JPH0830089A - Developing device - Google Patents

Abstract

PURPOSE:To provide a developing device capable of attaining noncontact development efficient in developing without development unevenness. CONSTITUTION:In the developing device carrying a two-component developer D to a developing region A by a developing sleeve 81 in which a magnet body 82 is fixedly provided and making toner soar up in a vibrating electric field to develop a latent image, a control electrode plate 84 constituted in such a manner that an electrode part 84a capable of applying a voltage is disposed on the top end part on the downstream side of the electrode plate 84 fixedly provided in the upstream part of the developing region A is provided and the top end part on the downstream side of the electrode plate 84 is set in a position where -0.05<=d3(-)-1.0(mm) is obtained when the distance between the top end on the downstream side of the control electrode plate 84 and the nearest position of an image forming body to the developing sleeve 81 is defined as d3(mm), where the upstream and downstream sides from the nearest position are positive and negative respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image in a non-contact manner using a one-component or two-component developer in an image forming apparatus such as an electrophotographic copying machine.

[0002]

2. Description of the Related Art A "powder cloud development method" (US Pat. No. 2,725,
No. 304) was known in recent years, but in recent years, an electrode plate was installed in the developing area, and an oscillating electric field was formed between the developing sleeve, which is a developer carrier, and the electrode plate to electrically form a toner cloud. A method of performing development has been proposed.

However, conventionally, the average particle diameter has generally been several tens of μm.
A developer consisting of magnetic carrier particles of a few hundred μm and non-magnetic toner particles with an average particle size of around 10 μm is used.Because the toner particles and further the carrier particles are coarse, delicate lines, dots, shade differences, etc. There is a problem that it is difficult to obtain a high-quality image that reproduces. Therefore, in order to obtain high image quality in this developing method, many efforts have been made in the past, such as resin coating of carrier particles and improvement of a magnet body in a developer carrying carrier, but still stable. The current situation is that a satisfactory image cannot be obtained. Therefore, it is considered necessary to make the toner particles and the carrier particles finer in order to obtain a high quality image. However, the average particle size of toner particles is 20 μm
In the following, especially when the particles are 10 μm or less, the influence of van der Waals force appears relatively to the Coulomb force at the time of development, the adhesion between the image forming body and the toner becomes strong, and the background portion of the image background is also strengthened. So-called fog to which toner particles adhere is generated, and it is difficult to prevent fog even by applying a DC bias voltage to the developer carrier. It becomes difficult to control the triboelectric charging of the toner particles, and aggregation easily occurs. On the other hand, when the carrier particles are made finer, the carrier particles also adhere to the electrostatic image portion of the image forming body. The reason for this is that the force of the magnetic bias decreases,
It is considered that the carrier particles adhered to the image forming body side together with the toner particles. Note that when the bias voltage increases, carrier particles also adhere to the ground portion of the image background. Since the above-mentioned side effects are more conspicuous in the atomization and a clear image cannot be obtained, it is difficult to actually atomize the toner particles and the carrier particles for that reason. It was

As a method for solving the above problems, a control electrode plate, which was filed by the applicant of the present invention, is provided in a developing region, and a bias voltage having an AC voltage component is applied to an electrode portion of the control electrode plate to generate an oscillating electric field. A developing method for developing a latent image by flying toner in a developer (JP-A-59-223467) or a non-contact developing method for controlling the central portion of the developing region and the layer thickness of the developer layer A method in which a leveling member is arranged between the leveling member and a DC bias voltage having a polarity opposite to the charging polarity of the toner particles is applied to the leveling member (JP-A-1-94368).
Issue).

[0005]

However, in the above-mentioned solution method, as shown in FIG. 8, at the tip of the control electrode plate 84 (or the leveling member), the toner or carrier scattered by an oscillating electric field is directed toward the upstream side. The scattered matter (Da) gradually accumulates. When the amount of the accumulated toner or carrier (Da) increases, there is a problem in that the toner adheres to or comes into contact with the image forming body to cause image stains and uneven streaks.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a developing device having high developing efficiency and performing non-contact development without image stains and unevenness.

Further, in a color image forming apparatus in which a toner image is superposed on an image forming body to form a multicolored image, and the multicolored image is collectively transferred onto a transfer material, an oscillating electric field causes another toner image to be transferred onto the toner image. There is a problem that so-called "color mixing" in which color toners adhere is likely to occur, but it is also intended to solve this problem.

