JPH06123998A - Magnetic toner and electrophotographic method - Google Patents

Abstract

PURPOSE:To provide a magnetic toner and an electrophotographic method using this toner with a simple and small-size high performance mechanism which gives high picture image density without fog and shows stable developing characteristics. CONSTITUTION:After an electrostatic latent image is formed by using an electrostatic latent image holding drum 1 having a magnet 2 fixed to the inside of the drum, the drum is brought into contact with a magnetic toner 7 in a developer reservoir 6 to attract the toner to the surface of the electrostatic latent image holding body by magnetic force. Further, by passing an electrode roller 8 containing a magnet 9 on which AC voltage is applied, the toner remains only in the picture image area and then developed. The magnetic toner 7 consists of an external additive and a toner base material consisting of at least a binder resin and a magnetic material. The specific surface area Sbm<2>/g of the toner base material, specific surface area Sjm<2>/g of the external additive, proportion Wjwt.%, of the added external additive, and specific surface area of the toner Stm<2>/g satisfy the relation of 0.10XSjXWj<=-(St-Sb)<=0.60XsjXWj, and Wj is 0.3-2.0wt.%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner used in printers and facsimiles and an electrophotographic method.

[0002]

2. Description of the Related Art Conventionally, as electrophotographic methods, there are a cascade developing method, a touchdown developing method, a jumping developing method and the like. Among them, the cascade development shown in US Pat. No. 3,105,770 is known as a developing method in which a developer is directly sprinkled on an electrostatic latent image carrier. The cascade development method
This is the first developing method used in electrophotographic copying machines.
Further, there is US Pat.
In this invention, it is described that the alternating electric field applied to the developing roller is used for the purpose of activating the movement of the toner, and the toner flies to the image portion and returns to the non-image portion on the way. Further, as a modification of the technique of applying the alternating electric field, there is a jumping development disclosed in Japanese Patent Publication No. 63-42256. This jumping developing method is a method in which toner is carried on a toner carrier and carried to a developing unit, where the toner is attached to the image part of the electrostatic latent image carrier by an alternating electric field. The technical idea of Japanese Patent Publication No. 63-42256 differs from the above-mentioned US Pat. No. 3,866,574 in that the toner reciprocates in the image portion and the non-image portion.

In order to further miniaturize development and improve image quality, a fixed magnet is included in the electrostatic latent image holding member, and the magnet is provided at a position facing the electrostatic latent image holding member with a predetermined gap. A developing method has been proposed in which an electrode roller is used and an alternating electric field is applied to the gap, and it is possible to further improve the image quality, reduce the size, simplify the apparatus, and reduce the cost.

As is well known, the toner for electrostatic charge development used in these developing methods is generally a resin component, a coloring component composed of a pigment or a dye, and a plasticizer, an additive component such as a charge control agent, and an external additive. It is composed by.

However, as the tendency toward higher image quality of copied images has become more and more remarkable in recent years, the surface adhering state of the external additive, which is a main constituent component of the toner, is required to have higher functionality than ever.

[0006]

However, with the above-mentioned structure, as is well known in the art, the cascade developing method is not good at reproducing solid images. Further, there is a problem that the device becomes large and complicated. Further, the developing device of US Pat.
There is a drawback that the device requires high accuracy, is complicated, and is expensive. In the jumping development method, it was essential to form a very uniform thin layer on a toner carrier carrying a toner layer. Further, in this method, so-called sleeve ghost development occurs in which the history of the previous image remains in the thin toner layer on the toner carrier and an afterimage appears in the image. Further, there is a drawback that the device is complicated and the cost is high.

Further, in the developing method used in the present invention in which the development is made compact and high performance, a fixed magnet is included in the electrostatic latent image holding member, and a magnet is provided at a position facing the electrostatic latent image holding member with a predetermined gap. It is a developing method that consists of an electrode roller having an electric field and an alternating electric field applied to the gap between the electrode roller and the electrode roller, which enables further downsizing, simplification of the apparatus, and cost reduction. It includes a surface that must rely on high performance toner characteristics. Although it is considered that this phenomenon is peculiar to this developing method, the layer of toner is not regulated, and the toner does not become triboelectrically charged and jumps into the developing field where the electrostatic latent image holder and the electrode roller rotate. Therefore, the toner is charged in the gap between the electrostatic latent image carrier and the electrode roller while reciprocating by an alternating electric field, and the charged toner particles are used for development. In other words, whether or not the toner reciprocates and is quickly charged is the key to achieving high image quality. In the toner of the external additive form of the toner used in the conventional one-component developing method and the two-component developing method, the external additive on the toner surface is liberated, and the external additive liberated on the toner surface portion is static. It is contact-charged with the latent electrostatic image carrier or the electrode roller, but the adhesive force between the contact-charged external additive and the toner is weak, so the toner does not reciprocate in an alternating electric field, so the toner charging is not promoted. .

