JP3168377B2 - Electrophotographic carrier, two-component developer and image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier in a developer used for developing an electric latent image or a magnetic latent image in an electrophotographic method or an electrostatic printing method. The present invention relates to a carrier for electrophotography, a two-component developer and an image forming method, which have significantly improved environmental characteristics.

[0002]

2. Description of the Related Art A carrier constituting a two-component developer is as follows.
The carrier is roughly divided into a conductive carrier and an insulating carrier.As the conductive carrier, oxidized or unoxidized iron powder is usually used.In a developer containing the iron powder carrier as a component,
There is a drawback that the triboelectric charging property with respect to the toner is unstable, and that a visible image formed by the developer is fogged. That is, with the use of the developer, toner particles adhere and accumulate (spent toner) on the surface of the iron powder carrier particles, so that the electric resistance of the carrier particles increases, the bias current decreases, and the frictional charge is increased. As a result, the image density of the visible image formed decreases, and fog increases. Therefore, when copying is continuously performed by an electronic copying apparatus using a developer containing an iron powder carrier, the developer deteriorates in a small number of times, so that it is necessary to replace the developer at an early stage, which results in a high cost. It will be.

[0003] A typical example of an insulating carrier is a carrier obtained by uniformly covering the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, or ferrite with an insulating resin. In a developer using this carrier, toner particles are less likely to fuse to the surface of the carrier than in the case of a conductive carrier, and at the same time, it is easy to control the triboelectric charging property between the toner and the carrier, and the durability is high. This is advantageous in that it is particularly suitable for high-speed electronic copiers in that it has excellent service life and a long service life.

There are various characteristics required for the insulating carrier, but particularly important characteristics are appropriate chargeability, impact resistance, abrasion resistance, good adhesion between the core and the coating material, and good charge distribution. Uniformity and the like.

In view of the above-mentioned required characteristics, conventionally used insulating carriers still have a problem to be improved, and the perfect carrier has not been known so far.
For example, examples in which an acrylic resin or the like is used as a carrier coating material are disclosed in JP-A-47-13954 and JP-A-60-1985.
-208765. In addition, those which particularly describe the molecular weight are disclosed in
It is disclosed in, for example, Japanese Patent Application Laid-Open No. 0-208767, and it is known that the chargeability of a coated carrier is stabilized by controlling the molecular weight to be constant. However, in order to attach the coating resin to the carrier core material, it is easily affected by the conditions of the apparatus and the environment in which the coating is performed, particularly humidity. Even if these are strictly controlled, the resin is stably attached to the core material. At present, there is no satisfactory material for providing sufficient chargeability and durability.

On the other hand, it has been proposed to improve the durability by using a resin having a small surface energy as a coating layer in order to prevent spent of a carrier such as toner fusion or the like. For example, silicone resin is used as a resin having a small surface energy. No.

[0007] Silicone resins have the advantage of high water repellency in addition to low surface tension. On the other hand, the silicone resin has a problem that it is easily peeled off when used for the coating layer because of poor adhesion.

In order to solve this problem, for example, a method using a resin-modified silicone resin (Japanese Patent Laid-Open No. 55-1275)
No. 69), a method of containing vinylsilane and reacting with another resin (JP-A-56-32149), a method using a mixture of trialkoxysilane and ethylcellulose (US Pat. No. 3,840,464), an organosilicone terpolymer. (US Pat. No. 3,849,127) using a mixture of styrene and polyphenylene resin has been proposed. However, a high temperature of 300 ° C. or more is required for forming the coating film, or a silicone resin and another resin may be used. There is a problem that the compatibility is poor and the coating film becomes non-uniform and the expected characteristics cannot be obtained. It has also been proposed to form a coating film at a relatively low curing temperature (Japanese Patent Laid-Open No. 55-12756).
No. 9) is liable to wear due to insufficient adhesiveness and insufficient toughness of the coating film. For example, carrier particles are hardly agitated in a developing section such as a high-speed copying machine for a long time. If the particles collide with the inner wall of the developing unit or the surface of the photoreceptor, or the particles collide with each other, the silicone resin coating layer is worn and peeled over time, and the frictional charge is changed from the charge between the toner and the silicone resin. Since the charge of the developer is changed, the charge amount of the developer is not kept constant, and the image quality is deteriorated.

Further, in recent years, the demand for high definition and high image quality of copying machines has been increasing in the market, and in the technical field, attempts have been made to achieve high image quality and color by reducing the particle size of toner. However, as the particle size becomes smaller, the surface area per unit weight increases, and the amount of charged electricity of the toner tends to increase.

Further, in color copying using a chromatic toner, continuous tone is an important factor affecting the image quality, and an edge effect in which only the peripheral portion of the image is emphasized after copying a large number of sheets occurs. Significantly impairs the gradation of the image. For example, a pseudo contour by an edge effect is formed in the vicinity of an actual contour, thereby deteriorating copy reproducibility including color reproducibility in color copying. Further, the image area used in the conventional black-and-white copy is 10% or less, and the image is almost a line image portion such as a letter, a document, a report, and the like. 20% or more, and solid images having gradation such as photographs, catalogs, maps, and pictures occupy a considerable frequency or area.

When a continuous copy is performed using such a document having a large image area, a copy having a high image density is usually obtained in the initial stage, but toner supply to the two-component developer gradually becomes insufficient. The replenishment toner and the carrier are mixed with each other in a state where the density is lowered or the charging is insufficient, which causes fogging or a partial toner density on the developing sleeve (indicating a mixing ratio of the toner and the carrier). Tends to increase or decrease, making it difficult to obtain image blur and uniform image density. This tendency is more remarkable when the diameter of the toner is reduced.

This is because the amount of toner included in the developer (that is, the toner concentration) is too low, or the rapid rise of triboelectric charging between the replenishment toner and the carrier in the two-component developer is poor and uncontrollable. It is considered that such insufficient development and fogging occur due to the fact that a toner having an insufficient charge is involved in the development. As a color developer, the ability to always output a high-quality image by continuous copying of a document having a large image area is essential. Conventionally, in order to cope with an original having a large image area and a very large amount of toner consumption, improvement of the developing device rather than improvement of the developer itself has been dealt with more. That is, in order to increase the chance of the developing sleeve contacting the electrostatic latent image, the peripheral speed of the developing sleeve is increased, or the size of the developing sleeve is increased.

