JP5106148B2 - Electrophotographic developer carrier, developer, and image forming method - Google Patents

Description

  The present invention relates to a carrier for an electrophotographic developer comprising magnetic core particles and a resin layer covering the particle surface, a developer using the carrier, and an image forming method using them.

An electrophotographic development method in which toner is supplied to the surface of a photoreceptor on which an electrostatic latent image has been formed to form a toner image in which the electrostatic latent image is visualized is a so-called one that contains only toner as a main component. There are a component development method and a two-component development method in which a glass bead, a magnetic carrier, or a coat carrier whose surface is coated with a resin and a toner are mixed and 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. . Further, since the toner amount supply capability to the development area is high, it is often used particularly for a high-speed machine.
In a digital electrophotographic system in which an electrostatic latent image is formed on a photoreceptor with a laser beam or the like and the latent image is visualized, a two-component development method that makes use of the above-described features is widely adopted.

In recent years, the minimum unit (1 dot) of the latent image has been minimized and the density has been increased in order to cope with higher resolution, improved highlight reproducibility, improved image graininess (graininess), and colorization. In particular, a development system capable of faithfully developing these latent images (dots) has become an important issue, and 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.
From the aspect of developer, toner particle size reduction and carrier particle size reduction have been studied, and various proposals have been made regarding the use of small particle size carriers.

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 coated with a resin and is used under a low development electric field, and has a problem that the developing ability is poor and the life is short because it is not coated with a resin.
In Patent Document 2, in an electrophotographic carrier having carrier particles, the carrier has a 50% average particle diameter (D ₅₀ ) of 15 to 45 μm, and the carrier 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, and 2% or less of carrier particles of 88 μm or more, the carrier Is the specific surface area S1 of the carrier measured by the air permeation method and the following formula:

によって算出される該キャリアの比表面積Ｓ２とが

The specific surface area S2 of the carrier calculated by

の条件を満たすことを特徴とする電子写真用キャリアが記載されている。

An electrophotographic carrier characterized by satisfying the following conditions is described.

It is disclosed that the following advantages can be obtained when this small particle size carrier is used.
(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) Since the surface area per unit volume is large and scumming is less likely to occur, the average charge amount of the toner can be reduced and a sufficient image density can be obtained. Therefore, the small particle size carrier can make up for problems in using the small particle size toner, and is particularly effective in drawing out the advantages of the small particle size toner.
(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, the conventional small particle size carrier as described in Patent Document 2 has a very big problem that carrier adhesion is likely to occur, and it has been a cause of occurrence of scratches on the photoreceptor and fusing rollers. It was difficult to put it into practical use.
In particular, when the carrier has a weight average particle size of less than 45 μm, the roughness is greatly improved and the image quality is improved. However, a carrier having an average particle size of less than 45 μm has a problem that carrier adhesion is very likely to occur, and high image quality cannot be maintained over time.

  On the other hand, Japanese Patent Application Laid-Open No. 11-38752 of Patent Document 3 describes a time constant. However, in this measurement, the time constant is measured in the contact state, and the R component in this time constant correlates with the static Log R measured using a conventional cell. This is not related to the time constant of the carrier, but to the time constant of the developer composed of the carrier and the toner.

  In recent years, carriers have a tendency to reduce the particle size in order to achieve high image quality and high reliability. Reducing the particle size of the carrier has a large surface area per unit weight (large specific surface area), making it difficult to release charges compared to a carrier with a large particle size. It has become.

As described above, the force Fc that causes carrier adhesion is related to the development potential, background potential, centrifugal force applied to the carrier, carrier resistance, and developer charge amount.
Therefore, it is effective to set each parameter so as to reduce Fc in order to prevent carrier adhesion, but it is closely related to development capability, background stain, toner scattering, etc., and it is difficult to change significantly. Currently.

JP 58-144839 A Japanese Patent No. 3029180 JP 11-38752 A

The main object of the present invention is to provide a carrier for an electrophotographic developer with a low occurrence of carrier adhesion at the initial stage and over time, a high image density and a good graininess (roughness), a developer using the carrier, and an image using these. It is to provide a forming method.
In particular, when the initial carrier adhesion occurs, the photoreceptor is immediately damaged, and the image is greatly deteriorated. Therefore, prevention of counter-charge type initial carrier adhesion is particularly important.

The inventors of the present invention have focused on changing the R portion of τ = R × C, and have arrived at the present invention. By changing the R component using a method that is completely different from the conventional one, Achieved to control the relaxation time.
In other words, it can be seen that the carrier having the resin film formed on the core material surface has the same physical properties such as carrier resistance, but has different relaxation times. By controlling this, carrier adhesion is greatly improved. I found that it can be improved. In other words, the carrier according to the present invention optimizes the electrical resistance characteristic that changes with time of the amount of charge remaining on the carrier, that is, the relaxation time, in addition to the static electrical resistance. .
Then, it has been found that applying this carrier to a developing system using a DC bias as a developing bias is extremely effective in preventing carrier adhesion, increasing image density, and preventing background contamination.

