JPH07319216A - Electrostatic charge image developing carrier - Google Patents

Abstract

PURPOSE:To obtain an output image having high and uniform density and high resolution without deposition of carrier, fog in the background of the image or trace of brushing in the solid part, by specifying the saturation magnetization and residual magnetization of an electrostatic charge image developing carrier comprising spherical magnetite particles coated with a resin when a specified magnetic field is applied on the carrier. CONSTITUTION:This electrostatic charge image developing carrier consists of substantially spherical magnetite particles as the core material coated with a resin. When 10kOe magnetic field is applied on the resin-coated electrostatic charge image developing carrier, the saturation magnetization sigmas and residual magnetization Br of the carrier are specified to 70 to 120emu/g and 30 to 240 Gauss, respectively. The saturation magnetization affects the mixing characteristics on a magnetic sleeve, namely, on the exchanging property of the developer in a developing area or the hardness of a magnetic brush head. The residual magnetization affects not only the mixing characteristics on the magnetic sleeve but also stirring and mixing characteristics of the developer in the developing machine, namely, the mixing property of the developer and a replenisher toner. By controlling the residual magnetization as well as the saturation magnetization to a proper range, high quality images can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for developing an electrostatic charge image used in electrophotography, electrostatic photography or electrostatic printing.

[0002]

2. Description of the Related Art A two-component developer applied to a magnetic brush developing method comprises a toner and a carrier for developing an electrostatic image (hereinafter referred to as a carrier). In many cases, iron powder or ferrite particles are used as the carrier. Is used.

However, iron powder has a large specific gravity of the particles,
When applied to a carrier to be mixed with toner, the stress applied to the toner and carrier particles increases due to mixing and stirring in the developing device. When the mechanical load applied to the developer is large, the performance of the toner and the carrier is deteriorated at an early stage, and the output image is roughened and the background portion is fogged. In addition, iron powder has extremely high magnetization, which causes the brush of the magnetic brush to become hard, and when applied to the magnetic brush development method, it disturbs the toner layer once developed and adversely affects the output image. Has become.

In order to avoid the above problems, ferrite particles are often used in conventional two-component developers. Ferrite particles have a smaller specific gravity and magnetization than iron powder, and the above-mentioned problems are less likely to occur, but on the other hand, since the volume resistivity is high, the developability is low and the output image density is low. In order to solve the problem, it has been attempted to increase the toner concentration or to add conductive fine particles to the carrier coating resin, but all of them have a problem of charging inhibition to the toner, which is satisfied. It is the current situation that no one with high performance has been obtained.

In order to obtain high image quality, it has been conventionally practiced to reduce the toner particle size. However, in the case of the two-component developer, it is necessary to reduce the particle size of the carrier according to the particle size of the toner in order to secure the charging site. However, if the particle size of the conventionally used ferrite carrier is made smaller, the ears of the magnetic brush become denser and the ears become harder, resulting in greater rubbing force of the magnetic brush, and The above-mentioned problems become more prominent, such as the smaller magnetization that occurs and carrier adhesion, and the practical problems are large.

[0006]

SUMMARY OF THE INVENTION The object of the present invention is to achieve high density and homogeneity without carrier adhesion, fog on the image background area, and solid area sweep even when the particle size of the carrier is reduced. And to provide a carrier for developing an electrostatic charge image capable of obtaining an output image having high resolution, and an electrophotographic method using the carrier.

[0007]

[Means for Solving the Problems] As a result of extensive studies to solve the above problems, it is effective to control the residual magnetization, which strongly affects the mixing characteristics as well as the saturation magnetization of the magnetic carrier used in the two-component developer. I found that.

Therefore, the above object of the present invention has been achieved by the following constitution.

A carrier for developing an electrostatic charge image in which substantially spherical magnetite particles are coated as a core material with a resin, and a saturation magnetization σs when a magnetic field of 10 kOe is applied to the carrier for developing an electrostatic charge image coated with the resin is 70. ~ 120emu / g, remanence B
An electrostatic charge image developing carrier characterized in that r is 30 to 240 Gauss.

