JPH11133751A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method which is very efficient in electrifying and capable of obtaining a high-quality image without an image fog and further, adopting a cleanerless system. SOLUTION: In the case a developer including toner and magnetic carriers is carried on the surface of a developer carrier having a magnet inside and delivered to a developing part 4C, to develop an electrostatic latent image on an image carrier facing a developer carrier, in the developing part 4C in which a developing magnetic field is formed, the image carrier 1C, whose surface resistance is 10<9> -10<14> Ω.cm is used and as the magnetic carriers, carriers of magnetic coat carriers which are constituted in such a manner that the surfaces of core grains having metallic oxide grains are coated with resin compositions are used. The carriers have characteristics as follows; a piece number average grain diameter is <=1-100 μm, a distribution cumulative value for <=1/2 grain diameter is <= several percent of 20 pieces, the resistivity of a core is >=1×10<10> Ω.cm, the resistivity of the carriers is >=10<12> Ω.cm, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming method for developing an electrostatic latent image formed on an image carrier with a magnetic brush of a developer having a toner and a magnetic carrier to obtain an image.

[0002]

2. Description of the Related Art A conventional image forming method will be briefly described below by taking a conventionally known image forming apparatus as an example. FIG. 3 shows a conventional copying machine.
When an image is formed using the copying machine, first, the document G is set on the document table 10 with the surface to be copied facing downward, and then copying is started by pressing the copy button. In the copying process, a unit 9 in which an original irradiation lamp, a short focus lens array, and a CCD sensor are integrated is used. First, scanning is performed while irradiating the original with the original irradiating lamp of the unit 9, and the original surface reflected light of the illumination scanning light is imaged by the short focus lens array to form a CC
It is incident on the D sensor. The CCD sensor has a light receiving section,
The light receiving unit of the CCD sensor converts an incident optical signal into a charge signal, and sequentially transfers the charge signal to the output unit in synchronization with a clock pulse in the light receiving unit of the CCD sensor. The unit converts the charge signal into a voltage signal, amplifies the signal, reduces the impedance, and outputs the signal. The analog signal obtained as described above is converted into a digital signal by performing well-known image processing and sent to a printer unit.

In the printer section, first, upon receiving the image signal, an electrostatic latent image is formed on an image carrier (hereinafter referred to as a photosensitive drum) as follows. First, the photosensitive drum 1 is configured to be driven to rotate around a center support shaft at a predetermined peripheral speed. In the rotation process, the charging unit 3 uniformly charges the photosensitive drum 1 to, for example, -650V. Receive processing. Then, the light L of the solid-state laser element, which is turned on and off in accordance with the image signal, is scanned on the uniformly charged surface using a rotating polygon mirror rotating at a high speed, thereby scanning the surface of the photosensitive drum 1. An electrostatic latent image corresponding to the original image is sequentially formed thereon.

FIG. 5 shows a schematic configuration of a laser scanning section 100 for scanning the light L of the solid-state laser device described above. In brief, when a laser beam is scanned by such a laser scanning unit 100, first, based on an input image signal, a light emission signal generator 10
1 causes the solid-state laser element 102 to blink at a predetermined timing. Laser light emitted from the solid-state laser element 102 is converted by the collimator lens system 103 into a substantially parallel light beam. Further, the laser beam is indicated by an arrow b in FIG.
The scanning is performed in the direction of arrow c by the rotating polygon mirror 104 that rotates at a high speed in the direction indicated by, and the _fθ lens group,
By 05a, 105b, and 105c, an image is formed on a spot on the scanning surface 106 such as a photosensitive drum. By the scanning of the laser beam as described above, an exposure distribution for one scanning of an image is formed on the scanned surface 106. Furthermore, if the scanned surface 106 is scrolled by a predetermined amount in the direction perpendicular to the scanning direction of the laser beam for each scan, an exposure distribution according to the image signal is obtained on the scanned surface 106.

Next, the electrostatic latent image formed on the photosensitive drum 1 as described above is visualized by the developer stored in the developing device 4. In a general developing method, when a non-magnetic toner is used as a developer, the developer is coated on a developer carrier (hereinafter, referred to as a sleeve) with a blade or the like, and the magnetic toner is used as the developer. Is coated with the developer on the sleeve by the magnetic force of the toner, and the developer is transported to the development area. As a method of developing the electrostatic latent image on the photosensitive drum with the developer coated on the sleeve as described above, first, a one-component non-contact developing method of developing the photosensitive drum 1 in a non-contact state, The one-component contact developing method in which the magnetic toner coated as described above is developed in contact with the photosensitive drum, using a developer as a two-component developer in which toner particles and a magnetic carrier are mixed. A two-component contact developing method in which the developer is conveyed by magnetic force and developed in contact with the photosensitive drum, and a two-component non-contact developing method in which the two-component developer is developed in a non-contact state with the photosensitive drum. It is roughly divided into four types. Among these, the two-component contact development method is often used from the viewpoint of high image quality and high stability. Such a method will be described with reference to FIG.

FIG. 4 is a schematic diagram of a developing device for two-component magnetic brush development to which the two-component contact developing method indicated by 4 in FIG. 3 is applied. In FIG. 4, reference numeral 11 denotes a developing sleeve, 12 denotes a magnet roller fixedly arranged in the developing sleeve 11,
13 and 14 are stirring screws for toner, 15 is a regulating blade arranged to form a thin layer of the developer on the surface of the developing sleeve 11, and 16 is a developing container for containing the developer. In this example, when the developing sleeve 11 is at least during development, the area closest to the photosensitive drum 1 is about 50
It is arranged so as to be 0 μm, and is set so that the developer carried on the sleeve 11 can be developed in a state of being in contact with the photosensitive drum 1.

As a developer used in the above-described two-component contact developing method, for example, as a toner particle, a negatively charged toner having an average particle diameter of about 6 μm produced by a pulverization method has an average particle diameter of 20 nm. About 1% by weight of titanium oxide or the like is externally added to the toner. The carrier has, for example, a saturation magnetization of 205 emu / c.
A magnetic ferrite carrier having an average particle size of m ³ of about 35 μm is used. As for the weight ratio of the toner and the carrier, a developer of 6:94 is used.