Therefore, as a means for promoting the reciprocating motion between the electrostatic latent image carrier and the electrode roller, a method of reducing the amount of the external additive added in order to reduce the liberated external additive is adopted. However, if the amount of the external additive such as silica is simply reduced, the toners agglomerate with each other and the toner cannot be conveyed, resulting in a decrease in the density or an increase in the adhesive force between the toner and the electrostatic latent image holding member. Ground fog is generated in the image area, which causes a deterioration in image quality. That is, simply reducing the amount of silica causes many adverse effects and cannot solve the problem.

In view of the above problems, the present invention is a developing method which can be further downsized, the apparatus can be simplified, and the cost can be reduced.
It is another object of the present invention to provide a magnetic toner and an electrophotographic method that achieve high image quality with low density and high density, are small in size, have a long life, and do not cause toner contamination in the apparatus.

[0010]

In order to solve the above problems, a magnetic toner and an electrophotographic method of the present invention are provided with an electrostatic latent image holder that moves by enclosing a fixed magnet, and the electrostatic latent image holder. A toner reservoir that faces the surface of the electrostatic latent image holding member and that magnetically attracts magnetic toner by the fixed magnet to supply magnetic toner, and a predetermined gap with the surface of the electrostatic latent image holding member at a position facing at least a part of the fixed magnet. A magnetic toner used in an electrophotographic method using a developing process in which an electrode roller having a magnet inside is installed at a position having a magnetic field and an alternating electric field is applied to the gap. The toner is composed of a toner base composed of at least a binder resin and a magnetic material and an external additive, and (1) the specific surface area of the toner base is S _b m ²
/ G, the specific surface area of the external additive is S _j m ² / g, the addition ratio of the external additive to the entire toner is W _j wt%, and the specific surface area of the toner is S _t m ² / g, the toner and the base are Difference in specific surface area S _t
-S _b is 0.10 x S _j x W _j ≤ S _t -S _b ≤ 0.60 x S _j
× W _j , and the proportion of the external additive in the whole toner is W _j of 0.3 to 2.0 wt%, and (2) the addition amount of the magnetic material is 20.0 with respect to the weight of the magnetic toner. The magnetic toner is characterized by being ˜60.0% by weight.

Further, according to the present invention, the electrostatic latent image holding member that moves by containing a fixed magnet, the magnetic toner, and the surface of the electrostatic latent image holding member are opposed to each other and magnetically attracted by the fixed magnet so that the magnetic A toner reservoir for supplying toner, and an electrode roller provided at a position facing at least a part of the fixed magnet and having a predetermined gap with the surface of the electrostatic latent image holding member and having a magnet inside. And (3) the magnetic toner is composed of at least a toner base and an external additive, and the toner base is small. Even if it is composed of a binder resin and a magnetic material, the specific surface area of the toner base is S _b m ² / g, the specific surface area of the external additive is S _j m ² / g, and the addition ratio of the external additive to the entire toner is _Is W _j wt% and the toner specific surface area is _St m ² / g, the difference S _t -S _b between the specific surface areas of the toner and the base is 0.10 × S _j × W _j ≤S _t -S _b ≤0.
60 × S _j × W _j , and the proportion of the external additive in the entire toner is W _j of 0.3 to 2.0% by weight. (4) The amount of the magnetic substance added is relative to the weight of the magnetic toner. 20.0-6
The electrophotographic method is characterized by using a magnetic toner of 0.0% by weight.

[0012]

According to the present invention, the electrostatic latent image holding member having the fixed magnet is used by the above structure, and the toner is sprinkled and magnetically adhered to the electrostatic latent image holding member on which the electrostatic latent image is formed. The electrostatic latent image carrier and the electrode roller are applied with an alternating electric field to reciprocate the toner for charging and development, and at the same time, the non-image area toner of the electrostatic latent image carrier is removed. Remove by electric power and magnetic force. That is, the present invention is a cascade development method in which a magnet is installed inside the electrostatic latent image holder and an alternating electric field is applied to the gap between the electrostatic latent image holder and the electrode to further reduce the size and improve the performance. The electrode roller portion circulates the toner in the toner retainer and at the same time collects the toner in the non-image portion of the electrostatic latent image. That is, it is the electrostatic latent image carrier that carries and carries the toner from the toner reservoir to the developing section. A bare surface of the electrode roller that does not carry the toner layer faces the electrostatic latent image holding member. The electrode roller and the electrostatic latent image carrier rotate in opposite directions.

