JP2667904B2 - Electrophotographic equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an electrophotographic apparatus such as a copying machine or a laser printer.

[Conventional technology]

The developing method of the recording apparatus using the electrophotographic method includes regular development and reversal development. Normal development is a method in which toner particles having a polarity opposite to the charge polarity of the electrostatic latent image formed on the photoconductor are attached to the latent image surface by, for example, the magnetic brush development method to create the same positive image as the original. Is. A typical electrophotographic apparatus to which the regular development method is applied is a copying machine. On the other hand, reversal development is a method of forming a negative-positive image by adhering toner particles where the charge is removed from the uniformly charged surface by light. Many laser printers and the like that output and record digital print information from a computer, facsimile, or the like use a reversal development method. The reason is,
When comparing the areas of the printed and non-printed areas of text consisting of characters and lines, the area of the printed area is usually much smaller.
The method of exposing only the portion to be printed by the exposure means using D, LCD, etc. to form an electrostatic latent image and attaching toner particles to the image by reversal development prolongs the life of the exposure means and the photoconductor. And the recording time can be shortened. However, in reversal development, toner particles having the same sign as the charge polarity on the photoconductor charging surface must be subjected to Coulomb repulsion from the charge on the charging surface and adhere to the exposed low-potential portion according to the lines of electric force. The effect is strong, and only the large area black area (solid black) edge is developed black, but the central area is difficult to develop and the image density is not sufficient, and toner is easily attached to the unexposed area and fog easily occurs. However, there is a problem different from regular development.

Therefore, techniques for solving these problems of the reversal developing method have been conventionally studied. For example, JP-A-54-89733
And a DC voltage substantially the same as the charging potential of the photoreceptor is applied to the sleeve of the developing device of the electrophotographic apparatus as described in JP-A-60-154261 and JP-A-60-154261. Means are one of them. The present inventor conducted an experiment similar to this using selenium (Se) which has been conventionally used as a photoconductor of an electrophotographic apparatus. However, in these methods, a magnetic carrier having an average particle diameter of 100 μm or more and an average particle diameter of a dozen or more μm, which have been generally used conventionally, are used.
A two-component developer in which the toner particles are mixed is effective, but a two-component developer in which the toner particles and the carrier particles are miniaturized for the purpose of obtaining a high-quality image has no effect. There are many spots and fog
A clear recorded image could not be obtained.

As described above, the conventional general two-component developer uses a magnetic carrier having an average particle diameter of 100 μm or more and toner particles having an average particle diameter of about 10 μm, but in such a developer, There is a problem that it is difficult to obtain a high-quality recorded image that reproduces fine lines, dots, differences in shading, and the like because each particle is coarse. Therefore, in order to obtain a high quality image, many studies have hitherto been made on, for example, a resin coating of carrier particles, a method of applying a bias voltage to a sleeve, and atomization of toner particles and carrier particles. Above all, the toner particles and the carrier particles are reduced to fine particles in an electrophotographic apparatus such as a laser printer, in contrast to the conventional recording density of 240 dpi (dots / inch) to 300 dpi, to increase the recording density to 400 dpi for higher quality of the recorded image. ~
It is effective when it is increased to 600dpi.

However, when the toner particles are fine particles having an average particle diameter of 10 μm or less, not only is it difficult to control the triboelectric charging of the toner particles, but also aggregation tends to occur. Further, the influence of the Van der Waals force on the Coulomb force acting on the toner particles during development due to the fine particles increases, so that the toner particles adhere to the image background and fog occurs. Further, when the carrier particles are made finer, the attraction force to the sleeve due to the magnetic force of the magnetic roll of the developing device becomes weaker, which is referred to as carrier scattering or carrier pulling, which scatters from the sleeve during development and adheres to the photoreceptor. The phenomenon appears and disturbs the recorded image. In particular, in reverse development, since the charge polarity of the charged surface of the photoconductor and the charge polarity of the carrier particles have different signs, carrier pulling is likely to occur.

[Problems to be solved by the invention]

As described above, in the conventional technique, since the side effects as described above due to the fine particles of the two-component developer and the problems inherent in the conventional reversal development method described above are added, the two-component developer in the form of fine particles is actually used in the electrophotographic apparatus. Was difficult to use for reversal development.

The present invention has been made to solve the above problems,
The purpose is to carry out reversal development by combining a photoconductor composed of an organic photoconductor and a developer composed of finely divided toner particles and carrier particles, so that there is no lack of density, density unevenness and fog, and high image quality. An object of the present invention is to provide an electrophotographic device capable of clear recording.

[Means for solving the problem]

In order to achieve the above object, the present invention provides an electrophotographic apparatus in which an electrostatic latent image formed on a photoreceptor is subjected to reversal development using a two-component developer. The organic photoconductor thus constituted is characterized in that the two-component developer is a mixture of toner particles having an average particle diameter of 10 μm or less and ferrite carrier having a resistivity of 10 ⁷ Ω · cm or more.

[Action]

The highly insulating surface of the organic photoconductor and the ferrite carrier with a high resistivity improve the image density by stably maintaining the electric field acting on the developing area by the bias voltage applied to the developing carrier, and improve the fine toner of 10μm or less. Adheres to the electrostatic latent image in the developing area to reproduce a high-definition and high-quality recorded image.

〔Example〕

First, in order to facilitate understanding of the present invention, an experiment, an experimental result, and a study performed by the inventor will be described.

FIG. 2 is a vertical side view of the electrophotographic apparatus. Charger
The photosensitive member 21 uniformly charged by 20 is exposed by the exposure unit 23 that operates according to the recording signal from the data recording unit 22 so that only the printed portion (the portion to which toner is attached) is exposed and the potential of that portion becomes low. And an electrostatic latent image is formed. Next, a toner having the same polarity as the charged polarity of the photoconductor 21 is supplied to the developing section by a sleeve 24A as a developer conveying member in the developing device 24, and is attached to a portion having a low latent image potential, so that the photoconductor is A toner image is formed on 21. This toner image is transferred from the paper cassette 26 via rollers 27 and 28 to the paper 29.
Is transferred by the transfer device 25. The paper 29 is separated from the photoconductor 21 by the paper removing static eliminator 30 and is sent to the fixing device 31. After the toner image on the paper 29 is fixed by the fixing device 31, the paper 29 is sent to the paper discharge tray 32. On the other hand, after removing excess toner on the surface of the photoconductor 21 by the cleaning device 33,
The residual charge is removed by the eraser 34, and the eraser 34 is used for the next recording step.

FIG. 1 is a vertical cross-sectional side view of the developing device 24 used in the electrophotographic apparatus of FIG. In the developer pool 35, there is a two-component developer 36 composed of a carrier and toner,
The toner is rubbed against the carrier by the rotation of the stirring screws 37 and 38, and is charged to a predetermined charge amount. The agitated two-component developer 36 includes a developing roll 40 having a fixed magnet roll 39.
Due to the rotation of the sleeve 24A, the developer is pumped up from the developer reservoir 35 and is conveyed in the rotation direction of the sleeve 24A. The thickness of the pumped up two-component developer 36 is regulated on the sleeve 24A by the doctor blade 41, a certain amount is supplied to the developing section, and the rest is turned back and passed through the scraper 42 to the toner concentration control sensor section 43. Be guided. The two-component developer 36 that has passed through the toner density control sensor unit 43 becomes a developer pool.
Collected at 35, repeat the same operation again.

On the other hand, the sleeve 24A passed the doctor blade 41 part
The upper two-component developer 36 is conveyed to the developing section in contact with the photoconductor 21 and used for development. Two-component developer 36 that has passed through the developing section
Is collected again in the developer reservoir 35. In the developing section, the toner adheres to the exposed area on the photoconductor 21 due to the action of the electric field created by the latent image potential of the photoconductor 21 and the DC bias voltage applied to the sleeve 24A from the bias power source 44.

In the two-component developer 36, the toner density, which is the mixing ratio of the toner and the carrier, must be kept constant in order to keep the recording characteristics constant. Therefore, the toner density control sensor
The toner concentration is monitored by 43, and when the toner is consumed by the development and the toner concentration of the two-component developer 36 decreases,
The toner is supplied from the toner hopper 46 by rotating the supply roller 45. In the drawing, reference numeral 47 denotes a stirring paddle provided at a position where the toner falls from the supply roller 45 so that the supplied toner immediately becomes compatible with the two-component developer 36 in the developing pool 35. To supply toner, use the toner cartridge.
The toner is conveyed to the toner hopper 46 from the inside by the rotation of the stirring blade 49. The stirring blade 49 is rotated simultaneously while the sleeve 24A is rotating.

The present inventor has studied using the electrophotographic apparatus shown in FIG. 2 and the developing device shown in FIG. 1 according to the method disclosed in JP-A-54-89733 and JP-A-60-154261. As described above, the recorded image has a low solid black density, has a lot of fog, and cannot print fine lines and dots clearly. As a result of various investigations, the main cause was that the Se photoreceptor was used, but in order to obtain a higher definition and higher quality image, it was necessary to adapt the developer and the reversal development process.

Hereinafter, the type of the photoconductor 21 and the type and characteristics of the toner and the carrier used for the two-component developer 36 by the present inventor, the gap between the photoconductor 21 and the sleeve 24A (hereinafter, referred to as a development gear), and the method of transporting the developer, By varying the stirring method, bias voltage, etc. and conducting experiments, it was found that these conditions are closely related in order to obtain a clear recorded image on the paper 29.

FIG. 3 to FIG. 7 are diagrams showing the results obtained by this experiment.

First, the difference in recording characteristics due to the difference in the photoconductor 21 will be described. As the photosensitive member 21, a cylindrical aluminum drum having Se deposited as a photosensitive layer to a thickness of about 60 μm, and an aluminum drum coated with an organic photoconductor as a photosensitive layer to a thickness of about 17 μm were used. . The drum had a diameter of 100 mm and a peripheral speed of 125 mm / s and was rotated clockwise. The potential of the unexposed portion of both photoconductors was 650 to 700.
With V, the potential of the exposed portion was set to 100 V or less. However, the charging polarity is S
While e is positive, the organic photoreceptor is negative.

The sleeve 24A and the doctor blade 41 are made of conductive non-magnetic aluminum. The developing roll 40 is
It is composed of a cylindrical sleeve 24A having a diameter of 40 mm and a cylindrical fixed magnet roll 39 inserted into the inside thereof. The fixed magnet roll 39 is fixed, and only the sleeve 24A is rotatable. The peripheral speed of the sleeve 24A is
It was made possible to change at a speed of 2 to 5 times the peripheral speed of, but the experiment was mainly carried out at a peripheral speed of 2.58 times. The number of magnetic poles of the fixed magnet roll 39 used was seven, and the intensity of the magnetic force was 850 gauss at the main pole located in the developing section. The developing gap is 1 mm, and the doctor blade 4
The doctor gap, which is the gap between 1 and the sleeve 24A, was set to 0.7 times the developing gap. The two-component developer 36 used was a mixture of a toner having an average particle diameter of 8 μm and a ferrite carrier having a resistivity of 10 ⁹ Ω · cm or more so that the toner concentration was 3% by weight. The charge polarity of the toner was adjusted by the charge control system contained in the toner so as to have the same polarity as the photoconductor 21 used.

FIG. 3 shows the result of examining the relationship between the magnitude of the bias voltage and the image density at the center of the solid black portion of the recorded image using the two types of photosensitive members 21. Curve A is the result for Se and curve B is the result for the organic photoconductor. In the case of Se, in the region where the bias voltage is small, the image density rises with the increase of the bias voltage, but it saturates up to around 200V, and if the bias voltage is further increased, uneven solid black occurs and the image density becomes unsatisfactory. It is not possible to increase the image density to a satisfactory level only by stabilization. This is due to the photoreceptor
It is considered that this is because the electric field on the surface of 21 is strengthened and a kind of breakdown occurs. JP-A-60-154261
Even if a bias voltage in which an alternating voltage is superposed on a direct current voltage is used as disclosed in Japanese Patent Laid-Open Publication No. 2003-242242, a clear recorded image cannot be obtained only by increasing the instability of the image density.

On the other hand, the organic photoconductor 21 does not have such a phenomenon, and the image density increases as the DC bias voltage increases, and a satisfactory image density can be obtained without using a complicated method such as superimposing an AC voltage on the DC bias voltage. To be The reason for this is that when the surface of the photoreceptor 21 in contact with the two-component developer 36 is an organic photoconductor, it is made of a highly insulating material such as polycarbonate. It is thought that this is because the previous breakdown is unlikely to occur.
From this result, it was found that it is advantageous to use an organic photoconductor whose surface is made of a material having a high insulating property for reversal development.

The next point is the resistivity of the carrier used for the two-component developer 36. FIG. 4 shows the results of examining the density change of the recorded image by changing only the resistivity of the carrier under the same recording conditions as described above using the organic photoconductor for the photoconductor 21. At this time, the bias voltage was set to -500V.
Carriers used two types: iron powder and ferrite. The resistivity of iron powder carrier is about 10 ⁴ Ω · cm as it is,
It can be changed up to about 10 ⁹ Ω · cm by coating the resin. Ferrite carrier, on the other hand, has a high resistivity as it is, about 10 ⁷ Ω · cm to 10 ⁹ Ω · cm, and 10 ¹⁴ Ω · cm by coating the resin.
The resistivity can be increased to about cm.

