JPS6339055B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION As a so-called jumping development method belonging to one-component development method, toner is uniformly applied to a carrier such as a sheet, and then the toner is opposed to an electrostatic image holding surface with a small gap maintained. A method is known in which toner is attracted from the carrier to the electrostatic image holding surface by the electric charge of the electrostatic image and developed (Japanese Patent Publication No. 41-9475, U.S. Pat. No. 2,839,400, etc.). . This method has the advantage that not only toner is not attracted to the non-image area where there is no static charge, but also there is no contact between the toner and the non-image area, so background fog is less likely to occur compared to other one-component developing methods. have.

However, this method has not yet been put into practical use due to the following drawbacks. One of the reasons for this is that it is difficult to uniformly apply toner to the support. There is a method of using a rigid and elastic blade to uniformly apply the coating, but unlike the case of applying a liquid, uneven coating is likely to occur.

Furthermore, even when the toner is applied relatively uniformly, it is difficult to uniformly separate the toner from the toner carrier during the development process. Furthermore, when the toner is separated from the toner and the distance from the latent image surface increases due to the mutually repelling charges of the toner, the developed image tends to be disturbed.

The present applicant has provided an electrostatic image developing device which eliminates such drawbacks and exhibits high fidelity and stable image quality (for example, Japanese Patent Application Laid-open Nos. 52-43037 and 55-18659).

These inventions are aimed at:

(1) Obtain a uniform toner layer using a simple device.

(2) Maintain an extremely thin toner layer with uniform thickness in the developing section.

(3) Obtain a toner layer that allows uniform toner separation from opposing electrostatic latent image surfaces.

As a result, in the non-image area, the toner layer is prevented from coming into contact with the non-image area, completely eliminating background fog development, and in the image area, a uniform and high-resolution toner image is obtained. It is an object of the present invention to provide a developing device configured to cause such a transition. For example, the above-mentioned Japanese Patent Application Publication No. 52
The invention of No.-43037, as illustrated in Figure 1,
a developer supporting means (sleeve) 2 provided opposite to the electrostatic image holding means 1 having an electrostatic image; a means for maintaining a constant gap between the electrostatic image holding means 1 and the developer supporting means 2; A means for supplying the magnetic developer 6 onto the developer support means 2, and a means for supplying the magnetic developer 6 onto the developer support means 2, and a thickness of the developer on the developer support means 2 such that the developer is applied to the non-image area of the electrostatic image holding means at least in the developing section. A magnetic field generating means (magnet) 3 is provided to regulate the thickness of the developer so that it does not come into contact with the developer, and a means (magnetic blade) is provided close to the developer supporting means in the magnetic field generated by the magnetic field generating means to regulate the thickness of the developer that stands up due to the magnetic field. ) 4. In the figure, a hopper 7 denoted by 5 is an auxiliary device for applying an alternating current bias between the electrostatic latent image support 1 and the sleeve 2 to improve image gradation and line reproducibility.

To explain this embodiment more specifically, there is no particular restriction on the electrostatic image holder, and any photoreceptor commonly used in the Caruson process can be used. It is also possible to use magnetic recording media. For example 80μ
A latent image potential (contrast) of 500 V was created on a thick selenium photosensitive plate, and the distance between the sleeve and the photosensitive plate was maintained at 0.5 mm.

Also, the distance between the sleeve surface and the magnetic blade is
When the magnetic field was maintained at 0.3 mm and a magnetic field of about 600 Gauss was generated from the magnetic pole 3a, a uniform toner coating layer with a thickness of about 70 microns was formed. The magnetic toner used at this time had a particle size of about 10 microns, and the potential of the formed toner layer was about 30V.

Under these conditions, the applicant was able to reproduce stable and good images, which had not been possible with two-component systems or one-component systems.

