JPH05127431A - Carrier for electrostatic charge image developing and its production - Google Patents

Abstract

PURPOSE:To obtain a resin coated carrier having good mechanical characteristics and water resistance and to increase the safeness of the carrier for environment by coating the carrier core material with water-base polyurethane and heating at specified temp. or higher to strengthen the coating. CONSTITUTION:This electrostatic charge image development carrier consists of the carrier core material coated with a compsn. containing at least water-base polyurethane. After coating the carrier core material with a compsn. containing at least water-base polyurethane, the carrier is subjected to heat treatment at >=80 deg.C. In the production process of the carrier, urethane resin soluble or dispersible in water is used. This urethane resin is obtd. by preparing a polyurethane polymer obtd. by the reaction of polyisocyanate having 2 or more isocyanate groups and polyols having >=2 hydroxyl groups and then making this polymer in a water-base form. To make the polyurethane in a water-base form, an emulsifier is used, or self-emulsification is effected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for electrostatic images of electrophotography and electrostatic recording, and more particularly to a dry two-component developer comprising a carrier and a toner.

[0002]

2. Description of the Related Art In electrophotography, a photosensitive member having a photoconductive layer is provided with a uniform surface charge in a dark place, and then an electrostatic image is formed by imagewise exposure, and the electrostatic image is developed. To form a visible image.

Generally, the method for developing such an electrostatic image is roughly classified into a wet developing method and a dry developing method. The wet developing method is a method of developing using a liquid developing agent in which various pigments and dyes are dispersed as fine particles in an insulating organic liquid, and the dry developing method is a method of developing carbon black in a natural or synthetic resin. Is a developing method using a toner containing a colorant such as the above. In this dry development method, a so-called bristle brush method using a developer containing only the toner as a main component, an impression method, a powder cloud method, or a mixture of the toner and a carrier made of iron powder or glass beads is used. There are so-called magnetic brush method and cascade method used as a developer.

By these developing methods, toner particles having a charge contained in the developer adhere to the electrostatic image to form a visible image. This visible image is transferred onto the photoreceptor as it is by heat, pressure, solvent vapor or the like, or is fixed onto paper or other record carrier.

Carriers of the dry two-component type developer which is the object of the present invention are roughly classified into conductive carriers and insulating carriers.

Oxidized or non-oxidized iron powder is usually used as the conductive carrier. In a developer containing the iron powder carrier as a component, the triboelectric chargeability against the toner is unstable, and the developer is not developed. There is a drawback that the visible image formed by the agent causes fogging. That is, as the toner particles adhere to the surface of the iron powder carrier particles as the developer is used, the electric resistance of the carrier particles increases, the bias current decreases, and the triboelectrification becomes unstable. The image density of the visible image is reduced and the fog is increased. Therefore, when copying continuously with an electronic copying machine using a developer containing an iron powder carrier, the developer deteriorates in a small number of times, so it is necessary to replace the developer at an early stage, so that good images can be continuously reproduced. I can't get it.

As the insulating carrier, iron,
A typical example is a carrier in which the surface of a carrier core material made of a ferromagnetic material such as nickel or ferrite is uniformly coated with an insulating resin. In the developer using this insulative carrier, the toner particles are much less fused to the carrier surface than in the case of the conductive carrier, and at the same time, the triboelectrification property between the toner and the carrier can be controlled and the durability can be improved. Is relatively excellent. It also has the advantage that it can be used in high-speed electronic copying machines. However, in this insulative carrier, the coating layer that covers the surface of the carrier core material has sufficient abrasion resistance (durability), and the coating layer is well fixed so that the toner film is not formed on the carrier surface. It is required to have an antistatic property and to obtain a charged state of a desired strength (charging property) by friction with a specific toner used together with a carrier.

That is, the insulating carrier is rubbed with other carrier particles, toner particles, container walls, etc. in the developing device. When the coating layer is abraded by the friction, the stability of the charging property caused by the friction with the toner is generated. Are lost, and the toner particles cannot be given a desired charge state. Further, even if the coating layer of the insulating carrier has sufficient abrasion resistance, if the adhesiveness to the core material is poor, the coating layer is peeled off or crushed by the above-mentioned friction, and the charging property is similarly lost. Like Furthermore, when toner adheres to the surface of the coating layer to form a coating, the charging characteristics also become unstable. In either case, it is necessary to replace the entire developer with a new one as soon as possible.

Conventionally, there has been no insulating carrier satisfying all of these.

