JPS619661A - Magnetic powder dispersed type microcarrier - Google Patents

Abstract

PURPOSE:To enhance fluidity in spite of small diameters, and to enable a visible image high in image quality to be formed for a long period by incorporating the mixture of a fluidity enhancing agent and a carrier powder specified in particle diameter contg. a fine magnetic powder dispersed into it in a binder resin with stirring. CONSTITUTION:The stirred mixture of the carrier powder formed by dispersing the fine magnetic powder having an average particle diameter of 10-50mum into the binder resin and the fluidity enhancer are used. Such a carrier is composed of the carrier particles and said enhancer, such as fine inorg. particles attached to the surfaces of the carrier particles, and it is superior in fluidity in spite of small diameter. Accordingly, toner concn. can be raised and its allowance can be enlarged, and high-density visible images can be obtained stably. A magnetic brush is formed delicately and softly, and sharpness and gradation of an image can be improved. When an oscillating electric field system is used, a jumping effect can be ensured and fog can be prevented. Since it is unnecessary to add a fluidity enhancer to the toner, deterioration of toner electrification controllability, and damge of a latent image bearing body, etc., can be prevented, and cleaning performance can be improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for developing an electrostatic latent image or a magnetic latent image formed in electrophotography, electrostatic recording, electrostatic inkiri method, etc. The present invention relates to the carrier used, and more specifically relates to a magnetic material-dispersed microcarrier.

[Technology background]

Generally, in electrophotography or electrostatic recording, in order to develop an electrostatic latent image formed on a latent image carrier made of a photoconductive photoreceptor or a dielectric material, toner, which is a colored fine powder, and a carrier are used. Two-component developers are widely used. This two-component developer uses agitation to cause friction between the toner and carrier to charge the toner to a specific polarity, and uses electrostatic attraction with the electrostatic charges that make up the electrostatic latent image to hold the toner as a latent image. Development is achieved by adhering the toner to the body, and it is relatively easy to control triboelectrification of the toner, and it is also possible to provide the developer with sufficiently high fluidity, making it possible to form sharp visible images. It has characteristics. However, with two-component developers, on the other hand, only the toner is consumed as development progresses, so the mixing ratio of toner to carrier (hereinafter referred to as "
The toner density is called 1. ) is within a certain range, the amount of toner replenishment must be strictly regulated. In other words, if the toner concentration is too low, sufficient image density cannot be obtained in the development process, and if the toner concentration is too high, the contact between the toner and the carrier will be insufficient, resulting in poor toner triboelectric charging control. This makes it difficult to obtain high image quality due to the occurrence of fog, etc., and in the end, the toner density needs to be adjusted within a specific tolerance range from both viewpoints.

By the way, in two-component developers that have been put to practical use in the past, the toner is composed of a group of particles with an average particle size of about 10-10 μm, while the carrier has an average particle size of about 70 μm.
It is composed of particles of ~200 μm. In most of these two-component developers, the average particle size of the carrier is considerably larger than the average particle size of the toner, and the ratio of the total surface area of the carrier to the total surface area of the toner is small, so it is difficult to prevent contact between the two. The toner concentration must be quite low (
On the other hand, from the point of view of image density, it is necessary to increase the toner density, and therefore the permissible 8@ area is narrow and it is difficult to obtain a visible image with stable image quality. have Furthermore, if the average particle size of the carrier is large, when a suitable magnetic brush development method is adopted as the development method, the ears of the magnetic brush formed on the developer transport carrier for transporting the developer will be rough. As a result, the sharpness of the visible image formed due to insufficient paper retention tends to be lowered in gradation.

In order to solve the above-mentioned problems, it is effective to reduce the average particle size of the carrier.
Japanese Patent No. 6134 discloses a small-diameter magnetic brush and image carrier formed by dispersing magnetic fine particles in an insulating resin.

However, such small-diameter gear carriers have a particle size that is not much different from that of toner, and since it is not possible to contain a large amount of magnetic material in the gear carrier particles, it is difficult to make the carrier particles have large magnetic properties. Due to this difficulty, the fluidity of the developer becomes insufficient, and as a result, the effect of reducing the diameter of the carrier cannot be fully realized.

