JP3146775B2 - Electrostatic image developing carrier, method for producing the same, and image forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for developing an electrostatic image 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. And an image forming method using the carrier.

[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] The magnetic brush method using a two-component developer includes:
There are problems such as a decrease in image density due to the deterioration of the charge of the developer, generation of remarkable stain on the background, image roughness and consumption of the carrier due to adhesion of the carrier to the image, and generation of image density unevenness. Charge deterioration of the developer is likely to occur due to sticking of toner components to the carrier coat layer or peeling of the coat, and when the coat layer is not uniform, when the environment changes such as humidity and temperature, or when toner is added. Alternatively, there is a tendency for background portion stains and the like to occur when the toner density is high.

The mechanism of adhesion of the carrier to the image is such that when the resistance of the carrier decreases due to unevenness or peeling of the coat layer, the induced charge is injected into the image area and the carrier adheres or the charge amount of the carrier is reduced. It is considered that because the upper limit control is insufficient, the charge amount of the carrier after development becomes excessive, and the carrier adheres to the edge portion.

As a coating method for making the coat layer more uniform and firm, there has been proposed a method in which a magnetic core material and a powder top coat material are mixed in a dry state, and a coating film is formed while heating and cooling. However, in consideration of the recent reduction in toner particle size and the lowering of the melting point of the toner material for improving the image quality, it cannot be said that the toner has a sufficient effect.

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above problems and to provide a carrier for developing an electrostatic charge image having the following features, a method for producing the same, and an image forming method. . Improves image quality maintenance due to changes in charging properties due to environmental fluctuations, improves background stains when toner is added, prolongs the life of the developer, prevents carrier adhesion, and ensures stable high image quality In addition, to suppress carrier consumption, to provide an image quality excellent in black solid and fine line reproduction, to prevent generation of scratches and black spots on a photoreceptor, and to efficiently manufacture a carrier for developing an electrostatic image.

[0007]

According to the present invention, there is provided a carrier for developing an electrostatic image, wherein the carrier is coated with magnetic core particles.
A carrier for developing an electrostatic image, wherein magnetic nucleus particles having a surface property index h of 3.0 to 5.0 represented by the following general formula are used. (2) The nucleus according to (1) above After mixing the particles and the coating resin in a dry state, heating and melting the coating resin, a method for producing a carrier for electrostatic image development characterized by coating core particles, and (3) A step of forming an electrostatic latent image on the electrostatic latent image holding member, a step of developing the electrostatic latent image on the electrostatic latent image holding member with a developer, and moving the developed image onto a transfer member And an image forming method comprising the steps of:
An image forming method using the carrier for developing an electrostatic image according to (1) as a developer in the developing step. h = A / {Σ0.03 × _{[W i / (ρ × r i} ) ]} where, A: BET specific surface area ^{_{(cm 2 / g) W i}} : particle size by weight percent (by sieving method) [rho: Magnetic True density of core particles (g / cm ³ ) r _i : radius of core particle by particle size (cm) (1/2 of the median value of the mesh size of two adjacent sieves ) Mesh size (μm): 150 , 105, 90, 75 , 63, 45 , 38, 26

[0008]

The present inventors have conducted intensive studies on the resin-coated carrier in order to solve the above-mentioned problems, and as a result, have improved the uniformity of the resin coating and controlled the fine irregularities on the surface of the magnetic core particles. Was found to be important, and the present invention was completed. If the surface of the magnetic core particles is too smooth without irregularities, the anchoring effect on the coating resin does not work effectively, and the coating state tends to be partially wiped. Further, when subjected to a mechanical action for a long period of time, the film tends to peel off. Therefore, it is desirable that moderate irregularities exist on the surface of the magnetic core particles.

In addition, when there are extremely deep and complicated irregularities, it is difficult to obtain the effect of the coating resin on the charging performance due to the penetration of the coating resin or the shortage of the coating resin. As a method for defining the surface state of such magnetic core particles, it is effective to use the above-mentioned surface property index. This surface property index is a ratio between the measured specific surface area and the spherical approximate theoretical surface area calculated from the particle size distribution and the true density. In order to solve the above-described problems of the invention, the surface property index h Was found to be an essential condition to be in the range of 3.0 to 5.0 . The carrier of the present invention can be produced also by a solution coating method.In particular, after the magnetic core particles and the coating resin are mixed in a dry state, the core resin particles are coated by heating and melting the coating resin. More preferably, it is manufactured by the following method.

