JPS6018068B2 - Magnetic brush development and cleaning method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to magnetic brush development and cleaning methods in electrophotographic copying machines.

In the magnetic brush development method, a powder developer containing a magnetic material is adsorbed onto the surface of a non-magnetic sleeve containing a magnet inside to form a magnetic brush layer, and this magnetic brush layer is used as an electrostatic latent image on the surface of a photoreceptor. In this method, the film is brought into contact with the film and developed.

Powder developers containing magnetic materials include two-component developers consisting of a magnetic carrier and non-magnetic toner, and one-component developers consisting only of magnetic toner.

In a two-component type, only the toner is consumed during development, so density management is required to keep the toner density constant. On the other hand, one-component magnetic toner has the advantage that it does not require control of toner concentration because it consists only of toner. However, when using a one-component magnetic toner as a developer, it is not possible to increase the thickness of the magnetic brush layer, and the ears of the magnetic brush do not stand up well. The gap with the sleeve must be sufficiently close.

As a result, for example, when the photoreceptor is drum-shaped, toner blocking occurs between the surface of the photoreceptor and the non-magnetic sleeve or uneven development occurs due to eccentricity of the drum. In addition, magnetic toner is used in a so-called two-rotation-one-copy system in which the same magnetic brush device is used to perform development in the first rotation of the photoreceptor drum and to clean the surface of the photoreceptor in the second rotation. In this case, the magnetic brush has weak bristles and cannot perform sufficient cleaning.

An object of the present invention is to use magnetic toner that does not require toner concentration control, while also eliminating its drawbacks, and to widen the gap between the photoreceptor surface and the non-magnetic sleeve. It is an object of the present invention to provide a magnetic brush development method and a cleaning method that can obtain ears strong enough to perform the following steps. The feature of this invention is that the developer is composed of a magnetic carrier and a magnetic toner, and the magnetic carrier is first adsorbed onto the surface of a non-magnetic sleeve, and a fixed amount of magnetic toner is supplied thereon to form a magnetic brush layer. It is.

As shown in Figure 1, there are multiple magnets la, lb, lc inside.
A fixed amount of magnetic carrier 3 is adsorbed in advance on the surface of a rotatable non-magnetic sleeve 2 on which a rotatable non-magnetic sleeve 2 is provided stationary.

The magnetic toner 4 is housed in a hopper 5, and is deposited onto the non-magnetic sleeve 2 from the lower opening □. The toner 4 and the carrier 3 have approximately the same particle size, and the toner 4 supplied onto the sleeve 2 is uniformly mixed with the carrier 3 on the rotating sleeve 2 .

Therefore, the toner concentration on the sleeve is determined by the combined supply amount of toner 4 since the amount of carrier 3 is constant. On the other hand, in a typical magnetic brush developing device, a doctor blade for regulating the layer thickness of the magnetic brush layer is provided with its tip close to the sleeve surface.

In the apparatus shown in FIG. 1, the right side plate 5a of the hopper 5 is
serves this purpose. Since the right side plate 5a also serves as a doctor, the amount of magnetic toner 4 in the hopper supplied onto the sleeve 3 is constant, and the layer thickness of the magnetic brush is also constant. Therefore, the toner concentration is also constant. The magnetic carrier and toner on the sleeve come into contact with the surface of the photoreceptor 6 at the position of the magnet ld.

Since the resin of magnetic toner contains pigment and the like, the attraction force to the magnet is smaller than that of the carrier. Therefore, the magnetic carrier remains attracted to the sleeve by the magnetic force of the magnet ld, and only the magnetic toner is separated and electrostatically adheres to the static latent image on the surface of the photoreceptor 6, and is developed. . The mechanism by which the magnetic toner adheres to the electrostatic latent image on the surface of the photoreceptor differs depending on the electrical resistance of the magnetic toner.

