JP2001296736A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a stable image over a long term by preventing a sweeping irregularity of image on an image carrier, the adhesion of carrier, a fogging and the lowering of image density even in the case of small particle diameter toner, and further preventing the fluctuation of toner particle size distribution. SOLUTION: A developing device 4 in which two-component developer is stored is provided with a 1st developer carrier 48 being a rotating body for carrying and feeding the two-component developer and a 2nd developer carrier 47 being a rotating body for carrying and feeding the toner. The 1st developer carrier carries and, conveys the two-component developer by magnetic field and supplies the toner to the 2nd developer carrier by electric field, and the 2nd developer carrier supplies the toner to the image carrier 1 by the electric field, then toner supplying force from the 2nd developer carrier to the image carrier is made stronger than that from the 1st developer carrier to the 2nd developer carrier.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electrostatic latent image on an image carrier using, for example, an electrophotographic method or an electrostatic recording method, and developing the electrostatic latent image using a developer. To a visible image, and then transferred and fixed to a recording material to obtain a permanent image,
For example, the present invention relates to an image forming apparatus such as a copying machine and a printer.

[0002]

2. Description of the Related Art Conventionally, there is an image forming apparatus using an electrophotographic system or an electrostatic recording system, which is an output means of an external device such as a copying machine or a computer, that is, a so-called printer. FIG. 6 shows a schematic configuration of an example of a conventional image forming apparatus for forming a black (Bk) monochrome image.

That is, an image forming apparatus using, for example, an electrophotographic method includes, for example, a drum-shaped electrophotographic photosensitive member as an image carrier rotatable in the direction of an arrow, that is, a photosensitive drum 1 at a central portion thereof. The charging roller 2 as the primary charging means is uniformly charged on the surface. Thereafter, the surface of the photosensitive drum 1 is exposed to, for example, a laser beam L emitted from the optical system 3 in response to the image signal, and an electrostatic latent image is formed on the surface. The electrostatic latent image reaches a position facing the developing device 4 with the rotation of the photosensitive drum 1 in the direction of the arrow, for example, using a developer having the same polarity as the charge of the photosensitive drum 1 by the primary charging roller 2. And is visualized by reversal development.

[0004] Thereafter, the toner image is electrostatically transferred onto the recording material P by a transfer charging roller 8 as a transfer means, and further fixed by a fixing device 9 by heat and pressure. A permanent image forms on it. After the transfer of the toner image is completed, the photosensitive drum 1 is removed from the cleaning device 1.
When 0 removes residual toner and the like, it is used for the subsequent image forming operation.

[0005] In the conventional image forming apparatus having the above-described schematic configuration, a different type of developing apparatus is known as a developing apparatus used for developing an electrostatic latent image on an image carrier. Hereinafter, some types of developing devices used in a conventional image forming apparatus will be described with reference to the drawings.

FIG. 8 shows a so-called “two-component developer” using magnetic carrier particles and non-magnetic toner particles as a developer.
1 shows a schematic configuration of an example of a two-component developing device. Non-magnetic toner particles (hereinafter simply referred to as “toner”) are not limited, but are negatively charged in this example. In addition, a magnetic substance such as ferrite is used as the magnetic carrier particles (hereinafter, simply referred to as “carrier”).

In the two-component developing device 4 shown in FIG. 8, the developing container 40 has an opening at a position facing the photosensitive drum 1, and the developer is held so that a part thereof is exposed outside the developing container 40 through the opening. A developing sleeve 41 as a body is supported by the developing container 40 so as to be rotatable in the arrow direction. The developing sleeve 41 is made of a non-magnetic metal member such as aluminum or stainless steel.
mm is a conductive sleeve. In addition, the gap between the developing sleeve 41 and the photosensitive drum 1 is brought about by the gap regulating members (not shown) provided at both ends in the longitudinal direction of the developing sleeve 41 contacting the image non-forming regions at both ends in the longitudinal direction of the photosensitive drum 1. It is configured to keep a predetermined interval.

Inside the developing sleeve 41, a magnet roller 43 as a magnetic field generating means is concentrically fixed to the developing container 40 while maintaining a predetermined gap with the developing sleeve 41. That is, the magnet roller 43 is not rotated.

In the developing container 40, a first stirring screw 44 as first and second developer stirring means is provided on the photosensitive drum 1 side and on the opposite side thereof with a partition wall 46 therebetween.
The second stirring screws 45 are provided rotatably in the directions of the arrows. The second stirring screw 45 stirs the two-component developer to be supplied with toner so that the toner and the carrier have a constant weight ratio by a toner concentration adjusting mechanism, that is, a toner / carrier ratio adjusting mechanism (not shown). And at the same time, transport to the first stirring screw 44 side. Furthermore,
The first stirring screw 44 stirs and transports the two-component developer so as to be uniform in the longitudinal direction of the developing sleeve 41. At this time, the toner is frictionally charged by being stirred with the carrier, and thus the toner adheres to the carrier.

In this way, the two-component developer conveyed in the direction of the developing sleeve 41 by the first and second stirring screws 44 and 45 is attracted onto the developing sleeve 41 by the magnetic force of the magnet roller 43,
It is carried on the developing sleeve 41. In addition, the developing container 40 is hung down on the developing sleeve 41 so as to be close to the developing sleeve 41.
A magnetic blade 42 is provided as a developer layer thickness regulating unit. As the developing sleeve 41 rotates, the two-component developer carried on the surface of the developing sleeve 41
The layer thickness is regulated by the magnetic field generated by the cooperation of the magnetic field and the magnetic pole N1, and a thin layer (two-component developer coating layer) C1 of the two-component developer is formed on the developing sleeve 41.

The formed thin layer of two-component developer (two-component developer coating layer) C1 is further carried and conveyed on the developing sleeve 41 to reach a developing area (developing nip) facing the photosensitive drum 1. Here, the developing sleeve 41 is maintained at a predetermined gap from the photosensitive drum 1 by the gap regulating member (not shown) as described above, but in the thin layer C1 of the two-component developer carried on the developing sleeve 41, The carrier is raised by the magnetic field generated by the magnet roller 43, so that the two-component developer comes into contact with the surface of the photosensitive drum 1.

The toner in the two-component developer that has reached the developing area in this manner is rotated in the direction of the arrow by the developing electric field generated by the developing bias voltage applied between the developing sleeve 41 and the photosensitive drum 1. The photosensitive drum 1 flies over the photosensitive drum 1 and adheres to an electrostatic latent image on the photosensitive drum 1, that is, an area where primary charge has been attenuated by exposure, and the electrostatic latent image is visualized.

In the developing area, the carrier of the two-component developer is strongly attracted to the developing sleeve by the magnetic force of the developing magnetic pole S1 of the magnet roller 43.
There is no transfer on the surface, and the developing sleeve 41
Carried and transported. The carrier is removed from the developing sleeve 41 by the repulsive magnetic field formed by the repulsive magnetic poles of the magnetic poles N2 and N3 of the magnet roller 43 together with the toner that has not contributed to the development, and is stirred again.

Next, a so-called non-magnetic one-component developing apparatus using only non-magnetic toner particles as a developer, that is, a non-magnetic one-component developer will be described. FIG. 9 shows a schematic configuration of an example of the non-magnetic one-component developing device.

In the non-magnetic one-component developing device 4 shown in FIG.
The developing container 40 contains toner particles (toner) which is an insulating non-magnetic one-component developer as a developer. The toner is not limited, but is negatively chargeable in this example. The developing container 40 has an opening at a position facing the photosensitive drum 1, and a developing sleeve 41 as a developer carrier is rotatable in the direction of an arrow so as to be partially exposed from the opening. Supported. The developing sleeve 41 is made of a nonmagnetic metal member such as aluminum or stainless steel, and has a diameter of, for example, 16 mm.
And a conductive sleeve. In addition, the gaps between the gap regulating members (not shown) provided at both ends in the longitudinal direction of the developing sleeve 41 abut on the non-image forming areas at both ends in the longitudinal direction of the photosensitive drum 1, so that the developing sleeve 41 is in contact with the photosensitive drum 1. A predetermined gap is maintained.

A stirring member 50 for stirring the toner is provided substantially at the center of the developing container 40 containing the toner.
It is provided rotatably in the direction of the arrow, agitates the toner, and transports the toner toward the contact area between the developing sleeve 41 and the toner stripping / supply roller 51.

The toner stripping / supply roller 51 is made of, for example, urethane sponge, and is in contact with the surface of the developing sleeve 41 at a predetermined penetration amount. This toner stripping /
The supply roller 51 is connected to the developing sleeve 4 as shown by the arrow.
The toner is preliminarily charged and supplied onto the developing sleeve 41 by rotating in the same direction (counterclockwise direction in FIG. 1) as in FIG.

Further, the developing container 40 is provided with a developing blade 52 as a developer layer thickness regulating means so as to be in contact with the surface of the developing sleeve 41. The toner supplied to the developing sleeve 41 by the toner stripping / supply roller 51 is regulated in layer thickness by the developing blade 52 with the rotation of the developing sleeve 41, and a thin layer of toner (toner coating) is formed on the developing sleeve 41. Layer C2 is formed. The toner is frictionally charged by the friction with the developing blade 52 at this time.

The amount of toner conveyed to the developing area (developing nip) depends on the amount of the developing blade 5
2 is determined by the contact thickness and the contact length. here,
The developing blade 52 is a so-called chip blade that is adhered or welded onto a thin metal plate 53 of phosphor bronze, stainless steel, or the like having a thickness of several hundred μm, and is uniformly placed on the developing sleeve 41 by the elasticity of the thin metal plate 53. Has been abutted. The contact condition of the developing blade 52 is determined by the material, thickness, penetration amount, and set angle of the thin metal plate 53, and the amount of toner carried and conveyed is 0.3 to 1. It is regulated to about 0 mg / cm ² .

The toner transported to the development area (development nip) with the layer thickness regulated as described above is caused by a development electric field generated due to a development bias voltage applied between the development sleeve 41 and the photosensitive drum 1 in the direction of the arrow. The toner flies over the rotating photosensitive drum 1, and the toner adheres to the electrostatic latent image on the photosensitive drum 1, that is, the area where the primary charge has been attenuated by exposure, and the electrostatic latent image is visualized. Further, the toner remaining on the developing sleeve 41 without contributing to the development is carried and transported by the developing sleeve 41 as it is, peeled off by the toner peeling / supply roller 51, collected in the developing container 40, and again. Stirred.

Further, as an intermediate developing method between the above two developing methods, that is, the two-component developing method and the non-magnetic one-component developing method, for example, as shown in FIG. (Toner) with magnetic carrier particles,
The toner is triboelectrically charged in the state of the two-component developer, and the two-component developer is supplied onto the first developer carrier 48 by a magnetic force to form a two-component developer thin layer (two-component developer coating layer) C1.
Then, only a toner is applied from the first developer carrier 48 to the second developer carrier 47 by an electric field to form a thin layer (toner coat layer) C2 of the toner, and finally the second layer C2 is formed. There is conventionally known a developing method of performing development by causing toner to fly from a thin layer of toner (toner coat layer) C2 from the developer carrying member 47 to the electrostatic latent image on the photosensitive drum 1. Hereinafter, in this specification, this developing method is referred to as a two-stage developing method.

More specifically, as shown in FIG. 10, in a conventional two-stage developing device, a two-component developer containing a toner and a carrier is contained in a developing container 40, and is used for stirring the two-component developer. The stirring member 44 stirs the two-component developer and the supply sleeve 4 as a first developer carrier.
Conveyed toward 8. The supply sleeve 48 is supported on the developing container 40 so as to be rotatable in the direction of the arrow, and a magnet roller 49 as a magnetic field generating means is fixed to the developing container 40 in a non-rotating manner. That is, the supply sleeve 48
The supply of the two-component developer to the developing sleeve 41 corresponds to the supply of the two-component developer to the developing sleeve 41 in the above-described two-component developing method.

The two-component developer supplied to the supply sleeve 48 is rotated by the rotation of the supply sleeve 48 in the direction of the arrow, and the magnetic blade 42 and the magnetic pole N1 serving as a developer layer thickness regulating means.
The thickness of the layer is regulated by the cooperation of the two-component developer, and a thin layer of a two-component developer (two-component developer coat layer) C1 is provided on the supply sleeve 48.
Is formed.

A thin layer of the two-component developer is applied to the supply sleeve 48.
With the rotation of, the toner is transported to a portion facing the developing sleeve 47 as the second developer carrier, and only the toner in the two-component developer is supplied to the supply sleeve 48 and the developing sleeve 4.
7 moves from the supply sleeve 48 onto the developing sleeve 47 by the electric field applied between the developing sleeve 7 and the developing sleeve 47, and a thin layer C2 of toner is formed on the developing sleeve 47.

The toner carried on the developing sleeve 47 is transported by a rotation of the developing sleeve 47 in the direction of the arrow to a developing area (developing nip) opposed to the photosensitive drum 1 and applied between the developing sleeve 47 and the photosensitive drum 1. The electric field generated due to the applied bias voltage flies over the photosensitive drum 1 and adheres to the electrostatic latent image on the photosensitive drum 1, and the electrostatic latent image is visualized.

Although the conventional black (Bk) single-color image forming apparatus and the developing apparatus provided in such an image forming apparatus have been described above, in each of the above-described developing methods, the toner itself is made non-magnetic, that is, the magnetic material is used. Is advantageous for forming a color image. Conventionally, a color image forming apparatus including the above-described developing devices has the following configuration.

FIG. 7 shows a schematic configuration of a full-color image forming apparatus as an example of a color image forming apparatus. For example, a case in which a non-magnetic one-component developing device is employed will be described. A negatively-charged non-magnetic non-magnetic material containing any of yellow (Y), magenta (M), cyan (C), and black (Bk) color materials is described. The developing devices 4Y, 4M, 4C, and 4Bk for each color that accommodate the one-component toner are incorporated in the rotary rotary 4a. At the time of full-color image formation, the rotary rotary 4a rotates, and the developing devices 4Y, 4M, 4
By arranging any one of C and 4Bk at a position facing the photosensitive drum 1, a toner image of a desired color can be formed on the photosensitive drum 1 at a desired timing.

That is, the surface of the photosensitive drum 1 is uniformly charged by the primary charging roller 2 and then subjected to color-separated image exposure L to form an electrostatic latent image on the photosensitive drum 1. Developer (toner) of each color electrostatically adheres to the electrostatic latent image corresponding to each color, and yellow (Y), magenta (M), cyan (C), and in some cases, black (Bk) At each timing, each monochrome toner image
It is formed on the photosensitive drum 1 for each single color. In this way, the toner images formed one by one on the photosensitive drum 1 are superimposed on the intermediate transfer drum 11 as an intermediate transfer member, and then the full-color toner image formed on the intermediate transfer drum 11 is transferred to the transfer charging roller. At 8, the images are collectively transferred onto the recording material P. Subsequently, the unfixed full-color toner image is fixed on the recording material P by the heat and pressure in the fixing device 9 to obtain a permanent image. Further, the photosensitive drum 1 and the intermediate transfer drum 11 on which the image transfer has been completed are subjected to the removal of residual toner and the like by the action of the cleaning device 10 and the cleaning roller 12, respectively.