The magnetic toner used in the electrophotographic method of the present invention is preferably an insulating one-component toner. If a one-component toner is used, the device structure can be simplified.

In the electrophotographic method of the present invention, the toner is once attached to the entire surface of the electrostatic latent image holder, and then the toner is reciprocated in the gap between the electrostatic latent image holder and the electrode roller by an alternating electric field. At the same time that the toner is charged, the toner in the non-image area is removed by electrostatic force and magnetic force by the electrode roller.

Therefore, in this method, the charging property due to the reciprocating motion of the toner in the electrostatic latent image carrier and the electrode roller in the alternating electric field greatly affects the image characteristics. In other words, if the reciprocating motion of the toner is not promoted, the electrostatic force will not be applied to the toner in the non-image area on the electrostatic latent image. It has been found that when the toner is adhered to the entire surface of the electrostatic latent image holding member in the image portion due to the background fog and the image is deteriorated, unevenness occurs in the solid image due to insufficient charging.

In order to realize high image quality, it is necessary in the present developing system to impart charge to the toner by reciprocating the toner by an alternating electric field in the gap between the electrostatic latent image carrier and the electrode roller. I understood it.

Therefore, the magnetic toner is composed of at least a toner matrix composed of a binder resin and a magnetic material and an external additive,
The specific surface area of the toner base is S _b m ² / g, the specific surface area of the external additive is S _j m ² / g, the addition ratio of the external additive to the entire toner is W _j wt%, and the toner specific surface area is _St. When m ² / g, the difference S _t −S _b between the specific surface areas of the toner and the base is 0.10 ×
It is preferable that S _j × W _j ≦ S _t −S _b ≦ 0.60 × S _j × W _j . More preferably _{0.15 × S j × W j ≦} S t over _{S b ≦ 0.55 × S j ×} W j.

If the difference S _t −S _b between the specific surface area of the toner and the base is larger than the exposure ratio of the external additive of 0.60 × S _j × W _j , the external additive on the surface of the toner is liberated. The external additive liberated on the surface portion is contact-charged with the electrostatic latent image carrier or the electrode roller, but the adhesive force between the contact-charged external additive and the toner is weak, so the toner reciprocates in an alternating electric field. Since it does not occur, the charging of the toner is not promoted. Therefore, the toner adhering to the non-image area is not subjected to an electrostatic force in the developing electric field, so that the toner in the non-image area cannot be removed to cause fog and deteriorate the image. It was also found that when the toner is attached, unevenness occurs in the solid image. If the difference S _t −S _b between the specific surface areas of the toner and the base is smaller than 0.10 × S _j × W _{j which is} the exposure ratio of the external additive, the distance between the base of the toner and the electrostatic latent image holder becomes short, and the molecule becomes small. Since the inter-force is large, the toner in the non-image area adheres strongly to the electrostatic latent image holder and cannot be removed by the electrostatic force generated by the electric field formation by the electrode roller for collection or the magnetic force generated by the magnet, and the image is deteriorated as a background fog. It was also found that when toner is attached to the entire surface of the electrostatic latent image holder, unevenness occurs in a solid image.

The addition amount of the external additive of the present invention is preferably 0.3 to 2.0% by weight based on the weight of the magnetic toner. It is more preferably 0.4 to 1.8% by weight.
When the addition amount of the external additive is 2.1% by weight or more, the external additive on the toner surface is released and adheres to the electrostatic latent image holding member, so-called filming occurs, and the electrostatic latent image is held during exposure. A development method that visualizes the exposed area without decreasing the body potential.In the so-called negative-positive reversal development method, white spots occur in the image area, and conversely, in the normal development method that visualizes the unexposed area, the non-image area It was found that the toner adhered to and black streaks occurred and the image quality was deteriorated. Further, the addition amount of the external additive is 0.
It has been found that when the content is 3% by weight or less, the toner particles agglomerate with each other, the fluidity of the toner is deteriorated, the conveyance failure occurs, and the image density is decreased.

At this time, the specific surface area value is measured by the usual BE.
The T measurement method is used. In the present invention, the model used is Shimadzu FlowSorb2-2300.

The external additive used in the magnetic toner of the present invention is preferably silica, alumina, or titania oxide fine particles.
More preferably, oxides of silica, alumina, titania, etc. are subjected to a hydrophobic treatment with a silane coupling agent, silicone oil, etc., and the hydrophobicity is preferably 50% or more.

