JPH07140730A - High-speed developing method for electrostatic charge image - Google Patents

Abstract

PURPOSE:To obtain the uniform image of a high density and sharp contour without a discontinuous a fine line by preventing a sweeping mark in development being irregularities in the toner layer of half-tone and solid parts, at the time of using in a high copying speed zone. CONSTITUTION:In a magnetic brush developing unit, the developing main magnetic pole position of a magnet roll 3 fixed inside a developer carrier 2 and composed of plural magnetic poles is set in the range of 5-20 deg. on the upstream side in the carrying direction of a developer, with respect to a plane connecting the center axes of the magnet roll 3 and an electrostatic charge image carrier 10 and simultaneously, the distance Hcut between a member 4 regulating the nap height of the bristle of a magnetic brush and the developer carrier 2 is 0.25-0.75mm, a developing nip distance Dsd is 0.30-0.80mm and 1.20<Dsd/Hcut<1.60 is set. Further, the moving linear velocity Vs (mm/s) of the periphery of the developer carrier 2 in a developing region and the moving linear velocity Vp (mm/s) of the periphery of the electrostatic charge image carrier 10 satisfy the inequality 1.0<=Vs/Vp<=3.0 (here, 400<=Vp<=800 and 400<=Vs<=2400).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed developing method for an electrostatic charge image used in electrophotography, electrostatic photography, electrostatic printing and the like.

[0002]

2. Description of the Related Art A developer composed of a magnetic carrier and a toner is widely used in a copying machine utilizing an electrophotographic method. When developing an electrostatic image, a magnetic brush of the developer is formed on the surface of a developer carrier. The toner image is formed by contacting and rubbing the magnetic brush with the electrostatic image carrier.

However, in a high-speed copying machine capable of obtaining a large number of copies in a short time, various problems occur when applying the present developing method.

Among them, the problem affecting the output image is that the electrostatic charge image carrier must be rotated at a high speed, so that the halftone of the electrostatic charge image or the toner layer developed in the solid part is Due to its high speed, there is a point that it is disturbed in the circumferential direction by rubbing of the magnetic brush, and so-called "sweep" is generated. This appears in the output image as problems such as unevenness in the solid portion and uneven density due to scratches, and breaks in fine line portions.

In addition, due to its high speed, the scattering amount of the magnetic carrier constituting the magnetic brush may increase due to the increase in centrifugal force, and a part of the magnetic carrier may adhere to the surface of the electrostatic image carrier. In that case, the magnetic carrier passes through the transfer section and the cleaning section while being attached, and the attached magnetic carrier damages the electrostatic image carrier. As a result, there is also a problem that the scar disturbs the electrostatic charge image, resulting in disorder of the output image. Further, the scratches caused by the adhered magnetic carrier reduce the durability of the electrostatic image carrier, which is a serious problem in practical use.

Conventionally, various methods have been taken to reduce the rubbing force of magnetic brushes. However, none of them are sufficient measures.

For example, a method of reducing the frictional force by minimizing the difference between the moving linear velocity of the peripheral surface of the developer carrying member and the moving linear velocity of the peripheral surface of the electrostatic charge image carrying member, and a developer carrying member. A method of reducing the rubbing force of the magnetic brush by widening the distance Dsd between the electrostatic charge image carrier and the electrostatic charge image carrier or reducing the height of the magnetic brush has been adopted. The amount of developer conveyed to the area is reduced, resulting in a decrease in image density.

Although a method of compensating for this decrease in image density by increasing the toner density in the developer has been proposed, a problem of toner scattering occurs remarkably in a high speed copying machine, and an appropriate countermeasure is taken. It can not be said.

[0009]

SUMMARY OF THE INVENTION The present invention provides a conventional developing method using a developer composed of a magnetic carrier and a toner such that the moving linear velocity Vp of the peripheral surface of the electrostatic image carrier exceeds 400 mm / s. By eliminating the disadvantages of using in the high-speed range, preventing halftones and development sweeps, which are disturbances of the toner layer in the solid area, and suppressing the adhesion of carriers to the electrostatic image carrier, It is intended to provide a developing method capable of preventing generation of scratches on the surface of a charge image carrier, obtaining a uniform image having a high density without causing breakage of fine lines and having a clear contour at high speed.

