JPH06167835A - Carrier for developing electrostatic charge image and its production - Google Patents

Abstract

PURPOSE:To produce a carrier for developing an electrostatic charge image preventing sticking, ensuring high image quality, inhibiting consumption, improving property of maintaining image quality against a change of electrostatic chargeability due to an environmental change, etc., and stably giving an image excellent in solid black and fine line reproduction. CONSTITUTION:This carrier for developing an electrostatic charge image is made of resin coated magnetic particles obtd. by mixing core particles of a magnetic substance with a resin soln. and vacuum-drying the mixture under stirring. The resin coated magnetic particles contain <=0.15wt.% residual volatile matter after vacuum drying. This electrostatic charge developing carrier is produced by mixing magnetic particle with resin solution, vacuum drying the mixture with a constant temp heater medium while stiring, and finishing the vacuum drying process when the temp. of the mixture is raised 10 deg.C higher them its minimum temp.

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 charge image formed by an electrophotographic method, an electrostatic recording method or the like with a two-component developer, and a method for producing the carrier. .

[0002]

2. Description of the Related Art A method of visualizing image information through an electrostatic charge image such as an electrophotographic method 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. It is widely used at present because it has functions such as good controllability because it shares functions such as conveyance and charging and is separated as a developer. In particular, a developer using a carrier coated with a resin has excellent charge controllability, and it is relatively easy to improve environmental dependency and stability over time. Further, as a developing method, a cascade method or the like has been used for a long time, but nowadays, a magnetic brush method using a magnetic roll as a developer carrying carrier is mainly used.

However, the magnetic brush method using a two-component developer lowers the image density due to charge deterioration of the developer,
Significant background stains and carrier adhesion to the image (This mechanism is because the resistance of the carrier decreases and induced charges are injected into the image area and the carrier adheres, and the upper limit of the charge amount of the carrier is controlled. Is insufficient, the charge amount of the carrier after development becomes excessive, and the carrier may adhere to the edge portion.) Image roughening and carrier consumption due to occurrence of uneven image density, etc. There's a problem. Further, in recent years, in the two-component development, the weight of the carrier is being further reduced in order to improve the image quality, and there is a tendency to use a smaller carrier diameter and further to use a magnetic substance dispersion type carrier in which a magnetic substance is kneaded and dispersed in a resin. . The magnetic substance-dispersed carrier can be obtained as a substantially spherical and lightweight carrier by spray cooling the kneading melt. Further, this magnetic substance-dispersed carrier has various advantages that it is excellent in fluidity, excellent in fine line reproduction and black solid uniformity, and that it can be coated with a resin to facilitate charge control. On the other hand, this magnetic substance-dispersed carrier also has a problem in that the chargeability varies due to the uniformity of coating and the effect of volatile components in the coating resin or core particles.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems in view of the actual state of the prior art. That is, an object of the present invention is to provide a carrier for developing an electrostatic charge image capable of stably obtaining a high quality image and a method for producing the carrier. Another object of the present invention is to provide a carrier for developing an electrostatic charge image, which can prevent carrier adhesion to ensure high image quality and suppress carrier consumption, and a method for manufacturing the same.
Still another object of the present invention is to provide a carrier for developing an electrostatic charge image and a method for producing the same, which can improve the image quality maintaining property due to a change in charging property due to environmental changes and the like. Another object of the present invention is to provide a carrier for developing an electrostatic charge image and a method for producing the same, which can obtain an image quality excellent in black solid and fine line reproduction.

[0005]

As a result of various studies, the present inventors have found that the residual volatile content of resin-coated magnetic particles is
By setting a certain amount or less for the carrier,
The inventors have found that the above objects can be achieved and completed the present invention. That is, the carrier for developing an electrostatic charge image of the present invention is coated with a resin by being mixed with a resin solution and then dried under reduced pressure, and the residual volatile content after drying under reduced pressure is 0.15% by weight or less with respect to the carrier. It is characterized by consisting of magnetic particles. Further, the method for producing a carrier for developing an electrostatic charge image of the present invention comprises mixing magnetic core particles with a resin solution and then coating the resin by drying the mixture under reduced pressure with stirring. It is characterized in that the heating is carried out at a substantially constant temperature, and the vacuum drying is terminated when the temperature rises by 10 ° C. or more above the minimum temperature of the heated mixture.