A known method is used as a method for producing the magnetic toner of the present invention. That is, the binder resin and other internal additives are mixed and dispersed by heating and kneading. As the heating and kneading method at this time, a known heating and kneading machine can be used. As the heating and kneading machine, it is possible to use an apparatus for heating a kneaded material such as a three-roll type, a single-screw type, a twin-screw type, and a banbury mixer type and applying a shearing force to knead the mixture. In this experiment, PCM30 manufactured by Ikegai Tekko KK was used. The present invention is not limited to this. The lumps are roughly crushed with a cutter mill, etc., then crushed with a jet mill crusher, fine powder particles are cut with an airflow classifier, a desired particle size distribution is obtained, and oxides of silica, alumina, titania, etc. are made hydrophobic. The toner is obtained by externally treating the external additive.

If necessary, the magnetic toner according to the present invention may be mixed with an appropriate pigment or dye for the purpose of controlling coloring and charge. Such pigments or dyes include carbon black, iron black, graphite, nigrosine, metal complexes of azo dyes, phthalocyanine blue, cerco oil blue, DuPont oil red, aniline blue, benzidine yellow, rose bengal and mixtures thereof. , The amount of charge, and the amount required for coloring are blended.

Further, the magnetic toner according to the present invention may further contain a release agent if necessary. Further, other types of additives can be blended if necessary. Examples thereof include external additives such as titanium and alumina, and abrasives such as tin oxide and strontium titanate.

Further, the magnetic toner according to the present invention contains a magnetic substance. Magnetic powders include iron, manganese, nickel,
There are metal powder such as cobalt and ferrite such as iron, manganese, nickel, cobalt and zinc. The average particle size of the powder is preferably 1 μm or less, particularly preferably 0.6 μm or less. The addition amount of the magnetic substance is preferably 20.0 to 60.0% by weight. It is particularly preferably 25 to 55% by weight. When the amount of the magnetic substance added is 60.0% by weight or more, the ratio becomes higher than that of the binder resin, and cold offset occurs during fixing on paper. Further, when the addition amount of the magnetic substance is 20.0% by weight or less, the ability to collect the toner from the electrostatic latent image holding member is weakened, and fog occurs in the non-image portion.

[0026]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an example of a developing process in which the magnetic toner of the present invention is used. The developing method is a one-component method. Reference numeral 1 is an organic electrostatic latent image carrier drum in which phthalocyanine is dispersed in polyester binder resin, 2 is a magnet fixed coaxially with the electrostatic latent image carrier 1, and 3 is a negative electrostatic charge of the electrostatic latent image carrier. A corona charger, 4 is a grid electrode for controlling the charging potential of the electrostatic latent image holder, 5 is a signal light, 6 is a toner reservoir, 7 is a magnetic one-component toner, 8 is a gap between the electrostatic latent image holder 1 and The non-magnetic electrode roller set by opening the door, 9 is a magnet installed inside the electrode roller 8,
Is an AC high voltage power source for applying a voltage to the electrode roller 8, 11 is a scraper made of polyester film for scraping off the toner on the electrode roller, and 12 is a transfer corona charger for transferring the toner image on the electrostatic latent image carrier onto paper. Is. Reference numeral 13 is a damper for smoothing the flow of the toner in the toner reservoir and for preventing the toner from being crushed by its own weight and clogged between the electrostatic latent image holder and the electrode roller. The magnetic flux density on the surface of the electrostatic latent image holder 1 is 600 Gs. The magnetic force inside the electrode roller was strengthened to improve the transportability. Further, the magnetic pole angle θ of the magnet 2 shown in the figure was set to 15 degrees. The electrostatic latent image holder 1 had a diameter of 30 mm and was rotated at a peripheral speed of 60 mm / s in the direction of the arrow in the figure for use.
The electrode roller 8 had a diameter of 16 mm, and was used by rotating it at a peripheral speed of 40 mm / s in the direction opposite to the advancing direction of the electrostatic latent image carrier (the direction of the arrow in the figure). The gap between the electrostatic latent image holder 1 and the electrode roller 8 was set to 300 μm.

The electrostatic latent image carrier 1 is attached to the corona charger 3 (applied voltage −4.5 kV, grid 4 voltage −500 V).
It was charged to -500V. The electrostatic latent image holder 1 was irradiated with laser light 5 to form an electrostatic latent image. At this time, the exposure potential of the electrostatic latent image carrier was -90V. Toner 7 was attached to the surface of the electrostatic latent image holding member 1 by a magnet in the toner reservoir 6. Next, the electrostatic latent image holder 1 was passed in front of the electrode roller 8. When passing through the uncharged area of the electrostatic latent image holder 1, the electrode roller 8 is supplied with 0 V by the AC high voltage power source 10.
An alternating voltage (frequency 1 kHz) of 750 V0-p (peak-to-peak 1.5 kV) superposed with the DC voltage was applied. After that, when passing through the electrostatic latent image holder 1 charged with −500V and having the electrostatic latent image written therein, the electrode roller 8 is superposed with a DC voltage of −350V by the AC high voltage power source 750V0-p (peak).・ Two peak 1.5
An alternating voltage (frequency 1 kHz) of kV) was applied. Then, the toner adhering to the charged portion of the electrostatic latent image holder 1 was collected by the electrode roller 8, and a negative-positive inverted toner image remained only on the image portion on the electrostatic latent image holder 1. The toner attached to the electrode roller 8 rotating in the direction of the arrow is removed by the scraper 11
It was scraped off and returned to the toner reservoir 6 again and used for the next image formation. The toner image thus obtained on the electrostatic latent image carrier 1 is transferred onto a sheet of paper (not shown) by the transfer charger 12, and then thermally fixed by a fixing device (not shown) to obtain a copied image. To be

The material composition and manufacturing method of the magnetic toner will be described below. (Example 1) Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as a binder resin, magnetite 33.0% by weight as a magnetic substance, and Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent 1.0 % By weight and 3.0% by weight of a low molecular weight polypropylene (manufactured by Sanyo Kasei) as a release agent are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.).
The mixture is heated and kneaded in, and finely crushed with a jet mill crusher IDS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder is cut by an air stream classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.) to obtain a volume average particle A toner base having a diameter of 8.0 μm and a specific surface area of 1.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the toner base, 1.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix at 0B (Mitsui Miike Co., Ltd.) and 2 at 2800 rpm
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating screen to complete a toner having a specific surface area of 1.80 m ² / g. That is, the addition amount W _j by weight of the toner specific surface area S _t m ² / specific surface area of g and maternal S _b a specific surface area of m ² / difference g is 0.10 m ² / g with an external additive S _j m ² / g Product multiplied by% is 1.00 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
to obtain toner is _{t-S b = 0.10 × S j ×} W j.

A copy test was conducted on 10000 sheets by the electrophotographic method of the present invention, and the image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 2 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as a binder resin, magnetite 33.0% by weight as a magnetic substance, and a Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent. 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the above toner base, 0.3% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix at 0B (Mitsui Miike Co., Ltd.) and 2 at 2800 rpm
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating sieve to complete a toner having a specific surface area of 1.73 m ² / g. That is, the difference between the toner specific surface area S _t m ² / g and the specific surface area S _b m ² / g of the base is 0.03 m ² / g, and the specific surface area S _j m ² / g of the external additive and the added amount W _j weight The value multiplied by% is 0.30 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
to obtain toner is _{t-S b = 0.10 × S j ×} W j.

A copy test was conducted on 10000 sheets of the electrophotographic method of the present invention, and the image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 3 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as a binder resin, magnetite 33.0% by weight as a magnetic substance, and a Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent. 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of the toner will be described below.
To the above-mentioned toner base, 2.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix at 0B (Mitsui Miike Co., Ltd.) and 2 at 2800 rpm
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating screen to complete a toner having a specific surface area of 1.90 m ² / g. That is, the addition amount W _j by weight of the toner specific surface area S _t m ² / specific surface area of g and maternal S _b a specific surface area of m ² / difference g is 0.20 m ² / g with an external additive S _j m ² / g The value multiplied by% is 2.00 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
to obtain toner is _{t-S b = 0.10 × S j ×} W j.

The electrophotographic method of the present invention was used to perform a copy test on 10,000 sheets, and the image density was measured with a reflection densitometer (Macbeth Co.) for evaluation. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 4 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as a binder resin, magnetite 33.0% by weight as a magnetic substance, and a Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent. 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the toner base, 1.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and add 1 at 2800 rpm.
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating screen to complete a toner having a specific surface area of 1.94 m ² / g. That is, the addition amount W _j by weight of the toner specific surface area S _t m ² / specific surface area of g and maternal S _b a specific surface area of m ² / difference g is 0.24 m ² / g with an external additive S _j m ² / g Product multiplied by% is 1.00 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
_A toner having _t −S _b = 0.24 × S _j × W _j was obtained.

