JP3141310B2 - Developer and image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer and an image forming method in electrophotography. More specifically, an image forming method including a charging step of charging by bringing a charging member to which a voltage is applied from the outside into contact with a member to be charged, and a cleaning step of removing a developer from the member to be charged, and the use thereof. Developer to be used.

[0002]

2. Description of the Related Art Conventionally, a corona discharger has been known as a charging means in an electrophotographic apparatus or the like. However, corona dischargers have problems such as the need to apply a high voltage and the generation of a large amount of ozone.

Therefore, recently, the use of contact charging means without using a corona discharger has been studied. Specifically, a voltage is applied to a conductive roller serving as a charging member, and the roller is brought into contact with a photosensitive member serving as a member to be charged, thereby charging the surface of the photosensitive member to a predetermined potential. If such a contact charging means is used, the voltage can be reduced as compared with a corona discharger, and the amount of generated ozone can be reduced.

[0004] However, when the contact charging means is used, there is a problem that poor charging occurs if sufficient contact with the member to be charged cannot be maintained. In the contact portion, if the residual developer is present on the surface of the photoreceptor, since the charging member has a predetermined contact pressure, the residual developer adheres to the surface of the charging member and the photoreceptor, and the image is affected. There is also a problem that is.

[0005] When such a phenomenon occurs, the latent image formation of the latent image carrier may be lost, or the transfer may be omitted.
The result is a defective image copy.

For this reason, the surface characteristics of the charging member are important and need to be strictly controlled. However, easiness of manufacturing including management of the material and surface shape, and matching with the inner layer, and cost are easy. Considering the surface, it is difficult to produce a charging member having surface characteristics satisfying all surfaces.

On the other hand, as a developer, a one-component developer consisting only of toner, especially a magnetic material, is used in order to solve various problems related to a two-component developer in accordance with miniaturization and simplification of operation of an electrophotographic apparatus and the like. Is used.

In a conventional image forming method using a developer containing a magnetic material, if a long-term repeated developing process (for example, copying) is continued, the fluidity of the developer deteriorates,
Normal frictional electrification cannot be obtained, and electrification tends to be nonuniform. In a low-temperature and low-humidity environment, a fogging phenomenon is likely to occur, which tends to cause a problem on an image. Further, when the adhesion between the binder resin and the magnetic material constituting the toner particles is weak, the magnetic material is removed from the surface of the toner particles by the repetitive development process, and tends to have an adverse effect such as a decrease in image density. There is.

In addition, when the dispersion of the magnetic substance in the toner particles is not uniform, small toner particles containing a large amount of the magnetic substance accumulate on the sleeve, and the image density is reduced and the density called the sleeve ghost is reduced. May be observed.

Further, these developers tend to be further finely divided in order to achieve high image quality. In such a magnetic developer, the developer itself has a strong polishing effect, and the surface of the photoconductor is strongly rubbed during image formation, so that the surface of the photoconductor is often scraped or damaged. There was a problem that the developer was fused. This problem is conspicuous when a contact member such as the above-mentioned charging member that is in contact with the surface of the photoreceptor with a predetermined contact pressure is used. ,
It can be difficult.

Further, in the contact charging device as described above, a DC voltage or a DC voltage obtained by superimposing an AC voltage is applied to the charging member and used. At this time, around the contact portion between the charging member and the photosensitive drum, Unusual charging of the residual developer and repetition of flying motion are repeated, which makes it difficult for the residual developer to be electrostatically attracted and embedded on the charging member and the surface of the photosensitive drum. Is very different from the case where non-contact charging means is used. In particular, this problem
The finer the developer, the more noticeable it appears. As a new problem, there is a concern that the life of the charging member is shortened, that is, frequent replacement is required.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a developer and an image forming method which solve the above-mentioned problems.

That is, an object of the present invention is to prevent contact between the charging member and the member to be charged by sufficiently preventing contamination of the charging member and the surface of the member to be charged (photoreceptor) such as residual developer. An image forming method that can be maintained, has a charging process that does not cause charging failure and charging unevenness, and ultimately extends the life of the charging member, that is, achieves a reduction in replacement frequency, and a developer used for the image forming method. To provide.

[0014]

That is, the present invention provides a method of charging a charging member having at least a polyester resin and having a surface layer having a center line average roughness (Ra) of 0.3 to 2.5 μm. An image forming method comprising: a charging step of applying a voltage to a charging member from the outside while being in contact with a body to charge the body to be charged; and a cleaning step of removing a developer from the body to be charged. A resin and a magnetic material, wherein inorganic fine particles are fixed to the surface of the magnetic material in a range of 0.2% by weight to 5% by weight based on the amount of the magnetic material, and the specific surface area (A ) [M ² / g], an increase in specific surface area after immobilizing inorganic fine particles on the surface of the magnetic material (B) [m ² / g], an amount of inorganic fine particles added to the magnetic material (C) [ wt%] and a specific surface area of the inorganic fine particles (D) [m ² / Is the following formula (1), formula (2) and formula (3) formula (1) 0.1 ≦ B / A ≦ 0.8 formula (2) B <30 × C formula (3) 0.4 ≦ An image forming method using a developer in a range of B / (0.01 × C × D) ≦ 2.5, and the above-mentioned developer used in this image forming method.

First, the contact charging step applicable to the image forming method of the present invention will be specifically described.

FIG. 1 is a schematic diagram showing one embodiment of a contact charging device for performing a contact charging step according to the present invention. In FIG. 1, reference numeral 1 denotes a photosensitive drum which is a member to be charged, which is formed by forming an organic photoconductor (OPC) 1b which is a photosensitive layer on an outer peripheral surface of a drum base 1a made of aluminum. Rotate at the speed of. Reference numeral 2 denotes a charging roller, which is a charging member brought into contact with the photosensitive drum 1 with a predetermined pressure, provided with a conductive rubber layer 2b on a metal core 2a, and further provided with a surface layer 2c which is a release coating on the peripheral surface thereof. Provided. Surface layer 2
c is preferably a release film in view of matching with the developer and the image forming method of the present invention.

