JP2000321841A - Electrophotographic image forming method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-grade color image with a small-sized high-speed device at a low cost. SOLUTION: In an electrophotographic image forming method in which a toner image is formed on a transfer material using an electrophotographic photoreceptor through at least electrifying, exposing, developing and transferring steps, plural electrophotographic photoreceptors 1 having >=1×1010 to <=1×1014 Ω.cm volume resistance of the surface layer are disposed, a multiple transferring step is carried out as the transferring step and the time T (sec) from image exposure to development satisfies the expressions T (sec)<=1×10-11×(volume resistance) (Ω.cm) and 1×10-15×(volume resistance) (Ω.cm) × film thickness (μm)<=T (sec), wherein film thickness is the film thickness of the surface layer of each electrophotographic photoreceptor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming method and an electrophotographic image forming apparatus, and more particularly to an electrophotographic image forming apparatus which is used in a multiple transfer process using a plurality of electrophotographic photosensitive members and realizes a high-quality image. The present invention relates to a forming method and an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art a) A toner image (charged fine particle developer) is formed on an electrophotographic photosensitive member or an electrostatic recording dielectric image carrier (hereinafter referred to as "photosensitive member") by an appropriate image forming process. Image), the toner image is transferred to a transfer material (transfer material, recording medium) such as paper, and the image is fixed and output as an image formed product (copy, print, hard copy).
2. Description of the Related Art A transfer type image forming apparatus (an electrophotographic copying machine, a facsimile, a laser beam printer, etc.) in which a photoreceptor is repeatedly used for image formation has been widely used.

In recent years, an electrophotographic process capable of faithfully reproducing a color image has been demanded, and several systems have been proposed. Among them, a plurality of photosensitive drums and a transfer member that holds a transfer material such as transfer paper take a synchronized configuration,
As a high-speed process, an apparatus adopting a multi-drum multiple transfer system in which three types of three primary colors or four-color images obtained by adding black to the three primary colors are successively superimposed on a transfer material to reproduce a color image is used.

B) In the transfer type image forming apparatus, when transferring the toner image from the photosensitive member side to the transfer material side, not all of the toner is actually transferred, but a part remains (transfer residual toner). Unless the transfer residual toner is removed from the photoreceptor, it is impossible to obtain a high-quality image free of dirt or the like in a repeated image forming process. For this reason, it is necessary to remove transfer residual toner from the photoconductor (photoconductor cleaning). Generally, a dedicated cleaning device (cleaner) is provided and provided to remove transfer residual toner from the photoreceptor.

The toner removed from the photoreceptor by the cleaning device becomes waste toner, but it is desirable that the waste toner does not come out from the viewpoint of environmental protection.

Therefore, the cleaning device is eliminated, and the transfer residual toner on the photoreceptor after the transfer is transferred to a charging device as a charging step means and / or a developing device as a developing step means in a charging step and / or a developing step of the photoreceptor. A transfer-type image forming apparatus of a cleaner-less system, which collects (simultaneously charges and cleans and cleans simultaneously) and reuses it, has also appeared.

[0007] Such an image forming apparatus of a cleanerless system is ecologically effective, and also makes it possible to reduce the size, weight and cost of the image forming apparatus.

C) As a charging step for uniformly charging the photosensitive member to a predetermined polarity and potential, a corona charger has been generally used. In this method, a corona charger is disposed so as to face a photoreceptor in a non-contact manner, and the surface of the photoreceptor is corona-charged by exposing the surface of the photoreceptor to a corona shower generated from the corona charger to which a high voltage is applied.

In recent years, contact charging devices have been put to practical use because they have advantages such as lower ozone and lower power than corona chargers.

[0010] The contact charging device is used for charging a charged object such as a photoreceptor.
A conductive charging member (contact charging member) such as a roller type (charging roller), a blade type, a fur brush type, or a magnetic brush type is brought into contact, and a predetermined charging voltage (charging bias) is applied to the contact charging member. The charged object is charged to a predetermined polarity and potential.

Contact charging mechanism (charging mechanism)
Has two types of corona charging system and direct charging system (charge injection charging system), and each characteristic appears depending on which one is dominant.

That is, as shown in the equation (D), the peak-to-peak voltage (Vpp) of the charging application alternating voltage is equal to the discharge starting voltage (Vt).
h) is less than twice that of the above formula (E)
The case where (F) is satisfied is the charge injection charging system.

A magnetic brush type contact charging device using a magnetic brush type contact charging member (magnetic brush charger) is used to transfer conductive magnetic particles directly to a magnet or magnetically on a sleeve containing a magnet. A magnetic brush-type contact charging member that is constrained to form and hold a magnetic brush portion of magnetic particles is disposed with the magnetic brush portion in contact with the photoreceptor, and a voltage is applied thereto to contact-charge the photoreceptor. And is preferably used from the viewpoint of stability of charging contact.

A conductive rubber roller (charge roller) made of conductive rubber in a roll shape, a brush made of conductive fibers (conductive fur brush), and the like are also preferably used as the contact charging member.

D) In an image forming apparatus of a cleanerless system using a contact charging device as a charging step of the photoreceptor, the transfer residual toner on the photoreceptor is transferred to a contact portion (charging area) between the contact charging member and the photoreceptor. It is carried and adhered to and mixed with the contact charging member, and is temporarily collected by the contact charging member (simultaneous charging cleaning).

The toner collected by the contact charging member has its charging polarity adjusted, and is sequentially electrically discharged from the contact charging member onto the photosensitive member.

The toner discharged from the contact charging member onto the photoreceptor is carried to a developing area opposite to the photoreceptor and a developing device as a developing process means, and is collected by the developing device (simultaneous development cleaning). Reused.

Simultaneous development and cleaning is a fogging bias (a potential difference between a DC component applied to a developing member of a developing device and a surface potential of the photoreceptor) when the transfer residual toner on the photoreceptor is developed in the subsequent photoreceptor. Fog removal potential difference Vba
ck).

The toner which is sequentially discharged from the contact charging member onto the photoreceptor is usually in a very small amount in a very thin layer in a uniformly scattered state, and substantially adversely affects the next image exposure step. Never. Further, generation of a ghost image due to the transfer residual toner pattern is also prevented.

The transfer residual toner on the photoreceptor after transfer of the toner image to the transfer material is often inverted in charge polarity by peeling discharge or the like at the time of transfer. It is difficult to collect at the same time as the development in the developing device. The contact charging member takes in the toner including the toner whose charge polarity is inverted, converts the toner into a regularly charged toner, and sequentially discharges the toner onto the photosensitive member, thereby enabling the developing device to collect the transfer residual toner at the same time as the development.

