JPH0792805A - Developing roller - Google Patents

Abstract

PURPOSE:To eliminate the need for fine adjustment of gap accuracy without the need for disposing a gap between an image carrying medium and a developing roller by having a columnar shaft and a conductive elastic layer having the hardness smaller than the surface hardness of this image carrying medium. CONSTITUTION:This developing roller 2 is composed of the columnar shaft 3 and the conductive elastic layer 4 disposed around the shaft 3. The elastic layer 4 is formed by packing ferromagnetic powder, such as ferrite powder and conducting agent, such as carbon black and carbon fibers, into a rubber material, such as urethane rubber. The developing roller 2 has preferably >=12 poles of magnetic poles in order to lessen unequal development and the volume resistivity of the elastic layer 4 is preferably <=10<9>OMEGA.cm. The developing roller 2 is brought into contact with a photosensitive drum and the run-out of the developing roller 2 itself is absorbed by providing the developing roller 2 with the elastic layer 4 in such a manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing roller used to convey a one-component magnetic toner, which is a magnetic developer, to a developing area.

[0002]

2. Description of the Related Art Conventionally, a developing roller has been used to supply a magnetic toner as a magnetic developer to an electrostatic latent image formed on the surface of an image carrier such as a photoconductor or a dielectric. .
The developing roller conveys the magnetic developer to the developing area by rotating while holding the magnetic developer with magnetic force. As a conventional developing roller, a roller formed by disposing a magnet member having a plurality of magnetic poles inside a sleeve formed of a non-magnetic metal material, or a magnet member not using a sleeve (for example, JP-A-63-223675) and the like are known.

[0003]

Conventionally, the developing roller is arranged close to the image carrier, and a predetermined gap (for example, about 0.5 mm) is provided between the two. The adjustment requires fairly strict accuracy. In particular, when a one-component magnetic toner is used as the magnetic developer, the developing roller, which is the developer conveying member, has 1/1
A deflection accuracy of about 00 to 3/100 mm is required. Further, if there is a gap between the image carrier and the developing roller, tailing or fronting is likely to occur in the image depending on the accumulation state of the magnetic toner, and the image quality deteriorates. Further, if a foreign substance larger than the magnetic toner is mixed in the magnetic developer, the photoconductor on the surface of the image carrier is damaged. Especially, in the developing roller having the sleeve,
Since the sleeve is made of a metal material (SUS, Al alloy, etc.), if a foreign matter having a size larger than the gap width is mixed, an image carrier (eg, OPC) made of a material softer than the sleeve will be generated. It will hurt you. Further, the developing roller of the type having a sleeve increases the cost because the sleeve is provided.

Therefore, the present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a developing roller which does not require strict gap accuracy and is inexpensive and which can obtain clear image quality. To provide.

[0005]

In order to achieve the above object, the present invention is arranged so as to face an image carrier having an electrostatic charge image on its surface and rotate while holding a magnetic developer on the surface. By doing so, in the developing roller that conveys the magnetic developer to the developing area, a cylindrical shaft and a plurality of magnetic poles that are provided around the shaft and have a plurality of magnetic poles on the surface, and the hardness of the image bearing member And a conductive elastic layer having a surface hardness smaller than the surface hardness. Furthermore, the volume resistivity of the elastic layer is 10 ⁹ Ω · cm or less.

[0006]

In the present invention, since the elastic layer is provided around the cylindrical shaft, the image bearing member can be placed in contact with the developing roller. The reason is that even if the image carrier and the developing roller are brought into contact with each other, the elastic layer absorbs the vibration of the developing roller. Therefore, it is not necessary to previously provide a gap between the image carrier and the developing roller, and fine adjustment of the gap accuracy is also unnecessary. Further, when this gap is eliminated, the trailing of the image and the forward pulling do not occur, and a clear image can be obtained. Because in the past,
This is because the tailing and the fronting of the image are caused mainly by the accumulation state of the magnetic toner in the gap.
Further, by making the hardness of the elastic layer smaller than the surface hardness of the image carrier, the surface of the image carrier is not damaged even when the developing roller is brought into contact with the image carrier. Further, even if a foreign substance larger than the magnetic toner is mixed in the magnetic developer, the elastic layer absorbs the influence of the foreign substance, so that the image carrier is not damaged. Conventionally, when a foreign substance larger than the gap provided in advance is mixed, the image carrier formed of a relatively soft material such as OPC is damaged. Further, since the sleeve is not provided on the developing roller and it is not necessary to consider the deflection accuracy, the cost of the developing roller becomes low.
Further, by making the elastic layer conductive, a predetermined bias voltage can be applied to the developing roller. On this occasion,
The volume resistivity of the elastic layer is preferably 10 ⁹ Ω · cm or less.