That is, the above-mentioned problems of the present invention are as follows: (1) “The core in a magnetic field having a magnetic core material particle and a resin layer covering the particle surface and having a weight average particle diameter Dw of 20 to 45 μm and 1000 oersted. The material particles have a magnetization of 40 to 100 emu / g, a carrier resistance (1000 V / 2 mm) · LogR · Ωcm of 11 to 17, and the resin layer contains conductive fine particles, and the carrier does not contain toner. A carrier for electrophotographic developer , wherein the carrier energy is given in the above and the carrier relaxation time τ is 150 seconds to 800 seconds ”,
(2) “consisting of a magnetic core material particle and a resin layer covering the particle surface, the weight average particle diameter Dw being 22 to 32 μm, and the ratio of the number average particle diameter Dp to the weight average particle diameter Dw (Dw / Dp) is a carrier for an electrophotographic developer in which 1 <(Dw / Dp) <1.20, and the content of particles having a particle size of less than 20 μm is 0 to 7% by weight, and particles of less than 36 μm The carrier for electrophotographic developer according to item (1), wherein the content is 80 to 100% by weight and the content of particles smaller than 44 μm is 90 to 100% by weight,
(3) "the paragraph (1) or the (2) Electrophotographic carrier for developer according to claim carrier core material is characterized by a MnMgSr ferrite"
(4) "The carrier for an electrophotographic developer according to any one of (1) to (3) above, wherein the carrier core material is Mn- based ferrite",
(5) "The carrier for an electrophotographic developer according to any one of (1) to (4) above, wherein the carrier core material is magnetite",
(6) The electrophotographic development according to any one of (1) to (5) above, wherein a core material having a bulk density of 2.15 to 2.70 g / cm ³ is used. Drug carrier ",
(7) An electrophotographic developer comprising a toner and a carrier, wherein the carrier according to any one of items (1) to (6) is used as the carrier. Photographic developer ",
(8) “An electrophotographic developer comprising a toner and a carrier, wherein the carrier is the carrier according to any one of items (1) to (6), and the carrier is covered with the toner. It is achieved by the electrophotographic developer described in item (7) above, wherein the toner has a charge amount of 15 to 30 μc / g when the rate is 50%.
(9) “Electrophotography for forming a toner image by visualizing the electrostatic latent image by supplying toner from a developer including a carrier and toner to the surface of the photoreceptor on which the electrostatic latent image has been formed by exposure. In the development method,
The carrier is composed of magnetic core material particles and a resin layer covering the surface of the core material particles. The resin layer includes conductive fine particles, and the carrier gives mechanical energy in a state where no toner is added. ones, and the weight average particle size of 20-45 [mu] m, 1000 oersteds magnetization 40~100emu / g of core material particles in a magnetic field, the carrier resistance (LogR when the distance between the electrodes was applied to 1000V voltage at 2mm ) Has a value of 11 to 17 Ω · cm, the carrier relaxation time τ is 150 seconds to 800 seconds, and a DC voltage is applied as a developing bias when supplying toner from the developer to the photoreceptor. Electrophotographic developing method characterized by that ",
(10) “The carrier has a weight average particle diameter Dw of 22 to 32 μm and a ratio (Dw / Dp) of the number average particle diameter Dp to the weight average particle diameter Dw of 1 <Dw / Dp <1.20. The content of particles having a particle size smaller than 20 μm is 0 to 7% by weight, the content of particles smaller than 36 μm is 80 to 100% by weight, and the content of particles smaller than 44 μm is 90 to 100% by weight. The electrophotographic developing method according to item (9), characterized in that,
(11) "The electrophotographic development method according to (9) or (10) above, wherein the core particles of the carrier are MnMgSr ferrite",
(12) "The electrophotographic developing method according to (9) or (10) above, wherein the core material particles of the carrier are Mn ferrite",
(13) "The electrophotographic developing method according to item (9) or (10) above, wherein the core particle of the carrier is magnetite",
(14) The bulk density of the core material particles of the carrier is 2.15 to 2.70 g / cm ³ , according to any one of (9) to (13), Electrophotographic development method ",
(15) “The toner supplied to the photoconductor is attached to the surface of the carrier, and the toner charge amount when the coverage of the carrier by the toner is 50% is 15 to 30 μc / g The electrophotographic development method according to any one of (9) to (14) above, characterized by:
(16) “After forming the toner image on the photoreceptor using the electrophotographic developing method according to any one of (9) to (15), the toner image is transferred to a recording medium. Thereafter, the image forming method is characterized in that the toner image transferred to the recording medium is fixed.

  As is clear from the following detailed and specific description, according to the present invention, by adopting the above configuration, the occurrence of carrier adhesion at the initial stage and with time is small, the image density is high, and the graininess is good (roughness). In addition, it is possible to provide a carrier for electrophotographic development, a developer, and an image forming method using these, which can have a stable charge imparting ability over a long period of time.

Hereinafter, the present invention will be described in detail and specifically.
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.
In the present invention, studies have been made on the adhesion of magnetic carriers. The magnetic carrier adhesion is caused by the carrier particles or the cut when the electric force to attach the carrier to the photoconductor becomes larger than the force that the carrier is bound to the magnetic brush (magnetic binding force-centrifugal force). Carrier adhesion occurs in the form of a magnetic brush. That is, when Fc is a force that causes carrier adhesion and Fm is a magnetic binding force, carrier adhesion occurs when the condition of Fc> Fm is satisfied. However, Fc (force causing carrier adhesion) = (function of centrifugal force, resin coated carrier resistance, electric field strength, charge amount), Fm (magnetic binding force) = (carrier magnetization) × (magnet magnetic field gradient) It is. In this case, the magnetization amount of one particle of carrier is (magnetization amount of one particle of carrier) = mass (g) × magnetization (emu / g) = ((4/3 · π · r ³ ) · ρ) × M It becomes. Where ρ is the true specific gravity of the carrier particles, r is the radius of the carrier particles, and M is the amount of magnetization per unit weight of the carrier particles.

As is apparent from this equation, since the amount of magnetization of one carrier particle is proportional to the third power of the carrier particle radius, r ³ , the magnetic binding force Fm rapidly decreases as the carrier diameter decreases. . Therefore, increasing the amount of magnetization of the particles and decreasing the centrifugal force to increase the magnetic binding force are effective for carrier adhesion. In order to increase the average magnetization amount of the core material particles, it is effective to increase the particle diameter of the core material and to obtain a composition capable of obtaining a large magnetization amount. Furthermore, it is important to reduce the variation in magnetization between particles.

Carrier adhesion is classified into two types, induction type and counter charge type, depending on the mechanism.
Inductive carrier adhesion is caused by the generation of induced charges in the carrier due to the electric field of the image area or the electric field of the non-image area (background part) because the resistance of the carrier is low. Furthermore, when the developing electric field is strong, the amount of induced charges becomes large, and carrier adhesion tends to occur and deteriorate.
The induced charge here means the charge that is directly injected into the carrier particle through the developing sleeve and stays in the particle, and the resulting charge is induced in the carrier material according to the strength of the external electric field. It is directly involved in carrier adhesion rather than charge due to polarization. Therefore, when the resistance of the toner is high, the toner becomes a spacer and the charge injection into the carrier hardly occurs. However, when the electric field in the developing area is strong, the toner on the carrier moves toward the image carrier or the developing sleeve in accordance with the gradient of the electric field strength, and the amount of toner on the carrier is reduced. Charges are easily injected along a series of carriers that are exposed and have low resistance. When the electric charge is injected, so-called induction type carrier adhesion occurs in which the carrier adheres to the photoconductor by the electric field in the developing region.
On the other hand, counter-charge type carrier adhesion is caused by accumulation of charge opposite to toner on the carrier due to frictional charging. That is, as the toner is developed or the toner drifts from the carrier (charged toner is sequentially separated from the carrier), charges (counter charge) having a polarity opposite to that of the toner are accumulated (expressed) in the carrier. Therefore, when the toner is developed on the electrostatic latent image carrier, charges having a polarity opposite to the toner polarity are accumulated in the carrier. Further, in the non-image portion of the electrostatic latent image carrier, the toner on the carrier moves away from the electrostatic latent image carrier, and the toner moves toward the developing sleeve, which is the developer carrier. Charge remains. This is also a counter charge. The latter countercharge occurs after some time (very short time) after the former countercharge, but in any case, the surface of the electrostatic latent image carrier and the developing sleeve are close to each other. -The speed of separation (for example, the rotational speed of the electrostatic latent image carrier) and the distance are also affected. Therefore, if the carrier resistance is high, it is difficult to alleviate the counter charge. Further, when the developer charge amount is large, the charge accumulation amount increases. Thus, the counter charge is that the carrier is charged to the opposite polarity to the toner.

Furthermore, when the electric field in the image area or the electric field strength in the non-image area (background area) is large, the counter-charge type carrier adhesion is deteriorated similarly to the induction type carrier adhesion.
Therefore, both the induction type and the counter charge type must be controlled so that the electric field strength does not become too large.

