JPH05216324A - Method for forming multi-color image - Google Patents

Abstract

PURPOSE:To provide a multi-color image forming method by which the sharpness and the successive copying property of a character picture image is improved and the excellent faithfulness of color tone without mixing the toner of the other colors is obtained by giving a vibration voltage obtained by superimposing a specified AC component and a DC bias component between a photosensitive body and a developing sleeve in a developing area and executing non-contact developing by using two- component developer. CONSTITUTION:In the developing device, N and S magnetic poles are disposed by avoiding the developing area where the developing sleeve 2 and the photosensitive body 1 come close to each other. Then, a horizontal magnetic field component is formed in the developing area and the bristle of a developer layer is laid without napping. Then, the developing is executed by impressing the voltage obtained by superimposing the DC voltage related to the prevention of fogging and developing density and the AC voltage related to the developing density and gradation on the sleeve 2 by a bias power source 8 and generating a vibration magnetic field in the developing area. The voltage which is almost equal to the potential of the non-image part of the body 1 or higher than it is used as the DC component and the voltage whose frequency is 5-20kHz, whose amplitude is within the range of 1.0-2.5VP-P is used as the AC component.

Description

Detailed Description of the Invention

[0001]

The present invention uses a two-component developer,
The present invention relates to a multicolor image forming method in which a parallel magnetic field is applied to a contact plane of a developing sleeve in a developing area to perform multiple development on a photoconductor.

[0002]

BACKGROUND OF THE INVENTION A two-component developer in which a toner and a magnetic carrier are mixed is easier to control triboelectric charging of the toner and less likely to cause aggregation of the toner, as compared with a one-component developer composed of a magnetic toner without using a magnetic carrier. Therefore, in the case of a color toner, which can effectively control the transfer of the toner by a bias electric field or the like, and can obtain the sharpness of the color, the toner is often used in spite of the management of the amount of the toner to the carrier. Has been.

As a developing device using such a developer, a developing sleeve is fixed and a built-in magnet having a plurality of N and S magnetic poles rotates in the circumferential direction, a developing sleeve and a magnet rotate together, and a developing device. It is often used that the sleeve rotates and the magnetic pole of the built-in magnet is fixed. Among them, the one in which the built-in magnet rotates has a problem that a large rotating force is required to rotate the magnet at a high speed, vibration is generated, and the rotating mechanism becomes complicated and strong and large-sized.
On the other hand, in the case where the magnetic pole of the built-in magnet is fixed, when the developer layer moves, the developer layer is wavy by the built-in magnetic pole,
There is a problem that if the developer layers have different layer thicknesses, they are amplified, and if the magnetic pole is provided in the developing area closest to the developing sleeve and the photoconductor, the effect is further emphasized. To be done.

In order to avoid the influence, a so-called horizontal magnetic field system has been proposed which suppresses the spike of the developer standing toward the surface of the photoconductor in the developing region (Japanese Patent Laid-Open Nos. 56-154769 and 60-60).
176069, 61-160764, etc.), it seems that there are insufficient points in the composition conditions, and the sharpness of the image and color reproducibility (color turbidity)
Is not yet satisfactory. In particular, character images made up of thin lines are inherited by successive generations of copying, and as the number of copying increases, the defects are amplified and the image quality becomes unreadable. Further, in multi-color multi-color development, color toner contamination occurs, resulting in color turbidity and poor color tone image quality.

[0005]

OBJECTS OF THE INVENTION The purpose of the present invention is to reflect the above situation and
In a non-contact developing system using a component type developer; (1) improvement of sharpness of character image and succession copying property, and (2) multicolor image forming method with good color tone fidelity without mixing of toner of other colors. In offer.

[0006]

The above object of the present invention is to sandwich a developing region between adjacent magnetic poles of a fixed magnet built in the developing sleeve in the developing region where the surface of the photoreceptor and the surface of the developing sleeve are closest to each other, and between the adjacent magnetic poles. In an image forming apparatus provided with a plurality of developing devices that generate magnetic fields parallel to the tangent planes in which the magnetic lines of force contact the developing sleeve surface in the developing area, between the photoreceptor and the developing sleeve in the developing area, 5 to 20 KHz, 1.0 ~
A multicolor image forming method in which an oscillating electric field in which an AC component of 2.5 KV _PP and a DC bias component are superimposed is applied and a two-component developer is used to perform non-contact development on a photoreceptor for each of the plurality of developing devices. Achieved by

In the embodiment of the present invention, the gap between the photoreceptor surface and the developing sleeve surface in the developing area is 0.1 to 0.5 mm,
In addition, the magnetic field lines in the direction of the normal line to the surface of the developing sleeve passing through each of the adjacent magnetic poles of the magnets contained in the developing sleeve have an opening angle of 30 to 70 degrees which sandwiches the developing region, and the magnetic field created by the magnetic lines of force in the normal line direction. It is preferable that the strength is 400 to 800 gauss.

