JP4700582B2 - Electrophotographic developer carrier and developer - Google Patents

Description

  The present invention relates to a carrier for an electrophotographic developer having a weight average particle diameter Dw of 22 to 32 μm, a developer, a developing method, and an image forming apparatus, each comprising a magnetic core material particle and a resin layer covering the particle surface. About.

The electrophotographic development system is a mixture of a so-called one-component development system that is mainly composed of toner, glass beads, a magnetic carrier, or a coated carrier whose surface is coated with a resin and toner. There are two-component development systems used.
Since the two-component development method uses a carrier and has a large triboelectric charging area for the toner, the charging characteristics are more stable than the one-component method, and it is advantageous for maintaining high image quality over a long period of time. . In addition, in the digital electrophotographic system that has a high toner amount supply capability to the development area, forms an electrostatic latent image on a photoreceptor with a laser beam or the like, and visualizes the latent image, A two-component development system that makes use of the above-mentioned features is widely adopted.

  In recent years, the minimum unit (1 dot) of the latent image has been minimized and increased in density in order to cope with resolution enhancement, highlight reproducibility, uniformity (granularity) improvement, and colorization. Development systems capable of faithfully developing these latent images (dots) have become an important issue. For this reason, various proposals have been made in terms of both process conditions and developer (toner, carrier). In terms of process, it is effective to make the developing gap close, to make the photoconductor thin, and to reduce the writing beam diameter, but there are still significant problems in terms of cost and reliability.

  On the other hand, as a developer, the reproducibility of dots is greatly improved by using a toner having a small particle diameter. However, the developer containing the small particle size toner still has problems to be solved such as generation of background stains and insufficient image density. In the case of a full color toner with a small particle size, a resin with a low softening point is used in order to obtain a sufficient color tone, but the spent amount to the carrier is increased and the developer is deteriorated as compared with the case of a black toner. As a result, toner scattering and background staining are likely to occur.

Various uses of small particle size carriers have also been proposed.
For example, Patent Document 1 proposes a magnetic carrier made of ferrite particles having a spinel structure and having an average particle size of less than 30 μm. This is a carrier that is not resin-coated, and is used under a low development electric field, and has a short development life because it has poor development capability and is not resin-coated.

  Further, in Patent Document 2, in an electrophotographic carrier having carrier particles, the carrier has a 50% average particle size (D50) of 15 to 45 μm and contains 1 to 20% of carrier particles smaller than 22 μm. 3% or less of carrier particles smaller than 16 μm, 2 to 15% of carrier particles of 62 μm or more, 2% or less of carrier particles of 88 μm or more, and a specific specific surface area An electrophotographic carrier is described.

When this small particle size carrier is used, the following advantages are obtained.
(1) Since the surface area per unit volume is large, sufficient frictional charge can be given to each toner, and the generation of low charge amount toner and reverse charge amount toner is small. As a result, the background stains are less likely to occur, the toner around the dots is less dusty and blurred, and the dot reproducibility is improved.
(2) The surface area per unit volume is large, and background stains hardly occur, and a sufficient image density can be obtained by development.
(3) The small particle size carrier is characterized in that it forms a dense magnetic brush and the flowability of the ears is good, so that the traces of the ears are hardly generated in the image.

  However, as the particle size of the carrier decreases, the magnetic binding force rapidly decreases at a ratio of the cube of the particle size, and the carrier adhesion is very likely to occur, in the form of carrier particles or cut magnetic brushes. Adhere to. As a result, it has been a very big problem to cause scratches on the photoreceptor and flaws on the fixing roller.

JP 58-144839 A Japanese Patent No. 3029180

  Accordingly, the main object of the present invention is to provide a carrier and a developer that do not cause such inconvenience, that is, good graininess, good charging stability, little background stain, and hardly cause carrier adhesion, and a developer. An image forming apparatus is provided.

  In order to solve the above-mentioned problems, the present inventors have intensively studied and, as a result, have a specific particle size distribution with a small particle size and a small content ratio of the small particle size particles, and voids existing inside the core material. It has been found that the above problem can be achieved by controlling the ratio of particles having a certain size or more to be low.

Usually, the carrier adheres to the background portion or the image portion of the image, when Fm <Fc, it is caused by adhering in the form of carrier particles or a cut magnetic brush.
However, Fm: Magnetic binding force, Fc: Force causing carrier adhesion.

  The present inventors conducted various analyzes and analyzes on the core material that easily adheres to the carrier with respect to the carrier having a small particle diameter, or the particle that has adhered to the carrier on the photoconductor. We found that there are many particles with voids.

  Ferrite particles obtained by mixing, pulverizing, granulating, and firing iron oxide and metal oxide often have fine voids inside the particles, and particles having large voids have a substantial mass. Therefore, the magnetization is reduced, the magnetic binding force on the developing sleeve is reduced, and carrier adhesion is likely to occur. In particular, it has been found that when the average particle size is reduced, the variation in magnetization per particle has a greater influence than the carrier having a large average particle size, and carrier adhesion tends to occur.

Since particles having large voids have a smaller mass than a volume, the magnetization per particle is also reduced. On the other hand, since the surface area of the carrier is substantially the same regardless of the presence or absence of voids, even if there are voids inside the particles, the counter charge of the toner accumulated in the carrier or the amount of induced charge has the same value. Therefore, it is considered that Fm <Fc and carrier adhesion occurs.
The state of voids existing inside the particles can be detected by various methods, but can also be easily quantified by the following method.

That is, the calculation of the equivalent circle diameter d μm of the void portion inside the particle and the equivalent circle diameter D μm of the area occupied by each particle with respect to the outside can be obtained by the following procedure.
Measuring equipment: X-ray microscope (TUX-3000W) Token Co., Ltd., 46KV, 200μA, focal size 0.6μm
Using an image processing software (Image-Pro PLUS Ver4.0: MEDIA CYBERNETICS), measure the void area in the X-ray microscope (TUX-3000W) photograph and the area occupied by void-containing particles. The equivalent circle diameter was calculated.
2,000 carriers were measured and analyzed by the method described above, and the ratio d / D of the equivalent circle diameter (d) of the voids and the equivalent circle diameter D of the area occupied by each particle with respect to the outside was determined. When the existence probability was examined, the relationship described in the following item (1) was clarified and the present invention was reached.
The equivalent circle diameter is expressed by the following equation.

