JP3227633B2 - Method for producing carrier for developing electrostatic image - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Methods for visualizing image information via an electrostatic image, such as electrophotography, are currently used in various fields. In the electrophotographic method, an electrostatic latent image is formed on a photoreceptor by a charging and exposing process, the electrostatic latent image is developed with a developer containing a toner, and visualized through a transfer and fixing process. The developer used here includes a two-component developer composed of a toner and a carrier, and a one-component developer used alone with a toner such as a magnetic toner. It has functions such as stirring, transporting, charging, and the like, and is separated into functions as a developer, so that it has characteristics such as good controllability and is widely used at present. 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 past, but a magnetic brush method using a magnetic roll as a developer conveyance unit is mainly used at present.

[0003] In recent years, negatively charged organic photoreceptors have become very popular, and reversal development in which an electrostatic image is recorded on an inorganic photoreceptor using a laser or the like is sometimes used. Even when a positively charged toner is used as well as a toner, a high quality developer is required. Therefore, it is desirable that the charging performance of the carrier can be freely controlled according to the charging polarity and charging strength of the toner. Furthermore, with the recent trend toward miniaturization and high-speed copiers and printers, developing units themselves also need to be miniaturized and driven at high speed.
There is a growing demand for improvements such as mechanical strength and stability over time for carriers.

[0004] In recent years, resin-coated carriers have been actively studied as carriers satisfying these required characteristics, and as the selection of coating resins has been diversified, the coating method has been changed to a coating resin solution dissolved in a solvent. A solution coating method of forming a film by removing the solvent after applying to the particles, or a dry melt coating method of dry-mixing core particles and coating resin particles and then heating to melt the coating resin to form a film. (Japanese Patent Laid-Open No. 54
JP-A-35735, JP-A-55-118047 and JP-A-60-170865) have been proposed.

[0005] Among such resin-coated carriers,
In particular, when coating a resin with poor solubility in solvents, such as a fluorine-based resin such as polyvinylidene fluoride, the solution coating method has poor film-forming properties and the coating is easily peeled off by mechanical stress, resulting in durability. Was low. The dry melt coating method has the advantages that there are few restrictions on solvent solubility, molecular weight, softening point, etc., the amount of coating resin can be selected relatively freely, and the control of characteristics such as chargeability and electrical resistance of the carrier can be arbitrarily controlled. is there. However, depending on the properties of the resin to be used, there still remains a problem that the carrier is not uniformly coated and the durability is reduced.

In particular, when a resin having high water repellency, such as a fluorine resin, is used as the coating resin, if even a small amount of moisture is present in the heating and melting step, the formation of a film is hindered and a uniform coating layer cannot be formed. There is. When the coating state of the carrier is non-uniform, the coating strength is reduced and the durability is reduced, and the exposed portion of the core particles increases,
This may cause toner contamination. This toner contamination on the carrier surface causes a decrease in the charge amount, and tends to cause image quality deterioration such as roughening of the solid image portion and contamination of the background portion. Furthermore, when two or more types of coated resin particles are used, it is difficult to uniformly disperse the resin particles due to the presence of moisture, and the coating state becomes uneven, so that a desired charge amount and film strength can be obtained. Often not.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems in the dry fusion coating method and to provide a method for producing a carrier for developing an electrostatic image having the following characteristics. To ensure uniform control of characteristics such as chargeability and electrical resistance by making the resin coating state uniform. Excellent durability and environmental safety, and suppresses deterioration of image quality due to toner contamination. In particular, it is an object of the present invention to provide a carrier which is excellent in charge retention and coating strength when forming a coating with a coating resin containing a highly water-repellent resin such as a fluororesin. To provide a safe and low-cost method for manufacturing a carrier without using a solvent.

[0008]

Means for Solving the Problems Specific embodiments of the present invention are as follows. (1) After mixing the magnetic core particles and the coating resin particles in a solid state, heating while stirring, coating the coating resin by melting, and further cooling to room temperature while stirring, for electrostatic image development. A method for producing a carrier for developing an electrostatic image, wherein the heating / melting step and / or the cooling step are performed under reduced pressure.

