JP2000147908A - Developing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing apparatus which prevents developer from being caused to scatter and spilling off, even when a developing roller is positioned within the height of the upper half of an image carrier and which ensures satisfactory image reproducibility. SOLUTION: An image roller (17) is positioned within the height of the upper half of an image carrier (1). Carrier is composed of a first carrier with an average particle diameter in the range of 70 μm-100 μm and second carrier with an average particle diameter in the range of 40 μm-70 μm. The percentage of the first carrier in the mixture is 30-60 wt.% and that of the second carrier is 70-40 wt.%. The saturation magnetizations of the first carrier and second carrier are 60-79 emu/g, and a developer with a resistance value of 109 Ωcm-1012 Ωcm is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to a developing device provided in an image forming apparatus such as a printer, and more particularly, to a developing device in which a magnetic brush formed on a developing roller is located at an upper half position of an image carrier.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, a plurality of developing devices provided in a two-color or multi-color image forming apparatus are arranged along the peripheral surface of an image carrier, and are sequentially known. An image is formed on the image carrier by the image forming means. A commonly known developing device has a developing roller provided so as to approach along the axial direction of the image carrier. For example, a two-component developer consisting of a toner and a carrier is attracted to the surface of the developing roller by the action of a magnet provided inside the developing roller to form a magnetic brush, and a magnetic brush is formed according to the electrostatic latent image formed on the surface of the image carrier. The brush moves only the toner to the image carrier side by contact or non-contact with the image carrier, and visualizes the image. The carrier remains on the surface of the developing roller, carries new toner, and is again used for development.

In such an apparatus, there is a case where the developing roller must be located at the upper half position of the image carrier due to the design due to the reduction in the diameter of the image carrier for downsizing or the like. In this case, gravity acts on the lower portion of the magnetic brush formed on the surface of the developing roller, so that the developer is easily separated from the surface of the sleeve. Therefore, if the developing device has a developing roller below the image carrier, a part of the casing may be extended to form a collecting plate to collect the spilled developer. However, when the developing roller is located above the image carrier, the developing roller comes into contact with the image carrier, so that the casing cannot be extended to provide the collecting plate, and the developer spills out of the developing device. The inside of the device will be soiled.

For this reason, when the developing roller is positioned in the upper half area of the image carrier, the carrier is inevitably increased in magnetization to strengthen the magnetic attraction to the surface of the developing roller and the developer drops. Must be prevented.

Changing the composition of a developer in a developing device
To provide a developing device that is less likely to scatter and fall
Can be As an example, increase the magnetization of carriers
Or increasing the particle size of the carrier
The carrier firmly on the developing roller surface
Agent leakage can be minimized. However,
The magnetic brush formed on the image roller has a short
The toner on the image carrier during image formation.
-The image is faded or the solid image is
The image cannot be reproduced. Generally, a career
A large particle size improves fluidity and reduces carrier scattering.
Disappears. Also, if the particle size of the carrier is small,
Good image, but carrier scattering
Will also increase. In addition, the carrier resistance is 10 ⁸Ω
cm or less, the toner charge is low, especially non-contact
In the type developed with, developer scattering becomes remarkable.
The inside of the main unit is contaminated. In addition,
Cause.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and makes the developer scatter even when the developing roller is positioned at the upper half position of the image carrier. It is an object of the present invention to provide a developing device which has good image reproducibility without spilling out.

[0007]

In order to solve the above-mentioned problems, a developing device of the present invention forms a magnetic brush on a developing roller using a two-component developer composed of a toner and a carrier to form an electrostatic latent image. In a developing device for forming a visible image by toner by bringing the magnetic brush into contact with or close to the formed image carrier, the developing roller is provided so as to be positioned at an upper half position of the image carrier; Are the first particles having an average particle diameter in the range of 70 μm to 100 μm.
And a second carrier having an average particle size in the range of 40 μm to 70 μm, and the mixing ratio of the second carrier is the first ratio.
A carrier is 30 to 60 wt% a and the second carrier is 70~40wt%, further and the resistance value saturation magnetization is a 60~79emu / g of the first carrier and the second carrier 10 ⁹ Ωcm to 10 ¹² Ωcm.