[0010]

[Means for solving the problem] Volume-based 50% particle diameter D50
(Μm), volume-based 25% particle size D25 (μm), 75% particle size D75
An electrostatic charge image bearing on which an electrostatic latent image is formed by using an electrophotographic developer composed of a magnetic carrier whose (μm) each satisfies the relation of 45 ≦ D50 ≦ 75 0.7 × D50 <D25 1.5 × D50> D75 The magnetic brush developing device is composed of a body, a developer carrier at a position facing the body, which conveys the developer to the developing area, and a magnet roll composed of a plurality of magnetic poles fixed inside the body. The position of the developing main magnetic pole of the roll is set in the range of 5 to 20 ° on the upstream side in the developer transport direction with respect to the surface connecting the central axes of the magnet roll and the electrostatic charge image bearing member, and more than the developing main magnetic pole. Further, a member for regulating the height of the magnetic brush bristles is located on the upstream side, the distance Hcut between the regulating member and the developer carrier is 0.25 to 0.75 mm, and further, between the developer carrier and the electrostatic image carrier. Development nip distance Dsd, which is the closest distance Is 0.30 to 0.80 mm, 1.20 <Dsd / Hcut <1.60, and the moving directions of the two are the same at that position, that is, the rotating directions are opposite to each other, and the developer carrier in the developing area is Moving linear velocity Vs (mm /
s), the moving linear velocity Vp (mm / s) of the peripheral surface of the electrostatic image carrier is 1.0 ≦ Vs / Vp ≦ 3.0 (where 400 ≦ Vp ≦ 800, 400 ≦ Vs
The above-described problems can be solved by a developing method using a high-speed developing device for an electrostatic charge image that satisfies the relationship of ≦ 2400).

The detailed structure of the present invention will be described below.

(Developing System) FIG. 1 shows an example of the construction of the developing device and the electrostatic charge image carrier used in the present invention.

The developing device 1 comprises a developing device main body 1A and a toner replenishing portion 1B, and a peripheral surface of a developer carrying member 2 incorporated in the developing device main body 1A is predetermined with respect to an electrostatic charge image carrying member 10. They are opposed to each other with an interval of, and are installed and set at a position where a developing area for developing the electrostatic charge image on the peripheral surface of the electrostatic charge image carrier 10 is developed. A main stirring member 9A and an auxiliary stirring member 9B are rotatably supported inside the developing device main body 1A.

The electrostatic charge image carrier 10 is a photoconductor having a photoconductive layer and rotates clockwise in FIG. 1 and a surface of the electrostatic charge image carrier is provided by a belt electrode 11 provided on the upstream side of the developing area. Is charged to a constant potential.

The charged electrostatic image carrier 10 has a developing area E.
And is exposed upstream to form a latent image, that is, an electrostatic image. After that, development is performed in the development area E.

The developer carrier 2 rotates counterclockwise in FIG. 1, and the closest distance in the developing area E between the peripheral surface of the developer carrier 2 and the peripheral surface of the electrostatic image carrier 10 is the development nip distance. It is called Dsd.

The magnet roll 3 contained in the developer carrying member 2 has a main magnetic pole N1 as a magnetic pole for development and a transport magnetic pole for transporting the developer on the outer peripheral surface of a non-magnetic rod material such as aluminum. It is a columnar magnet body having a plurality of auxiliary magnetic poles that play a role of.

Further, a magnetic brush spike height regulating member 4 for limiting the amount of the developer conveyed by the magnetic force of the magnet roll 3 to the amount necessary for the development, facing the peripheral surface of the developer carrying member 2. Is installed. The distance between the height control member 4 and the developer carrying member 2 is referred to as Hcut.

The developing device 1 is loaded with a developer consisting of toner and carrier, and the developer is stirred by the main stirring member 9A and the auxiliary stirring member 9B, and is then rotated on the outer circumference of the magnet roll 3 for development. The magnetic brush is formed by adhering to the outer peripheral surface of the agent carrier 2 and reaches the developing area E after the thickness of the developer layer is regulated by the spike height regulating member 4. A predetermined bias voltage is applied between the developer carrier 2 and the electrostatic image carrier to develop the image.

As the bias voltage applied between the developer carrier and the electrostatic charge image carrier, a DC voltage having the same polarity as the electrostatic charge image forming an electric field between the maximum and minimum potentials of the electrostatic charge image is applied. However, an AC voltage that forms an alternating electric field between the maximum and minimum potentials of the electrostatic charge image may be applied if necessary.

