JPH07333898A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To attain a high picture quality having a high image density and a low surface fogging by providing a process for transferring by transfer bias voltage after developing a electrostatic latent image and using a magnetic toner composed of respectively a specific binding resin, charge controlling agent and magnetic material. CONSTITUTION:In the electrophotographic method which includes a transfer process using a conductive elastic roller by the transfer bias voltage, the magnetic toner is constituted at least of a binding resin, magnetic material and charge controlling agent, and the binding resin has 1.0X10<4>-2.0X10<7> storage elastic modulus and is constituted of a styrene based polymer consisting essentially of styrene, the mixture or the like. And the charge controlling agent is constituted of at least a metal complex dye expressed by the formula. In the formula, X represents nitro group, sulfonamide group or a halogen atom, Y represents hydrogen atom, a halogen atom or into nitro group (where, except the case that both X and Y are nitro group), M represents chromium or cobalt atom, Further, the magnetic material is composed of a magnetic material particle having >=0.6g/cm<3> static bulk density.

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 copying machines, printers and facsimiles, and an electrophotographic method.

[0002]

2. Description of the Related Art In recent years, electrophotographic apparatuses are shifting from the purpose of office use to personal use, and there is a demand for a technology for realizing downsizing and maintenance-free operation.
Therefore, conditions such as maintainability such as recycling of waste toner and less ozone exhaust are required.

A printing process of an electrophotographic copying machine or printer will be described. First, an electrostatic latent image carrier (hereinafter referred to as a photoconductor) is charged for image formation. As a charging method, a conventionally used corona charger is used, and in recent years, a contact type charging method in which a conductive roller is directly pressed against the photoreceptor to reduce the amount of ozone generation is used. Charge the surface uniformly. After charging the photoreceptor,
In the case of a copying machine, a copy original is irradiated with light and reflected light is irradiated onto a photoconductor through a lens system. Alternatively, in the case of a printer, an image signal is sent to a light emitting diode or a laser diode as an exposure light source, and a latent image is formed on the photoconductor by turning the light on and off. When a latent image (high or low surface potential) is formed on the photoconductor, the photoconductor is visualized with toner (having a diameter of about 5 μm to 15 μm) which is precharged colored powder. The toner adheres to the surface of the photoconductor according to the level of the surface potential of the photoconductor, and is electrically transferred to the copy sheet. That is, the toner is charged positively or negatively in advance, and a charge having a polarity opposite to the polarity of the toner is applied from the back surface of the copy sheet and is electrically attracted. Up to now, a corona discharger has been widely used as the charge applying method as in the charging method, but in recent years, a transfer device using a conductive roller has been put into practical use in order to reduce the ozone generation amount. At the time of transfer, not all the toner on the photoconductor is transferred to the copy sheet, but a part of the toner remains on the photoconductor. This residual toner is scraped off by a cleaning blade or the like in the cleaning section to become waste toner.

Conventionally, there are a cascade developing method, a touch-down developing method, a jumping developing method and the like as a developing method for converting an electrostatic latent image into a visible image by an electrophotographic method. Among them,
Cascade development shown in US Pat. No. 3,105,770 is known as a developing method in which a developer is directly sprinkled on the photoreceptor. The cascade developing method is the first developing method used in a copying machine for electrophotography. Further, there is US Pat. No. 3,866,574 as a method of applying an AC bias to the developing roller to fly the one-component toner and develop the toner. According to the present invention, the AC bias 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 in the middle.

Further, as an improved technique for applying the AC bias, there is a jumping development disclosed in Japanese Patent Publication No. 63-42256. In this jumping developing method, toner is carried on a toner carrier, and a rigid or elastic regulating blade is installed on the toner carrier with a minute gap from the carrier. Then, the regulation blade regulates the toner in a thin layer, conveys the toner to a developing portion, and the toner is attached to the image portion of the photoconductor by an AC bias there. 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.

FIG. 3 shows U of Japanese Patent Laid-Open No. 48-69524.
SP2,807,233, JP-A-3-15558
4 is a schematic diagram showing a configuration of a toner image transfer device disclosed in Japanese Patent Publication No. 4 or the like. FIG. In FIG. 3, 100 is a transfer roller made of foamed or solid rubber and adjusted to a medium resistance of about 10 ⁷ Ω, 101 is a power source for applying voltage to the transfer roller, 102 is a photoconductor, and 103 is a transfer. Paper (copy paper) 104 is toner. The operation of the transfer device configured as described above will be described.

An image is formed on the surface of the photoconductor 102 by the above-mentioned toner. Now, the normal development in which the polarity of the photoconductor 102 is negative and the polarity of the toner 104 is positive is defined. The transfer roller 100 is in contact with the photoconductor 102 with a predetermined pressing force. The transfer paper 103 is pressed against the photoconductor 102 and comes into contact with the toner 104. The transfer roller 100 has toner 10
Since the negative voltage opposite to the polarity of No. 4 is applied from the power supply device 101, the toner 104 is transferred to the transfer paper 103.
Since the transfer roller 100 is in contact with the transfer paper 103, the voltage applied from the power supply 101 can be as low as several hundreds to 3000V. The transfer paper 103 includes the photoconductor 102 and the transfer roller 10.
After passing the contact point of 0, it is conveyed to a fixing unit (not shown). With such a transfer method, generation of harmful ozone can be suppressed to an extremely low level as compared with the conventional corona discharger.

As is well known, the toner for electrostatic charge development used in these developing methods is generally a resin component, a coloring component consisting of a pigment or a dye and a plasticizer, a charge control agent and, if necessary, a magnetic component. It is composed of additional components such as a body and a release agent. As the resin component, natural or synthetic resins are used alone or in a proper mixture.

Then, the above additives are premixed in an appropriate ratio, heated and kneaded by heat melting, finely pulverized by an airflow type collision plate system, and finely powdered to complete a toner base.
After that, an external additive is externally added to the toner base to complete the toner.

[0010]

However, in the above-mentioned structure, the cascade developing method is not good at reproducing a solid image, which is well known in the technical field of the developing method. Further, there is a problem that the device becomes large and complicated. Furthermore, US Pat.
The developing device of type 574 has a drawback that the device is required to have high accuracy and is complicated and costly. 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.

