JPH06348063A - Electrophotographic carrier - Google Patents

Abstract

PURPOSE:To provide an electrophotographic carrier showing high resolution, good reproducibility for a high-light part, and high reproducibility for fine lines by combining a core material having specified physical properties and a coating resin comprising a specified resin. CONSTITUTION:This electrophotographic carrier is obtd. by coating a resin core material with a resin. The core material is a magnetic material dispersion type containing a magnetic material dispersed in a binder resin. The carrier has 5-100mum particle size and <=3.0g/cm<3> bulk density, and the amt. of the magnetic material is 30-99mass% of the total weight of the carrier. The coating resin for the core material is a styrene-acryl copolymer containing 30-90mass% monomer ration of acryl component, 30000-70000 weight average mol.wt. of the copolymer, and 2-10 weight average mol.wt./number average mol.wt. By this constitution, accurate development for the original can be done for a long period even for high-speed development while preventing deposition of the carrier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic carrier which is mixed with a toner to form a developer for developing an electrostatic charge image, and more particularly to an electrophotographic carrier obtained by coating the surface of a carrier core material with a resin. Regarding career.

[0002]

2. Description of the Related Art US Pat. No. 2,29 as an electrophotographic method
Various methods are described in Japanese Patent No. 7,691, Japanese Patent Publication No. 42-23910 and Japanese Patent Publication No. 43-24748. These methods form an electrostatic latent image by irradiating the photoconductive layer with a light image corresponding to the original, and then, in the case of normal development, an opposite polarity is formed on the electrostatic latent image. The electrostatic latent image is developed by adhering colored fine powder called toner that it has, and after transferring the toner image to a transfer material such as paper as necessary, it is fixed by heat, pressure, heat and pressure, or solvent vapor. This is to obtain a copy.

In the step of developing the electrostatic latent image, toner particles charged to the opposite polarity to the latent image are attracted by electrostatic attraction and adhered to the electrostatic latent image (in the case of reversal development). In this case, a toner having a triboelectric charge having the same polarity as that of the latent image is used.) Generally, a method of developing such an electrostatic latent image with toner is roughly classified into a two-component system in which a small amount of toner and a carrier are mixed. There are a method of using a developer and a method of using a so-called one-component developer of toner alone without using a carrier.

Although the electrophotographic method has reached a satisfactory level for copying documents, due to the development of computers and the development of high-definition, full-color output images are subjected to alternation during digital image processing and development. Image quality and quality have been improved by various methods such as applying an electric field. Furthermore, in the future, further image quality improvement,
Higher quality is desired.

Conventionally, a two-component developer has been used to output a full-color image. In general, the carrier that constitutes such a two-component developer is roughly classified into a conductive carrier represented by iron powder and a so-called insulating carrier in which particles of iron powder, nickel, ferrite and the like are coated with an insulating resin. It When an alternating electric field is applied to measure high image quality, if the resistance of the carrier is low, the latent image potential leaks to the carrier, and a good developed image cannot be obtained. Therefore, the carrier needs to have a certain resistance or more. . When the carrier core is electrically conductive, it is preferably used by coating the carrier core. Further, ferrite having a high resistance to some extent, magnetic substance-dispersed resin particles and the like are preferably used as the core material.

In general, iron powder has a high magnetic force, and in the developing area where the toner in the developer develops the latent image, the magnetic brush of the developer becomes hard, resulting in blemishes, rubbing and the like. Therefore, it is difficult to obtain a high quality developed image. Therefore, in order to reduce the magnetic force of the carrier and achieve high image quality, ferrite or a magnetic material-dispersed resin carrier is preferably used.

Further, in the case of the magnetic substance-dispersed resin carrier, since the specific gravity is smaller than that of iron powder or ferrite, the strength of magnetization per unit volume becomes smaller and the share for toner is small, so that high image quality is obtained. In addition to high performance, high developer durability can be achieved.

In order to form a high-quality image, Japanese Patent Laid-Open No. 59-59
-104663 discloses that the value of saturation magnetization of carrier is 50.
It has been proposed that by setting the emu / g or less, a good developed image can be obtained without peeling. However, if a carrier with a smaller saturation magnetization value is used, fine line reproducibility is improved. As the distance from the magnetic pole increases, the phenomenon that the carrier adheres to the electrostatic image carrier (for example, the photosensitive drum) (carrier adhesion) becomes remarkable. Further, in the case of a magnetic substance dispersion type resin carrier, there is a problem that a low specific gravity is disadvantageous in carrier adhesion.

Further, Japanese Patent Publication No. 4-3868 proposes to use a so-called hard ferrite having a coercive force of 300 gauss or more as a carrier. However, this is a system for making full use of hard ferrite having a high coercive force as a carrier, and an increase in the size of the device cannot be avoided. In order to realize a compact high-quality color copier, it is preferable to use a developer carrier using a fixed magnetic core. In this case, a hard carrier having a high coercive force is
Due to the self-aggregating property, there is a problem that the transportability is rather deteriorated.

Further, Japanese Patent Laid-Open No. 2-88429 proposes to use a hard ferrite composed of a spinel phase and a magnet-plumbite phase containing a lanthanoid element as a carrier. In the developing system using an alternating electric field for obtaining a higher quality image, the charge leaks through the carrier and disturbs the image.

Therefore, in the developing system using the alternating electric field, it is necessary that the resistance of the carrier is higher than a certain level.

On the other hand, although there are various other characteristics required for the carrier, particularly important characteristics are appropriate charging property, pressure resistance against applied electric field, impact resistance, abrasion resistance, spent resistance, Examples include developability and productivity.

For example, when the developer is used for a long period of time,
Toner spent is generated by fusion of toner that does not contribute to development on the surface of the carrier, resulting in deterioration of the developer and accompanying deterioration of the image quality of the developed image.

In general, when the developer has a predetermined layer thickness on the sleeve by the developer layer thickness regulating member, and the developer is loaded by stirring in the developing machine, the developer is used for a long period of time. (A) The toner spent (b) Carrier destruction (c) Deterioration of the toner may occur, which easily causes deterioration of the developer and accompanying deterioration of the image quality of the developed image.

Therefore, in the carrier in which (a) to (c) are likely to occur, it is necessary to periodically replace the developer and it is uneconomical, so that the load on the developer is reduced. Alternatively, it is necessary to prevent the above (a) to (c) and extend the developer life by improving the impact resistance and the spent resistance of the carrier.

To solve the above problems, it is possible to reduce the specific gravity of the carrier and use a magnetic substance dispersion type resin carrier aiming at a light load on the developer.

However, in the above-mentioned magnetic substance-dispersed resin carrier, when a large amount of magnetic substance is not contained in the carrier particles, the saturation magnetization is small with respect to the particle size and carrier adhesion occurs on the photoconductor during development. There is a problem that it is not possible to be a drastic measure for extending the life of the developer, such as having to have a mechanism for replenishing the developer or collecting a carrier for adhering in the image forming apparatus. It has drawbacks.

When a large amount of the magnetic material is contained in the magnetic material-dispersed resin carrier, the amount of the magnetic material with respect to the binder resin increases, and the impact resistance becomes weak.
When the developer is made to have a predetermined layer thickness on the sleeve with the developer layer thickness regulating member, or due to stirring in the developing device or the like, the magnetic substance is apt to be missing from the carrier, resulting in deterioration of the developer. Since it easily occurs, even in this case, there is a drawback that it cannot be a drastic measure for extending the life of the developer.

When a large amount of the magnetic material is contained in the magnetic material-dispersed resin carrier, the resistance of the carrier is lowered due to an increase in the amount of the magnetic material having a low resistance, resulting in a high quality image. Therefore, in developing with an alternating electric field, there is also a drawback that an image defect is likely to occur due to leakage of a bias voltage applied during development.

Therefore, the above-mentioned magnetic substance-dispersed resin carrier with an increased amount of magnetic substance has a drawback that it cannot be a drastic measure for improving the developing property and extending the life of the developer. .

On the other hand, there is a method of dealing with the technique of coating a carrier with a resin, which is disclosed in JP-A-58-21750. According to the carrier coated with the above resin, the spent resistance, impact resistance,
The withstand voltage with respect to the applied voltage can be improved. Further, since the charging characteristics of the toner can be controlled by the charging characteristics of the resin to be coated, it is possible to impart desired charging to the toner by selecting the resin to be coated.