Further, it is preferable that the magnetic carrier particles of the two-component developer used have a diameter of 30 to 80 μm, and the magnetic susceptibility under a magnetic field of 500 oersteds is 20 to 50 emu / g.

Next, the present invention will be specifically described.

FIG. 1 is a sectional view showing an embodiment of an image forming apparatus according to the present invention. This image forming apparatus comprises an image reading system A, a laser writing system B, an image forming section C, etc., and forms a full-color image.

An original table made of a transparent glass plate or the like is provided above the image forming apparatus, and an original document D placed on the original table.
There is a document placing portion 11 composed of a document cover or the like for covering the first mirror unit 12 and the second mirror unit 12 in the apparatus body below the document table.
An image reading system A including a mirror unit 13, a main lens 20, a color CCD 23 and the like is provided. The first mirror unit 12 is provided with an exposure lamp 14 and a first mirror 15 and is mounted parallel to the document table and linearly movable in the horizontal direction of the drawing, and optically scans the entire surface of the document D. The second mirror unit 13 integrally includes a second mirror 16 and a third mirror 17, and linearly moves in the left-right direction at a speed half that of the first mirror unit 12 so as to always maintain a predetermined optical path length.
As a matter of course, the movement of the second mirror unit 13 is parallel to the platen like the first mirror unit 12. The image of the document D on the document table illuminated by the exposure lamp 14 is formed by the main lens 20 on the color CCD 23 through the first mirror 15, the second mirror 16 and the third mirror 17. There is. When the scanning is completed, the first mirror unit 12 and the second mirror unit 13 return to their original positions and wait until the next copy.

The image data of each color obtained by the color CCD 23 is image-processed and output from the laser writing system B as an image signal.

In the image forming section C, the toner image is transferred to the photosensitive drum.
A charger 35, an image exposure unit 55, and a developing device arranged around the periphery of 30.
36Y, 36M, 36C, 36BK, a transfer device 37, a separator 38, a cleaning device 39, a sheet feeding cassette 40 arranged near the photosensitive drum 30, a conveyor belt 44, a fixing device 45 and the like.

The order of arrangement of these developing devices in the rotational direction of the peripheral edge of the photosensitive drum is arbitrary because they are computer-controlled, but the developing devices 36Y, 36M, 36C and 36BK are arranged in this order.

With the above-described structure, each process of the image reading system A, the laser writing system B, and the image forming section C operates to form a color copy image. That is, the CP of the control unit
Under the control of U70 (not shown), the image signal from the image reading system A is input to the drive motor 31, the polygon mirror 32, and the writing system B including a semiconductor laser of 810 nm (not shown), an fθ lens, a correction lens and the like. And start the copy operation. That is, the photosensitive drum 30 rotates clockwise as shown by the arrow, is uniformly charged by the charger 35, and a yellow (Y) image corresponding to the image of the document D is written in the image exposure unit 55. Is performed by the laser beam from the laser writing system B, and an electrostatic latent image of the Y image is formed. The electrostatic latent image on the photosensitive drum 30 is the developing device 36Y.
Regular or reversal development is performed with the Y toner charged by the above, and a visible Y toner image is formed. That is, a DC or further AC bias voltage is applied to the developing sleeve of the developing device 36Y having a built-in magnet roll, and non-contact development is performed by a two-component developer which is a developing means to form a Y toner image. .. The photoconductor drum 30 on which the Y toner image layer is formed passes under the retracted cleaning device 39, and subsequently, charging by the charger 35 and laser beam writing of a magenta (M) image by the laser writing system B are performed. Then, an electrostatic latent image of a magenta (M) image is formed on the Y toner image layer. This latent image is a developing device 36M containing magenta toner.
Is developed to form an M toner image layer. Subsequently, similarly, a cyan (C) toner image layer and a black (BK) toner image layer having transparency to infrared semiconductor laser light are formed. A laminated multicolor toner image layer of each toner image is formed on the photoconductor drum 30, and is charged by the pre-transfer charger 47 and then transferred.