That is, the coating resin is dissolved in a ketone such as acetone or methyl ethyl ketone, an aromatic hydrocarbon such as toluene or xylene, or an organic solvent such as dioxane or tetrahydrofuran, and a carrier is prepared by using this solution by, for example, a dipping method or a spray method. Had been applied to. Since these organic solvents have relatively low boiling points, they have a large risk of explosion and have a great influence on the human body due to inhalation. Further, there has been a drawback that the equipment investment of the apparatus for recovering the used solvent is large and the cost is high.

Further, the resin-coated carrier has poor adhesion to the carrier core material, and the coating layer is peeled off or abraded due to long-term mixing and friction in the developing device, so that a proper charge amount is imparted to the toner. The charging ability was lowered, causing fogging and toner scattering. In addition, since the water resistance is poor, there is a drawback that the charging ability greatly depends on the environment.

[0012]

OBJECTS OF THE INVENTION In view of the above circumstances, the object of the present invention is: (1) Providing a method for producing a resin-coated carrier having high environmental safety (use of no organic solvent itself, elimination of explosion risk, odorless process) ), (2) Providing an inexpensive resin-coated carrier manufacturing method (no solvent recovery device required), (3) Providing a carrier having a coating having good mechanical properties, (4) Providing a coating having good water resistance. Providing a carrier with.

[0013]

The above object of the present invention is achieved by an electrostatic image developing carrier characterized in that the surface of a carrier core material is coated with a composition containing at least an aqueous polyurethane resin. It can be obtained by a production method in which the surface of the carrier core material is coated with a composition containing at least an aqueous polyurethane resin and then heat-treated at a temperature of 80 ° C. or higher.

In the production of the carrier used in the present invention, a water-soluble or dispersible urethane resin is used.

The urethane resin has 2 isocyanate groups.
It is obtained by making a polyurethane polymer aqueous by reacting a polyisocyanate having one or more hydroxyl groups with a polyol having two or more hydroxyl groups.

Examples of the compound having two or more isocyanate groups used in the present invention include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 2,4- and 2,6-tolylene diisocyanate. Mixture, crude tolylene diisocyanate, methylene diphenyl diisocyanate, crude methylene diphenyl diisocyanate,
4,4 ', 4 "-triphenylmethylene triisocyanate,
4,4'-dimethyldiphenylmethane-2,2 ', 5,5'-tetraisocyanate, xylene diisocyanate, hexamethylene-1,6-diisocyanate, lysine diisocyanate methyl ester, polymethylene polyphenyl isocyanate, hydrogenated methylene diphenyl isocyanate, m-Phenylene diisocyanate, naphthylene-1,5-diisocyanate, 1-methoxyphenyl-2,4-diisocyanate, diphenylmethane-4,4′-diisocyanate, 4,4 ′
-Biphenylene diisocyanate, 3,3'-dimethoxy-4,
4'-biphenyl isocyanate, 3,3'-dimethyl-4,4 '
-Biphenyl diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, isophorone diisocyanate and the like can be mentioned. It is also possible to use a so-called terminal isocyanate prepolymer obtained by using these organic polyisocyanates with respect to the polyfunctional hydrogen compound in a stoichiometric excess, for example, 4,4'- A terminal isocyanate prepolymer of diphenylmethane diisocyanate and poly-ε-caprolactone diol, polytetrahydrofuran ether diol and the like are included.

Examples of the polyol used in the present invention include low molecular weight polyols such as ethylene glycol, propylene glycol, glycerin, hexanetriol, and trimethylolpropane; for example, polyether polyol, polyester polyol, acrylic polyol, phenol resin polyol, epoxy. High molecular weight polyols such as polyols, butadiene polyols, polyester-polyether polyols, acrylics, styrenes, vinyl addition and / or dispersion polymer polyols, urea dispersion polyols, carbonate polyols and the like.

As a method for making polyurethane polyurethane aqueous,
There are cases where an emulsifier is used and cases where self-emulsification is not used. Self-emulsification means that the polyurethane itself is water-soluble or dispersible in water by adding a cationic functional group or anionic functional group. Is reacted with a tertiary amine having 2 or more groups, and the tertiary amino group is cationized with a quaternary emulsifier. (2) The polyurethane prepolymer is reacted with a tertiary amine having 2 or more hydroxyl groups, and then an acid Method of neutralizing with an aqueous solution and emulsifying, (3) having two or more hydroxyl groups 4
A method of reacting a primary salt, (4) a method of reacting a polyurethane prepolymer with a polyalkylene polyamine, and further reacting an epihalohydrin with an acid to cationize
(5) There is a method in which a polyurethane prepolymer is converted into a bis-bullet with a urea compound and quaternized with α-chloroacetamide. The method of obtaining anionic polyurethane is
(1) a method of reacting a polyurethane prepolymer with a diaminophenylcarboxylic acid salt to introduce an anionic hydrophilic group, (2) a method of reacting an isocyanate group at the end of the polyurethane prepolymer with a blocking agent such as sodium bisulfite, ( 3) A method in which an aromatic ring of a polyurethane prepolymer using an aromatic isocyanate is sulfonated, then neutralized with a tertiary amine, and further reacted with water to obtain an anionic polyurethane. (4) Polyurethane prepolymer and diamino There are a method of reacting with an aqueous solution of alkane sulfonate and a method of (5) reacting an acid having a hydroxyl group with a prepolymer, adding triethanolamine to form an ionomer, and then adding to water to form an emulsion.