(2) As the coating resin, a resin containing at least a resin having strong water repellency is used, and the heating / melting step and / or the cooling step are carried out under reduced pressure by reducing the pressure to 60,000 Pa or less. (1) The method for producing a carrier for developing an electrostatic image as described in (1). (3) The method for producing a carrier for developing electrostatic images as described in (2) above, wherein the resin having high water repellency is a fluororesin.

[0010]

According to the present invention, in the dry-type melt coating method, the process of melt-coating and cooling the coating resin is performed under reduced pressure to completely remove the water contained in the core particles and the coating resin particles. The object of the present invention is to improve the adhesion between the particles and the coating resin, to form a uniform coating, and to solve the above problems.

[0011] The degree of reduced pressure is 60,000 Pa or less, preferably 100 to 50,000 Pa, more preferably 500 to 50,000 Pa.
A range of up to 50,000 Pa is suitable. If the pressure in the mixer exceeds 60000 Pa, the resin coating state tends to be uneven, and toner contamination due to exposure of core particles and a decrease in durability due to a decrease in film strength are likely to occur. The degree of decompression becomes uniform as the degree of decompression becomes closer to vacuum, but it can be appropriately selected from the above range according to the desired charge amount and film strength.

As the coating resin used in the present invention, various resins can be used irrespective of the kind as long as the resin is mainly composed of a thermoplastic resin. Particularly suitable resins for the method of the present invention include the following. Examples of the fluorine-based resin include homopolymers or copolymers of vinyl fluorine-containing monomers such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, and monochlorotrifluoroethylene; examples of the acrylic resin include (meth) A) homopolymers of α─methylene aliphatic monocarboxylic acids such as acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and lauryl (meth) acrylate; Copolymers; styrenes such as styrene and methylstyrene, nitriles such as (meth) acrylonitrile, vinylpyridines such as 2-vinylpyridine and 4-vinylpyridine, and vinyl ethers with respect to these acrylic monomers. , Vinyl ketone , Olefins, methyl silicone, and the like obtained by copolymerizing silicones such as methylphenyl silicone. These coating resins may be used alone, or in combination with a toner, a plurality of types of resins may be used in combination to further increase the degree of freedom of charge adjustment.

The particle size of the coated resin particles is 1/3 of that of the core particles.
Hereinafter, preferably, the range of 1/1000 to 1/5 is suitable. If the ratio exceeds 1/3, it takes a long time to melt the coating resin and form a continuous film on the surface of the core particles, and thus lacks productivity. The compounding amount of the coating resin is about 0.2 to 10% by weight based on the carrier, preferably 0.5 to 3% by weight.
The range of% by weight is suitable for simultaneously satisfying the chargeability and the like.

The core particles used in the present invention include, but are not limited to, iron powder, ferrite powder, and granulated magnetite. The average particle size of the core particles is 10 to 500 μm, preferably 20 to 20 μm.
Those having a thickness of about 0 μm are used.

[0015] The conductivity of the coating layer is adjusted and the flow of the carrier is controlled.
For the purpose of improving the mobility and the like, inorganic fine particles, for example, Si
O_Two, TiO_Two, MgO, ZnO, BaSO_Four, ZrO
_Two, SnO_Two, CaO, Al_TwoO_Three, CaCO_Three, Mg
(OH)_Two, CeO_Two, MgCO _Three, MgSO_Four, Fe
_TwoO_Three, K_TwoO, Na_TwoO, CaO ・ SiO_Two,as well as,
Use by blending carbon black etc. with the coating resin
Can be. In the solution coating method, use a ball mill
It is necessary to disperse the fine particles in the resin solution.
In such a dry melt coating method, the core particles, the coating resin particles
Just add and mix the above fine particles at the same time, heat melting
In the process, it can be dispersed in the coating resin. Fine particles
The addition amount of the resin is 0.5 to 80 weight based on the amount of the coating resin.
%, Preferably in the range from 2 to 50% by weight.

The mixer used in the present invention comprises a heating, cooling,
As long as it has a decompression means, it does not matter what kind, but in order to enable selection of a wider coating resin amount,
Those having a stirring blade such as a rotary blade or a scraper capable of applying a forced shear force to the mixture are preferred. Specifically, a batch type kneader, a ribbon blender, a bonnie mixer and the like can be mentioned.

