JPH0259995B2 - - 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]

In an electronic copying machine, a copy image can generally be obtained by developing an electrostatic latent image formed on a photoreceptor, transferring the resulting toner image onto transfer paper, and fixing it.

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. 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. A developer stirring/supplying wheel 7 is rotatably provided at a predetermined location in the box 2 facing the sleeve 4. Further, 1a is a replenishment toner,
The box 2 is equipped with a mechanism for appropriately replenishing toner that is insufficient due to development.

For example, the magnet 4 is magnetized into seven poles as shown in FIG. 2, and has seven magnetic poles S ₁ , N ₁ , S ₂ , S ₃ ,
N ₂ , S ₄ , and N ₃ are arranged in this order in a counterclockwise direction in the figure. The magnetic pole _S1 constitutes a main developing pole. The distance between the main developing pole S ₁ and the adjacent magnetic pole N ₁ across the center connection line 9 of the photosensitive drum 8 and magnet roll 3 on the sleeve surface is 17.
~35mm, for example 27mm.

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 main developing 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, the developing electric field reaches its maximum value between 1.0 lines/mm and 10 lines/mm, as shown in Figure 8. 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, with insulating developers, after the toner is developed, the developing line electric field is also weakened by residual charges of the opposite polarity to the toner on the carrier on the surface of the developer layer. The drawback was that copies with a low so-called edge effect could be obtained.

[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 even when 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 line 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 the development electric field from attenuating due to charges of opposite polarity to the toner remaining on the photoreceptor, it is effective to quickly move a carrier having charges of opposite polarity to the toner away from the photoreceptor.

E _O = (V _O − V _B )/(S/Kd+dp/Kp) ...(1) However, E _O ; Developing electric field V _O ; Image potential V _B ; Bias potential S; Distance between the photosensitive drum and the developing sleeve Kd: Average dielectric constant dp of the developer; Thickness Kp of the photoconductor of the photoconductor drum; Dielectric constant of the photoconductor of the photoconductor drum [Configuration of the Invention] In the present invention, the main developing pole of the magnet roll,
In contrast, the distance on the sleeve surface between the adjacent magnetic poles across the center connecting line between the photosensitive drum and the magnet roll should be set at 5 to 15 mm along the roll surface.
In addition, as a value corresponding to this separation distance for a magnet roll of a normal diameter, the center angle between the main developing pole and the adjacent magnetic pole mentioned above is
The angle ranges from 16 degrees to 46 degrees, thereby strengthening the magnetic field between these magnetic poles, increasing the density of the brush-like developer, increasing its dielectric constant, and thus increasing the developing electric field. It is something.

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 toner development are quickly released together with the carrier away from the photoreceptor, and the developing electric field is This prevents the decline.

〔Example〕

The present invention will be explained in detail with reference to Examples below.

FIGS. 3 to 5 show magnet rolls in each embodiment of the present invention.

The magnet roll 11 shown in FIG. 3 has a diameter of
Rod-shaped magnets S ₁ , N ₁ , S ₂ , S ₃ ,
The device includes a device in which N ₂ , S ₄ , and N ₃ are embedded, respectively, and a nonmagnetic sleeve (not shown) rotatably provided outside the device. Magnet S ₁ ,
N ₁ , S ₂ , S ₃ , N ₂ , S ₄ , and N ₃ are arranged in this order in the counterclockwise direction in the figure. Magnet S ₁
constitutes the main developing pole. The distance on the sleeve surface between the main developing pole _S1 and the adjacent magnetic pole _N1 across the center connection line 13 between the photosensitive drum and the magnet roll is 13 mm.

The magnet roll 21 shown in FIG. 4 has a main developing pole S ₁ and a magnetic pole adjacent thereto across the center connection line 13 between the photosensitive drum and the magnet roll.
The separation distance from _N1 on the sleeve surface is 10 mm, and the same separation distance is 7 mm in the magnet roll 31 shown in FIG. In FIGS. 3 to 5, the magnetic poles other than magnetic poles S ₁ and N ₁ are arranged at appropriate angles to each other.

When copying an original having a gray solid density of 0.7 using these magnet rolls 11, 21, 31 and the conventional magnet roll 3 shown in FIG. The results shown in the figure were obtained.
The developer used at this time contained a carrier having a specific resistance value of 10 ¹² Ω·cm or more. According to this result, when the conventional magnet roll 3 is used, the solid black density is about 0.5, which indicates that a sufficient density cannot be obtained. On the other hand, when the magnet rolls 11, 21, and 31 of this embodiment are used, the solid black density is 1.15, 1.3, and 1.3, respectively.
It is found that the concentration is about 1.4, indicating that a sufficient concentration can be obtained. Also, from this result, the distance between the main developing pole S ₁ and the magnetic pole N ₁ on the sleeve surface is
In the case of 15 mm, the solid black density is approximately 1.0, which is higher than the original gray solid density of 0.7.

By the way, when copying was carried out using a developer containing magnet rolls 11, 21, and 31 and a carrier having a specific resistance value of 10 ¹² Ω·cm or more, it was not possible to obtain solid black with sufficient density as described above. However,
It was found that the concentration ratio of horizontal lines and vertical lines at low concentrations decreased. This seems to be because the developer is strongly condensed in the developing area due to the smaller separation angle between the main developing pole S ₁ and the magnetic pole N ₁ , 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 7 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 is even higher to about 1.5.

In the embodiments described above, a roll diameter of 37 mm was explained, but even if the roll diameter changes within the normal roll diameter range of 20 mm to 40 mm, the same can be achieved by developing the technical idea of the present invention. effect can be obtained. That is, in addition to forming a magnetic field to increase the density of the developer in the development area, a carrier with low magnetic force may be applied to increase the fluidity of the developer.

〔Effect of the invention〕

As explained above, according to the present invention, the distance between the magnetic poles in the developing area of the developing roll is in the range of 5 to 15 mm along the roll surface, and the center angle of these magnetic poles is in the range of 16 to 46 degrees. Since it was decided to perform development using a magnetic carrier having a specific resistance value of 10 ¹² ohm.cm or more and a saturation magnetization of 5 to 40 emu/g, 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 in a highly filled state in the developing section, it becomes easy to move, and the toner present inside the developing section can also contribute to the 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 photoreceptor is less likely to be scraped off, so a homogeneous image can be obtained, and lines of the same width in the vertical and horizontal directions can be obtained. The difference in these widths when the image is developed becomes smaller.

(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. A schematic front view showing a part of the magnet roll, FIG. 6 is a diagram shown to explain the solid black density of the copied image, and FIG. 7 is a diagram shown to explain the density ratio of horizontal lines and vertical lines in the copied image. FIG. 8 is a diagram showing the relationship between the number of lines within a unit width and the developing electric field. 11, 21, 31... Magnetrol, 12
... Magnetic support, S ₁ ... Main developing pole, N ₁ ...
...Magnetic pole adjacent to the main developing pole.

Claims (1)

[Scope of Claims] 1. In a two-component magnetic brush developing device using toner and a magnetic carrier having a specific resistance value of 10 ¹² Ω·cm or more, a main developing pole of a magnet roll, a photosensitive drum, and a magnetic carrier of the magnet roll are provided. The angle between adjacent magnetic poles across the center connecting line is in the range of 16 degrees to 46 degrees, and the distance between these magnetic poles is 5 to 15 mm along the roll surface, and the saturation magnetization of the magnetic carrier is 5 to 40 emu/g, and the main developing pole and the adjacent magnetic pole have different polarities.