JPH05249823A - Developing device - Google Patents

Abstract

PURPOSE:To restrain developer from scattering out of a developing part, to prevent the soiling of an optical system, of an electrostatic charging system and of a carrying system and to form a stable image over a long time by generating a one-way electrical field in a direction from an electrode member to a developer carrier. CONSTITUTION:A conductive member 8 as the electrode member is installed on the end part of a hopper 3 on the downstream side of the developing part A so that the member 8 may be opposite to a latent image holding member 6. A voltage having a polarity reverse to the surface potential of the latent image holding member 6, that means, the voltage having the same polarity as that of the charge of the toner is impressed on the conductive member 8 by a power source 9, and the power source 9 is provided with a circuit for rectifying the voltage from an alternate developing bias supply 7. In such a constitution, when the scattering toner generated in the developing part A comes flying to the gap between the conductive member 8 and the latent image holding member 6 by influenced by a motive power and the wind, etc., which is generated in following to the rotation of the photosensitive drum as the latent image holding member 6, the scattering toner is made to stick to the latent image holding member 6 by the electrical field between both members, so that the quantity of the toner scattering outside the developing device is remarkably reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a developing device for developing a latent image formed on the surface of a latent image holding member in electrophotography, electrostatic recording, magnetic recording and the like. In particular, the surface of the developer bearing member that holds the thin layer of toner is opposed to the surface of the latent image holding member (opposed with a minute gap, or contacted)
By doing so, the present invention relates to the improvement of the image forming apparatus of the type in which the toner is developed by selectively transferring the toner to the surface of the latent image holding member corresponding to the latent image pattern.

[0002]

2. Description of the Related Art FIG. 1 shows a schematic structure of a general one using a one-component magnetic toner of a developing portion in an image forming apparatus of this type (a surface of a latent image holding member and a thin toner layer are not in contact with each other). A so-called toner jumping development type developing device is shown).
In the figure, reference numeral 1 denotes a non-magnetic sleeve as a developer carrying member, which is rotationally driven in the direction of arrow a. Hereinafter, the member 1 will be referred to as a developing sleeve or simply a sleeve. Reference numeral 2 denotes a fixed magnet roll which is a magnetic field generating member inserted and arranged in the inner space of the sleeve 1. The developing sleeve 1 has the fixed magnet roll 2
Rotate around. A toner hopper 3 serves as a developer supplying means for the developing sleeve 1.
The toner hopper 3 is arranged so that the substantially right half peripheral surface thereof is inserted. Reference numeral 4 denotes a magnetic blade as a developer layer thickness regulating member, which has an appropriate minute gap α (eg 24
0 μ) is kept close to each other. The layer thickness of the magnetic toner is formed thinner than this gap α by the magnetic pole (N1) 21 facing the magnetic blade 4. 5 is hopper 3
The one-component magnetic toner 6 which is the developer accommodated in the inside of the developing sleeve 1 passes through the developing sleeve 1 on the side opposite to the hopper 3 side while maintaining a minute gap β (for example, 300 μ) between the developing sleeve 1 and the sleeve surface. An image holding member, which is the developing sleeve 1
The surface rotates in the b direction, which is the same direction as the closest rotation in the a direction. For the sake of convenience, the closest portion of both members 1 and 6 is referred to as a developing portion A.

The magnet roll 2 inserted in the inner space of the developing sleeve 1 has an upper surface position corresponding to the magnetic blade 4, a left side surface position corresponding to the developing section A, a lower surface position corresponding to the inner bottom surface of the hopper 3, and toner. Magnetic poles 21 (cut magnetic pole N1), 22 (developing magnetic pole S1), 23 (conveying magnetic pole N2), and 24 (conveying magnetic pole S) are located at the right side surface positions corresponding to the supply portion, respectively.
2) is arranged.

