JPH09146342A - Charging roller - Google Patents

Abstract

(57) Abstract: A charging roller is incorporated in an image forming apparatus to suppress sticking between a roller and a photosensitive drum, toner filming, contact charging noise, etc., which occur when copying is performed. A charging roller including a rotating shaft, a conductive elastic layer formed along the outer periphery of the rotating shaft, and a surface urethane layer formed on an outer peripheral surface of the conductive elastic layer, wherein the surface urethane layer is provided. Is formed by dispersing powder in urethane resin, and the surface roughness Rz of the surface urethane layer is adjusted to 0.2 to 5 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging member used in an image forming apparatus such as an electrophotographic apparatus, and more particularly to a charging roller.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic apparatus, a non-contact charging type wire has been conventionally used as a means for charging (including discharging) an image carrier such as an electrophotographic photosensitive member and an electrostatic recording derivative. Corona dischargers with shields have been mainly used.

Although the corona discharger has an advantage of being uniformly charged, it requires an expensive high voltage power source, requires a space such as itself and a shield space for the high voltage power source, and generates corona products such as ozone. However, there are various problems such as a relatively large number of additional means and mechanisms for coping with the problem, which are factors for increasing the size and cost of the device.

Therefore, recently, instead of such a corona discharger, a contact charging type has been used. The contact charging method is a charging member (conductive member) to which a voltage is applied.
The surface of the body to be charged is charged to a predetermined polarity and potential by bringing it into contact with the body to be charged. Compared with the non-contact charging method, it is possible to lower the charging voltage and generate less corona products such as ozone. The advantages are that the structure is simple and the cost can be reduced.

An example of an image forming apparatus adopting the contact charging system is disclosed in Japanese Patent Laid-Open No. 273844. FIG.
Shows a schematic configuration of a developing unit of such an image forming apparatus. In the figure, reference numeral 1 denotes a drum type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) as an image bearing member, which is rotationally driven in a direction of an arrow A at a predetermined peripheral speed. A charging roller 2 as a charging member contacts the outer peripheral surface of the photosensitive drum 1.
In the case of this example, the charging roller 2 follows the rotation of the photosensitive drum 1.
Also rotates while being partially elastically deformed.

The outer peripheral surface of the photosensitive drum 1 is uniformly charged by sliding contact with the charging roller 2, and when the outer peripheral surface is exposed 3 through the image to be copied of the object to be copied, the outer peripheral surface is statically exposed. A latent image is formed. With reference to FIG. 1, the latent image is visualized (developed) as a toner image with a negative charging polarity by reversal development by a developing sleeve 4 of a developing unit, and the toner image is fed from a paper feeding unit (not shown) to the photosensitive drum 1. And the transfer roller 5 is sequentially transferred to a transfer material 6 (copy paper) fed at a predetermined timing to a pressure contact nip portion (transfer site).

The transfer material 6 to which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and conveyed to a fixing means (not shown) where it is subjected to the toner image fixing and output as an image product. After the transfer material 6 is separated, the surface of the photosensitive drum 1 is cleaned by a cleaning blade 7 of a cleaning machine (cleaner) to remove residual adhered substances such as transfer residual toner, and further, an entire surface is irradiated with an eraser lamp (not shown). To zero potential and prepare for the next charging. In the figure, 8 indicates a power source.

Conventionally, alcohol-soluble nylon or urethane resin has been used for the surface layer of the charging roller 2. However, such a surface layer is formed on the photosensitive drum 1.
And the photosensitive drum 1 is easily contaminated. Further, there is a problem that the contact area of the charging roller 2 with the photosensitive drum 1 becomes large and the level of the charging sound rises accordingly.

The charging sound is a process in which an AC voltage is applied to the charging roller 2 to charge the photosensitive drum 1 to a predetermined potential at the time of copying in the above-mentioned image forming apparatus. .. is a sound generated by this slight vibration, and when this sound becomes loud, it gives an unpleasant feeling to the user and the people around it.

As a measure for reducing the charging noise, Japanese Patent Laid-Open No.
In 303860, a method is used in which elastomer (elastic body) particles are added to and dispersed in the resin material forming the surface layer of the charging roller 2 to roughen the surface (roughness Rz is about 7 to 30 μm).

However, if the surface is roughened too much (for example, Rz exceeds 5 μm), the toner not scraped off by the cleaner adheres to the surface of the charging roller 2 (filming), resulting in uneven charging. Come out.

[0012]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 4
Although the conventional technique disclosed in US Pat. No. 3,030,860 solves the problem of charging noise to some extent, it causes a new problem of toner filming and is not satisfactory.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a charging roller capable of reducing charging noise and suppressing toner filming.