Incidentally, conventionally, in order to improve the fluidity of a two-component developing agent, inorganic fine particles called a fluidizing agent have been added to the toner. However, in order to fully obtain the effect of adding this fluidity improver, it is necessary to add a considerable amount of the fluidity improver to the toner, and therefore, the fluidity improves over a wide range of the toner surface. Enhancing agents began to arrive,
Toner charge control performance deteriorates. Furthermore, since the fluidity improver is a hard inorganic fine particle such as silica, it damages the surface of the supporting member, and as a result, good development can be achieved over a long period of time. There is a problem in that the toner particles become embedded in the scratches formed on the image carrier, making it impossible to reliably clean the image carrier.

[Purpose of the invention]

The present invention has been made against the above background, and has excellent fluidity despite having a small diameter, and is capable of maintaining high charge controllability and IJ-ability of the toner. The object of the present invention is to provide a magnetic material-dispersed microcarrier that can achieve excellent development and form high-quality pJ images with good ladle developability over a long period of time.

[Structure of the invention]

The above object is to provide a magnetic material-dispersed microcarrier, which is formed by stirring and mixing carrier powder with an average particle size of 10 to 50 μm, in which fine magnetic powder is dispersed in a binder resin, and a fluidity improver. achieved by.

The present invention will be explained in detail below.

The magnetic material-dispersed microcarrier of the present invention is composed of a carrier powder and a fluidity improver made of inorganic fine particles that is mixed with the carrier powder and attached to the surface of the carrier particles, and the carrier powder is contained in a binder resin. It is formed by dispersing magnetic fine powder and further containing other additive components such as a coloring agent and a special electric control agent as necessary, and has an average particle size of 10 to 50 μm, preferably 15 to 4 μm.
The range is 0 μm.

Here, the mixing ratio of the fluidity improver to the carrier powder is 0.01 to 2% by weight, preferably 0.1 to 1% by weight.
% by weight. The mixing ratio of fluidity improver is 00
If it is less than 1% by weight, the fluidity of the carrier will be insufficient, and if it exceeds 2% by weight, the charge controllability of the carrier will tend to be impaired.

As a method for producing the carrier powder constituting the carrier of the present invention, conventionally known general toner manufacturing methods can be applied as is. That is, for example, a binder resin, a magnetic fine powder, a fluidity improver, and other additives added as necessary are premixed using a ball mill or the like and uniformly dispersed, and then kneaded using a heated roll. After that, it is cooled, pulverized, and classified if necessary.

As the binder resin in the present invention, various thermoplastic resins can be used, including addition type resins such as styrene resin, styrene-acrylic resin, styrene-butadiene resin, and acrylic resin, polyester resin,
Examples include condensation polymerization resins such as polyamide resins, and epoxy resins.

Among these resins, monomers for forming addition polymerization type resins include styrene, 0-methylstyrene, m-methylstyrene, p-7-methylstyrene, α-methylstyrene, p-ethylstyrene, 2.4- dimethylstyrene, p
-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p- Methoxystyrene.

p-Phenylstyrene, p-10 Rustyrene, 3.4-
Styrenes such as dichlorostyrene; ethylenically unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl fluoride; vinyl acetate, propionic acid Vinyl esters such as vinyl, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, ra2-chloroethyl acrylate, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, methacrylate Isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylamine ethyl methacrylate, diethylaminoethyl methacrylate α-methylene aliphatic monocarboxylic acid esters such as; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; vinyl methyl ketone, vinyl Vinyl ketones such as hexyl ketone and methyl isopropenyl ketone; N-vinylpyrrole, N-vinylcarbazole,
N such as N-vinylindole and N-vinylpyrrolidone
-Vinyl compounds; monoolefin monomers such as vinylnaphthalenes; diolefin monomers such as propadiene, butadiene, isoprene, chlorobrene, pentadiene, and hexadiene. These monomers can be used alone or in combination of two or more.

1. Monomers for forming the condensation polymerization resin include ethylene glycol, triethylene glycol, 1.
．． 2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butynediol, 1,4-bis(hydroxymethyl)cyclohexane, bisphenol A1 hydrogenated bisphenol A , polyhydric alcohols such as polyoxyethylenated bisphenol A and polyoxypropylenated bisphenol A, polyhydric amines such as ethylenediamine, tetramethylenediamine, pentamethylenediamine, piperazine, hexamethylenediamine, and maleic acid, fumaric acid, and mesacone. acids, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, cehatic acid, malonic acid, or esters of these with acid anhydrides or lower alcohols, riluin Examples include polyhydric carboxylic acids such as acid dimers.

