JPS58195863A - Developing device with magnetic brush - Google Patents

Abstract

PURPOSE:To enalbe stable development to high density with high quality over a long period of time, by turning a magnet roll and a non-magnetic sleeve in the same direction and using ferrite as a magnetic carrier for a developer. CONSTITUTION:A magnet roll 3 and a non-magnetic sleeve 4 are rotated at 400-200rpm, etc. in the direction (b) opposite from the direction (c) for conveying a two-component type developer 5 of a dry type using a magnetic carrier of ferrite which has prescribed grain sizes and good fluidity and does not scatter. Then, the developer 5 is agitated thoroughly and a magnetic brush consisting of the developer 5 which prevents the generation of sweeping stripes in the image formed with a substantial amt. of the developer is formed without scattering of the developer 5 and with soft tuft. As a result, the development to high density with high quality is accomplished stably over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention develops an electrostatic latent image formed on a charge holding member in an electrophotographic copying machine or the like with toner using a dry two-component developer consisting of toner and a magnetic carrier. The present invention relates to a magnetic brush image device.

Magnetic brush developing devices generally use a dry two-component developer consisting of a toner in which pigments or dyes such as carbon black are dispersed in a resin, and an iron powder carrier, and these toner and carrier are mixed and stirred to separate them from each other. The electrostatic latent image is developed with the toner by triboelectrically charging the toner to a polarity opposite to that of the electrostatic latent image to be developed and acting on the charge retention member. In this way, when toner and carrier are mixed and stirred and the toner is charged by mutual frictional charging, the adhesion of toner resin to the carrier surface reduces the charging effect of each other. It is preferable to use a carrier having a large specific surface area as a surface species, that is, a carrier having a small particle size. However, the iron powder carrier conventionally commonly used in magnetic brush developing devices has problems in miniaturization, and when miniaturized, it oxidizes and produces carriers whose magnetism has deteriorated, which is used as a charge retention member during development. It adheres to the surface and reduces the quality of the developed image! There is an L match.

As a dry two-component developer that solves these problems,
A method using a ferrite carrier has been proposed. Ferrite carriers are easy to miniaturize due to their manufacturing method, and
Because the chemical composition is stable and the magnetic properties are homogeneous down to the center, unlike iron powder carriers, it is possible to effectively maintain the triboelectric charging effect with the toner. Since the adsorption force of the carrier can be increased, adhesion of the carrier to the charge retention member can be effectively prevented. However, when a 7-elite carrier is used in a magnet-fixed-sleeve rotation type magnetic brush developing device that is generally used when conventional iron powder carriers are used to develop, for example, a solid electrostatic latent image, the direction of rotation of the magnetic brush is That is, there is a problem in that fine sweeping lines occur in the direction of rotation of the sleeve, making it impossible to obtain a uniform solid image.

This is thought to be because the ferrite carrier is magnetized more quickly than the iron powder carrier, and is rapidly magnetized even in a weak magnetic field, forming a hard magnetic brush.

In addition, microcarriers in which a magnetic material is fractionated in a resin have also been proposed. However, since this carrier contains resin, it becomes unusable in a high temperature atmosphere, and its storage is therefore troublesome. Furthermore, since the strength of the resin is low, it is easily destroyed by agitation, and the toner contained in the resin is also likely to adhere to it, making it impossible to effectively charge the toner and resulting in the inability to perform the required development. For this reason, a carrier in which a magnetic material is enriched in a resin cannot be used stably for a long period of time.

The purpose of the present invention is to solve the above-mentioned problems, and
tMagnetic brush development with an appropriate structure so that latent images can always be developed into high-quality images without deteriorating image quality! II device.

The present invention comprises a magnetic roller having magnetic poles of DI'e&, and a cylindrical non-magnetic sleeve that dips the outer circumferential surface of the magnetic roller, and dry two-component development consisting of toner and magnetic carrier is carried out on the non-magnetic sleeve. Convey the agent while holding it and have an eyta image! ! E In a magnetic brush developing device that develops an electrostatic latent image with toner by acting on a load holding member, a ferrite carrier is used as the magnetic carrier, and the magnetic roller and the non-magnetic sleeve are rotated in the same direction. It is said to be a special acid if it has such a structure.

The present invention will be described in detail below with reference to the drawings.

