JPH01191164A - Developing device - Google Patents

Abstract

PURPOSE:To obtain an excellent picture quality which is free from a line and a blur, and also, in which reproducibility of a horizontal thin line is satisfactory by providing an electrode for coming into contact with a developer which is constrained to a first developing roller between the first developing roller and a second developing roller, and applying a bias containing a DC component of the same direction polarity as the electrification polarity of a toner to the first developing roller. CONSTITUTION:An injection electrode 5 is provided on an adjacent part of the first developing roller 3 and the second developing roller 8 on the side opposite to a photosensitive body 100, and this injection electrode 5 is inserted into a developer layer which is constrained on the first developing roller 3. Also, to the injection electrode 5, a bias E2 is applied, and to the first developing roller 3, a voltage of the same direction polarity as the polarity of an electrified toner is applied, and to a carrier in the developer, charge of the same direction polarity as that of the toner is injected. In such a way, a directional property of an edge effect at the time of developing, and horizontal thin line reproducibility are improved, the image density is improved and an image with high quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a developing device such as an electrophotographic copying machine or printer using a two-component developer.

2. Description of the Related Art In recent years, as the amount of information processed has increased, the usage of electrophotographic image forming apparatuses has diversified. In other words, they are now being used not only as copying machines but also as printers for creating original documents, and products with even higher image quality and multifunctionality are required.

In such electrophotographic development, the charged toner used for development moves in one direction as the developing roll rotates and is supplied near the surface of the photoreceptor, whereas the latent image formed on the photoreceptor surface The electric field has a spatially complex shape. That is, the latent image electric field is strong at the edges of the image (referred to as the edge effect), and therefore the image obtained by development is an image with emphasized edges, which is typical of electrophotography. This phenomenon occurs due to the relationship between the moving direction of the developer and the electric field at the edge, and its effect differs depending on the direction of the edge. That is, the development density of edges and thin lines perpendicular to the direction of movement of the developer is low, resulting in a decrease in image quality.

The causes of such a decrease in image density are that the toner density in the white area near the photoreceptor decreases due to the bias potential applied to prevent fogging, and that the latent image electric field is localized in the case of thin lines. The toner may be shielded by the edge electric field of a nearby latent image, resulting in poor development, and the toner may be repelled from the latent image surface of the photoreceptor due to a reverse electric field generated near edges or thin lines.

This phenomenon is common to development methods using rolls, but is particularly noticeable in magnetic brush development using a two-component developer.

The two-component developing method is a developing method that enables high-speed copying and provides excellent image quality, but it has not yet provided sufficiently satisfactory image quality, particularly for creating original documents, such as those for printers.

The major drawbacks of such two-component development are that the toner concentration in the developer is usually low, less than 105, and the developer layer is thick. Therefore, in order to obtain a sufficient developed density, it is necessary to maintain a high relative speed of the developing roller with respect to the surface of the photoreceptor to supply sufficient toner and at the same time to remove space charges within the layer.

Generally, the amount of toner adhering to the photoreceptor surface is It is expressed as D=AθV/(1+1/Bθ).

Here, A and B are constants, ■ is the electric field in the direction perpendicular to the surface of the photoreceptor, and θ is the speed ratio of the circumferential speed of the sleeve on the developing roll to the surface of the photoreceptor. image density cannot be obtained. On the other hand, if θ is made thicker, image density can be obtained, but development defects at horizontal thin lines and image edges are likely to occur.

Problems to be Solved by the Invention In order to prevent such development defects, conventional methods have been taken such as increasing the toner concentration or increasing the carrier conductivity. However, if the toner concentration is increased, fogging is likely to occur, and if the carrier conductivity is increased, a static elimination effect will occur, causing streaks and blurring of the developed image.
Carrier adhesion is also likely to occur.

The present invention improves fogging, carrier adhesion, streaks on images,
To provide a developing device capable of obtaining excellent image quality without blurring and with good reproducibility of horizontal thin lines.