Further, in order to conduct electricity in the diameter direction, both the conductive rubber layer 2b and the surface layer 2c need to have a specific resistance in a medium resistance region. The resistance value in the present invention is preferably 10 ³ Ω to 10 ⁶ Ω for the conductive rubber layer 2b, and 10 ⁴ Ω to 10 ⁹ Ω when the surface layer 2c is provided.
As shown in FIG. 3, the resistance value is measured by winding a metal foil 4 having a width of 1 cm around the charging member, applying 250 V between the cored bar 2a and the metal foil 4, The subsequent current value is measured by the ammeter 6, and the resistance is measured based on the relationship of 250 [V] / current value “A” = resistance of the measuring section [Ω].

JIS K63 is used as the conductive rubber layer 2b.
20 at a hardness defined by an A-type hardness tester of No. 01
Preferably, the hardness is 80 °.

Reference numeral E denotes a power supply for applying a voltage to the charging roller 2, and supplies a predetermined voltage to the metal core 2 a of the charging roller 2. In FIG. 1, E indicates a DC voltage, but may be obtained by superimposing an AC voltage on a DC voltage.

In the present invention, the adhesion between the conductive rubber layer and the surface layer and the material and properties of the surface layer govern the strength of the charging member itself and determine the state of contact with the surface of the photoreceptor. I found it.

That is, it has been found that by adjusting them and combining them with a developer having good matching, the contamination of the surface of the charging member and the surface of the photosensitive member can be reduced, and the life of the charging member can be prolonged. .

In the charging roller shown in FIG. 1, for example, a polyether urethane layer in which carbon black is dispersed is used as the conductive rubber layer 2b, and the surface is polished in consideration of cost and ease of production. Adjust the shape.

Further, polyester, which is a low-cost material having good coating properties, is coated thereon by dipping to form a surface layer, and has a center line average roughness Ra of 0.3 to 2.5 μm according to JIS standard (B0601). Adjust so that

When Ra is less than 0.3 μm, the surface of the charging member and the surface of the photoreceptor easily adhere to each other. If a developer is interposed in the gap, contamination such as fusion or filming occurs on each surface. However, it is generally difficult to reach as long as the surface of the conductive rubber layer is formed by polishing. The surface of the conductive rubber layer can be further roughly polished and formed so that Ra of the surface layer exceeds 2.5 μm. In this case, however, the adhesion between the surface of the charging member and the surface of the photoreceptor can be improved. Adverse effects, such as deterioration of the developer, the possibility that the developer is easily buried in the concave portions of the charging member surface, and that the contamination easily proceeds.

As the resin material used for the conductive rubber layer in the present invention, besides polyether urethane, for example, EPDM, EPT, EPM, NBR, BR, BR, C
Synthetic rubbers such as R, thermosetting elastomers such as natural rubber, and thermoplastic elastomers such as vinyl chloride / vinyl acetate polyester / PVA are used alone or in combination.

As the conductive particles added to impart conductivity to the conductive rubber layer, conductive particles such as carbon black, zinc oxide, titanium oxide, and metal powder are used.

The polyester used for the charging member surface layer of the present invention is obtained by condensation of an alcohol and a carboxylic acid, and conventionally known polyesters are used.

Examples of the alcohol used include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol and the like. Dihydric alcohols such as diols, 1,4-bis (hydroxymethyl) cyclohexane, and etherified bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, and polyoxypropylene bisphenol A Examples of the carboxylic acid include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, and succinic acid Adipic acid, sebacic acid, malonic acid, anhydrides of these acids, dimers of lower alkyl ester and Rirein acid, divalent organic acids such as.

Further, a trihydric or higher polyhydric alcohol and / or
Alternatively, a trivalent or higher valent polycarboxylic acid may be used.

Examples of trihydric or higher polyhydric alcohols include sorbitol, 1,2,3,6-hexanetetrol,
1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose,
1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,
3,5-trihydroxymethylbenzene and the like. Examples of the trivalent or higher polycarboxylic acid include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 2,5,7-naphthalene. Tricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,2
4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2
-Methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, empol trimer acid, and acid anhydrides thereof.

It is also possible to use polyester and other resin materials in combination for the surface layer. As the resin material to be combined, a material having flexibility at normal temperature, such as polyamide, polyimide, fluororesin, silicon resin, and PVA, is used. In order to further impart conductivity, carbon black, zinc oxide, titanium oxide, Conductive particles such as metal powder may be added.

In the present invention, since the conductive rubber layer is used to support the electrodes, the conductive rubber layer is preferably flame-retardant, and particularly preferably has a flame retardancy of 94 HB or more according to UL-94 standard. preferable.

The thickness of the conductive rubber layer is preferably 1 to 5 mm. The thickness of the surface layer is 1 to 500 μm.
Is preferred.

In the above-described embodiment, the charging member is composed of the conductive rubber layer and the release coating. However, the present invention is not limited to this. For preventing leakage to the photoconductor between the conductive rubber layer and the surface of the release coating. For this purpose, a high resistance layer, for example, a hydrin rubber layer with small environmental fluctuation may be formed.

FIG. 2 is a schematic diagram showing another embodiment of the contact charging device for performing the contact charging step according to the present invention. The same members as those of the apparatus of FIG. 1 described above are denoted by the same reference numerals, and the description thereof will not be repeated.

The contact charging member 2 'of this embodiment is in the form of a blade which is brought into contact with the photosensitive drum 1 in a forward direction at a predetermined pressure, and the blade 2' is a metal supporting member 2 'to which a voltage is supplied. The conductive rubber 2'b is supported by a, and a surface layer 2'c serving as a releasable film is provided at a contact portion with the photosensitive drum 1. According to this embodiment, the same operation and effect as those of the above embodiment can be obtained without any trouble such as adhesion between the blade and the photosensitive drum.

The mechanical or electrical pressure applied between the charging member and the photosensitive member is an element according to the gist of the present invention, and the contact pressure of the charging member with the photosensitive member is 5 to 500 g.
/ Cm, the DC voltage applied to the charging member has an absolute value of 20
When an AC voltage is applied to 0 to 900 V, the peak-peak voltage is 500 to 5000 V, and the frequency is 50 to 3000 H.
It is desirable that z be adjusted respectively.

