JPH11272019A - Electrostatic charge image developing carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carrier which has excellent spent resistance, environmental resistance and a long life and which is gentle for the environment by coating the surface of a core material comprising a specified magnetic material with a specified resin containing a copolymer of a specified organopolysiloxane and radical polymerizable monomers. SOLUTION: The surface of a core material comprising a magnetic material expressed by (MnO)x (MgO)y (Fe2 O3 )z , wherein x+y+z=100 mol.%, with MnO, MgO and/or Fe2 O3 partly substituted with SrO, is coated with a resin containing a copolymer of organopolysiloxane expressed by the formula and radical polymerizable monomers. In the formula, R1 is a hydrogen atom or methyl group, x, y and z are numbers preferably ranging 35 to 45 mold, 5 to 15 mol.% and 45 to 55 mol.%, respectively, and are substituted with SrO preferably in the range of 0.35 to 5.0 mol.%. The proportion of the radical polymerizable monomers and the organopolysiloxane is controlled in such a manner that the proportion of the latter is 5 to 80 wt.%, preferably 20 to 60 wt.%, of the total amt. of the two.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a carrier for developing an electrostatic image.

[0002]

2. Description of the Related Art The developer of a two-component dry copying machine is composed of two components, a toner having a small particle size and a carrier having a larger particle size. The toner and the carrier are opposed to each other by friction generated by mixing and stirring the two components. It is electrostatically charged with the sign charge. The toner charged in this way is
A visible image is formed by electrostatically adhering to the electrostatic latent image formed on the photoreceptor, and copying is achieved by transferring this image to a transfer sheet and fixing it.

As a carrier, iron powder, magnetite, or (MO) _a (M'O) _b (Fe ₂ O ₃ ) _c has been conventionally used.
(In the formula, M and M ′ are metal elements, and a, b and c are integers.) Soft ferrite represented by, for example, Ni-Z
n ferrite, Cu-Zn ferrite or Cu-Z
An n-Mg ferrite or the like is used. In addition, in order to ensure durability of charging characteristics and environmental stability, these carriers are usually mainly used as a core material and the surface thereof is coated with a resin as a coating material.

However, Ni, Cu,
Carrier core materials containing metals such as Zn have been feared for adverse effects on the environment and have been shunned. Therefore, from the viewpoint of environmental friendliness, Li-Mn-based ferrites, Mn-Mg-based ferrites, etc. are proposed. Have been. Further, among Mn-Mg-based ferrites, a ferrite in which a part of the Mn-Mg-based ferrite is substituted with SrO for the purpose of reducing the variation in magnetization between carrier particles has been proposed (Japanese Patent Application Laid-Open No. 8-221).
No. 50).

[0005] As a carrier coating material,
For the purpose of improving the durability by preventing the spent phenomenon on the carrier surface by the toner component, a fluororesin or silicone resin having a small surface energy has been proposed. However, in a carrier in which such a resin is coated on the core material as described above, the adhesiveness between the coating material and the core material is reduced due to environmental changes and continuous copying,
As a result, there arises a problem that the durability and environmental stability of the above-described charging characteristics are deteriorated.

Accordingly, there has been proposed a carrier obtained by coating a core material such as ferrite with a resin-modified silicone resin whose main component is a copolymer with another polymerizable monomer among silicone-based resins (Japanese Patent Laid-Open No. Hei 10 (1994) -207). 8-179566).

On the other hand, in order to cope with the recent increase in the image quality level required for electrophotography, it has been required to use a carrier having a smaller diameter and a lower magnetic force in order to suppress the occurrence of carrier streaks. In such a carrier, since the magnetization per particle is low, there is also a problem that the carrier is likely to adhere (scatter) to the electrostatic latent image carrier during development.