  In recent years, the carrier tends to have a small particle size for high image quality and high reliability, and the magnetic brush becomes soft when the particle size of the carrier is reduced. Therefore, the development gap (gap between the photosensitive member and the development sleeve) is narrowed. I can do it. By narrowing the development gap, high development ability can be obtained, while the electric field in the background portion is also emphasized, and the problem that background contamination and carrier adhesion are likely to occur has become apparent. In addition, reducing the particle size of the carrier has a large surface area per unit weight, so that it is difficult to release charges as compared with a carrier having a large particle size, and particularly, counter-charge type carrier adhesion is a big problem.

  As described above, the force Fc that causes carrier adhesion is related to the development potential, background potential, centrifugal force applied to the carrier, carrier resistance, and developer charge amount. Therefore, it is effective to set each parameter so as to reduce Fc in order to prevent carrier adhesion. However, since it is closely related to development ability, background contamination, toner scattering, etc., it is difficult to change significantly. Is the current situation.

  The present inventors examined various factors in order to improve the counter-charge type carrier adhesion. As a result, it was found that reducing the relaxation time was effective, and the present invention was completed.

  In order to prevent counter-charge type carrier adhesion, it is important not to generate or accumulate counter charges. For this purpose, the following can be considered.

(I) To impart conductivity to the carrier. As the means, the resistance of the coat film applied to the carrier is lowered, the coat film thickness is reduced, the resistance adjuster is used in the coat layer, the low resistance filler is used, the electrical resistance of the core material particles Lowering the value.
(Ii) The amount of counter charge can be directly reduced by lowering the charge amount of the toner.
(Iii) In order to make the counter charge easy to escape, it is effective to reduce the carrier resistance, but to increase the number of times of contact with the developing sleeve by increasing the movement of the developer.
(Iv) In order to prevent the toner from moving in the direction of the developing sleeve in the non-image area, it is effective to reduce the speed of the developing sleeve relative to the photoreceptor and to reduce the electric field strength in the developing region.

  From the relationship (i) above, the carrier conductivity involves the electrical resistance R and the capacitance C of the carrier, so attention was paid to the relaxation time (τ) related to the electrical resistance R and the capacitance C of the carrier.

  The relaxation time (τ) in the present invention is expressed as τ = R × C. C is the capacity of the carrier and is almost determined by the material and volume of the core material and the coat film. On the other hand, the electrical resistance R can be obtained from the measured relaxation time and capacity. This electrical resistance R is obtained by packing a carrier in a conventionally known cell, applying a voltage to the gap, and measuring the current. It turned out to be very different from the normal static electrical resistance value. The reason for this is presumed that the movement of a very small amount of charge generated by frictional charging does not necessarily coincide with the cause of the electric resistance value obtained by measuring the current. Therefore, the phenomenon of carrier adhesion due to counter charge, which cannot be controlled by the value of electrical resistance obtained using a conventional cell, is made possible by controlling the relaxation time by the non-contact relaxation time measurement method described later. It is done.

  The carrier according to the present invention is intended to optimize the electrical resistance characteristics that change with time of the amount of charge remaining in the carrier, that is, the relaxation time, in addition to the static electrical resistance due to the cell. .

The conventional static electric resistance of the carrier can be obtained at a target level by using the carrier core material, the resistance of the coat film of the carrier, and the use of a resistance control agent for the coat film. In order to optimize the relaxation time of the carrier, when the carrier is manufactured, the formation state of the coating film on the surface is controlled (the extremely small area where the coating film does not exist, the invisible crack part, the irregular joint part, the coating film is extremely Or by applying mechanical energy without activating the toner in the carrier and activating the surface. Furthermore, specifically, the core surface of the coat carrier is not exposed, for example, the core material is exposed by non-uniform application, but it depends on controlling the variation of the film thickness of pinholes. It can also be obtained by controlling the aging, activation, shaving, filler, core material shape, and coating conditions of the coat carrier by controlling the mist diameter due to mechanical hazard of the coat carrier.
In other words, the carrier of the present invention optimizes the static resistance and the characteristics corresponding to the aging of the amount of charge remaining on the carrier, i.e., the relaxation time. This is achieved by non-homogenizing the coating resin layer covering the carrier core material. The coating resin layer in the present invention is a portion where any of the small areas is modified, and it is difficult to identify where the unmodified portion is by a microscope or visual inspection. This is probably because the modified site extends not only to the surface but also to the inside of the coating layer.

  As described above, the inventors of the present invention have focused on changing the R portion of τ = R × C, and have reached the present invention. By changing, we achieved controlling the relaxation time.

  In this way, it can be seen that the carrier in which the resin coat (coating film) is formed on the surface of the core material particles has different relaxation times even if the physical properties such as carrier resistance are the same, and by controlling this, It has been found that carrier adhesion can be greatly improved. Then, it has been found that applying this carrier to a developing system using a DC bias as a developing bias is extremely effective in preventing carrier adhesion, increasing image density, and preventing background contamination.

In the present invention, the relaxation time of the resin-coated carrier was measured using the apparatus shown in FIG. FIG. 1 is a schematic diagram relating to an apparatus for measuring the relaxation time of a carrier. Reference numeral (1) denotes an aluminum cell having a sample storage recess (1a) having a depth d = 0.3 mm. In the figure, reference numeral (4) is a noncontact electrometer detector (probe), and reference numeral (5) is a noncontact electrometer. A resin-coated carrier was piled up in the storage recess (1a) of the cell (1), and was cut with a metal blade to prepare a sample for relaxation time measurement. Note that the depth (d) of the cell (1) in this measurement is preferably about 0.1 mm to 2 mm because a distance corresponding to the developing photoreceptor of the image forming apparatus and the developing sleeve of the developing apparatus is suitable. With respect to the carrier filled in the cell (1), a corona charger to which a positive voltage of 5 KV was applied was swept at 150 mm / second in an environment of normal temperature and normal humidity (24 ° C., 60%), and the surface of the carrier was positive. Charged to the nature. Measures the charging potential V ₀ at the moment when charging of the sample is completed (t = 0 seconds), further measures the potential with respect to time from t = 0 seconds, and measures the potential data (V ₁ ) after 120 seconds. did. As the charging potential, a non-contact electrometer (MODEL 344 manufactured by TREC, 6000B-8 as a probe) was used.

  For the charged carrier, the relationship of the following formula (1) is generally established.

但し、式中、Ｖは、帯電からｔ秒後の表面電位、Ｖ₀は、キャリアへの帯電が終了した瞬間（ｔ＝０秒）の帯電電位、Ｒは、キャリアの電気抵抗、Ｃはキャリアの容量、τは緩和時間である。

Where V is the surface potential t seconds after charging, V ₀ is the charging potential at the moment when charging of the carrier is completed (t = 0 seconds), R is the electrical resistance of the carrier, and C is the carrier. , Τ is the relaxation time.

(1) Changing equation to the following equation (2), the surface potential V ₀ charging time t = 0, a predetermined time from the time of charging, for example, 120 seconds (t = 120) the surface potential V ₁ of the time elapsed measuring Then, the relaxation time τ can be calculated from the equation (2).