A plurality of developing devices are provided around the image carrier, and a developing roller provided in at least one of the developing devices is located at an upper half position of the image carrier. It is characterized by.

With such a configuration, even in a developing device in which the developing roller is located in the upper half position of the image carrier, the carrier in the developer is used by mixing a small particle size and a large particle size. In this case, a solid image is assigned to a carrier having a smaller size, and a line image is assigned to a carrier having a larger size to form a good image, and toner scattering and spillage are minimized.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view of an image forming apparatus provided with the developing device of the present invention. The image forming apparatus 30 includes:
For example, it is a two-color image that forms a red-black image, has a configuration using electrophotography, and has a photosensitive drum as the image carrier 1 at the center thereof.

A first corona charger 2 for uniformly charging the surface of the image carrier 1 so as to have a predetermined surface potential with the image carrier 1 as a center, and a first document read by a scanner or the like A first image projection device 3 for projecting data with an LED or the like to form a first latent image on the image carrier 1 and supplying a charged toner to the first latent image to form a toner image A first developing device 4, an AC corona eliminator 5 for discharging the surface of the image carrier 1 after the development of the first color by the first developing device, and a second device for recharging the surface of the image carrier 1 having been discharged. A corona charger 6, a second image projection device 7 for projecting the second document data read by a scanner or the like by an LED or the like to form a second latent image on the image carrier 1, Second development for forming a toner image by supplying charged toner to the latent image And location 8, formed on the image carrier 1 2
A transfer corona discharger 10 and a separation corona discharger 11 for transferring a color image to a transfer material sent from a paper feeding unit; a cleaning device 12 for removing toner remaining on the surface of the image carrier 1 after transfer; An eraser lamp 13 for uniformly eliminating the surface potential of the surface of the image carrier 1, which are arranged so as to sequentially act on the image carrier 1, and a two-color toner image is formed on the same image carrier surface; Form.

The first developing device 4 will be described in detail with reference to FIG. The first developing device 4 includes an opening 1 of the casing 14.
5 has a developing roller 17 provided so as to protrude therefrom.
A magnetic brush 16 is formed on the peripheral surface of the developing roller 17. For example, the developing roller 17 has a magnet 18 fixed inside, and the outer periphery thereof is provided so that a non-magnetic cylindrical sleeve 19 is rotatable. The magnetic brush 16 is formed on the surface 19. The magnetic brush 16 is regulated to a certain thickness by a regulating plate 20 provided in the casing 14. The inside of the developing device 4 is filled with a developer composed of a toner and a carrier, and the toner is charged by being stirred by stirring means 21 such as a stirring screw. Further, the toner consumed by the image formation is appropriately replenished from a toner hopper filled with replenishment toner (not shown) connected in the developing device.

The magnetic brush 16 formed on the peripheral surface of the developing roller 17 is developed by rubbing or non-contacting (jumping) the surface of the image carrier 1, and only the toner is applied to the surface of the image carrier according to the electrostatic latent image. To form a toner image.

In particular, in a two-color image forming apparatus or a color image forming apparatus, the number of developing devices is plural, and
The layout of the developing roller provided in the developing device is at least one in the upper half of the image carrier due to design. For this reason, the casing cannot be extended to provide the collecting plate 22 as shown in the second developing device, and further drops due to the action of gravity from below the developing roller to contaminate the inside of the device main body. I will.

In the developing device positioned above the image carrier as described above, the average particle size is 70 μm to 100 μm.
And the average particle size is 40 μm or more.
A second carrier having a range of 70 μm is used. The mixing ratio of the first carrier is 30 to 70 wt%,
Is 30 to 60 wt%, and the saturation magnetization of the first carrier and the second carrier is 60 to 79 em.
u / g and a resistance value of 10 ⁹ Ωcm to 10 ¹² Ω
cm carrier is used. The preferred range is 10
A carrier of ¹⁰ Ωcm to ^{10 11} Ωcm is used. As an example, the average particle diameter is 90 μm as the first carrier.
The second carrier has an average particle size of 60 μm (the range of 44 to 74 μm is 85 to 9%) with respect to 50 wt% of the carrier having a large particle size (the range of 74 to 105 μm includes 85 to 90%).
50% by weight of a carrier having a small particle diameter (including 0%), 5% by weight of a non-magnetic toner having an average particle diameter of 10 μm based on the total amount of the carrier, and stirring and mixing. The surfaces of the first and second carriers are coated with a resin such as silicon or acrylic to have a resistance value of 10 ¹¹ Ωcm. The saturation magnetization of the carrier was 63 emu.