Based on these results, the present inventors have found that the variation in magnetization between particles can be reduced by controlling the existence state of the voids and the number ratio thereof, and have reached the present invention.
That is, the above-described problems can be solved by the following specific means.
(1) “consisting of a core particle and a resin layer covering the particle surface, having a weight average particle diameter Dw of 22 to 32 μm and a ratio Dw / Dp of the weight average particle diameter Dw to the number average particle diameter Dp of 1 A carrier for an electrophotographic developer of ˜1.20, wherein the core particles are magnetically separated after removing fine powder with an ultrasonic vibration sieve, and the equivalent circle diameter of the projected cross section of the carrier core particles Is D μm, and the equivalent circle diameter of the projected cross section of the largest void existing inside the core material particle is d μm, the number ratio of particles satisfying 0.40 <(d / D) <1.0 is 0 to 2000. Electrophotographic developer carrier characterized in that the number is ppm.
( 2 ) "The carrier for an electrophotographic developer according to item (1), wherein the carrier core material is MnMgSr-based ferrite",
( 3 ) "Carrier for electrophotographic developer according to item (1) or (2), wherein the carrier core material is Mn ferrite",
( 4 ) "The carrier for an electrophotographic developer according to any one of (1) to ( 3 ) above, wherein the carrier core is magnetite",
( 5 ) An electrophotographic developer comprising a toner and a carrier, wherein the carrier according to any one of items (1) to ( 4 ) is used as the carrier. Developer ",
( 6 ) "An electrophotographic developer comprising a toner and a carrier, wherein the carrier is the carrier according to any one of the items (1) to ( 4 ), and the toner concentration is 7% by weight. An electrophotographic developer, wherein the charge amount of the toner is 10 to 50 μc / g, ”
( 7 ) "An electrophotographic developer comprising a toner and a carrier, wherein the carrier is the carrier according to any one of the items (1) to ( 4 ), and the weight average particle size of the toner An electrophotographic developer characterized by having a diameter of 3.0 to 9.0 μm ”;
( 8 ) "Electrophotographic development method characterized by using the developer according to any one of ( 5 ) to ( 7 )",
( 9 ) “The photosensitive member, the developer, and the developing sleeve are used, the distance between the developing sleeve and the photosensitive member is 0.4 mm or less, and an AC voltage and / or a DC voltage is applied as a developing bias. The electrophotographic developing method according to item ( 8 ),
( 10 ) "Image forming apparatus comprising developing means using developer according to any one of ( 5 ) to ( 7 )",
( 11 ) “The photosensitive member has the developing means, and the developing means uses a developing sleeve, the distance between the developing sleeve and the photosensitive member is 0.4 mm or less, and an AC voltage as a developing bias and And / or an image forming apparatus according to item ( 10 ), wherein a DC voltage is applied.
( 12 ) “A photosensitive member, a charging brush for charging the surface of the photosensitive member, and a developing unit including the electrostatic latent image developer according to any one of ( 5 ) to ( 7 ), A process cartridge comprising a blade for wiping off the developer remaining on the surface of the photoreceptor.

  As is clear from the following detailed and specific description, according to the present invention, the present invention has a specific particle size distribution with a small particle size and a small content ratio of the small particle size particles, and exists in the core material. By controlling the ratio of particles with a certain size or more, (1) good image uniformity (granularity), (2) good charging stability over time, and less likely to soil. (3) The carrier and the developer that are difficult to adhere to the carrier have a very excellent effect that a developing method and an image forming apparatus can be further provided.

  The electrophotographic developer carrier of the present invention (hereinafter also simply referred to as carrier) comprises magnetic core particles and a resin layer covering the surface thereof.

  It consists of a ferrite core material particle represented by the following general formula and a resin layer covering the particle surface, the weight average particle diameter Dw is 22 to 32 μm, and the ratio Dw of the weight average particle diameter Dw and the number average particle diameter Dp / Dp is a carrier for an electrophotographic developer having a value of 1 to 1.20, the equivalent diameter of the projected cross section of the carrier core particle is D μm, and the equivalent of the projected area of the largest void existing inside the core particle A carrier for an electrophotographic developer, wherein the number ratio of particles satisfying 0.40 <(d / D) <1.0 when the diameter is d μm is 0 to 5000 ppm.

The core material of the present application is a core material for carriers that is obtained by mixing, pulverizing and finely dispersing a metal oxide as a raw material of ferrite, followed by granulation, firing, and classification, and extremely small voids in the particles. .
In the present invention, the sintered core material is obtained by removing particles having large voids by using classification by ultrasonic vibration sieving or the like and a magnetic separation method in combination.
That is, the ferromagnetic material and ferrite (ferrimagnetic material) used as the carrier core material exhibit magnetization proportional to the mass with respect to the applied magnetic field and are bound to the magnetic field.
Using this magnitude of the binding force, particles with small magnetization (particles with a small mass with voids) are separated. When the magnetic separation is performed, particles having a small mass exist when the particle size distribution is wide. Therefore, if a classification process is performed in advance, particles having voids can be efficiently removed.
By using the classification process and magnetic sorting together, the number of spherical particles having the maximum voids as described above can be controlled to a low value as described above. Further, since the mass of the carrier particles with d / D = 0.40 is about 6% by weight as described above compared to the case where no voids are present, the shape of the particles is relatively small as in the present invention. In the case of core particles that are uniform and have a narrow particle size distribution range, it is also effective to separate the wind force. As described above, the magnetization (emu) per particle is reduced by about 6%, and development is performed. Since the binding force to the sleeve is small, separation using magnetic force is also effective.
Further, in order to remove the voids, the voids can be reduced by controlling the temperature rising pattern when firing the granulated particles.

  As the material of the core material, known magnetic materials can be used, and among them, the following MnMgSr ferrite, Mn ferrite, and magnetite can be preferably used.

但し、ｘ＋ｙ＋ｚ＝１００ｍｏｌ％であって、Ｍ、Ｎはそれぞれ、Ｎｉ、Ｃｕ、Ｚｎ、Ｌｉ、Ｍｇ、Ｍｎ、Ｆｅ、Ｓｒ、Ｃａなどであり、２価の金属酸化物と３価の鉄酸化物との完全混合物から構成されている。
また、Ｓｉ、Ｔｉ、Ｔａ，Ｎｂ，Ｖなどの添加物、およびＣａなどのアルカリ土類金属を含んでも良い。

However, x + y + z = 100 mol%, and M and N are Ni, Cu, Zn, Li, Mg, Mn, Fe, Sr, Ca, etc., respectively. Divalent metal oxide and trivalent iron oxide And consists of a complete mixture.
Further, additives such as Si, Ti, Ta, Nb, V, and alkaline earth metals such as Ca may be included.

[About Dw, Dp, and Dw / Dp above]
The carrier of the present invention comprises ferrite core material particles represented by the following general formula and a resin layer covering the particle surface, and preferably has a weight average particle diameter Dw of 22 to 32 μm.
When the weight average particle diameter Dw is larger than the above range, carrier adhesion is less likely to occur, but the toner is not developed faithfully with respect to the latent image, so that the variation in dot diameter increases and the graininess decreases. Further, when the toner concentration is high, the background is easily soiled. The carrier adhesion indicates a phenomenon in which a carrier adheres to an image portion or a background portion of an electrostatic latent image. The stronger each electric field, the easier the carrier adheres. In the image portion, the electric field is weakened by developing the toner, so that the carrier adhesion is less likely to occur compared to the background portion.
The carrier for an electrophotographic developer has a ratio Dw / Dp of the number average particle diameter Dp to the weight average particle diameter Dw of 1 to 1.20, more preferably 1 to 1.16. When the ratio is larger than 1.20, the ratio of fine particles is increased, and carrier adhesion is deteriorated.