Means for Solving the Problems The present invention provides a non-magnetic first developing roll having magnetic poles therein for transporting a developer having a magnetic component, and a second developing roll located close to both the first developing roll and the photoreceptor. A developing device having a roll, wherein an electrode is provided between the first developing roll and the second developing roll in contact with the developer bound by the first developing roll, and the electrode is charged with toner on the first developing roll. The present invention provides a developing device characterized by applying a bias including a DC component having the same polarity as the polarity.

Next, the present invention will be described in more detail by way of examples with reference to the drawings.

FIG. 1 is a sectional view showing a specific example of the device of the present invention. As shown in FIG. 1, the developing device 1 is disposed adjacent to a photoreceptor 100 that is rotationally driven in the direction of arrow a. The developing device 1
includes a first developing roll 3 that is close to the photoconductor and rotates with an internal magnet 4, and a second developing roll 8 that is provided close to both the first developing roll 3 and the photoconductor 100. These are housed in a casing 9 to which a developer storage tank 10 is attached.

Around the first developing roll 3 on the opposite side from the photoreceptor, centering on the vicinity of the first developing roll and the second developing roll, there is a roller whose tip has a constant interval with respect to the first developing roll. A regulating member 6 is provided to regulate the height of the carrier. On the other hand, a regulating blade 14 whose tip abuts on the lower surface of the second developing roll 8 is provided, a sealing member 15 for sealing the toner is provided on the upper surface, and on the side of the second developing roll 8,
Toner supply screw 7 that supplies toner by rotation
is provided.

Further, an injection electrode 5 is provided near the first developing roll 3 and the second developing roll 8 on the opposite side from the photoreceptor 100. The injection electrode 5 is inserted into a developer layer restrained on the first developer roll 3 .

A bias E1 and a bias E3 are applied to the first developing roll 3 and the second developing roll 8, respectively. AC in E3
Bias (200-2000V, 50-2000Hz
), are superimposed. Further, a bias E2 is applied to the injection electrode 5, and a voltage having a polarity in the same direction as the charged toner is applied to the first developing roll 3, so that the carrier in the developer is charged with a polarity in the same direction as the toner. inject.

As shown in FIG. 2, the injection electrode 5 has a thickness of 0°5 to i,6 and has an opening through which the toner passes.
It is made of an elongated metal plate (stainless steel, brass, aluminum, etc.) with a width of about 2 to 5+x, and is inserted into the developer on the first developing roll 3 using a thin support to maintain the necessary strength.

The shape of the injection electrode 5 may be a simple flat plate, but it may also be shaped to facilitate injection by inserting a large number of needle-like protrusions into the developer flow. In particular, when injecting charges by contacting the injection electrode with the flowing surface of the developer layer 2, it is necessary to insert needle-like protrusions into the layer to effectively apply charges to the middle of the developing layer. In addition, charge can also be injected by bringing a brush made of conductive fibers such as carbon fibers into contact with the surface of the developer layer. The voltage applied to the electrode 5 is 200~4000V
A range of is preferred.

Therefore, the bias voltages E, , E, applied to the first and second developer rolls, and the voltages E, applied to the injection electrode,
The optimum voltage varies depending on the photoreceptor characteristics, system speed, and required image development characteristics, but is approximately within the following range.

E, DC component 50-600vE, D
C component 200~4000VE3 DC component
50-100OVAC component 200-2000v (50-2000Hz) The first developing roll of the developing device of the present invention may be a known developing roll made of a conductive member with a roughened surface.

Similarly, as the second developing roll, a conductive roll made of a metal that is relatively stable in normal air, such as aluminum, stainless steel, or brass, is used. The surface of the roll is shot-blasted or etched to a depth of 10 to
The unevenness of 50 μm is provided to prevent the toner from slipping and facilitate the formation of a charged toner layer.

Note that between the second developing roll 8 and the photoreceptor 100, there is a
Provide a shoulder interval of 0 to 300μ.

The regulating member and the regulating blade are made of conventionally known materials,
Any structure can be suitably used.

As the developer used in the apparatus of the present invention, any conventionally known so-called two-component developer can be used, and as the toner, a normal two-component non-magnetic toner can be used.

