JPH0466513B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention is utilized in the technical field of developing devices used in electronic copying devices, and is particularly applicable to various types of display devices for image recording, printers, and facsimile electrophotographic devices. The present invention relates to a developing device applicable to the device.

(Prior Art and Problems) A fixed magnetic field generating means is disposed inside a rotatable cylindrical developer carrier made of a non-magnetic material, and the magnetic force generated by the magnetic field generating means is applied onto the developer carrier. The developer transported toward the developing section while being held by the developer is regulated to a predetermined layer thickness by the contact pressure of a thin rubber plate, etc., and then transferred to the latent image carrier in the developing section to form the latent image. 2. Description of the Related Art A developing device that develops a latent image on a carrier is known.

In this type of device, the developer carrying member rotates to hold the developer in the developer container again by magnetic force after passing through the developing section and conveys it to the developing section. At this time, in order to ensure that the developer is retained until it reaches the developing section, a magnetic field must be formed all around the developer carrier, at least in the range from the developer container to the developing section. Must be.

Therefore, conventionally, the magnetic field generating means has usually been made of four poles or more than four poles. Therefore, it had become expensive. If the developer carrier is made small in diameter, the magnetic field generating means will also be made small in diameter, and the number of poles can be reduced. However, even if the number of poles is simply reduced by making the diameter smaller, the magnetic force will decrease, resulting in poor developer conveyance and phenomena such as fog.

As described above, in conventional developing devices that use multi-polar magnet rollers, in order to generate sufficient magnetic force to obtain high-quality images, magnetic field generating means with a diameter larger than a certain degree or with a small number of poles are used. In this case, there is no choice but to use an expensive magnet with extremely strong magnetic force as a magnetic field generating means, which poses a major problem in manufacturing a small and inexpensive developing device.

Furthermore, after passing through the developing section, the developer carrier is
When returning to the developer container again, one of the plurality of poles of the magnetic field generating means is used to prevent developer from leaking from the gap on the entrance side between the developer container and the developer carrier as seen from the developer carrier. One pole is also provided with a sealing function at the above-mentioned gap position. For this reason as well, the magnetic field generating means must have four or more magnetic poles.

(Means for Solving the Problems) An object of the present invention is to solve the problems of a developing device having a multipolar magnetic field generating means as described above, and to make the developing device compact, inexpensive, and It is an object of the present invention to provide a developing device which can obtain good images and also has a sufficient sealing function in the above-mentioned gap.

In order to achieve the above object, the present invention includes a rotatable developer carrier that contains a developer and transports the developer on its surface by the magnetic force of a magnetic field generating means fixedly arranged in an internal space. The developer container is disposed in the container so as to partially protrude from the front opening of the developer container, and the protruding portion of the developer carrier is brought close to or in contact with the latent image carrier so that the developer carrier and the latent image are separated. In a developing device in which the developer carrier is installed in parallel with the developer carrier, the developer carrier has a cylindrical outer diameter of 5 mm or more and 25 mm or less, and the magnetic field generating means has magnetic poles at two positions around the circumference, and one pole is located at the aforementioned latent position. The other electrode is disposed in the internal space of the developer container at a position facing the image carrier, and is connected to the surface of the developer carrier at the exit side portion of the developer carrier at the opening of the developer container. a regulating member that comes into contact with the developer layer to regulate the thickness of the developer layer on the surface of the developer container; A magnetic member is disposed at a position upstream in the direction of movement of the developer carrier from the maximum magnetic force line position of the other pole, facing the developer carrier with a gap therebetween.

(Example) Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows a developing device according to a most preferred embodiment of the present invention. The developing device according to this embodiment will be explained by taking as an example a developing device using Carlson electrophotography, and since its overall configuration is already well known, the developing device according to the present invention will be described with reference to the photosensitive drum as the latent image carrier according to the present invention. , the developing device and the like provided near the outer periphery of the photoreceptor drum are illustrated in detail, and illustrations of the primary charging means, exposure means, cleaning means, etc. in the Carlson process are omitted.

In FIG. 1, a latent image carrier, that is, a photosensitive drum 1 is rotatably supported in the direction of arrow A, and a developing device is disposed near the outer edge of the photosensitive drum 1. As shown in FIG. A known photoconductor such as OPC is used as the photoconductor on the surface layer of the photoconductor drum 1, and the photoconductor is coated with a latent material by a known charging means, image exposure means, etc. An image is beginning to form.