Next, the transfer paper P fed out by the paper feed roller 41 one by one from the paper feed cassette 40 in which the transfer paper P which is the recording fixing material is accommodated is the toner image on the photosensitive drum 30. It is delivered onto the photoconductor drum 30 by a timing roller 42 which operates synchronously with the layers. This transfer paper P has
By the action of the transfer device 37, the toner image common layer on the photoconductor drum 30 is transferred, charged by the pre-transfer charger 47, and then separated from the photoconductor drum 30 by the transfer device 37 and the separator 38. After that, the copy sent to the fixing device 45 via the conveyor belt 44 and fixed by being nipped and pressed by the heat fixing roller and the pressure bonding roller is discharged to the tray outside the apparatus by the paper discharging roller 46.

Next, the development mode which is the main point of the present invention will be described with reference to the drawings.

FIG. 2 is an enlarged partial view for explanation showing only one of a plurality of developing devices according to the present invention as an example.

In the figure, 1 is a drum-shaped photosensitive member that rotates in the direction of the arrow to form an electrostatic latent image or the like, 2 is a non-magnetic conductive material such as aluminum or stainless steel,
Developing sleeve 3 which rotates in the direction of the arrow, 3 is a developing sleeve 2
Is a magnet in which a plurality of N and S magnetic poles which are built in, fixed and arranged in the circumferential direction are connected to each other, and the N and S magnetic poles are magnetized to have a predetermined magnetic flux density. 4 is the developer pool, 5 is the developer in which the toner and the magnetic carrier of the developer pool 4 are mixed,
The stirring rotor blades that make the toner and the magnetic carrier uniform and frictionally charge the toner, and 6 the developer in the developer reservoir 4 is attracted to the surface of the developing sleeve 2 by the magnetic force of the N and S magnetic poles of the magnet 3, and the rotation thereof A layer thickness control blade made of a magnetic material or a non-magnetic material for controlling the layer thickness of the developer layer that moves together, and 7 develops the developer layer that has passed through the development area where the developing sleeve 2 is close to the photoconductor 1. A cleaning blade 8 which removes from the surface of the sleeve 2 and returns it to the developer pool 4, applies a bias voltage to the developing sleeve 2 through a safety resistor 9, and an oscillating electric field between the substrate 1 and the photoreceptor 1 whose ground is grounded. A bias power source for controlling the transfer of toner from the developer layer to the photoconductor in the developing region,
Is a toner replenishing roller for replenishing the developer reservoir 4 with toner from the toner hopper.

When the fixed magnet 3 is located at the position where the N and S magnetic poles are arranged as in the conventional developing means, even if the layer thickness of the developer layer is regulated by the layer thickness regulating blade 6, This alone tends to cause inconsistencies in the layer thickness.

Therefore, in the developing device of the present invention, N, S
By arranging the magnetic poles so as to avoid the developing region where the developing sleeve 2 and the photoconductor 1 are close to each other, a horizontal magnetic field component is formed in the developing region, and the developer layer is laid down without standing. As a result, a uniform thin developer layer is realized in the developing area, and the layer thickness regulating blade 6 and the developing sleeve 2 are provided.
It is possible to perform stable development with good sharpness, with no gap between the layers and being unaffected by uneven layer thicknesses.

The arrangement of the magnetic poles will be described with reference to FIG. 2. The N and S magnetic poles are arranged at positions open at an angle θ of 30 to 70 ° between the center lines of the photoconductor 1 and the developing sleeve 2. preferable.

The strength of the magnetic field in the direction normal to the developing sleeve surfaces of the N and S poles adjacent to each other with the center line interposed therebetween is 400 to 800.
It is preferably Gauss. Further, it is preferable to reduce the diameter of the developing sleeve 2 so that the spikes of the developer layer at the positions of the N and S magnetic poles provided so as to avoid the center line position do not come into contact with the surface of the photoconductor 1. The preferable range is 40 to 10 mmφ. When a belt-shaped photosensitive member 1 is used, a belt driving roller may be provided in the developing area so as to satisfy the above conditions.