From the viewpoint of the triboelectrification property of the carrier, particularly the environmental dependence, the self-emulsification to make the aqueous solution is preferable.

By adding diamine or polyamine to the water-based polyurethane resin, chain extension and crosslinking reaction can be promoted, and mechanical strength and water resistance can be further improved. Further, it becomes possible to control the charging ability of the carrier by this addition amount.

As commercially available waterborne polyurethanes, Takelac W-610, W-620, W-630 and W-710 (manufactured by Takeda Pharmaceutical Co., Ltd.) can be used.

Next, a method of coating the carrier core material with the water-based polyurethane resin will be described.

The polyurethane resin is dissolved or dispersed in water to prepare a coating solution, which is applied to the surface of the carrier core material by, for example, a dry spray method to form a coating layer, and then heated to be used in the present invention. Get a career. The heating temperature must be 80 ℃ or higher.

Specifically, for example, in a fluidizing bed apparatus, a carrier gas core is raised to a height of equilibrium by an ascending pressurized gas flow, and the coating liquid is sprayed until the core falls again. Apply. This coating is repeated to form a coating layer in advance. When there is an aggregated carrier, it can be sieved to finally obtain the carrier of the present invention having a desired film thickness. The thickness of the coating layer is in the range of 0.05 to 20 μm, preferably 0.1 to 2 μm.

As the material of the carrier core material in the present invention, those conventionally used as the carrier core material such as sand, glass and metal can be used. In particular, a substance which is strongly magnetized in that direction by magnetism, For example, ferrite, magnetite, iron, cobalt, nickel, and other metals exhibiting ferromagnetism, or alloys or compounds containing these metals, but containing no ferromagnetic element, but exhibiting ferromagnetism by appropriate heat treatment Suitable alloys include, for example, alloys of the type called Heusler alloys such as manganese-copper-aluminum or manganese-copper-tin, or chromium dioxide. The particle diameter of these carrier core materials is 30 to 1000 μm, preferably 50 to 500.
μm. The carrier of the present invention has an absolute value of 5 to 40 μC / toner with respect to the toner used together under normal use conditions.
It is preferable to give a charge of g.

The carrier according to the present invention can form a two-component developer with an arbitrary toner. Among them, preferable toners include those using polyester resin or styrene / acrylic resin as the binder.

To produce the toner used in the present invention, a colorant is contained in the binder, various additives are added if necessary, and the mixture is mixed by a ball mill or the like.
The toner used in the present invention can be obtained through the steps of blending, pulverizing, and classifying.

It is possible to obtain it by a manufacturing method other than the above, for example, a spray drying method, an interfacial polycondensation method, a suspension polycondensation method, a solution polycondensation method, or the like.

The particle size of the toner obtained by the above method is 1
˜50 μm, preferably 5˜30 μm.

Specific examples of the colorant contained in the toner include, for example, carbon black, nigrosine dye, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, phthalocyanine blue or a mixture thereof. be able to.

Further, examples of the additive added as necessary include an offset preventive agent, a charge control agent and the like.

The above-mentioned developer is obtained by mixing the carrier of the present invention and the toner, and the mixing ratio thereof is preferably 0.3 to 20 parts by weight with respect to 100 parts by weight of the carrier.

[0033]

EXAMPLES Next, the present invention will be described in detail with reference to Examples.

(Manufacture of Carrier) Carrier 1 Water-based urethane resin "Takelac W-610" (manufactured by Takeda Pharmaceutical Co., Ltd., solid content 35%) 100 g, distilled water 400 ml was added,
A solution was prepared. This solution was spray-coated on 2 kg of spherical ferrite particles (average particle size 80 μm) as a carrier core material by a fluidized bed coating method, and then dried at 120 ° C. for 5 minutes,
The carrier 1 of the present invention was manufactured. This carrier 1 had a good fluidity without stickiness and no agglomeration.