Hereinafter, development is performed in which the electrostatic latent image formed on the photosensitive drum 1 as described above is visualized by a two-component magnetic brush method using the developing device 4 and a developer as described above. The process and the developer circulation system will be described with reference to FIG. First, the two-component developer pumped by the N ₂ pole with the rotation of the developing sleeve 11 is arranged perpendicular to the developing sleeve 11 in the process of being transported from the S ₂ pole to the N ₁ pole. The thickness is regulated by the regulating blade 15, and a thin layer is formed on the developing sleeve 11. Here a thin layer formed developer and conveyed to the main developing pole S ₁ pole, as shown schematically in the figure, brush is formed by the magnetic force. With the spike-shaped developer,
The electrostatic latent image on the photosensitive drum 1 is developed to form a toner image, and then the developer on the developing sleeve 11 is moved into the developing container 16 by the repulsive magnetic field formed by the N ₃ pole and the N ₂ pole. Will be returned.

The toner image formed on the photosensitive drum 1 as described above is first electrostatically transferred onto the transfer material P by the transfer charger 8 shown in FIG. 3, and thereafter, the transfer material P is separated. The image is electrostatically separated by the charger 7 and transported to the fixing device 6, where the image is output after being fixed by the fixing device 6. On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image is subjected to a process of removing adhered contaminants such as untransferred toner by the cleaner 5 and is repeatedly used for image formation.

A DC voltage and an AC voltage are superimposed and applied to the developing sleeve 11 from a power supply (not shown). For example, in the above-described conventional example, the DC voltage is -500.
V, as an AC voltage, V _pp = 1500 V, V _f = 2000
Hz is applied. In general, in the two-component magnetic brush developing method, when an AC voltage is applied, the developing efficiency is increased and the image quality is high, but on the contrary, there is a risk that fogging is likely to occur. For this reason, fogging is prevented by providing a potential difference between the DC voltage applied to the developing device 4 and the surface potential of the photosensitive drum 1, which is normally positively or negatively charged by corona discharge.

On the other hand, as the environmental consciousness has increased in recent years, a charging method of directly charging using a contact charging member without using corona discharge for charging the photosensitive drum has been used. In particular, the injection charging system is a system in which the amount of discharge when discharging the photoconductor is extremely small, and is very excellent. Here, the injection charging method means that charging is performed by injecting a charge into a trapping potential of the photoconductor surface material with a contact charging member, or a charge injection layer in which conductive particles are dispersed on the photoconductor surface is provided. In this case, the conductive particles are charged by a contact charging member to charge the conductive particles. Further, when a contact charging member is used, the surface resistance of the photosensitive drum is reduced by 10%.
^It has been found that when the resistance is as low as about ⁹ to 10 ¹⁴ Ω · cm, the charging efficiency can be improved. It should be noted that even in an amorphous silicon drum or the like aiming at high durability, the surface resistance is set to this level.

[0012]

However, as described above, the surface resistance of the photosensitive drum is reduced to 10 ⁹ to 10 ^14.
When the resistance is set to about Ω · cm, there is a problem that image fogging occurs. According to the study of the present inventors, it has been found that this fog occurs when the surface resistance of the photosensitive drum is set to a low resistance of 10 ⁹ to 10 ¹⁴ Ω · cm and development is performed by a contact two-component development method. . SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an image forming method which is extremely excellent in charging efficiency and in which an obtained image is a high quality image without fog. Another object of the present invention is to provide an image forming method which can adopt a cleanerless system and can realize a developing device which is small and does not generate waste toner.

[0013]

The above object is achieved by the present invention described below. That is, in the present invention, a developer containing at least a toner and a magnetic carrier is carried on a surface of a developer carrier, and is conveyed to a developing unit, and is developed by a developing magnetic pole of a magnet disposed inside the developer carrier. An image forming an image by developing an electrostatic latent image on an image carrier, which is disposed to face the developer carrier, with a developing device using the developer, in a developing section in which a developing magnetic field is formed; In the forming method, the developer carrier has a surface resistance of 10 ⁹ to 10 ⁹ .
Magnetic coated carrier having a low resistance layer of 10 ¹⁴ Ω · cm on its surface, wherein the magnetic carrier is formed by coating the surface of magnetic carrier core particles containing (1) metal oxide particles using a resin composition. (2) the specific resistance of the core particles of the magnetic carrier is 1 × 10 ¹⁰ Ω · cm or more, and the specific resistance of the magnetic coated carrier is 1 × 10 ¹² Ω · cm or more; Number average particle size of carrier is 1 to 1
The number distribution of the number distribution having a diameter equal to or less than 1/2 times the number average particle diameter is 20 number% or less, and (4) the shape factor SF-1 of the magnetic coated carrier is 100 to 130.
(5) An image forming method characterized in that the magnetic strength of the magnetic coated carrier at 1 kOe is 40 to 250 emu / cm ³ .

[0014]

Next, the present invention will be described in more detail with reference to preferred embodiments. In the image forming method of the present invention, as in the case of the two-component contact developing method using the two-component developer used in the above-described conventional example, a developer containing at least a toner and a magnetic carrier is provided inside a magnet. The developer is carried on the surface of the arranged developer carrier and transported to the developing section, and a developing magnetic pole of the magnet forms a developing magnetic field in the developing section. The developing section is arranged so as to face the developer carrier. The electrostatic latent image on the image carrier is developed using a developer to form an image. At this time, a low-resistance layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm is formed on the image carrier. And a carrier having the above five requirements as a carrier in the developer. That is, the charging efficiency is improved by making the surface resistance of the photosensitive drum as low as about 10 ⁹ to 10 ¹⁴ Ω · cm, while the use of a magnetic carrier having a specific physical property makes it possible to obtain a high fog free form. It is possible to provide high-quality images. Hereinafter, the magnetic carrier, toner, and image forming apparatus used in the present invention will be described.

First, the magnetic carrier used in the present invention is required to be a magnetic material-dispersed resin carrier coated with a high resin, and magnetic powder is dispersed in a binder resin as a carrier core material. Magnetic material-dispersed fine particles are used. Examples of the magnetic material used in this case include ferromagnetic metals such as iron, cobalt, and nickel; alloys or compounds containing ferromagnetic elements such as ferrite and magnetite hematite;
And the like.

Here, as the binder resin for forming the carrier core material used in the present invention by dispersing the magnetic material powder as described above, any resin obtained by polymerizing a vinyl monomer may be used. These can be used, and one or more of these can be used and polymerized. Other than the resin obtained by polymerizing a vinyl monomer, for example, polyester resins, epoxy resins, phenol resins, urea resins, polyurethane resins, polyimide resins, cellulose resins, non-vinyl condensation resins such as polyether resins, Alternatively, a mixture of these with the vinyl resin is used as a binder resin for dispersing the magnetic powder as described above.