As the magnetic core particles, ordinary ferrite powder or magnetite powder can be used. The controlling factors of the surface properties are the particle diameter of the raw material powder and the firing conditions.
As a raw material of the ferrite, an iron oxide such as Fe ₂ O ₃ , a metal oxide represented by MO such as Cu, Zn, Ni, or Mg, or a salt which finally becomes MO is used. In this method, the surface state after firing becomes smoother as the raw material is pulverized, refined, and uniformly mixed.

After calcining at a relatively low temperature in the range of 500 to 1000 ° C. for the purpose of keeping the raw material conditions constant,
In the pulverization method, the finer and more uniform the pulverization and mixing, the smoother the surface state after firing. Then, water is added to form a slurry, a binder resin, a dispersant, etc. are added, the mixture is granulated into a spherical shape by a spray dryer, classified, and then subjected to main firing.The higher the temperature of the main firing, the higher the surface smoothness. And the value of h tends to decrease. For granulated magnetite, F
Although e ₂ O ₃ or Fe ₃ O ₄ is used as a raw material, it is similar to ferrite in that the temperature at the time of miniaturization and firing of the raw material powder is a control factor of surface properties.

The coating resin used in the present invention includes copolymers of vinyl fluorine-containing monomers such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene, monochloroethylene and trifluoroethylene; styrene, Chlorostyrene,
Styrenes such as methylstyrene; 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 and ethyl methacrylate; dimethyl Nitrogen-containing acrylics such as aminoethyl methacrylate; nitriles such as acrylonitrile and methacrylonitrile; vinylpyridines such as 2-vinylpyridine and 4-vinylpyridine; vinyl ethers; vinyl ketones; olefins such as ethylene, propylene and butadiene A homopolymer or a copolymer of silicones such as methyl silicon and methyl phenyl silicon; Or the like can also be mentioned polyesters, including Le. Further, two or more of the above-mentioned combined resins may be mixed to form a coating composition.

The compounding amount of the coating resin is about 0.5 to 5% by weight, preferably 1.0 to 3.
The range of 0% by weight is suitable for simultaneously satisfying image quality, secondary obstruction, chargeability and the like. The nucleus particles used in the present invention have a substantially spherical shape such as ferrite particles and granulated magnetite, and any particles whose surface properties can be controlled can be used. Usually, those having an average particle size of about 20 to 120 µ can be used. For the production of the carrier, a heated kneader, a heated Henschel mixer, a UM mixer, a planetary mixer, or the like can be used.

The carrier of the present invention can be 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, parachlorostyrene, and α-methylstyrene; methyl acrylate, and ethyl acrylate. N-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, lauryl methacrylate, 2 methacrylic acid Α-methylene aliphatic monocarboxylic acid esters such as -ethylhexyl; 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 Kind Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and vinyl isopropenyl ketone; unsaturated hydrocarbons such as ethylene, propylene, isoprene, butadiene and the like, and halogenated unsaturated hydrocarbons such as chloroprene and the like; Or a copolymer obtained by combining two or more of those monomers, and a mixture thereof,
Rosin-modified phenol formalin resin, epoxy resin,
Non-vinyl condensed resins such as polyester resins, polyurethane resins, polyamide resins, cellulose resins, and polyether resins, and mixtures of these with the vinyl resins described above.

The colorant used for the toner includes carbon black, nigrosine dye, aniline blue, coco oil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue and mixtures thereof. As toner components other than the colorant, there are a charge control agent, an anti-offset agent, a fluidity improver, and the like, and may contain a magnetic fine powder as needed. Regarding the particle diameter of the toner, the smaller the diameter is, the higher the image quality tends to be.
A toner having an average diameter of about 0 μm is used.

[0016]

( Reference example )

(Manufacture of carrier) Cu-Zn ferrite having the following particle size distribution (manufactured by Powder Tech, true density ρ = 4.40, BET specific surface area A =
To 1390 cm ² / g), 3.0 parts by weight of a styrene-MMA copolymer (BR-52, manufactured by Mitsubishi Rayon Co., Ltd.) was mixed for 5 minutes using a small 1-liter kneader, and the heating medium temperature was set to 200 ° C. and 40 parts. After stirring and kneading for a minute, the heater was turned off, and the mixture was cooled for 50 minutes with stirring, and then sieved with a 105 μm sieve to obtain a carrier. (Particle size distribution: weight% between mesh openings) 90 to 75 μm: 0.5%, 75 to 63 μm: 15.6
%, 63 to 45 μm: 56.9%, 45 to 38 μm: 3
8.4%, 38 to 26 μm: 15.3% The surface property index h was determined to be 5.07.

(Production of Toner) A binder resin (styrene-n
87% by weight of butyl methacrylate), 8% by weight of carbon black (BPL manufactured by Cabot), 1% by weight of a charge control agent (TRH manufactured by Hodogaya Chemical Co., Ltd.), and 4% by weight of polypropylene wax (660P manufactured by Sanyo Chemical Co., Ltd.) Using
By a kneading and pulverizing method, a toner having an average particle size of 7.5 μ was obtained. (Preparation of Developer) A developer was prepared by mixing the above-mentioned toner and carrier so that the toner concentration became 5%.

(Evaluation) The developer was subjected to an image quality maintenance test using a 5039 modified machine manufactured by Fuji Xerox Co., Ltd. As a result, although carrier adhesion was slightly observed at the initial problem-free level, it quickly disappeared,
The image of the developer after copying 100,000 sheets had no problem, and the image quality retention was good.

Comparative Example 1 (Manufacture of Carrier) Cu—Zn ferrite having the following particle size distribution (manufactured by Powder Tech, true density ρ = 4.70, BET specific surface area A =
1188.5 cm ² / g), using 3.0 parts by weight of a styrene-MMA copolymer (BR-52 manufactured by Mitsubishi Rayon Co., Ltd.), resin coating was performed in the same manner as in Reference Example, and then 177 μm The carrier was obtained by sieving with a sieve. (Particle size distribution: weight% between mesh openings) 150 to 105 μm: 2.0%, 105 to 90 μm: 1
8.7%, 90-75 μm: 55.3%, 75-63 μm
m: 23.5%, 63-45 μm: 0.5% When the surface property index h was determined, it was 7.58.

(Preparation of Developer) A toner was prepared by mixing the toner of the reference example and the above carrier so that the toner concentration was 5%. (Evaluation) About this developer, Fuji Xerox Co., Ltd. 5039
An image quality maintenance test was performed using a modified machine. As a result, the developer had a slightly low initial chargeability, and fogging was observed in the background particularly in a high-temperature and high-humidity environment, and the image quality maintenance test was not performed.

Example 1 (Manufacture of Carrier) Cu—Zn—Mg ferrite (T
DK, true density ρ = 4.5, BET specific surface area A = 52
0 cm ² / g), 0.8 parts by weight of a polyvinylidene fluoride resin (KAYNAR7201 manufactured by Penwald Co., Ltd.) and 0.4 of a styrene-MMA copolymer (BR-52 manufactured by Mitsubishi Rayon Co., Ltd.) The resin coating was performed in the same manner as in Reference Example , using parts by weight, and then sieved with a 177 μm sieve to obtain a carrier. (Particle size distribution: weight% between mesh openings) 150 to 105 μm: 0.09%, 105 to 90 μm:
29.45%, 90-75 μm: 40.48%, 75-
63 μm: 17.34%, 63 to 53 μm: 10.92
%, 53-45 μm: 1.49%, 45-38 μm:
0.23% The surface property index h was determined to be 3.07.

(Production of Toner) Binder resin (styrene-n
(Butyl methacrylate) 87% by weight, carbon black (BPL manufactured by Cabot Corporation) 8% by weight, charge controlling agent (Bontron N04 manufactured by Orient Chemical Co., Ltd.) 1% by weight, and polypropylene wax (660P manufactured by Sanyo Chemical Co., Ltd.)
Using 4% by weight, a toner having an average particle size of 7.5 μ was obtained by a kneading and pulverizing method. (Preparation of developer) And toner concentration 5
%, A developer was prepared by mixing the above toner and carrier. (Evaluation) The developer was subjected to an image quality maintenance test using a V500 modified machine manufactured by Fuji Xerox Co., Ltd. As a result, there was no carrier adhesion, and there was no problem with the image of the developer after copying 100,000 sheets, and the image quality was maintained well.

