JP2623986B2 - 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 carrier for developing an electrostatic image used for developing an electrostatic 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. Since they share functions such as transport and charging and are separated in function as a developer, they have characteristics such as good controllability and are widely used at present. In particular, a developer using a resin-coated carrier is excellent in charge controllability, and it is relatively easy to improve environmental dependency and temporal stability. As a developing method, a cascade method or the like has been used in the past, but at present, a magnetic brush method using a magnetic roll as a developer carrier is mainly used.

[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. The mechanism of carrier attachment to the image is
When the resistance of the carrier decreases, the induced charge is injected into the image area and the carrier adheres, or the charge amount of the carrier after development becomes excessive due to insufficient control of the upper limit of the charge amount of the carrier. It is considered that the carrier adheres to the edge portion.

In recent years, negatively charged organic photoreceptors have become widespread, and even in the case of inorganic photoreceptors, the reversal development method of recording an electrostatic image using a laser or the like has been frequently used. That is, there is a high demand for a high-quality developer even for a positively charged toner.

As a carrier for a positively charged toner, a carrier coated with a fluorine-containing resin has been proposed. However, fluorine-containing resins such as polyvinylidene fluoride have poor adhesion to the core particles, and in many cases, the charge retention is insufficient in long-term use. In addition, the coating material is detached during use, lowering the electrical resistance of the carrier, which tends to cause carrier adhesion, black spots and density unevenness due to the detached coating material. JP-A-54-1108
Japanese Patent Publication No. 39 proposes the use of an adhesion-imparting resin for the purpose of improving the adhesion of the negatively-chargeable resin to the core particles, but it was not always possible to obtain a sufficient effect.

[0006] In order to improve the adhesion of the coating material to the core particles, a high-temperature treatment at 200 ° C or higher has been performed. However, when a resin containing a high concentration of fluorine is exposed to a high temperature, a fluorine-containing resin is exposed. Generation of harmful gases such as hydrogen hydride is inevitable,
In addition to the durability of the equipment, there is a risk of causing problems such as safety and health and environmental destruction. It is not impossible to lower the melting point of the fluorine-containing resin by copolymerization or the like, but it has been found that lowering the melting point tends to lower the strength of the coat layer and also lowers the charge retention performance. .

Further, there is known a coating method for improving adhesion by using a solution of a fluorine-containing resin. However, solvents such as DMF used therein have a high boiling point and are highly toxic. There were drawbacks.

[0008]

SUMMARY OF THE INVENTION The present invention solves the above problems, improves the charge retention of a carrier containing a fluorine-containing resin coating material, prevents carrier adhesion, and ensures stable image quality. , Suppresses the consumption of carriers, enables application to high-quality developers for reversal development for organic photoreceptors and inorganic photoreceptors, makes it easier to control the developer to an appropriate charge amount, and reduces static charge. An object of the present invention is to provide a method for efficiently producing an image developing carrier.

[0009]

Means for Solving the Problems The present invention relates to nuclear particles and
After being mixed with the coating resin in a dry state, the mixture is heated to
The covering resin is melted, and the core particles are coated to form an electrostatic image.
In the method for producing an image carrier , the softening point is 150
℃ and less of the fluorine-containing resin, soft than the fluorine-containing resin
Production of the electrostatic image developing carrier, which comprises using a second resin had low reduction point 30 ° C. or more as the coating resin
Is the way .

[0010]

According to the present invention, the charge controllability, the charge retention and the strength of the coating layer can be greatly improved by using the fluorine-containing resin and the second resin having different softening points as described above. Was. Although the reason for this is not necessarily clear, it is considered that the difference in softening point causes a difference in compatibility.

The fluorine-containing resin used in the present invention preferably has a softening point in the range of 80 to 150 ° C.
If the temperature exceeds ℃, the temperature of the carrier manufacturing equipment will be 200 ℃
It is necessary to make the above, and a normal coating cannot be performed. On the other hand, when the temperature is lower than 80 ° C., agglomeration is apt to occur at the time of production, and the yield of the carrier having a desired particle size is significantly reduced. As the combined resin, a resin having a softening point lower than that of the fluorine-containing resin by 30 ° C. or more is used. However, if the temperature is extremely low, the fluidity of the carrier is deteriorated and toner contamination is caused. Is preferred.