(Developer) A known developer carrier can be used in the present invention. Aluminum, stainless steel, etc. can be used as the material. Further, in order to convey the developer to the developing area at a high speed and stably for a long period of time, it is effective to perform a surface roughening treatment such as a thermal spraying treatment or a sandblasting treatment on the surface of the developer carrying member.

The outer diameter of the developer carrying member is 40 to 80 mmφ,
It is preferable to use one having a diameter of 50 to 70 mm.

Further, the developing main magnetic pole N1 used for the magnet roll inside the developer carrying member has a magnet width of 10 to 30 mm,
Good results can be obtained by using a magnetic flux density of 800 to 1400 Gauss, preferably 900 to 1200 Gauss. Moreover, it is preferable to use a magnetic pole having a magnetic flux density of 400 to 800 Gauss as the auxiliary magnetic pole.

Further, the position of the developing main magnetic pole N1 is appropriately set in the range of 0 to 30 ° on the upstream side in the developer conveying direction, but preferably, it is set in the range of 5 to 20 ° to obtain better results. .

When the total number of main magnetic poles and auxiliary magnetic poles is at least 4, preferably 5 to 10, the high-speed transportability of the developer is very stable.

Further, a member for regulating the height of the magnetic brush bristles is arranged further upstream than the main developing magnetic pole, and the distance Hcut between the regulating member and the developer carrying member is appropriately in the range of 0.25 to 0.75 mm. However, better results can be obtained by setting the range of 0.30 to 0.65 mm.

Further, it is necessary to dispose the electrostatic charge image carrier at a position facing the developer carrier. In that case, the developing nip distance which is the closest distance between the developer carrier and the electrostatic image carrier. A suitable range of Dsd is 0.30 to 0.80 mm, but more preferred results are obtained by setting it in a range of 0.45 to 0.75 mm.

Further, it is very important to set the distance ratio between Dsd and Hcut in order to reduce the rubbing force of the magnetic brush and simultaneously obtain a high quality image. Specifically, better results are obtained when the Dsd / Hcut distance ratio is in the range of 1.20 to 1.60, preferably 1.25 to 1.50.

Regarding the rotation directions of the electrostatic image carrier and the developer carrier, the peripheral surfaces of the electrostatic charge image carrier and the developer carrier move in the same direction, that is, the rotation directions are opposite to each other, and the development in the development region proceeds. Moving linear velocity Vs (mm /
s), moving linear velocity Vp (mm / s) on the peripheral surface of the electrostatic image carrier
However, good results are obtained when the range is 1.0 ≦ Vs / Vp ≦ 3.0 (however, 400 ≦ Vp ≦ 800). However, in order to obtain a more remarkable effect, it is preferable to set 1.2 ≦ Vs / Vp ≦ 2.6 (however, 400 ≦ Vp ≦ 800).

(Toner) The toner used in the present invention is
Known ones can be used. Specifically, it is a toner including at least a binder resin and a colorant, and may be a toner to which a release agent, a charge control agent, a fluidizing agent, and a magnetic material are further added as necessary. Known materials are used for the constituent materials.

The volume-based 50% particle diameter of the toner used in the present invention is preferably in the range of 5 to 15 μm.
More preferably, as the particle size distribution, toner having a particle size of 0.4 times or less of the volume-based 50% particle size is 10 vol% or less of the whole on the fine powder side, and 2.5% of the volume-based 50% particle size on the coarse powder side. Toner with a particle size more than double is 0.5
If the content is less than vol%, the uniformity of the mixing of the toner in the developer and, by extension, the uniformity of the output image can be increased, and better results can be obtained.

A known method can be used as the method for producing the toner.

(Magnetic Carrier Core Material) As the magnetic carrier or core material thereof that can be used in the present invention, a substance that is strongly magnetized in its direction by a magnetic field can be used.

More specifically, iron, ferrite, magnetite and other nickel, cobalt, and other ferromagnetic metals, or alloys or compounds containing these metals can be used. The term “ferrite” as used herein is a general term for magnetic compounds containing iron and is not limited to spinel type.

Of these, ferrite is preferable because it is relatively easy to keep the magnetization within an appropriate range.