Next, the operation of developing using the apparatus of the present invention will be explained with reference to FIG. As shown in FIG. 1, the first developing roll 3 moves in the direction of arrow (b), and the second developing roll
and toner supply screw 7 are indicated by arrows (C), respectively.
It is rotated by a drive source (not shown) in the direction of arrow (d), the developer moves in the direction of the first developing roll 3, and the toner is supplied to the second developing roll 8.

The developer forms ears of magnetic carrier on the surface of the first developing roll 3 by the internal magnet 4 . Chiolia and toner in the developer move toward the photoreceptor while being triboelectrically charged as the first developing roll 3 rotates, and reach the tip of the regulating member 6, where the height of the brush is controlled.

The developer 2 on the first developing roll 3 that has passed the tip of the regulating member 6 is transferred to the injection electrode 5 inserted near the part adjacent to the roll 8.
After contacting and injecting charges, the photoreceptor passes through the vicinity of the first developing roll 8 toward the photoreceptor and is subjected to development.

On the other hand, the second developing roll 8 is supplied by the toner supply screw 7.
The toner supplied to the surface of the developing roller is conveyed while being in contact with the surface of the second developing roll. The toner is frictionally charged by the regulation blade 14 and forms a thin layer. Regulation blade 1
4, the toner passes through the developer 2, which is restrained on the surface of the first developing roll 3, on the magnetic pole of the first developing roll 3.
(mixture of magnetic carrier and toner).

Here, a bias E3 of 1% is applied to each of the first developing roll 3 and the second developing roll 8. E,
In addition to DC bias, AC bias (200 to 200
0 V, 50 to 2000 Hz) are superimposed, and the charged toner 13 on the second developing roll 8 is connected to the second developing roll,
It reciprocates between the first developing roller 3 and the developer. This reciprocating motion creates an equilibrium between the layer of charged toner 13 on the second developing roll 8 and the developer 2, and stabilizes the layer thickness of the charged toner 13 and the toner concentration in the developer 2.

The toner also has the opportunity to make sufficient contact with the carrier in the developer material 2. Therefore, most of the toner I3 on the surface of the second developing roll 8 is replaced with the charged toner in the developer 2 due to such contact and application of the AC bias.
Uniformly charged toner layer 13 with increased charge amount and good development performance
form.

Here, in order to give the charged toner 13 the necessary layer thickness, a bias voltage E is applied to the injection electrode. Said E1,
The value of E is determined in advance by other factors necessary for good development, such as the characteristics of the photoreceptor, the development speed, the required development density, fog, etc. is applied to maintain the layer of charged toner 13 at the required thickness. That is, when a voltage with a polarity in the same direction as the charged toner is applied to the injection electrode 5 with respect to the first developing roll 3, a charge with a polarity in the same direction as the toner is injected into the carrier, and a space charge is generated in the developer layer. do. This space charge generates an electric field between the developer layer 2 and the second developing roll 8, attracting the toner to the surface of the second developing roll 8, and forming a charged toner layer 13 with a required thickness. Therefore, the layer thickness of the charged toner 13 is controlled by the DC voltage applied to the injection electrode 5.

Next, the thin layer of charged toner 13 is conveyed to the photoconductor surface by the rotation of the second development roll 8 after passing through the vicinity of the first development roll. Moves to the charged part on the photoconductor surface. An AC voltage of 50 to 2000 Hz and 200 to 2000 V is superimposed on the bias E, which gives vibration to the charged toner 13 and facilitates its movement. In this way, the electrostatic image on the surface of the photoreceptor is first developed by the charged toner on the surface of the second developing roll 8 (-component development). The surface potential of the photoreceptor 100 is usually 50
0 to tooov. On the other hand, the DC of the second developing roll 8
Although the bias component varies depending on the characteristics of the photoreceptor and the effective voltage frequency of the superimposed AC component, a value lower than the optimum value for normal one-component development is selected. Therefore, the adhesion to fine lines and solid black is good, but the two-component development by the first developing roll 3 is carried out with considerable fog remaining on the white background.

On the other hand, the developer on the developing roller 3 that has passed close to the first developing roller 8 moves further and reaches the photosensitive drum 100.
The photoreceptor drum 100 The toner image is moved onto the electrostatic latent image formed on the surface of the toner image and developed.