The fluorine-containing resin used in the present invention includes vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene,
Monochloroethylene, copolymers of vinyl fluorine-containing monomers such as trifluoroethylene,
In addition, as the combined resin, 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; acrylonitrile And nitriles such as methacrylonitrile; 2-vinylpyridine;
4. Use of vinylpyridines such as vinylpyridine; vinyl ethers; vinyl ketones; olefins such as ethylene, propylene and butadiene; and homopolymers or copolymers of silicons such as methylsilicon and methylphenylsilicon. And bisphenol,
Polyesters containing glycol and the like can also be used.

The compounding amount of the coating resin is 0.2 to 10% by weight based on the total amount of the fluorine-containing resin and the combined resin with respect to the carrier.
The range is preferably about 0.5 to 3% by weight.

Examples of the core particles used in the present invention include ordinary iron powders, ferrites, and magnetite granules, and those having a particle size of usually about 30 to 200 μm can be used.

In the method for producing the carrier of the present invention, a heating type kneader, a heating type Henschel mixer, a UM mixer or the like can be used. Can also be used.

The carrier of the present invention is used as a two-component developer by mixing with a toner. The toner is obtained by dispersing a colorant or 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. Α-methylene aliphatic monocarboxylic acids such as n-propyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate Esters; 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 and vinyl isopro Vinyl ketones such as phenyl ketone, ethylene, propylene,
Polymers composed of monomers such as unsaturated hydrocarbons such as isoprene and butadiene and their halides, halogenated unsaturated hydrocarbons such as chloroprene and the like, or copolymers obtained by combining two or more of these monomers Polymers, and mixtures thereof, further rosin-modified phenol formalin resin, epoxy resin, polyester resin, polyurethane resin, polyamide resin, cellulose resin, non-vinyl condensation resin such as polyether resin or these and the vinyl resin And mixtures thereof.

Examples of the colorant used in the toner include carbon black, nigrosine dye, aniline blue, chaco 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 flowability improver, and the like, and may contain a magnetic fine powder if necessary.

[0019]

Example A fluorine-containing resin and a combined resin were blended with Cu-Zn ferrite core particles having an average particle size of 80 µm as shown in Table 1, and mixed with a 5 L small kneader for 5 minutes.
After setting the temperature of the heating medium at 195 ° C. and stirring and kneading for 40 minutes, the heater was turned off and the mixture was cooled for 50 minutes with stirring.
Thereafter, the mixture was sieved with a 177 μ sieve to obtain a carrier.
Also, a binder resin (styrene @ n-butyl methacrylate)
84% by weight, carbon (Cabot BPL) 10% by weight, charge controlling agent (Orient Chemical Bontron N04)
A toner having an average particle size of 11 μm was obtained by a kneading and pulverizing method using 2% by weight and 4% by weight of polyethylene wax (Mitsui Petrochemical 400P). Then, a developer was prepared by mixing the toner and the carrier so that the toner concentration became 4%. About these developers, Fuji Xerox FX5
An image quality maintenance test was performed using a 017 modified machine. As shown in the test results in Table 1, the developers of the examples had no problem in the image after copying 50,000 sheets and also had good image quality retention. In the developer of the comparative example in which the difference in softening point between the fluorine-containing resin and the combined resin is 30 ° C. or less, carrier adhesion occurs at a low concentration in the initial image quality, and the image quality after 50,000 sheets has uneven density and background stain. , Carrier consumption also showed a large value.

[Table 1]

[0020]

According to the present invention, by adopting the above structure, the charge retention of the carrier can be improved.
The carrier is prevented from adhering to the image, and excellent image quality free from density unevenness and background contamination can be obtained. 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 Continuation of the front page (56) References JP-A-2-250063 (JP, A) JP-A-2-93547 (JP, A) JP-A-2-27365 (JP, A) JP-A-62-1987 138859 (JP, A) JP-A-60-176053 (JP, A) JP-A-60-176052 (JP, A) JP-A-63-27858 (JP, A) JP-A-62-106475 (JP, A)

Claims (1)

(57) [Claims] (1) A core particle and a coating resin are mixed in a dry state.
After being combined, the mixture is heated to melt the coating resin,
Method for producing carrier for developing electrostatic images by coating particles
In, a fluorine-containing resin having a softening point of 150 ° C. or less,
Method for producing a carrier for developing electrostatic images, which comprises using the above fluorine-containing resin from the second resin have a low softening point is 30 ° C. or more as the coating resin.