Keeping the magnetization within a proper range is an important factor in the high-speed development of the present invention. This is because when the magnetization is extremely high, the toner having a small particle size is likely to be damaged, and the durability of the developer may be deteriorated. This is more noticeable in high speed copying machines.
On the other hand, if the magnetization is too low, scattering of magnetic carriers occurs, which adversely affects the output image. This is also a problem that appears prominently in high-speed copying machines.

Therefore, the magnetic carrier used in the present invention or the core material used for the magnetic carrier is 1000 O
It is preferable that the saturation magnetization of e in the external magnetic field is 40 to 120 emu / g and the coercive force is 0 to 100 Oe, but the saturation magnetization is 5
Even better results are obtained when a material having a coercive force of 0 to 100 emu / g and a coercive force of 0 to 30 Oe is used.

Further, since ferrite has a smaller specific gravity than iron powder or nickel powder, it becomes easy to mix and agitate with the toner, and the toner concentration in the developer is made uniform, and the charge amount with the toner is optimized. It is preferable in that Specifically, the specific gravity is preferably 4.0 to 5.5.

Further, ferrite is preferable because it is relatively easy to control the volume resistivity. In the present invention 500
The volume resistivity of the magnetic carrier when V is applied is 1 × 10 ⁸ to 1
Good results are obtained with x10 ¹⁴ Ω · cm, preferably 5 × 10 ^{11 to} 5 × 10 ¹³ Ω · cm.

The particle size of the magnetic carrier that can be used in the present invention is such that the volume-based 50% particle size D50 is 45 to 75 μm.

The reason is 50% by volume of the magnetic carrier.
When the particle size is too small, magnetic carriers are likely to adhere to the electrostatic charge image bearing member, which may cause scratches on the electrostatic charge image bearing member. Further, if the volume-based 50% particle size is excessively large, the specific surface area of the magnetic carrier becomes small, and it becomes difficult to properly triboelectrically charge a required amount of toner, which causes image defects such as background fog.

As the particle size distribution of the magnetic carrier, volume-based 50% particle size D50 (μm), volume-based 25% particle size D25.
(Μm) and volume-based 75% particle size D75 (μm) satisfy the relations of 45 ≦ D50 ≦ 75 0.7 × D50 <D25 1.5 × D50> D75 respectively, the homogeneity necessary for the developer is obtained,
An output image having a uniform density can be obtained even in a high developing speed region.

(Magnetic Carrier Coating Layer) The magnetic carrier used in the present invention may have a resin coating layer provided on the surface of the magnetic particles, if necessary. In that case, as the resin for coating the magnetic particles, a resin obtained by a known polymerization method can be used.

As the coating resin which can be used in the present invention, known resins can be used. Specifically, styrene resins, acrylic resins, vinyl resins, ethylene resins, polyamide resins, polyesters. Such as resin
Alternatively, a resin composed of a copolymer or a mixture of two or more of these can be used.

Specific examples of the resin production method include a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, a bulk polymerization method, and an in-situ polymerization method.
A polymerization method or the like can be used.

As a method for coating the surface of the magnetic particles with the obtained resin, a known coating method can be used.

Specific examples of the method for coating the surface of the magnetic particles with the resin include a method of spraying the dispersion solution of the resin obtained by the above-mentioned method on the surface of the magnetic particles, a method of immersing the magnetic particles in the dispersion solution, and the like. A resin layer is formed on the magnetic particle surface by a wet coating method or by electrostatically adhering the atomized coating resin to the magnetic particle surface, and then applying either or both heat and mechanical stress to the magnetic particle. A dry coating method of coating and immobilizing can be used.

When the resin coating is performed, the coating amount of the resin on the magnetic particles is preferably 0.1 to 10% per unit weight of the magnetic particles, although it depends on the specific gravity of the resin.

(Developer) The developer used in the present invention is
Although it is composed of a magnetic carrier and a toner, a third component such as a lubricant, a cleaning aid and a fluidizing agent may be mixed if necessary.

Further, the toner concentration setting in the developer used in the present invention is slightly different depending on the specific gravity of the toner or the magnetic carrier, but the weight ratio is 3 to 10% with respect to the magnetic carrier.
It is preferable to mix them in the range of 4 to 8%.