Examples of the means for heating the mixture include a method in which a jacket is attached to the mixing tank to circulate steam and a heating medium and heat transfer heating, and a direct heating method in which hot air is blown into the mixing tank. However, it is not limited to these. Examples of the cooling method include, but are not limited to, a method of switching a heat medium or the like of a steam jacket to a refrigerant, a method of blowing cool air, and the like.

The carrier of the present invention is mixed with
Used as a component developer. The toner is obtained by dispersing a colorant and the like in a binder resin. Examples of the binder resin used in the toner include styrenes such as styrene and chlorostyrene; vinyl acetate, vinyl propionate, and vinyl butyrate;
Vinyl esters such as vinyl benzoate; methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, octyl (meth) acrylate, dodecyl (meth) acrylate, phenyl (meth) acrylate Α-methylene aliphatic monocarboxylic acid esters such as;
Vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone; and homopolymers or copolymers such as olefins. In particular, typical binder resins include polystyrene, styrene-acrylate copolymer, styrene-methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, and styrene-maleic anhydride. Copolymers, polyethylene, polypropylene and the like can be mentioned. Furthermore, polyester resin, polyurethane resin, epoxy resin, silicone resin, polyamide resin, modified rosin, and paraffin wax can be exemplified.

Colorants used in the toner include carbon black, aniline blue, calcoil blue, chrome yellow, ultramarine blue, Dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, and rose bengal. And the like can be exemplified as typical ones.

Various additives such as a cleaning aid and a fluidity promoter can be added to the toner used in the present invention, if necessary. The toner used in the present invention is preferably fine particles having an average particle diameter of 30 μm or less, and preferably 3 to 20 μm.

The developer containing the carrier and the toner is as follows:
It is used to develop an electrostatic latent image formed on a photoconductor or an electrostatic recording medium. For the photoreceptor, an inorganic photoconductive material such as selenium, zinc oxide, cadmium sulfide, and amorphous silicon, and an organic photoconductive material such as a phthalocyanine pigment and a bisazo pigment are used. A dielectric such as polyethylene terephthalate is used as the electrostatic recording medium. The electrostatic latent images formed on these are developed by a developing method such as a magnetic brush method or a touch-down method, and are transferred to transfer paper such as paper.
It is fixed and becomes a copy or printed matter. Then, the toner remaining on the surface of the photoconductor or the like is cleaned.

[0022]

[Example 1]

(Manufacture of carrier) 100 parts by weight of Cu-Zn ferrite (3009, manufactured by TDK) having an average particle size of 80 µm was pulverized with vinylidene fluoride / 3-fluoroethylene copolymer (KF1,500, manufactured by Kureha Chemical Co., Ltd.). One part by weight of particles having a particle diameter of 8 μm was blended, put into a planetary mixer having a heatable jacket and a capacity of 30 liters capable of reducing pressure, and mixed at room temperature for 5 minutes under reduced pressure of 8000 Pa. Then, while maintaining the above-described reduced pressure state and stirring and mixing for 40 minutes while circulating the heating medium at 200 ° C. through the jacket, circulating the cooling medium at 20 ° C. through the jacket.
Stirred for minutes. Thereafter, the mixture was sieved with a 177 μm sieve to obtain a carrier.

(Production of Toner) Binder resin (styrene-n
86% by weight of butyl methacrylate), 8% by weight of carbon black (R330 manufactured by Cabot), 2% by weight of a charge controlling agent (Nigrosine Bontron NO4 manufactured by Orient Chemical Co., Ltd.), and polypropylene wax (6 manufactured by Sanyo Chemical Co., Ltd.)
60P) 4% by weight and an average particle size of 1
1 μm of toner was obtained.

Example 2 (Manufacture of carrier) Cu-Zn-M having an average particle size of 80 μm
g 1 part by weight of vinylidene fluoride / 3-fluoroethylene copolymer having an average particle diameter of 8 μm (KF1500, manufactured by Kureha Chemical Co., Ltd.) and 100 parts by weight of ferrite (C08, manufactured by Fuji Electric Chemical Co., Ltd.) 10 μm diameter styrene-methyl methacrylate copolymer (manufactured by Mitsubishi Rayon Co., Ltd., BR
50 pulverized products) were put into a planetary mixer having a jacket capable of heating and having a decompressible capacity of 30 liters, and mixed at normal temperature and normal pressure for 10 minutes. Then, the pressure in the mixer was reduced to 1000 Pa,
After stirring and mixing for 40 minutes while circulating a heating medium at a temperature of 40 ° C. through the jacket, the pressure in the mixer was returned to atmospheric pressure, and stirring was performed for 40 minutes while circulating a refrigerant at 20 ° C. through the jacket.
Thereafter, the mixture was sieved with a 177 μm sieve to obtain a carrier.