The developing device has a developer container 4 having an opening 4a on the front surface and containing a one-component or two-component developer therein, and partially protrudes from the developer container 4 with a gap in between the photoreceptor drum 1. It has a developing sleeve 2 which is a rotatable developer carrier arranged and facing the opening, and a regulating member 5 made of, for example, urethane rubber, which is made of a non-magnetic thin plate and is in elastic contact with the developing sleeve 2. Further, within the developing sleeve 2, a magnet roll 3 as a magnetic field generating means having two magnetisms 3a and 3b is fixedly arranged. Unlike multipolar magnet rolls, which are made by pasting multiple magnets together, such bipolar magnet rolls can be made from a single magnet, so they are easy to manufacture, and the magnetic poles exhibit The magnetic force exerted by the magnetic roll is extremely strong compared to the magnetic force exerted by the magnetic poles of a multipolar magnet roll of the same diameter.

The developing sleeve 2 as described above rotates in the direction of arrow B (counterclockwise), and one-component or two-component developer is attached to the surface of the developing sleeve 2 by the magnetic force of the magnet roll 3. Then, it is carried out to the outside of the developing device, that is, to the developing area. In this embodiment, a predetermined gap is set between the developing sleeve and the photoreceptor drum. However, if the two are in contact with each other, even if a so-called elastic developing sleeve is used. Applicable.

A developing bias power source is connected to the developing sleeve 2. That is, by forming an alternating electric field in which a DC component is superimposed between the developing sleeve 2 and at least the image portion of the latent image carrier, the outer circumferential surface of the photosensitive drum 1 of the developing sleeve 2 and The developer is configured to transfer the developer bound to the development areas (areas) that are close to each other onto the photoreceptor drum 1 and develop the latent image formed on the photoreceptor drum 1. There is.

Next, a description will be given of the magnet roll, which is a magnetic field generating means fixedly disposed within the developing sleeve 2, and in particular, the position of its magnetic pole.

Of the two poles 3a and 3b of the magnet roll 3, 3b is located at the developing section closest to the photosensitive drum 1, while 3a is located at the opening 4a of the developer container 4. That is, both poles 3a and 3b
are located on opposite sides of the center of the magnet roll 3, but are preferably located on opposite sides of the magnet roll 3.
It is located approximately on one diameter line. By doing so, the range of the magnetic field produced by both magnetic poles is utilized to the maximum extent possible, and a sufficient amount of developer is deposited on the developing sleeve 2. If the magnetic pole 3a is not within the opening 4a of the container 4, the amount of developer adhering to the developing sleeve will be insufficient, causing image unevenness during development.

However, even if the bipolar magnet roll 3 described above is adopted as a conventional one with a relatively large diameter, the developing device tends to have poor developer conveyance. This is because conventionally, by employing a multipolar magnet roll, there are multiple magnetic poles that contribute to developer conveyance in addition to the magnetic poles for the developing section, whereas the above-mentioned bipolar magnet roll has This is because there is only one corresponding magnetic pole. Further, due to this, the entrance side (lower side in the figure) of the opening 4a of the developer container 4 does not have any sealing function, which may cause leakage of the developer.

However, it has been found that even with the bipolar magnetic roll 3, the developer can be sufficiently transported and a high-quality image can be obtained by reducing the diameter of the developing sleeve 2, even though there is a problem regarding the transportability of the developer. did. This point is one of the features of the present invention. In particular, it was confirmed that the outer diameter of the developing sleeve was 5 to 25 mm. Further, a magnetic member 10 is disposed on the developer container 4 in order to promote the above-mentioned transportability and prevent leakage of the developer from the developer container.
The position of the magnetic member 10 is within the magnetic field region of the magnetic pole 3a of the two poles of the magnet roll 3, which is directed toward the inside of the developer container 4, and
It is set upstream of the developing sleeve 2 from the maximum magnetic force line position.

