JPS648328B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method in a copying machine using a magnetic brush including a rotatable sleeve and a magnet fixedly disposed within the sleeve.

Conventionally, as a developing method in a copying machine, a method using a so-called magnetic brush, which includes a rotatable sleeve and a magnet fixedly arranged within the sleeve, is known. A two-component developer consisting of a carrier of iron powder and toner is held in the form of brush-like spikes on the outer peripheral surface of the sleeve by the magnetic action of the magnet, and is transported toward the photoreceptor as the sleeve rotates. The developing effect is achieved by directly slidingly contacting the latent image surface of the photoreceptor. The developing pressure with which the developer carried by the magnetic brush presses the developing surface, that is, the strength of the sliding contact force of the brush-like ears against the latent image surface of the photoreceptor, has a subtle influence on the developing effect, and In the case of a single image, it is difficult to obtain an image with sufficient image density, especially for an image including a solid image, without traces of the tip, without white spots on the solid tip, and without background smearing. . This is because when the brush is brought into strong contact with the latent image surface of the photoreceptor, the amount of toner supplied to the latent image surface is sufficient and uniform, resulting in a uniform black solid image with no unevenness in shading. Although it has the advantage of improving solid image uniformity and improving image density,
Due to the capacity and resistance of the developer, the speed at which the developer approaches the photoreceptor, etc., the leading edge of a solid image is not reproduced uniformly, resulting in a concave and jagged pattern, so-called tip marks, which cause line images (especially (horizontal lines) may not be reproduced, and in the case of letters, the sharpness may be significantly impaired.In addition, the potential at the tip of the tip changes due to sudden changes in the latent image in relation to the developer capacity and time constant. The smaller the capacitance, the higher the potential at the tip and the smaller the potential difference with the latent image, resulting in the disadvantage of so-called solid tip white spots, where toner movement is difficult to occur and development is insufficient.

On the other hand, if the brush is brought into weak sliding contact with the latent image surface of the photoreceptor, it has the advantage of not producing tip marks or white spots on the solid tip, but on the other hand, the image density is insufficient and background smear occurs. It has the disadvantage of

As a means to overcome the drawbacks of the single developing sleeve system described above, there is a method in which a plurality of magnetic brushes are arranged in a row facing the photoreceptor, and the strength of the developer holding power of each magnetic brush is varied. The strength of the developer retention force is determined by the orientation of the magnetic poles relative to the photoreceptor and the selection of the magnetic field line distribution, but if the carrier's bonding force is too large, the magnetic brush tip will forcefully press the latent image surface. This causes the same drawback as the single developing sleeve method due to rubbing. Another drawback is that setting the degree of developer retention strength, that is, determining the position of the magnet with respect to the photoreceptor, and assembling the magnet are troublesome.

The present invention solves the above-mentioned drawbacks and provides a developing method for a copying machine that can obtain a high-quality copy image with sufficient image density and uniformity of the solid image, without causing tip marks or blank spots on the solid tip. The purpose is to

This purpose is to provide a plurality of magnetic brushes, each including a rotatable sleeve and a magnet fixedly arranged within the sleeve, adjacent to each other, and to arrange each of the magnetic brushes to face the latent image surface of the photoreceptor. In the developing device of the copying machine, the moving speed on the outer circumferential surface of the sleeve is set such that the developing pressure with which the developer carried by each of the magnetic brushes presses the latent image surface is gradually increased in the moving direction of the latent image surface. This is achieved by a developing method in which the latent image surface is gradually accelerated in the direction of movement of the latent image surface.

Hereinafter, the present invention will be explained based on the illustrated developing device suitable for carrying out the present invention. The figure shows a main part configuration diagram of a developing device in a copying machine to which the present invention is applied. In the figure, a photosensitive drum 1 is driven to rotate at a constant speed in the direction of the arrow, and its outer peripheral surface is uniformly charged with a predetermined charge, and a latent image is formed by projecting a light image of an image to be copied. It forms a surface 1a.
The photoconductor 1 then passes through a dry-type developing device 2, where a two-component developer containing electrostatically charged toner is adsorbed onto the surface of the electrostatic latent image, and the electrostatic latent image is transferred to the toner. It is visualized (developed) by The developing device 2 is disposed below the photoreceptor drum 1, and includes a developer container 4 containing a developer 3, a pumping magnetic brush 5 that supplies the developer 3 to a developing magnetic brush,
It consists of two developing magnetic brushes, that is, a first-stage magnetic brush 6 and a second-stage magnetic brush 7, which convey the developer supplied from the pumping magnetic brush 5 to the latent image surface 1a of the photoreceptor and bring it into sliding contact. There is. In this embodiment, two parts are used for development along the moving direction of the latent image surface 1a.
Although the present invention is not limited to this example, it goes without saying that a plurality of magnetic brushes may be used. Each magnetic brush has a sleeve S ₅ , S ₆ , which is rotationally driven in the direction of the arrow.
S ₈ and magnets M ₅ , M ₆ , M ₇ fixedly arranged inside the sleeves S ₅ , S ₆ , S ₇ , and the developer adheres to the outer circumferential surface of the sleeve by the magnetic force of the magnets and rotation of the sleeve.・Be transported. That is, the magnetic brush 5 for pumping up the developer 3 disposed at the lower part of the developer container 4 holds the developer 3 on the outer peripheral surface of the sleeve S ₅ like a brush-shaped ear by the action of the magnet M ₅ and moves it in the direction of the arrow. When it reaches the top of the sleeve S ₅ , it moves to the bottom of the second stage developing magnetic brush 7, and the sleeve
The sleeve S ₇ is held like a brush-like ear by the action of the magnet M ₇ on the outer peripheral surface of the sleeve S ₇ and moved in the direction of the arrow as the sleeve S 7 rotates. Latent image surface 1a
The latent image surface 1a is conveyed toward a portion facing the latent image surface 1a, and is brought into direct sliding contact with the latent image surface 1a to perform a developing action. A portion of the developer 3 adheres to the surface of the latent image surface 1a at the portion where the second stage magnetic brush 7 and the latent image surface 1a face each other;
A portion of the developer 3a that did not adhere to the surface of the latent image surface 1a falls into the developer container 4, and the rest is moved by the adjustment plate 9 to the lower right part of the first stage magnetic brush 6 in the figure. , so a magnet is placed on the outer circumferential surface of sleeve S ₆ .
The sleeve S ₆ is held like a brush-like tip by the action of the sleeve S 6, and as the sleeve S ₆ rotates, it is conveyed toward the opposing part of the latent image surface 1a, where it comes into sliding contact with the latent image surface again and is developed. perform an action. The developer 3b that has not adhered to the surface of the latent image surface 1a is scraped off from the outer peripheral surface of the first stage magnetic brush 6 by the scraping plate 10 and collected into the developer container 4.