However, a problem with this method is that it is difficult to maintain a stable image because the balance of "forces" acting during the developing process is complicated. That is, the adhesion force of the toner to the sleeve 2 during development is:
These are the attraction force toward the sleeve surface due to the charge of the toner, the attraction force toward the sleeve surface due to the magnetism of the toner, and the attraction force between the toners or between the toners and the sleeve due to adhesion. On the other hand, in the direction of the latent image, there is an electrostatic force drawn by the electric field created by the latent image and an electrostatic force due to the developing bias 7. Furthermore, the kinetic energy (centrifugal force) of the toner acts in the tangential direction.

A good image is maintained by maintaining the balance of these complex "forces," but our experiments revealed the following drawbacks. That is, when development was carried out for a long time, the image density decreased significantly. Furthermore, this phenomenon was remarkable when the developing bias was a direct current system. It has become clear that one of the major causes of this is that a magnetic field is applied during development. In other words, the stronger the magnetic force acting on the toner during development, the less toner moves toward the latent image. When used for a long time, the ratio of relatively strongly magnetized toner increases, resulting in deterioration of development characteristics. It has also become clear that the balance between electric and magnetic forces is disrupted due to the tribo and magnetization during development. The amount of magnetism that the toner has during development depends on the content of the magnetic material dispersed in the toner, the size of the toner (amount of magnetic material), or the magnetization characteristics of the magnetic material. This shows that the magnetic force acting on the toner is constantly changing, as the toner gradually becomes magnetic due to contact friction with the cut blade.

In our experiments, we were able to eliminate the aforementioned deterioration in development characteristics by eliminating such unstable factors, that is, by eliminating the magnetic field that acts during development.

That is, although the magnetic cut blade method is a very effective means for coating the sleeve with a uniform layer of toner, the advantage of applying a magnetic field during the developing process has not been well recognized. For example, in Japanese Patent Laid-Open No. 54-43037 proposed by the present applicant, there is an explanation of applying a magnetic field during the developing process to make use of the toner "hodachi" phenomenon to make it easier to blow the toner away, but this is particularly important. Although these are not essential, it was possible to maintain a good image by selecting the distance between the latent image surface and the sleeve, the latent image between them, the developing bias conditions, etc.

The present invention was developed as a result of experimental research against the above-mentioned technical background, and in the developing method shown in Figure 1, the present invention is based on the fact that no magnetic field is applied to the area where the latent image is to be developed. It is characterized by:

That is, the present invention provides a developer support means provided opposite to a latent image holding means, a means for supplying magnetic developer in which each particle is charged onto the developer support means, and a developer support means. In a developing method having a means for regulating the thickness of the upper developer at least in the developing section to a thickness such that the developer does not come into contact with the non-image area of the latent image holding means, a magnetic field is applied to the area where the latent image is substantially developed. This is a developing method characterized by the fact that it does not act.

FIG. 2 shows the basic configuration of the present invention, in which a magnetic pole 8 is located only at a position facing the magnetic blade 4 for coating the sleeve 2 with a uniform toner layer.
, and there is no magnetic field in the developing area where the sleeve 2 and the photosensitive drum 1 face each other. In this case, a magnetic pole necessary for pumping up and conveying the toner in the sleeve 2 may be provided at the rear of the blade 4 in the rotational direction of the sleeve, if necessary.

FIG. 3 shows an example in which a plurality of transport magnetic poles 9 ₁ to 9 _o are provided in order to give sufficient triboelectricity to the toner after passing through the position of the cut magnetic pole 8.

In the present invention, the toner is more likely to fly, but it is preferable in the present invention to apply an AC bias from the power supply 7 to accelerate development by reciprocating the developer as in the example shown in FIG. However, it is preferable to use them together. The bias may be direct current.

Example A 500V latent image is formed on a photosensitive drum having a 30μ Mylar (trade name) layer formed on the surface of the photosensitive layer, and the drum is opposed to the sleeve 2 with a gap of 300μ and rotated in the same direction.

Iron blade 4 is connected to sleeve 2 with a gap of 150μ.
It faced magnet 8 of 700 gauss. The formation of a toner layer of about 5 toner particles in the interstices was observed under a microscope. The toner has the following composition and an average particle size of approximately
It is 15-20μ.