[0008]

The object is to carry a developer to a development area by a developer carrying carrier, and to form an oscillating electric field between an image forming body and the developer carrying carrier for non-contact development. In the developing device, a plate-shaped member that is a control electrode plate is arranged upstream of the closest position between the image forming body and the developer transport carrier, and the set position of the plate-shaped member downstream side tip is This is achieved by a developing device characterized by being set on the downstream side of the closest position.

In the developing device, the distance between the downstream end of the plate member and the closest position is d3 (mm),
However, when the upstream side from the closest position is positive and the downstream side is negative, -0.05 ≤ d3 ≤ -1.0 (mm), and the plate-shaped member is provided with an electrode portion at its tip. The use of an electrode plate is a preferred embodiment.

[0010]

FIG. 3 is a schematic diagram showing an example of a color image forming apparatus provided with the developing device of the present invention as a suitable developing means.

In FIG. 3, reference numeral 1 denotes a photoconductor belt which is a belt-shaped image forming body made of a flexible belt coated or vapor-deposited with a photoconductor, and the photoconductor belt 1 includes rotary rollers 2 and 3. It is installed between and is conveyed in the clockwise direction by driving the rotating roller 2.

Reference numeral 4 denotes a guide member fixed to the main body of the apparatus so as to be inscribed in the photoconductor belt 1. The photoconductor belt 1 is tensioned by the action of a tension roller 5, so that the inner peripheral surface of the guide member 1 becomes the guide member. Rub 4

6 is a scorotron charger as a charging means, and 7
Is a laser writing device using a laser beam as an image exposing means, and 8A to 8D are developing devices of the present invention which are a plurality of developing means each containing a developer of a specific color, and these image forming means are photosensitive members. It is arranged at a portion of the belt 1 in contact with the guide member 4.

Each of the developing devices 8A, 8B, 8C and 8D will be described in detail later. For example, each of the developing devices 8A, 8B, 8C and 8D accommodates yellow, magenta, cyan and black developers, respectively. Each developing sleeve 81 having a diameter of 10 to 30 mm is kept, and has a function of making the latent image on the photosensitive belt 1 visible by a non-contact reversal developing method. Unlike the contact development, the non-contact development has an advantage that it does not hinder the movement of the photosensitive belt 1.

A transfer device 12 and a cleaning device 13 are a blade 13a of the cleaning device 13 and a toner discharge roller.
13b is kept at a position apart from the surface of the photoconductor belt 1 during image formation and is pressed against the surface of the photoconductor belt 1 as shown in the figure only during cleaning after image transfer.

The process of forming a color image by such a color image forming apparatus is performed as follows.

First, in the formation of a multicolor image according to the present embodiment, an original image is obtained by a color image image data input unit (not shown) in which an image pickup device scans, and this data is processed by an image data processing unit to obtain image data. Created and temporarily stored in the image memory. Next, this image data is taken out at the time of recording and is input to the recording unit, for example, the color image forming apparatus shown in FIG. That is, when image data, which is a color signal output from an image reading apparatus separate from the color image forming apparatus, is input to the laser writing apparatus 7, the laser writing apparatus 7 is a semiconductor as a writing light source (not shown). A laser beam (writing light) generated by a laser passes through a collimator lens and a cylindrical lens (not shown), is rotationally scanned by a rotary polygon mirror 74 rotated by a drive motor 71, and has an fθ lens 75 and a cylindrical lens 76.
After that, the optical path is bent by the two mirrors 77 and 78 in the meantime, and the image is written by being projected onto the peripheral surface of the photosensitive belt 1 to which a uniform charge is previously given by the charger 6 of the scorotron to perform main scanning. Is done.

When scanning is started, the laser beam is detected by an index sensor (not shown), and the laser beam modulated by the first color signal is transferred to the photosensitive belt 1.
On the peripheral surface of. Therefore, a latent image corresponding to the first color is formed on the peripheral surface of the photosensitive belt 1 by the main scanning by the laser beam and the sub-scanning by the conveyance of the photosensitive belt 1. This latent image is developed by the developing device 8A in which yellow (Y) toner (visual medium) is loaded in the developing means, and a toner image is formed on the belt surface. The obtained toner image is separated from the peripheral surface of the photosensitive belt 1 while being held on the belt surface, which is a cleaning device 13 as a cleaning means.
Blade 13a and toner discharge roller 13b
Enter the next image forming cycle.

That is, the photoconductor belt 1 is recharged by the charger 6, and then the second color signal is input to the laser writing device 7, and the belt is processed in the same manner as in the case of the first color signal described above. Writing is performed on the surface to form a latent image. The latent image is developed by the developing device 8B loaded with magenta (M) toner as the second color.