Carrier 2 Carrier 2 was obtained in the same manner as Carrier 1 using water-based urethane resin "Takelac W-630" (manufactured by Takeda Pharmaceutical Co., Ltd., solid content 35%).

Carrier 3 Carrier 3 was obtained in the same manner as Carrier 1 except that 0.5 g of hexamethylenediamine was added to the urethane resin aqueous solution of Carrier 1.

Carrier 4 Polystyrene (molecular weight Mw = 10,000) 30 g, toluene 500 ml
2 kg of spherical ferrite particles (average particle size 80 μm) as a carrier core material
Was spray-coated by a fluidized bed coating method and dried at 70 ° C. for 5 minutes to prepare a carrier 4 for comparison.

(Production of Toner) Toner 1 Copolymer 100 obtained by reacting styrene, methyl methacrylate, and butyl methacrylate (molar ratio 50/20/30)
Parts by weight, carbon black "Mogul L" (manufactured by Cablack) 10 parts by weight, low molecular weight polypropylene "Viscole"
660 p "(manufactured by Sanyo Kasei Co., Ltd.), kneaded by a heating roll, cooled, coarsely crushed, further finely pulverized by an ultrasonic jet mill, and classified by an air classifier to obtain colored fine particles. It was

Hydrophobic silica fine powder "Aerosil R-972" (manufactured by Aerosil) to 100 parts by weight of the colored fine particles.
0.8 parts by weight were mixed with a V-type mixer to obtain a toner having an average particle size of 11 μm.

(Preparation of Developer) 1,96 parts by weight of carrier and 1,4 parts by weight of toner were mixed with a YGG mixer (manufactured by Yayoi Co., Ltd.) at 100 rpm for 20 minutes to prepare a developer.

Carriers 2 to 4 are used in the same manner as developers 2 to 4
Was prepared.

(Evaluation of Developer) The developer was 5 at a temperature of 33 ° C. and a relative humidity of 80% by a modified electrophotographic copying machine “U-Bix5000” (manufactured by Konica Corporation).
Ten thousand running tests were performed.

For the evaluation, the coverage rate, charge amount, image, continuous copy number (durability), specific resistance, and image quality of 5th generation copy were examined, and the results are summarized in Table 1.

[0044]

[Table 1]

The meanings of the terms in Table 1 are as follows.

The "coverage" was obtained by calcining the coated carrier at high temperature and calculating the weight of the resin relative to the carrier core material from the amount of carbon dioxide produced. The manufactured carrier was used before the start of running. After running, the developer was washed with water containing a surfactant to remove the toner, and a carrier dried at 40 ° C. for 24 hours was used.

The "charge amount" is the value of the triboelectric charge amount per 1 g of the developer measured by the flow-off method.

"Dmax" represents the maximum image density, and is represented by the relative density of the developed image when the image density of the original image is 1.3.

The "fog" is expressed by the relative density of the developed image when the density of the original image is 0.

"5th generation copy" means 1 copy of the original image.
This is the fifth copy when the first-generation copy is the second-generation copy. The image quality of the fifth generation copy is indicated by x when it is less than the practical level, Δ when it is at the practical level limit, and by ◯ when it is better than the practical level.

"Durability" means that the fog value of the developed image is 0.
It is the number of copies when the value becomes 03 or more or the value of Dmax becomes 0.7 or less. In addition, the number of copies when the 5th generation copy has reached the practical level is also shown. It should be noted that the number of copied sheets of "50,000 sheets or more" means that neither the fogging value nor the Dmax value reached the above-mentioned limit value even after copying 50,000 sheets.

The "specific resistance" was calculated from the value of the current flowing in the carrier layer under the condition that the electrode area was 1 cm ² and the load was 1 kg, with 100 V applied in 1 cm of the carrier layer. For the measurement, the manufactured carrier was used at the start of running, and the carrier from which the toner was removed by blow-off after the start of running was used.

[0053]

By using an aqueous polyurethane resin for the carrier coating layer, it is not necessary to use an organic solvent, there is no danger of explosion and the process is odorless, and there is no need to recover the solvent. An inexpensive resin-coated carrier can be obtained.

The obtained resin-coated carrier has good mechanical properties and water resistance.

Claims (2)

[Claims] 1. A carrier for electrostatic image development, characterized in that the surface of a carrier core material is coated with a composition containing at least an aqueous polyurethane resin. 2. A method for producing a carrier for electrostatic image development, which comprises coating the surface of a carrier core material with a composition containing at least an aqueous polyurethane resin and then heat-treating it at a temperature of 80 ° C. or higher.