In the one-component development described above, there is still a large amount of fog and development is not complete, but furthermore, by coming into contact with the two-component developer 2 conveyed by the first developing roll 3, fogging on the white background is prevented and unnecessary toner is removed. . To remove this unnecessary toner, a bias voltage EI is applied to the first developing roll 3.
is important, and normally the voltage in the opposite direction to the toner charge is 50
Appropriate values can be obtained in the range of ~600 .

In the two-component development by the first developing sleeve 3, on the contrary, a slightly higher DC bias voltage is applied, and toner fog is sufficiently removed. Since toner is already sufficiently attached to solid black areas and the like by the second developing roll, image density can be obtained even if the efficiency of two-component development is quite low, and there is no problem of carrier adhesion.

In the first development by the second developing roll, the toner has already been supplied to the necessary areas, so in the second two-component development, the circumferential speed ratio θ between the sleeve and the photoreceptor is set high as in normal development. There's no need.

Therefore, the rotation speed of the second developing roll is low, and the anisotropy of the edge effect is extremely small. Moreover, even if there is fog in the development by the first and second developing rolls 8, there is no problem. Therefore, the distance between the control electrode surface that holds the charged toner layer and the photoreceptor surface can be made much wider than in normal one-component development, making it possible to handle high-speed development without the risk of damage to the photoreceptor surface by foreign objects. becomes possible.

In this embodiment, the first developing roll 3 is of a rotating type with a fixed inner pole magnet, but is not particularly limited to this; the roll and the inner pole are rotated, only the inner pole is rotated, or the roll surface is magnetized. Rotation of a fixed magnet or the like is used.

FIG. 3 is a sectional view showing another embodiment of the device of the present invention;
The figure is a perspective view showing an injection electrode used for this. In this embodiment, the regulating member 6 is attached downward from the casing 9, and maintains a predetermined distance from the top of the first developing roll 3. The injection electrode 5 shown in FIG. 4 is attached to the regulating member 6, and its tip with a plurality of openings is inserted into the developer on the first developing roll 3. Note that a stirring blade 11 for stirring the developer is provided in the developer storage tank 10, and a toner supply roller 12 is provided above the storage tank 10.

The biggest problem with conventional one-component development methods is to always stably form a toner layer that is uniform and has the required amount of charge, and it is extremely difficult to form a stable charged layer using normal methods. Therefore, it is difficult to put it to practical use except for special purposes, such as when using magnetic toner or when using color toner with a small amount of toner.

The feature of the present invention is thus the method of forming a uniformly charged toner layer, which has been extremely difficult with conventional component development methods. According to the present invention, it is possible to create a stable and uniformly charged toner layer with the required amount of charge, and the two-component developing brush (first The toner concentration in the developer 2 (development) is also maintained almost constant and stable, and no special toner supply device or toner concentration stabilization device is required.

Effects of the Invention According to the developing device of the present invention, the directionality of the edge effect during development and the reproducibility of horizontal fine lines are improved, the image density is improved, and a high-quality image can be obtained. The risk of damage to the developer roll and photoreceptor surface is reduced, and the problems of one-component and two-component development are eliminated while providing high speed development.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing a specific example of the developing device of the present invention;
FIG. 2 is a front view showing the injection electrode used in the specific example of FIG. 1, FIG. 3 is a schematic sectional view showing another specific example of the device of the present invention, and FIG. 4 is the injection electrode used in this specific example. FIG. The main symbols in the figure are as follows. l: developing device, 2: developer, 3: first developing roll, 5:
Injection electrode, 8: second developing roll, 13: charged toner. Patent applicant Minolta Camera Co., Ltd.

Claims (1)

[Claims] (1) A developing device having a non-magnetic first developing roll that has magnetic poles arranged inside and conveys a developer having a magnetic component, and a second developing roll that is close to both the first developing roll and the photoreceptor. An electrode is provided between the first developing roll and the second developing roll in contact with the developer bound by the first developing roll, and the electrode has a DC polarity in the same direction as the charging polarity of the toner with respect to the first developing roll. A developing device characterized by applying a bias containing a component.