JPH03138674A - Developing device - Google Patents

Abstract

PURPOSE:To prevent developing irregularities generating in an image forming body and carrier attachment by using a magnet rotor, wherein N and S magnets are alternately arranged, for a developer conveying carrier, forming a developer layer on the surface and developing a latent image on the surface of an image forming body. CONSTITUTION:The magnet rotor 102 employs a plastic magnet rotor including N and S magnets as magnetic members placed on an Al roller for the developer conveying carrier. A developer regulating body 104 composed of a magnetic bar close to or abutting on the periphery of the magnet rotor 102 faces the periphery of the magnet rotor 102 provided close to the image forming body 1, and a developer thin layer is formed. As the image conveying carrier 102 rotates, a latent image on the image forming body 1 is non-contact developed in a developing area 2 to form a toner image. A bias including an AC component is applied to the image conveying carrier 102 and the aluminum shaft of a rotating shaft via resistance element R and passed through a magnet part of low resistance, whereby a vibrating electric field is created between the image forming body an the surface of the magnet rotor. Thus, development irregularities generating in the image forming body can be prevented.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a developing device that converts an electrostatic latent image formed on an image forming body into a visible image, which is used in an electrostatic recording device such as a copying machine.

[Conventional technology]

Conventionally, a magnetic bluff development method is generally known as a development method using a developer containing a magnetic material. Below, the outline of the magnetic plan development method will be explained. A developer transporting carrier having a built-in fixed or rotatable magnet is provided at a position close to an image forming body made of a photoreceptor. When the developer is fully brought into contact with a part of the developer transport carrier and the magnet 7 or one or both of the developer transport carriers rotate, spikes of developer are formed on the circumferential surface of the developer transport carrier. The toner particles are attracted to the latent image of the image forming body, and the toner particles are attracted to the latent image of the image forming body, and the toner particles are attracted to the latent image of the image forming body. A visual image is formed. Since the development transport carrier has a built-in magnet, it has the disadvantage that the number of parts is increased and the driving method is complicated. On the other hand, it may be possible to simplify the groove path by using a magnet rotating body in which a magnet is used as a direct development transport carrier. When a one-component developer containing magnetic toner is used, a uniform developer layer can be formed on the magnetic rotor as disclosed in JP-A-61-42672. It is known from JP 60-254161 and U, S, P 4707428. The reason for this is thought to be that the magnetic force of the magnetic toner is small and the particle size is small. However, with magnetic toners, it is difficult to obtain color, charge stability, and developer layer stability, and it is necessary to use a two-component developer.

[Problems to be solved by the invention]

However, when a two-component developer consisting of a magnetic carrier and a toner is used, and the magnetic rotating body described above is used as a developer transport carrier, the pitch of the developer layer corresponding to the magnetic poles is formed, so the latent image formed on the image forming body is There are two problems: uneven development, which appears as a development pinch, occurs when the image is developed, and the carrier adheres to the image forming body. In view of the above problems, the present invention prevents uneven development and carrier adhesion that occur on an image forming body when a two-component developer made of a magnetic carrier is used and a magnetic rotating body is used as a developer transport carrier. An object of the present invention is to provide a developing device for the purpose of.

[Means to solve the problem]

The present invention achieves the above object by supplying a developer consisting of a magnetic carrier and toner to a developer transport carrier, and forming an oscillating electric field on the developer transport carrier to develop a latent image on the surface of an image forming body. In the developing device, the surface developer transport carrier is a magnetic rotating body in which magnetic bodies are alternately arranged in NS,
It is characterized in that a developer layer is formed on the surface of the image forming body to develop the latent image on the surface of the image forming body. Further, if the magnetic carrier is characterized in that the developer layer and the developer layer having an average particle diameter of 15 to 50 μm are provided at intervals, even more remarkable effects can be obtained.

[For use]