Therefore, the applicant of the present invention has found that the electrophotographic method of the present invention can realize downsizing and high performance of development (Japanese Patent Laid-Open No. 5-72).
890). In the developing method of this electrophotographic method, unnecessary toner in the non-image area is removed by a photoreceptor containing a fixed magnet and a toner recovery electrode roller (hereinafter referred to as an electrode roller) having a magnet facing the photoreceptor with a predetermined gap. It is a configuration to be removed. Therefore, this developing method faithfully reproduces a solid image, does not generate a sleeve ghost, and enables further downsizing, simplification, and cost reduction of the apparatus.

However, in order to obtain high image quality by using this developing method, higher performance toner characteristics are required.
Since this developing method does not use a regulating blade that regulates the toner in a thin layer, the toner is conveyed to the developing field, which is a space having a narrow gap between the photoconductor and the electrode roller, without regulating the layer. Therefore, there are few places and spaces required for the toner to be triboelectrically charged to obtain a desired charge amount, and the toner requires higher charging characteristics than ever before.

With a toner having a low charge amount, unevenness occurs in a solid black image portion and a halftone image portion, and background fog increases in a non-image portion. Since the probability of contact with the developing member is low, a satisfactory triboelectrification amount cannot be obtained. Further, the triboelectric chargeability varies among the toners, and uniform toner chargeability cannot be obtained.

In the magnetic toner, the magnetic material is internally added to the binder resin. Conventionally, toner is pulverized and finely divided by an airflow type collision plate method. Since magnetic particles having a resistance lower than that of the binder resin are present, the magnetic toner has a drawback that it is difficult to obtain a high charge amount.

Therefore, in the magnetic toner, in the binder resin,
A charge control agent such as a dye is internally added in order to have a negative charging property. As a result, the charging polarity of the toner can be strongly negatively charged. As an example of using a metal complex salt dye in a toner, for example, Japanese Patent Publication No. 4-6397 and Japanese Patent Publication No.
There are JP-A No. 1-112915, JP-B No. 41-20153, JP-B No. 51-29827 and the like, which show that high charging characteristics for the purpose of charge control can be obtained.

However, when a charge control agent of a metal complex salt dye and a magnetic substance are added to the magnetic toner in the binder resin, the magnetic substance and the metal complex salt dye having different specific gravities are added and mixed, and the binder resin is mixed when heat-melted and kneaded. There is a drawback that the dispersibility in the inside deteriorates. Although the detailed cause is unknown, it is considered that the particles repelled electrostatically and the cohesiveness became stronger.

When the dispersibility is deteriorated, the amount of the oppositely charged toner particles is increased and the toner adheres to the non-image area, that is, so-called background fog is increased and the image quality is deteriorated.

In the electrophotographic method of the present invention, toner is first sprinkled on the electrostatic latent image holding member and developed. The toner is always in contact with the entire surface of the photoconductor, and 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 by magnetism and electrostatic force. Therefore, if the dispersibility of the charge control agent or the internal additive such as a magnetic substance in the toner varies, the consumed toner is extremely biased, and, for example, toner particles in which the magnetic substance is unevenly distributed remain, and The consumption of particles in which a large amount of the control agent is unevenly distributed progresses, the charging characteristics of the toner change during long-term use, and the image density decreases.

In the electrophotographic method of the present invention, a conductive elastic roller is used. The transfer method using the conductive elastic roller has problems such as hollow characters, hollow lines, and toner scattering around the characters.

When the toner on the photoconductor is transferred onto the transfer paper by using the transfer roller, the transfer roller is in contact with the photoconductor at a predetermined pressure. For this reason, characters and lines are edge-developed, where the amount of toner is large and the toner is concentrated, the pressure is higher than in the areas without toner, causing aggregation of toner due to pressure, A so-called "blank" occurs that is not transferred to the transfer paper. Low liquidity,
Remarkably appears in toner with a low charge amount. The transfer of the toner onto the transfer paper onto the photoconductor is carried out by the attraction between the charged electric charge of the toner and the electric charge opposite to the charged electric charge of the toner applied from the outside. When the toner charge amount is low, the toner easily scatters around the characters where no toner exists.

In view of the above problems, the present invention provides an electrophotographic method which realizes high image density and high image quality such as low background fog in a developing method which enables further downsizing, simplification and cost reduction of the apparatus. To provide.

Another object of the present invention is to provide an electrophotographic method capable of preventing hollow defects and scattering during transfer in a low ozone process using roller transfer.

It is another object of the present invention to provide an electrophotographic method capable of achieving long-life and image stability without causing deterioration of toner charge amount and fluidity even when used for a long period of time, aggregation is not generated. .

[0024]

In order to solve the above problems, the magnetic toner and the electrophotographic method of the present invention use the magnetic toner to visualize the electrostatic latent image formed on the electrostatic latent image carrier. And a conductive elastic roller that is in contact with the electrostatic latent image holding member. The transfer paper is inserted between the electrostatic latent image holding member and the conductive elastic roller, and And a transfer step of transferring the magnetic toner, which visualizes the electrostatic latent image on the electrostatic latent image holding member by a transfer bias voltage applied to an elastic roller, onto the transfer paper. The magnetic toner is composed of at least a binder resin, a magnetic substance, a charge control agent, and an external additive, and the binder resin has a storage elastic modulus of 1.0 × 10 ^{4 to} 2.0 × 1.
0 ⁷ (dyn / cm ² ) (a storage elastic modulus measuring device is a viscoelastic spectrometer, measuring conditions are 200 ° C., 20 Hz)
And a mixture of styrene-based polymer containing styrene as a main component or a mixture of styrene-based polymers containing styrene as a main component, or a styrene-based copolymer containing styrene as a main component or styrene-based containing styrene as a main component A mixture of copolymers, the charge control agent is at least a metal complex salt dye represented by the general formula (Formula 1), and the magnetic material is at least a quiet density 0.6 g.
The electrophotographic method uses a magnetic toner composed of magnetic particles having a density of at least ³ / cm ³ .

Further, the present invention is an electrophotographic method using a magnetic toner containing a charge control agent in an amount of 0.01 to 5.0% by weight based on the weight of the magnetic toner.