[0014]

In order to achieve the above object, the present invention provides a charging member having a surface layer whose surface roughness Rz is adjusted to 5 μm or less. According to the present invention, in a charging roller including a rotating shaft, a conductive elastic body layer formed along the outer periphery thereof, and a surface urethane layer formed on the outer peripheral surface of the conductive elastic body layer,
The surface urethane layer is formed by dispersing powder in urethane resin, and the surface roughness Rz of the surface urethane layer is
Is adjusted to 0.2 to 5 μm. In the present invention, the particle size of the powder dispersed in the surface urethane layer is preferably in the range of 1 to 10 μm.

[0015]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described below with reference to the drawings.

FIG. 2 shows a sectional view of an embodiment of the charging roller of the present invention. In the figure, 9 is a rotating shaft, 10 is a conductive elastic layer, and 11 is a surface urethane layer.

The conductive elastic body layer 10 is typically a polyurethane or rubber member (composition) molded in the form of an elastic body (elastomer) or foam containing a conductivity-imparting agent. In particular, a conductive rubber layer is preferable in the present invention.

The rubber composition that can be used for the conductive rubber layer includes polynorbornene rubber and ethylene-
Examples thereof include propylene rubber, chloroprene rubber, acrylonitrile rubber, silicone rubber and the like. These rubbers are
It can be used alone or as a mixed rubber of two or more kinds.

In order to impart conductivity, these rubber compositions are mixed with a conductivity-imparting agent and used. Examples of suitable conductivity-imparting agents include publicly known carbon black (furnace-based carbon black or ketjen black) and metal powder such as tin oxide. The conductivity-imparting agent is used in an amount of about 5 to about 50 parts by weight based on the total amount of the rubber composition.

In addition to the rubber base material, the foaming agent, and the conductivity-imparting agent, the rubber composition may be blended with a chemical for rubber and a rubber additive, if necessary, to give a conductive foamed rubber composition.
Chemicals for rubber, as rubber additives, vulcanizing agents such as sulfur and peroxide, vulcanization accelerators such as zinc white, stearic acid, sulfenamide-based, thirium-based, thiazole-based,
It is possible to use vulcanization accelerators such as granidine-based, amine-based, phenol-based, sulfur-based and phosphorus-based antioxidants, or antioxidants, ultraviolet absorbers, ozone deterioration inhibitors, tackifiers, etc. Further, various reinforcing agents, friction coefficient adjusting agents, and inorganic fillers such as silica, talc, and clay may be arbitrarily selected and used.

As a material for forming the surface urethane layer 11,
A urethane resin material, particles and, if desired, a conductivity imparting agent are used.

The particles used in the present invention may be either an inorganic substance or an organic substance, but in the case of an inorganic substance, silica powder is particularly preferable. Examples of organic substances include urethane resin particles, nylon particles, silicon rubber particles, and epoxy resin particles. These particles alone or
Used as a mixture of more than one species. Suitable particles have a surface roughness Rz of the surface urethane layer 11 of 0.2 to 5 μm as described later.
It is sufficient to select a substance that can be adjusted to the above range, but if the particle diameter of the particles is in the range of 1 to 10 μm, the desired surface roughness range can be easily achieved. If the particle size exceeds 10 μm, the surface roughness R
z also exceeds 5 μm and does not serve the intended purpose. On the contrary, if the particle size is less than 1 μm, the surface roughness Rz is less than 0.2 μm, which also fails the intended purpose.

The reason why the surface roughness Rz is set in the range of 0.2 to 5 μm is that if the thickness exceeds 5 μm, the filming of the toner on the roller surface becomes remarkable.
If it is less than the above range, the adhesion between the charging roller 2 and the photosensitive drum 1 is increased, that is, the contact area is increased, and the charging noise cannot be suppressed.

As the conductivity-imparting agent to be blended in the surface urethane layer 11, carbon black, tin oxide and the like can be mentioned as in the above.

The mixing ratio of the powder to the urethane resin material is preferably about 5 to about 20 parts based on 100 parts by weight of the urethane resin and dispersed.

The charging roller 2 of the present invention can be manufactured, for example, as follows. That is, first, a metal rotary shaft (core bar) is placed in a molding die having a cylindrical molding space.
9 is filled with a conductive elastic layer forming material in a molding die,
By conducting vulcanization, the conductive elastic body layer 10 is formed on the outer peripheral surface of the rotating shaft 9. Next, the rotary shaft 9 on which the conductive elastic layer 10 is formed is taken out from the molding die. On the other hand, a urethane resin material, granules, a conductivity-imparting agent and other additives are mixed, and this mixture is mixed and stirred using a ball mill or the like to prepare a surface urethane layer forming material mixture. Then, this mixture is applied by a dip method, a roll coating method, a spray coating method, or the like to the surface of the rotating shaft on which the conductive elastic layer 10 is formed to have a uniform thickness, dried, and cured by heating to obtain the structure shown in FIG. The charging roller 2 having a two-layer structure as shown can be manufactured.

The charging roller 2 thus obtained is
Roughness Rz of the surface of the surface urethane layer 11 which is the outermost layer
Is formed to have a thickness of 0.2 to 5 μm.

In the present invention, the charging roller is formed, but the technique of the present invention can be applied to a developing roller, a transfer roller, a transfer belt and the like which are similarly used in an image forming apparatus.

