JPS61166558A - Image forming device - Google Patents

Abstract

PURPOSE:To make an image forming device small-sized and low-cost by sharing a partial power source of bias power sources among plural developing devices. CONSTITUTION:A power source 39 applies a bias voltage including an oscillating voltage component as occasion demands to a developing sleeve 31 through a protective resistance 40 to generate the electric field which controls the motion of a toner between the developing sleeve 31 and an image forming body 1. This power source 39 is constituted by connecting a DC bias power source 39a and an AC bias power source 39b in series, and the bias power source 39 is shared among developing devices 5-8. The resistance value of the protective resistance 40 is changed to adjust the voltage applied to the sleeve 31.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an image forming apparatus, and more specifically, the present invention relates to an image forming apparatus, and more specifically, the present invention relates to an image forming apparatus that repeatedly forms and develops an electrostatic image on an image forming body. The present invention relates to an image forming apparatus that forms a toner image.

Prior Art As a color image forming method as described above, Japanese Patent Application Laid-Open No. 1986-
Methods described in Japanese Patent Application Laid-open No. 144452, Japanese Patent Application Laid-Open No. 116553/1982, and Japanese Patent Application Laid-open No. 58-11-554 are known.

An image described in JP-A-56-144452 is formed and developed with a first developing device, and then an electrostatic image is formed on the same charged surface with a second exposure means, and then the image is developed. A method of developing with a second developing device, further forming an electrostatic image on the same charging surface with a third exposure means, and developing it with the third developing device to form a color image on an image forming body. Therefore, a separate exposure means is required for each repeated electrostatic image formation, which not only increases the size and cost of the image forming apparatus, but also
The synchronization of the exposure of each exposure means to the image forming body is also related to the installation position of each exposure means, so there are problems in that synchronization control is troublesome and color shift is likely to occur.

Further, each development in this method is performed by a forced development method in which toner charged to the same polarity is attached to an electrostatic image in which the potential of the exposed portion is lower than the potential of the background portion. In this forced development method, a toner charged to the same polarity as that of the image forming member is used as a developer so that the toner does not adhere to the background area.

Therefore, in the reversal development method, the toner is repelled by the background potential and fog is less likely to occur, but at the same time, the toner also adheres to the electrostatic image, making it difficult to obtain a sufficient developed density. The method described in Japanese Patent Application Laid-Open No. 56-144452 is a non-contact method in which the second and subsequent development by the reversal development method is performed without bringing the developer layer formed in the developing device into contact with the surface of the image forming body. This method uses jumping development conditions, and according to this method, it is difficult to obtain sufficient developed density unless a strong bias voltage is applied to the developing device to force the toner to adhere to the electrostatic image. In addition, stains are likely to occur due to toner scattering, and if a strong bias voltage is applied to the developing device, the bias voltage may leak to the image forming body, etc.
There is a problem in that toner of another color tends to adhere to a previously developed toner image or toner tends to adhere to the background area.

JP-A-58-116553 and JP-A No. 58-1165
The method described in Japanese Patent Application Laid-open No. 56-144452 is substantially the same as that in Japanese Patent Application Laid-Open No. 144452/1983 in that the electrostatic image formation and development are performed using different devices each time the image is formed. However, it similarly has the problems of being large and expensive, making it difficult to control the exposure synchronization of each exposure means, and easily causing color shift. However, in the method described in JP-A-58-116554, each development by the reversal development method is performed under contact development conditions in which a developer layer formed in a developing device rubs the surface of the image forming body. In addition, it is possible to obtain a sufficient developed density in the reversal development method, thereby alleviating the problem that the toner easily scatters, and the method described in JP-A-58-116553. Furthermore, in the second and subsequent electrostatic image formations, the surface of the image forming body is recharged before exposure using a charger installed before each exposure means, thereby making it possible to This method differs from the method described in JP-A-56-144452 in that it prevents toner of a different color from adhering to areas to which toner has adhered during subsequent development. However, in these methods, since the second and subsequent developments are also performed under contact development conditions, the toner adhered in the previous development may be displaced in the subsequent development, or the toner may be mixed into the developer of the subsequent development device. There is a big problem that it is easy to get mixed with other substances.