For example, in FIG. 1, the magnetic member 10 is located on the bisector Z of the N and S poles of the magnet roll 3, or on the downstream side of the bisector Z with respect to the rotational direction of the developing sleeve 2 and at the N pole. It is installed on the upstream side. By arranging the magnetic member 10 at the lower part of the developer container 4 so as to face the developing sleeve 2, a part of the N-pole magnetic lines of force can be concentrated on the magnetic member 10 at the lower part of the developer container 4. Become. Comparing this with the case of a conventional two-pole magnet roll, for example, in a conventional device as shown in FIG. It is widely spread outside. For this reason, the adhesion of the developer to the developing sleeve is weak, and the transportability of the developer is also reduced, resulting in retention, leakage, and scattering of the developer. On the other hand, in this embodiment, as shown in FIGS. 2A and 2B, when the magnetic member 10 is provided, the lines of magnetic force are located between the two poles and have a high density around the magnetic member, and It is along the surface of the developing sleeve 2. Therefore, the adhesion of the developer to the developing sleeve 2 is strong, the transportability of the developer is improved, and it is possible to prevent retention, leakage, scattering, etc. of the developer. Here, the second
In Figure A, the direction of rotation of the developing sleeve 2 is set so that the magnetic force between the S developing pole and the magnetic plate 10 is stronger than that between the N pole and the magnetic plate 10. A magnetic plate 10 is arranged on the upstream side.
Therefore, although some developer remains on the developing sleeve 2 at portion C in FIG. 2A, the magnetic plate 10
Unlike the conventional case shown in FIG. 5, the magnetic force between the developing sleeve 2 and the north pole is strong, so as the developing sleeve 2 rotates, the developer is transported toward the developing container 4 side. In addition, in FIG. 2B, the developer does not stagnate on the upstream side of the magnetic member 10 and is transported satisfactorily.

Next, while comparing the device of this embodiment with other conventional devices, an experiment was conducted regarding its image gradation, and the results will be shown with reference to FIG.

In Figure 3, the surface voltage value of the photosensitive drum (hereinafter abbreviated as SD bias) after subtracting the DC component voltage value applied to the developing sleeve is plotted on the horizontal axis, and the image density value D after copying is plotted using Macbeth RD514 (registered trademark). The vertical axis is the result of measuring the reflection density using a 3D printer, and the outer diameter of the developing sleeve is shown as a parameter.
In this experiment, development was performed using a jumping development method.

In the jumping development method, a dark area potential of -700V and a light area potential of -700V are placed on an OPC photoreceptor drum using a known method.
A latent image potential of 200V is formed, the distance between the developing sleeve and the photoreceptor drum is maintained at, for example, approximately 300 μm in this example, and -
By superimposing an alternating current bias of 1.3 KV and 1.5 KHz on a 250 V direct current, the developer, for example, one-component magnetic toner, is caused to fly from the developing sleeve to the latent image on the photoreceptor drum for development.

The experimental conditions for each curve shown in FIG. 3 are as follows.

Curve: The outer diameter of the developing sleeve is 32 mm, and the inner space has a curve on the surface of the developing sleeve.
A four-pole magnet roll that emits an external magnetic field of 1000G (Gauss) is fixed.

Curve: The outer diameter of the developing sleeve is 20 mm, and the inner space has a curve on the surface of the developing sleeve.
A four-pole magnet roll that emits an external magnetic field of 800G (Gauss) is fixed.

Curve: The outer diameter of the developing sleeve is 10 mm, and the inner space has a curve on the surface of the developing sleeve.
A four-pole magnet roll that emits an external magnetic field of 500G (Gauss) is fixed.

Broken curve: The outer diameter of the developing sleeve is 10 mm, and the inner space has a
A two-pole magnet roll that emits an external magnetic field of 750G (Gauss) is fixed.

That is, the curves ~ are the experimental results for the developing device using the conventional multi-pole (quadrupole) magnet roll, and the broken curve is the experimental result for the developing device using the bipolar magnet roll of this embodiment.

From the results in Figure 3, when the SD bias is 0V, the concentration of the curve is higher than the other curves.

Curves and dashed curves are gentler than other curves.

This is clearly the case.

The above-mentioned phenomenon is so-called fog, and when it comes to curved image quality, the adhesion of developer to the white background portion of the copied image becomes noticeable, which poses a problem in use.

Further, the above development indicates good gradation properties. The steeper the rise of the curve, the harder it is to bring out the gradation of the image.On the other hand, the dashed curve in the figure has a gentler slope and is better for bringing out the gradation of the image. It can be said.

Overall, from the above experimental results, it can be concluded that in the case of a curved image, there is no scattering or fogging, a sufficient Dmax is obtained, and an image with no unevenness and extremely rich gradation can be obtained. It was also confirmed that this tendency was the same even when the outer diameter of the developing sleeve was in the range of 5 to 25 mm.