Furthermore, the core material of the present carrier has a diameter equivalent to a circle of the projected cross section of the core material particle of D μm, and a diameter equivalent to a circle of the projected cross section of the largest void existing inside the core material particle is d μm, 0.40 <( d / D) A carrier for an electrophotographic developer, wherein the number ratio of particles satisfying 1.0 is from 0 to 5000 ppm, typically from 500 to 5000 ppm.
The carrier particles with d / D = 0.40 have a mass reduced by about 14% by weight compared to the case where no voids exist, that is, the magnetization (emu) per particle is reduced by about 6%. The binding force on the sleeve is small. In a sintered type core material, a plurality of voids often exist in one particle.

In the present invention, the weight average particle diameter Dw referred to for the carrier, the carrier core material, and the toner is calculated based on the particle diameter distribution (relationship between the number frequency and the particle diameter) of the particles measured on the basis of the number.
The weight average particle diameter Dw in this case is represented by the following formula.

式（１）中、Ｄは各チャネルに存在する粒子の代表粒径（μｍ）を示し、ｎは各チャネルに存在する粒子の総数を示す。なお、チャネルとは、粒径分布図における粒径範囲を測定幅単位に分割するための長さを示すもので、本発明の場合には、２μｍの等分長さ（粒径分布幅）を採用した。

In the formula (1), D represents a representative particle size (μm) of particles present in each channel, and n represents the total number of particles present in each channel. The channel indicates a length for dividing the particle size range in the particle size distribution diagram into measurement width units. In the present invention, the channel has an equal length of 2 μm (particle size distribution width). Adopted.

Further, as the representative particle size of the particles existing in each channel, the lower limit value of the particle size stored in each channel was adopted.
In the present invention, the number average particle diameter Dp of the carrier and the carrier core material particles is calculated based on the particle diameter distribution of the particles measured on the basis of the number. The number average particle diameter Dp in this case is represented by the following formula.

式（２）中、Ｎは計測した全粒子数を示し、ｎは各チャネルに存在する粒子の総数を示し、Ｄは各チャネル（２μｍ）に存在する粒子粒径の下限値を示す。

In formula (2), N represents the total number of particles measured, n represents the total number of particles present in each channel, and D represents the lower limit value of the particle size present in each channel (2 μm).

As a particle size analyzer for measuring the particle size distribution in the present invention, a Microtrac particle size analyzer (model HRA9320-X100: manufactured by Honeywell) was used.
The measurement conditions are as follows.
[1] Particle size range: 100-8 μm
[2] Channel length (channel width): 2 μm
[3] Number of channels: 46
[4] Refractive index: 2.42

[Number ratio of particles having d / D of 0.40 to 1.0 is 0 to 2000 ppm]
The particles satisfying 0.40 <(d / D) <1.0 in the carrier more preferably have a number ratio of 0 to 2000 ppm. By reducing the number ratio in the carrier, carrier adhesion is further improved.

[About the material of the carrier core]
The inventors of the present invention have made it possible for the magnetization related to the magnetic binding force of the carrier to be 40 emu / g or more, more preferably 70 emu / g or more when the magnetic field of 1000 oersted (Oe) is applied. It has been found that adhesion is improved. The upper limit is not particularly limited, but is usually about 150 emu / g.
If the magnetization of the carrier core particles is smaller than the above range, carrier adhesion tends to occur, such being undesirable.

As the material for the core particles constituting the carrier of the present invention, various conventionally known magnetic materials are used.
The magnetization can be measured as follows.
A BH tracer (BHU-60 / manufactured by Riken Denshi Co., Ltd.) is used, and 1.0 g of carrier core particles are packed in a cylindrical cell and set in an apparatus. The magnetic field is gradually increased and changed to 3000 oersted, then gradually reduced to zero, and then the opposite magnetic field is gradually increased to 3000 oersted. Further, after gradually reducing the magnetic field to zero, a magnetic field is applied in the same direction as the first. In this way, the BH curve is shown, and the 1000 oersted magnetization is calculated from the figure.

Examples of the core particles that are 50 emu / g or more when a 1000 oersted magnetic field used in the carrier of the present invention is applied include, for example, ferromagnetic materials such as cobalt, magnetite, hematite, Li-based ferrite, and Mn—Zn-based materials. Examples thereof include ferrite, Cu—Zn ferrite, Ni—Zn ferrite, Ba ferrite, and Mn ferrite.
Ferrite is a sintered body generally represented by the following formula.

但し、ｘ＋ｙ＋ｚ＝１００ｍｏｌ％であって、Ｍ、Ｎはそれぞれ、Ｎｉ、Ｃｕ、Ｚｎ、Ｌｉ、Ｍｇ、Ｍｎ、Ｆｅ、Ｓｒ、Ｃａなどであり、２価の金属酸化物と３価の鉄酸化物との完全混合物から構成されている。
また、Ｓｉ、Ｔｉ、Ｔａ，Ｎｂ，Ｖなどの添加物、およびＣａなどのアルカリ土類金属を含んでも良い。

However, x + y + z = 100 mol%, and M and N are Ni, Cu, Zn, Li, Mg, Mn, Fe, Sr, Ca, etc., respectively. Divalent metal oxide and trivalent iron oxide And consists of a complete mixture.
Further, additives such as Si, Ti, Ta, Nb, V, and alkaline earth metals such as Ca may be included.

  In the present invention, the core particles having a magnetization of 70 emu / g or more when a magnetic field of 1000 oersted is applied more preferably includes, for example, magnetite-based, Mn-Mg-Sr-based ferrite, and Mn-based ferrite. .

[Electrophotographic developer of the present invention]
In the electrophotographic developer comprising the toner of the present invention and a carrier, the carrier is any one of the carriers described above, and the toner charge amount at a toner concentration of 7% by weight is 15 to 35 μc / g. An electrophotographic developer having better soiling and carrier adhesion can be obtained.
In the developer comprising the carrier and toner of the present invention, the ratio of the toner weight to the carrier is 2 to 20%, preferably 3 to 15%. In the developer of the present invention, the toner charge amount when the toner concentration is 7% is preferably 10 to 50 μc / g, more preferably 15 to 35 μc / g.
When the charge amount is lower than 10 μc / g, background staining and toner scattering increase. On the other hand, if it is larger than 50 μc / g, carrier adhesion tends to occur. If it is less than 35 μc / g, the carrier adhesion is very good.