FIG. 1 is a block diagram showing a schematic configuration of a developing device according to the present invention. The developing device of the present invention is characterized in that it has a structure that particularly prevents development unevenness from occurring in the toner image formed on the image forming body when magnetic brush development is performed using only the magnetic rotating body. Magnet rotary body +02 employs a plastic magnetic rotary body formed by alternating NS magnetic poles provided with a thickness of 1 to 5 mm on an AO roller and containing a magnetic member such as ferrite as a developer transport carrier. This magnetic rotating body is made of a semiconductive material having a thickness of 10' to 10<12 >Ω·cm so that a sufficient developing electric field is generated when a bias is applied to the AQ roller. A developer transport body +04 consisting of a magnetic rod that is close to or in contact with the circumferential surface of the magnet rotating body 102 provided close to the image forming body 1 faces, forms a thin layer of developer, and forms a thin layer of developer. 102 is a developing device that employs a magnetic brush developing method configured to rotate in the direction of the arrow and non-contact develop the latent image on the image forming body l in the developing area 2 to form a toner image, thereby eliminating unevenness in the phenomenon. In order to do this, a bias having an alternating current component is applied to the aluminum shaft of the rotating shaft of the image carrying carrier 102 through the resistive element R, and the vibration is generated between the image forming body and the surface of the magnet rotating body by applying a bias having an alternating current component to the aluminum shaft of the rotating shaft and passing it through the low resistance magnet part. A developing bias circuit 120 that generates an electric field is provided. Here, the development pitch width will be explained. FIG. 2 is a conceptual diagram for explaining the development pitch width. In the figure, when the image forming body l on which a latent image has been formed is rotated in the same direction and at the same speed as the developer transport carrier 102, the developer 1 carried by the developer transport carrier 102 by magnetic force is The toner inside moves along the force of the developing electric field and adheres to the surface of the image forming body 1. The width to which the toner periodically adheres on the surface of the image forming body 1 is the development pitch width L1.
I will call it. This development pitch width L i (mm) is determined by the linear velocity V i, V m (mm/5ec) between the image forming member and the developer transport carrier, and the distance L NS (mm) between the magnetic poles on the developer transport member. In other words, the relationship of Li-(Vi/Vm) LNS is established.In order to eliminate this development pitch, the magnetic pole spacing distance LN
It is conceivable to reduce S or to reduce the Vi/Vm ratio (increase the rotational speed of the developer transport carrier). However, increasing the number of magnetizations causes a decrease in magnetic force, which causes carrier adhesion, and increasing Vm causes developer scattering and development directionality to become noticeable. Further, even if the development pitch becomes smaller, it will be more noticeable in the reproduction of halftones and halftone dots, and this problem has not fundamentally been solved. The present invention takes into account that the development pinch is caused by the periodic formation of the magnetic brush conveyed to the development section by the magnetic rotating body, which makes toner supply and development electric field non-uniform. This is a concrete example of eliminating development pitch unevenness by actively using electrical action that does not depend on action. The oscillating electric field employed in the present invention acts to return toner to the developer transport carrier 102 from areas where a large amount of toner has adhered, and in areas where toner has adhered, the toner is transferred to the image forming body.
It has the effect of acting to supply Here, what is noteworthy about two-component developers is that although the carrier transports the toner unevenly according to the magnetic poles, the oscillating electric field acts to pull or attract the toner from the carrier and the image forming body. As a result, it has the effect of making the development of the image forming body uniform. A major role in this is that the 1-ner is non-magnetic and is not affected by magnetism once it is separated from the carrier. The reason why the development pitch can be made uniform even if the development pitch is changed by using the oscillating electric field is thought to be that the above-mentioned uniformity effect is achieved in the moving direction of the image forming body l. In order to exhibit the uniformity effect, it is desirable that the development pitch width Li falls within a specified range experimentally. The conditions for this development pitch to disappear are the image forming body 1 and the magnet rotating body 102.
It was consistent with the average development width obtained by fixing and applying a development bias for a certain period of time. That is, it matched the average value of the development width when the magnetic poles N were opposed to each other and when the magnetic poles were opposed to each other. Although this value varied depending on the bias conditions, the maximum value was 5 mm. From the above, Ll is 5
It is preferably within mm. Even in contact magnetic plan development where the image forming body and the developer layer on the developer transport carrier are in contact with each other, the non-uniformity of the developer acts on the photoreceptor and similarly causes development pitch. Also in this case, the vibration of the toner has the effect of improving uniformity. In other words, the purpose is to make the toner developed by the oscillating electric field uniform. The conditions for this will be described below. (1) In order to achieve uniformity of toner, it is necessary that the development width be wide. That is, it is preferable that the phenomenon pinch width Li is 5 mm or less with respect to the development width on the magnetic pole and between the magnetic poles, which sets the development width, typically the average value thereof. (2) It is preferable that the oscillating electric field oscillates its frequency r 10 times or more with respect to the phenomenon pinch width Li. If the frequency of the oscillating electric field is not sufficient to oscillate 10 times with respect to the development pitch ll Li , toner uniformity will be insufficient and the toner image formed on the image forming body will be undulated. Expressing this mathematically, f≧10·(V i/L i). (3) It is preferable that the oscillating electric field sufficiently vibrates the toner. This oscillating electric field has the effect of causing the toner once attached to the image forming body to move in a reverse direction in the magnetic pole facing portion where toner tends to adhere, and promoting the movement of the toner to the image forming body between the magnetic poles. This condition is preferably 0.2≦VAc/df (v Ac/d -1500)/f≦1.0. Here, VAc and f are the amplitude (V) and frequency (Hz) of the AC component of the developing bias (7), and d is the gap between the image forming body and the magnet rotating body. (4) Carrier In the developing device of the present invention, the average particle size is 15 to 50 μm.
By using a developer consisting of a magnetic carrier and toner, the unevenness of the developer layer formed on the magnetic rotating body 102 is reduced. Furthermore, by using a high-resistance carrier, it is possible to make the developing electric field generated in the developing section uniform, to prevent discharge and leakage, and to form a high oscillating electric field. The developing device of the present invention employs contact and non-contact development, and more preferably, by employing non-contact development,
It is possible to prevent magnetic carrier from adhering to the latent image on the image forming body, and to perform development with a uniform toner density without development pitch unevenness.

