JPH03223778A - Dry type developing device - Google Patents

Abstract

PURPOSE:To prevent generation of a void in an image by impressing bias voltage of a greater absolute value than the bias voltage of the electrostatic latent image but of the same polarity. CONSTITUTION:A counter electrode 9 is installed between the developing pat and the developing part restriction member 7 to face a developing sleeve 3 provided with enough space left from the developer on the developing sleeve which has its nap height restricted by a developer restriction member 7, so that it does not come into contact with it. The bias voltage of a greater absolute value than the bias voltage of the electrostatic latent image but of the same polarity is impressed on the developing sleeve 3 by a DC voltage power source circuit E2. Therefore, before the developing part is reached by a magnetic brush on the developing sleeve 3, an electric field of the same polarity as the image part is impressed on the magnetic brush, the tendency the toner to evade to the sleeve side is controlled, and the toner T on a leading tip of the magnetic brush 15 can be left in a plenty state. Thus, the void can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magnetic brush type developing device.

[Prior art and problems to be solved by the invention] In image forming devices such as copying machines, facsimiles, and printers, dry type developing devices are widely used in those that form electrostatic latent images on latent image carriers. It is used.

In such a developing device, a magnetic brush made of developer is formed on the circumferential surface of a developing sleeve that is provided with a magnetic field generating means inside, and this magnetic brush is brought into contact with an electrostatic latent image on a latent image carrier to generate a magnetic brush. A magnetic brush type developing device is known that electrostatically transfers toner in a developer constituting the image to an electrostatic latent image and visualizes the electrostatic latent image.

Such developing devices are roughly divided into two types: one in which the moving direction of the developer on the developing sleeve is the same as the moving direction of the latent image carrier, and the other in which the moving direction of the developer on the developing sleeve is the same as the moving direction of the latent image carrier. Development by the former type is sometimes called developed image, and development by the latter type is sometimes called reverse development.

In such a developing device, for example, in the case of a development method, image defects as shown in FIG. 6 tend to occur at the rear end of the image area in high density areas and halftone areas. Such image defects are generally referred to as white spots, and in the case of the reverse development method, similar white spots are likely to occur at the leading edge of the image area.

In order to deal with this problem, conventionally there are cases where the number of developing sleeves is increased to perform multi-stage development. Moreover, the structure of the developing device becomes unnecessarily complicated and its cost also increases.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dry developing device that prevents the above-mentioned white spots on images and further improves image quality without complicating the device configuration.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a developing device which is placed opposite to a latent image carrier, to which a bias voltage of the same polarity as the electrostatic latent image formed on the latent image carrier is applied, and which is provided with a magnetic field generating means inside. A spike-shaped developer is supported on the circumferential surface of a developer-carrying member, and dry development is performed by moving the spike-shaped developer into contact with the surface of the latent image carrier. In a dry type developing device configured to regulate the amount of developer on a developer carrying member, the area between the developing section where development is performed and the developer regulating member does not come into contact with the spike-shaped developer on the developer carrying member. facing the developer carrying member with an interval of
A configuration is proposed in which a counter electrode is provided to which a bias voltage having the same polarity as the electrostatic latent image and having a larger absolute value than the bias voltage is applied.

Further, it is advantageous if the counter electrode is constituted by a rotatably driven electrode roller, and a cleaning member is provided for cleaning toner adhering to the roller.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a drum-shaped photoreceptor, which is an example of the configuration of a latent image carrier, and is rotatably driven in the direction of the arrow in the drawing by a drive device (not shown). This photoreceptor 1 has a dry developing device W according to an embodiment of the present invention.
43 are deployed in close opposition.

Here, taking the electrophotographic copying machine shown in FIG. 5 as an example,
How an electrostatic latent image is formed on a photoreceptor will be explained below.

The photoreceptor 1 is composed of, for example, an organic photoreceptor (○pc),
As will be described later, an electrostatic latent image is formed on the photoreceptor, and in one example, the polarity thereof is negative (-). Therefore, the toner in the developer described later is charged to a positive (+) polarity opposite to that of the toner.

First, to explain the optical system, the halogen lamp 31
The light emitted from the original 32 hits the first mirror 33,
The image passes through the second mirror 34, the third mirror 35, the lens 36, the fourth mirror 37, the fifth mirror 38, the sixth mirror 39, and the dust-proof glass 40 in this order, and is projected onto the photoreceptor 1.

The dustproof glass 40 is provided to prevent floating objects from entering the optical system.

This copying machine is equipped with a zoom magnification function in 1% increments from a maximum of 200% to a minimum of 50%. Also,
This copying machine is equipped with an automatic density adjustment system that detects the background density of the original 32 using an optical fiber and corrects the developing bias described later based on the detected background density, thereby making it possible to obtain an image with a clear background. It is being

Around the photoreceptor 1, there is a charging section 41. An eraser 42, a developing device 43, a static eliminating section 44, a transfer separation section 45, a cleaning section 47, and the like are arranged.