The charge amount of the developer can be measured by the following method. This is shown in FIG.
A certain amount of developer is put into a conductor container (cage) (15) equipped with metal mesh at both ends. The mesh (made of stainless steel) has a mesh size between the toner and the carrier (particle size 20 μm), and is set so that the toner passes between the meshes. When compressed nitrogen gas (1 kgf / cm ² ) is blown from the nozzle for 60 seconds to cause the toner to jump out of the gauge, a carrier having a polarity opposite to that of the toner charge remains in the cage.
The charge amount Q and the mass M of the protruding toner are measured, and the charge amount per unit mass is calculated as the charge amount Q / M. The toner charge amount is expressed in μc / g.

[Electrophotographic development method of the present invention]
When a toner having a weight average particle diameter of 3.0 to 5.0 μm and any one of the carriers (1) to (5) is used as a developer, the graininess is particularly improved and further high image quality is achieved. .

[Image forming apparatus of the present invention]
When a toner having a weight average particle diameter of 5 μm or less and any one of the carriers (1) to (5) is used as a developer, the graininess is particularly improved, and further high image quality is achieved.

The developer of the present invention comprises the carrier and toner.
The carrier of the present invention has a resistivity (LogR · cm) of preferably 11.0 to 16.0, more preferably 12.0 to 14.0.
When the resistivity of the carrier is lower than 11.0, when the developing gap (the closest distance between the photosensitive member and the developing sleeve) becomes narrow, charges are induced in the carrier and carrier adhesion is likely to occur. When the linear velocity of the photosensitive member and the linear velocity of the developing sleeve are large, a tendency of deterioration is observed. In addition, it is remarkable when an AC bias is applied. Usually, a color toner developing carrier is generally used having a low resistance in order to obtain a sufficient toner adhesion amount.
It has been found that a sufficient image density can be obtained by using a carrier having the above resistance range under an appropriate toner charge amount.
On the other hand, when the value is larger than 16.0, charges having a polarity opposite to that of the toner are likely to be accumulated, and the carrier is easily charged to cause carrier adhesion.

The carrier resistivity can be measured by the following method.
As shown in FIG. 5, a cell (11) made of a fluororesin container containing electrodes (12a) and (12b) having a distance between electrodes of 2 mm and a surface area of 2 × 4 cm is filled with a carrier (13), A DC voltage of 100 V is applied, the DC resistance is measured with a high resistance meter 4329A (4329A + LJK 5HLVLVWDQFH OHWHU; manufactured by Yokogawa Hewlett-Packard Co., Ltd.), and the electrical resistivity LogR · Ωcm is calculated.
When filling the carrier resistance, fill the cell until it overflows, and after tapping the entire cell 20 times, use a non-magnetic horizontal spatula on the top surface of the cell along the top edge of the cell. Scrape flatly in one operation. No pressure is required during filling.

The carrier resistivity can be adjusted by adjusting the resistance of the coating resin on the core particles and controlling the film thickness. Moreover, it is also possible to add conductive fine powder to the coating resin layer for carrier resistance adjustment. As the conductive fine particles, conductive ZnO, metal or metal oxide powder such as Al, _SnO 2 doped with SnO ₂ or the various elements that have been prepared in a variety of _{ways, TiB 2, ZnB 2, MoB} 2 , etc. Borides, silicon carbide, polyacetylene, polyparaphenylene, poly (para-phenylene sulfide), conductive polymers such as polypyrrole and polyaniline, carbon black such as furnace black, acetylene black and channel black.
These conductive fine powders can be obtained by the following methods: a dispersing machine using a medium such as a ball mill or a bead mill after the conductive fine powder is put into a solvent used for coating or a resin solution for coating, or a blade rotating at high speed. Can be uniformly dispersed.

  As described above, various conventionally known resins can be used as the usable resin used in the production of the carrier, and a silicone resin containing a repeating unit represented by the following formula is preferably used.

In the above formula (3), R ¹ represents a hydrogen atom, a halogen atom, a hydroxy group, a methoxy group, a lower alkyl group having 1 to 4 carbon atoms, or an aryl group (such as a phenyl group or a tolyl group), and R ² represents carbon. A C 1-4 alkylene group or an arylene group (such as a phenylene group) is shown.

In the aryl group of the above formula (3), the carbon number is 6 to 20, preferably 6 to 14. This aryl group includes an aryl group derived from benzene (phenyl group), an aryl group derived from a condensed polycyclic aromatic hydrocarbon such as naphthalene, phenanthrene, and anthracene, and a chain polycyclic aromatic such as biphenyl and terphenyl. An aryl group derived from a group hydrocarbon is included.
Various substituents may be bonded to the aryl group.

  In the present invention, a straight silicone resin can be used as the silicone resin. Examples thereof include KR271, KR272, KR282, KR252, KR255, KR152 (manufactured by Shin-Etsu Chemical Co., Ltd.), SR2400, SR2406 (manufactured by Toray Dow Corning Silicone).

In the present invention, a modified silicone resin can be used as the silicone resin. Examples of such materials include epoxy-modified silicone, acrylic-modified silicone, phenol-modified silicone, urethane-modified silicone, polyester-modified silicone, and alkyd-modified silicone.
Specific examples of the modified silicone resin include epoxy modified product: ES-1001N, acrylic modified silicone: KR-5208, polyester modified product: KR-5203, alkyd modified product: KR-206, urethane modified product: KR-305 ( As mentioned above, Shin-Etsu Chemical Co., Ltd.), epoxy-modified product: SR2115, alkyd-modified product: SR2110 (manufactured by Toray Dow Corning Silicone), and the like.

Furthermore, in this invention, it is also possible to use what is shown below individually or in mixture with the said silicone resin.
Polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, Styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer) Polymer, styrene-phenyl acrylate copolymer, etc.), styrene-methacrylate copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, Styrene-phenyl methacrylate copolymer, etc.) Styrenic resins such as styrene-α-chloroacrylic acid methyl copolymer, styrene-acrylonitrile-acrylic acid ester copolymer, epoxy resin, polyester resin, polyethylene resin, polypropylene resin, ionomer resin, polyurethane resin, ketone resin, ethylene -Ethyl acrylate copolymer, xylene resin, polyamide resin, phenol resin, polycarbonate resin, melamine resin, fluorine resin and the like.

As a method for forming the resin layer on the surface of the carrier core particles, a known method such as a spray drying method, a dipping method, or a powder coating method can be used.
In particular, the method using a fluidized bed type coating apparatus is effective for forming a uniform coated film.
The thickness of the resin layer formed on the surface of the carrier core particles is usually 0.02 to 1 μm, preferably 0.03 to 0.8 μm.

Moreover, the carrier in any one of (1)-(5) with favorable durability can be obtained by making an aminosilane coupling agent contain in the resin coating layer which consists of the above-mentioned silicone resin.
Examples of the aminosilane coupling agent used in the present invention include the following. The content is preferably 0.001 to 30% by weight.

  The toner used in the present invention contains a colorant, fine particles, a charge control agent, a release agent and the like in a binder resin mainly composed of a thermoplastic resin. Can be used. This toner can be an amorphous or spherical toner prepared by various toner production methods such as a polymerization method and a granulation method. Either magnetic toner or non-magnetic toner can be used.

