JPH0822141A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To realize high picture quality by using a magnetic toner comprising fine particles essentially comprising melamine as the main component and having a specified average particle size and the like, and using negative charge silica fine particles having a specified BET specific surface area measured by nitrogen adsorption. CONSTITUTION:The magnetic toner used for this electrophotographic method consists of a binder resin, magnetic material and external additive. The external additive consists of fine particles essentially comprising melamine and having 0.01-12mum average particle size and 0.1-50m<2>/g BET specific surface area by nitrogen adsorption, and negative charge hydrophobic silica fine particles having 50-350m<2>/g BET specific surface area measured by adsorption of nitrogen. An electrostatic latent image formed on a photoreceptor drum 1 is visualized with the magnetic toner 7. While a transfer paper 16 is inserted and carried between the phptpreceptor drum 1 and a transfer roller 13, the visualized image of the magnetic toner 7 on the photoreceptor drum 1 is transferred to the paper 16 by applying bias voltage for transfer on the transfer roller 13. Thereby, the high picture quality with high image density and low surface fog is realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic method used in copying machines, printers and facsimiles.

[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 touchdown developing method, a jumping developing method and the like as a developing method for making an electrostatic latent image visible by an electrophotographic method. 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 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. In this 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,
In the non-image part, it is explained that it returns 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
The configuration of the toner image transfer device disclosed in Japanese Patent Publication No. 4 is shown.
FIG. In FIG. 3, 40 is foaming or solid
Made of body condition rubber, 10 ⁷Adjusted to a medium resistance of about Ω
And a transfer roller 41 for supplying voltage to the transfer roller.
Source, 42 photoconductor, 43 transfer paper (copy paper), 44
Toner. Operation of the transfer device configured as described above
Is shown.

On the surface of the photoconductor 42, the above-mentioned toner image is formed. Now, the normal development in which the polarity of the photoconductor 42 is negative and the polarity of the toner 44 is positive is defined. The transfer roller 40 is in contact with the photoconductor 42 with a predetermined pressing force. The transfer paper 43 is pressed against the photoconductor 42 and comes into contact with the toner 44. Since a negative voltage opposite to the polarity of the toner 44 is applied to the transfer roller 40 from the power supply device 41, the toner 44 is transferred to the transfer paper 43. The transfer roller 40 is a transfer paper 43.
The voltage applied from the power source 41 is several hundreds
It can be as low as 3000V. The transfer paper 43 passes through the contact point between the photoconductor 42 and the transfer roller 40 and 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, a natural or synthetic resin is used alone or in a suitable 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 574 developing device has the disadvantage that high precision is required for the device, and it is complicated and expensive. In the jumping development method, it was essential to form a very uniform thin layer on the toner carrier carrying the toner layer. In addition, this method often causes so-called sleeve ghost development, in which the history of the previous image remains in the thin toner layer on the toner carrier and the afterimage appears in the image. Further, there is a drawback that the device is complicated and the cost is high.

Therefore, the inventors of the present invention have proposed the electrophotographic method of the present invention which can realize the downsizing of development and the high performance (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 and higher fluidity characteristics than ever before.

The low-fluidity toner causes unevenness in the solid black image area and the halftone image area, and increases the background fog in the non-image area. This phenomenon remarkably appears in the toner having low fluidity. This is because a toner having a low fluidity has a low probability of coming into contact with the developing member, so that a sufficient triboelectric charge amount cannot be obtained.
Further, the triboelectric chargeability varies among the toners, and uniform toner chargeability cannot be obtained.

Conventionally, in order to improve the fluidity of the toner, a means for adding silica or the like as an external additive (Japanese Patent Publication No. 54-1).
No. 6219), it has been proposed to use silica fine powder which is further hydrophobized. (JP-A-46-5782)
JP-A-48-47345, JP-A-48-4734
No. 6). For example, silica fine powder which has been hydrophobized by reacting silica fine powder with an organic silicon compound such as dimethyldichlorosilane to replace the silanol group on the surface of the silica fine powder with an organic group is used. However, although the fluidity of the toner is improved by the addition of an external additive such as silica, the silica fine particles have a strong cohesive property, so that suspended matters such as silica particles increase. In addition, the floating silica has strong adhesion to the photoconductor.