Furthermore, in the embodiment of the present invention, the non-magnetic thin plate 5 having elasticity is provided so that one side thereof is in contact with the developing sleeve. It is possible to adopt a configuration with a wider section, and it is possible to widen the design specification range of the developer configuration. As a result, a sufficient distance for transporting the developer on the developing sleeve to the regulating member can be ensured, so that triboelectric charging of the developer can be sufficiently and stably achieved.

Such an effect can be obtained even when a magnetic member is included.

In addition to the case where the non-magnetic thin plate contacts in the subordinate direction with respect to the rotational direction of the developing sleeve as in the above-described embodiment, the present invention also provides contact with the non-magnetic thin plate in the opposite direction to the rotational direction of the developing sleeve. Applicable even if there is contact. FIG. 4 shows an embodiment in which a non-magnetic thin plate is brought into contact with the developing sleeve in a direction opposite to the rotating direction. This example also shows the same effect as when the contact form of the non-magnetic thin plate is oriented in the direction of rotation of the sleeve, and there is no scattering or fogging, Dmax is sufficient, and there is no unevenness. Images with very rich tonality can be obtained.

Further, the non-magnetic thin plate may be a thin plate of phosphor bronze or stainless steel, or may have rubber fixed to the contact portion with the developing sleeve.

Incidentally, it is preferable that the surface of the developing sleeve is provided with irregularities of 0.5 to 5 μm by a known method in order to improve the frictional charging of the toner and the conveyance of the developer.
In this example, a #400 sandblasted aluminum sleeve was used.

(Effects of the Invention) As described above, according to the present invention, scattering and fogging can be avoided by using a small-diameter bipolar magnet roll as a magnetic field generating means without using a large-diameter or expensive magnet roll. Not only is it possible to obtain images with excellent gradation, but the magnetic pole for taking in the developer is placed on the opposite side of the developing section, making development possible by making the most of the magnetic force of the two-pole magnet roll. It is possible to provide a developing device in which agent is supplied and a good image with no unevenness can be obtained. Moreover, it contributes to miniaturization of the entire device. Furthermore, the above-mentioned magnetic member may be disposed at the opening of the developer storage container on the entrance side when viewed from the developer carrier, and the developer may be restrained at this portion to improve its transportability. As a result, there is an effect that developer retention, leakage, and scattering in the above-mentioned portions are eliminated.

[Brief explanation of the drawing]

FIG. 1 is a vertical sectional view showing a schematic configuration of an embodiment of the present invention, FIGS. 2A and B are views showing the state of magnetic lines of force around the magnetic member of the device shown in FIG.
Figure 4 is a longitudinal cross-sectional view showing the general configuration of another embodiment of the present invention, and Figure 5 is a diagram showing the state of magnetic lines of force in the conventional apparatus. be. 1... Latent image carrier (photosensitive drum), 2... Developer carrier (developing sleeve), 3... Magnetic field generating means (magnet roll), 3a, 3b... Magnetic poles,
4... Developer container, 4a... Opening, 5... Regulating member, 10... Magnetic member.

Claims (1)

[Scope of Claims] 1. A rotatable developer carrier that conveys developer on its surface by the magnetic force of a magnetic field generating means fixedly arranged in an internal space is attached to a developer container in which developer is stored. The developer carrier is disposed in the container so as to partially protrude from the front opening, and the protruding portion of the developer carrier is brought close to or in contact with the latent image carrier so that the developer carrier and the latent image carrier are parallel to each other. In the installed developing device, the developer carrier has a cylindrical outer diameter of 5 mm or more and 25 mm or less, the magnetic field generating means has magnetic poles at two positions around the circumference, and one pole faces the latent image carrier. The other electrode is disposed in the internal space of the developer container, and is in contact with the surface of the developer carrier at the outlet side portion of the developer carrier in the opening of the developer container. a regulating member for regulating the thickness of the developer layer of the developer container, the part of the opening of the developer container on the entrance side of the developer carrier is within the magnetic field region of the other pole and the line of maximum magnetic force of the other pole; A developing device characterized in that a magnetic member is disposed facing the developer carrier with a gap at a position upstream in the moving direction of the developer carrier. 2. The developing device according to claim 1, wherein the two poles of the magnetic field generating means are located on approximately one diameter line of the developer carrier. 3. The developing device according to claim 1, wherein the regulating member is formed of a non-magnetic thin plate that has elasticity and comes into contact with the developer carrier.