However, also in the above resin-coated carrier, when the amount of the coating resin is large and the resistance of the carrier is high, the charge amount of the toner becomes large in a low humidity environment.
The so-called toner charge-up phenomenon easily occurs,
Further, when the amount of the coating resin is small, the resistance of the carrier becomes too low, so that there is a problem in that it is difficult to control the coating amount such that an image defect is likely to occur due to leakage of the developing bias voltage.

When the coat state is not uniform, the carrier is partially charged up, and the electrostatic force thereof causes carrier adhesion especially in a developing system using an alternating electric field for improving image quality. Problems arise.

Further, depending on the coating resin, even if the resistance of the carrier coated with the resin is considered to be an appropriate resistance in measurement, image defects are apt to occur due to leakage of the developing bias voltage, or charging in a low humidity environment is performed. There are some cases where the up phenomenon occurs easily, and the coated carrier made of the above resin also has a problem that its control is difficult when the developability is taken into consideration.

As described above, the high image quality, especially the highlight reproducibility is satisfied at the same time while preventing carrier adhesion.
Moreover, a sufficient developer carrier that can be used for a long period of time has not yet been obtained.

[0026]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic carrier which solves the above problems.

It is an object of the present invention to provide an electrophotographic carrier capable of performing development faithful to an original document (that is, faithful to a latent image) for a long period of time while preventing carrier adhesion.

A further object of the present invention is to provide an electrophotographic carrier excellent in high resolution, good reproducibility of highlight portions and high fine line reproducibility.

A further object of the present invention is to provide a carrier for electrophotography which can obtain a high quality developed image without carrier adhesion even at high speed development.

A further object of the present invention is to provide an electrophotographic carrier which can obtain a developed image of high quality without carrier adhesion even in the development of an alternating electric field.

A further object of the present invention is to provide an electrophotographic carrier applicable to a small-sized developing device using a fixed magnetic core type developer carrying member for obtaining a high quality image.

A further object of the present invention is to provide an electrophotographic carrier capable of maintaining a high quality image without deterioration of the developer even when copying a large number of sheets and without deterioration of the image.

[0033]

The present invention relates to an electrophotographic carrier having a carrier core material surface coated with a resin, wherein the carrier has an average particle size of 5 to 100 .mu.m.
m, the bulk density is 3.0 g / cm ³ or less, the carrier is formed of fine particles made of a soft magnetic material, and the magnetic fine particles have three-dimensional shape anisotropy in at least a uniaxial direction. The ratio of the major axis to the minor axis is greater than 1, the magnetic fine particles constituting the carrier have an orientation of 30% or more, and the magnetic characteristics of the carrier are that the strength of magnetization (σ ₁₀₀₀ ) in a magnetic field of 1000 Oersted is 30 to 150 emu
/ Cm ³ , and further, the magnetic properties of the carrier satisfy the following formulas (1) and (2), and the resin coating the surface of the core material is composed of a styrene-acrylic copolymer, Acrylic component monomer ratio in coalescence is 30-9
0% by mass, the weight average molecular weight of the copolymer is 30,000 to 70,000, and the weight average molecular weight /
The present invention relates to a carrier for electrophotography, which has a number average molecular weight of 2 to 10. In the following, this carrier is particularly referred to as “invention 1”.

[0034]

[Equation 4]

[Wherein σ ₁₀₀₀ is the strength of magnetization (emu / cm ³ ) at 1000 Oersted, and σ ₃₀₀
Is the strength of the magnetization at 300 Oersted (emu /
cm ³ ). ]

[0036]

[Equation 5]

[Wherein σ ₁₀₀ is the strength of magnetization (emu / cm ³ ) at 100 Oersted, and σ r is
Magnetization strength at 0 Oersted (emu / cm ³ )
Indicates. ]

Further, the present invention provides an electrophotographic carrier comprising a magnetic material-dispersed resin core material obtained by dispersing a magnetic material in a binder resin and coating the resin with a particle diameter of 5 to 100 μm. And the bulk density is 3.0 g / cm ³ or less, and the content of the magnetic material is 3 with respect to the total amount of the carrier.
0 to 99% by mass, the magnetic fine particles dispersed in the carrier have a major axis / minor axis> 1, three-dimensional uniaxial shape anisotropy, and 30% or more orientation. The strength of magnetization ( ₁₀₀₀ ) at 1000 Oersted after the magnetic properties of the carrier are magnetically saturated is 30 to 150 emu / cm ³ , and the strength of magnetization at a magnetic field of 0 Oersted (residual Magnetization: σ
r) is 25 emu / cm ³ or more, and the coercive force is 300.
It is less than Oersted, and at that time, the resin satisfying the above formula (1) and coating the surface of the core material is composed of a styrene-acrylic copolymer, and the monomer ratio of the acrylic component in the copolymer is 30 to 30. 90% by mass, and the copolymer has a weight average molecular weight of 30,000 to 700.
And the weight average molecular weight / number average molecular weight is 2
The present invention relates to a carrier for electrophotography, characterized in that In the following, this carrier is particularly referred to as "the present invention 2".

The present invention will be described in detail below.

The carrier of the present invention improves various problems of the conventional carrier, and provides a carrier capable of performing development faithful to an original, that is, faithful to a latent image, for a long period of time while preventing carrier adhesion. The reason for this is considered to be as follows.

In order to faithfully develop the latent image,
It is important to set the strength of carrier magnetization to 30 to 150 emu / cm ³ in the magnetic field at the developing pole. This is because the strength of the magnetic field at the developing pole is generally about 1000 Oersted, and the strength of the magnetization of the carrier at that time is weak, so that the magnetic brush of the developer becomes short and dense,
Furthermore, since the magnetic brush becomes softer, development faithful to the latent image can be achieved.

As described above, since the magnetic brush is short, dense, and soft, the developing efficiency is improved, and higher fidelity developing is achieved, especially in the developing in which an alternating electric field that vibrates the developer is applied to the developing portion. You can

Another effect of the present invention is to prevent deterioration of image quality and maintain an initial high quality image.
By using such a carrier with a low magnetic force, when the developing sleeve containing the fixed magnet is coated with the two-component developer, the mutual magnetic coupling force between the carrier brushes near the regulating member is weak, and Since it is soft, it does not take much market share with the toner, so high-quality images can be maintained for a long period of time.

Further, the softening of the magnetic brush reduces the load from the developer layer thickness regulating member, and
Since the magnetic substance-dispersed resin carrier is lighter than the conventional iron or ferrite carrier, the load due to stirring in the developing device is small, and the deterioration due to the durability of the developer can be significantly reduced.

Further, as a result of a detailed examination, carrier adhesion is likely to occur at a magnetic field strength of 0 to 300 Oersted, and does not occur or is unlikely to occur when the carrier magnetization strength at that time is high to some extent. It has been found. Further, the carrier adhesion is also influenced by the bias condition of the development, and particularly when developing by an alternating electric field, when the carrier has a certain amount of electric charge as compared with a DC electric field, the carrier is easily transferred to the electrostatic latent image carrier, and the carrier is not transferred. Magnetic force is required to hold the developing sleeve. Therefore, in order to suppress carrier adhesion, the strength of magnetization in the low magnetic field is required.

In the present invention 1, as shown by the hysteresis curve in FIG. 1, the magnetization strength σ ₁₀₀₀ at 1000 Oersted is 30 to 150 emu / cm ³ , which is smaller than that of the conventional carrier, but is 0 to 100 Oersted. By rapidly raising the magnetization intensity to increase the magnetization intensity at 0 to 300 oersteds, carrier adhesion can be prevented while achieving high image quality.

In addition, in the present invention 2, as shown in FIG. 4, by performing a treatment for orienting the magnetic fine particles dispersed in the carrier in the uniaxial direction by 30% or more, the strength of the residual magnetization is further enhanced, and FIG. Σ as shown in the hysteresis curve of
_{Although 1000} is 30 to 150 emu / cm ^{3 which} is smaller than that of a conventional carrier, a resin carrier having a strong magnetization intensity of 0 to 300 oersted can be used to simultaneously achieve high image quality and prevention of carrier adhesion.