Further, from the relationship of equation (2), the carrier discharge characteristics can be obtained with (V ₁ / V ₀ ) as the vertical axis and the elapsed time t as the horizontal axis, and the relaxation time τ can be obtained from the discharge characteristics. FIG. 2 is a graph showing carrier discharge characteristics. Curve 1 shows a carrier having a short relaxation time, curve 2 shows a carrier having a moderate relaxation time, and curve 3 shows a carrier having a large relaxation time. Yes. From this figure, if the elapsed time t when (V ₁ / V ₀ ) = 1 / e (= 0.3678) is obtained, that is, t at the points P1, P2, and P3 shown in FIG. Since τ = t, which is the carrier relaxation time showing each curve, it can be easily obtained.

  Among the carriers thus measured, those having a relaxation time τ of 150 seconds to 800 seconds have good carrier adhesion, as will be described later. More preferably, a carrier having a relaxation time τ of 200 seconds to 700 seconds is good. When the relaxation time τ is less than 150 seconds, induction-type carrier adhesion is likely to occur, and when it is 800 seconds or more, counter-charge-type carrier adhesion is likely to occur.

  In addition, as the basic structure of the carrier in the present invention, it is composed of core particles having magnetism and a resin layer covering the surface thereof, and selection of the particle diameter of these carriers and the core particles serving as the carrier skeleton is important. is there. The carrier used in the developing method of the present invention has a weight average particle diameter Dw in the range of 20 to 45 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 electrostatic latent image, and the variation in the dot diameter increases and graininess (roughness). Decreases.

  In addition, when a carrier having a weight average particle diameter Dw smaller than 20 μm is used, particles with small magnetization are present throughout the magnetic brush, and the carrier adhesion is rapidly deteriorated.

  Further, in the carrier particles having a weight average particle diameter Dw of 22 to 32 μm, sharp particles in which particles smaller than 36 μm are 80% by weight or more, more preferably 82% by weight or more and the content of particles smaller than 44 μm are 90% by weight or more. A carrier coated with a resin having a particle size distribution has a small variation in magnetization of each carrier particle, and carrier adhesion can be greatly improved by a developing method in which a DC bias is applied.

  In particular, the content of particles having a particle size smaller than 20 μm is in the range of 0-7 wt%, the content of particles smaller than 36 μm is 80-100 wt%, and the content of particles smaller than 44 μm is 90-100 wt%. A carrier coated with a resin having a sharp particle size distribution becomes smaller in variation in magnetization of each carrier particle, and can greatly improve carrier adhesion.

  In the present invention, the weight average particle diameter Dw referred to with respect to the carrier and the carrier core material particles 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 expressed by the following formula (3).

上式中、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等分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の長さを採用した。
また、各チャネルに存在する粒子の代表粒径としては、各チャネルに保存する粒子径の下限値を採用した。本発明において粒径分布を測定するための粒度分析計としては、マイクロトラック粒度分析計（モデルＨＲＡ９３２０−Ｘ１００：Ｈｏｎｅｗｅｌｌ社製）を用いた。その測定条件は以下のとおりである。

In the above formula, D represents the 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 equally dividing the particle size range in the particle size distribution diagram. In the present invention, a length of 2 μm is 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. 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.

(I) Particle size range: 100-8 μm
(II) Channel length (channel width): 2 μm
(III) Number of channels: 46
(IV) Refractive index: 2.42

  Further, in the carrier particles having a weight average particle diameter Dw of 22 to 32 μm, sharp particles in which particles smaller than 36 μm are 80% by weight or more, more preferably 82% by weight or more and the content of particles smaller than 44 μm are 90% by weight or more. A carrier coated with a resin having a particle size distribution has a small variation in magnetization of each carrier particle, and carrier adhesion can be greatly improved by a developing method in which a DC bias is applied.

  Further, the carrier used in the present invention is preferably a carrier having a sharper particle size distribution and uniform particle size, and in addition to the above-mentioned regulation of the weight average particle diameter Dw, the carrier and the carrier regulated by the number average particle diameter Dp. Preferably, core material particles are used.

  This number average particle diameter Dp is calculated based on the particle size distribution of the particles measured on the basis of the number. In this case, the number average particle diameter Dp is expressed by the following formula (4).

上記（４）式中、Ｎは計測した全粒子数、ｎは各チャンネルに存在する粒子の総数を示し、Ｄは各チャンネル（２μｍ）に存在する粒子径の下限値を示す。

In the above formula (4), 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 diameter 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 shown in the above (I) to (IV).

  Further, in the carrier according to the present invention, a predetermined magnetization is required because it is necessary to form a magnetic brush, and the amount of magnetization of such a carrier is the amount of magnetization when a magnetic field of 1000 oersted (Oe) is applied. 40 to 100 emu / g, more preferably 50 e to 90 mu / g. When it becomes less than 40 emu / g, carrier adhesion tends to occur, and when it becomes 100 emu / g or more, the head trace of the magnetic brush becomes strong.

  The amount of magnetization can be measured as follows. Using a BH tracer (BHU-60 / manufactured by Riken Denshi Co., Ltd.), 1 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, a BH curve is drawn, and a magnetic moment of 1000 Oersted is calculated from the drawing.

  The amount of magnetization of such carriers is basically determined by the magnetic material that becomes the core particles. Examples of the core particles that are 40 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 iron and cobalt, magnetite, hematite, Li-based ferrite, and MnZn-based materials. Examples thereof include ferrite, CuZn ferrite, NiZn ferrite, Ba ferrite, and Mn ferrite. Ferrite is a sintered body generally represented by the following chemical formula (1).

但し、ｘ＋ｙ＋ｚ＝１００ｍｏｌ％であって、Ｍ、Ｎはそれぞれ、Ｎｉ、Ｃｕ、Ｚｎ、Ｌｉ、Ｍｇ、Ｍｎ、Ｓｒ、Ｃａ等であり、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。本発明において、より好ましく用いられる１０００エルステッドの磁場を印加したときの磁気モーメント（磁化量）が４０ｅｍｕ／ｇ以上の芯材粒子としては、例えば、鉄系、マグネタイト系、ＭｎＭｇＳｒ系フェライト、Ｍｎ系フェライトなどが挙げられる。

However, x + y + z = 100 mol%, and M and N are Ni, Cu, Zn, Li, Mg, Mn, Sr, Ca, etc., respectively, and the divalent metal oxide and the trivalent iron oxide Consists of a complete mixture. In the present invention, the core particles having a magnetic moment (magnetization amount) of 40 emu / g or more when a magnetic field of 1000 oersted is more preferably used are, for example, iron-based, magnetite-based, MnMgSr-based ferrite, Mn-based ferrite. Etc.

  The core particles used in the carrier of the present invention are crushed particles of magnetic material, or in the case of core materials such as ferrite and magnetite, the primary granulated product before classification is classified, and the sintered particles are classified. It can be obtained by mixing a plurality of particle powders after classification into particle powders having different particle size distributions by treatment.

  As a method of classifying the core particles, conventionally known classification methods such as a sieving machine, a gravity classifier, a centrifugal classifier, and an inertia classifier can be used, but the productivity is easy and the classification point can be easily changed. Therefore, it is preferable to use an air classifier such as a gravity classifier, a centrifugal classifier, or an inertia classifier.