The present invention will be described in more detail below.

The saturation magnetization is a mixing characteristic on the magnetic sleeve,
That is, it affects the replacement performance of the developer in the developing area and the hardness of the magnetic brush ears.

When the saturation magnetization is high, the magnetic brush is too hard, and the toner existing on the side closer to the magnetic sleeve in the developing area remains trapped in the magnetic brush, which makes it difficult to develop. Further, since the magnetic brush is hard, the rubbing force in the developing area increases, and the toner once developed is scraped off. Therefore, the developability tends to be insufficient,
On the output image, image defects such as density decrease, density unevenness, and swaths occur. On the other hand, when the saturation magnetization is low, the spikes of the magnetic brush are lowered, and the developer carrying ability of the magnetic sleeve is also lowered, so that the amount of the developer carried to the developing area is insufficient.
Therefore, the developability is lowered and the density of the output image is lowered.

The remanence magnetism affects not only the mixing characteristics on the magnetic sleeve but also the stirring characteristics of the developer in the developing unit, that is, the mixing characteristics of the developer and the replenishment toner.

If the residual magnetism is high, the developer in the developing device tends to be agglomerated, and the stress applied to the developer becomes excessive due to an increase in mixing and stirring torque, and the durability of the developer deteriorates. This is because an image defect such as a decrease in image density or fog on the background portion occurs as the number of copies increases.

On the other hand, if the residual magnetism is low, the cohesive force of the developer is insufficient, so that carrier adhesion occurs in the developing area, which causes image defects. Further, in the stirring and mixing area, the developer cannot be appropriately stressed by stirring due to the same reason, and the mixing property between the replenished toner and the developer becomes insufficient. As a result, in many cases, the toner is introduced into the development area before the toner can be sufficiently charged. Toner with an insufficient amount of charge is scattered around the developing device and adheres to the photoconductor regardless of the latent image, which causes image defects such as contamination of the output image and fogging on the background portion.

To improve the mixing characteristics of the two-component developer,
It is important to use a magnetite carrier composed of hematite and wustite as a carrier to keep the saturation magnetization and the residual magnetism within an appropriate range.

When the developer comprising the carrier of the present invention is used, even if the carrier has a small particle size, high developability can be ensured while suppressing carrier adhesion and a high quality output image can be obtained.

As the core material used in the carrier of the present invention, substantially spherical magnetic particles are used. The term "substantially spherical" as used herein means that the ratio of the minor axis / major axis of the core material particles is 0.7 to 1.0.
Means what is. The measurement can be easily performed by an electron micrograph. Specifically, the minor axis / major axis ratio was determined for any of 300 carriers photographed, and the average value was calculated. When the ratio of the minor axis / major axis of the core material particles is 0.7 or less, uneven mixing of the developer is likely to occur in the developing machine, which makes the toner charge amount unstable and causes fog or toner scattering.

The volume average particle diameter of the core material is preferably 20 to 150 μm, more preferably 30 to 80 μm.
You can use m.

The volume average particle size can be measured by using a laser diffraction particle size analyzer "HELOS" (manufactured by JEOL Ltd.). When the volume average particle size is 20 μm or less,
Carrier adhesion easily occurs, which is a practical problem. When the volume average particle size is larger than 150 μm, the magnetic brush lacks uniformity, image density unevenness is likely to occur, and the reproducibility of fine lines is poor.

The volume resistivity of the core material is preferably 1 × 10 ⁴ to 1 × 10 ¹² Ωcm, more preferably 1 × 1.
Good performance can be obtained by using a material in the range of 0 ⁵ to 1 × 10 ¹⁰ Ωcm. If this value is 1 × 10 ⁴ Ωcm or less, carrier adhesion to the photoconductor occurs, which poses a serious problem in practical use.
When it is 1 × 10 ¹² Ωcm or more, sufficient developability cannot be obtained and the image density becomes insufficient.