When the magnetic carrier used in the present invention is manufactured as described above, the specific resistance of the core particles of the magnetic carrier is 1 × 10 ¹⁰ Ω · cm or more, and the specific ratio of the magnetic coated carrier obtained is One having a resistance of 1 × 10 ¹² Ω · cm or more is used. According to the study of the present inventors, when the specific resistance of the core particles is smaller than 1 × 10 ¹⁰ Ω · cm, or when the specific resistance of the coated carrier particles is 1 × 10 ¹² Ω.
It was found that when the diameter was smaller than cm or less, rough and fogging caused by charge leakage to the photoreceptor drum was severely generated.

Further, as the magnetic carrier used in the present invention, a small particle size carrier having a number average particle size of 1 to 100 μm or less is used. That is, in general, the particle size of the carrier needs to be as small as possible from the viewpoint of high image quality. Therefore, when the number average particle size of the carrier exceeds 100 μm, fine line reproducibility and gradation It is difficult to form an image having excellent properties. In the present invention, further from this viewpoint, the number average particle size is 10 to
It is preferred to use a carrier in the range of 60 μm.
The method of measuring the carrier particle size used in the present invention will be described later. What is important in the present invention is that the carrier has a particle size distribution such that the number distribution cumulative value of 1/2 or less the number average particle size of the carrier is 20% by number or less. If the cumulative value of the number distribution having a half diameter or less exceeds 20% by number, it is not preferable in that the carrier adhesion increases as described above and the charging of the toner becomes poor.

The magnetic coated carrier used in the present invention comprises:
Spherical shape having a shape factor SF-1 of 100 to 130 is used. The shape coefficient will be described in the description of the toner.

Further, the magnetic coated carrier used in the present invention must have a magnetic property of 40 to 250 emu / cm ³ at 1 kOe, and more preferably, as a magnetic property. 50-230 emu / c
It is preferred to use a carrier with a low magnetic force such as in the range of m ³ . As described above, the intensity of magnetization of the carrier is appropriately selected depending on the carrier particle size. When the magnetization intensity exceeds 250 emu / cm ³ , the density of the developing brush formed on the developing sleeve at the developing electrode decreases, and the spike length becomes longer and the rigidity increases. As a result, sweeping unevenness occurs on the copied image, and the durability of the developer deteriorates due to a large number of copies, which causes image deterioration such as half-tone roughness and carrier adhesion due to peeling of the coating material. Also, 40 emu / c
If it is less than m ³ , the magnetic force of the carrier will be insufficient, causing the carrier to adhere or the toner transportability to deteriorate.

Next, the toner constituting the developer used in the present invention together with the magnetic carrier as described above will be described. As the toner used in the present invention, any conventionally known toner can be used. In the present invention, in particular, the shape factor SF-1 is 100 to 130, and SF-2
Of approximately 100 to 115 is preferably used. Note that S representing the shape factor used in the present invention.
The values of F-1 and SF-2 are obtained as follows. That is, 100 toner images are randomly sampled using an FE-SEM (S-800) manufactured by Hitachi, Ltd., and the image information is introduced into an image analysis device (Luzex3) manufactured by Nireco via an interface and analyzed. And calculate the values obtained by the following formulas as shape factors SF-1 and SF, respectively.
-2. The shape factor of the carrier was measured by the same method. SF-1 = [(MXLNG) ² / AREA] × (π / 4)
× 100 SF-2 = (PERI / AREA) × (1 / 4π) × 1
00 (AREA: toner projection area, MXLNG: absolute maximum length, PERI: circumference)

The shape factor SF-1 of the toner obtained as described above indicates the degree of spherical shape of the toner particles. When the shape factor SF-1 is larger than 140, the shape gradually changes from spherical to irregular. Also, SF-2
Indicates the degree of unevenness of the toner particle surface, and if it is larger than 120, the unevenness of the toner particle surface becomes remarkable. The functions and effects that these toner shapes can have on the image forming method are to minimize the influence of the photosensitive member charging member on the toner surface and to suppress the generation of reactive low molecular weight components in the toner as much as possible. It is in. From the above, it is preferable that the toner used in the present invention has a spherical shape in which the surface area of the toner particles is as small as possible.

For this reason, in the present invention, it is preferable to use a toner in which part or all of the toner is formed by a polymerization method. In particular, the polymerized toner formed by polymerizing the monomer composition in the aqueous dispersion medium is present as pre-toner (monomer composition) particles in the aqueous dispersion medium, and the monomers of the pre-toner particles are generated by a polymerization reaction.
The obtained toner particles are spherical and can be obtained with considerably smooth surface properties, so that the effects of the present invention can be further enhanced. In contrast, SF
If -1 exceeds 140 or SF-2 exceeds 120, fogging of the obtained image may increase and durability of the toner may be slightly deteriorated, which is not preferable.

Further, by giving the toner a core / shell structure and forming the shell portion by a polymerization method to produce the toner, the toner preferably used in the image forming method of the present invention can be more easily obtained. . Also in this sense, in the present invention, a toner having a core / shell structure is preferably used. As a function of the core / shell structure, it goes without saying that blocking resistance can be imparted without impairing the excellent fixability of the toner.

The volume average particle diameter of the toner particles is 4 to
Those having a size of about 15 μm are suitably used in the present invention. Here, the volume average particle diameter of the toner was measured by the following measuring method in the present invention. In addition, the particle size of the above-mentioned carrier was measured by the same method. The particle size distribution of the toner can be measured by various methods, but in the present invention, the measurement was performed using the following measuring apparatus. That is, an interface (manufactured by Nikkaki) and a CX-i for outputting a number average distribution and a volume average distribution using a Coulter Counter TA-II type (manufactured by Coulter) as a measuring device.
A personal computer (Canon) was connected.
As an electrolyte solution used at this time, about 1% NaCl aqueous solution was prepared using primary sodium chloride.

The measuring method is as follows.
0.1 to 5 ml of a surfactant (preferably an alkylbenzene sulfonate) as a dispersant in 00 to 150 ml
In addition, a sample solution is further prepared by adding 0.5 to 50 mg of a measurement sample. The electrolytic solution in which such a sample is suspended is subjected to dispersion treatment using an ultrasonic disperser for about 1 to 3 minutes, and the particle size distribution of particles of 2 to 40 μm is measured by using the above-described measuring device using a 100 μm aperture as an aperture. To determine the volume distribution. From these determined volume distributions, the volume average particle size of the sample is obtained.