In the above-described embodiment, the roller-shaped or blade-shaped charging member is used. However, the present invention is not limited to this, and the present invention can be applied to other shapes.

The photoreceptor used in the present invention includes, in addition to organic photoconductors, amorphous silicon, selenium, Zn
O or the like can also be used. In particular, when amorphous silicon is used for the photoconductor, compared to the case where other materials are used, even if the softening agent of the conductive rubber layer adheres to the photoconductor even to a small extent, the image flow becomes severe, so The effect of providing the insulating coating is great.

In the cleaning step according to the present invention, the photosensitive drum after transfer of the toner image is generally wiped off by a cleaning member such as a blade or a roller of a cleaner to remove residual toner and other contaminants after transfer. The surface is cleaned and repeatedly used for image formation.

Further, such a cleaning step can be performed simultaneously in a charging step, a developing step, or a transfer step relating to electrophotography.

Examples of the surface material of the latent image carrier used in the present invention include silicone resin, vinylidene chloride, ethylene-vinyl chloride, styrene-acrylonitrile, styrene-methyl methacrylate, styrene, polyethylene terephthalate, and polycarbonate. There is no limitation, and other monomers or copolymerization or blending between exemplified resins can be used.

The present invention is particularly effective for an image forming apparatus in which the diameter of the latent image carrier is less than 30 mm. This is because, in the case of a small-diameter drum, even if the linear pressure is the same, the curvature is large, and the pressure is likely to be concentrated at the contact portion.

It is considered that the same phenomenon occurs in the belt photoreceptor, and the present invention is also effective for an image forming apparatus having a radius of curvature of 25 mm or less at the transfer portion.

Next, a developer applicable to the developing step and the cleaning step in the image forming method of the present invention will be described.

The developer of the present invention has at least a binder resin and a magnetic substance, and is contained in an amount of 0.2 to 5% by weight based on the amount of the magnetic substance.
The inorganic fine particles are fixed on the surface of the magnetic material in the range of weight%, and the specific surface area (A) [m ² /
g], the amount of increase in specific surface area (B) [m ² / g] after the fixing treatment of the inorganic fine particles on the surface of the magnetic material, the amount of the inorganic fine particles added to the magnetic material (C) [% by weight], and The specific surface area (D) [m ² / g] of the inorganic fine particles is determined by the following formula (1), formula (2) and formula (3): formula (1) 0.1 ≦ B / A ≦ 0.8 formula (2) B <30 × C Formula (3) It is preferable that the range of 0.4 ≦ B / (0.01 × C × D) ≦ 2.5 is satisfied.

The developer of the present invention, having the above-described structure, can adhere to the surface of the charging member or the surface of the photosensitive drum even if a small amount of the residual developer remains on the photosensitive drum after the cleaning step. Is extremely unlikely to occur, and the contamination itself is reduced, so that the life of the charging member itself can be prolonged, and the frequency of replacement can be reduced.

The reason why the developer according to the present invention exhibits the above-mentioned effects is not clear, but is presumed as follows.

When the developer of the present invention is used repeatedly, the magnetic material contained therein is exposed to the surface of the developer by fixing inorganic fine particles to the surface by mechanical treatment and adjusting the physical properties to the above-mentioned range. The presence of the inorganic fine particles on the magnetic material provides a polishing effect and has an effect of preventing the developer from sticking to the photoreceptor.

On the other hand, under environmental conditions such as high temperature and high humidity, the chargeability is impaired by moisture adhering to the surface of the developer, and the image density is easily lowered and the image quality is easily deteriorated. Therefore, preferably, in the developer of the present invention, the occurrence of the above-described problems can be prevented by subjecting the inorganic fine particles added to the magnetic material to a hydrophobic treatment to improve the chargeability under high temperature and high humidity. .

Further, the surface treatment agent improves the releasability from the photoreceptor, and has the effect of suppressing the occurrence of voids.

The inorganic fine particles are added to the magnetic material in the range of 0.2 to 5% by weight, and fixed to the magnetic material by mechanical treatment. If the addition amount of the inorganic fine particles is less than 0.2% by weight, the polishing effect cannot be obtained, and if it exceeds 5% by weight, it becomes difficult to completely fix the inorganic fine particles, and the fixing property is deteriorated by the released inorganic fine particles, Developability also deteriorates.

Further, the specific surface area (A) [m ² / g] of the magnetic material before the inorganic fine particles are attached, and the specific surface area increase (B) [m ² / g] after the inorganic fine particles are fixed on the surface of the magnetic material. It is important that is in the range of the equation below.

0.1 ≦ B / A ≦ 0.8 Equation (1) It is preferable that the value be 0.3 to 0.6.

When the value is less than 0.1, the effect of adding the inorganic fine particles cannot be obtained, and when it exceeds 0.8, the fixing property is affected. Further, problems such as a decrease in image quality and a failure to obtain a sufficient density are likely to occur not only in a situation where the charge amount tends to decrease such as under high temperature and high humidity, but also in a normal environment. Similarly, the amount of increase in specific surface area (B) [m ² / g] and the amount of inorganic fine particles added (C) [% by weight] must be within the range of the following formula.

B <30 × C Formula (2) Preferably, B <20 × C, and more preferably, B <15 × C.

(B) exceeds the range of the formula (2) when very fine inorganic fine particles are used, or when the magnetic substance or the inorganic fine particles are crushed and pulverized by extreme mechanical pressure. However, in the former case, aggregation between the inorganic fine particles is so severe that it is difficult to uniformly disperse and fix the particles on the magnetic material, and it is difficult to obtain a uniform magnetic material. In the latter case, a large number of crushed materials are mixed, and this is a factor that largely alienates the fixing property and the developing characteristics.

Further, the amount of inorganic fine particles added to the magnetic material (C) [% by weight] and the specific surface area (D) [m
² / g] and (B) are within the range of the following formula.

0.4 ≦ B / (0.01 × C × D) ≦ 2.5 Formula (3) Preferably, it is 0.6 to 1.8.