Further, the present invention is an electrophotographic method using a magnetic toner containing a magnetic substance in an amount of 15 to 70% by weight based on the weight of the magnetic toner.

Further, in the present invention, the external additive is a negatively charged hydrophobic silica fine powder surface-treated with silicone oil, and the magnetic content is 0.1 to 5.0 parts by weight based on 100 parts by weight of the magnetic toner. This is an electrophotographic method using a toner.

Further, the present invention is the electrophotographic method in which the elastic member of the elastic roller is a urethane foam to which a conductivity-imparting agent is added in the transfer step.

Further, the present invention is the electrophotographic method in which the conductivity-imparting agent dispersedly added to the urethane foam in the transfer step is a lithium salt.

Further, according to the present invention, a fixed magnet is contained and moved.
The electrostatic latent image holding member, the toner hopper, and the electrostatic latent image holding member.
Place a magnet inside at a position with a specified gap from the surface of the holder.
And a toner recovery electrode roller having
After forming an electrostatic latent image on the holder,
Magnetic toner is magnetically applied to the surface of the electrostatic latent image holding member.
The magnetic toner on the surface of the electrostatic latent image carrier.
Support the electrostatic latent image carrier and move the electrostatic latent image carrier.
Of the electrostatic latent image holding member facing the toner collecting electrode roller.
The magnetic toner remains in the image area and the magnetic toner in the non-image area
A developing process in which toner is collected by the toner collecting electrode roller,
A conductive elastic roller that contacts the electrostatic latent image carrier
Between the electrostatic latent image carrier and the conductive elastic roller.
Insert the transfer paper into the conductive elastic roller.
On the electrostatic latent image holder by the transfer bias voltage applied
Transfer the toner that visualized the electrostatic latent image of
Transfer process and holding of the electrostatic latent image partially during the transfer process
Removal of the toner remaining on the body from the electrostatic latent image carrier
And a cleaning step of
The magnetic toner contains at least a binder resin, a magnetic material,
A charge control agent, an external additive, and the binder resin,
Storage elastic modulus 1.0 × 10^Four~ 2.0 x 10⁷(Dyn /
cm ²) (A storage elastic modulus measuring device
The measurement conditions are 200 ° C and 20Hz).
Styrene-based polymer or
A mixture of styrene-based polymers containing mainly ethylene,
Is a styrene-based copolymer or a styrene-based copolymer.
From a mixture of styrene-based copolymers containing mainly ethylene
And the charge control agent has at least the general formula
Which is composed of a metal complex dye represented by Chemical Formula 1, and
The magnetic material is at least quiet density 0.6g / cm³Since
Use magnetic toner composed of magnetic particles above
It is an electrophotographic method.

Further, the present invention is an electrophotographic method using a magnetic toner containing a charge control agent in an amount of 0.01 to 5.0% by weight based on the weight of the magnetic toner.

Further, the present invention is an electrophotographic method using a magnetic toner containing a magnetic substance in an amount of 15 to 70% by weight based on the weight of the magnetic toner.

Further, in the present invention, the external additive is negatively charged hydrophobic silica fine powder surface-treated with silicone oil, and the magnetic content is 0.1 to 5.0 parts by weight based on 100 parts by weight of the magnetic toner. This is an electrophotographic method using a toner.

Furthermore, the present invention is the electrophotographic method in which the elastic member of the elastic roller is a urethane foam to which a conductivity-imparting agent is added in the transfer step.

Further, the present invention is the electrophotographic method in which the conductivity-imparting agent dispersedly added to the urethane foam in the transfer step is a lithium salt.

Further, the present invention is an electrophotographic method in which the magnetic toner is a one-component toner.

[0037]

In the electrophotographic method according to the present invention, an electrostatic latent image holder containing a fixed magnet is used, and toner is sprinkled and magnetically adhered to the electrostatic latent image holder on which the electrostatic latent image is formed. It is configured such that the toner is carried and conveyed to a portion, an AC bias is applied to the electrode roller, and the toner in the non-image portion of the electrostatic latent image holding member is removed by electrostatic force and magnetic force.

That is, the electrophotographic method presented in the present invention is a cascade development method in which a magnet is installed inside the electrostatic latent image holding member and an AC voltage is applied to the electrodes to further reduce the size and improve the performance.

In the electrophotographic method of the present invention, the development is almost completed when the toner is first sprinkled on the electrostatic latent image carrier. 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 hopper 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 according to the present invention is preferably an insulating one-component toner. When the one-component toner is used, the mixing and stirring mechanism of the carrier and the toner, which is necessary for the two-component development, and the toner concentration control are unnecessary, so that the apparatus configuration can be simplified.

Since the developing method in the electrophotographic method according to the present invention has a simple structure, there are few toner charging occasions, it is difficult to obtain high charging characteristics, and if the dispersibility of the toner deteriorates, selective consumption is increased. proceed.

Further, when combined with a transfer process using a conductive elastic roller as the transfer means, the magnetic toner is required to have a higher chargeability than in the conventional case in order to prevent hollowing out during transfer and scattering around the characters.

In the developing process having a simple structure and the transfer process using a conductive elastic roller, stable high-quality images can be obtained unless the toner is charged more highly than before and the uniform dispersibility of the internal additive is not maintained. I can't.

Therefore, by using a metal complex salt dye as the charge control agent, a high negative charging property can be obtained, and the rising property of charging can be improved. However, when magnetic particles are added,
There was a tendency that the dispersibility deteriorated and the charge amount decreased, resulting in non-uniform charging.

However, at this time, the quietness density is 0.6 g / c
m ³ or more, further moved by the use of magnetic particles is density 1.1 g / cm ³ or more to improve the dispersibility of the metal complex dye of the present invention. As a result, although the magnetic particles are added, the negative charging property is improved and the highly charging toner property is obtained. It is considered that this is because the flowability of the magnetic material itself is improved, the cohesiveness is weakened, and the dispersibility is improved. Further, it is presumed that the charge control agent also has the effect of releasing the aggregation.