The gap Dsd between the developing sleeve 2 and the photosensitive member 1 is 0.
It is preferably set to 1 to 0.5 mm. That is, the spread of the lines of electric force is small and the sharpness of the image is improved. This gap Dsd is 0.
If it is narrower than 1 mm, it becomes difficult to form a developer layer that uniformly develops, and it becomes impossible to supply sufficient toner to the developing area, so that stable development cannot be performed. On the other hand, when the gap is much larger than 0.5 mm, the counter electrode effect is lowered and sufficient development density is lost. That is, in the present invention, the condition is set so that the developer layer does not contact the surface of the photoconductor 1 and is as close as possible, but Dsd is 0.
If it is narrowed down to about 3 mm, the succession copyability of character images can be extended from the third generation to the fifth generation. However, in the multi-color multi-layer development, the mixed tendency of the color toners appears and the fidelity of the color tone deteriorates. In the present invention, the mixing tendency is eliminated by adjusting the oscillating electric field developing bias.

In the development under an oscillating electric field in the present invention, a bias voltage 8 is applied to the developing sleeve 2 by superimposing a DC voltage related to fogging prevention and development density and an AC voltage related to development density and gradation. Apply a voltage,
As a result, an oscillating electric field is generated in the developing area. As the DC component, a range of 50 to 600 V which is substantially equal to or higher than the non-image portion potential of the photoconductor 1 is used, and as the AC component, a frequency of 5 to 20 KHz and an amplitude of 1.0 to 2.5 V _PP . Used. If the frequency of the AC component is too low, the vibration pitch appears in the development, and if it is too high, the development cannot follow the vibration of the electric field, and the development density decreases, resulting in a clear high-quality image. Cannot be reproduced. Although the amplitude of the AC component is related to the frequency, the greater the amplitude, the more vibrating the developer layer and the greater the effect.However, on the other hand, fogging is likely to occur and insulation such as a lightning phenomenon occurs. Destruction is also likely to occur. However, if the carrier particles of the developer are insulated by a resin or the like and are further spherical, dielectric breakdown is prevented and fogging can be prevented by the direct current component. The surface of the developing sleeve 2 may be covered with a resin or an oxide film for insulation or semi-insulation, or unevenness may be provided on the surface to improve the transportability of the developer layer.

Further, since the oscillating electric field weakens the bond between the toner particles and the carrier particles, the adhesion of the carrier particles accompanying the toner particles to the photoconductor 1 is also reduced. Particularly in the case of the non-contact developing method, in the image area and the non-image area, the toner particles having a large charge amount vibrate under an oscillating electric field, and the carrier particles also vibrate depending on the strength of the electric field.
Since the toner particles are selectively transferred to the image area on the surface of the photoconductor 1, the adhesion of the carrier particles to the surface of the photoconductor 1 is significantly reduced. In this case, there is a problem that the toner particles vibrating in the non-image area are easily scattered depending on the electric field. The same applies to carrier particles. this is,
This can be prevented by slowing down the rotation of the developing sleeve 2 and appropriately reducing the conveying speed of the developer layer.

In the developing mode of the present invention, since the transfer of toner can be effectively controlled by the oscillating electric field as described above, a two-component developer containing toner having an average particle diameter of 10 μm or less can be used. ..

When the average particle diameter of the toner is reduced, the toner particles qualitatively decrease in the charge amount in proportion to the square of the particle diameter.
Although the adhesive force such as the Van der Waals force becomes relatively large and it becomes difficult to separate from the carrier particles, according to the present invention, in the non-contact developing method, the effective transfer control of the toner by the oscillating electric field is performed. Toner particles having a low charge amount almost never migrate to the non-image area, and are not rubbed against the surface of the photoconductor, and are not attached to the photoconductor by frictional charging. Will be used up to.

The resins used in the toner according to the present invention include styrene resins, vinyl resins, ethyl resins,
Examples include rosin-modified resins, acrylic resins, polyamide resins, epoxy resins, polyester resins, etc., to which a colorant such as carbon and, if necessary, a fixability improver, charge control, etc. are added, to produce conventionally known toner particles. It can be made by a method similar to the method.

Further, the toner particles are spray-dried,
Alternatively, when the developer is spheroidized by the spheroidizing treatment after the granulation, the flowability of the developer is improved and aggregation is less likely to occur, and the uniform mixing property with the carrier, the transportability and the charging property are also improved.

As the colorant, dyes and pigments are generally used, but pigments having high weather fastness are widely used.
Examples of the pigment include black pigments such as carbon black and graft-treated carbon black, and examples of color pigments such as cyan or green pigment include C.I. I. Pigment Blue-1
5, C.I. I. Pigment Blue-15: 2, C.I. I. Pigment Blue 15: 3, C.I. I. Pigment Blue 1
6, C.I. I. Pigment Blue 60, C.I. I. Pigment Green 7 and the like.