Although these countermeasures improve the developing ability, the inside of the apparatus is contaminated by toner scattering from the developing device,
Overload on the driving of the developing device may significantly limit the life of the device. In addition, in some cases, a large amount of developer is charged into the developing device to compensate for the lack of developing ability of the developer. However, these problems also increase costs due to an increase in the weight of the copier and an increase in the size of the device. As described above, this results in overload on the driving of the developing device, which is not very preferable.

[0014]

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

That is, an object of the present invention is to provide an electrophotographic carrier, a two-component developer, and an image forming method which do not cause a decrease in image density and no blurring even when continuous copying of a color original having a large image area is performed. It is in.

It is a further object of the present invention to provide a two-component carrier for electrophotography and an image forming method, which has clear image characteristics without fog and has excellent durability stability.

Another object of the present invention is to provide a carrier for electrophotography, a two-component developer, and an image forming method, in which the image density is less dependent on the environment.

[0018]

The present invention has solved the above-mentioned problems by the following constitution.

That is, the present invention relates to a ferrite component represented by the following formula (I): formula (I) (Fe ₂ O ₃ ) _x (MO) _{1 -x} (where M is Li, Mn, Mg, Ca, Al , Si and Sr represent one or more metal elements selected from the group consisting of x, x represents a weight fraction, and 0.2 ≦
x ≦ 0.95. ) 100 parts by weight of Bi ₂ O ₃
Is a carrier for electrophotography in which the surface of a magnetic carrier core material containing 0.05 to 5 parts by weight is coated with a crosslinkable silicone resin and / or a fluorine-containing resin, and the resin coating amount is based on 100 g of the magnetic carrier core material. Ag coverage
When the specific surface area of the coated carrier is Scm ² / g, the following relationship (a / S) × 10 ⁴ = 2 to 40 (where a is 0.01 to 20) is satisfied; The present invention relates to a carrier for electrophotography, wherein the carrier has a current value of 20 to 300 μA (the present invention 1).

Still another aspect of the present invention relates to a carrier wherein the surface of the magnetic carrier core material according to the present invention 1 is coated with a resin, and at least a weight average particle size of 0.001 to 0.2 as an external additive.
a toner having a weight average particle diameter of 1 to 9 μm containing inorganic fine particles of μm (Invention 2).

Still another aspect of the present invention is to rotate a magnet roller and a developer carrier among a developer carrier and a magnet roller incorporated therein, or to fix a magnet roller to carry a developer carrier. Rotate the body,
A two-component color developer containing at least a carrier and a color toner is circulated and conveyed over the developer carrier, and the latent image is developed with the color toner in the developing region of the latent image carrier and the developer carrier opposed thereto. In an image forming method for developing and transferring a toner image formed on a latent image carrier onto a transfer material, the carrier and the toner according to the second aspect of the present invention, and the developing method comprises: DC /
The present invention relates to an image forming method which is a developing method for developing a latent image with toner by applying at least an AC superposed electric field (the present invention 3).

The present inventors have conducted various studies and studies to improve the above-mentioned conventional problems. As a result, a carrier obtained by coating a carrier having a specific composition with a resin having a specific composition is effective in improving various characteristics. The present inventors have found that the present invention 1 has been completed.

That is, the present inventors have made intensive studies on the image density, highlight reproducibility, and fine line reproducibility of a two-component developer, and as a result, when a carrier having a specific carrier resistance and fluidity is used, the high reproducibility is obtained. They have found that high image quality with excellent image density, highlight reproducibility, fine line reproducibility, etc. can be achieved.

In order to increase the resistance of the carrier core material, for example, Japanese Patent Application Laid-Open No. 61-200551 discloses
Additives that do not affect magnetic properties have been proposed.
Although these additives do increase the carrier resistance,
The durability of the developer is not always satisfactory, such as the rise of toner charge and toner sticking, and the center particle size is very coarse between 150 and 250 mesh, making it possible to continuously copy original documents with a high image ratio. Further improvements are desired.

On the other hand, various coated carriers coated with a large amount of resin have been proposed in order to increase the carrier resistance. However, when the resin coating reduces the carrier fluidity, especially when the carrier particle size is reduced, the carrier is rather reduced. The mixing property of the toner is deteriorated, and image deterioration, fogging and the like are generated, and improvement is required.

However, as the carrier used in the present invention, a carrier core material having a large volume resistance is used, and the surface of the carrier core material is thin-layered with a crosslinkable silicone resin having a small surface free energy or / and a fluorine-containing resin. The coating is very effective for high image quality and high stability even if the carrier particle size is reduced without impairing the carrier fluidity.

The ferrite composition which can be used in the present invention is represented by the formula (I). If x is smaller than 0.2, desired magnetic properties cannot be obtained and carrier adhesion and transportability are reduced. When x exceeds 0.95, Bi ₂ O ₃
Even if a large amount is added, the resistance is reduced, and as a result, the resin coating amount is increased, and the carrier fluidity is reduced.

Further, the coating resin suitably used in the present invention includes a curing agent represented by the following general formula (II):

[0029]

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More preferably, the following general formula (III)
An aminosilane coupling agent represented by R _m Si—Y _n (III) (wherein, R represents an alkoxy group, Y represents a hydrocarbon group containing an amino group, m represents an integer of 1 to 3, n represents an integer of from 3 to 1). When a reactive silicone resin containing (a) is coated, a good adhesion and chargeability are achieved even when a thin layer is coated on a carrier core material, and a very high level is achieved. A long-life carrier with high performance can be obtained.

JP-A-2-33159 also discloses that the above-mentioned general formulas (II) and (III) are contained. However, in the present invention, the OH held in the carrier core material is used. It is characterized by reacting the above-mentioned reactive silicone resin with the base or residual moisture / adsorbed moisture, and as a result, a coated carrier with improved strength can be obtained even with a thin layer coat, which is different from the above invention. Things. Therefore, as a carrier core material composition preferably used in the present invention, Li having an appropriate affinity for water is used.
₂ O, CaO, MgO, and the like are preferable in terms of production stability and storage stability because ferrite particles are easily homogenized and spheroidized and contain a suitable amount of water.

Further, the carrier of the present invention desirably has a specific surface property and the following particle size distribution.

That is, the carrier used in the present invention is a carrier having a small average particle size, a uniform small particle size carrier having a uniform particle size by controlling the abundance of fine powder and coarse powder, and having a certain degree of unevenness on its surface. It is a career that I made.
Therefore, even if the resin is coated with a resin having a small free energy, the transportability of the toner is good and the rise of the triboelectric charging property with the toner is also preferably improved.

