JPS63269180A - Developing device - Google Patents

Abstract

PURPOSE:To miniaturize the whole device by providing a magnetic brush with a toner feeding means and a toner recovering means. CONSTITUTION:The developing device for applying toner 25 to a latent image 16 on a latent image carrier 11 such as a photosensitive body and developing the latent image 16 by a developing means 17 has the magnetic brush 24 for supplying toner 25 to the latent image 16, a toner feeding means 24 for supplying toner 25 to the brush 14, a toner electrostatically charging means 27 for forcedly charging the toner 25 supplied to the means 24, a toner recovering means 18 for recovering the toner 25 left on the brush 14 after development. Since the stirring of carrier and toner in the developing device is removed, various stirring mechanisms and a stirring space of the developing device using developer consisting of two components can be omitted.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device that applies toner to an electrostatic latent image formed on a latent image carrier such as a photoreceptor and uses this as a head image. This type of developing device is used in copying machines.

Used in electrophotographic devices such as facsimiles and printers.

The above-described developing devices include those that use a so-called dry two-component developer (mainly composed of carrier and toner) and those that use a so-called one-component developer (mainly composed only of toner).

Generally, in a developing device that uses a dry two-component developer consisting of carrier and toner, as shown in FIG. It is provided. After the toner supplied from the toner hopper 5 is sufficiently mixed and stirred with the carrier by the stirring mechanism such as the stirring roller 2, the toner is supplied to the developing roller 6 as a developer carrier, and a layer is formed on the surface of the developing roller 6. form a magnetic brush.

The thickness of this adhered developer layer is regulated to a constant thickness by a doctor blade 7.

The developing roller 6 has a plurality of magnets 9 inside the sleeve 8.
By rotating at least one of the sleeve 8 and the magnet 9 in a fixed direction, a magnetic brush formed on the surface of the sleeve 8 is moved in a fixed direction. When the magnetic brush comes into contact with the photoreceptor drum 10 as a latent image carrier, the electrostatic latent image formed on the photoreceptor drum 10 is developed into a head image. After development, the magnetic brush, that is, the carrier and toner are scraped into the developing tank 1, and mixed and stirred again by a stirring mechanism such as the stirring roller 2.

As described above, the two-component developer requires sufficient agitation and mixing in order to maintain uniformity of toner concentration or to charge the toner well.

The conventional developing device using the two-component developer described above has the advantage of stabilizing image quality, but for this purpose, the developer must be sufficiently stirred as described above. In order to perform sufficient stirring, various stirring mechanisms are required, and sufficient space is required to form a stirring channel.

Furthermore, the carrier is required to have good fluidity in order to obtain good stirring characteristics. In particular, carriers that exhibit cohesive properties even after the magnetic field is removed due to residual magnetism cannot be applied to a developing device based on the above-mentioned stirring mechanism. Moreover, frequent stirring will lead to faster carrier fatigue.

There is a problem with durability.

On the other hand, in order to solve the drawbacks of the developing apparatuses using such two-component developers, various developing apparatuses have been developed in which the mixing and stirring of the developer is omitted and the developer is hung. These developing devices include those that supply toner by attaching toner to the surface of a charging roller and then bringing the charging roller into contact with a magnetic brush, and others that use a magnetic brush to supply toner to the developing roller. There is a device that supplies toner to form a thin layer of toner on the developing roller.

However, the former method has the disadvantage that the toner concentration on the developing roller tends to be uneven, and the latter method has the problem that the developer still needs to be sufficiently mixed and stirred.

In view of the above-mentioned points, the present invention uses a dry two-component developer to maintain the stability of images, while providing an entire device that could not be achieved with conventional dry two-component developing devices. The purpose is to achieve smaller size, improved handling, and improved durability.

The present invention, which achieves the above object, is a developing device that applies toner to a latent image on a latent image carrier such as a photoreceptor to form a head image, and includes a magnetic flux that supplies the toner to the latent image. a brush, a toner supply means for supplying toner to the magnetic brush, a toner charging means for forcibly charging the toner supplied to the toner supply means, and a toner recovery means for collecting toner remaining on the brush after development. A developing device having means.