When mixing the magnetic carrier and the toner, a conventionally known mixer can be used.
It is preferable that the stress applied to the developer at that time is small. Specifically, a rotation type mixer such as a V-type mixer, a W-cone mixer, a rocking mixer can obtain better results than a stirring type mixer such as a Henschel mixer.

(Electrostatic Charge Image Bearing Member) As the electrostatic charge image bearing member used in the present invention, a conventionally known photoreceptor can be used. Specifically, various organic photoconductors, amorphous silicon photoconductors, selenium photoconductors and the like can be used.

(Particle size measuring method) The volume standard particle size of the magnetic carrier or toner used in the present invention can be determined by a laser diffraction particle size distribution measuring device HELOS (manufactured by JEOL Ltd.).

(Magnetic characteristic measuring method) The magnetic characteristic of the magnetic carrier used in the present invention is a direct current magnetization characteristic automatic recording apparatus.
It can be determined by Model 3257-35 (made by Yokogawa Electric Corp.).

[0055]

[Function] The disadvantages of using the conventional developing method using a developer composed of a magnetic carrier and toner in a high copying speed range are solved, and the development sweep, which is a disturbance of the halftone or solid toner layer, is eliminated. In addition to this, by preventing the magnetic carrier from adhering to the electrostatic charge image carrier, the occurrence of scratches on the surface of the electrostatic charge image carrier is prevented, the fine lines are not broken, the density is high and the contour is uniform. In order to obtain clear images at high speed, as a result of diligent studies, the height and shape of the brush of the magnetic brush, the shape and size of the development area, the moving linear velocity of the peripheral surface of the developer carrier and the electrostatic image carrier. It was found that it is effective to keep the above in an optimum range and to make the particle size distribution of the developer uniform.

[0056]

EXAMPLES Magnetic carriers A, B, C and D having the particle size distribution shown in Table 1 were prepared.

The magnetic carriers A to D were composed of spherical Cu-Zn ferrite particles, and 2% of styrene / methylmethacrylate copolymer resin was added to the weight of the magnetic particles.
It is a coated resin-coated carrier.

[0058]

[Table 1]

The magnetic carrier of this example had a saturation magnetization of 58 [emu / g], a coercive force of substantially 0 [Oe] below the detection limit, and a volume resistivity of 2.1 × 10 ¹³ [Ωcm. ] The resin-coated carrier of was used.

The toner used was obtained in the following manner.

To 100 parts by weight of polyester resin, 2 parts by weight of carnauba wax as a release agent and 10 parts by weight of carbon black as a colorant are mixed and melt-kneaded by a kneader. After that, the mixture was cooled, coarsely crushed, and finely pulverized to obtain two kinds of toner having volume-based 50% particle diameters of 8.0 μm and 6.8 μm. Thereafter, as a fluidizing agent, 1 part by weight of silica fine particles was externally added and mixed with 100 parts by weight of the toner to obtain toners a and b used in this example.

The particle size distribution of this toner is shown in Table 2. Toner a was mixed with magnetic carriers A and C, and toner b was mixed with magnetic carriers B and D to obtain the developer of this embodiment.

[0063]

[Table 2]

In the preparation of the developer, the toner and the magnetic carrier obtained as described above are set so that the weight ratio of the toner to the magnetic carrier is 5%, and the mixture is put into a V-type mixer and mixed to form a toner. A developer used in the examples. The developers using the magnetic carriers A, B, C and D are referred to as developers A, B, C and D, respectively.

The copying machine is Konica U-Bix5082 (Konica
A modified machine (made by Co., Ltd.) was used. This remodeling machine, if necessary, the moving linear velocity of the electrostatic charge image carrier, the peripheral surface of the developer carrier,
The distance Dsd between them, the Hcut distance in the developing device, and the developing main magnetic pole position can be arbitrarily changed.

The developing conditions other than the above are as follows.

Electrostatic charge image potential: 850-60V Development bias potential: DC 200V Developer carrier: Outer diameter 60 mmφ Made of aluminum (spraying the surface) Electrostatic image carrier: Outer diameter 108 mmφ Selenium photoreceptor Main magnetic pole: Magnetic flux Density 1050 Gauss, magnetic pole width 18 mm, number of auxiliary magnetic poles: 4 (evaluation method) -Image density A solid portion with an original density of 1.30 was copied, and the relative reflection density of the output image with respect to a blank sheet was measured. A Macbeth densitometer was used for density measurement, and image density of 1.25 or higher was judged to be good.