The applicant first solved the problems of the above-mentioned conventional method, made it possible to reduce the size and cost of the device, made it easy to control the synchronization of image exposure, and obtained sufficient developed density by non-contact jumping development. has proposed a color image recording method in which the formation of electrostatic images is repeated using the same device (Japanese Patent Application No. 184381/1983) as an image forming method that can prevent mixed adhesion of toners of different colors.

By the way, in conventional image forming apparatuses, a bias power supply for applying AC bias to the developing device is attached to each developing device, and it is conceivable to turn these on and off individually. A high-voltage power supply for bias is required depending on the number of
If you try to shorten the lead wires to prevent AC power loss, you will be subject to placement constraints. ), (iii) AC high-voltage power supplies are expensive, resulting in high costs. The problem remains.

C. Purpose of the Invention It is an object of the present invention to provide an image forming apparatus that solves the above-mentioned remaining problems, facilitates design, and enables further downsizing and cost reduction of the image forming apparatus. It is said that

2. Structure of the invention, that is, the present invention provides an image forming apparatus having a plurality of developing devices using a developing bias power source, in which at least one of the bias power sources is shared by the plurality of developing devices. The present invention relates to an image forming apparatus characterized in that:

Bias power supplies include DC power supplies and AC power supplies, and the above-mentioned "sharing" includes what a DC power supply does, but sharing an AC power supply does not include the above (i), (
This method is particularly effective in solving problems 11) and (iii).

E, Example Hereinafter, the present invention will be explained in detail with reference to illustrated examples.

In the recording device shown in FIG. 1, 1 is a drum-shaped image rotating in the direction of the arrow. 2 is a charger that uniformly charges the surface of the image forming body 1; 4 is image exposure for each color of a color image; 5 to 8 are toners of different colors such as yellow, magenta, cyan, and black; The developing devices used as developers, 9 and 10 are used as necessary to facilitate the transfer of a color image formed by superimposing a plurality of color toner images onto the recording medium P on the image forming body 1. 11 is a transfer device, 12 is a fixing device for fixing the toner image transferred to the recording medium P, and 13 is one or both of a static elimination lamp and a corona discharger for static elimination. A static eliminator 14 consisting of a combination adheres to the surface of the image forming body 1 after the color image has been transferred to remove residual toner on the surface, and by the time the first development has been performed reaches the surface. is a cleaning device having a cleaning blade and a fur brush that are separated from the surface of the image forming body 1.

Here, the charger 2 may be a charger such as the one shown in the figure, which can provide a stable charge with less influence from the previous charge, especially if the charger 2 superimposes charge on the surface of the image forming body 1 that is already charged. It is preferable to use a Scorotron corona leaver. In addition, in the case of a recording device that uses a drum-shaped image forming body 1 like this recording device, the image exposure 4 is performed by filtering slit n light such as that used in ordinary monochrome flag/electrophotographic copying μ. It is also possible to use a laser beam scanner that is filtered for each color, but in order to record clear color images, it is preferable to use a laser beam scanner as shown in FIG.

The laser beam scanner shown in FIG. 2 is a laser beam emitted from a laser 21 such as a He-Ne laser, which is 0N10FFed by an acousto-optic modulator 22, deflected by a mirror scanner 23 consisting of an octahedral rotating polygon mirror, and then imaged. Image exposure 4 is formed by scanning the surface of the image forming body 1 at a constant speed through the f-theta lens 24. Note that 25 and 26 are mirrors, and 27 is a lens for enlarging the diameter of the beam incident on the imaging r-θ lens 24 in order to reduce the diameter of the beam on the image forming body 1. 2nd for forming image exposure 4
If a laser beam scanner like the one shown in the figure is used, it is possible to easily form electrostatic images of different colors in a shifted manner, as will be described later, and it is possible to record clear color images as desired. but,
The image exposure 4 is not limited to dot exposure using light or a laser beam on a slit as described above;
It may be obtained using EDJPcRT, liquid crystal, or optical fiber transmission material.

In a recording apparatus in which the image forming body can take a flat state such as a belt shape, the image exposure can also be flash exposure.

Further, the developing devices 5 to 8 preferably have a structure as shown in FIG. 3.

