging device according to the present invention is provided on the charging member via the gap holding member for holding a minute gap between the surface of the charging member and the surface of the photosensitive member. A charging device for suppressing fluctuation of the air gap by biasing the charging member toward the surface of the photoconductor by a biasing means, and uniformly charging the surface of the photoconductor by discharge in the air gap, wherein the charging member is JIS A50. It is made of rubber having a rubber hardness of not less than °.

Therefore, when the charging member is urged to the surface of the photosensitive member by the urging means provided in the charging member, the generation of the depression at the surface of the charging member contacting the space holding member is suppressed. .. Therefore, the space formed between the surface of the photoconductor and the surface of the charging member is reliably held at a constant value corresponding to the thickness of the space holding means, and the space resistance of the space is maintained at a constant value. As a result, the surface potential of the photoconductor after charging becomes uniform, and good copy image quality can always be obtained.

[Brief description of drawings]

FIG. 1 is a front view having a partial cross section showing the configuration of a charging device according to the present invention.

FIG. 2 is a side view showing a configuration of a main part of the charging device of FIG.

FIG. 3 is a cross-sectional view showing various aspects of the structure of the charged body.

FIG. 4 is a front view showing a configuration of a conventional charging device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (photosensitive member) 2 Charging roller (charging member) 2b Elastic rubber layer (rubber) 3 Insulating tape (gap holding means) 6 Spring (biasing means) ts Gap

Claims (1)

[Claims] 1. A biasing means provided on the charging member for biasing the charging member toward the surface of the photoconductor through a gap holding member for holding a minute gap between the surface of the charging member and the surface of the photoconductor. In this charging device, the fluctuation of the voids is suppressed, and the surface of the photoconductor is uniformly charged by the discharge in the voids. The charging member is formed of rubber having a rubber hardness of JISA 50 ° or more. A charging device characterized by the above.