In order to increase the bulk specific gravity of the magnetic material, it is preferable to subject the magnetic material to degassing or to treat the surface with an organic material or the like. This surface treatment is titanium coupling treatment,
A silane coupling treatment or a surface treatment with a silicone resin, an acrylic resin, a styrene resin, a polyester resin, or the like can be considered.

When the quietness density is 0.6 g / cm ³ or less, the dispersibility of the magnetic material itself is poor and the dispersibility in the binder resin is deteriorated. Further, when the mobility density is 1.1 g / cm ³ or less, the cause is unknown, but the kneading property at the time of heat melting is poor and the dispersibility of the charge control agent is deteriorated.

The addition amount of the magnetic material is preferably 15 to 70% by weight based on the weight of the magnetic toner. 15
If it is less than 50% by weight, the toner scattering increases, and if it is 70% by weight, the fixing property deteriorates.

The charge control agent is preferably added in an amount of 0.01 to 5.0% by weight based on the weight of the magnetic toner. 0.01
If it is less than weight%, high negative chargeability cannot be obtained. If it is 5.0% by weight or more, the fluidity is lowered under high humidity and the image quality is deteriorated.

The magnetic toner according to the present invention uses a styrene resin having a storage elastic modulus of 1.0 × 10 ^{4 to} 2.0 × 10 ⁷ dyn / cm ² . It has been found that by using this resin, a uniform kneading torque is applied during hot melt kneading, for example, when kneading is performed by a twin-screw extruder, and the dispersibility of the internal additive is greatly improved. It is speculated that the resin itself has appropriate meltability and viscoelasticity.

Storage elastic modulus of 1.0 × 10 ⁴ dyn / cm ²
In the following cases, torque is hardly applied during kneading and dispersibility is not improved. In addition, the generation of fine powder increases during crushing. 2.
When it is 0 × 10 ⁷ dyn / cm ² or more, the elasticity becomes too strong, the kneading ability is lowered, and the pulverizability is deteriorated.

The measurement of dynamic viscoelasticity is a measurement method which looks at the temperature dependence for a certain frequency or the frequency dependence for a certain temperature, and the storage elastic modulus can be calculated from the response to stress at a certain frequency. The resin was melted to prepare a plate-shaped sample, which was sandwiched between cone plate-shaped sample supports, and the temperature dependence when a constant frequency was applied was measured. The measuring device is Rh manufactured by Rheometrics
eometricsDynamic Spectrom
It was carried out using eter (RDS-2).

Further, when negatively charged hydrophobic silica fine particles whose surface is treated with silicone oil are used as an external additive, a magnetic toner having a high negatively charged property can be obtained, which leads to improvement in image quality. This is because the silanol groups, which are hydrophilic groups, present on the surface of the silica fine particles are completely covered and the siloxane groups are present on the surface, and the silica fine particles have a high negative chargeability.

However, since the material itself has a high chargeability, the secondary agglomeration is strong, and many silica agglomerates are present, which promotes the deterioration of fluidity, the generation of white spot noise due to the silica soul, and the occurrence of filming. This phenomenon is remarkable when the dispersibility of the internal additive of the toner base is poor. Therefore, it has been found that by externally treating the toner base of the present invention in which the internal additive is uniformly dispersed, the generation of silica aggregates can be significantly suppressed. The cause is unknown, but it is presumed that the use of an electrostatically uniform toner base can eventually suppress the occurrence of silica aggregation. It was found that this has the effect of improving the fluidity of the toner and also enhancing the charging property.

Further, at this time, silica is BE due to nitrogen adsorption.
When the T specific surface area is 50 to 350 m ² / g, the characteristics are further improved.

BET specific surface area due to nitrogen adsorption of 50 m ²
If it is less than / g, the fluidity of the toner will decrease. When the BET specific surface area due to nitrogen adsorption is 350 m ² / g or more, the aggregating property becomes strong, and even if the BET specific surface area is mixed with the toner base of the present invention, the agglomeration cannot be suppressed.

As described above, by using the magnetic toner of the present invention, a high negative charging property can be obtained and the rising property of charging can be improved. In addition, the dispersibility of the metal complex dye and the magnetic substance is improved. As a result, although the magnetic particles are added, the negative charging property is improved and the highly charging toner property is obtained. Therefore, by using a magnetic toner that can maintain high fluidity and high chargeability in a developing method that enables further downsizing, simplification, and cost reduction of the apparatus, an image with high image density and low background fog can be obtained. In addition, in the transfer process using the conductive elastic roller, when toner such as characters and lines is concentrated, even if the toner is transferred with a predetermined pressing force, it is difficult for the toner particles to agglomerate, and a clear image with no voids Is obtained.

Further, even if it is used for a long period of time, there is no deterioration in fluidity and charge amount, a high image density without background fog is obtained, and it is possible to maintain a good image with little selective consumption.

[0059]

EXAMPLES The magnetic toner according to the present invention is manufactured by the following method.

The toner is mixed, kneaded, pulverized, externally added, and if necessary classified. The mixing treatment is a treatment in which a binder resin, a charge control agent, a magnetic material, and other internal additives such as a release agent and a pigment, which are added as necessary, are uniformly dispersed by a mixer equipped with a stirring blade. Is used.

In the kneading process, the mixed material is heated to disperse the internal additive in the binder resin by shearing force. The kneading at this time can be performed using a known heating kneader. 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. The agglomerates obtained by the kneading treatment are roughly pulverized by a cutter mill or the like, and then finely pulverized, and fine powder particles are further cut if necessary to obtain a desired particle size distribution.

The fine pulverization method at this time includes an air flow type and a mechanical type, but a mechanical pulverizing method is preferable. Examples of the pulverizing method include a rotary mechanical pulverizing method.

In the method of finely crushing by a collision plate method crushing such as an air flow type jet mill crusher, since the toner is smashed by hitting the collision plate, the crushed toner has an indefinite shape. It has a drawback that a large amount of fine powder is generated. Furthermore, it is considered that the charge control agent, which is a metal complex dye internally added to the resin during the pulverization, is likely to be exposed in the form of protrusions on the surface of the toner base, resulting in uneven chargeability of the toner and deterioration of the image.