Solid Area Sweep: A solid area having a document density of 1.00 was copied and judged by visually observing the output image. When there was no scratch-like image disturbance in the paper feeding direction, the result was “good” and when there was occurrence, it was poor and was “poor”.

Fine line break A fine line having a line width of 100 μm drawn in a direction perpendicular to the paper feeding direction was copied, and the output image was magnified with a microscope and visually judged. If there are no fine line breaks and there is no problem, it is "○", if there are two or less fine line breaks per 100 mm of fine line, it is "△", and if more fine line breaks occur, it is a defect. "

-Adhering carrier Determined by visual observation of the output image. The case where the carrier adhesion did not occur and there was no problem was evaluated as “◯”, and the case where the carrier adhesion was confirmed and was defective was evaluated as “x”.

Drum Scratch Continuous copying was carried out at 10 kC, after which the electrostatic image carrier (photosensitive drum) was taken out, and the presence or absence of scratches in the moving direction of the peripheral surface was judged by visual observation. The case where no scratch was observed was good and was “Good”, and the case where scratch was seen in the moving direction of the peripheral surface was bad and was bad.

(Evaluation Conditions) Table 3 shows the evaluation conditions for the examples and comparative examples.

[0073]

[Table 3]

(Evaluation Results) Table 4 shows the evaluation results under the above evaluation conditions.

[0075]

[Table 4]

[0076]

By using the developing method of the present invention, it is possible to eliminate the drawbacks of using a conventional developing method using a developer composed of a magnetic carrier and a toner at a high speed, and obtain a high quality image at a high speed. You can

Specifically, it is possible to prevent the development sweep, which is the halftone and the disturbance of the toner layer in the solid portion, and to suppress the adhesion of the carrier to the electrostatic charge image bearing member, so that the surface of the electrostatic charge image bearing member is suppressed. It is possible to prevent scratches from occurring, and as a result, it is possible to quickly obtain an image with high density, uniform and clear contours, without breaks in fine lines.

[Brief description of drawings]

FIG. 1 is a sectional view of a developing device according to the present invention.

[Explanation of symbols]

 1 developing device (electrostatic charge image carrier) 2 developer carrier 3 magnet roll 4 magnetizing member 10 electrostatic charge image carrier 21 DC constant current power supply 22 AC constant current power supply E development area Hcut magnetic spike forming gap Hsd development unit Gap Vs Development potential (bias voltage)

Claims (1)

[Claims] 1. A volume-based 50% particle size D50 (μm), a volume-based 25% particle size D25 (μm), and a 75% particle size D75 (μm) are 45 ≦ D50 ≦ 75 0.7 × D50 <D25 1.5 ×, respectively. An electrophotographic developer composed of a magnetic carrier satisfying the relationship of D50> D75 is used, and the electrostatic charge image carrier on which an electrostatic latent image is formed, and a position opposite to the electrostatic image carrier are conveyed to the developing area. It is composed of a magnetic brush developing device composed of a developer carrier and a magnet roll composed of a plurality of magnetic poles fixed inside the developer carrier, and the main developing magnetic pole position of the magnet roll is the center of the magnet roll and the electrostatic image carrier. A member for controlling the height of the magnetic brush is set in the range of 5 to 20 ° on the upstream side in the developer conveying direction with respect to the surface connecting the shafts, and a member for regulating the height of the magnetic brush is located further upstream than the main developing magnetic pole. When the distance Hcut between the member and the developer carrier is 0.25 to 0.75 mm Furthermore, the developing nip distance Dsd, which is the closest distance between the developer carrier and the electrostatic image carrier, is 0.30 to 0.80 mm, 1.20 <Dsd / Hcut <1.60, and both of them at that position. The moving directions are the same, that is, the rotating directions are opposite to each other, and the moving linear velocity Vs (mm /
s), the moving linear velocity Vp (mm / s) of the peripheral surface of the electrostatic image carrier is 1.0 ≦ Vs / Vp ≦ 3.0 (where 400 ≦ Vp ≦ 800, 400 ≦ Vs
A high-speed developing method using a high-speed developing device for electrostatic images, which satisfies the relationship of ≦ 2400).