When a pressing force is applied to the photoconductor during the process of forming an image, the silica suspended matter serves as nuclei, which strikes the photoconductor to cause scratches, which triggers the adhesion of toner onto the photoconductor. The so-called toner filming occurs. Further, in the magnetic toner containing the magnetic substance internally, the magnetic substance particles are exposed on the surface at the time of pulverization, so that the photoconductor is likely to be scratched, which promotes the occurrence of filming. When this filming occurs, the surface potential is less likely to drop when the charged photoconductor is exposed, and, for example, in the reversal development, an image defect that a solid black image portion becomes white is generated.

Further, the suspended matter of silica adheres to the solid black image portion to generate white spot noise. The pressing force on the photoconductor has a force received from the cleaning blade in the cleaning section.

In the electrophotographic method of the present invention, the transfer roller is in contact with the photoconductor at a constant pressure in the transfer step.

In the electrophotographic method of the present invention, the toner is first sprinkled on the entire surface of the electrostatic latent image holding member in the developing step,
It is developed. Therefore, compared with the conventional method, the toner and the photoconductor are in contact with each other for a long time, and silica is more likely to be attached.

Therefore, as compared with the conventional electrophotographic method, the toner filming is more likely to occur.

On the other hand, in order to avoid filming, the use of a so-called polyvinylidene fluoride powder as the friction reducing substance is disclosed in, for example, Japanese Patent Publication No. 48-8136.
Nos. 48-8141, 51-1130, and the like. Further, JP-A-48-47
In Japanese Patent No. 345, it is proposed to add both a friction reducing substance and an abrasive substance to the toner. According to this, it is effective for avoiding the photoconductor filming phenomenon, but when a friction reducing substance is added, low electrical resistance substances such as paper powder and ozone adducts that adhere to the surface of the photoconductor by repeated use can be obtained. There is a drawback that the removal becomes difficult to perform, and the latent image on the photoconductor is significantly impaired by the low electric resistance, especially in a high temperature and high humidity environment.

In the electrophotographic method of the present invention, the transfer roller is in contact with the photosensitive member. Therefore, simply adding an abrasive, a friction-reducing substance, or the like, does not transfer to the transfer roller, does not supply it to the cleaning unit, and cannot remove the toner filming effect.

There are also examples in which other abrasives such as alumina, titania, and zirconia are externally added to the toner. However, these substances adversely affect the charging characteristics of the toner, lowering the image density and increasing the background fog. I will invite you.

Further, in the electrophotographic method of the present invention, since the toner is always in contact with the entire surface of the photosensitive member, simply adding fine particles such as an abrasive and a friction-reducing substance,
If you continue to take originals with a low blackening rate, the toner consumption will be low, and the selective consumption of only fine particles such as abrasives and friction-reducing substances will increase. There is a problem that the effect on

If the polishing agent, the friction reducing substance and the like remain adhered to the cleaning blade, the effect on filming continues, but when the transfer residual waste toner comes to the cleaning blade, these fine particles are generated together with the waste toner. Removed from the cleaning blade,
The effect will decrease.

Further, the transfer method using the conductive elastic roller has problems such as hollow characters, missing 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 for realizing high image density and high image quality with low background fog in a developing method which enables further downsizing, simplification and cost reduction of the apparatus. To do.

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.

Another object of the present invention is to provide an electrophotographic method capable of preventing filming of a photoconductor even in long-term use.

It is another object of the present invention to provide an electrophotographic method in which the charge amount and fluidity of the toner are not deteriorated even after long-term use, aggregates are not formed, and the life is extended.