The magnetic materials constituting the magnetic fine powder in the present invention include substances that are extremely strongly magnetized in the direction of a magnetic field;
For example, metals such as iron, cobalt, nickel, iron including ferrite, magnetite, hematite, etc.
Alloys or compounds that contain ferromagnetic elements such as cobalt and nickel, or alloys that do not contain ferromagnetic elements but become ferromagnetic through appropriate heat treatment;
For example, alloys called Heusler alloys containing manganese and copper, such as manganese-copper-aluminum or manganese-copper-tin, or chromium dioxide can be used.

It is desirable that the magnetic fine powder has an average particle size of about 0.05 to 3 μm. In addition, the usage ratio of magnetic fine powder is
30-80% by weight relative to the carrier, preferably 50-7%
It is desirable to have 5 layers of leaves.

Examples of the material of the inorganic fine particles constituting the fluidity improver in the present invention include silicon dioxide (silica), aluminum oxide (alumina), and titanium oxide (titania), which have a unit particle size of 1 to 50 mμ. It is said to be a fine particle in the midsummer range.

Specific examples of commercial products of the above-mentioned exemplified compounds are as follows.

Silicon dioxide: [3oJ, r2ooJ, r3
ooJ.

r380J, [0X5oj, rTT600J,
rMOX80J.

rMOX17oJ, rcOKs4J, rR-972
J (all manufactured by Nippon Aerosil Co., Ltd.) Aluminum oxide: [Aluminum oxide CJ (
Titanium oxide = [Titanium oxide P25J (manufactured by Nippon Aerosil Co., Ltd.) In the present invention, additives such as a coloring agent and a charge control agent may be included as necessary.

Such colorants include carbon black, aniline blue (C, I, 150405), calco oil blue (
C, I, l'4azoec Blue 3), Chrome Yellow (C, I, ff114090), Ultramarine Blue (C, I.

77103), DuPont Oil Red (C, I, 26105), Quinoline Yellow (C, I, l'!x
47005), methylene blue chloride (C,I,
52015), phthalocyanine blue (C, I, l
'474160), malachite green off-salate (C9Ii 42000), lamp black ((,I
77266 ), Rose Bengal (C, I, %45
435), mixtures thereof, and others.

Further, as the charge control agent, for example,
B'ettschwarz HBN (B'ettsc
hwarz H,BN: CII) N[L2615
0), alcohol-soluble nigrosine (Nigros
in: C, I, 7% 50415), Sudan Chief Schwarz BB (Sudantiefschwarz
BB: Solvent black 3: C, I.

7426150), Brilliant Spirit Schwarz TN
TN: 7 Alpen, Fapriken, Bahia)
, Zaponschwarz X
Ceres Schwarz (R) G (Ceresscbw) with negative triboelectric charging
arz (R・) G: Falpen, Favriken,
Bahia 11), Cromorgenschwarz ETOO (Ch
romogen schwarz ETOO: C,
1, N1114645), Azo oil blank (5F1
) (Azo-Oi 1-Black (R): National, manufactured by Aniline), Spin Black TR, H (
Dyes such as Hodogaya Chemical Co., Ltd.), Bontron 534 (Orient Chemical Co., Ltd.) and pigments such as phthalocyanine blue can be praised. Further, oxidized carbon black and resins having positive or negative charge control groups can be considered as a type of charge control agent.

Further, in order to improve the compatibility of these charge control agents with the resin component, they can be added in the form of salts formed with higher fatty acids, or a compatibility improver can be added separately.

The toner to be mixed with the carrier of the present invention to form the developer is not particularly limited, and any known toner can be used, but the toner has an average particle size of 20 μm or less, preferably 8 to 12 μm.
In this case, a fluidity improver as described above is added to the toner,
It is preferable that the content is 0.01 to 5% by weight.

The two-component developer composed of the carrier and toner of the present invention can be used in conventional dry developing methods such as the cascade method, bristle brush method, and magnetic brush method, and is particularly suitable for the magnetic plan method. Can be used.