  Further, as the carrier used in the present invention, the characteristics of the electric resistance are also an important factor. In the carrier particles of the present invention, the electric resistivity logR is an applied electric field of 1000 V / 2 mm shown in FIG. Using a cell, it can be measured by the following method.

  As shown in FIG. 3, 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) as a sample, A DC voltage of 1000 V is applied between both electrodes, a DC resistance is measured with a high resistance meter 4329A (4329A + LJK 5HVLVWDQFH OHWHU; manufactured by Yokogawa Hewlett-Packard Co., Ltd.), and an electrical resistivity logR is calculated. When filling the carrier particle resistance, the carrier (13) is filled until it overflows into the cell (11), and then the entire cell (11) is tapped 20 times. Using a spatula, it was scraped flat along the upper end of the cell (11) by a single operation.

  In the carrier of the present invention, the electrical resistivity (log R) measured by such a method is preferably in the range of 11.0 to 17.0 Ω · cm, and in the range of 11.5 to 16.5 Ω · cm. More preferably. When the resistivity logR of the carrier is less than 11.0 Ω · cm, when the developing gap (the closest distance between the photosensitive member and the developing sleeve) is narrowed, charges are induced in the carrier and carrier adhesion is likely to occur. When it is larger than 17.0 Ω · cm, the edge effect becomes strong and the image density of the solid image portion becomes low. On the other hand, when LogR is greater than 17.0 Ω · cm, charges having the opposite polarity to the toner are likely to be accumulated, and the carrier is charged and carrier adhesion is likely to occur.

The resistivity of the carrier can be adjusted by adjusting the resistance of the coating resin on the core particles and controlling the thickness of the coating layer. Moreover, it is also possible to add conductive fine powder to the coating resin layer for carrier resistance adjustment. Examples of the conductive fine powder include conductive metals such as ZnO and Al, or cerium oxide, alumina, for example, metal oxides such as SiO ₂ and TiO ₂ having a hydrophobic surface, SnO ₂ prepared by various methods, and various _{SnO 2, TiB 2, ZnB 2} , borides such as MoB ₂ that doped with elements, silicon carbide, polyacetylene, polyparaphenylene, poly (para - phenylene sulfide) polypyrrole, a conductive polymer such as polyethylene, furnace black, Examples thereof include carbon black such as 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. The dispersion for forming a coating layer is prepared by uniformly dispersing by using a stirrer equipped with, and the carrier can be prepared by applying the dispersion for forming a coating layer to the core material particles.

  As the resin used for the carrier coating layer, various conventionally known resins can be used, and a silicone resin containing a repeating unit represented by the following chemical formula is preferably used.

上記式中、Ｒ¹は水素原子、ハロゲン原子、ヒドロキシ基、メトキシ基、炭素数１〜４の低級アルキル基、またはアリール基（フェニル基、トリル基など）を示し、Ｒ²は炭素数１〜４のアルキレン基、またはアリーレン基（フェニレン基など）を示す。

In the above formula, 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 (phenyl group, tolyl group, etc.), and R ² represents 1 to C carbon atoms. 4 alkylene group or an arylene group (such as a phenylene group).

  In the aryl group of the above formula, the carbon number thereof 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 also 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 the resin 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 -An ethyl acrylate copolymer, a xylene resin, a polyamide resin, a phenol resin, a polycarbonate resin, a melamine resin, a fluorine resin, or the like can be suitably mixed with the silicone resin.

  In the present invention, a carrier having good durability can be obtained by adding an aminosilane coupling agent to the coating layer made of the silicone resin.

  Examples of the aminosilane coupling agent used in the present invention include those represented by the following chemical formula. The content is preferably 0.001 to 30% by weight.

  As a method for forming the resin coating layer on the surface of the carrier core material 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 coating layer.

  The thickness of the coating layer on the surface of the carrier core particles is usually 0.02-1 μm, preferably 0.03-0.8 μm. Since the thickness of the coating layer is extremely small, the carrier having the coating layer formed on the surface of the core particle and the carrier core particle have substantially the same particle size.

In this case, although the bulk density of the carrier affects the carrier adhesion, the bulk density of the carrier recommended in the present invention is 2.15 to 2.70 g / cm ³ , more preferably 2.25 to 2.60 g / cm ³ . When the carrier is porous, or the surface irregularities are large and the bulk density is less than 2.15, the substantial magnetization per particle is increased even if the amount of magnetization (emu / g) of 1 KOe of the core particle is large. Since the value is small, it is disadvantageous for carrier adhesion.

To increase the bulk density, it is possible to increase the firing temperature. However, it is preferable that the core particles be less than 2.7 g / cm ³ because the core particles are easily fused and difficult to disintegrate. More preferably, it is less than 6 g / cm ³ .

According to the metal powder-apparent density test method (JIS-Z-2504), the carrier according to the present invention has a bulk density of 25 cm ³ made of stainless steel, which is allowed to flow naturally from an orifice having a diameter of 2.5 mm. After pouring the carrier into the cylindrical container until it overflows, the upper surface of the container is scraped flat with a single operation along the upper end of the container using a nonmagnetic horizontal spatula. If it is difficult to flow with an orifice having a diameter of 2.5 mm, the carrier naturally flows out from the orifice having a diameter of 5 mm. This operation, the carrier weight that flowed into the container is divided by the volume 25 cm ³ of the vessel to determine the weight of the carrier per 1 cm ^3. This is defined as the bulk density of the carrier.

  In the present invention, it is preferable to use a developer having a toner charge amount of 15 to 30 μc / g when the carrier coverage with the toner is 50%. When the charge amount is less than 30 μc / g, the accumulation of counter charge is suppressed, and thus carrier adhesion is more preferable. However, when the charge amount is less than 15 μc / g, scumming tends to occur, which is not preferable.

  The charge amount of the toner in the developer can be measured by the following method. FIG. 4 is a schematic diagram of an apparatus for measuring the charge amount of toner in the developer. In the figure, reference numeral (15) denotes a nozzle for discharging the compressed gas (16) and blowing off the toner (T) adhering to the carrier (C) in the blow-off cage (17) to the outside of the cage (17). ) Is an electrometer that measures the potential of the carrier in the blow-off cage (17).

In order to measure the charge amount of the toner in the developer using this apparatus, a certain amount of developer with the toner attached to the surface of the carrier is used, and a conductor having a stainless steel metal mesh (19) at both ends is used. Place in blow-off cage (17). The mesh (19) has a mesh size between the toner (T) and the carrier (C) having a particle size (mesh size of 20 μm) so that only the toner (T) passes between the meshes (19). Is set. Compressed nitrogen gas 16 (1 kgf / cm ² ) is blown from the nozzle (15) for 60 seconds to cause the toner T to jump out of the cage (17). In this way, when the toner (T) is blown off from the carrier (C), the carrier (C) is charged with a polarity opposite to that of the toner. The charge amount Q and the mass M of the ejected toner are measured and measured per unit mass. Is calculated as the charge amount (Q / M) of the toner. In this case, the toner charge amount is expressed in μc / g. In addition, it is calculated by the following formula below the carrier coverage with toner.

