JP2954326B2 - Two-component developer carrier - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a carrier for a two-component developer used in electrophotography, and more particularly, to a durable carrier.
The present invention relates to a carrier for a two-component developer, which provides a high-quality image during development and is suitable for use in high-speed development.

(Prior Art) In the field of electrophotography, two-component magnetic developers are widely used as a means for developing an electrostatic latent image.
In this development method, the two-component composition is agitated to cause triboelectric charging to charge and adhere the toner around the carrier particles, and then the composition is supplied onto a developing sleeve having a magnet therein, A magnetic brush made of this composition is formed, and the magnetic brush is rubbed against an electrophotographic photosensitive surface having an electrostatic latent image, thereby forming a visible toner on the photosensitive plate.

Normally, a voltage is applied between the photosensitive surface and the developing sleeve, and the potential difference between the electrostatic latent image on the photosensitive surface and the electrostatic latent image is particularly large. Adhered to the image, development of the electrostatic latent image is achieved.
On the other hand, the magnetic carrier is attracted by the magnet in the sleeve, and the charged charge has the same polarity as the charge of the electrostatic latent image, so that the magnetic carrier remains on the sleeve. Therefore, it is understood that in such a developing method, the physical, electrical, and magnetic characteristics of the magnetic carrier have a great influence on the developed image quality.

Conventionally, iron powder carriers have been widely used as magnetic carriers, but have recently been replaced with sintered ferrite particles. Sintered ferrite particles are characterized in that chemical properties and magnetic properties are more stable than iron powder carriers, and that the particle size and magnetic properties are easily controlled.

Japanese Patent Application Laid-Open No. 63-2076, which is proposed by the present applicant, discloses a two-component developer for electrophotography comprising a ferrite carrier and a visible toner, wherein the ferrite carrier has a relationship between an applied electric field and a current density. There is proposed a two-component developer composed of ferrite particles which is directly related to a Schottky plot, that is, a half value of electric field strength and a natural logarithm of current density.

In the above prior art, the Schottky effect is a phenomenon in which a saturation current further increases due to an increase in an applied electric field during electron emission. In which conductivity control by Schottky emission is used.

(Problems to be Solved by the Invention) However, the conventional magnetic carrier made of sintered ferrite particles has a large electric resistance near the bias electric potential at a low electric field side, and has a large electric resistance near a developing electric field at a high electric field side near a developing electric field. If the electric resistance is set to be small on the low electric field side, the resistance is further reduced on the high electric field side, and a brush mark or the like is generated in a solid image portion. On the other hand, if the electric resistance is set high on the low electric field side, the resistance will be higher than necessary even on the high electric field side, and the edge effect will easily occur, causing the image solid part to reduce the density and requiring the toner on the character and line image parts. The toner is excessively developed and the toner consumption becomes excessive. Also,
Background fog, in which toner adheres to the entire surface of the transfer paper, is likely to occur.

In addition, although ferrite particles have chemical stability compared to iron powder carriers, since they are sintered particles, the mechanical strength of the particles is not yet sufficient compared to iron powder carriers, and developer There is a disadvantage that the particles are broken during use and their life is relatively short. Further, if the sintered ferrite particles having a relatively large particle size are used as a developer and the development is performed with the development sleeve-photoreceptor (DS-DS) relatively narrow, the above problem becomes a serious problem. .

Accordingly, an object of the present invention is to provide a carrier for a two-component developer in which the density of the solid image portion is sufficiently satisfied without causing an edge effect, and the toner is not consumed more than necessary.

Another object of the present invention is to provide a carrier for a two-component developer in which the carrier life when used in magnetic brush development is extended.

In addition, the present inventors, when performing a normal speed development,
It has been found that it is desirable that the average particle size of the carrier particles is in the range of 30 to 50 μm when clearly displaying a solid image portion. However, in recent high-speed development, the carrier particles have a volume-based central particle size of 70 to 100 μm. It was found that it was desirable to set the range, and it was also found that fine line image portions could be clearly developed and reproduced in high-speed development.

Accordingly, it is an object of the present invention to provide a two-component developer carrier capable of sharpening a fine line image portion during high-speed development.