【Example】

Next, embodiments of the present invention will be described based on the accompanying drawings. FIG. 3 is a block diagram showing a schematic configuration of an embodiment of the phenomenon device of the present invention. The image forming body 1 is a photoreceptor such as an OPC formed in the shape of a drum or a belt, rotates in the direction of the arrow at a predetermined linear velocity Vi, and forms an electrostatic latent image on its surface by being charged and exposed. By loading a developer consisting of a magnetic carrier and toner into the developing device 100, a low, steep, uniform height spike is formed on the developer transport carrier 102. The developing device 100 rotates in the opposite direction to a developer transport carrier 102 that transports the developer stored in a developer tank in a housing to a developing area, and rotates in the opposite direction to the developer transport carrier 102 to achieve an appropriate density. A supply roller 103 that supplies the developer of the same amount, a developer amount regulator 104 that regulates the amount of developer supported on the surface of the developer transport carrier 102, and a developer amount regulator 104 that regulates the amount of developer carried on the surface of the developer transport carrier 102; a sponge member 105 for scraping off the developer after development on the surface of the developer transport carrier 102, a scraper 106 for scraping off the developer after development, and first and second stirring members 109 and 110 for stirring the developing agent after development and the newly replenished toner. It has been established. Note that the first stirring member 109 and the @2 stirring member +10 are screw-shaped members having a left-handed helical angle and rotating in mutually opposite arrow directions. The toner and magnetic carrier transported to the rear side by the thrust of the second stirring member 110 are transferred to the first stirring member 109 side through the stirring partition plate +11 having a cutout at the rear side, and are transported to the front side by the thrust. During this time, the developer is sufficiently triboelectrically charged by the mixing action of the toner and carrier, and is deposited in a layer on the circumferential surface of the developer transport carrier 102 by the spongy supply roller 103 rotating in the direction of the arrow. The developer transport carrier 102 is a 20 m diameter AQ flora with a diameter of 14 mm and is formed by containing a magnetic material such as ferrite.
It is a magnetic rotating body in which magnetic poles of equal magnetic force are arranged alternately in NS on a cylindrical member made of a plastic material of 3 mm, and rotates at a predetermined linear velocity Vm in the same direction or in the opposite direction with respect to the image forming body 1. If Vm=Vi is set, since the developer transport carrier 102 is a 20I cylindrical member,
The development pinch radius Li is 5 mm or less, that is, the distance between magnetic poles LN.
In order to make S 5 mm or less, 12 or more NS alternating magnetic poles are magnetized on the magnet rotating body 102, and Vm=2Vi
In this case, in order to make the distance LNS between the magnetic poles 5 mm or less, the magnetic rotating body 102 must be magnetized with six or more alternate magnetic poles of NS. The magnetic rotating body 102 of this embodiment has V m −2V i (V i −100 mm/
5ec), 12 poles of NS alternating magnetic poles are magnetized, and the development pitch L1 is set to about 2.5 mm, satisfying the condition of 5 mm or less. Further, a developing bias circuit 1 applies a bias having an AC component of 3 Ktlz to the developer transporting carrier 102 via a resistive element R in order to widen the developing width.
20 is provided. This frequency is f≧10・(Vi/L
i) is satisfied. The developer amount regulating body 104 is a cylindrical rod-shaped member having rigid magnetism, and is fixed with a screw 107b via the spring member 108 of the housing 101, so that the developer transport carrier 1
A constant load is applied to 02 without intervening developer, and
The amount of developer supported on the developer transport carrier 102 is regulated by being pressed by the attractive force caused by the magnetic force induced by the developer transport carrier 102 . As a developer regulating method, it is insufficient to place a normal non-magnetic plate facing a rotating magnet at a distance in order to form a thin layer of developer. For this purpose, it is preferable to directly act on the magnet rotating body using a suppressing means such as the above-mentioned magnetic plate or magnetic bar, opposing means with a gap, or suppressing means such as an elastic plate made of rubber or the like. In particular, since a strong magnetic field acts on the magnetic pole opposing portion of the magnetic regulating means and the magnet rotating body due to magnetic action, that portion is likely to be thinned. This cancels out the effect of the magnetic brush becoming convex on the magnetic pole portion of the magnet rotating body, and makes the unevenness of the developer layer uniform. Further, it is desirable that the surface of the magnet rotating body has irregularities of 1 to 10 .mu.m for stable conveyance of the developer. After development, the developer layer formed on the developer transport carrier 102 is scraped off by a scraper 106 to remove the adhering developer. In the figure, a sponge roller 105 is disposed close to the scraper 106 and is driven to rotate on the upstream side in the developer transport direction. This prevents developer from accumulating on the scraper 106. It can be placed in contact with or in close proximity to the sponge roller 105. Alternatively, a magnetic bar or the like may be placed in contact with or in close proximity to each other. It is also desirable that these rotate. The distance between the developer transport carrier 102 and the image forming body l is 50 to 20
00 μm is preferred. If the surface distance between the developer transport carrier 102 and the image forming member l becomes too narrow than 50 μm, it will be difficult to form magnetic brush ears that uniformly develop the surface, and it will be difficult to form sufficient toner particles. It becomes impossible to supply the toner to the developing device, and stable development is no longer performed. Furthermore, if the gap exceeds 2000 μm, the opposing electrode effect will deteriorate, making it impossible to obtain sufficient image quality. Furthermore, it becomes necessary to apply high vibration VL and TL pressures during development, and carrier adhesion is likely to occur due to magnetic deterioration. In this way, if the distance between the developer transport carrier 102 and the image forming body l becomes extreme, it becomes impossible to appropriately set the thickness of the developer layer on the developer transport carrier and the developing electric field. When the distance is in the range of 50 μm to 2000 μm, the thickness of the developer layer and the developing electric field can be appropriately formed. Therefore, it is preferable to set the gap and the thickness of the developer layer to conditions such that the ears of the magnetic brush do not come into contact with the surface of the image forming body 1 without applying an oscillating electric field, and are as close as possible to the surface of the image forming body 1. . This is because carrier adhesion to the toner developed latent image, scratches due to friction of the magnetic brush, and fogging can be prevented. Furthermore, development under an oscillating electric field is performed using a magnet rotating body 10.