This figure shows the structure of an example of the magnetic brush developing device of the present invention, which is adapted from a playback type machine. This electrophotographic copying machine is equipped with an 88 series electrophotographic photosensitive drum which rotates in the direction of arrow A, and a static @# image formed by a well-known electrophotographic method is transferred onto this PIB optical drum using a dry method consisting of toner and ferrite carrier. A toner image is developed by the magnetic brush developing device 12 according to the present invention using a two-component developer, transferred onto recording paper by a well-known bias roller transfer device (not shown), and then fixed and copied. This is what you get. In this example, the magnetic brush developing device 2 includes a magnetic roller 8 in which four N poles and S tanks each having a magnetic force of approximately 800 Gauss are arranged alternately at approximately equal intervals on a circle l#I, and this magnetic roller 8'. f) i distributed power close to the outer peripheral surface
[Equipped with a cylindrical non-magnetic sleeve 4 made of aluminum with a diameter of 375 m +, these magnetic rollers δ and the non-magnetic sleeve 4 are shown by arrows f - The magnetic roller 8 rotates at a higher speed than the non-magnetic sleeve 4 in the same direction. By doing so, the developer 5 is conveyed on the non-magnetic sleeve 4 in the direction of the arrow H, which is opposite to the direction of the arrow opening, and brought into contact with the /IB9 drum, thereby developing the **a image with toner. Ferrite carrier accommodates developer I! 66 and toner 71
1) Toner MM roller 9 accommodated in t-* collar 8
The rotation of the developer container 6 keeps the toner concentration in the kJim agent almost at a predetermined value, which is 9% by weight in this example.
The toner and ferrite carrier in the developer storage section 6 are mixed and stirred by the rotation of the stirring blade 10, and due to mutual frictional electrification, the toner is charged with a polarity opposite to that of the static 1tfIJ image formed on the photosensitive drum 1. The charged toner and the ferrite carrier are regulated by a doctor blade 1 to transport the charged toner and the ferrite carrier onto the non-magnetic sleeve 4.
A scraper 12 scrapes off the developer 5 on the non-magnetic sleeve 4 after the developing action.

In the configuration described above, the developer 5 conveyed on the non-magnetic sleeve 4 moves in the convex direction of the arrow as it rolls while finely moving upwards due to changes in the magnetic field caused by the rotation of the magnetic roller 8. The type of movement changes depending on the particle size of the ferrite carrier, and the average particle size is approximately 10
If it is more than 0μ, the fluidity will be poor, or
■If it is below, there is a problem that it will scatter and contaminate the surrounding area.

Therefore, in this example, a ferrite carrier having an average particle diameter of about 10 to 100 μm is used.

Further, according to various experiments, the developer 5 can be stirred if the rotational speed of the magnetic roller 8 is approximately 40 Orpm or more, that is, the number of magnetic pole changes with respect to the ferrite carrier is 8200 times/min or more. It is possible to effectively prevent the occurrence of sweeping marks in the developed image due to the intense rotation, but the rotation speed is approximately 2000 rpm, m (
When the number of magnetic pole changes exceeds 16,000 times/min, as is generally known, eddy currents generated within the non-magnetic sleeve 4 cause the non-magnetic sleeve 4 to generate heat and toner to scatter. Therefore, in this example, the magnetic roller 8 is approximately 4
00~g o o o rpm, that is, the number of magnetic pole changes is approximately 8200~160.00 times/min, preferably 150
Rotate at less than 0 rpm (number of magnetic pole changes 12,000 times/min).

However, if only the magnetic roller 8 is rotated at high speed, the developer 5 moves d! due to changes in the magnetic field. The temperature is getting faster and the nest is about the same time! ! There is a problem that the amount of developer 5 that acts on the nine-drum drum decreases, resulting in a low degree of development. For this reason, in this example, the non-magnetic sleeve 4 is rotated in the opposite direction to the conveying direction of the developer 5 as indicated by the arrow C, that is, in the same direction as the rotation direction of the magnetic roller 8 as indicated by the arrow opening. The conveyance is braked to increase the amount of developer 5 that acts on the photosensitive drum 1 per nest position time.

In this way, a soft ridge can be formed without causing heat generation or toner scattering due to eddy current in the non-magnetic sleeve 4, and a sufficient amount of developer 5 can be applied to the photosensitive drum 1.
Therefore, it is possible to obtain a developed image with sufficient density without any scratches.