In the charging section 41, a high voltage is applied to the charge wire 41a in the dark to cause corona discharge, and negative charges are uniformly placed on the photoreceptor l. The potential of the photoreceptor 1 at this time is set to, for example, -800V. By performing the above-mentioned image projection on such a uniformly charged surface,
An electrostatic latent image is formed on the surface of the photoreceptor 1. This electrostatic latent image is then visualized as a toner image by the developing device 43.

A grid 41b is arranged between the charge wire 41a and the photoreceptor 1 in order to control the potential uniformly and constant.

The eraser 42 illuminates the charged photoreceptor 1 to erase unnecessary charges and facilitate cleaning. The eraser 42 is made of a long LED, and performs re-erasing and tip erasing.

The static eliminator 44 includes a pre-transfer static eliminator lamp 44a and a static eliminator lamp 44b. Both are turned on at the same time as the main motor (not shown) starts, and the photoreceptor is irradiated with light that erases the residual charge on the photoreceptor while being diffused by a filter.

The transfer separation unit 45 causes a transfer charger 45a to transfer the toner image onto the paper 49 while bringing the paper 49, which is a transfer material sent out from the registration roller 48, into close contact with the photoreceptor 1, and also transfers the toner image onto the paper 49 using a separation charger 45b. Separate the paper from 1. If separation is not possible, the separation claws 50 force the separation. The separated paper is conveyed to the fixing section 52 side by the conveyor belt 51.

The cleaning section 47 includes a cleaning brush 47a and a cleaning blade 47b for scraping off residual toner on the photoreceptor 1. Cleaning blade 47b
is configured with center-point support so that the left and right contact pressure is equalized.

The cleaning brush 47a is rotated in the same direction as the photoreceptor 1. This cleaning brush 47a has a function of removing foreign matter such as pieces of paper that are difficult to remove with the cleaning blade 47b. The toner scraped off by the cleaning brush 47a and the cleaning blade 47b is collected in a toner collecting section 47c.

The fixing section 52 applies a certain temperature and pressure to the paper sent from the conveyance section to fuse the toner image onto the paper. The temperature of the heater 52b is controlled while the thermistor 52a detects the temperature.

Here, in FIG. 1, reference numeral 2 denotes a developing tank having an opening in a portion facing the photoreceptor 1, and inside this developing tank 2, a non-magnetic cylindrical developing sleeve 3 is placed in the opening. It is provided so that a part of the circumferential surface faces the part.

Note that the gap between the photoreceptor 1 and the developing sleeve 3 is set to, for example, about 0.75 images.

A magnet 4, which is an example of a magnetic field generating means, is provided inside the developing sleeve 3, which is opposed to the photoreceptor 1 with such a gap. This magnet has a agent pumping pole 48, a agent transporting pole 4b, a developing pole 4c, etc., and in this example, along with other magnetic poles (not shown), the polarity of the magnetic poles is alternately positive and negative in the circumferential direction of the developing sleeve 3. They are fixedly arranged at regular intervals from the inner surface of the sleeve 3.

In addition to the developing sleeve 3, the magnet 4 may be rotated,
It is well known that only the magnet 4 may be rotated.

Moreover, an integral roller-shaped magnet may be used as the magnet 4.

The developing tank 2 contains a two-component developer containing toner and a magnetic carrier. On the other hand, toner is contained in a toner hopper 11 attached to the developing tank 2, and as the toner replenishment bar 12 rotates, the toner is sprinkled onto the toner replenishment roller 13, and the toner replenishment roller 13 rotates. The developer is supplied into the developer tank 2 through the slitter 14.

The developer supplied with toner is stirred by the rotation of two stirring members 5, 6, and at this time, the toner and the magnetic carrier are frictionally charged to have opposite polarities. In this example, the toner is positively charged. In this manner, the developer is drawn up by the stirring member 6 and supplied to the circumferential surface of the developing sleeve 3 while being triboelectrically charged.

The supplied developer is attracted toward the developing sleeve by the magnetic force of the magnet 4 inside the developing sleeve 3, and is carried on the circumferential surface of the developing sleeve.

It is carried in the direction of rotation of the developing sleeve. At this time, the developer on the same circumferential surface stands up in spikes at each magnetic pole, forming a magnetic brush of the developer.