Preferably, by applying an oscillating bias voltage to 2. Further, as the bias voltage, a voltage that is a superimposition of a direct current voltage that prevents toner particles from adhering to non-image areas and an alternating current voltage that makes it easier for toner particles to separate from carrier particles is used. In the above-described apparatus, when the electrostatic image on the image forming body 1 is developed by setting the magnet rotating body 102 to the image forming body 1 so that the surface gap is in the range of 50 to 2000 μm, the magnet The magnetic brush formed on the surface of the rotating body 102 moves as the magnetic rotating body 102 rotates, thereby stably and smoothly passing through the gap between the image forming body 1 and the image forming body 1. This gives a uniform development effect to the surface of the toner, making it possible to develop with a stable high toner density. In order to prevent the occurrence of fog in which the developer is prevented from scattering and to improve the developing effect, an image forming body is provided in which the magnetic rotating body 102 has an alternating current component vibrated by the developing bias circuit 120 and the bias voltage is grounded. The voltage is applied between the base of No. 1 and the base of No. 1. As mentioned above, this bias voltage has a preferable DC component that prevents fogging, and an AC component that gives vibration to the magnetic brush to improve the developing effect. Note that normally a voltage approximately equal to the non-image area potential is used for the DC voltage component, and a voltage approximately equal to the potential of the non-image area is used for the AC voltage component.
z, preferably l-5kHz frequency and 100-50
A voltage with an amplitude of 00V is used. Note that if the frequency of the AC voltage component is too low, the development pitch will not be resolved, and if it is too high, the developer will not be able to follow the vibrations of the electric field, resulting in a decrease in development density and the inability to obtain clear, high-quality images. There is a tendency to say. In addition, the voltage value of the AC voltage component is also related to the frequency, but the higher the voltage value, the more the magnetic plan will vibrate and the more effective it will be. It also makes dielectric breakdown more likely to occur. However, the fact that the developer carrier particles are insulated by a resin or the like and further made spherical not only makes the developing electric field uniform but also prevents dielectric breakdown, and the occurrence of fog can also be prevented by using the DC voltage component. Note that the surface of the magnet rotating body +02 to which the AC Vl voltage is applied may be insulated or semi-insulated with a resin or oxide film. Although FIG. 3 shows a developer conveying method and an example of applying an oscillating bias voltage to the magnet rotating body 102, the developing method of the present invention is not limited thereto. The developing effect can also be improved by extending several electrode wires around the developing area between the magnetic brushes 1 and 2 and applying an oscillating voltage to them. In that case as well, a direct current bias voltage may be applied to the magnet rotating body 102, or oscillating voltages of different frequencies may be applied. Furthermore, the developing device of the present invention can be similarly applied to reversal development and the like. In that case, the DC voltage component is set to a voltage approximately equal to the receiving potential in the non-image background portion of the image forming body l. Furthermore, the developing device of the present invention can also be applied to a color image recording method in which a color image is formed by repeating latent image formation and development. The magnetic carrier preferably used in the present invention will be described below. Magnetic carrier particles improve the agitation performance of toner and carrier and the transportability of developer, and also improve the charge control performance of toner, which has the effect of making it difficult for toner particles and toner particles and carrier particles to aggregate together. However, in general, when the average particle size of the magnetic carrier particles is large, the electrostatic latent image is developed while being vibrated by an electric field because the ears of the magnetic carrier formed on the magnetic carrier +02 are rough. Even if you do, pinch unevenness tends to appear in the toner image. (2) Since the toner concentration in the panicle is low, problems such as a high concentration phenomenon not occurring occur. In order to solve this problem, the average particle size of the carrier particles can be reduced.
As a result of experiments, it was found that the effect begins to appear when the average particle size is 50 μm or less, and in particular, when the average particle size is 30 μm or less, the problem (①) does not substantially occur. In addition, the problem (2) can be solved by making the magnetic carrier finer particles, which increases the toner concentration in the ears and enables high-density development. However, if the carrier particles are too fine, (1) they will adhere to the surface of the image forming body together with the toner particles, or (2) they will easily scatter. These developments are also related to the strength of magnetization acting on the carrier particles and the resulting magnetization of the carrier particles, but generally speaking, a tendency gradually begins to appear when the average particle size of the carrier particles becomes 15 μm or less. , it becomes noticeable at 5 μm or less. A portion of the carrier particles adhering to the surface of the image forming body will be transferred onto the recording paper together with the toner, and the remaining portion will be removed from the surface of the image forming body along with the residual toner by a cleaning device such as a blade or a fabric brush. With conventional carrier particles made only of magnetic material, (1) the carrier particles migrate onto the recording paper;