Coverage (%) = (Wt / Wc) × (ρc / ρt) × (Dc / Dt) × (1/4) × 100 (5)
In the above formula (5), Dc is the weight average particle diameter (μm) of the carrier, Dt is the weight average particle diameter (μm) of the toner, Wt is the weight of the toner (g), Wc is the weight of the carrier (g), ρt Represents the true density (g / cm ³ ) of the toner, and ρc represents the true density (g / cm ³ ) of the carrier.

  Next, the toner used in the present invention will be described.

  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; examples of acrylic binders include polymethyl methacrylate and polybutyl methacrylate. 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. Is mentioned.

  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 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. For this purpose, it is generally effective to externally add hydrophobized metal oxide fine particles and fine particles such as lubricants as fluidity improvers, and metal oxides, organic resin fine particles, metal soaps and the like as additives. It is possible to use. Specific examples of these additives include fluorine resins such as polytetrafluoroethylene, lubricants such as zinc stearate, abrasives such as cerium oxide and silicon carbide; for example, inorganic surfaces such as SiO ₂ and TiO ₂ whose surfaces are hydrophobized. Examples thereof include fluidity-imparting agents such as oxides; those known as anti-caking agents, and surface-treated products thereof. In order to improve the fluidity of the toner, hydrophobic silica is particularly preferably used.

  In the toner used in the present invention, the weight average particle diameter Dt is 9.0 to 3.0 μm, preferably 7.5 to 3.5 μm. The ratio of the toner to the carrier is 2 to 25 parts by weight, preferably 3 to 20 parts by weight, per 100 parts by weight of the carrier. The toner particle size was measured using a Coulter counter (manufactured by Coulter Counter).

  The developing method of the present invention is a method of developing the electrostatic latent image formed on the photoreceptor using the developer containing the carrier and toner according to the present invention. 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.

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

  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. 5 is a schematic view showing a developing unit of the image forming apparatus for explaining the electrophotographic developing method of the present invention. In FIG. 5, the developing unit is arranged to face the photosensitive drum (20) as a latent image carrier. The provided developing device (40) is mainly composed of a developing sleeve (41) as a developer carrying member, a developer accommodating member (42), a doctor blade (43) as a regulating member, a support case (44) and the like. Has been.

  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. 6 is a cross-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), a charging member (32), an exposure system (33), a developing device (40), a transfer roller (50), a cleaning device (60), a static elimination lamp ( In this example, the surface of the charging member (32) is not in contact with the surface of the photoreceptor (20) with a gap of about 0.2 mm, and the charging member (32). When the photosensitive member (20) is charged by the charging, the charging member (32) is charged by an electric field in which an alternating current component is superimposed on a direct current component by voltage application means (not shown), thereby charging unevenness. Can be reduced, which is effective. 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. A photoconductor (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. Formation of a latent image by laser light modulated in accordance with image information irradiated from the optical exposure 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) Is done.

  Laser light is emitted from a semiconductor laser, and the surface of the image bearing member, that is, the photosensitive member (20) is scanned in the direction of the rotational axis of the photosensitive member (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 (21) and carrier particles (23) supplied on a developing sleeve (41) which is a developer carrying member in the 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 an AC voltage is applied from the voltage application mechanism (not shown) to the developing sleeve (41) between the exposed portion and the non-exposed portion of the photoreceptor (20). A developing bias with superimposed is applied.

On the other hand, a recording medium (for example, paper) (80) is fed from a paper feeding mechanism (not shown), and is synchronized with the leading edge of the image by a pair of upper and lower registration rollers (not shown). The toner image is fed between the transfer roller (50) and the toner image is transferred to the recording medium (80). At this time, it is preferable that a potential opposite to the toner charging polarity is applied to the transfer roller (50) as a transfer bias. Thereafter, the toner image is transferred, and the recording medium (80) is conveyed to a fixing device (90) comprising heating and pressure rollers, and the toner image on the recording medium (80) is fixed by the fixing device (90). Are ejected.
Further, the toner particles remaining on the photoreceptor (20) are collected into the toner collection chamber (62) in the cleaning device (60) by the 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 is not limited to a monochrome type provided with one photoconductor (20) and developing device (40), but a plurality of photoconductors, for example, four, yellow, magenta, cyan, black, etc. A full-color type in which a plurality of developing devices corresponding to the respective colors are arranged in parallel along the conveyance path of the recording medium (80) corresponding to the photoreceptor (20) may be used.

Hereinafter, the present invention will be specifically described by way of examples. In addition, this invention is not limited to the Example illustrated here.
Hereinafter, the present invention will be described using examples and comparative examples. However, "part" represents a weight part.

Toner production example (toner production example)
Polyester resin 100 parts Quinacridone-based magenta pigment 3.5 parts Fluorine-containing 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 particle diameter of 5.8 μm and a true specific gravity of 1.20.
Further, 1.5 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 toner I.

[Example of carrier production]

(Carrier production example 1)
The following composition was dispersed with a homomixer for 10 minutes to prepare a coating layer forming solution.
Silicone resin (SR2411 manufactured by Toray Dow Corning Silicone / 20% solid content) 100 parts H ₂ N (CH ₂ ) ₃ Si (OC ₂ H ₅ ) ₃ 5 parts Alumina particles (volume average particle size: 0.35 μm) 20 parts 300 parts of toluene

  Next, using a fluidized bed type coating apparatus, carrier core material particles (a) having the properties shown in Production Example 1 in Table 1 (particle size: 38.9 μm, CuZn-based ferrite particles, 1 KOe magnetization: 56 emu / g ) On the surface of each particle of 5 kg, the above-mentioned silicone resin solution was applied at a rate of 30 g / min in an atmosphere of 90 ° C., and further heated at 230 ° C. for 2 hours to obtain carrier A (0). Carrier A (0) has a resin film thickness of 0.45 μm, and a resistance LogR of 16.3 Ω · cm when 1000 V is applied in the cell shown in FIG. 3 (hereinafter referred to as 1000 V / 2 mm), as shown in FIG. The relaxation time τ measured by the method was 1195 seconds. The film thickness was adjusted by the amount of the coating solution.

  Next, 500 g of the carrier A (0) was placed in a turbuler shaker mixer and stirred, 2 g of the carrier was taken out every 5 minutes, and the carrier relaxation time τ was measured by the method shown in FIG. Carriers when the stirring time is 5 minutes, 10 minutes, and so on are indicated as carrier A (5), carrier A (10), and so on. As shown in Table 3, the relaxation time of each carrier is carrier A (5) = 1054 seconds, carrier A (10) = 927 seconds, carrier A (15) = 828 seconds, carrier A (20) = 705, respectively. Second, carrier A (30) = 578 seconds. Further, the resistance LogR after 30 minutes was 16.4 Ω · cm.