When the value of B / (0.01 × C × D) is less than 0.4, the strength of the mechanical treatment is weak, and the inorganic fine particles do not adhere to the surface of the magnetic material and are released. It is assumed that the mechanical treatment is too strong and that the inorganic fine particles are buried in the surface of the magnetic material. When a magnetic material in such a state is used for a developer, it is difficult to obtain the intended performance.

When the value of B / (0.01 × C × D) exceeds 2.5, the inorganic fine particles or the magnetic material is crushed by an extreme mechanical pressure to be pulverized. As described above, this is a factor that causes a problem.

By satisfying the above conditions, it is possible to obtain a magnetic developer in which inorganic fine particles are firmly fixed on the surface of a magnetic material without generating free inorganic fine particles, and the inorganic fine particles fall off when used repeatedly. Without causing
The object of the present invention can be achieved.

From the above, the developer according to the present invention is:
Matching with the charging step according to the present invention is extremely good, and it is possible to provide an image forming method that makes full use of the ability of the charging step according to the present invention and always performs good image formation. It is possible to contribute ecologically by reducing.

The magnetic material to be combined with the inorganic fine particles of the present invention includes a metal composed of ferromagnetic elements such as ferrite and magnetite, iron, cobalt and nickel, or an alloy or compound containing the same, or a strong magnetic material. An alloy that does not contain an element, but becomes ferromagnetic by appropriate heat treatment or the like, for example, a type called a Heusler alloy containing manganese and copper such as manganese-copper-aluminum or manganese-copper-tin. Alloy, or chromium dioxide, and the like. Further, the shape of the magnetic material is not particularly limited, and a magnetic material having any shape such as a sphere, an octahedron, and a hexahedron can be used. The content ratio of the fine powder of these magnetic substances can be 30 to 150 parts by weight, preferably 40 to 120 parts by weight, based on 100 parts by weight of the binder resin. Further, the magnetic fine particles can also be used as a black or brown pigment.

The inorganic fine particles to be added to the magnetic material in the present invention include, for example, silica fine powder, titania fine powder, alumina fine powder, zirconium oxide fine powder, magnesium oxide fine powder, zinc oxide fine powder, cerium oxide fine powder and the like. But not limited thereto, such as inorganic oxides, boron nitride fine powder, aluminum nitride fine powder, carbon nitride fine powder and the like.

The surface treating agent to be applied to these inorganic fine particles includes:
Oil treatment and various coupling agents can be used.

Examples of the oil treatment include treatment with dimethyl silicone oil, methyl hydrogen silicone oil, alkyl-modified silicone oil, α-methylstyrene-modified silicone oil, chlorophenyl silicone oil, fluorine-modified silicone oil, and the like. As the coupling agent treatment, for example, dimethyldichlorosilane, trimethylchlorosilane, allyldimethylchlorosilane, hexamethyldisilazane, allylphenyldichlorosilane, benzyldimethylchlorosilane, vinyltrimethoxysilane, γ-methacryloxypropyltrisilane Examples of the treatment include methoxysilane, vinyltriacetoxysilane, divinylchlorosilane, and dimethylvinylchlorosilane. However, the treatment is not particularly limited.

The method of surface treatment is not particularly limited, and a known method is used. For example, as a method of oil treatment, inorganic fine particles and oil may be directly mixed using a mixer such as a Henschel mixer, or a method of spraying oil onto the inorganic fine particles may be used. Alternatively, the varnish may be formed by mixing with inorganic fine particles and then removing the solvent.

Similarly, as a method of treating with a coupling agent, for example, a dry treatment in which a vaporized silane coupling agent is reacted with a cloud of inorganic fine particles by stirring or the like, or a silane coupling in which inorganic fine particles are dispersed in a solvent. The treatment can be performed by a generally known method such as a wet method in which an agent is dropped.

The method for fixing the inorganic fine particles on the surface of the magnetic material of the present invention by mechanical treatment is not particularly limited as long as the physical properties described in the claims are satisfied. That is, methods such as a ball mill, a roll mill, a batch kneader, a Nauta mixer, and a mix muller are used.

The binder resin in the developer according to the present invention is:
Those obtained by polymerizing one or more kinds of monomers selected from styrenes, acrylic acids, methacrylic acids and derivatives thereof are preferable from the viewpoint of developing characteristics and charging characteristics. Examples of monomers that can be used include styrenes such as styrene, α-methylstyrene, vinyltoluene, and chlorostyrene. Acrylic acids, methacrylic acids and derivatives thereof include acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, n-tetradecyl acrylate, and n-acrylate
Acrylates such as hexadecyl, lauryl acrylate, cyclohexyl acrylate, diethylaminoethyl acrylate, dimethylaminoethyl acrylate, and the like. Similarly, methacrylic acid, methyl methacrylate ク リ ethyl methacrylate, propyl methacrylate, methacrylic acid. Butyl, amyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, decyl methacrylate, dodecyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, phenyl methacrylate, 2-hydroxyethyl methacrylate, 2 methacrylate 2 Methacrylates such as hydroxypropyl, dimethylaminoethyl methacrylate, glycidyl methacrylate, and stearyl methacrylate; In addition to the above-mentioned monomers, a small amount of other monomers as long as the object of the present invention can be achieved, such as acrylonitrile, 2-vinylpyridine, 4-vinylpyridine, vinylcarbazole, vinylmethylether, butadiene, isoprene, maleic anhydride, Maleic acid, maleic acid monoesters, maleic acid diesters, vinyl acetate and the like may be used.

As the crosslinking agent used in the binder resin according to the present invention, divinyl benzene,
Bis (4-acryloxypolyethoxyphenyl) propane, ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexane Diol diacrylate, neopentyl glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate,
Polyethylene glycol # 200, # 400, # 600
Diacrylate, dipropylene glycol diacrylate, polypropylene glycol diacrylate, polyester type diacrylate (MANDA Nippon Kayaku),
And those obtained by replacing the above acrylates with methacrylates.