Polystyrene (Picola Stik D-125)
100 parts Charge control agent (Pomelo First Black B)
2. Carbon black (Regal 400R) 6. Magnetite (Toda Kogyo EPT-500) 40. When development was repeated using these combinations, the tendency shown in Figure 4 was confirmed. Curve 1 shows the density change when the developing magnetic pole 3a (800 Gauss) shown in Figure 1 is placed, and curve 2 shows the density change in the case of the present invention without the developing magnetic pole, which shows that the density drop is small even if development is continued for a long time. It represents.

Figure 5 shows the residual magnetism (amount of magnetization) of the toner remaining on the developing sleeve in the example shown in Figure 1.
As time passes, the average amount of magnetization of toner increases. This seems to be due to the increase in the proportion of those that are strongly magnetized by rotation of the sleeve and those that are strongly magnetized from the beginning.

The difference between curves 1 and 2 in FIG. 4 is not explained only by the change in the amount of magnetization of the toner in FIG.
For example, the meaning of the curve shown in FIG. 6 is also important. FIG. 6 shows the particle size distribution of the toner remaining at the end and the initial toner when approximately 1000 g of toner was put into the developing device 5 and copying was carried out for 5 hours. The initial toner has a center value around 13μφ as shown in curve 1.
The amount of toner below 5μ and above 20μ is quite small and is close to the so-called normal distribution. However, when examining the distribution of residual toner, as shown in curve 2, it is less than a few microns or less than 20 microns.
The tightening ratio of the above toner increases.

The toner in the area in FIG. 6 has a relatively small particle size, and the toner in this area is also electrically
It also tends to physically adhere strongly to the sleeve. That is, the smaller the toner, the larger the mirror image force between the toner and the sleeve due to the triboelectric toner.
In addition, the chance of contacting the uneven portions of the sleeve surface increases, making it difficult for the sheet to protrude toward the latent image side.

The toner in one region has a large particle size and mass, so it tends to be difficult to fly, but the toner in this type of one-component developer is insulating and does not rotate sufficiently on the sleeve, so the amount of tribo is low. It has been confirmed that the particle size does not increase in proportion to the particle size.

On the other hand, the amount of magnetism in toner increases to a degree close to the cube of the particle size. Therefore, toner with a large particle size gradually remains without contributing to development, and as a result, from a durable perspective, the development density gradually decreases. decline is inevitable. Such a problem would not occur if the particle size was uniform in terms of composition, but this is practically impossible, and fluctuations in development density are unavoidable.

In the system without a developing magnetic pole or the system in which the magnetic field is weakened according to the present invention, a distribution curve 3 similar to the initial distribution curve 1 in FIG. 6 is obtained.
In this case, toner with small particle size still tends to remain, but since large particles are effectively developed, the density visually becomes higher, which is advantageous in terms of development.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a developing device which is a premise of the present invention, Fig. 2 is a block diagram of an apparatus for carrying out the method of the present invention, Fig. 3 is a block diagram of another embodiment of the present invention, and Fig. 4 is a block diagram of a developing device that is a premise of the present invention.
The figure is a curve diagram showing the relationship between development concentration and development time.
FIG. 5 is a graph showing the relationship between magnetization amount and development time, and FIG. 6 is a graph showing the toner particle size distribution curve at the initial stage of development and after long-term development. 1 is a latent image holding means, 2 is a developer supporting means, 3,
8 and 9 are magnets, 4 is a magnetic blade, 5 is a developer,
6 is toner, 7 is bias power supply.

Claims (1)

[Scope of Claims] 1. A developer support means provided opposite to the latent image holding means, means for supplying a magnetic developer in which each particle is electrically charged onto the developer support means, and the developer In a developing method having means for controlling the thickness of the developer on the supporting means to a thickness that does not allow the developer to come into contact with the non-image area of the latent image holding means at least in the developing section, A developing method characterized by not applying a magnetic field. 2. The developing method according to claim 1, characterized in that an alternating current voltage is applied between the latent image holding means and the developer supporting means. 3. A developing method according to claim 1, characterized in that a DC voltage is applied between the latent image holding means and the developer supporting means.