To measure the volume resistivity of the core material, specifically, about 1 g of the core material is filled in an insulating cylindrical container having a cross-sectional area of 1.0 cm ² in an environment of room temperature of 20 ° C. and relative humidity of 50%. ,
After obtaining the height of the sample under a load of 500 g, an electric field of DC100V is applied to measure the current value. The volume resistivity was calculated from the obtained sample height and current value by the following formula.

[0023]

[Equation 1]

Further, in the carrier of the present invention, it is necessary to coat the surface of the spherical magnetic particles as the core material with a resin. When using magnetic particles whose surface is not resin-coated as a carrier,
Due to the high surface energy, the toner is apt to be fused to the carrier surface due to the stirring stress in the developing device, and as a result, the charge imparting ability of the carrier is deteriorated with long-term use, which causes fog and image roughening.

As the resin that can be used for coating the carrier of the present invention, known materials that can impart the necessary charging property can be used. Specifically, styrene resins, acrylic resins, styrene / acrylic resins can be used. Resin, ester-based resin, urethane-based resin, olefin-based resin, phenol-based resin, carbonate resin, ketone-based resin, fluorine-based resin, silicon-based resin or modified product thereof, or a copolymer of two or more of these Alternatively, a resin made of a mixture can be used.

Specific examples of the resin production method include a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, a bulk polymerization method, and an in-situ polymerization method.
A polymerization method or the like can be used.

In the present invention, one of the above resins may be used, and if necessary, two or more of these resins may be used in combination.

The volume resistivity of the coating layer of the carrier is 1 ×
Those in the range of 10 ¹⁰ to 1 × 10 ¹⁴ Ωcm give good results. If this value is 1 × 10 ¹⁰ Ωcm or less, the charge imparting ability to the toner is low, causing fog and toner scattering.
There is a big problem in practical use.

On the other hand, when it is 1 × 10 ¹⁴ Ωcm or more, sufficient developability cannot be obtained and the image density becomes insufficient. The method for measuring the volume resistivity of the coating layer is basically the same as that for the core material, but the measurement sample is pelletized by a molding machine. Approximately 0.2 g of material forming the coating layer when molding
Is charged into a molding machine and subjected to compression molding at a surface pressure of 500 kgf / cm ^{2 for} 30 seconds to prepare pellets having a cross-sectional area of 1 cm ² . The volume resistivity of the thus obtained pellets was measured under the same conditions as for the core material.

The preferable coating amount of the resin that can be used for coating the carrier of the present invention needs to be slightly changed depending on the specific gravity of the resin, but in many cases, it is preferably 0.5 to 5.0 wt% with respect to the core material. More preferably 1.0 to 3.0 wt%
The ones give good results. If the resin coating amount is 0.5 wt% or less, the surface of the core material is likely to be exposed when used for a long period of time, and the same problem as in the case where the resin is not coated occurs.
Further, when the resin coating amount is 5.0 wt% or more, the fluidity of the carrier becomes low, so that uneven mixing of the developer is likely to occur in the developing device, the toner charge amount becomes unstable, and fogging and toner scattering may occur. Cause.

As a method for coating the core material surface of the carrier of the present invention with a resin, a known method can be used. Specifically, the resin dispersion solution obtained by the above-mentioned method is applied to the core material surface. A spraying method, a wet coating method such as a method of immersing the core material in a dispersion solution, or electrostatically attaching a finely divided coating resin to the core material surface of a carrier,
Then, a dry coating method can be used in which a resin layer is adhered and fixed on the surface of the core material of the carrier by applying one or both of heat and mechanical stress to the surface of the core material.