[0007]

EXAMPLE An example of the present invention will be described with reference to FIG. First, FIG. 3 shows a developing device using the developing roller according to the present invention.
Shown in. The photoconductor drum 1 rotates in the direction of arrow A, and an electrostatic charge image (not shown) is formed on its surface by charging and exposure. The developing roller 2 is rotatably arranged so as to face the photosensitive drum 1, and a developing area C is formed between the photosensitive drum 1 and the developing roller 2. At this time, the developing roller 2 is arranged in contact with the photosensitive drum 1. The conveying speed of the developing roller 2 is the same as that of the photosensitive drum 1.
It is preferable to set the transfer speed to about 1 to 3 times.

A longitudinal section of the developing roller 2 is shown in FIG.
The X-X cross section of the developing roller 2 is shown in FIG. The developing roller 2 is a conductive rubber roller having a plurality of magnetic poles on its surface. Specifically, the developing roller 2 includes a cylindrical shaft 3 and a conductive elastic layer 4 provided around the shaft 3. The elastic layer 4 is made by filling a rubber material such as urethane rubber, silicone rubber or butyl rubber with a ferromagnetic powder such as ferrite powder or a rare earth magnet and a conductive agent such as carbon black or carbon fiber. The developing roller 2 preferably has 12 or more magnetic poles in order to reduce uneven development, and preferably has a surface magnetic flux density of 100 G or more in order to prevent toner from scattering from the developing roller 2.

The manufacturing method is as follows. A rubber material filled with a ferromagnetic powder and a conductive agent is mixed with sulfur and a vulcanization accelerator as a raw material. Sharpen. Then, by magnetizing, a conductive rubber roller having a plurality of magnetic poles on its surface is manufactured. The volume resistivity of the elastic layer 4 is preferably 10 ⁹ Ω · cm or less, more preferably 10 ⁵ Ω · c.
m or less. In this way, the elastic layer 4 is provided on the developing roller 2 so that the developing roller 2 can be brought into contact with the photosensitive drum 1 and absorb the vibration of the developing roller 2 itself.

Here, if the developing roller 2 is composed only of a magnet member (sintered magnet, resin magnet, etc.) of a relatively hard material, and the developing roller 2 is simply brought into contact with the photosensitive drum 1, a comparison is made. The photosensitive layer (OPC) 1a on the surface of the photosensitive drum 1 made of a soft material is damaged by the magnet member. In order to prevent this, it is necessary to provide the elastic layer 4 on the developing roller 2.
At this time, the surface hardness of the developing roller 2 must be smaller than that of the photosensitive layer 1a on the surface of the photosensitive drum 1. This is because the hardness of the elastic layer 4 depends on the photosensitive layer 1a of the photosensitive drum 1.
This is because if the hardness is larger than the hardness, the photosensitive layer 1a will be damaged when the developing roller 2 is brought into contact with the photosensitive drum 1. The surface hardness of the elastic layer 4 is 60 °.
The following (JIS A) is desirable.

The elastic layer 4 is made conductive so that the bias voltage from the bias power source 8 can be applied to the developing roller 2. To reverse develop an electrostatic latent image formed on the photoconductor drum 1 or to prevent background fog, the developing roller 2 to which the magnetic developer 5 is attached
A certain voltage must be applied to the surface of the. Normally, since the bias voltage is applied to the shaft 3, if the insulating elastic layer is used, the voltage will not be applied to the surface of the developing roller 2. Therefore, in the present invention, the elastic layer 4 is made conductive. In order to impart conductivity to the elastic layer 4, it is filled with a conductive agent such as carbon black, carbon fiber or metal powder.

The magnetic developer 5 is a one-component magnetic toner and is contained in a developer tank 6. At the outlet of the developer tank 6, a blade member 7 is arranged in pressure contact with the developing roller 2. Then, the magnetic developer 5 on the developing roller 2
Is regulated in thickness by the blade member 7 (formed of urethane rubber, stainless steel, etc.) and is triboelectrically charged to be conveyed to the developing area C. The magnetic developer 5 attracted to the surface of the developing roller 2 by magnetic force is conveyed in the same direction as the developing roller 2 by rotating the developing roller 2 in the direction of arrow B by an appropriate driving means (not shown). When the charged magnetic developer 5 whose thickness is regulated by the blade member 7 reaches the developing area C, the magnetic brush formed there slides on the surface of the photosensitive drum 1 to develop the electrostatic charge image. .

Next, the present invention will be described based on experimental examples. First, 5 parts of a styrene-n-butyl methacrylate copolymer (M _w = 21 × 10 ⁴ , M _n = 1.6 × 10 ⁴ ) were used.
5 parts by weight (wt%), magnetite (Toda Kogyo EP
40 parts by weight of T-500, 3 parts by weight of polypropylene (Viscole 550P manufactured by Sanyo Kasei Co., Ltd.), and 2 parts by weight of a charge control agent (oil black BY) are kneaded and pulverized, then classified, and then hydrophobic silica. (Aerosil R972 manufactured by Nippon Aerosil Co., Ltd.) is externally added (0.5 parts by weight) to give a magnetic toner having a volume average particle diameter of 8.5 μm, a specific resistance of 10 ¹⁴ Ω · cm, and a triboelectric charge amount (TEC) of −15 μc / g. Got

The average particle size (volume) of the toner was measured by a particle size analyzer (manufactured by Coulter Electronics Co., Coulter Counter Model TA-II). Further, the triboelectric charge amount is measured by a blow-off triboelectric charge amount measuring device (TB-200 manufactured by Toshiba Chemical Co., Ltd.) by mixing a standard carrier (KBN-100 manufactured by Hitachi Metals) and toner (toner concentration 5% by weight). did. The volume resistivity of the toner is measured by filling a cylinder made of Teflon (trade name) with an inner diameter of 3.05 mm with several tens of mg of the sample, and applying a load of 0.1 kg DC4KV.
It was measured with an electric field of / cm.