However, in the method of mechanically finely pulverizing with a rotating body, the toner is pulverized in such a manner that the surface of the toner is peeled off.
This is a method of pulverizing toner by the so-called peel effect. Therefore, the charge control agent, which is a metal complex dye internally added to the resin when crushed as seen in the collision plate method, is not exposed in the form of protrusions on the surface of the toner base, and the particles are crushed in the shape of a corner. , The chargeability of the toner becomes uniform. Further, since the toner is spherical, the powder fluidity is greatly improved.

This system includes a turbo mill manufactured by Turbo Kogyo Co., Ltd. and a crypttron crusher manufactured by Kawasaki Heavy Industries Ltd., but a crypttron crusher having a long stroke in which the residence time of the toner in the crusher mill is long is preferable.

External additives are externally added to the magnetic toner base particles thus obtained. A known method such as a Henschel mixer or a super mixer is used for the external addition treatment.

The binder resin of the magnetic toner according to the present invention is a vinyl polymer obtained by polymerizing or copolymerizing vinyl monomers. Examples of the monomer styrene constituting the binder resin include styrene, α-methylstyrene, styrene such as P-chlorostyrene and its substitution products, and examples of the acrylic acid alkyl ester include acrylic acid, methyl acrylate and acryl. Ethyl acid, butyl acrylate, dodecyl acrylate, octyl acrylate, isobutyl acrylate, hexyl acrylate, alkyl methacrylates, for example, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate,
Examples include monocarboxylic acids having a double bond such as isobutyl methacrylate, dodecyl methacrylate, and hexyl methacrylate, and substituted products thereof.

As a method for producing these copolymers, known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization and emulsion polymerization are adopted.

The copolymer used in the magnetic toner according to the present invention preferably contains a styrene-based component as a 50 to 95% by weight component. 50% by weight of styrene
If it is less than the above range, the melting property of the toner is poor, the fixing property is insufficient, and the pulverizability is deteriorated.

The magnetic toner according to the present invention contains the binder resin as a main component as described above, but other known polymers or copolymers may be used, if necessary, in addition to such a main component. . For example, there are polyester resin, epoxy resin, polyurethane resin, and the like.

To the magnetic toner according to the present invention, by adding the negatively-charged hydrophobic silica fine particles surface-treated with the polydimethyl silicone oil represented by the general formula (Formula 2), the high-chargeability of the present invention can be improved. A combination of the charge control agent having the above and the magnetic particles having a high quiet density can bring out the effect of further drawing out the negative charging property.

[0072]

[Chemical 2]

The silica fine particles are preferably silica fine particles produced by vapor phase oxidation of a silicic acid halogen compound, and, for example, those utilizing the thermal decomposition oxidation reaction in oxyhydrogen flame of silicon tetrachloride gas. The general formula of the reaction is shown in (Chemical Formula 3).

[0074]

[Chemical 3]

The preferred silicone oil for surface-treating the silica fine particles used in the present invention is polydimethyl silicone oil, and in addition, alkyl-modified silicone oil, fluorine-modified silicone oil and the like are preferable.

As the surface treatment method, a known technique is used, and a method of mixing using a mixer such as a Henschel mixer or a method of spraying silicone oil may be used.

The amount of silica added is preferably 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the magnetic toner. In order to prevent the toner particles from coagulating, the addition amount of 0.1 parts by weight or more is necessary, and if it is 5.0 parts by weight or more, the floating silica increases.

Further, the magnetic toner according to the present invention may further contain a release agent such as WAX if necessary.

Further, the magnetic toner according to the present invention contains magnetic particles. The magnetic particles include metal powders of iron, manganese, nickel, cobalt, etc., ferrites of iron, manganese, nickel, cobalt, zinc, etc. Magnetite fine particles having an average particle diameter of 1 μm or less, particularly preferably 0.6 μm or less are preferable.

Next, the electrophotographic method of the present invention will be described with reference to the drawings. The present invention is not limited to this.

(Embodiment 1) FIG. 1 is a sectional view of an electrophotographic apparatus according to an embodiment of the electrophotographic method of the present invention. The developing method is a one-component developing method. Reference numeral 1 denotes an organic photoreceptor, and a charge generation layer in which a charge generation substance of τ type metal-free phthalocyanine (manufactured by Toyo Ink) is dispersed in polyvinyl butyral resin (Elec BL-1 manufactured by Sekisui Chemical Co., Ltd.) on an aluminum conductive support, Polycarbonate resin (Mitsubishi Gas Chemical Z-
200) and a charge transport layer containing 1,1-bis (P-diethylaminophenyl) -4,4-diphenyl-1,3-butadiene (T-405 manufactured by Anan) are sequentially laminated. 2 is a magnet fixed coaxially with the photoconductor 1,
Reference numeral 3 is a corona charger for negatively charging the photoconductor, 4 is a grid electrode for controlling the charging potential of the photoconductor, and 5 is signal light.

The developing device for visualizing the latent image after exposure includes a magnetic one-component toner 7; a toner hopper 6 for supplying the magnetic toner 7 to the surface of the photoconductor 1; and a gap 8 with the photoconductor 1. A non-magnetic electrode roller set by opening the magnet, 9 a magnet installed inside the electrode roller 8, 10 an AC high-voltage power supply for applying a voltage to the electrode roller 8, and 11 a polyester film for scraping off toner on the electrode roller The electrode roller 8 collects the excess toner in the non-image area.

Reference numeral 12 is a damper for smoothing the flow of the toner in the toner hopper and for preventing the toner from being crushed by its own weight and clogged between the photosensitive member and the electrode roller.

Reference numeral 13 denotes a transfer roller for transferring the toner image on the photoconductor onto the paper, which is set so as to come into contact with the photoconductor 1. The transfer roller is an elastic roller in which a conductive elastic member is provided around a shaft made of a conductive metal. The pressing force to the photoconductor 1 is 0 per transfer roller 13 (about 216 mm).
~ 2000g, preferably 500-1000g.
This was measured from the product of the spring coefficient and the contraction amount of the spring for pressing the transfer roller 13 against the photosensitive member 1. The contact width with the photoreceptor is about 0.5 mm to 5 mm. The rubber hardness of the transfer roller 13 is 80 degrees or less by the Asker C measurement method (measurement using a block piece, not the roller shape), and preferably 30 degrees.
-40 degrees. In the present invention, the elastic roller 13 has a diameter of 6
A conductive urethane elastomer in which a foamable lithium salt was internally added to the periphery of a shaft having a diameter of 10 mm and having a resistance value of 10 ⁷ Ω (an electrode was provided on the shaft and the surface, and 500 V was applied to both electrodes) was used. Outer diameter of the entire transfer roller 13 is 16.4 mm
The hardness was 40 degrees in Asker C. Transfer roller 1
3 was brought into contact with the photoconductor 1 by pressing the shaft of the transfer roller 13 with a metal spring. The pressing force was about 1000 g. The present invention is not limited to this material.