Examples of magenta or red pigments include C.I. I.
Pigment Red 2, C.I. I. Pigment Red 3,
C. I. Pigment Red 5, C.I. I. Pigment Red 6, C.I. I. Pigment Red 7, C.I. I. Pigment Red 15, C.I. I. Pigment Red 16, C.I.
I. Pigment Red 48: 1, C.I. I. Pigment Red 53: 1, C.I. I. Pigment Red 57: 1,
C. I. Pigment Red 122, C.I. I. Pigment Red 123, C.I. I. Pigment Red 139, C.I.
I. Pigment Red 144, C.I. I. Pigment Red 149, C.I. I. Pigment Red 166, C.I. I.
Pigment Red 177, C.I. I. Pigment Red 1
78, C.I. I. Pigment Red 222 and the like.

Yellow or orange pigments include C.I.
I. Pigment Yellow 12, C.I. I. Pigment Yellow 13, C.I. I. Pigment Yellow 14, C.I. I.
Pigment Yellow 15, C.I. I. Pigment Yellow 17, C.I. I. Pigment Yellow 93, C.I. I. Pigment Yellow 94, C.I. I. Pigment Yellow 13
8, C.I. I. Pigment Orange 31, C.I. I. Pigment Orange 43 and the like.

These organic and inorganic pigments can be adjusted to a desired color tone by selecting one or a plurality of them in combination as desired.
The amount of pigment added is selected from about 2 to about 20 parts, preferably about 3 to 15 parts, based on the resin.

Next, when the average particle size of the magnetic carrier is large,
The state of the developer layer formed on the developing sleeve becomes rough, and even if vibration is applied by an oscillating electric field, unevenness in the toner image easily appears, and the toner concentration in the developer layer becomes low, making high-density development difficult. Become. Further, when the average particle size of the carrier is small, if the carrier particles are too fine, they tend to adhere to the surface of the photoconductor together with the toner particles and scatter. These phenomena are greatly related to the strength of the magnetic field acting on the carrier particles as a developing condition, and the strength of the magnetization of the carrier particles corresponding thereto.

The magnetic carrier particles may be composed of only a magnetic material, or the magnetic material particles may be coated with a resin.

As a result of various studies as described above, the magnetic carrier of the two-component developer according to the present invention has an average particle size of 30 to 80 μm and a magnetic field of
A suitable condition is that the magnetic susceptibility at 500 oersteds is 20 to 50 emu / g. In the case of toner, the average particle size is also a weight average particle size, and is a value measured by a Coulter counter manufactured by Coulter or Omnicon Alpha manufactured by Boschrom.

The magnetic substance used in the above magnetic carrier includes metals such as iron, chromium, nickel and cobalt, or their compounds and alloys such as ferric tetroxide, γ-ferric oxide and dioxide. Examples thereof include particles of ferromagnetic or paramagnetic materials such as chromium, manganese oxide, ferrite, and manganese-copper alloy.

By forming the carrier particles from a resin or the like and preferably having a spherical shape, the developer layer formed on the developing sleeve becomes uniform and a high bias voltage is applied to the developing sleeve. Gives the effect of being able to apply. That is, when the carrier particles are made into particles by a resin or the like, (1) in general, there is no tendency to be easily magnetized and adsorbed in the long axis direction, a developer layer is uniformly formed, and a region having a locally low resistance is formed. And (2) the resistance of the carrier particles is increased, and the edge portions as seen in the conventional carrier particles are eliminated, so that the electric field is not concentrated on the edge portions. As a result, even if a high bias voltage is applied to the developing sleeve, the effect of preventing the electrostatic latent image from being disturbed by the discharge to the photoconductor and the breakdown of the bias voltage is given. The ability to apply this high bias voltage can sufficiently bring out the effect of the high bias voltage in the development under the oscillating electric field in the present invention.

Furthermore, the resistivity of the carrier particles is 10 ⁸ Ωcm.
Above all, it is particularly preferable that the insulating magnetic particles are formed so as to have a resistance of 10 ¹³ Ωcm or more. This resistivity is 0.50 for particles
After tapping in a container with a cross-sectional area of cm ² ,
It is a current value when a load of 1 kg / cm ² is applied on the packed particles and a voltage that generates an electric field of 1000 V / cm is applied between the load and the bottom electrode. If this resistivity is low, the developing sleeve When a bias voltage is applied to the carrier particles, charges are injected into the carrier particles, and the carrier particles adhere to the photoconductor.
Alternatively, the breakdown of the bias voltage is likely to occur.

