JPH01191166A - Developing device - Google Patents

Abstract

PURPOSE:To improve horizontal fine line reproducibility and to improve image density by allowing a first developing roll to have plural divided electrodes being parallel to a rotary shaft and providing a means for applying a different bias potential to a part being adjacent to a second developing roll and a part being adjacent to a photosensitive body in said electrodes. CONSTITUTION:The first developing roll 3 has many stripe-like control electrodes 14 divided in parallel to its rotary shaft on the surface of an insulating roll, and the control electrodes 14 conduct to a contact terminal 12 provided on the roll end part, respectively. Two voltage supply brushes 11a, 11b are brought into contact with the contact terminal 12, and a bias voltage E2 and a bias voltage E1 are always supplied to the control electrode 14 of the second developing roll 8 side and the control electrode 14 of the photosensitive body side, respectively. Accordingly, the roll surface does not have a uniform potential on the whole surface but controlled to a different surface potential in the peripheral direction. In such a way, an excellent picture quality which is free from the increase of fog, adhesion of a carrier, a line and a blurring, and also, in which the reproducibility of a horizontal fine line is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device such as an electrophotographic copying machine or a 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 electric field formed on the surface of the photoreceptor 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 photoconductor 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 especially 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, and to simultaneously supply sufficient toner and remove space charges within the layer.

Generally, toner adhesion ff1D to the photoreceptor surface is D=AOV/
It is expressed as (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 increased, 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 is produced, causing streaks and blurring, and carrier adhesion is also likely to occur.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that is free from increased fogging, carrier adhesion, streaks, and blurring, and can provide excellent image quality 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 the first developing roll has a plurality of divided electrodes parallel to the rotation axis, and a portion adjacent to the second developing roll and a portion adjacent to the photoreceptor. The object of the present invention is to provide a developing device characterized in that it is provided with means for applying different bias potentials.

Main 1 One-component development is performed by the second developing roll, and then, at the portion where the first developing roll approaches the photoreceptor, two-component development is performed using a bias electric field to remove unnecessary toner from the photoreceptor.

EXAMPLES Next, the present invention will be explained 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 the arrow &. The developing device
a first developing roll 3 that is close to the photoreceptor and has a fixed magnet 4 therein and rotates; a regulating member that has a distal end spaced a certain distance from the first developing roll 3 and regulates the height of the carrier; 6. A second developing roll 8 disposed in a region close to the first developing roll between the regulating member 6 and the developing area X and also close to the photoreceptor, and a casing 9 that accommodates these. . The casing 9 has a partition 9 inside.
a, a first storage chamber 9b that accommodates the first developing roll 3 and a second storage chamber 9c that accommodates the second developing roll 8 are formed, and the first storage chamber 9b contains toner and A developer 2 made of a magnetic carrier is contained, and a second
Only toner is stored in the storage chamber 9c.

The first developing roll 3 has a large number of striped control electrodes 14 divided parallel to its rotation axis on the insulating roll surface, and holds the developer 2 made of toner and carrier. Rotate in the direction.

The width of the control electrode in the dividing direction is preferably equal to or less than the effective development width of the surface of the development roll. Such microelectrodes are made by applying a metal evaporation layer provided on a disconnection layer (20 to 100 μm thick) or chemically plating metallizing, then applying photoresist and optically baking and etching. An electrode obtained by a method or the like is used. Furthermore, fine grooves parallel to the axis, for example 1 to 5 per mm, are created on the insulating layer on the roll surface, a paint containing carbon black, metal powder, etc. is applied onto these grooves, and a regulating blade is used to groove the grooves. You can also create striped electrodes by removing the paint on the peaks between the two. Alternatively, the electrodes may be formed by printing.

Figure 2 is the control electrode! FIG. 3 is a perspective view showing the structure of a brush that supplies a bias voltage to 4, and FIG. 3 is a schematic diagram showing the structure of a contact terminal with which the brush comes into contact. The control electrodes 14 are electrically connected to contact terminals 12 provided at each end of the roll. The contact terminal 12
The two voltage supply brushes 11a and llb are in contact with the second voltage supply brush 11a and llb.
A bias voltage E is always applied to the control electrode 14 on the developing roll 8 side.
, but - the bias voltage E1 is always supplied to the control electrode 14 on the photoconductor side. Therefore, the roll surface is -
Rather than having different potentials, the surface potentials are controlled to differ in the circumferential direction.

The bias E is preferably controlled to a DC voltage of 50 to 600V, for example. On the other hand, the optimum value of the bias E is determined in relation to the bias E3 applied to the second developing roll. Bias E3 usually includes DC voltage and ACT, pressure (5
50H2~:2kHz) is applied to 0v~2, and it is preferable to superimpose an AC component and a DC component between E and E3.

Next, this second developing roll 8 faces the fixed magnetic pole of the first developing roll 3, and is arranged parallel to the first developing roll axis with a gap sufficient to allow the spikes of developer to pass therethrough. Moreover, the roll 8 simultaneously has a 100 to 30
They are provided at a distance of 0 μπ.

