JPH0619208A - Electrostatic charge image developing carrier and production thereof - Google Patents

Abstract

PURPOSE:To produce an electrostatic charge image developing carrier excellent in charge maintainability, capable of preventing its deposition on a picture, capable of easily obtaining a high-quality picture uniform in density and free from stain and with the consumption remarkably reduced. CONSTITUTION:Nuclide grains having <=60mum average grain diameter, >=6.0 true density and >=60emu/g magnetic susceptibility at 1kOe and 3.0wt.%, based on the grain, of a coating resin are mixed in a dry state, the mixture is heated to melt the resin, hence the grain is coated with the resin, and an electrostatic charge image developing carrier is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic charge image developing carrier used for developing an electrostatic latent image formed by an electrophotographic method, an electrostatic recording method or the like with a two-component developer, and a method for producing the same. Regarding

[0002]

2. Description of the Related Art A method of visualizing image information through an electrostatic latent image such as electrophotography is currently used in various fields. In the electrophotographic method, an electrostatic latent image is formed on a photosensitive member by a charging and exposing process, the electrostatic latent image is developed with a developer containing toner, and then transferred and fixed to be visualized. The developer used here includes a two-component developer composed of a toner and a carrier and a one-component developer such as a magnetic toner which is used alone as a toner. In the two-component developer, the carrier is a developer. It is widely used at the present time because it has functions such as good controllability because it is divided into functions such as stirring, carrying, and charging and is separated as a developer. In particular,
A developer using a resin-coated carrier has excellent charge controllability, and is relatively easy to improve in environmental dependency and stability over time. Further, as a developing method, a cascade method or the like has been used in the old days, but at present, a magnetic brush method using a magnetic roll as a developer conveying unit is mainly used.

In the magnetic brush method using a two-component developer,
There are problems such as a decrease in image density due to charge deterioration of the developer, a remarkable stain on the background portion, image roughness and carrier consumption due to carrier adhesion to the image, and further uneven image density. The mechanism of carrier attachment to the image is
When the carrier resistance decreases, the induced charge is injected into the image area to attach the carrier, or the upper limit control of the charge amount of the carrier is insufficient, and the charge amount of the carrier after development becomes excessive. It is considered that the carrier adheres to the edge portion. Further, in recent years, in the two-component developer, the diameter of the carrier is becoming smaller for the purpose of improving the image quality, and of course, the diameter of the ferrite core is made smaller, and further the magnetic material is kneaded and dispersed in the resin, and then pulverized and classified. There is a tendency to use a small diameter carrier having a diameter of 20 to 60 microns. However, when the diameter of the carrier is reduced, carrier adhesion becomes a serious problem. In order to avoid this, it is necessary to more precisely control the chargeability of the carrier. Further, in the case of the above magnetic substance-dispersed carrier, the exposure of the magnetic substance to the carrier surface or the detachment of the magnetic substance is unavoidable at the time of pulverization, and the occurrence of scratches on the photoconductor, the generation of black spots, and the environmental fluctuation of the charging property may occur. It becomes a problem.

[0004]

Therefore, the present invention is intended to solve the above problems and provide a carrier for developing an electrostatic image having the following features and a method for producing the same. Prevents carrier adhesion to ensure stable high image quality, suppresses carrier consumption, prevents damage to the photoconductor and black spots, improves image quality maintenance due to changes in charging due to environmental changes, black solid And excellent reproducibility of fine lines, efficient production of carriers for electrostatic image development.

[0005]

The present invention provides a core particle having an average particle size of 60 microns or less and a true density of 6.0 or more and 1K.
A carrier for electrostatic charge image development, characterized in that a magnetic material having a magnetic susceptibility of 60 emu / g or more in Oe is used, and the surface of the magnetic material is coated with a resin in an amount of more than 3.0% by weight, and
After mixing the core particles and the coating resin in a dry state, the core resin is heated to melt the coating resin, and the core particles are coated. .

