JPH0256674B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developing device for 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 consisting of toner and magnetic carrier. A magnet roll 3 is provided at a predetermined location within the box 2. 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 . 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 1 differ depending on the model, but the former is about 1.0 to 2.0 mm and the latter is 1.5 to 3.0 mm.
The ratio is less than 0.8. A developer stirring/supplying wheel 7 is rotatably provided at a predetermined location in the box 2 facing the sleeve 4. Reference numeral 1a denotes replenishment toner, and box 2 is equipped with a mechanism for appropriately replenishing toner that is insufficient during development.

The developer 1b in box 2 of this developing device is
First, the pick-up magnetic pole _S3 of the magnet 4 is picked up onto the sleeve 5 by the wheel 7 rotating in the direction of the arrow. The picked up developer 1b is conveyed by rotation of the sleeve 5 in the direction of the arrow, and is controlled by a regulating plate 6 to an optimum amount.
Thereafter, the developer 1b is further conveyed by the rotation of the sleeve 5, and forms brush-like spikes at the developing magnetic pole _S1 of the magnet 4. The toner in this brush-shaped developer 1b 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 portion between the photosensitive drum 8 and the sleeve 5). , development is performed. At this time, a portion of the toner in the developer 1b remains without adhering to the electrostatic latent image. Therefore, the developer 1b consisting of the magnetic carrier and some toner remains on the surface of the sleeve 5 after development. The remaining developer 1b is further conveyed by the rotation of the sleeve 5 and is picked off between the magnetic poles S ₂ and S ₃ of the magnet 4. 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 methods called conductive magnetic brush development methods and insulating magnetic brush development methods, respectively, based on the electrical characteristics of the carrier.

In the former conductive magnetic brush development method, charge is injected from the development sleeve because the resistance of the developer layer is low, and the area near the surface of the developer layer serves as a counter electrode, so the development 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, this 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 and the background becomes smeared.

On the other hand, in the insulating magnetic brush development method using a carrier with a specific resistance value of 10 ¹² Ω・cm or more, as shown in Figure 5, the developing electric field reaches its maximum value between 1.0 lines/mm and 10 lines/mm. The reproducibility of fine lines is excellent. However, in solid black areas, the developing electric field becomes weaker because no charge is injected from the developing sleeve. Furthermore, in the case of an insulating developer, after the toner is developed, the developing electric field is also weakened by residual charges of opposite polarity to the toner on the carrier on the surface of the developer layer. The drawback was that it produced a copy with an edge effect.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and provides a developing device capable of obtaining solid black with sufficient density using a developer containing a carrier having a specific resistance value of 10 ¹² Ω·cm or more. The purpose is to

[Consideration of 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 according to equation (1) below. In order to prevent attenuation of the developing electric field due to charges of opposite polarity to the toner, it is effective to quickly move a carrier having a charge of opposite polarity to the toner away from the photoreceptor.

E ₀ = (V ⁰ - V _B )/(S/Kd, d _P / K _P ) ...(1) However, E ₀ ; Developing electric field V ₀ ; Image potential V _B ; Bias potential S; Photosensitive drum and developing Distance between sleeves Kd; Average dielectric constant d _P of developer; Thickness K _P of photoconductor of photoconductor drum; Dielectric constant of photoconductor of photoconductor drum [Configuration of the Invention] In the present invention, the developer regulating plate and the magnet The ratio of the gap between the rolls and the gap between the magnet roll and the photosensitive drum is set to 0.85 to 1.05, thereby strongly compressing the brush-like developer in the development area.
The idea is to increase its density, increase its dielectric constant, and thus increase the developing electric field.

Furthermore, as a carrier, its saturation magnetization is 5~
By using 40 emu/g, the migration of the developer in the developing area is improved, and thus the charges of opposite polarity to the toner remaining on the carrier surface after the toner movement are quickly dissipated away from the photoreceptor along with the carrier, and the developing electric field is 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. If the gap ratio is 0.85 or less, the brush-shaped developer 1 cannot be strongly compressed in the development area, and its density cannot be sufficiently increased. On the other hand, if the gap ratio is 1.05 or more, the density of the developer in the developing area can be sufficiently increased, but the developer 1 may overflow in the developing area and spill downward, causing blurring on the copied image. It is not desirable because it makes you feel like