The magenta (M) toner image is formed in the presence of the previously formed yellow (Y) toner image.

Reference numeral 8C is a developing device having cyan (C) toner, which forms a cyan (C) toner image on the surface of the belt in the same manner as the first and second colors.

Further, 8D is a developing device having a black toner, which forms a black toner image on the surface of the belt by superposing it by the same processing as the above-mentioned color. A DC or even AC bias voltage is applied to each developing sleeve 81 of each of these developing devices 8A, 8B, 8C and 8D, and non-contact development is performed by a two-component developer that is a developing means.
The photosensitive belt 1 whose base is grounded is developed in a non-contact manner.

The color toner image thus formed on the peripheral surface of the photosensitive belt 1 is sent from the paper feeding cassette 14 through the paper feeding guide 15 by applying a high voltage having a polarity opposite to that of the toner at the transfer portion. It is transferred to the transfer material.

That is, the transfer material contained in the paper feed cassette 14 is carried out by the rotation of the paper feed roller 16 and one of the uppermost layers is carried out, and the timing is adjusted with the image formation on the photosensitive belt 1 via the timing roller 17. And is supplied to the transfer device 12.

The transfer material which has received the toner image is surely separated from the photosensitive belt 1 which suddenly changes its direction along the rotating roller 2 and goes upward, and the toner image is fused by the fixing roller 18. After being fixed, the paper is discharged onto the tray 20 via the paper discharge roller 19.

On the other hand, the photosensitive belt 1 which has been transferred to the transfer material is further conveyed and the blade 13a and the toner discharge roller 13b are brought into pressure contact with each other, and the residual toner is removed by the cleaning device 13 to finish the operation. Then, the blade 13a is separated again, and a little later, the toner discharge roller 13b is separated, and a new image forming process is started.

As the color image forming apparatus using the developing device of the present invention, the belt-shaped image forming body is described, but an image forming apparatus having a drum-shaped image forming body can be similarly used. .

The developing devices 8A to 8D have the same structure, and will be denoted by reference numeral 8 below.

FIG. 1 is a schematic sectional view showing an embodiment of the developing device of the present invention, showing an example in which one of the magnetic poles of the magnet body exists in the developing area. In the drawing, reference numeral 81 denotes a developing sleeve which is a developer carrying carrier whose surface is made into a rough surface by processing such as sandblasting, and which is made of a non-magnetic material such as aluminum, and is rotatable in the direction of the arrow in the drawing. Reference numeral 82 denotes a magnet body fixed in the developing sleeve 81 and having a plurality of N and S magnetic poles in the circumferential direction. One magnetic pole 82a of the magnet body 82 is located at the closest position between the developing sleeve 81 and the photosensitive belt 1. It is arranged in the development area A and is referred to as a main magnetic pole.
The developing sleeve 81 and the magnet body 82 form a developer carrying carrier. Each magnetic pole including the main magnetic pole 82a of the magnet body 82 is 500
The magnetic flux is magnetized to a magnetic flux density of ˜1,500 gauss, and the magnetic force forms a layer of the magnetic developer D on the developing sleeve 81, that is, the magnetic brush moves in the same direction by the rotation of the developing sleeve 81 and moves in the developing area. Transported to A. The magnetic brush formed on the developing sleeve 81 does not come into contact with the surface of the photosensitive belt 1 and maintains a gap between the developing sleeve 81 and the regulating blade 86 and the developing sleeve.
The gap between 81 and the photoconductor belt 1 is adjusted.

Reference numeral 84 is a plate in which an electrode portion 84a to which voltage can be applied is provided on the downstream end of an insulating member 83 provided on the upstream side of the developing area A in contact with / close to the layer of the developer D. The control electrode plate is a strip-shaped member, the insulating member 83 is a member also serving as a leveling member made of an electrical insulator such as polyester, polyimide, glass epoxy, polyethylene terephthalate, and polyamide imide, and the electrode portion 84a is made of a conductive material such as metal. It is made of a material and is integrally provided linearly on the tip of the insulating member 83. Reference numerals 85A and 85B are stirring screws for stirring the developer D to make the components uniform, and 86 is a developer regulating means formed of a non-magnetic material or a magnetic material for regulating the layer thickness and amount of the developer D. A regulating blade, 87 is a cleaning blade for removing the magnetic brush passing through the developing area A from the developing sleeve 81, 88 is a developer reservoir, 89 is a casing, and 89a.
Is a support portion provided in the casing 89 for supporting the fixed portion of the insulating member 83. 90 is a holding plate which is an example of a fixing member, and 90s is a control electrode plate 84 which holds the holding plate 90 on the supporting portion 89a.
Is a set screw for fixing so as to press toward the developing sleeve 81.