The latent image holding member 6 is, for example, an xerographic photoreceptor on which an electrostatic latent image is formed by the Carlson process, and an insulating layer on the surface on which the electrostatic latent image is formed by the NP process described in Japanese Patent Publication No. 42-23910. A photoreceptor having an electrostatic latent image, an insulator on which a latent image is formed by an electrostatic recording method, an insulator on which an electrostatic latent image is transferred by a transfer method, or an electrostatic latent image (or a potential latent image or a magnetic latent image) by another appropriate method. Is a member that holds and forms.

The peripheral speed of the member 6 at the developing portion A and the peripheral speed of the toner layer on the developing sleeve 1 must be equal. This is because, as described in JP-A-55-120042, if the peripheral speeds of the two are different, the directionality appears in the developed image. Therefore, in the developing section A, the peripheral speed of the developing sleeve 1 is higher than that. Taking advantage of the fact that the peripheral speed of the carried toner layer is slightly higher, the peripheral speed of the developing sleeve 1 is made slightly slower than the peripheral speed of the latent image holding member 6, so that the developed image due to the directionality is This is to eliminate unevenness.

The latent image holding member 6 and the developing sleeve 1 in FIG. 1 are driven by gears (not shown).
In FIG. 1, reference numeral 7 denotes a bias power supply for forming an alternating electric field between the developing sleeve 1 and the latent image holding member 6, which is an alternating current, an alternating current superposed with a direct current, a distorted wave alternating current, a rectangular wave, a pulse wave, etc. The alternating voltage is supplied and its value is preferably 1000 to 2000 V in peak-to-peak value. As an example of using such a developing bias, Japanese Patent Publication No. 58-323
Development is carried out by the developing method described in Japanese Patent Publication No. 75 or Japanese Patent Publication No. 58-32377.

[0007]

Conventionally, when a bias voltage is applied to the minute gap β in the developing section A, the toner T coated in a thin layer on the developing sleeve 1 is formed between the sleeve and the latent image holding member. It flies in the space and is developed according to the surface potential of the latent image holding member 6. During this flight, a very small amount of toner separates from the sleeve at the developing portion A due to gravity, a laminar flow caused by the rotation of the latent image holding member 6, etc., and is attached to both the latent image holding member 6 and the developing sleeve 1. There is a case in which the toner does not wear and becomes a scattered toner, which stains equipment such as a charger in the image forming apparatus. When the scattered toner adheres to the optical device or the charger, the surface potential on the latent image holding member 6 is disturbed, which causes a problem that white streaks, black streaks, black spots, etc. occur on the copy image. Further, when the scattered toner drops on the copy sheet conveying path, the copy sheet is contaminated.

(Object of the Invention) The present invention suppresses the scattering of the developer from the developing section in the above-mentioned conventional example.
It is an object of the present invention to provide an image forming apparatus capable of forming a stable image for a long period of time by preventing the optical system, the charging system, and the conveying system from being contaminated.

[0009]

In order to achieve the above-mentioned object, the present invention forms a developer layer on the surface of a developer transport carrier and generates an oscillating electric field between the developer transport carrier and the image carrier.
In a developing device that develops a latent image on the surface of the image carrier with toner, an electrode member is provided in a portion of a frame of a developing device that surrounds the outside of the developer transport carrier and is close to the image carrier, and the oscillating electric field is applied to the electrode member. By applying an AC voltage and a DC voltage having the same phase as that between the electrode member and the developer transport carrier, a unidirectional electric field is generated from the electrode member toward the developer transport carrier. It is a feature.

[0010]

2 is a schematic sectional view of a developing device portion of an image forming apparatus according to the present invention. Reference numeral 8 in the drawing denotes a conductive member which is an electrode member and is provided at the end of the hopper 3 on the downstream side of the developing unit A so as to face the latent image holding member 6. A power source 9 applies a voltage having a polarity opposite to the surface potential of the latent image holding member, that is, a voltage having the same polarity as the electric charge of the toner to the conductive member 8, and has a circuit for rectifying the voltage from the alternate developing bias power source 7. .. Members having the same functions as those in FIG. 1 are designated by the same reference numerals.