In general, a magnetic material having a large residual magnetization has a large coercive force. It is a magnetic material such as so-called hard ferrite such as a so-called permanent magnet, and as described above, the mixing property with the toner due to self-aggregation and the developer transportability become poor, and the developer carrying member becomes a rotating magnetic core applicator. , A large and special developing device is required. However, the present invention does not use such a general hard magnetic material as a carrier, but uses a carrier having a low coercive force, so that even a small-sized developing device using a fixed magnetic core type developer carrier can be mixed with toner. It is possible to achieve a developer having excellent properties and developer transportability.

When the surface of the carrier of the present invention was observed by a scanning electron microscope, it was found that the resin used in the present invention, which was composed of the styrene-acrylic copolymer or the mixture of the styrene-acrylic copolymer and the fluorine-containing resin, It was observed that the carrier had excellent binding properties with the core material and that the surface of the carrier was thinly and uniformly coated.

That is, when the surface of the carrier is divided into minute parts, and when the coat is uniform, impact resistance, resistance value, and charge imparting property to the toner are equal in every part. Is considered to indicate.

On the other hand, when the coat is non-uniform, it is considered that the impact resistance, the resistance value, and the charge imparting property to the toner are different in each part of the carrier surface. Therefore, for example, since the measurement of the resistance value is an evaluation method when the carrier is viewed from a macro standpoint, even if the resistance value is considered to be an appropriate resistance in the measurement, if the coat is non-uniform, Have charge, carrier adhesion may occur, or image defects may easily occur due to leakage of the developing bias voltage, and high-quality images cannot be obtained.

The carrier used in the present invention 1 is required to have the following magnetic characteristics of the carrier particles.

That is, the magnetization intensity (σ ₁₀₀₀ ) at 1000 Oersted is 30 to 150 emu / cm ^3.
It is necessary to be. In order to achieve higher image quality, it is preferably 30 to 120 emu / cm ³ . When it is higher than 150 emu / cm ^3, the density of the developer brush at the developing pole is not so different from the conventional one, and it becomes difficult to obtain a high quality toner image. 30e
If it is less than mu / cm ³ , the magnetic binding force at 0 to 300 oersteds is also reduced, and carrier adhesion is likely to occur.

Further, it is the rising speed of the magnetization strength in a magnetic field of 0 to 100 Oersted, and it is important to satisfy the following formula.

[0055]

[Equation 6]

If it is less than 0.15, the rising of the magnetization strength is slow, and the magnetization strength until reaching 300 oersted is not sufficient, so that no effect can be obtained for carrier adhesion.

Further, in order to obtain a high quality image, it is necessary to satisfy the following formula.

[0058]

[Equation 7] More preferably, this value is 0.30 or less.

If it exceeds 0.40, it becomes difficult to prevent the carrier from adhering while achieving the high image quality of the present invention. That is, if a value that satisfies σ ₁₀₀₀ is taken, high image quality is achieved, but carrier adhesion is likely to occur. Also, σ
_{When the} value is set to satisfy the value of ₃₀₀ , carrier adhesion can be prevented, but the value of σ ₁₀₀₀ becomes large, so that it becomes difficult to obtain a high quality image as in the present invention.

The first aspect of the present invention achieves the above magnetic characteristics by setting the degree of orientation of the magnetic fine particles in the carrier to 30% or more and simultaneously satisfying the expressions (1) and (2).

In the carrier used in the second aspect of the present invention, the magnetic properties of the carrier particles must be as follows.

Σ _{1000 of} carrier particles is 30 to 150e
It is the same as in the first aspect of the present invention that it is necessary to be mu / cm ³ .

The strength of remanent magnetization is 25 emu / c.
It must be m ³ or more. If it is less than 25 emu / cm ³ , the contrast potential is increased particularly for high image quality, or carrier adhesion is likely to occur in a developing system using an alternating electric field, and the carrier-adhered portion is defective in the transfer process after development. As a result, high quality images cannot be obtained.

Furthermore, the coercive force must be less than 300 Oersted. If it is 300 oersteds or more, the carrier itself is self-aggregated, resulting in poor mixing property with the toner. Particularly, the carrier cannot move easily in the developing sleeve including the fixed magnet, and the carrier is transported on the developing sleeve. Therefore, a high quality image cannot be obtained because the coating property of the developer is deteriorated.

Further, it is necessary to increase the strength of the magnetization in the vicinity of the magnetic field of 0 to 300 Oersted. That is, in the second aspect of the invention, it is necessary to perform a treatment for orienting the magnetic fine particles dispersed in the carrier by 30% or more, and at that time, it is necessary to satisfy the above formula (1).

Here, the orientation degree of the magnetic particles dispersed in the carrier of the present invention is defined by the orientation probability of the magnetic particles having the shape anisotropy used in the present invention, and manufactured by Hitachi Ltd. Field emission scanning electron microscope (F
Using E-SEM) S-800, the orientation of the magnetic fine particles on the carrier surface (carrier cross section in the case of a magnetic substance-dispersed resin carrier) is statistically processed and measured. The case of a magnetic material-dispersed resin carrier will be specifically described. 100 or more magnetic particles having shape anisotropy used in the present invention were randomly extracted from 10 randomly selected carrier cross-sectional photographs, and the magnetic field direction was considered to be within ± 15 °. Calculate the ratio of those facing within the range. Here, the sample of the carrier cross section is prepared by dispersing and solidifying the carrier in the epoxy resin in a parallel magnetic field, and then cutting the plastic-embedded sample with a microtome FC4E (manufactured by REICHERT-JUNG).

For example, when a flat magnetic material is used, as shown in FIG.
As shown in, the major axis is oriented in the direction perpendicular to the direction of the magnetic field, and the orientation within the range of ± 15 ° was counted to obtain the orientation degree. When a needle-shaped magnetic material is used, it is shown as in FIG.

The measurement of the magnetic characteristics in the present invention is
Riken Denshi Co., Ltd. DC magnetization B-H characteristic automatic recording device B
Performed using HH-50. The magnetic characteristic value is obtained from a hysteresis curve at the time when a magnetic field of ± 1 kilo-oersted is created. The sample is prepared in a state where the carrier is packed in a cylindrical plastic container so as to be sufficiently dense in a strong magnetic field such that it is sufficiently saturated, and has a constant volume of 0.332 cm ³ . The magnetization moment is measured in this state, and the strength of the magnetization per unit volume is obtained from this.

In order to achieve the above-mentioned magnetic characteristics in the carrier of the present invention 1, an amorphous alloy magnetic material having a shape anisotropy with a maximum diameter (major axis) of 2 μm or less can be used as the magnetic material. For example, Fe-Si system, F
e-Si-B system, Co-Fe-Si-B system, Fe-Si
-BC system, Fe-W-Ni-Mo system, Co-Zr system,
Magnetic materials such as Fe-Zr system and Ni-Zr system can be used alone or in combination. In order to impart shape anisotropy to these alloys, a method of mechanically flattening during quenching can be used. Further, an iron-based metal oxide having a shape anisotropy with a maximum diameter (major axis) of 2 μm or less can be used alone or as a mixture with the amorphous alloy. For example, magnetite _{(Fe · Fe 2 O 3)} , Ni -based, Ni-Zn-based, Mn-
Zn-based, Mn-Mg-based, Li-based, Li-Ni-based, Li-
Cu-based, Cu-Zn-based, Cu-Zn-Mg-based, Mn-M
A g-Al type, a Co-Fe type, or the like can be used. In order to impart shape anisotropy to these iron-based metal oxides, some additives are added, liquid properties and concentration are controlled during crystal growth, temperature control during firing, and heat treatment such as quenching are performed. Perform processing such as applying.

The magnetic substance dispersed in the carrier of the present invention 2 is a metal oxide magnetic material of 1 μm or less, for example,
Hexagonal plate crystals such as Ba-based ferrite, Sr-based ferrite, Pb-based ferrite, or γ-Fe ₂ O ₃ -based, Co
Acicular magnetic material such as acicular ferrite acicular magnetite or the like, or a mixture of particles having shape anisotropy, or particles having shape anisotropy and a soft magnetic material such as soft ferrite. Can be used.

In the case of a magnetic substance dispersion type resin carrier, the carrier of the present invention can be obtained by mechanically or magnetically orienting the magnetic substance fine particles at the time of injection molding. The carrier of the present invention can be obtained by granulating and polymerizing.

In the case of a sintered type carrier, it can be obtained by orienting in a magnetic field during granulation of carrier particles. At this time, it is important to maintain the shape anisotropy and the amorphous state by sintering, and it is necessary to perform heat treatment such as quenching.