An image was prepared using the above magnetic toner under the following conditions. An OPC drum (outer diameter 30 mm) was used as the photosensitive drum 1, and this was rotated at a peripheral speed of 60 mm / sec. On the other hand, the developing roller 2 includes a cylindrical shaft 3 (outer diameter 6 mm, length 280 mm) and an elastic layer 4.
(Outer diameter 20 mm, length 227 mm). The elastic layer 4 is filled with 100 parts by weight of rubber (urethane), 100 to 500 parts by weight of ferromagnetic powder (Sr ferrite powder), and 10 to 30 parts by weight of a conductive agent (carbon black, carbon fiber, etc.). . Sulfur and a vulcanization accelerator are kneaded and cast into this, followed by vulcanization, external polishing and magnetization.

As described above, four types of developing rollers having 16 magnetic poles and a surface magnetic flux density of 150 gauss or more were prepared. Table 1 shows the main components and characteristics of each roller. Then, these developing rollers 2 were rotated at a speed of 120 mm / sec. Then, the developing gap (photosensitive drum 1
And the developing roller 2) are almost zero. That is, the developing roller 2 is arranged so as to be substantially in contact with the photosensitive drum 1.

[0017]

[Table 1] (Note) Volume resistivity is the value measured by the Hoeston bridge method.

Then, the surface potential (charging portion) of the photosensitive drum 1 was set to -650 V, and a DC bias voltage of -530 V was applied to the developing roller 2 to perform reversal development. next,
The toner image obtained by development is corona-transferred onto plain paper, and then fixed with a heating roller (fixing temperature 160 ° C., fixing pressure 0.
8 kg / cm). As a result, the image density is N
O. No. 1 developing roller is 1.45. No. 2 developing roller is 1.40. No. 3 developing roller is 1.38.
The developing roller of No. 4 was 1.32, and each developing roller was free from fog and a clear image without tailing was obtained.

As described above, when the developing roller 2 having the elastic layer 4 is used and development is carried out in a state of being in contact with the photosensitive drum 1, a stable image can be obtained from the initial stage to 50,000 sheets. It could be confirmed. On the other hand, using a developing roller having no rubber layer (having a cylindrical magnet magnetized with 6 poles (800G on the sleeve) inside a SUS304 sleeve with an outer diameter of 20 mm) and developing the photosensitive drum When developing is performed with a gap (about 0.1 to 0.3 mm) between the roller and
(Rotated at rpm), a bad image with tailing was obtained.

[0020]

According to the present invention, since the developing roller can be arranged in contact with the image bearing member, it is not necessary to provide a gap between the image bearing member and the developing roller, and the gap precision can be finely adjusted. Is unnecessary. In addition, image tailing,
Pre-drawing does not occur and a clear image can be obtained. Further, by making the hardness of the elastic layer smaller than the surface hardness of the image carrier, the surface of the image carrier is not damaged even when the developing roller is brought into contact with the image carrier. further,
Even if a foreign substance larger than the magnetic toner is mixed in the magnetic developer, the elastic layer absorbs the influence of the foreign substance, so that the image carrier can be prevented from being damaged. Further, since the sleeve is not provided, the cost of the developing roller can be reduced. As described above, it is possible to provide an inexpensive sleeveless developing roller that does not require strict gap accuracy and can obtain a clear image quality.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a developing roller according to the present invention.

FIG. 2 is a sectional view of the developing roller of FIG. 1 according to the present invention, taken along line XX.

FIG. 3 is a diagram showing a configuration of a developing device using a developing roller according to the present invention.

[Explanation of symbols]

 1 Photoconductor drum 2 Developing roller 3 Shaft 4 Elastic layer 5 Magnetic developer 7 Blade member

Claims (2)

[Claims] 1. A developing roller which is arranged so as to face an image carrier having an electrostatic charge image on its surface, and which rotates while holding a magnetic developer on its surface to convey the magnetic developer to a developing area. , A cylindrical shaft and a plurality of magnetic poles provided on the surface around the shaft,
A developing roller having a conductive elastic layer whose hardness is smaller than the surface hardness of the image carrier. 2. The volume resistivity of the elastic layer is 10 ⁹ Ω
The developing roller according to claim 1, wherein the developing roller has a size of not more than cm.