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

As shown in FIG. 1, a photosensitive drum 11 serving as a latent image carrier is rotationally driven in the direction of arrow A, that is, clockwise, by a drive mechanism (not shown). This photoreceptor drum 11 is made of an organic photoreceptor (OPC), and the polarity of the electrostatic latent image formed on the photoreceptor drum 11 is negative (
Therefore, toner for development, which will be described later, is charged to a positive (+) polarity, which is the opposite polarity.

Furthermore, the vicinity of the photoreceptor drum 11 (photoreceptor drum 1
A non-magnetic cylindrical sleeve 12 made of aluminum or the like is disposed in the gap 1Wn) with respect to the magnet 1. Inside this cylindrical sleeve 12, a developing magnet roller 13 having a plurality of different magnetic poles arranged alternately is provided at a constant interval from the inner surface of the cylindrical sleeve 12. A magnetic brush 14 containing magnetic carrier and toner is formed on the surface of the cylindrical sleeve 12 by the magnetic force. This magnetic brush 14 is moved in the direction of arrow B, that is, clockwise, by rotation of at least one of the cylindrical sleeve 12 and the developing magnet roller 13.

As the carrier constituting the magnetic brush 14, 40 g of resin-coated carrier having an average particle diameter of 100 μm is used.

Further, the cylindrical sleeve 12 and the photosensitive drum 11
, a developing bias voltage of the same polarity is applied by the power supply circuit 15. While moving, the magnetic brush 14 on the cylindrical sleeve 12 contacts the photoreceptor drum 11 on which the electrostatic latent image 16 is formed, and applies toner to the electrostatic latent image 16 to form a head image 17. being done.

In addition, in this embodiment, the cylindrical sleeve 12 has an outer diameter of 20
In addition, as the developing magnet roller 13, one in which the surface magnetic force of the cylindrical sleeve 12 is about 900 Gauss is used. As a result, the height of the magnetic brush 14 is preferably 0.3 to 5 mm, preferably 0.7 to 2 mm.
■It can be done.

In addition, the above-mentioned developing bias is applied to prevent background smearing and adjust image density. In this embodiment, the latent image potential is set to 180 ov, the background potential is set to 150 V, and the developing bias is The voltage is set to 1150V. Note that the final developing bias value is determined depending on the original density or the user's wishes.

Further, there is a toner collection roller 18 that collects residual toner from the magnetic brush 14 after completing development.

It is installed in the upper part of the cylindrical sleeve 12 with a gap 1.

A predetermined bias voltage for toner collection is applied to the toner collection roller 18 by a power supply circuit 19 .

This toner collection bias voltage is set to the same polarity as the latent image, that is, negative (-), in order to collect the toner remaining on the magnetic brush 14, and is set to the same level as the development potential, that is, toner In this embodiment, the bias voltage for toner recovery is -
It is set to 100 to -400v.

In this case, it is not necessary to collect all the toner contained in the magnetic brush, and it is sufficient to selectively collect the toner near the surface of the magnetic brush. That is, the minimum condition is to eliminate the difference in toner concentration distribution on the magnetic brush 14 caused by development. For example, Kurobe,
The difference in toner consumption between the halftone area and the background area should be equalized.

Generally, the toner adhesion amount of a two-component developer is 0.8 to 1.0 square meters per unit area, and the relative speed of the photosensitive drum 11 and magnetic brush 14 is approximately 1=3. Toner is being supplied to the latent image 16 in this state. That is,
The magnetic brush 14 has a density of 0.27 to 0.33 per unit area.
This means that the toner supply capacity is only +1g. Therefore, if toner is collected to exceed this toner supply capacity, the toner concentration distribution on the magnetic brush 14 will be
This results in uniformity and completely cancels out the effects of development.

To explain this point in more detail, bulk specific gravity 24
Based on the characteristics of a very common two-component developer with a toner concentration of 3%, the weight of a magnetic brush with a height of 1 cm is:

Since it is 0.2g per unit area and the toner contained in it is 6■, the toner that actually contributes to development is:
It accounts for only about 5% of magnetic brushes.

In other words, it is sufficient to collect toner equivalent to 5% of this amount.
Since 11g/aJ of toner is unevenly distributed near the surface of the magnetic brush by the toner supply roller described later,
The difference in toner consumption can be effectively eliminated.

Further, the toner collection roller 18 is rotationally driven in the direction of arrow C, that is, in the clockwise direction. This is to prevent the collected toner from adhering to the magnetic brush 14 again.