The saturation magnetization σs of the carrier coated with the resin by the above method is σs when a magnetic field of 10 kOe is applied.
Of 70 to 120 emu / g, preferably 80 to 100 emu / g can be used. If the saturation magnetization is higher than 120 emu / g, the magnetic brush becomes hard and the developability tends to be insufficient. As a result, image defects such as density reduction, density unevenness, and sweeps occur on the output image. On the other hand, when the saturation magnetization is lower than 70 emu / g, the amount of the developer conveyed to the developing area is insufficient, so that the developability is lowered and the density of the output image is lowered. Further, the remanent magnetism Br of the resin-coated carrier by the above method is 3 when the magnetic field of 10 kOe is applied.
It is possible to use one that is 0 to 240 Gauss, preferably 50 to 120 Gauss. When the residual magnetism is higher than 240 Gauss, the developer in the developing device tends to be agglomerated, and the stress applied to the developer by stirring becomes excessive and the durability of the developer decreases. On the other hand, when the residual magnetism is lower than 30 Gauss, the replenishment of the toner and the developer is insufficiently mixed, and in many cases, toner having an insufficient charge amount is generated. The poorly charged toner scatters around the developing device and causes image defects such as fogging.

To measure the saturation magnetization and remanence of the resin-coated carrier of the present invention, a DC magnetization characteristic automatic recording device 32 is used.
It can be determined using a 57-35 type (made by Yokogawa Electric Corp.). The measurement conditions are shown below.

The carrier to be measured has a room temperature of 20.
Use the one that has been conditioned for 2 hours in an environment of ℃ and relative humidity of 50%. A carrier is filled in an acrylic cylinder having a height of 20 mm and an inner diameter of 15.8 mm, and the sample weight W [g] is obtained. After that, the acrylic cylinder filled with the carrier was set in the above DC magnetization characteristic automatic recording device, a magnetic field of 10 kOe was applied, and y
A magnetic hysteresis curve with the magnetic flux density B (Gauss) on the axis and the magnetic field strength H (Oe) on the x axis is obtained.

An example of the magnetic hysteresis curve is shown in FIG.

When a magnetic field of 10 kOe is applied on the x-axis, (0.0)
The time when the magnetic flux density on the y-axis reaches Bm gradually increases from a, and when the magnetic field is next weakened, the magnetic flux density does not become 0 even if the magnetic field becomes 0, and a magnetic flux b remains. In order to return the magnetism of b in the magnetic flux density B on the y-axis to 0, if the magnetic field is strengthened in the opposite direction, the magnetic flux density becomes 0 at the point of c. If the magnetic field is further increased, the magnetic field is saturated at the point d. From there, if the magnetic field is weakened again and the magnetic field becomes 0 at the point e, the residual magnetic flux of Oe remains, and if the magnetic field is further strengthened in the positive direction, the magnetic flux becomes 0 at the point f.

The saturation magnetization σs is calculated by the following conversion formula using the magnetic flux density Bm when a magnetic field of 10 kOe is applied.

Saturation magnetization σ _S = Bm / (4π · W) W: measured carrier weight (g) Further, the residual magnetism Br is the magnetic flux density B after application of a magnetic field of 10 kOe.
Is obtained ((0b + 0e) / 2 in the figure).

The following method can be used for producing a core material used in a resin-coated carrier having the magnetic properties required for the present invention.

After pulverizing the raw material α-Fe ₂ O ₃ , it was heated and reduced at a temperature of 500 to 700 ° C. for several hours in a reducing atmosphere such as hydrogen, and the obtained iron oxide was mixed with water. Use slurry.

This slurry is sprayed with a spray dryer, granulated, and then sintered. In this case, an inert gas atmosphere such as nitrogen or a reducing gas atmosphere should be selected as the atmosphere for the sintering process, and the sintering temperature should be within the range of 1050 to 1250 ° C and the sintering time within the range of 2 to 6 hours. Is preferred. Then, the core material used in the present invention is obtained through the steps of crushing and classification. When controlling the magnetic properties, it is possible to keep the saturation magnetization within an appropriate range by controlling the raw material purity, the reduction process, and the sintering process conditions, and the residual magnetism by controlling the sintering process atmosphere, temperature, and time. it can.