[0021]

When a plurality of photosensitive members are used as a high-speed color process, the size of the apparatus becomes large, and it is not suitable for miniaturization and cost reduction.

However, Japanese Unexamined Patent Publication No. Hei 6-3921 discloses a method in which a charge is directly injected into a photoreceptor and a certain charge is performed.
Japanese Patent Application Laid-Open No. Hei 4-34566 proposes an electrophotographic apparatus using a magnetic brush and having no cleaner, and a so-called injection charging cleanerless system in which both are combined. Various attempts to reduce the size and cost of a high-speed color process by using this system have been started.

However, even in the case of this system, in order to reduce the size and speed of the apparatus, 1) the outer diameter of the photoconductor should be 40 mm or less. 2) The non-magnetic sleeve used for the magnetic brush charger should be φ.
3) Set the peripheral speed of rotation (process speed) of the photoconductor to 100 mm or less.
It is necessary to restrict the distance to mm / sec or more.

In addition, as shown in Japanese Patent Application Laid-Open No. 9-288406, when used for injection charging, the charging member serves to satisfactorily inject charges into the charge injection layer of the photoreceptor, It must also have a role to prevent the charging member and the photoconductor from being energized and destroyed due to concentration of the charging current on the generated defect such as a pinhole.

Therefore, the resistance of the magnetic particles of the charging member is such that the resistance between the voltage applied portion and the portion in contact with the photosensitive member is 1 × 10
⁴ Ω to 1 × 10 ⁹ Ω, preferably 1 × 1
Is preferably 0 ⁵ Ω~1 × 10 ⁸ Ω. When the resistance value of the charging member is less than 1 × 10 ⁴ Ω, pinhole leak tends to occur. When the resistance value exceeds 1 × 10 ⁹ Ω, good charging tends to be difficult.

In order to control the resistance of the charging member within the above range, the volume resistance of the charging member must be 1 × 10 ⁴ Ω.
cm × 1 × 10 ⁹ Ωcm, particularly preferably 1 × 10 ⁵ Ωcm to 1 × 10 ⁸ Ωcm.

The volume resistance of the magnetic particles used in the charging member is measured by using an electric resistance measuring device shown in FIG. That is, the cells are filled with particles,
The electrode 101 and the electrode 102 are arranged so as to be in contact with the filler particles. Here, 103 is an insulator, 104 is an ammeter, 1
05 is a voltmeter, 106 is a constant voltage device, 107 is magnetic particles, and 108 is a guide ring.

In such an electric resistance measuring apparatus, the volume resistance value is measured by applying a voltage between the electrodes 101 and 102 and measuring the current flowing at that time. The measurement conditions were as follows: the contact area S of the filled particles with the cell was 2 cm ² , the thickness d was 1 mm, the load on the upper electrode was 10 kg, and the applied voltage was 100 V in an environment of 23 ° C. and 65%.

On the other hand, the photosensitive member used for injection charging is supported.
The layer farthest from the body, that is, the charge injection layer
I do. The volume resistivity of this charge injection layer is sufficient
Volume resistance to prevent image deletion
Resistance value is 1 × 10^Ten~ 1 × 10 ¹⁴Ωcm is preferred
New

The method of measuring the volume resistance value of the charge injection layer referred to here is that the surface has a gap of 180 μm / length 59 μm.
A 3 mm thick surface layer was applied by bar coating on a polyethylene terephthalate (PET) film on which a gold-shaped comb-shaped electrode was vapor-deposited. In this environment, a voltage of 100 V is applied in the environment described above, and measurement is performed from a current value flowing.

In general, when the volume resistance is less than 1 × 10 ¹⁰ Ωcm, the charged charges are not held in the surface direction, so that image deletion is apt to occur. On the other hand, if it exceeds 1 × 10 ¹⁴ Ωcm, the charged charge from the charging member cannot be sufficiently injected and held, so that poor charging tends to occur.

However, when the charging member and the photoreceptor are used under the above conditions 1), 2) and 3), dot images are disturbed (image deletion) or image density is poor (insufficient sensitivity).
May occur, and particularly in an image such as a color image that requires faithful reproducibility, high quality may not be maintained.

[0033]

The present inventors have studied the above problems and found that the volume resistivity was 1 × 10 ¹⁰ Ωcm.
As described above, a high-quality image can be obtained even in a small high-speed color image process in which a plurality of photoconductors each having a density of 1 × 10 ¹⁴ Ωcm or less are arranged, and the transfer process is repeated once for each photoconductor on one transfer material. The conditions that can be obtained have been found.

That is, according to the present invention, there is provided an electrophotographic image forming method for forming a toner image on a transfer material through at least the steps of charging, exposing, developing and transferring on an electrophotographic photosensitive member. 10 ¹⁰ Ω · cm or more, 1 × 10 ¹⁴
A plurality of photoconductors having a resistance of less than Ω · cm are arranged, and the transfer process is repeated once for each photoconductor for one transfer material, and the image on the transfer material by the first transfer is second and subsequent times. Is a multiple transfer process in which images on the photosensitive member are sequentially superimposed in synchronization with each other, and a time T (second) from image exposure to development.
Is an image forming method or an electrophotographic image forming apparatus characterized by satisfying the following expressions (A) and (B) at the same time.

T (second) ≦ 1 × 10 ⁻¹¹ × volume resistance (Ω · cm) (A) 1 × 10 ⁻¹⁵ × volume resistance (Ω · cm) × film thickness (μm) ≦ T (second (B) (Film Thickness: Film Thickness of Electrophotographic Photoreceptor Surface Layer) Further, there is provided an image forming method or an image forming apparatus in which the charging step is performed by contact charging.

The charging step is charge injection charging, and the present invention is an image forming method or an image forming apparatus using a magnetic brush charger.

Further, there is provided an image forming method or an image forming apparatus of a cleanerless system for recovering transfer residual toner on a photoreceptor surface after transferring a toner image to a transfer material in a charging step and / or a developing step.

[0038]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The case where the electrophotographic image forming method of the present invention is applied to the electrophotographic apparatus shown in FIG. 1 will be described. In FIG. 1, A is a printer main body, and B is an image reader (image reading device) mounted thereon.
1 is a photosensitive drum, and 7 is a transfer member. The photosensitive drum and the transfer member may be driven in conjunction with a gear, a belt, or the like, or may have independent drive systems. In any case, the photosensitive drum and the transfer member need to overlap the first and second color images at the time of transfer, and control for synchronization is performed. This electrophotographic apparatus can be used as an output device such as a copying machine, a printer, a facsimile, and the like.

