JPS6087373A - Developing device - Google Patents

Abstract

PURPOSE:To obtain solid black with sufficient density even when a developer containing carriers with large specific resistance is used by setting the ratio of gaps of a specifying plate and a photosensitive body to a magnet roll to 0.85-1.05. CONSTITUTION:The ratio of the gap between the magnet roll 4 and the specifying plate 6 which specifies the amount of the developer and the gap between the magnet roll 4 and photosensitive body 8 is set to 0.85-1.05. When the ratio of the gaps is <=0.85, the development napped in a brush shape can not be compressed highly in a development area and a dielectric constant and a developing electric field are not increased by increasing the degree of congestion. When the gap ratio is >=1.05, the developer overflows to fall down, causing blur. Therefore, even when the developer contains carriers with >=10<12>OMEGA.cm, solid black with sufficient density is obtained by setting the gap ratio to 0.85-1.05 to obtain an image of good quality with good area image reproducibility.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a developing device in an electronic copying machine or the like.

[Prior art]

An electronic copying machine uses a photosensitive drum having a photosensitive member (photoconductor) provided on the surface of a metal drum. In such an electronic copying machine, the surface of a photosensitive drum is charged and exposed to form an electrostatic latent image. The electrostatic latent image is developed with toner.

The toner image thus obtained is transferred to plain paper and fixed to obtain a copy image.

Some developing devices of such electronic copying machines use a two-component developer consisting of toner and a magnetic carrier for conveying the toner, and perform development by a magnetic brush development method.

FIG. 1 shows an example of such a conventional developing device. This developing device includes a box 2 containing a developer 1b made of toner and magnetic carrier. Magnets 4 to 3 are placed at designated locations in box 2.
is provided.

The magnet roll 3 has a structure in which a non-magnetic sleeve 5 is rotatably provided outside a magnet 4. The magnet 4 is made of a cylindrical isotropic ferrite magnet, and is magnetized into seven poles as shown in FIG. A developer regulating plate 6 is provided at a predetermined location facing the surface of the sleeve 5.
is provided. The regulating plate 6 is attached to the box 2, and its tip is appropriately spaced from the surface of the sleeve 5. The gap between the regulating plate 6 and the sleeve 5 and the gap between the sleeve 5 and the photosensitive drum l vary depending on the model, but the former is about 1.0 to 2.0 mm, and the latter is about 1.5 to 3.0 mm. O'm
m, the ratio is less than 0.8. box 2
A developer stirring/supplying wheel 7 is rotatably provided at a predetermined location facing the sleeve 4 inside.

Reference numeral 1a denotes replenishment toner, and the box 2 is equipped with a mechanism for appropriately replenishing toner that is insufficient during development.

The developer 1b in the box 2 of this developing device is first picked up onto the sleeve 5 by the pickup magnetic pole 83 of the magnet 4 by the wheel 7 rotating in the direction of the arrow. This picked up developer 1b is transferred to the sleeve 5.
It is conveyed by rotation in the direction of the arrow, and is controlled by the regulating plate 6 to an optimum amount.

Thereafter, the developer 1b is further conveyed by the sleeve 50 rotations, and forms brush-like spikes at the developing magnetic pole 81 of the magnet 4. The toner in this brush-like developer lb adheres to the electrostatic latent image formed on the surface of the photosensitive drum 8 rotating in the direction of the arrow in the development area (the closest part between the photosensitive drum 8 and the sleeve 5). , development is performed.

At this time, a portion of the toner in the developer lb remains without adhering to the electrostatic latent image. Therefore, the surface of the sleeve 5 after development is coated with a developer 1b consisting of a magnetic carrier and some toner.
remains. This remaining developer 1b is further conveyed by the rotation of the sleeve 5, and the magnetic pole S2.53 of the magnet 4
Picked off between. This makes it possible to newly supply the developer 1b to the surface of the sleeve 5 for the next development.