The electrophotographic method of the present invention was used to perform a copying test on 10,000 sheets, and the image density was measured by a reflection densitometer (Macbeth Co.) and evaluated. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 5 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as a binder resin, magnetite 33.0% by weight as a magnetic substance, and a Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent. 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the above toner base, 0.3% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and add 1 at 2800 rpm.
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating screen to complete a toner having a specific surface area of 1.79 m ² / g. That is, the addition amount W _j by weight of the toner specific surface area S _t m ² / specific surface area of g and maternal S _b a specific surface area of m ² / difference g is 0.09 m ² / g with an external additive S _j m ² / g The value multiplied by% is 0.30 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
to obtain toner is _{t-S b = 0.30 × S j ×} W j.

A copy test was conducted on 10000 sheets by the electrophotographic method of the present invention, and the image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 6 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as binder resin, magnetite 33.0% by weight as magnetic substance, Cr-containing azo dye as charge control agent (Hodogaya Chemical Co., Ltd.) 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the above-mentioned toner base, 2.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and add 1 at 2800 rpm.
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating screen to complete a toner having a specific surface area of 2.20 m ² / g. That is, the difference between the toner specific surface area S _t m ² / g and the specific surface area S _b m ² / g of the base is 0.50 m ² / g, and the specific surface area S _j m ² / g of the external additive and the addition amount W _j weight The value multiplied by% is 2.00 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
_A toner having _t -S _b = 0.25 × S _j × W _j was obtained.

The electrophotographic method of the present invention was used to perform 10,000 copying tests, and the image density was measured by a reflection densitometer (Macbeth Co.) and evaluated. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 7 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as binder resin, magnetite 33.0% by weight as magnetic substance, Cr-containing azo dye as charge control agent (Hodogaya Chemical Co., Ltd.) 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the toner base, 1.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix at 0B (Mitsui Miike Co., Ltd.) and mix at 2800 rpm.
External addition processing was performed for a minute. Finally, the aggregate was extracted with a vibrating sieve to complete a toner having a specific surface area of 2.30 m ² / g.
That is, the toner specific surface area S _t m ² / g and the specific surface area S _{b of the base material}
m ² / g difference 0.60 m ² / g in an external additive having a specific surface area S _j of
The product of m ² / g and the addition amount W _j wt% is 1.00 m ² /
g, and the difference S _t −S _b between the specific surface areas of the toner and the base is S _t
To obtain a toner which is over _{S b = 0.60 × S j ×} W j.

The electrophotographic method of the present invention was used to perform a copying test on 10,000 sheets, and the image density was measured by a reflection densitometer (Macbeth Co.) for evaluation. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 8 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as a binder resin, magnetite 33.0% by weight as a magnetic substance, and a Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent. 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the above toner base, 0.3% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and mix at 2800 rpm.
External addition processing was performed for a minute. Finally, the aggregate was extracted with a vibrating screen to complete a toner having a specific surface area of 1.88 m ² / g.
That is, the toner specific surface area S _t m ² / g and the specific surface area S _{b of the base material}
m ² / g difference 0.18 m ² / g in an external additive having a specific surface area S _j of
The value obtained by multiplying m ² / g by the added amount W _j wt% is 0.30 m ² /
g, and the difference S _t −S _b between the specific surface areas of the toner and the base is S _t
To obtain a toner which is over _{S b = 0.60 × S j ×} W j.

A copying test was conducted on 10000 sheets of the electrophotographic method of the present invention, and the image density was measured by a reflection densitometer (Macbeth Co.) and evaluated. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

Example 9 Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as a binder resin, magnetite 33.0% by weight as a magnetic substance, and a Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent. 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the above-mentioned toner base, 2.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and mix at 2800 rpm.
External addition processing was performed for a minute. Finally, the aggregate was extracted with a vibrating sieve to complete a toner having a specific surface area of 2.90 m ² / g.
That is, the toner specific surface area S _t m ² / g and the specific surface area S _{b of the base material}
m ² / g difference 1.20 m ² / g in an external additive having a specific surface area S _j of
The value obtained by multiplying m ² / g by the added amount W _j wt% is 2.00 m ² /
g, and the difference S _t −S _b between the specific surface areas of the toner and the base is S _t
To obtain a toner which is over _{S b = 0.60 × S j ×} W j.

The electrophotographic method of the present invention was used to perform a copy test on 10,000 sheets, and the image density was measured with a reflection densitometer (Macbeth) and evaluated. As a result, the horizontal lines are not disturbed and the toner is not scattered, the solid is uniform, the fog is 5 or less per mm ² , and the density is 1.4.
An image of extremely high resolution and high quality, in which the lines of lines / mm were reproduced, was obtained.