In the developing section, which is the closest part between the photoconductor 1 and the developing sleeve 3, the toner in the developer forms an electrostatic latent image as the spikes of the developer move while contacting the surface of the photoconductor 1. The electrostatic latent image is electrostatically transferred to a toner image, and the electrostatic latent image is visualized as a toner image. In this example, the direction of movement of the developer is the same as the direction of movement of the surface of the photoreceptor 1, and in this case, the development is called darkening. Note that the linear velocity of the developing sleeve 3 is, for example, 3 times the linear velocity of the surface of the photoreceptor 1.
．． It is set to about 5 times. Further, as the carrier constituting the magnetic brush, for example, a resin-coated carrier having an average particle diameter of 100 μm is used.

Further, the developing sleeve 3 used has a diameter of, for example, 30 m, and the magnetic force on the surface of the developing sleeve due to the magnet 4 is set to, for example, about 800 Gauss.

Here, before performing development, the developing sleeve 3
A blade-shaped developer regulating member 7 provided on the upstream side in the moving direction of the upper developer scrapes off excess developer on the developing sleeve and regulates the amount of developer. There is. Note that the scraped developer is returned to the developing tank 2 by the separator 8.

Here, a bias voltage having the same polarity as that of the electrostatic latent image is applied to the developing sleeve 3 by a DC voltage power supply circuit E, and due to this application, toner is spread between the photoreceptor 1 and the developing sleeve 3. Although the toner is electrostatically attracted toward the latent image area of No. 1, a developing electric field is generated that prevents toner from adhering to the background area. As described above, the bias voltage can also be called a developing bias, and is applied to prevent background smearing and adjust image density.

In the developing device of this embodiment, the latent image potential is, for example, -800V.
As a result, the background potential is set to -40V, and the aforementioned developing bias voltage is set to -200V. Note that the final developing bias value is determined depending on the original density or the user's desire.

Here, between the developing section and the developer regulating member 7, there is provided an interval such that the developer on the developing sleeve whose brush height is regulated by the developer regulating member 7 does not come into contact with the developing sleeve 3. A counter electrode 9 is provided so as to face each other, and the counter electrode 9 is sandwiched between an insulator 10 and insulated from the developing tank 2 .

During image formation, a bias voltage having the same polarity as the electrostatic latent image and having a larger absolute value than the bias voltage applied to the developing sleeve 3 is applied to the counter electrode 9 by the DC voltage power supply circuit E2. That is, a bias voltage of about -400 V, for example, having the same polarity as the bias voltage applied to the developing sleeve 3 is applied. On the other hand, as mentioned before, the developing sleeve 3 has a voltage of -200V.
A bias voltage of is applied.

Here, in this type of magnetic brush type developing device.

In the case of a developed image, white spots as shown in FIG. 6 tend to occur at the rear end of the image area in high-density areas and half-tone areas. or,
In the case of reverse development, white spots are likely to occur at the leading edge.

The cause of this is a phenomenon in which toner moves on the magnetic brush from the tip of the magnetic brush toward the peripheral surface of the developing sleeve due to the electric field in the non-image area (background area) that exists on the rear end side of the 5 image area. It is explained that this is because of the (toner drift model).

That is, the electric field in the image area of the photoreceptor acts to draw the toner toward the photoreceptor, whereas the electric field in the non-image area acts to pull the toner away from the photoreceptor. This prevents background stains, but since the toner moves on the magnetic brush due to the electric field in the non-image area, the magnetic brush moves from the non-image area as the developing sleeve 3 rotates. Even if the toner moves to the image area, it becomes easier to move to the developing sleeve side, so it takes more time for the toner to move to the image area, and for a while, the toner is not used for development. It will be in a state where it will not be done. This is thought to cause the white spots mentioned in Section 7.

By applying the aforementioned bias voltage to the counter electrode 9, an electric field having the same polarity as the image area is applied to the magnetic brush on the developing sleeve 3 before the magnetic brush reaches the developing area. As a result, the tendency of the toner to retreat toward the developing sleeve is suppressed, and as schematically shown in FIG. 4, the toner T at the tip of the magnetic brush 15 can be kept in an abundant state. by this,
Even if the magnetic brush moves from the non-image area on the photoreceptor to the image area with the rotation of the developing sleeve, the toner can be directly visualized, making it possible to prevent the above-mentioned white spots. It is.

Note that FIGS. 2 and 3 show embodiments in which the bias voltage application method is changed, and even in this embodiment, the same function as the embodiment shown in FIG. 1 can be achieved.

Incidentally, in the embodiment described above, the counter electrode 9 is fixedly disposed close to the developing sleeve 3 with an interval such that it is supported by the developing sleeve 3 and does not come into contact with the developer. A small amount of toner adheres to the developing sleeve 3 and the counter electrode 9, thereby weakening the electric field between the developing sleeve 3 and the counter electrode 9, which may reduce the effectiveness of the counter electrode.