Further, in the present invention, it is preferable that the toner surface is coated with an external additive as described above so that the influence of the photosensitive member charging member can be released to a certain external additive. . The external additive of the toner used at this time is 1/10 of the weight average particle diameter of the toner particles in view of the durability of the external additive when added to the toner.
It is preferable to use one having the following particle size. Here, the particle size of the additive means the average particle size of the toner particles obtained by observing the surface of the toner particles with an electron microscope. As the external additive of the toner used in the present invention, for example, aluminum oxide, titanium oxide, strontium titanate,
Metal oxides such as cerium oxide, magnesium oxide, chromium oxide, tin oxide, and zinc oxide; nitrides such as silicon nitride;
Examples thereof include carbides such as silicon carbide, metal salts such as calcium sulfate, barium sulfate, and calcium carbonate; fatty acid metal salts such as zinc stearate and calcium stearate; carbon black; and silica.

These external additives are used in an amount of 0.01 to 10 parts by weight, more preferably about 0.05 to 5 parts by weight, based on 100 parts by weight of the toner particles. These external additives may be used alone or in combination of two or more, but it is more preferable to use each of them after the hydrophobic treatment.

In the image forming method of the present invention, the above-described two-component developer composed of the toner and the carrier is used. The weight ratio of the toner and the carrier is 2 to 20: 98 to 80. , More preferably 2 to 10:
It is preferable to use 98 to 90 developers.

In the image forming method of the present invention, the developer having the above-described structure is used to perform development using a developing device as shown in FIG. An image is formed by applying a voltage. For example, -500 V as a DC voltage, as the AC _{voltage, V pp = 1,500V, V f} = 2,000Hz is applied. In the present invention, by using a specific magnetic carrier having the above-described characteristics in such a configuration, it is possible to effectively prevent image fogging which has conventionally occurred.

Further, by using the spherical toner having the above-described configuration and having a very high transfer efficiency, a cleaner-less device in which cleaning is performed simultaneously with development by the developing device 4 from which the cleaner is removed can be realized. That is, the transfer residual toner is slightly left on each photosensitive drum 1 of each image forming unit after the transfer process. As such a small amount of transfer residual toner on the image forming unit, there are a mixture of a toner having a positive polarity and a toner having a negative polarity due to discharge. In this way, the transfer residual toner in which the positive and negative toners are mixed is conveyed to the primary charger of 17C. As described above, the charging device 17C of the present embodiment includes the non-magnetic sleeve 11 in which the magnet fixed inside is contained.
Magnetic particles having a volume resistance of 10 ⁷ Ω · cm and a particle diameter of 25 μm are supported, and the magnetic particles rotate while contacting the photosensitive drum 1 (see FIG. 1). Then, when the transfer residual toner is conveyed to the primary charger of 17C, the transfer residual toner is mixed with the magnetic particles serving as the contact charging member, and the polarity is all negatively charged.
Spitted up. In this way, the untransferred toner discharged on the photosensitive drum 1 with its polarity uniformed in the primary charging step is then collected in the developing device by the fog removing electric field during development.

Here, in the case of a system for simultaneously collecting transfer residual toner during development as described above, if the image area in the rotation direction is longer than the circumferential length of the photosensitive drum 1, the transfer residual toner is not collected. , And other image forming steps (charging → image exposure → development → transfer). Such a cleanerless developing device can be achieved by a primary charger using a corona charger, but by using a direct charger having such a contact charging member, the transfer residual toner is temporarily removed as described above. A system that takes in the charger and discharges it to the drum 1 becomes possible. In such a system, even if a very large amount of transfer residual toner occurs in some time, the primary charger functions as a buffer, and a large amount of toner to be collected is conveyed into the developing device. This is preferable because there is no risk of inferior collection. That is,
Direct charging, in particular, by using a charger using magnetic particles as a contact charging member, can realize a cleaner-less system of higher quality.

As a preferred embodiment of the present invention, a method of charging by injecting a charge with a contact charging member into the trap potential of the photoreceptor surface material as described above, or dispersing conductive particles on the surface of the photoreceptor is preferred. By providing a charge injection layer, and by using an injection charging method in which the conductive particles are charged and charged by a contact charging member, the amount of discharge when the photoconductor is charged can be extremely reduced. It becomes possible. Therefore, even when the surface resistance of the photosensitive drum is as low as about 10 ⁹ Ω · cm to about 10 ¹⁴ Ω · cm as in the image forming method of the present invention, it is efficient when these injection charging methods are used. Chargeability can be obtained. Conventionally, when a photosensitive drum having such a low-resistance surface resistance is used, there has been a problem that image fogging occurs.
By using the magnetic coated carrier used in the present invention, a good image without fog can be obtained. Further, if a method is used in which the developing device also performs a cleaning process for collecting the transfer residual toner remaining on the image carrier, the transfer residual toner is collected and reused in the next step and thereafter, so that the The toner can be eliminated. Further, when the cleaning process is also performed by the developing device, there is a great advantage in terms of space, and the device can be significantly reduced in size.

[0034]

EXAMPLES Examples and comparative examples of the present invention will be described below.
The present invention will be described in more detail. (Embodiment 1) First, an apparatus according to a first embodiment to which the image forming method of the present invention is applied will be described with reference to FIG. In the apparatus shown in FIG. 1, a plurality of (four in the figure) image forming units are provided, and the transfer belt 30 serving as a transfer material transporting means extends vertically through these image forming units.
Are arranged. Furthermore, in this example, by using a spherical toner formed by a polymerization method as a constituent material of the developer, it is not necessary to perform a process of removing adhered contaminants such as transfer residual toner on the photosensitive drum after the transfer of the toner image. An image forming process system capable of recovering transfer residual toner at the same time as development without using a drum cleaner is employed.

The configuration of the above image forming apparatus will be described in detail. As shown in FIG. 1, in the apparatus, four units having the same configuration of a magenta unit (UM), a cyan unit (UC), a yellow unit (UY), and a black unit (UBk), which are image forming units, are provided. Although provided, units for four colors will be described below with UC as a representative.