Next, a method of applying an oscillating electric field to the developer layer on the developer transporting carrier surface, which is suitable for developing an electrostatic latent image using a two-component developer constituted by the carrier of the present invention, is described. The brush development method will be described. The developer transport carrier for supplying the developer to the developing space can be the same as the conventional one to which a bias voltage can be applied. A structure in which a rotating magnet body having & number of magnetic poles is provided can be preferably used. In such a developer transport carrier, the rotation of the rotating magnet causes the developer layer supported on the surface of the sleeve to move in an undulating manner, so that new developer is supplied one after another. Even if there is some degree of non-uniformity in the thickness of the developer layer on the sleeve surface, the effect of this should be sufficiently covered by the above-mentioned wavy undulations so that it does not become a problem in practice. First, it is preferable that the developer conveying speed due to the rotation of the rotating magnet or the rotation of the sleeve is almost the same as or faster than the moving speed of the electrostatic image carrier. Further, it is preferable that the rotation of the rotating magnet and the rotation of the sleeve are carried in the same direction.

Image reproducibility is better in the same direction than in the opposite direction. However, it is not limited to these.

In addition, it is preferable that the developer layer supported on the developer transport carrier has a uniform thickness. It is preferable to scrape it off to form a uniform layer. The gap between the developer transport carrier and the electrostatic image carrier is expressed by the number 1.
0 to 2000 μm is preferable. If the gap between the developer transport carrier and the electrostatic image carrier becomes narrower than several tens of microns, it will be difficult to form magnetic brush ears that will develop uniformly in the developing space. It is no longer possible to supply toner particles from a large tank to the developing space, making it difficult to perform stable development.
When zm is greatly exceeded, the weight of the counter electrode becomes too low, making it difficult to obtain a sufficient image density, and toner sticking to the contours of the electrostatic charge field increases more than the center of the electrostatic charge field. The edge effect and effect also depend on the dog.

Also, does the gap and the thickness of the developer cause the magnetic brush ear to remain static under conditions where the oscillating electric field is not evenly distributed? It is particularly preferable to set the conditions so that the surface of the image carrier does not come into contact with the surface of the image carrier and is as close as possible to the surface of the image carrier. This is because the toner f9 is prevented from being swept by the magnetic brush and from being fogged.

Preferably, the oscillating electric field is created by applying an oscillating bias voltage to the sleeve of the developer transport carrier. Further, as the bias voltage, it is preferable to use a voltage that is a combination of a DC voltage that prevents toner particles from adhering to non-image areas and an AC voltage that makes it easier for the toner particles to separate from the carrier particles. However, the present invention is not limited to these methods.

An example of a specific apparatus that can be used to carry out the above-described development process is shown in FIG. In Figure 1, 1
1 is a drum-shaped electrostatic charge image carrier made of a photoreceptor such as Se, which rotates in the direction of the arrow, and an electrostatic charge image is formed on its surface by a charging photosensitive device (not shown). 2 is a sleeve made of a non-magnetic material such as aluminum; 3 is a magnet body provided inside the sleeve 2 and having a plurality of N and S magnetic poles along the circumference; the sleeve 2 and the magnet body 3 form a developer transport carrier; is configured. These sleeve 2 and magnet body 3 are relatively rotatable, and in the illustrated example, sleeve 2 is rotated in the direction of the arrow, and magnet body 3 is fixed. N of magnet body 3,
The eight magnetic poles are normally magnetized to a magnetic flux density of 500 to 1,500 Gauss, and the magnetic force forms a layer of developer material, ie, a magnetic brush, consisting of brush-like spikes on the surface of the sleeve 20. 4 is a regulating blade made of magnetic or non-magnetic material that regulates the height and amount of the magnetic brush; 5 is a cleaning blade that removes the magnetic brush that has passed through the developing space A from above the sleeve 2; Since the surface of the sleeve 2 comes into contact with the developer reservoir in the developer reservoir 6, the developer reservoir is thereby supplied.
This is a stirring screw that stirs the developer mixture to make the components uniform.