The present invention will be described in detail below. In the present invention, the carrier for developing an electrostatic charge image comprises resin-coated magnetic particles (hereinafter, referred to as magnetic particles) obtained by immersing the magnetic core particles in a resin solution and then drying under reduced pressure. The residual volatile content of the magnetic particles after drying under reduced pressure must be 0.15% by weight or less based on the carrier. If the residual volatile content is more than 0.15% by weight with respect to the carrier, the chargeability with the toner becomes unstable, and the chargeability is lowered in the initial stage of copying, and the background portion of the image is stained. Also, the chargeability rises due to the temperature rise inside the developing machine during continuous copying, and the image density decreases,
In addition, uneven image density due to carrier adhesion and scratches on the photoconductor occur. In the present invention, the smaller the residual volatile content, the more the effect of improving the chargeability at the initial stage of copying and the temperature rise inside the developing machine at the time of continuous copying. If it is 0.15% by weight or less, the initial purpose is achieved.

The magnetic core particles in the present invention are magnetic substance-dispersed particles in which a known magnetic fine powder such as magnetite is dispersed in a resin by melt-mixing a resin and magnetic fine powder and spray cooling. Other examples include magnetic substance-dispersed particles obtained by a kneading and pulverizing method, ordinary ferrite, magnetite granules, and the like. Among these, substantially spherical magnetic substance dispersion type particles obtained by melt-kneading a resin and magnetic substance fine powder and spray cooling are particularly preferable. These magnetic core particles are usually used as particles having a particle size of about 30 to 200 μm. In the case of magnetic substance-dispersed particles, a binder resin is used as a constituent component, and as the binder resin, a polyolefin-based compound which is a polymer of ethylene, propylene, butylene, isobutylene, or the like; a styrene-based monomer and an acrylic-based monomer Homopolymers or copolymers such as;
Polyester; polyurethane; epoxy resin; polyamide resin and the like can be used.

The coating resin used in the present invention includes styrenes such as styrene, chlorostyrene and methylstyrene; methyl methacrylate, methyl acrylate, propyl acrylate, lauryl acrylate, methacrylic acid, acrylic acid, butyl methacrylate and butyl. Α-Methylene aliphatic monocarboxylic acids such as acrylate, 2-ethylhexyl acrylate and ethyl methacrylate; nitriles such as acrylonitrile and methacrylonitrile; vinyl pyridines such as 2-vinylpyridine and 4-vinylpyridine; vinyl ethers; vinyl ketones Olefins such as ethylene, propylene and butadiene; homopolymers or copolymers of silicones such as methyl silicone and methylphenyl silicone; vinylidene fluoride, tetrafuro Ethylene, hexafluoropropylene, monochlorotrifluoroethylene polyfluoroethylene, monochloroethylene ethylene, copolymers of vinyl based fluorine-containing monomers such as trifluoroethylene ethylene; bisphenols, polyesters containing glycol.

In the present invention, in order to coat the magnetic core particles with the above resin, the above resin is dissolved in a suitable solvent to prepare a resin solution, and this resin solution is mixed with the magnetic core particles, The obtained mixture may be dried under reduced pressure with stirring using a heating medium heated to a predetermined temperature. In this case, the compounding amount of the coating resin is 0.2 to 3 of the carrier.
It is adjusted so as to be in the range of about 0.5% by weight, preferably 0.5 to 2% by weight. For the reduced pressure drying, a stirring reduced pressure dryer, specifically, a reduced pressure heating kneader, a reduced pressure heating Henschel mixer, a reduced pressure heating fluidized bed, a reduced pressure heating planetary mixer, or the like can be used.