In this case, the sleeve S ₇ of the second stage magnetic brush 7 disposed on the downstream side in the moving direction of the latent image surface 1a has an outer circumferential surface velocity of the sleeve S7 disposed on the downstream side in the moving direction of the latent image surface 1a. The rotation speed of the sleeve S ₆ of the first-stage magnetic brush 6 is set to be faster by a predetermined amount. The first stage sleeve S ₆ and the second stage sleeve S ₇ may be interlocked and connected to each other by a transmission belt or a gear, and in this case, the reduction ratio of the transmission belt or gear is determined by the transmission belt or the gear. It may be set as appropriate between the two.

In this embodiment, the latent image surface 1a is first developed by the first stage magnetic brush 6, but the latent image surface 1a is first developed by the first stage magnetic brush ₆ .
Since the speed of the outer peripheral surface of the brush is slow, the brush-like ears are weak against the latent image surface, that is, the developing pressure is low. Therefore, the image density is insufficient and the development results in a slight amount of background smudge, but there are almost no traces of the tip and no white spotting occurs at the solid tip. Next, development is performed by the second stage magnetic brush 7, but since the speed of the outer peripheral surface of the sleeve _S7 is fast, the brush-like bristles are strong against the latent image surface, that is, the developing pressure is high. Therefore, the first
For areas where the image density was insufficient after development with the stage magnetic brush 6, it was replenished to a sufficient level by development with the second stage magnetic brush 7, and at the same time, due to the scavenging effect of the magnetic brush, it was found to have adhered to the background part. Unnecessary toner is also removed. Although the first stage was insufficient for the tip marks and white spots on the solid tip, the toner was attached and developed, so the electric field between the developer and the photoconductor was not large enough to cause abnormalities and was stable. Development is performed.

Another embodiment of the invention is to reduce the sleeve diameter of the first stage magnetic brush 6 and increase that of the second stage. In this case, the product of the rotational speed ratio of each sleeve and the diameter ratio of each sleeve becomes the ratio of the outer peripheral surface speed of each sleeve. Of course, the outer circumferential surface speed of the sleeve in the first stage must be smaller than that in the second stage.

In the above description, the rotation direction of the sleeves S ₆ and S ₇ of each developing magnetic brush is opposite to that of the photoreceptor 1 as shown by the arrow direction. The direction of rotation of the sleeve has an effect on the tip trace described above. That is, when the rotation direction of the sleeve is in the opposite direction, it appears at the tip as described above, and when it is in the forward direction, it appears at the rear end. The larger the linear speed difference between the photoreceptor and the sleeve, the more likely it is to appear, and therefore, it is more likely to appear in the reverse direction than in the forward direction. When only the sleeve 6 is in the forward direction, the amount of developer, the interval between the developing magnetic brushes, and the strength of the magnetic field are adjusted so that the first magnetic brush can be replaced by a magnetic roller and the second magnetic brush By inducing a magnetic field to form a brush around the developer, it is possible to cause the developer to slowly "twirl around" mainly due to the moving flow of the developer on the adjusting plate 9. In this case, developer adheres to the outer peripheral surface of the first stage magnetic roller, and development is performed with a small developing pressure.

In the above explanation, a cylindrical photoreceptor is shown, but the photoreceptor referred to in the present invention is an endless belt-shaped photoreceptor, or a so-called photoreceptor in which a photoconductive layer is formed on a support such as paper. It also includes photosensitive paper.

[Brief explanation of the drawing]

The figure is a cross-sectional view of the main part of a dry developing device in a copying machine to which the present invention is applied. 1a...Photoconductor latent image surface, 3...Developer, 6...
1st magnetic brush, 7... 2nd magnetic brush.

Claims (1)

[Scope of Claims] 1. Magnetic brushes including a plurality of rotatable sleeves disposed along the moving direction of the latent image surface of the photoreceptor and magnets fixedly disposed within each of the sleeves are arranged adjacent to each other. In a developing device of a copying machine, in which each of the magnetic brushes is arranged to face the latent image surface of the photoreceptor, the developing pressure at which the developer carried by each of the magnetic brushes presses the latent image surface is: In order to gradually increase the moving speed of the latent image surface in the moving direction of the latent image surface, the moving speed of the developer on the outer peripheral surface of the sleeve disposed on the upstream side of the moving direction of the latent image surface is on the downstream side in the moving direction of the latent image surface. A developing method for a copying machine, characterized in that the moving speed of developer on the outer circumferential surface of a sleeve disposed in the sleeve is increased.