The image forming process is basically performed in the order of charging, exposing, developing and transferring, and by repeating these sequentially on each photosensitive drum, a color image is reproduced by performing color superposition. First, after a charge is applied to the surface of the photoreceptor by the charger 3, a laser controlled by a digital image signal sent from a reading device or an information processing device such as a computer, a storage device, a communication device, or the like, an LED, A minute light image in the form of a dot is irradiated onto the photoreceptor from a light source such as a liquid crystal shutter. The light image generates charge carriers in the photoreceptor and erases the surface charge of the photoreceptor to form a minute electrostatic latent image in the form of dots. The image signal is color-separated into three colors of cyan, magenta and yellow, or four colors obtained by adding black thereto, and after an electrostatic latent image is formed on a photoconductor corresponding to each color, Are successively developed by the developing devices corresponding to the colors.

The image developed by the developer is transferred to a transfer material such as transfer paper in a transfer step. The transfer material is electrostatically or mechanically fixed to the surface of the transfer member 7 in order to transfer a three-color or four-color image to one transfer material in a multiplex manner. Also, the image starting point and the image area of each photosensitive drum 1 and the transfer member 7 are always synchronized at least during the multiple transfer process of the same image to the same transfer material so that there is no shift of each color image during the multiple transfer. Controlled.

[0041]

Embodiments of the present invention will be described below.

Example 1 (1) Image Reader B In the image reader B of the electrophotographic image forming apparatus shown in FIG. 1, reference numeral 10 denotes a fixed document table (a transparent plate such as glass).
The document G is placed on the upper surface of the document table 10 with the surface to be copied facing downward, and a document pressure plate (not shown) is placed thereon.

Reference numeral 9 denotes an image reading unit provided with a document irradiation lamp 9a, a short focus lens array 9b, a CCD sensor 9c, and the like. When a copy start signal is input, the unit 9 is driven forward from the home position on the left side of the document table under the document table 10 to the right side along the lower surface of the document table to reach a predetermined forward end point. When it reaches, it is driven backward and returned to the initial home position.

In the forward drive process of the unit 9, the downward image surface of the placed set document G on the document table 10 is sequentially illuminated and scanned by the document irradiating lamp 9a of the unit 9 from the left side to the right side. The scanning light reflected from the document surface is converted by the short focus lens array 9b into the CCD sensor 9a.
An image is incident on c.

The CCD sensor 9c includes a light receiving section, a transfer section, and an output section. The light signal is converted into a charge signal in the CCD light receiving unit, and the transfer unit sequentially transfers the light signal to the output unit in synchronization with the clock pulse. The output unit converts the charge signal into a voltage signal, amplifies the signal, reduces the impedance, and outputs the voltage signal. The analog signal thus obtained is subjected to well-known image processing, converted into a digital signal, and sent to the printer main unit A.

That is, the image information of the document G is photoelectrically read by the image reader B as a time-series electric digital pixel signal (image signal).

(2) Printer Body A a) 1 is a rotating drum type electrophotographic photosensitive member as an image carrier. The photoreceptor 1 is driven to rotate at a predetermined peripheral speed (process speed) in a clockwise direction a shown by an arrow about a central support shaft. The photoreceptor 1 of this example is a photoreceptor having a diameter of about 30 mm, and is driven to rotate at a peripheral speed of 115 mm / sec. The photoreceptor 1 will be described in detail in section (3) below.

B) In the rotation process, the photosensitive member 1 is uniformly primary-charged to a predetermined polarity and potential by a magnetic brush contact charging device in this example. In this example, approximately -500
V is uniformly primary charged. Reference numeral 3 denotes a magnetic brush charger as a magnetic brush contact charging member. The magnetic brush charger 3 will be described later in detail in (4).

C) The one-side charged surface of the rotary photoreceptor 1 is modulated by the laser exposure means (laser scanner) 2 in accordance with the image signal sent from the image reader B side to the printer body A side. By performing the scanning exposure with the laser light L, an electrostatic latent image corresponding to the image information of the original G that is photoelectrically read by the image reader B is sequentially formed on the surface of the rotating photoconductor 1.

The laser exposure means 2 comprises a solid-state laser element 2a, a rotating polygon mirror (polygon mirror) 2b, an f-θ lens group 2c, a deflecting mirror 2d and the like. On / off emission control of the solid-state laser element 2a is performed at a predetermined timing by a light emission signal generator (not shown) based on the input image signal. The laser light emitted from the solid-state laser element 2a is converted into a substantially parallel light beam by a collimator lens system, scanned by a rotating polygon mirror 2b rotating at high speed, and exposed through an f-θ lens group 2c and a deflecting mirror 2d. An image is formed on the body 1 in a spot shape.

The photosensitive member 1 is scanned by such laser beam scanning.
An exposure distribution for one scanning of an image is formed on the surface, and an exposure distribution according to an image signal is obtained on the rotating photoreceptor surface by sub-scanning by rotating the photoreceptor 1. That is, the light of the solid-state laser element 2a whose ON / OFF light emission is controlled in accordance with the image signal is scanned by the rotating polygon mirror 2b which rotates at a high speed on the one-side charged surface of the rotating photosensitive body 1 so that the surface of the rotating photosensitive body 1 , An electrostatic latent image corresponding to the scanning exposure pattern is sequentially formed. That is, the potential of the exposed portion irradiated with the laser beam drops on the surface of the rotating photoconductor 1 (bright portion potential), and corresponds to the exposure pattern by the contrast with the potential of the non-exposed portion not irradiated (dark portion potential). The formed electrostatic latent image is formed.

D) The electrostatic latent image formed on the surface of the rotating photoreceptor 1 is successively developed as a toner image by the developing device 4 in the case of the present embodiment, and is reversely developed. The configuration of the developing device 4 will be described later in detail in section (5).

E) On the other hand, the transfer material P stacked and stored in the paper feed cassette 5 is fed out and fed one by one by the paper feed roller 5a, and is transferred by the registration roller 5b at a predetermined control timing. The sheet is fed to a transfer section 7e, which is a contact nip section between the transfer member 7 and the transfer device 7 as a transfer unit, and the toner image on the photosensitive member 1 side is electrostatically transferred to the transfer material P side.

The transfer device 7 in this embodiment is a belt transfer device. An endless transfer belt 7a is suspended between a driving roller 7b and a driven roller 7c. They are driven to rotate at substantially the same peripheral speed.
A transfer charging blade 7d is provided inside the endless transfer belt 7a.
The transfer portion (transfer nip portion) 7e is formed by bringing a substantially intermediate portion of the belt portion on the ascending side of the belt 7a into contact with the surface of the photosensitive drum 1 by the blade 7d.

