JPS61148457A - Developer - Google Patents

Abstract

PURPOSE:To maintain the specified image density without controlling toner density by constituting a developer in such a manner that the difference in the respective residual magnetization of a magnetic carrier and magnetic toner has <=1emu/g relation. CONSTITUTION:The magnetic carrier 1a and magnetic toner 1b on a developing sleeve 4 form independently ears as the brush-shaped ears of the carrier 1a and the toner 1b in the starting stage of development. The thickness of the developer 1 napping on the sleeve 4 in the above-mentioned manner is controlled by a doctor blade 6 to develop the electrostatic latent image formed on a photosensitive drum 7 to form the sensible image in the sliding contact part. The developer 1 sticking to the sleeve 4 is connected like chains near the sleeve 4 and is hardly separated when the carrier 1a and toner 1b having a small difference in the residual magnetization of <1emu/g are used in combination. The toner 1b of the same amt. as the consumed toner is thus stuck freshly to the sleeve 4. The developing characteristic is less changed and the specified image density is obtd. in the above-mentioned manner, by which the good image is obtd. without controlling the toner density.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a developer used in an electrophotographic copying machine or a printer using electrophotographic technology.

In particular, the present invention relates to a secondary developer having a magnetic toner and a magnetic carrier.

[Prior art]

The developer used in the above-mentioned electrophotographic copying machine and the like is normally placed in a developing device, and the developing method differs depending on the constituent components of the developer. For example, development is carried out using a developer containing a mixture of non-magnetic toner and magnetic carrier.
There are a component development method, a primary development method in which development is performed using only low-resistance or high-resistance magnetic toner as a developer, and a development method in which development is performed by mixing a magnetic carrier with high-resistance magnetic toner.

[Problems with conventional technology]

When developing using the conventional developing method as described above, for example, when a first-order developer is used, the following problems arise. In other words, magnetic toner with a low resistance of 10 ohms or less is difficult to transfer to plain paper, and
Magnetic toner having a high resistance of 13Ω or more also has the problem that when the thickness of the magnetic toner adhering to the developing sleeve is controlled to be constant, the magnetic toner aggregates and blocking occurs.

On the other hand, the secondary development method using non-magnetic toner and magnetic carrier requires extremely precise toner concentration control. In addition, the development method using high-resistance magnetic toner and magnetic carrier has the advantage that the magnetic carrier prevents agglomeration of magnetic toner, which is a problem in component development methods, and does not require highly accurate toner concentration control. However, even if it is a rough control, toner concentration control is still required.

In addition, we investigated how many copies could be made without using this toner density controller using a developer consisting of high-resistance magnetic toner and magnetic carrier, and the results are as follows. That is, when using a developer having an appropriate toner concentration range of 50 to 60% by weight (hereinafter referred to simply as %), which will be described later.

If 100 g of a developer with a concentration of 60% is initially put into the developing device, only 400 copies can be made until the toner concentration of this developer reaches 50% when copying consumes 50 mg of toner per sheet.

Here, the appropriate toner density range means a toner density range in which substantially the same level of image density can be obtained for the same photoreceptor surface potential when copying is performed continuously without toner replenishment. Normally, this appropriate toner concentration range is at most about 10% as described above. In the above example, when the toner density exceeds 60%, it becomes difficult to reproduce the image;
If it is less than 0%, the two images will be reproduced darkly and problems such as scumming will occur. Figure 2 shows the relationship between the surface potential of the photoreceptor and the density of the reproduced image.
%, 80% (hereinafter referred to as development characteristics).This characteristic diagram shows that if the photoreceptor potential is constant, the range in which the image density does not change is very narrow. I understand. Therefore, in a developing device using conventional developer, a control device must be installed to control the toner concentration within a very narrow range.Furthermore, when replenishing toner with this toner concentration control device, the toner spreads around the surrounding area. Problems such as toner scattering and toner spillage also occur.

[Purpose of the invention]

In view of the above-mentioned conventional drawbacks, the present invention makes it possible to obtain an extremely wide appropriate toner concentration range when a mixture of a fet toner and a magnetic carrier is used as a developer, and furthermore, provides a development method that eliminates the need to control toner concentration. The purpose is to make this method possible by using this developer.

[Key points of the invention]

In order to achieve the above object, the present invention provides a developer comprising a magnetic toner and a magnetic carrier.

The difference between the residual magnetization of the magnetic toner and the residual magnetization of the magnetic carrier after passing through a magnetic field of less than 1000 Oe is 1
It is characterized by being less than emu/g.