This will be described in more detail.

As the carrier, the 50% average particle size of the carrier is 15 to 60 μm, preferably 20 to 45 μm, and the carrier particles smaller than 22 μm are 1 to 20%, preferably 2 to 15%, more preferably 4 to 45%. It is 12% and the carrier particles smaller than 16 μm are 3% or less, preferably 2% or less, more preferably 1% or less.

If the amount of the fine powder exceeds the above-mentioned value, it becomes difficult to uniformly coat the resin on the carrier core material, causing the carrier to adhere or preventing the toner from being charged smoothly.
Image results such as fog are generated. If the carrier particles having a particle size of less than 22 μm are less than 1%, the magnetic brush will be in a sparse state, causing image deterioration such as a decrease in solid uniformity and a decrease in fine line reproducibility.

Further, the amount of coarse particles of the carrier having a size of 62 μm or more closely correlates with the sharpness of an image, and needs to be 2 to 20%. If it exceeds 20%, the toner carrying ability of the carrier is reduced, the scattering of the toner to the non-image portion is increased, the resolution of the image is reduced, and the highlight reproducibility is reduced. On the other hand, if the content is less than 2%, even if the carrier is a thin-layer coated carrier, the fluidity of the carrier is reduced, that is, the fluidity of the developer is reduced, and the ability to impart charge to the toner is reduced,
It becomes difficult to obtain a stable image.

As a core material of a ferrite carrier containing the above-mentioned metal oxide, for example, JP-A-59-111159
JP-A-58-123551, JP-A-55-123551
No. 5406, etc., but these are not intended to improve the carrier fluidity and durability in a thin coat, not only because the particle size distribution is not controlled, and are different from the present invention. It is.

JP-A-2-33159 also discloses that the above-mentioned metal oxide may be contained. However, this also positively controls the surface of the carrier core material, improves the carrier fluidity, and improves the toner carrying capacity. There is no suggestion to increase the improvement, which is different from the present invention.

The curing agent in the present invention includes, for example, those shown below.

[0041]

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The addition amount is 0.1 to 10 parts by weight, preferably 0.5 to 10 parts by weight, based on 100 parts by weight of the solid siloxane component.
It is preferable to add 5 parts by weight. If less than 0.1 parts by weight,
If the cross-linking effect is not sufficient and the amount exceeds 10 parts by weight, the residue cannot be sufficiently removed or a compound with an insufficient reaction remains, and the charging characteristics and strength are reduced.

Further, the amount of the resin to be covered is determined by the carrier core material 1
When the coating amount for 00 g is ag and the specific surface area of the coated carrier is Scm ² / g, the following relationship (a / S) × 10 ⁴ = 2 to 40 (where a is 0.01 to 20 It is necessary to satisfy the following relationship (a / S) × 10 ⁴ = 5 to 30 (where a is 0.01 to 20). When the amount of coating is in relation, the fluidity of the carrier is not impaired, and extremely excellent properties including durability and chargeability are exhibited.

In order to make the present invention more effective, a is preferably from 0.02 to 1.8, and more preferably from 0.05 to 1.5.

By using the carrier in the toner to which the inorganic fine particles of the present invention are externally added, carrier deterioration does not occur even when copying a large number of sheets, and an initial high-quality image can be retained. Further, in any environment, it is possible to obtain good chargeability and charge rising characteristics.

The general formula (I) used for the carrier of the present invention
Examples of the aminosilane coupling agent represented by II) include the following.

[0047]

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One or more of these can be used. Among them, those preferably used in the present invention include:
The following coupling agents having at least one nitrogen atom having one hydrogen atom in terms of compatibility, reactivity, and stability.

[0049]

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The addition amount is 0.1 to 8 parts by weight, preferably 0.3 to 5 parts by weight, based on 100 parts by weight of the solid siloxane component.
Parts by weight are preferred. If the amount is less than 0.1 part by weight, a sufficient effect of addition cannot be obtained, resulting in deterioration of chargeability and a decrease in coating strength.
If the amount exceeds 8 parts by weight, a sufficient reaction is not performed, and conversely, the coating strength is reduced.

In the present invention, the coupling agent may further be represented by the following general formula (IV): R _4-a —Si—Xa (IV) (where R _4-a represents a vinyl group, a methacryl group, an epoxy group) , An amino group, a mercapto group, or a derivative thereof, and X represents a halogen or an alkoxy group).

Examples of such a coupling agent include the following. (14) CH ₃ ＣＨCH—Si— (OCH ₃ ) ₃ (15) CH ₃ —Si— (OCH ₃ ) ₃ (16) CH ₃ —Si— (OC ₂ H ₅ ) ₃

In order to coat the resin on the carrier core material, a method of dissolving the resin composition in an appropriate solvent, immersing the core material in the obtained solution, and then removing the solvent, drying and baking at a high temperature, Alternatively, a method in which the core material is suspended in a fluidizing system, the above-mentioned copolymer solution is sprayed and applied, dried and baked at a high temperature, or simply mixed with a powder or an aqueous emulsion can be used.

In the present invention, preferably used are
A method using a mixed solvent containing 0.1 to 5 parts by weight of water, preferably 0.3 to 3 parts by weight of water in a solvent containing a polar solvent such as ketones and alcohols is based on reactive silicone resin. It is desirable to firmly adhere to the material. If the amount of water is less than 0.1 part by weight, the hydrolysis reaction of the reactive silicone resin is not sufficiently performed, and it is difficult to coat the surface of the carrier core material in a thin and uniform manner. It becomes difficult, and conversely, the coating strength decreases.

Next, in the present invention, at least a weight average particle size of 0.001 to 0.2 μm is used as an external additive of the toner.
Another feature is that the developer is a toner comprising a toner having a weight average particle diameter of 1 to 9 μm containing inorganic fine particles of the present invention (the present invention 2).

In particular, surface-treated titanium oxide and alumina are preferred. That is, the alumina and titanium oxide fine particles themselves have a substantially neutral charge, and the toner to which they are added generally has a slower rise in charge. However, in combination with the carrier described in the first aspect of the present invention, even in a toner containing titanium oxide and alumina fine particles, a very good rise of charging is achieved, and an original having a large image area such as a full-color original can be continuously formed. Even when copying or printing out, image quality deterioration such as fogging and image density reduction does not occur.