The reduction in the diameter of the carrier leads to an increase in the electrical resistance between particles in the magnetic brush layer of the carrier in the developing region, and it is necessary to appropriately adjust the electrical resistance of the magnetic brush layer in order to obtain proper developability and image quality. Occurs.
One method of adjusting the electric resistance is to reduce the thickness of the resin coat layer of the carrier. However, when the carrier has insufficient adhesiveness with the resin core material, the coat layer is peeled off at the time of durability. This causes a new problem that carrier characteristics fluctuate. Further, when the resin coating layer of the carrier is made thinner, there is also a problem that the environmental stability of the charging characteristics is reduced due to an increase in the partial exposure of the carrier core material.

As described above, in the conventional resin-coated carrier, the durability and environmental stability of the carrier are ensured despite the improvement of the core material and the coating resin, and the image quality is improved by reducing the diameter of the carrier. It is difficult to measure.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a carrier for developing an electrostatic charge image which is excellent in spent resistance and environmental resistance, has a long service life and is environmentally friendly. With the goal.

The present invention is also capable of avoiding carrier adhesion (scattering), and is excellent in spent resistance, environmental resistance and image quality.
It is an object of the present invention to provide a long-life and environmentally friendly carrier for developing electrostatic images.

[0012]

According to the present invention, there is provided the following general formula (I): (MnO) _x (MgO) _y (Fe ₂ O ₃ ) _z (I) (where x + y + z = 100 mol%) The surface of the core material obtained by substituting a part of MnO, MgO and / or Fe ₂ O ₃ of the magnetic substance represented by SrO is represented by the following general formula (II);

Embedded image (Wherein, R ₁ is a hydrogen atom or a methyl group). An electrostatic image development characterized by being coated with a resin containing a copolymer of an organopolysiloxane and a radical polymerizable monomer. For carrier.

[0013] The present invention also relates to a method for producing a polymer having an average particle diameter of 25 to 45 µm.
And the carrier for developing an electrostatic image.

The carrier core material of the present invention is obtained by substituting a part of Mn-Mg ferrite having a predetermined composition with SrO. Specifically, the core material is a magnetic material represented by the following general formula (I); (MnO) _x (MgO) _y (Fe ₂ O ₃ ) _z (I) (where x + y + z = 100 mol%). Wherein a part of MnO, MgO and / or Fe ₂ O ₃ is replaced by SrO, and x, y and z are preferably in the ranges of 35 to 45 mol%, 5 to 15 mol% and 45 to 55 mol%, respectively. Of these, SrO is preferably substituted in the range of 0.35 to 5.0 mol%. If the SrO substitution amount is less than 0.35 mol%, the obtained carrier particles have too low magnetization, so that the carriers are likely to scatter and cause the carrier to adhere to the photoreceptor. On the other hand, when the substitution amount exceeds 5.0 mol%, the carrier tends to aggregate due to generation of residual magnetization and coercive force.

As described above, the carrier of the present invention is environmentally friendly because the SrO-substituted Mn-Mg ferrite is used as the core material. Further, since the carrier core material of the present invention is partially substituted with SrO, it is possible to reduce the variation in magnetization between particles as compared with the conventional ferrite carrier core. In addition, it is considered that carrier adhesion (scattering) to the electrostatic latent image carrier during development can be suppressed to a low level.

The method for producing the carrier core material of the present invention is not particularly limited as long as a core material having the above composition is obtained, but the carrier core material can be easily produced in the following manner. First, MnO, MgO and Fe ₂ O ₃ are 35 to 4 respectively.
5 mol%, 5 to 15 mol% and 45 to 55 mol%
% Of each oxide, and a predetermined amount of SrO or SrCO ₃ which is finally SrO, and water is usually added thereto, and the mixture is added for 1 hour by a wet ball mill or a wet vibration mill. As described above, the mixture is preferably pulverized and mixed for 1 to 20 hours. The thus obtained slurry is dried, further pulverized, and then temporarily calcined at a temperature of 700 to 1200 ° C. If it is desired to further reduce the apparent density, the calcination step may be omitted. After calcination, it is further 15 μm or less, preferably 5 μm, in a wet ball mill or wet vibration mill.
m or less, more preferably 2 μm or less, after adding a dispersant, a binder, etc., if necessary, after adjusting the viscosity,
The granulation is performed, the temperature is maintained at 1000 to 1500 ° C. for 1 to 24 hours, and the main firing is performed. The fired product is pulverized and classified.
If necessary, the surface may be reoxidized at a low temperature after a slight reduction with hydrogen at a temperature of 700 to 1000 ° C.