Next, the toner used in each of the above-described developing methods will be described. Conventionally, as a method for producing a toner, a resin, a release agent containing a low softening point substance, a colorant, a charge control agent, and the like are uniformly dispersed using a pressure kneader, an extruder, or a media disperser, and then the Production of toner (pulverized toner) by a so-called pulverization method in which a target is crushed under a target or jet stream to finely pulverize the toner to a desired particle size, and further subjected to a classification process to sharpen the particle size distribution to produce the toner. Methods are known.

In addition, there is a method described in Japanese Patent Publication No. 56-13945, which uses a disk or a multi-fluid nozzle to atomize a molten mixture into air to obtain a spherical toner. Further, Japanese Patent Publication No. 36-10231,
9-53856, JP-A-59-61842, a method of directly producing a toner using a suspension polymerization method, and a method in which a monomer is soluble and a polymer obtained by polymerization is insoluble. Emulsification represented by a dispersion polymerization method in which a toner is directly produced by using an aqueous organic solvent as described above, or a soap-free polymerization method in which a toner is produced by direct polymerization in the presence of a water-soluble polar polymerization initiator. It is possible to produce a toner (polymerized toner) by a so-called polymerization method such as a polymerization method.

When a toner is produced by a method including polymerization among the above-mentioned toner production methods, a toner having a spherical shape and a smooth surface can be easily obtained. Therefore, the polymerized toner has the following advantages.

That is, by making the toner shape spherical, the fluidity of the toner is improved, and the mechanical stress of the toner is reduced. Further, by using the spherical toner, it is possible to obtain the transfer efficiency up to nearly 100%. Further, in the case of irregular-shaped toner such as pulverized toner, when the pressing force of the roller-shaped transfer means (transfer roller) 8 is high, the toner is
(Or, the intermediate transfer drum 11) is mechanically pressed to cause transfer failure, that is, so-called “missing characters” easily occurs. However, with the spherical toner, “missing characters” does not easily occur.

In recent years, for example, as a part of improving image quality of an electrophotographic image forming apparatus, a reduction in toner particle size has been required. Since the energy required to crush the particles is proportional to the square of the particle size of the toner -2, it is difficult to reduce the particle size of the toner by the crushing method. On the other hand, in the production of toner by the polymerization method, toner particles are generated using a chemical reaction, so that the particle size of the toner can be easily reduced and a sharp particle size distribution can be easily obtained. This is a toner manufacturing method suitable for forming an image.

Here, a method of measuring the toner shape will be described, and the shape factor SF- of the toner used in this specification will be described.
1. Define SF-2. That is, FE-S manufactured by Hitachi, Ltd.
Using an EM (S-800), 100 toner images were randomly sampled, and the image information was introduced into an image analyzer (Luzex3) manufactured by Nicole via an interface, analyzed, and calculated by the following equation. The obtained values are defined as shape factors SF-1 and SF-2. (SF-1) = {(MAXLNG) ² / AREA} ×
(Π / 4) × 100 (SF-2) = {(PERI) ² / AREA} × (1 /
4π) × 100 As understood from FIG. 11, the shape factor SF-1 is a numerical value indicating the ratio of the roundness (spherical degree) of the shape of the spherical material, and is obtained by projecting the spherical material on a two-dimensional plane. Let MXLNG be the absolute maximum length of the resulting elliptical figure, and let AREA be the projected area. The shape factor SF-2 is a numerical value indicating the degree of unevenness of the spherical substance, and the peripheral length of the projected figure is PERI. When the shape factor SF-1 is larger than 140, the shape gradually changes from a spherical shape to an irregular shape, and when the shape factor SF-2 is larger than 120, irregularities on the toner surface become remarkable.

Next, the average particle size and the particle size distribution of the toner used in this specification are defined to be measured by the following apparatus and method. That is, the coulter counter TA-
Interface (Nikkaki) and PC980 that output number distribution and volume distribution using Type II (manufactured by Coulter)
1 Connect a personal computer (manufactured by NEC).
In addition, a 1% aqueous sodium chloride solution is prepared using primary sodium chloride as an electrolytic solution. Instead of the Coulter Counter TA-II, for example, ISOTONR-II
(Coulter Scientific Japan) or Coulter Multisizer (Coulter) can be used.

The measuring method is as follows.
In 50 ml, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant, and 2 to 20 mg of a measurement sample is further added. The aqueous charge solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser,
The volume distribution and the number distribution were calculated by measuring the volume and the number of toner particles having a particle size of 2 μm or more by using a 100 μm aperture as the aperture with a Coulter Counter TA-II.

From the volume distribution determined by the above measurement method,
Volume-based volume average particle diameter (Dv: median value of each channel is a representative value of the channel) and volume variation coefficient (S
v) was determined. Further, from the number distribution obtained by the above-described measurement method, the number-based length average particle diameter (Dl) and the length variation coefficient (Sl) were obtained.

Further, the weight-based coarse powder amount (8.00 μm or more) determined from the volume distribution and the number-based fine powder amount (5 μm or less) determined from the number distribution were determined.

The length variation coefficient S1 was determined by the following equation: length variation coefficient (S1) = (σ / D1) × 100 (%). Here, σ is the standard deviation of the number-based particle size distribution.

[0040]

The conventional image forming apparatus employing each of the above-described developing devices has the following problems.

First, when the two-component developing device 4 shown in FIG. 8 is used as the developing device 4, the toner itself is non-magnetic, and the carrier and the toner are stirred and mixed, and the carrier on which the toner adheres is conveyed by magnetic force. Therefore, in the two-component developing device 4, the supply of the two-component developer onto the developing sleeve 41 and the regulation of the layer thickness of the two-component developer can be performed by the magnetic force, so that the two-component developing device 4 can be uniformly and appropriately formed on the developing sleeve 41. It is easy to obtain a thin layer (two-component developer coating layer) C1 of a two-component developer having a large thickness. The toner can obtain a charge by frictional charging with a carrier, and can stably obtain a uniform and high toner charge amount. There are advantages such as.

However, in the two-component developing device, the thin layer C1 of the two-component developer, which is carried and conveyed in a state in which the carrier stands on the developing sleeve 41,
As a result, not only the toner but also the carrier comes into contact with the surface of the photosensitive drum 1. Therefore, the carrier peels off the toner image (visible image) on the photosensitive drum 1 and causes a large number of image defects with a size equal to the carrier particle size (about 30 to 100 μm), and uneven image, so-called “ Sweep unevenness ".

This phenomenon becomes remarkable especially when the toner is reduced in particle size in order to achieve high resolution. That is, when reducing the particle size of the toner, the specific surface area of the carrier is increased by lowering the weight content of the toner in the two-component developer, so that the toner is provided with good triboelectric charging.
However, as the weight content of the carrier in the two-component developer increases, the probability that the carrier peels off the toner image increases, and image unevenness easily occurs.

Further, when the carrier is reduced in particle size in order to use a toner having a small particle size, the magnetic force per particle of the carrier is reduced, so that it is difficult to restrain the carrier by the magnetic force on the developing sleeve 41. Become. Therefore, the carrier having a small particle diameter easily adheres to the photosensitive drum 1 in the development area (development nip). That is, not only the toner but also the carrier easily moves on the photosensitive drum 1 and is further transferred onto the recording material P, so that the quality of an image formed on the recording material P is significantly reduced.

As described above, in the image forming apparatus employing the two-component developing device, the stable triboelectric charging of the toner,
It was difficult to achieve both image unevenness and prevention of carrier from adhering to the photosensitive drum 1, and it was difficult to reduce the particle size of the toner.

Next, when the non-magnetic one-component developing device 4 shown in FIG. 9 is used as the developing device 4, the toner itself is made non-magnetic and applied directly to the developing sleeve 41 without using a carrier. Accordingly, in the non-magnetic one-component developing device 4, only the toner comes into contact with the photosensitive drum 1, and image unevenness caused by the carrier contacting the photosensitive drum 1 as occurs in the two-component developing device. Does not occur. The carrier does not adhere to the photosensitive drum 1. There is an advantage.

However, in the non-magnetic one-component developing device, only one of the developing blade 52 and the developing sleeve 41 is used.
Since toner is charged by frictional charging in a contact area (regulation nip) of about 2 mm, stable toner friction differs from stirring and mixing a carrier having a sufficient surface area and toner in a two-component developing method. It is difficult to charge. Therefore, when the particle diameter of the toner is reduced in the non-magnetic one-component developing method, the toner becomes non-uniform and unstable, and the density unevenness such as a decrease in the density in the image area and the toner (noise ) Adhesion, so-called increase in fog, etc. occurs, and a good formed image cannot be obtained.

In the non-magnetic one-component developing method, the supply of toner to the developing sleeve 41 and the regulation of the thickness of the toner layer cannot be controlled by the magnetic force. It is necessary to bring the supply rotating member into contact with the developing sleeve 41. Therefore, in the non-magnetic one-component developing device in which the toner is pressed against the developing sleeve 41 by the rotating member serving as the toner stripping / supplying roller 51, for example, toner aggregation is likely to occur. Is used, the fluidity of the toner particles is deteriorated, so that a uniform toner coat cannot be obtained on the developing sleeve 41, and image unevenness often occurs.

Further, the small particle size toner increases the surface area of the toner in the same volume, making uniform triboelectric charging difficult. Therefore, although reducing the toner particle size in the conventional non-magnetic one-component developing device has the advantage of improving the spatial resolution of the formed image, the non- The toner (noise) adheres to the toner, so-called fog and density unevenness such as a decrease in the density in an image portion are easily generated, which makes it difficult to design a non-magnetic one-component developing apparatus.

On the other hand, when the two-stage developing device 4 shown in FIG. 10 is used as the developing device 4, the toner itself is made non-magnetic, stirred and mixed with the carrier, and then passed through a two-stage carrying and conveying process using a magnetic field and an electric field. Since the electrostatic latent image on the photosensitive drum is developed, good triboelectric charging of the toner can be obtained by using a carrier even when using a toner having a small particle diameter, similarly to the two-component developing device. Since the supply of the two-component developer by the magnetic force and the regulation of the layer thickness are included, uniform and appropriate supply of the developer can be realized. In the development area (development nip), a second developer carrier (development sleeve) 47 carries and transports a thin layer of toner (toner coat layer) C2 on the surface, and can be in a carrier-free state. Since the carrier is not brought into contact with the photosensitive drum 1, it is possible to form a high-quality image without “sweeping unevenness” of the image due to the contact of the carrier with the photosensitive drum 1 and without attaching the carrier onto the photosensitive drum 1. Become. There is an advantage.

That is, the two-stage developing device basically has the advantages of the two-component developing device and the non-magnetic one-component developing device described above.

However, in the two-stage developing device,
There is a problem that it is difficult to maintain high-quality images during long-term use. That is, in the two-stage developing method, an electric field is used to supply the toner from the first developer carrier (supply sleeve) 48 to the second developer carrier (development sleeve) 47. The toner is easily supplied selectively depending on the weight specific charge of the toner. Here, the weight specific charge of the toner is a value of Q / W obtained by dividing the charge Q of the toner by the weight W of the toner, and is referred to as “tribo” in this specification.

More specifically, since the toner tribo is correlated with the toner particle diameter r (Q / W∝1 / r), a toner having a specific particle size distribution is supplied onto the developing sleeve 47 by an applied electric field. You. Therefore, in long-term use, only toner of a specific particle size is consumed by development,
The particle size distribution of the toner in the developing container 40 changes, and the ratio of the toner that can be supplied to the developing sleeve 47 by the electric field decreases. As a result, the amount of toner coating on the developing sleeve 47 decreases, and image density unevenness such as a decrease in image density occurs.

Further, according to the two-stage developing method, the toner is supplied from the supply sleeve 48 to the developing sleeve 47 by contacting the two-component developer, whereas the toner is not developed in the developing region (developing nip). It is necessary to fly between the sleeve 47 and the photosensitive drum 1, and the photosensitive drum 1
The supply capability of the toner to the developing sleeve 47 is lower than the supply capability between the supply sleeve 48 and the developing sleeve 47. Therefore, only the toner having a tribo that is suitable for flying onto the photosensitive drum 1 contributes to the development due to the electric field applied between the developing sleeve 47 and the photosensitive drum 1. Similarly to the supply of the toner to the toner 47, the toner on the developing sleeve 47 is further selected and consumed according to the tribo of the toner or, in other words, the particle diameter of the toner.

As described above, by selectively consuming the toner in two stages, the fluctuation of the toner particle size distribution in the developing container 40 is further deteriorated, and the long-term stability of the developing device is significantly deteriorated.

Accordingly, an object of the present invention is to stably provide a uniform and high charge amount to a toner even when a toner having a small particle diameter is used as a toner in a two-component developer, It is possible to supply the developer to the image carrier, and it is possible to prevent unevenness of the image on the image carrier, adhesion of the carrier, fog and a decrease in the image density, and further suppress the toner particle size distribution fluctuation. An object of the present invention is to provide an image forming apparatus capable of forming a stable image over a long period of time by preventing such an image.

[0057]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
In an image forming apparatus including a developing device for developing an electrostatic latent image formed on an image carrier into a visible image, the developing device includes a two-component developer including a toner and a carrier as a developer. A first developer carrier that is a rotating body for carrying and transporting the two-component developer, and a second developer carrier that is a rotating body for carrying and transporting the toner,
The first developer carrier carries and transports the two-component developer by a magnetic field, and further supplies the toner to the second developer carrier by an electric field, and the second developer carrier The body supplies the toner to the image carrier by an electric field, and the toner is supplied from the first developer carrier to the second developer carrier from the second developer carrier. An image forming apparatus characterized in that a supply force of the toner to the image carrier is increased.

According to one embodiment of the present invention, the second developer carrier is more than the maximum value of the electric field intensity applied between the first developer carrier and the second image carrier. The maximum value of the electric field intensity applied between the image carrier and the image carrier is increased.

According to another embodiment of the present invention, at least the surface of the second developer carrier has a volume resistivity of 10 ^5.
A resistive layer having a resistance of Ωcm or more and 10 ¹⁰ Ωcm or less is provided.
Preferably, the resistance layer is a phenol resin in which carbon black and graphite are dispersed.

According to another embodiment of the present invention, the second developer carrier is a rotating body including a resistive elastic layer, and is pressed against the image carrier. Preferably, the resistance elastic layer has a volume resistivity of 10 ⁵ Ωcm or more and 10 ¹⁰ Ωcm or more.
The hardness is 30 degrees or more in Asker C hardness and 6
0 degrees or less. Further preferably, the resistance elastic layer is a silicone rubber in which at least carbon black is dispersed.

According to another embodiment of the present invention, the length variation coefficient of the toner is 10% or more and 30% or less.
According to a preferred embodiment, the toner has a shape factor SF-1 of 100 to 140, and a shape factor SF-2 of 10 to 10.
0 to 120.

According to another embodiment of the present invention, a part or all of the toner contained in the two-component developer is formed by a polymerization method. Preferably, the polymerization method is a dispersion polymerization method.

According to still another embodiment of the present invention, the carrier has a volume resistivity of 10 ⁸ Ωcm or more and 10 ¹⁵ Ωcm.
cm or less.

[0064]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 shows a schematic configuration of an image forming apparatus according to the present invention. According to the present embodiment, the image forming apparatus is a black (Bk) single-color image forming apparatus. However, it should be understood that the present invention is not limited to this, and can be applied to a color image forming apparatus. .

In the image forming apparatus, a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1 is rotatably supported in the direction of an arrow. When the image forming operation starts, the primary charging roller 2 uniformly charges the surface of the photosensitive drum 1. In this embodiment, the surface of the photosensitive drum 1 is uniformly charged to a negative polarity (−700 V) by the primary charging roller 2. The surface of the photosensitive drum 1 is irradiated with a laser beam L emitted by the optical system 3 in response to an image signal, and an image portion (-150 V) where primary charging of the photosensitive drum 1 is attenuated, that is, an electrostatic latent image Is formed.

Thereafter, as the photosensitive drum 1 rotates, the electrostatic latent image reaches a region facing the developing device 4 and is developed with toner to become a toner image (visible image). According to this embodiment, the development is reversal development, that is, the toner having the same polarity (negative polarity) as the primary charge adheres to the attenuated portion of the primary charge as described above.

On the other hand, the recording material P stored in the cassette 5
Is fed by a feed roller 6 and is conveyed by a conveying means 7 to a transfer area where the photosensitive drum 1 and the transfer charging roller 8 abut, in synchronization with the formation of the toner image on the photosensitive drum 1.

In this manner, the transfer charging roller 8 transfers the toner image formed on the photosensitive drum 1 to the conveyed recording material P.
Is transferred electrostatically to the top. Thereafter, the recording material P is transferred to the fixing device 9.
And the toner image is fixed by heat and pressure. The photosensitive drum 1 on which the transfer has been completed is subjected to removal of residual toner by a cleaning device 10 having a blade-shaped cleaning member to prepare for the subsequent image formation.

Next, the developing device 4 provided in the image forming apparatus of the present invention will be described in more detail. FIG. 2 shows a schematic configuration of an embodiment of the developing device according to the present invention.

The developing device 4 includes a polymerized toner (negatively chargeable) having a volume average particle size of 5 μm manufactured by a dispersion polymerization method,
Silicone resin is added to ferrite particles, which are magnetic materials, in an amount of about 0,0.
A two-component developer obtained by mixing a magnetic carrier having a volume average particle diameter of 30 μm applied at a thickness of 1 μm at a fixed ratio by a toner concentration (toner / carrier ratio) adjusting mechanism (not shown) is stored in a developing container 40. are doing. In the present embodiment, the weight mixing ratio of the toner to the carrier is 5% by weight.
% Is set.

In the developing container 40, a partition 46 is interposed.
The first stirring screw 44 and the second stirring screw 45 have spiral screws formed as first and second stirring means on the photosensitive drum 1 side and the opposite side, respectively.
Are rotatably provided in the directions of the arrows. The second stirring screw 45 stirs the two-component developer and conveys it to the first stirring screw 44 side. The first stirring screw stirs the two-component developer and conveys the developer toward a supply sleeve 48 as a first developer carrier. Here, a screw is formed in the first and second stirring means 44 and 45, and the two-component developer is also conveyed in the longitudinal direction of the supply sleeve 48, so that the amount of the two-component developer is also increased in this longitudinal direction. It can be made uniform. Further, at this time, the toner is frictionally charged by the first and second stirring screws 44 and 45 conveying and stirring the toner and the carrier at the same time.

The developing container 40 has a part opened on the photosensitive drum 1 side, and is located at the opening to supply a supply sleeve 48 as a first developer carrier and a second developer carrier. Is supported by the developing container 40 so as to be rotatable in the direction of the arrow. According to this embodiment, the supply sleeve 48 is made of aluminum and has a diameter of 12 mm.
The sleeve. Further, the surface of the supply sleeve 48 is brought into contact with the surface of the developing sleeve 47 which is opposed by the gap regulating members (not shown) provided at both ends in the longitudinal direction abutting on the developing sleeve 47 as the second developer carrier. A constant gap of 500 μm is maintained. In this embodiment, the supply sleeve 48 rotates at a peripheral speed of 200 mm / sec.

Inside the supply sleeve 48, a magnet roller 49 as a magnetic field generating means is arranged concentrically with the supply sleeve 48 and with a predetermined gap from the supply sleeve 48. The magnet roller 49 is used for the developing container 4
It is fixed at 0, is non-rotating, and has five magnetic poles N2, S3, S2, and N1 in the rotation direction of the supply sleeve 48 from the magnetic pole S1 facing the developing sleeve 47 in order.
The magnetic pole S1 is a developer supply pole (800 Gs), the magnetic pole N1 is a developer layer thickness regulation pole (700 Gs), and N2 (600 Gs).
Denotes a developer blowing prevention pole, and magnetic poles S2 and S3 denote developer repelling poles (400 Gs). Note that the appended value is the maximum value of the absolute value of the magnetic flux density in the magnetic field generated by each magnetic pole.

The two-component developer conveyed toward the supply sleeve 48 by the first and second stirring screws is attracted by the magnetic force of the magnet roller 49 and supplied onto the supply sleeve 48. Above the magnetic pole N1, a magnetic blade 42 as a developer layer thickness regulating means hanging from the developing container 40 onto the supply sleeve 48 is provided so as to be close to the supply sleeve 48. The layer thickness of the upper two-component developer is regulated by the magnetic force in cooperation with the magnetic pole N1, and a thin layer (two-component developer coat layer) C1 of the two-component developer is formed. In the present embodiment, the amount of the two-component developer conveyed to the area facing the developing sleeve 47 is set to 50.
mg / cm ² .

In a developing sleeve 47 as a second developer carrying member arranged at a position facing the photosensitive drum 1 of the developing device 4, a gap regulating member (not shown) provided at both ends in the longitudinal direction thereof is photosensitive. By contacting the image non-forming regions at both ends in the longitudinal direction of the drum 1, a distance of 300 μm is maintained with respect to the opposing surface of the photosensitive drum 1. Developing sleeve 4
7 rotates at a peripheral speed of 170 mm / sec.

The two-component developer carried and conveyed on the supply sleeve 48 and arrived at the toner supply area facing the developing sleeve 47 is developed by the magnetic field generated by the magnet roller 49 in a state where the carrier carrying the toner is raised. Due to the electric field applied between the supply sleeve 48 and the developing sleeve 47 in contact with the surface of the sleeve 47, only the toner adheres to the surface of the developing sleeve 47, and a thin layer of toner (toner coat layer) C2 is formed on the surface of the developing sleeve. I do. Since the carrier is strongly attracted to the supply sleeve 48 by the magnetic force of the magnetic pole S1 of the magnet roller 49, the carrier does not move and adhere on the developing sleeve 47.

The toner not contributing to the supply of the toner onto the developing sleeve 47 is transferred to the magnet roller 4 together with the carrier.
The repulsive magnetic poles S2 and S3 (substantially 0 Gs) collect the toner into the developing container and agitate again.

The developing roller 47 is supplied by the supply roller 48.
The toner that forms the thin layer C2 of the toner having the coating amount of 0.5 mg / cm ² thereon along with the rotation of the developing sleeve 47,
An electric field generated due to a developing bias voltage applied between the developing sleeve 47 and the photosensitive drum 1 reaches the developing area opposed to the photosensitive drum 1 and flies from the developing sleeve 47 onto the photosensitive drum 1, and is exposed to light. The toner image is selectively adhered to the electrostatic latent image (image portion -150V, non-image portion -700V) on the drum 1 to form a toner image.

The basic configuration and operation of the developing apparatus of this embodiment have been described above. The features of the present invention will be described in more detail.

First, according to the present embodiment, the supply sleeve 4
8 has a DC voltage of -500 V with respect to the developing sleeve 47.
Is supplied to supply the negatively-charged toner in the two-component developer onto the developing sleeve 47. At this time, in order to suppress a current flowing from the supply sleeve 48 to the developing sleeve 47 via the carrier, and to prevent potential fluctuation and heat generation of the developing sleeve 47, it is desirable to use a carrier having a high resistance. Although not limited, in the present embodiment, the ferrite particles are coated with a silicone resin, and the volume resistivity of the carrier is set to 10 ¹⁰ Ωcm. If the volume resistance of the carrier is less than 10 ⁸ Ωcm, problems such as potential fluctuation and heat generation of the developing sleeve 47 occur due to current leaking to the developing sleeve 47 via the carrier.
If the volume resistivity of the carrier is larger than 10 ¹⁵ Ωcm,
Since an image defect occurs due to charge of the carrier, the volume resistivity of the carrier is preferably 10 ⁸ Ωcm to 10 ¹⁵ Ωcm.

Next, according to this embodiment, the developing sleeve 4
7 denotes a conductive column 47a made of aluminum and a resistance layer 4
7b. The resistance layer 47b is, but not limited to, a phenol resin in which carbon black and graphite are dispersed in the present embodiment, is applied to the surface of the conductive column 47a with a thickness of 50 μm, and has a volume resistivity of 1 μm.
Forming a 0 ⁶ [Omega] cm the resistance layer 47b.

The resistance layer 47b is coated on the developing sleeve 47
Reduces the reflection power of the attached toner, and the toner
By making it easier to fly to the
The ability to supply toner to the optical drum 1 is improved. Resistance layer
The volume resistivity of 47b is 10 ^FiveΩcm or more is preferable,
10^FiveIf less than Ωcm, the effect of lowering the toner mirror power
Was inadequate. Also, the volume resistivity of the resistance layer 47b
Limit the charge remaining on the surface of the developing sleeve 47 during development.
10 to suppress^TenPreferably less than Ωcm
No.

According to the present embodiment, the developing sleeve 47
Is applied with a bias voltage in which an alternating voltage having a frequency of 2 kHz and a peak-to-peak voltage of 2 kV is superimposed on a DC voltage of -500 V. Here, as long as the toner supplied onto the developing sleeve 47 is any type of toner, that is, the tribo of each toner particle (in other words, the particle size of the toner)
Irrespective of this, in order to be able to supply onto the photosensitive drum 1, the maximum value of the electric field strength (hereinafter referred to as “developing electric field”) between the developing sleeve 47 and the photosensitive drum 1 must be supplied. It is desirable that the electric field strength between the sleeve 48 and the developing sleeve 47 (hereinafter, referred to as “supply electric field”) be larger than the maximum value.

That is, in this embodiment, although not limited, a DC voltage of -1 kV is applied to the supply sleeve 48 to the developing sleeve 47, and as described above, The gap distance between the developing sleeve 47 and the supply sleeve 4 is 300 μm.
8 is set to 500 μm, and by applying an alternating voltage of 2 kVpp between the developing sleeve 47 and the photosensitive drum 1, the maximum value of the developing electric field in the image area on the photosensitive drum 1 is 4.5 V / μm. By making the supply electric field larger than the maximum value 1 V / μm, the developing sleeve 4
7, the ability to supply toner to the photosensitive drum 1 from above is increased. In this way, the toner supplied onto the developing sleeve 47 is supplied onto the photosensitive drum 1 irrespective of the toner particles.

If the maximum value of the developing electric field is not more than the maximum value of the supply electric field, a toner layer which does not fly by the developing electric field is formed on the developing sleeve 47, and the image density is lowered. Since the selection of the toner to be consumed occurs, the fluctuation of the toner particle size distribution in the developing container 40 also increases, and an appropriate image output cannot be obtained.

Further, according to this embodiment, the toner is formed by a dispersion polymerization method. Dissolve 60 g of polyvinylphenol in 600 g of methanol, and add styrene 1
00 g, 25 g of n-butyl acrylate and 10 g of azobisisobutyronitrile were added, mixed in a 5-liter flask, and refluxed in a nitrogen stream for 15 hours to produce particles. Furthermore, after adding oil black as a coloring agent,
After refluxing for 1 hour and cooling to room temperature, solid-liquid separation and washing with methanol were performed, and after drying, the volume average particle diameter was 5 μm,
Colored particles having a length variation coefficient of 20% were obtained.

In the structure of the image forming apparatus according to the present invention, in order to form a high-quality image over a long period of time, as shown in this embodiment, the toner length variation coefficient is suppressed to 30% or less. Is desirable. When the length variation coefficient is larger than 30%, uneven use such as a decrease in image density and an increase in fog tend to occur due to long-term use. Note that the toner length variation coefficient is set to 10% or more because the increase in production cost is suppressed while the density variation is suppressed. Hereinafter, this phenomenon will be described in more detail with reference to the drawings.

FIGS. 3 and 4 show the particle size distribution of the toner in the developing container 40. FIG. The charge amount of each toner particle depends on the particle size of the toner. If the particle size is too large, the charge amount per weight, that is, the weight-specific charge (tribo, Q / W) is insufficient, and the supply sleeve 48 to the developing sleeve When the toner is not supplied to the toner 47 and the toner particle size is too small, the toner particles have too large a triboelectricity, which makes it difficult for the toner to fly from the developing sleeve 47 to the photosensitive drum 1. Therefore, the toner consumed by the development depends on each particle size.

That is, when a polymerized toner having an initial particle size distribution shown by the solid line in FIG. 4A and having a length variation coefficient of 50% is used as a comparative example, a toner having a narrow range of particle size distribution shown by a broken line in FIG. Only the particles fly on the photosensitive drum 1 and contribute to development. As a result, while the image formation is repeated, the toner particle size distribution in the developing container 40 changes to the particle size distribution as shown in FIG. 4B, and the toner density having a particle size appropriate for development is reduced. Image formation becomes difficult, and density unevenness such as a decrease in image density and an increase in fog occur.

On the other hand, according to the present invention, when using a toner having an initial particle size distribution shown by the solid line in FIG. 3A and having a length variation coefficient of 20%, the photosensitive drum 1 shown by the broken line in FIG.
Since there is almost no difference between the particle size distribution of the toner flying upward and contributing to the development and the initial particle size distribution (solid line), even if image formation is repeated, as shown in FIG. The toner particle size distribution does not change, and it is possible to suppress the fluctuation of the toner particle size distribution even when the image forming apparatus is used for a long time, and it is possible to stably form a high-quality image.

In this embodiment, a polymerized toner manufactured by a dispersion polymerization method is used. In this embodiment,
Preferably, the above-mentioned effects are effectively exhibited by using a toner having a shape factor SF-1 = 100 to 140 and a shape factor SF-2 = 100 to 120, that is, a spherical and smooth toner. In the pulverized toner manufactured by the pulverization method,
Even if the classification is repeated and the length variation coefficient is 30% or less,
Since each toner particle is irregular, the charge amount of the toner becomes non-uniform, and it is difficult to obtain the effects of the present invention. But,
The pulverized toner having a length variation coefficient of 30% or less is subjected to the above-described sphering process, and the shape factor SF-1 of the toner is set to 100 to
0, by setting the shape factor SF-2 to 100 to 120,
The present invention can be suitably used, and the same effect as in the case of using the polymerized toner is obtained.

As described above, it is spherical and smooth, that is, the shape coefficient SF-1 = 100 to 140, and the shape coefficient SF-2 = 1.
The toner having a particle size of 00 to 120 can be easily prepared by a polymerization method.
And can be manufactured at low cost, but preferably,
In particular, by producing by a dispersion polymerization method that can easily obtain a sharp particle size distribution, the classification step can be simplified and the production efficiency can be increased.

As described above, according to the image forming apparatus of this embodiment,
By mixing and stirring the toner and the carrier, a uniform and high charge amount can be given to the toner, and the amount of the developer can be uniformly and appropriately regulated by the magnetic force.
7 is provided with a resistive layer to increase the toner supply power of the developing sleeve, and by making the intensity of the developing electric field larger than the supplied electric field intensity, the toner is prevented from being selectively consumed by tribo. 30% length variation coefficient
The following makes it possible to further suppress the selective consumption of the toner.

Embodiment 2 FIG. 5 shows another embodiment of the developing device according to the present invention. According to the present embodiment, the image forming apparatus performs development by causing a developing roller 54 including an elastic member to contact the surface of the photosensitive drum 1 instead of the developing sleeve 47 in the first embodiment as a second developer carrier. Otherwise, the configuration is basically the same as that of the first embodiment. Members having the same functions are denoted by the same reference numerals, and detailed description thereof will be omitted.

According to the present embodiment, the toner produced by dispersion polymerization having a volume average particle diameter of 3 μm and a length variation coefficient of 18%, and a magnetic carrier having a volume average particle diameter of 30 μm have a toner concentration (toner / carrier The mixture is mixed at a weight mixing ratio of 3% by a (ratio) adjustment mechanism (not shown), and is contained in the developing container 40 as a two-component developer. Although not limited, in this embodiment, the magnetic carrier is a polymerized carrier in which iron oxide is dispersed in a phenol resin, and is suitable for producing a carrier having a small particle size and high resistance. In addition, a carrier having a small particle diameter has an effect of expanding a contact area with respect to a toner having a small particle diameter as used in the present embodiment, thereby favorably triboelectrically charging each toner particle.

As in the first embodiment, the first and second stirring screws 44 and 45 convey the two-component developer toward the supply sleeve 48 while stirring. Also, supply sleeve 48
Are contained in a magnet roller 49, the two-component developer is supplied by a magnetic force onto a supply sleeve 48, and the layer thickness is regulated by cooperation between a magnetic blade 42 as a developer layer thickness regulating means and a magnetic pole N1. And coat amount 40mg / c
An m ² two-component developer thin layer C1 is formed.

The supply sleeve 48 includes developing rollers 54 and 50
A gap of 0 μm is maintained. A DC voltage of -300 V and an alternating voltage of 1 kV peak-to-peak voltage are applied to the supply sleeve 48 with respect to the developing roller, and in a region facing the thin layer C1 of the two-component developer and the developing roller 54, Only the negatively charged toner adheres to the developing roller 54, and no carrier exists on the developing roller 54;
A toner thin layer C2 having a coating amount of 0.4 mg / cm ² is formed.

Although not limited, in the present embodiment, the developing roller 54 is formed by disposing silicone rubber whose resistance is adjusted by dispersing carbon black as a conductive agent on the surface layer of a mandrel 54a having an outer diameter of 4 mm, as an elastic member. That is, a roller having an outer diameter of 16 mm formed as the resistance elastic layer 54b.
The resistance elastic layer 54b has a volume resistivity of 10 ⁷ Ωcm,
The hardness is 40 degrees on an Asker C hardness tester (total weight 500 g).

The toner carried on the developing roller 54 is
The rotation of the developing roller 54 reaches a region (developing nip) where the photosensitive drum 1 and the developing roller 54 come into contact with each other. The developing bias voltage applied between the developing roller 54 and the photosensitive drum 1 causes the developing bias voltage to be applied on the photosensitive drum 1. Adheres to the electrostatic latent image of
Form a toner image.

The embodiment of the basic configuration and operation of the developing device according to the present invention has been described above. The features of the present invention embodied in the present embodiment will be described in more detail.

First, in this embodiment, the developing roller 54
Is made to have a volume resistivity of 10 ⁷ Ωcm, similarly to the resistance layer 47b of the developing sleeve 47 in the first embodiment,
The reflection force of the toner on the developing roller 54 generated by the toner tribo is reduced, and the power of supplying the toner from the developing roller 54 to the photosensitive drum 1 is increased. In this embodiment, the surface layer of the developing roller 54, that is, the resistance elastic layer 5 is also used.
The volume resistivity of 4b is desirably set to 10 ⁵ Ωcm or more and 10 ¹⁰ Ωcm or less. Preferably, the hardness of the resistance elastic layer 54b is 30 degrees or more in Asker C hardness, and
0 degrees or less.

In this embodiment, the supply sleeve 48
By superimposing the alternating voltage between the developing roller 54 and the developing roller 54, even when a toner having a small particle diameter and a large adhesive force to the carrier is used as in the present embodiment, the developing roller 54 Thus, a sufficient amount of toner can be supplied. Further, by superimposing an alternating voltage between the supply sleeve 48 and the developing roller 54, the photosensitive drum 1
Even after passing through the developing area where the developing roller 54 abuts, the thin layer of the toner remaining on the developing roller 54 is disturbed, so that the development history is not reflected in the subsequent image forming process. There is.

Further, according to this embodiment, the developing roller 54 is applied with a developing bias voltage of -500 V with respect to the photosensitive drum 1, and the developing roller 54 contacts the photosensitive drum 1 with a contact pressure of 30 gf / cm. Therefore, the electric field strength (developing electric field) near the contact point between the developing roller 54 and the photosensitive drum 1 is larger than the maximum electric field strength (supply electric field) between the developing roller 54 and the supply sleeve 48 which are not in contact with each other. The maximum value can be increased, and the ability to supply toner from the developing roller 54 to the photosensitive drum 1 is increased. That is, the maximum value of the developing electric field in the image area on the photosensitive drum 1 is 25 V / μm, which is larger than the maximum value of the supply electric field of 1.6 V / μm.

Thus, the toner supplied onto the developing roller 54 is supplied onto the photosensitive drum 1 irrespective of the tribo of each toner particle. Is suppressed by contributing to the development, and as a result, the particle size distribution of the toner in the developing container 40 fluctuates.

Further, according to this embodiment, since the length variation coefficient of the toner is 18%, the particle diameter of the toner supplied onto the developing roller 54 is almost the same as that of the toner contained in the developing container 40. That is, even when the image forming apparatus is used for a long period of time, the density of toner having a particle size suitable for development does not decrease. Accordingly, it is possible to suppress a variation in the particle size distribution of the toner over a long period of time, and to form a high-quality image with little image deterioration.

On the other hand, in the image forming apparatus of this embodiment,
When a toner having a length variation coefficient of more than 30% is used,
If the image forming apparatus is used for a long time, the developing container 40
In this case, the toner particle size distribution fluctuated, and the image density decreased and the density unevenness occurred. Therefore, in the image forming apparatus having the configuration of the present embodiment, it is desirable that the toner length variation coefficient is 30% or less. In order to suppress an increase in toner manufacturing cost, the toner length variation coefficient is set to 10% or more. Also in this embodiment, the shape factor SF-1 of the toner is 100 to 140, and the shape factor SF-2 is 10
It is desirable to set it to 0 to 120.

As described above, according to the image forming apparatus of this embodiment,
By mixing and stirring the toner and the carrier, a uniform and high charge amount can be given to the toner, and the amount of the developer can be uniformly and appropriately regulated by the magnetic force.
Is provided with a resistive elastic layer 54b to increase the toner supply force of the developing sleeve, and the developing roller 54 is pressed against the photosensitive drum 1 to increase the developing electric field strength more than the supplied electric field strength with a simple configuration. Is prevented from being selectively consumed by the tribo, and by further reducing the toner length variation coefficient to 30% or less, it is possible to further suppress the selective consumption of the toner.

[0109]

As described above, the image forming apparatus according to the present invention relates to an image forming apparatus provided with a developing device for developing an electrostatic latent image formed on an image carrier into a visible image. The developing device contains a two-component developer containing a toner and a carrier as a developer, and a first developer carrier that is a rotating body for carrying and transporting the two-component developer, and for carrying and transporting the toner. A second developer carrier that is a rotating body of the first developer carrier, the first developer carrier carries and transports a two-component developer by a magnetic field, and further applies toner to the second developer carrier by an electric field. The second developer carrier supplies the toner to the image carrier by an electric field, and the second developer carrier is supplied with toner from the first developer carrier to the second developer carrier. It is configured to increase the supply power of the toner from the carrier to the image carrier. By mixing and agitating the carrier, even when using a toner having a small particle diameter, a uniform and high charge amount is stably given to the toner, and a uniform and appropriate amount of the developer is supplied to the image carrier by a magnetic force. And the density of the image on the image carrier due to contact with the image carrier, such as uneven sweeping of the image and adhesion of the carrier, poor charging of the toner, fog due to aggregation, and a decrease in image density. In addition, it is possible to prevent unevenness and the like, and furthermore, it is possible to form a stable image over a long period of time by preventing toner particle size distribution fluctuation due to selective consumption of toner by tribo. I can play.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram showing one embodiment of a developing device according to the present invention.

FIG. 3 is a graph illustrating a variation in particle size distribution of a toner according to the present invention.

FIG. 4 is a graph illustrating a variation in particle size distribution of a toner according to a comparative example.

FIG. 5 is a schematic configuration diagram showing another embodiment of the developing device according to the present invention.

FIG. 6 is a schematic configuration diagram illustrating an example of a conventional image forming apparatus.

FIG. 7 is a schematic configuration diagram illustrating an example of a conventional color image forming apparatus.

FIG. 8 is a schematic configuration diagram illustrating an example of a conventional two-component developing device.

FIG. 9 is a schematic configuration diagram illustrating an example of a conventional non-magnetic one-component developing device.

FIG. 10 is a schematic configuration diagram illustrating an example of a conventional two-stage developing device.

FIG. 11 is a diagram for explaining shape factors SF-1 and SF-2.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum (image carrier) 2 primary charging roller (primary charging unit) 3 optical system 4 developing device 8 transfer charging roller (transfer unit) 9 fixing device 10 cleaning device 11 intermediate transfer drum (intermediate transfer member) 42 magnetic blade ( (Developer layer thickness regulating means) 44 First stirring screw (first stirring member) 45 Second stirring screw (first stirring member) 46 Partition wall 47 Developing sleeve (second developer carrier) 48 Supply sleeve (second One developer carrier) 49 Magnet roller (magnetic field generating means) 54 Developing roller (second developer carrier)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03G 9/10 G03G 9/08 384 9/113 9/10 351 15/06 101 15/08 507L 507E 507X

Claims (13)

[Claims] 1. An image forming apparatus comprising: a developing device for developing an electrostatic latent image formed on an image carrier into a visible image, wherein the developing device includes a toner and a carrier as a developer. A first developer carrying member that contains a two-component developer and is a rotator for carrying and conveying the two-component developer, and a second developer carrying member that is a rotator for carrying and conveying the toner The first developer carrier carries and transports the two-component developer by a magnetic field, and further supplies the toner to the second developer carrier by an electric field, and the second developer carrier The developer carrier supplies the toner to the image carrier by an electric field, and the second developer is supplied from the toner supply force from the first developer carrier to the second developer carrier. Increasing the supply power of the toner from the carrier to the image carrier. An image forming apparatus symptoms. 2. The method according to claim 1, further comprising: determining a difference between a maximum value of an electric field intensity applied between said first developer carrying member and said second image carrying member. 2. The method according to claim 1, wherein the maximum value of the intensity of the electric field applied therebetween is increased.
Image forming apparatus. 3. A resist layer having a volume resistivity of 10 ⁵ Ωcm or more and 10 ¹⁰ Ωcm or less is provided on at least the surface of the second developer carrier.
Image forming apparatus. 4. The image forming apparatus according to claim 3, wherein said resistance layer is a phenol resin in which carbon black and graphite are dispersed. 5. The image forming apparatus according to claim 1, wherein the second developer carrier is a rotating body including a resistance elastic layer, and is pressed against the image carrier. Image forming apparatus. 6. The resistive elastic layer has a volume resistivity of 10 ^5.
Ωcm or more and 10 ¹⁰ Ωcm or less, and hardness is Aske
The image forming apparatus according to claim 5, wherein the rC hardness is 30 degrees or more and 60 degrees or less. 7. The image forming apparatus according to claim 5, wherein said resistance elastic layer is made of silicone rubber in which at least carbon black is dispersed. 8. The method according to claim 1, wherein at least an alternating electric field is formed between the first developer carrier and the second developer carrier. Image forming device. 9. The image forming apparatus according to claim 1, wherein the length variation coefficient of the toner is 10% or more and 30% or less. 10. The shape factor SF-1 of the toner is 10
The image forming apparatus according to any one of claims 1 to 9, wherein 0 to 140 and shape factor SF-2 are 100 to 120. 11. The image forming apparatus according to claim 1, wherein a part or all of the toner contained in the two-component developer is formed by a polymerization method. 12. The image forming apparatus according to claim 11, wherein said polymerization method is a dispersion polymerization method. 13. The carrier has a volume resistivity of 10 ^8.
The image forming apparatus according to any one of claims 1 to 12, wherein the value is not less than Ωcm and not more than 10 ¹⁵ Ωcm.