As the titanium oxide or alumina fine particles preferably used in the present invention, anatase type titanium oxide or amorphous titanium oxide or alumina fine particles which have been subjected to a surface treatment while hydrolyzing a coupling agent in the presence of water may have a stable charge. It is extremely effective in terms of conversion and fluidity.

The use of anatase-type titanium oxide has been proposed in, for example, Japanese Patent Application Laid-Open No. 60-112052. However, anatase-type titanium oxide has a small volume resistivity of about 10 ⁷ Ωcm, and When used, the charge leaks particularly quickly under high humidity, which is not always satisfactory in terms of the stabilization of the charge, and needs improvement.

Further, as an example of the toner containing hydrophobic titanium oxide, Japanese Patent Application Laid-Open No. Sho 59-52255 proposes a toner containing titanium oxide treated with alkyl trialkoxysilane. ,
Certainly, although the electrophotographic properties have been improved, the surface activity of titanium oxide is inherently low and unified particles are formed at the processing stage and the hydrophobicity is not uniform, which is not always satisfactory. Was.

The present inventors have conducted intensive studies on the stability of the charging property of the toner. As a result, the specific coupling agent was treated while hydrolyzing in the presence of water, and the average particle diameter was 0.001.
Anatase type or amorphous titanium oxide or amorphous alumina having a hydrophobicity of 20 to 80% with a hydrophobicity of 20 to 80% can be subjected to a uniform hydrophobic treatment, and there is no coalescence between particles. Toner
They have found that they are extremely effective in stabilizing charging and imparting fluidity.

That is, surface treatment is performed while anatase type or amorphous titanium oxide or amorphous alumina fine particles are mechanically dispersed to have a primary particle size in the presence of water, or while the coupling agent is hydrolyzed while atomizing. So that coalescence of the particles is unlikely to occur,
In addition, it was found that the repelling action between the particles by the treatment worked, and the fine particles were surface-treated in a state of almost primary particles.

Further, when the surface is treated while hydrolyzing the coupling agent in the presence of water, a mechanical force for dispersing the fine particles into the primary particles is applied, so that the fine particles such as chlorosilanes and silazanes are used. It is not necessary to use a coupling agent that generates a gas, and it is also possible to use a highly viscous coupling agent, which was previously unreactive in the gas phase and could not be used. Is overwhelming.

The coupling agent may be any of a silane coupling agent, a titanium coupling agent and the like. Particularly preferably used is a silane coupling agent of the general formula R _m SiY _n R: Arukookishi group m: 1 to 3 integer Y: alkyl group vinyl group, glycidoxy group, a hydrocarbon group containing a methacrylic group n: 1 Represented by an integer of -3, for example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane , Dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane and the like. That. Particularly _{preferred, C α H 2α + 1 -Si} (OC β H 2β + 1) 3 α = 4~12, a beta = 1 to 3.

Here, when α in the general formula is smaller than 4, processing becomes easy, but sufficient hydrophobicity cannot be achieved.
If α is larger than 12, the hydrophobicity is sufficient, but the coalescence of the particles is increased, and the fluidity-imparting ability is reduced. On the other hand, if β is larger than 3, the reactivity is lowered and the hydrophobic treatment is not sufficiently performed. Therefore, in the present invention, α is 4 to 12, preferably 4 to 8, and β is 1 to 3, preferably 1 to 2.

The treatment amount is 1 to 50 parts by weight, preferably 3 to 40 parts by weight, based on 100 parts by weight of the fine particles, and the degree of hydrophobicity is 20 to 98%, preferably 30 to 90%.
%, More preferably 40 to 80%.

That is, if the degree of hydrophobicity is less than 20%, the charge amount is greatly reduced due to long-term storage under high humidity, and a mechanism for accelerating the charge on the hard side is required. If the degree exceeds 98%, the resistance of the fine particles increases, and it becomes difficult to control the charge of the external additive itself. As a result, the toner is charged up under low humidity.

Further, the particle size is 0.0
01 to 0.2 μm is good. If the particle size is larger than 0.2 μm, toner charging due to poor fluidity becomes non-uniform, resulting in toner scattering and fogging. 0.0
When the thickness is smaller than 01 μm, the toner is easily embedded on the surface of the toner, so that the toner deteriorates quickly and the durability is reduced. This tendency is more remarkable in the color toner having the sharp melt property.

Further, the light transmittance of the fine particles treated as described above at a light length of 400 nm is preferably 40% or more.

That is, the external additive used in the present invention 2 has a very small primary particle diameter of 0.2 to 0.001 μm. Are not dispersed but may be present as secondary particles. Therefore, no matter how small the primary particle diameter is, the effect of the second aspect of the present invention is reduced if the effective diameter acting as a secondary particle is large. However, the higher the light transmittance at 400 nm, which is the lower limit wavelength in the visible region, the smaller the secondary particle size, the better the results such as the ability to impart fluidity and the sharpness of the projected image of the OHP in the case of color toner. it can. The reason for choosing 400 nm is the boundary region between ultraviolet and visible light, which is の of the light wavelength.
Since it is said that the particles having the following particle diameters are transmitted, the transmittance at wavelengths longer than that is naturally increased, and is not meaningful.

Further, the present inventors have found that the crystal form of alumina or titanium oxide determined by X-ray diffraction is amorphous with no peak or lattice constant (a) is 3.78 °,
It has been confirmed that the lattice constant (b) is anatase-type titanium oxide having 9.49 °.

The titanium oxide described above works well when combined with a toner having the following particle size distribution. That is, when the particle size of the toner is reduced, the surface area per weight increases, and excessive charging due to rubbing tends to occur. On the other hand, the effect of fine particles that can control charging and impart fluidity is great. The content of the fine particles suitable for the present invention is 0.5 to 5% by weight, preferably 0.7 to 3% by weight, and more preferably 1.0 to 2.5% by weight.

In the toner according to the present invention, the toner particles having a particle diameter of 4 μm are 10 to 70% by number of the total number of particles, preferably 15 to 60% by number. When the toner particles having a particle size of 4 μm or less are less than 10% by number, the amount of non-magnetic toner particles effective for high image quality is small. In particular, as the toner is used by continuing copy or printout, the effective non-magnetic toner The particle component is reduced, the balance of the particle size distribution of the non-magnetic toner is deteriorated, and the image quality may be gradually reduced. The tendency is remarkable especially when combined with the carrier according to the present invention. On the other hand, if the content exceeds 20% by number, toner particles are likely to aggregate with each other, and the toner particles are liable to become larger than the original particle size, resulting in rough image quality, reduced resolution, or poor latent image quality. The density difference between the edge portion and the inside becomes large, and the image tends to be slightly hollow.