Furthermore, a scraping blade 21 is provided on the toner collection roller 18.
is attached.

The collected toner is scraped off by the scraping blade 21, and the scraped toner is returned to the toner hopper 23 side.

Furthermore, a toner supply roller 2 is provided at the lower part of the cylindrical sleeve 12, that is, at the downstream part of the magnetic brush 14.
4 is installed in contact with the magnetic brush 14 with a gap of 1 m from the cylindrical sleeve 12.

The toner supply roller 24 is rotationally driven in the direction of the arrow, that is, in the counterclockwise direction, by a rotational drive mechanism (not shown). As a result, the toner 25 stored in the toner hopper 23 is sent to the magnetic brush 14 side.

In this case, the toner supply roller 24 has a function of uniformly regulating the height of the ears of the magnetic brush 14, contributing to eliminating uneven image density.

Further, a toner regulation blade 26 is pressed against the toner supply roller 24 . The toner layer regulating blade 26 causes the toner 25 to adhere to the toner supply roller 24 in a uniform thin layer, and also to frictionally charge the toner 25.

Furthermore, a charging assisting member 27 made of a sponge roller or the like is placed in contact with the toner supply roller 24 in order to further enhance the function of frictionally charging the toner 25 and to evenly adhere the toner to the toner supply roller 24. ing.

Furthermore, a predetermined toner supply bias voltage is applied to the toner supply roller 24 and the charging auxiliary member 27 by a power supply circuit 28, and this toner supply bias voltage causes the toner 25 to move toward the magnetic brush 14. This results in good metastasis. As will be described later, the bias voltage for toner supply is set to +50 to +400 V with the opposite polarity to the latent image, that is, the same polarity as the charged toner.

A bias voltage for toner potential control by a power supply circuit 30 is applied to the toner further regulating blade 26, and the toner 25 is maintained at a predetermined potential by this bias voltage for toner potential control. As the bias voltage for toner charging, any polarity and voltage can be selected, as will be described later.

FIG. 2 shows the relationship between the bias voltage Vi applied to the toner regulation blade 26 and the toner potential Vt. In this figure, the toner potential Vt is taken on the vertical axis, and the blade applied voltage Vi is taken on the horizontal axis.
The relationship line is displayed using (b) as a parameter.

As is clear from this figure, as the value of the blade applied voltage Vi increases, the toner potential Vt increases, and this tendency remains the same for both positively chargeable toner (a) and negatively chargeable toner (b). do not have.

That is, it can be seen from this that the range of selection of toner materials, which was previously limited in terms of triboelectric charging properties, has been expanded. or,
Since the polarity of one toner can be arbitrarily controlled, it can be seen that reversal development can be easily performed by selecting the respective polarities and applied voltages of the power supply circuits 15, 19, 28.

The most important feature is that the present invention guarantees that deterioration or change in triboelectric charging characteristics that tends to occur over time is guaranteed, so that stable images can always be obtained.

As a means for controlling the toner potential, in addition to applying a voltage to the regulating blade 26 as in this embodiment, there is also a means for charging the toner by corona discharge between the blade 26 and the cylindrical sleeve 12 for development. A member may be provided.

The power supply circuit 15 that provides the developing bias voltage is equipped with an encoder that divides the output power into 4 bits and converts it into a signal, and a signal representing the output value of the developing bias voltage is sent to a control circuit (not shown). is being applied. This control circuit includes an arithmetic circuit that calculates an appropriate toner supply bias voltage value corresponding to the developing bias voltage value. The output signal of the control device is applied to a power supply circuit 28 that provides a bias voltage for toner supply, thereby determining the bias voltage value for toner supply. For example, the difference between both bias voltages is controlled to always be constant.

The toner collection roller 18 and the toner supply roller 24
The material may be any material that can provide an electrical bias effect between it and the cylindrical sleeve 12, and may be metal, conductive rubber, or the like.