Since toner particles in the developer reservoir 6 are consumed when development is performed, toner particles T in the toner hopper 8 are replenished as appropriate. 9 is a toner particle T in the developer reservoir 6
It is a supply roller that has a recessed part on the surface where it drops. A bias power source 10 applies a bias voltage to the sleeve 2 via a protective resistor 11, and is applied between the base 1a of the special holiday 1 and the sleeve 2. As this bias voltage, for example, a weight voltage of a DC voltage and an AC voltage is used.The DC component prevents fogging, and the AC component vibrates the magnetic brush to improve the developing effect. This DC voltage component usually has a voltage approximately equal to or higher than the non-direct voltage component, for example, 50 to 6
00■ voltage is used, and the AC voltage component has a frequency of 1
00Hz~10K]-1z, preferably 1~5K
Voltages from 100v to 10KV in Hz are used. In addition,
The DC voltage component may be lower than the non-direct potential when the toner particles contain a magnetic material. If the frequency of the AC voltage component is too low, the effect of imparting vibration will be reduced by 74%, and if it is too high, the developer will not be able to follow the vibrations of the electric field, resulting in a decrease in image density, making it impossible to obtain a clear, high-quality image. This tendency appears. Also, the voltage of the AC voltage component is
Although it is related to the frequency, the higher the frequency, the more the magnetic brush is vibrated and the more effective it is, but if the frequency is too high, fogging is likely to occur and dielectric breakdown such as that caused by lightning strikes is also likely to occur, which is undesirable.

In the above-described apparatus, the gap between the sleeve 2 and the electrostatic image carrier 1 is set to be in the range of several tens to 2000 μm, so that the electrostatic image on the electrostatic image carrier 1 can be seen. When this is done, the magnetic brush formed on the surface of the sleeve 20 will move on the sleeve 2 while vibrating because the magnetic flux density on the surface changes as the sleeve 20 rotates, thereby causing the electrostatic image carrier to 1 stably and smoothly, and at this time imparts a uniform developing effect to the surface of the electrostatic image carrier 10, making it possible to stably develop a high image density.

Furthermore, for example, if several electrode wires are stretched around the development area between the developer transporting member and the electrostatic image carrier and a vibrating voltage is applied to them, the magnetic brush will not be vibrated. The developing effect can be improved. In that case as well, a direct current bias voltage may be applied to the developer transport carrier, or oscillating voltages of different frequencies may be applied.

Further, the above-described method can be similarly applied to reversal development and the like. In that case, the DC voltage component is set to a voltage approximately equal to the receiving potential in the non-image background portion of the electrostatic image carrier. Furthermore, the above-described method can also be applied when the image to be developed is a magnetic latent image.

〔Effect of the invention〕

The carrier of the present invention has the following effects.

(1) Since the carrier of the present invention is formed by stirring and mixing a fluidity improver with carrier powder, it has excellent fluidity even if the carrier particles have a small diameter.

As a result, the effects of using a small-diameter carrier, i.e., (a) high toner concentration and wide tolerable range, making it possible to stably obtain visible images with high image density; and (b) magnetic brush development method. In the development process, the magnetic brush ears become suitably delicate and flexible, ensuring the advantages of being able to obtain highly reproducible visible images with good sharpness and gradation. It becomes possible to set 2.

In particular, in the magnetic brush development method that uses a method of applying an oscillating electric field to the development space, the carrier has good fluidity as described above, so that the particles constituting the developer behave as unit particles. As a result, it is possible to reliably obtain the jumping effect due to the oscillating electric field, and it is possible to achieve fog-free development with good dust repellency.

(2) Since the carrier of the present invention contains a fluidity improver, it can have sufficient fluidity as a developer, and therefore, it is not necessary to include a fluidity improver in the toner at all. Or even if it is needed, it can be in small amounts. As a result, there are negative effects that occur when toner contains a large amount of fluidity improver, such as (a) deterioration of toner charge controllability due to the fluidity improver adhering over a wide range of the toner surface;
b) Damage to the latent image carrier due to the fluidity improver adhering to the toner surface can be avoided, and development and cleaning of the latent image carrier can be satisfactorily achieved over a long period of time.

〔Example〕

Examples of the present invention will be described below, but the present invention is not limited thereto. Note that "parts" represent parts by weight.