As the binder resin for the toner, the following can be used alone or in combination.
Styrene binder resins such as polystyrene, polyvinyltoluene and other styrene and substituted homopolymers, styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-acrylic Acid methyl copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate Copolymer, styrene-α-chloromethacrylic acid methyl copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene -Isoprene copolymer, styrene- Styrene copolymers such as oleic acid copolymers and styrene-maleic acid ester copolymers; acrylic binders such as polymethyl methacrylate and polybutyl methacrylate, and in addition, polyvinyl chloride, polyvinyl acetate, polyethylene , Polypropylene, polyester, polyurethane, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or aliphatic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax Etc.

Further, the polyester resin can further reduce the melt viscosity while ensuring the stability during storage of the toner, as compared with the styrene-based or acrylic-based resin. Such a polyester resin can be obtained, for example, by a polycondensation reaction between an alcohol and a carboxylic acid.
Examples of the alcohol include diols such as polyethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-propylene glycol, neopentyl glycol, 1,4-butenediol, , 4-Bis (hydroxymethyl) cyclohexane, bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A and other etherified bisphenols, which are saturated or unsaturated having 3 to 22 carbon atoms Divalent alcohol units substituted with a hydrocarbon group, other divalent alcohol units, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaesitol, dipentaes Tolu, tripentaerythritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, tri Mention may be made of trihydric or higher alcohol monomers such as methylolethane, trimethylolpropane and 1,3,5-trihydroxymethylbenzene.

  Examples of the carboxylic acid used to obtain the polyester resin include monocarboxylic acids such as palmitic acid, stearic acid, and oleic acid, maleic acid, fumaric acid, mesaconic acid, citraconic acid, terephthalic acid, cyclohexanedicarboxylic acid, and succinic acid. Acids, adipic acid, sebacic acid, malonic acid, divalent organic acid monomers in which these are substituted with saturated or unsaturated hydrocarbon groups having 3 to 22 carbon atoms, anhydrides of these acids, lower alkyl esters and Dimer from linolenic acid, 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1, 2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl 2-methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid embol trimer acid, anhydrides of these acids, etc. The body can be mentioned.

  Epoxy resins include polycondensates of bisphenol A and epochrohydrin, such as epomic R362, R364, R365, R366, R367, R369 (above, Mitsui Petrochemical Co., Ltd.), Epototo YD-011, YD-012, YD-014, YD-904, YD-017 (above, manufactured by Tohto Kasei Co., Ltd.) Epochs 1002, 1004, 1007 (above, manufactured by Shell Chemical Co., Ltd.) Things.

  Examples of the colorant used in the present invention include carbon black, lamp black, iron black, ultramarine, nigrosine dye, aniline blue, phthalocyanine blue, Hansa Yellow G, rhodamine 6G lake, calco oil blue, chrome yellow, quinacridone, and benzidine yellow. Conventionally known dyes and pigments such as rose bengal, triallylmethane dyes, monoazo dyes, disazo dyes, and dyes can be used alone or in combination.

  It is also possible to make a magnetic toner by adding a magnetic material to the toner. As the magnetic material, ferromagnetic powders such as iron and cobalt, fine powders such as magnetite, hematite, Li-based ferrite, Mn-Zn-based ferrite, Cu-Zn-based ferrite, Ni-Zn ferrite, and Ba ferrite can be used.

  For the purpose of sufficiently controlling the triboelectric chargeability of the toner, so-called charge control agents such as metal complex salts of monoazo dyes, nitrohumic acid and its salts, salicylic acid, naphthoic salts, dicarboxylic acid Co, Cr, Fe, etc. , A quaternary ammonium compound, an organic dye, and the like can be contained.

Furthermore, a release agent may be added to the toner used in the present invention as necessary.
As the release material, low molecular weight polypropylene, low molecular weight polyethylene, carnauba wax, microcrystalline wax, jojoba wax, rice wax, montanic acid wax and the like can be used alone or in combination, but are not limited thereto. is not.

Additives can be added to the toner. In order to obtain a good image, it is important to impart sufficient fluidity to the toner.
As the external additive, general hydrophobized inorganic fine particles can be used in addition to the inorganic fine particles, but the average particle size of the hydrophobized primary particles is 1 to 100 nm, more preferably 5 nm to 70 nm. It is desirable to include inorganic fine particles. Moreover, it is preferable that the specific surface area by BET method is 20-500 m < ² > / g.

Any known one can be used as long as the conditions are satisfied. For example, silica fine particles, hydrophobic silica, fatty acid metal salts (such as zinc stearate and aluminum stearate), metal oxides (such as titania, alumina, tin oxide, and antimony oxide), fluoropolymers, and the like may be contained.
Particularly suitable additives include hydrophobized silica, titania, titanium oxide, and alumina fine particles. As silica fine particles, there are HDK H 2000, HDK H 2000/4, HDK H 2050EP, HVK21, HDK H 1303 (Clariant Japan) and R972, R974, RX200, RY200, R202, R805, R812 (Nippon Aerosil). . Further, as titania fine particles, P-25 (Nippon Aerosil), STT-30, STT-65C-S (above Titanium Industry), TAF-140 (Fuji Titanium Industry), MT-150W, MT-500B, MT-600B MT-150A (taker above). Particularly, the hydrophobized titanium oxide fine particles include T-805 (Nippon Aerosil), STT-30A, STT-65S-S (above Titanium Industry), TAF-500T, TAF-1500T (above Fuji Titanium Industry), MT -100S, MT-100T (above Taka), IT-S (Ishihara Sangyo), etc.
In order to obtain hydrophobized inorganic fine particles, silica fine particles, titania fine particles, and alumina fine particles, hydrophilic fine particles are treated with a silane coupling agent such as methyltrimethoxysilane, methyltriethoxysilane, or octyltrimethoxysilane. Can be obtained.

  In the toner used in the present invention, the weight average particle diameter Dt is 3.0 to 9.0 μm, more preferably 3.0 to 5.0 μm. The toner particle size was measured using a Coulter Counter (manufactured by Coulter Counter).

[Image forming apparatus of the present invention]
The carrier according to any one of (1) to (5) above is used as the carrier, the charge amount of the toner when the toner concentration is 7% is 10 to 50 μc / g, and the weight average particle diameter of the toner is An electrophotographic developing method using 3.0 to 9.0 μm, the distance between the developing sleeve and the photosensitive member is 0.4 mm or less, and applying an AC voltage as a developing bias. Low image quality can be obtained.
The developing method of the present invention is a method of developing a latent image using the carrier, toner and developer of the present invention described above. In this method, when an AC voltage obtained by superimposing an AC voltage on a DC voltage is applied as an externally applied developing bias, a sufficient image density can be obtained. In particular, the granularity of highlights is improved.

