JPH0348600Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Technical Field of the Invention] The present invention relates to a developing device such as an electrophotographic copying machine or a printer using electrophotographic technology that obtains stable high image quality. [Prior art and its problems] In the conventional two-component development method, it was necessary to strictly control the content of toner in carrier to 4%±0.5%. This is because at high densities, toner scattering and scumming occur, and at low densities, image density decreases and carrier drag occur. On the other hand, a developing method using only a one-component magnetic toner without using a carrier has advantages such as no need for density control and a simple structure.
However, the disadvantage is that uniformly charging high-resistance toner by frictional charging or charge injection is unstable because there is no carrier, resulting in a lack of stability in image quality, and the narrow doctor gap causes toner to It has drawbacks such as easy clogging and white streaks. On the other hand, as an intermediate concept between one-component and two-component development, there is a method in which one-component magnetic toner is mixed into the carrier. For example, one-component magnetic toner with a particle size of 10 μm is added to a resin mixed carrier with a particle size of about 20 μm.
% to 50% of the developer is used, and the rotation of the magnet roll and sleeve sufficiently mixes the carrier and toner to obtain good image quality. Compared to ordinary two-component developers, this type of system has the advantage that the toner density tolerance range is as wide as about ±10%, and strict toner control is not required. However, as a disadvantage, compared to a one-component developer, it requires toner concentration control, and the structure is complicated because the magnet roll and sleeve are both rotated. Another method is to use a developer containing about 50% (by weight) of magnetite or ferrite carrier one-component magnetic toner (particle size 10 to 12 μm) with a particle size of 40 μm to 50 μm, and use a magnet roll as a developing device. There is a developing method that uses a fixed sleeve rotation method. This has a wider toner concentration range than the two-component development method, and it is possible to obtain a certain level of image quality even at about 30% to 80%. However, the drawback is that the limit of the toner concentration range for obtaining good image quality is 50%±10%. FIG. 2 shows the .gamma. characteristic, that is, the V-D curve (the horizontal axis is the photoreceptor surface potential V, and the vertical axis is the image density D) when the toner density is varied from 20% to 60%. Generally speaking, as for development characteristics, the copy density changes depending on the density of the developer. The correlation depends on the potential of the photoreceptor and the concentration of the developer. Since a method is usually used to stabilize the potential of the photoreceptor, the development characteristics are determined by the residual potential of the photoreceptor depending on the amount of exposure and the toner concentration of the developer. In FIG. 2, as the toner density decreases, the maximum density decreases, but the image density increases. Table 1 shows the results of measuring the height of the developing main pole for the above reasons.

[Purpose of invention]