(Comparative Example 1) Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as binder resin, magnetite 33.0% by weight as magnetic substance, Cr-containing azo dye as charge control agent (Hodogaya Chemical Co., Ltd.) 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the toner base, 1.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and add 1 at 2800 rpm.
External addition processing was performed for a minute. Finally, the aggregate was extracted with a vibrating sieve to complete a toner having a specific surface area of 2.45 m ² / g.
That is, the toner specific surface area S _t m ² / g and the specific surface area S _{b of the base material}
m ² / g difference 0.75 m ² / g in an external additive having a specific surface area S _j of
The value obtained by multiplying m ² / g by the added amount W _j wt% is 1.00 m ² /
g, and the difference S _t −S _b between the specific surface areas of the toner and the base is S _t
A toner having −S _b = 0.75 × S _j × W _j was obtained.

A copying test was conducted on 10,000 sheets of the image by the electrophotographic method of the present invention, and the image density was measured by a reflection densitometer (Macbeth Co.) and evaluated. As a result, the horizontal lines were disturbed and the toner was scattered, and the toner adhered to the non-image area, fog was generated, and 120 particles / mm ² of toner were observed on the paper surface, resulting in an extremely low-quality image. .

(Comparative Example 2) Styrene acrylic resin (manufactured by Sanyo Kasei) 63.0% by weight as binder resin, magnetite 33.0% by weight as magnetic material, Cr-containing azo dye as charge control agent (Hodogaya Chemical Co., Ltd.) 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the toner base, 1.0% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive.
Mix with 0B (Mitsui Miike Co.) and 4 at 2800 rpm
External addition was performed for 5 minutes. Finally, the aggregate was extracted with a vibrating sieve to complete a toner having a specific surface area of 1.74 m ² / g. That is, the difference between the toner specific surface area S _t m ² / g and the specific surface area S _b m ² / g of the base is 0.04 m ² / g, and the specific surface area S _j m ² / g of the external additive and the addition amount W _j weight The value multiplied by% is 1.00 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
_A toner having _t −S _b = 0.04 × S _j × W _j was obtained.

The electrophotographic method of the present invention was used to perform a copying test on 10,000 sheets, and the image density was measured by a reflection densitometer (Macbeth Co.) and evaluated. As a result, toner adhered to the non-image area, fog was generated, and 120 particles / mm ² of toner were observed on the paper surface, resulting in an extremely low-quality image.

(Comparative Example 3) 63.0% by weight of styrene-acrylic resin (manufactured by Sanyo Kasei) as a binder resin, 33.0% by weight of magnetite as a magnetic substance, Cr-containing azo dye as a charge control agent (Hodogaya Chemical Co., Ltd.) 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the above-mentioned toner base, 0.2% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and add 1 at 2800 rpm.
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating sieve to complete a toner having a specific surface area of 1.74 m ² / g. That is, the difference between the toner specific surface area S _t m ² / g and the specific surface area S _b m ² / g of the base is 0.04 m ² / g, and the specific surface area S _j m ² / g of the external additive and the addition amount W _j weight The value multiplied by% is 0.20 m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
to obtain toner is _{t-S b = 0.20 × S j ×} W j.

A copy test was conducted on 10,000 sheets of the electrophotographic method of the present invention, and the image density was measured by a reflection densitometer (Macbeth Co.) and evaluated. As a result, toner adhered to the non-image area, fog was generated, and 120 particles / mm ² of toner were observed on the paper surface, resulting in an extremely low-quality image.

(Comparative Example 4) 63.0% by weight of styrene-acrylic resin (manufactured by Sanyo Kasei) as a binder resin, 33.0% by weight of magnetite as a magnetic substance, and Cr-containing azo dye (manufactured by Hodogaya Chemical Co., Ltd.) as a charge control agent. 1.0% by weight, as a release agent, low molecular weight polypropylene (manufactured by Sanyo Kasei) 3.0% by weight
Are mixed by a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.), and the mixture is heated and kneaded by a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko Co., Ltd.) and jet mill crusher IDS.
Finely pulverized with a 2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and fine powder was cut by an air flow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.), and the volume average particle size was 8.0 μm and the specific surface area was 1. A toner base having a weight of 0.70 m ² / g was obtained.

The surface treatment of toner will be described below.
To the above toner base, 2.1% by weight of silica fine particles having a specific surface area of 100.0 m ² / g, which had been hydrophobized with silicone oil, was added as an external additive, and a Henschel mixer FM2 was used.
Mix with 0B (Mitsui Miike Co., Ltd.) and mix at 2800 rpm.
External addition treatment was performed for 0 minutes. Finally, the aggregate was extracted with a vibrating sieve to complete a toner having a specific surface area of 2.40 m ² / g. That is, the addition amount W _j by weight of the toner specific surface area S _t m ² / specific surface area of g and maternal S _b a specific surface area of m ² / difference g is 0.70 m ² / g with an external additive S _j m ² / g % Multiplied by 2.10m ²
/ G, and the difference S _t −S _b between the specific surface area of the toner and the base is S
_A toner having _t -S _b = 0.33 × S _j × W _j was obtained.