[0006]

In order to prevent the carrier adhesion to the small-diameter carrier, it is important to control the charging property to a lower level to prevent the excessive charge of the carrier at the time of development and suppress the electrostatic attraction force to the photoconductor. However, it is not easy to achieve compatibility with charge retention. In order to suppress the above-mentioned attraction force, it is necessary to increase the carrier magnetic force which is the drag force, but the increase of the carrier magnetic force tends to be more disadvantageous due to the smaller diameter. In order to increase the magnetic force per carrier with a small diameter, it is effective to increase the magnetic force of the magnetic substance and increase the true density. However, in a normal ferrite magnetic material, the true density is about 4.0 to 5.0, and the magnetic susceptibility is insufficient at around 40 to 50 emu / g at 1 KOe. Further, the carrier in which magnetic powder such as magnetite is dispersed in the resin has the effects of high charge retention and high image quality due to the small diameter carrier, but when the loading amount of magnetite is about 80% by weight. It becomes the upper limit, carrier adhesion,
There is a problem that comet is generated due to the release of the fine magnetic powder. On the other hand, the carrier that coats the ferrite core particles does not have the problem of releasing the fine magnetic powder even if the diameter is reduced, but the magnetic force of the carrier is small and the specific gravity is also light, so that the carrier does not adhere to the photoreceptor. It cannot be avoided, and good image quality cannot be obtained.

However, the use of a magnetic material having a small diameter, high density, and high magnetic susceptibility as in the present invention can solve the above problems, but a magnetic material having such physical properties can be used in iron powder or alloy powder. However, when these magnetic materials are used, if the uniformity of the coating is not maintained, the resistance will be lowered with time and the photoreceptor will be damaged. In order to solve this problem, the amount of coating resin should be increased significantly, but in the past, there was a limit to coating iron powder with a high amount of resin, and in ordinary fluidized beds, the amount of coating resin was 2% by weight. The degree was the limit. However, according to the method for producing a carrier of the present invention, the restriction on the amount of coating resin is greatly relaxed, and it becomes possible to coat small-sized iron powder etc. with a resin amount exceeding 3.0% by weight. In this way, high density in the center of the carrier,
A magnetic material with a high magnetic susceptibility is arranged, and its surface can be completely covered with resin to avoid the problem of a decrease in resistance value and the problem of scratches on the photoconductor, and the magnetic material dispersion type Secondary problems caused by magnetic powder or free magnetic powder on the surface of the carrier, which are seen in the carrier, are also prevented, and the problem of carrier adhesion is solved. Furthermore, since the resin is completely thickly coated, the influence on the chargeability of the core particles can be neglected, and the chargeability can be easily controlled by blending the coating resin.

Examples of the core particles used in the present invention include, in addition to ordinary iron powder and iron oxide powder, metals such as nickel, steel, zinc, cobalt, manganese, chromium and rare earths, and alloys thereof. The average particle size is usually 20 to 6
It is possible to use one having a thickness of about 0 μm. If it exceeds 60 μm, it is difficult to achieve both a line image and a solid black image, and it is difficult to obtain high image quality. Also, the true density is below 6.0, and 1K
When the magnetic susceptibility at Oe is less than 60 emu / g,
Even with a high coating resin amount exceeding 3.0% by weight, a sufficient effect cannot be obtained for carrier adhesion. Also, when the resin coating amount is 3.0% by weight or less, dielectric breakdown may occur due to the small coating amount. Therefore, 3.
A coating amount of more than 0% by weight is necessary, but 3.2% by weight or more is particularly preferable from the viewpoint of maintainability and durability.

The coating resin used in the present invention includes vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene, trifluoroethylene, and other vinyl-based fluorine-containing monomer copolymers; styrene, chlorostyrene, Styrenes such as methyl styrene; α-methylene aliphatic monocarboxylic acids such as methyl methacrylate, methyl acrylate, propyl acrylate, lauryl acrylate, methacrylic acid, acrylic acid, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate; dimethyl Nitrogen-containing acrylics such as aminoethylmethacrylate; Nitriles such as acrylonitrile and methacrylonitrile; 2-vinylpyridine, 4-vinylpyridine, etc. Nyl pyridines; vinyl ethers; vinyl ketones; olefins such as ethylene, propylene and butadiene; homopolymers or copolymers of silicons such as methyl silicon and methyl phenyl silicon can be used, and further bisphenol, glycol, etc. Polyesters containing can also be used. It is also possible to mix two or more of the above-mentioned combination resins to form a coating composition for positively and negatively charged toner. The coating amount of the coating resin is more than 3% by weight with respect to the carrier,
A range of about 20% by weight, preferably 3.2 to 10.0% by weight is suitable for simultaneously satisfying image quality, secondary obstacles, charging properties and the like.

The carrier for developing an electrostatic image of the present invention can be produced by the method described in detail in the Japanese Patent Application No. 3-29816 application previously proposed by the present inventors. The resin is mixed with the resin in a dry state and then heated to melt the resin for coating and coat the core particles. For example, under a condition of applying a high shearing force or a condition of simply stirring, while magnetically mixing the magnetic core particles and at least the coating resin fine particles in a dry manner, after heating the softening point of the coating resin or higher, A carrier for developing an electrostatic charge image can be manufactured by mixing and cooling to the following temperatures. For manufacturing the above carrier, a heating type kneader, a heating type Henschel mixer,
A UM mixer, a planetary mixer or the like can be used.