When the magnetic toner has a high resistance, the magnetic toner is triboelectrically charged due to friction with the side wall of the hopper and the carrier, and development is performed by the electrostatic attraction force of the static latent image to this charge. Therefore, the material must be determined based on the triboelectrification series so that the magnetic toner is charged in a manner opposite to the gutter properties of the electrostatic latent image. On the other hand, when the magnetic toner has a low resistance, an opposite polarity charge is induced in the magnetic toner due to electrostatic transfer due to the charge of the electrostatic latent image, and this causes the magnetic toner to be attracted to the electrostatic latent image. be done. Since development is carried out by adhering only the toner to the static latent image, the carrier is not consumed and remains on the sleeve 2 in a constant amount. In order to use the carrier for a long period of time without fatigue deterioration, it is preferable to keep the resistance of the carrier to be low so that it is not charged. As described above, according to the present invention, since a magnetic carrier having a large magnetic attraction force is used together with a magnetic toner, the formed magnetic brush layer is sufficiently thick and has a strong texture.

Therefore, the gap between the sleeper 2 and the surface of the photoreceptor 6 can be made sufficiently wide. In order to further widen this gap, the magnetic flux density of the magnet ld located at this position should be made larger than that of the magnet la near the doctor 5a, and the height of the ears should be made higher. On the other hand, if the spikes are too strong, the electrostatic grain image will be scratched during development and the developed image will be damaged, resulting in the so-called rain phenomenon, so an appropriate spike strength must be selected.

This depends on the mixing ratio of carrier to toner on the sleeve. The more carriers there are, the stronger the ears will be. However, this is related to toner concentration. That is, as the amount of carrier increases, the toner concentration decreases. The toner density is related to the developer density, and the strength of the spikes is related to the cleanability.

FIG. 2 shows this relationship. When the mixing ratio is gradually increased from 1 for toner and 0 for carrier, the developed density gradually decreases as shown by curve A, and the cleaning performance gradually improves as shown by curve B. Assuming that the practically acceptable range of developer density is from 0.5 to 1.0, and that of cleaning performance is from 0.75 to 1.0, carrier/toner is needed to satisfy both. The mixing ratio is
A range C extends from the intersection of curve B and the allowable lower limit value of cleaning performance to the intersection point of curve A and the allowable lower limit value of developer density. Using a mixing ratio in this range allows effective development and cleaning to be performed by the same magnetic brush device. However, in order to make development and cleaning more effective, it is sufficient to increase the amount of toner in the mixing ratio during development and to increase the amount of carrier during cleaning.

As described above, in the present invention, since the amount of carrier is constant, this is done by changing the amount of toner to be supplied. The amount of toner is controlled by doctor 5 in FIG.
This is done by advancing and retracting a with respect to the surface of the sleeve 2. During development, the doctor 5a is moved backward to increase the amount of toner supplied, and during cleaning, it is moved forward to decrease the amount of toner supplied. As described above, according to the present invention, since the gap between the surface of the photoreceptor and the sleeve can be widened, a degree of leeway is created in the design, and toner blocking and uneven phenomena do not occur. In addition, the thickness of the magnetic brush layer can be made sufficiently thick and the bran can be made strong.
When the same magnetic brush device is used for both development and cleaning, both can be effectively performed.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic diagram showing an example of a magnetic brush device to which the present invention is applied, and FIG. 2 is a diagram showing the relationship between the carrier-toner mixing ratio, developer concentration, and cleaning performance in the present invention. It is a graph. 1... Magnet, 2... Non-magnetic sleeve, 3... Magnetic carrier, 4... Magnetic toner, 5
...Hopper, 5a...Doctor, 6...
...Photoreceptor. Pig illustration 2

Claims (1)

[Claims] 1 A powder developer is adsorbed on the surface of a non-magnetic sleeve containing a magnet inside to form a magnetic brush layer, and this magnetic brush layer is brought into contact with the surface of a photoreceptor to develop an electrostatic latent image and to form a magnetic brush layer on the surface of the photoreceptor. In the magnetic brush development and cleaning method, in which cleaning is performed separately in the same device,
The powder developer is composed of a magnetic carrier and a magnetic toner, and first, the magnetic carrier is attracted to the surface of the non-magnetic sleeve to form a magnetic brush, and a fixed amount of magnetic toner is supplied onto the magnetic brush. 1. A method for developing and cleaning with a magnetic brush, characterized in that development is performed using a magnetic brush, and cleaning is performed by supplying a smaller amount of the magnetic toner onto the magnetic brush than during development.