By taking such a composition and orientation form, the strength of the magnetization at 1000 Oersted (σ
₁₀₀₀ ) is 30 to 150 emu / cm ³ , and it is possible to obtain a carrier having magnetic characteristics in which the rise of the magnetization strength is faster.

In the carrier of the present invention, in the case of a magnetic substance-dispersed resin carrier, the content of the magnetic substance with respect to the total amount of the carrier is 30% by mass or more, preferably 50% by mass or more. If the amount is less than 30% by mass, carrier adhesion to the photoconductor tends to occur. In addition, it becomes difficult to control the specific resistance of the carrier. Further, if the content of the magnetic material exceeds 99%, the adhesion between the magnetic material and the binder resin becomes poor.

The specific resistance of the carrier of the present invention is 10 ⁸ to 10
It is preferably in the range of ¹³ Ω · cm. 10 ⁸ Ω ・ c
When it is less than m, in the developing method in which a bias voltage is applied, a current easily leaks from the developing sleeve to the surface of the photoconductor in the developing area, and it is difficult to obtain a good toner image. On the other hand, if it exceeds 10 ¹³ Ω · cm, a charge-up phenomenon is likely to occur under a condition such as low humidity, which tends to cause deterioration of the toner image such as density, transfer failure, and fog.
In the present invention, the measurement method as shown in FIG. 5 is used to measure the specific resistance. That is, the cell A is filled with the carrier,
A method is used in which the electrodes 1 and 2 are arranged so as to be in contact with the filled carrier, a voltage is applied between the electrodes, and a current flowing at that time is measured to obtain a specific resistance. In the above measuring method, since the carrier is a powder, the filling rate may change, and the specific resistance may change accordingly, which requires caution. The measurement conditions of the specific resistance in the present invention are as follows: contact area S between the filled carrier and the electrode S = about 2.3 cm ² , thickness d
= Approx. 1 mm, upper electrode 2 load 275 g, applied voltage 10
Set to 0V.

In view of keeping the specific resistance of the carrier of the present invention within the above range, the specific resistance can be easily controlled by coating the low-resistance core material with the resin of the present invention. The coating state of the resin is closely related to the characteristics of the carrier. For example, if there is a site where the resistance is partially the same even though the resistance is the same in measurement, the residual charge tends to cause carrier adhesion. . Therefore, in order to obtain good developability, it is important to keep the resistance of each part of the carrier surface substantially the same by uniform resin coating.

The resin coated on the carrier of the present invention is a styrene-acrylic copolymer or a mixture of a styrene-acrylic copolymer and a fluorine-containing resin.

The styrene-acrylic copolymer that can be used here refers to a copolymer of a styrene derivative and acrylic acid esters and a copolymer of a styrene derivative and methacrylic acid esters. The following compounds can be mentioned as specific examples of the monomers constituting these styrene-acrylic copolymers. That is, as the styrene derivative, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p- tert-butyl styrene, pn-hexyl styrene, pn-octyl styrene, pn-nonyl styrene, pn-decyl styrene, pn-dodecyl styrene, p-methoxy styrene, p-chloro styrene, 3,4-dichlorostyrene, m-nitrostyrene, o-nitrostyrene, p-nitrostyrene and the like can be mentioned.

Examples of acrylates include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, and the like.
2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate and the like can be mentioned.

Further, as the methacrylic acid esters, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate,
Isobutyl methacrylate, n-octyl methacrylate,
Dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate and the like can be mentioned.

In the present invention, the coating resin styrene-
The monomer ratio of the acrylic component in the acrylic copolymer is preferably 30 to 90% by mass. If the amount is less than 30% by mass, the coating uniformity sufficient to contribute to the present invention cannot be obtained, and the toner has insufficient charge stability. On the other hand, if it is more than 90% by mass, uniform coatability is obtained, but the strength against impact resistance is insufficient.

Further, the weight average molecular weight of the coating resin used in the present invention is indispensably 30,000 to 70,000,
In addition, it is essential that the weight average molecular weight / number average molecular weight is 2 to 10. When the weight average molecular weight is less than 30,000, the strength against impact resistance of the carrier cannot be obtained,
When it is more than 70,000, the coat uniformity with respect to the carrier core is deteriorated, and the strength of the carrier and further the charging stability become poor. More importantly, even if the weight average molecular weight is within this range, the effect of the present invention cannot be obtained unless the weight average molecular weight / number average molecular weight is within the range of 2 to 10. Weight average molecular weight /
If the number average molecular weight is less than 2, the coating resin is uniformly coated, but the impact resistance is poor. When the weight average molecular weight / number average molecular weight is more than 10, the coat uniformity with respect to the carrier core is deteriorated, and the strength of the carrier and desired charge stability cannot be obtained.

As described above, the coating resin of the carrier core material of the present invention contains the styrene-acryl-based resin in order to increase the spent resistance of the carrier and the charging stability of the developer exhibiting the positive charging property. It is also possible to use a mixture of a polymer and a fluororesin. Examples of the fluorine-containing resin mixed with the styrene-acrylic copolymer include polyvinyl fluoride, polyvinylidene fluoride, polytrifluoroethylene, halofluoropolymers such as polytrifluorochloroethylene, polytetrafluoroethylene, polyperfluoro. Propylene, copolymer of vinylidene fluoride and acrylic monomer, copolymer of vinylidene fluoride and trifluorochloroethylene, copolymer of tetrafluoroethylene and hexafluoropropylene, vinyl fluoride and vinylidene fluoride Of a copolymer of vinylidene fluoride and tetrafluoroethylene, a copolymer of vinylidene fluoride and hexafluoropropylene, a terpolymer of tetrafluoroethylene and vinylidene fluoride and a non-fluorinated monomer Like fluoroterpoly Chromatography, and the like.

The mixing ratio of these fluororesins to the styrene-acrylic copolymer is 5:95 to 95: 5 by mass ratio (mass of the fluororesin: mass of the copolymer). is necessary. Content of the fluorine-containing resin is 5% by mass
When the amount is less than the range, the charging property may be slightly inferior depending on the type of the coating material when used as a developer exhibiting positive charging property. When the content of the fluorine-containing resin exceeds 95% by mass, the negative charging property is obtained. Not only is the charge stability of the developer exhibiting characteristics deteriorated, but also the wettability deteriorates, making uniform coating on the core material difficult.

The weight average molecular weight of the fluorine-containing resin is preferably 50,000 to 400,000, more preferably 100,000 to 250,000. If it is less than 50,000, impact resistance tends to be insufficient, and if it is 40
When it exceeds 0000, uniform coating on the core material becomes unstable.

In the present invention, the molecular weight and the molecular weight distribution of the carrier coat resin are the values obtained by GPC (gel permeation chromatography) in light of a calibration curve obtained by using monodisperse standard polystyrene. .

The measurement conditions are shown below.

(GPC measurement conditions) Apparatus: GPC-150C (Waters) Column: Shoredex KF 7 stations (Showa Denko) Temperature: 40 ° C. Solvent: THF Flow rate: 1.0 m / min Sample: 0.15% Inject sample 0.4m

Next, as a method of resin-coating the core material, considering that the core material is made of resin, a treatment method in which the coating resin is rapidly coated so that the core materials do not adhere to each other is desirable. It is preferable to use a treatment method in which the selection of a solvent that dissolves the coating resin and the conditions such as treatment temperature and time are sufficiently controlled, and coating and drying are simultaneously performed in such a manner that the core material is always allowed to flow.
The amount of resin coating depends on the true specific gravity of the core material,
The optimum value must satisfy the following relational expression.

[0090]

[Equation 8] More preferably,

[0091]

[Equation 9] Is.

If the amount of the coating resin is less than 1/2 × mass%, it is difficult to coat the surface of the core material uniformly, and even if the coating can be performed, it cannot be said that the carrier has sufficient strength.

On the other hand, if it exceeds 50 / X mass%, it becomes difficult to coat uniformly, and it becomes impossible to control the resistance to the optimum value, which is a feature of the present invention. Further, the coating resin that could not be coated is singly released and generated, and adheres to the photoconductor to cause image deterioration.