CR rubber, NBR, S are used for the elastic body of the roller.
Examples of the rubber include i rubber and fluororubber, and urethane foam is preferable. Then, as the conductivity-imparting agent for imparting conductivity, carbon black or a lithium salt such as Li ₂ O is a preferable material.

Reference numeral 14 is a thrust guide made of a conductive member for introducing the transfer paper to the transfer roller 13, and reference numeral 15 is a conveyance guide in which the surface of the conductive member is covered with an insulating material. The plunge guide 14 and the transport guide 15 are grounded directly or through a resistor. Reference numeral 16 is a transfer sheet, and 17 is a voltage generating power source for applying a voltage to the transfer roller 13.

Reference numeral 18 is a cleaning blade for scraping off the residual toner after transfer, 19 is a cleaning box for storing the waste toner, and 23 is a waste toner.

An elastic urethane blade was used as the cleaning blade, but a fur brush to which a bias was applied,
A similar result is obtained with a conductive metal roller.

The magnetic flux density on the surface of the photoreceptor 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 diameter of the photoconductor 1 is 30 mm and the peripheral speed is 60 m.
It was used by rotating in the direction of the arrow in the figure at m / s. The diameter of the electrode roller 8 is 16 mm and the peripheral speed is 40 mm / s.
It was used by rotating it in the direction opposite to the traveling direction (direction of arrow in the figure). The gap between the photoconductor 1 and the electrode roller 8 is 300μ
set to m.

The photoconductor 1 is connected to the corona charger 3 (applied voltage-
-50 at 4.5kV, voltage of grid 4 -500V)
It was charged to 0V. The photoconductor 1 was irradiated with laser light 5 to form an electrostatic latent image. At this time, the exposure potential of the photoconductor 1 was −90V. Toner 7 was attached to the surface of the photoconductor 1 by a magnet in the toner hopper 6. Next, the photoconductor 1 was passed in front of the electrode roller 8. When passing through the uncharged area of the photoconductor 1, an AC high voltage power source 10 superimposes a DC voltage of 0V on the electrode roller 8 and an AC voltage of 750V0-p (peak-to-peak 1.5kV) (frequency 1k).
Hz) was applied. After that, when the photoconductor 1 charged with −500V and having the electrostatic latent image written thereon passes, the electrode roller 8
750V 0-p (peak-to-peak 1.5) with a DC voltage of -350V superposed by an AC high-voltage power supply 10.
An alternating voltage (frequency 1 kHz) of kV) was applied. Then, the toner adhering to the charged portion of the photoconductor 1 is removed by the electrode roller
Then, a toner image in which only the image portion was negative-positive inverted was collected on the photoconductor 1. The toner adhering to the electrode roller 8 rotating in the direction of the arrow was scraped off by the scraper 11, returned to the inside of the toner hopper 6 and used for the next image formation. The toner image thus obtained on the photoconductor 1 is transferred onto the transfer paper by the transfer roller 13 and then thermally fixed by a fixing device (not shown) to obtain a copied image.

Examples of the magnetic toner of the present invention will be described. The present invention is not limited to this.

Table 1 shows an example of the material composition of the magnetic toner A1 of the present invention. As the magnetic material, deaerated magnetite was used.

[0093]

[Table 1]

The measurement results of fluidity and charge amount of each magnetic toner are shown in (Table 2). Flowability was defined as static bulk density. For the measurement, a powder tester PT-E type manufactured by Hosokawa Micron was used. The charge amount was measured by the blow-off method by weighing 0.2 g of the sample and blowing it for 180 sec at an air pressure of 0.2 kgf / cm ² . As the measurement conditions, a non-coated ferrite carrier was mixed at a toner concentration of 10%, put in a 100 ml polyethylene bottle, and stirred at a rotation speed of 60 rpm for 10 minutes.

[0095]

[Table 2]

The production of the magnetic toner of the present invention will be described. A mixture other than the external additives shown in (Table 1) is mixed with a Henschel mixer FM20B (manufactured by Mitsui Miike Co., Ltd.). The mixture is a twin-screw kneading extruder PCM30 (made by Ikegai Tekko Co., Ltd.)
Knead by heating. The kneaded product is roughly crushed to a size of 2 mm or less with a coarse crusher Rotoplex (manufactured by Alpine). Then, fine pulverization is performed with a Kryptron pulverizer KTM0 type (manufactured by Kawasaki Heavy Industries Ltd.). The pulverized material is cut into fine powder with an airflow classifier DS2 type (manufactured by Nippon Pneumatic Mfg. Co., Ltd.). By the above treatment, magnetic toner base particles having an average particle diameter of 8 μm were obtained.

Thereafter, an external additive was added to the Henschel mixer FM2.
OB (manufactured by Mitsui Miike Co., Ltd.) was externally added.

Using the electrophotographic apparatus shown in FIG. 1, a copy test was conducted using the magnetic toner A1 of the present invention. The image density was measured by a reflection densitometer (Macbeth) and evaluated.
As a result, an extremely high-resolution and high-quality image is obtained, in which horizontal lines are not disturbed, toner is not scattered, hollow characters are not present, and a solid black image is uniform and 16 lines / mm with a density of 1.4 are reproduced. Was given. A high-density image having an image density of 1.4 or more was obtained. No background fog has occurred in the non-image area.

Then, a long-term copying test of 10,000 sheets was conducted. After 10,000 sheets, there was no deterioration in the fluidity of the toner, a high charge amount was maintained, and a copy image of high density and low-level fog comparable to the initial image was obtained.