As polyfunctional crosslinking agents, pentaerythritol triacrylate, trimethylolethane triacrylate, trimethylolpropane triacrylate, tetramethylolmethanetetraacrylate, oligoester acrylate and its methacrylate, 2,2-bis (4-methacryloxy, Polyethoxyphenyl) propane, diallyl phthalate, triallyl cyanurate,
Triallyl asocyanurate, triallyl isocyanurate, triallyl trimellitate, diarylchlorendate and the like.

In the developer using the resin according to the present invention, besides the above-mentioned binder resin component, the content of the binder resin component is smaller than the content of the binder resin component within the range not adversely affecting the effect of the present invention. May be contained.

For example, silicone resin, polyester,
Polyurethane, polyamide, epoxy resin, polyvinyl butyral, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin such as low molecular weight polyethylene or low molecular weight polypropylene, aromatic petroleum resin, chlorinated paraffin, For example, paraffin wax.

As the colorant contained in the developer according to the present invention, generally known dyes and pigments can be used.
Examples of such dyes and pigments include, for example, carbon black, nigrosine dye, lamp black, Sudan black S
M, First Yellow G, Benzidine Yellow, Pigment Yellow, India First Orange, Irgazine Red, Paranitroaniline Red, Toluidine Red, Carmin FB, Permanent Bordeaux F
RR, Pigment Orange R, Risor Red 2
G, rake red C, rhodamine FB, rhodamine B
Lake, methyl violet B lake, phthalocyanine blue, pigment blue, brilliant green B, phthalocyanine green, oil yellow GG, Zapon First Yellow CGG, Kayaset Y963,
Kayaset YG, Sumiplast Yellow GG, Zapon Fast Orange RR, Oil Scarlet, Sumiplast Orange G, Orazol Brown B, Zapon First Scarlet CG, Aizen Spiron Red BEH, Oil Pink OP, etc. can be applied. These colorants are generally used to obtain a capsule toner for a two-component developer, and are used in an amount of 5 to 20 with respect to the core material binder.
It is preferred to add it in a proportion of weight%.

As the charge control agent contained in the developer according to the present invention, a conventionally known charge control agent is selected. As specific examples of the positive charge control agent, generally, nigrosine, carbon number 2
Azine dyes containing up to 16 alkyl groups (Japanese Patent Publication No.
No. 1627), basic dyes (for example, CI Bas)
ic Yellow 2 (CI.41000), C.I.
I. Basic Yellow 3, C.I. I. Basi
c Red 1 (CI. 45160), C.I. I. Ba
sic Red 9 (CI. 42500), C.I. I.
Basic Violet 1 (CI. 4253)
5), C.I. I. Basic Violet 3 (C.I.
I. 42555), C.I. I. Basic Violet
10 (CI. 45170), C.I. I. Basic
Violet 14 (CI. 42510), C.I. I. B
asic Blue 1 (CI. 42025), C.I.
I. Basic Blue 3 (CI. 5100)
5), C.I. I. Basic Blue 5 (CI.4
2140), C.I. I. BasicBlue 7 (C.I.
I. 42595), C.I. I. Basic Blue 9
(CI. 52015), C.I. I. Basic Blu
e24 (CI. 52030), C.I. I. Basic
Blue 25 (CI.52025), C.I. I. B
asic Blue 26 (CI.44025),
C. I. Basic Green 1 (CI. 420)
40), C.I. I. Basic Green 4 (C.I.
I. Lake pigments of these basic dyes (for example, phosphotungstic acid, phosphomolybdic acid, phosphomolybdic acid, tannic acid, lauric acid, gallic acid, ferricyanide, ferrocyanide, etc.). , C.I. I. Sovent Black
3 (C.I. 26150), Hansa Yellow G (C.I.
I. 11680), C.I. I. Moldrant Bla
ck11, C.I. I. Pigment Black 1
etc.

Further, for example, polyamide resins such as quaternary ammonium salts such as benzolmethyl-hexadecyl ammonium chloride and decyl-trimethyl ammonium chloride, vinyl polymers containing an amino group, and condensation polymers containing an amino group can be used. ,
Preferred are nigrosine, quaternary ammonium salts, triphenylmethane-based nitrogen-containing compounds, polyamides and the like.

Specific examples of the negative charge control agent include the monoazo dyes described in JP-B-41-20153, JP-A-42-27596, JP-A-44-6397, and JP-A-45-26478. Metal complexes, furthermore, nitroamine acids and salts thereof described in JP-A-50-133338 or C.I. I. Dyes and pigments such as 14645, JP-B-55-42752, JP-B-58
No. 41508, JP-B-58-7384, JP-B-59-7385 and the like, Zn, Al, C of salicylic acid, naphthoic acid and dicarboxylic acid
Metal complexes such as o, Cr, Fe, etc., sulfonated copper phthalocyanine pigments, nitro groups, styrene oligomers into which halogens are introduced, and chlorinated paraffins can be exemplified. In particular, from the viewpoint of dispersibility, a metal complex salt of a monoazo dye, and a metal complex of salicylic acid, alkyl salicylic acid, naphthoic acid, and dicarboxylic acid are preferable. The addition amount of these charge control agents minimizes adverse effects such as a reduction in developing power and a decrease in environmental stability due to contamination of the developing sleeve surface by the charge control agents while maintaining good triboelectricity as described above. For 100 parts by weight of the binder resin.
An addition amount of 1 to 3 parts by weight is preferred.

In the developer according to the present invention, an ethylene olefin polymer may be used together with a binder resin as a fixing aid.

Here, those applied as an ethylene-based olefin homopolymer or ethylene-based olefin copolymer include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and ethylene-ethyl acrylate copolymer. There is an ionomer having a polyethylene skeleton, or the like, and the above copolymer preferably contains 50 mol% or more (more preferably, 60 mol% or more) of an olefin monomer.

Next, an electrophotographic method using a developer using the resin according to the present invention will be described.