Image density becomes region satisfying if 10 ⁷ Omega · cm or more ferrite Canon rear using resistivity, the best is 10 ⁹
This is the case when a carrier having a resistivity of Ω · cm to 10 ¹² Ω · cm is used. At a higher resistivity, the image density is slightly reduced.
Generally, lowering the resistivity of the carrier improves the developability and improves the image density. However, in the case of reversal development, the developing gear gap is narrow and the bias voltage is high, so the insulating property is high. Even if an organic photoconductor having a surface is used for the photoreceptor, the use of an iron powder carrier having a low resistivity tends to cause a kind of breakdown on the surface of the photoreceptor 21 as described above, and the image Not only does the density not increase, but the density unevenness increases. From this result, the average particle size was 10 μm.
It has been found that ferrite carriers having a resistivity of 10 ⁷ Ω · cm or more are suitable for reversal development using the following toners.

In the case of using finely divided toner, it is necessary to reduce the particle size of the carrier in order to increase the stirring property. FIG. 5 shows the results obtained by changing the size of the carrier particles and the toner density under the same conditions as above, and determining the image density, the fog and the limit of the carrier pull. If the average particle size of the carrier particles is large, the chargeability of the toner deteriorates and fog occurs, so that the toner density of the two-component developer 36 cannot be increased and the image density is low. On the other hand, as the particle size of the carrier is reduced, carrier pulling tends to occur and the problem of further deterioration in fluidity occurs, and those having an average particle size of 50 μm or less cannot be used practically. For this reason, in the case of a toner having an average particle diameter of 8 μm, the carrier particle diameter conforming to the average particle diameter was in the range of 60 μm to 100 μm. From the above, it was found that the particle size of the carrier suitable for reversal development was in the range of 7.5 times to 12.5 times the particle size of the toner used.

If the size distribution of small particles with respect to the average particle size becomes large in the carrier used, carrier pulling easily occurs.
If the particle size distribution is set to be 0% or less, the margin for carrier drawing increases, which is preferable.

Various studies were conducted on the resin coating of the carrier, but no noticeable effect was found. This is because the ferrite carrier itself has a high resistivity. Therefore, in this electrophotographic apparatus, either resin coated or not resin coated may be used.

Next, the study of toner suitable for reversal development will be described. As described in the prior art, in order to improve the definition and image quality of a recorded image of an electrophotographic apparatus, as described in Japanese Patent Publication No.
It is effective to make the particles having a size of about 13 μm into fine particles of 10 μm or less. However, when the toner diameter is reduced, the surface area increases even with the same weight, and the contact between the toners increases, so that the fluidity becomes poor or the toners easily aggregate. Therefore, there is a problem in that the toner replenishing portion to the developing portion is likely to be clogged and stable replenishment cannot be achieved. In addition, if the toner diameter is reduced even in the developing device, the mixing and stirring characteristics with the carrier are deteriorated, and the replenished toner is not easily charged to a predetermined charge amount. As a result, the electrostatic adhesion of the toner to the carrier is weak, the scattering is increased and the inside of the apparatus becomes dirty, and the scattered toner causes fogging on a white background portion of an image which does not need to adhere the toner. There is.

Therefore, as a result of various studies by the present inventor, these problems were found in the reversal development using a fine particle toner having an average particle diameter of 10 μm or less by optimizing the particle size distribution of the fine particle toner, the materials constituting the toner and the external additives Was found to be reduced.

First, regarding the particle size distribution of the toner, as a result of various studies, in the case of reversal development using a toner having an average particle size of 10 μm or less, a small particle size of 0.65 times or less of the average particle size is 3% by weight. A toner having a particle size distribution of 1% or less by weight and having a large particle size of 2 times or more of the average particle size was suitable. The reason for this is that small-diameter toner particles are difficult to use in development and tend to remain because they have strong adhesion to the carrier.
In particular, when 3% or more of the toner particles having a small particle diameter of 0.65 times or less of the average particle diameter is contained in a weight ratio, the tendency is strongly problematic.

Next is the optimization of the materials and external additives that make up the toner. In the reversal development, the electric field for attracting the toner in the central portion of the solid black to the photoconductor 21 is weak as described in the section of the related art. Therefore, as described above, even if a measure for narrowing the developing gap and strengthening the electric field by the bias voltage is taken, the toner adhesion amount in the solid black central portion is essentially small. Therefore, the present inventor has considered changing the amount of carbon contained in the toner so that a sufficient image density can be obtained even when the amount of toner is small.

FIG. 6 shows the result of examining the relationship between the amount of carbon and the density of a recorded image using toner having a different amount of carbon as the developer of the electrophotographic apparatus of FIG. The amount of carbon contained in a toner conventionally used for a two-component developer is about 6%. For toner having an average particle size of 10 μm or less,
As shown in FIG. 6, the amount of carbon contained in the toner is 6
%, A sufficient image density cannot be obtained. In this study, the amount of carbon is preferably 8% or more and 15% or less by weight. If the amount of carbon is further increased, the resistivity of the toner decreases, the chargeability of the toner deteriorates, and fog occurs in the recorded image.

From 8% by weight or more of carbon contained in toner
15% or less of toner and 2% by weight of silica fine powder
When the following and magnetic particles are used by adding externally in the range of 1% by weight or less, the fluidity of the toner is improved, the cohesiveness can be improved, and the stirring and charging property is also improved, which is suitable for long-term continuous reversal development. On the other hand, it was found that there is almost no deterioration of the developer and it can be used stably. When hydrophobic silica is externally added to a toner containing vinyl resin as the main binder resin, the fluidity is improved and aggregation of toner particles is reduced, but if this toner is continuously used for a long period of time, it will be mixed and stirred in the developing device. It was found that the characteristics changed, and the replenished toner was not easily charged. As a result, a phenomenon of deterioration of the developer such as fogging and unevenness of image density is caused.

A close examination of the cause revealed that there were two problems. The first problem is that the hydrophobic silica added to the toner separates from the toner and moves to the carrier surface,
The second problem with covering the carrier surface is that the toner adheres to the carrier surface due to repeated use for a long time (toner filming). As a result of investigating various methods for solving these problems, by using externally adding magnetic fine particles having a smaller particle size than the toner particles in the toner or the developer, the deterioration of the developer due to continuous use is deteriorated. I found that there was almost no phenomenon. The magnetic fine particles to be externally added are smaller in particle size than the toner particles, and the material may be the same as that used for the conventional magnetic carrier. Among them, ferrite or magnetite, which can be easily pulverized, is suitable. I can tell you.

The above is the conditions for the developer. Next, the conditions for the developing device 24 that develops the electrostatic ray image formed on the photoconductor 21 using such a developer will be described.

The development gap, which is the gap between the photoconductor 21 and the sleeve 24A, needs to be sandwiched in order to bring out the effect of the electric field created by the bias voltage in the reversal development as described above. Seventh
The figure shows the result obtained by using the two-component developer 36 in the electrophotographic apparatus of FIG. 2 to determine the relationship between the development gap and the image density. From these results, it was found that when reversal development is performed using the two-component developer 36, a development gap of 1 mm or less is suitable.

The amount of the two-component developer 36 supplied to the developing area is regulated by the gap (doctor gap) on the sleeve 24A by the doctor blade 41. The size of the doctor gap is determined when the developing gap is 1 mm or less. It does not significantly affect the development gap, but it is 0.
If the ratio is not less than eight times, the two-component developer 36 is clogged by the developing gap, and the photosensitive member 21 and the sleeve 24A are easily locked. Therefore, in the present electrophotographic apparatus, the developing gap is set to 1 mm or less and the doctor gap is set to 0.8 times or less of the developing gap at the same time.

The transport speed of the two-component developer 36 is preferably 2 to 5 times the moving speed of the photosensitive member 21, and especially 2.5 to 3.5 times the image reproducibility. Since the transport speed of the two-component developer 36 is determined by the peripheral speed of the sleeve 24A, it is set and used so that the wind speed of the sleeve 24A satisfies the above condition. Also, two-component developer
When the transporting direction of 36 was the same as the moving direction of the photoconductor 21, a high-quality recorded image was obtained. When the conveying direction of the two-component developer 36 is set to the opposite direction to the moving direction of the photoconductor 21, the sliding action of the two-component developer 36 has a strong effect of scraping the toner image once developed, resulting in a sweep in the recorded image. Therefore, a clear recorded image cannot be obtained.

In this electrophotographic apparatus, the developing gap is 1 mm or less, and the parallelism of this gap is d ± 0 with respect to the gap d.
When it is within the range of 1d, there is no density difference between the right end and the left end of the image,
An image with a uniform density is obtained. The developing gap may be set in this way at the time of manufacturing the apparatus, but the photoconductor 21 and the two-component developer 36 have a life and must be replaced according to the number of printed sheets of paper 29. Therefore, the photoconductor 21 and the developing device 24
It is necessary that the developing device can be taken out of the apparatus main body, can be more easily mounted, and the developing gap can be set accurately. Conventionally, as one method, a contact ring with a diameter larger by 2d than the diameter of the sleeve 24A
There is a method of setting the developing device 24 by providing this ring on both ends of the photoconductor 21. However, this method is good during the initial period when the contact ring is not worn, but if the contact ring is worn, the development gap fluctuates and uneven density of the recorded image occurs.

Therefore, the present inventor does not use this method, and
As shown in the figure, a photoreceptor member 50 holding the photoreceptor 21 and a developing unit 24 are each independently detachable from the electrophotographic apparatus main body, and a pin 52 provided on a side plate 51 of the electrophotographic apparatus main body, Positioning holes provided in part of the photoconductor holding member 50
The developing device 24 and the photoconductor 21 are accurately positioned by fitting together the 53 and the positioning hole 54 provided in a part of the developing device 24, so that the parallelism of the developing gear is obtained. As shown in FIG. 9, the photosensitive member holding member 50 and the developing device 24 are inserted into and fixed to the apparatus main body by bearings 56, 57 provided on a side plate 55 on the back side of the apparatus main body, and the drum shaft 58 of the photosensitive member 21 and Developing roll 4
The shaft 59 of 0 is fitted so that the photosensitive member holding member 50 and the developing device 24 are fitted when the developing device 24 is inserted into the apparatus main body. The photosensitive member holding member 50 has a positioning hole 53 fitted to a pin 52 provided on a side plate 51 on the insertion side of the apparatus main body, and a screw 60 fitted to a screw hole 62 for fixing. In the developing device 24, the positioning hole 54 is similarly fitted to the pin 52 provided on the side plate 51 on the insertion side of the apparatus main body, and further the screw 61 is fitted and fixed to the screw hole 63. By sharing one pin 52 in this way, the developing device 24 and the photosensitive member
Since the position of 21 can be accurately determined, the developing gear can also be set accurately.

Furthermore, if the driving of the photoconductor and paper conveyance and the driving of the developing device system are performed by the same system such as a belt and a chain, a slight fluctuation occurs in the feeding speed of the photoconductor and paper conveyance system due to the fluctuation of the load of the developing device. Causes image unevenness. In particular, in the present invention, since the development gap is narrow in reversal development, the image forming process is more susceptible to this speed fluctuation than in the conventional system. By the way, the rotation of the photosensitive member and the conveyance of the paper must be at the same speed, but the rotation speed of the sleeve of the developing device does not need to be the same. Therefore, in the electrophotographic apparatus shown in FIG. 2, the driving of the developing device and the driving of the photosensitive member and the sheet conveying system are separated, and the driving of the developing device is independently driven. With this arrangement, the speed of the photosensitive member and the paper transport system does not fluctuate due to the load fluctuation of the developing device, and the image quality is improved.

 Hereinafter, examples of the present invention will be specifically described.

Embodiment 1 FIGS. 1 and 2 show an embodiment of a developing device and an electrophotographic apparatus using the present invention. The photoconductor 21 is a polycarbonate containing a charge generation layer containing phthalocyanine, which is an organic pigment, as a main component on an aluminum drum to a thickness of 0.5 μm, and a 30% by weight ratio of an oxadol derivative as a charge carrier layer on the charge generation layer. Was used to form an organic photoconductor having a two-layer structure. The volume resistivity of the photoconductor 21 is
It was 10 ¹⁵ Ω · cm.

The photoconductor 21 has a diameter of 100 mm and a peripheral speed of 125 mm / s and rotates clockwise. The potential of the surface of the photoconductor 21 is −650 V in the unexposed portion corresponding to the background portion of the image, and the applied voltage of the charger 20 and the exposure amount of the exposure unit 23 so that the exposed portion corresponding to the image recording portion is −100 V or less. It was adjusted. The output voltage of the bias power supply 44 applied to the sleeve 24A was -500V.

Aluminum, which is a conductive nonmagnetic material, is used for the sleeve 24A and the doctor blade 41 of the developing device 24. The developing roll 40 includes a cylindrical sleeve 24A having a diameter of 40 mm and a cylindrical fixed magnet roll 39 inserted therein, and only the sleeve 24A rotates counterclockwise to transport the developer 36. The peripheral speed of the sleeve 24A is 322.5 mm / s, which is 2.58 times the peripheral speed of the photoconductor 21. The number of magnetic poles of the fixed magnet roll 39 is seven, and the strength of the magnetic force is such that the magnetic flux density at the main pole located in the developing section is 850 gauss. The development gear tape was set to 1 mm and the doctor gear tape was set to 0.6 mm.

The toner is composed of styrene-acrylic resin as a main component, 10% by weight of carbon black, and 3% by weight of a chromium alloy dye as a charge controlling agent. Small particles with a particle size of 0.65 times or less of the particle size are 3% or less by weight ratio, and large particles with a particle size of 2 times or more the average particle size are 1% or less by weight ratio, and then fine silica powder 1% by weight and fine particles of magnetite 0.5% by weight as magnetic particles were externally added. When the particle size distribution of this toner was measured, the average particle size was 8 μm, 5.2 μm or less was 1.3% by weight, and those having an average particle size of 16 μm or more was 0.3% by weight.

Carrier used was ferrite mainly composed of copper-zinc, the surface of which was coated with a silicon resin to a thickness of about 0.2 μm. The carrier resistivity was 10 ¹² Ω · cm. The size of the carrier is 70 μm with an average particle size of 91 μm.
The particles classified so that the particles having a particle diameter of μm or less become 5% or less were used.

As the two-component developer 36, a mixture of the toner and the carrier such that the toner concentration becomes 3% by weight was used.
The toner density was detected by a toner density sensor unit 43 in the developing device 24, and was controlled to be within ± 0.5% around 3%. The charge amount of the toner at this time was −20 μC / g.

As a result of reversal development under the above conditions, the resulting paper 29
The upper recorded image was high in image density, free from uneven density and fog, and was clear and high quality. Subsequently, continuous printing of 50,000 sheets was performed while successively replenishing toner so that the toner concentration of the two-component developer 36 became constant. As a result, the image density was almost constant, the fog was small, and a high-quality and stable recorded image was obtained. Could be obtained.

Embodiment 2 This embodiment is an electrophotographic apparatus using the developing device 24 having the same structure as that of Embodiment 1, but the different points are as follows.

The potential of the surface of the photoconductor 21 is −600 V for the unexposed portion corresponding to the background portion of the image, and −100 V for the exposed portion corresponding to the image recording portion. It was adjusted. Further, the bias voltage applied to the sleeve 21A was −450V.

In the developing device 24, the peripheral speed of the sleeve 24A was set to 385 mm / s, the developing gap was set to 0.8 mm, and the doctor gap was set to 0.6 mm.

The toner is obtained by pulverizing a styrene-acryl resin as a main component, containing 8% by weight of carbon black and 3% by weight of a chromium alloy dye as a charge controlling agent, and has an average particle size and particle size distribution. Further, the mixing ratio of the external additive was the same as in Example 1.

Carrier is a ferrite whose main component is copper-zinc, the surface of which is not coated with a resin. The resistivity of the carrier was 10 ⁹ Ω · cm. The size of the carrier is 6% with an average particle size of 85 μm and a particle size of 65 μm or less.
Those classified as follows were used. In other words, the average particle size is 0.76 times (≒ 65μm / 85μm)
% Or less.

The toner concentration of the two-component developer 36 is ± 0.5 around 3.5%.
%. At this time, the toner charge amount was −22 μC / g.

As a result of reversal development under the above conditions, the recorded image had high image density, no density unevenness and no fog, and high image quality and sharpness as in Example 1. Continuously, two-component developer
When continuous printing of 50,000 sheets was performed while replenishing toner successively so that the toner density of 36 became constant, the image density was
It was possible to obtain a stable recorded image with high image quality with almost constant density and little fog.

Embodiment 3 This embodiment is an electrophotographic apparatus using a developing unit 24 having the same configuration as that of Embodiment 2, but different points are as follows.