In the present invention, the residual volatile content is 0.15.
In order to adjust the content to be less than or equal to wt%, the temperature may be reduced and dried using the temperature of the mixture of the magnetic core particles and the resin solution as an index. When the mixture of the magnetic core particles and the resin solution is dried under reduced pressure while stirring, the solvent evaporates from the mixture, and the heat of vaporization gradually lowers the temperature of the mixture. When drying is further continued, the solvent does not evaporate, and conversely, the temperature of the resin solution-immersed magnetic core particles begins to rise. In this specification, the temperature at this point is referred to as the minimum temperature of the mixture. If the drying under reduced pressure is continued under stirring and the drying is terminated when the temperature becomes higher than the above minimum temperature by 10 ° C. or more, the residual volatile content can be reduced to 0.15% by weight or less. Further, in the present invention,
After the above mixture is dried, it may be taken out from the stirring vacuum dryer, and then vacuum dried again at a temperature higher by 10 ° C. or more than the temperature at the time of taking out. This treatment is effective not only for magnetic substance-dispersed particles in which a magnetic substance is dispersed in resin, but also for magnetic substance nuclear particles using a material that easily contains volatile components in the nuclear particles.

The carrier for developing an electrostatic image of the present invention is mixed with a toner and used as a two-component developer. The toner is a binder resin in which a colorant or the like is dispersed, and examples of the binder resin used in the toner include styrenes such as styrene, parachlorostyrene, and α-methylstyrene; methyl acrylate, acrylic acid. Α-methylene aliphatic monocarboxylic acids such as ethyl, n-propyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate and 2-ethylhexyl methacrylate. Acid 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, vinyl isop Vinyl ketones such as lopenyl ketone,
Polymers of monomers such as unsaturated hydrocarbons such as ethylene, propylene, isoprene, butadiene and their halides, halogenated unsaturated hydrocarbons such as chloroprene, or a combination of two or more of these monomers Copolymer obtained by, and a mixture thereof, further rosin-modified phenol formalin resin, epoxy resin, polyester resin, polyurethane resin, polyamide resin,
Examples include non-vinyl condensation resins such as cellulose resins and polyether resins, or mixtures of these with the vinyl resins.

As the colorant used for the toner, carbon black, nigrosine dye, aniline blue, calcoil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue, or a mixture thereof can be mentioned. .
Further, known other components such as a metal salicylate, a metal-containing azo compound, a charge control agent such as nigrosine or a quaternary ammonium salt, and an offset preventive agent such as low molecular weight polypropylene, low molecular weight polyethylene and wax can be added. . Preferably, the weight average molecular weight is 500 to 5
000 low molecular weight polypropylene is preferred. To make a toner, the above toner materials are mixed using a Banbury mixer, a kneader coater, a CM mixer, an extruder, etc., melt-kneaded, pulverized and classified to have an average particle diameter of about 30 μm or less, particularly 3 μm or less. It is preferable to use fine particles of 20 to 20 μm. Further, a fluidizing agent such as silica, titania, or alumina, or an external additive such as a cleaning aid or a transfer aid such as polystyrene fine particles, polymethylmethacrylate fine particles, or polyvinylidene fluoride fine particles can be used. In particular, the average primary particle size is 5 nm to 30
Hydrophobic silica of nm is preferably used.

[0013]

When the magnetic core particles are coated with a resin, volatile components remain on the magnetic particles after drying.
When magnetic particles are used as carriers, they affect various points. That is, when the residual volatile content increases, the chargeability of the toner becomes unstable and the chargeability is initially lowered, or the temperature inside the developing machine during continuous copying increases,
As a result, the charging property is increased, and as a result, problems such as background stains initially occurring, image density decrease during continuous copying, density unevenness due to carrier adhesion, and photoconductor scratches occur. In particular, in the case where the magnetic core particles are ferrite particles that are not sufficiently sintered, or in the case of magnetic core particles in which magnetic fine powder is dispersed in a resin, volatile components permeate inside the core particles. The amount of volatile matter remains is large, and the above problem becomes remarkable. However, if the residual volatile content is set to 0.15% by weight or less of the carrier weight as in the present invention, the above problems are solved, the image quality maintainability with respect to the change in chargeability due to environmental changes and the like, and the carrier adhesion Is prevented, and a high-quality image excellent in black solid and fine line reproducibility can be stably obtained. The above treatment in the present invention is particularly effective in the case of magnetic substance-dispersed particles in which the resin and magnetic fine powder are melt-kneaded, spray-cooled, and the magnetic fine powder is dispersed in a substantially spherical resin.