Further, both rollers 18 and 24 can be installed so as to be in contact with each other at a ratio of 50% to 100% of the height of the magnetic brush 14. However, if the absolute value of the air gap is 1 mm or less, the air gap can be set to exceed 100%. In this case, it is essential to use electrical bias means. Furthermore, the outer diameters of both the rollers 18 and 24 can be arbitrarily selected, but due to the demand for miniaturization, the outer diameter of the cylindrical sleeve 12 is 80% or less, or the absolute value is 5 to 60 mm, preferably 8 mm. The amount of toner supplied to the magnetic brush 14, which is preferably set to ~40 m, is
4 and the supply roller 24, the supply amount may be controlled by making the rotational speed of the toner supply roller 24 variable; that is, the toner concentration can be controlled by means of a known sensor. By detecting the rotation speed of the toner supply roller 24, the rotation speed of the toner supply roller 24 can be controlled. An example of toner concentration detection is a means of detecting and calculating the opposite concentration of toner on the toner collection roller 18.

Next, an agitator 29 is provided in the toner hopper 23 to prevent toner blocking. At this time, if the toner scraped off from the toner collection roller 18 by the scraping blade 21 is supplied as close to the agitator 29 as possible, the mixing efficiency of the once collected toner and the new toner can be increased.

In this type of developing device, first, the toner hopper 2
The toner 25 in the toner 3 is fed and held by the toner supply roller 24 by the rotation of the toner supply roller 24 and the charging auxiliary member 27. The retained toner is triboelectrically charged while being uniformly made into a thin layer by the toner layer regulating blade 26 .

Then, under a predetermined toner supply bias voltage, the toner 25 is supplied and transferred to the magnetic brush 14 in a uniform thin layer.

The magnetic brush 14 supplied with toner is attached to the photosensitive drum 1
The electrostatic latent image 16 formed on the photosensitive drum 11 is developed.

After the development is completed, a difference in toner density (unevenness) corresponding to the image will occur on the magnetic brush 14, but the residual toner on the magnetic brush 14 is removed from the toner collection roller 18 side by the bias voltage force for toner collection. will be transferred and collected. As a result, the difference in toner density between the magnetic brushes 14 is eliminated and the toner density is made uniform. That is, after collecting the toner, the magnetic brush 14 leaves the toner collecting roller 18 with a uniform toner concentration distribution, and moves toward the toner supply side again.

Further, the bias voltage value for toner supply given by the power supply circuit 28 is controlled based on the developing bias voltage value given by the power supply circuit 15. That is, a new amount of toner is supplied to the magnetic brush 14 in accordance with the amount of toner consumed by development. As a result, the amount of toner consumed and the amount of toner supplied can be balanced, and oversupply or undersupply of toner can be avoided.

Next, the third example of a copying machine that employs the above-mentioned developing device will be explained.
A functional explanation will be given based on the diagram.

First, to explain the optical system, light emitted from the halogen lamp 31 hits the original 32, the first mirror 33, the second mirror 34, the third mirror 35, the lens 36, and the fourth mirror 37.
and the dust-proof glass 38 in order, and the photoreceptor drum 11
imaged on top. The dustproof glass 38 is provided to prevent floating objects from entering the optical system. Note that this device is equipped with a zoom magnification function in 1% increments from a maximum of 200% to a minimum of 50%. Further, an automatic density adjustment system is provided that detects the background density of the document 32 using an optical fiber and corrects the development bias based on the detected background density, thereby making it possible to obtain an image with a clear background.

Around the photosensitive drum 11, a charging section 40. Eraser 4
1. A developing bag [42, a static eliminating section 43, a transfer separation section 44, a cleaning section 45, etc. are arranged.

In the static eliminator 4o, a high voltage is applied to the charge wire in the dark to cause corona discharge, and the photoreceptor drum 11 is uniformly charged with negative charges. At this time, the potential of the photosensitive drum 11 is set to -800V as described above. Air is fed from the front of the charger 40a to increase discharge efficiency. A wire with a diameter of 0.08 nn is used as the charge wire, and the surface of this wire is coated with carbon. Further, a grid is arranged between the charge wire and the photoreceptor drum 11 to control the potential uniformly and constant. Also.

A charge cleaner is attached that cleans dirt on the charger by inserting and removing the charger 40a.

The eraser 41 illuminates the charged photoreceptor drum 11 to erase unnecessary charges and facilitate cleaning. The eraser 41 is made of a long LED, and performs site erase and tip erase.

Two thermistors are attached to the erase board, one is used for hard and the other is used for software, and bias correction is performed.

As the developing device 42, the one described in FIG. 1 is employed.

The static eliminator 43 includes a pre-transfer static eliminator 43a and a static eliminator lamp 43.
It has b. Both lights are turned on at the same time as the main motor 46 starts, and light is emitted to erase residual charges on the photosensitive drum 11 while being diffused by a filter.