The step of developing the electric latent image using a developer includes the above-described magnetic brush method, cascade developing method, powder cloud method, and the conductive method described in US Pat. No. 3,909,258. JP-A-53-53.
There is a method using a high-resistance magnetic developer described in JP-A-31136. The toner using the resin according to the present invention is also suitable for a developing method using a so-called one-component developer containing magnetic particles. In the process of transferring the developed image to the transfer-receiving member, an electrostatic transfer method such as a corona transfer method or a method of applying a bias to the contact transfer member is used.

In recent years, methods such as charging and / or transfer and / or charge elimination using corona discharge from a member not in contact with the photoreceptor onto the photoreceptor involve generation of ozone. A method of applying a bias directly through a contact member has attracted attention. With the shift to such a method according to the image forming method of the present invention, a conventional copying machine
There is a possibility that the activated carbon filter often attached to the printer may be removed. In such a case, the developer of the present invention has a remarkable effect.

Further, in the developer using the binder resin according to the present invention, a blade cleaning method, a fur brush cleaning method, or the like is applied to the step of removing the residual toner on the photosensitive layer or the insulating layer. Particularly, it is suitable for a blade cleaning method.

The specific surface area of the magnetic material of the present invention (after the inorganic fine particles were adhered) was determined by a BET method using a specific surface area measuring apparatus Autosorb 1 (manufactured by Yuasa Ionics) by nitrogen adsorption. The specific surface area (A) of the magnetic material before the inorganic fine particles were attached was calculated by the following equation. Further, the amount of increase (B) in the specific surface area due to the adhesion treatment of the inorganic fine particles was determined from these differences.

A = 6 / (ρ × d ₁ ) × E A: Specific surface area (g /
m ² ) ρ: Density of the magnetic material (= 5.2) d ₁ : Number average particle size (μm) of the magnetic material after the inorganic fine particle adhesion treatment (photograph of the magnetic material by TEM, Here, the coefficient E is represented by the following value based on the value of the sphericity ψ of the magnetic material.

When と き ≧ 0.8 1.35 When ψ <0.8 1.70 The sphericity in the present invention is calculated by the following equation.

[0089]

(Equation 1) The sphericity ψ is obtained by arbitrarily selecting 100 magnetic particles from a TEM photograph, measuring the maximum length and the minimum length, and then averaging the calculated values.

[0090]

The basic structure and features of the present invention have been described above. The method of the present invention will be specifically described below with reference to examples. However, these do not limit the embodiments of the present invention at all. still,
Parts in the examples are parts by weight.

<Production Example of Magnetic Material> (Magnetic Material 1) BET surface-treated on commercially available spherical magnetite (φ = 0.92) having a BET specific surface area of 6.6 m ² / g.
0.8% by weight of silica fine powder having a specific surface area of 280 m ² / g was mixed by a mix muller and fixed on the surface of magnetite to produce a magnetic substance 1. Table 1 shows the physical properties and the like of the obtained magnetic body 1.

30 g of this magnetic material 1 was placed in an Erlenmeyer flask, 200 cc of methanol was added, and the mixture was thoroughly stirred.
Then, the cleaning liquid was discarded while preventing the magnetic substance 1 from flowing out using a magnet. Thereafter, 200 cc of methanol was added again, and the mixture was stirred well, and the washing liquid was discarded in the same manner as the previous time. After repeating this again, the magnetic material 1
Was dried and the amount of silica on the surface was quantified by fluorescent X-ray measurement. As a result, 95% or more of the silica was detected as compared to before the washing, and it was confirmed that the silica was fixed on the magnetite surface.

(Magnetic substance 2) BET specific surface area 5.0 m ² /
g of commercially available spherical magnetite (φ = 0.90) and 0.8% by weight of a silica fine powder having a BET specific surface area of 170 m ² / g added thereto in the same manner as in the case of the magnetic body 1 except that Generated. Table 1 shows the physical properties and the like of the obtained magnetic body 2.

The magnetic material 2 was washed in the same manner as the magnetic material 1 and the silica was quantified. As a result, 95% or more of the silica before washing was detected, and it was confirmed that the silica was fixed on the magnetite surface. Was done.

(Magnetic Material 3) A 2.0% by weight alumina fine powder having a surface-treated BET specific surface area of 90 m ² / g was added, and a magnetic material was prepared in the same manner as the magnetic material 1 except that a ball mill was used in the mixing device. 3 was generated. Table 1 shows the physical properties and the like of the obtained magnetic body 3.

The magnetic material 3 was washed in the same manner as the magnetic material 1 and the amount of alumina was determined. As a result, 95% or more of the alumina before washing was detected, and it was confirmed that the alumina was fixed on the magnetite surface. Was done.

(Magnetic Material 4) A magnetic material 4 was produced in the same manner as the magnetic material 1 except that 0.8% by weight of a silica fine powder having a BET specific surface area of 380 m ² / g, which had not been subjected to surface treatment, was added. Table 1 shows the physical properties and the like of the obtained magnetic body 4.

The magnetic material 4 was washed with water in the same manner as the magnetic material 1 and the silica was quantified. As a result, 95% or more of the silica before washing was detected, and the silica was fixed on the magnetite surface. Was confirmed.

(Comparative magnetic body 1) BE used in magnetic body 1
A commercially available spherical magnetite (φ = 0.92) having a T specific surface area of 6.6 m ² / g was used as Comparative Magnetic Material 1. Table 1 shows the physical properties and the like of the comparative magnetic body 1.

(Comparative Magnetic Material 2) A comparative magnetic material 2 was produced in the same manner as the magnetic material 1 except that the amount of the surface-treated silica fine powder having a BET specific surface area of 80 m ² / g was changed to 0.6% by weight. . Table 1 shows the physical properties and the like of the obtained comparative magnetic body 2.

(Comparative Magnetic Material 3) A comparative magnetic material 3 was manufactured in the same manner as the magnetic material 4 except that the mixture was very weakly mixed using a Henschel mixer. Table 1 shows the physical properties and the like of the obtained comparative magnetic body 3.

The ratio B / (0.01 × C × D) of the increase in the BET specific surface area and the theoretical increase in the BET specific surface area due to the silica fine powder adhering treatment is as low as 0.20 for the comparative magnetic substance 3. It was found that the amount of silica present on the magnetite surface was very small relative to the amount of silica charged, and the silica was not fixed on the magnetite surface but was released.