As shown in FIG. 5, the electrode portion 84a is made by bonding a conductive material such as metal into a linear shape with a circular or quadrangular cross section and bonding it to the tip of an insulating member 83 made of an insulating material. Stick with an agent (Figs. 5 (a), (b), (g),
(H)), a notch 83a is provided at the tip of the insulating member 83 and sandwiched between them (FIGS. 5C and 5D), and a recess 83c is provided at the tip of the insulating member 83 and embedded therein (FIG. e),
In addition to the method (f)) and the like, as shown in FIG. 6, a conventionally known printed circuit board manufacturing method is used, and glass epoxy, polyimide, paper phenol or the like is used as the insulating member 83, and a conductive material such as copper foil is used. After the members are laminated, an etching process is performed to attach the electrode portion 84a to the tip of the insulating member 83.
Can be formed. The electrode portion 84a may be covered with an insulating resin for preventing unnecessary discharge and for rust prevention. 84b is a terminal portion for applying a bias voltage.

Further, it is preferable that the electrode portion 84a is installed only on the downstream side of the closest position between the control electrode plate and the developing sleeve via the developer. If the electrode portion 84a spreads to the upstream portion, there arises a problem that toner is scattered on the upstream side due to an oscillating electric field between the electrode portion 84a and the developing sleeve.

The insulating member 83 of the control electrode plate 84 is a developing sleeve.
When the developer D is conveyed onto the 81, the developer D is slightly curved because the developer D enters between the insulating member 83 and the developing sleeve 81, and the insulating member 83 faces the developing sleeve 81 with a slight gap. Or, the developing sleeve 81 faces the developing sleeve 81 in a state where there is almost no gap, that is, in a state of being in contact with / close to the layer of the developer D. The point on the developing sleeve 81 that is in contact with / proximity is called a proximity point and is represented by 81b.

The thickness t1 of the insulating member 83 and the electrode portion 84a
Thickness t2 of the control electrode plate 84 (see FIG. 6).
(B) shows (1 / 10,000) d when the closest distance between the photosensitive belt 1 in the developing area A and the developing sleeve 81 is d1.
1- (2/3) d1, especially (1 / 1,000) d1- (1/2) d1
Is preferred. If it is larger than (2/3) d1, the gap between the photoconductor belt 1 and the electrode portion 84a becomes narrow, so that the electrode portion 84a easily contacts the surface of the image forming body 1 and image distortion easily occurs. On the other hand, if it is (1 / 10,000) d1 or less, current easily flows from the developing sleeve 81, causing a voltage drop and a reduction in developing efficiency.

The circumferential length m of the electrode portion 84a is preferably 0.05 to 5 mm, and particularly preferably 0.1 to 1 mm, though it depends on the diameter of the developing sleeve 81 and the conveying speed. If it is less than 0.05 mm, a sufficient cloud cannot be generated, and if it is more than 5 mm, the electrodes will vibrate and toner will scatter in the upstream portion from the closest position.

The surface roughness Rz1 (μm) of the developing sleeve 81 and the surface roughness Rz2 (μm) of the surface of the insulating member 83 of the control electrode plate 84 facing the developing sleeve 81 are preferably Rz1> Rz2, and Rz1> Rz2.
When z1 ≦ Rz2, the developer D carried on the developing sleeve 81 is prevented from being carried by the insulating member 83a, and the developing area A is reached.
As a result, the amount of toner conveyed to the toner decreases and the image density decreases. Rz
1 is in the range of 0.2 μm to 20 μm, and Rz2 is in the range of 0.02 μm to 5.0 μm, which is preferable in order to obtain good transportability and an image of high density without image distortion. The surface roughness Rz
Was measured with a standard length of 2.5 mm using Surftest-402 manufactured by Mitutoyo in accordance with JISB0601.

Further, when an experiment was conducted on the set position of the control electrode plate 84, the following results were obtained.