A cooled electrode tube is used as the pre-transfer static eliminator 43a.

The transfer separation unit 44 causes the transfer charger 44b to transfer the toner to the paper side while bringing the paper sent out from the registration roller 44a into close contact with the photoreceptor drum 11, and separates the paper from the photoreceptor drum 11 using the separation charger 44c. This is how it was done.

In the event that separation is not possible, the paper separated forcibly by the separating claw 47 after one separation is transported to the fixing unit 48 side by the transport belt 44d.

The cleaning section 45 includes a fur brush 45a for scraping off residual toner on the photoreceptor drum 11 and a cleaning blade 45b. cleaning blade 45
b is configured to be supported at a single point in the center so that the left and right contact pressures are equalized. The fur brush 45a is rotated in the same direction as the photosensitive drum 11. This fur brush 45a has a function of removing foreign matter such as pieces of paper that are difficult to remove with the cleaning blade 45b. The toner scraped off by the fur brush 45a and cleaning blade 45b is discharged to the outside by a toner collection coil 45c and collected into a bottle.

The fixing section 48 applies a certain temperature and pressure to the paper sent from the conveyance section to fuse the toner onto the paper. The heater 48b (loOV750
W) temperature control is performed.

In the above-described apparatus, a cylindrical sleeve is used as the magnetic brush carrier, but a belt-shaped magnetic brush carrier may also be used.

In this embodiment, the charged toner is once transferred to a magnetic brush (or fur brush), and the latent image is developed with this magnetic brush. Carrier as magnetic brush (
Or in a fur brush. Since the toner (fur) does not need to have the function of triboelectrically charging the toner or the photoreceptor, there is no worry that the toner, whose polarity is controlled to a predetermined value by forced charging, will lose or reverse its charge during development. On the other hand, in conventional developing devices, a roller that carries positively or negatively charged toner is used as a developing roller. Particularly, in order to improve the image quality, in a system in which a developing roller is brought into contact with a photoreceptor carrying an electrostatic latent image to develop the image, depending on the material of the photosensitive layer, the material of the toner, and the material of the developing roller, a 1gA image may be produced. A frictional charging phenomenon occurs between the roller and the photoreceptor. In this case, the potential of the toner that has been forcibly charged will fluctuate, making it impossible to obtain the desired development characteristics.

Effects According to the present invention, the magnetic brush is provided with a toner supply means and a toner recovery means, thereby eliminating the need to stir the carrier and toner within the developing device. Various stirring mechanisms and stirring spaces can be omitted, making it possible to significantly downsize the entire device.

It is possible to facilitate handling similar to the one-component development method. Moreover, by omitting stirring, early fatigue of the carrier can be prevented, and furthermore, the image stability and flexibility of the two-component development system can be maintained as they are.

In particular, the present invention further provides such characteristics,
Even when toner consumption is high in color copying, printing, etc., a large amount of toner can be supplied without stirring, and stable images with little density change and image deterioration can be obtained.

Furthermore, since the toner supplied to the toner supply means is forcibly charged, a constant charging potential can always be applied to the toner regardless of the frictional charging characteristics of the toner, and stable image quality can be obtained. Can be done. Furthermore, since the polarity of the toner can be arbitrarily obtained, a normal image, an inverted image, etc. can be freely selected and easily obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a developing device in an embodiment of the present invention;
Fig. 2 is a diagram showing the relationship between bias value and image density, Fig. 3 is a longitudinal cross-sectional view of a copying machine to which the developing device according to the present invention is applied, and Fig. 4 is a longitudinal cross-sectional view of a general developing device. It is. 11... Photosensitive drum 12... Cylindrical sleeve 14... Magnetic brush 16... Electrostatic latent image 18... Toner collection roller 24... Toner supply roller 25... Toner

Claims (1)

[Scope of Claims] A developing device that applies toner to a latent image on a latent image carrier and uses this latent image as a head image, comprising: a magnetic brush that supplies toner to the latent image; and toner charged on the magnetic brush. a toner supplying means for supplying the toner, a toner charging means for forcibly electrically charging the toner supplied to the toner supplying means separately from the above-mentioned charging, and collecting the toner remaining on the magnetic brush after development. A developing device comprising a toner collecting means.