The carrier of the present invention is mixed with a toner to prepare a toner.
Used as a component developer. The toner is a binder resin in which a colorant or the like is dispersed. Examples of the binder resin used in the toner include styrenes such as styrene, parachlorostyrene, and α-methylstyrene; methyl acrylate, ethyl acrylate. , N-propyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate,
Α-methylene aliphatic monocarboxylic acid esters such as lauryl methacrylate and 2-ethylhexyl methacrylate;
Vinyl nitriles such as acrylonitrile and methacrylonitrile; vinyl pyridines such as 2-vinyl pyridine and 4-vinyl pyridine; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc. Vinyl ketones; polymers of monomers such as unsaturated hydrocarbons such as ethylene, propylene, isoprene, butadiene and halogenides thereof, halogenated unsaturated hydrocarbons such as chloroprene, or
Copolymers obtained by combining two or more of these monomers, and mixtures thereof, and further rosin-modified phenol formalin resin, epoxy resin, polyester resin, polyurethane resin, polyamide resin, cellulose resin, polyether resin, etc. Examples of the non-vinyl-condensed resin, or a mixture of these with the vinyl-based resin.

The colorant used in the toner may be carbon black, nigrosine dye, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue, or a mixture thereof. As the toner component other than the colorant, a salicylic acid metal salt, a metal-containing azo compound, nigrosine, a charge control agent such as quaternary ammonium salt, low molecular weight polypropylene, low molecular weight polyethylene,
Known components such as an anti-offset agent such as wax and a fluidity improver can be added, and among them, a low molecular weight polypropylene having a weight average molecular weight of 500 to 5000 is particularly effective. In addition, you may contain a magnetic substance fine powder as needed. The toner is manufactured by blending the above toner materials and mixing them using a Banbury mixer, a kneader coder, a CM mixer, an extruder, etc., melt kneading, and pulverizing and classifying to obtain an average particle size of about 30 μm or less, particularly It is preferable that the particle size is 3 to 20 μm.
Furthermore, silica, titania, fluidizing agents such as alumina, polystyrene fine particles, polymethylmethacrylate fine particles,
External additives such as cleaning aids such as polyvinylidene fluoride fine particles or transfer aids can be used, and among them, hydrophobic silica having a primary particle size of 5 to 30 nm is particularly effective.

[0013]

EXAMPLES The present invention will be described in more detail below with reference to examples. However, the present invention is in no way limited by these examples. (Example 1) 100 parts by weight of irregular-shaped iron oxide powder (true density: 7.4, 7.41 KOe magnetic susceptibility: 65 emu / g) manufactured by Powder Tech Co., Ltd. having an average particle size of 40 μm was added to KYNAR7201 (polyfluoride manufactured by Penwort Co., Ltd.). 2 parts by weight of vinylidene) and 1.5 parts by weight of styrene MMA copolymer manufactured by Mitsubishi Rayon Co., Ltd. are mixed with a 1 L small kneader for 5 minutes, the heat medium temperature is set to 200 ° C., the mixture is stirred and kneaded for 40 minutes, and then the heater is turned off. Cooled for 50 minutes with stirring. afterwards,
A carrier was obtained by sieving with a 75 μm sieve. Further, a binder resin (styrene-n-butyl methacrylate) 86% by weight, carbon black (BPL manufactured by Cabot Co.) 8% by weight, a charge control agent (Bontron N0 manufactured by Orient Chemical Co., Ltd.)
4) 2% by weight and 4% by weight of polypropylene wax (660P manufactured by Sanyo Kasei Co., Ltd.) were used to obtain a toner having an average particle size of 9μ by a kneading and pulverizing method. Then, the above toner and carrier were mixed to obtain a developer so that the toner concentration was 6%. About this developer, VI made by Fuji Xerox Co., Ltd.
An image quality maintenance test was conducted using a modified VACE500 machine. As a result, the developer had no problem in the image after copying 100,000 sheets, and the image quality maintaining property was good. In addition, the consumption of the carrier was also small. Furthermore, high temperature and high humidity (30 ℃, 80
% RH), low temperature and low humidity (10 ° C, 20% RH) 5 each
When an image sustainability test was carried out on 10,000 sheets, there was no problem with the image and the image maintainability under each environment was also good.

