JPH035579B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic brush developing method for developing an electrostatic latent image in an electrophotographic copying machine, an electrostatic recording device, or the like.

As one of the developing methods for electrophotographic copying machines, etc.
There is a one-component magnetic brush development method that uses magnetic toner as a one-component developer. In this case, a high-resistance magnetic toner is used to ensure the transfer of the image onto plain paper, but in this case there is a problem that the quality of the developed image is poor. In order to solve this problem, two magnetic brush rolls are used to bring the latent image close to or in contact with the magnetic brushes twice.
Several methods have been proposed for performing multiple development processes. However, in this developing method using two magnetic brush rolls, the developing device becomes large and complicated, and the unique problems associated with performing development twice have not been solved.

The above-mentioned development method uses two magnetic brush rolls (hereinafter referred to as development rolls) to carry out two development processes.The first development is developed so that the image density is high enough to cause fogging, and the second development is performed so that the image density is high enough to cause fogging. In the second development, development is performed to remove fog and excess toner adhering to the image area, thereby obtaining a high quality image.

As a developing device conventionally used in such a developing method, for example, in JP-A-56-14268, as shown in FIG. 1, a first developing roll is connected to a developer tank, and a second developing roll is connected to a developer tank. It is arranged separately from the first developing roll. Also, JP-A-55-
No. 138766, as shown in Figure 2, describes an example of using two developing devices, each of which has a developer tank and functions as a developing device even when used alone.
No. 73058 describes an example in which two developing rolls are embedded in a developer tank as shown in FIG.

In the example shown in Figure 1, in order to develop a high-density image including the background part with the first developing roll, a large amount of toner is consumed when continuous development is performed, so a large capacity developer tank is required. However, since the second developing roll collects excess toner such as background fog, it has the disadvantage that toner accumulates and overflows. In addition to the same disadvantages as the example of FIG. 1, the example of FIG. 2 requires just twice the space and cost as compared to a conventional developing device using a single developer roll. In the example in Figure 3, the first and second
Since the two developing rolls are connected by a common developer tank, toner will not flow out from the developer tank or accumulate on one roll, but if continuous development is performed, the density will change. I found out that the drawback is that the image quality fluctuates.

This drawback will be explained in detail using the graph of FIG.

FIG. 4a is an example of the particle size distribution of the one-component magnetic toner injected into the developing machine in terms of weight.
In general, with one-component magnetic toner, it is thought that this is mainly due to the relationship with the magnetic force that acts on the toner, but toner with a small particle size is easier to develop, especially in areas with low latent image potential such as the background. A large amount of toner with a small diameter is developed. In other words, the particle size distribution of the toner developed by the first developing roll is
As shown in Figure b. As a result, toner having a particle size distribution as shown in c in FIG. 4, which is the difference between a and b in FIG. 4, remains on and in the vicinity of the first developing roll, that is, toner having a bias towards large particle sizes. As the proportion of toner with a large particle size increases, the development density decreases and the roughness of the image becomes noticeable, although this is thought to be mainly related to magnetic force. On the other hand, the second developing roll collects the toner of the fogged part with particularly small particle size among the developed toner, that is, the toner having the particle size distribution as shown in FIG. 4d. At the top, the proportion of toner with small particle size increases. However, the second developing roll
Since the main purpose of this setting is to collect excess toner from the image developed by the first developing roll, the toner with small particle size on the second developing roll is actually hardly developed. It cannot be expected to compensate for the aforementioned decrease in development density and roughness of the image. It will be clear that such development is particularly noticeable in devices such as those shown in FIGS. 1 and 2 in which the first and second developer rolls are separated.

As shown in the example of FIG. 3, two developing rolls are connected by one developer tank, and a means for stirring the entire developer tank is provided, so that the toner on each of the first and second developing rolls, that is, the If the toners shown in FIG. 4c and d are mixed, the fluctuation speed of the image will be slightly reduced, but the distribution of the toner as a whole in the developer tank will gradually shift to the larger particle size side, causing a decrease in density.

An object of the present invention is to provide a developing method that can stably supply and transport toner even when continuous development is performed using two magnetic rolls. Another object of the present invention is to provide a developing method that can maintain stable, high-quality images that do not cause a decrease in density or image roughness.

It is an object of the present invention to convert the electrostatic latent image on the latent image carrier into a first
In a magnetic brush development method in which development is performed using magnetic toner held on a developing roll and a second developing roll, the first developing roll is developed without moving the toner from the first developing roll to the second developing roll within the developing machine. A portion of the toner on the latent image carrier that has been excessively developed by the roll is magnetically collected to a second developing roll, and the excess toner on the second developing roll approaches the second developing roll. This can be achieved by a magnetic brush developing method characterized in that the magnetic brush is returned to the first developing roll and refluxed.

The developing method of the present invention will be explained in detail with reference to FIG.

1 and 2 indicate magnetic rolls, which are cylindrical magnetic rolls that are rotatably disposed concentrically with the sleeve inside a hollow cylindrical sleeve made of non-magnetic material (aluminum, stainless steel, resin, etc.). have. Although the figure shows an example in which the magnet is fixed and the sleeve is rotated to convey toner, the magnet or both the sleeve and the magnet may be rotated. Reference numerals 3 and 4 indicate trimmer blades, which function to regulate the thickness of the toner layer conveyed on the sleeve and supplied to the latent image carrier 11 side to a constant amount. As the toner is consumed in development, new toner is replenished from the toner tank (hopper) 5 onto the first developing roll.