[Embodiments of the invention]

First, a first embodiment of the present invention will be described in detail with reference to the drawings.

The developer 1 of the present invention includes a magnetic toner 1b and a magnetic carrier 1a.
The magnetic toner 1b contains 60% by weight of magnetite in styrene-acrylic resin and has a volume average particle size of 1.
It is about 4μm, 1ooo Oersted (hereinafter referred to as O
After passing through the magnetic field (indicated by e), the residual magnetization (σrv) is 3.9
emu/g. In addition, the magnetic carrier 1a is composed of ferrite particles with a volume average particle diameter of 45 μm and has a density of 1000 (O
After passing through the magnetic field e), the residual magnetization (σrc) is 3.3 emu
/g≠ exists.

The developer 1 having the above structure is put into the hopper 2a of the developing device 2 whose schematic structure is shown in FIG.

Inside the developing device 2, there is further provided a developing sleeve 4 having a diameter of 20 mm which rotates in the direction of the arrow 3, and main poles N1, N2, . A magnet roll 5 having Sl and S2 is provided. Further, a doctor blade 6 is provided on the developing sleeve 4 with a gap of 0°2511 from the developing sleeve 4 to regulate the thickness of the developer 1 adhering to the developing sleeve 4 to be constant. Also, the developer sleeve 4.

It is provided near the photoreceptor drum 7 rotating in the direction of arrow 7a, and is configured to form a magnetic brush on the developing sleeve 4 corresponding to the main pole N1 of the magnet roll 5 to rub the surface of the photoreceptor drum 7. The photosensitive drum 7 at this sliding portion
The distance between the developing sleeve 4 and the developing sleeve 4 is as narrow as 0.5 mm.

The operation will be described below in the case where the developer 7 of the present invention having a toner concentration of 80% is introduced into the developing device configured as described above and continuous copying is performed.

First, at the start of development (here, "start of development" refers to the time when magnetic carrier 1a and magnetic toner 1b are put into the developing device 2 for the first time and development is started), magnetic toner 1b and magnetic carrier l
The brush-like ears of magnetic carrier 1a and magnetic toner 1b on the developing sleeve 4 are not sufficiently mixed with magnetic carrier 1a and magnetic toner 1b, as shown in FIG. 4(a). The ears form independently. The development characteristics at this time are the same as those without the magnetic carrier 1a.

As described above, at the start of development when the magnetic toner 1b has a high concentration, the state of formation of the ears is almost the same as that at the start of conventional development shown in FIG.

The thickness of the developer 1 that has formed spikes on the developing sleeve 4 is regulated by the doctor blade 6.

The electrostatic latent image formed on the photoreceptor drum 7 is visualized at the rubbing portion. Repeat the process further.

When continuous copying is performed, the magnetic carrier 1a and the magnetic toner 1b have residual magnetization (σr) of approximately the same magnitude, so even if the toner concentration decreases to, for example, 20%, the image density will be As shown in Figure 1, there is almost no difference from the time at the start of development (at 80% toner concentration). That is, when the magnetic carrier 1a and the magnetic toner 1b, which have a small difference in residual magnetization, are used in combination as in this embodiment, the developer 1 adhering to the developing sleeve 4 is connected in a chain shape near the developing sleeve 4.

Far away, the same amount of magnetic toner as consumed 1
b newly adheres to the developing sleeve 4. In other words, even if the toner concentration decreases to about 20% due to continuous copying, the condition of the ears remains the same as at the start of development, as shown in FIG. 4 (C1). As a result, the development characteristics do not change.Also, as the toner concentration decreases due to continuous copying, the agitation properties change, as shown in this example, when the developer 1 with large residual magnetization In the case of , it is so small that it has almost no effect on the degree of stirring.

Therefore, for example, the residual magnetization of the magnetic carrier 1a and the magnetic toner 1b is 1.1 emu/g and 3.9 emu/g.
The development characteristics shown in Figure 5 when using the same developing device and developing under the same developing conditions are as follows. It won't happen.

That is, in the case of FIG. 5, as shown in FIG. 4(b),
The magnetic toner 1b that stands in spikes on the developing sleeve 4 at the start of development has a large residual magnetization, and once the magnetic toner has adhered to the developing sleeve 4, other developer 1 is hardly agitated, but the magnetic carrier 1a has small residual magnetization,
Even after it adheres to the developing sleeve 4, it separates from the developing sleeve 4 and mixes well with the developer l in the pumper 2a without being chained together with the magnetic toner 1b.