There is a problem that carrier particles easily fall off, and (2) when the carrier particles remaining on the surface of the image forming body are removed by a cleaning device, the surface of the image forming body consisting of a photoreceptor is easily damaged. These problems (1) and (2) can be solved by forming magnetic carrier particles together with a substance that can be fixed to recording paper, such as resin. That is, by covering magnetic particles with a substance that can fix magnetic carrier particles to recording paper, or by covering magnetic particles with a substance that can fix magnetic particles to recording paper, or by covering magnetic particles with a substance that can fix magnetic particles to recording paper containing dispersed magnetic powder. By forming the carrier particles on the recording paper, the carrier particles attached to the recording paper are also fixed by heat and pressure, and when the carrier particles are removed from the surface of the image forming body 1 by the cleaning device, the carrier particles are also fixed on the image forming body 1. No more scratching the surface. In such magnetic carrier particles, the carrier particles have an average particle size of 5 to 15 μm or less, and even if the carrier particles may migrate to the surface of the image forming member 1 or the recording paper, the magnetic carrier particles as described in (2) above can be used. The problem causes little trouble in practice. Incidentally, if carrier adhesion occurs as in the case (2) above, it is effective to provide a recycling mechanism. From the above, the average particle size of the magnetic carrier particles is 50 μm.
Hereinafter, the thickness is preferably 5 μm or more, particularly preferably 30 μm or less, and 15 μm or more. Note that the average particle diameter is
It is the weight average particle diameter measured with a counter (manufactured by Coulter) and Omnicon Alpha (manufactured by Posh-Lomb). Such magnetic carrier particles are made of metals such as iron, chromium, nickel, cobalt, etc. as in conventional magnetic carrier particles, or compounds or alloys thereof, as magnetic substances.
For example, triiron tetroxide, γ-ferric oxide, chromium dioxide,
Ferromagnetic particles such as manganese oxide, ferrite, manganese-copper alloy, or the surface of these magnetic particles can be coated with styrene resin, vinyl resin, ethylene resin, rosin modified resin, acrylic resin, polyamide resin, Epoquine resin, Particles coated with a resin such as polyester resin or obtained by preparing a resin containing dispersed magnetic particles are subjected to particle size selection using a conventionally known average particle size selection means such as an air classifier. The spherical carrier has no directionality of magnetization, and a developer layer is formed uniformly. There are no edges in the carrier particles, and the electric field does not concentrate on the edges, so even if a high bias voltage is applied to the developer transport carrier, there are advantages such as blurring of the image due to discharge and breakdown of the bias voltage. have The fact that this high uniform bias voltage can be applied means that when development under an oscillating electric field in the present invention is performed by applying a bias voltage because it oscillates, it is possible to fully exhibit the effects described below. can. Further, the carrier particles that exhibit the above-mentioned effects have a resistivity of 10"Ωcm or more, particularly 101
Preferably, insulating magnetic particles are formed to have a resistance of 3 Ω·cm or more. This resistivity reduces the particle size to 0.5 cm2
After tapping it into a container with a cross-sectional area of
A load of l kg/cm2 was applied to the packed particles, and a voltage of 1000 V/cm was applied between the electrode that also served as the load body and the bottom electrode.
This value is obtained by reading the current value when applying a voltage that generates an electric field of cm. If this resistivity is low, not only will the non-uniformity of the developing electric field be emphasized, but also the bias voltage will be applied to the magnet rotating body 102. When this voltage is applied, charges are injected into the carrier particles, making it easier for the carrier particles to adhere to the surface of the image forming body, or for bias voltage breakdown to occur more easily. To summarize the above, the magnetic carrier particles used in the developing device of the present invention are spherical so that the ratio of the long axis to the short axis is 3 times or less, and there are no protrusions such as needle-shaped parts or etched parts. , the resistivity is preferably 10'Ω·cm or more,
It is particularly preferable that the resistance is 1013 Ω·cm or more. Such magnetic carrier particles are made of magnetic particles that are as close to spherical as possible and are coated with a resin. Alternatively, it can be produced by dispersing magnetic powder in a resin, pulverizing the solidified product, and then forming it into a bed shape, or by spray drying a mixed solution containing magnetic powder and resin. In order to restrain the carrier on the magnetic rotating body, it is preferable to set the surface magnetization of the magnetic rotating body to 400 to 1000 Gauss. Also, the saturation magnetization of the carrier is 20~80e
It is preferable to set it to mu/g. If the magnetization of the non-remagnet rotating body or the carrier is small, the uniformity of the magnetic brush improves, but if carrier adhesion occurs and the magnetization is large, the unevenness of the magnetic brush becomes large, making it difficult to eliminate development pitch unevenness. Next, regarding toner, as the average particle size of toner particles becomes smaller, the amount of charge steadily decreases in proportion to the square of the particle size, and the adhesion force such as 7 Anderwaalska becomes relatively large. This may make it difficult for the toner particles to separate from the carrier particles, or once the toner particles are attached to the image forming body 1.