(Means for Solving the Problems) According to the present invention, in the magnetic carrier for a two-component developer used with the toner, the internal pore ratio based on the area is 3%.
The sintered ferrite particles containing 80% by weight or more of particles formed in the range of from about 30% to about 30%. The electric resistance at an electric field strength of 2500 V / cm is 1 × 10 ^{7 to} 1 × 10 ¹¹ Ω · cm. The development electric field dependency defined by the ratio of the resistance (R2500) and the electric resistance (R5000) at an electric field strength of 5000 V / cm is 1.5.
~ 20, and the volume-based central particle size is 70 ~ 110μ
m, and a carrier for a two-component developer excellent in high-speed development.

The carrier may have an apparent density in the range of 2.0 to 3.0 g / cc.

In the carrier, the sintered ferrite particles are 20 to
It has a flow rate of 30 seconds / 50 g (JIS Z2502).

The carrier may be characterized in that the sintered ferrite particles have a specific surface area (BET method) of 0.02 to 0.20 m ² / g.

The carrier may have a saturation magnetization in a range of 40 to 60 emu / g.

Further, according to the present invention, in a magnetic carrier for a two-component developer used with a toner, a sintered ferrite particle containing 80% by weight or more of particles formed in an area-based internal pore ratio of 3 to 30% is used. The electric resistance at an electric field strength of 1500 V / cm is 1 × 10 ^{6 to} 1 × 10 ¹⁰ Ω · cm, and the ratio of the electric resistance (R1500) to the electric resistance (R150) at an electric field strength of 150 V / cm. Is 5 depending on the developing electric field
20 to 20 and the volume-based central particle size is 30 to 50 μm
And a carrier for a two-component developer.

(Function) The present inventors consider that carrier particles each having a specific range of internal pore rate, electric resistance, and particle size are defined as magnetic carriers of a two-component developer. The present invention has been found to be able to eliminate fog and excessive consumption of toner and brush marks all at once, to extend the life of the carrier, and to provide a sufficient toner density to a solid image portion during development. It has been reached.

When high-speed development is performed, which is different from normal development, the volume-based central particle size of the two-component developer carrier is increased to increase the fluidity of the carrier itself and to increase the carrier 1
The inventors have found that when the saturation magnetization per unit is increased, carrier adhesion during high-speed development is prevented, and a fine line image portion is clearly reproduced.

In the present specification, a brush mark is a phenomenon in which many white fine stripes are generated in a solid image, and a carrier pull is a phenomenon in which an electrostatic latent image is developed not only by toner but also by a carrier. The tailing is similar to fogging in that toner adheres to portions other than the regular image, but tailing refers to a phenomenon in which toner adheres to the periphery of the regular image.

The magnetic carrier used in the present invention is 3 to 30 on an area basis.
It is important to use a magnetic carrier containing a specific amount of ferrite particles having an area-based internal pore ratio of 5% to 25%. The area-based internal pore ratio is obtained by cutting a carrier particle with a microtome so that it passes through the center, It is the value obtained by

The area-based internal pore ratio of the sintered ferrite particles affects the electrical resistance of the particles. That Figure 1 is a graph showing the dependence of the electrical resistance to the applied voltage of the magnetic carrier, the line A is 50% of less than conventional sintered ferrite carrier (P _R 3%, greater than 30% P _R For 10%, D _E = 25), line B is the sintered ferrite carrier (R _R ) used in the present invention.
90% for 3-30%, D _E = 5).
FIG. 1 shows that the carrier has a median particle size of 70 to
This shows ferrite carrier particles used for high-speed development in the range of 110 μm. The volume-based central particle diameter means the particle diameter of particles located at the center of the distribution in a state where the particle group is distributed in volume. The second
The figure shows a carrier whose average particle size based on the volume of the carrier is in the range of 30 to 50 μm. The difference between FIG. 1 and the measurement range of the electric field strength is that the particle size is small.
This is because, when the measurement is performed at a high electric field strength, the measurement particles are scattered and an accurate value cannot be obtained.

Generally, when considering the electrical resistance as a magnetic carrier,
When the electric field strength is low, the contribution of the surface resistance of the carrier particles is large, and when the electric field strength is high, the contribution of the internal resistance of the carrier particles is large. The resistance at low electric field strength becomes the resistance value, and the internal resistance mainly becomes the resistance value at high electric field strength. As shown in FIGS. 1 and 2, it is understood that the resistance value of the carrier whose internal pore ratio satisfies the above range is not significantly changed by the electric field strength. It is understood that does not change.

