JPS5917832B2 - Denshisha Shingen Zosouchi - Google Patents

Description

[Detailed description of the invention] The present invention relates to an electrophotographic dry developing device.

Specifically, the present invention relates to an improvement of a developing device that uses magnetic toner as a developer. In electrophotography, conventional methods for developing electrostatic latent images with toner include cascade, fur brush, powder cloud, and magnetic brush methods.

The former three methods have drawbacks such as difficulty in reproducing halftones, an increase in the size of the developing device, and contamination of the device due to toner scattering. On the other hand, those using a magnetic brush have the advantage that the developing device is small, the reproducibility of intermediate tones is good, and it is suitable for high-speed copying. However, since this magnetic brush method uses a developer containing a magnetic carrier and chargeable colored toner,
If the toner content ratio decreases, scratch marks caused by the carrier may occur in the image area, whereas if it increases, toner fog may occur in the non-image area. Furthermore, since this developing method involves attaching toner charged by frictional charging between the carrier and toner to the electrostatic latent image on the photoreceptor, the surface condition of the carrier has a large influence on the copied image. In other words, in a carrier that has deteriorated due to fatigue, that is, a carrier whose surface condition has changed, it becomes difficult to cause triboelectric charging depending on the physical and chemical condition of the carrier surface, so that toner adhesion to the photoreceptor becomes incomplete and, on the contrary, Carrier fog (that is, development in which degraded carrier adheres to the entire image surface, or development in which carrier noticeably adheres to the vicinity of the boundary between black and white images), etc., occurs. Therefore, a developing method using a developer without a carrier, that is, magnetic toner, can be considered, but since the mass of magnetic toner is several tens of times larger than that of general resin toner, it is difficult to develop a smooth surface. It has a property that it is difficult to adhere to a photosensitive plate or photosensitive paper, and as a result, complete development may not be possible. By the way, a conventional method is known in which a magnetic toner is made of a material with low resistance (102 to 105 ΩCTfL) and developed by adhering it to a conductive magnetic member.

This is a method of visualizing an image using the electrostatic force between the latent image charge and the charge of opposite polarity induced through a magnetic member by the latent image charge, but since the toner resistance is low, it is easy to avoid rubbing. There are drawbacks such as the latent image area being neutralized during repetition, or the toner being easily charged to the same polarity as the latent image due to the latent image charge, resulting in a negative image. Furthermore, it is extremely difficult to transfer the developed toner onto plain paper. This was also a phenomenon caused by the fact that the toner has a low resistance and therefore easily converts to any polarity. The present invention uses a highly insulating (1010 to 1012 ΩCT!L) magnetic toner (hereinafter referred to as toner) as a developer, and eliminates the above-mentioned drawbacks by applying electric charge evenly to the particle surface of the toner, An object of the present invention is to provide an electrophotographic developing device for obtaining good copy materials.

In the present invention, while the toner magnetically attracted on the surface of an insulating non-magnetic cylinder (hereinafter referred to as a sleeve) rotates on the sleeve surface due to changes in magnetic poles and is conveyed, the toner contacts an electrode provided on the sleeve surface. It is characterized in that it is brought into contact and then separated, charged, and then charged to a substantially uniform charge and subjected to development.

In other words, the magnetic toner particles receive rotational force due to alternating changes in the magnetic poles N and S in the sleeve, and are conveyed while rotating over an electrode area on the sleeve surface that is sufficiently wide compared to the toner particle size. A charge is uniformly applied to the surface of the toner particles. Embodiments of the present invention will be described in more detail below with reference to the drawings.

FIG. 1 is a drawing showing an embodiment of a copying machine equipped with a developing device according to the present invention.

Figure ◆ In this case, having an insulating layer on the surface = layer structure Photosensitive plate 1 is primarily charged by a corona discharger 2, AC static electricity is removed by a corona discharger 3, simultaneous light image exposure is performed by an optical system 4, and the entire surface is further exposed by a light source 5. For example, Japanese Patent Publication No. 42239
The electrostatic latent image is formed by the process described in No. 10 or other known processes.