[0017] The carrier of the present invention comprises the surface of the core material,
The following general formula (II);

Embedded image (In the formula, R ₁ is a hydrogen atom or a methyl group.) The resin is coated with a resin containing a copolymer of an organopolysiloxane and a radical polymerizable monomer.

The organopolysiloxane constituting the coating layer of the carrier of the present invention has a vinyl group at the terminal as represented by the above-mentioned general formula (II), so that it can be combined with other radically polymerizable monomers. By copolymerizing, it is possible to graft-polymerize onto a polymer chain composed of other radically polymerizable monomers, and when the obtained copolymer is coated on a carrier core material, silicon is coated on the outside of the carrier. The structure is rich in components. In addition, since a portion composed of a monomer having an affinity for the carrier is abundantly present on the carrier side, the adhesion between the carrier and the coating layer is good, and the surface of the coated carrier has excellent release properties. Can be provided. As a result, the coated carrier of the present invention can be made to have little peeling of the coating layer and to be excellent in spent resistance and environmental resistance.

Further, one of the features of the coated carrier of the present invention is good fluidity, and it is possible to impart a good charge rising property even when the diameter of the toner is reduced. This is thought to be caused by the relatively short main chain of the organopolysiloxane of the present invention.

The radical polymerizable monomer which forms a copolymer with the organopolysiloxane of the general formula (II) has an affinity for the core material of the coated carrier and can be copolymerized with the above-mentioned organopolysiloxane. Methyl acrylate, ethyl acrylate, butyl acrylate, β-hydroxypropyl acrylate, β acrylate
Acrylate monomers such as -hydroxyethyl, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-hydroxyethyl methacrylate,
Methacrylate monomers such as glycidyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl acrylate, dimethylaminopropyl methacrylamide And vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, p-ethylstyrene, vinyl acetate, and vinyl chloride, N-laurylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide. For example, a maleimide-based monomer such as ethylene, or propylene can be used. Preferred are methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate. One of these radical polymerizable monomers may be used alone, or a plurality of them may be used as a mixture.

The proportion of the radical polymerizable monomer and the organopolysiloxane of the general formula (II) is 5 to 80% by weight, preferably 20 to 20% by weight of the total amount of the organopolysiloxane of the general formula (II). It is desirable to use ６０60% by weight. If the amount is less than 5% by weight, the releasability and environmental resistance effects of the siloxane are impaired, and if it is more than 80% by weight, the adhesion to the magnetic particles is reduced.

As a method of radically copolymerizing the above-mentioned radical polymerizable monomer and organopolysiloxane to obtain a coating material of a coated carrier, there are generally used known suspension polymerization, emulsion polymerization, and the like. A solution polymerization method, a bulk polymerization method and the like can be used as appropriate, but from the viewpoint of productivity, the solution polymerization method is preferred. As a solvent or a polymerization initiator used in the solution polymerization method, any of those conventionally used can be used.

The particle size of the coated carrier of the present invention is at least 20 μm (average particle size) from the viewpoint of preventing the carrier from adhering (scattering) to the electrostatic latent image carrier, and the image quality such as the occurrence of carrier streaks is reduced. 70μ at most from the point of prevention of reduction
m is desirable. Further, the average particle size of the carrier of the present invention is more preferably 25 to 45 μm.
This is because by setting the average particle size to be 25 μm or more and 45 μm or less, prevention of carrier adhesion and prevention of deterioration of image quality can be more reliably achieved.