[0031]

In order to solve the above-mentioned problems, the electrophotographic method of the present invention comprises a developing step in which an electrostatic latent image formed on an electrostatic latent image carrier is visualized with a magnetic toner. A conductive elastic roller that comes into contact with the electrostatic latent image holding member, inserts a transfer sheet between the electrostatic latent image holding member and the conductive elastic roller, and applies the transfer paper to the conductive elastic roller. Transfer bias voltage to transfer the magnetic toner, which visualizes the electrostatic latent image on the electrostatic latent image carrier, to the transfer paper, and a part of the electrostatic latent image carrier during the transfer process. A cleaning step of removing the magnetic toner remaining on the electrostatic latent image holding member from the electrostatic latent image holding member, wherein the magnetic toner comprises at least a binder resin, a magnetic material, and an external additive, The external additive has at least an average particle size of 0. 01～12Myuemu, the particles BET specific surface area by nitrogen adsorption as a main component melamine is 0.1 to 50 m ² / g, negatively chargeable hydrophobic BET specific surface area by nitrogen adsorption is a 50~350m ² / g The electrophotographic method uses a magnetic toner composed of silica fine particles.

Further, the present invention is an electrophotographic method using a magnetic toner in which negatively charged hydrophobic silica fine particles are surface-treated with silicone oil.

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 fine particles containing melamine as a main component are 0.01 parts by weight with respect to 100 parts by weight of the magnetic toner.
This is an electrophotographic method using a magnetic toner containing ˜5.0 parts by weight.

Further, in the present invention, the negatively chargeable hydrophobic silica fine particles are contained in an amount of 0.1 to 100 parts by weight of the magnetic toner.
The electrophotographic method uses a magnetic toner containing 5.0 parts by weight.

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.

Furthermore, the present invention is an 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 magnet is housed inside a fixed latent magnet, a moving electrostatic latent image holder, a toner hopper, and a position having a predetermined gap from the surface of the electrostatic latent image holder. And a toner recovery electrode roller having the same, and after the electrostatic latent image is formed on the electrostatic latent image holder, the toner is magnetically attached to the surface of the electrostatic latent image holder located in the toner hopper. By suction, the toner is carried on the surface of the electrostatic latent image holding member, the electrostatic latent image holding member is moved, and is made to face the toner collecting electrode roller, and the image is formed on the electrostatic latent image holding member. The electrostatic latent image holding member is provided with a developing step in which toner is left and toner in the non-image portion is collected by the toner collecting electrode roller, and a conductive elastic roller that contacts the electrostatic latent image holding member. While inserting the transfer paper between the conductive elastic roller, The transfer step of transferring the toner, which visualizes the electrostatic latent image on the electrostatic latent image carrier by the transfer bias voltage applied to the conductive elastic roller, to the transfer paper, and part of the transfer step during the transfer step. A cleaning step of removing the magnetic toner remaining on the electrostatic latent image carrier from the electrostatic latent image carrier, wherein the magnetic toner contains at least a binder resin, a magnetic material, and an external additive. And the external additive has an average particle size of at least 0.
01-12 μm, the BET specific surface area due to nitrogen adsorption is 0.
1 to 50 m ² / g of melamine-based fine particles and nitrogen adsorption of BET specific surface area of 50 to 350 m ²
/ G of negatively charged hydrophobic silica fine particles and a magnetic toner comprising the same.

Further, the present invention is an electrophotographic method using a magnetic toner in which negatively charged hydrophobic silica fine particles are surface-treated with silicone oil.

Furthermore, 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, according to the present invention, the fine particles containing melamine as a main component are contained in an amount of 0.01 per 100 parts by weight of the magnetic toner.
This is an electrophotographic method using a magnetic toner containing ˜5.0 parts by weight.

Further, in the present invention, the negatively charged hydrophobic silica fine particles are contained in an amount of 0.1 to 100 parts by weight of the magnetic toner.
The electrophotographic method uses a magnetic toner containing 5.0 parts by weight.

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.

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

[0045]

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 another portion, an AC bias is applied to the electrode roller, and the non-image portion toner of the electrostatic latent image holder 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. The bare surface of the electrode roller that does not carry the toner layer faces the electrostatic latent image holder. The electrode roller and the electrostatic latent image holder rotate in opposite directions.