Further, particles having a particle size of 8 μm or more
0.0% by volume, preferably 3.0 to 1%.
8.0 vol% is good. If the content is more than 20.0% by volume, the image quality is deteriorated, and the development is performed more than necessary, that is, the toner is overloaded, which leads to an increase in toner consumption. on the other hand,
When the content is less than 2.0% by volume, there is a possibility that the image quality may be reduced due to a decrease in fluidity regardless of how the toner formulation is devised.

In order to further improve the effects of the present invention, in order to improve the chargeability and fluidity of the toner,
More than 40% by number of particles having a particle size of 5.04 μm or less 9
0% by number or less, preferably more than 40% by number and 80% by number or less, and particles having a particle size of 10.08 μm or more
-6% by volume, preferably 0-4% by volume.

The toner according to the present invention may contain a charge control agent in order to stabilize the charge characteristics. At that time, a colorless or light-colored charge control agent that does not affect the color tone of the toner is preferable. Examples of the negative charge control agent in this case include an organic metal complex such as a metal complex of an alkyl-substituted salicylic acid (for example, an aluminum complex or a zinc complex of di-tert-butylsalicylic acid). When the negative charge control agent is blended with the toner, 0.1 to 100 parts by weight of the binder resin is used.
It is good to add 10 to 10 parts by weight, preferably 0.5 to 8 parts by weight.

When the two components are prepared by mixing the carrier and the toner according to the present invention, the mixing ratio is preferably 2 to 12% by weight, preferably 3 to 9% by weight as the toner concentration in the developer. Results are obtained. Toner density is 2
If the amount is less than 12% by weight, the image density is low and the image becomes unpractical. If the amount is more than 12% by weight, fog and scattering in the machine are increased, and the useful life of the developer is shortened.

As the coloring agent used in the present invention, known dyes and pigments such as phthalocyanine blue, induslen blue, peacock blue, permanent red, lake red, rhodamine lake, Hansa yellow, permanent yellow and benzidine yellow are widely used. can do. The content thereof is 12 parts by weight or less, preferably 0.5 to 9 parts by weight, based on 100 parts by weight of the binder resin so as to reflect sensitively on the permeability of the OHP film.

Additives may be added to the toner of the present invention as needed as long as the properties of the toner are not impaired. Examples of such additives include Teflon, zinc stearate, and polyvinylidene fluoride. Lubricants, fixing aids (eg, low molecular weight polyethylene, low molecular weight polypropylene, etc.), and organic resin particles.

In the production of the toner of the present invention, the constituent materials are well kneaded with a hot kneader such as a hot roll, kneader, extruder, etc., and then obtained by mechanical pulverization and classification, or in a binder resin solution. After dispersing a material such as a colorant in the method obtained by spray drying, or
After mixing the predetermined material with the monomer that should constitute the binder resin,
Each method such as a polymerization toner production method of obtaining a toner by polymerizing this emulsion suspension can be applied.

As the binder used in the toner of the present invention, various material resins conventionally known as toner binder resins for electrophotography are used.

For example, styrene-based copolymers such as polystyrene, styrene-butadiene copolymer and styrene-acrylic copolymer, and ethylene-based copolymers such as polyethylene, ethylene-vinyl acetate copolymer and ethylene-vinyl alcohol copolymer Copolymer, phenolic resin, epoxy resin, acrylic phthalate resin, polyamide resin, polyester resin, maleic acid resin and the like. In addition, the production method of any resin is not particularly limited.

Among these resins, the effect of the present invention is remarkable when a polyester resin having high negative chargeability is used. That is, the polyester-based resin has excellent fixability and is suitable for a color toner, but has a strong negative charging ability and tends to be excessively charged. However, when the polyester resin is used in the composition of the present invention, the harmful effects are improved and excellent. A toner is obtained.

In particular, the following equation

[0084]

Embedded image

(Wherein R is an ethylene or propylene group, x and y are each an integer of 1 or more, and x +
The average value of y is 2-10. A) a carboxylic acid component comprising a divalent or higher carboxylic acid or an acid anhydride thereof or a lower alkyl ester thereof (for example, fumaric acid, maleic acid, maleic anhydride, phthalic acid) Acid, terephthalic acid, trimellitic acid, pyromellitic acid, etc.) are more preferred because they have sharp melting properties.

In the present invention, the latent image is developed with toner by applying at least a DC / AC superimposed electric field between the latent image holding member and the developing carrier using the above-mentioned developer. One feature is that the image forming method is a development method (the present invention 3).

That is, although a two-component developing method of DC / AC superposition has been known, the peak electric field intensity at the time of DC / AC superposition is extremely large, so that bias leakage or charge injection of latent image charges into carriers is performed. In order to prevent the latent image from being disturbed by the above, a low-resistance carrier core material is coated with a large amount of resin and used as a high-resistance type carrier. However, long-term stability has been impaired due to a decrease in carrier fluidity caused by coating a large amount of resin.

In the present invention, however, since a high-resistance carrier core material is coated with a thin layer of a resin having a small surface energy, a high-resistance carrier having good carrier fluidity is achieved, resulting in bias leakage and carrier adhesion. ,
High image quality without image deterioration such as charge injection was achieved over a long period of time.

In order to make the present invention more effective, the current value of the carrier is 20 to 300 μA, preferably 30 to 250 μA, more preferably 40 to 200 μA.
A is desirable.

If the current value is smaller than 20 μA, the transfer of charges on the surface of the carrier is not sufficiently performed, and the ability to impart charge to the toner is reduced, so that fogging and toner scattering occur. On the other hand, if it is larger than 300 μA, carrier adhesion to the drum, bias leak, etc. are likely to occur,
Image defects occur.

The current value was measured as follows. Weigh 800 g of carrier and expose to environment for at least 15 minutes. (Indoor temperature: 22 to 25 ° C., humidity: 50 to 54%) An apparatus having a built-in magnet roller and provided with a counter electrode at a distance of 1 mm facing a conductive sleeve provided with a spike regulating blade is prepared. The carrier is magnetically attracted between the sleeve and the counter electrode. Rotate the magnet roller in the sleeve to contact the counter electrode, apply a DC voltage of 500 V between the sleeve and the counter electrode, measure the voltage drop across the 1 MΩ and 10 KΩ resistors, and calculate the current value from this value Ask for.