When the scattered toner generated in the developing section A is affected by gravity and wind caused by the rotation of the photosensitive drum, which is the latent image holding member 6, when it comes into the gap between the conductive member and the latent image holding member. In addition, the amount of toner that adheres to the latent image holding member due to the electric field between them and is scattered outside the developing device is significantly reduced.

Although the one-component magnetic toner is used in the embodiment shown in FIG. 2, the non-magnetic toner that cannot utilize the magnetic binding force is generally used for the toner scattering during the development than the magnetic toner that can use the developing magnetic pole. The amount of scattering increases when there is.
Therefore, the effect of the present invention is great in the case of a developing device using non-magnetic toner. FIG. 3 shows an embodiment of the present invention when a non-magnetic toner is used as the developer.

FIG. 3 is a sectional view of a developing device to which the present invention is applied. In FIG. 3, the photosensitive member 6 which is a latent image holding member
Moves in the direction of arrow a. A non-magnetic developer carrier 1 for holding the developer is provided to the photoconductor 6 through a gap. In the present embodiment, the carrier 1 is cylindrical, but in the form of a web that moves endlessly. Is also good. The same applies to the photoconductor 6. Along with the movement of the photoconductor 6, the developer carrier 1 is rotated in the direction of arrow b. In order to supply the non-magnetic toner to the developer carrier 1, the magnetic particles 14
And a developing container 10 holding the non-magnetic toner 15 is provided. The developing container 10 has an opening near its lower portion, and the developer carrying member 1 is provided in the opening. Since the developer carrying member 1 is partially exposed to the outside through the opening, the surface thereof moves from the inside of the developing container 10 to the outside thereof, and then returns to the inside thereof. An envelope is formed in the lower part of the developing container 10 so as to enclose the lower part of the developer carrying member 1, so that the developer does not leak to the outside. Inside the developer carrying member 1, a fixed magnetic field generating means for generating a fixed magnetic field, that is,
The magnet 11 is fixedly provided. Therefore, only the developer carrying member 1 rotates. The magnet 11 has N and S magnetic poles.

A magnetic particle layer composed of magnetic particles 14 or a mixture containing magnetic particles and a non-magnetic developer (toner) 15 is formed on the surface of the developer carrying member 1, and a non-magnetic developing layer is formed on the magnetic particle layer. A layer of agent 15 is formed, and the upper and lower layers are
It has a layered structure. Reference numeral 12 is a magnetic blade made of a magnetic material that is a magnetic particle restraining member,
When the magnetic particles 14 are rotated in the direction,
Is constrained in the developing container 10 and only the nonmagnetic developer 15 is applied thinly and uniformly on the developer carrier 1. The magnetic blade 12 is formed by bending an iron plate, and
It is fixed to 0. The distance between the tip of the magnetic blade 12 and the developer carrying member 1 is 100 to 1000 μ, preferably 200 to 500 μ, and 250 μ in this embodiment. If this distance is smaller than 100 μ, there is a drawback that magnetic particles are clogged and pushed out of the blade. Again 1
If it is larger than 000 μm, a large amount of non-magnetic toner leaks due to vibration, and a thin layer cannot be formed.

Incidentally, only the non-magnetic development is carried on the developer carrier 1.
The method of thinly coating the above is described in detail in Japanese Patent Application No. 58-151028 of the applicant of the present invention, and thus detailed description thereof will be omitted.

A magnetic particle circulation area limiting member 13 made of a non-magnetic material is installed above the magnetic blade 12 to prevent the magnetic particles from rising on the magnetic blade, and the magnetic particles leak from the magnetic blade portion due to unnecessary circulation. This prevents the amount of magnetic particles in the developing container from decreasing. At the bottom of the developing container 10, facing the north pole of the magnet 11, L
A letter-shaped magnetic plate 16 is installed. The magnetic plate 16 forms a magnetic brush of magnetic particles between itself and the developer carrying member 1, and plays the role of a magnetic seal for preventing leakage of magnetic particles or non-magnetic developer from the developing container. Further, in the lower part of the developing container 10, a developer collecting portion 17 is provided on the upstream side of the magnetic plate 16 for magnetic sealing with respect to the moving direction of the developer carrying member 1. The developer collecting portion 17 collects the developer scattered between the magnetic plate 16 and the developer holding member, or the developer released from the developer carrier after development.

