JPH02304458A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To record with high quality and cleanness by reversal developing with the combination of a photosensitive body constituted from an organic photo conductive body and developer constituted from particulated toner particles and carrier particles. CONSTITUTION:A surface of a photosensitive body 21 in the electrophotographic device which carries out reversal developing of an electrostatic latent image which is formed on the photosensitive body 21 utilizing two component developer 36 of the organic photoconductive body which is constituted from material of high insulation, and the two component developer 36 is made to be a mixture of toner particles with an average diameter of the particle smaller than 10mum and ferritic carrier with electrical resistance of over 10<7>OMEGA.cm. That is, electric field which affects a developing range by bias voltage impressed on a developer carrier is maintained stable by the surface with the high insulation of the organic photo conductive body and ferritic carrier with the high electrical resistance. Thus image density is improved, fine toner particle of 10mum and less are stuck to the electrostatic latent image in the developing range, and a recording image of high definition and high image quality is reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to electrophotographic devices such as copying machines and laser printers.

[Conventional technology]

Developing methods for recording apparatuses using electrophotography include regular development and reversal development. Regular development is a method in which toner particles with a polarity opposite to that of the charge polarity of the electrostatic latent image formed on the photoreceptor are attached to the latent image surface using, for example, magnetic brush development, to create a positive image that is the same as the original. It is. A typical electrophotographic apparatus that uses a regular development method is a copying machine.

On the other hand, reversal development is a method of creating a negative-positive image by attaching toner particles to a portion of a uniformly charged surface from which the charge has been removed by light. Many laser printers and the like that output and record digital print information from computers, facsimiles, etc. use a one-reversal developing force type. The reason for this is that when comparing the areas of printed and non-printed parts of text consisting of characters and lines, the area of the printed part is usually much smaller, so lasers, LEDs, etc.
A method of exposing only the area to be printed using an exposure means such as an LCD to create an electrostatic latent image, and then attaching toner particles to that image through reversal development can extend the life of the exposure means and photoreceptor. In addition, it is possible to shorten the recording time. However, in reversal development, toner particles with the same polarity as the charge polarity on the charged surface of the photoconductor must receive Coulomb repulsion from the charge on the charged surface and adhere to the exposed low-potential area along the lines of electric force, which causes the edge effect. Only the edges of large black areas (solid black) that appear strongly are developed black, but the central areas are difficult to develop, resulting in insufficient image density, and toner tends to adhere to unexposed areas and cause fogging. There are different problems than developing.

Therefore, techniques for solving these problems of the reversal development method have been studied. For example, JP-A-54-897
Applying a DC voltage that is almost the same as the charged potential of the photoreceptor to the sleeve of a developing device of an electrophotographic device, as described in Japanese Patent Application Laid-open No. 33 and Japanese Patent Application Laid-open No. 154261/1983,
Furthermore, means for superimposing an alternating current voltage is also one of them. The inventor conducted a similar experiment using selenium (Ss), which has been conventionally used as a photoreceptor in electrophotographic devices. However, these methods are effective for conventional two-component developers that are a mixture of magnetic carrier with an average particle size of 100 μm or more and toner particles with an average particle size of more than 10 μm; A two-component developer in which the toner particles and carrier particles are made finer to obtain high-quality images is not effective; it lacks density, has uneven density, and has fog, making it impossible to obtain clear recorded images. There wasn't.

In addition, as mentioned above, the conventional general two-component developer is
A magnetic carrier with an average particle size of 100 μm or more and toner particles with an average particle size of more than 10 μm are used, but in such a developer, each particle is coarse, so fine lines, dots, differences in density, etc. There is a problem in that it is difficult to obtain high-quality recorded images that reproduce images. Therefore, in order to obtain high-quality images, conventional methods include coating carrier particles with resin and applying a bias voltage to the sleeve.

Many studies have been made, such as making toner particles and carrier particles finer. Among these, finer particles of toner particles and carrier particles are used in electrophotographic devices such as laser printers, which are capable of printing at conventional speeds of 240 dpi (dots/inch) to 300 dpi.
This is effective when the recording density is increased to 400 dpi to 600 dpi in order to improve the quality of recorded images.

However, if the toner particles are made into fine particles with an average particle diameter of 10 μm or less, not only will it be difficult to control the triboelectric charging of the toner particles, but agglomeration will likely occur. Furthermore, as the particles become smaller, the effect of van der Waals force on the Coulomb force acting on the toner particles during development increases, and the toner particles also adhere to the background of the image, resulting in fogging. In addition, as the carrier particles become atomized, the attraction force to the sleeve due to the magnetic force of the magnetic roll of the developing device becomes weaker, resulting in a phenomenon called carrier scattering or carrier pulling, in which the carrier particles scatter from the sleeve and adhere to the photoreceptor during development. A phenomenon appears and disturbs the recorded image. In particular, in reversal development, carrier attraction tends to occur because the charge polarity of the charged surface of the photoreceptor and the charge polarity of the carrier particles are of opposite signs.

[Problem to be solved by the invention]

As described above, in the conventional technology, since the above-mentioned side effects caused by the fine particles of the two-component developer and the inherent problems of the conventional reversal development method described above are added, it is difficult to use the fine-grained two-component developer in an actual electrophotographic apparatus. It was difficult to use it for reversal development.

The present invention was made to solve the above problems, and its purpose is to perform reversal development by combining a photoreceptor made of an organic photoconductor and a developer made of finely divided toner particles and carrier particles. By doing so, it is an object of the present invention to provide an electrophotographic apparatus that can record clear images with high image quality without insufficient density, uneven density, or fog.

[Means to solve 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 reversely developed using a two-component developer, in which the photoreceptor has a surface made of a highly insulating material. The two-component developer consists of toner particles with an average particle size of 10 μm or less and a resistivity of 107Ω·1.
It is characterized by being a mixture of the above ferrite carriers.

(Function) The highly insulating surface of the organic photoconductor and the high-resistivity ferrite carrier keep the electric field acting on the development area stable by the bias voltage applied to the development carrier, improving image density and improving image density to 10 μm or less. The fine toner adheres to the electrostatic latent image in the development area and reproduces a high-definition, high-quality recorded image.

〔Example〕

First, in order to aid understanding of the present invention, experiments conducted by the present inventor, the results of the experiments, and their discussion will be explained.

FIG. 2 is a longitudinal sectional side view of the electrophotographic apparatus.

The photoreceptor 21 uniformly charged by the charger 20 is exposed to the exposure means 2 operated by a recording signal from the data recording section 22.
3, only the printed portion (the portion to which the toner is attached) is exposed to light, the potential of this portion is lowered, and an electrostatic latent image is formed. Next, toner having the same polarity as the charging polarity of the photoreceptor 21 is supplied to the developing section by the sleeve 24A as a developer conveying member in the developing device 24, and is deposited on the portion of the photoreceptor 21 where the latent image potential is low. A toner image is formed on 21.

This toner image is transferred from the paper cassette 26 to the printers 27 and 2.
The image is transferred by the transfer device 25 onto the paper 29 sent through the paper 8 . The paper 29 is separated from the photoreceptor 21 by a paper-separating static eliminator 30 and sent to a fixing device 31. After the toner image on the paper 29 is fixed by the fixing device 31, the paper 29 is sent to a paper discharge tray 32. On the other hand, after excess toner on the surface of the photoreceptor 21 is removed by a cleaning device 33, residual charges are removed by an eraser 34, and the photoreceptor 21 is used for the next recording process.

FIG. 1 is a longitudinal sectional side view of a developing device 24 used in the electrophotographic apparatus shown in FIG. Inside the developer reservoir 35 is a two-component developer 36 composed of carrier and toner, and as stirring screws 37 and 38 rotate, the toner rubs against the carrier and is charged to a predetermined amount of charge. The agitated two-component developer 36 is drawn up from the developer reservoir 35 by the rotation of the sleeve 24A of the developing roll 40 having the fixed magnet roll 39 and is conveyed in the rotational direction of the sleeve 24A. The thickness of the pumped two-component developer 36 on the sleeve 24A is regulated by the doctor blade 41, a certain amount is supplied to the developing section, and the rest is folded back and passed through the scraper 42 to the toner concentration control sensor part 43. guided by. The two-component developer 36 that has passed through the toner concentration control sensor portion 43 is collected in a developer reservoir 35.
Repeat the same action again.

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

The two-component developer 36 must maintain a constant toner concentration, which is the mixing ratio of toner and carrier, in order to maintain constant recording characteristics. Therefore, the toner concentration is monitored by the toner concentration control sensor part 43, and when the toner is consumed during development and the toner concentration of the two-component developer 36 decreases, the toner is replenished from the toner hopper 46 by rotating the replenishment roller 45. 1, reference numeral 47 is
The replenished toner is immediately transferred to the two-component developer 3 in the developing unit 35.
This is a stirring paddle provided at a position where the toner falls from the replenishment roller 45 so as to be similar to 6. Toner for replenishment is transported from inside the toner cartridge 48 to the toner hopper 46 by rotation of the stirring blade 49. The stirring blade 49 is made to rotate simultaneously while the sleeve 24A is rotating.

The present inventor used the electrophotographic apparatus shown in FIG. 2 and the developing device shown in FIG.
I investigated using the method shown in Publication No. 54261, etc., but
As explained above, the recorded image had a low solid black density and a lot of fogging, and even fine lines and dots could not be printed clearly.6 After various studies, we found that the main reason for this was the use of an Ss photoreceptor. However, in order to obtain even higher definition and higher quality images.