Incidentally, the magnetic characteristics of the carrier are affected by the magnet roller built in the developing sleeve, and greatly affect the developing characteristics and the transportability of the developer.

In the present invention, of the developing sleeve (developer carrying member) and the magnet roller incorporated therein, for example, the magnet roller is fixed and the developing sleeve is rotated alone, and the carrier made of magnetic particles is insulated from the carrier. When the two-component developer composed of color toner is circulated and transported on the developing sleeve, and the two-component developer develops the electrostatic latent image held on the surface of the electrostatic latent image holding member, the magnet roller When a magnetic pole density having a repulsive pole is used, the magnetic flux density in the developing region is 500 to 1200 gauss, and the saturation magnetization of the carrier is 20 to 70 Am ² / kg, the image uniformity and gradation reproducibility in color copying are excellent. is there.

If the saturation magnetization exceeds 70 Am ² / kg (for an applied magnetic field of 3000 Oersteds),
At the time of development, the brush-like spikes formed by the carrier and the toner on the developing sleeve facing the electrostatic latent image on the photoreceptor are firmly tightened, and the gradation and the reproduction of halftone are deteriorated. On the other hand, if it is less than 20 Am ² / kg, it becomes difficult to hold the toner and the carrier on the developing sleeve satisfactorily, and problems such as deterioration of carrier adhesion and toner scattering are likely to occur. Furthermore, if the residual magnetization and coercive force of the carrier are too high, good transportability of the developer in the developing device is hindered, and image defects such as blurring and uneven density in a solid image are likely to occur. It will be reduced. Therefore, in order to maintain the developability in color copying, unlike ordinary black-and-white copying, the residual magnetization is 10 Am ² / kg or less, preferably 5 Am ² / k.
g, more preferably substantially 0, and the coercive force is 40
It is important that it is less than Oersted (3000 Oersted, relative to the applied magnetic field), preferably less than 30 Oersted, more preferably less than 10 Oersted.

Hereinafter, the measuring method in the present invention will be described.

(1) Measurement of Magnetic Properties of Carrier A BHU-60 type magnetization measurement device (manufactured by Riken Keizai) is used. About 1.0 g of a measurement sample is weighed, packed in a cell having an inner diameter of 7 mmφ and a height of 10 mm, and set in the above-mentioned apparatus. In the measurement, an applied magnetic field is gradually applied to change the maximum to 3,000 Oe. Next, the applied magnetic field is decreased, and finally a hysteresis curve of the sample is obtained on the recording paper. From this, the saturation magnetization, residual magnetization, and coercive force are obtained.

(2) Measurement of carrier particle size distribution The measurement was carried out using an SRA type microtrac particle size analyzer (Nikkiso Co., Ltd.) with a range of 0.7 to 125 μm.

(3) Fog density measurement method The fog was evaluated by using REFLECTOME manufactured by Tokyo Denshoku Co., Ltd.
The measurement was performed using TER MODELTC-6DS, and the cyan toner image was calculated using the following formula using an amber filter. The smaller the value, the less fog.

Fog (reflectance) (%) = reflectance of standard paper (%) − reflectance of non-image portion of sample (%)

(4) Specific surface area test method A specific surface area test method is performed using a Shimadzu powder specific surface area measuring device (SS-100 type) according to the following procedure. 1) Turn on the power of the autoslidac of the powder tester to fill the sample iron powder and adjust it to 100V. 2) Tap the changeover switch of the powder tester to adjust the timer to 1 minute (50 times ± 1 time / 1 minute). 3) Place a screen in a plastic sample tube, lay a sheet of filter paper on it, and put the sample on it up to 1/3 of the sample tube. 4) Set the sample tube on the tap stand of the powder tester and press the start button (1 minute tap). 5) Place the sample in the tapped sample tube 2/3 of the sample tube
Insert up to 6) Perform the same operations as in 4 above. 7) Insert the supplementary tube (plastic) onto the sample tube, and put the sample on the heap from above. 8) Perform the same operations as in the above 4 and 6. 9) Remove the tapped sample tube from the tap stand, extract the supplementary tube, and cut the excess sample with a spatula. 10) Fill water up to the S scale of the measuring tube with specific surface area. 11) Connect the sample tube to the measuring tube (after filling the sample, apply grease to the contact surface). 12) Open the lower outlet cock and check that the water level of the
Start the stopwatch as it passes through the scale (the bottom runoff is received in a beaker). 13) Measure the time when the water surface drops to 20 scales (unit is cc). 14) Remove the sample cylinder and measure the weight of the sample. 15) Silicic acid with specific surface area

The specific surface area is calculated by the following formula.

[0102]

(Equation 1)

SW: Specific surface area of powder cm ² / g e: Porosity of sample packed layer ρ: Density of powder g / cm ³ η: Viscosity coefficient of fluid g / cm · sec L: Thickness of sample layer cm Q: The amount of fluid permeating the sample layer cc ΔP: Pressure difference between both ends of the sample layer g / cm ² A: Cross-sectional area of the sample layer cm ² t: Time required for fluid (air) of Qcc to permeate the sample layer sec W : Weight of sample g

[0104]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples. “Parts” means “parts by weight”.

(Production Examples 1 to 3 of Carrier Core Material) Li ₂ O
20 parts, CaO 5 parts, Fe ₂ O ₃ to 75 parts Bi ₂ O ₃
Was added and mixed, water was added and mixed, and the mixture was granulated, fired at 1100 ° C., adjusted for particle size as shown in Table 1, and then subjected to an average particle size of 35. 7 μm, 3
Ferrite carrier core materials (saturated magnetization: 65 Am ² / kg) A, B, C of 5.1 μm and 36.8 μm were obtained.

(Production Example 4 of Carrier Core Material) MgO 25
A ferrite carrier core material (saturated magnetization 60 Am ² / kg) D was obtained in the same manner as in Production Example 1 except that ₃ parts of Bi ₂ O ₃ were used for 5 parts of MnO, 5 parts of MnO, and 70 parts of Fe ₂ O ₃ .