That is, the distance between the downstream end of the control electrode plate 84 and the closest position 81a between the developing sleeve 81 and the photosensitive belt 1 (image forming member) is d3 (mm), but upstream from the closest position. When the side is positive and the downstream side is negative, this distance d3
Image density due to the change in development efficiency when is changed,
A graph of FIG. 4 is obtained to show the relationship between the degree of contamination of the electrode portion 84a at the tip of the control electrode plate 84 due to toner or carrier attachment. The development efficiency does not change when d3 is positive, that is, when the tip of the control electrode plate 84 is located upstream of the closest position 81a, but decreases as it moves downstream. However, there is no problem up to -1.0 mm, but when -1.0 mm or less, the decrease in image density becomes remarkable, and at -2 mm,
The image density is significantly reduced. It was also found that the stain on the electrode portion 84a started to decrease when d3 was +0.5 mm or less, and almost no stain was generated when d3 was −0.05 mm.

From this, the control electrode plate 84, which is a plate-like member, is inserted into the developing area A, and the d3 thereof is within the following range (hatched area in FIG. 4) -0.05≤d3≤-1.0 (mm). If the control electrode plate 84 is installed so that the electrode portion 84a can be prevented from being soiled without lowering the developing efficiency. Although inserting the control electrode plate 84 into the developing area A lowers the developing efficiency, in the present invention, the following oscillating electric field is formed between the electrode portion 84a of the control electrode plate 84 and the developing sleeve 81. Improves the developing efficiency.

That is, the developing sleeve 81 is provided with a protective resistance R1 by a DC bias power source E1 and an AC bias power source E2.
A bias voltage in which an AC component is superimposed on a DC component is applied via the. In addition, a DC bias power source E is attached to the electrode portion 84a.
A bias voltage of only a DC component is applied from 3 through the protection resistor R2. It is preferable to apply a DC voltage having the same polarity as the toner to the electrode portion 84a from the viewpoint of preventing toner adhesion.

When the DC voltage applied to the developing sleeve 81 is equal to the DC voltage applied to the electrode portion 84a, the DC bias power source E1 can be shared as shown in FIG. It is possible to avoid complication.

In the developing device 8 of the present invention, by applying the bias voltage as described above, it is possible to control the alternating electric field (which will be referred to as a second oscillating electric field) formed between the photosensitive belt 1 and the developing sleeve 81. A first oscillating electric field is generated between the electrode portion 84a of the electrode plate 84 and the developing sleeve 81.

In the color image forming apparatus, if the OPC photosensitive member that is negatively charged is used as the photosensitive member of the photosensitive belt 1 and reverse development is performed, and the photosensitive member is charged to, for example, -800 V, the electrode portion 84a. Is applied to the developing sleeve 81, and a bias voltage of -750V + AC voltage component is applied to the developing sleeve 81. The AC component has a frequency of 100 to 20 KHz, preferably 1 to 10 KHz, and a peak-to-peak voltage (V _PP ) of 200 to 2,000.
V. In this case, since the electrode portion 84a is provided closer to the developing sleeve 81 than the photosensitive belt 1, the strength of the first oscillating electric field is higher than the strength of the second oscillating electric field.

The first vibrating electric field causes the toner particles of the developer D that have reached the vicinity of the electrode portion 84a to vibrate in the direction of the lines of electric force thereof, so that the toner particles are separated from the carrier and fly to form cloud haze-shaped toner. The cloud can be generated sufficiently. The toner cloud is assisted in the flight toward the latent image on the photoconductor belt 1 by the second oscillating electric field, and the control electrode plate 84 is set at an appropriate position, so that uniform development is performed.

At this time, since the AC bias is applied only to the developing sleeve 81, the first oscillating electric field and the second oscillating electric field have the same phase, and the toner particles are oscillated from the first oscillating electric field to the second oscillating field. Smooth transition to electric field.

The waveform of the above AC component is not limited to a sine wave,
It may be a rectangular wave or a triangular wave. Although the frequency is also related, the higher the voltage value is, the more the magnetic brush of the developer D is vibrated, and the separation and flight of the toner particles from the carrier particles are facilitated. Dielectric breakdown easily occurs. The generation of fog is prevented by a direct current component, and the insulation breakdown is caused by coating the surface of the developing sleeve 81 with a resin, an oxide film, or the like so as to be insulating or semi-insulating, or the carrier particles of the developer D having an insulating property as described later. It can be prevented by using carrier particles.

