JP2500906B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming 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.
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 image forming apparatus having a simple structure and high image quality. Further, the present invention provides an excellent image forming apparatus that can handle high-speed processes.

[0007]

In order to solve the above problems, the present invention is directed to a moving electrostatic latent image holding member and the electrostatic latent image holding member fixed inside the electrostatic latent image holding member. A fixed magnet that shows two or more magnetic poles on the surface of the image holding member, a means for forming an electrostatic latent image on the electrostatic latent image holding member, and the electrostatic latent image holding member on which the electrostatic latent image is formed. A developer reservoir for supplying a magnetic developer to the image portion and the non-image portion of the body, and a predetermined gap with the surface of the electrostatic latent image holding member are installed, and the moving direction of the electrostatic latent image holding member is set. An electrode roller that moves in the opposite direction, a means for applying a DC voltage to the electrode roller that superimposes an AC voltage that removes the magnetic developer in the non-image area on the electrostatic latent image carrier, and a means for applying the DC voltage to the electrode roller. An image forming apparatus comprising: a removing member that scrapes off the magnetic developer.

[0008]

The present invention uses an electrostatic latent image holder containing a fixed magnet that does not rotate. A magnetic developer is sprinkled and magnetically attached to the electrostatic latent image holder on which an electrostatic latent image is formed, and the electrode roller is attached. It is configured such that the toner is carried and conveyed to another portion, an AC bias is applied to the 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 is a cascade development method which is improved in size and performance by adding two improvements in that a fixed magnet that does not rotate is installed inside the electrostatic latent image carrier and an AC voltage is applied to the electrodes. is there. In the present invention, development is almost completed when toner is first sprinkled on the electrostatic latent image holding member. The electrode roller part circulates the toner in the developer reservoir and at the same time collects the toner in the non-image part 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), the magnetic developer is once attached to the entire surface of the electrostatic latent image holder 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 electrode roller of the present invention and a conventional method, for example, Japanese Patent Publication No. 63-42256.
The difference from the developing roller of the publication is as follows. (1) It is the electrostatic latent image carrier that carries and carries the magnetic developer from the developer reservoir 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, in the electrode roller of the present invention, the bare surface always faces 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 electrode roller rotates in the opposite direction.

That is, in the present invention, the electrostatic latent image carrier carries the magnetic developer from the developer reservoir to the developing section, and the toner collected by the bare electrode roller is immediately removed from the developing section by the reverse rotation. It is a composition.

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 that has returned to the roller from the image portion of the electrostatic latent image holding member due to the reciprocating motion is again You can return to the original image section. 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 electrode roller in the present invention is as follows.
"Reciprocating motion of toner" disclosed in Japanese Patent Laid-Open No. 3-42256
Instead, it is assumed to be close to the “activation of toner movement” shown in US Pat. No. 3,866,574. Here, in the present invention, since the toner is collected on the bare surface of the electrode roller, there is a new effect that the sleeve ghost phenomenon caused by the uneven thickness of the toner layer, 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 is unnecessary because the electrode roller does not carry the developer layer. By rotating the electrostatic latent image holder and the electrode roller in opposite directions, the magnetic developer does not get stuck in the developing nip portion and is smoothly transferred from the electrostatic latent image holder to the electrode roller. Since the developer amount regulating blade is not provided, the cost of the device can be reduced. Further, since the transfer movement of the magnetic developer can be used also as the rotation movement of the electrostatic latent image holding member, the structure of the developing device can be simplified and the entire apparatus can be downsized.

Further, in the present invention, the moving direction of the electrode roller is set to be opposite to the moving direction of the electrostatic latent image holding member, and the moving speed of the electrode roller is set to be lower than the moving speed of the electrostatic latent image holding member. Moreover, the bare electrode roller can precisely remove the toner on the electrostatic latent image carrier. as a result,
(1) No unevenness in the developing direction is generated, (2) horizontal line resolution is high, and (3) sufficient image density is obtained.

Here, the magnet inside the photoconductor is, for example, as shown in FIG.
It is preferable that two or more magnetic poles appear on the surface of the photosensitive member, as shown in, since the transportability of the magnetic developer is improved.

Further, in the present invention, the magnetic developer supplying section can magnetically attract the magnetic developer by the internal magnet of the electrostatic latent image holding member to supply a large amount to the electrostatic latent image holding member. That is, since the developing width is large, it is possible to provide an excellent developing device having a simple structure of the entire device and capable of supporting high-speed processes.

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 may be used as long as it is a charging device such as a roller charging device made of an elastic rubber material or a conductive fur brush charging device and used in a normal device.

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. 30
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 electrode roller. Further, in order to improve the transportability of the developer and the motility of the toner during 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 electrode roller. It is preferable to set it at the closest position 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, and it is natural that this value becomes small when the diameter of the photoconductor is large.

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 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 to promote the formation of the magnetic developer layer.

In the present invention, a developer reservoir having an opening on the surface of the electrostatic latent image carrier is used. The magnetic developer directly contacts the electrostatic latent image carrier from the developer reservoir, and the magnetic developer is magnetically attracted to the electrostatic latent image carrier regardless of whether or not it is charged. The width of the opening of the developer reservoir facing the electrostatic latent image holder in the moving direction of the electrostatic latent image holder is required to be 5 mm or more, and preferably 10 to 15 mm.
When this width is 5 mm or less, the image density becomes extremely low.

The magnetic developer 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 electrode roller. in this way,
It has been found that when the fluidity of the toner is poor, the toner in the non-image portion adheres strongly to the electrostatic latent image holder 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, 1
In the case of component toner, it is not particularly necessary to provide a charging member for charging the toner, and if silica particles are added to the toner, when the toner comes into 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.

In the present invention, a two-component developer comprising toner and magnetic carrier can be used. The toner used in the present invention is obtained by dispersing a color pigment such as carbon black or phthalocyanine in a binder resin such as an acrylic resin or a polyester resin, pulverizing and classifying. The toner may be a powder obtained by spray drying, or a powder chemically obtained by a pearl polymerization method, an emulsion polymerization method, or the like. Further, the toner particles may be directly mixed with a carrier, or silica particles or fluororesin fine powder may be adhered to the surface of the toner. The average particle diameter of the toner used is preferably 15 μm or less, but 12 μm
A sharper image can be obtained by the following.

The carrier used in the present invention is made of a magnetic substance such as iron powder or ferrite powder, or a powder whose surface is coated with a resin, or a fine powder such as ferrite powder or magnetite, in a proportion of about 30 to 80%, and styrene. A magnetic powder that is dispersed and mixed in a resin, an epoxy resin, a styrene-acrylic resin, and pulverized and classified is used. The average particle size of the carrier is 30
The thickness is preferably 0 μm or less, but particularly 150 μm or less, the toner can be uniformly charged.

The distance between the electrode roller and the electrostatic latent image carrier is
100 μm to 700 μm when a one-component toner is used
Degree: 400 μm to 2 m when using a two-component developer
It is installed about m away.

The material of the electrode roller may be conductive.
When the fluidity of the developer is poor, if the electrode roller is made of a magnetic material, the magnetic lines of force from the magnet inside the electrostatic latent image carrier reach the electrode roller, and 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 electrode roller may be a polished one, or may be one in which the surface is made uneven by sandblasting or the like or a groove is carved.

The 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 electrode roller is preferably opposite in polarity to the magnetic pole of the magnet inside the electrostatic latent image holding member.

An alternating voltage is applied to this 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 in the range of approximately 50 Hz to 5000 Hz, preferably in the range of 300 to 3000 Hz. The value of the AC voltage is the value of zero to peak, which is about 0.5 to 3 of the charging potential of the electrostatic latent image holding member.
A double value is preferable, and a value of 0.5 to 2 is preferable. 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 normal development, a good positive image can be obtained by setting the value to be equal to or higher than the background potential of the electrostatic latent image carrier by several tens of percent.

When the rotating direction of the electrode roller is opposite to the moving direction of the electrostatic latent image holding member at the developing position,
High image quality can be obtained, and the device configuration can be simplified.

In order to effectively remove the fog on the electrostatic latent image carrier, it is preferable to increase the moving speed of the electrode roller. On the other hand, the slower the moving speed of the electrode roller, the more carefully the toner on the electrostatic latent image carrier can be removed. The speed of the electrode roller is preferably in the range of 0.3 to 2.0 times the moving speed of the electrostatic latent image carrier.

The developer adhering to the electrode roller is scraped off by a removing member provided in the developer reservoir and returned to the developer reservoir again. The removing member is preferably electrically insulated so as not to affect the electrode roller. Therefore, for example, a plastic such as a polyester film is preferable for the removing member. The removing member may be made of stainless steel, phosphor bronze plate, or the like, but at this time, in order not to electrically affect the electrode roller, make sure that it does not come into electrical contact with anything other than the electrode roller. Needs to be insulated. Furthermore,
A rubber blade or a roller to which a voltage is applied may be used as the removing member.

[0032]

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

Concrete Embodiment 1 FIG. 2 shows an embodiment of the image forming apparatus of the present invention. In FIG. 2, 6 is an organic photoconductor drum in which phthalocyanine is dispersed in a polyester binder resin, 7 is a magnet which is fixed coaxially with the photoconductor 6 and has 7 magnetic poles which do not rotate, and 8 is a negative charge on the photoconductor. Corona charger, 9 is a grid electrode for controlling the charging potential of the photoconductor, 1
0 is a signal light, 11 is a developer reservoir, 12 is an average particle size of about 10
A negatively chargeable magnetic one-component toner of μm, and 13 is a toner guide. The magnet 7 has magnetic poles of three poles attracting each other at a portion facing the developer reservoir 11, and magnetic poles of four poles mutually repelling at a repulsive magnetic field portion 14 on the opposite side with respect to the axis. . Reference numeral 15 is an electrode roller made of stainless steel having magnetism, 16 is an AC high voltage power source for applying a voltage to the electrode roller, 17 is a scraper made of a polyester film for scraping off toner on the electrode roller, and 18 is a paper image of a toner image on the photoconductor. It is a transfer corona charger that transfers to.
Reference numeral 19 is a recovery unit for recovering the toner splashed by the repulsive magnetic field unit 14. The magnetic flux density on the surface of the photoconductor 6 is 800
It is Gs. The photoconductor 6 has a diameter of 30 mm and a peripheral speed of 30 m.
It was rotated at m / s.

The magnetic one-component toner used was composed of 70% polyester resin, 25% ferrite, 3% carbon black, and 2% oxycarboxylic acid metal complex, and 0.4% colloidal silica was added externally. (All were weight%).

The operation of the image forming apparatus configured as described above will be described below with reference to FIG. Photoconductor 6
Was charged to -500V by a corona charger 8 (applied voltage-4kV, grid 9 voltage-500V). 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 was -100V. On the surface of the photoconductor 6, a magnetic one-component toner 12 is stored in a developer reservoir 11
It is attached by magnetic force inside. At this time, the toner was charged to approximately −3 μC / g. Next, the photoconductor 6 having the toner layer attached thereto was passed in front of the electrode roller 15. The electrode roller 15 was installed at a distance of 300 μm from the photoconductor 9. A high voltage power supply 16 is applied to the electrode roller 15 so that the electrode roller 15 shown in FIG.
400 of the waveform shown in FIG.
An AC voltage (frequency 300 Hz) of V0-p (peak-to-peak 800V) was applied. The toner layer on the photoconductor 6 moves between the photoconductor 6 and the electrode roller 15, and the toner in the non-image area gradually moves to the side of the photoconductor 6
A negative-positive inverted toner image remained only on the image portion on the upper portion. The toner adhering to the electrode roller 15 rotating in the direction of the arrow was scraped off by the scraper 17 and returned to the developer reservoir 11 to be used for the next image formation. The toner image thus obtained on the photoconductor 6 is transferred onto a sheet of paper (not shown) by the transfer charger 18, and then a fixing device (not shown).
It was fixed by heat. On the other hand, the toner remaining on the photoconductor 6 after the transfer is transferred to the photoconductor 6 by the repulsive magnetic field portion 14 as the photoconductor 6 moves.
It is splashed from the surface and collected in the collection unit 19. In some cases, the toner repelled in the repulsive magnetic field portion is partially returned to the surface of the photoconductor, but at this time, the portion passing through the repulsive magnetic field portion adheres to the surface of the photoconductor in a dispersed state. Subsequent charging exposure has virtually no effect.