(Example 2) The material composition of the magnetic toner A2 of the present invention is shown in (Table 3).

[0101]

[Table 3]

Using the electrophotographic apparatus shown in FIG. 1, a copying test was conducted with the magnetic toner A2 of the present invention. The image density was measured by a reflection densitometer (Macbeth) and evaluated.
As a result, an extremely high-resolution and high-quality image is obtained, in which horizontal lines are not disturbed, toner is not scattered, hollow characters are not present, and a solid black image is uniform and 16 lines / mm with a density of 1.4 are reproduced. Was given. A high-density image having an image density of 1.4 or more was obtained. No background fog has occurred in the non-image area.

Then, a long-term copying test of 10,000 sheets was conducted. After 10,000 sheets, there was no deterioration in the fluidity of the toner, a high charge amount was maintained, and a copy image of high density and low-level fog comparable to the initial image was obtained.

(Embodiment 3) FIG. 2 shows a sectional view of an electrophotographic apparatus of an embodiment of the electrophotographic method of the present invention. The developing method is a one-component developing method. Reference numeral 1 denotes an organic photoreceptor, and a charge generation layer in which a charge generation substance of τ type metal-free phthalocyanine (manufactured by Toyo Ink) is dispersed in polyvinyl butyral resin (Elec BL-1 manufactured by Sekisui Chemical Co., Ltd.) on an aluminum conductive support, Polycarbonate resin (Mitsubishi Gas Chemical Z-
200) and a charge transport layer containing 1,1-bis (P-diethylaminophenyl) -4,4-diphenyl-1,3-butadiene (T-405 manufactured by Anan) are sequentially laminated. Reference numeral 3 is a corona charger for negatively charging the photoconductor, 4 is a grid electrode for controlling the charging potential of the photoconductor, and 5 is signal light.

The developing device for visualizing the latent image after exposure has a magnetic one-component toner 7, a magnet inside, and a non-magnetic developing sleeve 3 set with a gap between the photosensitive member 1 and the photosensitive member 1.
2, a toner popper 31, a rigid toner layer regulating doctor blade 33, and a power source 34 for applying a bias to the developing sleeve 32.

Reference numeral 13 denotes a transfer roller for transferring the toner image on the photoconductor to the paper, which is set so as to come into contact with the photoconductor 1. The transfer process and the cleaning process have the same configurations as those of the first embodiment shown in FIG.

Using the electrophotographic apparatus shown in FIG. 2, a copy test was conducted with the magnetic toner A1 of the present invention. The image density was measured by a reflection densitometer (Macbeth) and evaluated.
As a result, an extremely high-resolution and high-quality image is obtained, in which horizontal lines are not disturbed, toner is not scattered, hollow characters are not present, and a solid black image is uniform and 16 lines / mm with a density of 1.4 are reproduced. Was given. A high-density image having an image density of 1.4 or more was obtained. No background fog has occurred in the non-image area.

Then, a long-term copying test of 10,000 sheets was conducted. After 10,000 sheets, there was no deterioration in the fluidity of the toner, a high charge amount was maintained, and a copy image of high density and low-level fog comparable to the initial image was obtained.

(Example 4) A copying test was conducted using the magnetic toner A2 of the present invention using the electrophotographic apparatus shown in FIG. The image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, an extremely high-resolution and high-quality image is obtained, in which horizontal lines are not disturbed, toner is not scattered, hollow characters are not present, and a solid black image is uniform and 16 lines / mm with a density of 1.4 are reproduced. Was given. A high-density image having an image density of 1.4 or more was obtained. No background fog has occurred in the non-image area.

Then, a long-term copying test of 10,000 sheets was conducted. After 10,000 sheets, there was no deterioration in the fluidity of the toner, a high charge amount was maintained, and a copy image of high density and low-level fog comparable to the initial image was obtained.

Comparative Example 1 Table 4 shows an example of the material composition of the magnetic toner B1.

[0112]

[Table 4]

The fine pulverization was carried out by a crushing method of an airflow type collision plate method. The other manufacturing method is the same as that of the first embodiment.

Using the electrophotographic method of FIG. 1 shown in Example 1, a copy test was conducted with magnetic toner B1. The image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, a large amount of toner scatters, voids in characters occur, uneven solid black images occur, a low image density and a large amount of background fog make it impossible to obtain a practical image.

In the long-term copying test, the image density decreased and the background fog in the non-image area increased. In addition, the scratches on the photoconductor were remarkably generated, and filming also occurred, so that a practical image could not be obtained.

Comparative Example 2 Table 5 shows an example of the material composition of the magnetic toner B2.

[0117]

[Table 5]

The pulverizability was poor and the production efficiency was lowered. (Comparative Example 3) A toner was experimentally manufactured with the same composition as in Example 1 except that the addition amount of the magnetic material was 10% by weight. Due to the large amount of toner scattering, practical characteristics could not be obtained.

(Comparative Example 4) The addition amount of the magnetic material was 80% by weight.
A toner was trial-produced with the same composition as in Example 1 except for the above. The amount of electrification was low, and there was a lot of background fog, and practical properties could not be obtained.

Comparative Example 5 A toner was experimentally prepared with the same composition as in Example 1 except that the amount of the charge control agent added was 7% by weight. Due to the large amount of toner scattering, practical characteristics could not be obtained.

(Comparative Example 6) The amount of silica added was 0.0% by weight.
A toner was experimentally manufactured with the same composition as in Example 1 except that the content was 5%. Poor fluidity and lots of background fog, and practical properties could not be obtained.

(Comparative Example 7) The amount of silica added was 6.0 by weight.
A toner was experimentally manufactured with the same composition as in Example 1 except that the content was changed to%. A lot of floating silica was not obtained, and practical properties could not be obtained.

[0123]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, an electrostatic latent image holding member that contains a fixed magnet and moves, is installed at a position having a predetermined gap with the surface of the electrostatic latent image holding member, and is internally provided. A developing step including an electrode roller having an electrode roller having a magnet,
By adding a metal complex salt dye and a magnetic material having a quiet density of 0.6 g / cm ³ or more to an electrophotographic method having a transfer step using a conductive elastic roller and a cleaning step, high charging and charging can be achieved. Excellent rising characteristics can be obtained. In addition, the dispersibility of the magnetic material and the charge control agent is improved, whereby high image density such as high image density and low background fog can be realized even in long-term use in a high-performance, small-sized, low-cost developing method.