Conditions for the electrostatic latent image are usually set so that the latent image potential in the dark area is +400 to +600 and the potential of the latent image in the bright area is -50 to -150. The electrostatic latent image is visualized by the magnetic toner of the developing device 6 according to the present invention, and the magnetic toner is transferred onto the transfer material T by the transfer charger 7, and then transferred to the transfer material by the fixing device 8. Examples of magnetic toner include 40 parts of polystyrene, 60 parts of magnetite,
It is conceivable to mix 3 parts of carbon and use the following manufacturing method.

First, the mixture was subjected to a vibration mill for 15 minutes, then a roll mill at 150°C, followed by coarse pulverization with a hammer mill, and fine pulverization with a dinit mill to obtain a powder of 5μ or less and a melting temperature of 30°C or less. By removing these, a good magnetic toner can be obtained. FIG. 2 shows an embodiment of the developing device according to the present invention.

In the figure, 1 is a photoreceptor having an electrostatic latent image, which rotates in the direction of the arrow. 9 is a developer container containing toner 10 as a developer; 11 is a magnetic roller that rotates in the direction of the arrow; around the magnetic roller is a fixed non-magnetic insulating sleeve 12;
is provided.

Further, an electrode 13 made of a non-magnetic conductive material is formed on at least a portion of the sleeve surface, and a bias source 14 is formed.
A negative bias voltage is applied from The alternating changes in the magnetic poles N and S due to the rotation of the magnet roller are caused by the regulating member 1.
For example, 0.5-1.5m77! A rotational force is applied to the toner, which is regulated to a certain amount with a thickness of , so that it rolls on the sleeve. In other words, as shown by the spiral arrow P, the toner is transported while rotating along the sleeve surface.
Before reaching the development area A, the electrostatic latent image is charged by contact separation with the electrode 13 to an appropriate amount of charge having a polarity opposite to that of the electrostatic latent image. The charged toner stands in spikes due to the magnetic poles in the development area A, and develops the electrostatic latent image on the photoreceptor. In the above developing device, since the thickness of the toner in the developing area A is 0.5 to 1.5 mm, the contact with the photoreceptor is shallow, and a large amount of toner causes toner scattering and non-image areas. Although there is less toner fog, it is thought that the developing ability tends to decrease due to a lack of toner, but the amount of toner sent to the developing area A is increased by increasing the number of poles of the magnetic roller and increasing the rotational speed of the magnetic roller. ,
Developing ability can be improved.

The drum facing portion of the sleeve is made of a non-magnetic insulating material. This has the purpose of preventing toner fog on non-image areas. That is, the entire sleeve is made of a conductive member,
When a bias voltage is applied (usually 100 to 1000), a potential difference of several hundred is generated between the drum and the non-image area, and toner easily adheres to the non-image area. Therefore, the above solid? The above-mentioned drawbacks can be prevented by configuring the portion of the non-magnetic sleeve that faces the photoreceptor with an insulating material. FIG. 3 is a diagram showing image reproduction characteristics by the developing device according to the present invention.

The X-axis shows the bias voltage applied to the electrode on the sleeve, and the Y-axis shows the reproduced image density. The solid line shows the image reproducibility of the dark area latent image potential, and the broken line shows the image reproducibility of the bright area latent image potential. When the bias voltage is 0, image reproduction is performed without contrast, with low image density in dark areas and high image density in bright areas. This is a phenomenon that occurs because the toner polarity and charge amount are unstable in a one-particle developing system, and negative image fog usually occurs around positive images. In addition, dirt may also occur due to contact between the printner and the photosensitive drum. As the sleeve bias voltage increases, through the process of toner contacting and separating from the electrode,
The toner is charged to the same polarity as the electrode polarity. As a result, the dark latent image is uniformly visualized by the uniformly charged toner, and the toner in the bright latent image is electrostatically repelled, resulting in a high-quality image without fogging. As the applied voltage is further increased, the toner is overcharged and the fog density of the bright image increases. This is a phenomenon in which the potential on the surface of the developer sleeve shifts to negative due to toner charging, and as a result, a high electric field is generated between the photosensitive plate and the sleeve, causing toner to adhere to the photosensitive plate. At the same time, the negatively overcharged toner neutralizes the negative charge of the dark latent image more quickly, and as a result, the amount of toner adhering to the photosensitive plate decreases, and the image density also decreases. Appropriate applied voltage for bias is influenced by various factors such as sleeve diameter, toner material, and conveyance amount, but in this example, -800 to -1500V was a good voltage range. FIG. 4 shows another embodiment.