By the way, magnetic brush development methods include those called conductive magnetic brush development methods and insulating magnetic brush development methods, respectively, based on the electrical characteristics of carriers.

In the former conductive magnetic brush development method, charge is injected from the developing sleeve due to the low resistance of the developer layer, and the area near the surface of the developer layer acts as a counter electrode.
The developing electric field is relatively large.

Therefore, such a developing method has the advantage that a sufficient solid black density can be obtained and the reproducibility of an area image is good. However, such a developing method has disadvantages in that the reproducibility of fine lines is poor, and if the photosensitive drum has scratches or the like, the bias voltage leaks, resulting in staining of the background area.

On the other hand, in the insulating magnetic brush development method using a carrier with a specific resistance value of 1012 Ω·cm or more, as shown in FIG.
Since the developing electric field reaches its maximum value between 1.09477 mm and 10 lines/mm, the reproducibility of fine lines is very excellent. However, in solid black areas, the developing electric field becomes weaker because no charge is injected from the developing sleeve. Furthermore, with insulating developers, after the toner is developed, the developing electric field is weakened by residual charges of opposite polarity to the toner on the carrier on the surface of the developer layer. This method had the disadvantage that it produced a copy that was highly effective.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a developing device capable of obtaining solid black with sufficient density even when using a developer containing a carrier having a specific resistance value of 1012 Ω·cm or more. [Discussion of the invention] In order to increase the developing electric field using an insulating developer, it is effective to increase the dielectric constant of the developer in the developing area in the following equation (1), and the toner In order to prevent the development electric field from attenuating due to charges of opposite polarity to the toner remaining on the carrier after moving to the photoreceptor, it is effective to quickly move the carrier with a charge of opposite polarity to the toner away from the photoreceptor. .

Eo-(■o Va) / (S/, +d, p/
Kp )...(1) However, Eo; Developing electric field ■o; Image potential ■8; Bias potential S; Distance between the photosensitive drum and developing sleeve Kd; Average dielectric constant d of the developer; Photosensitive drum Thickness KP of the photoconductor; dielectric constant of the photoconductor of the photoconductor drum [Structure of the invention] In the present invention, the ratio of the gap between the developer regulating plate and the magnet roll and the gap between the magnet roll and the photoconductor drum is from 0.85 to
1.05, thereby strongly compressing the brush-like developer in the development area, reducing its density and increasing its dielectric constant, thus increasing the development electric field. .

Furthermore, as a carrier, its saturation magnetization is 5 to 40 e m
The use of u'/g improves the migration of the developer in the developing area, and thus, the charges of opposite polarity to the toner remaining on the carrier surface after the toner movement are quickly released together with the carrier away from the photoreceptor, thereby reducing the developing electric field. This prevents the decline.

〔Example〕

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

In this embodiment, the ratio of the gap between the developer regulating plate 6 and the sleeve 5 and the gap between the sleeve 5 and the photosensitive drum 1 (hereinafter simply referred to as gap ratio) is set to 0.85 to 1.05. The gap ratio is 0.
If it is less than 85, the brush-like spiked developer 1 cannot be strongly compressed in the development area, and its density cannot be sufficiently increased. - When the ratio of the blade gap is 1.05 or more, the density of the developer in the developing area can be sufficiently increased; This is not desirable as it may cause blurring.

Using a developer containing a carrier with a specific resistance value of 10'2 Ωcm or more with four types of gap ratios of 0.85, 0.9, 1.05 and 0.8, a gray color with a density of 0.7 was used. When a solid document was copied, the solid black density of the copied image was as shown in FIG. 3. The one with a gap ratio of 0.8 refers to the one with the maximum gap ratio among the above-mentioned Jurai developing devices. Further, at this time, the gap between the regulating plate 6 and the sleeve 5 and the gap between the sleeve 5 and the photosensitive drum 1 are 1.28 mm when the gap ratio is 0.85, and 1.28 mm when the gap ratio is 0.85.
．． It should be about 5mm, and 1.35mm for 0.9,
It should be about 1.5mm, with a 1.05 beam, 57
mm, 1,"5 mm, and for 0.8 mm, 1,2 mm, and 1.5 mm. According to these results, when the gap ratio is 0.8, solid black It can be seen that the density is about 0.5, and it is not possible to obtain a sufficient density.On the other hand, when the gap ratio is 0.85, 9, and 1.05, the density of solid black is 1, respectively.
．． The values are approximately 0, ■, and 2.1.3, indicating that a sufficient concentration can be obtained.

By the way, when copying was carried out using a developer containing a carrier with a gap ratio of 0.85. was obtained, but it was found that the density ratio of low density horizontal lines and vertical lines decreased. This seems to be because the developer is strongly condensed in the development area due to the gap ratio increasing, and as a result, the visualized image on the photosensitive drum is rubbed off.

When the developer carrier used at this time was examined, it was found that the saturation magnetization was 70 emu/H.

In this way, a developer containing a carrier with high saturation magnetization,
The magnetic force of the magnet roll causes the carriers to strongly bond to each other, creating a stiff spike.

Therefore, with such a developer, migration in the development area is poor, and therefore, when strongly condensed, the visualized image on the photosensitive drum is likely to be rubbed off. Therefore, if a developer containing a carrier with a saturation magnetization of 5 to 40 emu/g is used, the binding force between the carriers due to magnetic force is weak, and the microclision in the development area is good, so it is strongly Even if it condenses, it is unlikely that the visualized image on the photosensitive drum will be rubbed off.

For this reason, when we used each of the two types of developers mentioned above to copy an original with gray lines at a density of 0.2, the density ratio of horizontal lines and vertical lines in the copied image was as shown in Figure 4. The results were obtained. According to this result,
When a developer Δ containing a carrier with a saturation magnetization of 70 emu/g is used, the density ratio of horizontal lines and vertical lines in the copied image is 60.
%, indicating that a sufficient concentration ratio cannot be obtained. On the other hand, the saturation magnetization is 5 to 40 emu/g.
It can be seen that when the developer B containing the carrier is used, the density ratio of the horizontal line to the vertical line of the copied image is about 90%, and a nearly sufficient density ratio can be obtained. In addition, when the latter developer is used, the density of solid black can be further increased since the micro-collision in the development area is good.

〔Effect of the invention〕

As explained below, according to the present invention, the specific resistance value is 10
Even if a developer containing a carrier of 12 Ω/cm or more is used, it is possible to obtain solid black with sufficient density, and excellent reproduction of low-density line images can be obtained, thus improving the reproducibility of area images. You can get good quality images.

[Brief explanation of the drawing]

Figure 1 is a schematic front view showing an example of a conventional developing device;
The figure is a schematic front view showing a part of the magnet roll of the same device, and FIGS. Figure 4 is a diagram to explain the density of solid black. Figure 4 is a diagram to explain the density ratio of horizontal lines and vertical lines in a copied image. Figure 5 is the relationship between the number of lines per unit width and the developing electric field. FIG. 1b...Developer, 3...Macnet roll, 4...Magnet, 5...Sleeve, 6...Developer regulation plate, 8...Photosensitive drum. Applicant: Fuji Xerox Co., Ltd. Representative: Patent Attorney Ume Yu Yamanouchi 1 Figure 2 Figure 3 Solid A P61 Ripe upper b Takashi Shigeru

Claims (1)

[Scope of Claims] 1. In an electronic copying machine using a two-component developer consisting of toner and a magnetic carrier that conveys the toner, a magnetic roll is provided facing the photosensitive drum, and a magnet is picked up on the magnetic roll. It is equipped with a regulating plate that regulates the amount of developer that is applied, and the gap between the rigid plate and the magnet roll and the gap between the magnet roll and the photosensitive drum is set to 0.85.
1.05. 2. The magnetic carrier of the developer has a saturation magnetization of 5 to 4.
2. The developing device according to claim 1, wherein a developing device having a concentration of 0 emu/g is used.