FIG. 7 shows the results of changing the frequency and the peak-to-peak voltage of the AC component applied to the developing sleeve 81 in the above embodiment. In FIG. 7, the range shaded with horizontal lines is the range where fogging is likely to occur, the range shaded with vertical lines is the breakdown where dielectric breakdown is likely to occur, and the range shaded with diagonal lines is the range where image quality degradation is likely to occur. There is a preferable range in which a stable and clear image can be obtained. As is clear from the figure, the range in which fogging is likely to occur changes according to changes in the AC component. Further, the low frequency region shaded with dots in the figure is a range where uneven development occurs due to the low frequency.

In the embodiment described above, one of the magnetic poles of the magnet body is used.
However, in addition, when adjacent magnetic poles of the magnet body are equally spaced apart from the developing area with the developing area sandwiched between them, one of the adjacent magnetic poles is close to the developing area. There is a case where one is located far away from the developing area, but basically neither of them is changed. Further, a developing device shown in FIG. 2 is used, in which a magnetic one-component developer or a non-magnetic one-component developer is used, and the developer D is conveyed by the rough surface of the developing sleeve 81 without the magnet body 82. In the same manner, the same effect can be obtained by providing the control electrode plate 84 between the photoconductor belt 1 and the developing sleeve 81 and making the installation conditions the same as in the developing device shown in FIG. (85c in FIG. 2 is a fur brush for supplying the developing property 81 to the developing sleeve 81 while stirring the developing property, and 86 is a restricting blade made of elastic rubber for restricting the amount of the developer D conveyed. 1 is the same as that in FIG. 1, so detailed description thereof will be omitted.) As described above, the developing device of the present invention keeps the developer D in non-contact with the photosensitive belt 1 which is an image forming member. 1
Also, a toner cloud is generated by the second oscillating electric field to improve separation and flight to the photosensitive belt 1 and prevent carrier particles from adhering to the photosensitive belt 1. It is possible to use it to develop a high quality image by using a two-component developer D composed of carrier particles and toner particles as described below or a toner as described below. It is preferable to use the following one-component developer D.

Generally, when the average particle size of the magnetic carrier particles is large, the state of the ears of the magnetic brush formed on the developing sleeve 81 becomes rough. Therefore, even if the electrostatic latent image is developed while being vibrated by the electric field. However, there is a problem that unevenness is likely to appear in the toner image and the toner density at the ears becomes low, so that high-density development is not performed. To solve this problem, the average particle size of the magnetic carrier particles should be reduced, and as a result of experiments, it was found that the above problems do not occur when the weight average particle size is 50 μm or less. However, if the particle size of the magnetic carrier is too small, the magnetic carrier tends to adhere to the surface of the photoconductor belt 1 together with the toner particles and scatter easily. These phenomena are related to the strength of the magnetic field acting on the carrier and the strength of the magnetization of the carrier due to it, but in general, the above tendency gradually begins to appear when the weight average particle diameter of the magnetic carrier becomes 15 μm or less. It becomes noticeable at 5 μm or less. Therefore, in this developing device, the magnetic carrier of the developer D preferably has a weight average particle diameter of 50 μm or less, particularly preferably 30 μm or less and 5 μm or more. When the magnetic carrier is spherical, the stirring property of the toner particles and the carrier particles and the transport property of the developer D are improved, and the charge controllability of the toner is further improved. It is preferable because it prevents aggregation of particles.

Such a magnetic carrier is a metal such as iron, chromium, nickel, cobalt or the like, or a compound or alloy thereof, such as iron tetroxide, γ-oxidation, which is the same as a conventional magnetic carrier as a magnetic substance. Spherical particles of ferromagnets or paramagnetic materials such as ferric iron, chromium dioxide, manganese oxide, ferrite, manganese-copper alloys, or the surface of these magnetic particles is styrene resin, vinyl resin, Ethylene resin, rosin modified resin,
Resin such as acrylic resin, polyamide resin, epoxy resin, polyester resin, silicone resin, etc., spherical coating with these copolymer resins or fatty acid wax such as palmitic acid, stearic acid, or containing dispersed magnetic fine particles. The particles obtained by forming spherical particles of the resin or fatty acid wax described above can be obtained by performing particle size selection by a conventionally known average particle size selection means.