Therefore, as shown in FIG. 1, the internal pore ratio has a significant effect on the electric resistance of the developer carrier and also has a significant effect on the developing electric field dependence. It is important that the carrier for developer in high-speed development has a volume-based central particle diameter of 70 to 100 μm, particularly 80 to 100 μm. The dependence on the development electric field is defined by the following equation (2). The value to be used.

In the formula, R ₂₅₀₀ is the electric resistance value (Ω · cm) of the magnetic carrier measured at an electric field strength of ₂₅₀₀ V / cm, and R ₅₀₀₀ is the electric field strength of 5
The electric resistance (Ω · cm) of the magnetic carrier measured at 000 V / cm is shown.

The developing electric field dependency has the following meaning. The electric resistance of the denominator in the equation (2) is obtained with an electric field strength of 5000 V / cm. The electric field strength applied to the magnetic brush during development, that is, the electric field strength between the photoconductor and the developing sleeve is almost equal to this value. . A bias voltage is applied to the developing sleeve, the voltage is usually in the range of 100 to 300 V, and the developing limit is 350
It is set in the range of ~ 700V. The width between the photosensitive member and the developing sleeve (between DS) is set to a width of 0.05 to 0.13 cm. Therefore, the intensity of the developing electric field applied to the magnetic brush at the time of the development is as described above. Electrical resistance of the molecule of formula (2)
The electric field intensity of 2500 V / cm is obtained because the electric field intensity only by the bias voltage applied to the developing sleeve has almost this value, which mainly affects carrier adhesion and background fog.

When the area-based internal pore ratio of the ferrite carrier particles is within the above-mentioned range, it has a significant effect on the development electric field dependence of electric resistance, and when the internal pore ratio in the particles increases, the denominator of the formula (2) is obtained. Increasing R ₅₀₀₀ while decreasing R ₂₅₀₀ in the molecule. In other words, it has the effect of bringing the internal resistance closer to the surface resistance of the sintered ferrite. this is,
This is a remarkable difference from the conventional sintered ferrite particles in which the dependence of the electric resistance on the developing electric field is extremely large.

Dependence of carrier on development electric field (D _E ) in high-speed development
It is important to adjust to be in the range of 1.5 to 20. The development electric field dependence refers to the rate of change in the resistance of the carrier when no electric field is applied to the carrier and when the electric field is applied. This is based on the charge state of the carrier when the electric field is changed. It is also a thing. In the present invention, since the development electric field dependence of the carrier is in the above range,
Along with achieving low carrier resistance on the low voltage side,
Higher carrier resistance on the high voltage side is achieved, and background fog, excessive consumption of toner (decrease in toner transfer rate), brush marks, and the like are eliminated, and an image with excellent gradation can be formed.

In the present invention, when the content of the particles formed to have an area-based internal pore ratio (P _R ) of 3 to 30% is less than 50% and the proportion of the particles having an internal pore ratio of less than 3% increases, No matter how the substrate is adjusted, it becomes difficult to control the developing electric field dependence (D _E ) within the range specified in the present invention, which tends to cause brush marks and carrier pulling. When the content of the particles having (P _R ) of more than 30% increases, the image density tends to be inferior in terms of maintainability, gradation, and carrier durability. Further, the content of particles formed to have an internal pore ratio (P _R ) of 3 to 30% is
If it is less than 80%, the above effects such as maintenance of image density are not sufficiently exhibited.

For carriers used for high-speed development, etc., the value of R ₂₅₀₀ is 1 × 10 ⁷
To 1 × 10 ¹¹ Ωcm, especially 1 × 10 ^{8 to} 5 × 10 ¹⁰ Ωcm
It is also important in image quality to select a value within the range. By satisfying such a range of the electric resistance value and the pore ratio, the range of the electric resistance value of the carrier on the low electric field side and the electric resistance value of the carrier on the high electric field side are almost determined. In these ranges, developer brush marks, carrier pulling, and background fog do not occur.

The present invention also provides a carrier with an apparent density of 2.0 to 3.0 g / c.
c, preferably in the range of 2.2 to 2.8 g / cc.
When a carrier having an apparent density within these ranges is used in a two-component developer in the above range, the saturation magnetization per carrier particle is high and stable, and carrier adhesion during high-speed development is prevented, resulting in excellent image quality at high speed. I will provide a.