By using the carrier and toner under the above-mentioned conditions, it is possible to provide a developing device which provides a good image and has less scattering and less spillage. That is, by using a carrier having a saturation magnetization of 60 to 79 emu / g, a strong magnetic brush is formed to some extent on the surface of the developing roller to improve the fluidity of a large-sized carrier and reduce carrier scattering. Reproduce halftone with a small carrier. A good image can be obtained within the range of the above conditions.

If the average particle size of the first carrier exceeds 100 μm under the above-described conditions, the charge amount of the toner increases, and the density of the solid image cannot be maintained. On the other hand, when the average particle size of the second carrier is less than 40 μm, the charge amount of the toner becomes small, and the developer is easily scattered.

If the saturation magnetization of the carrier is less than 60 emu / g under the above-described conditions, the adsorption of the developer to the sleeve surface by the action of the magnet inside the developing roller is not sufficient, and the developer is scattered. If the saturation magnetization of the carrier exceeds 79 emu / g, the magnetic brush formed on the peripheral surface of the sleeve will be in a hard state, so that the toner image will have unevenness.

The mixing ratio of the first carrier and the second carrier is from 30:70 to 60:40 by weight. Under the conditions described above, the mixing ratio of the first carrier is 6
When the content is higher than 0 wt%, an image having insufficient halftone is formed, and when the content of the second carrier is less than 40 wt%, the image density becomes insufficient and the carrier is easily scattered.

Further, when the resistance of the carrier is less than 10 ⁹ Ωcm under the above-mentioned conditions, the charge amount of the toner becomes small and a solid image having a sufficient density can be obtained, but the developer is liable to be scattered. On the other hand, if the resistance exceeds 10 ¹² Ωcm, the charge amount increases, and a sufficient image density cannot be obtained.

[0021]

As described above, the developing roller is provided at the upper half position of the image carrier, and even if it is not possible to extend the casing at the lower portion to provide a sufficient collecting plate, the first carrier and the developing carrier can be used. By setting the second carrier and the above conditions, the carrier can be prevented from adhering to the image carrier, and a solid image and a good line image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an image forming apparatus provided with a developing device according to the present invention.

FIG. 2 is a schematic sectional view showing an example of a developing device according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image carrier 2 first corona charger 3 first image projection device 4 first developing device 5 AC corona discharger 6 second corona discharger 7 second image projection device 8 second development device 10 Transfer corona discharger 11 Separation corona discharger 12 Cleaning device 13 Eraser lamp 14 Casing 15 Opening 16 Magnetic brush 17 Developing roller 18 Magnet 19 Sleeve 20 Restriction plate 21 Stirrer 22 Collection plate 30 Image forming device

Claims (2)

[Claims] 1. A magnetic brush is formed on a developing roller using a two-component developer composed of a toner and a carrier, and the magnetic brush is brought into contact with or close to an image carrier on which an electrostatic latent image is formed. In the developing device for forming a visual image, the developing roller is provided so as to be located at a position of an upper half of the image carrier, and the carrier has a first carrier having an average particle diameter in a range of 70 μm to 100 μm. And a second carrier having an average particle size in the range of 40 μm to 70 μm. The mixing ratio of the first carrier is 30 to 60 wt% and the second carrier is 70 to 40 wt%.
%, and the saturation magnetization of the first carrier and the second carrier is 60 to 79 emu / g, and the resistance value is 10 ⁹ Ωcm to 10 ¹² Ωcm. 2. A plurality of developing devices are provided around the image carrier, and a developing roller provided in at least one of the developing devices is located at an upper half position of the image carrier. The developing device according to claim 1, wherein: