JPH073608B2 - Development method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a developing method in electrophotography, and more particularly to forming an image of high density and high quality using an amorphous silicon photoconductive layer. To a developing method for

2. Description of the Related Art Amorphous silicon photoconductor layers have high surface hardness, are sensitive to light of long wavelength side, and have good sensitivity themselves. Attention is paid to the body.

However, according to the research conducted by the present inventors, although amorphous silicon has the above-mentioned excellent characteristics, it is difficult to provide the photoconductive layer in a sufficiently thick layer in terms of manufacturing technology and manufacturing cost. However, the layer thickness is actually limited to a relatively small range of 10 to 35 μ, which is considerably thinner than that of the selenium photosensitive layer. Due to the small thickness of the amorphous silicon layer, the surface potential at the time of charging that can be formed on the photoconductive layer is also limited to the range of 200 to 400 V, which is much smaller than that of the selenium photosensitive plate, and it is forcibly forced. Since raising the charging potential causes dielectric breakdown of the photosensitive layer,
There is a problem that the potential contrast of the formed charge image is low. Thus, when developing with a normal two-component developer, the image density of the toner image is lowered, and if an attempt is made to improve the image density by force, toner scatter or fog density becomes high. There are drawbacks.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a method capable of forming a toner image with high density and excellent quality on an amorphous silicon photoconductive layer.

Another object of the present invention is to provide a developing system capable of forming a toner image excellent in sharpness and density from an electrostatic image having low potential contrast.

Yet another object of the present invention is to provide a developing method for an amorphous silicon based photoconductor using a combination of a ferrite carrier having specific electrical characteristics and an electroscopic toner having specific particle size characteristics. There is.

According to the present invention, an electrostatic image formed on an amorphous silicon photoconductive layer having a thickness of 10 to 35 μm is developed by a two-component developer including a magnetic carrier and an electrophotographic toner. Using ferrite sintered reduced particles as the magnetic carrier, and the content of the electroscopic toner having a median diameter of 10 to 14 μm and a particle diameter of 5 μm or less is substantially zero. A volume resistivity of 1 × 10 ¹³ Ω-cm or more is used, and a dynamic magnetic brush resistance measured as a magnetic brush of the magnetic carrier alone is 6 × 10 ^{4 to} 2.5 ×.
There is provided a developing method characterized in that the developing condition is set so as to fall within a range of 10 ⁶ Ω.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.

In FIG. 1 for explaining an electrophotographic method to which the developing method of the present invention is preferably applied, an amorphous silicon photoconductor layer 2 is provided on the surface of a metal drum 1 which is driven and rotated. There is. Around this drum, a main charging corona charger 3; an image exposure mechanism composed of a lamp 4, an original supporting transparent plate 5 and an optical system 6; a developing mechanism 8 having toner 7; a toner transferring corona charger 9; a paper separating corona charger 1
0; a static elimination lamp 11; and a cleaning mechanism 12 are provided in this order.

First, the photoconductor layer 2 is charged by the corona charger 3 with a constant polarity charge. Next, the original to be copied with the lamp 4
Illuminate 13 and expose photoconductor layer 2 with the light beam image of the original through optical system 6 to form an electrostatic latent image corresponding to the original image. The electrostatic latent image is developed with the toner 7 by the developing mechanism 8. The transfer paper 14 is supplied so as to come into contact with the drum surface at the position of the toner transfer charger 9, and a corona charge having the same polarity as the electrostatic image is made from the back surface of the transfer paper 14 to transfer the toner image to the transfer paper 14. . Transfer paper with toner image transferred
14 is electrostatically separated from the drum by the charge removal of the separation corona charger 10 and sent to a processing area such as a fixing area (not shown).

After the toner transfer, the photoconductor layer 2 is entirely exposed by the static elimination lamp 11 to erase the residual charge, and then the cleaning mechanism.
By 12, the residual toner is removed.

In the present invention, in the development of the above-mentioned electrostatic latent image, a two-component developer comprising a combination of low electrical resistance sintered ferrite particles and high electrical resistance electroscopic toner particles having specific particle size characteristics. To use.

Magnetic Carrier In the present invention, first of all, a ferrite carrier is used among various magnetic carriers. Ferrite carriers have a smaller specific gravity and a smaller saturation magnetic flux density than ordinary iron powder carriers, so the ears formed are soft, and as a result, during development, the sleeve for development or the magnet inside the sleeve does not rotate. It is known to have the advantage of requiring less torque.

Further, the use of the ferrite carrier has the advantage that the magnetic properties of the developer magnetic brush are stable over a long period of time, and the amount of spent toner generated is small.

However, as already mentioned, the ferrite carrier particles have a volume resistivity higher by about two to three orders of magnitude than the iron powder carriers. Therefore, a two-component magnetic developer composed of a combination of a normal ferrite carrier and a sensible toner does not give a high-concentration toner image to the development of an electrostatic image on a selenium-based photoconductor. It has been found that when used in the development of electrostatic images on crystalline silicon-based photoreceptors, it gives remarkably low image densities.

The ferrite carrier used in the present invention has a dynamic electric resistance of 6 × 10 ^{4 to} 2.5 × as a magnetic brush of the carrier alone.
10 ⁶ Ω, preferably 6 × 10 ^{4 to} 7.2 × 10 ⁵ Ω, in particular 1 × 10 ^{5 to} 5.8 × 10 ⁵ Ω, which is a remarkable feature of the ferrite reduced sintered particles. That is, an ordinary ferrite carrier generally has a high volume resistivity of 1 × 10 ¹⁰ Ω · cm or more and a dynamic electric resistance of 1 × 10 ⁹ Ω or more. Recently, Japanese Unexamined Patent Publication No. 59-48774 discloses the use of a ferrite shaped product having a molar ratio of divalent metal oxide component per Fe ₂ O ₃ of 0.85 or less as a carrier for electrophotographic development. However, the volume resistivity of this carrier is still 8.5 even if lower than that of ordinary ferrite.
It is on the order of × 10 ^{6 to} 2 × 10 ⁹ Ω · cm, which is unsatisfactory for the purpose of developing an electrostatic latent image on an amorphous silicon photoconductor at a high density.

The present invention uses the ferrite sintered reduced particles obtained by reducing the ferrite sintered particles with hydrogen as a magnetic carrier, so that the carrier alone has a dynamic electric resistance of 6 × 10 ^{4 to} 2.5. It is possible to set the developing conditions so as to be in the range of × 10 ⁶ Ω, and combine this carrier with electroscopic toner particles having a volume resistivity of 1 × 10 ¹³ Ω-cm or more to obtain a thickness of 10 to 10 35 μm
By developing the electrostatic image formed on the amorphous silicon-based photoconductive layer, the toner image excellent in sharpness and density was successfully formed from the electrostatic image with low potential contrast. is there.

In the present specification, the dynamic electric resistance as a magnetic brush is an electric resistance value dynamically measured under the developing condition by the magnetic brush, and means a value obtained by the following method. That is, an aluminum electrode drum having the same size as the electrophotographic photosensitive drum is installed by replacing the photosensitive drum with the photosensitive drum, and a developer is supplied onto the developing sleeve to form a magnetic brush, and the magnetic brush is rubbed against the electrode drum. Then, a voltage is applied between the sleeve and the drum to measure a current flowing between the sleeve and the drum, and the calculated resistance value is meant. For the measurement, apply a voltage of 50V for the developer consisting of toner and carrier, and apply a voltage of 20V for the case of forming a magnetic brush by the carrier alone and applying a voltage of 20V. The developing conditions of the developing device (for example,
(Drum-sleeve distance, magnetic brush movement speed, etc.)
Measure according to. That is, it is understood that the resistance value obtained by this measurement is a resistance value suitable for the developing device in the copying machine to be used. Hereinafter, the electric resistance measured by this measuring method is referred to as the DS resistance.

Generally, if the charging potential is E, the developing current is i, and the electric resistance of the developer magnetic brush is R, the following equation E = iR (1) is considered to be established. Assuming that the density of the toner image is proportional to the developing current i, the developing current (i) is extracted as large as possible by lowering the resistance (R) of the magnetic brush for the photoconductor having a small charging potential (E). It may be possible. Further, in order to reduce the electric resistance R of the developer magnetic brush, the electric resistance of the magnetic carrier, that is, DS
It may be possible to lower the resistance.

However, the inventors of the present invention have found that the relationship between the electric resistance of the magnetic brush under dynamic and developing conditions and the density of the toner image is not the hyperbolic relationship of the above formula (1) but a constant electric resistance. It has been found that there is a bending point at the value, and the image density is dramatically improved below this bending point. FIG. 2 is a plot showing the relationship between the resistance and the toner image density under the dynamic and developing conditions of the developer magnetic brush, which the present inventors previously applied (Japanese Patent Application No. 59-84000). It will be apparent that the combination of an amorphous silicon photoreceptor and a ferrite carrier developer results in the above-mentioned critical point.

As is clear from FIG. 2, when a normal toner is used, from the viewpoint of forming a high-density and high-quality toner image on an amorphous silicon-based photoreceptor, a developer magnetic brush is used. Electrical resistance (D-S
It is necessary to set the resistance) in the range of 4 × 10 ⁶ Ω to 5 × 10 ⁷ Ω, particularly 8 × 10 ⁶ Ω to 4 × 10 ⁷ Ω.

The resistance of the developer magnetic brush as a whole naturally depends on the resistance of the carrier particles and the resistance of the toner particles, but the electric resistance of the toner particles is important for the transfer of the toner image from the surface of the photosensitive layer to the transfer paper. If the volume resistance of the toner particles is lower than 1 × 10 ¹³ Ω-cm, the transfer efficiency of the toner particles may be lowered and the toner image may be scattered or the contour may be broadened during transfer. However, it cannot be lowered below the reference value. In this sense, it is effective to use a carrier having a relatively low electric resistance.

In the present invention, the D-S resistance of the ferrite carrier is limited to the above-mentioned upper limit from the viewpoint of dramatically improving the image density. Further, the density of the toner image is rather decreased when the resistance of the carrier magnetic brush becomes smaller than a certain value, and when the electric resistance becomes too small, the charge of the electrostatic image leaks through the magnetic brush. As a result, a fine white background pattern (brush mark) or the like is generated in the solid black image portion. From this point of view, in the present invention, the DS resistance of the carrier is limited to the above lower limit value or more.

The low D-S resistance ferrite carrier used in the present invention is obtained by reducing the sintered ferrite particles so that the D-S resistance falls within the above range, preferably hydrogen reduction. The raw material sintered ferrite particles are known per se, and known sintered ferrite particles, particularly spherical sintered ferrite particles, are advantageously used. The composition of ferrite is also known, and is generally called soft ferrite, such as, but not limited to, Zn-based ferrite, Ni-based ferrite, Cu-based ferrite, Mn-based ferrite, Mn-Zn-based ferrite, Mn. -Mg-based ferrite, Cu-Zn-based ferrite, Ni-Zn-based ferrite, Mn-Cu-Zn-based ferrite, and the like. The preferred ferrite is atomic weight percent
And Fe35 to 65%, Cu5 to 15%, Zn5 to 15% and Mn0
To Cu-Zn or Cu-Zn-Mn based ferrite composed of 0.5% to 0.5%.

This sintered ferrite particle is, for example, 300 to 5 in a hydrogen stream.
The reduction is carried out at a temperature of 00 ° C, especially 340 to 420 ° C. The required treatment time varies depending on the temperature and the amount of hydrogen aeration, but generally speaking, from 30 minutes to 1 hour, the product D-S
Select a time for which the resistance falls within the above range. It is recognized that this reduction causes the metal component of at least the surface portion of the sintered ferrite particles to shift to an oxide having a low oxidation state, that is, a state having a low valence, thereby causing a decrease in electric resistance. The reduction treatment is preferably performed in a hydrogen atmosphere, but carbon monoxide can also be used.