When a document containing gray solids with a density of 0.7 was copied using a developer containing carriers with four types of gap ratios of 0.85, 0.9, 1.05, and 0.8 and a resistivity value of 10 ¹² Ωcm or more. The results shown in FIG. 3 were obtained as the solid black density of the copied image. The gap ratio of 0.8 refers to the one with the maximum gap ratio among the conventional developing devices described above. Also, 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 have a gap ratio.
For 0.85, it is about 1.28mm, 1.5mm, for 0.9, it is 1.35mm, about 1.5mm, and for 1.05, it is about 1.28mm, 1.5mm.
1.57mm, 1.5mm, 1.2mm, 1.5 for 0.8
It was about mm. According to this result, the gap ratio is
When it is 0.8, the density of solid black is about 0.5, which shows that it is not possible to obtain a sufficient density. On the other hand, when the gap ratio is 0.85, 0.9, and 1.05, the solid black density is 1.0, 1.2, and 1.2, respectively.
It is found that the concentration is about 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 gap ratios of 0.85, 0.9, and 1.05 and a resistivity value of 10 ¹² Ωcm or more, it was not possible to obtain solid black with sufficient density as described above. However, 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 becoming large, and as a result, the visualized image on the photosensitive drum is rubbed off.

When the carrier of the developer used at this time was examined, it was found that the saturation magnetization was 70 emu/g. In a developer containing carriers with such high saturation magnetization, the carriers are strongly bonded to each other by the magnetic force of the magnet roll, creating hard spikes.
Therefore, it is believed that such a developer has poor migration in the development area, and therefore, when it is strongly condensed, it rubs off the visualized image on the photosensitive drum. Therefore, the saturation magnetization is 5~
When using a developer containing 40emu/g of carrier,
With this type of developer, the magnetic binding force between carriers is weak and migration in the development area is good, so even if it is strongly condensed, it is unlikely to rub off the visualized image on the photosensitive drum. It will be done.

For this reason, when we used each of the two types of developers mentioned above to copy a document with gray lines at a density of 0.2, we obtained the results shown in Figure 4 as the density ratio of horizontal lines and vertical lines in the copied image. was gotten. According to this result, the saturation magnetization is 70emu/g.
When using developer A containing a carrier of
It can be seen that a sufficient concentration ratio cannot be obtained. On the other hand, when developer B containing a carrier with a saturation magnetization of 5 to 40 emu/g is used, the density ratio between horizontal lines and vertical lines in the copied image is approximately 90%, and an almost sufficient density ratio can be obtained. It turns out that you can do it.
Furthermore, when the latter developer is used, the migration in the development area is good, so that the solid black density can be further increased.

〔Effect of the invention〕

As explained above, according to the present invention, it has a specific resistance value of 10 ¹² ohm cm or more, and a saturation magnetization of 5
Since a magnetic carrier of ~40 emu/g is used and the ratio of the distance between the regulating plate and the magnet roll to the distance between the magnet roll and the photosensitive drum is set to 0.85 to 1.05, the following effects are obtained.

(a) Due to the low magnetic force of the carrier, the binding force between magnetic carrier particles due to the magnetic field is weakened. As a result, even if the developer is highly filled in the developing section, it is easy to move, and the toner present inside the developing section can also contribute to development.

(b) During development, charges of opposite polarity corresponding to the charges of the developed toner are likely to be separated from the vicinity of the photoreceptor due to the high fluidity of the developer, so it is possible to suppress the decrease in the developing electric field. can.

(c) The spikes of the developer are no longer strong, and the toner electrostatically adsorbed on the photoconductor is less likely to be scraped off, resulting in a homogeneous image, and lines of the same width in the vertical and horizontal directions. The difference in these widths becomes smaller when the image is developed.

(d) Since the collision force between the magnetic carriers is reduced, toner and externally added materials are less likely to fuse to the surface of the magnetic carriers, and the life of the developer can be extended.

[Brief explanation of drawings]

FIG. 1 is a schematic front view showing an example of a conventional developing device, FIG. 2 is a schematic front view showing a part of the magnet roll of the same device, and FIGS. 3 and 4 show an example of the present invention. These diagrams are shown for explanation, of which Figure 3 is a diagram shown to explain the solid black density of a copy image, and Figure 4 is a diagram shown to explain the density ratio of horizontal lines and vertical lines of a copy image. , FIG. 5 is a diagram showing the relationship between the number of lines in a unit width and the developing electric field. 1b...Developer, 3...Magnetrol, 4
... Magnet, 5 ... Sleeve, 6 ... Developer regulation plate, 8 ... Photosensitive drum.

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 magnet roll is provided facing the photosensitive drum, and a pick-up is placed on the magnet roll. The magnetic carrier used for development is 10 ^{to 12} ohm.
It has a specific resistance value of cm or more and a saturation magnetization of 5 to 5 cm.
40 emu/g, and the ratio of the distance between the regulating plate and the magnet roll to the distance between the magnet roll and the photosensitive drum is 0.85 to 1.05.