The amount of the coating material for covering the core material is 0.2 to 1.5% by weight, preferably 0.3% by weight, based on the core material.
１1% by weight. If the amount is less than 0.2% by weight, the core material cannot be uniformly coated, and the environmental resistance deteriorates. If the amount is more than 1.5% by weight, the electric resistance as a carrier layer increases. Too much, resulting in insufficient toner developability. On the other hand, if the coating is more than 1.5% by weight, it is meaningless because the coating is already sufficiently formed, and it is economically disadvantageous.

To coat the coating material on the carrier core material, for example, the obtained copolymer is dissolved in an appropriate solvent such as methyl ethyl ketone, methyl isobutyl ketone, dioxane, etc. The treatment may be performed by the method or the like so as to achieve the above-mentioned coating amount.
In addition, coating can also be performed by immersing the carrier core material in a coating resin solution and drying.

The carrier of the present invention as described above can be used in any type of developing device for developing using a two-component developer. Among them, the carrier of the present invention reduces the distance between the developer carrying member and the developer regulating member compared to the conventional developing device to reduce the amount of developer carried to the developing region, and reduces the amount of the developer carrying member in the developing region. This is very effective for a developing device in which the distance between the image bearing member and the image bearing member is slightly wider than that of the conventional developing device, and a DC voltage and an AC voltage are superimposed on the developer carrying member.

This type of developing device will be described with reference to FIG. FIG. 1 is a schematic diagram showing a configuration of a developing device according to one embodiment of the present invention. The main body 10 of the developing device is provided with a developer carrier 11 facing the image carrier 1 on which an electrostatic latent image is formed by a known process. The developer carrier 11 has a cylindrical shape, and has a magnet roller 11a on the inner peripheral side. The developer 2 contained in the apparatus main body 10 is supplied to the surface of the developer carrier 11 by a developer supply member 12 such as a bucket roller.

The developer 2 thus supplied is supplied to the developer carrier 1 by the magnetic force of the magnet roller 11a.
The developer carrier 11 is conveyed by being rotated while the developer carrier 11 is held on the surface of the developer carrier 1. After the developer 2 conveyed by the developer carrier 11 is regulated to a certain amount by the regulating member 13, the developer 2 reaches a developing area where the developer carrier 11 and the image carrier 1 face each other. The electrostatic latent image formed on the carrier 1 is developed by supplying toner.

Further, the developing device includes a developer carrier 11
The DC power supply 14 and the AC power supply 15 apply a voltage in which an AC voltage is superimposed on a DC voltage. This allows
Development is performed by applying an electric field in which an AC electric field is superimposed on a DC electric field to a developing region where the developer carrier 11 and the image carrier 1 are opposed to each other.

In the above-described developing device, the amount of the developer transported to the developing area by the developer carrier is preferably 1.0 to 15 mg / cm ² , more preferably 3 to 15 mg / cm ^2.
-10 mg / cm ² . 1.0mg / cm ^{2 of} developer
If the amount is smaller, the amount of toner supplied to the image carrier tends to be insufficient, and the image density tends to decrease. If the transport amount of the developer is more than 15 mg / cm ² , the layer thickness of the developer on the developer carrier becomes thicker, so that the carrier tends to remain on the carrier after development, and the carrier adheres to the image carrier. It will be easier. In order to secure such a transport amount, the distance between the developer regulating member and the developer carrier is set to 0.1 to 0.6 m.
m, preferably 0.4 to 0.5 mm. The distance (Ds) between the developer carrier and the image carrier in the developing area is preferably 0.2 to 0.5 mm,
More preferably, it is 0.3 to 0.4 mm. 0.2mm
If it is narrower, the carrier particles tend to adhere to the image carrier,
If it is wider than 0.5 mm, the image density tends to decrease.

Further, the image agent carrier is specifically -300
DC voltage of ~ -450V and frequency of 3-5kHz,
It is desirable to apply a rectangular wave AC voltage of 1.0 to 1.6 kV. When the DC voltage exceeds -300 V, the density tends to decrease, and when the DC voltage is less than -450 V, background fogging easily occurs. If the frequency is less than 3 kHz, background fogging tends to occur, and if it exceeds 5 kHz, the density tends to decrease. If the AC voltage is less than 1.0 kV, the concentration tends to decrease, and if it exceeds 1.6 kV, leak noise tends to occur.

In the above-described developing device, the distance between the developer carrying member and the developer regulating member is made narrower than that of the conventional developing device, so that the amount of the developer conveyed to the developing area is suppressed. The developer supplied into the apparatus can be efficiently used for development without waste. Further, in the developing device, the distance between the developer carrier and the image carrier in the developing area is slightly wider than that of the conventional developing device, and the DC voltage and the AC voltage are superimposed on the developer carrier so that the developer is superposed. Since the carrier vibrates, the developer on the developer carrier is supplied to the image carrier in a state where the developer carrier and the image carrier are not in contact with each other, so that the carrier adheres to the image carrier. This makes it possible to provide an image which is difficult to obtain and has excellent image quality. Furthermore, by using the carrier of the present invention set to a specific particle size, carrier adhesion can be more effectively prevented, and an extremely good image can be easily provided.

The developer used in such a developing device comprises at least the carrier and the toner of the present invention. The carrier of the present invention is desirably used so that the toner content is 3 to 20% by weight, preferably 5 to 15% by weight. When the toner content is less than 3% by weight, the image density tends to decrease, and when the toner content is more than 20% by weight, background fog due to toner scattering tends to occur.

The toner constituting the developer is prepared by using a binder resin, a colorant and other desired additives which have been widely used in the field of electrophotography, and comprises a kneading / pulverizing method, a suspension polymerization method, and an emulsifying method. It can be produced by other known methods such as a polymerization method, an emulsion dispersion granulation method, and an encapsulation method. The volume average particle diameter of the toner is desirably set to 5 to 10 μm, preferably 6 to 8 μm from the viewpoint of image quality and environmental resistance. Hereinafter, the present invention will be described more specifically with reference to examples.

[0035]

EXAMPLES (Production of core material A) MnO was 35 mol%,
MgO and 15 mol%, 49.5 mol% of Fe ₂ O ₃ and SrCO ₃ to 0.5 mol%, 5 by a wet ball mill
After crushing, mixing and drying for an hour, the mixture was kept at 850 ° C. for 1 hour and calcined. This was pulverized by a wet ball mill for 7 hours to reduce the average particle size to 3 μm or less. An appropriate amount of a dispersant and a binder are added to this slurry, and then granulated and dried by a spray drier, and then 1200
The temperature was maintained at 4 ° C. for 4 hours to perform main firing. Thereafter, the resultant was crushed and further classified to obtain a core material A as ferrite particles having an average particle diameter of 35 μm. Analysis of the components of the granulated ferrite particles revealed that MnO was 35 mol% and M
gO is 14.5 mol%, SrO is 0.5 mol%, F
e ₂ O ₃ was 50 mol%.

(Production of core material B) Core material B was replaced with an average particle having the same composition as core material A in the same manner as in the production method of core material A, except that the crushing conditions after the main firing were weakened. Diameter 50μ
m were obtained as ferrite particles. (Production of core material C) A core material C having the same composition as the core material A and having an average particle diameter of 20 μm was produced in the same manner as in the production method of the core material A, except that the crushing conditions after the main firing were strengthened. Obtained as ferrite particles.

(Production of core material D)
5.5 mol%, 31.5 mol% of ZnO, and F
Except that 53 mol% of e ₂ O ₃ was used, the core material D was replaced with C having an average particle diameter of 35 μm in the same manner as in the method of manufacturing the core material A.
Obtained as u-Zn ferrite particles. When the component analysis of the granulated ferrite particles was performed, CuO was found to be 16.0.
mol%, ZnO 31.0 mol%, Fe ₂ O ₃ 5
3.0 mol%. The above component analysis was performed using an atomic absorption spectrometer (SAS-7500; manufactured by Seiko Instruments Inc.).

(Coating resins A and B) stirrer,
In a 500 ml flask equipped with a condenser, a thermometer, a nitrogen inlet tube and a dropping device, methyl ethyl ketone (M
EK), and kept at 80 ° C. under a nitrogen atmosphere, and with stirring, add methyl methacrylate (M
MA) 50.0 parts, 3-methacryloxypropyl tris (trimethylsiloxy) silane (MPTS) 50.0 parts and 1,1′-azobis (cyclohexane-1-carbonitrile) (V-40) 1 part in MEK 100 parts The resulting solution was dropped into the reaction vessel over 2 hours, copolymerized, and aged for 5 hours to obtain a coating resin A. In the present specification, as the coating resin B, a commercially available silicone resin (solid content concentration 20% by weight,
SR-2411; manufactured by Dow Corning Toray Silicone Co., Ltd.).

(Production of Toner) Polyester resin (T
g: 58 ° C., Tm: 100 ° C.) and a magenta pigment (CI Pigment Red 184) were charged and kneaded in a pressure kneader so that the weight ratio of resin: pigment was 7: 3. After cooling the obtained kneaded material, it was pulverized with a feather mill to obtain a pigment master batch. 93 parts by weight of the polyester resin, 10 parts by weight of the pigment masterbatch, and 2 parts by weight of a charge control agent (zinc salicylate complex: E-84: manufactured by Orient Chemical Industry Co., Ltd.) were mixed with a Henschel mixer. The mixture was kneaded with a kneading device. The obtained kneaded product was cooled, coarsely pulverized by a feather mill, finely pulverized by a jet mill, and classified to obtain toner particles having a volume average particle diameter of 7 μm. To the toner particles, 0.6 wt% of hydrophobic silica (H2000, manufactured by Hoechst Japan) and 0.6 wt% of hydrophobic titania (STT30A, manufactured by Titanium Industry) are added as external additives. These were mixed with a Henschel mixer and subjected to an addition treatment to obtain a toner.

Example 1 The above coating resin A was treated with methyl ethyl ketone (ME
K), a resin solution having a solid content of 3% by weight was prepared, and the solution was coated with a spira coater (manufactured by Okada Seiko Co., Ltd.) so that the coating resin amount was 0.7% by weight with respect to the core material A. After drying, the particles were classified with a screen mesh having openings of 75 μm to obtain a resin-coated carrier.

Example 2 A resin-coated carrier was obtained in the same manner as in Example 1 except that core material B was used instead of core material A.

Example 3 A resin-coated carrier was obtained in the same manner as in Example 1, except that the core material C was used instead of the core material A.

Comparative Example 1 A resin-coated carrier was obtained in the same manner as in Example 1 except that coating resin B was used instead of coating resin A.

Comparative Example 2 A resin-coated carrier was obtained in the same manner as in Example 1 except that core material D was used instead of core material A.

8 parts by weight of the toner was mixed with 92 parts by weight of the carriers obtained in the above Examples and Comparative Examples to obtain a developer. These developers were evaluated according to the evaluation methods described below. The modified copier is a remodeled developing machine of a commercially available copier (CF900; manufactured by Minolta Co., Ltd.), and has a configuration schematically shown in FIG. The distance (Ds) between the body and the developer conveying member is adjusted to 0.3 mm, the amount of the developer conveyed to the developing area is adjusted to 8 mg / cm ² , and the distance between the image carrier and the developer conveying member is adjusted. A rectangular wave AC voltage having a peak-peak value (V _pp ) of 1.4 kV, a frequency of 3 kHz, and a DC voltage of -400 V were applied therebetween.

(Environmental friendliness)
A sample containing i, Cu or Zn was evaluated as “x”, and a sample not including any metal was evaluated as “Δ”.