[0014]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. (Production of Magnetic Nucleus Particles) The following composition is heated and melted and kneaded by a pressure type kneader, granulated by a spray cooling method using a disc type spraying device, and sieved for magnetic particle nuclei having an average particle size of 80 μm. The particles were obtained. Polyethylene (400P, Mitsui Petrochemical Industry Co., Ltd.) 30% by weight Magnetite powder (EPT1000, Toda Industry Co., Ltd.) 70% by weight

(Resin coating of magnetic core particles) To 40 kg of the magnetic core particles obtained, 12 kg of a chloroform solution (concentration 2.8 to 6.0% by weight) of polymethylmethacrylate (weight average molecular weight 15,000) was added. After mixing and mixing, according to the composition and coating process conditions of Table 1, resin was coated by performing vacuum drying under stirring with a vacuum type kneader heated to 55 ° C. under stirring. Resin coated magnetic core particles 1 to 5 were obtained. These were used as carriers for electrostatic image development. (Measurement of Residual Volatile Content) The residual volatile content was measured by the following method. About 50 g of each carrier of the sample was precisely weighed, transferred to a warm vacuum dryer for chemical experiments, and 5
While heating to 0 ° C, the pressure was reduced by a vacuum pump with a trap, dried at 10 mmHg or less for 1 hour, and then taken out.
After cooling to room temperature, it was weighed to quantify the volatile loss. The results are shown in Table 1.

(Production of Toner and Developer) Binder Resin (Styrene-n-Butyl Methacrylate) 84% by Weight Carbon Black (BPL, Cabot Co.) 10% by Weight Polypropylene Wax (660P, Sanyo Kasei Co., Ltd.) 5% by Weight Polyethylene wax (400P, manufactured by Mitsui Petrochemical Industry Co., Ltd.) 1% by weight The above composition was kneaded and pulverized to obtain a toner having an average particle diameter of 11μ. Next, the obtained toner was added to a carrier so as to have a concentration of 6% and mixed to obtain each developer.

(Image Quality Maintainability Test) Each developer was subjected to an image quality maintainability test of up to 50,000 sheets under a high temperature and high humidity environment using a modified machine of Fuji Xerox FX5039. The results are shown in Table 1.

[0018]

[Table 1]

[0019]

INDUSTRIAL APPLICABILITY According to the present invention, the residual volatile content of resin-coated magnetic core particles after drying under reduced pressure is set to 0.
When the content is 15% by weight or less, carrier adhesion is prevented and high image quality is ensured, carrier consumption is suppressed, and image quality maintainability is improved against changes in chargeability due to environmental changes and the like. It is possible to stably obtain an image of high quality with excellent solid black and fine line reproduction. The manufacturing method of the present invention, melt kneading resin and magnetic fine powder, spray cooling,
It is particularly effective in the case of magnetic substance dispersion type particles in which magnetic substance fine powder is dispersed in a substantially spherical resin.

Claims (3)

[Claims] 1. After mixing a resin solution and magnetic core particles,
A carrier for developing an electrostatic charge image, comprising magnetic particles which are coated with a resin by being dried under reduced pressure with stirring and which has a residual volatile content of 0.15% by weight or less after drying under reduced pressure. 2. The magnetic substance core particles are magnetic substance-dispersed particles obtained by melt-mixing magnetic substance fine powder and resin and then granulating by spray cooling. Electrostatic charge image developing carrier. 3. After mixing the magnetic core particles with the resin solution,
In the method for producing a carrier for developing an electrostatic charge image by performing resin coating by drying the mixture under reduced pressure with stirring, the drying under reduced pressure is performed using a heating medium having a substantially constant temperature, and at that time, the minimum temperature exhibited by the heated mixture is exhibited. The method for producing a carrier for developing an electrostatic charge image, characterized in that the drying under reduced pressure is terminated when the temperature rises by 10 ° C. or more.