The transfer material P is conveyed to the transfer portion 7e on the upper surface of the ascending belt portion of the belt 7a. When a predetermined transfer bias is supplied from the transfer bias application power supply S3 to the transfer charging blade 7d at the time when the leading end of the transport transfer material P enters the transfer portion 7e, charging of the opposite polarity to the toner from the back side of the transfer material P is performed. Then, the toner images on the photoconductor 1 are sequentially transferred onto the upper surface of the transfer material P.

F) The transfer belt 7a also serves as a means for transporting the transfer material P from the transfer unit 7e to the fixing device 6, and the transfer material P that has passed through the transfer unit 7e is separated from the surface of the rotary photoreceptor 1 and transferred. The toner image is conveyed and introduced to the fixing device 6 by the belt 7a, and the toner image is thermally fixed and discharged to the discharge tray 8 as a copy or a print.

G) The printer main body A of this embodiment does not include a dedicated cleaning device (cleaner) for removing the transfer residual toner remaining on the surface of the rotary photoreceptor 1 after the transfer of the toner image onto the transfer material P. This is a cleaner-less system device in which the device 4 also serves as a cleaning unit that collects transfer residual toner remaining on the surface of the photoconductor 1. This will be described in detail in (6) below.

(3) Photoreceptor 1 The photoreceptor 1 used in this example is a negatively charged OPC photoreceptor having a charge injection layer on the surface and manufactured in the following manner.

Conductive titanium oxide: 10 parts by weight (tin oxide coating, average primary particle size: 0.4 μm) Phenol resin precursor (resol type): 10 parts by weight Methanol: 10 parts by weight Butanol: 10 parts by weight were dispersed in a sand mill, and then the outer diameter was 30 mm and the length was 35 mm.
Dip coating on a 7.5 mm aluminum cylinder
By curing at 40 ° C., the volume resistance is 5 × 10 ⁹ Ωcm,
A conductive layer having a thickness of 20 μm was provided.

Next, the following methoxymethylated nylon (the degree of methoxymethylation is about 30%): 10 parts by weight

[0061]

Embedded image

After mixing and dissolving 150 parts by weight of isopropanol, dip coating was performed on the conductive layer, and 1 μm
m undercoat layer was provided.

Next, the diffraction angles 2θ ± 0.2 ° in the X-ray diffraction spectrum of CuKα are 9.0 °, 14.2 °, 2 °
TiOPc having strong peaks at 3.9 ° and 27.1 °
After 4 parts by weight, 2 parts by weight of polyvinyl butyral (trade name: Eslec BM2, manufactured by Sekisui Chemical) and 60 parts by weight of cyclohexanone were dispersed for 4 hours by a sand mill using a φ1 mm glass bead, 100 parts by weight of ethyl acetate was added thereto, and the electric charge was added. A dispersion for a generating layer was prepared. This was applied by dip coating to provide a 0.3 μm charge generation layer.

Next, the following triphenylamine: 10 parts by weight

[0065]

Embedded image

Polycarbonate resin (bisphenol Z, molecular weight 20,000): 10 parts by weight Monochlorobenzene: 50 parts by weight Dichloromethane: 15 parts by weight After stirring and mixing, dip coating was performed on the charge generation layer.
A 0 μm charge transport layer was provided.

Next, the following acrylic monomer: 30 parts by weight

[0068]

Embedded image

Ultrafine tin oxide particles having an average particle size of 400 ° before dispersion: 50 parts by weight 2-methylthioxanthone as a photopolymerization initiator: 3 parts by weight Ethanol: 150 parts by weight in a sand mill Time dispersed.

A film was formed by dip coating the above-prepared solution on the above-mentioned charge transporting layer, and 800 W / cm.
Light curing was performed for 60 seconds at a light intensity of
C. for 2 hours in hot air to obtain a surface layer. At this time, the thickness of the obtained surface layer was 3 μm.

When the volume resistance of the charge injection layer on the surface of the photoreceptor 1 thus obtained was measured, it was 2 × 10 ¹⁰ Ω.
cm.

(4) Magnetic Brush Charger 3 The magnetic brush charger 3 as a contact charging member is of a sleeve rotating type in the case of this embodiment.

As shown in the model diagram of FIG. 2, the magnetic brush charger 3 is composed of a fixed magnet roller 3a and an aluminum or the like having an outer diameter of 16 mm provided rotatably and concentrically on the magnet roller 3a. A non-magnetic sleeve 3b;
This is a horizontally long member elongated in the generatrix direction of the photoconductor 1, including a magnetic brush portion 3 c of charging magnetic particles (magnetic carrier) adhered and held in a brush shape by the magnetic force of the internal magnet roller 3 a on the outer peripheral surface of the sleeve.

The magnetic brush portion 3c is brought into contact with the surface of the photosensitive member 1 with a predetermined contact width. The contact part n1 is a charged area (charged part). In this example, the width of the charged area n1 formed by bringing the magnetic brush portion 3c into contact with the photoconductor 1 was adjusted to be about 6 mm.

As described above, the non-magnetic sleeve 3b is rotated by the driving system (not shown) in the clockwise direction indicated by the arrow b, that is, in the rotation direction of the photosensitive member 1 in the charging portion n1, which is the contact portion of the magnetic brush portion 3c with the photosensitive member 1. Is rotated in the counter direction at a predetermined peripheral speed. In this embodiment, the non-magnetic sleeve 3b is driven to rotate at 160 mm / sec with respect to the rotational speed of the photoconductor 1 of 110 mm / sec. The rotation of the non-magnetic sleeve 3b causes the non-magnetic sleeve 3
The magnetic brush portion 3c, which is magnetically restrained and held on the outer peripheral surface of the non-magnetic sleeve 3b,
b in the same direction as in FIG.
Rub the surface.

A predetermined charging bias is applied to the non-magnetic sleeve 3b by the charging bias application power supply S1. In this example, the non-magnetic sleeve 3b is applied with an oscillating voltage on which a direct current voltage (DC): -500 V alternating voltage (AC, Vpp): amplitude Vpp 0.7 kV is superimposed as a charging bias (A
C bias application method), approximately -500 V on one surface of the rotating photoconductor
To be contact-charged.

The higher the relative rotation speed between the photosensitive member 1 and the magnetic brush charger 3 is, the better the charging uniformity tends to be.

As the magnetic particles for charging constituting the magnetic brush portion 3c, a resin carrier formed by dispersing magnetite as a magnetic material in a resin and dispersing carbon black for conductivity and resistance adjustment, or ferrite And the like may be used in which the surface of a single magnetite, such as ferrite, is oxidized and reduced to adjust the resistance, or the surface of a single magnetite, such as ferrite, is coated with a resin and the resistance is adjusted.