A conductive member 8 for preventing developer scattering according to the present invention is provided in the vicinity of the photosensitive member 6 at the lower end of the developing container 10. A voltage having the same polarity as the charging polarity of the non-magnetic developer used is applied to the conductive member 8, and the floating developer generated mainly in the developing process is adhered to the photoconductor to prevent the developer from scattering outside the developing container. To prevent. Reference numeral 7 in the drawing denotes a developing bias power source, which supplies an alternating bias voltage applied to the developer carrying member. Further, 9 is a power source for rectifying the alternating voltage from the developing bias power source 7 and applying a voltage to the conductive member for preventing the developer scattering. In this embodiment, the polarity is the same as the charging polarity of the non-magnetic developer. The rectifier circuit element (diode) is inserted in the direction.

The conductive member 8 may be a magnetic material, but it is preferably a non-magnetic material so as not to disturb the magnetic field of the developing device. In this embodiment, a copper plate having a thickness t = 0.6 mm, a width 6 mm and a length 210 mm is used. The latent image holding member 6 was arranged so as to face the latent image holding member 6 at a distance of 0.8 mm. Alternate development bias power supply 7 has a frequency of 1.6
Rectification using a Y10EA high withstand voltage diode manufactured by Hitachi Ltd. as a power source 9 for the conductive member 8 using a sine wave alternating current having a peak-to-peak value of 1.3 kV _PP and a DC component of -300 V superimposed. , V _H = + 250V, V
_When a half-wave current of _L = + 130V was obtained and applied to the conductive member 8, the amount of scattered developer could be reduced to 1/2 to 1/5 as compared with the case where no voltage was applied. still,
In the figure, 8a is a sheet made of an insulating material, which prevents magnetic particles from causing insulation failure between the conductive member 8 and the developer carrying member 1 when a small amount of magnetic particles leak from the developing container.

In the above-described embodiment, a current rectified by one diode is applied to the conductive plate member 8 from the developing bias power source 7, but AC is used as the developing bias and a DC component having a polarity opposite to that of the toner is used. When the superposed ones are used, a sufficient voltage may not be obtained. This is because, in a developing device of the type in which the DC component of the developing bias is adjusted for developing density adjustment, the amount of toner scattered may increase depending on the value of the DC component. Therefore, FIG. 4 shows a circuit for applying a constant voltage regardless of the value of the DC component. FIG. 4 schematically shows the developing device, and the same members as those in FIG. 3 are designated by the same reference numerals. Reference numeral 18 in the figure is a diode, and by inserting a capacitor 19 of about 100 pF between the developing bias power source 7 and the diode 18, the DC component can be cut off.
A constant voltage was applied to the conductive member 8 and a stable scattering prevention effect could be obtained.

In order to further enhance the effect stably obtained in the embodiment of FIG. 4, as shown in FIG.
When one more zero is added to form a voltage doubler rectifier circuit, V
A half-wave current of _H = 1200V and _VL = 900V can be obtained, and when this is applied to the conductive member 8, the amount of developer scattering is 1/2 to 1 with respect to that without forming the voltage doubler rectifier circuit.
We were able to reduce it to a stable 20th place. Although the rectified voltage is directly applied to the conductive member in the present embodiment and the embodiments of FIGS. 3 and 4, it is also preferable to apply a rectified voltage to a complete DC power source through a smoothing circuit. Further, a multiple voltage rectification circuit such as triple voltage rectification may be formed within a range that does not damage the photosensitive drum.

