JPH06161266A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To provide an electrophotographic device which is simple and small in size and ensures high resolution. CONSTITUTION:The device uses a photosensitive drum 6 which incorportates a fixed magnet 7. After an electrostatic latent image is formed, it is brought into contact with magnetic toner 12 in a toner hopper 11, and the developer is attracted to the surface of the photosensitive body by a magnetic force. Further, when a toner recovering electrode roller 13 to which an AC voltage is applied is passed, the toner remains only in the image part, and the part is developed and visualized. The rotating direction of the toner recovering electrode roller 13 is made opposite the advancing direction of the photosensitive body, and the rotating speed of the roller 13 is made eaqual to or higher than that of the photosensitive body. Thus, the electrophotographic device which is small, ensures high image quality, and is excellent in the adaptation of high speed is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus applicable to printers, facsimiles and the like.

[0002]

2. Description of the Related Art Conventional electrophotographic developing methods include a cascade developing method, a touchdown developing method, a jumping developing method and the like. Among them, a cascade developing method shown in US Pat. No. 3,105,770 is known as a developing method in which a developer is directly sprinkled with a developer. The cascade developing method is the first developing method used in an electrophotographic copying machine.

Further, an AC bias is applied to the developing roller 1
U.S. Pat. No. 38 as a method for flying and developing a component toner
There is 66574. In this invention, it is explained that the AC bias applied to the developing roller is used for the purpose of activating the movement of the toner, and that the toner reaches the image portion and flies back on the way in the non-image portion.

Further, as a modification of the technique of applying the AC bias, there is a jumping developing method disclosed in Japanese Patent Publication No. 63-42256. This jumping developing method is a developing method in which toner is carried on a toner carrier and conveyed to a developing unit, where the toner is attached to the image part of the photoconductor by an AC bias. This Japanese special public Sho 63-42
The technical idea of the 256 publication is that the toner reciprocates in the image portion and the non-image portion in the above-mentioned US Pat.
It is different from 866574.

[0005]

As is well known in the art, the cascade development method is not good at reproducing solid images. Further, there is a problem that the device becomes large and complicated. Further, US Pat.
The 6574 developing device has a drawback that the device is required to have high accuracy and is complicated and high in cost. In the jumping development method, since a photoreceptor is developed by a toner carrier carrying a toner layer, it is essential to form an extremely uniform thin layer on the toner carrier in order to obtain high image quality. Further, in this method, a so-called sleeve ghost phenomenon often occurs in which a history of the previous image remains in the thin toner layer on the toner carrier and an afterimage appears in the image. Further, there is a drawback that the device is complicated and the cost is high.

In view of the above problems, it is an object of the present invention to provide an electrophotographic method and apparatus having a simple structure and high image quality. Further, the present invention provides an excellent electrophotographic apparatus which can cope with a high speed process.

[0007]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides an electrostatic latent image holding member which holds an electrostatic latent image and which includes a fixed magnet and moves, and the electrostatic latent image holding member. A toner hopper that magnetically attaches magnetic toner to the body surface by the fixed magnet, and an alternating current that is installed with a gap between the electrostatic latent image holding member and the electrostatic latent image to collect the magnetic toner attached to the non-image portion of the electrostatic latent image. An electrophotographic apparatus having a toner recovery electrode roller to which a voltage is applied, the traveling direction is opposite to the traveling direction of the electrostatic latent image holding member, and the moving speed of which is faster than the moving speed of the electrostatic latent image holding member. is there.

[0008]

The present invention uses an electrostatic latent image holder containing a fixed magnet that does not rotate. A developer is sprinkled and magnetically adhered to the electrostatic latent image holder on which an electrostatic latent image is formed. The toner is carried and conveyed to the roller portion, an AC bias is applied to the toner collecting electrode roller, and the non-image portion toner of the electrostatic latent image holding member is removed by electrostatic force and magnetic force. That is,
The present invention improves the size and performance of the cascade development method by adding two improvements to the electrostatic latent image carrier, in which a magnet that does not rotate is fixedly installed and an AC voltage is applied to the electrodes. In the present invention, the development is almost completed when the toner is first sprinkled on the electrostatic latent image carrier. The toner collecting electrode roller section circulates the toner in the toner hopper and at the same time collects the toner in the non-image section of the electrostatic latent image.

The technical idea of the present invention will be described with reference to FIG. Reference numeral 1 is an electrostatic latent image holder on which an electrostatic latent image is formed, 2 is toner, 3 is a developing electrode, 4 is a magnet, and 5 is a power source. In the conventional method, as shown in (b), toner is attached to the image portion of the electrostatic latent image holding member to obtain the toner image of (c). On the other hand, in the present invention, as shown in (d), magnetic toner is once attached to the entire surface of the electrostatic latent image holding member by magnetic force, and then (e).
As shown in (1), the toner is taken from the non-image portion by the magnetic force and the electrostatic force. That is, the conventional example is a “developing method for adhering toner to the image portion”, and the present invention can be said to be a “developing method for stripping off toner in unnecessary non-image portion”.

Due to such a difference in technical idea, the toner collecting electrode roller of the present invention and a conventional method, for example, Japanese Patent Publication No. 63-
Differences from the developing roller disclosed in Japanese Patent No. 42256 are as follows. (1) It is the electrostatic latent image carrier that carries and carries the developer from the toner hopper to the developing section. (2) In the conventional developing roller, the surface carrying the toner layer is always opposed to the electrostatic latent image holding member. On the other hand, the toner collecting electrode roller of the present invention always has a bare surface facing the electrostatic latent image holding member. (3) In the conventional example, the developing roller and the electrostatic latent image carrier move in the same speed and in the same direction. However, in the present invention, the toner recovery electrode roller rotates in the opposite direction.

That is, in the present invention, the electrostatic latent image carrier conveys the developer from the toner hopper to the developing section, and the toner collected by the bare toner collecting electrode roller is immediately removed from the developing section by the reverse rotation. Is.

Due to such a difference in structure, the following difference in action and effect occurs. If the electrostatic latent image holding member and the roller move at the same speed and in the same direction as in Japanese Patent Publication No. 63-42256, the toner returned from the image portion of the electrostatic latent image holding member to the roller due to the reciprocating motion is again. You can return to the image section with. However, when the roller rotates in the reverse direction as in the present invention, once the toner moves to the roller side, the surface of the electrostatic latent image holding member facing next is different from the original electrostatic latent image holding member surface, and therefore the toner is the same again. You cannot go back to the place. That is, assuming that reciprocating motion occurs in the image portion in the reverse rotation as in the present invention, a visible image with toner cannot be obtained in principle. Therefore, the effect of the AC voltage applied to the toner recovery electrode roller in the present invention is not the "reciprocating motion of toner" disclosed in Japanese Patent Publication No. 63-42256, but "activation of toner motion" disclosed in U.S. Pat. No. 3,866,574. It is supposed to be close to.
Here, in the present invention, since the toner is collected on the bare surface of the toner collecting electrode roller, there is a new effect that the sleeve ghost phenomenon due to the unevenness of the toner layer thickness, which has been a problem in the past, does not occur.

Furthermore, in the present invention, there is no developer amount regulating blade which is usually used for the developing roller. This becomes unnecessary because the toner collecting electrode roller does not carry the toner layer. By rotating the electrostatic latent image holder and the toner collecting electrode roller in opposite directions, the developer is not blocked in the developing nip portion and is smoothly transferred from the electrostatic latent image holder to the toner collecting electrode roller. . Since the developer amount regulating blade is not provided, the cost of the device can be reduced. Further, since the transport movement of the developer can be used also as the rotation movement of the electrostatic latent image holding member, the construction of the developing device can be simplified and the entire apparatus can be downsized.

Further, in the present invention, since the developer is in contact with the electrostatic latent image on the surface of the electrostatic latent image holding member for a longer time than in the conventional magnetic brush developing method, the developing efficiency is extremely high and the high speed adaptability is excellent. It's easy to understand.

As the charging device used in the present invention, a commonly used corona charger and a scorotron charger having a grid electrode are used. Further, any type of charging device such as a roller charging device made of an elastic rubber material or a conductive fur brush charging device can be used as long as it is a charging device normally used in an electrophotographic apparatus.

The present invention uses an electrostatic latent image carrier containing a magnet. This magnet does not rotate but only the electrostatic latent image carrier rotates. At this time, if the magnet and the electrostatic latent image holder are supported coaxially, there is an advantage that the mechanism for driving the electrostatic latent image holder can be simplified and the magnetic pole position can be easily adjusted.
The maximum magnetic flux density of the magnet inside the electrostatic latent image carrier used in the present invention needs to be 300 gauss or more on the surface of the electrostatic latent image carrier, and is preferably 500 to 1200 gauss. Thirty
When it is 0 Gauss or less, the effect of the magnetic force is weakened, the uniformity of the image is lost, and the toner is easily clogged with the toner collecting electrode roller. Further, in order to improve the transportability of the developer and the mobility of the toner at the time of development, the magnetic pole position of the magnet inside the electrostatic latent image holding member is set to the electrostatic latent image holding member and the toner collecting electrode roller. It is preferable to set it at the position closest to or at a position upstream thereof. This angle θ is preferably in the range of 0 ° to 30 °. The range of the magnetic pole angle is based on the assumption that the diameter of the photoconductor drum is 30 mm. For example, when the diameter of the photoconductor is large,
Obviously, this value will be small.

As the electrostatic latent image carrier used in the present invention, zinc oxide, selenium, cadmium sulfide, amorphous silicon, or an organic photoconductor using phthalocyanine or an azo pigment can be used. Needless to say, ordinary electrostatic recording paper or the like may be used. The surface of the electrostatic latent image carrier may be roughened by sandblasting or the like in order to accelerate the formation of the developer layer.

In the present invention, a toner hopper having an opening on the surface of the electrostatic latent image carrier is used. The developer is configured to directly contact the electrostatic latent image holder from the toner hopper, and the developer is magnetically attracted to the electrostatic latent image holder regardless of whether or not it is charged.

The magnetic toner used in the present invention is preferably an insulating one-component toner. If a one-component toner is used, the device configuration can be simplified. The one-component toner used in the present invention is obtained by dispersing powder of magnetite or ferrite together with a charge control agent in a binder resin such as styrene resin or acrylic resin, pulverizing and classifying. This toner may be a powder obtained by spray drying or a powder chemically obtained by a pearl polymerization method or the like. The average particle diameter of the toner used is preferably 15 μm or less, but if it is 12 μm or less, a sharper image can be obtained.

In this electrophotographic method, the toner is once attached to the entire surface of the electrostatic latent image holding member, and then the toner in the non-image portion is removed by the toner collecting electrode roller. It was found that with this method, if the fluidity of the toner is poor, the toner in the non-image area adheres strongly to the electrostatic latent image carrier and cannot be removed, resulting in background fog and degrading the image. When silica fine particles are externally added to the surface of the toner, the fluidity of the toner is improved, the non-electrostatic adhesion force to the electrostatic latent image holding member is reduced, and the effect of eliminating fog is obtained. At this time, it was found that the silica particles not only contribute to the improvement of the fluidity but also contribute to the charging of the toner. In this electrophotographic method, in the case of a one-component toner, it is not necessary to particularly provide a charging member for charging the toner. If silica particles are added to the toner, when the toner comes in contact with the charged electrostatic latent image holding member, It was found that the charge was transferred from the side of the electrostatic latent image holder to the side of the toner to charge the toner to the same polarity as that of the electrostatic latent image holder. The silica fine particles are also called colloidal silica.

The distance between the toner collecting electrode roller and the electrostatic latent image holding member is 100 μm when one-component toner is used.
They are set apart by about 700 μm.

The material of the toner collecting electrode roller may be conductive. When the fluidity of the developer is poor, if the toner recovery electrode roller is made of a magnetic material, the magnetic force lines from the magnet inside the electrostatic latent image holder reach the toner recovery electrode roller.
As a result, the developer transportability is improved. Examples of such a material include soft iron, magnetic stainless steel, nickel and the like. The surface of the toner collecting electrode roller may be a polished one, or may be one having a roughened surface by sandblasting or the like or a grooved one.

The toner recovery electrode roller may be a non-magnetic roller having a magnet fixed inside. For example, there is a configuration in which a magnet is inserted into a cylinder made of non-magnetic stainless steel or aluminum.
The magnetic pole of the magnet inside the toner recovery electrode roller is preferably opposite in polarity to the magnetic pole of the magnet inside the electrostatic latent image holding member.

An AC voltage is applied to the toner collecting electrode roller. Of course, a pulse waveform or a triangular wave may be used as long as an alternating electric field is effectively applied to the electrostatic latent image holder. The frequency of this alternating voltage varies depending on the image forming process speed, and is approximately 50 Hz to 5000 Hz.
And preferably in the range of 300 to 3000 Hz. The value of AC voltage is zero to peak
The value of k is approximately 0.5 of the charging potential of the electrostatic latent image carrier.
Is preferably 3 to 3 times, more preferably 0.5 to 2 times. In the case of reversal development, if the value of the DC voltage superimposed on the AC voltage is set equal to or lower than the charging potential of the electrostatic latent image carrier by several tens of percent, a good negative-positive reversal image can be obtained. . On the other hand, in the case of regular development, it is equal to the background portion potential of the electrostatic latent image holding member or several ten
% If set to a high value, a good positive image can be obtained.

The rotation direction of the toner collecting electrode roller is
When the developing position is set in a direction opposite to the traveling direction of the electrostatic latent image holding member, high image quality is obtained and the apparatus structure is simplified.

In order to effectively remove the fog on the electrostatic latent image carrier, it is preferable to increase the moving speed of the toner collecting electrode roller. The speed of the toner collecting electrode roller is preferably in the range of 1 to 2 times the moving speed of the electrostatic latent image holding member.

The toner attached to the toner collecting electrode roller is scraped off by a scraper provided in the toner hopper, and the toner is returned to the toner hopper again. The scraper is preferably electrically insulated so as not to affect the toner collecting electrode roller. Therefore, for example, plastic such as polyester film is preferable for this scraper. This scraper has
It is possible to use stainless steel or phosphor bronze plate, but in this case, in order to prevent the toner recovery electrode roller from being electrically affected, insulate the parts other than the toner recovery electrode roller from electrical contact. There is a need.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An electrophotographic apparatus of the present invention will be described below with reference to the drawings.

Specific Example 1 In FIG. 2, 6 is an organic photosensitive drum in which phthalocyanine is dispersed in a polyester binder resin, and 7 is a photosensitive body 6.
A non-rotating magnet fixed coaxially with 8 is a corona charger for negatively charging the photoconductor, 9 is a grid electrode for controlling the charging potential of the photoconductor, 10 is a signal light, 11 is a toner hopper, and 12 is a magnetic 1 Component toner, 13 is a non-magnetic toner collecting electrode roller set with a gap from the photoconductor 6,
14 is a non-rotating magnet installed inside the toner recovery electrode roller 13, 15 is an AC high-voltage power supply for applying a voltage to the toner recovery electrode roller 13, and 16 is a polyester film for scraping off the developer on the toner recovery electrode roller. The scraper 17 is a transfer corona charger that transfers the toner image on the photoconductor onto paper. Reference numeral 18 is a damper for smoothing the flow of the developer in the toner hopper and for preventing the developer from being crushed by its own weight to cause clogging between the photoconductor and the toner collecting electrode roller. The magnetic flux density on the surface of the photoconductor 6 is 600 Gs. The magnetic flux density on the surface of the toner recovery electrode roller 13 is 800 Gs. The magnetic force inside the toner collecting electrode roller is made stronger than the magnetic force inside the photoconductor to improve the transportability. The magnetic pole angle θ of the magnet 7 shown in the figure was set to 15 °. The diameter of the photoconductor 6 is 30 m
It was used by rotating in the direction of the arrow in the figure at m and a peripheral speed of 60 mm / s. The diameter of the toner collecting electrode roller 13 is 16 mm,
The photosensitive member was rotated at a peripheral speed of 80 mm / s in the direction opposite to the traveling direction of the photoconductor (the direction of the arrow in the figure). The gap between the photoconductor 6 and the toner recovery electrode roller 13 was set to 300 μm.

As the magnetic one-component developer, fine particle insulating magnetic one-component toner having a particle size of 8 μm was used. The composition of the magnetic one-component toner is 70% polyester resin, 25% ferrite,
Carbon black 3%, Oxycarboxylic acid metal complex 2%
Further, 1% of colloidal silica was externally added and used (all are% by weight).

The photoconductor 6 is charged with a corona charger 8 (applied voltage-
4.5kV, voltage of grid 9 -500V), -50
It was charged to 0V. The photoconductor 6 was irradiated with a laser beam 10 to form an electrostatic latent image. At this time, the exposure potential of the photoconductor is −
It was 90V. Toner 12 was attached to the surface of the photoconductor 6 in the toner hopper 11 by magnetic force. Next, the photoconductor 6 was passed in front of the toner collecting electrode roller 13. When the photoconductor 6 passes through the uncharged region, the toner recovery electrode roller 13 is superposed with a DC voltage of 0 V by the AC high-voltage power supply 15 at 750 V0-p (peak-to-peak 1.5.
An alternating voltage (frequency 1 kHz) of kV) was applied. After that, when the photoconductor 6 charged with −500V and having the electrostatic latent image written thereon is passed, a DC voltage of −350V is superposed on the toner collecting electrode roller 13 by the AC high voltage power source 7
An AC voltage (frequency 1 kHz) of 50V0-p (peak-to-peak 1.5kV) was applied. Then, the toner was collected from the photoconductor 6 toward the toner collecting electrode roller 13, and a negative-positive inverted toner image remained only on the image portion on the photoconductor 6. The toner adhering to the toner collecting electrode roller 13 rotating in the direction of the arrow was scraped off by the scraper 16 and returned to the toner hopper 11 again for the next image formation. The toner image thus obtained on the photoconductor 6 is
After being transferred onto paper (not shown) by the transfer charger 17, it was heat-fixed by a fixing device (not shown).

[0032]

According to the present invention, an electrophotographic method and apparatus having a simple structure and high image quality can be obtained. Further, an excellent electrophotographic apparatus that can handle high-speed processes can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view explaining a difference in technical idea between a conventional method and the present invention.

FIG. 2 is a configuration diagram of an electrophotographic apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 6 Photoconductor 7 Magnet 8 Corona Charger 9 Grid Electrode 10 Laser Exposure 11 Toner Hopper 12 Magnetic Toner 13 Toner Recovery Electrode Roller 14 Magnet 15 AC High Voltage Power Supply 16 Scraper

Claims (1)

[Claims] 1. An electrostatic latent image holder that holds an electrostatic latent image and moves by containing a fixed magnet; and a toner hopper that magnetically attaches magnetic toner to the surface of the electrostatic latent image holder by the fixed magnet. The electrostatic latent image holder is installed through a gap, and an AC voltage for collecting the magnetic toner adhering to the non-image portion of the electrostatic latent image is applied, and the traveling direction of the electrostatic latent image holder advances. An electrophotographic apparatus having a toner collecting electrode roller, which is in a direction opposite to the direction and whose moving speed is higher than the moving speed of the electrostatic latent image holding member.