The magnetic particles have an average particle diameter of 10 to 100 μm and a saturation magnetization of 20 to 250 emu / c.
m ³ and a resistance of 1 × 10 ² to 1 × 10 ¹⁰ Ω · cm are preferable. Considering the presence of insulation defects such as pinholes in the photoreceptor 1, the resistance is 1 × 10 ⁵ Ω · cm or more. It is preferable to use

In order to improve the charging performance, it is better to use one having as small a resistance as possible. In this embodiment, magnetic particles having an average particle diameter of 25 μm, a saturation magnetization of 200 emu / cm ³ and a resistance of 5 × 10 ⁵ Ω · cm are used. Using.

Here, the resistance value of the magnetic particles for charging was measured by placing 2 g of magnetic particles in a metal cell having a bottom area of 228 mm ² , applying a load of 6.6 kg / cm ² , and applying a voltage of 100 V. are doing.

(5) Developing device 4 In general, the developing method of an electrostatic latent image is roughly classified into the following four types.

A. The non-magnetic toner is coated on the sleeve with a blade or the like, and the magnetic toner is coated by a magnetic force, transported, and developed in a non-contact state with the photoreceptor (one-component non-contact development).

B. A method in which the toner coated as described above is developed in contact with the photoreceptor (one-component contact development).

C. A method in which a mixture of toner particles and a magnetic carrier is used as a developer and conveyed by magnetic force to develop in a state of contact with a photoreceptor (two-component contact development).

D. A method of developing the above two-component developer in a non-contact state (two-component non-contact development).

From the viewpoints of high image quality and high stability, c
Component contact development is widely used.

The developing device 4 in this embodiment is a two-component contact developing device (two-component magnetic brush developing device). In the model diagram of FIG. 3, reference numeral 41 denotes a developing sleeve which is driven to rotate in a counterclockwise direction c as indicated by an arrow, 42 denotes a magnet roller fixedly arranged in the developing sleeve 41, 43/44 denotes a developer stirring screw, and 45 denotes a developing screw. A regulating blade disposed to form the agent T on the surface of the developing sleeve 41 in a thin layer, 46 is a developing container, and 47 is a toner hopper for replenishment.

The developing sleeve 41 is arranged so that the area closest to the photoconductor 1 is at least about 500 μm at least during development, and a thin layer of the developer T formed on the surface of the developing sleeve 41 is 1 is set so as to be able to be developed in a state of contact. n2 is a developer contact area (development area, development site) with respect to the photoconductor 1.

The two-component developer T used in this example is a mixture of the toner particles t and the developing magnetic carrier c.

In this example, a negatively chargeable spherical toner (negative toner) having an average particle diameter of 6 μm and produced by a suspension polymerization method was used as the toner particles t.

The magnetic carrier c has a saturation magnetization of 2
A magnetic carrier having an average particle size of 35 μm of 05 emu / cm ³ was used.

Then, the toner t and the magnetic carrier c
Was mixed at a weight ratio of 6:94 and used as a developer T.

The developing sleeve 41 is driven to rotate at a predetermined peripheral speed in a counterclockwise direction c indicated by an arrow, which is a forward direction to the rotation direction of the photosensitive member 1 in the developing region n2. With the rotation, the developer T in the developing container 46 is pumped by the S ₂ pole of the magnet roller 42 to the surface of the developing sleeve 41 and transported. In the process of being transported, the developer T is arranged perpendicular to the developing sleeve 41. The layer thickness is regulated by the regulating blade 45, and a thin layer of the developer T is formed on the developing sleeve 41. The developer formed as a thin layer brush is formed by the magnetic force when conveyed to a developing pole S1 is conveying pole N ₁ to the developing region n2 correspondence. The electrostatic latent image on the surface of the rotating photoconductor 1 is developed as a toner image in the developing area n2 by the toner t in the developer T formed in the spike shape. In this example, the electrostatic latent image is reversely developed.

The developing sleeve 41 that has passed through the developing area n2
The upper developer thin layer enters the developing container 46 with the subsequent rotation of the developing sleeve 41, is separated from the developing sleeve 41 by the repulsive magnetic field of the N ₃ pole and the N ₂ pole, and the developer is accumulated in the developing container 46. Is returned to.

[0096] DC voltage and AC voltage is applied from the power source S ₂ to the developing sleeve 41. In this example, a DC voltage; -350 V alternating voltage; Vpp = 1500 V, Vf = 3000 Hz is applied.

In general, in the two-component developing method, when an alternating voltage is applied, the developing efficiency is increased, and the quality of the image becomes high. On the contrary, there is a risk that fogging is liable to occur. For this reason, fog is generally prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photoconductor 1. More specifically, the photoconductor 1
A bias voltage having a potential between the potential of the exposed portion and the potential of the non-exposed portion is applied.

The potential difference for preventing fogging is called a fogging potential (Vback). Due to this potential difference, toner adheres to a non-image area (non-exposed portion) on the surface of the photoreceptor 1 during development on the surface of the photoreceptor 1. In addition, in the cleanerless system, the transfer residual toner on the surface of the photoconductor 1 is also collected (simultaneous cleaning with development).

The toner concentration is monitored by a sensor (not shown) for detecting the toner concentration of the developer T in the developing container 46. The toner t in the developer T is consumed for developing the latent image. When the density is lower than the predetermined density level, the replenishment toner hopper 47
Is replenished. By this toner replenishing operation, the toner concentration of the developer T is constantly maintained at a predetermined level.

(6) Cleanerless System The printer A of this embodiment is provided with a dedicated cleaning device (cleaner) for removing transfer residual toner remaining on the surface of the rotating photoconductor 1 after the transfer of the toner image onto the transfer material P. This is a cleaner-less system device in which the developing device 4 also serves as a cleaning unit that collects the transfer residual toner remaining on the surface of the photosensitive member 1.

After transfer of the toner image onto the transfer material P, the transfer residual toner remaining on the surface of the rotating photoconductor 1 is brought into contact with the magnetic brush portion 3 c of the magnetic brush charger 3 by the rotation of the photoconductor 1. It is carried to a certain charging area n1.

In the charging area n1, the photosensitive member 1
The surface is rubbed by the magnetic brush portion 3c of the magnetic brush charger 3, so that the transfer residual toner carried to the charged area n1 is disturbed and moved on the surface of the photoreceptor 1, and the pattern at the time of the transfer remaining is broken. At the same time, the toner is attached to and mixed with the magnetic brush portion 3c and temporarily collected by the magnetic brush charger 3.