Comparative Example 2 (Manufacture of Carrier) Cu—Zn—Mg ferrite (T
DK Corporation, true density ρ = 4.61, BET specific surface area A = 2
80 cm ² / g), polyvinylidene fluoride resin (KAYNAR7201 manufactured by Penwald Corporation).
8 parts by weight, and a styrene -MMA copolymer (Mitsubishi Rayon Co., Ltd. BR-50) with 0.4 parts by weight, Example
Resin coating was performed in the same manner as in Example 1, and then sieving was performed with a 177 μm sieve to obtain a carrier. (Particle size distribution: weight% between mesh openings) 150 to 105 μm: 0.03%, 105 to 90 μm:
26.94%, 90-75 μm: 43.83%, 75-
63 μm: 17.77%, 63 to 53 μm: 10.09
%, 53-45 μm: 1.29%, 45-38 μm:
The surface property index h was determined to be 1.70.

(Preparation of Developer) Then, the toner of Example 1 and the above carrier were mixed to prepare a developer so that the toner concentration became 5%, and a V500 modified machine manufactured by Fuji Xerox Co., Ltd. was used. An image quality maintenance test was performed. As a result, with this developer, image density unevenness due to carrier adhesion was slightly observed at the beginning, and the background stain started to be generated after copying 10,000 sheets. After 20,000 sheets, the background stain became remarkable, and the test was terminated. . In addition, a large number of scratches were observed on the photoreceptor due to carrier adhesion, and black spots were observed on the image.

Example 2 In the reference example , a Cu—Zn ferrite having the following particle size distribution (manufactured by Powder Tech, true density ρ = 4.45, B
ET specific surface area A = 1260 cm ² / g)
A carrier was produced in the same manner as in the reference example . Particle size distribution: weight% between each mesh opening 90 to 75 μm: 0.8%, 75 to 63 μm: 18.0
%, 63-45 μm: 60.3%, 45-38 μm: 1
5.0%, 38 to 26 μm: 5.9% The surface property index h was found to be 4.83. When the above carrier was tested in the same manner as in the Reference Example , no carrier adhesion occurred, and the image of the developer after copying 150,000 sheets had no problem and the image quality retention was good.

[0026]

According to the present invention, by adopting the above structure, the charge retention 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 free from uneven density and background contamination. In addition, the amount of carrier consumption can be significantly reduced. Further, by mixing the coating resin and the core particles in a dry state in advance and then melt-coating, efficient production of the carrier is enabled.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masao Mochizuki 1600 Takematsu, Minamiashigara-shi, Kanagawa Fuji Xerox Co., Ltd. (56) References JP-A-4-147269 (JP, A) JP-A-5-100492 ( JP, A) JP-A-2-163758 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/10

Claims (3)

(57) [Claims] 1. A carrier for developing an electrostatic charge image coated with a resin having magnetic nucleus particles, wherein magnetic nucleus particles having a surface property index h represented by the following general formula of 3.0 to 5.0 are used. Characteristic carrier for developing electrostatic images. h = A / {Σ0.03 × _{[W i / (ρ × r i} ) ]} where, A: BET specific surface area ^{_{(cm 2 / g) W i}} : particle size by weight percent (by sieving method) [rho: Magnetic True density of core particles (g / cm ³ ) r _i : radius of core particle for each particle size (cm) (のof the median value of openings of two adjacent sieves) Sieve opening (μm): 150 , 105, 90, 75 , 63, 45 , 38, 26 2. An electrostatic charge image wherein the core particles according to claim 1 and the coating resin are mixed in a dry state, and then heated to melt the coating resin and coat the core particles. A method for producing a developing carrier. 3. A step of forming an electrostatic latent image on an electrostatic latent image holding member, a step of developing the electrostatic latent image on the electrostatic latent image holding member with a developer, and An image forming method comprising the step of transferring onto a transfer member, wherein the carrier for developing an electrostatic image according to claim 1 is used as a developer in the developing step.