(Production Example 5 of Carrier Core Material) Li ₂ O 2
0 parts, Al ₂ O ₃ 15 parts, Fe ₂ O ₃ 65 parts, Bi ₂ O ₃
Ferrite carrier core material (saturated magnetization 48 Am ² / kg) E in the same manner as in Production Example 1 except that 1.5 parts were used.
I got

(Production Example 6 of Carrier Core Material) CaO 3
Parts, SrO 27 parts, Fe ₂ O ₃ 70 parts, Bi ₂ O ₃ 1
In the same manner as in Production Example 1, a carrier core material (saturated magnetization: 55 Am ² / kg) F having an average particle size of 39.2 μm was obtained using the same parts.

(Production Example 7 of Carrier Core Material) MgO 20
Part, 3 parts of SiO ₂ , 77 parts of Fe ₂ O ₃ , Bi ₂ O ₃ 2
In the same manner as in Production Example 1, a carrier core material (saturation magnetization: 65 Am ² / kg) G having an average particle size of 28.7 μm was obtained.

(Production Examples 1 to 3 of Carrier) Toluene 20
, 20 parts of butanol, 20 parts of water and 40 parts of ice are placed in a four-necked flask, and while stirring, 40 parts of a mixture of 15 mol of CH ₃ SiCl _{3 and} 10 mol of (CH ₃ ) ₂ SiCl ₂ are added, and further 30 minutes. After stirring, a condensation reaction was performed at 60 ° C. for 1 hour. Thereafter, the siloxane was sufficiently washed with water and dissolved in a mixed solvent of toluene, methyl ethyl ketone and butanol to prepare a silicone varnish having a solid content of 10%.

The silicone varnish contained 2.0% by weight of ion-exchanged water and 2.0% by weight of the siloxane solids.

[0112]

Embedded image And 3.0% by weight

[0113]

Embedded image Was added simultaneously to prepare a carrier coating solution I.

The coating solution I was applied to a coating machine (manufactured by Okada Seiko Co., Ltd .:
Spiral coater) was applied to the above-mentioned carrier core materials A to C so that the resin coating amount was 1.0% by weight to obtain coating carriers 1 to 3, respectively.

(Manufacturing Example 4 of Carrier) Carrier 4 was obtained in the same manner as above, except that the resin coating amount was applied to carrier core material A to be 4.0% by weight.

(Carrier Production Examples 5 and 6) Carriers 5 and 6 were obtained in the same manner except that the resin coating amount I was applied to the carrier core materials D and E to 1.5% by weight.

(Preparation Example 7 of Carrier) 50 parts of a polyvinylidene fluoride-polytetrafluoroethylene copolymer and 50 parts of a styrene-methyl methacrylate copolymer were dissolved in a mixed solvent of toluene and methyl ethyl ketone to obtain a solid component 10
% Coating solution II was made. The coating solution II was applied to the carrier core material B so that the resin coating amount was 1.5% by weight, and a coating carrier 7 was obtained.

(Production Examples 8 and 9 of Carriers) Carriers 8 and 9 were obtained in the same manner except that the resin coating amount I was applied to carrier cores F and G so as to be 1.0 part and 2.5 parts. Was.

(Carrier Production Example 10) A coating carrier 10 was obtained by using the same coating solution III except that the aminosilane coupling agent was not used in the carrier coating solution I.

Table 1 summarizes the characteristic values of the above carriers.

(Production Example 1 of Toner) Polyester resin obtained by condensing propoxylated bisphenol with fumaric acid and 100 parts of trimellitic acid 5 parts of carbon black 4 parts of aluminum complex of di-tert-butylsalicylic acid 4 parts of a Henschel mixer The mixture was sufficiently preliminarily mixed, melt-kneaded by a twin-screw extruder, cooled, coarsely pulverized to about 1 to 2 mm using a hammer mill, and then finely pulverized by an air jet pulverizer. The obtained finely pulverized product was classified to obtain a black powder having a weight average particle size of 5.8 μm.

100 parts of the above colored powder and n-C in an aqueous medium
1.5 parts of anatase-type titanium oxide fine powder (i) treated with 20 parts of ₄ H ₉ -Si- (OCH ₃ ) ₃ was mixed with a Henschel mixer to obtain a black toner a. Hydrophobicity of titanium oxide fine powder (i) 60%, primary particle diameter 30 μm, 400
The light transmittance in nm was 65%.

(Production Example 2 of Toner) In Production Example 1 of toner, titanium tetraisopropoxide was oxidized at 300 ° C. at low temperature in place of titanium oxide fine powder (i), and at the same time, helium gas was added in the gas phase to the carrier gas. 1.5 parts of amorphous titanium oxide fine powder (ii) treated with 20 parts of nC ₄ H ₉ —Si— (OCH ₃ ) ₃ in the presence of water vapor
The mixture was mixed with a Henschel mixer to obtain a black toner b. The titanium oxide fine powder (ii) had a hydrophobicity of 70%, a primary particle diameter of 20 μm, and a light transmittance of 75% at 400 nm.

(Production Example 3 of Toner) A black toner c was obtained in the same manner as in Production Example 1 of toner except that amorphous alumina was used instead of the fine titanium oxide powder (i). 65% hydrophobicity of amorphous alumina, primary particle diameter 15μm,
The light transmittance at 400 nm was 65%.

Example 1 The above-described black toner a and carrier 2 were mixed at a toner concentration of 7% to prepare a developer, and a color copier CLC700 was used.
(Manufactured by Canon) at a development contrast of 300 V,
23 ° C using an original document with an image area ratio of 25%
Table 2 shows the results of image output of 40,000 sheets under / 65% RH. From Table 2, it can be seen that the above-mentioned developer has a small variation in the printing durability test and is very good.

Table 2 also shows the results of the following examples and comparative examples.

Comparative Examples 1 and 2 The same operation as in Example 1 was carried out except that the carriers 1 and 3 were used instead of the carrier 2 in Example 1, and the results were lower than those in Example 1. This is presumably because the carrier 1 was not added with Bi ₂ O ₃ , so that the carrier current value was large, the latent image was disturbed, and the solid uniformity was poor. Further, it is considered that the carrier 3 was too large in Bi ₂ O _3, so that a uniform ferrite phase including the surface could not be achieved, and the resin could not be uniformly coated, so that the charge stabilization of the toner was not achieved. .

Comparative Example 3 The same operation as in Example 1 was carried out except that the carrier 4 was used. In particular, highlight reproducibility was lowered. This is because the amount of resin coating was increased to reduce the carrier current value,
It is considered that the carrier fluidity was impaired and the mixing property with the toner was reduced.

Examples 2, 3, 4 The same procedure as in Example 1 was carried out except that carriers 5, 6, and 7 were used, and good results were obtained.