Further, in the same manner as in Example 1, the comparative magnetic material 3 was washed and the amount of silica was determined. Only 60% of the amount of silica after washing was detected relative to the amount of silica before washing, and the release of silica was confirmed by washing. This result also confirmed that silica was not fixed to the magnetite surface as described above.

(Comparative Magnetic Material 4) The comparative magnetic material was prepared in the same manner as the magnetic material 1 except that the addition amount of the silica fine powder used in the comparative magnetic material 2 was 2.0% by weight and the mixture was very strongly mixed using a ball mill. Body 4 was produced. Table 1 shows the physical properties and the like of the obtained comparative magnetic body 4.

The ratio B / (0.01 × C × D) of the increase in the BET specific surface area and the theoretical increase in the BET specific surface area due to the silica fine powder adhesion treatment of the comparative magnetic substance 4 was as high as 3.44, It was found that the magnetite or silica fine powder was crushed to produce fine powder.

[0106]

[Table 1]

Example 1 Styrene-butyl acrylate-divinylbenzene copolymer 100 parts (copolymerization ratio 80 / 19.5 / 0.5, weight average molecular weight 320,000) Magnetic substance 1 100 parts Low molecular weight polypropylene 4 parts Chromium complex of monoazo dye 2 parts The above mixture was melt-kneaded in a twin-screw kneading extruder heated to 140 ° C, the cooled kneaded material was coarsely pulverized by a hammer mill, and the coarsely pulverized product was finely pulverized by a jet mill. The obtained finely pulverized product was classified and removed with a multi-segment classifier to obtain a magnetic toner having a weight average particle size of 6.8 μm. 1.0% by weight of hydrophobic silica was externally added to and mixed with the magnetic toner to obtain a developer.

Next, the photosensitive drum and the charging roller are: the outer diameter of the photosensitive drum: 24 mmφ the outer diameter of the charging roller: 12 mmφ The hardness of the charging roller: 54.5 ° (ASKER-C) Conductive rubber layer: carbon black Dispersed polyether urethane layer having a thickness of 3 mm Surface layer: In the contact charging device shown in FIG. 1 having a polyester layer having Ra of 0.9 μm (thickness of about 5 μm), the contact pressure on the photoreceptor is 60 g / cm. , The voltage applied to the charging member is DC-3
Using an image forming apparatus (Canon LBP-A404) with 45 V, AC 1700 Vpp, and frequency 150 Hz,
With the above-mentioned developer, a real image test for forming an image by the reversal development method continuously 5000 times at a print speed of 4 sheets (A4) / min was conducted at normal temperature and normal humidity (25 ° C., 60% RH), and high temperature and high humidity (30 ° C.). ℃, 90% RH) and low temperature and low humidity (15 ℃, 1
0% RH), the printout image was evaluated, and at the same time, the state of the charging member and the surface of the photoreceptor were observed.

As a result, there was no adhesion of the residual developer on the charging member and the surface of the photosensitive drum in any of the environments. Further, the obtained image was good.

Then, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was further continued. As a result, even after the actual photographing of 20,000 sheets, the developer was not fixed on the surface of the charging member and severe stains were not observed. Was.

Example 2 The same as Example 1 except that the contact charging member was a blade type (see FIG. 2) having a Ra of 1.5 μm and a surface layer (thickness of 10 μm) made of polyester resin. In each environment, a continuous shooting test of 3000 sheets was performed under each environment.

As a result, no residual developer was fixed on the charging member and the surface of the photosensitive drum in any of the environments. Further, the obtained image was good.

Further, in the same manner as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued.
Even after the actual photographing of 50,000 sheets, there was no particular abnormality on the surface of the charging member.

Example 3 A developer was obtained in the same manner as in Example 1 except that the magnetic material 2 was used.

Next, this developer was used in the same image forming apparatus as in Example 1, and was continuously used in each environment in the same manner as in Example 1.
A real-image test of 000 sheets was performed.

As a result, there was no fixation of the residual developer on the charging member and the surface of the photoreceptor in any of the respective environments. Further, the obtained image was good.

Further, in the same manner as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued. After the actual photographing of 20,000 sheets, there was no particular abnormality on the surface of the charging member.

Example 4 A developer was obtained in the same manner as in Example 1 except that the magnetic material 3 was used.

Next, this developer was used in the same image forming apparatus as in Example 1, and was continuously used in each environment in the same manner as in Example 1.
A real-image test of 000 sheets was performed.

As a result, no residual developer was fixed on the charging member and the surface of the photoreceptor in any of the environments. Further, the obtained image was good although the image density was slightly low under a high temperature and high humidity environment.

Further, as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued.
No abnormalities were found on the surface of the charging member even after the actual printing of 50,000 sheets.

Example 5 A developer was obtained in the same manner as in Example 1 except that the magnetic material 4 was used.

Next, this developer was used in the same manner as in Example 1 except that the same image forming apparatus as in Example 1 was replaced with a transfer roller having an electric resistance of 10 ¹⁰ Ωcm or less when a direct current of 100 V was applied. In each environment, a continuous shooting test of 3000 sheets was performed.

As a result, no residual developer was fixed on the charging member and the surface of the photosensitive member in any of the environments. In addition, the obtained image gradually decreased in image density under a high-temperature and high-humidity environment, and was slightly fogged under a low-temperature and low-humidity environment.

Further, as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued.
No abnormalities were found on the surface of the charging member even after the actual copying of 20,000 sheets.

Comparative Example 1 A developer was obtained in the same manner as in Example 1 except that Comparative Magnetic Material 1 was used.

Next, this developer was used in the same image forming apparatus as in Example 1, and was continuously used in each environment in the same manner as in Example 1.
A real-image test of 000 sheets was performed.

As a result, a point-like residual developer was found to adhere to the surface of the photoreceptor and the surface of the charging roller in a high-temperature, high-humidity environment. Further, in the obtained image, spot-like white spots, so-called white spots, occurred.