Example 1 Polyester resin [Dialec MB/5CJ (manufactured by Diamond Jamrock Co., Ltd.) 100 parts Magnetite r EPT-1000J (manufactured by Toda Kogyo Co., Ltd.) 185 parts or more of substances were mixed in a ball mill, further kneaded with two rolls, and then ground. It was classified to obtain carrier powder with an average particle size of 25 μm. Then add 0.0% to this carrier powder.
Hydrophobic silica fine powder corresponding to 4% by weight [-972J
(manufactured by Nippon Aerosil Co., Ltd.) was added and stirred to obtain a carrier of the present invention. This will be referred to as "Career 1."

Example 2 Addition ratio of hydrophobic silica fine powder in Example 1: 0.4
A carrier of the present invention was obtained in the same manner as in Example 1 except that the amount was 0.2% by weight. This is called [career illusion].

Comparative Example 1 "Yaria" was obtained in the same manner as in Example 1 except that the hydrophobic silica fine powder in Example 1 was not added.
Comparison carrier l'.

<Manufacture of toner> 1) Toner a Styrene-n-butyl methacrylate copolymer (1#
Mass composition ratio 70:30) 100 parts carbon black "#30" (manufactured by Mitsubishi Kasei Corporation) 15 parts After kneading with this roll, the mixture was crushed and classified to obtain a non-magnetic toner powder with an average particle size of 12 μm. Then, to this toner powder, hydrophobic silica fine powder [11,-972J'' corresponding to 0.2% by weight of
' (manufactured by Nippon Aerosil Co., Ltd.) was added and mixed to obtain a toner. This is referred to as "toner a".

2) Toner b Addition ratio of hydrophobic silica fine powder in toner a: 0.2
A toner was obtained in the same manner as Toner A except that the weight % was changed to 0.4 weight %. This is called ``Toner Tsukasa.''

3) Toner C Addition ratio of hydrophobic silica fine powder in toner a: 0.2
A toner was obtained in the same manner as toner a except that the weight % was changed to 0.6 weight %. This is referred to as "toner C". ” <Live-action test> Live-action test 1 A developer was prepared by mixing each of the above carriers and each toner at a weight ratio of 85:15 in the combinations shown in Table 1. Electrophotographic copying machine 1'-U-Bix 1200j that adopts the law
(manufactured by Konishi Roku Photo Industry Co., Ltd.) was used for actual copying tests, and the image density and cleaning resistance of the resulting copied images were determined. In other words, cleaning failures of the electrostatic image carrier occurred during continuous copying tests. I checked the number of copies.

The results are listed in Table 1. Furthermore, an electrophotographic copying machine [U
- In the modified Bix 1200 J, the shortest distance between the electrostatic image carrier and the sleeve is 0.70 m,
The distance between the regulating blade and the sleeve for regulating the height of the magnetic brush is 055 mm.

1st front length copying test 2 The r used in the actual copying test 1 as an electrophotographic copying machine
The u-Bix 120 oJ modified machine was further modified, and (a) the distance between the regulating blade and the sleeve was set to 0.30+nm to keep the developer layer and the static image carrier in a non-contact state;
(o) A direct current of 1250 cm between the electrostatic image summation member and the sleeve [a, field and 800 V, 1.5 K) f
The photo test was carried out in the same manner as photo test 1, except that a modified rlJ-Bix1200j machine was used to apply an alternating current electric field of The number of cleaning cycles was determined. The results are shown in Table 2.

Table 2 From the results in Table 1 and Table 2, it can be seen that the developer using the carrier of the present invention has ii! II image density was excellent, and no cleaning defects occurred even after 30,000 continuous copies. On the other hand, in the developer using the comparative carrier, one image is insufficient because it does not contain the carrier or the fluidity improver, and a large amount of the fluidity improver is added to improve the fluidity of the developer. It has been found that the use of toners containing such materials causes cleaning failures very quickly.

[Brief explanation of drawings]

FIG. 1 is an explanatory sectional view schematically showing an example of a group of developing devices that can be used to perform a developing process using a developer using a carrier of the present invention. 1... Electrostatic charge image summation shield 2... Sleeve 3..., magnet body 4... Regulation blade 5... Cleaning blade

Claims (1)

[Claims] 1) A magnetic substance-dispersed microcarrier comprising a carrier powder having an average particle size of 10 to 50 μm, in which fine magnetic powder is dispersed in a binder resin, and a fluidity improver.