The photoreceptor 6 is charged again by the corona charger 8,
Used in the next imaging step. As a result, a sharp image with no toner scattering was obtained.

In the embodiment, the repulsive magnetic field portion is provided with a recovery unit for recovering the splashed toner. However, since the toner repulsed once and adhered again to the surface of the photoconductor is well dispersed, the amount of the toner may be small. If it does not affect the next process. Therefore, if the magnetic field configuration is such that the dispersed toner adheres to the surface of the photoconductor again, the recovery unit 19 may be omitted.

Concrete Example 2 The constitution of FIG. 4 is different from the constitution of FIG. 2 in that the magnetic developer is a two-component developer in which toner and carrier are mixed. Further, the electrode roller 20 is provided with a fixed magnet 21 that does not rotate. Other configurations are the same as those in FIG. The toner used consisted of 93% of styrene acrylic resin, 5% of carbon black and 2% of metal complex of oxycarboxylic acid, and 0.1% of colloidal silica was added externally (all are% by weight). A two-component developer 22 prepared by mixing a ferrite powder carrier having a particle diameter of 100 μm and a toner, the surface of which was coated with a silicone resin, was placed in the developer reservoir 11 and attached to the surface of the photoconductor 6 by magnetic force. When the photoconductor 6 on which the electrostatic latent image is formed is passed through the developer 22, the two-component developer 2
2 was adsorbed on the surface of the photoconductor. Further, when passing through the electrode roller 20, only the toner in the image portion passed through the electrode roller 20, and a toner image was obtained on the photoconductor 6. The obtained toner image was transferred onto paper (not shown) by the transfer charger 18, and then heat-fixed by a fixing device (not shown). On the other hand, after the transfer, the photoconductor 6 was charged again by the corona charger 8 and used in the next image forming step. As a result, a sharp image with no toner scattering was obtained.

[0039]

According to the present invention, an image forming apparatus having a simple structure and high image quality can be obtained. Further, an excellent image forming 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 image forming apparatus according to a first embodiment of the present invention.

FIG. 3 is a schematic diagram showing a waveform of an AC voltage used in the first embodiment of the present invention.

FIG. 4 is a configuration diagram of an image forming apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 6 Photosensitive Member 7 Magnet 8 Corona Charger 9 Grid Electrode 10 Laser Exposure 11 Developer Reservoir 12 Magnetic Developer 15/20 Electrode Roller 21 Magnet 16 AC High Voltage Power Supply 17 Scraper

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location G03G 15/09 101 G03G 15/09 101 21/00 350 21/00 350

Claims (1)

(57) [Claims] 1. A moving electrostatic latent image holder, and a fixed magnet fixed inside the electrostatic latent image holder and having two or more magnetic poles on the surface of the electrostatic latent image holder. A means for forming an electrostatic latent image on the electrostatic latent image holder, and an entire surface of the electrostatic latent image holder on which the electrostatic latent image is formed ,
A developer reservoir for supplying by attaching magnetic one-component toner, is installed has a surface with a predetermined gap between the electrostatic latent image holding member, moves in a direction opposite to the movement direction of said electrostatic latent image holding member
The magnetic one-component toner of the non-image area on the electrostatic latent image carrier.
An electrode roller to remove over has a means for applying a DC voltage obtained by superposing an AC voltage to the electrode roller, and a removing member for scraping off the magnetic developer adhering to the electrode roller, further said fixed magnet At a position approximately opposite to the electrode roller
The closest position between the electrostatic image carrier and the electrode roller.
An image forming apparatus characterized in that it is located on the upstream side .