The apparent density is usually determined by the density of the particles themselves, the particle size, the shape, etc., and the apparent density of the carrier is affected by the range of the pore ratio and the range of the particle size of the ferrite particles, and is greatly related to these. Is clear. Therefore, it is understood that the effect on the stirring load and the effect on the saturation magnetic susceptibility are achieved by combining these.

Further, the saturation magnetization of the carrier is 40 to 60 emu / g, particularly 45
It is important to be in the range of ~ 55 emu / g. When the saturation magnetization of the carrier is within the above range, the brush of the developer brush formed on the surface of the developing sleeve can be kept soft, thereby improving the image quality. In addition, since the saturation magnetization of the carrier is in such a range and the amount of the saturation magnetization is high, carrier pulling and the like can be prevented, and reduction between DS can be achieved.

FIG. 2 is a graph showing the dependence of the electric resistance on the applied voltage of the magnetic carrier, and the line A is a conventional sintered ferrite carrier (50% for those having an internal pore ratio of less than 3%, 30% 45% and 30% internal pore rate
And 5% which exceeds, for D _E = 50), line B sintered ferrite carrier used by the present invention (internal porosity of 3%
Less than 5%, internal pore rate 3 to 30% 85
% And 10% if the internal pore rate exceeds 30%, and D _E =
11.5). FIG. 2 relates to a carrier for improving the reproducibility of a solid image portion. The carrier has a volume-based central particle diameter of 30 to 50 μm, particularly 35 μm.
It is important that the thickness is in the range of from about 45 μm to about 45 μm.

In the formula, R ₁₅₀₀ is the electric resistance value (Ω · cm) of the magnetic carrier measured at an electric field strength of 1500 V / cm, and R ₁₅₀ is the electric field strength of 15 V / cm.
Electrical resistance of magnetic carrier measured at 0 V / cm (Ω
· Cm). The development electric field dependence is expressed by the equation (3) because the particle size of the carrier particles is small, and when the measurement is performed at a high electric field, the carrier particles move on the electric field, so that the accuracy is lacking. It is.

In the present invention, it is important to adjust the developing electric field dependence (D _E ) of the carrier particles so as to be in the range of 5 to 20. If the value of the development dependency is smaller than 5, the formed image is likely to cause tailing, and toner is likely to be scattered during development. This is considered because the carrier resistance at the time of charging is too low and the toner charge amount is reduced.
On the other hand, if this value is larger than 20, brush marks are likely to occur. This is presumably because the carrier resistance when the bias voltage is applied is too low, causing charge leakage on the photoconductor surface.

For the carrier, the value of R ₁₅₀₀ is 1 × 10 ^{6 to} 1 × 10 ¹⁰ Ω · c
It is also important from the viewpoint of image quality to select m so as to be in the range of 1 × 10 ^{7 to} 5 × 10 ⁹ Ω · cm. When this value is less than the above range, brush marks and carrier pulling tend to occur. On the other hand, when the value is more than the above range, the development of the solid image portion is not performed well.

In the present invention, it is also important to contain the sintered ferrite particles having the above characteristics in an amount of 80% by weight or more based on the total magnetic carrier. If the amount of the sintered ferrite particles falls below the above range, the above-mentioned effect according to the present invention is exhibited. Will not be.

The magnetic brush ears on the developing sleeve can be softened by making the carrier contain 20 to 40% by weight of fine particles having a particle size under 400 mesh (37 μm). 40 of this particle size
Exceeding the weight percentage tends to cause carrier pulling,
If the amount is less than 20% by weight, the ears become hard and the image quality tends to be worse than that in the above range.

The carrier preferably has a saturation magnetization of 50 to 60 emu / g. When the saturation magnetization of the carrier is within the above range, the brush of the developer brush formed on the surface of the developing sleeve can be kept soft, thereby improving the image quality.

By incorporating these properties into the carrier particles, a two-component developer can provide excellent image quality and better compatibility within the apparatus, especially at high speed development.

(Embodiment) Hereinafter, a preferred embodiment according to the present invention will be described in detail. In the description of the present invention, it is roughly divided into a magnetic carrier and a toner. Hereinafter, the description will be made sequentially.

Magnetic Carrier The carrier is mainly made of sintered ferrite particles, and the ferrite particles have a ferrite composition known per se. As a magnetic material pigment, for example, zinc oxide (ZnFe)
₂ O ₄ ), yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium iron oxide (Cd ₃ Fe ₅ O ₁₂ ), gadolinium oxide (Gd ₃ Fe)
₅ O ₁₉ ), copper iron oxide (CuFe ₂ O ₄ ), lead iron oxide (PbFe
₁₂ O ₁₉ ), iron neodymium oxide (NdFeO ₃ ), barium iron oxide (BaFe ₁₂ O ₁₉ ), magnesium iron oxide (MgFe ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ) ,
And the like, or one or more compositions. Preferred ferrites are at least one metal component selected from the group consisting of Cu, Zn, Mg, Ni, etc.
Soft ferrite containing more than one species, such as copper-zinc-
Magnesium ferrite. Particularly preferred ferrites are 35-70% Fe ₂ O _{3 in} mole%, 5-15% CuO, ZnO
Ferrite consisting of 5 to 35% and MnO of 0 to 40%.

Generally, as the primary particle size of the oxide particles constituting ferrite increases, the internal pore ratio increases, and conversely, as the primary particle size decreases, the internal pore ratio tends to decrease. On the other hand, in the production of ferrite particles by sintering, the higher the degree of sintering, the lower the internal pore ratio.For example, the higher the sintering temperature, the lower the internal pore ratio. As the sintering time becomes longer, the internal pore ratio tends to decrease. Of course, when the grain size of the ferrite raw material or the intermediate becomes fine, sintering proceeds under milder conditions as compared with the case where the grain size is coarse, so it is necessary to pay attention to these combinations.

The method of producing the internal pore-containing sintered ferrite is, of course, not limited to this, but as an example, the primary particle size is 0.1 to 2.0 μm.
The metal oxide raw material or the intermediate may be used, molded into predetermined granules, and sintered at a temperature of 900 to 1500 ° C. for 5 to 50 hours. FIG. 3 is a sketch of a micrograph (magnification: 800 times) showing the internal structure of the sintered ferrite particles used in the present invention.

In the present invention, the area-based internal pore ratio is 3 to 30%, particularly 5 to 25% from the ferrite composition based on the above method.
And the sintered ferrite particles having the pore ratio are adjusted so as to be contained in an amount of 80% by weight or more with respect to the whole magnetic carrier. If the internal pore ratio exceeds 30%, the durability tends to be poor. In addition, when the proportion of particles having an internal pore ratio of less than 3% is large, it is difficult to adjust the developing electric field dependence.

In high-speed development, the volume-based average particle size of the carrier particles is such that the volume-based central particle size is 70 to 110 μm, particularly 8 μm.
It is in the range of 0 to 100 μm. When the particle size is below the above range, the saturation magnetization is reduced in combination with the apparent density in development, and carrier adhesion is likely to occur in high-speed development. On the other hand, if the ratio exceeds the above range, the magnetic brush on the developing sleeve surface becomes difficult to form during development, so that the image quality deteriorates. The electric resistance of the carrier at an electric field strength of 2500 v / cm is 1 × 10 ^{7 to} 1 × 10 ¹¹ , especially 1 × 10 ^{8 to} 5 ×
It is important to be in the range of 10 ¹⁰ Ω · cm, and it is important that the developing electric field dependence (D _E ) is in the range of 1.5 to 20. In order to adjust the electric resistance value within the above range, Can be obtained by changing the compounding ratio of the ferrite composition and the pore ratio within the above range.

Also, the apparent density of the carrier is 2.0 to 3.0 g / cc, especially 2.
It is set to satisfy the range of 2 to 2.8 g / cc. When the apparent density exceeds the above-mentioned range, the stirring load at the time of development becomes large and the saturation magnetic susceptibility becomes low, so that carrier adhesion in high-speed development cannot be prevented. Carrier saturation magnetization is 40
It is preferably in the range of from 60 to 60 emu / g, especially from 45 to 55 emu / g. The saturation magnetization of the sintered ferrite particles can be adjusted to the above range by changing the ferrite composition described above. If the saturation magnetization is lower than the above range, carrier pulling occurs in the development, and if the saturation magnetization is higher than the above range, the brush of the magnetic brush formed on the developing sleeve becomes hard and the image quality deteriorates.

Further, in order for the solid image portion to perform excellent development with high density, the center particle diameter based on the volume of the carrier is 30 to 70 μm.
m, particularly preferably 35 to 50 μm. Also, 40
It is desirable that fine particles having a particle size of 0 mesh under are contained in an amount of 20 to 40% by weight per carrier.

In this case, it is important that the electric resistance of the carrier at an electric field strength of 1500 v / cm is in a range of 1 × 10 ^{6 to} 1 × 10 ¹⁰ , particularly 1 × 10 ^{6 to} 5 × 10 ⁹ Ω · cm. It is important that the electric field dependence (D _E ) is in the range of 5 to 20, the saturation magnetization of the carrier is in the range of 50 to 60 emu / g, and the apparent density is 1.8 to 2.5 g / cc, especially 2.0 to 2.5 g / cc. It is desirable to satisfy the range of 2.3g / cc.

In these carrier particles, the fluidity (JIS Z2502) of the particles can be adjusted within a range of 20 sec / 50 g to 30 sec / 50 g, particularly 20 to 28 sec / 50 g. When the flow rate of the carrier particles is less than the above range, it becomes difficult to manufacture, but when the above range is exceeded, the shape of the carrier particles becomes distorted, the crushing resistance is reduced, and the internal pore strength is affected. give.

Further, in the present invention, by making the primary particles of the carrier composition uniform, the specific surface area of the ferrite particles can be increased.
A range of 0.02 to 0.2 m ² / g is obtained. The specific surface area is measured by the BET method. If the specific surface area of the particles exceeds the above range, the above-mentioned internal pores may affect the surface, and the particles are easily broken.

Toner As the toner, any of a colored toner having visible and fixing properties can be used. A particulate composition having a particle size of 5 to 30 microns in which a coloring pigment, a charge control agent, and the like are dispersed in a binder resin is used. used. As the resin, a thermoplastic resin or an uncured or precondensed thermosetting resin is used. Suitable examples thereof include, in order of importance, vinyl aromatic resin such as polystyrene, acrylic resin, polyvinyl acetal, polyester, epoxy resin, phenol resin, petroleum resin, olefin resin and the like.

Examples of the coloring agent include various pigments such as carbon black, quinacridone pigments, rhodamine pigments, thioindigo pigments, azo pigments, phthalocyanine pigments, nitro pigments, CI Solvent Red 49, CI Solvent Red 1
9, CI Solvent Blue 70, CI Solvent Blue 7
0, CI Solvent Yellow 19, CI Solvent Yellow
21 mag is used.

As a control agent, for example, nigrosine base (CI 5041
5), oil-soluble dyes such as oil black (CI 26150),
Metal complex salts such as metal-containing azo dyes, salicylic acid, naphthoic acid and fatty acid metal soaps are used as required.

The median toner particles used in the present invention have a median type of 5 particles.
It is desirable to have a particle size characteristic of from 3 to 35 μm, especially from 7 to 20 μm.

Two-component developer The magnetic carrier composed of ferrite particles and the toner described above are in an amount ratio of 90% by weight or more, particularly 92 to 98% by weight, and 10% by weight or less, particularly 2 to 8% by weight of the magnetic carrier. To form a two-component developer. After mixing and stirring the developer in this amount ratio, the developer is supplied onto a developing sleeve provided with a magnet therein, and is rubbed against the surface of the photoreceptor having an electrostatic image to form a toner image. The toner image is transferred onto copy paper and brought into contact with a heating roller to obtain a copy having the fixed toner image.

(Effect of the Invention) According to the present invention, a sintered ferrite having an area-based internal pore ratio, electric resistance, and particle size in a specific range is used as a carrier for a two-component developer in a specific range. Accordingly, the density of the solid image portion can be sufficiently satisfied without causing an edge effect in the formed toner image. Moreover, the life of the developer is long and the toner is not consumed more than necessary. Also, by making the particle size of the carrier constant, it is suitable for high-speed development.

