JPH0217110B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a carrier that constitutes an electrostatic image developer together with a toner, and in particular coats the carrier core material with a specific resin to improve durability and obtain high-quality images. The present invention relates to a negatively chargeable carrier for electrostatic image development. [Prior Art] In electrophotography, a photoreceptor made of a photoconductive element is given a uniform surface charge in a dark place, an electrostatic image is formed by imagewise exposure, and this electrostatic image is developed. A visible image is formed. Generally, methods for developing such electrostatic images are broadly classified into wet developing methods and dry developing methods. The wet development method uses a liquid developer made by dispersing various pigments and dyes as fine particles in an insulating organic liquid, while the dry development method uses carbon black in a natural or synthetic resin. This is a developing method that uses fine electrostatic detection powder, which is a toner that contains a colorant dispersed therein. In addition to the so-called bristle brush method, impression method, and powder cloud method using a developer containing only the above-mentioned toner as a main component, this dry development method includes a method in which the above-mentioned toner is mixed with a carrier made of iron powder or glass beads, etc. There are the so-called magnetic brush method and the cascade method, which use the body as a developer. By these developing methods, electrostatic particles such as toner particles having electric charge contained in the developer adhere to the electrostatic image to form a visible image. This visible image is transferred directly onto a photoreceptor or onto paper or other image support by heat, pressure, solvent vapor, etc., and then fixed. The present invention relates to a developer carrier used in the magnetic brush method and cascade method among the above-mentioned development methods, that is, a carrier for imparting a desired charge to the toner by being stirred together with the toner. [Problems to be Solved by the Invention] Generally, carriers are broadly classified into conductive carriers and insulating carriers. Oxidized or unoxidized iron powder is usually used as the conductive carrier, but in a developer containing this iron powder carrier, the triboelectric charging properties of the toner are unstable, and the formation by the developer is unstable. There is a drawback that fog occurs in the visible image. That is, as toner particles adhere to the surface of iron powder carrier particles as a developer is used, the electrical resistance of the carrier particles increases and the bias current decreases, and the triboelectricity becomes unstable, resulting in the formation of toner particles. The image density of the visible image decreases and fog increases. Therefore, if a developer containing an iron powder carrier is used for continuous copying with an electronic copying device, the developer deteriorates after a few copies, making it necessary to replace the developer early, making it difficult to continue producing good images. I can't get it. A typical example of an insulating carrier is a carrier in which the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, or ferrite is uniformly coated with an insulating resin. In a developer using this insulating carrier, toner particles are less likely to fuse to the carrier surface than in the case of a conductive carrier, and at the same time, the frictional electrification between the toner and the carrier can be controlled, resulting in increased durability. is relatively excellent. Another advantage is that it can be used in high-speed electronic copying machines. However, in this insulating carrier, it is necessary that the coating layer covering the surface of the carrier core material has sufficient abrasion resistance (durability) and that the coating layer is good enough to prevent toner from forming a film on the carrier surface. It is required to have anti-sticking properties and to be able to obtain a charging state of a desired magnitude and polarity by friction with a specific toner used together with a carrier (charging property). That is, the insulating carrier is rubbed against other carrier particles, toner particles, the container wall, etc. in the developing device, but when the coating layer is worn away by this friction,
The stability of the charging characteristics caused by friction with the toner is lost, and as a result, it is not possible to impart a desired charging state to the toner particles. Furthermore, even if the coating layer of the insulating carrier has sufficient friction resistance, if its adhesion to the core material is poor, the coating layer will peel off or crumble due to the friction described above, and the charging characteristics will similarly deteriorate. become lost. Furthermore, if toner adheres to the surface of the coating layer to form a film, the charging characteristics will become unstable. In either case, it becomes necessary to quickly replace the entire developer with a new one. Conventionally, as a technique for improving such defects, a technique is known in which the surface of the carrier core material is coated with a fluoro compound such as perfluoroalkane or perfluoroalkyl (see Japanese Patent Laid-Open No. 117638/1983). However, in this technology, since the compound containing the coating layer has a relatively low molecular weight, the coating strength is weak and the friction resistance has not been significantly improved, resulting in poor durability and unstable triboelectrification. Ta. Therefore, as a technique for increasing the coating strength, a technique is known in which the coating is coated with a polymer containing a fluorinated acrylate or methacrylate having a specific structure as a monomer component (see Japanese Patent Application Laid-Open No. 53-97435). However, although the carrier had improved coating strength, it was found that performance deteriorated under high speed and repeated use over a long period of time, and there were problems with durability. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a negatively charging carrier for electrostatic image development that can increase image density, has durability even in high-speed and long-term use, and has stable triboelectric charging characteristics. . [Means for Solving the Problems] The negatively chargeable carrier for electrostatic image development according to the present invention contains at least 50 wt% or more of a monomer represented by the following general formula (1) on the surface of the carrier core material. Molecular weight/intrinsic viscosity obtained from the monomer mixture [η] 0.01
2.0, preferably 0.1 to 1.0, or a composition containing the polymer. General formula (1) [In the formula, R ¹ represents a hydrogen atom or a methyl group,
n represents 1 or 2; m represents 1 or 2; ] Hereinafter, the present invention will be explained in detail. In this specification, the molecular weight/intrinsic viscosity [η] of a polymer refers to a value measured at 35°C in methyl ethyl ketone or m-xylene hexafluoride solvent. The carrier coating material according to the present invention has a molecular weight and an intrinsic viscosity [η] of 0.01 obtained from a monomer mixture containing 50 wt% or more of the monomer represented by the above general formula (1).