The first developing roll performs excessive development that causes fog. In the example shown in FIG. 5, a developing bias having a polarity opposite to that of the electrostatic latent image is applied. Next, with the second developing roll, fog and excess toner around and on the image are removed from the toner developed with the first developing roll. In the example shown in FIG. 5, this function is performed by applying a developing bias having the same polarity as that of the electrostatic latent image. The toner removed by the second developing roll once stays behind the second trimmer blade 4, but as the amount of staying toner increases, some of it is placed close to the second developing roll. It is magnetically attracted to the first developing roll side. As a result, the toner once collected from the drum is also refluxed again and supplied for development by the first development roll.

In this case, if the two developing rolls are placed too close together, the space for arranging the second trimmer blade will be restricted, and if they are placed too far apart, the toner will not be transferred magnetically. Magnetic flux density on sleeve surface is 500 to 1000
With Gaussian magnetic rolls, such toner transfer between two rolls is possible by arranging the two rolls such that the distance between them is approximately 20 mm or less at the closest point.

In this manner, in the developing method of the present invention, the relatively small particle size toner collected from the drum onto the second developing roll and the relatively large particle size toner remaining on the first developing roll are separated. Since they are mixed and supplied to the latent image, the particle size distribution is close to that of new toner. The first developing roll is connected to the outlet of the toner hopper, and as the toner is consumed, new toner in the hopper is gradually transferred to the first developing roll.
is supplied onto the developing roll. That is, the toner is transferred from the hopper to the first developing roll to the drum (latent image carrier) to the second developing roll (some of it goes to the drum).
Reflux is repeated in the order of the first developing roll.
In this process, the new toner supplied from the hopper, the toner on the first developing roll, and the toner collected on the second developing roll are mixed, and the toner particles on the first developing roll have the greatest effect on the developed image quality. The diameter distribution remains stable and constant.

Next, another feature of the present invention will be explained in comparison with the conventional two-roll type developing device shown in FIG. In the developing device shown in FIG. 6, the developer supplied for the first development by the first development roll is first sent to the second development roll for the second development before being returned to the hopper after one rotation. After that, it is returned to the hopper or the first developing roll. Although such a reflux route did not pose a major problem when using a two-component developer, it was found that it was not preferable when using a single-component toner, particularly a high-resistance single-component toner.
In the toner layer immediately after the first developing roll performs the developing action, for example, a portion where the toner is transferred to the drum side has a potential of opposite polarity to the developed toner, that is, the same polarity as the latent image. In this way, the potential of the toner layer immediately after the development action differs depending on the location, so if this is transferred as it is to the second development roll and the second development is performed, the developed image will be uneven. In addition to this, depending on the case, it may be necessary to change the magnitude of the developing bias applied to the second developing roll.

The potential of the toner layer described here can be restored to a uniform and constant potential by once passing the toner layer through the gap formed by the trimmer blade. Therefore, as in the apparatus used in the developing method of the present invention shown in FIG. 5, a trimmer blade is provided for each of the first and second developing rolls, and the toner layer is brought into contact with each trimmer blade each time the roll goes around. By doing so, fluctuations in the potential of the toner layer can be prevented.

FIG. 7 is a diagram showing another embodiment of the present invention.
In the example shown in FIG. 5, the sleeve is rotated so that the toner is moved in the same direction as the drum at the developing position for both the first and second developing rolls, but in the example shown in FIG. At the position, the sleeve is rotated so that the toner moves in a direction opposite to the direction of movement of the drum. In such cases as well, by providing a trimmer blade at a position close to the middle between the first developing roll and the second developing roll, the hopper →
First developing roll → drum → second developing roll →
The toner can be conveyed through a path called the first developing roll. In both the examples shown in FIG. 5 and FIG. 7, at least the first developing roll needs to convey the toner in the same direction as the moving direction of the latent image carrier at the developing position. This is because the first developing roll must have the function of developing excess toner, but it is difficult to provide such a function when the toner moves in the opposite direction to the latent image. Although it is possible to forcibly perform excessive development by adjusting the developing bias, etc., in that case, the image quality will be significantly degraded.

FIG. 8 is a diagram showing still another embodiment of the present invention. In the examples shown in FIGS. 5 and 7, the first developing roll is disposed on the upper side and the second developing roll is disposed on the lower side, but the developing method of the present invention is not limited to this. It goes without saying that similar functions can be obtained even when the first developing roll is disposed on the lower side and the second developing roll on the upper side as shown in FIG. 8 depending on the moving direction of the latent image carrier.

As described above, in the developing method of the present invention, the toner is stably transported and supplied, and the toner does not spill, be concentrated in one place, or overflow. In addition, there is no fluctuation in density or image quality that occurs due to selective consumption of toner particles with smaller particle sizes among the entire toner, and stable image quality can be obtained.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, and FIG. 6 are cross-sectional views showing a conventional developing device. FIGS. 4a to 4d are graphs showing toner particle size distribution. Figures 5 and 7
8 and 8 are cross-sectional views showing an embodiment of a developing device used in the present invention. Symbols in the figure: 1... First developing roll; 2... Second developing roll; 3... First trimmer blade; 4... Second trimmer blade; 5... Hopper; 6, 7... Bias power supply; 10...toner, 11...latent image carrier drum.

Claims (1)

[Claims] 1 In a magnetic brush development method in which an electrostatic latent image on a latent image carrier is developed with magnetic toner held on a first development roll and a second development roll, the development is performed from the first development roll to the second development roll. A part of the toner on the latent image carrier that has been excessively developed by the first developing roll is magnetically collected to the second developing roll without moving the toner inside the machine, and the toner is transferred onto the second developing roll. A magnetic brush developing method characterized in that an excess amount of toner is returned to a first developing roll close to a second developing roll and refluxed.