JPH01191163A - Developing device - Google Patents

Abstract

PURPOSE:To execute a satisfactory reproduction of a thin line and development at high speed with high density by executing one-component development by a second developing roller, and subsequently, executing two-component development by a bias electric field in a part where a first developing roller approaches a photosensitive body, and eliminating unnecessary toners from the photosensitive body. CONSTITUTION:An electrostatic image on the surface of a photosensitive body is developed (one-component development) by electrifying toners 13 on the surface of a developing roller first. A developer on the first developing roller 3, which has passed through an adjacent part to the second developing roller 8 moves further and carried to an opposed part (a developing area X) to a photosensitive drum 100. Subsequently, by an electric field based on a potential difference between the surface potential of the photosensitive drum 100 and a bias voltage E1 which has applied to the first developing roller 3, said developer moves onto an electrostatic latent image which is formed on the surface of the photosensitive drum 100, forms a toner image and executes the development. Accordingly, fog of a white ground and unnecessary toners are eliminated. In such a way, an excellent picture quality in which reproducibility of a horizontal thin line is satisfactory 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 degree of development of edges and thin lines perpendicular to the direction of movement of the developer is low, resulting in a deterioration 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 to the surface of the photoreceptor, supply a sufficient amount of toner, and at the same time remove space charges within the layer.

Generally, toner adhesion ff1D to the photoconductor surface is D=Aθv/
It is expressed as (1+l/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 that has magnetic poles arranged therein 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. a developing device having a roll, wherein the second developing roll has a plurality of divided control electrodes parallel to the rotation axis, and a portion close to the first developing roll and a portion close to the photoreceptor. and means for applying different bias potentials to the
The present invention provides a developing device characterized in that a toner supply means for supplying toner to a second developing roll is provided.

One-component development is performed by the second developing roll, and then two-component development is performed using a bias electric field at the portion where the first developing roll approaches the photoreceptor 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 an example of the integrated device of the present invention. As shown in FIG. 1, the developing device 1 is arranged adjacent to a photoreceptor 100 that is rotationally driven in the direction of arrow a. The developing device 1
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 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. Further, the roll 8 is also provided at a distance of IOθ to 300μ with respect to the photoreceptor surface.

Further, the second developing roll 8 has a large number of striped control electrodes 14 divided parallel to its rotation axis on the insulating roll surface, and rotates in the direction of arrow C while holding the charged toner 13. . 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 second development roll. Such microelectrodes can be formed by depositing a metal layer on an insulating layer (20 to 100 μm shoulder), or by chemically plating metallizing, applying photoresist, optically baking, and etching. Electrodes obtained by such methods are used. Furthermore, fine grooves parallel to the axis, for example, 1 to 5 per hole, 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 cut the grooves. The electrodes may be created in stripes by removing the paint on the peaks between the two. Alternatively, the electrodes may be formed by printing.

FIG. 2 is a perspective view showing the structure of a brush that supplies a bias voltage to the control electrode 14, 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 11aSllb are in contact with each other, and the control electrode 14 on the first developing roll 3 side is always supplied with a bias voltage E, and the control electrode 14 on the photoreceptor side is always supplied with a bias voltage E. Ru. Therefore, the roll surface does not have a negative potential over the entire surface, but is controlled to have different surface potentials in the circumferential direction.

The bias El is preferably controlled to a DC voltage of 150 to 500V, for example.

The DC voltage applied to the bias E, has the same direction polarity as the DC bias applied to E, and is 50 to 5 in absolute value lower than El.
A range as high as 00V is practically sufficient. This value is selected so that the toner concentration in the carrier and the thickness of the charged toner layer on the control electrode roll are the values necessary to achieve the desired developed image quality. It depends. Et does not necessarily require an AC bias, but 50-2kV, preferably 200-2kV.
lk■, 50 Hz to 2 kHz, preferably 20
Preferably, an AC bias from 0 to 500 Hz is superimposed. Within this range, the toner concentration in the carrier is stabilized, and practically good characteristics can be obtained.

Next, regarding the bias E, the AC voltage is important, but in order to control the development characteristics and fog and obtain the best development characteristics, it is usually 500 V or less, preferably 50~3Q.
It is preferable to apply a DC bias of about OV. E,
The AC voltage superimposed on the
kHz range, preferably 200V to 1kV, 200
The range is Hz=2kHz.

Further, 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 that controls the charging and thin layer of the toner. 15 are placed. The second storage chamber 9c is supplied with a conveyance screw or the like so that toner can be replenished as needed from a replenishment hopper (not shown).

God is good enough to provide the means.

The first developing roll 3 is made of a conductive material such as aluminum whose surface has been roughened by blasting, and the first developing roll 3 is made of a conductive material such as aluminum whose surface has been roughened by blasting, or a metal core coated with rubber, plastic, etc., which is made conductive with carbon or the like. It can be anything. Instead of the developing roll, an endless belt with a roughened moving surface may be used as the toner carrier.

A stirring blade 5 for stirring the toner is provided in the toner storage tank of the casing 9.

For the stirring blade 5, the regulating member 6, and the regulating blade 15, any of conventionally known materials and structures can be suitably used. 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 E8 and Et are superimposed between the developer on the developing roll 8, and the charged toner in the developer 2 and the charged toner 13 on the second developing roll 8 are superimposed. A kind of equilibrium is established between the layers due to the reciprocating motion of the charged toner. Due to this balancing action, the first developing roll 3
The toner concentration in the upper developer and the thickness of the charged toner layer on the second developing roll 8 are maintained approximately constant.

The consumed toner is supplied to the surface of the second developing roll 8 by the toner supply screw IO, 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 photoreceptor surface by the rotation of the second developing roll 8, and moved to the image charging portion of the photoreceptor by the bias E and the photoreceptor surface potential. The AC14 pressure is superimposed on the bias E3, which gives vibration to the charged toner 13 and facilitates its movement.

In this way, the electrostatic image on the photoreceptor surface is first developed (-component development) by the charged toner 13 on the developing roll.
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 and faces the photosensitive drum 100 (developing area (X)).
), the electrostatic latent image formed on the surface of the photoreceptor drum 100 is caused by an electric field based on the potential difference between the surface potential of the photoreceptor drum 100 and the bias voltage E1 applied to the first developing roll 3. to form a toner image and perform development.

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 further removed by coming into contact with the two-component developer 2 conveyed by the first developing roll 3. The bias voltage E applied to the first developing roll 3 is important for removing this unnecessary toner.
The voltage is in the opposite direction to the normal toner charge! Appropriate values can be obtained in the range of 50-500v.

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. In addition, even when the toner concentration in the carrier is low, carrier adhesion does not occur, and the carrier with small particle size
Allows for fine-grained development. 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 single-component development, making it possible to handle high-speed development without the risk of damage to the photoreceptor surface due to foreign matter. .

With conventional one-component development, it is difficult to perform good development of fine lines without fogging, but according to the present invention, good reproduction of fine lines and high-speed, high-density development are possible.

Here, the first developing roll 3 is a sleeve rotating quib with a fixed inner pole magnet, but is not particularly limited to this. 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. This allows for good reproduction of fine lines and high-speed, high-density development. 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 a specific example of the 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, IO = toner supply screw,
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 second developing roll has two developing rolls.
The developing roll has a plurality of divided control electrodes parallel to the rotation axis, and different bias potentials are applied to a portion of the electrodes that are close to the first developing roll and a portion that is close to the photoreceptor. What is claimed is: 1. A developing device comprising: a toner supplying means for supplying toner to a second developing roll;