The average particle size of the carrier particles of the present invention is 5 to
It is necessary to be 100 μm, and more preferably 20 to 80 μm. If it is less than 5 μm, carrier adhesion to the photoconductor is likely to occur, and if it exceeds 100 μm, the magnetic brush at the developing pole becomes coarse, and it is difficult to obtain a high-quality toner image. In the present invention, 300 or more particles of the carrier are randomly extracted by an optical microscope, and the horizontal Feret diameter is measured as the carrier particle diameter by an image processing analysis device Luzex3 manufactured by Nireco.

The bulk density of the carrier of the present invention is 3.0 g /
It should be less than or equal to cm ³ . 3.0 g / cm ³
When it exceeds, the centrifugal force applied to one carrier particle becomes large due to the rotation of the developing sleeve in comparison with the force that the carrier is magnetically held on the developing sleeve, and the carrier is easily scattered. The bulk density of the carrier of the present invention is measured by JI
Performed according to the method described in S Z 2504.

In the constitution of the carrier of the present invention, the binder resin used for the core material includes all resins obtained by polymerizing vinyl monomers. Examples of the vinyl-based monomer here include styrene and o-
Methyl styrene, m-methyl styrene, p-methyl styrene, p-phenyl styrene, p-ethyl styrene,
2,4-dimethylstyrene, pn-butylstyrene,
p-tert-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, pn-dodecylstyrene, p-methoxystyrene, p-chloro. styrene,
3,4-dichlorostyrene, m-nitrostyrene, o-
Styrene derivatives such as nitrostyrene and p-nitrostyrene, and ethylene and unsaturated monoolefins such as ethylene, propylene, butylene and isobutylene; unsaturated diolefins such as butadiene and isoprene; vinyl chloride, vinylidene chloride and bromide Vinyl halides such as vinyl and vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate and vinyl benzoate; methacrylic acid and methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, methacrylic acid Acid isobutyl, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate,
Α-Methylene aliphatic monocarboxylic acid esters such as stearyl methacrylate and phenyl methacrylate; acrylic acid and methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-acrylate Acrylic esters such as octyl, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate; maleic acid, maleic acid half ester; vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl Vinyl ethers such as ethers; vinyl methyl ketone, vinyl hexyl ketone,
Vinyl ketones such as methyl isopropenyl ketone; N-
N-vinyl compounds such as vinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrrolidone; vinylnaphthalenes; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile and acrylamide; acrolein and the like. The polymer obtained by polymerizing one or more of these is used.

In addition to resins obtained by polymerizing vinyl monomers, non-vinyl condensation resins such as polyester resins, epoxy resins, phenol resins, urea resins, polyurethane resins, polyimide resins, cellulose resins and polyether resins, or these resins. And a mixture of the above vinyl-based resin can be used.

As the method for producing the carrier in the present invention, the binder resin and the magnetic fine particles are mixed in a desired amount ratio, and the mixture is heated at an appropriate temperature by using a heating and melting mixing device such as a three-roll or an extruder. After kneading, the magnetic fine particles are mechanically or magnetically oriented at the time of injection molding, and after cooling and pulverizing and classifying, a core material obtained is obtained. The obtained core material is collided with a plate at a high speed, and the energy is used to heat-melt the surface of the plate for spherical treatment.

Alternatively, as another method for obtaining the core material, magnetic fine particles, a polymerization initiator, a suspension stabilizer, etc. are added to a monomer solution of a binder resin used for the core material and dispersed, and then the mixture is subjected to a magnetic field. There is also a method of using a suspension polymerization method in which granulation polymerization is carried out in.

The sphericity of the carrier of the present invention is preferably 2 or less. The carrier of the present invention has a sphericity of more than 2,
The fluidity as a developer becomes poor, and the shape of the magnetic brush becomes poor at the developing pole, which makes it difficult to obtain a high-quality toner image. The sphericity of the carrier of the present invention is measured by randomly measuring the carrier with a field emission scanning electron microscope S-800 manufactured by Hitachi, Ltd.
Image processing analysis device Luz manufactured by Nireco
The shape factor derived by the following equation is obtained using ex3.

[0101]

[Equation 10]

[In the formula, MX LNG represents the maximum diameter of the carrier, and AREA represents the projected area of the carrier. ]

The closer the sphericity is to 1, the closer it is to a sphere.

The toner used in combination with the carrier of the present invention has a weight average particle diameter of 1 in order to obtain a high quality image.
˜20 μm, preferably 4 to 10 μm. The weight average particle diameter of the toner can be measured by various methods, but in the present invention, it is measured using a Coulter counter.

Further, in order to obtain a higher quality image, the degree of toner aggregation is preferably low, preferably 30% or less. The cohesion degree used in the present invention is measured as follows.

Powder tester (Hosokawa Micron Co., Ltd.)
From top to 60 mesh, 100 mesh, 200 mesh
Set the sieves in three stages in the order of h, and place 5 g of the sample weighed on the sieve gently and oscillate 1 at a voltage of 17V.
After 5 seconds, the weight of the toner remaining on each sieve is measured, and the aggregation degree is calculated according to the following formula.

[0107]

[Equation 11]

In order to reduce the degree of cohesion, it is preferable to use a fluidity improver such as silica, titanium oxide or alumina internally or externally added to the toner. In particular, it is preferable to externally add a fluidity improver having hydrophobicity to the toner.

[0109]

EXAMPLES The present invention will be described below with reference to examples. These do not limit the invention in any way. In addition,% and parts in the following formulations indicate mass% and parts by mass.

(Example 1) Styrene-methyl methacrylate (80/20) 30% Flat Co ₇₀ Fe ₅ Si ₁₀ B ₁₅ 70% (maximum diameter 1 μm, thickness 0.07 μm)

The above materials were sufficiently premixed with a Henschel mixer, melt-kneaded twice with a three-roll mill, cooled, and then roughly crushed with a hammer mill into chips having a particle size of about 5 mm, and then at 200 ° C. Through the heated extruder, the magnetic fine particles in the binder resin are mechanically oriented by an injection molding machine, and then the molten magnetic substance-dispersed resin is cooled while applying a magnetic field of 10 kilo Oersted, pulverized again, and A powder of about 2 mm was obtained. Then, it was pulverized to a particle size of about 50 μm by an air jet pulverizer. Further, the finely pulverized product obtained is mechano-mill MM.
-10 (manufactured by Okada Seiko Co., Ltd.) and mechanically spheroidized.
The pulverized finely pulverized particles were further classified to obtain magnetic substance-dispersed resin particles. The particle diameter of the obtained magnetic material-dispersed resin particles was 46 μm.

The surface of the obtained magnetic substance-dispersed resin carrier was coated with the following resin.

Styrene-2-ethylhexyl methacrylate (40/60) Mw / Mn = 2.9, Mw = 42000

10% of the above resin was dissolved in a mixed solvent of acetone and methyl ethyl ketone (mixing mass ratio = 1: 1) so that the resin coating amount was 0.5% from the above-mentioned calculation formula,
A carrier coat solution was prepared. This carrier coat solution is applied by an applicator (Okada Kogyo Co., Ltd .: Spiracoater)
The core material was applied while simultaneously applying and drying. The obtained magnetic substance-dispersed resin carrier after coating was dried at a temperature of 90 ° C. for 2 hours to remove the solvent, and a resin-coated magnetic substance-dispersed resin carrier in which the surface of the magnetic substance-dispersed resin carrier was coated with a resin coat layer was obtained. . The particle size of the carrier was the same as before coating. As a result of cross-sectional observation by FE-SEM, the degree of orientation of the magnetic fine particles was 60%.

The physical properties of the obtained carrier are summarized in Table 1.

On the other hand, polyester resin obtained by condensing propoxylated bisphenol and fumaric acid 100 parts Copper phthalocyanine pigment 5 parts Di-tert-butylsalicylic acid chromium complex salt 4 parts

After sufficiently pre-mixing the above materials, melt-kneading, cooling, and using a hammer mill, the particle size is about 1 to 2 mm.
Coarsely crushed to a degree. Then, it was pulverized by an air jet pulverizer. Further, the obtained finely pulverized product was classified to obtain a negatively chargeable cyan powder (toner) having a weight average diameter of 8.4 μm.

100 parts of the cyan toner and 1.0 part of silica fine powder hydrophobized with hexamethyldisilazane were mixed to prepare a cyan toner having silica fine powder on the toner particle surface.