Further, in the same manner as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued. However, the white spots on the image gradually deteriorated, and the charging roller was replaced at 6,000 sheets. I had to help.

Further, the image density was slightly low in a low-temperature and low-humidity environment, and some fog occurred.

Comparative Example 2 Using the developer of Comparative Example 1 in the same image forming apparatus as in Example 2, a photographic test of 2,000 sheets was continuously conducted under each environment in the same manner as in Example 1.

As a result, streak-like residual developer was found to adhere to the surface of the photoreceptor and the surface of the charging blade under a high temperature and high humidity environment. Further, the obtained image had a density difference in image density in addition to a partial white spot phenomenon, and lacked sharpness.

Further, in the same manner as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued. However, the image defect deteriorated, and the charging blade had to be replaced at the time of 5000 sheets. No longer.

Comparative Example 3 A developer was obtained in the same manner as in Example 1 except that Comparative Magnetic Material 2 was used.

Next, Ra of the surface of the developer was set to 3.1 μm.
Using the same image forming apparatus as in Example 1 except that m was used, a continuous shooting test of 2,000 sheets was continuously performed under each environment in the same manner as in Example 1.

As a result, many spot-like residual developers were found to adhere to the surface of the photoreceptor and the surface of the charging roller under a high temperature and high humidity environment. In addition, many white spots occurred in the obtained image. Further, the image density had a difference in shading, and lacked sharpness.

Further, in the same manner as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued. However, the image defect became worse, and the charging roller had to be replaced at 4000 sheets. No longer.

Comparative Example 4 A developer was obtained in the same manner as in Example 1 except that Comparative Magnetic Material 3 was used.

Next, this developer was used in the same image forming apparatus as in Example 1, and was continuously used in each environment in the same manner as in Example 1.
A real-image test of 000 sheets was performed.

As a result, many spot-like residual developers were found to adhere to the surface of the photoreceptor and the surface of the charging roller under a high-temperature and high-humidity environment. In addition, many white spots occurred in the obtained image, and the image density gradually decreased.

Further, in the same manner as in Example 1, the developer was replenished, the photosensitive member was replaced, and the actual photographing test was continued. However, the white spots on the image deteriorated. I had to do it.

Further, the image density was slightly low even under a low-temperature and low-humidity environment, and fog occurred.

Comparative Example 5 A developer was obtained in the same manner as in Example 1 except that Comparative Magnetic Material 4 was used.

Next, this developer was used in the same image forming apparatus as in Example 1, and was continuously used in each environment in the same manner as in Example 1.
A real-image test of 000 sheets was performed.

As a result, the image density was low under each environment and was not suitable for practical use.

[0146]

As described above, according to the present invention, a good contact state between the charging member and the member to be charged (photosensitive member) can be sufficiently maintained, and the developer can be applied to the charging member and the member to be charged. By improving the fixing property, it is possible to prevent poor charging due to contamination of the developer on the charging member and the surface of the member to be charged, thereby always forming a good image.

Further, by reducing the contamination of the charging member, the service life can be prolonged, and it is possible to contribute to the reduction of waste by prolonging the replacement cycle.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of a contact charging device for performing a contact charging step according to the present invention.

FIG. 2 is a schematic configuration diagram showing another embodiment of a contact charging device for performing a contact charging step according to the present invention.

FIG. 3 is an explanatory diagram of a method for measuring the resistance of the charging device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Latent image carrier (photosensitive drum) 2, 2 'Charging member 4 Electrode (50-micrometer aluminum sheet) 5 DC power supply 6 DC ammeter

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shunji Suzuki 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Akihiko Nakazawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-6-130718 (JP, A) JP-A-60-26350 (JP, A) JP-A-58-91463 (JP, A) JP-A-2-73367 (JP, A) A) JP-A-61-53660 (JP, A) JP-A-4-274455 (JP, A) JP-A-4-155361 (JP, A) JP-A-2-306274 (JP, A) JP-A-2 -271366 (JP, A) Patent 2986139 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/08

Claims (2)

(57) [Claims] 1. A charging member containing at least a polyester resin and having a surface layer having a center line average roughness (Ra) of 0.3 to 2.5 μm is brought into contact with a member to be charged, and a voltage is externally applied to the charging member. Is applied to the member to be charged, and a cleaning step of removing the developer from the member to be charged is a developer used in an image forming method, comprising at least a binder resin and a magnetic material. Then, inorganic fine particles are fixed to the surface of the magnetic material in the range of 0.2% by weight to 5% by weight based on the amount of the magnetic material, and the specific surface area (A) of the magnetic material before the inorganic fine particles are adhered [m ² / g ], The amount of increase in specific surface area (B) [m ² /
g], the amount of inorganic fine particles added to the magnetic material (C) [% by weight], and the specific surface area of inorganic fine particles (D) [m ² / g]
Is a range of the following formulas (1), (2) and (3). Equation (1) 0.1 ≦ B / A ≦ 0.8 Equation (2) B <30 × C Equation (3) 0.4 ≦ B / (0.01 × C × D) ≦ 2.5 2. A charging member containing at least a polyester resin and having a surface layer having a center line average roughness (Ra) of 0.3 to 2.5 μm is brought into contact with a member to be charged, and a voltage is externally applied to the charging member. And a cleaning step of removing the developer from the charged body, wherein at least a binder resin and a magnetic body are provided, and the amount of the magnetic body is increased. The inorganic fine particles are fixed to the surface of the magnetic material in the range of 0.2% by weight to 5% by weight, and the specific surface area (A) [m ² / g ] of the magnetic material before the inorganic fine particles are adhered to the surface of the magnetic material. the increase in the specific surface area after the fixing process is performed in the inorganic fine particles (B) [m ² /
g], the amount of inorganic fine particles added to the magnetic material (C) [% by weight], and the specific surface area of inorganic fine particles (D) [m ² / g]
Wherein a developer having the following formulas (1), (2) and (3) is used. Equation (1) 0.1 ≦ B / A ≦ 0.8 Equation (2) B <30 × C Equation (3) 0.4 ≦ B / (0.01 × C × D) ≦ 2.5