JPH11282213A - Carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carrier having stable resistance for a long time with which a developer having good durability and a long life without spent of a toner can be obtd. and a copy image showing good reproducibility of dots and a good roughness state in a halftone area can be obtd. SOLUTION: This carrier has the following properties. A magnetic material having the relation of (major axis/minor axis)>1 is used, and fine particles of the magnetic material shows 30 to 150 emu/cm<3> magnetization in 1000 Oe magnetic field, >=25 emu/cm<3> magnetization in 0 Oe magnetic field after the magnetic material is magnetically saturated, and <300 Oe coercive force. The carrier particles have 5 to 100 μm average particle size, <=3.0 g/cm<3> bulk density and 30 to 99 wt.% content of the magnetic material. The particle consists of a core material coated with a resin having >=10<13> Ω.cm specific resistance at 22 deg.C and 55% RH. Carrier particles having >=90% coating rate of the resin on the carrier core surface are >=80% in number of the whole particles, and the carrier has 10<8> to 10<13> Ω.cm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated carrier comprising an electrostatic image developer mixed with a toner.

[0002]

2. Description of the Related Art U.S. Pat.
7, 691, JP-B-42-23910 and JP-B-43-24748 describe various methods. In each of these methods, an electrostatic latent image is formed by irradiating a photoconductive layer with a light image corresponding to a document, and the electrostatic latent image is developed using colored fine powder called toner. Accordingly, a toner image is transferred onto a transfer material such as paper, and then fixed by heating, pressurizing, or solvent vapor to obtain a copy.

In the process of developing the electrostatic latent image, normally, toner particles charged to the opposite polarity to the latent image are attracted by electrostatic attraction and adhered on the electrostatic latent image (reversal). In the case of development, a toner having a triboelectric charge having the same polarity as the charge of the latent image is used). Generally, as a method of developing such an electrostatic latent image using the toner, the toner is roughly divided into a small amount on a medium called a carrier. There are a method using a dispersed so-called two-component developer and a method using a so-called one-component developer of a toner alone without using a carrier.

[0004] Although the electrophotographic method has reached a satisfactory level for document copying, a full-color image output image required by the development of computers and high-definition images is subjected to digital image processing and application of an alternating electric field during development. And the like, high image quality and high quality have been achieved. Further higher image quality and higher quality are desired in the future.

[0005] Conventionally, to output a full-color image,
A two-component developer is used. Generally, the carrier constituting such a two-component developer is formed by coating a conductive carrier typified by iron powder and the surface of iron powder, nickel or ferrite with an insulating resin, or by coating magnetic fine particles with an insulating resin. It is roughly classified into so-called insulating carriers whose resistance is increased by dispersing them inside. When an alternating electric field is applied to achieve high image quality, if the resistance of the carrier in the developer is low, the carrier leaks the latent image potential and a good image cannot be obtained. is necessary. Therefore, when the core material of the carrier is conductive, it is preferable to cover the surface with an insulating resin or the like before use. Ferrite or magnetic substance dispersed resin fine particles having a somewhat high resistance are preferably used as carriers.

In general, since iron powder has a high magnetic force, when iron powder is used as a carrier in a developer, a magnetic brush of the developer becomes hard in a developing region where a toner in the developer develops a latent image. Therefore, high-quality images cannot be obtained due to the occurrence of nicks and rough edges. Therefore, a ferrite or resin carrier is preferably used also in order to reduce the magnetic force of the carrier to achieve high image quality. In order to form a high-quality image, Japanese Patent Application Laid-Open No. Sho 59-104,663 discloses that a ferrite particle having a carrier saturation magnetization value of 50 emu / g or less is used to obtain a good image without nicks. It has been proposed that the use of a carrier with a small saturation magnetization improves the reproducibility of fine lines, but the carrier is placed on an electrostatic latent image carrier (for example, a photosensitive drum) as the distance from the magnetic pole increases. The phenomenon of carrier adhesion (carrier attachment) becomes significant. Further, in the case of a magnetic material-dispersed resin carrier, a small specific gravity is disadvantageous in adhering the carrier.

Japanese Patent Publication No. 4-3868 proposes using so-called hard ferrite having a coercive force of 300 gauss or more as a carrier. However, this is a system for using hard ferrite having a high coercive force as a carrier, and an increase in the size of the device is inevitable. It is preferable to use a developer carrier with a fixed magnetic core in order to realize a compact, high-quality color copier. The carrier of hard ferrite having a high coercive force has a self-aggregating property, and consequently the developer transportability Gets worse.

Further, Japanese Patent Application Laid-Open No. 2-88,429 proposes to use a hard ferrite composed of a spinel phase and a magnet plumbite phase containing a lanthanoid element as a carrier.
Since the hard ferrite has conductivity, it is not preferable in a developing system using an alternating electric field for obtaining a high-quality image in that charge leaks through carriers to disturb development. Therefore, the carrier used in the developing system using the alternating electric field needs to have a certain degree of electrical resistance. As described above, a sufficient developer carrier that satisfies the high image quality, particularly the reproducibility of highlight while preventing the carrier from adhering to the electrostatic latent image carrier has not yet been obtained.

[0009]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a coated carrier which solves the above-mentioned conventional problems. Another object of the present invention is to faithfully adhere to a document while preventing carrier adhesion to an electrostatic latent image carrier, that is,
An object of the present invention is to provide a carrier excellent in high resolution, high highlight reproducibility and high fine line reproducibility by faithfully developing an electrostatic latent image. It is another object of the present invention to provide a carrier that does not leak the latent image potential even in the development of an alternating electric field, and that provides good developed image quality.

[0010]

The above object is achieved by the present invention described below. That is, the present invention provides the following (1) to
(3). (1) A magnetic material-dispersed carrier obtained by dispersing a magnetic material in a binder resin, wherein the magnetic fine particles are (long axis /
(Small axis)> 1 and the magnetic fine particles have a magnetization intensity (σ1000) of 30 to 150 e at a magnetic field of 1,000 Oe after magnetically saturated.
mu / cm ³ , the magnetization intensity (residual magnetization: σr) at a magnetic field of 0 Oe is 25 emu / cm ³ or more;
The coercive force is less than 300 Oersted, the volume average particle size of the carrier is 5 to 100 μm, and the bulk density is 3.0.
g / cm ³ or less, and the content of the magnetic substance is 30 to 99% by weight.

(2) The specific resistance of the carrier is 10 ⁸ to 10
The coated carrier according to (1), which has a resistance of ¹³ Ω · cm.

(3) When the measured electric field is 5,000 V / cm, the coated carrier having a coating layer having a predetermined thickness has a specific resistance of 0.5 μm smaller than the predetermined thickness. The coated carrier according to any one of (1) and (2), which has a specific resistance of at least 1 and at most 10 ⁴ times.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The carrier of the present invention improves the drawbacks of the conventional carrier and prevents the carrier from adhering to the electrostatic latent image carrier, and faithfully reproduces the electrostatic latent image. The reason why development and high image quality can be maintained over a long period of time is considered to be as follows. In order to perform faithful development on a latent image, it is important to reduce the intensity of carrier magnetization in the magnetic field at the development pole. This is because the magnetic strength of the carrier is weak, and the magnetic brush of the carrier is short, dense and soft, so that development faithful to the latent image can be achieved. By making the magnetic brush short, dense, and soft in this way, the developing efficiency is increased particularly in the development in which an alternating electric field that oscillates the developer is applied to the developing section, and high-quality and faithful development can be performed. . Generally, the strength of the magnetic field at the developing pole is about 1,000 Oersted, so the magnetic characteristics of the carrier of the present invention are also the same as the strength of magnetization (σ1,000
), And the value is 30 to 150 emu / cm.
³ , preferably ³⁰ to 150 emu / cm ³ .

Another advantage of the present invention is that deterioration of image quality can be prevented and an initial high-quality image can be maintained because such a carrier having a low magnetic force is used to enclose a fixed magnet. When coating the developer carrier with a two-component developer, the magnetic coupling force between the carriers as a magnetic brush near the regulating member is weak, and the ears are soft, so the toner does not share much. Further, since the resin carrier is lighter in weight than the conventional iron / ferrite-based carrier, the load caused by stirring in the developing device is small, the deterioration of the developer is greatly reduced, and a high-quality image can be maintained for a long time.

Furthermore, carrier adhesion to the electrostatic latent image carrier is likely to occur when the magnetic field strength is 0 to 300 Oe, and does not or hardly occurs when the carrier has a relatively high magnetization strength. In addition, the adhesion of the carrier to the electrostatic latent image carrier is also affected by the bias condition of the development. In particular, in the case of performing the development by the alternating electric field, the carrier shifts to the electrostatic latent image carrier when the carrier has a charge compared to the DC electric field. The magnetic force is required to hold the carrier to the developer carrier. Therefore, in order to suppress the carrier from adhering to the electrostatic latent image carrier, it is necessary to have a certain degree of magnetization in the magnetic field. Generally, a magnetic material having a large remanent magnetization has a large coercive force, and becomes a hard ferrite like a so-called permanent magnet. That is, if a magnetic material having a large residual magnetization is used for the magnetic substance in the carrier, poor mixing with the toner and poor developer transportability due to self-aggregation are likely to occur as described above. A large and special developing device having such a developer carrier is required. The present invention does not use such a general magnetic material such as hard ferrite as a magnetic material in a carrier, but by using magnetic particles having a low coercive force such that the coercive force is less than 300 Oe, Even a small developing device using a fixed magnetic core type developer carrier provides a carrier having good mixing properties with toner and good developer transportability.

The magnetic properties of the carrier particles of the present invention must be as follows. That is, intensity of magnetization in a magnetic field of 1,000 oersted after magnetically saturated (σ1000) is 30~150emu / cm ^3, in order further to achieve a high image quality, 30~100emu / cm ³
It is preferred that When it is larger than 150 emu / cm ^3, the density of the magnetic brush of the carrier at the developing pole is not different from the conventional one, and it is difficult to obtain a high quality image. 30
If it is less than emu / cm ³ , the magnetic binding force will decrease, and carriers will adhere to the electrostatic latent image carrier.

The intensity of the remanent magnetization is 25 emu / cm
^It is necessary to be ³ or more. If it is less than 25 emu / cm ³ , particularly in a developing system using a high contrast potential for high image quality or using an alternating electric field having a large amplitude, carrier adhesion to the electrostatic latent image carrier is likely to occur. In the subsequent transfer process, a high-quality image is hardly obtained because the transfer portion of the carrier causes transfer failure or the like.

Furthermore, it is necessary that the coercive force be less than 300 Oersted. If it is more than 300 Oersteds, the carrier itself will self-aggregate, resulting in poor mixing with the toner. In particular, in the case of a developer carrier containing a fixed magnet, the carrier can easily move on the developer carrier. In addition, the transportability of the developer is deteriorated, and the coating state of the developer on the developer carrier is deteriorated, so that it is difficult to obtain a high-quality image.

Next, the present invention will be described in more detail. The degree of orientation of the magnetic substance dispersed in the binder resin of the carrier of the present invention is defined by the orientation probability of the magnetic substance having shape anisotropy used in the present invention, and is measured by a field emission scanning electron microscope (FE-SEM). S-800 (Hitachi, Ltd.)
Was measured by statistically processing the orientation of the magnetic fine particles on the cross section of the carrier. Specifically, 100 or more magnetically anisotropic magnetic materials used in the present invention are randomly extracted from 10 randomly extracted carrier cross-sectional photographs, and the direction of the magnetic field is considered to be considered. ± 15 °
The ratio of those facing the range of was calculated. The sample of the cross section of the carrier is prepared by dispersing and solidifying the carrier in an epoxy resin in a parallel magnetic field, and then embedding the plastic embedding sample in a microtome FC4E (REICHERT-JUN).
(Company G).

The measurement of the magnetic properties of the carrier in the present invention is performed using a DC magnetization BH characteristic automatic recording apparatus BHH-50 (manufactured by Riken Denshi Co., Ltd.). Generally, the developing pole in the developing device has a magnetic field of 1,000 Oe, and in the present invention, the magnetic characteristics of the carrier create a magnetic field of 10 kOe, and the magnetic field is 1,000, 300 and 0 Oe based on the hysteresis curve of the carrier at that time. Of the carrier (σ1000, σ300, and σr) and the coercive force of the carrier are obtained.

In the present invention, the magnetic properties are measured by loosely placing a sample in a cylindrical plastic container, performing strong packing under a magnetic field of 10 kOe, fixing the sample, and measuring the magnetic properties in that state. . The measured value in this state is used as the magnetic characteristic of the present invention. At this time, the volume of the sample holder was 0.332 cm ³ , and the intensity of magnetization per unit volume was determined from this.

In order to achieve the above-mentioned magnetic characteristics which are the characteristics of the carrier of the present invention, the magnetic material is a metal oxide magnetic material of 1 μm or less, for example, hexagonal ferrite such as Ba ferrite, Sr ferrite and Pb ferrite. Crystalline plate-like magnetic material, or needle-like magnetic material such as γ-Fe2O3-based, Co-based ferrite and acicular magnetite, etc. alone, by mixing these particles with shape anisotropy, or by shape anisotropy And a soft magnetic material such as soft ferrite can be used as a mixture. Examples of the orientation means at this time include kneading or injection molding in a magnetic field, and a method of cooling in a magnetic field after kneading, or a combination thereof.

The content of the magnetic substance with respect to the total amount of the carrier of the present invention is 30% by weight to 99% by weight, preferably 5% by weight.
0% by weight or more. If the content is less than 30% by weight, the above-mentioned desired magnetic properties cannot be obtained as a carrier, and it becomes difficult to control the specific resistance of the carrier. On the other hand, if the content of the magnetic substance exceeds 99% by weight, the adhesiveness between the magnetic substance and the binder resin becomes poor.

Further, by using the carrier of the present invention after being magnetically saturated, it is easy to achieve the characteristic magnetic characteristics of the present invention. As a method of magnetic saturation, there is a method in which carrier particles are exposed to a magnetic field of 10 kOe by a DC electromagnet.

As the binder resin usable in the present invention, an insulating resin having a specific resistance of 10 ¹³ Ωcm or more at 22 ° C. and 55% RH can be suitably used. The method for measuring the specific resistance of the resin will be described later. As the insulating resin used for the purpose of the present invention described above, it is preferable to use a thermosetting resin from the viewpoint of improving the coverage when multiple coating is performed.

It is preferable that the specific resistance of the binder resin is equal to or higher than a predetermined value. Specifically, it is necessary that the binder resin has a resistance of 10 ¹³ Ωcm or more at an electric field intensity of 5 × 10 ⁴ V / m. If the specific resistance is lower than the above range, the leakage of electric charge through the carrier and / or the injection of electric charge are not sufficiently improved, and the dot image is disturbed, so that it is difficult to achieve the object of the present invention such as high image quality and high definition.

The specific resistance of the coated carrier of the present invention is 1
0 it is preferably in the range of ^{8 ~10 13 Ω} · cm. 10
^If it is less than ⁸ Ω · cm, in the developing method in which a bias voltage is applied, current leaks from the developer carrier to the surface of the photoreceptor in the developing area, and it is difficult to obtain a good image. 10 ¹³
If it exceeds Ω · cm, a charge-up phenomenon is caused under conditions such as low humidity, which tends to cause image deterioration such as low density, poor transfer or fog.

The volume average particle size of the coated carrier of the present invention is:
The range is preferably 5 to 100 μm, more preferably 20 to 100 μm.
８０80 μm. If it is smaller than 5 μm, the carrier tends to adhere to the electrostatic latent image carrier. On the other hand, if it exceeds 100 μm, the magnetic brush of the carrier at the developing pole becomes coarse, and it is difficult to obtain a high quality image. In addition, the particle diameter of the carrier of the present invention is extracted at least 300 randomly using an optical microscope, and the image processing and analysis software Image-Pro Plus is used.
The particle diameter of the carrier particles was defined as the horizontal Feret diameter analyzed by s (produced by Planetron Co., Ltd.).

Next, the specific resistance difference between the coated carrier of the present invention and the conventional coated carrier is that the specific resistance of the coated layer is constant in the conventional product, but the specific resistance of the coated layer in the carrier of the present invention is not. The outer surface is designed to be lower. In the conventional product, the specific resistance of the coated carrier aggregate rapidly decreases as the coating layer becomes thinner.
The resistivity of a coated carrier with a μm thin coating layer is several orders of magnitude lower than that of a normal product.

As described above, in the coated carrier of the present invention, since the specific resistance of the coating layer is lower than that of the surface, even if the coating layer is worn and thinned, the specific resistance does not decrease as compared with the conventional product. Then, when the measured electric field is 5,000 V / cm, the specific resistance of the carrier having the coating layer having the predetermined thickness is at least 1 times that of the case having the coating layer having a thickness smaller by 0.5 μm than the film thickness. The specific resistance of the coating layer is preferably adjusted so as to be 1000 times or less, preferably 1 time or more and 100 times or less. The reason for specifying the measurement electric field is that the specific resistance of the high-resistance powder easily depends on the electric field. The coated carrier of the present invention is a method in which the coating layer has a multilayer structure and the type or amount of the resistance adjusting agent in each layer is changed stepwise, or the type or amount of the resistance adjusting agent in a single film is continuously changed during coating. The latter is preferred. In the present invention, a conductive material such as carbon black or a metal oxide is used for the resistance adjusting agent, but the former which is effective in a small amount is preferable. Then, a coating layer may be formed on the carrier surface by a spraying method, an immersion method, or the like, using a coating layer forming liquid in which one or more of the above-described resistance modifiers are dispersed.

As described above, the specific resistance of the coating layer of the coated carrier of the present invention is changed stepwise or continuously. The coating layer is formed such that the resistance is low as a whole.
If the resistance in a single film is to be changed continuously, start coating layer formation using a coating layer forming solution in which a low-efficiency resistance control agent is dispersed, and then adjust the high-concentration resistance during coating layer formation. The coating layer may be formed by gradually adding a liquid containing an agent to the coating layer forming liquid, thereby gradually increasing the resistance adjusting agent concentration in the forming liquid. In this case, the resistance adjusting agent may be used alone or as a mixture of two or more types, or an additive such as a dispersing aid for the resistance adjusting agent may be added.

The various measuring methods used in the present invention are described below. (1) Measurement of Specific Resistance of Carrier A cell is filled with a carrier, two electrodes are arranged in contact with the filled carrier, a voltage is applied between the electrodes, and a current flowing at that time is measured. A method for determining the resistance was used. In the above-mentioned measuring method, since the carrier is a powder, a change occurs in the filling rate, and accordingly, the specific resistance may change. The measurement conditions of the specific resistance in the present invention are as follows: the contact area S between the filled carrier and the electrode.
= About 2.3 cm ² , thickness d = about 1 mm, load on the upper electrode 2 = 180 g, and applied voltage = 100V.

(2) Measurement of Magnetic Characteristics The magnetic characteristic value of the carrier powder is a magnetic field of ± 1 kOe, and a magnetic field of 10 kΩ is obtained from the hysteresis curve at that time.
The magnetization at 00 Gauss was determined. The sample was prepared so that the carrier was packed in a cylindrical plastic container so as to be sufficiently dense. In this state, the magnetization moment is measured, and the magnetization moment per unit volume is determined based on the measurement.

(3) Measurement of triboelectric charge The toner and the carrier of the present invention are mixed so that the weight of the toner becomes 5%, and mixed with a Turbula mixer for 60 seconds. This developer is placed in a metal container equipped with a 500-mesh conductive screen at the bottom, and is suctioned by a suction machine. The amount of frictional charge is calculated based on the difference in weight before and after suction and the potential accumulated in a condenser connected to the container. Ask. At this time, the suction pressure is 250
mmHg. By this method, the triboelectric charge amount is calculated using the following equation. Q (μC / g) = (C × V) × (W1−W2) −1 (where W1 is the weight before suction, W2 is the weight after suction, C is the capacity of the capacitor, and V is This is a potential accumulated in a capacitor.) As a method for producing a carrier of the present invention, the binder resin and the magnetic fine particles are mixed in a desired quantitative ratio, and the mixture is heated and melted by, for example, a three-roll or extruder. Kneading is performed at an appropriate temperature using a kneading apparatus, and the magnetic fine particles are oriented mechanically, magnetically, or a combination thereof during injection molding. After cooling the kneaded material, the particles obtained after pulverizing and classifying the material are collided with a plate at a high speed, and the surface is heat-melted with the energy to perform a spheroidizing treatment.

The magnetic fine particles used in the present invention include: ferromagnetic metals such as iron and cobalt; iron oxides such as magnetite, hematite and ferrite; various alloys and compounds; fine powders of these magnetic materials are dispersed in a binder resin. Resin nucleus particles; Of these, the use of resin core particles is particularly preferable because image quality is improved. The resin core particles are produced by the following method or the like, but are not limited thereto. (1) A thermoplastic resin and a magnetic fine powder are melted and kneaded, then pulverized and classified appropriately. Further spheroidization can be achieved by hot air treatment. (2) After the thermosetting resin and the magnetic fine powder are melted and kneaded, a curing agent is added and the mixture is thermally cured, and the obtained cured product is pulverized and classified. (3) After the binder resin and the magnetic fine powder are melted and kneaded, the kneaded material is cooled and solidified by spraying it into a relatively low-temperature air flow without solidifying the kneaded material. (4) After dissolving the thermosetting resin in the solvent, dispersing the magnetic fine powder, spray-granulating and drying, and further heat-curing to classify. (5) A phenol and an aldehyde are reacted and cured in an aqueous medium in the presence of a magnetic fine powder, a suspension stabilizer, and a base catalyst. That is, it is produced by a reaction method.

[0036]

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples. They do not limit the invention in any way. The percentages and parts in the following formulations are% by weight and parts by weight unless otherwise specified. Toner Production Example 1 Styrene-acrylic resin (CPR300: manufactured by Mitsui Chemicals, Inc.) 85 parts Carbon black (# 44: manufactured by Mitsubishi Chemical Corporation) 8 parts Metal-containing azo dye (S-34: manufactured by Orient Chemical Co., Ltd.) 2 parts Wax ( High Wax NP195: manufactured by Mitsui Chemicals, Inc. 5 parts The mixture of the above formulation is kneaded with a hot roll at 115 ° C., cooled and solidified, and the kneaded material is pulverized and classified by a jet mill to obtain a negatively chargeable toner having an average particle diameter of 8 μm. 1 was obtained.

Toner Production Example 2 Styrene-acrylic resin (CPR100: manufactured by Mitsui Chemicals, Inc.) 85 parts Carbon black (# 44: manufactured by Mitsubishi Kasei Corporation) 8 parts Nigrosine dye (Nigrosine EX: manufactured by Orient Chemical Co., Ltd.) 2 parts Wax ( High Wax NP195: manufactured by Mitsui Chemicals, Inc. 5 parts The mixture having the above formulation is kneaded with a hot roll at 115 ° C., cooled and solidified, and the kneaded material is pulverized and classified with a jet mill to obtain a positively chargeable toner having an average particle diameter of 10 μm. 2 was obtained.

Toner Production Example 3 100 parts by weight of a polyester resin obtained by condensing propoxylated bisphenol and fumaric acid 5 parts by weight of copper phthalocyanine pigment 5 parts by weight of chromium complex salt of di-tert-butylsalicylic acid 4 parts by weight were sufficiently preliminarily mixed. Then, the mixture was melt-kneaded, cooled and coarsely pulverized using a hammer mill to a particle size of about 1 to 2 mm. Next, it was pulverized by a pulverizer using an air jet method.
Further, the obtained finely pulverized product was classified using an elbow jet classifier to obtain a negatively chargeable cyan powder having a weight average particle size of 6.0 μm, and 100 parts by weight of the powder. Silica fine powder hydrophobized with hexamethyldisilazane
7 parts by weight and 0.3 parts by weight of alumina fine powder were mixed by a Henschel mixer to obtain a cyan toner 3.

Example 1 A 3% Zn-doped γ-Fe 2 O 3 (horizontal Feret diameter: major axis = 1.0 μm, minor axis = 0.14 μm) was modified with a silicone-modified epoxy resin [ES-1001N, Shin-Etsu Silicone 6 × 10 ¹⁴ Ω · cm (22 ° C.,
55% RH)] to prepare a 10% by weight carrier coating solution using toluene as a solvent so that the binder resin amount becomes 2% by weight. This coating solution was applied onto the above-mentioned core material using a solvent immersion type coating apparatus. After drying the obtained carrier in a dryer at a temperature of 140 ° C. for 1 hour and curing, the carrier fixed in the dryer was crushed, immediately classified and cooled to obtain coated carrier particles. After cooling the coated carrier thus obtained to room temperature, the above-mentioned binder resin is coated again with 1% by weight of the resin by a solvent immersion type coating device. I got
The particle size of the obtained carrier particles was 41 μm. The cured film obtained under the curing conditions at this time has a Tg of 6
7 ° C.

As a result of measuring the coverage of the obtained carrier particles with the resin by an electron microscope, the carrier particles having a coverage of 90% or more accounted for 94% by number, and the carrier particles having a resin coverage of 95% or more accounted for 94%. It was 65% by number.

When the specific resistance of the carrier particles was measured, it was 5 × 10 ¹⁴ Ω · cm. Further, the amount of the resin coated on the surface of the carrier particles is measured by a thermobalance (TGA-
7: PerkinElmer)
It was 2.8% by weight. Also, as a result of measuring the magnetic characteristics of the carrier particles, the magnetic characteristics at that time were σ1000 =
It was 52 emu / cm ³ (the packing density of the sample was 3.50 g / cm ³ ).

As a result of an image output test in combination with Toner 1, the density of the solid image was as high as 1.50, there was no roughness, and the reproducibility of the halftone portion and the line image portion was good. Further, despite the high speed rotation of the developer carrying member, no carrier was adhered to the electrostatic image portion or the non-electrostatic image portion due to carrier scattering and carrier development. Further, after the developing device was idled at a speed of 200 rpm for 30 minutes, an image output test was performed. As a result, there was no particular problem with the image quality after idling, and no carrier adhesion was observed in both the image area and the non-image area. The magnetic brush ears of the developer carrier were dense, and the solid density, the halftone area, and the reproducibility of the line image area were good.

Example 2 Silicone acrylic resin KR-9706 (manufactured by Shin-Etsu Silicone Co., Ltd.) was added to the carrier core particles used in Example 1 using toluene as a solvent so that the binder resin amount was 2% by weight, and 10% by weight. % Of the carrier coating solution was prepared. This coating solution was coated on a carrier core material in the same manner as in Example 1 to obtain carrier particles. The glass transition point of the binder resin coated with the carrier obtained at this time was 63 ° C. The particle size of the obtained carrier particles was 40 μm. The obtained carrier particles had a coating ratio of 90% with the binder resin of 91 number%, and a resin coating ratio of 9%.
Those with 5% or more were 65% by number. The specific resistance of the carrier particles was 4 × 10 ¹⁴ Ω · cm. Further, the coating amount was 2.5% by weight. Also, σ100
0 = 52 emu / cm ³ (packing density of sample: 3.51 g / cm ³ ).

As a result of an image output test in combination with Toner 1, the density of the solid image was as high as 1.50, there was no roughness, and the reproducibility of the halftone portion and the line image portion was good. Further, despite the high speed rotation of the developer carrying member, no carrier was adhered to the electrostatic image portion or the non-electrostatic image portion due to carrier scattering and carrier development. Further, after the developing device was idled at a speed of 200 rpm for 30 minutes, an image output test was performed. As a result, there was no particular problem with the image quality after idling, and no carrier adhesion was observed in both the image area and the non-image area. The magnetic brush ears of the developer carrier were dense, and the solid density, the halftone area, and the reproducibility of the line image area were good.

Example 3 Silicon alkyd resin KR-5206 (manufactured by Shin-Etsu Silicone Co., Ltd.) was added to the carrier core particles used in Example 1.
To prepare a 10% by weight carrier coating solution using toluene as a solvent so that the binder resin amount becomes 2% by weight. This coating solution was coated in the same manner as in Example 1, cured at 150 ° C. for 1 hour, crushed at 100 ° C., classified and cooled to obtain carrier particles. This step was repeated twice to obtain high coverage carrier particles having a resin coating amount of 3.7% by weight. At this time, the glass transition temperature of the carrier coating resin was less than 30 ° C. The particle size of the obtained carrier particles was 45 μm. Further, 90% or more of the obtained carrier particles have a resin coverage of 90% or more.
Further, those having a coverage of 95% or more were 63 number%. The specific resistance of the carrier particles is 1 × 10 ¹³ Ω · c
m. Further, the coating amount was 3.7% by weight.
Also, σ1000 = 52 emu / cm ³ (packing density of the sample: 3.51 g / cm ³ ).

As a result of an image output test in combination with Toner 2, the density of the solid image was as high as 1.50, there was no roughness, and the reproducibility of the halftone portion and the line image portion was good. Further, despite the high speed rotation of the developer carrying member, no carrier was adhered to the electrostatic image portion or the non-electrostatic image portion due to carrier scattering and carrier development. Further, after the developing device was idled at a speed of 200 rpm for 30 minutes, an image output test was performed. As a result, there was no particular problem with the image quality after idling, and no carrier adhesion was observed in both the image area and the non-image area. The magnetic brush ears of the developer carrier were dense, and the solid density, the halftone area, and the reproducibility of the line image area were good.

Example 4 Coating was carried out in the same manner as in Example 1 except that the crushing temperature was changed to 100 ° C. to obtain carrier particles. The particle size of the obtained carrier particles was 42 μm. The coverage of the obtained carrier particles with the binder resin was 81% when the resin coverage was 90% or more, and 60% when the resin coverage was 95% or more. The specific resistance of the carrier particles is 3
× 10 ¹⁴ Ω · cm. Further, the coating amount was 2.1% by weight. Also, σ1000 = 50 emu / cm ³
(Packing density of sample: 3.36 g / c
m ³ ). The magnetic brush ears of the developer carrier are dense,
Solid part density, reproducibility of halftone part and line image part were also good.

Example 5 Coating was performed in the same manner as in Example 2 except that the crushing temperature was changed to 100 ° C. to obtain carrier particles. The particle size of the obtained carrier particles was 42 μm. The coverage of the obtained carrier particles with the binder resin was 83% by number with a resin coverage of 90% or more, and 61% by number with a coverage of 95% or more. The specific resistance of the carrier particles is 2
× 10 ¹⁴ Ω · cm. Further, the coating amount was 2.3% by weight. Also, σ1000 = 55 emu / cm ³
(Packing density of the sample: 3.36 g / cm ³ ).

The carrier and the toner 2 have a toner concentration of 5.
The mixture was mixed to 8% by weight to obtain a developer. Using this developer, an image was formed under the same developing conditions as in Example 1.
As a result, the supply of the developer on the developing sleeve is sufficient, the density of the solid image is high, there is no dot roughness due to electric charge leakage, the reproducibility of the halftone portion, and the reproducibility of the line image are also improved. It was good. Also, 1
Even after the image durability test of 000 sheets, the toner exhibited good durability without fluctuation in the solid density, generation of fog in the non-image portion, and toner scattering which is considered to be caused by a decrease in the triboelectric charge. .

Example 6 As magnetic fine particles, γ-Fe ₂ O ₃ (horizontal Feret diameter, major axis 0.9 μm, single axis 0.12 μm, average particle diameter 41)
Coating was carried out in the same manner as in Example 1 except that μm) was used. The coverage of the carrier particles with the binder resin was 9%.
98% by number is 0% or more, resin coverage 95%
The above was 73% by number. In addition, the amount was 23%. The specific resistance of the carrier particles is 3 × 10 ¹⁴ Ω · cm.
Met. Further, the coating amount was 3.3% by weight. Σ1000 = 78 emu / cm3 (packing density of sample 2.1 g / cm3).

Comparative Example 1 The magnetic fine particles used in Example 1 were coated with the binder resin used in Example 1 using 5% by weight of a carrier coating solution using toluene as a solvent so that the resin content was 1.5% by weight. Was prepared.
The coating was performed by volatilizing the solvent while continuously applying shear stress to the coating solution. The carrier particles were dried at 150 ° C. for 1 hour, cooled to room temperature, crushed, and classified with a 100-mesh sieve to obtain carrier particles. The particle size of the obtained carrier particles was 42 μm. Further, the obtained carrier particles were further added to the same coating solution by 1.5% by weight.
Was applied. The coverage of the carrier particles with the binder resin is 45% by number when the resin coverage is 90% or more, and 10% by number when the resin coverage is 95% or more. Did not. The specific resistance of the carrier particles was 2 × 10 ⁹ Ω · cm. Further, the coating amount was 3.0% by weight. Also, σ100
0 = 50 emu / cm ³ (packing density of the sample 3.36 g / cm ³ ).

A test was conducted in the same manner as in Example 1 except that the obtained carrier was used. As a result, the supply of the developer on the developing sleeve was sufficient and the density of the solid image was sufficient. As a result, an image was obtained in which the roughness of the dots was severe and the reproducibility of the halftone portion and the reproducibility of the line image were significantly reduced. Further, as the endurance of the actual machine progresses, the toner is scattered due to a reduction in the triboelectric charge amount due to the contamination of the carrier core by the toner having a small particle diameter. High image quality was not achieved.

Comparative Example 2 The magnetic fine particles used in Example 1 were coated with the resin used in Example 1 and a 5% by weight carrier coating solution was prepared using toluene as a solvent so that the resin amount was 1% by weight. This coating solution was coated using a fluid bed type coating device Spira Coater (manufactured by Okada Seiko Co., Ltd.) to obtain carrier particles. The carrier particles were dried in a dryer at 140 ° C. for 1 hour to obtain a carrier. The obtained carrier was cooled to room temperature, crushed and classified, and then the above coating step was repeated three times using the same coating solution to obtain a coated carrier having a resin coating amount of 2.8%. The particle size of the obtained carrier particles is 4
It was 2 μm. Further, the coverage of the obtained carrier particles with the resin was 67% by number when the resin coverage was 90% or more.
The ratio of resin coverage was 95% or more, and 56% by number. The specific resistance of the carrier particles is 2 × 10 ¹⁰ Ω · c
m. Further, the coating amount was 2.9% by weight.
Also, σ1000 = 50 emu / cm ³ (packing density of the sample 3.36 g / cm ³ ). A test was carried out in the same manner as in Example 1 except that the obtained carrier was used. As a result, an image having extremely poor image quality was obtained as in Comparative Example 1, and further, the image quality was significantly reduced due to durability.

Comparative Example 3 Fe ₂ O ₃ 50 mol% ZnO 25 mol% CuO 25 mol% The above materials were weighed and mixed using a ball mill.
The mixed powder was calcined and then pulverized. The pulverized sample was made into a slurry, and the slurry was granulated with a spray drier, and the granulated powder was sintered. The obtained sintered powder was classified by an air classifier to obtain magnetic fine particles having an average particle size of 48 μm. The obtained core material was substantially spherical, and the specific resistance was 5.2 × 10 ⁹ Ω · cm. The same resin as in Example 1 was coated on the core material in the same manner as in Example 1 to obtain a carrier of Comparative Example. When a test similar to that of Example 1 was performed using the carrier described above, no carrier was adhered to the electrostatic image portion or the non-electrostatic image portion. In the above, roughness of the halftone portion and disturbance of the line occurred. In addition, image deterioration after a 30-minute durability test was observed.

[0055]

According to the coated carrier of the present invention, in the developing process in which an alternating electric field is applied and the developer brush contacts the surface of the photoreceptor by improving the resin covering ratio of the carrier, the leakage of the electric charge and the carrier are particularly suppressed. This has the effect of reducing both of the charge injection into the substrate and improving image reproducibility. In addition, by using the carrier having an improved resin coverage according to the present invention, a long-life developer having good durability without toner spent, etc. is provided as a developer together with a small particle size toner. However, it has become possible to provide a carrier having a stable carrier resistance, a high image quality and a high definition, and capable of obtaining a copied image with good dot reproducibility and halftone roughness.

Claims (3)

[Claims] 1. A magnetic material-dispersed carrier obtained by dispersing a magnetic material in a binder resin, wherein a magnetic material having a ratio of (major axis / minor axis)> 1 is used as the magnetic fine particles, and The magnetic fine particles have a magnetization intensity (σ1000) of 30 to 1,000 at a magnetic field of 1,000 Oe after magnetically saturating.
150 emu / cm ³ , the magnetization intensity (residual magnetization: σr) at a magnetic field of 0 Oe is 25 emu / cm ³ or more, the coercive force is less than 300 Oe, and the volume average particle size of the carrier is 5 to 100 μm. , The bulk density is 3.0 g / cm ³ or less, and the content of the magnetic substance is 30.
Coated carrier that is ~ 99% by weight. 2. A carrier having a specific resistance of 10 ⁸ Ω · 10 ¹³ Ω ·
2. The coated carrier according to claim 1, wherein 3. When the measured electric field is 5,000 V / cm, the specific resistance of a coated carrier having a coating layer of a predetermined thickness is as follows:
Claim is less than 10 ⁴ times 1 times the resistivity coated carrier having a 0.5μm small thickness coating of the predetermined thickness of 1
Or the coated carrier according to 2.