[0029]

The present invention will be further described below with reference to Examples and Comparative Examples, but these do not limit the scope of the present invention. All parts are parts by weight.

(Examples 1 and 2) The following materials were blended as materials for forming the conductive elastic body layer, and mixed by a ball mill and stirred to prepare a composition for the conductive elastic body layer.

Polynorbornene rubber 100 parts Ketjen black 30 parts Naphthene-based oil 300 parts Further, a vulcanizing agent, a vulcanization accelerator, a vulcanization accelerating aid and additives were appropriately blended according to a conventional method.

In a mold having a cylindrical molding space (cavity), a core metal made of stainless steel, which is a rotating shaft, is placed, the cavity is filled with the above composition, and the mold is vulcanized (vulcanization conditions:
The temperature is 150 ° C., the time is 45 minutes, and the conductive elastic layer (rubber hardness JISA 20, electric resistance 1 × 1) is provided on the outer periphery of the core metal.
0 ⁴ Ω · cm ² ) was formed.

Separately, as the surface urethane layer-forming material, the raw materials were blended as shown in Table 1 below, and were mixed and stirred by a ball mill to prepare a composition for the surface urethane layer.

Then, the cored bar on which the conductive elastic layer is formed is dipped in the composition for surface urethane layer to coat the surface layer, dried, and then heat-treated at 140 ° C. for 1 hour, A surface urethane layer having a film thickness of about 80 μm was formed. Thus, the charging roller of the present invention was manufactured.

The surface roughness Rz of the surface of the charging roller thus obtained was set as follows using a surface roughness meter Surfcom-550A manufactured by Tokyo Seimitsu Co., Ltd. That is, big up: 0.2, stylus: 0.8, cutoff: 0.8,
Measuring distance: 4 mm, measuring speed: 0.3 mm / sec
Set to.

Comparative Examples 1 and 2 In the same manner as in Examples, the compositions for the surface urethane layer were prepared by using the raw materials shown in Table 1, and the compositions were applied to the core metal having the conductive elastic layer used in the Examples. Applied to produce a charging roller. The surface roughness Rz of the obtained charging roller was measured, and this is also shown in Table 1. No powder was dispersed in the surface urethane layer of the charging roller of Comparative Example 2.

Characteristic Test of Charging Roller The charging roller obtained from the above Examples and Comparative Examples was incorporated into an electrophotographic copying machine as shown in FIG. 1 and the following characteristic test was conducted. Table 2 shows the results.

A) Charging Sound The noise level generated during copying was measured. The charging noise measurement test method is described in, for example, JP-A-5-273844, No. 16.
Although it is described in the 10th line to the 34th column of the column, the present test was also performed in accordance with the item 6 of ISO 7779.

B) Toner filming After copying, the charging roller was removed and the toner adhesion was visually observed.

C) Sticking to the photosensitive drum If a sticking occurs during copying, an abnormal image is generated. This was visually determined. For example, in the case of a solid black image, white streaks or white spots were found.

[0041]

[Table 1]

[0042]

[Table 2]

The charging roller of Comparative Example 1 is substantially the roller disclosed in Japanese Patent Application Laid-Open No. 4-303860, and although the level of the charging sound is low, there are problems such as toner filming and sticking to the photosensitive drum. . The charging roller of the example has a charging sound level similar to that of the roller of the comparative example 1, but is improved in filming of the toner and fixing to the photosensitive drum.

[0044]

As described above, according to the present invention, the surface roughness Rz of the surface urethane layer, which is the outermost layer of the charging roller, is adjusted to a suitable range.

Therefore, in the charging roller of the present invention, the filming of the toner on the roller surface is suppressed and the charging is uniformly performed, so that the image quality is improved. Further, the charging roller of the present invention does not stick to the photosensitive drum, no abnormal image is generated, and the surface of the drum and the roller is kept in a continuously usable state for a long time.

In addition, in the charging roller of the present invention, the charging noise is suppressed to a low level and the noise is prevented.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an example of an image forming apparatus using a contact charging device.

FIG. 2 is a cross-sectional view of a charging roller that is an embodiment of the present invention.

[Explanation of symbols]

 1 Photosensitive Drum 2 Charging Roller 3 Exposure 4 Developing Roller 5 Transfer Roller 6 Transfer Material 7 Cleaning Blade 8 Power Supply 9 Rotating Shaft 10 Conductive Elastic Layer 11 Surface Urethane Layer

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Claims (2)

[Claims] 1. A charging roller comprising a rotary shaft, a conductive elastic layer formed along the outer periphery of the rotary shaft, and a surface urethane layer formed on the outer peripheral surface of the conductive elastic layer. A charging roller, wherein the layer is formed by dispersing powder in urethane resin, and the surface roughness Rz of the surface urethane layer is adjusted to 0.2 to 5 μm. 2. The charging roller according to claim 1, wherein the particle size of the powder is in the range of 1 to 10 μm.