The use of the spherical carrier particles coated with a resin or the like as described above, in addition to the above-mentioned effect, makes the layer of the developer D formed on the developer carrying carrier uniform, and Also, the effect that a high bias voltage can be applied to the developer carrier is given. That is, the fact that the carrier particles are spherical carrier particles coated with a resin or the like means that (1) in general, the carrier particles are easily magnetized and adsorbed in the long axis direction, but the spheroidization eliminates the directionality thereof, and therefore the developer layer Are uniformly formed to prevent locally low resistance regions and uneven layer thickness.
(2) As the resistance of the carrier particles is increased, the edge portion as seen in the conventional carrier particles is eliminated, and the electric field is not concentrated on the edge portion. As a result, a high bias voltage is applied to the developer carrier. However, the photoconductor belt 1
It is effective in preventing the electrostatic latent image from being disturbed by discharging on the surface and the bias voltage from breaking down. The fact that this high bias voltage can be applied means that the effects as described above in the development under the oscillating electric field of the present invention can be sufficiently exerted. And, the above-mentioned wax is also used for the spheroidizing of the carrier particles having the above effects, but from the viewpoint of the durability of the carrier, it is preferable to coat the above-mentioned spherical magnetic particles with a resin. Further, it is preferable that the carrier particles are formed of magnetic particles having an insulating property in which the resistivity of the carrier particles is 10 ⁸ Ωcm or more, particularly 10 ¹³ Ωcm or more. The resistivity, after tapping putting particles into a container having a cross section of 0.50 cm ^2, 1Kg / on packed particles cm ²
Is obtained by reading the current value when a voltage that generates an electric field of 1,000 V / cm is applied between the load and the bottom electrode. If this resistivity is low, the developer transport carrier When a bias voltage is applied to the carrier particles, charges are injected into the carrier particles, and the carrier particles are likely to adhere to the surface of the photosensitive belt 1 or the breakdown of the bias voltage is likely to occur.

In summary, the magnetic carrier particles are spherical so that at least the ratio of the major axis to the minor axis is 3 times or less, there are no protrusions such as needles and edges, and the resistivity is high. Is 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm or more is a proper condition. Further, such magnetic carrier particles are obtained by increasing the resistance of spherical magnetic particles by forming an oxide film or the like. It is produced by subjecting to spheroidizing treatment or obtaining dispersed resin particles by a spray drying method.

Next, the toner particles will be described. Generally, when the average particle size of toner particles is small, the amount of charge qualitatively decreases in proportion to the square of the particle size, and the adhesive force such as the Van der Waals force is relatively large, and the toner particles are easily scattered. While fogging easily occurs, it becomes difficult to separate from the carrier particles of the magnetic brush. In the conventional magnetic brush developing method, such a problem becomes remarkable when the average particle diameter is 10 μm or less. In the developing device of the present invention, this problem is solved by developing with a magnetic brush under a double oscillating electric field. That is, the toner particles attached to the ears of the magnetic brush are
The toner is strongly vibrated in the first oscillating electric field and easily separates from the spikes to form a toner cloud.
The inertial force due to the rotation of the sleeve, the centrifugal force due to the oscillating electric field, and the like cause the toner particles to be carried to the immediately adjacent developing area A, and the toner particles are faithfully adsorbed to the electrostatic latent image under the second oscillating electric field. At this time, the electrode portion 84a is provided only on the downstream side of the insulating member 83 and the closest contact 81a of the developing sleeve 81, so that no cloud is generated in an unnecessary portion other than the developing area. The weakening of the bond between the toner particles and the carrier particles by the oscillating electric field reduces the adhesion of the carrier particles accompanying the toner particles to the photoconductor belt 1, and the ears of the magnetic brush are kept in non-contact with the surface of the photoconductor belt 1. However, the toner particles having a large charge amount with respect to the carrier particles are selectively transferred to the electrostatic latent image under the oscillating electric field as described above, so that the adhesion of the carrier particles to the photosensitive belt 1 is significantly increased. Reduce.

As the average particle size of the toner becomes large, as already mentioned, the roughness of the image becomes noticeable. Usually, for developing with fine lines arranged at a pitch of about 10 lines / mm, a toner with an average particle size of about 20 μm does not cause any problem, but if a finely divided toner with an average particle size of 10 μm or less is used, the resolution will be improved. Is significantly improved, and it gives a clear high-quality image that faithfully reproduces the tone difference. For the above reason, the average particle size of the toner is 20 μm or less, preferably 1 to 10 μm. Further, since the toner particles follow the electric field, the charge amount of the toner particles is 3 μC / g.
It is desirable that it is larger (preferably 3 μC / g to 100 μC / g). Especially when the particle size is small, a high charge amount is required.

Such a toner can be obtained by a method such as a pulverization / granulation method, a suspension polymerization method, an emulsion polymerization method and the like similar to the conventional toner. That is, it is possible to use a toner in which spherical or amorphous non-magnetic or magnetic toner particles in the conventional toner are selected by the average particle size selection means. Further, the toner particles may be magnetic particles containing magnetic fine particles. In this case, the amount of the magnetic fine particles is 60 wt% or less, especially 30%.
Those that do not exceed wt% are preferable. When the toner particles contain magnetic particles, the toner particles are affected by the magnetic force contained in the developer carrying carrier, so that the uniform forming property of the magnetic brush is further improved and the fogging Generation is prevented, and toner particles are less likely to be scattered. However, if the amount of the magnetic substance contained is too large, the magnetic force between the carrier particles becomes too large,
It becomes impossible to obtain a sufficient developing density, and the magnetic fine particles come to appear on the surface of the toner particles.
It may be difficult to control triboelectric charging, or toner particles may be easily damaged.

In summary, in the developing device of the present invention, as the preferable toner particles, the resin as described for the carrier particles and the fine particles of the magnetic substance are used, and the coloring component such as carbon and the electrification as required. It is composed of particles having an average particle size of 20 μm or less, particularly preferably 1 to 10 μm, which can be produced by the same method as a conventionally known method for producing toner particles by adding a control agent and the like.

For the developing device of the present invention, a developer in which the spherical carrier particles and the toner particles as described above are mixed in the same proportion as in the conventional two-component developer is preferably used. Further, if necessary, a fluidizing agent for improving fluidity of particles and a cleaning agent useful for cleaning the surface of the image bearing member are mixed. As the fluidizing agent, colloidal silica, silicon varnish, metal soap, nonionic surface active agent or the like can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicon or fluorine surface active agent or the like can be used. You can

[0058]

According to the developing device of the present invention having the above-described configuration, the distance between the downstream end of the control electrode plate, which is a plate-like member, and the closest position between the image forming body and the developing sleeve is d3. (Mm) However, when the upstream side of the closest position is positive and the downstream side is negative, the position is set to −0.05 ≦ d3 ≦ −1.0 (mm), and the electrode portion of the control electrode plate and the developing sleeve are set. By forming an oscillating electric field between the developing device and the developing device, it is possible to provide a developing device that has high developing efficiency and performs non-contact developing without image stains and uneven streaks.

Further, in a color image forming apparatus in which a toner image is superposed on an image forming body to form a multicolored image, and the multicolored image is collectively transferred onto a transfer material, an oscillating electric field causes another toner image to be transferred onto the toner image. It has become possible to provide a color image forming apparatus which has no so-called "color mixture" in which color toners adhere and which has good developing efficiency.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a developing device of the present invention.

FIG. 2 is a schematic cross-sectional view showing another embodiment of the developing device of the invention.

FIG. 3 is a schematic configuration diagram showing an example of a color image forming apparatus including the developing device of the present invention.

FIG. 4 is a graph showing a relationship between an installation position of a control electrode plate, electrode contamination, and image density.

FIG. 5 is a cross-sectional view showing another form of the insulating member and the electrode portion of the control electrode plate.

FIG. 6 is a perspective view and an enlarged sectional view showing an example of a control electrode plate.

FIG. 7 is a graph showing a preferable range of an AC component of a developing sleeve bias voltage.

FIG. 8 is a diagram illustrating conventional non-contact development.

[Explanation of symbols] 1 photoconductor belt (image forming body) 6 scorotron charger 7 laser writing device 8, 8A, 8B, 8C, 8D developing device 81 developing sleeve 81a closest contact (to image forming body) 81b proximity point ( (To the control electrode plate of the developing sleeve) 82 Magnet 83 Insulation member 84 Control electrode plate (plate member) 84a Electrode portion 86 Regulation blade A Development area D Developer E1, E3 DC bias power supply E2 AC bias power supply R1, R2 protection resistance

Claims (3)

[Claims] 1. A developing device that carries a developer to a developing area by a developer carrying carrier, and forms an oscillating electric field between an image forming body and the developer carrying carrier to perform non-contact development. A plate-like member that is a control electrode plate is arranged upstream of the closest position between the forming body and the developer transport carrier, and the setting position of the plate-like member downstream end is set to the downstream side from the closest position. A developing device. 2. The distance between the downstream end of the plate-shaped member and the closest position is d3 (mm), where -0.05 ≦ d3 when the upstream side is positive and the downstream side is negative from the closest position. The developing device according to claim 1, wherein ≦ −1.0 (mm). 3. The developing device according to claim 1, wherein the plate-shaped member is a control electrode plate having an electrode portion provided at a tip portion thereof.