A resin-coated magnetic material-dispersed resin carrier and a toner were mixed so as to have a toner concentration of 5% to obtain a developer. This is a Canon full color laser copier CLC
Images were displayed using a modified machine that is a modification of -500.
FIG. 6 shows a schematic diagram of the developing area portion of the developing device and the photosensitive drum at this time. The distance between the developing sleeve and the developer regulating member is 400 μm, and the process speed is 350 m.
m / sec, the peripheral speed ratio between the developing sleeve and the photosensitive drum is 1.4: 1, and the developing conditions are as follows: the magnetic field strength of the developing pole is 1000 Oersted and the alternating electric field is 2000V.
_PP , frequency was 3000 Hz, and the distance between the sleeve and the photosensitive drum was 500 μm. At this time, as a result of microscopic observation of the brush rising of the developing brush near the developing pole on the developing sleeve, it was found that the brush was dense and the brush length was short.

As a result of the image output test, the supply of the developer on the developing sleeve was sufficient, and the density of the solid image was 1.
The value was as high as 54, there was no roughness, and the reproducibility of the halftone portion and the reproducibility of the line image were good. further,
Despite the sleeve rotating at high speed, carrier adhesion to the image area and non-image area due to carrier scattering and carrier development was not observed. In addition, the developing device is 20
There was no particular problem with regard to the image quality in the image formation after the idle rotation was carried out for 60 minutes at the speed of 0 rpm, and the carrier adhesion was very good.

(Comparative Example 1) In terms of molar ratio, Fe ₂ O ₃ = 62
Mol%, ZnO = 16 mol%, and CuO = 22 mol% were weighed and mixed using a ball mill. This is granulated, sintered and then classified to give an average particle size of 50μ.
m ferrite particles were obtained. The shape of the carrier obtained at that time was almost spherical, and the smoothness was excellent. This sintered core was coated with the following resin.

Styrene-2-ethylhexyl methacrylate (40/60) Mw / Mn = 20.2, Mw = 110,000

A carrier coating solution was prepared by dissolving 10% in toluene so that the coating resin amount was 0.5%.

Similar to Example 1, the above carrier coating solution was applied to the above ferrite carrier core to obtain a resin coated carrier. When the obtained resin-coated carrier was observed with an electron microscope, the coated state was not uniform, and the resin was locally thickly coated.

The carrier particle size after coating was almost the same as that before coating. Table 1 shows the physical properties of the obtained carrier.

A test similar to that of Example 1 was conducted using this carrier. It was observed that the magnetic brush of the developer on the developing pole was rough, and the roughness in the halftone portion was observed on the image, and at the same time, some carrier adhesion was recognized. Further, as in the case of Example 1, the image forming test was conducted after the idle rotation for 60 minutes.
It was found that image deterioration such as halftone shading and transfer deficiency in solid areas was more remarkable than that of No. 1, and toner deterioration due to magnetic shear was large. Peeling of the coating resin was seen in the shaking test, image unevenness in the image output test,
And carrier adhesion was observed. Further, in the image forming test under low humidity, the density of the solid image was lower than that in Example 1.

(Example 2) Phenol 20% Formaldehyde 10% (Formaldehyde about 37%, Methanol about 10%, the rest is water) Flat Co ₇₀ Fe _4.95 Cr _0.05 Si ₁₀ B ₁₅ 70% (maximum diameter 0.9 μm thickness 0.05 μm)

Ammonia using the above materials as a basic catalyst,
Using calcium fluoride as a polymerization stabilizer, the mixture was stirred in an aqueous phase, gradually heated to a temperature of 80 ° C., and polymerized in a magnetic field for 2 hours. The polymer particles thus obtained were classified to obtain a magnetic substance-dispersed resin carrier core.

The surface of this magnetic substance-dispersed resin carrier core was coated with the following resin.

Styrene-phenyl acrylate copolymer (50/50) 50% Mw / Mn = 4.5, Mw = 56000 Vinylidene fluoride-tetrafluoroethylene copolymer (75:25) 50% Mw = 210000

At this time, the carrier showed a good coated state. As a result of FE-SEM observation, the degree of orientation of the magnetic substance was 6
It was 2%. Table 1 shows the physical properties of the obtained carrier.

The same tests as in Example 1 were carried out on the above carrier except that the contrast potential was lowered.
In the initial and idle rotation durability tests, both images and carrier adhesion were good.

Example 3 Flat Co _70.3 Fe _4.7 Si ₁₀ B ₁₅ (maximum diameter 1.0 μm, thickness 0.05 μm)

A slurry was obtained by applying a magnetic field to the above magnetic material in a 3% PVA aqueous solution. This was granulated to about 50 μm using a spray dryer, and then reacted at 1000 ° C. for 2 hours. This was rapidly cooled to obtain particles having a particle size of 47 μm. Example 2 was formed on the surface of the particles in the same manner as in Example 1.
The resin used in 1. was coated. Table 1 shows the physical properties of the obtained carrier particles.

When the same tests as in Example 1 were conducted using the above carrier, both the initial image quality and the image quality after endurance were good, and there was no problem with carrier adhesion. Also,
Even in the idle rotation test, there was no particular problem with the roughness of the halftone portion, image quality, and carrier adhesion.

Example 4 The surface of the carrier core used in Example 2 was coated with the following resin.

Styrene-phenyl acrylate copolymer (50/50) Mw / Mn = 4.5, Mw = 56000

At this time, the carrier showed a good coated state. Table 1 shows the physical properties of the obtained carrier. When the same test as in Example 1 was performed, both the image and the carrier adhesion were good in the initial and idle rotation durability tests.

Example 5 A carrier core material similar to that of Example 3 was coated with the following resin in the same manner as in Example 3 to obtain a carrier.

Styrene-diethylhexyl methacrylate copolymer (40/60) 50% Mw / Mn = 2.9, Mw = 42000 Vinylidene fluoride-tetrafluoroethylene copolymer (75:25) 50% Mw = 210000

As the toner, styrene-2-ethylhexyl acrylate-100 parts dimethylaminoethyl methacrylate copolymer (monomer composition mass ratio = 80: 15: 5) copper phthalocyanine 4 parts low molecular weight polypropylene 5 parts

A material was prepared in the same manner as in Example 1 using the above materials. The weight average diameter at that time was 7.9 μm. To 100 parts of the above particles, 1.2 parts of positively chargeable colloidal silica treated with amino-modified silicone oil was mixed with a Henschel mixer to obtain a positively chargeable blue toner. The carrier and the toner were mixed so as to have a toner concentration of 5% to obtain a developer. This is a modified copy machine made by Canon NP4835 (sleeve peripheral speed 210mm / se
c, developing bias: 2000 V _PP , 2000 Hz, and the distance between the sleeve and the photosensitive drum was 500 μm), and an image forming durability test was conducted in the same manner as in Example 1. As a result, in the same manner as in Example 1, both the image and the carrier adhesion were good in the image output durability test.

The physical properties of the carrier of the present invention are shown in Table 1, and the evaluation results are shown in Table 2. ◎ in Table 2
Is very good, ◯ is good, Δ is good, and × is bad.

[0144]

[Table 1]

[0145]

[Table 2]

(Example 6) Styrene-isobutyl acrylate copolymer (80/20) 28% 3% Zn-doped γ-Fe ₂ O ₃ 72% (horizontal ferret diameter: major axis = 1.0 μm, minor axis = 0.14 μm)

The above materials were sufficiently premixed with a Henschel mixer, melt-kneaded with a three-roll mill at least two times or more, and after cooling, had a particle size of about 5 using a hammer mill.
After roughly crushing into chips of about mm, the magnetic powder in the binder resin is mechanically oriented by an injection molding machine, the molten resin containing the magnetic material is cooled in a magnetic field, and then crushed to a diameter of about 2 mm. A powder was obtained. Then, it was pulverized to a particle size of about 50 μm by an air jet pulverizer.
Further, the obtained finely pulverized product was put into MechanoMill MM-10 (manufactured by Okada Seiko) and mechanically spheroidized. The spheroidized finely pulverized particles were further classified to obtain a magnetic substance-dispersed resin carrier core. The particle size of the obtained carrier core was 48 μm, and the specific resistance was 2.2 × 10 ¹⁰ Ω · cm. FE
As a result of cross-section observation by -SEM, the degree of orientation of the magnetic fine particles was 55%.

The surface of the obtained magnetic substance-dispersed resin carrier was coated with the following resin.

Styrene-2-ethylhexyl methacrylate (40/60) Mw / Mn = 2.9, Mw = 42000

10% of the above resin was dissolved in a mixed solvent of acetone and methyl ethyl ketone (mixing mass ratio = 1: 1) so that the resin coating amount would be 0.5% from the above calculation formula,
A carrier coat solution was prepared. This carrier coat solution is applied by an applicator (Okada Kogyo Co., Ltd .: Spiracoater)
The core material was applied while simultaneously applying and drying. The obtained magnetic substance-dispersed resin carrier after coating was dried at a temperature of 90 ° C. for 2 hours to remove the solvent, and a resin-coated magnetic substance-dispersed resin carrier in which the surface of the magnetic substance-dispersed resin carrier was coated with a resin coat layer was obtained. .

The physical properties of the obtained carrier are summarized in Table 1. The magnetic measurement was performed after the carrier was saturated with magnetization in a magnetic field of 10 kilo Oersted.

On the other hand, polyester resin obtained by condensing propoxylated bisphenol and fumaric acid 100 parts Phthalocyanine pigment 5 parts Di-tert-butylsalicylic acid chromium complex salt 4 parts

The above materials were sufficiently premixed with a Henschel mixer, melt-kneaded with a three-roll mill three times, cooled, and then coarsely pulverized with a hammer mill to a particle size of about 1 to 2 mm. Then, it was pulverized by an air jet pulverizer. Further, the obtained finely pulverized product was classified to obtain a negatively chargeable cyan powder (toner) having a weight average diameter of 8.2 μm.

100 parts of the above-mentioned cyan toner and 0.4 part of silica fine powder hydrophobized with hexamethyldisilazane were mixed by a Henschel mixer to prepare a cyan toner having silica fine powder on the toner particle surface.

After the carrier was saturated and magnetized in a magnetic field of 10 kilo Oersted, the carrier and the toner were mixed in an environment of 23 ° C./60% RH so that the toner concentration was 5% to obtain a developer. Images were printed on this using a full color laser copying machine CLC-500 modified by Canon. FIG. 6 shows a schematic view of the developing area of the developing device and the photosensitive drum at this time. The distance between the developing sleeve and the developer regulating member is 400 μm, the peripheral speed ratio between the developing sleeve and the photosensitive drum is 1.4: 1, and the developing condition is that the magnetic field strength of the developing pole is 1000 oersted, alternating. Electric field 2200V
_PP , frequency was 3000 Hz, and the distance between the sleeve and the photosensitive drum was 500 μm. At this time, as a result of observing with a microscope the spikes of the developing brush near the developing pole on the developing sleeve, it was found that the spikes were dense and the spike length was short.

As a result of the image output, the density of the solid image was sufficient and there was no roughness, and particularly the reproducibility of the halftone portion and the reproducibility of the line image were very good. Further, carrier adhesion was good in both the image area and the non-image area. Further, the developing device was idly rotated at a speed of 200 rpm for 40 minutes. As a result, there was no particular problem regarding image quality, and carrier adhesion was very good.

Comparative Example 2 Fe ₂ O ₃ 60 mol% ZnO 23 mol% CuO 17 mol%

The above materials were weighed and mixed using a ball mill. The mixed powder was fired and then ground. The crushed sample was made into a slurry, and the slurry was granulated with a spray dryer to sinter the granulated powder. The obtained sintered powder is classified by an air classifier, and the average particle size is 49 μm.
To obtain carrier particles. The shape of the carrier obtained at that time is almost spherical, and the specific resistance is 6.7 × 10 ⁹ Ω ・
It was cm.

Instead of the carrier coating solution used in Example 6, styrene-2-ethylhexyl methacrylate (40/6) was used.
0) Mw / Mn = 20.2, Mw = 110,000

10% was dissolved in toluene so that the amount of the coating resin was 0.5% to prepare a carrier coating solution.

Similar to Example 6, the above carrier coating solution was applied to the above ferrite carrier core to obtain a resin coated carrier. When the obtained resin-coated carrier was observed with an electron microscope, the coated state was not uniform, and the resin was locally thickly coated.

The same test as in Example 6 was conducted using this carrier. It was observed that the magnetic brush of the developer at the developing pole was rough, and the image was jarring at the halftone portion. In addition, as in Example 6, 4
When an image output test was performed after performing idle rotation for 0 minutes, image deterioration such as halftone roughness and transfer bleeding at solid portions was remarkable as compared with Example 6, and toner due to magnetic shearing was observed. It turned out that the deterioration was large. Peeling of the coating resin was observed in the shaking test, and image unevenness and carrier adhesion were observed in the image display test. Further, in the image forming test under low humidity, the density of the solid image was lower than that of Example 6.

(Example 7) Styrene-isobutyl acrylate copolymer (80/20) 26% Ba ferrite (flat) 30% (mol% Fe ₂ O ₃ : ZnO: BaO = 70: 15: 15) Cu -Zn ferrite 44% _{(mol% Fe 2 O 3: CuO:} ZnO = 60: 20: 20)

After melting and kneading the above materials in the same manner as in Example 6, extrusion molding is carried out in a magnetic field to orient the magnetic particles in the binder, and after cooling, pulverization and classification are carried out in the same manner as in Example 6, Further, spheroidizing treatment was performed to obtain a magnetic substance-dispersed resin carrier core. The specific resistance of the obtained carrier core was 2.4 × 10 ¹⁰ Ω · cm. The obtained carrier core was coated in the same manner as in Example 6. Also, FE-
As a result of cross-section observation by SEM, the degree of orientation was 60%. Table 3 shows the physical properties of the obtained carrier. Further, this carrier was tested in the same manner as in Example 6. As a result, as in the case of Example 6, both image and carrier adhesion were good.

Example 8 Using the same formulation as in Example 6, the mixture was heated in a container to a temperature of 70 ° C. and dissolved to obtain a monomer mixture. Further, while maintaining the temperature at 70 ° C., the initiator azobisisonitrile was added and dissolved to prepare a monomer composition. 2c containing 1.2 cm ³ of 1% PVA aqueous solution
Pour into a m ³ flask and use a homogenizer at 70 ° C for 2
The composition was granulated by stirring at 500 rpm for 10 minutes. Then, polymerization was performed in a magnetic field at 70 ° C. for 10 hours while stirring with a paddle stirrer. After the completion of the polymerization reaction, the reaction product was cooled, and the obtained magnetic substance-dispersed styrene acrylic slurry was washed and filtered. This was dried to obtain a magnetic substance-dispersed resin carrier core. The particle diameter of the obtained magnetic substance-dispersed resin carrier core was 51 μm, and the specific resistance was 1.3 × 10 ¹⁰ Ω · c.
It was m. The orientation degree was 62%.

The surface of this magnetic substance-dispersed resin carrier core was coated with the following resin.

Styrene-phenyl acrylate copolymer (50/50) 50% Mw / Mn = 4.5, Mw = 56000 Vinylidene fluoride-tetrafluoroethylene copolymer (75:25) 50% Mw = 210000

A resin-coated carrier was obtained by using a carrier coating solution in which 10% was dissolved in methyl ethyl ketone so that the coating resin amount was 0.5%. When a test similar to that of Example 6 was performed using this carrier, good results were obtained as in Example 6.

Example 9 Phenol 10% Formaldehyde 5% (Formaldehyde about 37%, Methanol about 10%, balance water) Sr Ferrite 23% (Molar ratio Fe ₂ O ₃ : SrO: CaO = 80: 17: 3) ) Cu-Zn ferrite 62% (molar ratio _{Fe 2 O 3: CuO: ZnO} = 60: 15: 25)

Ammonia using the above materials as a basic catalyst,
Using calcium fluoride as a polymerization stabilizer, while stirring in water, the temperature was gradually raised to 80 ° C., and polymerization was performed in a magnetic field for 2 hours. The polymer particles obtained were classified to obtain a magnetic substance-dispersed resin carrier core. The obtained core has a particle size of 46 μm and a specific resistance of 2.0 × 10 ⁹ Ω.
・ It was cm. The orientation degree was 52%. When the surface of the obtained carrier core was coated with the same resin as in Example 6 in the same manner as in Example 8, a good coated state was exhibited. The physical properties of the obtained carrier are shown in Table 3. When the same test as in Example 6 was performed on the above carrier, both the image and the carrier adhesion were good. (Example 10) γ-instead of the magnetic material used in Example 9
A polymerized carrier was prepared in the same manner as in Example 9 using Fe ₂ O ₃ . At that time, the amount of magnetic material is 70%, and the rest is resin. The particle size of the obtained carrier core was 50 μm, and the specific resistance was 9.2 × 10 ⁵ Ω · cm. The orientation degree was 63%. When the surface of the obtained carrier core was coated with the same resin as in Example 6 in the same manner as in Example 8, the same coated state as in Example 9 was exhibited. Table 3 shows the physical properties of the obtained carrier. When the same test as in Example 6 was performed on the above carrier, both the image and the carrier adhesion were good in the image development durability test.

(Example 11) As a toner, styrene-2-ethylhexyl acrylate-100 parts Dimethylaminoethyl methacrylate copolymer (monomer composition mass ratio = 80: 15: 5) Copper phthalocyanine 4 parts Low molecular weight polypropylene 5 parts

The above material was produced in the same manner as in Example 6. The weight average diameter at that time was 7.9 μm. To 100 parts of the above particles, 1.2 parts of positively chargeable colloidal silica treated with amino-modified silicone oil was mixed with a Henschel mixer to obtain a positively chargeable blue toner.
The carrier of Example 6 and the above toner are mixed in a toner concentration of 5%.
To obtain a developer. This is a Canon copier NP4835 modified machine (sleeve peripheral speed 210 mm / s
ec, developing bias: 2000 V _PP , 2000 Hz, and the distance between the sleeve and the photosensitive drum was 500 μm). As a result, in the same manner as in Example 6, both the image and the carrier adhesion were good in the image output durability test.

[0173]

[Table 3]

[0174]

[Table 4]

[0175]

INDUSTRIAL APPLICABILITY The present invention uses a carrier coated with a resin on a core material in which a magnetic material having shape anisotropy is magnetically oriented in a uniaxial direction. In a low magnetic field such as 0 to 300 Oersted, the magnetization strength of the carrier can be quickly raised, and the coating resin can be uniformly coated, thereby improving the image quality even in the initial copy and a large number of copies. At the same time, an electrophotographic carrier having excellent durability without sticking the carrier on the electrostatic latent image carrier is achieved.

Further, the magnetic substance-dispersed resin carrier of the present invention lowers the magnetic properties of the carrier at the developing pole and orients the magnetic substance dispersed in the carrier to raise the residual magnetization and further maintain it. Providing a carrier that does not adhere to the carrier on the image in addition to the high durability under a light load, which is the characteristic of resin carrier, while improving the high image quality, halftone reproducibility and fine line reproducibility by not increasing the force To do.

[Brief description of drawings]

FIG. 1 is a schematic diagram schematically showing a first quadrant of a magnetic characteristic curve (hysteresis curve), where the horizontal axis represents the external magnetic field (Oersted) and the vertical axis represents the strength of magnetization of a carrier per unit volume. Show.

FIG. 2 is another schematic diagram schematically showing a hysteresis curve, in which the numerical value shown in the frame is (σ ₁₀₀₀ −σ
The value is ₃₀₀ ) / σ ₁₀₀₀ .

FIG. 3 is a schematic view schematically showing the carrier of the present invention, showing how flat magnetic particles are dispersed in a resin.

FIG. 4 is another schematic view schematically showing the carrier of the present invention, showing a state in which acicular magnetic particles are dispersed in a resin.

FIG. 5 is a schematic view schematically showing an electric resistance measuring device.

FIG. 6 is a schematic view schematically showing a developing device and a photosensitive drum.

[Explanation of symbols]

 1 Lower Electrode 2 Upper Electrode 3 Insulator 4 Ammeter 5 Voltmeter 6 Constant Voltage Device 7 Carrier 8 Guide Ring 20 Photoreceptor Drum (Electrostatic Latent Image Carrier) 21 Developer Container 22 Developer Carrier 23 Fixed Magnetic Core 23a- e Magnetic pole 24 Developer regulating member 25 Carrier returning member 26 Toner 27 Developer 30 Toner replenishing roller 31 Developer conveying roller 32 Developer stirring roller 40 Alternating electric field applying means

Claims (7)

[Claims] 1. An electrophotographic carrier having a carrier core material surface coated with a resin, wherein the carrier has an average particle size of 5 to 100 μm and a bulk density of 3.0 g / cm 3.
³ or less, the carrier is formed of fine particles made of a soft magnetic material, and the magnetic fine particles have three-dimensional shape anisotropy in at least one axis direction, and the ratio of the major axis to the minor axis is 1
30% of the magnetic fine particles constituting the carrier are larger.
With the above orientation, the magnetic properties of the carrier are
Magnetization strength at 000 Oersted (σ ₁₀₀₀ ) is 3
0 to 150 emu / cm ³ , further, the magnetic properties of the carrier satisfy the following formulas (1) and (2), and the resin coating the surface of the core material is composed of a styrene-acrylic copolymer, The monomer ratio of the acrylic component in the copolymer is 30 to 90% by mass, the weight average molecular weight of the copolymer is 30,000 to 70,000, and the weight average molecular weight / number average molecular weight is 2 to 10. An electrophotographic carrier characterized by the above. [Equation 1] Wherein, sigma ₁₀₀₀ indicates 1000 of magnetization in Oe strength of ^{(emu / cm 3), σ} 300 shows the magnetization intensity at 300 Oe and (emu / cm ^3). ] [Equation 2] Wherein, sigma ₁₀₀ represents 100 of magnetization of Oe strength of (emu / cm ^3), σr shows 0 of magnetization in oersteds intensity (emu / cm ^3). ] 2. The resin coating the surface of the core material is a styrene-acrylic copolymer mixed with a fluororesin, and the mixing ratio of the fluororesin to the styrene-acrylic copolymer is a mass ratio. The carrier for electrophotography according to claim 1, wherein (the mass of the fluororesin: the mass of the copolymer) is 5:95 to 95: 5. 3. The carrier core material is a magnetic substance-dispersed resin carrier having a binder resin and a magnetic substance as main essential components, and the content of the magnetic substance is 30 to 99% by mass relative to the total amount of the resin carrier. The shape of the magnetic fine particles dispersed in the resin carrier has three-dimensional uniaxial shape anisotropy, and the degree of orientation is 30% or more. The electrophotographic carrier according to 2. 4. The carrier has a specific resistance of 10 ⁸ to 10 ¹³ Ω.
The carrier for electrophotography according to claim 1, wherein the carrier is cm. 5. An electrophotographic carrier comprising a magnetic material-dispersed resin core material obtained by dispersing a magnetic material in a binder resin, the resin having a particle diameter of 5 to 100 μm.
And the bulk density is 3.0 g / cm ³ or less, the content of the magnetic material with respect to the total amount of the carrier is 30 to 99% by mass, and the magnetic material fine particles dispersed in the carrier are
The major axis / minor axis> 1, three-dimensional uniaxial shape anisotropy, 30% or more orientation treatment, and 1000 after the magnetic characteristics of the carrier are magnetically saturated. Magnetization strength (σ ₁₀₀₀ ) in Oersted is 30 to 1
50 emu / cm ³ , and the strength of magnetization (remanent magnetization: σr) in a magnetic field of 0 Oersted is 25 emu / cm ^3.
And above, the coercive force is less than 300 Oersted,
At that time, the following formula is satisfied, the resin coating the surface of the core material is composed of a styrene-acrylic copolymer, and the monomer ratio of the acrylic component in the copolymer is 30 to 90% by mass, and A carrier for electrophotography, wherein the copolymer has a weight average molecular weight of 30,000 to 70,000 and a weight average molecular weight / number average molecular weight of 2 to 10. [Equation 3] [Wherein σ ₁₀₀₀ and σ ₃₀₀ represent the magnetization intensity (emu / cm ³ ) at 1000 and 300 oersteds after magnetic saturation, respectively. ] 6. The resin coating the surface of the core material is a styrene-acrylic copolymer mixed with a fluororesin, and the mixing ratio of the fluororesin to the styrene-acrylic copolymer is a mass ratio. The carrier for electrophotography according to claim 5, wherein the mass of the fluororesin: the mass of the copolymer is 5:95 to 95: 5. 7. The specific resistance of the carrier is 10 ⁸ to 10 ¹³ Ω.
The carrier for electrophotography according to claim 5 or 6, wherein the carrier is cm.