First, a cylindrical photosensitive drum 1C as an electrostatic latent image carrier rotates and moves in the direction of arrow a as shown in FIG. 17C, which is provided so as to face the photosensitive drum 1C, is a primary charger, and the photosensitive drum 1C is uniformly negatively charged by the charger 17C as follows. That is, the charger 17C is provided with a non-magnetic sleeve carrying magnetic particles as a contact charging member,
The photosensitive drum 1 is attached to the magnetic particles carried on the sleeve.
Since C is configured to rotate while being in contact with the photosensitive drum 1C, the photosensitive drum 1C is negatively charged when a peak-to-peak 700V AC bias on which a DC voltage of -650V is superimposed is applied to the sleeve. In this example, as a nonmagnetic sleeve having such a function, a magnet fixed inside is included, and the magnet carries an iron powder having a volume resistance of 10 ⁷ Ω · cm and a particle size of 25 μm. Using.

As the contact charging member for charging the photosensitive drum 1C which can be used in the present invention, in addition to the above magnetic particles such as iron powder, for example, conductive fibers such as carbon fibers can be used. It is also preferred to use. In addition to the above magnetic particles, other than iron powder, for example,
0 particle size of about 15~35μm at ^{6 ~10 8 Ω} · cm or so, ferromagnetic metals such as cobalt and nickel; ferrites, iron or the like magnetite hematite, cobalt, or an alloy containing an element exhibiting ferromagnetism such as nickel Compounds and the like can be used.

Reference numeral 18C in FIG. 1 denotes an image exposure section, which is provided on the downstream side in the rotation direction of the photosensitive member 1C with respect to the primary charger 17C, and uses an LED to image the photosensitive member 1C. Expose the part. Reference numeral 4C denotes a developing device, which is provided further downstream than the exposure position of the photoconductor 1C and is installed adjacent to the photoconductor 1C. In this example, a spherical negatively charged toner produced by a polymerization method is included in the developing device 4C. Reference numeral 19 denotes a material to be transferred, and here, copy paper is used. Reference numeral 20 denotes a paper feeding unit for supplying the transfer material 19.

Reference numeral 30 denotes a transfer belt, which is a photosensitive drum 1
It is driven in the a direction in contact with C. Transfer belt 30
Is, for example, an endless belt in which conductive particles such as carbon are dispersed in a resin such as polycarbonate or rubber having high mechanical strength and flexibility, and has a resistance value of 10 ⁹ to It is preferable to use one adjusted to 10 ¹³ Ω · cm and the thickness to 0.1 to 1 mm. In this example, a resistor having a resistance value of 10 ¹² Ω · cm and a thickness of 0.5 mm was used. Reference numeral 31 denotes a driving roller, and 32 denotes a support roller. These are driving means for stretching and driving the transfer belt 30.

Reference numeral 25C denotes a transfer blade, which is preferably installed so as to sandwich the transfer belt 30 at the transfer position and face the photosensitive drum 1C as shown in the figure. This transfer blade 25C is, for example, a base material of 10 ⁹ to 10
^It is preferably formed of a semiconductor layer of ¹¹ Ω · cm. In this example, a polyurethane material having a resistance value of 10 ¹⁰ Ω · cm was used. Reference numeral 38 denotes a toner image fixing device, which is disposed adjacent to the drive roller 31 of the transfer and conveyance belt 30.

The structure of the photosensitive drum 1C used in the first embodiment of the present invention will be described. The photosensitive drum 1C used in the present invention has a surface resistance of 10 ⁹
One having a low resistance layer of 10 to 10 ¹⁴ Ω · cm is used.
By controlling the surface resistance in this way, the efficiency of direct charging is improved, and a high-quality image can be obtained. Table 1 shows the evaluation results on the effect on the chargeability and the effect on the occurrence of image deletion when the surface resistance of the photosensitive drum is changed.

The chargeability is measured as a charge potential, and the usable degree was evaluated by A to D. The evaluation criteria are as follows. A: very good B: good C: bad D: very bad

The image deletion is a phenomenon caused by the fact that the charged electric charge on the surface of the photosensitive drum is not retained when the surface of the photosensitive drum becomes low resistance, and the potential is attenuated. The degree was evaluated by A to D. The evaluation criteria are as follows. A: very good B: good C: bad D: very bad

Table 1: Evaluation results of surface resistance, chargeability and image deletion of photosensitive drum

From the above Table 1, as the photosensitive drum,
It can be seen that those having a surface resistance in the range of 10 ⁹ to 10 ¹⁴ Ω · cm are suitable for the direct charging method. In addition, when such a photosensitive drum is used, since the discharge phenomenon is extremely reduced, the generation of discharge products such as ozone is also extremely reduced.

The photosensitive drum 1C as described above is obtained by the following configuration. First, in this example, a drum base made of aluminum or the like having a diameter of about 30 mm was used, and an undercoat layer was provided as the first layer. The undercoat layer is not necessarily required, but is for preventing the occurrence of moire due to the reflection of light exposure. For example, in this example, the undercoat layer was formed of a conductive layer made of polyurethane having a thickness of 20 μm. In addition, as the undercoat layer, on the substrate as described above,
0.1-0.5μ thick made of polyamide alcohol
It may be composed of about m conductive layers.

The second layer provided thereon is a positive charge injection preventing layer, which prevents the positive charge injected from the drum base from canceling out the negative charge charged on the surface of the photosensitive drum 1C. Play a role. As the second layer, in this example, a medium-resistance layer having a thickness of about 0.1 μm and a resistance adjusted to 10 ⁶ Ω · cm by using an amilan resin and methoxymethylated nylon was used.

The third layer formed on the second layer is a charge generation layer. In this example, the third layer was formed as a layer having a thickness of about 0.3 μm in which a disazo pigment was dispersed in an acrylic resin. As a result, positive and negative charge pairs are generated by the exposure.

The fourth layer formed on the above-mentioned third layer is a charge transporting layer. In this example, the fourth layer was formed using a p-type semiconductor in which hydrazone was dispersed in a polycarbonate resin. In the present invention, the charge transport layer may be formed using an acrylic resin or the like.

Further, a fifth layer formed on the fourth layer
The eye is a surface layer, and in this example, a polycarbonate resin,
Teflon (Dupont's trademark PTFE) and surface resistance
SnO for dropping_Two2 dispersed with low-resistance particles such as
It was formed using a layer of about μm. In the present invention,
Alternatively, the surface layer may be formed using an acrylic resin or the like.
No. The photoconductor driver used in this example configured as described above is used.
1C has a surface resistance of 10¹³Ω · cm. In addition, above
The photoconductor 1C as described above is limited to OPC (organic photoconductor).
It can be realized with an a-Si drum,
Durability can be realized.

