JP2500905B2 - 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 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.
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, an object of the present invention is to provide an electrophotographic 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]

In order to solve the above problems, the present invention is directed to an electrostatic latent image holder that contains a fixed magnet and moves, and an electrostatic latent image is formed on the electrostatic latent image holder. Means for forming, a developer reservoir for supplying a magnetic developer composed of a magnetic carrier and toner to the image portion and the non-image portion of the electrostatic latent image holding member on which the electrostatic latent image is formed, and the electrostatic latent image An electrode roller that is installed with a predetermined gap from the surface of the image holding member and that moves in a direction opposite to the moving direction of the electrostatic latent image holding member, and toner in the non-image portion on the electrostatic latent image holding member An image forming apparatus comprising: a means for applying a DC voltage on which an AC voltage to be removed is superimposed to the electrode roller; and a removing member for scraping off the magnetic developer adhering to the electrode roller.

[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 to be carried and conveyed to a portion, an AC bias is applied to the electrode roller, and the non-image portion developer 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 in which a magnet is installed inside the electrostatic latent image carrier and an AC voltage is applied to the electrodes, thereby improving the size and performance. In the present invention, the development is almost completed when the developer is first sprinkled on the electrostatic latent image carrier. The electrode roller part circulates the developer in the developer reservoir and at the same time collects the developer 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 developer from the developer reservoir to the developing section. (2) In the conventional developing roller, the surface carrying the developer layer is always opposed to the electrostatic latent image carrier. 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 developer from the developer reservoir to the developing section, and the developer 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 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 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 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 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, 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.

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. 30
If it is 0 Gauss or less, the effect of the magnetic force is weakened, the uniformity of the image is lost, and the developer is easily clogged with the electrode roller. Further, in order to improve the transportability of the developer and the mobility of the developer 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 electrode roller. It is preferable to set it at the closest position 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, 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 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 developer reservoir having an opening on the surface of the electrostatic latent image carrier is used. The developer is configured to come into direct contact with the electrostatic latent image holding member from the developer reservoir, and the developer is magnetically attracted to the electrostatic latent image holding member 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.

In the present invention, a two-component developer comprising a toner and a magnetic carrier is 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 if it is 12 μm or less, a sharper image can be obtained.

The carrier used in the present invention is 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
It is installed at a distance of about 400 μm to 2 mm. 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 AC 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 developer 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 attached to the electrode roller is scraped off by a removing member provided in the developer reservoir, and the developer is 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. Further, as the removing member, a rubber blade or an electrode roller to which a voltage is applied can be used.

[0028]

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

Concrete Example 1 FIG. 2 shows an example of the electrophotographic 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
Reference numeral 0 is a signal light, 11 is a developer reservoir, 12 is a two-component developer in which toner and carrier are mixed, 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. . The electrode roller 15 is provided with a fixed magnet 16 that does not rotate. Reference numeral 17 is an AC high voltage power source for applying a voltage to the electrode roller, 18 is a scraper made of a polyester film for scraping off the toner on the electrode roller, and 19 is a transfer corona charger for transferring the toner image on the photoconductor onto paper. Reference numeral 20 denotes a recovery unit that recovers the toner splashed by the repulsive magnetic field unit 14. The magnetic flux density on the surface of the photoconductor 6 is 8
00 Gs. The photoconductor 6 has a diameter of 30 mm and a peripheral speed of 3
It was rotated at 0 mm / s. 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). Inside the developer reservoir, the surface is coated with silicone resin and the particle size is 10
A two-component developer in which a ferrite powder carrier of 0 μm and a toner were mixed was added. The operation of the electrophotographic apparatus configured as described above will be described below with reference to FIG.

The photosensitive member 6 is connected to the corona charger 8 (applied voltage-4
It was charged to -500V at a voltage of the grid 9 of -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 is -100.
It was V. The magnetic developer 12 is magnetically attached to the surface of the photoconductor 6 in the developer reservoir 11. Next, the photoconductor 6 having the developer 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. The electrode roller 15 has a high voltage power supply 17
As a result, 400V0-p (peak-to-peak 800 with the waveform shown in FIG.
V) AC voltage (frequency 300 Hz) was applied. The toner layer on the photoconductor 6 moves between the photoconductor 6 and the electrode roller 15, so that the toner in the non-image portion gradually moves to the electrode roller 15 side, and the toner image on the photoconductor 6 is negative-positive inverted only in the image portion. Remained. Electrode roller 15 rotating in the direction of the arrow
The toner adhering to the upper portion was scraped off by the scraper 18, returned to the inside of the developer reservoir 11 and used for the next image formation.
The toner image thus obtained on the photoconductor 6 was transferred onto a sheet of paper (not shown) by the transfer charger 19 and then thermally fixed by a fixing device (not shown). As a result, a sharp image with no toner scattering was obtained.

Concrete Example 2 In FIG. 4, 21 is an organic photoconductor drum in which phthalocyanine is dispersed in polyester binder resin, 22 is a non-rotating magnet fixed coaxially with the photoconductor 21, and 23 is a minus photoconductor. A corona charger that charges the surface of the photoreceptor, 24 a grid electrode that controls the charging potential of the photoconductor, 25 a signal light, 2
6 is a developer reservoir, 27 is a magnetic two-component developer consisting of toner and carrier, 28 is a magnetic stainless steel electrode roller set with a gap of 500 μm from the photoconductor 21,
29 is an AC high voltage power supply for applying a voltage to the electrode roller, 30
Is a scraper made of a polyester film that scrapes off the developer on the electrode roller, and 31 is a transfer corona charger that transfers the toner image on the photoconductor onto paper. The magnetic flux density on the surface of the photoconductor 21 is 800 Gs. The diameter of the photoconductor 21 is 30
mm and the peripheral speed was 60 mm / s. The toner was composed of 93% of styrene-acrylic resin, 5% of carbon black and 2% of metal complex of oxycarboxylic acid, and 0.5% of colloidal silica was externally added (all in% by weight).
The carrier has a surface coated with silicone resin and a particle size of 1
A ferrite powder of 00 μm was used. The magnetic pole of the magnet 22 was set at an angle of 30 ° upstream from the closest position of the electrode roller.

The operation of the electrophotographic apparatus configured as described above will be described below with reference to FIG. Photoconductor 2
1 is a corona charger 23 (applied voltage-4 kV, grid 2
4 voltage of -500V) and charged to -500V. The photoconductor 21 was irradiated with a laser beam 25 to form an electrostatic latent image. At this time, the exposure potential of the photoconductor was -100V.
The magnetic developer 27 was magnetically attached to the surface of the photoconductor 21 in the developer reservoir 26. Next, the photoconductor 21 was passed in front of the electrode roller 28. When passing through the uncharged area of the photoconductor 21, an AC high voltage power supply 29 is applied to the electrode roller 28, and an AC voltage of 500 V 0-p (peak to peak 1 kV) (frequency 500 Hz) is applied so that no DC voltage is superimposed.
Was applied. After that, when the photoconductor 21 charged with −500V and having the electrostatic latent image written thereon is passed, 500V0-p (peak-to-peak) in which a DC voltage of −350V is superimposed on the electrode roller 28 by an AC high-voltage power supply 29. 1k
V) AC voltage (frequency 500 Hz) was applied. Then, the developer moved between the photoconductor 21 and the electrode roller 28, and a negative-positive inverted toner image remained only on the image portion on the photoconductor 21. The developer attached to the electrode roller 28 rotating in the direction of the arrow is scraped off by the scraper 30,
It was returned to the developer reservoir 26 again and used for the next image formation. The toner image thus obtained on the photoconductor 21 was transferred onto paper (not shown) by the transfer charger 31 and then thermally fixed by a fixing device (not shown). As a result, a sharp image was obtained without any brush marks of the developer or toner scattering.

[0033]

According to the present invention, an electrophotographic 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 the 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 electrophotographic apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 6 Photoconductor 7 Magnet 8 Corona Charger 9 Grid Electrode 10 Laser Exposure 11 Developer Reservoir 12 Magnetic Developer 15 Electrode Roller 16 Magnet 17 AC High Voltage Power Supply 18 Scraper

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location G03G 15/06 101 G03G 15/06 101 15/09 15/09 Z 21/00 350 21/00 350

Claims (1)

(57) [Claims] 1. An electrostatic latent image holder that includes a fixed magnet and moves, means for forming an electrostatic latent image on the electrostatic latent image holder, and the electrostatic latent image on which the electrostatic latent image is formed. A developer reservoir for supplying a magnetic developer composed of a magnetic carrier and a toner is provided on the entire surface of the image holding member, and the electrostatic latent image holding member is installed with a predetermined gap from the surface of the electrostatic latent image holding member. moves in a direction opposite to the movement direction of the latent image holder
Magnetic carrier on the electrostatic latent image carrier and toner in the non-image area
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 .