In FIG. 3, 31 is a developing sleeve made of a non-magnetic material such as aluminum or austenitic stainless steel;
32 is a magnet body provided inside the developing sleeve 31 and has a plurality of magnetic poles in the circumferential direction; 33 is a layer thickness regulating plate that regulates the thickness of the developer layer formed on the developing sleeve 31; and 34 is a developing sleeve. 31 is a scraper blade that removes the developer layer after development from above; 35 is a stirring rotor that stirs the developer in the developer reservoir 36; 37 is a toner hopper;
8 is a toner replenishment roller that has a recess on its surface for toner to enter and replenishes toner from a toner hopper 37 to a developer reservoir 36; 39 a developing sleeve 31 via a protective resistor 40;
A power source for applying a bias voltage including an oscillating voltage component in some cases to the developing sleeve 31 and forming an electric field for controlling the movement of the toner between the developing sleeve 31 and the image forming body 1;
A DC bias power supply 39a and an AC bias power supply 39b are connected in series, and as shown in FIG. 1, the bias power supply 39 is shared by each developing device 5, 6, 7, and 8. The protective resistor 40 is also used to adjust the voltage applied to the sleeve 31 by changing its resistance value.

FIG. 3 shows that the developing sleeve 31 and the magnet body 32 rotate in the directions of the arrows, but even if the developing sleeve 31 is fixed, the magnet body 32 is fixed, or the developing sleeve 31 and the magnet body 32 are fixed, The sleeve 31 and the magnet body 32 may rotate in the same direction. When the magnet body 32 is fixed, normally, in order to make the magnetic flux density of the magnetic pole facing the image forming body 1 larger than the magnetic flux density of other magnetic poles, the magnetization is strengthened or a magnetic pole of the same or different polarity is attached thereto. The two magnetic poles may be placed close to each other.

In such a developing device, the magnetic pole of the magnet body 32 is usually 500.
It is magnetized to a magnetic flux density of ~1500 Gauss, and its magnetic force attracts the developer in the developer reservoir 36 to the surface of the developing sleeve 31, and the thickness of the attracted developer is regulated by the layer thickness regulating blade 33. A developer layer is formed, and the developer layer moves in the same direction as the rotation arrow direction of the image forming body 1 or in the opposite direction (the same direction in the figure), so that the surface of the developing sleeve 31 is brought into contact with the surface of the image forming body 1. The electrostatic image on the image forming body 1 is developed in the opposing development area, and the remaining part is left on the scraper blade 3.
4, the developer sleeve 31 is removed from the surface of the developer sleeve 31 and returned to the developer reservoir 36. The development is repeated in order to superimpose the color toner images, at least for the second and subsequent development, so that the toner attached to the image forming body 1 in the previous development will not be displaced in the subsequent development. It is preferable to use non-contact jumping development conditions. FIG. 3 shows a state in which development is performed under non-contact jumping development conditions.

The above-mentioned "non-contact" means that there is no potential difference between the developer chief sleeve 31 and the image forming member 1 (the image forming member is not charged and no developing bias is applied), and the two are spaced apart from each other by a predetermined distance. This means that they are arranged opposite each other so that the developer does not come into contact with the image forming body 1.

At the time of development, an oscillating electric field is generated at the opposing positions due to a bias in which direct current and alternating current are superimposed, and the developer flies from the developing sleeve 31 to the image forming body 1 while being loosened, and is deposited on the image forming body 1. A developer image is formed. By doing this, damage to the developer image (for example, a toner image) that has already been formed on the image forming body 1 during the second and subsequent development can be avoided. It is possible to avoid the occurrence of color mixture due to the developer flowing back into the developer transport carrier 2 and mixing into the subsequent developing device which stores a developer of a different color from the preceding developer.

Furthermore, the developing devices 5 to 8 use non-magnetic toner, which does not require the toner to contain a black or brown magnetic substance, can obtain a toner with a clear color, and can easily control the charging of the toner. It is preferable to use a so-called two-component developer which is mixed with a magnetic carrier. Details of the developer will be described later.

The above is the configuration of the developing device preferably used in the image forming apparatus of the present invention, but the present invention is not limited thereto.
No. 6-18659, No. 56-144452, No. 58-
You may use the developing device as described in each publication of 116553-116554. However, Japanese Patent Application No. 58-57446 and No. 5B-96 filed earlier by the applicant
It is preferable to use non-contact jumping development conditions using a two-component developer as described in the specifications of Nos. 900-96903 and 58-97973.