Therefore, in the embodiment shown in FIG. 4a, the opposing electrode is constituted by an electrode roller 109 which is rotated in an appropriate direction, and this roller 109 is in contact with a cleaning member consisting of a blade 100. This electrode roller 109
Also, the developing section where development is performed and the developer regulating member 7 are arranged close to and opposite to the developing sleeve 3 with an interval that does not come into contact with the spike-shaped developer on the developing sleeve 3, and are stationary. A bias voltage having the same polarity as the electrolatent image and having a larger absolute value than the bias voltage applied to the developing sleeve 3 is applied, and functions in the same manner as the counter electrode 9 in the previous embodiment. It is something. The electrode roller 109 is insulated from the developing tank 2, and the electrode roller 10
9, there is no difference from the previous embodiment in that voltage can be applied even in the form shown in FIGS. 2 and 3.

The difference is that the toner that has adhered to the electrode roller 109 is removed from the blade 1 as the roller 109 rotates.
00, and the surface of the electrode roller 109 can always be kept clean. Therefore, it is possible to prevent a decrease in the electric field between the electrode roller 109 and the developing sleeve 3,
It is possible to maintain the effect of the counter electrode described above and always form high-quality images. The other configurations in FIG. 4a are not substantially different from those in FIG. 1, and the same parts are given the same reference numerals.

Note that any appropriate leaning members other than the blade 100,
For example, it goes without saying that a fur brush roller or the like may be used as appropriate.

Note 1: For example, as in the technique disclosed in Japanese Patent Application Laid-Open No. 54-130127, the developer regulating member itself is set to have the same polarity as the electrostatic latent image, and is applied with a voltage higher than the first bias voltage applied to the developing sleeve. A system in which a second bias voltage that is large in absolute value is applied has already been proposed, but in this example, the developer regulating member to which the second bias voltage is applied directly performs development. Since a large amount of toner adheres to this regulating member because it is in contact with the agent, the electric field caused by the second bias voltage is weakened early. The effect of applying voltage weakens earlier than in the configuration of the embodiment of the present invention.

Furthermore, when the developer regulating member and the developing section are separated, the toner at the tip of the magnetic brush is moved toward the developing sleeve due to the effect of the first bias voltage while the developer is being conveyed from the developer regulating member to the developing section. As a result, the preventive effect of Yabari 1, which is the original white area, cannot be expected. In the case of the example of the present invention, the roles of the developer regulating member 7 and the counter electrode 9 are shared, and such a problem can be prevented.

In addition, in the embodiments described so far, a cylindrical developing sleeve is used as the developer carrying member, but in addition to this,
It is also possible to use a belt-shaped developer carrying member.

〔Effect of the invention〕

As described above, according to the present invention, white spots that occur at the leading edge or trailing edge of high-density areas and half-tone areas are less likely to occur, without complicating the device configuration or increasing the device cost. can.

- It is possible to achieve higher image quality.

[Brief explanation of drawings]

Fig. 1 is a schematic sectional view of a developing device according to an embodiment of the present invention, Figs. 2 and 3 are schematic sectional views of the actual flow side, and Fig. 4 is a schematic sectional view of a developing device according to an embodiment of the present invention. A diagram for explaining that toner is concentrated due to the action of the counter electrode, FIG. 4a is a schematic cross-sectional view showing an embodiment in which the counter electrode is constituted by an electrode roller, and FIG. 5 is an electrophotographic copying machine equipped with the above-mentioned developing device. FIG. 6 is a schematic diagram of an example of the machine, and is a diagram for explaining that white spots occur at the rear end of the image. 1...Drum-shaped photoreceptor 3 as a latent image carrier...Developing sleeve as a developer carrying member, developer regulating member, counter electrode 09...Electrode roller 43...Developing device

Claims (2)

[Claims] (1) A bias voltage of the same polarity as the electrostatic latent image formed on the latent image carrier is applied to the circumferential surface of a developer carrying member that is placed opposite to the latent image carrier and has a magnetic field generating means provided inside. , carries a spike-shaped developer, and performs dry development by moving the spike-shaped developer into contact with the surface of the latent image carrier, and before performing the development, the developer on the developer carrying member is controlled by a developer regulating member. In a dry-type developing device that regulates the amount of developer, a gap is placed between the developing section where development is performed and the developer regulating member so that the developer does not come into contact with spike-shaped developer on the developer carrying member. 1. A dry type developing device, comprising a counter electrode to which a bias voltage having the same polarity as the electrostatic latent image and having a larger absolute value than the bias voltage is applied so as to face the supporting member. (2) The dry developing device according to claim 1, wherein the counter electrode is constituted by a rotationally driven electrode roller, and a cleaning member for cleaning toner adhering to the roller is provided.