If it adheres to the non-image area of the surface, it cannot be easily removed by rubbing with a conventional magnetic brush, causing fogging. In the conventional magnetic plan development method, such problems became noticeable when the average particle size of toner particles was 10 μm or less. The developing device of the present invention solves this problem by performing development using a magnetic brush under an oscillating electric field. That is, the toner particles to which the developer layer is attached tend to move away from the developer layer and move to the image area and non-image area of the surface of the image forming body 1 due to the electrically applied vibrations, and also become easier to separate from the developer layer. When the developer layer rubs the surface of the image forming body 1, the toner particles attached to the non-image area of the image forming body 1 can be easily removed or moved to the image area. When the agent layer thickness is formed to be thinner than the gap between the surface of the image forming body 1 and the magnet rotating body 102, toner particles with a low charge amount hardly migrate to the image area or non-image area, and the image Since the toner is rubbed against the surface of the image forming body 1, it is no longer attached to the image forming body 1 due to frictional electrification, and toner particles having a particle size of about 1/7 m can now be used. Therefore, it is possible to obtain a clear toner image with good reproducibility in which the electrostatic latent image is faithfully developed. Furthermore, since the oscillating electric field weakens the bond between toner particles and carrier particles, adhesion of carrier particles accompanying toner particles to the surface of the image forming member is also reduced. In particular, the thickness of the developer layer is set to be thinner than the gap between the surface of the image forming body and the surface of the rotating magnet 102.
In this case, carrier adhesion to the image forming body 1 is also reduced. On the other hand, as described above, under the alternating magnetic field caused by the rotation of the magnet rotating body 102, the bond between developer particles is weakened, making it easier for the developer to scatter, so it is necessary to reduce the centrifugal force of the developer toward the development area. be. Therefore, it is desirable that the linear velocity of the magnet rotating body 102 is 1 to 3 times the linear velocity of the image forming body. On the other hand, as the average particle size of the toner increases, the roughness of the image becomes more noticeable as described above. Normally, toner with an average particle size of about 20μII+ is not a problem in practice when developing paper sheets lined up with a pinch of about 10 lines/mm.However, if fine particles with an average particle size of 10μm or less are used The resolution has been significantly improved, and it is now possible to produce clear, high-quality images that faithfully reproduce the differences in shading. For the above reasons, the average particle size of toner is 20μ.
A suitable condition is less than m, preferably less than 10 μm. Further, in order for the toner particles to follow the electric field, it is desirable that the average charge amount of the toner particles be larger than 1 to 3 μC/g (preferably 3 to 300 μC/g). Particularly when the particle size is small, a high amount of charge is required. Such toner can be obtained in the same manner as conventional toner. That is, it is possible to use a toner in which spherical or amorphous nonmagnetic or magnetic toner particles in conventional toners are sorted by an average particle size sorting means. Among these, it is preferable that the toner particles are magnetic particles containing only a small amount of magnetic particles. In particular, it is preferable that the amount of magnetic fine particles does not exceed 30% by weight in the L.Qi particles. If the toner particles contain magnetic particles,
Since the toner particles are influenced by the magnetic force of the magnet included in the magnetic rotating body, the uniform formation of the magnetic brush is further improved, fogging is prevented, and toner particles are less likely to scatter. Become. However, if the amount of magnetic material contained is too large, the magnetic force between the carrier particles and the carrier particles becomes too large, making it impossible to obtain a sufficient developing density. It becomes difficult to control triboelectric charging, toner particles are easily damaged, and they tend to aggregate with carrier particles. In particular, in the case of color toners, it is preferable to use non-magnetic toners that do not contain magnetic substances. Further, the toner used in the present invention is preferably spherical. The spherical shape of the i-toner has favorable effects on improving the fluidity of the toner, stirring, transporting, and charging the developer. The spheroidization of the toner can be carried out by known methods such as granulation polymerization and treatment with hot air. As described above, the toner preferably used in the developing device of the present invention uses the resin described above for the carrier and furthermore fine particles of magnetic material, to which a coloring component such as carbon and a charge control agent, etc. are added as necessary. The toner particles are processed into spherical particles having an average particle diameter 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. In the developing device of the present invention, it is preferable to use a developer in which carrier particles and toner particles are mixed in the same ratio as in a conventional two-component developer, as described above. A fluidizing agent for improving the fluidity and sliding of the particles, a cleaning agent for cleaning the surface of the image forming body, and the like are mixed. As a fluidizing agent, colloidal silica, inorganic fine particles such as titanium oxide fine particles, and PMM
Organic fine particles such as A and the like can be used, and fatty acid metal salts and the like can be used as the cleaning agent. Figure 4 shows the linear velocity of negatively charged OPC at 1001 m/s.
The gap d between the image forming body l moving at ec and the magnet rotating body 102 moving at the same speed and in the same direction is 1-0 mm, the developer layer is 0.5 mm, and the charging potential of the image forming body l is -600 V. The amplitude VAC of the AC component when the DC component of the developing bias is set to -500V and the frequency of the AC component is set to 1 kHz.
The graph shows the relationship between the toner image density and the image density of the toner image that is reversely developed on the exposed portion (potential is approximately OV) on the image forming body 1. Here, the magnet rotating body has a diameter of 15 mm. Number of magnetic poles: 10. The surface magnetic field is 400 Gauss. The carrier is an insulating spherical carrier made of ferrite particles coated with resin (particle size 25μm, resistance 1014Ω).
"cm, magnetization 50 emu/g). On the other hand, a spherical toner with a particle size of 5 μm was used. Anrica was used as an external additive. The toner concentration was adjusted to 10 wt% as a developer. Horizontal axis EAC is the value obtained by dividing the amplitude of the AC component by the gap d.
Curves A, B, and C shown in the figure have average charge amounts of -30μC/g, -20μC/g, and -15μ, respectively.
These results were obtained using a material whose charge was controlled to C/g. The three curves A, B, and C all have the amplitude E of the alternating electric field.
When the AC was 200 V/mm or more, the effect of the alternating current component appeared, and when the AC was 2500 V/mm or more, it was observed that the image density formed on the image forming body 1 decreased. Figure 6 shows the frequency of the AC component of the developing bias at 2,5 kH.
z, under the same conditions as in the experiment shown in Figure 4. It shows the change in image density when the amplitude EAC of the alternating current electric field is changed. According to this experimental example, the amplitude EAc of the alternating current electric field is 50
When the voltage exceeds 0V/mm, the image density increases and the voltage exceeds 4kV/mm.
When the thickness exceeded mm, it was observed that the density of the image previously formed on the image forming body 1 decreased and a part of the toner image was destroyed. As can be seen from the experimental results shown in Figs. 5 and 6, the image density changes greatly after reaching a certain value of the AC electric field amplitude EAC, but this value varies depending on the average band of the toner.
Does not depend too much on 5Lfire. The reason for this can be considered as follows. In other words, in a two-component developer, the toner is charged by friction with the carrier and mutual friction between the toners, and the amount of charge of the toner is distributed over a certain range, and the toner with a relatively large amount of charge is preferentially charged. It is thought that it will be developed. Even if the average charge amount is controlled by charge control, and even if the charge amount of the toner that is actually developed is controlled, there is no difference in the average charge amount of the toner that is actually developed; It is thought that the difference in the realized image characteristics is observed to be small. Now, when the same experiment as in FIGS. 4 and 5 was carried out while changing the conditions, the results shown in FIG. 7 were obtained when the relationship between the amplitude EAC of the alternating current electric field and the frequency f was summarized. In FIG. 7, the area indicated by a is an area where development pitch unevenness is likely to occur depending on the frequency, the area indicated by b is an area where the effect of the alternating current component is not suppressed and the development pitch unevenness is not resolved, and C
The region indicated by 1 is a region where the toner adhering to the image forming body 1 tends to return from the image forming body 1 to the magnet rotating body 102 and has a low density, and is also a region where breakdown is likely to occur. d
, e is a region where the effect of the alternating current component appears, high density is obtained, and there is no development pitch unevenness, and among these, e is a particularly preferable region where neither image density nor image unevenness occurs. This area e
is an electric field condition in which the image density is saturated as the electric field strength EAC increases, and the subsequent image density is slightly decreased. The area of 2 Jt et al. is divided by straight lines g, h, and i. These g. h, 1 give experimentally equal concentrations on the line, respectively. This result shows that there is an appropriate range for the amplitude EAC of the alternating current electric field and its frequency f in order to develop a toner image with an appropriate density, and this is thought to be due to the reasons described below. . In a region where the image density tends to increase with respect to the amplitude EAC of the alternating current electric field, for example, in the density curve A of FIG. 4, the amplitude E of the alternating electric field
In the region where AC is 0.2 to 1.2 kV/mm, the AC component of the developing bias has a large contribution due to the force acting on the toner in the direction exceeding the threshold for flying from the sleeve 20. As the toner becomes stronger, more and more toner is used for development. Therefore, as the amplitude EAC of the AC electric field increases, the image density increases. For this reason, the influence of the presence or absence of magnetic poles on development in the developing section of the magnet rotor cannot be sufficiently resolved. On the other hand, in a region where the image density is saturated with respect to the amplitude EAC of the AC electric field, for example, curve A in FIG. 4, the amplitude EA of the AC electric field (
Regarding the region beyond that including the vicinity of 1.2 kV/mm, this development can be explained as follows. That is, it is considered that in this region, as the amplitude EAC of the alternating current electric field increases, the toner vibrates more strongly, causing the toner attached to the image forming body l to fly backwards. Therefore, it is possible to eliminate the influence that the presence or absence of a magnetic pole in the developing section of the magnet rotating body has on the development. In such a situation, it is also important that the amount of toner that can be supplied to the development area in a certain period of time is limited. For this reason, the image density is considered to be saturated with respect to the amplitude EAC of the AC electric field. These conditions are preferable for eliminating development pitch unevenness. When the amplitude EAC of the alternating current electric field further increases, the image forming body 1
A phenomenon also occurs in which the charge on the surface of the toner leaks, making it difficult for the toner to be developed. In reality, it is considered that these factors combine to keep the image density constant even if the amplitude EAC of the alternating current electric field increases. If the amplitude EAC of the alternating current electric field is increased to, for example, the amplitude φa of 2.5 kV/mm or more under the conditions where curve A in FIG. The larger the alternating current component is, the more unevenness due to carrier adhesion appears, to a degree similar to that of the broken line. Based on the above experimental results, the inventor determined that, during each development, the amplitude of the AC component of the developing bias is vAc(v), the frequency f
(Hz) and the gap d (mm) between the image forming body l and the magnet rotating body 102, 0.2≦VA(/(d-f)BvAc/d)-1500)/r(,,1 ,0
It was concluded that if development is carried out under the conditions that are satisfied, development can be carried out on the image forming body 1 without any unevenness at an appropriate density. In order to obtain uniform and sufficient image density, it is particularly desirable that 0.8≦V Ac/(d−f ). [Effects of the Invention] As explained above, the present invention supplies a two-component developer consisting of a magnetic carrier and a toner to a developer transport carrier,
In a developing device that develops a latent image on the surface of an image forming body by applying an alternating current voltage to the developer carrying body, development unevenness that occurs on the image forming body when a magnetic rotating body is used as the developer carrying body. It is possible to provide a developing device that can prevent this from occurring.

[Brief explanation of the drawing]

FIG. 1 is a brochure diagram showing a schematic configuration of a developing device of the present invention, FIG. 2 is a conceptual diagram for explaining the developing width, and FIG. 3 is a schematic diagram of an embodiment of a developing device of the present invention. The block diagrams, FIGS. 4 and 5 are diagrams showing the relationship between image density and the developing electric field, and FIG. 6 is a diagram showing the relationship between the frequency and the developing electric field. l...Image forming body 100...Developing device 102...Magnetic rotating body 103 as a developer transport carrier...Sponge roller 106...Scraper 120...Developing bias circuit D...Developer T...toner layer

Claims (3)

[Claims] (1) In a developing device that supplies a developer consisting of a magnetic carrier and toner to a developer transport carrier, and develops a latent image on the surface of an image forming body by forming an oscillating electric field on the developer transport carrier, the developing device A developing device characterized in that the agent transport carrier is a magnetic rotating body in which magnetic bodies are alternately arranged in NS, and a developer layer is formed on the surface of the carrier to develop a latent image on the surface of the image forming body. (2) The developing device according to claim 1, wherein the magnetic carrier has an average particle size of 15 to 50 μm. (3) The developing device according to claim 1 or 2, wherein the image forming member and the developer layer on the developer carrying member are provided with a gap between them.