In this figure, 16 is an auxiliary electrode placed at a distance of 3 to 10 m1L from the part corresponding to electrode 13 on the sleeve. It is applied from 17. This auxiliary electrode 1
6 increases the electric field strength between the electrodes 13 and 16, and the toner can be charged more efficiently.
FIG. 5 is a diagram showing still another embodiment of the developing device according to the present invention.

As described in the image characteristics shown in FIG. 3, as the negative bias potential is increased in the embodiment shown in FIG. As shown, toner also adheres to the bright areas of the photosensitive plate.

In order to prevent this drawback, a second electrode 18 made of a conductive member is formed on the surface of the sleeve facing the developing section, and a bias voltage is applied from a bias source 19. At this time, the second electrode needs to be arranged only in the developing area so that the toner charge charged by the first electrode 13 is not removed. Further, the bias voltage of the second electrode 18 needs to be selected to a potential that prevents fogging of bright areas of the photoreceptor and does not damage the toner charge. In this example, O■ was appropriate.

As described above, the present invention uses a one-component developer made of highly insulating magnetic toner in a fixed sleeve type electrophotographic developing device having a rotatable magnetic member inside, and uses a one-component developer made of a highly insulating magnetic toner to attach the photoreceptor on the outer circumferential surface of the sleeve. An electrode made of a non-magnetic conductive material is provided on the outer periphery of the sleeve in front of the developing area, with which the supplied developer comes in contact with and moves. Since a bias voltage with a polarity opposite to that of the latent image is applied, the magnetic toner can be charged while rotating by the above-mentioned electrodes in addition to the above-mentioned structure of the magnetic roller and sleeve. As a result, a uniform charge can be applied to the surface of the toner particles, and as a result, a good visible image without fogging can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of an example of an electrophotographic apparatus equipped with a developing device according to the present invention, FIG. 2 is a vertical cross-sectional view of an example of a developing device according to the present invention, and FIG. Graphs of reproduced image density by the developing device, FIGS. 4 and 5 are longitudinal sectional views of other embodiments of the developing device according to the present invention. 1... Photoreceptor, 10... Magnetic toner,
11...) magnet roller, 12...
... Sleeve, 13 ... Sleeve upper electrode, 16
...Auxiliary electrode, 18...Second electrode on the sleeve.

Claims (1)

[Claims] 1. In a fixed sleeve-type electrophotographic developing device having a rotatable magnetic member inside, a one-component developer made of highly insulating magnetic toner is used, and the developer is placed opposite the photoreceptor on the outer surface of the sleeve. The developing area is made of a non-magnetic insulating material, and an electrode made of a non-magnetic conductive material is provided on the outer periphery of the sleeve in front of the developing area, with which the supplied developer comes in contact with and moves, and the electrostatic latent image formed on the photoreceptor is attached to this electrode. An electrophotographic developing device characterized by being provided with means for applying a bias voltage of opposite polarity. 2. In the specified invention, an auxiliary electrode is provided at a position corresponding to the above electrode and separated from the developer moving in contact with the above electrode, and the auxiliary electrode is grounded or biased with a polarity opposite to the polarity on the sleeve. An electrophotographic developing device characterized in that a voltage is applied to the auxiliary electrode. 3. In the specific invention, a second electrode is provided on the outer peripheral surface of the sleeve at a portion facing the photoconductor, and a bias voltage that prevents fogging of bright areas of the photoconductor and does not damage the charge of the developer is applied to the second electrode. An electrophotographic developing device characterized in that a voltage is applied to an electrode.