Therefore, the formation of spikes of the developer 1 on the developer sleeve 4 at the rubbing portion is caused by the magnetic carrier 1a and the magnetic toner 1b being mixed together to form spikes, as shown in FIG. Unlike the spike formation shown in FIG. 4(b) at the start, charge injection into the magnetic toner 1b at the tip of the spike is more likely to occur, resulting in deviations in development characteristics.

The development conditions and the magnetic toner 1b were the same as described above, and only the magnetic carrier 1a was made of iron oxide powder with a volume average particle diameter of 42 μm, and the residual magnetization after passing through a magnetic field of 1000 (Oe) was 2.5 emu/g. Even when there is a change, the development characteristics change and deviate as shown in FIG. 7 for the same reason.

Other embodiments of the invention will now be described below.

The developing device and developing conditions used are the same as those used in the first embodiment of the present invention shown in FIG.
C contains 40% by weight of magnetite in a styrene-acrylic resin and has a volume average particle size of 15 μm, and 100
The residual magnetization (σr) after passing through a magnetic field of 0 (Oe) is 1.8
emu/g is used, and a magnetic carrier with residual magnetization of 1.1 emu/g after passing through a magnetic field of 1000 (Oe) is used.

When the developer 8 of this embodiment is used, the development process is the same as described above, but from the start of development, the ears on the developing sleeve 4 are agitated by slight rotation of the developing sleeve 4, and as shown in FIG. As shown, the magnetic toner IC and the magnetic carrier 1a are mixed to form an ear. Continuous copying is performed in the same manner as described above with such spike formation, and even if the toner concentration decreases, the degree of agitation of the developer 8 and the condition of the spikes do not change. Further, although the amount of charge on the magnetic toner IC and the magnetic carrier 1a increases slightly due to continuous copying, it is not large enough to affect the development characteristics.

Therefore, in the developer 8 of this embodiment as well, the magnetic carrier 1
Since the difference in residual magnetization between a and the magnetic toner IC is small, continuous copying is performed, and the development characteristics hardly change even if the toner concentration decreases.

As shown in the above two examples, the magnetic toners lb, lc
The difference between the residual magnetization of the magnetic carrier and the residual magnetization of the magnetic carrier is l e
When it is less than mu/g, the change in development characteristics is small and the image density becomes constant, and a good image can be obtained without controlling the toner density. Therefore, between the residual magnetization (σ) of the magnetic carrier 1a and the residual magnetization (σrc) of the magnetic toner 1b or 1c, σPT−σrc<1 em
By using developer 1 or 8 that satisfies the u/g relationship.

Appropriate development can be performed in an extremely wide toner concentration range.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the difference between the residual magnetization of the magnetic carrier and the residual magnetization of the magnetic toner is 1 emu.
By configuring the developer so that the relationship is equal to or less than /g, a constant image density can be maintained without controlling the toner density. Therefore, it is not necessary to provide a toner density control device in the developing device, and problems such as toner scattering and toner spillage that occur when toner is replenished by the toner density control device can also be solved.

[Brief explanation of drawings]

FIG. 1 is a development characteristic diagram using the developer of the present invention. Figure 2 is a development characteristic diagram using a conventional developer, Figure 3 is a block diagram of a developing device using the developer of the present invention, and Figure 4 (al,
(C) is a block diagram showing a state in which the developer of the present invention stands up; FIG. 4 tb> is a block diagram showing a state in which a conventional developer stands up;
FIG. 5 is a development characteristic diagram using a conventional developer, FIG. 6 is a block diagram showing the spiked state of the conventional developer, and FIG. 7 is a development characteristic diagram using a conventional developer. FIG. 8 is a diagram showing the structure of the developer of the present invention in a standing state. 1.8...Developer, 2...Developer. 3.7a...Arrow, 4...Developing sleeve, 5...Magnet roll. 6...Doctor blade, 7...Photosensitive drum. Patent Applicant Casio Computer Co., Ltd. Same as above
Casio Electronic Industries Co., Ltd. Patent Attorney Dai
Yoshiyuki SugaFigure 4Figure 5Figure 7Figure 8

Claims (1)

[Claims] In a developer having a magnetic toner and a magnetic carrier,
The difference between the residual magnetization of the magnetic toner and the residual magnetization of the magnetic carrier after passing through a magnetic field of less than 1000 Oe is 1
A developer characterized in that it is less than emu/g.