The present invention was developed in view of the above-mentioned drawbacks of the conventional technology, and is a developing method using a magnetite or ferrite carrier as a carrier, a developer using a one-component magnetic toner as a toner, and a developing device with a magnet roll fixed and a rotating sleeve. However, it is an object of the present invention to provide a developing method that maintains a constant V-D curve and obtains stable characteristics even when the toner concentration is varied from 30% to 80%. [Summary of the invention] In order to achieve the above object, the present invention uses a developer consisting of a magnetic carrier and a magnetic toner, in which the magnetic toner accounts for approximately 30% by weight or more, and has a rotating sleeve in which a fixed magnet is disposed. In the apparatus, the center of the magnetic pole is located at the upstream side and the downstream side in the rotational direction of the image carrier at the closest point between the image carrier and the rotating sleeve, which are disposed facing the rotating sleeve. and adjacent developing magnetic poles having mutually different polarities and arranged within a range of approximately 20° or more and 50° or less from a line connecting the center of the rotating sleeve, and the magnetic force of the developing magnetic pole that is located on the downstream side of the developing magnetic poles. is larger than the magnetic force of the developing magnetic pole located upstream. [Embodiments of the invention] Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of the developing device of the present invention, and FIG. 3 is a block diagram of the developing device of the present invention equipped with a scraper. In FIG. 1, 1 is a developing device, and developer 3
consists of a carrier 4 made of magnetite or ferrite carrier and a one-component magnetic toner 5, and the toner 5 is mixed and regulated to a thickness of 0.3 mm by a doctor 2. Toner 5 has a magnetic material content of 55% and a volume resistivity value.
10 ^12~14 Ωcm. 6 is a sleeve that rotates counterclockwise. The magnet roll 7 is fixed and has a four-pole configuration of N ₁ , S ₁ , N ₂ , and S ₂ . The main pole N ₁ is mainly used for developing latent images,
S ₁ is used to improve image quality. Other N ₂ , S ₂
is mainly used for conveying developer. Reference numeral 8 denotes a photoreceptor made of Se, OPC, etc., which rotates in the direction of the arrow (clockwise in the figure) while maintaining an electrostatic latent image corresponding to the original image on its surface. N ₁ is a magnetic force of 650 Gauss, magnetic pole width is 5 mm, and θ ₁
is 32°. S ₁ has a magnetic force of 800 Gauss, a magnetic pole width of 7 mm, and θ ₂ of 45°. The regulated developer 3 comes into contact with the photoreceptor 8 by the rotation of the sleeve 6 made of a non-magnetic material, but since the center of the developing ear is largely shifted from the center of the photoreceptor, the developing agent 3 is not sufficiently developed. First, development is performed in the slightly shifted developer reservoir 7A. This developer reservoir 7A hardly changes even if the toner concentration changes by about 30% to 80%, so stable development is performed. The reason for this is that at the center of the developer ear, the magnetic lines of force 9 are highly dense and are directed toward the center of the magnet roll, whereas in the developer reservoir 7A, the lines of magnetic force are tilted and lie horizontally, so the change in the height direction of the developer 3 is very large. This is because there are few. However, since development is performed off-center from the center of the developing ear, toner tends to adhere excessively around the thin lines. An auxiliary reservoir 7B with _one pole is used to remove this to increase sharpness and to remove background stains when they occur. Since the auxiliary reservoir 7B is located in the direction away from the photoreceptor 8 with respect to the developing reservoir 7A, the reservoir is small and the image quality can be sufficiently improved without reducing the image density. Also, developer reservoir 7A
For the same reason, it is hardly affected by changes in toner concentration. The reason why the magnetic force of the main developing pole N ₁ is lower than that of S ₁ is to improve the image quality by making the developing brush softer and to reduce the collapse of thin lines, and also to reduce the difference in image density due to the difference in toner density. There is a purpose to This requires _N1
The poles are preferably provided at θ ₁ =20° to 50°. On the other hand, S ₁
The reason why the magnetic force is large is to prevent the developer 3 from scattering. For this purpose, it is preferable to provide the S ₁ pole in the range of θ ₂ =20° to 50°. As mentioned above, the main pole is separated into two parts (N ₁ and S _{1 )} , one pole is used for development and the other pole is used for improving image quality, and the center of each pole is connected to the center of the photoreceptor and the center of the developing roll. The developing pole was placed 20° to 50° above and below the line, and the width of the magnetic force of the developing pole was narrower than that of the pole for improving image quality, and the density of the magnetic force was weakened. As a result, even if the toner density is changed from 30% to 80%, the V-D curve hardly changes as in the conventional method, and the image quality can be greatly improved. Further, since the carrier is mixed, triboelectric charging properties are improved and image stability during continuous use is also good. Using this method, you can add toner (developer) for the required number of sheets into the hopper of the developing device.
It is possible to make several thousand copies without the need for toner control until the density reaches the equivalent of %, making it especially suitable for low-speed machines. Generally, when the toner concentration is less than 30%, a phenomenon called carrier drag occurs in which carriers adhere to the photoreceptor. FIG. 3 shows an example in which a scraper is attached to the sleeve surface as a way to prevent this. Since the structure is such that the developer does not go over the scraper when the concentration decreases and the developer volume becomes below a certain level, the developer is not transported when the concentration decreases, thus preventing carrier drag. [Effects of the invention] As explained in detail above, the image characteristics are constant over a wide range of toner concentration of the developer (a mixture of a ferromagnetic carrier containing no resin and a one-component magnetic toner) from 30% to 80%. Furthermore, due to the carrier mixture, sufficient friction and charging can be obtained, and stable high image quality can be obtained. Although it is technically a two-component developer, it can be used as a single-component developer, meaning that the toner concentration range is extremely wide, so once the developer is put into the developer, thousands of copies can be made without special toner replenishment. . Moreover, the structure is simple and the cost is low.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the developing device of the present invention, Figure 2 is a diagram of the relationship between the photoreceptor surface potential and image density when the toner density is varied, and Figure 3 is a block diagram of the developing unit equipped with a scraper. It is. 1...Developer, 2...Doctor, 3...Developer, 4...
Carrier, 5...Toner, 6...Sleeve, 7...Magnet, 7A...Developer reservoir, 7B...Auxiliary reservoir, 8...
Photoreceptor, 9... lines of magnetic force, 10... scraper.

Claims (1)

[Scope of utility model registration request] In a developing device that uses a developer consisting of a magnetic carrier and a magnetic toner and in which the magnetic toner accounts for approximately 30% by weight or more and has a rotating sleeve in which a fixed magnet is disposed, an image carrier is disposed facing the rotating sleeve. The center of the magnetic pole is approximately 20° or more from the line connecting the center of the image carrier and the center of the rotating sleeve on the upstream and downstream sides in the rotational direction of the image carrier at the closest point between the image carrier and the rotating sleeve.
It has adjacent developing magnetic poles that are arranged within a range of 50° or less and have mutually different polarities, and the magnetic force of the developing magnetic pole placed on the downstream side of the developing magnetic poles is greater than the magnetic force of the developing magnetic pole placed on the upstream side. A developing device characterized by: