JPH086381A - Developing device - Google Patents

Abstract

PURPOSE:To provide a developing device stably having a high developing property without causing an image disturbance during intermittent copying by accurately installing a control electrode. CONSTITUTION:This developing device 8 has a control electrode 84 arranged with a voltage applicable electrode section 84a supported by an insulating member 83 located near or in contact with a developer D layer at the upstream section of the development region A of a developing sleeve 81 capable of being applied with the AC bias voltage superimposed with DC voltage on AC voltage. When development is started, the following processes are implemented: (1) the process to apply DC voltage to the electrode section 84a, (2) the process to start the rotation of the developing sleeve 81, and (3) the process to apply the AC bias voltage to the developing sleeve 81. At least the process (1) is implemented prior to the process (3).

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 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, but in recent years, a control wire or an electrode has been installed especially in the developing area, and an oscillating electric field is formed between the developing sleeve and the electrode to electrically form a toner cloud. Therefore, an example of performing cloud development has been proposed.

For example, a) Japanese Patent Laid-Open No. 56-27158 discloses that
A method in which a plurality of wires parallel to each other are provided between the image forming body and the developing sleeve that are not in contact with each other, and an alternating voltage is applied so that the polarities of the adjacent wires are reversed to fly the developer is known. It is disclosed.

Further, (b) Japanese Patent Application Laid-Open No. 57-198470 discloses that
A grid is provided between an image forming body that holds a latent image and a developing sleeve that holds toner, and DC and / or AC or one of them is applied as a bias voltage between the grid and the developing sleeve. Is disclosed.

Further, c) Japanese Patent Laid-Open No. 3-121678 discloses that
There is disclosed a method in which an electrode is installed in a developing region which is closest to an image forming body and a developing sleeve, and an alternating electric field is applied to disperse and fly a toner to perform development.

[0006]

However, the above-mentioned prior art has the following problems.

(1) It is difficult to arrange and maintain the wire (grid) with high accuracy by the methods (1) and (2), and by the method (3), the wires are exposed in the axial direction of the developing sleeve. Swelling occurs. It is difficult to install the electrodes so as to prevent the poor position accuracy, the unevenness, and the waviness, which causes image irregularity such as uneven streaks in the copy image.

(2) In any of the above-mentioned prior arts, in intermittent copying in which development and stopping are repeated, it takes time for the output of the power source to rise at the start of development, so the image density of the first half of the copied image becomes insufficient. easy.

(3) Further, when the development is stopped, the toner accelerated by the grid and the electrodes still exists in the development space, so that a stain such as a fog occurs on the image.

The object of the present invention is to provide the above (1), (2),
By solving the problem of (3), a control electrode corresponding to a wire or an electrode is accurately installed in a narrow space, and the resolution is high,
It is an object of the present invention to provide a developing device capable of stably obtaining a high-density image free from image irregularities such as uneven streaks and fogging even during intermittent copying.

[0011]

The first means (first invention) for solving the problems (1) and (2) described above is development in which an AC bias voltage in which a DC voltage is superimposed on an AC voltage can be applied. In a developing device having a control electrode provided with an electrode portion capable of applying a voltage, which is supported by an insulating member close to or in contact with the developer layer, at the upstream portion of the developing area of the sleeve, at the start of development, a) Performing each step of applying a DC voltage to the electrode portion, b) starting rotation of the developing sleeve, c) applying the AC bias voltage to the developing sleeve, and at least the step a) Is carried out prior to the step (c) above.

A second means (second invention) for solving the problems (1) and (3) is a developing area of a developing sleeve to which an AC bias voltage in which a DC voltage is superimposed on an AC voltage can be applied. In a developing device having a control electrode having an electrode portion to which a voltage can be applied, which is supported by an insulating member close to or in contact with the developer layer, is provided in the upstream portion, d) the electrode portion Electrically floating, e) stopping the rotation of the developing sleeve, f) electrically floating the developing sleeve,
Alternatively, at least the step of setting the applied AC bias voltage to 0 V is performed, and at least the step (f) is performed before the step (d).

[0013]

FIG. 2 is a schematic structural view showing an example of a color image forming apparatus equipped with the developing device of the present invention as a suitable developing means.

In FIG. 2, 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 rotating 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 thereof is the guide member. Rub 4

6 is a scorotron charger which is 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 developer of yellow, magenta, cyan and black, and has a predetermined gap from the photosensitive belt 1. Keep each developing sleeve
81, and has a function of visualizing the latent image on the photoreceptor belt 1 by a non-contact reversal development 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 color image forming process by the color image forming apparatus is carried out as follows.

First, the formation of a multicolor image according to this embodiment is shown in FIG.
Image forming system. That is, the original image is obtained by the color image image data input section (a) scanned by the image pickup device, and this data is obtained by the image data processing section (b).
Then, the image data is created by performing the arithmetic processing in (1) and is temporarily stored in the image memory (C). Next, this image data is taken out at the time of recording and inputted to the recording unit (d), for example, the color image forming apparatus of 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, passes through an fθ lens 75 and a cylindrical lens 76, and is in between. The optical path is bent by the individual mirrors 77 and 78, and is projected onto the peripheral surface of the photoconductor belt 1 to which uniform charge is previously applied by the charger 6 of the scorotron, and main scanning is performed to form a bright line.

On the other hand, when scanning is started, the laser beam is detected by an index sensor (not shown), and the first
The laser beam modulated by the color signal of (1) scans the peripheral surface of the photosensitive belt 1. 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 passes under the blade 13a of the cleaning device 13 and the toner discharge roller 13b as the cleaning means, which is separated from the peripheral surface of the photosensitive belt 1 while being held on the belt surface, and the next image forming cycle is performed. to go into.

That is, the photosensitive 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.

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

A developing device 8C has a cyan (C) toner, and 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 superimposing 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 having received the transfer of 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 and the operation is completed. 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, a 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.

FIG. 1 is a schematic sectional view showing an embodiment of the developing device of the present invention, and a sectional view of the main part, showing an example in which one of the magnetic poles of the magnet body is present in the developing area. Is not limited to this.

In the figure, reference numeral 81 denotes a developing sleeve which is a developer carrying carrier made of a non-magnetic material such as aluminum and is rotatable in the direction of the arrow in the figure. 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. The developing sleeve 81 and the magnet body 82 constitute a developer carrying carrier. Each magnetic pole of the magnet body 82 is magnetized to a magnetic flux density of 500 to 1,500 gauss, and the magnetic force forms a layer of magnetic developer D on the developer sleeve 81, that is, a magnetic brush. Is rotated in the same direction and is conveyed to the developing area 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, so that the developing sleeve
The gap between 81 and the regulation blade 86 and the gap between the developing sleeve 81 and the photosensitive belt 1 are adjusted.

Reference numeral 84 is a control electrode in which a voltage-applicable electrode portion 84a is disposed on the downstream end of an insulating member 83 provided on the upstream side of the developing area A in proximity to or in contact with the layer of the developer D. so,
The insulating member 83 also functions as a leveling member made of an electrical insulator such as polyester, polyimide, glass epoxy, polyethylene terephthalate, or polyamide imide, and the electrode portion 84a is made of a conductive material such as metal and the tip of the insulating member 83. It is linearly provided integrally on the part. 85A and 85B are agitation screws for agitating the developer D to make the components uniform, 86
Is a regulating blade which is a developer regulating means provided to regulate the amount of the transported developer D, 87 is a cleaning blade for removing the developer layer passing through the developing area A from the developing sleeve 81, and 88 is developing Agent reservoir, 89 is casing,
89a is a casing 89 for supporting the fixed portion of the insulating member 83.
Is a support portion provided in the. A pressing plate 90 is an example of a fixing member, and a fixing screw 90S is a fixing screw for fixing the pressing plate 90 to the supporting portion 89a and pressing the control electrode 84 toward the developing sleeve 81.

As shown in FIG. 3, in the control electrode 84, an electrode portion 84a made of a conductive material such as metal in a linear shape with a circular or quadrangular cross section is adhered to the tip portion of an insulating insulating member 83. Stick with an agent (Figs. 3 (a), (b), (g),
(H)), a notch 83a is provided at the tip of the insulating member 83 and sandwiched between them (FIGS. 3C and 3D), 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), etc., as shown in FIG. 4 with specific dimensions, a conventionally known printed circuit board manufacturing method is used,
By using glass epoxy, polyimide, paper phenol, or the like as the insulating member 83 and laminating a conductive member such as copper foil and then performing an etching process, the electrode portion 84a can be formed at the tip of the insulating member 83. . Electrode part 84
A may be coated with an insulating resin to prevent unnecessary discharge and to prevent rust. 84b is a terminal portion for applying a bias voltage.

The insulating member 83 of the control electrode 84 is the developing sleeve 81.
When the developer D is conveyed upward, the developer D enters between the insulating member 83 and the developing sleeve 81, so that the developer D is slightly curved and the insulating member 83 faces the developing sleeve 81 with a slight gap. 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 close to or in contact with the layer of the developer D.

In order to prevent the generation of unnecessary toner cloud in the upstream portion of the transport and to obtain a stable transport amount, the entire electrode portion 84a is, as shown in FIG. 1B, the control electrode 84 of the developing sleeve 81. The developing sleeve 81 is formed so as to be disposed only on the side of the closest position 81a of the developing belt 81 to the photosensitive belt 1 than the closest position 81b thereof. The length of the electrode portion 84a in the circumferential direction (horizontal direction) is 0.05 depending on the diameter of the developing sleeve 81 and the conveying speed.
.About.5 mm, particularly 0.1 to 1 mm is preferred. If it is less than 0.05 mm, a sufficient toner cloud cannot be generated, and if it is more than 5 mm, the toner is charged by vibration and becomes excessively charged, so that the developing property is deteriorated.

The thickness t (FIG. 4A) of the control electrode 84, which is the sum of the thickness of the insulating member 83 and the thickness of the electrode portion 84a, is defined as the development area A.
The closest distance between the photosensitive belt 1 and the developing sleeve 81 is d1
Then, (1 / 10,000) d1 to (2/3) d1, especially (1
/ 1,000) d1 to (1/2) d1 is preferable. 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 contrary (1 / 10,00
When the value is 0) d1 or less, the current from the developing sleeve 81 easily flows in, a voltage drop occurs and the developability deteriorates.

In the insulating member 83 of the control electrode 84, the gap between the upper end of the electrode portion 84a on the photosensitive belt 1 side and the photosensitive belt 1 is (2/3) d1 or less, and the lower end portion on the developing sleeve 81 side and the developing sleeve 81. The one that can support the electrode part 84 is selected so that the gap between and is (1 / 10,000) d1 or more, but strength and vibration prevention,
From the viewpoint of preventing contact with the photosensitive belt 1, the thickness t1 is (1
It is preferably / 100) d1 to (3/5) d1.

The width of the developing sleeve 81 in the rotation axis direction is W1,
The width of the insulating member 83 (the axial length of the developing sleeve 81) of the control electrode 84 is W2, the width of the electrode portion 84a (the axial length of the developing sleeve 81) is W3, and the developer D on the developing sleeve 81 is D3. Assuming that the width of the layer is W4, as shown in FIG. 5, W2>W1>W3>
As W4, a terminal portion 84b for applying a DC voltage E3 to the electrode portion 84a is also provided in a portion outside the width W4 of the developing area to prevent generation of unnecessary toner cloud.

The control electrode free end length is L (mm) (FIG. 1), the height from the surface of the developing sleeve 81 to the tip of the electrode portion 84a of the electrode portion 84 is d2 (mm), the photosensitive belt 1 and the developing sleeve 81.
The closest distance 81a to the electrode 84a and the horizontal distance between the tip of the electrode 84a on the downstream side are d3 (mm) (d3 is − on the downstream side of development from the closest position 81a, and + on the upstream side). When the diameter is R (mm), it is preferable that R / 400 ≤ L ≤ 2R / 3 R / 400 ≤ d2 ≤ 3R / 10 0 ≤ d3 ≤ 2R / 3.

When the control electrode free end length L is less than R / 400, it is not possible to obtain a sufficient vibration space for the toner to fly, and when it is greater than 2R / 3, the control electrode 84 is formed when an alternating electric field is formed.
Vibrates, and a stable image cannot be obtained.

When the height d2 of the tip of the electrode portion 84a is less than R / 400, electric discharge is likely to occur on the surface of the developing sleeve 81, causing image disturbance, and when d2 is greater than 3R / 10,
It is not possible to form an alternating electric field that is strong enough for the toner to fly.

Regarding d3, if it is less than 0, a sufficient developing property cannot be obtained because it covers the developing region, and if it is more than 2R / 3, it is too far from the developing region and sufficient developing property cannot be obtained.

The surface roughness Rz1 (μm) of the developing sleeve 81 and the roughness Rz2 (μm) of the surface of the insulating member 83 of the control electrode 84 facing the developing sleeve 81 are preferably Rz1> Rz2, and Rz1 ≦.
When Rz2 is reached, the developer D conveyed onto the developing sleeve 81
Is prevented from being conveyed by the insulating member 83a, so that the amount of toner conveyed to the developing area A is reduced and the image density is reduced. Rz1 is 0.2
The range of μm to 20 μm and Rz2 of 0.02 μm to 5.0 μm are preferable in order to obtain a high density image with good transportability and no image distortion. The surface roughness Rz is JIS
According to B0601, the measurement was performed with a standard length of 2.5 mm using Surftest-402 manufactured by Mitutoyo.

Position of control electrode 84 closest to developing sleeve 81
The pressure contact force at 81b is 0.1 g / cm or more and 40 g / cm or less,
It is preferably 0.5 g / cm or more and 25 g / cm or less.

When the amount is less than 0.1 g / cm, the control electrode 84 is the developer D.
It vibrates due to the fluctuation of the layer and the developing property becomes unstable.
If it is higher than / cm, the developer D layer is excessively regulated by the control electrode 84, and the conveyance failure occurs.

Further, an AC bias voltage in which a DC component is superimposed on an AC component is applied to the developing sleeve 81 by a DC bias power source E1 and an AC bias power source E2 via a protective resistor R1. 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.

In FIG. 1, S1 is a developing sleeve 81 and a protective resistor R1.
And a changeover switch S2 provided between the electrode section 84a
And a protection resistor R2. These changeover switches S1 and S2 are changed over as shown by a solid line or a broken line by the control of the CPU of a control unit (not shown) to turn ON / OFF the bias voltage applied to the developing sleeve 81 and the electrode member 84a, thereby applying the bias voltage. Can be set to a floating state indicated by a broken line.

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 above bias voltage, 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 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 the reversal 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 developer D which has reached near the electrode portion 84a in the direction perpendicular to the line of electric force by the first strong oscillating electric field.
Since the toner particles are vibrated, it is possible to separate and fly the toner particles from the carrier and sufficiently generate a haze-shaped toner cloud. This toner cloud is second
The weak oscillating electric field assists the flight toward the latent image on the photosensitive belt 1 and allows uniform development.

As described above, since the toner flying is performed by the weak oscillating electric field, the toner image is superposed on the image forming body to form a multicolor image, and the multicolor image is collectively transferred onto the transfer material. In the process, so-called "color mixing" in which toner of another color adheres to the toner image is unlikely to occur.

At this time, the AC bias voltage is the developing sleeve.
Since it is applied only to 81, the first oscillating electric field and the second oscillating electric field have the same phase, and the toner particles are smoothly transferred from the first oscillating electric field to the second oscillating 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 DC component, and the dielectric breakdown is caused by coating the surface of the phenomenon 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.

As described above, the developing device of the present invention keeps the magnetic developer in non-contact with the photosensitive belt 1 which is an image forming body, and generates the toner cloud by the first and second oscillating electric fields. , The separation and flight to the photoconductor belt 1 are improved, the selective adsorption to the electrostatic image is improved, and the carrier particles are prevented from adhering to the photoconductor belt 1. Therefore, the toner particles or the carrier particles are fine particles. Is used to develop a high-quality image, and it is preferable to use the following developer D composed of carrier particles and toner particles.

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 in a conventional magnetic carrier as a magnetic substance. Spherical particles of ferromagnet or paramagnetic material such as ferric iron, chromium dioxide, manganese oxide, ferrite, manganese-copper alloy, or the surface of these magnetic particles is styrene resin, vinyl resin, Resins such as ethyl resin, rosin-modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, silicone resin and their copolymer resins are spherically coated with fatty acid wax such as palmitic acid and stearic acid, or Conventionally, particles obtained by making spherical particles of resin or fatty acid wax containing dispersed magnetic fine particles Obtained by a particle size selected in average particle 径選 by means of knowledge.

The use of spherical carrier particles coated with a resin or the like as described above, in addition to the effects described above, 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, 1 kg 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 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 is likely to occur, 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, since the electrode portion 84a is provided only on the downstream side of the closest position 81b between the insulating member 83 and the developing sleeve 81, no cloud is generated in an unnecessary portion other than the developing area A. Further, the toner particles having a low charge amount hardly move to the image portion or the non-image portion, and the toner does not rub against the photosensitive belt 1, so that the toner particles may adhere to the photosensitive belt 1 by frictional charging. Gone, 1 μm
Even toner particles having a certain toner particle size can be used. 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 diameter 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 reasons, the average particle size of the toner is 20 μm or less, preferably 10 μm or less. Since the toner particles follow the electric field, the charge amount of the toner particles is 1 μC /
g to more than 3 μC / g (preferably 3 μC / g to
30 μC / g) is desirable. 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 or an emulsion polymerization method 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 transport carrier, so that the uniform forming property of the magnetic brush is further improved, and moreover, fog is not generated. 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 further 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 10 μm or less, which can be produced by a method similar to a conventionally known method for producing toner particles by adding a control agent and the like.

For the developing device 8 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

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 above developing apparatus, at the start of development (a) the changeover switch S2 is turned on to turn the electrode portion 8
Applying a DC voltage from the power source E3 or E1 to 4a,
(B) a step of starting the rotation of the developing sleeve 81,
(C) Each of the steps of applying the AC bias voltage by the power supplies E1 and E2 to the developing sleeve 81 by turning on the changeover switch S1 is performed, and at least the step (A) is performed from the step (C). Will be done first.

By performing the step (a) before the step (c), a strong electric field can be instantly formed between the developing sleeve 81 and the electrode portion 84a, and the instability of the rising of the AC power source E2 is reduced. it can. If the step (c) is performed first, the effective gap between the developing sleeve 81 and the photosensitive belt 1 is reduced by the dielectric constant of the insulating member 83, so that the strong first vibration described above between the electrode 84a is generated. Even if an electric field is not formed, unstable development will occur. By performing the step (a) first, the strong first oscillating electric field described above can be formed, and stable development can be performed.

Therefore, the following process sequence is preferable.

A): (a) → (b) → (c) b): (b) → (b) → (c) c): (a) → (c) → (b) d) :( b) ) → (c) and (b) {(c) and (b) are performed at the same time} Of the above, the particularly preferable process sequence is (b) → (b) →
By rotating the developing sleeve 81 first in the order of (c), it is possible to perform development with the developer D with sufficient charging.

Further, in the above developing device, at the end of development, (d) a step of turning off the switch S2 of the electrode portion 84a to make it electrically floating, (e) stopping the rotation of the developing sleeve 81. Step (f) The developing sleeve 81 is set in an electrically floating state by turning off the changeover switch S1 or at least a CP not shown
Each step of the steps of turning off the outputs of the power supplies E1 and E2 by the control of U and setting the applied AC bias voltage to 0 V is performed, and at least the step (f) is performed before the step (d). To do so.

By turning off the AC bias voltage of the developing sleeve 81 first, the developing sleeve 81 and the electrode portion 84a
Strong electric field between the developing sleeve 81 and the photoconductor belt 1
Since the weak electric field between and can be instantly extinguished, an unnecessary toner cloud is not formed and fogging that occurs at the end of copying can be prevented. Since only a weak oscillating electric field is formed in the developing space between the developing sleeve 81 and the photosensitive belt 1, the toner moving speed is small, and the toner is unnecessarily transferred to the photosensitive belt 1 after the AC bias voltage is turned off. Does not adhere.

Therefore, the following process sequence is preferable.

A): (f) → (d) → (f) b): (f) → (f) → (d) c): (f) → (f) → (d) d): (f) ) → (e) and (d) {(e) and (d) are performed at the same time} Of the above, a particularly preferable process sequence is (e) → (d) →
By rotating this developing sleeve 81 at the end in the order of (e), electrical ON / OFF with fast response is performed first and the electrode section
Discharge between 84a and the developing sleeve 81 can be prevented.

(Experimental Example) In the apparatus shown in FIGS. 1 and 2,
A spherical magnetic carrier having a weight average particle diameter of 30 μm and a resistivity of 10 ¹⁴ Ωcm or more obtained by coating a surface of a methyl methacrylate / styrene copolymer resin on spherical ferrite particles having a magnetization strength of 50 emu / g, Obtained by a pulverization granulation method having a weight average particle diameter of 8 μm, which is composed of 100 parts by weight of styrene-acrylic resin (Haimer up110 manufactured by Sanyo Kasei), 10 parts by weight of carbon black (MA-100 manufactured by Mitsubishi Kasei), and 5 parts by weight of nigrosine as toner. The non-magnetic particles were used. Under the condition that the toner particle ratio of each developer D in the developer pool 88 of the developing device is 10 wt% with respect to the carrier particles, the average charge amount of each toner at the time of development was -18 μC / g.

The photoconductor belt 1 is an OPC photoconductor, the peripheral speed is 180 mm / sec, the maximum potential of the electrostatic latent image formed on the photoconductor belt 1 is −800 V, the outer diameter of the developing sleeve 81 is 30 mm,
The rotation speed is 150 rpm, the thickness of the developer D layer is 0.3 mm, and L = 10 m.
m, in the developing area, d1 = 0.5 mm, d2 = 0.3 mm,
d3 = 0.5 mm. Further, glass epoxy having a thickness of 0.1 mm is used as the insulating member 83 of the control electrode 84, and as shown in FIG. 4, the electrode portion 84a having a horizontal width of 0.3 mm is provided at the tip of the surface of the photosensitive belt 1 side. Was formed by a laminate etching method using a 0.02 mm-thick copper foil,
The surface roughness Rz1 of the developing sleeve 81 is 2.7 μm, and the insulating member 83
The surface roughness Rz2 is set to 0.3 μm, and the position of the downstream end of the electrode portion 84a is set to an angle 5 about the rotation axis O of the upstream developing sleeve 81 from the closest position 81a between the developing sleeve 81 and the photosensitive belt 1. And the position of the magnetic pole in the developing area A of the magnet body 82 was set near the closest position, and the following experiment was conducted by the color image forming apparatus of FIG. 2 equipped with the developing device.

The bias voltage applied to the developing sleeve 81 is a DC component voltage of −750 V, an AC component frequency of 8 KHz,
The peak-peak voltage was 1,200 V, and the DC component voltage applied to the electrode portion 84a was -750 V.

The following four steps (a) to (d) show the order of ON / OFF of bias voltage application at the start and end of development and ON / OFF of rotation of the developing sleeve 81. about,

[0080]

[Table 1]

Intermittent copying was performed up to 50,000 copies, such as stopping after copying one black monochrome image, then stopping after copying another one, and in each case, the resolution was high and the streaks were uneven. It was possible to obtain a stable high-density copy image with no fog or the like and no lack of density at the leading edge of the copy image.

Although the present embodiment has been described with respect to the developing device using the two-component developer, it can be applied to the developing device using other non-magnetic one-component developer and magnetic one-component developer.
Needless to say, a magnetic latent image can be visualized under similar developing conditions as long as the toner of the developer has magnetism.

[0083]

EFFECTS OF THE INVENTION The present invention has the above-described structure. A) The control electrode can be accurately installed in a narrow space and can be stably maintained during operation. It is possible to obtain a high-density color image without disturbance.

B) Even if the intermittent copying is performed, the image is not disturbed, stable high developing property is obtained, and a high-density copied image can be obtained.

It is possible to provide an excellent developing device having the effects described above.

[Brief description of drawings]

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

FIG. 2 is a schematic configuration diagram showing an example of a color image forming apparatus including a developing device of the present invention.

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

FIG. 4 is an enlarged side view and a perspective view showing an example of the control electrode of FIG.

FIG. 5 is a bird's-eye view showing a relationship of widths of a developing sleeve, a control electrode, a developer layer, and the like.

FIG. 6 is a block diagram illustrating an image forming system.

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

[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 position (developing sleeve to image forming body) 81b closest position ( (To the control electrode of the developing sleeve) 82 Magnet 83 Insulating member 84 Control electrode 84a Electrode 86 Control blade 90 Holding plate A Development area D Developer E1, E3 DC bias power supply E2 AC bias power supply R1, R2 Protection resistance S1, S2 Changeover switch

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hiroyuki Nomori Inventor Hiroyuki Nomori 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company

Claims (2)

[Claims] 1. A voltage-applied voltage supported by an insulating member close to or in contact with a developer layer is provided at an upstream portion of a developing area of a developing sleeve to which an AC bias voltage in which a DC voltage is superimposed on an AC voltage can be applied. In a developing device having a control electrode provided with an electrode part, a) a step of applying a DC voltage to the electrode part at the start of development, b) a step of starting rotation of the developing sleeve, and c) a developing sleeve. A developing device, wherein each step of applying the AC bias voltage is performed, and at least step (a) is performed before step (c). 2. A voltage-applied voltage supported by an insulating member close to or in contact with a developer layer is provided at an upstream portion of a developing area of a developing sleeve to which an AC bias voltage in which a DC voltage is superimposed on an AC voltage can be applied. In a developing device having a control electrode provided with an electrode section, d) a step of electrically floating the electrode section at the end of development, e) a step of stopping the rotation of the developing sleeve, and f) the development The sleeve is in an electrically floating state,
Or at least the step of setting the applied AC bias voltage to 0 V, and at least the step (f) is performed before the step (d).