(Carrier production example 2)
Carrier B (0) was prepared in exactly the same manner as Carrier Production Example 1 except that the carrier core material particles (b) (particle size 27.9 μm CuZn ferrite particles, 1 KOe magnetization 57 emu / g) were used as the carrier core material. Obtained. Carrier B (0) had a resin film thickness: 0.32 μm, a resistance LogR of 1000 V / 2 mm: 16.2 Ω · cm, and the relaxation time measured by the method shown in FIG. 1 was 1127 seconds. The film thickness was adjusted by the amount of the coating solution. In the same manner as in Carrier Production Example 1 described above, this carrier B (0) was placed in a turbula shaker mixer and stirred, 2 g of the carrier was taken out every 5 minutes, and the carrier relaxation time was measured by the method shown in FIG. τ was measured.

  The carrier relaxation times in this case are carrier B (5) = 976 seconds, carrier B (10) = 844 seconds, carrier B (15) = 705 seconds, carrier B (20) = 601 seconds, carrier B ( 30) = 474 seconds. Further, the resistance LogR after 30 minutes was 16.0 Ω · cm.

(Carrier production example 3)
The carrier C (0) is the same as the carrier production example 1 except that the carrier core material is changed to carrier core material particles (c) (MnMgSr ferrite particles having a particle size of 27.6 μm, 1 KOe magnetization amount 71 emu / g). ) Carrier C (0) had a resin film thickness: 0.32 μm, a resistance LogR of 1000 V / 2 mm, 16.4 Ω · cm, and the relaxation time measured by the method shown in FIG. 1 was 1103 seconds. The film thickness was adjusted by the amount of the coating solution.

  In the same manner as in Carrier Production Example 1 described above, this carrier C (0) was placed in a tumbler shaker mixer and stirred, 2 g of the carrier was taken out every 5 minutes, and the carrier relaxation time was measured by the method shown in FIG. τ was measured. The carrier relaxation times in this case are carrier C (5) = 962 seconds, carrier C (10) = 794 seconds, carrier C (15) = 623 seconds, respectively, as shown in the carrier C column of Table 3. Carrier C (20) = 554 seconds and carrier C (30) = 412 seconds. Further, the resistance LogR after 30 minutes was 16.2 Ω · cm.

(Carrier Production Example 4)
Except for changing the carrier core material to carrier core material particles (d) (Mn ferrite particles having a particle diameter of 27.2 μm, 1 KOe magnetization of 75 emu / g), the carrier D (0) was prepared in exactly the same manner as in Production Example 1. Obtained. Carrier D (0) had a resin film thickness: 0.33 μm, a resistance LogR of 1000 V / 2 mm: 16.2 Ω · cm, and the relaxation time measured by the method shown in FIG. 1 was 1138 seconds. The film thickness was adjusted by the amount of the coating solution.

  The carrier D (0) was placed in a turbula shaker mixer and stirred in the same manner as in the carrier production example 1 described above, 2 g of the carrier was taken out every 5 minutes, and the carrier relaxation time was measured by the method shown in FIG. τ was measured. The carrier relaxation times in this case are carrier D (5) = 934 seconds, carrier D (10) = 742 seconds, carrier D (15) = 554 seconds, as shown in the carrier D column of Table 3. Carrier D (20) = 474 seconds and carrier D (30) = 377 seconds. Further, the resistance LogR after 30 minutes was 16.0 Ω · cm.

(Carrier Production Example 5)
Except for changing the carrier core material to carrier core material particles (e) (magnetite particles having a particle diameter of 26.9 μm, 1 KOe magnetization amount 74 emu / g) and reducing the amount of the coating solution to 1/3, completely the same as in Production Example 1 In the same manner, carrier E (0) was obtained. Carrier E (0) had a resin film thickness: 0.08 μm, a resistance LogR of 1000 V / 2 mm: 12.3 Ω · cm, and the relaxation time measured by the method shown in FIG. 1 was 811 seconds.

  This carrier E (0) was stirred in a turbula shaker mixer in the same manner as in the carrier production example No1 described above, and 2 g of the carrier was taken out every 5 minutes. τ was measured. The carrier relaxation times in this case are carrier E (5) = 578 seconds, carrier E (10) = 412 seconds, carrier E (15) = 241 seconds, respectively, as shown in the carrier E column of Table 3. Carrier E (20) = 187 seconds and Carrier E (30) = 122 seconds. Further, the resistance LogR after 30 minutes was 10.4 Ω · cm.

  Using the core particle carriers (a) to (e) having the characteristics shown in Table 1, carriers A (0) to E (30) having carrier characteristics as shown in Table 3 were prepared.

(Development of developer and evaluation 1)
Using the carrier A (0) to carrier E (30) obtained in the above carrier production example and the toner obtained in the toner production example, toner (13.1 parts) is added to 100 parts of the carrier, The mixture was stirred with a ball mill for 5 minutes to prepare a developer of 11.6% by weight. The coverage of the toner with respect to the carrier was 50%. In this case, carrier A (20) is implemented in Example 1, carrier B (20) is implemented in Example 2, carrier C (20) is implemented in Example 3, carrier D (20) is implemented in Example 4, and carrier E (20) is implemented. Example 5 Carrier A (0) is Comparative Example 1, Carrier A (15) is Comparative Example 2, Carrier B (0) is Comparative Example 3, Carrier C (0) is Comparative Example 4, Carrier D (0) is compared A developer was prepared using Example 5, Carrier E (0) as Comparative Example 6, and Carrier E (30) as Comparative Example 7, image formation was performed, and the image quality was confirmed. The image was created using Imagio Color 5000 (Ricoh Digital Color Copier / Printer Combined Machine) under the following development conditions. Incidentally, the characteristics of the carrier manufactured in this way are as shown in Table 2.

Development gap (photosensitive member-developing sleeve): 0.3 mm
Doctor gap (Developing sleeve-Doctor): 0.7mm
Photoconductor linear velocity: 245 mm / sec
(Developing sleeve linear velocity) / (photosensitive member linear velocity): 1.5
Writing density: 600 dpi
Charging potential (Vd): -750V
Potential after exposure of the portion corresponding to the image portion (solid document): −100V
Development bias: DC-550V

  For the image created as described above, (1) counter charge type carrier adhesion, (2) induction type carrier adhesion, (3) image density, (4) granularity, (5) background stain, (6) A characteristic test for evaluation of soiling after 20K running was conducted and evaluated. The results are shown in Table 4. In addition, the characteristic test method and its evaluation method are as follows.

(1) Counter-charge type carrier adhesion (carrier adhesion 1): The charging potential (Vd) is fixed at −750 V, the developing bias (Vb) is fixed at DC-450 V, the background portion (unexposed portion) is developed, and the photoconductor The number of carriers adhering to the upper 30 cm ² was directly counted to evaluate the carrier adhesion.
The symbols described in the table are ◎: very good, ○: good, ×: poor (× is an unacceptable level).

(2) Induction-type carrier adhesion (carrier adhesion 2): Evaluation of carrier adhesion by directly counting the number of carrier adhesion in the solid portion of the solid image (30 mm × 30 mm) of IMAGIO COLOR 5000 under the development conditions described above. went.
The symbols described in the table are ◎: very good, ○: good, ×: poor (× is an unacceptable level).