The electrophotographic method of the present invention was subjected to a copy test on 10,000 sheets for evaluation. As a result, toner adheres to the electrostatic latent image carrier, so-called filming occurs, the potential of the electrostatic latent image carrier does not decrease during exposure, white spots occur in the image area, and extremely low. It became a quality image.

[0068]

INDUSTRIAL APPLICABILITY As described above, the present invention provides an electrostatic latent image holding member which includes a fixed magnet and moves, and a predetermined position with respect to the surface of the electrostatic latent image holding member which is opposed to a part of the fixed magnet. A magnetic toner used in an electrophotographic method having a developing step in which an alternating electric field is applied to the gap, the magnetic roller being installed at a position having a gap of It consists of a specific range of the product of the specific surface area difference and the specific surface area of the external additive to be added and the addition amount, and by specifying the addition amount of the external additive, further downsizing of the device, simplification, and cost reduction can be achieved. It is possible to provide a magnetic toner and an electrophotographic method that realize a possible developing method and achieve a high image quality of low density fog at a high density by a magnetic toner.

[Brief description of drawings]

FIG. 1 is a sectional view showing a main part of an electrophotographic apparatus in which a magnetic toner and an electrophotographic method according to an embodiment of the present invention are used.

[Explanation of symbols]

 1 Electrostatic Latent Image Holder Drum 2 Fixed Magnet Enclosed in Electrostatic Latent Image Holder 6 Toner Reservoir 7 Magnetic Toner 8 Electrode Roller 9 Magnet Installed Inside Electrode Roller 12 Transfer Corona Charger 13 Damper

Claims (4)

[Claims] 1. An electrostatic latent image holder that includes a fixed magnet and moves, and a toner reservoir that faces the surface of the electrostatic latent image holder and that is magnetically attracted by the fixed magnet to supply magnetic toner. An electrode roller that is installed at a position facing at least a part of the fixed magnet and has a predetermined gap with the surface of the electrostatic latent image holding member, and has a magnet inside a predetermined inside, A magnetic toner used in an electrophotographic method using a developing process in which an alternating electric field is applied to the gap, wherein the magnetic toner comprises at least a toner base and an external additive, and the toner base is at least a binder. It is composed of a resin and a magnetic substance, and the specific surface area of the toner base is S _b m ² / g, the specific surface area of the external additive is S _j m ² / g, and the addition ratio of the external additive to the entire toner is W _j wt%, the toner specific surface area S _t m ² / When, × difference S _t over S _b of the specific surface area of the toner and maternal _{0.10 S j × W j ≦ S} t over S _b ≦ 0.60
A magnetic toner characterized in that xS _j × W _j , and the proportion of the external additive in the entire toner is W _j of 0.3 to 2.0% by weight. 2. The magnetic toner according to claim 1, wherein the addition amount of the magnetic material is 20.0 to 60.0% by weight based on the weight of the magnetic toner. 3. An electrostatic latent image holding member which moves by containing a fixed magnet.
The magnetic toner and the surface of the electrostatic latent image holding member.
The magnetic toner is magnetically attracted by the fixed magnet.
For supplying toner to at least one of the fixed magnets.
At a position facing the surface of the electrostatic latent image holding member.
Installed at a position with a fixed gap and has a magnet inside
An electrode roller, and an alternating electric field is printed in the gap.
An electrophotographic method using an applied developing step, wherein the magnetic toner comprises at least a toner base and an external additive.
The toner base is composed of at least a binder resin and a magnetic material.
And the specific surface area of the toner base is S _bm²/
g, the specific surface area of the external additive is S_jm²/ G, occupy the whole toner
The external additive addition rate is W_j% By weight, toner specific surface area is S_t
m²/ G, the difference S in specific surface area between the toner and the base_t-S
_bIs 0.10 x S_j× W_j≤ S_t-S_b≤0.60 x S_j× W
_jAnd the proportion of the external additive in the entire toner is W_jBut
Magnetic toner which is 0.3 to 2.0% by weight
A method for electrophotography, characterized in that 4. The electrophotographic method according to claim 3, wherein the magnetic toner is used in an amount of 20.0 to 60.0% by weight based on the weight of the magnetic toner.