[Brief description of drawings]

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

FIG. 2 is a sectional view showing a main part of an electrophotographic apparatus in which an electrophotographic method according to an embodiment of the present invention is used.

FIG. 3 is a sectional view showing an outline of a transfer device.

[Explanation of symbols]

 1 Photoconductor drum 2 Fixed magnet contained in photoconductor 3 Corona charger 4 Grid electrode 6 Toner hopper 7 Magnetic one-component toner 8 Electrode roller 9 Magnet installed inside electrode roller 11 Scraper 13 Transfer roller 14 Inrush guide 15 Transport Guide 16 Transfer paper 18 Cleaning blade 19 Waste toner box 23 Waste toner

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G03G 9/08 15/08 507 L 15/16 G03G 9/08 325 346 375 (72) Inventor Tatematsu Hideki 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (13)

[Claims] 1. An electrostatic latent image formed on an electrostatic latent image carrier
A developing step of visualizing with a magnetic toner; and a conductive elastic roller contacting the electrostatic latent image holding member.
Between the electrostatic latent image carrier and the conductive elastic roller.
Insert the transfer paper into the conductive elastic roller.
On the electrostatic latent image holder by the transfer bias voltage applied
Transfer the magnetic toner that visualizes the electrostatic latent image of
An electrophotographic method including a transfer step of transferring to a paper, wherein the magnetic toner is at least a binder resin, a magnetic substance, and a charge control agent.
The binder resin has a storage elastic modulus of 1.0 × 10.^Four~ 2.0
× 10⁷(Dyn / cm ²) (The storage elastic modulus measuring device
Elasticity spectrometer, measurement condition is 200 ℃, 20H
z) and styrene based on styrene
Polymer or styrene-based polymer containing styrene as a main component
Or a styrene-based resin containing styrene as a main component.
Styrene-based copolymer based on polymer or styrene
And a charge control agent represented by the general formula (Formula 1)
And a magnetic substance having a quiet density of 0.6 g / cm.³
Use of magnetic toner composed of magnetic particles
An electrophotographic method characterized by: [Chemical 1] 2. The electrophotographic method according to claim 1, wherein the charge control agent is a magnetic toner containing 0.01 to 5.0% by weight based on the weight of the magnetic toner. 3. The magnetic material comprises 15 to 15 parts by weight of the magnetic toner.
The electrophotographic method according to claim 1, wherein a magnetic toner containing 70% by weight is used. 4. A magnetic toner 10 wherein the external additive is fine powder of negatively charged hydrophobic silica surface-treated with silicone oil.
The electrophotographic method according to claim 1, wherein the magnetic toner is used in an amount of 0.1 to 5.0 parts by weight based on 0 parts by weight. 5. The electrophotographic method according to claim 1, wherein in the transferring step, the elastic member of the elastic roller is a urethane foam to which a conductivity-imparting agent is added. 6. The electrophotographic method according to claim 1, wherein the conductivity-imparting agent dispersedly added to the urethane foam in the transfer step is a lithium salt. 7. An electrostatic latent image holding member that moves by containing a fixed magnet.
The toner hopper, the surface of the electrostatic latent image carrier, and
A toner cartridge with a magnet inside is located at a position with a constant gap.
An electrostatic latent image on the electrostatic latent image holder having a collecting electrode roller.
After the formation of the
The magnetic toner is magnetically attracted to the surface of the latent image carrier,
The magnetic toner is carried on the surface of the electrostatic latent image carrier,
The electrostatic latent image holder is moved to move the toner recovery electrode roll.
The magnetic latent image carrier on the image portion of the electrostatic latent image carrier.
The magnetic toner in the non-image area remains in the toner recovery
A developing step of collecting with a polar roller; and a conductive elastic roller that comes into contact with the electrostatic latent image holding member.
Between the electrostatic latent image carrier and the conductive elastic roller.
Insert the transfer paper into the conductive elastic roller.
On the electrostatic latent image holder by the transfer bias voltage applied
Transfer the toner that visualized the electrostatic latent image of
Transfer step and before partially remaining on the electrostatic latent image carrier during the transfer step.
Cleaner for removing toner from the electrostatic latent image carrier
And an electrophotographic method, wherein the magnetic toner comprises at least a binder resin, a magnetic material, and an electric charge.
The binder resin has a storage elastic modulus of 1.0 × 10.^Four~ 2.0
× 10⁷(Dyn / cm ²) (The storage elastic modulus measuring device
Elasticity spectrometer, measurement condition is 200 ℃, 20H
z) and styrene based on styrene
Polymer or styrene-based polymer containing styrene as a main component
Or a styrene-based resin containing styrene as a main component.
Styrene-based copolymer based on polymer or styrene
And a charge control agent represented by the general formula (Formula 1)
And a magnetic substance having a quiet density of 0.6 g / cm.³
Using a magnetic toner composed of the above magnetic particles
An electrophotographic method characterized by the following. 8. The electrophotographic method according to claim 7, wherein the charge control agent is a magnetic toner containing 0.01 to 5.0% by weight based on the weight of the magnetic toner. 9. The magnetic material comprises 15 to 15 parts by weight of the magnetic toner.
The electrophotographic method according to claim 7, wherein a magnetic toner containing 70% by weight is used. 10. A magnetic toner 1 wherein the external additive is fine powder of negatively charged hydrophobic silica surface-treated with silicone oil.
8. The electrophotographic method according to claim 7, wherein the magnetic toner is used in an amount of 0.1 to 5.0 parts by weight with respect to 00 parts by weight. 11. The electrophotographic method according to claim 7, wherein the magnetic toner is a one-component toner. 12. The electrophotographic method according to claim 7, wherein in the transfer step, the elastic member of the elastic roller is a urethane foam to which a conductivity-imparting agent is added. 13. The electrophotographic method according to claim 7, wherein the conductivity-imparting agent dispersedly added to the urethane foam in the transfer step is a lithium salt.