Example 5 The same operation as in Example 1 was carried out except that toner b was used, and good results were obtained.

Comparative Example 4 The procedure of Example 1 was repeated, except that the core material B without resin coating was used instead of the carrier 2, and the image deteriorated.

Example 6 The developing electric field of the CLC700 was modified so as to be DC only.
When image formation was performed in the same manner as in Example 1 except that no AC electric field was applied, the image quality was slightly lower than in Example 1 in all cases.

Examples 7, 8, and 9 The same procedure as in Example 1 was carried out except that the carriers 8, 9, and 10 were used, and good results were obtained.

Example 10 The same operation as in Example 1 was carried out except that toner c was used, and good results were obtained.

[0135]

[Table 1]

[0136]

[Table 2]

[0137]

According to the present invention electrophotographic carrier of the present invention, Bi ₂
For ferrite carrier core material of a specific composition containing O ₃ ,
Since the carrier is a thin layer coated with a cross-linkable silicone resin and / or a fluorine-containing resin, the carrier fluidity is good, and the charging ability is stabilized for a long time,
It has excellent characteristics for high image quality.

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI G03G 9/08 361 (56) References JP-A-60-227265 (JP, A) JP-A-60-127244 (JP, A) JP 6-110254 (JP, A) JP-A-5-61259 (JP, A) JP-A-6-83115 (JP, A) JP-A-8-511108 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/10

Claims (9)

(57) [Claims] 1. A ferrite component represented by the following formula (I): Formula (I) (Fe ₂ O ₃ ) _x (MO) _1-x (where M is Li, Mn, Mg, Ca, Al, Si and Represents one or more metal elements selected from the group consisting of Sr, x represents a weight fraction, and 0.2 ≦
x ≦ 0.95. ) 100 parts by weight of Bi ₂ O ₃
Is a carrier for electrophotography in which the surface of a magnetic carrier core material containing 0.05 to 5 parts by weight is coated with a crosslinkable silicone resin and / or a fluorine-containing resin .
The coating amount is ag, and the specific surface area of the coated carrier is Sc.
When m ² / g, the following relationship (a / S) × 10 ⁴ = 2 to 40 (where a is 0.01 to 20) is satisfied, and the current value of the carrier is 20 to 300 μA. electrophotographic carrier which is characterized in that there. 2. A carrier having a 50% average particle size of 15 to 15%.
60 μm and smaller than 22 μm
-20%, and 3% of carrier particles smaller than 16 μm.
% Of the carrier particles having a particle size of 62 μm or more.
% Content and, electrophotographic carrier according to claim 1, characterized in that it contains less than 3% or more of the carrier particles 88 .mu.m. 3. The method according to claim 1, wherein the carrier and the toner are reduced.AlsoTwo
In a component developer,  The carrier is a ferrite represented by the following formula (I):
Component Formula (I) (Fe_TwoO_Three)_x(MO)_1-x (Where M is Li, Mn, Mg, Ca, Al, Si and
One or more selected from the group consisting of Sr
X represents a weight fraction, and 0.2 ≦
x ≦ 0.95. ) Bi for 100 parts by weight_TwoO_Three
Carrier core material surface containing 0.05 to 5 parts by weight of
Is a carrier coated with a resin,The coating amount of the resin is based on 100 g of the magnetic carrier core material.
The coating amount is ag, and the specific surface area of the coated carrier is Sc.
m ^Two / G (A / S) × 10 ^Four = 2 to 40 (where a is 0.01 to 20) The filling, A current value of the carrier is 20 to 300 μA,  The toner has a weight average particle diameter of 1 to 9 μm,And
As an external additive, at least a weight average particle size of 0.001 to 0.
2μm inorganic fine particlesWithTwo-component system characterized by
Developer. 4. The two-component developer according to claim 3 , wherein the coating resin of the carrier is a crosslinkable silicone resin and / or a fluorine-containing resin. 5. The carrier has a 50% average particle size of 15 to 15.
60 μm and smaller than 22 μm
-20%, and 3% of carrier particles smaller than 16 μm.
% Of the carrier particles having a particle size of 62 μm or more.
The two-component developer according to claim 3 , wherein the two-component developer contains 3% or less of carrier particles having a particle size of 88 μm or more. 6. A developer carrier and a magnet roller built therein, wherein both the magnet roller and the developer carrier are rotated, or the magnet roller is fixed and the developer carrier is rotated, and the carrier and the carrier are rotated. The two-component color developer having at least the color toner is circulated and conveyed on the developer carrier, and the latent image is developed with the color toner in the developing region of the latent image carrier and the developer carrier opposed thereto. In an image forming method for transferring a toner image formed on an image carrier onto a transfer material, the carrier is a ferrite component represented by the following formula (I): Formula (I) (Fe ₂ O ₃ ) _x (MO) _{1 -x} (wherein, M represents one or more metal elements selected from the group consisting of Li, Mn, Mg, Ca, Al, Si and Sr, x represents a weight fraction, and 0.2 ≦
x ≦ 0.95. ) 100 parts by weight of Bi ₂ O ₃
Is a carrier in which the surface of a magnetic carrier core material containing 0.05 to 5 parts by weight is coated with a crosslinkable silicone resin and / or a fluorine-containing resin, and the resin coating amount is 100 g of the magnetic carrier core material.
The coating amount is ag, and the specific surface area of the coated carrier is Sc.
When m ² / g, the following relationship (a / S) × 10 ⁴ = 2 to 40 (where a is 0.01 to 20) is satisfied, and the current value of the carrier is 20 to 300 μA. The toner has a weight average particle diameter of 1 to 9 μm, and has at least a weight average particle diameter of 0.001 to 0.1 as an external additive.
The image forming method characterized by have a 2μm inorganic fine particles. 7. A developing method for developing a latent image with toner by applying at least a DC / AC superimposed electric field between a latent image holding member and a developer carrying member. The image forming method according to claim 6 , wherein: 8. The method according to claim 8, wherein the coating resin of the carrier is a crosslinkable silicone.
Corn resin and / or fluorine-containing resin
The image forming method according to claim 6, wherein: 9. The carrier having a 50% average particle size of 15 to 6%.
0 μm and the carrier particles smaller than 22 μm
3% carrier particles smaller than 16 μm containing 20%
2% to 20% of carrier particles having a particle size of 62 μm or more
3% or less of carrier particles of 88 μm or more
9. The image forming method according to claim 6, wherein: