JPH06222620A - Electrostatic charge image developing carrier - Google Patents

Abstract

PURPOSE:To provide the carrier with which excellent image quality is obtainable at the stable electrostatic charge quantity even in an initial period and after copying of many sheets by subjecting the carrier to a heat treatment and specifying the amt. of the magnetic powder to be exposed on the carrier surface with respect to the weight of the carrier. CONSTITUTION:The electrostatic residual image developing carrier formed by dispersing the magnetic powder into a binder resin is subjected to the heat treatment and is so formed that the amt. of the magnetic powder exposed on the carrier surface is 10 to 25wt.% of the weight of the carrier. The carrier is obtd. by heat treating the particles which are obtd. by mixing a binder resin and the magnetic powder under heating at a prescribed mixing ratio and pulverizing and classifying the mixture after cooling, the particles which are obtd. by dispersing the magnetic powder into a resin soln. formed by dissolving the binder resin into the solvent and spray drying this soln. or the particles which are obtd. by dispersing the magnetic powder obtd. by a wet process granulation method, such as suspension polymn. method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier used as a developer for developing an electrostatic latent image, and more particularly to a carrier prepared by dispersing magnetic powder in a binder resin.

[0002]

2. Description of the Related Art As a developer used in an electrophotographic copying machine or printer, a two-component developer comprising a toner and a magnetic carrier such as iron powder is known. In the developing method using such a two-component developer,
The magnetic strength between the carrier particles is too high, the ears of the magnetic brush become hard, and problems such as white stripes appear in a black solid image. In addition, since the iron powder carrier has a low volume specific electric resistance of the carrier itself, when the toner concentration in the developer decreases due to continuous use, the charge on the electrostatic latent image carrier escapes through the carrier and the latent image carrier becomes latent. There are problems that the image is disturbed, a defect occurs in the image, and the carrier is attached to the image portion due to the injection of charges from the developing sleeve to the carrier. Further, if a hard carrier such as iron powder adheres to the electrostatic latent image carrier, the surface of the electrostatic latent image carrier may be damaged when the residual toner is removed.

In order to solve such a problem, a binder type carrier has been proposed in which magnetic fine powder is dispersed in a binder resin. The binder-type carrier has a lower magnetization in a magnetic field in a general developing device than a carrier such as iron powder, can form soft ears, and can obtain an excellent image without white lines due to the carrier. have.

However, even with such a binder type carrier, although it exhibits excellent characteristics in the initial state, problems such as toner fog and a decrease in image density occur as the number of copies increases.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances.
An object of the present invention is to provide a carrier that has a stable toner charge amount even after initial copying and after copying a large number of sheets, and that provides excellent image quality.

[0006]

According to the present invention, in a carrier for developing an electrostatic latent image in which magnetic powder is dispersed in a binder resin, the carrier is heat-treated and exposed on the carrier surface. The present invention relates to an electrostatic latent image developing carrier in which the amount of magnetic powder is 10 to 25% by weight based on the weight of the carrier.

The inventors of the present invention have the above-mentioned problems of toner fog during printing and lowering of image density because the charge control agent, which is a component of the toner during printing, adheres to the carrier surface or the carrier itself mixes. It has been found that this is caused by a change in the triboelectrification performance of the carrier due to activation under stress. It has been found that there is a close relationship between the above problem and the surface condition of the carrier, and the above problem can be solved by controlling the amount of magnetic powder exposed on the carrier surface within a predetermined range.

In the carrier of the present invention, the amount of magnetic powder exposed on the carrier surface is 10 to 25 relative to the weight of the carrier.
%, Preferably 15-25% by weight. When the amount of the exposed magnetic powder is less than 10% by weight, the toner charge amount changes largely due to the spent toner components and the mixing stress, and the stability during repeated use is impaired. Also, 25
If it is more than wt%, the stability against environmental changes is impaired.

The carrier of the present invention comprises particles obtained by heating and mixing a binder resin and magnetic powder at a predetermined mixing ratio, cooling and pulverizing and classifying the particles, and magnetic powder in a resin solution prepared by dissolving the binder resin in a solvent. It can be obtained by heat-treating particles obtained by dispersing and spray-drying the solution, or particles obtained by dispersing magnetic powder obtained by a wet granulation method such as suspension polymerization.

As shown in FIG. 1, it is desirable that the heat treatment is carried out by jetting a carrier into an air stream to instantaneously perform heat treatment. As such a heat treatment apparatus, for example, a suffusing system (manufactured by Nippon Pneumatic Mfg. Co., Ltd.) is used. ) And the like can be used, and the heating temperature is preferably about 150 to 350 ° C.

By such heat treatment, the surface condition of the carrier can be modified, and a carrier having excellent durability without desorption of magnetic powder even when repeatedly used can be obtained.

Further, it is preferable to cool the carrier by heating it and then introducing cooling air or cooling a pipe or the like. Such cooling reduces carrier adhesion to carrier walls or carrier aggregation and improves yield.

The flow rate of the heating air stream and the supply rate of the carrier in the heat treatment may be appropriately selected depending on the temperature of the heating air stream, the particle size of the carrier, the specific gravity, the thermal characteristics of the binder resin, and the like.

The exposed amount of magnetic powder of the carrier can be adjusted by appropriately selecting the amount of magnetic powder to be added, the temperature of heat treatment, the number of heat treatments, and the like. That is, in order to reduce the exposure amount of the magnetic powder, the amount of the added magnetic powder may be decreased, the temperature of the heat treatment may be increased, the number of heat treatments may be increased, the suction air speed in the cyclone may be decreased, and the like. The reverse operation may be performed to increase the exposure amount of the magnetic powder. These operations may be appropriately combined so as to obtain the desired magnetic powder exposure amount without impairing the characteristics of the carrier.

The carrier current of the carrier of the present invention is 20
˜150 nA, preferably 30 to 100 nA. When the carrier current is less than 20 nA, the initial charge amount becomes too high, and when it is more than 150 nA, the charge amount becomes low.
The carrier current is measured by setting a predetermined amount of the carrier 20 in the sleeve 21 and applying a voltage from the DC power supply 23 while rotating the sleeve 21 or the magnet roller 22 in the measuring device shown in FIG. Sleeve 21
Is a current value obtained by measuring the current flowing through the carrier 20 and the regulation blade 24 with the ammeter 25.

The binder resin used in the carrier of the present invention is, for example, polystyrene resin or poly (meth) resin.
Acrylic resins, styrene-acrylic copolymer resins, polyolefin resins, polyester resins, epoxy resins and the like can be used.

The magnetic powder used in the carrier of the present invention includes, for example, metals such as iron, nickel and cobalt, these metals and zinc, antimony, aluminum, lead and tin,
Alloys or mixtures with metals such as bismuth, beryllium, manganese, selenium, tungsten, zirconium, vanadium, mixtures with metal oxides such as iron oxide, titanium oxide, magnesium oxide, and ferromagnetic ferrite, magnetite and mixtures thereof. Can be used.

The particle size of these magnetic powders is preferably 5 μm or less, preferably 2 μm or less, and more preferably 0.1 to 1 μm, in terms of uniform dispersion in the binder.

The mixing ratio of the binder resin and the magnetic powder is
The amount of magnetic powder is 100 to 900 parts by weight, preferably 200 to 600 parts by weight, based on 100 parts by weight of the resin. If the blending amount of the magnetic powder is more than 900 parts by weight, the magnetic powder will be made into secondary particles and will not be uniformly dispersed, and the carrier will become brittle. If the amount of the magnetic powder is less than 100 parts by weight, sufficient magnetism cannot be obtained.

The average particle size of the carrier is 20 to 100 μm,
It is preferably 30 to 60 μm. If the average particle size of the carrier is smaller than 20 μm, the carrier is likely to adhere to the electrostatic latent image bearing member, and if it is larger than 100 μm, uneven brushing occurs like a normal iron powder carrier, and a clear image cannot be obtained. .

The carrier of the present invention may contain a dispersant such as carbon black, silica, titania or alumina. By including the dispersant, the uniform dispersibility of the magnetic powder in the binder resin can be improved. The content of the dispersant is preferably 0.01 to 3% by weight based on the carrier.

Next, the heat treatment of the present invention will be specifically described with reference to FIG. As shown in FIG. 1, the high-temperature high-pressure air generated by the hot air generator 1 is injected from the hot air injection nozzle 6 through the introduction pipe 2. On the other hand, the carrier particles (sample) are conveyed from the fixed quantity feeder 4 by a predetermined amount of pressurized air through the introduction pipe 2 ′ and are jetted into the hot air stream from the sample jet nozzle 7 provided around the hot air jet nozzle 6. It In this case, it is preferable that the sample jet nozzle 7 is provided with a predetermined inclination with respect to the hot air jet nozzle 6 so that the jet flow of the sample jet nozzle 7 does not cross the hot air flow.
Further, the number of the sample injection nozzles 7 may be one or more, but in order to improve the dispersibility of the sample in the hot air flow, a plurality of the nozzles facing each other with the predetermined inclination (preferably It is desirable to provide 2 to 3 sample injection nozzles. When using a plurality of sample injection nozzles, carriers are jetted from each sample injection nozzle toward the central part of the hot air stream at the predetermined inclination, and the carrier particles collide with each other at an appropriate force in the central part of the hot air stream. It is preferable to sufficiently disperse the carrier particles in a hot air stream and heat-treat each carrier particle uniformly. The carrier particles thus jetted are brought into contact with the hot air of high temperature instantaneously and uniformly heat-treated.

Next, the heat-treated carrier particles are immediately cooled rapidly by the cold air introduced from the cooling air introduction section 8. Due to such rapid cooling, adhesion to the device wall and aggregation of carrier particles are eliminated, and the yield is improved. The carrier particles are then collected by the cyclone 9 via the inlet tube 2 ",
Collect in the product tank 11. The carrier air after the carrier particles are collected further passes through the bag filter 12 to remove fine powder, and then is discharged into the atmosphere through the blower -13. The cyclone 9 is provided with a cooling jacket 10 to cool carrier particles in the cyclone with cooling water to prevent agglomeration.

[0024]

EXAMPLES Next, specific examples of the present invention will be described, and it will be clarified that the carriers according to the examples of the present invention are excellent by giving comparative examples.

Production Example of Carrier 100 parts by weight of polyester resin (Tufton NE-1110: manufactured by Kao Corporation) and ferrite powder (MFP-2: TD)
K) 500 parts by weight, carbon black (Ketjen Black EC: Lion Yushi Co., Ltd.) 2 parts by weight, and silica (# 200: Nippon Aerosil Co., Ltd.) 1.5 parts by weight, and then melted. The mixture was kneaded, and the kneaded product was cooled and then pulverized and classified to obtain magnetic particles having an average particle diameter of 55 μm. The magnetic particles were heat-treated under the conditions shown in Table 1 below using a suffusing system (manufactured by Nippon Pneumatic Mfg. Co., Ltd.). Table 1 shows the exposure amount of the magnetic powder and the carrier current value of the obtained carrier.

[0026]

[Table 1]

Measurement of exposure amount of magnetic powder The magnetic powder used as a carrier is dissolved in dilute hydrochloric acid and the spectral transmittance is measured using a spectrophotometer. The transmittance is 50% and the magnetic powder is contained in the solution. Obtain a calibration curve with the amount.

A carrier as a sample and dilute hydrochloric acid are weighed and mixed in a glass bottle for 30 minutes to elute the magnetic powder on the surface of the carrier.

This eluate is filtered, the spectral transmittance of the filtrate is measured with a spectrophotometer, the wavelength at which the transmittance is 50% is determined, and the content of magnetic powder in the filtrate is obtained from the calibration curve.

Measurement of Carrier Current The carrier current was measured using the apparatus shown in FIG. The measurement conditions are as follows.

-Distance between regulation blade and sleeve: 0.65 mm-Sleeve rotation speed: 50 rpm-DC power supply voltage: 500 V-Sample amount: 3 g Under the above measurement conditions, the carrier 20 is set in the sleeve 21 and the sleeve 21 is rotated. While DC power supply 23
To apply a voltage. Sleeve 21 to carrier 20
And the current flowing through the ammeter 22 through the regulation blade 24 is measured.

Toner Preparation Component Weight part Styrene-n-butyl methacrylate resin 100 (Softening point: 132 ° C., glass transition temperature: 60 ° C.) Carbon black 8 (MA # 8: manufactured by Mitsubishi Kasei Co., Ltd.) Nigrosine dye 5 (Bontron N-01: manufactured by Orient Chemical Industry Co., Ltd.) The above materials were thoroughly mixed with a ball mill and then kneaded on a three-roll mill heated to 140 ° C. After leaving the kneaded mixture to cool,
It was roughly crushed and then finely crushed with a jet mill. Next, air classification was performed to obtain a toner having an average particle size of 14 μm.

Measurement of Initial Toner Charge Amounts 1 to 6 of the carriers 1 to 6 and the toner obtained by the above toner adjustment were mixed with a toner rotator using a vial rotator.
The developer was adjusted by mixing for 0 minutes, and the toner charge amount was measured under the conditions of 25 ° C. and humidity of 65%. The results are shown in Table 2.

Measurement of Toner Charge Amount when Using Carrier in + Side Deterioration State The evaluation of the + side deterioration state means that the number of contacts between the carriers increases when the toner density decreases during printing durability.
The evaluation is based on the assumption that the carrier is activated and the triboelectricity of the toner is high.

Carriers 1 to 6 were individually put in a polybin and mixed for 3 hours to deteriorate the carrier to the + side. These carriers and the toner obtained by adjusting the above toner were mixed at a toner mixing ratio of 5% by using a vial rotator.
The developer was adjusted by mixing for 0 minutes, and the toner charge amount was measured under the conditions of 25 ° C. and humidity of 65%. The results are shown in Table 2.

Measurement of Toner Charge Amount During Use of Carrier in Degraded Side-Evaluation of deteriorated state means that the charge control agent of the toner adheres (spents) to the carrier during printing to cause triboelectric chargeability to the toner. Is an evaluation that assumes a state in which

To the carriers 1 to 6, 0.01% by weight of the charge control agent (nigrosine dye) used in the toner was attached to deteriorate the carriers to the negative side. These carriers and the toner obtained by adjusting the toner described above are mixed at a toner mixing ratio of 5% for 10 minutes using a vial rotator to adjust the developer, and the toner charge amount is adjusted under the conditions of 25 ° C. and humidity of 65%. Was measured. The results are shown in Table 2.

[0038]

[Table 2]

The developers prepared by using the carriers 1 to 6 were evaluated by actual copying using an electrophotographic copying machine EP-470Z (manufactured by Minolta Camera Co., Ltd.). The results are shown in Table 3.

In the table, the fog is visually evaluated for the toner fog on the white background portion of the image, ◯ means that it is not a practical problem, and x means that the fog is conspicuous and there is a problem as image noise. In the evaluation of the image density (ID), ◯ means that a sufficient image density was obtained, Δ means that the image density is slightly low, and × means that the image density is low and there is a problem in practical use. Show.

[0041]

[Table 3]

The developer using Carriers 1 to 6 obtained a practical charge amount in the initial state, but the developer using Carrier 6 had a high charge amount and an image density of + in the + side deterioration state. It was confirmed to decrease. It was also confirmed that the developer using the carrier 1 has a low charge amount and fog occurs in the negative side deterioration state.

Reference Experimental Example 1 The carrier current value was changed by changing the amount of magnetic powder added to the carrier, the number of heat treatments and the heat treatment temperature, and the relationship between the carrier current value and the initial toner charge amount was investigated.

It is to be noted that each carrier and the toner obtained by the above toner adjustment are mixed for 10 minutes using a vial rotator at a toner mixing ratio of 5% to adjust the developer.
The toner charge amount was measured under the conditions of ° C and 65% humidity, and the conditions of 30 ° C and 85% humidity. The results are shown in Table 4.

[0045]

[Table 4]

(* 1) Toner charge amount 1 (μc / g) is 2
Measured value at 5 ° C and 65% humidity.

(* 2) Toner charge amount 2 (μc / g) is 3
Measured value at 0 ° C and 85% humidity.

An appropriate toner charge amount is 12 to 18 μc / g in a normal environment (25 ° C., humidity 65%), and 10 μc / g or more is required even in a high temperature and high humidity environment (30 ° C., humidity 85%). Is.

Therefore, from the results shown in Table 4, it is necessary that the carrier current value is 20 to 150 nA, preferably 30 to 100 nA.

Reference Experimental Example 2 The relationship between the surface state of the heat-treated carrier and the suction air velocity in the cyclone after the heat treatment was investigated.

With respect to the heat-treated carrier, the cyclone suction air velocity was changed between 5 and 30 m / s, and the magnetic powder exposure amount and the carrier current value were measured. The results are shown in Table 5.

[0052]

[Table 5]

From this result, the suction air velocity is 20 m /
It can be seen that when s is exceeded, the magnetic powder exposure amount of the carrier and the carrier current value increase. It is presumed that this is because the surface of the heat-treated carrier is roughened by collision with the inner wall of the cyclone when it enters the cyclone,
It is considered that when the suction air velocity is high, the energy with which the carrier collides with the inner wall of the cyclone is large, the residence time in the cyclone becomes long, and the surface state of the carrier deteriorates. Further, if the suction air velocity is too low, the carrier transportation amount is limited, so the suction air velocity is required to be about 10 m / s. Therefore, it is considered that the collection air velocity in the cyclone is preferably 10 to 20 m / s.

[0054]

INDUSTRIAL APPLICABILITY The carrier of the present invention has excellent initial charging characteristics and stable charging characteristics upon repeated use.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a heat treatment apparatus.

FIG. 2 is a schematic diagram of a measuring device for measuring a carrier current value.

[Explanation of symbols]

 1 hot air generator 4 fixed quantity feeder 5 carrier particles 6 hot air jet nozzle 7 sample jet nozzle 8 cooling air inlet 9 cyclone 10 cooling jacket

Claims (1)

[Claims] 1. A carrier for electrostatic latent image development comprising magnetic powder dispersed in a binder resin, wherein the carrier is heat-treated, and the amount of magnetic powder exposed on the surface of the carrier is the weight of the carrier. A carrier for developing an electrostatic latent image of 10 to 25% by weight.