(Example 2) 100 parts by weight of an amorphous iron oxide powder (true density: 6.9, 1 KOe magnetic susceptibility: 63 emu / g) manufactured by Heganes Co., having an average particle size of 60 μm was used, and methylphenyl manufactured by Toray Dow Corning Co., Ltd. 3.5 parts by weight of a silicone resin and 2 parts by weight of a styrene MMA copolymer manufactured by Mitsubishi Rayon Co., Ltd. were mixed with a 1 L small kneader for 5 minutes to obtain a heat medium temperature of 200.
After the temperature was set to 0 ° C. and the mixture was stirred and kneaded for 40 minutes, the heater was turned off, and the mixture was cooled for 50 minutes while stirring. Then 105μ
Sieve with a m sieve to obtain a carrier. Also, 87% by weight of a binder resin (styrene-n-butyl methacrylate), 8% by weight of carbon black (BPL made by Cabot Corporation), 1% by weight of a charge control agent (TRH made by Hodogaya Chemical Co., Ltd.), and polypropylene wax (Sanyo Chemical Co., Ltd.). Toner having an average particle size of 9 μ was obtained by a kneading and pulverizing method using 4% by weight of 660P manufactured by K.K. Then, the above toner and carrier were mixed to obtain a developer so that the toner concentration was 5%. An image quality maintenance test was performed on this developer using a modified FX5039 machine manufactured by Fuji Xerox. As a result, the developer had no problem in the image after copying 100,000 sheets, and the image quality maintaining property was good. In addition, the consumption of the carrier was also small. further,
Under high temperature and high humidity (30 ℃, 80% RH), low temperature and low humidity (10
When an image maintainability test was performed on each of 50,000 sheets under a condition of 20 ° C. and 20% RH, there was no problem with the image and the image maintainability under each environment was also good.

Comparative Example 1 100 parts by weight of an amorphous iron oxide powder (true density: 6.8, 1 KOe magnetic susceptibility: 62 emu / g) manufactured by Heganes Co., having an average particle size of 80 μm was used, and methylphenyl manufactured by Toray Dow Corning Co., Ltd. 2.0 parts by weight of silicone resin and 0.5 of styrene MMA copolymer manufactured by Mitsubishi Rayon Co., Ltd.
A carrier was obtained in the same manner as in Example 2 except that parts by weight were compounded. Under the conditions other than the above, a developer was obtained in the same manner as in Example 2 and an image quality maintenance test was conducted. As a result, a slight solid black brush-like unevenness was observed in the initial image quality, and the density was remarkably reduced after 50,000 sheets. It was observed. Further, during the sustainability test, carrier adhesion was observed due to charge injection, and the decrease in concentration was remarkable under high temperature and high humidity.

(Comparative Example 2) 100 parts by weight of spherical iron oxide powder (true density 6.5, 1 KOe magnetic susceptibility 53 emu / g) manufactured by Powder Tech Co., Ltd. having an average particle size of 50 μm was added to methylphenyl manufactured by Toray Dow Corning Co., Ltd. A carrier was obtained in the same manner as in Example 2 by mixing 3.0 parts by weight of a silicone resin and 2.0 parts by weight of a styrene MMA copolymer manufactured by Mitsubishi Rayon Co., Ltd. Under the conditions other than the above, a developer was obtained in the same manner as in Example 2 and an image quality maintenance test was conducted. As a result, a slight solid black brush-like unevenness was observed in the initial image quality, and the density was remarkably reduced after 50,000 sheets. It was observed. Further, carrier adhesion was remarkably generated, the photoreceptor was scratched, and the concentration was significantly reduced under high temperature and high humidity.

[0017]

According to the present invention, by adopting the above-mentioned constitution, the charge maintaining property of the carrier can be improved,
As a result, it is possible to prevent the carrier from adhering to the image, and it is possible to obtain excellent image quality without density unevenness and background stain. In addition, it has become possible to significantly reduce the consumption of carriers. Further, by mixing the coating resin and the core particles in a dry state in advance and then performing melt coating, it is possible to efficiently manufacture the carrier.

Claims (2)

[Claims] 1. A core particle having an average particle size of 60 μm or less, a true density of 6.0 or more, and a magnetic susceptibility of 60 e at 1 KOe.
A carrier for developing an electrostatic charge image, which comprises a magnetic substance having a mu / g or more and a resin coating of more than 3.0% by weight on the surface of the magnetic substance. 2. An average particle size of 60 microns or less and a true density of 6.
A core particle having a magnetic susceptibility of 0 or more and 1 KOe of 60 emu / g or more, and a coating resin exceeding 3.0 wt% thereof are mixed in a dry state, and then heated to melt the coating resin,
A method for producing a carrier for developing an electrostatic charge image, which comprises coating core particles.