As described above, the conditions for obtaining a high-quality developed image that satisfies both the image quality and FA change by rotating the stone roller 8 and the non-magnetic sleeve 4 in the same direction are the particle size of the ferrite carrier, the magnetic roller The number of poles and rotation speed of the magnetic sleeve 8, the diameter and rotation speed of the non-magnetic sleeve 4, etc. are major factors, but expressing these in a general relationship means that the movement of the developer 5 conveyed on the non-magnetic sleeve 4 is It's difficult because I'm lazy. However, it is easy to find I&optimal conditions by changing the combination of these factors. For example, using a ferrite carrier having a particle size distribution shown in Fig. 2 with an average particle diameter of 80μ, the rotation speed of the magnetic roller δ is 11000 rpm, the rotation speed of the nonmagnetic sleeve 4 is 5 Orpm, and a solid electrostatic latent carrier is used. When the image was developed, it was possible to obtain a high-quality developed image that was uniform and had a high degree of a.The particle size distribution of the ferrite carrier shown in Figure 2 was measured using a particle size distribution measuring device that uses laser light diffraction ( Product name: Microdrug Co., Ltd.
+ machine). In addition, as a comparative example, when a similar static 1ta image was developed by stopping the rotation of the non-magnetic sleeve and rotating only the magnetic roller 8 at 1000 rpm, only a developed image with low density was obtained although there were no sweeping marks. Ta. Fourth, the same #1. When a similar electrostatic latent image was developed using a conventional magnetic brush developing device using a magnet-fixed-sleeve rotating system, only low-quality developed images with noticeable scratches were obtained.

Note that the present invention is not limited to only the example described above, and numerous modifications and changes are possible.

For example, in the above-mentioned example, the rotation *t of the magnet roller 8 was rotated faster than that of the non-magnetic sleeve 1 so that the developer 6 was conveyed in the opposite direction to the rotation direction of both. The same effect can be obtained even if the rotation of the magnetic roller 4 is made faster than that of the magnetic roller 3 and the developer 5 is conveyed in the same direction as the rotational direction of both. In this case, the rotation of the magnet roller 8 serves as a brake on the conveyance of the developer 5.

As described above, according to the present invention, a ferrite carrier that can be easily miniaturized and has high magnetic permeability is used as a carrier for a dry two-component developer, and a magnetic roller having a plurality of magnetic poles and a non-magnetic sleeve are moved in the same direction. This allows the magnetic brush to be made soft, and the amount of developer applied per unit time to the charge retaining member having the electrostatic latent image to be sufficiently increased. a High-quality development with high darkness can be stably performed at long light intervals.

[Brief explanation of drawings]

Figure #lI is a cross-section Ek1 diagram showing an example of the magnetic brush developing device of the present invention. FIG. 1 is a diagram showing the particle size distribution of the ferrite carrier used in the magnetic brush developing device according to the present invention. l...Electronic photosensitive drum 2...Magnetic brush developing device lid 8...Magnetic roller 4...Non-magnetic sleeve 6...Developer 6...Developer storage section 7
...Toner 8...Toner hopper 9...
・Toner supply roller 10...Agitating blade 11...Doctor blade] 2...Scraper.

Claims (1)

[Scope of Claims] L A magnetic roller having a plurality of magnetic poles and a cylindrical non-magnetic sleeve that covers the outer 1M surface of the magnetic roller, and a dry-type toner and a magnetic carrier formed on the non-magnetic sleeve. In a magnetic brush developing device that develops an electrostatic latent image with toner by conveying the two-component developer while holding it and causing it to act on a charge holding member having a static WLa image, a ferrite carrier is used as the magnetic carrier. A magnetic brush developing device characterized in that the magnetic roller and the non-magnetic sleeve are configured to rotate in the same direction. Turtle As the ferrite carrier, the average particle size is approximately 10
2. The magnetic brush developing device according to claim 1, wherein a magnetic brush developing device having a diameter of 100 μm is used. & The magnetic brush developing device according to claim 1, wherein the magnetic roller is configured to rotate so that the number of magnetic pole changes relative to the ferrite carrier is approximately 8,200 to 16,000 times/minute.