It was necessary to adapt the developer and the reversal development process.

The following 9 inventors have determined the type of photoreceptor 21, the two-component developer 36,
Types and characteristics of toner and carrier used for photoreceptor 21
and the gap between the sleeve 24A (see below).

development gap), developer transport method and stirring method,
By experimenting with various changes in bias voltage, etc., it was found that in order to obtain a clear recorded image on the paper 29, these conditions are closely related.

FIGS. 3 to 7 are diagrams showing the results obtained from this experiment.

First, differences in recording characteristics due to differences in photoreceptor 21 will be explained. The photoreceptor 21 used was a cylindrical aluminum drum on which Se was vapor-deposited as a photosensitive layer to a thickness of about 60 μm, and a cylindrical aluminum drum coated with an organic photoconductor as a photosensitive layer to a thickness of about 17 μm on the same aluminum drum. . The diameter of the drum is Looml, and the peripheral speed is 125■/S
rotated it clockwise. In addition, the potential of the unexposed part of the rain photoconductor is 650 to 700V, and the potential of the exposed part is 100V.
I made it below. However, while Se has a positive charge polarity, the organic photoreceptor has a negative charge polarity.

For the sleeve 24A and the doctor blade 41, conductive and non-magnetic aluminum was used. Developing roll 40
is composed of a cylindrical sleeve 24A with a diameter of 40 m and a cylindrical fixed magnet roll 39 inserted into the sleeve.The fixed magnet roll 39 is fixed and the sleeve 2
Only 4A is rotatable. Although the circumferential speed of the sleeve 24A could be varied from 2 to 5 times the circumferential speed of the photoreceptor 21, experiments were mainly conducted at a circumferential speed of 2.58 times. The number of magnetic poles of the fixed magnet roll 39 used is 7, and the strength of its magnetic force is as follows.

The magnetic flux density at the main pole located in the developing section was 850 Gauss. The development gap is IIIWI, and the doctor blade is 4.
The doctor gap between the sleeve 24A 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 size of 8 μm and a ferrite carrier having a resistivity of 10 9 Ω·1 or more such that the toner concentration was 3% by weight. The charging polarity of the toner was adjusted using a charging control system contained in the toner so that it had the same polarity as the photoreceptor 21 used.

FIG. 3 shows the results of investigating the relationship between the magnitude of the bias voltage and the image density at the center of a solid black part of the recorded image using the two types of photoreceptors 21. Curve A is the result for Se, and curve B is the result for organic light. This is the result of a conductor.

In the case of Se, in the region where the bias voltage is small, the image density increases as the bias voltage increases, but it becomes saturated at about 20OV, and if the bias voltage is increased further, unevenness occurs in the solid black and the image density becomes poor. It is not possible to increase the image density to a satisfactory level even if it becomes stable. This is considered to be because the electric field on the surface of the photoreceptor 21 is strengthened by increasing the bias voltage, and a type of breakdown occurs. As shown in Japanese Patent Application Laid-Open No. 60-154261, using a bias voltage in which an alternating current voltage is superimposed on a direct current voltage only increases the instability of the image density, but it is not possible to obtain a clear recorded image. There wasn't.

On the other hand, the organic photoconductor 21 does not have such a problem, 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 a DC bias voltage. It will be done. The reason for this is that when the surface of the photoreceptor 21 that the two-component developer 36 comes into contact with is an organic photoconductor, it is made of a highly insulating material such as polycarbonate, so it is less sensitive than a semiconductor material such as Se. ,
This is thought to be because the previous breakdown is less likely to occur. From this result, it was found that it is advantageous to use an organic photoconductor whose surface is made of a highly insulating material for reversal development.

The next important point is the resistivity of the carrier used in the two-component developer 36. FIG. 4 shows the results of examining changes in the density of a recorded image under the same recording conditions as described above using an organic photoconductor as the photoreceptor 21 and changing only the resistivity of the carrier. At this time, the bias voltage was set to -500V. Two types of carriers were used: iron powder and ferrite.

The resistivity of the iron powder carrier is approximately 104Ω as it is, but it increases to approximately 101Ω by coating it with resin.
It can be changed up to 1Ω・1. On the other hand, the ferrite carrier has a high resistivity as it is, ranging from about 10 7 Ω· to 10 e Ω·, and by further coating it with resin, the resistivity can be increased to about 10 14 Ω·.

The image density can be satisfied by using a ferrite carrier with a resistivity of 107Ω・1 or higher, and the best is 10Ω.
This is the case when using a carrier with a resistivity of 9Ω·1 to 1012Ω·■. If the resistivity is higher than that, the image density will decrease slightly. In addition, it is generally thought that lowering the resistivity of the carrier improves developability and improves image density.
In the case of reversal development, the development gap is narrow and the bias voltage is high, so even if an organic photoconductor with a highly insulating surface is used as a photoreceptor, the iron powder gear has low resistivity. If the rear is used, a type of breakdown on the surface of the photoreceptor 21 as described above tends to occur, and not only does the image density not increase, but density unevenness increases. From this result, for reversal development using toner with an average particle size of 10 μm or less, 10
It was found that a ferrite carrier with a resistivity of 7Ω·1 or more is suitable.

When using a finely divided toner, it is necessary to reduce the carrier particle size in order to improve stirring performance. FIG. 5 shows the results of determining the image density, fogging, and carrier pull limits under the same conditions as above, varying the carrier particle size and toner density. If the average particle diameter of the carrier particles is large, the charging properties of the toner will deteriorate and fog will occur, making it impossible to increase the toner concentration of the two-component developer 36 and resulting in low image density. On the other hand, as the particle size of the carrier is reduced, carrier pull tends to occur and fluidity becomes worse, and carriers with an average particle size of 50 μm or less cannot be used practically. Therefore, in the case of a toner with an average particle size of 8 μm, the particle size of a carrier suitable for this is within the range of 60 μm to 100 μm.Since the particle size is 0 or more, the particle size of a carrier suitable for 1 reversal development is , 7.5 times to 12 times the particle size of the toner used
．． It was found that the value was within the range of 5 times.

If the distribution of particles smaller than the average particle size in the carrier used increases, carrier pull will occur more easily, so the proportion of small carriers with a particle size of 0.8 or less relative to the average particle size should be 10% or less. Such a particle size distribution increased the margin for carrier attraction, which was preferable.

Various resin coatings for the carrier were investigated, but no particularly noticeable effects were found. This is because the ferrite carrier itself has a high resistivity. Therefore, in a single electrophotographic device, either one coated with resin or one not coated may be used.

Next, consideration of toner suitable for reversal development will be explained.

As explained in the prior art section, in order to improve the definition and quality of images recorded by electrophotographic devices, the diameter of toner particles used has conventionally been reduced to 11 to 13 μm, as described in Japanese Patent Publication No. 11103/1983. It is effective to make the particles into particles of 10 μm or less. However, when the toner diameter is reduced, the surface area increases even with the same weight, and the toners come into contact with each other more, resulting in poor fluidity and a tendency for the toners to aggregate with each other. Therefore, there is a problem that the toner replenishing section for the developing section is easily clogged, making it impossible to replenish the toner stably.

In addition, if the toner diameter is reduced in the developing device, the mixing and agitation characteristics with the carrier deteriorate, making it difficult for the replenished toner to reach the desired charge level. lFt will no longer occur. As a result, the electrostatic adhesion of the toner to the carrier is weak, causing more scattering, which not only pollutes the inside of the device, but also causes the problem that the scattered toner sticks to the white background of the image where toner does not need to be attached, causing fogging. be.

Therefore, as a result of various studies, the inventors of the present invention found that: (1) cloth for particle size of finely divided toner; (2) optimization of materials and external additives constituting the toner; We have found that these problems can be reduced.

First, as a result of various studies regarding the particle size distribution of toner,
In the case of reversal development using toner with an average particle size of 10 μm or less, small particles with a weight ratio of 0.65 times or less than the average particle size account for 3% or less, and large particles with a weight ratio of 2 times or more the average particle size. Toners having a particle size distribution of 1% or less by weight were preferred. The reason for this is that toner with a small particle size has a strong adhesion to the carrier, so it is difficult to be used in development and tends to remain.

Particularly, when particles with a small particle diameter of 0.65 times or less than the average particle diameter of toner particles are contained in an amount of 3% or more by weight, this tendency is strong and becomes a problem.

Next is the optimization of the materials and external additives that make up the toner. In reversal development, as explained in the prior art section, the electric field that tries to attract the toner in the center of the solid black area to the photoreceptor 21 is weak, so as explained above, the electric field due to the bias voltage is reduced by narrowing the development gap. Even if measures are taken to strengthen the toner, the amount of toner adhering to the central part of the solid black cow is essentially small. Therefore, one of the present inventors has considered changing the amount of carbon contained in the toner so that sufficient image density can be obtained even with a small amount of toner.

FIG. 6 shows the results of investigating the relationship between the amount of carbon and the density of the recorded image using toners with different amounts of carbon as the developer of the electrophotographic apparatus shown in FIG.

The amount of carbon in toners conventionally used in two-component developers is around 6% at most. Average particle size is 10μm
In the following toners, sufficient image density cannot be obtained when the amount of carbon contained in the toner is 6% as shown in the results in Figure 6. In this study, the amount of carbon is 8% or more to 15% by weight. The following were suitable. When the amount of carbon was increased more than that, the resistivity of the toner decreased, the charging property of the toner deteriorated, and fogging occurred in the recorded image.

The amount of carbon contained in the toner is 8% or more by weight to 1
Add 2% by weight of fine silica powder to less than 5% toner.
When the following and magnetic fine particles are externally added in a weight ratio of 1% or less, the fluidity of the toner can be improved, the cohesiveness can be improved, the stirring IF conductivity can also be improved, and long-term continuous use of reversal development can be achieved. However, it was found that there was almost no deterioration phenomenon of the developer, and it could be used stably. Externally adding hydrophobic silica to a toner whose main binder is vinyl resin improves fluidity and reduces toner aggregation, but if this toner is used continuously over a long period of time, mixing and agitation in the developing device may occur. It was found that the characteristics changed and the replenished toner became difficult to charge. As a result, developer deterioration phenomena such as increased fogging and uneven image density occurred.

After carefully investigating the cause of this problem, we found that there are two problems. The first problem is that the hydrophobic silica added to the toner separates from the toner and migrates to the carrier surface, covering the carrier surface. This is a phenomenon in which toner sticks (toner filming). As a result of examining various methods to solve these problems, we found that by externally adding magnetic fine particles with a smaller particle size than the toner particles to the toner or developer, the deterioration of the developer due to continuous use could be reduced. We found that there were almost no phenomena. The externally added magnetic fine particles must have a particle size smaller than that of the toner particles, and the material may be the same as that used for conventional magnetic carriers. Among them, ferrite and magnetite, which are easily pulverized, are suitable. I understand.

The above are the conditions regarding the developer, and next, the conditions regarding the developing device 24 which develops the electrostatic latent image formed on the photoreceptor 21 using such developer will be described.

As explained above, the development gap, which is the gap between the photoreceptor 21 and the sleeve 24A, needs to be narrowed in order to bring out the effect of the electric field created by the bias voltage in reverse development. FIG. 7 shows the above two-component developer 3 in the electrophotographic apparatus shown in FIG.
6 is used to determine the relationship between the development gap and image density. From this result, when performing reversal development using the two-component developer 36, it was found that a development gap of 1+m or less is suitable.

The amount of the two-component developer 36 supplied to the development area is regulated by the gap (doctor gap) on the sleeve 24A caused by the doctor blade 41.

The size of this doctor gap is that the development gap is 10
If it is less than 111, it will not have much effect on the image density, but if it is not set to 0.8 times or less than the development gap, the two-component developer 36 will become clogged in the development gap, and the photoreceptor 21 and sleeve 24A will likely lock. There was a problem. Therefore, in a single electrophotographic apparatus, the developing gap is set to 1 mm or less, and the doctor gap is also set to 0.8 times or less of this developing gap.

The transport speed of the two-component developer 36 was preferably 2 to 5 times the moving speed of the photoreceptor 21, and among them, the image reproducibility was excellent when the transport speed was 2.5 to 3.5 times. The transport speed of the two-component developer 36 is determined by the circumferential speed of the sleeve 24A.
The circumferential speed of 4A is set and used so as to meet the above conditions. Furthermore, when the two-component developer 3G was transported in the same direction as the moving direction of the photoreceptor 21, high-quality recorded images were obtained.

When the direction of conveyance of the two-component developer 36 is opposite to the direction of movement of the photoreceptor 21, the sliding action of the two-component developer 36 has a strong effect of scraping off the once developed toner image, resulting in scratches on the recorded image. Therefore, clear recorded images cannot be obtained.

In this electrophotographic device, the development gap is 1a! As shown below, the parallelism of this gap is d±0.
If it is within the range of 1d, there will be no difference in density between the right and left ends of the image, and an image with uniform density will be obtained.

The developing gap can be set in this way when manufacturing the device, but the photoconductor 21 and the two-component developer 36 have a limited lifespan and must be replaced according to the number of sheets of paper 29 printed. The developing device 24 must be able to be taken out from the main body of the apparatus, be easily installed, and be able to accurately set the developing gap. Conventionally, one of the methods is to provide a contact ring with a diameter 2d larger than the diameter of the sleeve 24A on the shaft of the sleeve 24A, and to set the developing device 24 by applying this ring to both ends of the photoreceptor 21. . However, although this method is good in the initial stage when the abutment ring is not worn, when the abutment ring wears out, the development gap changes, causing density unevenness in the recorded image.

Therefore, the inventor did not use this method.

As shown in FIG. 8, the photoreceptor member 50 holding the V6 light body 21 and the developing device 24 are each independently removable from the main body of the electrophotographic apparatus, and pins are provided on the side plate 51 of the main body of the electrophotographic apparatus. 52, the positioning hole 53 provided in a part of the photoreceptor holding member 50 and the positioning hole 54 provided in a part of the developing unit 24 are commonly fitted, so that the developing unit 24 and the photoreceptor 21 can be accurately aligned. The development gap was positioned to ensure parallelism. The photoreceptor holding member 50 and the developing unit 24 are inserted into and fixed in the apparatus main body using bearings 56 and 57 provided on a side plate 55 on the back side of the apparatus main body, as shown in FIG.
The shaft 58 of the drum of the photoreceptor 21 and the shaft 59 of the developing roll 40 are fitted into each other when the photoreceptor holding member 50 and the developer @ 24 are inserted into the main body of the apparatus. The photoreceptor holding member 50 is fixed by fitting a positioning hole 53 into a pin 52 provided on a side plate 51 on the insertion side of the apparatus main body, and further fitting a screw 60 into the screw hole 62. The developing device 24 is fixed by fitting the positioning hole 53 into the pin 52 provided on the side plate 51 on the insertion side of the apparatus main body in the same way, and further fitting the screw 61 into the screw hole 63. By sharing one pin 52 in this manner, the positions of the developing device 24 and the photoreceptor 21 can be determined accurately, and the developing gap can also be set with high precision.

Furthermore, if the photoreceptor and paper transport drive and the developer system are driven by the same system, such as a belt or chain, slight fluctuations in the feed speed of the photoreceptor and paper transport system will occur due to changes in the load on the developer. The image becomes uneven. In particular, in the present invention,
Because the development gap is narrow in reversal development, the image forming process is more susceptible to speed fluctuations than conventional systems. Incidentally, although the rotation of the photoreceptor and the conveyance of the paper must be at the same speed, it is not necessary that the rotation speed of the sleeve of the developing device be the same.

Therefore, in the electrophotographic apparatus shown in FIG. 2, the driving of the developing unit and the driving of the photoreceptor and paper conveyance system are separated.

The developing device is now driven independently. In this way, the speed of the photoreceptor and paper transport system does not fluctuate due to load fluctuations on the developing device, and image quality can be improved.

Examples of the present invention will be specifically described below.

Embodiment 1 FIGS. 1 and 2 show an embodiment of a developing device and an electrophotographic apparatus using the present invention. The photoreceptor 21 is constructed by coating an aluminum drum with a charge generation layer mainly composed of phthalocyanine, an organic pigment, to a thickness of 0.5 μm, and then applying an oxadol derivative as a charge transport layer thereon at a weight ratio of 30 μm.
A two-layer organic photoconductor coated with 16.5 μm thick polycarbonate comprising The body resistivity of the photoreceptor 21 was 101!5 Ω·■.

The diameter of the photoreceptor 21 is 100 nn, and the peripheral speed is 125 m.
/s to rotate clockwise. The voltage applied to the charger 20 and the exposure amount of the exposure means 23 are adjusted so that the potential on the surface of the photoreceptor 21 is -650V in the unexposed area, which is the background of the image, and -100V or less in the exposed area, which is the image recording area. It was adjusted. Also, a bias power supply 44 applied to the sleeve 24A
The output voltage was -500V.

Sleeve 24A of developing device 24 and doctor blade 41
Aluminum, which is a conductive non-magnetic material, was used.

The developing roll 40 has a cylindrical sleeve 2 with a diameter of 40 mm.
4A and a cylindrical fixed magnet roll 39 inserted therein, only the sleeve 24A rotates counterclockwise to convey the developer 36. The peripheral speed of the sleeve 24A is 322, which is 2.58 times the peripheral speed of the photoreceptor 21.
．． It was set to 511 fl/s. The number of magnetic poles of the fixed magnet roll 39 was seven, and the strength of the magnetic force was such that the magnetic flux density at the main pole located in the developing section was 850 Gauss. The development gap was set to 1 m, and the doctor gap was set to 0.6 m+.

The main component of the toner is styrene-acrylic resin.

A material containing 10% by weight of carbon black and 3% by weight of chromium alloy dye as a charge control agent is pulverized,
In addition, small particles with an average particle size of 8 μm and 0.65 times or less of the average particle size account for 3% or less by weight, and large particles with an average particle size of more than twice the average particle size account for 1% or less by weight. After that, 1% by weight of fine silica powder and 0.5% by weight of fine magnetite powder were externally added as magnetic fine particles. When we measured the particle size distribution of this toner, we found that
The weight ratio of particles with an average particle size of 8 μm and 5.2 μm or less is 1.3.
% and those with a diameter of 16 μm or more were 0.3% by weight.

The carrier used was a ferrite whose main component was copper-zinc, the surface of which was coated with silicone resin to a thickness of about 0.2 μm. The resistivity of the carrier is 10izΩ・l
Met. In addition, the size of the carrier is an average particle size of 91μ
The particles were classified so that 5% or less of the particles had a particle size of 7 μm or less.

The two-component developer 36 used was a mixture of the above toner and carrier so that the toner concentration was 3% by weight.

The toner concentration was detected by a toner concentration sensor section 43 in the developing device 24, and was controlled to be within a range of ±0.5% around 3%. The amount of charge on the toner at this time is -20μ
C/g.

Paper 29 obtained as a result of reversal development under the above conditions
The above recorded image had high image density, no density unevenness or fog, and was high quality and clear.

Subsequently, 500 sheets were continuously printed while sequentially replenishing the toner so that the toner concentration of the two-component developer 36 remained constant.The image density was almost constant and there was little fogging, resulting in a high quality and stable recorded image. was able to obtain.

Embodiment 2 This embodiment is an electrophotographic apparatus using the developing device 24 having the same configuration as in Embodiment 1, but the differences are as follows.

The potential on the surface of the photoreceptor 21 is -600 V for the unexposed area, which is the background of one image, and -11 V for the exposed area, which is the recording area of one image.
The applied voltage of the charger 20 and the exposure amount of the exposure means 23 were adjusted so that the voltage was 00 V or less. Further, the bias voltage applied to the sleeve 24A was set to -450V.

The developing device 24 has a circumferential speed of the sleeve 24A of 385 m/s.
The development gap is 0.8@m, the doctor gap is 0, and the two toners set at 6 mL knee are mainly composed of styrene-acrylic resin, 8% by weight of carbo black, and charge control. The powder contained 3% by weight of a chromium alloy dye as an agent, and the average particle size, particle size distribution, and mixing ratio of external additives were the same as in Example 1.

The carrier used was ferrite whose main component was copper-zinc, and whose surface was not coated with resin. The resistivity of the carrier was 109Ω·l. The size of the carrier used was one classified so that the average particle size was 85 μm and 6% or less of the particles had a particle size of 65 μm or less.

The toner concentration of the two-component developer 36 was controlled to be within a range of ±0.5% around 3.5%.

The charge amount of the toner at this time was -22 μC/g.

As a result of performing reversal development under the above conditions, as in Example 1, the recorded image had a high image density, was free from density unevenness and fogging, and was of high quality and clear. Next, two-component developer 3
When I continuously printed 500 sheets while replenishing the toner sequentially so that the toner density of 6 was constant, the image density was almost constant and there was little fogging, and I was able to obtain a high quality and stable recorded image. .

Embodiment 3 This embodiment is an electrophotographic apparatus using the developing device 24 having the same configuration as that of Embodiment 2, except for the following differences.

The toner is made by pulverizing a material whose main component is polyester resin, 10% by weight of carbon black, and 3% by weight of chromium alloy dye as a charge control agent, and the average particle size is 6 μm. The particles are classified so that the weight ratio of particles with a small particle size of 0.65 times or less than 0.65 times the average particle size is 3% or less, and the large particle size of 2 times or more the average particle size is 1% or less by weight. The powder used was 2% by weight, and 1% by weight of fine ferrite powder was externally added as magnetic fine particles. When the particle size distribution of this toner was measured, it was found that the average particle size was 6 μm, 2.3% by weight was 3.6 μm or less, and 0.5% by weight was 12 μm or more.

The carrier used was ferrite whose main component was barium-zinc, and the surface of which was coated with styrene-acrylic resin. The resistivity of the carrier was 1010Ω±mark. The carrier size is 48 mm with an average particle size of 60 μm.
The particles used were classified so that particles with a particle size of μm or less were 8% or less.

The toner density of the two-component developer 36 is within ±0.0% around 3%.
It was controlled to be within a range of 5%. The charge amount of the toner at this time was -18 μC/g.

As a result of performing reversal development under the above conditions, the recorded image had a high image density and was free from density unevenness and fog.

The image quality was similar to or higher than that of Example 1 and was clearer. Subsequently, 500 sheets were continuously printed while sequentially replenishing the toner so that the toner concentration of the developer remained constant.The image density was almost constant, with little fogging, and a high quality and stable recorded image was obtained. was completed.

〔Effect of the invention〕

As explained above, the present invention comprises a photoreceptor made 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·1 or more. By performing reversal development in combination with a two-component developer, there is no lack of density, uneven density, or fog.

It is possible to provide an electrophotographic device that can record clear images with high image quality.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional side view of a developing device according to an embodiment of the present invention, and FIG.
The figure is a vertical side view of an electrophotographic apparatus according to an embodiment of the present invention, FIG. 3 is a characteristic diagram showing the difference in bias voltage and image density due to different photoreceptors, and FIG. A characteristic diagram showing density changes. Figure 5 is a characteristic diagram showing the image density, fog, and carrier pull limit obtained by varying the carrier particle size and toner concentration under the same conditions. Figure 6 is a characteristic diagram showing the toner carbon content and image. A characteristic diagram showing the relationship with the concentration of
Figure 7 is a characteristic diagram showing the relationship between development gap and image density.
FIG. 8 is a perspective view showing a setting section of the developing device, and FIG. 9 is a longitudinal sectional side view showing the positioning structure of the photoreceptor and the developing device. 21... Photoreceptor, 24... Developing device, 24A... Sleeve, 35... Developer reservoir, 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 blade, 50...
- Photoreceptor holding member, 51... electrophotographic device main body side plate,
52... Pin, 53.54 Fig. 1 Fig. 2 26... Paper cassette 34... Eraser Fig. 3 Fig. 4 Carrier resistivity [Ω/port] Fig. 5 Fig. 6 Carbon amount [chi] Figure 7 Development gap (grip) Figure 8

Claims (1)

[Claims] 1. A two-component developer that is used by mixing and stirring a toner whose main component is a resin mixed with carbon and a charge control agent and a carrier made of a magnetic material is transported to a development area. A direct current bias voltage is applied between the developing conveyor and the photoreceptor that forms the electrostatic latent agent, and the toner is attached to the uniformly charged surface of the photoreceptor where the electric charge has been removed by exposure by an exposure means. In an electrophotographic apparatus using a reversal development method, the photoreceptor is an organic photoconductor, the toner of the two-component developer is an average particle size of 10 μm or less, and the carrier is a ferrite having a resistivity of 10^7 Ω·cm or more. An electrophotographic device characterized in that it is a carrier. 2. In an electrophotographic apparatus in which an electrostatic latent image formed on a photoconductor is reversely developed using a two-component developer, the photoconductor is an organic photoconductor, and the particle size distribution of the toner of the two-component developer is , whose average particle size is 10 μm or less, and 3% or less by weight of small particles that are 0.65 times or less than the average particle size,
An electrophotographic device characterized in that the weight ratio of particles having a large particle size that is twice or more the average particle size is 1% or less. 3. In an electrophotographic apparatus in which an electrostatic latent image formed on a photoreceptor is reversely developed using a two-component developer, the photoreceptor is an organic photoconductor, and the toner of the two-component developer is The average particle size is 10 μm or less, and the amount of carbon contained in the toner is from 8% to 15% by weight, and further contains 2% or less of silica fine powder and 2% or less of magnetic fine particles by weight. An electrophotographic device characterized by containing 1% or less of external additives. 4. In an electrophotographic apparatus in which an electrostatic latent image formed on a photoreceptor is reversely developed using a two-component developer, the photoreceptor is an organic photoconductor, and the two-component developer has a carrier of 10 A ferrite carrier having a resistivity of ^7Ω・cm or more, with an average particle size of 100 μm or less, and a small particle size of 0.8 times or less of the average particle size, with a weight ratio of 10% or less. An electrophotographic device characterized by having a certain particle size distribution. 5. In the electrophotographic apparatus according to claim 1, the gap between the developer transport member and the photoreceptor in the development region is 1 mm or less, and a regulating member provided to regulate the thickness of the developer on the developer transport member. An electrophotographic apparatus characterized in that the gap between the developing conveying body and the developing conveying body is 0.8 or less with respect to the gap between the developing conveying body and the photoreceptor. 6. In the electrophotographic apparatus according to claim 5, the member for holding the photoreceptor and the member for holding the development conveyor are each independently removable from the main body of the electrophotographic apparatus, and are attached to a side plate of the main body of the electrophotographic apparatus. The developer transport member and the photoreceptor are positioned by fitting the provided pin into a hole provided in a part of the photoreceptor holding member and a hole provided in a part of the member holding the developer transport member. An electrophotographic device characterized by: 7. The electrophotographic apparatus according to claim 1, wherein the development transport member and the photoreceptor move in the same direction in the development area. 8. In the electrophotographic apparatus according to claim 1, the developer transporting member that conveys the two-component developer to the development area, the developer stirring member, and the stirring member in the toner cartridge storing toner for replenishment are synchronized. An electrophotographic device characterized in that the device is rotated by rotating the device. 9. In the electrophotographic apparatus according to claim 8, a stirring member for the developer and the developer, a replenishment roller for replenishing the toner to the developer and the conveyor, and stirring in the toner cartridge that stores the toner for replenishment. Put the parts together,
An electrophotographic apparatus, characterized in that the electrophotographic apparatus is rotatably driven separately from a drive section of the electrophotographic apparatus main body.