Further, when only a DC voltage is applied as a developing bias, carrier adhesion and edge effect are greatly improved, and a margin for dirt is increased, so that the toner coverage with respect to the carrier can be increased, and the toner charge amount And the developing bias can be lowered, and the image density can be increased.
Further, when only a DC voltage is applied as a developing bias, carrier adhesion and edge effect are greatly improved, and a margin for dirt is increased, so that the toner coverage with respect to the carrier can be increased, and the toner charge amount And the developing bias can be lowered, and the image density can be increased.

[About the process cartridge of the present invention]
The photosensitive member, a charging brush for charging the surface of the photosensitive member, a developing unit for developing the electrostatic latent image formed on the surface of the photosensitive member using the carrier and a developer, and the photosensitive member A process cartridge comprising a blade for wiping off the developer remaining on the surface of the body can be employed in an electrophotographic system.

Next, examples of the electrophotographic developing method and the electrophotographic developing apparatus of the present invention will be described in detail with reference to the drawings. However, these examples are for explaining the present invention and are not intended to limit the present invention. Absent.
FIG. 6 is a schematic diagram for explaining the electrophotographic developing method and developing apparatus of the present invention, and the following modifications also belong to the category of the present invention.
In FIG. 6, a developing device (40) disposed opposite to a photosensitive drum (20) as a latent image carrier includes a developing sleeve (41) as a developer carrier and a developer containing member (42). It is mainly composed of a doctor blade (43) as a regulating member, a support case (44) and the like.
To a support case (44) having an opening on the side of the photosensitive drum (20), a toner hopper (45) as a toner storage portion for storing the toner (21) is joined. In the developer accommodating portion (46) that accommodates the developer composed of toner (21) and carrier particles (23) adjacent to the toner hopper (45), the toner particles (21) and carrier particles (23) are agitated. In addition, a developer stirring mechanism (47) is provided for imparting friction / release charges to the toner particles.

Inside the toner hopper (45), a toner agitator (48) and a toner replenishing mechanism (49) are disposed as toner supplying means rotated by a driving means (not shown). The toner agitator (48) and the toner replenishing mechanism (49) send out the toner (21) in the toner hopper (45) toward the developer container (46) while stirring.
A developing sleeve (41) is disposed in a space between the photosensitive drum (20) and the toner hopper (45). The developing sleeve (41), which is driven to rotate in the direction of the arrow by a driving means (not shown), has a relative position relative to the developing device (40) in order to form a magnetic brush made of carrier particles (23). A magnet (not shown) is provided as magnetic field generating means.
A regulating member (doctor blade) (43) is integrally attached to the side of the developer accommodating member (42) facing the side attached to the support case (44). In this example, the regulating member (doctor blade) (43) is disposed in a state where a certain gap is maintained between the tip thereof and the outer peripheral surface of the developing sleeve (41).

  Using such an apparatus without limitation, the developing method of the present invention is performed as follows. That is, with the above configuration, the toner (21) sent out from the toner hopper (45) by the toner agitator (48) and the toner replenishing mechanism (49) is transported to the developer accommodating portion (46), where the developer agitation is performed. By stirring by the mechanism (47), a desired friction / peeling charge is imparted, and the carrier particles (23) and the developer are carried on the developing sleeve (41) as a developer, and the outer peripheral surface of the photosensitive drum (20). A toner image is formed on the photosensitive drum (20) by being transported to the opposite position and only the toner (21) is electrostatically coupled with the electrostatic latent image formed on the photosensitive drum (20). Is done.

  FIG. 7 is a sectional view showing an example of an image forming apparatus having such a developing device. Around the drum-shaped image carrier, that is, the photosensitive drum (20), an image carrier charging member (32), an image exposure system (33), a development (device) mechanism (40), a transfer mechanism (50), and a cleaning mechanism. (60), a static elimination lamp (70) is arranged. In this example, the surface of the image carrier charging member (32) is not spaced apart from the surface of the photoreceptor (20) by about 0.2 mm. When the photosensitive member (20) is charged by the charging member (32) in the contact state, the photosensitive member (32) is applied to the photosensitive member by an electric field obtained by superimposing the alternating current component on the direct current component by a voltage applying means (not shown). By applying charging, it is possible and effective to reduce charging unevenness. The image forming method including the developing method is performed by the following operation.

  A series of image forming processes can be described by a negative-positive process. An image carrier (20) represented by a photoconductor (OPC) having an organic photoconductive layer is neutralized by a static elimination lamp (70), and is uniformly negatively charged by a charging member (32) such as a charging charger or a charging roller. A latent image is formed by laser light emitted from the laser optical system (33) (in this example, the absolute value of the exposed portion potential is lower than the absolute value of the non-exposed portion potential).

  Laser light is emitted from a semiconductor laser and scans the surface of the image carrier, that is, the photoreceptor (20) in the direction of the rotation axis of the image carrier (20) by a polygonal polygon mirror (polygon) that rotates at high speed. . The latent image formed in this way is developed from a mixture of toner particles and carrier particles supplied on a developing sleeve (41) which is a developer carrying member in the developing device, developing means or developing device (40). The toner is developed to form a visible toner image. At the time of developing the latent image, a voltage of an appropriate magnitude or AC is applied to the developing sleeve (41) from a voltage application mechanism (not shown) between the exposed portion and the non-exposed portion of the image carrier (20). A developing bias with a superimposed voltage is applied.

On the other hand, a transfer medium (for example, paper) (80) is fed from a paper feed mechanism (not shown), and is synchronized with the leading edge of the image by a pair of upper and lower registration rollers (not shown). And the transfer member (50) to transfer the toner image. At this time, it is preferable that a potential opposite to the polarity of toner charging is applied to the transfer member (50) as a transfer bias. Thereafter, the transfer medium or intermediate transfer medium (80) is separated from the image carrier (20) to obtain a transfer image.
Further, the toner particles remaining on the image carrier are collected into a toner collection chamber (62) in the cleaning mechanism (60) by a cleaning blade (61) as a cleaning member.
The collected toner particles may be transported to a developing unit and / or a toner replenishing unit by a toner recycling unit (not shown) and reused.
The image forming apparatus may be a device in which a plurality of the developing devices described above are arranged and the toner images are sequentially transferred onto the transfer medium, then sent to the fixing mechanism, and the toner is fixed by heat or the like. It is also possible to use a device that transfers a plurality of toner images to the transfer medium and transfers them all together onto a transfer medium and performs the same fixing.

  FIG. 8 shows another process example using the electrophotographic developing method according to the present invention. The photosensitive member (20) is provided with at least a photosensitive layer on a conductive support and is driven by driving rollers (24a) and (24b) to be charged by a charging roller (32), image exposure by a light source (33), and development. Development with the apparatus (40), transfer with the charger (50), exposure before cleaning with the light source (26), cleaning with the brush-like cleaning means (64) and the cleaning blade (61), and static elimination with the static elimination light source (70) are repeated. Done. In FIG. 8, the photoconductor (20) (of course, the support is translucent in this case) is irradiated with pre-cleaning exposure light from the support side.