(Chargeability (Environmental Resistance))
After storing for 24 hours in a 15% environment (L / L) and for 24 hours in an environment of 30 ° C. and 85% (H / H), the charge amount was measured in each environment. The environmental resistance was evaluated using these measured values. It was ranked according to the following. In addition, 〇 is a desirable level, △ is a level that has some problem but is practically usable, and X is a level that has a large problem and cannot be practically used. In addition, 20,000 under the environment of 25 ° C. and 55% by the above modified copier is used.
After storing the developer after copying 0 sheets under each environment as described above, the charge amount was measured under each environment, and the environment resistance was similarly evaluated. 〇: △ Q ≦ 10 μC / g and Q (HH) ≧ 15 μC / g
And Q (LL) ≦ 35 μC / g; Δ: ΔQ ≦ 15 μC / g and Q (HH) ≧ 10 μC / g
And Q (LL) ≦ 40 μC / g; ×: ΔQ> 15 μC / g or Q (HH) <10 μC / g
Or Q (LL)> 40 μC / g; (however, ΔQ = | Q (LL) −Q (HH) |)

(Coating Material Peeling Amount) The above-mentioned improved copier equipped with a developer was used at 25 ° C. and 55% environment.
0000 sheets were copied, and the peeling amount of the carrier coating material after the 20,000 sheets were copied was measured by a roasting method.

(Carrier scattering) 20,000 in an environment of 25 ° C. and 55% with the above improved copier equipped with a developer.
Sheets were copied, the carrier consumption was calculated from the carrier amounts before continuous copying and after 20,000 sheets were copied, and evaluated according to the following ranking. Δ: Carrier consumption <5%; Δ: 5% ≦ Carrier consumption ≦ 10%; ×: Carrier consumption> 10%.

(Image Texture) The image density variation of the copied image was measured. As a measuring method, a microdensitometer (manufactured by Abe Design Co., Ltd .; Model 2405) was used to measure the image density in a 10 μm × 100 μm area portion of a halftone image having an image density of 0.4 every 5 μm, and the standard deviation thereof was used. Was used as an index of texture. The evaluation was performed according to the following ranking. 〇: Standard deviation was 0.04 or less; Δ: Standard deviation was more than 0.04 and less than 0.05; ×: Standard deviation was 0.05 or more.

The above evaluation results are shown in Table 1 below together with the carrier core material and the coating material obtained in each of the examples and comparative examples.

[Table 1]

From the above results, the carrier of the present invention is environmentally friendly, has good adhesion of the coating material to the core material, and has little peeling of the coating layer during the durability. It is considered to show. Also,
It has been clarified that by using a carrier having a specific particle size, an image having good texture can be obtained with little carrier adhesion.

In the present specification, the measurement of the charge amount was performed by a film charge measurement method.

[0054]

The carrier of the present invention is excellent in spent resistance and environmental resistance, has a long life and is environmentally friendly. Further, by setting the particle size of the carrier of the present invention to a specific particle size, it is possible to avoid carrier adhesion (scattering) and to provide an image excellent in image quality.

[Brief description of the drawings]

FIG. 1 shows a schematic configuration diagram of an example of a developing device suitable for using a developer containing a carrier of the present invention.

[Explanation of symbols]

1: image carrier, 2: developer, 10: developing device body, 1
1: developer carrier, 11a: magnet roller, 12:
Developer supply member, 13: developer regulating member, 14: DC power supply, 15: AC power supply.

Claims (2)

[Claims] 1. MnO of a magnetic material represented by the following general formula (I): (MnO) _x (MgO) _y (Fe ₂ O ₃ ) _z (I) (where x + y + z = 100 mol%) , MgO and / or Fe ₂ O ₃ are partially substituted with SrO to give a surface of a core material having the following general formula (II): (Wherein, R ₁ is a hydrogen atom or a methyl group). An electrostatic image development characterized by being coated with a resin containing a copolymer of an organopolysiloxane and a radical polymerizable monomer. For carrier. 2. The electrostatic image developing carrier according to claim 1, wherein the average particle diameter is 25 to 45 μm.