~2.0, preferably 0.1 to 1.0, the polymer itself may be used, or it may be a composition containing the polymer. The monomer represented by the above general formula (1) is characterized by the structure of -(CF ₂ ) mH, which is a fluoro-containing substituent,
It is particularly distinctive in that it contains a hydrogen atom, and is different from conventional substituent structures. That is, to the best of the inventor's knowledge,
Only perfluoroalkyl groups as described in Japanese Patent No. 97435 are known, and substituents containing hydrogen atoms are not known. As a result of extensive research, the present inventors have discovered that by using the carrier unique to the present invention, it is possible to obtain high-quality images and to improve the adhesion with the core material. Although this may be due to this, they have found that the solvent solubility of the polymer can be significantly improved, and the carrier itself can be manufactured extremely easily. In the present invention, if the monomer component is less than 50 wt%, the triboelectric charging properties will be insufficient, causing fogging, and if the amount is further reduced, an oppositely charged toner will be produced. Furthermore, toner adhesion is more likely to occur due to the increase in surface tension. Examples of monomer components (second component) other than those mentioned above used in the present invention include acrylic (methacrylic) acid, methyl acrylic (methacrylate), ethyl acrylic (methacrylate), butyl acrylic (methacrylate), and acrylic (methacrylic) acid. Examples include benzyl methacrylate, acrylic amide, cyclohexyl acrylate, glycidyl acrylate, hydroxyethyl acrylate, styrene, vinyl acetate, ethylene, propylene, isoprene, etc. . Polymers (including copolymers) used in the present invention
Specific examples include, but are not limited to, the following: [Exemplary compounds] As the coating material for the carrier according to the present invention, a composition containing the above-mentioned polymer and other substances can also be used.
Examples include polymers or copolymers made of the compounds described in Publication No. 97435, and blend compositions can be obtained by incorporating them. As mentioned above, the carrier coating resin in the present invention may be a polymer of a monomer alone, a copolymer containing other monomers, or a blend of the above polymer or copolymer with the above other components. In either case, the object of the present invention can be achieved. The content of the polymer of the present invention in the composition (blend) is 50 wt% or more. In manufacturing the carrier used in the present invention, the above polymer or composition is dissolved in an organic solvent to prepare a coating solution, and the coating solution is applied to the surface of the carrier core material by, for example, a dry spray method to form a coating layer. Thereafter, the carrier used in the present invention is obtained by further heating or standing. Specifically, for example in a fluidized bed apparatus, the carrier core is raised to an equilibrium height by means of a rising pressurized gas stream, and then the coating liquid is sprayed on by the time the core falls again.
This application is repeated to form a coating layer in advance. Incidentally, if there is agglomerated 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 μm to 20 μm, preferably 0.1 μm to
It is in the range of 2μm. The organic solvent used in the above production may be any solvent as long as it dissolves the resin containing the polymer of the present invention as a main component, but examples include acetone, ketones such as methyl ethyl ketone, tetrahydrofuran, dioxane, dimethyl sulfoxide, or any of these. A mixed solvent etc. is used. The material of the carrier core material in the present invention is as follows:
Materials conventionally used as carrier core materials such as sand, glass, and metal can be used, but in particular, materials that are strongly magnetized in the direction of a magnetic field, such as ferrite and magnetite, can be used.
ferromagnetic metals such as iron, cobalt, and nickel;
or alloys or compounds containing these metals;
Alloys that do not contain ferromagnetic elements but become ferromagnetic through appropriate heat treatment, such as alloys called Heusler alloys such as manganese-copper-aluminum or manganese-copper-tin, or chromium dioxide. etc. can be mentioned as suitable ones. The particle size of these carrier core materials is 30~
1000 μm, preferably 50-500 μm. The carrier of the present invention has an absolute value of 5 to 40 μC/g with respect to the toner used together under normal usage conditions.