  FIG. 9 shows an example of the process cartridge of the present invention. This process cartridge uses the carrier of the present invention, the photoconductor (20), the proximity brush-shaped contact charging means (32), the developing means (40) for storing the developer of the present invention, and the cleaning means. This is a process cartridge that integrally supports a cleaning unit having at least a cleaning blade (61) and is detachable from the main body of the image forming apparatus. In the present invention, the above-described components can be integrally combined as a process cartridge, and the process cartridge can be configured to be detachable from a main body of an image forming apparatus such as a copying machine or a printer.

Hereinafter, the present invention will be described using examples and comparative examples. In the following, “parts” represents parts by weight.
Toner Production Example (Toner Production Example 1)
Polyester resin 100 parts Quinacridone-based magenta pigment 4.0 parts Fluorinated quaternary ammonium salt 4 parts The above components are thoroughly mixed in a blender, melt-kneaded in a twin-screw extruder, allowed to cool, and then milled And then finely pulverized with a jet airflow fine pulverizer, and further classified with an air classifier to obtain toner base particles having a weight average average particle diameter of 6.8 μm.
Further, 0.8 parts of hydrophobic silica fine particles (R972: manufactured by Nippon Aerosil Co., Ltd.) were added to 100 parts of the toner base particles, and mixed with a Henschel mixer to obtain a toner I.

(Toner Production Example 2)
A base toner was prepared in exactly the same manner as in Toner Production Example 1 to obtain a toner II having 1.2 parts of hydrophobic silica fine particles (R972: manufactured by Nippon Aerosil Co., Ltd.) having a weight average particle diameter of 4.5 μm.

(Manufacture example 1 of a core material)
Carrier core material particles (a) having the properties shown in Table 1 (magnetization 55 emu / g of CuZn-based ferrite 1 KOe) were prepared. This core material was obtained by subjecting CuZn ferrite to classification and void removal treatment by the following method.
That is, first, classification is performed using a vibration sieve machine equipped with an ultrasonic oscillator, and then a main pole magnet (about 1000 mm) is used using a developer of IMAGIO COLOR 4000 (Ricoh's digital color copier / printer combined machine). Gauss) was replaced with a weak 250-gauss magnet, creating a device that can be driven by a single developer.
The classified core material was put into this apparatus, and the single developing device was driven for 10 minutes under the following conditions.
Doctor gap (developing sleeve-doctor): 0.30mm
Development sleeve linear velocity: 150 mm / sec
As a result, some of the core particles were scattered and separated from the position of the main pole of 250 Gauss. Most of these particles have large voids.
Furthermore, the particles were classified again using a vibration sieve equipped with an ultrasonic oscillator to obtain true spherical type ferrite core particles (a) shown in Table 1.

(Carrier production example 1)
Silicone resin (SR2411 manufactured by Toledo Corning Silicone) was diluted to obtain a silicone resin solution (solid content: 5%).
Using a fluidized bed coating apparatus, the above-mentioned silicone resin solution is applied on the surface of each of 5 Kg of carrier core particles (a) (CuZn ferrite 1 KOe magnetization 55 emu / g) having the properties shown in Table 1. It is applied at a rate of 30 g / min in an atmosphere of 90 ° C., and further heated at 230 ° C. for 2 hours to have a weight average particle diameter Dw = 27.9 μm, Dw / Dp = 1.13, 1 KOe magnetization 55 emu / g carrier Carrier A having a thickness of about 0.27 μm was obtained.
With respect to this carrier, the size and the number of voids were examined for 2000 particles using an X-ray microscope (TUX-3000W).
When the equivalent circular diameter of the projected cross section of the carrier core particle is D μm and the equivalent circular diameter of the projected cross section of the largest void existing inside the core particle is d μm, 0.40 <(d / D) <1.0 It was found that the number of the particles was 8, which was a ratio of 4000 ppm.

(Carrier Production Example 2 to Production Example 10)
Using the ferrite core material of Table 1 in the same manner as in Production Example 1, Carrier B to Carrier J were produced in the same manner as in Production Example 1.
In carrier G, 10 parts of H ₂ N (CH ₂ ) ₃ Si (OC ₂ H ₅ ) ₃ was added to the coating material to adjust the charge amount of the carrier.
The characteristics of each carrier and the number of carrier particles having voids corresponding to 0.4 <(d / D) <1.0 in the core were examined.
The examination results are shown in Table 1.

(Development and evaluation of developer)
Various developers were produced using the toners I and II obtained in the above toner production examples 1 and 2 and the carriers A to J obtained in carrier production examples 1 to 10.
Further, an image was formed using the obtained developer, and a characteristic test such as an image quality confirmation and a reliability test was performed.
The image was created using Imagio Color 4000 (Ricoh Digital Color Copier / Printer Combined Machine) under the following development conditions.
Development gap (photosensitive member-developing sleeve): 0.35 mm
Doctor gap (Development sleeve-Doctor): 0.65mm
Photoconductor linear velocity 200mm / sec
(Developing sleeve linear velocity / photosensitive member linear velocity) = 1.80
Writing density: 600 dpi
Charging potential (Vd): -600V
Potential after exposure of the portion corresponding to the image portion (solid document) (Vl): −150V
Development bias: DC voltage -500V / AC bias component: 2KHZ, -100V to -900V, 50% duty
Quality evaluation was performed on transfer paper. However, carrier adhesion was observed by transferring the state after development and before transfer onto the adhesive tape from the photoreceptor.

The test methods employed in the following image forming examples are as follows.
(1) Image density:
Under the above development conditions, the center of a solid portion of 30 mm × 30 mm is measured at five locations with an X-Rite 938 spectrocolorimeter and the average value is obtained.

(2) Dirt:
The dirt on the background under the above development conditions was evaluated in 10 stages. The higher the rank, the less soiling, rank 10 being the best.
Evaluation method / The number of toner adhering to the background portion (non-image portion) on the transfer paper was counted and converted to the number of adhering per 1 cm ² to obtain the background stain rank. Each rank and the number of adhered toners (pieces / cm ² ) are as follows.
<Rank>
Rank 10: 0 to 36
Rank 9: 37-72
Rank 8: 73-108
Rank 7: 109-144
Rank 6: 145-180
Rank 5: 181 to 216
Rank 4: 217-252
Rank 3: 253-288
Rank 2: 289-324
Rank 1: 325 or higher

(3) Granularity:
The granularity (brightness range: 50 to 80) defined by the following formula was measured, and the numerical value was replaced with a rank as shown below (rank 10 was best).
Granularity = exp (aL + b) ∫ {WS (f)} ^1/2 VTF (f) df
L: Average brightness f: Spatial frequency (cycle / mm)
WS (f): power spectrum of brightness fluctuation VTF (f): visual spatial frequency characteristics a, b: coefficient L: average brightness f: spatial frequency (cycle / mm)
WS (f): Lightness fluctuation power spectrum VTF (f): Visual spatial frequency characteristics a, b: Constant <Rank>
Rank 10: -0.10 to 0
Rank 9: 0-0.05
Rank 8: 0.05-0.10
Rank 7: 0.10 to 0.15
Rank 6: 0.15 to 0.20
Rank 5: 0.20 to 0.25
Rank 4: 0.25 to 0.30
Rank 3: 0.30-0.40
Rank 2: 0.40 to 0.50
Rank 1: 0.50 or more FIG. 10 shows image samples of each rank. In addition, an enlarged sample of the image of the example is shown.