That is, the preferred magnetic carrier for the present invention is
It is preferable that the particles are spherical particles having an average particle size of 30 to 80 μm, a magnetic field of 500 oersteds is 20 to 50 emu / g, and a resistivity of 10 ⁸ Ωcm or more, more preferably 10 ¹³ Ωcm or more.

In the developing mode of the present invention, a developer in which the above-described toner and magnetic carrier are mixed in the same proportion as in the conventional two-component developer is preferably used.

If necessary, the developer may be mixed with a fluidizing agent for improving fluidity and slippage of particles, a cleaning agent useful for cleaning the surface of the photoreceptor, a fixability improving agent, a charge control agent and the like. As the fluidizing agent, colloidal silica, silicone varnish, metal soap or nonionic surface active agent can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicone or fluorine surface active agent can be used. You can

Known fixability improvers are used. Generally, a polyolefin type is used.
For example, low molecular weight polyethylene, low molecular weight polypropylene, oxidized polyethylene and polypropylene,
Acid-modified polyethylene and polypropylene are used. These can be introduced into polymer particles by a conventional method, after being melted, dispersed in water and added in the form of emulsion during emulsion polymerization or seed emulsion polymerization. It is preferable to add it during seed emulsion polymerization so that it can be made to exist as polyolefin fine particles on the particle surface, which is preferable from the viewpoint of improving fixability.

Further, a polyethylene wax emulsion marketed under the trade name "HYTEC" (manufactured by Toho Chemical Industry Co., Ltd.) can be used for the same purpose.

A charge control agent having a known structure is similarly used.

As the charge control agent, a nigrosine-based electron-donating dye, a metal salt of naphthenic acid or a higher fatty acid, an alkoxylated amine, a quaternary ammonium salt, an alkylamide, a metal complex, a pigment, or a fluorine treatment is used as a charge control agent. An electron-accepting organic complex such as an activator, which is negatively charged
Examples thereof include chlorinated paraffin, chlorinated polyester, and sulfonylamine of copper phthalocyanine.

In the present invention, by using the above-mentioned developer and developing conditions, stable and excellent sharpness can be achieved without fog and clouding of color tone in multicolor multi-layer development. It is also suitably used for reversal development.

[0049]

EXAMPLES Next, specific examples of the present invention will be described.

Example 1 Machine used: Full-color copying machine Development conditions: ・ Reverse development ・ Blank paper potential V _H = -850 V ・ Black part potential _VL = -50 V ・ DC development bias potential V _DC = -750 V ・ AC development bias rectangular wave The peak-to-peak potential V _PP corresponds to the change of Dsd and the maximum toner development amount is almost the same (here, about 0.7 to 0.8 mg /
It was adjusted in the range of 0.23 to 3.3KV so that it would be cm ² ).

Linear velocity ratio V _s / V _p = 2.2 between developing sleeve and photoconductor Linear velocity (V _p ) 140 mm / sec Developer: For full color copying machine Toner diameter d _T = 8.5 μm, toner concentration T _C = 7 wt% Carrier diameter d _C = 45 μm Table 1 shows examples and comparative examples in the case of using 8.5 μm toner. Distance Dsd between developing sleeve and photoconductor is 0.05-0.7m
m, the number of copy generations (successive copyability) and the amount of contamination with good character reproducibility when the AC development bias frequency was changed from 4.5 to 21 KHz. The values in Table 1 are picked up and shown in FIGS.

[0052]

[Table 1]

The condition that the character reproducibility is good up to the fifth generation is that Dsd is 0.1 to 0.5 mm and f is less than 21 KHz.
On the other hand, the condition that the contamination is 0.8 wt% and does not adversely affect the hue of the other color toner and the color tone fidelity is good is as follows.
Dsd was 0.05 mm or more and f was 5 KHz or more.

Therefore, the conditions for good character reproduction and contamination were Dsd in the range of 0.1 to 0.5 mm and f in the range of 5 to 20 KHz.

Evaluation method (b) Successive copyability 5.5 points The copy copy of Japanese characters was enlarged, and the number of copy generations capable of maintaining a good state in which it was not blurred and was hardly broken was visually determined.

(B) Contamination First, the amount of toner adhered to the area of the A4 tip 50 mm is 0.7 to 0.8 mg.
A solid image of / cm ² is formed on the drum, and then the developing sleeve of the developing machine containing only the carrier is recharged and the developing bias of the developing machine is applied in the unexposed state. After repeating this 500 times, the concentration of the toner mixed in the carrier was taken as the contamination amount.

Example 2 Development conditions and developers are as shown below.

Others were the same as in Example 1, and the evaluation was performed in the same manner.

AC development bias rectangular wave The peak-to-peak voltage V _PP is in the range of 0.27 to 3.7 KV so that the maximum toner development amount is almost the same (about 0.4 to 0.5 mg / cm ² ) according to the change of Dsd. I adjusted it with.

Toner diameter d _T = 5 μm, toner concentration T _C =
5 wt% Table 2 shows examples and comparative examples when 5 μm toner is used. Based on these data, the relationship between Dsd and the character reproducibility is shown in FIG. 5, and the relationship between the AC bias frequency f and the contamination amount is shown in FIG.

[0061]

[Table 2]

The condition that the character reproducibility was good up to the fifth generation was that Dsd was 0.1 to 0.5 mm and f was less than 21 KHz. If Dsd is smaller than 0.1, a part of the developer is connected to cause "sweep" to disturb the image. On the other hand, if it is larger than 0.5 mm, the inheritance copyability of the characters is deteriorated and some of the characters are blurred. f is 21 KHz
Even if it is larger, it will be the same and will be blurred.

On the other hand, since the amount of contamination that does not adversely affect the hue of the other color toner was about 0.6 wt%, the condition for satisfying this is that Dsd is 0.05 mm or more and f
Was over 5 KHz.

Therefore, the conditions for good character reproducibility and contamination are Dsd of 0.1 to 0.5 mm and f of 5
It was in the range of ~ 20KHz.

[0065]

According to the development mode of the present invention, the
It has an excellent effect that it is possible to reproduce an image with high succession in copying character images and high color tone fidelity.

[Brief description of drawings]

FIG. 1 is a sectional view of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged view of a developing device for explaining a developing aspect of the present invention.

3A and 3B are relationship diagrams showing the characteristics of the embodiment when d _T = 8.5 μm.

4A and 4B are relationship diagrams showing characteristics of a comparative example when d _T = 8.5 μm.

5A and 5B are relationship diagrams showing the characteristics of the embodiment when d _T = 5.0 μm.

6A and 6B are relationship diagrams showing characteristics of a comparative example when d _T = 5.0 μm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Development sleeve 3 Magnet body 4 Developer reservoir 5 Stirring rotor blade 6 Layer thickness regulation blade 7 Cleaning blade 8 Bias power supply 9 Safety resistance 10 Toner supply roller

Claims (4)

[Claims] 1. In the developing area where the surface of the photosensitive member and the surface of the developing sleeve are closest to each other, the developing area is sandwiched between the adjacent magnetic poles of the fixed magnet built in the developing sleeve, and the magnetic field lines generated between the adjacent magnetic poles are the magnetic fields of the developing area. In an image forming apparatus equipped with a plurality of developing devices, each of which produces a magnetic field parallel to a tangential plane in contact with the developing sleeve surface, an alternating current of 5 to 20 KHz and 1.0 to 2.5 KV _PP is applied between the photoconductor in the developing area and the developing sleeve. A multicolor image forming method in which an oscillating electric field in which a component and a DC bias component are superimposed is applied and a two-component developer is used to perform non-contact development on a photoconductor for each of the plurality of developing devices. 2. The multicolor image forming method according to claim 1, wherein the gap between the photosensitive body surface and the developing sleeve surface in the developing area is set to 0.1 to 0.5 mm. 3. The magnetic field strength produced by the magnetic force lines in the direction of the normal to the surface of the developing sleeve passing through each of the adjacent magnetic poles of the magnets contained in the developing sleeve is 400 to 800 gauss, and the lines of magnetic force in the direction of the normal are developed. The method for forming a multicolor image according to claim 1 or 2, wherein an opening angle between the regions is 30 to 70 degrees. 4. The magnetic carrier particle of the two-component developer has a diameter of 30 to 80 μm, and has a magnetic susceptibility of 20 to 50 emu / g under a magnetic field of 500 oersteds. Multicolor image forming method.