  (3) Image density: The center of a solid portion of 30 mm × 30 mm in the above development conditions was measured at five locations with an X-Rite 938 spectrocolorimeter and the average value was obtained.

  (4) Granularity: The granularity (brightness range: 50 to 80) defined by the following formula was measured, and the numerical values were evaluated by replacing them with ranks as follows.

  (5) Background stain: The stain on the background portion on the image was visually evaluated. The symbols described in the table are ◎: very good, ○: good, ×: poor (× is an unacceptable level).

  (6) Evaluation of background stain after 20K running: For a developer that has run 20K sheets on a character image chart with an image area ratio of 6% while replenishing toner, the same background stain as in (5) above. Was evaluated.

  As is clear from the results shown in Table 4, each example has (1) counter-charge type carrier adhesion, (2) induction type carrier adhesion, and (3) image density as compared with the comparative examples. , (4) granularity, (5) background dirt, and (6) background dirt after 20K running. In particular, in Examples 2-5, the relaxation time is small, the counter-charge type carrier adhesion is small, the image density is high, and the relaxation time is within 200 to 700 seconds. In addition, the adhesion of the induction type carrier is also suppressed, and the granularity and the soiling characteristics after 20K running also show better results than those of Examples 1 and 5.

(Development of developer and evaluation 2)
Evaluation was performed in the same manner as in (Development of developer and evaluation 1) except that the development bias was changed to the following conditions. The results are shown in Table 5.
A developer was prepared using the carriers A to I obtained in the carrier production example and the toner obtained in the toner production example, image formation was performed, and the image quality was confirmed. The image was created using Imagio Color 5000 (Ricoh Digital Color Copier / Printer Combined Machine) under the following development conditions.
・ Development gap (photosensitive member-developing sleeve): 0.3 mm
・ Doctor gap (developing sleeve-doctor): 0.7mm
-Photoconductor linear velocity: 245 mm / sec
・ (Developing sleeve linear velocity) / (photosensitive member linear velocity): 1.5
-Write density: 600 dpi
・ Charging potential (Vd): -750V
-Potential after exposure of the portion corresponding to the image portion (solid document): -100V
Development bias: DC −500V / AC bias component: 2 KHz, −100 V to −900 V, 50% duty

It is a schematic diagram of the measuring apparatus which measures the relaxation time of the carrier of the Example by this invention. Is a graph showing the relationship between the potential ratio of the carrier for explaining the relaxation time of the carrier and (V / V ₀₎ decay time and. It is a perspective view of the cell for measuring the electrical resistance of a carrier. It is a schematic diagram of a measuring device for measuring the charge amount of toner in a carrier. 1 is a cross-sectional view illustrating a schematic configuration of a developing device according to an embodiment used in the present invention. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment used in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Photoconductor 21 Toner 23 Carrier 32 Charging device 33 Exposure mechanism 40 Developing device 50 Transfer roller 60 Cleaning device 80 Recording medium 90 Fixing device

Claims (16)

It consists of a core material particle having magnetism and a resin layer covering the particle surface, the weight average particle diameter Dw is 20 to 45 μm, the magnetization of the core material particle in a magnetic field of 1000 oersteds is 40 to 100 emu / g, and carrier resistance (1000V / 2mm) · LogR · Ωcm is a carrier of 11 to 17, wherein the resin layer contains conductive fine particles, and the carrier is provided with mechanical energy in a state where no toner is added . A carrier for an electrophotographic developer, wherein the relaxation time τ is 150 seconds to 800 seconds. It consists of a core material particle having magnetism and a resin layer covering the particle surface, the weight average particle diameter Dw is 22 to 32 μm, and the ratio of the number average particle diameter Dp to the weight average particle diameter Dw (Dw / Dp) is A carrier for an electrophotographic developer in which 1 <(Dw / Dp) <1.20, the content of particles having a particle size smaller than 20 μm is 0 to 7% by weight, and the content of particles smaller than 36 μm is 80 2. The carrier for an electrophotographic developer according to claim 1, wherein the content of particles of ˜100 wt% and smaller than 44 μm is 90 to 100 wt%. Electrophotographic developer carrier according to claim 1 or 2 the carrier core material is characterized by a MnMgSr ferrite. The carrier for an electrophotographic developer according to any one of claims 1 to 3, wherein the carrier core material is Mn- based ferrite. The carrier for an electrophotographic developer according to any one of claims 1 to 4, wherein the carrier core material is magnetite. 6. The carrier for an electrophotographic developer according to claim 1, wherein a core material having a bulk density of 2.15 to 2.70 g / cm ³ is used. An electrophotographic developer comprising a toner and a carrier, wherein the carrier according to any one of claims 1 to 6 is used as the carrier. An electrophotographic developer comprising a toner and a carrier, wherein the carrier is the carrier according to any one of claims 1 to 6, and charging of the toner when the coverage of the carrier by the toner is 50%. The electrophotographic developer according to claim 7, wherein the amount is 15 to 30 μc / g. In the electrophotographic development method of forming a toner image by visualizing the electrostatic latent image by supplying toner from a developer containing a carrier and toner to the surface of the photoreceptor on which the electrostatic latent image is formed by exposure,
The carrier is composed of magnetic core material particles and a resin layer covering the surface of the core material particles. The resin layer includes conductive fine particles, and the carrier gives mechanical energy in a state where no toner is added. ones, and the weight average particle size of 20-45 [mu] m, 1000 oersteds magnetization 40~100emu / g of core material particles in a magnetic field, the carrier resistance (LogR when the distance between the electrodes was applied to 1000V voltage at 2mm ) Has a value of 11 to 17 Ω · cm, the carrier relaxation time τ is 150 seconds to 800 seconds, and a DC voltage is applied as a developing bias when supplying toner from the developer to the photoreceptor. An electrophotographic developing method characterized by the above.   The carrier has a weight average particle diameter Dw of 22 to 32 μm and a ratio (Dw / Dp) of the number average particle diameter Dp to the weight average particle diameter Dw of 1 <Dw / Dp <1.20, which is smaller than 20 μm. The content of particles having a particle size is 0 to 7% by weight, the content of particles smaller than 36 μm is 80 to 100% by weight, and the content of particles smaller than 44 μm is 90 to 100% by weight. Item 10. The electrophotographic development method according to Item 9.   11. The electrophotographic developing method according to claim 9, wherein the core material particles of the carrier are MnMgSr ferrite.   The electrophotographic developing method according to claim 9, wherein the core material particles of the carrier are Mn ferrite. The electrophotographic developing method according to claim 9 or 10, wherein the core material particles of the carrier are magnetite. The electrophotographic developing method according to claim 9, wherein a bulk density of the core material particles of the carrier is 2.15 to 2.70 g / cm ³ .   The toner supplied to the photosensitive member is attached to the surface of the carrier, and the toner charge amount when the coverage of the carrier by the toner is 50% is 15 to 30 μc / g. 15. The electrophotographic developing method according to any one of 9 to 14.   16. A toner image formed on a photoreceptor using the electrophotographic developing method according to claim 9, and then transferred to a recording medium, and then transferred to the recording medium. An image forming method comprising fixing an image.

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