Sintered reduced ferrite particles used generally have an average particle size of 30.
Those in the range from .about.100 microns, especially 35 to 45 microns are preferred. The above-mentioned D-S resistance, that is, the dynamic resistance of the magnetic brush also depends on the particle size of the carrier particles, and by decreasing the particle size of the ferrite carrier, the resistance of the magnetic brush can be set to an arbitrary low value. It is clear that it can be adjusted to This is considered to be because the number of contact points in the magnetic brush or between the magnetic brush and the sleeve or the surface of the photosensitive layer is increased by reducing the particle size of the ferrite carrier.

Toner The toner used is 1 × 10 ¹³ Ω from the viewpoint of transferability described above.
It must have an electrical resistance of −cm, in particular at least 5 × 10 ¹³ Ω-cm. Moreover, of course,
The toner particles must be colored toners having electroscopic and fixing properties. A granular composition in which a color pigment, a charge control agent and the like are dispersed in a binder resin is used. As the resin, a thermoplastic resin or a thermosetting resin of an uncured or initial condensation product is used. Suitable examples thereof are vinyl aromatic resins such as polystyrene, acrylic resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenol resins, petroleum resins, olefin resins, etc., in the order of importance. As the pigment, for example, one or more kinds of carbon black, cadmium yellow, molybdenum orange, pyrazolone red, fast violet B, phthalocyanine blue, etc. are used, and as the charge control agent, for example, nigrosine base (CI 50415), Oil-soluble dyes such as oil black (CI 26150) and spirone black, metal naphthenic acid salts, and fatty acid metal soaps are used as necessary.

It is also extremely important that the electrophotographic toner particles used in the present invention have particle size characteristics such that the median diameter is 10 to 14 μm and the content of particles having a particle size of 5 μm or less is substantially zero.

Heretofore, it has been known to use a sensible toner having a particle size of 5 to 35 μm for a two-component developer.
However, in the toner manufactured by the known pulverization / classification method, even though the particle size is adjusted to be in the range of 5 to 35 μm, fine particles of 5 μm or less are necessarily mixed,
The content of fine particles of 5 μm or less still reaches 0.5 to 2% by volume.

On the other hand, in the present invention, the median diameter of the toner particles is set in the range of 10 to 14 μm, particularly 12 to 13 μm, and the content of particles having a particle size of 5 μm or less is suppressed to substantially zero. By substantially zero is meant the fact that commercially available particle size analysis techniques, such as the Coulter Counter method, do not detect particles with a size below 5 μm.

Therefore, in the present invention, in order to form a high-density image from an electrostatic image of low potential contrast on an amorphous silicon photoconductor, the content of particles having a particle size of 5 μm or less should be substantially zero. It is extremely critical to do so.

This criticality becomes apparent with reference to the diagram of FIG. FIG. 3 is a diagram in which the surface potential of the amorphous silicon photoconductor is plotted on the abscissa and the image density is plotted on the ordinate. The plots marked with ◯ contain 0.8% by volume of particles having a particle size of 5 μm or less.
When the toner of No. 2 is used, the plot with * indicates the case of using the toner of which the content of particles having a particle size of 5 μm or less is substantially zero. Referring to FIG. 3, by using a toner that does not substantially contain particles having a particle size of 5 μm or less,
The fact that a remarkably high density image formation is possible over a wide surface potential range becomes clear. Such facts
This was first observed in the case of an amorphous silicon photoconductor having a low potential contrast, and was not observed at all in the case of a selenium photosensitive plate having a high potential contrast, which was even unexpected.

FIG. 4 is a diagram in which the number of continuous copies is plotted on the horizontal axis and the image density is plotted on the vertical axis. The plots ◯ and * have the same meanings as in FIG. From FIG. 4 as well, it is understood that setting the content of particles having a particle size of 5 μm or less to substantially zero is extremely critical in suppressing the tendency of image density to decrease with time.

Further, by making the content of particles having a particle size of 5 μm or less substantially zero, the fluidity of the developer can be improved and the developing workability can be improved.

It is also important that the median diameter of the toner is within the above range. If the median diameter is larger than the above range, the resolving power tends to decrease, and if it is smaller than the above range, the developing workability and the fixability such as offset are likely to occur. Tends to get worse.

In order to make the content of particles having a particle size of 5 μm or less substantially zero, it is sufficient to perform a highly accurate classification operation such as applying the toner obtained by the kneading / pulverization method to two or more classification operations.

Two-component developer Ferrite carrier and electrophotographic toner are generally 100: 6
It is preferable to use it in a weight ratio of 100 to 11: 1. This quantity ratio also affects the electric resistance of the magnetic brush of the developer. That is, when the amount ratio of the ferrite carrier increases, the electric resistance of the magnetic brush of the developer tends to decrease. The optimum ratio of the two is closely related to the specific surface areas of the ferrite carrier and the electrophotographic toner. In a preferred embodiment of the present invention, the toner concentration (Ct%) of the mixture forming the magnetic brush is In the formula, Sc is the specific surface area of the ferrite carrier (cm ² / g: measured value by the permeation method), St is the specific surface area of the toner (cm ² / g: based on the average particle size measured using a Coulter counter, It is the effective specific surface area calculated assuming that the toner is a true sphere. When the radius obtained from the average particle size is r (cm) and the true specific gravity of the toner is ρ (g / cm ³ ), St = 3 / r · ρ), k is a number from 0.80 to 1.07, and development is performed at a density that satisfies

First, the term Sc / (St + Sc) on the right side of the above equation (2)
Is a term related to the specific surface area of the carrier and the toner,
Specifically, it is a numerical value representing the ratio of the surface area occupied by the carrier to the total surface area of the composition obtained by mixing the carrier and the toner in equal weight (hereinafter simply referred to as the carrier surface area occupancy rate).

Therefore, in this aspect of the present invention, when the electrostatic image is developed with the two-component developer under the condition that the carrier surface area occupancy rate or its neighborhood value is equal to the toner density, The density is improved, the fog density is reduced, the resolution is improved, and the gradation is improved.

Toner concentration (Ct%) and carrier surface area occupation ratio (Sc / (St
+ Sc),%) can be evaluated by determining the ratio of the two, that is, k = Ct / [Sc / (St + Sc)] coefficient k.

This coefficient k differs depending on the shape of the ferrite carrier used, but in the present invention, this coefficient k has been described above.
A value of 0.80 to 1.07, especially in the range of 0.90 to 1.04 for spherical ferrite particles, high image density, low fog density, high resolution and excellent gradation can be obtained. In addition, an effect is achieved in which there is almost no deterioration even after continuous copying of 10,000 sheets.

As the photoconductor amorphous silicon-based photoconductor layer, any known material is used, and for example, amorphous silicon deposited on the substrate by plasma decomposition of silane gas is used.
This may be doped with hydrogen, halogen, or the like, and further doped with a periodic group III or group V element such as boron or phosphorus.

The physical properties of a typical amorphous silicon photoconductor are as follows: dark conductivity of 10 ^-12 Ω ^-1 · cm ^-1 , activation energy <0.85 eV,
Photoconductivity> 10 ^-7 Ω ^-1 cm ^-1 , optical bandgear 1.7
˜1.9 eV, the amount of bound hydrogen is 10 to 20 atomic%, and the dielectric constant of the film is in the range of 11.5 to 12.5.

This amorphous silicon photoconductive layer can be positively or negatively charged depending on the doping species, and the voltage applied to the corona charger is generally in the range of 5 to 8 KV.

According to the present invention, the amorphous silicon photoconductor layer has a thickness of 10
To 35 μm, and as a result, there is a remarkable advantage that a high-density image can be formed even when the charging potential is extremely small. Moreover, the use of a photosensitive layer having a small film thickness not only provides a significant advantage in reducing the cost of the photosensitive member, but also prevents light diffusion in the photosensitive layer, resulting in the formation. There is also an advantage that the resolution of the toner image is improved.

The invention is illustrated in the following examples.

Example In order to investigate the relationship between the DS resistance of the ferrite carrier and the copy, a copying machine equipped with each mechanism shown in FIG. 1 was used, and toner and 4.0 × 10 ^{4 to} 8.5 × 10 ⁶ were used. Duplicate tests were carried out with a developer consisting of a ferrite carrier having a certain D-S resistance in the .OMEGA. Range.

The copying machine was used under the following conditions.

Photoreceptor: 90-mm-diameter Al substrate with boron doped a-
Photoreceptor with Si: H deposited to a thickness of 20 μm by glow discharge decomposition method Image exposure light source: Light intensity 60 μW / cm on photoreceptor surface
White fluorescent lamp set to ² (however, spectral intensity of 600 nm or more is 10 μW / cm ² or less) Static erasing light source: green light emitting cold cathode discharge tube Cleaning unit: blade cleaning method Main charging: corona charger (+6.2 KV applied) Transfer charge: 〃 (+ 5.7KV applied) Copy speed: Photoconductor drum rotation speed 16cm / sec Development part: Sleeve rotation speed 23cm / sec Development magnet strength 1000 gauss Ear cutting interval 1.0mm Development area: Photoconductor and development sleeve Both were rotated clockwise and the gear between D and S was fixed at 1.5 mm.

The same toner was used as the developer, and a developer was used in combination with a ferrite carrier having various dynamic electric resistances within the above-mentioned range.

(A) Ferrite carrier Electric resistance (20V applied DS resistance): 4.0 × 10 ^{4 to} 8.51 × 10 ⁶
Ω Incidentally, for the measurement of the D-S resistance, the above-mentioned conditions of the copying speed, the developing portion and the developing region are used as they are, and instead of the photosensitive drum, an Al electrode drum having the same diameter as the drum is mounted, and the sleeve and the drum It is a value calculated by applying a voltage of 20 V between and and measuring the current flowing between them.

Saturation magnetization: All about 70 emu / g Central particle size: All about 40 μm (b) Toner (i) Composition Hymer SBM-73 (Styrene resin: Sanyo Kasei KK
...... 87 parts by weight Viscole 550P (low molecular weight polypropylene: manufactured by Sanyo Kasei KK) …… 5 parts by weight Special black 4 (carbon black: manufactured by Degussa) …… 5.5 parts by weight Bontron S-32 (dye: Orient Chemical Co., Ltd.) Company) …… 1.
5 parts by weight (ii) Preparation The mixture having the above composition was sufficiently melted and kneaded and dispersed in a hot three-roll mill, and the kneaded product was taken out and cooled, and then 2 mm by a group crusher (Rotprex cutting mill: made by Alpine). Coarsely pulverized to a size of about 5 μm and then finely pulverized with an ultra high speed jet mill (manufactured by NIPPON PNEUMATIC MFC Co.LTD) to prepare a toner having a particle size of about 5 to 20 μm.
What should be noted here is to adjust to a toner (hereinafter referred to as fine powder cut toner) in which classification is repeated until the content of fine particles of 5 μm or less becomes substantially zero (volume% conversion). The specific surface area of this toner was 4360 cm ² / g, and the volume resistivity was 4.5 × 10 ¹⁴ Ω · cm.

These ferrite carriers and toner were mixed so as to have an appropriate toner concentration in view of the relationship of specific surface area, and the developers shown in Table 1 were prepared.

Table 2 shows the physical properties of a developer prepared by using a toner (hereinafter referred to as a normal toner) prepared to have a particle size of about 5 to 20 μm by a normal classification operation, and the fine cut toner and the normal toner. The particle size distribution is shown in Table 3.

(A commercially available Coulter counter was used to measure the particle size distribution.) The results of copying tests using the developers A to G and A'to G'shown in Tables 1 and 2 are 4 and It is shown in Table 5.

In the table, for ID, the reflection density of a solid part having a photoreceptor surface potential of 250 V developed and transferred under the condition of applying a developing bias of 80 V is shown.

As for brush marks, x: there are many brush marks, Δ: there is little, ◯: there is no brush mark, and for gradation, x: the low density region cannot be reproduced.

Δ: Low density can be reproduced, but lack of gradation in high density range.

Good: Gradation from low density area to high density area.

Means

Based on these experimental results, the graph of FIG. 5 was created to make it easier to judge that the difference between the normal toner and the fine powder cut toner appears as a remarkable difference when the amorphous silicon photoconductor is used. did.

The graph of FIG. 5 shows D of the carrier in Tables 1 and 2.
4 shows the relationship between -S resistance and ID in Tables 3 and 4. With reference to this graph, it is clear that the normal toner and the fine powder cut toner show similar tendencies, but the latter has a significantly higher image density.

Also, from the experimental results shown in Table 4, the DS of the carrier
Resistance is 8.0 × 10 ^{4 to} 25 × 10 ⁶ Ω (B, C, D, E in the table)
When the developer of F) was used, a high density copy was obtained. Among these B to E developers, the DS resistance of the carrier is 1.0 × 10 ^{5 to} 7.1 × 10 ⁵ Ω (C, D in the table,
The image E) has a high image density (ID), is excellent in gradation and resolution, and a clear copy image free from white marks due to brush marks, fog, and edge effect and tailing phenomenon was obtained. The image densities of the developers C and D were particularly high.

Further, from the graph of FIG. 5, there is an ID peak in the range of 4 × 10 ⁶ Ω to 5 × 10 ⁷ Ω in the DS resistance of the developer formed by combining the fine powder cut toner and the ferrite carrier. It is understood that when a developer in this range is used, a high-quality copy having an image density of 1.25 or more can be obtained.

Thus, it was confirmed that a developing method can be provided in which excellent developing characteristics can be obtained when a developer combined with the above carrier is used for an amorphous silicon photoconductor using a fine powder cut toner.

[Brief description of drawings]

FIG. 1 is a diagram for explaining an electrophotographic method suitable for carrying out the developing method of the present invention. In the figure, 2 is an amorphous silicon photoconductor layer, 3 is a main charging corona charger, and 4 is a corona charger. An exposure lamp, 8 is a developing mechanism, 9 is a transfer corona charger, 11 is a discharge lamp, and 12 is a cleaning mechanism. FIG. 2 is a graph showing the relationship between the D-S resistance of the developer and the ID, and FIG. 3 is a graph showing the relationship between the surface potential of the amorphous silicon photoconductor and the image density. The mark shows the case where the normal toner is used, and the mark * shows the case where the fine powder cut toner according to the method of the present invention is used. FIG. 4 is a graph showing the relationship between the number of continuous copies and the image density when the developing method of the present invention is used, and FIG. 5 is the dynamic resistance of the developer using fine powder cut toner and normal toner, respectively. It is a graph which shows.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location G03G 15/09 Z (72) Inventor Kazuo Yamamoto 1-2-2 Tamatsukuri, Higashi-ku, Osaka-shi, Osaka 3 Tako Kogyo Co., Ltd. (72) Inventor Yoshinobu Yamagami 1-2-2 Tamazoi, Higashi-ku, Osaka-shi, Osaka Mita Kogyo Co., Ltd. (56) Reference JP 59-139056 (JP, A) JP 59 -172660 (JP, A)

Claims (1)

[Claims] 1. An electrostatic image formed on an amorphous silicon photoconductive layer having a thickness of 10 to 35 .mu.m is developed by using a two-component developer composed of a magnetic carrier and an electrostatic toner. The method uses ferrite sintered reduction particles as the magnetic carrier, and the electrophotographic toner has a median diameter of 10
To 14 μm and a particle size of 5 μm or less, the content is substantially zero, and the volume resistivity is 1 × 10 ¹³ Ω-cm or more. Resistance is 6 × 10 ^{4 to} 2.5 × 10 ⁶
A developing method characterized in that the developing conditions are set so as to fall within a range of Ω.