The toner is composed of polyester resin as a main component, carbon black in a weight ratio of 10%, and a chromium alloy dye as a charge control agent in a weight ratio of 3%. The toner is crushed, and the average particle size is 6 μm. The particles having a small particle size of 0.65 times or less are classified so that the weight ratio is 3% or less and the large particles having a diameter of 2 times or more the average particle size is 1% or less. 2% by weight and 1% by weight of fine powder of ferrite as magnetic fine particles were used as external additives. When the particle size distribution of this toner was measured, the average particle size was 6 μm and the average particle size was 3.6 μm.
2.3% by weight or less was 0.5 μm and 0.5% by weight was 12 μm or more.

Carrier used was ferrite containing barium-zinc as a main component, the surface of which was coated with a styrene-acrylic resin. The resistivity of the carrier was 10 ¹⁰ Ω · cm. The size of the carrier used was classified so that particles having an average particle diameter of 60 μm and a particle diameter of 48 μm or less became 8% or less.

The toner concentration of the two-component developer 36 is ± 0.5 around 3%.
%. At this time, the charge amount of the toner was −18 μC / g.

As a result of performing reversal development under the above conditions, the recorded image was high in image density and free from density unevenness and fogging, and was clear with high image quality as in Example 1 or higher. Subsequently, continuous printing of 50,000 sheets was performed while successively replenishing the toner so that the toner concentration of the developer became constant.The image density was almost constant, the fog was small, and a high-quality and stable recorded image was obtained. I was able to.

〔The invention's effect〕

As described above, the present invention comprises a photoreceptor composed of an organic photoconductor, toner particles atomized to have an average particle size of 10 μm or less, and ferrite carrier particles having a resistivity of 10 ⁷ Ω · cm or more. By performing reversal development in combination with the two-component developer to be provided, it is possible to provide an electrophotographic apparatus capable of performing high-quality and clear recording without density insufficiency, density unevenness and fog.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional side view of a developing device according to an embodiment of the present invention, FIG.
FIG. 4 is a vertical sectional side view of an electrophotographic apparatus according to an embodiment of the present invention, FIG. 3 is a characteristic diagram showing a difference in bias voltage and image density due to a difference in photoconductor, and FIG. 4 is a resistivity of a carrier and a recorded image. FIG. 5 is a characteristic diagram showing the density change, FIG. 5 is a characteristic diagram showing the image density and the limit of fogging and carrier pulling obtained by variously changing the size of the carrier particles and the toner concentration under the same conditions, and FIG. Characteristic diagram showing the relationship with the concentration of
FIG. 7 is a characteristic diagram showing a relationship between the developing gear and the image density,
FIG. 8 is a perspective view showing a setting portion of the developing device, and FIG. 9 is a vertical sectional side view showing a positioning structure of the photoconductor and the developing device. 21 ... Photoconductor, 24 ... Developer, 24A ... Sleeve, 35 ...
... developer pool, 36 ... developer, 40 ... developing roll, 41 ...
… Doctor blade, 44… Bias voltage, 45… Supply roller, 46… Toner hopper, 47… Stirring paddle, 48…
... toner cartridge, 49 ... stirring blades, 50 ... photosensitive member holding member, 51 ... electrophotographic apparatus main body side plate, 52 ... pin,
53,54 ... Positioning holes.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location G03G 15/08 506 G03G 9/10 321 (56) References JP-A-63-208861 (JP, A) JP-A JP-A-63-301960 (JP, A) JP-A-60-170660 (JP, A) JP-A-1-167847 (JP, A)

Claims (1)

(57) [Claims] 1. An electrophotographic apparatus for reversal developing an electrostatic latent image formed on a photoreceptor by applying a DC bias voltage between a developing carrier and the photoreceptor using a two-component developer. The component developer toner has an average particle diameter of 6 to 10 μm.
And the amount of carbon contained in the toner is 8 to
10%, silica fine powder as an external additive is added in an amount of 1 to 2% by weight, and magnetic fine particles are added in an amount of 0.5 to 1% by weight, and the particle size distribution of the toner is 0.65 of the average particle size. 3% or less by weight ratio of those having a small particle size of 2 times or less, and 1% or less by weight ratio of a large particle size having at least twice the average particle size. A ferrite carrier having a content of 6 to 8% or less and a resistance value of 10 ⁷ to 10 ¹² Ωcm having a particle size of 0.76 to 0.8 times the average particle size is used. The gap of the photosensitive member is 1 mm or less, and the gap between the developing member and the regulating member that regulates the thickness of the developer on the developing member is relative to the gap between the developing member and the photosensitive member. 0.8
An electrophotographic apparatus characterized by the following.