Example 3 (Manufacture of carrier) 100 parts by weight of Cu-Zn ferrite (F150, manufactured by Powder Tech) having an average particle size of 85 μm were mixed with vinylidene fluoride and 3-fluoroethylene having an average particle size of 8 μm. One part by weight of the polymer was blended, put into a planetary mixer having a heatable jacket and a capacity of 30 liters capable of reducing pressure, and mixed at normal temperature and normal pressure for 10 minutes.
Then, the mixture was stirred and mixed for 40 minutes under a normal pressure while circulating a heating medium at 200 ° C. through a jacket. Then, the pressure in the mixer was reduced to 5500 Pa, and the mixture was stirred for 40 minutes while circulating a refrigerant at 20 ° C. through the jacket. Thereafter, the mixture was sieved with a 177 μm sieve to obtain a carrier.

Comparative Example 1 (Manufacture of Carrier) A carrier was obtained in the same manner as in Example 1, except that the inside of the mixer was always kept at atmospheric pressure, and other conditions were the same as in Example 1.

[Comparative Example 1] (Manufacture of carrier) A carrier was obtained in the same manner as in Example 2 except that the inside of the mixer was always kept at atmospheric pressure, and the other conditions were the same as in Example 2.

(Evaluation) A developer was prepared by mixing the carriers of Examples 1 to 3 and Comparative Examples 1 and 2 with the toner of Example 1 so that the toner concentration was 6%. The developer was subjected to an image quality maintenance test using a modified product of a Vision 400 manufactured by Fuji Xerox Co., Ltd., and the results are shown in Table 1.
As is evident from Table 1, the coating state observed by a scanning microscope (SEM) photograph shows that the carriers of Examples 1 to 3 all formed a uniform continuous film, whereas the carrier of Comparative Example 1 was a nucleus. Many exposed portions of the particles were observed, and in the carrier of Comparative Example 2, the dispersion state of the two kinds of coating resins was non-uniform, and the film thickness was non-uniform. The dispersion state was measured by taking photographs of carrier particles with a scanning electron microscope (SEM),
The image was analyzed and judged. The image quality maintenance was performed according to Example 1.
Comparative Examples 1 to 3 showed good results even after copying 100,000 sheets from the initial stage.
After copying million sheets, the background became heavily stained, and the carrier was consumed much. In Comparative Example 2, carrier adhesion to the non-image portion occurred from the beginning, and the background portion was stained after copying 100,000 sheets.

[0029]

[Table 1]

[0030]

According to the present invention, by adopting the above constitution, a uniform resin film can be formed on the surface of the core particles, and a carrier having excellent image quality maintenance can be provided. .

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-345172 (JP, A) JP-A-1-204073 (JP, A) JP-A-4-268572 (JP, A) JP-A-6-268 19210 (JP, A) JP-A-4-264564 (JP, A) JP-A-4-452 (JP, A) JP-A-2-160032 (JP, A) JP-A-3-188650 (JP, A) JP-A-6-51565 (JP, A) JP-A-5-173371 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/10

Claims (3)

(57) [Claims] 1. An electrostatic charge image in which magnetic core particles and coating resin particles are mixed in a solid state, heated with stirring to melt and coat the coating resin, and further cooled to room temperature with stirring. A method for producing a carrier for developing an electrostatic image, wherein the heating / melting step and / or the cooling step are performed under reduced pressure. 2. A coating resin comprising at least a resin having a strong water repellency, wherein the pressure is reduced to 60,000 Pa or less, and the heating / melting step and / or the cooling step are performed under reduced pressure. 2. The method for producing an electrostatic image developing carrier according to item 1. 3. The method for producing a carrier for developing an electrostatic image according to claim 2, wherein the resin having high water repellency is a fluorine resin.