(Experimental Example) Experimental Example 1 The carriers of the experimental samples 1-1 to 1-8 have the characteristics shown in Table 1, and together with the carrier, 100 parts by weight of a styrene-acrylic polymer were used as a visible toner. Based on 10 parts by weight of carbon black, 1.0 part by weight of metal-containing azo dye, and 1.5 parts by weight of low molecular weight polypropylene, 100 parts by weight of toner particles having a median diameter of 13 μm obtained by a conventional method are mixed with 0.3 parts by weight of hydrophobic silica and alumina. The two-component developer was obtained by adjusting the surface-treated toner composition at 0.15 parts by weight to a toner concentration of 5%. Using this developer, high-speed development was carried out using a DC-4555 (trade name, manufactured by Mita Kogyo Co., Ltd.), and a printing durability test was performed on 50,000 sheets (developing potential difference: 500 V, bias potential: 250 V). Was. Table 1 shows the test results.
Shown in

Experimental Example 2 The carriers of Experimental Samples 2-1 to 1-10 have the characteristics shown in Table 2, and together with each carrier, the same toner composition as in Experimental Example 1 was used so that the toner concentration became 9%. This was adjusted to obtain a two-component developer. Using this developer, a printing durability test of 50,000 sheets (developing potential difference: 570 V, bias potential: 250 V) was performed using a DC-4055 (trade name, manufactured by Mita Kogyo Co., Ltd.).
Table 2 shows the test results.

[Brief description of the drawings]

1 and 2 show the relationship between the resistance of the carrier and the electric field strength, and FIG. 3 shows the internal particle structure of the carrier of the present invention based on an electron micrograph.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hidenori Asada 1-2-28 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Inside Mita Kogyo Co., Ltd. (72) Inventor Shigeki Yamada 1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka No. 28 Inside Mita Kogyo Co., Ltd. (56) References JP-A-58-23032 (JP, A) JP-A-59-228664 (JP, A) JP-A-63-2076 (JP, A) JP-A-2- 146061 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G03G 9/10 321

Claims (11)

(57) [Claims] 1. A magnetic carrier for a two-component developer used together with a toner, wherein the area-based internal pore ratio is 3 to 30.
% Of sintered ferrite particles containing at least 80% by weight of particles formed in the range of 1% to 1 × 10 ^{7 to} 1 × 1 at an electric field strength of 2500 V / cm.
0 ¹¹ Ω · cm, the developing electric field dependence defined by the ratio of the electric resistance (R2500) to the electric resistance (R5000) at an electric field strength of 5000 V / cm is 1.5 to 20, and the volume basis Having a center particle diameter of 70 to 110 μm. 2. The carrier according to claim 1, wherein the apparent density is in the range of 2.0 to 3.0 g / cc. 3. The sintered ferrite particles are 20 to 30 seconds / 50 g.
The carrier according to claim 1, wherein the carrier has a fluidity (JIS Z2502). 4. The sintered ferrite particles have a particle size of 0.02 to 0.20 m ^2.
2. The carrier according to claim 1, wherein the carrier has a specific surface area (BET method) of / g. 5. The carrier according to claim 1, wherein the saturation magnetization is in a range of 40 to 60 emu / g. 6. A magnetic carrier for a two-component developer used together with a toner, wherein the area-based internal pore ratio is 3 to 30.
% Of sintered ferrite particles containing 80% by weight or more of particles formed in the range of 1% to 1 × 10 ^{6 to} 1 × 1 at an electric field strength of 1500 V / cm.
0 ¹⁰ Ω · cm, and the developing electric field dependency defined by the ratio of the electric resistance (R1500) to the electric resistance (R150) at an electric field strength of 150 V / cm is 5 to 20, and is based on volume. A carrier for a two-component developer, wherein the carrier has a center particle diameter of 30 to 50 μm. 7. The carrier according to claim 6, wherein the apparent density is in the range of 1.8 to 2.5 g / cc. 8. The carrier according to claim 6, wherein particles having a particle size of 400 mesh (37 μm) or less are contained in an amount of 20 to 40% by weight based on the whole. 9. The sintered ferrite particles are 20 to 30 seconds / 50 g.
The carrier according to claim 6, wherein the carrier has a fluidity (JIS Z2502). 10. The sintered ferrite particles have a particle size of 0.02 to 0.20.
7. The carrier according to claim 6, wherein the carrier has a specific surface area (BET method) of m ² / g. 11. The carrier according to claim 6, wherein the saturation magnetization is in a range of 50 to 60 emu / g.