Since the developing method in the electrophotographic method according to the present invention has a simple structure, there are few toner charging opportunities and it is difficult to obtain high charging characteristics.

In the electrophotographic method of the present invention, a conductive elastic roller is used as the transfer means. At this time, the magnetic toner is required to have a high fluidity and a high charging property in order to prevent the voids in the transfer and the scattering around the characters.

Further, when combined with the developing method in the electrophotographic method according to the present invention, the magnetic toner is required to have higher fluidity and higher electrification property than ever before in order to prevent hollow defects during transfer and scattering around characters. .

In the developing process having a simple structure and the transfer process using a conductive elastic roller, a stable and high-quality image cannot be obtained unless the toner is kept to have higher fluidity and higher chargeability than ever before. Furthermore, it is necessary to improve the printing durability against toner filming on the photoconductor more than ever before. Therefore, when negatively charged hydrophobic silica fine particles whose surface is treated with silicone oil are used as an external additive, the negatively charged property is improved. A high magnetic toner can be obtained, which leads to an 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.

However, the BET specific surface area due to nitrogen adsorption is 5
By using negatively chargeable hydrophobic silica surface-treated with a silicone oil represented by the general formula (Chemical Formula 1) at 0 to 350 m ² / g, and further mixing with the melamine fine particles of the present invention to perform external addition treatment, It was found that the generation of silica aggregates can be greatly suppressed. The cause is unknown, but it is presumed that the silica and the melamine fine particles are mixed during the external addition process, and the shearing force is applied to the silica to loosen the agglomerates. It was also found that this has the effect of improving the fluidity of the toner and also enhancing the charging property. It was also found that the transfer roller can be prevented from falling out, and the fluidity and chargeability are stable, and a high-quality image can be obtained.

[0054]

Embedded image

At this time, the polymerization degree n is preferably 10 to 100. When the polymerization degree n is 10 or less, it is difficult to obtain high negative chargeability. If the degree of polymerization n is 100 or more, the surface treatment becomes uneven.

The BET specific surface area due to nitrogen adsorption is 50
When it is less than m ² / g, the fluidity of the toner is lowered. 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 melamine fine particles of the present invention, the agglomeration cannot be suppressed.

However, it is difficult to suppress the occurrence of toner filming on the photosensitive member only by eliminating the silica agglomerates and obtaining a uniform dispersion. Since silica is added to the toner by a mixing process, it is impossible to completely suppress the free silica, so that it is inevitably attached to the photoreceptor. The silica is driven into the photoconductor by some kind of stress, and toner filming occurs using it as a trigger. The stress is the cleaning blade and the transfer roller. Particularly in the electrophotographic method according to the present invention,
Since the toner is attached to the entire surface of the photoconductor during development, the toner and the photoconductor are always in contact with the entire surface as compared with the conventional one-component developing method, and thus toner filming is more likely to occur.

However, by using the melamine fine particles as an external additive, it is possible to prevent unnecessary damage to the photoconductor,
It is possible to remove foreign matter attached to the photoconductor.

The melamine microparticles are separated from the toner and independently adhere to the photoconductor, are supplied to the cleaning section without being transferred to the transfer material in the transfer step, and adhere to the cleaning blade. When the melamine fine particles adhere to the cleaning blade, the effect of lowering the frictional resistance can be eliminated, and the foreign matter adhered to the photoconductor can be removed.

At this time, the melamine fine particles had an average particle size of 0.
01-12 μm, the BET specific surface area due to nitrogen adsorption is 0.
By using the fine particles of 1 to 50 m ² / g, the dispersibility of the fine particles is improved, the fine particles are uniformly attached to the magnetic toner base particles, and they effectively act on the filming.

Further, in the electrophotographic method according to the present invention, since the toner is adhered to the entire surface of the photosensitive member during development, for example, in the case of a toner to which the inorganic fine particles are added, the inorganic fine particles are released from the toner and selectively selected on the photosensitive member without limitation. If attached, the consumption of only the fine particles will proceed. If a document with a low blackening rate is continuously taken, only fine particles will be consumed, and the effect on filming will gradually decrease.

However, by adding the melamine fine particles of the present invention, the melamine fine particles are appropriately held by the magnetic toner base particles, so that the toner is always in contact with the entire surface of the photoconductor. Even if a manuscript having a low blackening rate is continuously taken, the selective and unlimited consumption of only the melamine fine particles can be suppressed.

As a result, melamine fine particles are present as long as the magnetic toner remains, and while recycling the waste toner,
The effect on filming continues even after long-term use.

Further, by using fine particles in which the melamine fine particles have the opposite polarity charging property to the toner base particles and the charge amount is +5 to +90 μC / g by the blow-off measurement method, the dispersibility of the particles is further improved. , Uniformly adheres to the magnetic toner base particles, and effectively acts on filming.

If the melamine fine particles have the opposite polarity charging property, the melamine fine particles are supplied to the cleaning blade portion without adhering to the transfer roller, which is very effective for filming.

When the average particle diameter is 0.01 μm or less, the dispersibility of the melamine fine particles is deteriorated and aggregates are increased, resulting in image defects. Also, the BET specific surface area due to nitrogen adsorption is 50 m.
^{If it is 2} / g or more, the dispersibility is similarly deteriorated, aggregates are increased, and image defects occur.

When the average particle diameter is 12 μm or more, the toner particles are separated from the toner base particles and give unnecessary damage to the photoreceptor. When the BET specific surface area due to nitrogen adsorption is 0.1 m ² / g or less, coarse particles increase and the coarse particles are separated from the toner base particles to give unnecessary damage to the photoreceptor.

When the charge amount becomes +5 μC / g or less, the melamine fine particles are severely detached from the toner base particles,
Selective consumption progresses. In addition, the amount of the toner that adheres to the transfer roller also increases, and the effect on filming decreases. If it is +90 μC / g or more, the charging property of the toner itself is affected and the background fog occurs.

As described above, in the electrophotographic method using the magnetic toner of the present invention, a magnetic toner capable of maintaining high fluidity and high chargeability by a developing method which enables further downsizing, simplification and cost reduction of the apparatus. By using, a high image density and a low ground fog image can be obtained, and in a transfer process using a conductive elastic roller, when toner such as characters and lines is concentrated, transfer is performed with a predetermined pressing force. However, aggregation of toner particles does not easily occur, and a clear image with no voids can be obtained.

[0070]

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.

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 for uniformly dispersing the binder resin, the charge control agent, the magnetic material, and other internal additives such as a release agent and a pigment, which are added as necessary, by a mixer equipped with a stirring blade. Then, a known processing method 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 mass obtained by the kneading treatment is roughly pulverized by a cutter mill or the like, and then finely pulverized by a jet mill pulverization or the like, and fine powder particles are further cut by an airflow classifier as necessary to obtain a desired particle size distribution.

Mechanical crushing and classification are also possible. For example, there is a method of injecting toner into a minute gap between a fixed stator and a rotating roller. Known methods are used in both cases.

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 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 in addition to the main component as required. . For example, there are polyester resin, epoxy resin, polyurethane resin, and the like.

To the magnetic toner according to the present invention, fine particles containing a melamine resin represented by the general formula (Formula 2) as a main component are added, and melamine has a proper slip property and a proper hardness, and By having a nitrogen group, it is possible to obtain positive charge of opposite polarity to the magnetic toner base particles.

[0081]

Embedded image

Melamine resin is obtained by the reaction of melamine and formalin. The reaction is carried out in an addition polymerization type reaction of melamine and formaldehyde, or in a condensation reaction form. Melamine and formaldehyde (37% formalin aqueous solution) are added to an alkaline catalyst in a reaction vessel to heat the melamine while adjusting the pH. A resin is obtained.

The addition amount of the melamine fine particles is 10
0.01 to 5.0 parts by weight is preferable with respect to 0 parts by weight.
If the amount is 0.01 parts by weight or less, the effect on filming is small, and if the amount is 5.0 parts by weight or more, the cohesiveness is increased and the photoreceptor is uselessly scratched.

To the magnetic toner according to the present invention, negatively charged hydrophobic silica fine particles surface-treated with silicone oil are added. 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 a thermal decomposition oxidation reaction in oxyhydrogen flame of silicon tetrachloride gas. The general formula of the reaction is shown in (Chemical Formula 3).

[0085]

Embedded image

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

A known technique is used as the surface treatment method, 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.

If necessary, a suitable pigment or dye is added to the magnetic toner according to the present invention for the purpose of controlling coloring and charge. Examples of such pigments or dyes include carbon black, iron black, graphite, nigrosine, metal complexes of azo dyes, phthalocyanine blue, DuPont oil red, aniline blue, benzidine yellow, rose bengal, and mixtures thereof, etc., and charge amount, The amount required for coloring is blended.

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 a magnetic substance. As magnetic powder, 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 is preferably 15 to 70% by weight. When the addition amount is 15% by weight or less, the toner scattering tends to increase, and when the addition amount is 70% by weight or more, the toner charge amount tends to decrease and the image quality tends to deteriorate.

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 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 generating layer in which a charge generating 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 2 is a non-rotating magnet fixed coaxially with the photoconductor 1, 3 is a corona charger for negatively charging the photoconductor, 4 is a grid electrode for controlling the charging potential of the photoconductor, 5
Is the 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 between the photoconductor 1 and the gap. A non-magnetic electrode roller set to open, 9 is a non-rotating magnet installed inside the electrode roller 8, 10 is an AC high voltage power source for applying a voltage to the electrode roller 8, and 11 is polyester for scraping off toner on the electrode roller The scraper is made of a film, and the electrode roller 8 collects 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 being clogged between the photosensitive member and the electrode roller.

Reference numeral 13 is a transfer roller for transferring the toner image on the photoconductor to the paper, and 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 foaming lithium salt was internally added to the periphery of a mm shaft was used, and the resistance value was 10 ⁷ Ω (electrodes were provided on the shaft and the surface, and 500 V was applied to both electrodes). 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 is 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. 14 is a transfer roller for the transfer paper 1
A rush guide made of a conductive member to be introduced into 3 and a conveying guide 15 having an insulating coating on the surface of the conductive member. The plunge guide 14 and the transport guide 15 are grounded directly or through a resistor. 16 is a transfer paper, 17 is a transfer roller 13
It is a voltage generating power supply that applies a voltage to the.

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

Although an elastic urethane blade was used as the cleaning blade, a fur brush to which a bias was applied,
Similar results are obtained with a conductive metal roller.

The magnetic flux density on the surface of the photoconductor 1 is 600 Gs. The magnetic force inside the electrode roller was strengthened to improve 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 rotated at m / s in the direction of the arrow in the figure and used. 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 transferred to the electrode roller 8
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 base particles of the present invention.

[0104]

[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.

[0106]

[Table 2]

The measurement of the charge amount of the melamine fine particles is the same as the condition for measuring the charge amount of the magnetic toner. The difference is that instead of the non-coated ferrite carrier, the coarsely crushed magnetic toner base particles before crushing have an opening diameter of It was used after being sieved with a mesh having a diameter of 100 μm. Mixed concentration is 3
%.

The specific surface area is measured by an ordinary BET measuring method,
Shimadzu specific surface area measuring device FlowSorb2-2
300 was used.

The production of the magnetic toner of the present invention will be described. The mixture shown in (Table 1) was used as a Henschel mixer FM.
Mix with 20B (Mitsui Miike). The mixture is heated and kneaded with a twin-screw kneading extruder PCM30 (manufactured by Ikegai Tekko KK). 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 jet mill pulverizer IDS-2 type (made by Nippon Pneumatic Mfg. Co., Ltd.). Air flow classifier DS2
Cut fine powder with a mold (made by Nippon Pneumatic Mfg. Co., Ltd.). By the above treatment, magnetic toner base particles having an average particle diameter of 8 μm were obtained. Then, the external additive was externally added.

The material composition of the magnetic toner A1 of the present invention is shown in (Table 3).

[0111]

[Table 3]

Hydrophobic silica treated with melamine fine particles and polydimethyl silicone oil was used as an external additive.

As shown in Table 2, it is understood that the magnetic toner A1 has high fluidity and high charging property.

Using the electrophotographic apparatus shown in FIG. 1, 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. There is no decrease in the fluidity of the toner after 10,000 sheets, a high charge amount is maintained, and filming does not occur on the photoreceptor. High density, comparable to the early images,
A copy image of the lowland fog was obtained.

(Embodiment 2) FIG. 2 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 generating layer in which a charge generating 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 in FIG. 1 of the first embodiment.

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. There is no decrease in the fluidity of the toner after 10,000 sheets, a high charge amount is maintained, and filming does not occur on the photoreceptor. High density, comparable to the early images,
A copy image of the lowland fog was obtained.

(Comparative Example 1) A magnetic toner B1 was manufactured as a trial with the same composition and formulation as in Example 1 except that the external additives were different.
Table 4 shows the material composition of the magnetic toner B1.

[0122]

[Table 4]

Only the hydrophobic silica surface-treated with dimethyldichlorosilane was used as the external additive.

Using the electrophotographic apparatus shown in FIG. 1 of 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, the image density was slightly low and the image was heavily fogged.

In the long-term copying test, toner filming occurred after about 2000 sheets.

(Comparative Example 2) Using the electrophotographic apparatus of Example 2 shown in FIG. 2, a copying test was conducted using magnetic toner B1. The image density was measured by a reflection densitometer (Macbeth) and evaluated. As a result, the image density was slightly low and the image was heavily fogged.

In the long-term copying test, toner filming occurred after about 2000 sheets.

(Comparative Example 3) The addition amount of the magnetic material was 10% by weight.
A toner was trial-produced with the same composition as in Example 1 except for the above. 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 silica added was changed to 0.05 part by weight. The fluidity was poor and practical properties could not be obtained.

(Comparative Example 6) A toner was experimentally manufactured with the same composition as in Example 1 except that the amount of silica added was 6 parts by weight.
There were many silica aggregates and many white spots adhered to the solid black image area, and practical properties could not be obtained.

(Comparative Example 7) The amount of melamine fine particles added was 6
A toner was trial-produced with the same composition as in Example 1 except that the parts by weight were used. Many aggregates of fine melamine particles were generated, and many scratches were generated on the photoreceptor, so that practical characteristics could not be obtained.

[0133]

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,
An electrophotographic method comprising a transfer step using a conductive elastic roller and a cleaning step, wherein a toner having high fluidity and high chargeability is obtained by containing melamine fine particles and silica fine particles surface-treated with silicone oil. In high-performance, small size, low cost development method, high density,
It is possible to achieve high image quality in low-lying fog.

Further, it is possible to provide an electrophotographic method capable of preventing a hollow portion at the time of transfer, suppressing the occurrence of toner filming on the photoconductor even when used for a long time, and obtaining a stable image.

[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 Photoreceptor Drum 2 Fixed Magnet 3 Enclosed in Photoreceptor 3 Corona Charger 4 Grid Electrode 6 Toner Hopper 7 Magnetic Toner 8 Electrode Roller 9 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 the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 15/16 103 G03G 9/08 372 374

Claims (14)

[Claims] 1. A developing step of visualizing an electrostatic latent image formed on an electrostatic latent image holder with magnetic toner, and a conductive elastic roller contacting the electrostatic latent image holder, A transfer sheet is inserted between the electrostatic latent image holder and the conductive elastic roller, and the electrostatic latent image on the electrostatic latent image holder is applied by a transfer bias voltage applied to the conductive elastic roller. A transfer step of transferring the magnetic toner visualized to the transfer paper, and a cleaning step of removing the magnetic toner partially remaining on the electrostatic latent image holder from the electrostatic latent image holder during the transfer step. The magnetic toner is composed of at least a binder resin, a magnetic material, and an external additive, and the external additive has an average particle diameter of 0.01 to 12 μm.
m, BET specific surface area due to nitrogen adsorption is 0.1 to 50 m ²
/ G of melamine as a main component, and a BET specific surface area due to nitrogen adsorption of 50 to 350 m ² / g
An electrophotographic method comprising using a magnetic toner comprising the negatively-charged hydrophobic silica fine particles of 2. The electrophotographic method according to claim 1, wherein a magnetic toner in which the negatively-charged hydrophobic silica fine particles are surface-treated with silicone oil is used. 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. The electrophotographic method according to claim 1, wherein the magnetic toner contains fine particles containing melamine as a main component in an amount of 0.01 to 5.0 parts by weight based on 100 parts by weight of the magnetic toner. . 5. The electrophotographic method according to claim 1, wherein the magnetic toner contains 0.1 to 5.0 parts by weight of the negatively chargeable hydrophobic silica fine particles with respect to 100 parts by weight of the magnetic toner. . 6. The electrophotographic method according to claim 1, wherein in the transfer step, the elastic member of the elastic roller is a urethane foam to which a conductivity-imparting agent is added. 7. 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. 8. An electrostatic latent image holder that moves by enclosing a fixed magnet, a toner hopper, and a toner recovery member having a magnet inside at a position having a predetermined gap from the surface of the electrostatic latent image holder. An electrode roller, after forming an electrostatic latent image on the electrostatic latent image holder, magnetically attract magnetic toner to the surface of the electrostatic latent image holder located in the toner hopper, The magnetic toner is carried on the surface of the electrostatic latent image carrier,
The electrostatic latent image holding member is moved to face the toner collecting electrode roller, magnetic toner is left in the image portion of the electrostatic latent image holding member, and magnetic toner in the non-image portion is collected by the toner collecting electrode roller. And a conductive elastic roller that is in contact with the electrostatic latent image holder, and a transfer paper is inserted between the electrostatic latent image holder and the conductive elastic roller. And a transfer step of transferring the magnetic toner, which visualizes the electrostatic latent image on the electrostatic latent image holding body by a transfer bias voltage applied to a conductive elastic roller, onto the transfer paper. A cleaning step of removing the magnetic toner partially remaining on the electrostatic latent image holding member from the electrostatic latent image holding member during the transfer step, wherein the magnetic toner is at least bound. Resin, Sex body, is composed of an external additive, the external additive is at least an average particle diameter 0.01~12μ
m, BET specific surface area due to nitrogen adsorption is 0.1 to 50 m ²
/ G of melamine as a main component, and a BET specific surface area due to nitrogen adsorption of 50 to 350 m ² / g
An electrophotographic method comprising using a magnetic toner composed of negatively charged hydrophobic silica fine particles. 9. The electrophotographic method according to claim 8, wherein a magnetic toner in which the negatively chargeable hydrophobic silica fine particles are surface-treated with silicone oil is used. 10. The magnetic material is 15 parts by weight based on the weight of the magnetic toner.
9. The electrophotographic method according to claim 8, wherein a magnetic toner containing about 70% by weight is used. 11. The electrophotographic method according to claim 8, wherein the magnetic toner contains fine particles containing melamine as a main component in an amount of 0.01 to 5.0 parts by weight based on 100 parts by weight of the magnetic toner. . 12. The electrophotographic method according to claim 8, wherein the negatively chargeable hydrophobic silica fine particles are used in the amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the magnetic toner. . 13. The electrophotographic method according to claim 8, wherein in the transfer step, the elastic member of the elastic roller is a urethane foam to which a conductivity-imparting agent is added. 14. The electrophotographic method according to claim 8, wherein the conductivity imparting agent dispersedly added to the urethane foam in the transfer step is a lithium salt.