The magnetic brush unit 3 of the magnetic brush charger 3
transfer residual toner adhering to and mixing with the magnetic brush part 3c
By frictional charging with the magnetic particles for charging constituting
The toner is recharged to the normal charge polarity (negative in this example) including the toner whose charge polarity is inverted. That is, the toner is converted into a normally charged toner.

The toner in the magnetic brush portion 3 c, which has been converted into the normally charged toner, is discharged onto the photoreceptor 1 by an electric repulsion generated by the charging bias applied to the magnetic brush charger 3.

In this way, the toner is converted into the normally charged toner, and the magnetic brush portion 3 c of the magnetic brush charger 3 transfers the photosensitive member 1
The toner discharged upward is conveyed to the developing area n2, which is a portion where the photosensitive member 1 and the developing sleeve 41 of the developing device 4 are opposed by the subsequent rotation of the photosensitive member 1, and is collected by the developing device 4 at the fog removal potential Vback. (Development simultaneous cleaning).

Normally, the toner sequentially discharged from the magnetic brush charger 3 as a contact charging member onto the photosensitive member 1 is
It is a very thin layer in a small amount and in a uniformly dispersed state, and does not substantially adversely affect the next image exposure step. Further, generation of a ghost image due to the transfer residual toner pattern is also prevented.

(7) Time from Image Exposure to Development In Example 1, the distance (perimeter) on the photoconductor from image exposure to the development area n2 in the electrophotographic apparatus (FIG. 1) used. Was adjusted to 20 mm. At this time, the time from image exposure to development is 0.
18 seconds.

This is because the following formulas (A) and (B)
Were satisfied, and when the image was evaluated, a high-quality image was obtained in fact.

0.18 (T: second) ≦ 1 × 10 ⁻¹¹ × 2 × 10 ¹⁰ (volume resistance: Ωcm) (A) -1 1 × 10 ⁻¹⁵ × 2 × 10 ¹⁰ (volume resistance: Ωcm) × 3 (film thickness μm) ≦ 0.18 (T: second) (B) -1 (Example 2) In the apparatus of Example 1, the incident position of the image exposure was moved to the developing device side as much as possible. The distance on the photoreceptor from the image exposure to the development area n2 is 4.5.
mm. The time from image exposure to development at this time is 0.04 seconds.

This is based on the above formulas (A) and (B)
Were satisfied, and the image was evaluated. As a result, a high-quality image was obtained.

0.04 (T: second) ≦ 1 × 10 ⁻¹¹ × 2 × 10 ¹⁰ (volume resistance: Ωcm) (A) -2 1 × 10 ⁻¹⁵ × 2 × 10 ¹⁰ (volume resistance: Ωcm) × 3 (film thickness: μm) ≦ 0.04 (T: second) (B) -2 (Comparative Example 1) In the apparatus used in Example 1, the incident position of the image exposure was moved away from the developing device side, and the image exposure was performed. The position of the image exposure was adjusted so that the distance on the photosensitive member from the point of reaching the developing area n2 was 33 mm. At this time, the time from image exposure to development is 0.3 second.

Although the expression (B) was satisfied as described below, the expression (A) was not satisfied, and the image was evaluated. As a result, the dot image portion was disturbed. That is, in the photoreceptor having the surface layer having a volume resistance of 2 × 10 ¹⁰ Ωcm, if the time from the image exposure to the development takes 0.3 seconds or more, the latent image cannot be held, and it is considered that the image flow has occurred. It is.

0.3 (T: second) ≦ 1 × 10 ⁻¹¹ × 2 × 10 ¹⁰ (Volume resistance: Ωcm) (A) -3 does not hold, and 1 × 10 ⁻¹⁵ × 2 × 10 ¹⁰ (Volume Resistance: Ωcm) × 3 (thickness: μm) ≦ 0.3 (T: seconds) (B) -3 (Example 3) In the apparatus used in Example 2, the photosensitive member 1 used was changed to the following. The other device configuration was the same as the device of Example 2.

Photoreceptor 2 used in Example 3: An aluminum cylinder, a conductive layer, an undercoat layer, a charge generation layer, and a charge transport layer were prepared in the same manner as in Example 1; A surface layer having a thickness of 4 μm was obtained in the same manner as in Example 1, except that the polymerization initiator 2-methylthioxanthone was changed to 10 parts by weight.

The surface resistance of the thus-obtained photosensitive member 2 was measured and found to be 2 × 10 ¹² Ωcm.

Since the distance on the photosensitive member from the image exposure of the used image evaluation apparatus to the development area n2 is 4.5 mm, and the time required for the distance is 0.04 seconds, the following equation is used. Both (A) and (B) were satisfied, and a high-quality image was obtained in fact.

0.04 (T: sec) ≦ 1 × 10 ⁻¹¹ × 2 × 10 ¹² (volume resistance: Ωcm) (A) −4 1 × 10 ⁻¹⁵ × 2 × 10 ¹² (volume resistance: Ωcm) × 4 (film thickness: μm) ≦ 0.04 (T: second) (B) -4 (Example 4) In the apparatus used in Example 3, the incident position of image exposure was set as far as possible from the developing device side. However,
The distance from the image exposure to the development area n2 on the photoconductor was 55 mm. At this time, the time from the image exposure to the development is 0.5 second.

This is based on the following formulas (A) and (B)
Were satisfied, and the image was evaluated. As a result, a high-quality image was obtained.

0.5 (T: second) ≦ 1 × 10 ⁻¹¹ × 2 × 10 ¹² (volume resistance: Ωcm) (A) -5 1 × 10 ⁻¹⁵ × 2 × 10 ¹² (volume resistance: Ωcm) × 4 (film thickness: μm) ≦ 0.5 (T: seconds) (B) -5 (Example 5) In the apparatus used in Example 4, the photosensitive member 2 used was changed to the following, and other apparatuses were used. The configuration was the same as that of the device of Example 4.

Photoconductor 3 used in Example 5: An aluminum cylinder, a conductive layer, an undercoat layer, a charge generation layer, and a charge transport layer were prepared in the same manner as in Example 4, and the surface layer was formed by using a light source. A surface layer having a thickness of 5 μm was obtained in the same manner as in Example 4, except that the amount of the polymerization initiator, 2-methylthioxanthone, was changed to 30 parts by weight.

The surface resistance of the photoreceptor 3 thus obtained was measured and found to be 8 × 10 ¹³ Ωcm.

The distance on the photoreceptor from the image exposure of the used image evaluation apparatus to the development area n2 is 55 mm, and the time required for it is 0.5 second. 2) Both (B) were satisfied, and a high-quality image was obtained in fact.

0.5 (T: sec) ≦ 1 × 10 ⁻¹¹ × 8 × 10 ¹³ (volume resistance: Ωcm) (A) −6 1 × 10 ⁻¹⁵ × 8 × 10 ¹³ (volume resistance: Ωcm) × 5 (film thickness: μm) ≦ 0.5 (T: seconds) (B) -6 (Comparative Example 2) In the apparatus used in Comparative Example 1, the photosensitive member 3 was used, and the other device configurations were the same as those in Comparative Example 1. Same as the equipment.

The distance on the photoreceptor from the image exposure of the used image evaluation apparatus to the development area n2 is 33 mm, and the time required for it is 0.3 second.

Although the above expression (A) was satisfied as described below, the above expression (B) was not satisfied. When the image was evaluated, the image density was low. That is, 8 × 10
^In a photoreceptor having a surface layer with a volume resistance of ¹³ Ωcm, if the time from image exposure to development is only 0.3 seconds, photocarriers generated by image exposure cannot move sufficiently between surface layers,
It seems that the sensitivity was poor.

0.3 (T: second) ≦ 1 × 10 ⁻¹¹ × 8 × 10 ¹³ (volume resistance: Ωcm) (A) -7 1 × 10 ⁻¹⁵ × 8 × 10 ¹³ (volume resistance: Ωcm) × 5 (thickness: μm) ≦ 0.3 (T: second)... (B) -7 does not hold. <Regarding Photoconductor> a) The photoconductor used in the present invention has a highly releasable surface. For example, it is also possible to uniformly disperse a fluorine-based resin powder in the surface layer.

Specific examples of the fluororesin powder include polymers such as tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, vinylidene fluoride, vinyl fluoride, and perfluoroalkyl vinyl ether; Is used.

The particle diameter of the fluororesin powder is 0.01 to 5 μm.
m and a molecular weight of 3000-5.
It can be used in the range of 000000.

The fluororesin powder is dispersed as a photosensitive layer composition together with a binder resin. As a dispersion method, a sand mill, a ball mill, a roll mill, a homogenizer, a nanomizer, a paint shaker, an ultrasonic wave, or the like is used. At the time of dispersion, a fluorine-based surfactant, a graft polymer, a coupling agent, or the like may be additionally used.

The content of the fluororesin powder in the outermost surface layer of the photoreceptor is preferably 4 to 70% by weight, more preferably 10 to 55% by weight. If it is less than 4% by weight, the surface energy is not sufficiently reduced, and if it exceeds 70% by weight, the film strength of the surface layer is reduced.

Examples of the binder resin in which the fluororesin powder is dispersed include polyester, polyurethane, polyarylate, polyethylene, polystyrene, polybutadiene,
Polycarbonate, polyamide, polypropylene, polyimide, polyamideimide, polysulfone, polyallyl ether, polyacetal, nylon, phenolic resin, acrylic resin, silicone resin, epoxy resin, urea resin, allyl resin, alkyd resin, butyral resin, and the like. In addition, reactive epoxy, (meth)
Acrylic monomers and oligomers can also be used after mixing and curing.

B) The photosensitive layer used in the present invention has a single layer or a laminated structure.

In the case of a laminated structure, a charge generation layer for generating photocarriers and a charge transport layer for moving carriers are laminated. The surface layer may be formed on either the charge generation layer or the charge transport layer.

The single-layer photosensitive layer can have a thickness of 5 to 100 μm, more preferably 10 to 60 μm.

The charge generation material and the charge transport material are 20 to 80.
%, More preferably 30 to 70% by weight. In the laminated photoreceptor, the thickness of the charge generation layer is 0.0
It is from 0.01 to 6 μm, more preferably from 0.01 to 2 μm. The amount of the charge generating material is 10 to 100% by weight, more preferably 40 to 100% by weight.

The thickness of the charge transport layer is 5 to 100 μm, more preferably 10 to 60 μm. The amount of charge transport material is between 20 and 80% by weight, more preferably between 30 and 70% by weight.

C) As the charge generating material used in the present invention, phthalocyanine pigments, polycyclic quinone pigments, azo pigments, perylene pigments, indigo pigments, quinacridone pigments,
Examples include azulenium salt dyes, squarylium dyes, cyanine dyes, pyrylium dyes, thiopyrylium dyes, xanthene dyes, quinone imine dyes, triphenylmethane dyes, styryl dyes, selenium, selenium-tellurium, amorphous silicon, and hardened cadmium.

D) The charge transporting materials used in the present invention include pyrene compounds, carbazole compounds, hydrazone compounds, N, N-dialkylaniline compounds, diphenylamine compounds, triphenylamine compounds, triphenylmethane compounds, pyrazoline compounds, and styryl compounds. And stilbene compounds.

E) The electrophotographic photosensitive member used in the present invention has a charge injection layer on the surface of the photosensitive layer. The thickness of the charge injection layer can be 0.01 to 40 μm, and more preferably 0.1 to 30 μm. The charge injection layer may contain the above-described charge generation material or charge transport material, or a conductive material such as a metal and its oxide, nitride, salt, alloy, and carbon.

As the binder resin used for the charge injection layer, polyester, polyurethane, polyarylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide,
Polyamide imide, polysulfone, polyallyl ether, polyacetal, nylon, phenolic resin, acrylic resin, silicone resin, epoxy resin, urea resin, allyl resin, alkyd resin, butyral resin, and the like. Furthermore, reactive epoxy and (meth) acrylic monomers and oligomers can be used after mixing and curing.

F) The conductive support used in the electrophotographic photoreceptor used in the present invention is made of iron, copper, nickel, aluminum, titanium, tin, antimony, indium, lead,
Metals and alloys such as zinc, gold, and silver, oxides thereof, carbon, and conductive resins can be used. The shapes include a cylindrical shape, a belt shape, and a sheet shape. The conductive material may be molded, but may be applied as a paint or may be deposited.

G) An undercoat layer may be provided between the conductive support and the photosensitive layer. The undercoat layer is mainly made of a binder resin, but may contain the conductive material or the acceptor. Examples of the binder resin for forming the undercoat layer include polyester, polyurethane, polyarylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide, polyamideimide, polysulfone, polyallylether, polyacetal, nylon, phenolic resin, and acrylic resin. , Silicone resin, epoxy resin, urea resin, allyl resin, alkyd resin, butyral resin and the like.

H) As a method for producing the electrophotographic photosensitive member used in the present invention, methods such as vapor deposition and coating are used. For coating, a bar coater, knife coater, roll coater, attritor, spray, dip coating, electrostatic coating, powder coating, or the like is used.