(4) Carrier adhesion:
When carrier adhesion occurs, it may cause damage to the photosensitive drum and the fixing roller, resulting in a decrease in image quality. Even if the carrier adheres, only a part of the carrier is transferred to the paper.
An image pattern of 2 dot lines (100 lpi / inch) is created in the sub-scanning direction, developed by applying a DC bias of 400 V, and transferred with adhesive tape between the two dot line lines (area 100 cm ² ). The numbers were replaced with ranks as shown below. Rank 10 is the best.
<Rank>
Rank 10: 0
Rank 9: 1-10 Rank 8: 11-20 Rank 7: 21-30 Rank 6: 31-50 Rank 5: 51-100 Rank 4: 101-300 Rank 3: 301-600 Rank 2: 601-1000 Rank 1: 1000 or more

(5) Soil after 50K run:
The running evaluation of 50,000 sheets was performed using a magenta toner I used for initial image output or a character image chart with an image area ratio of 6% while supplying toner I. The background of the background under the above development conditions was evaluated for rank according to the same criteria as (2).

( Reference Example 1)
7 parts of toner I was added to carrier A (93 parts) and stirred for 20 minutes with a ball mill to prepare a 7.0 Wt% developer. The toner charge amount was −24 μc / g.
Next, using Ricoh's Imagio Color 4000 under the above development conditions, the image quality was first confirmed by the above-described measurement evaluation method.
The image density was 1.67, the background stain rank was 8, the graininess was rank 7, and the carrier adhesion was rank 8. Subsequently, 50,000 running evaluations were performed using a character image chart with an image area ratio of 6%. After running 50,000 sheets, the background stain was confirmed. The background stain was a good level of rank 8, and the high image quality was maintained.

(Examples 1 and 2, Reference Examples 2 to 4 and Comparative Examples 1 to 5 )
Evaluation was performed in exactly the same manner as in Reference Example 1 except that the combination of toner and carrier was changed as shown in Table 2 to produce a developer of 7 wt%.
Table 1 shows carrier production examples (carrier core material characteristics and carrier characteristics), and Table 2 shows quality evaluation results in the examples and comparative examples.

It is a core sample in which many voids can be seen in one particle by an X-ray microscope. It is an enlarged photograph by the X-ray microscope of the particle | grains in which a space | gap exists. It is the photograph by the X-ray microscope of the core material sample with comparatively few space | gap inside particle | grains. FIG. 6 is a diagram illustrating a method for measuring the charge amount of a developer according to the present invention. It is a perspective view of the resistance measurement cell used for the measurement of the electrical resistivity of a carrier. It is a figure explaining an example of the developing apparatus suitable for performing the electrophotographic developing method of this invention. 1 is a diagram illustrating an example of an image forming apparatus suitable for executing an image forming method using an electrophotographic developing method of the present invention. It is a figure explaining another example of the image forming apparatus suitable for performing the image forming method using the electrophotographic developing method of this invention. It is a figure explaining an example of the process cartridge of the present invention. It is the figure (enlarged view) which showed the rank of the highlight uniformity of the image in the Example of this invention, and the image sample.

Explanation of symbols

11 cell 12a electrode 12b electrode 13 carrier 15 conductor container (cage)
20 Photosensitive drum 21 Toner 23 Carrier 24a Driving roller 24b Driving roller 26 Exposure light source 32 before cleaning Image carrier charging member 33 Image exposure system 40 Developing device 41 Developing sleeve 42 Developer containing member 43 Developer supply regulating member (doctor blade)
44 Support case 45 Toner hopper 46 Developer container 47 Developer agitation mechanism 48 Toner agitator 49 Toner supply mechanism 50 Transfer mechanism 60 Cleaning mechanism 61 Cleaning blade 62 Toner recovery chamber 64 Brush-like cleaning means 70 Static elimination lamp 80 Intermediate transfer medium

Claims (12)

It consists of a core material particle and a resin layer covering the particle surface, the weight average particle diameter Dw is 22 to 32 μm, and the ratio Dw / Dp between the weight average particle diameter Dw and the number average particle diameter Dp is 1-1.20. The core material particles are magnetically separated after removing the fine powder with an ultrasonic vibration sieve, and the equivalent circular diameter of the projected cross section of the carrier core material particles is D μm. When the equivalent circular diameter of the projected cross section of the largest void existing inside the material particles is d μm, the number ratio of particles satisfying 0.40 <(d / D) <1.0 is 0 to 2000 ppm. An electrophotographic developer carrier characterized by the above. The carrier for an electrophotographic developer according to claim 1, wherein the carrier core material is MnMgSr ferrite. Electrophotographic developer carrier according to claim 1 or 2 the carrier core material is characterized by a Mn ferrite. The carrier for an electrophotographic developer according to any one of claims 1 to 3 , wherein the carrier core material is magnetite. An electrophotographic developer comprising a toner and a carrier, wherein the carrier according to any one of claims 1 to 4 is used as the carrier. An electrophotographic developer comprising a toner and a carrier, the carrier being the carrier according to any one of claims 1 to 4 , wherein the toner charge amount at a toner concentration of 7% by weight is 10 to 50 μc / g. An electrophotographic developer, comprising: An electrophotographic developer comprising a toner and a carrier, wherein the carrier is the carrier according to any one of claims 1 to 4 , and the weight average particle diameter of the toner is 3.0 to 9.0 µm. An electrophotographic developer characterized by the above. Electrophotographic developing method which comprises using the developer according to any one of claims 5 to 7. Photoreceptor, wherein the developer using the developing sleeve, the distance between the developing sleeve and the photosensitive member is not more 0.4mm or less, and claim 8, characterized in that an AC voltage is applied and / or the DC voltage as a developing bias The electrophotographic development method according to 1. An image forming apparatus wherein a developing means using a developer according to any one of claims 5 to 7. A photosensitive member, the developing unit, the developing unit using a developing sleeve, a distance between the developing sleeve and the photosensitive member is 0.4 mm or less, and an AC voltage and / or a DC voltage as a developing bias The image forming apparatus according to claim 10 , wherein: is applied. A photosensitive member, a charging brush for charging the surface of the photosensitive member, a developing unit including the electrostatic latent image developer according to any one of claims 5 to 7 , and a developer remaining on the surface of the photosensitive member. A process cartridge comprising a blade for wiping.

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