In this example, even if any one of the developing devices 5, 6, 7, 8 shown in FIG. The developing device is, for example, kept away from the image forming body 1 so that the developer does not fly to the image forming body 1, or the sleeve 31 is
It is necessary to take measures such as providing a developer stripping blade (not shown) that can come into contact with and detach from the developer to stop the developer supply.

The structure of the bias power supply is shown in the block diagram in FIG. 4, and the other parts are the same as those of the first embodiment.

Since the timing at which bias needs to be applied to each developing device is different, the bias power supply shown in FIG. This is done so that the bias is applied only to the developing device during development.

Using such an apparatus, images were recorded and formed according to the timing chart shown in FIG. Switching is preferably performed when the AC bias shown in FIG. 5 is not applied.

In addition, the applied bias voltage (''i]! flow component, waveform,
frequency) can also be programmed independently for each electrostatic image. In addition, by detecting the potential of each electrostatic image and the developing device, and feeding hacking the detection results,
Image formation can be performed under optimal conditions.

An example of the image forming process in the above embodiment 1.2 is shown in a flowchart as shown in FIG. In the figure, the second image exposure is shown, and the subsequent steps are omitted.

Figure 6 shows that an electrostatic image is formed by an electrostatic image forming method in which the exposed part becomes an electrostatic image and the non-exposed part becomes a background part, and development is performed by using toner that is charged with the opposite polarity to the background part. 1 illustrates an example of the invention being carried out. This is the first
According to the recording apparatus shown in the figure, the surface of the image forming body 1 in an initial state, which has been neutralized by the static eliminator 13, cleaned by the cleaning device 14, and has a potential of O, is charged by the charger 2 in the first rotation. A first charge is applied to the charged surface as shown in FIG.
Rotational exposure is performed, and the electrostatic image obtained thereby is developed for the first time by the developing devices 5 to 8 that use a developer of a color toner corresponding to the first image exposure 4, and the toner T is Since the potential of the electrostatic image that has fallen due to adhesion is still lower than the background potential, a second charge is uniformly applied again by the charger 2 in the second rotation (here, the static eliminator 13
Charging may be performed after the surface potential of the image forming body 1 is set to O by uniformly removing the charge using a charge removal lamp (only a charge removal lamp may be used). ) A second image exposure is performed on the charged surface by image exposure 4 for a color different from the previous one so that the potential of the electrostatic image area becomes approximately O, and the obtained electrostatic image is developed with a toner of a color corresponding to the image. toner T by another developing device using
A second development is carried out by ``, and the third and fourth electrostatic image formation and development are repeated in the same manner, and a fourth development is carried out to form a color image in which color toner images are superimposed. When the image forming member 1 is rotated, the pre-transfer charger 9 and the pre-transfer exposure lamp 10 are operated until the image has passed, and then the transfer device 11L transfers the color image to the recording material P which is fed in synchronization with the rotation of the image forming member 1. The transferred color image is fixed on the recording medium P by the fixing device 12, and the surface of the image forming body 1 to which the color image has been transferred is neutralized by the static eliminator 13 and cleaned by the cleaning device 14, so that the initial state is This is an embodiment of the present invention in which one cycle of color image recording is completed by returning to the state. That is, the charging for each electrostatic image formation is performed by the charger 2, and the image exposure is also performed by the same slit exposure device equipped with filter switching means or the same exposure device created by the laser beam scanner shown in FIG. 2, for example. Because the process is performed by be exposed. Note that the charge removal by the charge remover 13 between the previous development and the next charge can be omitted. In order to avoid color mixing, it is preferable to set the DC bias in the development process to a higher value in later stages. Correspondingly, the charging potential may also be set higher in sequence.

Details of the image forming conditions in Example 1.2 are as follows.

The image forming body 1 had a CdS photoreceptor surface layer, and its one circumferential speed was 1801 m/sec. This image forming body 1
The surface of the sample was charged to -500 V using a charger 2 using a scorotron corona discharger, and the charged surface was exposed to laser light corresponding to the blue component of the image. As a result, the image forming body 1
A background area was formed in which the electrostatic image potential of the exposed area was -50V and the potential of the non-exposed area was -500V. This electrostatic image was first developed using a developing device 5 as shown in FIG.

The developing device 5 contains 50wt% magnetite in the resin.
The average particle size of the dispersed particles is 20μm, and the magnetization is 30emμ/
g, a carrier with a resistivity of 1014 Ωcmn, a styrene-acrylic resin containing 10 parts by weight of a benzine derivative as a yellow pigment, and other charge control agents, with an average particle size of 1
A developer consisting of a negatively charged non-magnetic toner of 0 μm was used under conditions such that the ratio of toner to carrier was 25 wt %. Further, the outer diameter of the developing sleeve 31 is 30 fins, the rotation speed is loorpm, the magnetic flux density of the N and S magnetic poles of the magnet body 32 is 100 Gauss, the rotation speed is 11000 rpm, the thickness of the developer layer in the development area Q, 7 mm, the gap between the developing sleeve 31 and the image forming body 1 was 0.8 mm, and the non-contact jumping developing conditions were such that a superimposed voltage of -400 V DC voltage and 3 KHz, 1000 V AC voltage was applied to the developing sleeve 31. According to

While the electrostatic image was being developed by the developing device 5, the other developing devices 6 to 8 shown in FIG. 3 were maintained in a non-developing state as shown in FIG. 4. That is the developing sleeve 31
The developing sleeve 3 can be disconnected from the power source 39 and left in a floating state, or grounded, or actively disconnected from the developing sleeve 39.
1, charging of the toner is achieved by applying a DC bias voltage of opposite polarity, and it is particularly preferable to apply a DC bias voltage. The developing devices 6 to 8 are also developed under the same non-contact jumping developing conditions as the racking device 5, but there is no need to remove the developer layer on the developing sleeve 31 or separate the developing sleeve from the image forming body. However, it is even better.The developing device 6 uses a developer in which the toner in the developing device 5 is changed to a toner containing polytungstophosphoric acid as a magenta pigment instead of a yellow pigment. used a developer in which the toner was changed to a toner containing steel phthalocyanine as a cyan pigment, and a developer in which the toner was changed to a toner containing carbon blank as a black pigment was used in the developing device 8. Of course, color toners based on other pigments or dyes can also be used.
For the color to be developed, the static eliminator 13 and the charger 2 were operated to recharge to 1600 cm (the static eliminator does not need to be operated).

A second image exposure is performed on the life charger using a laser exposure tip corresponding to the green component of the image, and then the developing sleeve 3
1 has a DC voltage of -500 cm and a frequency of 3 KHz, 1000
A second development of the magenta toner was performed using the developing device 6 under non-contact jump pink developing conditions in which a weight voltage of an AC voltage of V was applied. Similarly, the third development of cyan toner is performed by the laser exposure and development device 7 in response to the charge and the red component of the image, and the third development of the cyan toner is performed by the laser exposure and development device 8 in response to the charge and the black component of the image. The development was repeated a fourth time. In addition, in the development after the second development, the image forming body 1
The amplitude and frequency of the DC bias component and AC component of the voltage applied to the developing sleeve 31, the selection time of the time selection conversion, etc. are appropriately changed in accordance with changes in the surface potential, development characteristics, and color reproducibility. did. In particular, gradually increasing the charging potential and gradually increasing the DC bias has the effect of preventing color mixing of toners.

When the fourth development is performed and a four-color image is formed on the image forming body 1, the image is easily transferred by the pre-transfer charger 9 and the pre-transfer exposure lamp 10, and then transferred to the recording body by the transfer device 11. The image was transferred to P and fixed by the fixing device 12. The image forming body 1 on which the color image has been transferred is neutralized by the static eliminator 13, and residual toner is removed from the surface by contact with the cleaning blade or fur brush of the cleaning device 14, and the surface on which the color image has been formed is cleaned. One cycle process of color image formation is completely completed at the time of passing through the device 13.

The color images recorded in the above manner were clear with sufficient density in each color.

In this example, an image forming apparatus with a different image forming process from the image forming apparatus used in Example 1.2 is used, and FIG. 7 is a schematic diagram thereof.

The feature of this method is that a mosaic filter (
The objective is to perform color separation using a photoreceptor having B, G, R). (Patent No. 59-83096).

In the figure, reference numeral 41 indicates a mosaic filter (B) on the photoreceptor layer.

G, R) rotates in the direction of arrow a during a copying operation.

While rotating, the photosensitive drum 41 is irradiated with light as necessary, and is charged over its entire surface by a charging electrode 104, while being subjected to alternating current or corona discharge of the opposite sign to that of the electrode 104 from an electrode 105 having an exposure slit. Exposure of the original is provided and the primary electrostatic imaging process is completed. Next, the developing device 7 is fully exposed to blue light obtained by the combination of the light source 6B and the light source blue filter F8 and loaded with yellow toner.
Developed with Y. Furthermore, it is charged by the charger 15Y.

Next, the light source 6G, the green light source filter FG, the entire surface is exposed by linear color light from the light source 6G, and the developing device 7M equipped with magenta toner.
A multicolor image is formed on the photosensitive drum through development by a developing device 7C loaded with cyan toner, charging by a charging device 15M, full exposure to red light from a light source 6R1 and a red light source filter 6R, and development by a developing device 7C loaded with cyan toner. The obtained multicolor toner image is transferred by a transfer electrode 109 onto a paper 108 fed by a paper feeding means (not shown).

The sheet carrying the multicolor toner image to be transferred is separated from the photosensitive drum by a separation electrode and fixed by a fixing device (not shown) to form a completed multicolor copy, which is then discharged outside the machine. After the transfer, the photosensitive drum 41 is used again after being irradiated with a neutralizing light as necessary to eliminate static electricity with a neutralizing electrode 111, and removing toner remaining on the surface with a cleaning blade 112.

For the developing devices 7Y, 7M, and 7C, the developing devices shown in FIG. A bias power supply 139 consisting of a power supply 139b
Development is performed using a non-contact jumping method.

FIG. 8 is a block diagram of a bias power supply 139 that applies a bias to the developing devices 7Y, 7M, and 7C.

The bias power supply 139 is connected to each developing device from different positions on the secondary side of the transformer, and sequentially lowers the output to the developing devices 7Y, 7M, and 7C shown in FIG. (the amplitude of the electric field strength is successively reduced) to prevent the toner image formed on the image forming body by the previous stage development from being destroyed during the latter stage development. Also, even if one of these developing devices is in progress, a bias is applied to the other developing devices, so if you want to operate only a specific developing device, you may want to operate the unused developing device. Do as in Example 1.

Next, a developer suitable for use in the present invention will be explained.

First, regarding the carrier, the fact that the magnetic carrier particles are spherical improves the agitation performance of the toner and carrier and the transportability of the developer, making it difficult to smudge. However,
In the present invention, if the average particle size of the magnetic carrier particles is large, (1) the condition of the ears of the magnetic brush formed on the developer transport carrier is rough; therefore, an electrostatic image cannot be developed while being vibrated by an electric field; Also, unevenness tends to appear in the toner image, and the toner concentration at the tip is low (so high-density development cannot be performed).
Such problems may occur. To solve this ■ problem,
It is sufficient to reduce the average particle size of the carrier particles, and as a result of experiments, it has been 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 (2) does not substantially occur.

Further, the @ problem is solved by making the magnetic carrier particles finer than the problem (■), and the toner concentration in the spike increases, allowing high-density development to be performed. However, if the carrier particles are too fine, they tend to adhere to the surface of the image bearing member together with the toner particles or are easily scattered.

These phenomena are caused by the strength of the magnetic field acting on the carrier particles,
This is also related to the strength of magnetization of the carrier particles,
According to experiments 9, a tendency gradually begins to appear when the average particle size of carrier particles becomes 15 μm or less, and becomes noticeable when the average particle size is 5 μm or less. The carrier particles adhering to the surface of the image bearing member of the present invention are usually dark colored, and some of them migrate onto the recording paper together with the toner, and have a serious adverse effect on the image quality.

From the above, the average particle size of the magnetic carrier is 50 μm.
The appropriate conditions are below, particularly preferably 30 μm or less, 5 μm or more, particularly preferably 15 μm or more, and it is preferable that the particle size is spherical. In addition, the particle size is Coulter Counter (Coulta! U) Omnicon Alpha (Bausch & Lomb)
This is the weight average particle diameter determined by

Such magnetic carrier particles are made of metals such as iron, chromium, nickel, cobalt, etc., or compounds or alloys thereof, as in conventional magnetic carrier particles.
For example, triiron tetroxide, γ-ferric oxide, chromium dioxide,
Particles of ferromagnetic or paramagnetic substances such as manganese oxide, ferrite, and manganese-copper alloys are made fine, preferably spherical, or the surfaces of these magnetic particles are preferably coated with styrene resin or vinyl resin. , spherically coated with a resin such as ethyl resin, rosin-modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, or fatty acid wax such as palmitic acid or stearic acid, or more preferably coated with magnetic fine particles. By pulverizing or granulating and polymerizing particles of dispersed resin or fatty acid wax to form preferably spherical particles, the particles obtained are subjected to particle size selection using a conventionally known mean particle size classification method. can get.

In addition to the above-mentioned effects, forming the carrier particles into a spherical shape using a resin or the like as described above makes the developer layer formed on the developer transport carrier uniform, and also increases the It also has the effect of making it possible to apply a bias voltage.

In other words, the fact that the carrier particles are made spherical by resin etc. generally means that carrier particles tend to be magnetized and attracted in the long axis direction, but by sphericalization, this directionality is lost, and therefore the developer layer is formed uniformly. (2) In addition to increasing the resistance of the carrier particles, there is no edge part as seen in conventional carrier particles, and the edge part As a result, even if a high bias voltage is applied to the developer transport carrier, electrostatic +
This provides the effect that no disturbance of the 11 image or breakdown of the bias voltage occurs. The fact that this high bias voltage can be applied means that if development under an oscillating electric field in a preferred embodiment of the present invention is performed by applying an oscillating bias voltage, the effects described below can be fully achieved. This means that you can make the most of it. As mentioned above, wax is also used as carrier particles that have the above effects, but,
From the viewpoint of the durability of the carrier, it is preferable to use a resin such as the one described above, and furthermore, it is preferable that the carrier particles have a resistivity of 1.
It is preferable that insulating magnetic particles are formed to have a resistivity of 0.9 Ωcm or more, especially 10"3 or more. This resistivity is
After tapping the particles into a container with a cross-sectional area of 0.50CI11, l kg/
Apply a load of ctl and set a distance of 1000 between the load and the bottom electrode.
This value is obtained by reading the current value when applying a voltage that generates an electric field of V/cm.If this resistivity is low, when a bias voltage is applied to the developer transport carrier, the carrier particles will be charged. is injected, making it easier for carrier particles to adhere to the surface of the image carrier, or for bias voltage breakdown to occur more easily.

In summary, the magnetic carrier particles are spherical so that the ratio of the major axis to the minor axis is at least 3 times or less,
There are no protrusions such as needles or edges, and the resistivity is 108Ωc.
A proper condition is that the resistance is 1013 Ωcm or more, preferably 1013 Ωcm or more. And, such magnetic carrier particles are
For high-resistance spherical magnetic particles or resin-coated carriers, choose magnetic particles that are as spherical as possible and coat them with resin; for carriers that have a dispersion of magnetic fine particles, use fine magnetic particles as much as possible. It is manufactured by performing a spheroidization treatment after forming dispersed resin particles, or by obtaining dispersed resin particles by a spray drying method.

Next, regarding toner, in general, as the average particle size of toner particles in a two-component developer becomes smaller, the amount of charge qualitatively decreases in proportion to the square of the particle size, and relatively As the adhesion force increases, it becomes difficult for the toner particles to separate from the carrier particles, or the toner particles once form an image carrier. In the conventional magnetic brush development method, such problems became noticeable when the average particle size of toner particles was 10 μm or less. The developing method of the present invention solves this problem by performing development using a developer layer, a so-called magnetic brush, under an oscillating electric field. That is, the toner particles attached to the developer layer are
Due to the electrically applied vibrations, it is easy to separate from the developer layer and move to the image area and non-image area on the image bearing member surface, and it also becomes easy to separate from the developer layer.

Then, toner particles with a low charge amount almost never migrate to the image area or non-image area, and since they are not rubbed against the surface of the image carrier, they are no longer attached to the image carrier due to frictional charging. Toner particles with a particle size of about 1 μm have come to 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 image bearing surface is also reduced. In the image area and non-image area, toner particles with a large amount of charge vibrate under an oscillating electric field, and depending on the strength of the electric field, the carrier particles also vibrate, so that the toner particles selectively move to the image area on the image carrier surface. , the adhesion of carrier particles to the surface of the image carrier is significantly reduced.

1,' On the other hand, as the average particle size of the toner increases, as mentioned above, the roughness of the image becomes noticeable.

Generally speaking, toner with an average particle size of about 20 μm has no practical problem for developing fine lines arranged in a pinch of about 10 lines/m* with good resolution, but fine toner particles with an average particle size of 10 μm or less are fine. When used, the resolution is significantly improved, and it becomes possible to provide clear, high-quality images that faithfully reproduce shading differences. For the above reasons, the appropriate condition for the particle size of the toner is that the average particle size is 20 μm or less, preferably 10 μm or less. Further, in order for the toner particles to follow the electric field, it is desirable that the amount of charge of the toner particles be greater than 1 to 3 μC/g (preferably 3 to 100 μC/g). Particularly when the particle size is small, a high amount of charge is required. Also, the resistivity is 10
It is preferable that the resistance is at least gΩcm, preferably at least 10'3 Ωam. 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 magnetic particles, particularly when the amount of magnetic fine particles is 60W.
It is preferable that the amount does not exceed t%, but in order to obtain color clarity, a small amount of 30-t% or less is preferable. When the toner particles contain magnetic particles, the toner particles are influenced by the magnets included in the developer transport carrier, which further improves the uniform formation of the magnetic brush and reduces fogging. The occurrence of toner particles is prevented, and scattering of toner particles also becomes less likely to occur. However, if the amount of magnetic material contained is too large, the magnetic force between it and the carrier particles becomes too strong (too much,
It becomes impossible to obtain a sufficient developing density, and fine magnetic particles also appear on the surface of the toner particles, making it difficult to control triboelectric charging, making it easier to damage the toner particles, and causing damage to the carrier particles. It is easy to aggregate between the two.

To summarize the above, the preferred toner in the image forming method 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 have 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.

In the image forming method of the present invention, a developer in which the above-described spherical carrier particles and toner particles are mixed in the same proportion as in a conventional two-component developer is preferably used, but this also includes: If necessary, a fluidizing agent to improve the fluidity and sliding of the particles, a cleaning agent to help clean the surface of the image carrier, and the like are mixed. As a fluidizing agent,
Colloidal silica, silicon face, metal soap, nonionic surfactants, etc. can be used, and as cleaning agents, fatty acid metal salts, organic group-substituted silicones, fluorine, etc. can be used.

In Examples 1, 2, and 3, clear color images were recorded, and by using only one bias power source, the image forming apparatus could be downsized and manufacturing costs could be reduced. In particular, in Examples 2 and 3, there is no need to take any special plain text measures to prevent color mixture other than the bias power supply (the above effect is great).

In the above embodiment, the bias power source is shared by each developing device, but only the AC bias power source is shared by each developing device, and the DC bias power source is provided for each developing device. It is also possible to apply a voltage.

As described in detail, the present invention allows at least a portion of the bias power source to be shared by a plurality of developing devices, which facilitates the design of the image forming device and reduces its size and cost. Cost reduction becomes possible.

[Brief explanation of the drawing]

The drawings all show embodiments of the present invention, and FIGS. 1 and 7 are a schematic diagram of an image forming apparatus, FIG. 2 is a schematic diagram of a laser beam scanner, and FIG. 3 is a cross-sectional diagram of a developing device. 4 and 8 are block diagrams of the AC bias power supply, FIG. 5 is a timing chart of the image forming process, and FIG. 6 is a flow chart of the image forming process. In addition, in the symbols shown in the drawings, 1.41... Image forming body 5.6.7.8.7Y, 7M, 7C...Development Device 31...Developer conveying sleeve 32...
......Magnet body 39.139......Bias power supply 39a,
139a...DC bias power supply 39b,
139b・・・・・・AC bias power supply 40.1
40......Protective resistance T...
It is a developer (toner). Agent Patent Attorney Hiroshi AisakaFigure 1Figure 2Figure 3Figure 4Figure 8Figure 7Figure 1Tuna

Claims (1)

[Scope of Claims] 1. In an image forming apparatus having a plurality of developing devices that use a bias power source for development, at least some of the bias power sources are shared by the plurality of developing devices. An image forming apparatus characterized by: 2. The image forming apparatus according to claim 1, wherein the AC bias power supply is used for a plurality of developing devices by being switched to each developing device over time.