Known toners can be used in the present invention. Specifically, at least a binder resin,
It is a toner composed of a colorant, and may further contain a release agent, a charge control agent, a magnetic material, a fluidizing agent, etc., if necessary. Known materials are used for the constituent materials.

As a method for producing the toner used in the present invention, a known method can be used. Specifically, the constituent materials are mixed, melt-kneaded, and then subjected to a cooling step, followed by pulverization and classification to obtain a toner, or a polymerization method such as emulsion polymerization or suspension polymerization to obtain a toner. Etc. can be mentioned.

The volume average particle diameter of the toner is preferably 1/30 to 1 / the volume average particle diameter of the carrier.
Use of 2, more preferably 1/20 to 1/5, gives good results. The volume average particle diameter of the toner can be measured by using a laser diffraction particle size analyzer “HELOS” (manufactured by JEOL Ltd.) as in the case of the carrier.

When the volume average particle diameter of the toner with respect to the carrier of the present invention is 1/30 or less, the carrier is too large as compared with the toner and the toner is compressed and deformed by the carrier due to stirring of the developer in the developing device. Since the toner is easily fused to the surface of the carrier, when used for a long time,
The charge imparting ability is deteriorated, and it causes fog and image roughness.

Further, when the volume average particle diameter of the toner with respect to the carrier of the present invention is 1/2 or more, the carrier cannot give a sufficient charge amount to the toner by stirring the developer in the developing device. , The toner charge amount becomes unstable,
This may cause fogging and toner scattering.

In order to use as a two-component developer, it is necessary to previously mix the carrier and the toner.

The mixing ratio of the carrier and the toner of the present invention is
Although it is necessary to change the specific gravity or the particle size of the carrier or the toner to some extent, in many cases, it is preferable to set the toner in the range of 2.0 to 10.0 wt% with respect to the carrier. When the mixing ratio of toner is 2.0 wt% or less, the amount of toner conveyed to the developing area is insufficient and the output image density becomes insufficient. If the toner mixing ratio is 10.0 wt% or more,
The amount of toner becomes excessive with respect to the carrier, the toner cannot sufficiently contact with the carrier, and the toner charge amount becomes unstable, which causes fogging and toner scattering.

When mixing the carrier and toner of the present invention, a conventionally known mixer can be used, but it is preferable that the stress applied to the developer at that time is small. Specific examples thereof include a V-type mixer, a W-cone mixer, and a rotation-type mixer such as a rocking mixer, which gives better results than a stirring-type mixer such as a Henschel mixer.

As the developing device applied to the developer used in the present invention, a developing device comprising an agitating and mixing part of the developer, a developer conveying part for conveying the developer to the developing region, and a toner replenishing part can be used. . As the structure of the stirring and mixing unit of the developer, a stirring and mixing system used in a known developing device can be used.

The developer transporting section is configured to contain a fixed magnetic roll and to transport the developer to the developing area by rotating the non-magnetic sleeve on the outer periphery by utilizing its magnetic force. You can use one.

As the material of the non-magnetic sleeve of the developer carrying section used in the present invention, aluminum, stainless steel or the like can be used. Further, in order to stably convey the developer to the developing area, it is effective to use a non-magnetic sleeve surface to which a surface roughening treatment such as a thermal spraying treatment or a sandblasting treatment has been applied.

The magnetic roll fixed inside the developer transport unit used in the present invention is composed of a plurality of magnetic poles for the purpose of transporting and developing the developer.

Good results can be obtained by using one magnetic pole or a plurality of magnetic poles that act for development and having a magnetic flux density of 600 to 1400 Gauss, preferably 800 to 1200 Gauss.

Further, the position of the magnetic pole for development is centered on the position where the developing sleeve and the photoconductor are closest to each other, and is preferably within a range of ± 30 ° with respect to the rotation axis of the developing sleeve, but preferably ± 15. Better results are obtained with a range of °.

It is preferable to use a magnetic pole having a magnetic flux density of 400 to 800 Gauss as the magnetic pole that acts for transportation.

If the total number of magnetic poles for transportation is at least 3, preferably 4 to 8, the developer transportability is very stable.

[0058]

The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

-Preparation of Carrier- In carrying out the present invention, seven kinds of carriers were prepared and used as shown in Table 1. As the coating resin, a methylmethacrylate / butylmethacrylate = 7/3 copolymer resin (volume resistivity 2.5 × 10 ¹³ Ωcm) was used. The resin coating method used was a method in which the core material was fluidized and the resin solution was sprayed.

List of carriers

[0061]

[Table 1]

-Preparation of Toner- The toner used for carrying out the present invention was prepared by the following method. However, the toner used in the present invention is not limited to this production method.

Carnauba wax 2 wt% as a release agent and carbon black as a colorant with respect to polyester resin
12 wt% was mixed and melt-kneaded with a twin-screw kneader.

Then, after cooling and coarse crushing steps, fine pulverization and air classification were carried out to obtain colored particles having a volume average particle size of 8.0 μm. After that, 0.5 wt% of hydrophobic silica fine particles were externally added and mixed with the colored particles as a fluidizing agent to obtain a toner used in the examples of the present invention.

-Preparation of Developer- 1692 g of each of the seven carriers shown in Table 1 and 108 g of each toner were charged into a V-type mixer and mixed for 10 minutes to obtain a toner concentration of 6.0 wt%. A developer was prepared.

Example 1 Developer 1 prepared using carrier No. 1 in Table 1 was used as U-Bix
The performance of the developer 1 was evaluated by putting it in a modified 5076 (manufactured by Konica) and continuously copying 50,000 sheets.

FIG. 2 is a sectional view schematically showing the magnetic pole arrangement of the developing sleeve of the developing device of the copying machine used in this embodiment. In FIG. 2, the position of the developing magnetic pole 3 is centered on the closest position between the developing sleeve 6 and the photoconductor 9, and the developing sleeve 6
The magnetic pole fixing shaft 7 is installed at a position of + 5 ° upstream of the developer transport.

In the present invention, the developing magnetic pole 3 is used.
Used a 10 mm wide and 1000 Gauss magnetic flux density.
The carrier magnetic poles 1, 2, 4, and 5 were installed in the developing sleeve 6 as shown in FIG. 2, and the magnetic flux density was 700, 750, 750, and 600 Gauss from the carrier magnetic pole 1, respectively.

The results of Example 1 are shown in Table 2.

Examples 2, 3 and 4 The developer 1 is the developer Nos. 2 and 3 and 4, respectively.
Continuous 5 as in Example 1 except that 3 and 4 were used, respectively.
10,000 copies were made and the performance of each of the developers 2, 3 and 4 was evaluated. The results are shown in Table 2 below.

Comparative Example 1 Continuous development of 50,000 sheets was carried out in the same manner as in Example 1 except that the developer 5 made of carrier No. 5 was used instead of the above developer, and the performance of the developer 5 was evaluated. The results are shown in Table 2 below.

Comparative Example 2 The performance of the developer 6 was evaluated by continuously copying 50,000 sheets in the same manner as in Example 1 except that the developer 6 made of carrier No. 6 was used instead of the above developer. The results are shown in Table 2 below.

Comparative Example 3 The performance of the developer 7 was evaluated by continuously copying 50,000 sheets in the same manner as in Example 1 except that the developer 7 made of carrier No. 7 was used instead of the above developer. The results are shown in Table 2 below.

-Evaluation-The performance of the developer was evaluated by the following methods and criteria.

(Image Density) A solid image having an original density of 1.30 was copied and the relative reflection density of the output image with respect to a blank sheet was measured. A Macbeth densitometer was used for density measurement, and image density of 1.30 or higher was judged to be good. The evaluation was performed on the first copy (also referred to as the initial copy) and the 50,000th copy.