The second developing roll 8 of the developing device of the present invention may be made of a conductive member such as aluminum whose surface has been roughened by blasting, or may be made of rubber, plastic, etc. with a metal core made conductive with carbon or the like. It may be coated.

Instead of the developing roll, an endless belt with a roughened moving surface may be used as the toner carrier.

Inside the second storage chamber 9c, there is a toner supply screw 10° that moves the toner toward the second developing roll 8 while preventing blocking of the stored toner, and a regulation blade 15 that controls the charging and thin layer of the toner. Placed. Note that the second storage chamber 9c may be provided with a replenishing means such as a conveyance screw so that toner can be appropriately replenished from a replenishment hopper (not shown).

The regulating member 6 and the regulating blade 15 may be made of conventionally known materials and structures. Further, as the developer, any conventionally known so-called two-component developer 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.
(not shown). The developer 2 forms ears of magnetic carrier on the surface of the first developing roll 3 by the internal magnet 4 . As the first developing roll 3 rotates, the carrier and toner in the developer are triboelectrically charged and move toward the photoreceptor.
The tip reaches the tip of the regulating member 6, and the height of the ears is regulated.

Furthermore, the developer 2 conveyed on the developing roll 3 is transferred to the second
It reaches the vicinity of the developing roll 8. The first developing roll 3 and the second developing roll
A DC component and an AC component corresponding to the difference between E1 and E3 are superimposed between the developer on the developing roll 8, and the charged toner in the developer 2 and the charged toner layer on the second developing roll 8 are superimposed. 13, a kind of equilibrium effect is established due to the reciprocating movement of the charged toner. Due to this balancing action, the toner density in the developer on the first developing roll 3 and the second developing roll 8 are reduced.
The thickness of the top charged toner layer remains approximately constant. The consumed toner is supplied to the surface of the second developing roll 8 by the toner supply screw 10, and is kept at a constant thickness by the action of the regulating blade 15 and charged at the same time to form a uniform layer of charged toner 13. Form.

The charged toner 13 layer on the second developing roll 8 is conveyed to the surface of the photoreceptor by the rotation of the second developing roll 8, and moved to the image charging portion of the photoreceptor by the bias E3 and the surface potential of the photoreceptor. The AC voltage is superimposed on the bias E3, and the charged toner 1
3 to make it easier to move.

In this way, the electrostatic image on the photoreceptor surface is first developed (-component development) by the charged toner 13 on the developing roll surface.
Even with this alone, there is still a large fog and the development is not complete.

On the other hand, the developer (carrier + toner) on the first developing roller 3 that has passed through the vicinity of the second developing roller 8 moves further to the area facing the photoreceptor drum 100 (developing area (X)).
), the photoreceptor drum 10
The toner image is moved onto the electrostatic latent image formed on the surface of 0 to form a toner image, and development is performed.

In the one-component development described above, the fog is still large and the development is not complete, but the fog on the white background and unnecessary toner are removed by contacting the two-component developer 2 conveyed by the first developing roll 3. The bias voltage E1 applied to the first developing roll 3 is important for removing this unnecessary toner.
Normally, an appropriate value can be obtained in the range of 150 to 500 V with a voltage in the opposite direction to the toner charging.

In the second two-component development, since the toner has already been supplied to the necessary areas in the first development, there is no need to increase the sleeve photoreceptor circumferential speed ratio θ unlike in normal development, and the rotation speed of the sleeve can be reduced. The anisotropy of the edge effect is extremely small. Further, even if there is fog, there is no problem in the development by the second developing roll 8. Therefore, the distance between the control electrode surface that holds the charged toner layer and the photoreceptor surface can be made much larger than in normal one-component development, making it possible to handle high-speed development and imaging without the risk of damage to the photoreceptor surface due to foreign matter. becomes possible.

Here, the first developing roll 3 is of a rotating sleeve type with a fixed inner pole magnet, but is not particularly limited to this type. Both rotations and the like are used.

The striped control electrodes may be connected by ordinary resistance, or a high-resistance protective coating layer containing dispersed carbon black or the like may be provided on the electrode surface.

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 thin lines are improved, and the image density is improved. Furthermore, since it becomes possible to reduce the rotational speed of the developing roll, scattering of developer is reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an example of a developing device of the present invention;
FIG. 2 is a perspective view showing the structure of a brush that applies a bias to the control electrode, and FIG. 3 is a schematic diagram showing the structure of a contact terminal. The main symbols in the figure are as follows. 1: developing device, 3: first developing roll, 6: regulating blade, 8: second developing roll, 14: control electrode. Patent applicant Minolta Camera Co., Ltd.

Claims (1)

[Claims] (1) A first non-magnetic developing roll that is provided facing the photoreceptor, has a magnetic pole inside, and conveys a developer having a magnetic component; A developing device having two developing rolls, wherein the first developing roll has two developing rolls.
The developing roll has a plurality of divided electrodes parallel to the rotation axis, and means for applying different bias potentials to a portion of the electrodes that are close to the second developing roll and a portion that is close to the photoreceptor. A developing device characterized by being provided with.