In the image forming method of the present invention using the above-described image forming apparatus, a developer containing at least a toner and a magnetic carrier is used. In the present invention, the following 5 is used as the magnetic carrier. Use one that satisfies the two requirements. (1) A magnetic coated carrier obtained by coating the surface of a magnetic carrier core particle containing metal oxide particles with a resin composition. (2) The specific resistance of the magnetic carrier core particles is 1 × 10 ¹⁰ Ω ·
cm or more, and the specific resistance of the magnetic coated carrier is 1
× 10 ¹² Ω · cm or more. (3) The magnetic coated carrier has a number average particle size of 1 to 10
0 μm, and the cumulative distribution value of the number distribution having a diameter equal to or less than 倍 times the number average particle diameter is 20 number% or less. (4) The magnetic coated carrier has a shape factor SF-1 of 10
0 to 130. (5) The magnetic coat carrier has a magnetization intensity of 40 to 250 emu / cm ³ at 1 kOe.

Hereinafter, a method for producing the magnetic carrier having the above-described physical properties used in this example will be described.・ 7 parts by weight of phenol ・ 10.5 parts by weight of formalin solution (formaldehyde about 40%, methanol about 10%, balance is water) ・ Magnetite lipophilized with 0.5 part by weight of γ-aminopropyltrimethoxysilane ( Α-Fe ₂ O ₃ (particle size 0) treated with lipophilic treatment with 0.5 part by weight of γ-aminopropyltrimethoxysilane (particle diameter: 0.25 μm, specific resistance: 5.1 × 10 ⁵ Ω · m) .60 μm, specific resistance 7.8 × 10 ⁹ Ω · m) 35 parts by weight

The magnetite and α-Fe ₂ used here
The lipophilic treatment of O ₃ is performed by adding 0.5 parts by weight of γ-aminopropyltrimethoxysilane to 100 parts by weight of each metal oxide, and adding 30 parts at 100 ° C. in a Henschel mixer.
This was done by mixing and stirring for minutes. Hereinafter, the lipophilic treatment of the metal oxide used in the examples was performed in the same manner.

The above materials and 28% by weight as a basic catalyst
Of ammonia water and 20 parts by weight of water were placed in a flask, heated to 85 ° C. for 40 minutes while stirring and mixing, and reacted and cured for 3 hours. Then 30 ° C
After cooling to 100 parts by weight of water, the supernatant was removed, and the precipitate was washed with water and air-dried. Next, this was dried at 70 ° C. under reduced pressure (5 mmHg or less) to obtain spherical particles in which magnetite and hematite were bound using a phenol resin as a binder. The coarse particles were removed from the particles by a 60-mesh sieve, and the number average particle diameter was 28 μm.
Got a career core. The resulting core has a resistance of 8.0.
× 10 ¹⁰ Ω · cm.

Next, 100 parts by weight of the carrier core particles obtained above, 0.5 part by weight of phenol, 0.75 part by weight of a formalin solution, 0.2% of a 28% by weight aqueous ammonia solution
In a flask, 50 parts by weight of water and 50 parts by weight of water were heated and maintained at 85 ° C. for 40 minutes while stirring and mixing, and reacted and cured for 3 hours. Thereafter, the mixture was cooled to 30 ° C., 50 parts by weight of water was added, the supernatant was removed, and the precipitate was washed with water and air-dried. Next, this was dried at 180 ° C. under reduced pressure (5 mmHg or less) to obtain coated carrier particles whose surface was coated with a phenol resin. The repolymerized core thus obtained has a number average particle size of 28 μm and a resistance of 2.
It was 1 × 10 ¹² Ω · cm.

On the surface of the coated carrier particles obtained above, all the substituents were methyl groups and OH groups were added to the terminals where the ratio of bifunctional to trifunctional silicon was 5:95 with respect to 100 parts by weight of the particles. 0.5 parts by weight of tolate silicone resin,
0.025 parts by weight of γ-aminopropyltrimethoxysilane and 0.025 parts by weight of n-propyltrimethoxysilane were coated by the following method. First, a carrier coat solution was prepared using toluene as a solvent so that the resin composition was 10% by weight. The solvent was volatilized while continuously applying shear stress to the coating solution to coat the carrier core. The obtained coated carrier particles are mixed with 180
After curing at 2 ° C. for 2 hours and crushing, only aggregated coarse particles were removed with a 100-mesh sieve to obtain carrier particles. The obtained carrier particles have a number average particle size of 28 μm.
And the number distribution cumulative value of the particle size distribution of 14 μm or less (1/2 diameter) is 0% by number, and the shape factor SF-1 is 104%.
Met.

Here, a method of measuring the carrier particle size employed in the present invention will be described. The particle size of the carrier of the present invention is determined by randomly extracting 300 or more carrier particles having a particle size of 0.1 μm or more by a scanning electron microscope (100 to 5,000 times), and using an image processing analysis device Luzex3 manufactured by Nireco Corporation.
, The carrier average particle diameter is measured with the horizontal Feret diameter, and the number average particle diameter is calculated. Based on the number-based particle size distribution measured under these conditions, the cumulative ratio of the number average particle size smaller than 1/2 times the diameter cumulative distribution is determined, and the cumulative value equal to or smaller than the 1/2 size diameter cumulative distribution is calculated.

Next, a method for measuring the magnetic properties of the carrier particles employed in the present invention will be described. The magnetic properties of the carrier are measured using an oscillating magnetic field type magnetic property automatic recording device BHV-30 manufactured by Riken Denshi Co., Ltd. Specifically, the magnetic characteristic value of the carrier particles is obtained by generating an external magnetic field of 1 kOe and obtaining the intensity of magnetization at that time. The carrier for measurement is prepared in a state of being packed in a cylindrical plastic container so as to be sufficiently dense. In this state, the magnetization moment is measured, and the actual weight when the sample is placed is measured to obtain the magnetization intensity (emu / g). Next, the true specific gravity of the carrier particles was measured using a dry automatic densimeter Acupic 13
30 (manufactured by Shimadzu Corporation), and multiplying the above-obtained magnetization intensity (emu / g) by the true specific gravity, the magnetization intensity per unit volume of the present invention (emu / c)
m ³ ).

A method for measuring the specific resistance of the carrier core particles and the coated carrier employed in the present invention will be described. The specific resistance of the carrier is determined by filling the cell with the carrier, arranging electrodes 1 and 2 so as to be in contact with the filled carrier, applying a voltage between these electrodes, and measuring the current flowing at that time. A method for determining the resistance was used. In the above-mentioned measuring method, it is necessary to pay attention to the fact that the carrier is a powder, so that the filling rate changes and the specific resistance sometimes changes. The measurement conditions for the specific resistance of the carrier used in the present invention are as follows: the contact area S between the filled carrier and the electrode is about 2.3 cm ² , and the thickness d is about 1 m.
m, the load of the upper electrode 2 was 180 g, and the applied voltage was 100 V.

Next, the toner used in the image forming method of the present invention will be described. In this example, a toner produced by the following polymerization method was used. [Production Method of Polymerized Toner A] 450 parts by weight of a 0.1 M Na ₃ PO ₄ aqueous solution is added to 710 parts by weight of ion-exchanged water, heated to 60 ° C., and then a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) ) And stirred at 12,000 rpm. To this, 68 parts by weight of a 1.0 M CaCl ₂ aqueous solution was gradually added to obtain an aqueous medium containing Ca ₃ (PO ₄ ) ₂ .

On the other hand, (monomer) styrene 165 parts by weight n-butyl acrylate 35 parts by weight (colorant) I. Pigment Blue 15: 3 15 parts by weight (charge control agent) Metal salicylate compound 3 parts by weight (polar resin) Saturated polyester (acid value 14, peak molecular weight: 8,000) 10 parts by weight (release agent) Ester wax (melting point 70) The above formulation was heated to 60 ° C. and uniformly dissolved and dispersed at 12,000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). Into this, 10 parts by weight of a polymerization initiator 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved to prepare a polymerizable monomer composition.

The above polymerizable monomer composition is charged into the aqueous medium obtained above, and the mixture is heated at 60 ° C. under a nitrogen atmosphere.
The mixture was stirred at 11,000 rpm for 10 minutes with a K-type homomixer to granulate a polymerizable monomer composition. Thereafter, the temperature was raised to 80 ° C. while stirring with a paddle stirring blade, and the reaction was performed for 10 hours. After completion of the polymerization reaction, residual monomers were distilled off under reduced pressure, and after cooling, hydrochloric acid was added to dissolve calcium phosphate, followed by filtration, washing and drying to obtain cyan colored suspension particles. The obtained colored suspension particles have a weight average particle size (D4) of about 5.6 μm and a number average particle size (D1) of 4.
5 μm, the cumulative value of the number distribution of 径 times the number average particle diameter or less was 6.3 number%, and the cumulative value of the volume distribution of the twice or more weight average particle diameter was 0% by volume. .

For 100 parts by weight of the colored suspended particles,
2.0 parts by weight of hydrophobic silica having a specific surface area of 200 m ² / g by a BET method was externally added to obtain a suspension polymerization toner A. The shape factor SF-1 of the obtained toner A is 101
, Nearly spheric, and the residual monomer content is 480 ppm
Met. The coverage by the external additive was 65%.

Hereinafter, the polymerized toner A of the specific example described above will be described.
And a magnetic-coated carrier in a weight ratio of 8:92 to obtain a developer. The developing device shown in FIG. went. At this time, a DC voltage of -500 V and an AC voltage of V _PP =
1,500 V and _Vf = 2,000 Hz are applied.

The specific resistance of the core particles of the carrier used in this example was 8 × 10 ¹⁰ Ω · cm as described above, and the specific resistance of the coated carrier particles was 2.1 × 10 ¹² Ω · cm. However, the use of such carrier particles did not cause image fogging, which occurred conventionally, on the photosensitive drum having a surface resistance of 1 × 10 ¹³ Ω · cm used in this example. On the other hand, the specific resistance of the core particles is 1
The case where the resistivity is smaller than × 10 ¹⁰ Ω · cm or the case where the specific resistance of the coated carrier particles is smaller than 1 × 10 ¹² Ω · cm was examined. It was found that rough and fogging caused by charge leakage occurred violently.

(Comparative Example) Cu-Zn ferrite particles having a number average particle size of 45 μm were used as the core particles of the carrier. The specific resistance of the core particles was 4.0 × 10 ⁸ Ω · cm. This was coated with the same resin composition as in Example 1 to obtain coated carrier particles of a comparative example having a resin-coated surface. The obtained coated carrier particles have a number average particle size of 45 μm and a particle size distribution of 22.5 μm (1/1).
The cumulative value of the number distribution of 2 × or less was 18.8% by number, and the shape factor SF-1 of the coated carrier particles was 118. The specific resistance is 4.4 × 10 ¹⁰ Ω · cm, and the magnetization intensity at 1 kOe (σ ₁₀₀₀ ) = 305 e
mu / cm ³ (true specific gravity of coated carrier particles: 5.02 g / cm ³ ). A magnetic carrier having such characteristics is mixed with the same polymerized toner A as used in Example 1 (toner: carrier = 8: 92 (weight ratio)) to obtain a developer. As a result, severe roughening and image fogging occurred.

(Embodiment 2) Next, a second embodiment of the present invention will be described with reference to FIG. As shown in FIG.
Also in the embodiment, similarly to the above-described first example, an image forming unit capable of integrally performing the respective steps of charging, exposure, development, and pre-exposure around the photosensitive drum is provided for each toner color, that is, UM. , UC, UY, and UBk. As in the case of the first example, a spherical toner formed by a polymerization method is used as the toner, and an image is formed by a process in which the transfer residual toner on the drum is simultaneously collected at the time of development by a developing device without cleaning the drum. To form.

However, what is different from the first example is that the transfer material is not carried and conveyed on the transfer belt and the toner images of the respective colors are transferred onto the transfer material 19 in a multiplex manner. The transfer body 50 is stretched by a driving roller 31, a support roller 32, and a backup roller 27, and the toner images of each color are multiplex-transferred onto the intermediate transfer body 50, and the composite toner image is transferred by the paper feed roller 20 to be transferred. Lumber 19
The backup roller 27 and the secondary transfer roller 2
After the transfer at 6, the fixing unit 38 fixes the image.

The intermediate transfer member 50 used in the present example has a PTFE (polytetrafluoroethylene) layer (10) as a dielectric layer on the surface of urethane rubber (10 ³ to 10 ¹⁴ Ω · cm).
⁽¹⁴ Ω · cm or more). The other components are almost the same as those in the first example described above, and the description is omitted. The intermediate transfer member 50 is not limited to the above, and for example, polyethylene terephthalate, polybutylene fluoride, or the like can be preferably used.

Hereinafter, according to the image forming method having the above-described configuration, first, a magenta toner image is formed on the photosensitive drum of the magenta unit UM by the same process as in the first example, and the transfer electric field formed by the transfer blade is used. The toner image is transferred onto the intermediate transfer body 50. Next, as the intermediate transfer member 50 rotates, the intermediate transfer member 5
The magenta toner image on 0 is conveyed, and the cyan toner image is multiplex-transferred onto the intermediate transfer body 50 by the next cyan unit UC. In the same manner, the charge adjustment and the multiple transfer are performed in yellow and black in the same manner. Finally, the transfer is collectively transferred onto the transfer material 19 by the secondary transfer roller 26, and the fixing device 3
The image is fixed at 8 and an image is formed. In the second embodiment of the present invention using the image forming apparatus having the above-described configuration, a photosensitive drum having a low surface resistance of 1 × 10 ¹⁰ Ω · cm was used as the photosensitive drum. As the carrier constituting the developer, the same resin-coated carrier as that described in the first example was used. As a result, as in the case of Example 1, a high-quality image in which image fogging was prevented was obtained.

[0071]

As described above, according to the present invention, there is provided an image forming method which is extremely excellent in charging efficiency and provides a high quality image without fog. Further, according to the present invention, since a cleaner-less system can be realized, a small-sized apparatus which does not generate waste toner is provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view illustrating a color image forming apparatus applied to a first embodiment of the present invention and a conventional example.

FIG. 2 is a schematic sectional view of a color image forming apparatus applied to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a color image forming apparatus illustrating a conventional example of the invention.

FIG. 4 is a schematic sectional view of a developing device of a color image forming apparatus for explaining a conventional example of the present invention.

FIG. 5 is an explanatory diagram of a laser beam scanner used in a conventional example of the present invention.

[Explanation of symbols]

1, 1C: Photosensitive drum 2: Exposure unit 3: Charger 4, 4C: Developing device 5: Cleaner 6: Fixing device 7: Transfer charger 8: Separation charger 9: Unit 10: Document table 11: Developing sleeve 12: Magnet roller 13: stirring screw 14: stirring screw 15: regulating blade 16: developer container 17C: primary charger 18C: image exposing section 19: transfer material (copy paper) 20: sheet feeding section 25C: transfer blade 26: 2 Next transfer roller 27: Backup roller 30: Transfer belt 31: Driving roller 32: Support roller 38: Fixing device 40: Power supply 50: Intermediate transfer member 100: Laser scanning unit 101: Light emission signal generator 102: Solid state laser element 103: Collision meter lens system 104: the rotary polygonal mirror _105a, 105b, 105c: f θ lens group 106 The surface to be scanned UBK: black image forming unit UY: yellow image forming unit UC: cyan image forming unit UM: the magenta image forming unit G: document

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[Procedure amendment]

[Submission date] April 7, 1998

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claim 1

[Correction method] Change

[Correction contents]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

[0013]

The above object is achieved by the present invention described below. That is, in the present invention, a developer containing at least a toner and a magnetic carrier is carried on a surface of a developer carrier, and is conveyed to a developing unit, and is developed by a developing magnetic pole of a magnet disposed inside the developer carrier. An image forming an image by developing an electrostatic latent image on an image carrier, which is disposed to face the developer carrier, with a developing device using the developer, in a developing section in which a developing magnetic field is formed; in the method for forming, said image bearing member has a surface resistance of 10 ⁹ to 10
^The magnetic carrier has a low resistance layer of ¹⁴ Ω · cm on the surface, and the magnetic carrier is a magnetic coated carrier obtained by coating the surface of a magnetic carrier core particle containing (1) metal oxide particles using a resin composition. (2) the specific resistance of the core particles of the magnetic carrier is 1 × 10 ¹⁰ Ω · cm or more, and the specific resistance of the magnetic coated carrier is 1 × 10 ¹² Ω · cm or more;
(3) Number average particle diameter of magnetic coated carrier is 1 to 100
μm, the cumulative value of the number distribution having a diameter equal to or less than 倍 times the number average particle diameter is 20 number% or less, (4) the shape factor SF-1 of the magnetic coated carrier is 100 to 130, (5) An image forming method, wherein the magnetic strength of the magnetic coated carrier at 1 kOe is 40 to 250 emu / cm ³ .

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI G03G 15/08 507 G03G 9/10 351 (72) Inventor Ryo Inoue 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (5)

[Claims] 1. A developer containing at least a toner and a magnetic carrier is carried on a surface of a developer carrying member and transported to a developing section. The developer is developed by a developing magnetic pole of a magnet disposed inside the developer carrying member. In the developing section where the magnetic field is formed,
In an image forming method of forming an image by developing an electrostatic latent image on an image carrier that is arranged to face the developer carrier by a developing device using the developer, the developer carrier is The magnetic carrier has a low-resistance layer having a surface resistance of 10 ⁹ to 10 ¹⁴ Ω · cm on the surface, and the magnetic carrier is formed by using a resin composition on the surface of (1) magnetic carrier core particles containing metal oxide particles. Coated magnetic carrier,
(2) The specific resistance of the core particles of the magnetic carrier is 1 × 10 ¹⁰ Ω
Cm or more, and the specific resistance of the magnetic coated carrier is 1 × 10 ¹² Ω · cm or more. (3) The number average particle diameter of the magnetic coated carrier is 1 to 100 μm, and the number average particle diameter is 1 to 100 μm. The cumulative distribution value of the number distribution having a diameter of / 2 or less is 20
(4) the magnetically coated carrier has a shape factor SF-1 of 100 to 130, and (5) the magnetically coated carrier has a magnetization intensity of 4 at 1 kOe.
An image forming method, wherein the pressure is from 0 to 250 emu / cm ³ . 2. The image forming method according to claim 1, wherein the image carrier is charged by a contact charging member, and an image exposure is performed by an exposure unit to form an electrostatic latent image on the image carrier. 3. The image forming method according to claim 2, wherein the contact charging member is a conductive fiber, and the fiber is brought into contact with the image carrier to charge the image carrier. 4. The image forming method according to claim 2, wherein the contact charging member is a magnetic particle, and the magnetic particle is brought into contact with the image carrier to charge the image carrier. 5. The cleaning device according to claim 1, wherein after the image developed with the developer is transferred to the transfer material, the developing device also performs a cleaning process for recovering the transfer residual toner remaining on the image carrier. Image forming method.