(Resolution) A fine line image was copied and the number of fine lines reproduced per 1 mm width of the output image was evaluated.
It should be noted that the larger the number of reproduced fine lines, the higher the resolution, and the image was judged to be good. The evaluation was performed on the 50,000th copy image.

(Sweep) After 50,000 copies were made, a solid image having an original density of 1.00 was copied, and the output image was visually observed for judgment. When there was no scratch-like image disturbance in the paper feeding direction, the result was “good” and when there was occurrence, it was poor and was “poor”.

(Fog) After copying 50,000 sheets, a blank original was copied and the relative reflection density of the output image with respect to the blank was measured. A Macbeth densitometer was used for density measurement, and image density of 0.005 or less was judged to be good.

(Density unevenness) After copying 50,000 sheets, ten solid images each having a document density of 1.00 were continuously copied, and the relative reflection densities of the output images with respect to white paper were measured for all 10 sheets. When the difference between the maximum value and the minimum value of each density data of the 10 sheets was 0.02 or less, it was judged as good, and when the difference was more than that, it was judged as bad and marked as bad.

(Adhering to carrier) Judgment was made by visually observing the output images from the first copy to the tenth copy. The case where the carrier adhesion did not occur and there was no problem was evaluated as “◯”, and the case where the carrier adhesion was confirmed and was defective was evaluated as “x”.

The above results are shown in Table 2 below.

[0082]

[Table 2]

Examples 1 to 4 As is clear from the data in Table 2, in Examples 1 to 4 using the developer of the present invention, high image density and high resolution were maintained from the initial stage of copying, and swept and fog densities were maintained. It was possible to obtain a high-quality image without density unevenness and carrier adhesion all the time.

Particularly, in Examples 1 and 2 in which the developer having a residual magnetism in the range of 50 to 120 Gauss was used, the image density at the initial stage of copying was much better than others, and 50,000 copies were made. Even with the eyes, there is almost no difference from the image density at the initial stage of copying, and it can be seen that the deterioration of the image density is extremely small. Further, the resolution and fog density of Examples 1 and 2 are also better than others, and the effects are remarkably excellent. Comparative Example 1 As is apparent from the data in Table 2, the image was low from the initial stage of copying and the resolution was insufficient. Further, carrier adhesion occurs, which is a practical problem.

Comparative Example 2 As is clear from the data in Table 2, when 50,000 copies were made, sweep marks were noticeable in the solid area and the fog density was extremely high, which caused fog. . Further, density unevenness also occurred, and it was not possible to obtain a high-quality image.

Comparative Example 3 As is clear from the data in Table 2, the image density was rather low from the initial stage of copying and the resolution was insufficient. Also, 5
When 10,000 sheets were copied, the solid areas had conspicuous sweeps and uneven density.

[0087]

When the carrier for developing an electrostatic charge image which is the two-component developer of the present invention and the electrophotographic method using the carrier are used, carrier adhesion, fogging on the image background portion, and sweeping of solid areas are prevented. In addition, it is possible to obtain an output image having high density, high homogeneity, and high resolution for a long period of time.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an example of a magnetic hysteresis curve in the present invention.

FIG. 2 is a sectional view schematically showing an example of a photoconductor and a developing sleeve used in the present invention.

[Explanation of symbols]

 1, 2, 4, 5 Conveying magnetic pole 3 Developing magnetic pole 6 Developing sleeve 7 Magnetic pole fixed shaft 8 Thickness regulating member 9 Photoconductor

Claims (1)

[Claims] 1. A carrier for developing an electrostatic charge image, which comprises resin coating of substantially spherical magnetite particles as a core material,
A carrier for electrostatic image development, which has a saturation magnetization σs of 70 to 120 emu / g and a residual magnetism Br of 30 to 240 Gauss when a magnetic field of 10 kOe is applied to the resin-coated carrier for electrostatic image development.