A brass plate having a thickness t of 1.0 mm, a width of 6 mm and a length of 210 mm is arranged as the conductive member 8 so as to face the latent image holding member 6 at an interval of 1.2 mm. The half-wave current obtained by the power supply 9 by the voltage rectification circuit was applied to the conductive member 8 as a complete DC through the smoothing circuit. This direct current is changed in the range of -400V to + 400V, a paper (not shown) is placed below the developing device, and the original with an image ratio of 6% is changed to 5%.
When the amount of toner scattered on the above-mentioned paper after passing 00 sheets was measured by a Macbeth reflection densitometer, the result as shown in FIG. 6 was obtained. As a result, it was revealed that the scattering was reduced when a voltage of +100 V or higher was applied to the conductive member, and the scattering amount was remarkably reduced when a voltage of +200 V or higher was applied. Therefore, in the present invention, it is preferable to apply a voltage of +100 V or more, preferably +200 V or more, which has the same polarity as that of the toner, to the conductive member. Further, when +100 V or more is applied, toner hardly adheres to the conductive member, and −100
It was confirmed that the conductive member was almost covered with the toner when V or more was applied, that is, when the polarity was opposite to that of the toner.

In the present invention, the scattering of toner can be prevented by applying a voltage having the same polarity as that of the toner to the conductive member even when reversal development is performed. Further, in the description of the embodiments of the present invention, the example in which the conductive member is provided at the lower end of the hopper or the developing container of the developing device has been shown, but the conductive member is provided separately from the developing device, for example, in the image device. It may be configured to be attached to.

Incidentally, Japanese Utility Model Laid-Open No. 58-100345 discloses an example in which a voltage having the same polarity as that of toner is applied to the electrode plate. However, in the present invention, a voltage is applied to the conductive member from the alternating developing bias power source through a rectifying circuit. Since it does not require an independent power source for the conductive member, the image forming apparatus can be downsized,
There is an advantage that it can be formed at low cost.

In the description of the embodiments of the present invention, the developing device for keeping the developer in contact with the latent image holding member and performing the jumping development has been described as an example. The present invention can also be applied to an apparatus for developing by contacting the latent image holding member with.

[0025]

As described above, according to the present invention, it is possible to greatly reduce the amount of scattered developer, and the contamination in the image forming apparatus is reduced, so that the optical system and the charging system are not contaminated for a long period of time. Therefore, there is an effect of obtaining a stable and good image.

[Brief description of drawings]

FIG. 1 is a sectional view of a conventional developing device.

FIG. 2 is a sectional view of a developing device showing an embodiment of the present invention.

FIG. 3 is a sectional view showing another embodiment of the present invention.

FIG. 4 is a schematic view showing another embodiment of the present invention.

FIG. 5 is a schematic view showing still another embodiment of the present invention.

FIG. 6 is a graph showing the amount of developer scattered.

[Explanation of symbols]

 1 Developer Carrier 2 Magnet 4 Magnetic Blade 5 Magnetic Toner 6 Latent Image Holding Member 7 Alternate Development Bias Power Supply 8 Conductive Member 9 Rectifier Circuit 11 Magnet 12 Magnetic Blade

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hatsue Tajima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. A developing device for forming a developer layer on a surface of a developer carrying carrier, generating an oscillating electric field between the developer carrying carrier and an image carrier, and developing a latent image on the surface of the image carrier with toner. In, in the developing device frame surrounding the outside of the developer transport carrier, an electrode member is provided in a portion close to the image carrier, and an alternating voltage and a direct current voltage having the same phase as the oscillating electric field are applied to the electrode member, A developing device, wherein a unidirectional electric field is generated between the electrode member and the developer transport carrier in a direction from the electrode member to the developer transport carrier. 2. The developing device according to claim 1, wherein a part of the electrode member is arranged so as to have a surface facing the image carrier surface. 3. The developing device according to claim 1, wherein a developer layer thickness on the surface of the developer transport carrier is formed thinner than a gap between the image carrier and the developer transport carrier.