<Others> 1) The present invention is not limited to the embodiment described above.

2) As a method for developing an electrostatic latent image, the two-component contact developing method has been described in the embodiments, but other developing methods may be used. Preferably, one-component contact development or two-component contact development, in which the developer is developed in contact with the photoreceptor, is effective in enhancing the simultaneous recovery effect during development.

3) The magnetic brush charger 3 as a contact charging member is a magnet roller 3a-fixed, a non-magnetic sleeve 3
Although a so-called sleeve rotation type charger of b-rotation was used, the invention is not limited to this charger configuration. For example, a system in which the magnet roller 3a rotates with the same configuration or a system in which the magnet roller itself rotates with only the magnet roller 3a can be used by performing a conductive treatment on the roller surface.

The contact charging member need not be the magnetic brush charger 3.

4) As the waveform of the primary charging alternating voltage component for the contact charging member, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. For example, a DC power supply is periodically turned on and off.
F includes the voltage of the rectangular wave formed by the F.

When an AC bias component is included in the developing bias applied to the developing device, the AC bias is the same as described above.

5) The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly and primarily charged to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head and an electron gun to form an electrostatic latent image corresponding to the target image information. Write and form.

6) The transfer method may be roller transfer, plate transfer, corona discharge transfer, or the like. An intermediate transfer member may be used instead of the transfer drum and the transfer belt.

7) Image Carrier 1, Charging Means 3, Developing Device 4
It is also possible to adopt a device configuration of a detachable type with a process cartridge which is detachable and replaceable with the image forming apparatus main body.

[0153]

As described above, according to the present invention,
In a process having multiple transfer steps using a plurality of photoconductors, and in a process using a photoconductor in which the surface layer has a volume resistance of 1 × 10 ¹⁰ Ωcm or more and 1 × 10 ¹⁴ Ωcm or less, a small-sized, high-speed, low-cost An electrophotographic image forming method and apparatus capable of obtaining a high-quality color image can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing an image forming apparatus to which an image forming method of the present invention is applied.

FIG. 2 is a cross-sectional view of a magnetic brush charger provided in the image forming apparatus of FIG.

FIG. 3 is a cross-sectional view of a developing device provided in the image forming apparatus of FIG. 1;

FIG. 4 is a schematic diagram schematically showing an electric resistance measuring device.

[Explanation of symbols]

 Reference Signs List A Printer body B Image reader 1 Photoconductor drum (image carrier) 2 Laser exposure means 3 Magnetic brush charger (contact charging member) 5 Paper feed cassette 6 Fixing device 7 Transfer device 8 Paper discharge tray P Transfer material 101 Main electrode 102 Upper electrode 103 Insulator 104 Ammeter 105 Voltmeter 106 Voltage regulator 107 Magnetic particles 108 Guide ring

Claims (10)

[Claims] In an electrophotographic image forming method for forming a toner image on a transfer material through at least the steps of charging, exposing, developing and transferring using an electrophotographic photosensitive member, the surface layer has a volume resistance of 1 × 10 ¹⁰ Ω · cm or more, 1 × 10 ¹⁴ Ω · c
m, and the transfer step is repeated once for each electrophotographic photosensitive member with respect to one transfer material, and is performed on the transfer material by the first transfer. This is a multiple transfer step in which the images on the electrophotographic photosensitive member from the second time on are sequentially superimposed on the image synchronously, and the time T (second) from image exposure to development is expressed by the following formula (A):
An image forming method characterized by simultaneously satisfying (B). T (second) ≦ 1 × 10 ⁻¹¹ × volume resistance (Ω · cm) (A) 1 × 10 ⁻¹⁵ × volume resistance (Ω · cm) × film thickness (μm) ≦ T (second)・ (B) (Film thickness: film thickness of electrophotographic photosensitive member surface layer) 2. The electrophotographic image forming method according to claim 1, wherein said charging step is performed by contact charging. 3. The electrophotographic photosensitive member surface is charged by applying only a DC voltage Vdc (V) to the electrophotographic photosensitive member from a charging member used in the charging step.
3. The relationship between a DC voltage Vdc (V) applied from the charging member to the electrophotographic photosensitive member and a dark potential Vd (V) of the electrophotographic photosensitive member satisfies the following expression (C).
2. The electrophotographic image forming method according to 1. | Vdc−Vd | ≦ 200 (V) (Equation (C)) 4. A peak-to-peak voltage Vpp of an alternating voltage Vac (V) from a charging member used in the charging step to a direct current voltage Vdc (V) to the electrophotographic photosensitive member.
(V) satisfies the following equation (D): Vpp <2 Vth Equation (D) ∴Vth (discharge start voltage V) = √ (7737.7 × D) + 312 + 6.2
× D D = L (film thickness of photosensitive layer μm) / K (relative dielectric constant of photosensitive layer) Further, the relationship between applied voltages Vdc and Vpp (V) and dark potential Vd (V) of A electrophotographic photosensitive member is 4. The electrophotographic image forming method according to claim 2, wherein the following formulas (E) and (F) are satisfied. | Vdc−Vd | ≦ 200 (V) Expression (E) | Vd |> | Vpp / 2 | + | Vdc | − | Vth | Expression (F) 5. The electrophotographic image forming method according to claim 2, wherein said charging step is performed by contact charging using a magnetic brush charger. 6. The transfer residual toner on the surface of the electrophotographic photosensitive member after the transfer of the toner image to the transfer material is recovered in the charging step and / or the developing step, and the electrophotographic photosensitive member is repeatedly used for image formation. The electrophotographic image forming method according to claim 2. 7. The electrophotographic image forming method according to claim 2, wherein an electrophotographic photosensitive member having an outer diameter of φ40 mm or less is used. 8. The device according to claim 1, wherein the charger includes a fixed magnet roller,
A non-magnetic sleeve having an outer diameter of 20 mm or less provided concentrically and rotatably and externally on the magnet roller, and charging magnetic particles attached and held on the outer peripheral surface of the sleeve in a brush shape by the magnetic force of an internal magnet roller ( The sleeve is a rotary type consisting of a magnetic brush part of a magnetic carrier), and
6. A contact nip width between the magnetic particles and the electrophotographic photosensitive member in a rotation direction of 8 mm or less.
8. The electrophotographic image forming method according to any one of items 7 to 7. 9. The electrophotographic image forming apparatus according to claim 2, wherein the electrophotographic photosensitive member is driven to rotate around a central support shaft at a peripheral speed (process speed) of 100 mm / sec or more. Method. 10. An electrophotographic image forming apparatus using the electrophotographic image forming method according to claim 1.