It is preferable that the electric charge be given as follows. The carrier according to the present invention can constitute a two-component developer with any toner. Among these, preferred toners include those using polyester resin or styrene/acrylic resin as a binder. Polyester resin is obtained by polycondensation of alcohol and carboxylic acid, and the alcohols used include, for example, ethylene glycol, diethylene glycol, triethylene glycol,
Diols such as 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,4-bis(hydroxymethyl)cyclohexane, and bisphenol A, etherified bisphenols such as hydrogenated bisphenol A, polyoxyethylenated bisphenol A, and polyoxypropylenated bisphenol A;
Other dihydric alcohol monomers may be mentioned. Examples of carboxylic acids include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, malonic acid, Examples include anhydrides of these acids, dimers of lower alkyl esters and linoleic acid, and other divalent organic acid monomers. As the polyester resin used in the present invention, it is preferable to use not only a polymer composed only of the above difunctional monomers but also a polymer containing a component composed of trifunctional or higher polyfunctional monomers. Examples of such polyfunctional monomers, such as trivalent or higher polyhydric alcohol monomers, include sorbitol, 1,
2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose,
1,2,4-butanetriol, 1,2,5-pentatriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3 , 5-trihydroxymethylbenzene, and others. In addition, as trivalent or higher polyvalent carboxylic acid monomers,
For example, 1,2,4-benzenetricarboxylic acid,
1,3,5-benzenetricarboxylic acid, 1,2,
4-cyclohexanetricarboxylic acid, 2,5,7
- Naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-
Mention may be made of methylenecarboxypropane, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, Empol trimer acid, anhydrides of these acids, and others. It is desirable that the above-mentioned polyfunctional monomer component is contained in a proportion of 20 to 30 mol % in each of the alcohol component or acid component as a structural unit in the polymer. As for styrene/acrylic resin, JP-A-50
-Contains the α,β-unsaturated ethylenic monomer described in Publication No. 134652 as a structural unit, and has a weight average molecular weight (Mw)/number average molecular weight (Mn) of 3.5
~40 resins can be used. The content of the polyester resin or styrene/acrylic resin is preferably 30 to 95 wt% based on the total amount of the toner. In order to produce the toner used in the present invention, a coloring agent is contained in the binder, various additives are added as necessary, and the toner is mixed in a ball mill or the like, and through the steps of kneading, pulverization, and classification. It is possible to obtain toner used in In addition, it can also be obtained by a manufacturing method other than the above, such as spray drying, interfacial polycondensation, suspension polycondensation, or solution polycondensation. The particle size of the toner obtained by the above method is 1~
It is 50 μm, preferably 5 to 30 μm. Specific examples of colorants contained in toner include:
For example, carbon black, nigrosine dye, aniline blue, calco oil blue, chrome yellow, ultramarine blue, methylene blue,
Mention may be made of rose bengal, phthalocyanine blue, or mixtures thereof. Further, examples of additives that may be added as necessary include offset inhibitors, charge control agents, and the like. The developer described above 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 per 100 parts by weight of the carrier. [Effects of the Invention] Since the carrier of the present invention uses a copolymer containing a specific monomer having a side chain with a fluorine atom as a monomer component as a material for its coating layer,
It has the following effects: high quality images can be obtained, adhesion to the core material is improved, triboelectric charging properties are very stable during long-term use, and the material is highly durable. Furthermore, since the polymer of the present invention has high solubility in organic solvents, it has the advantage that it can be easily manufactured by a dry spray method or a dipping method.
In other words, for carriers coated with conventional fluorine-based resins, since fluorine-based resins have low solvent solubility, firing methods were used as a means of fixing the core material and resin in the manufacturing method. There were some shortcomings. For example, a technique in which the surface of the carrier core material is coated with a copolymer of tetrafluoroethylene and hexafluoropropylene as a fluorocarbon resin, and an epoxy resin or polyurethane as a modifier (see JP-A-47-17435) In order to bond the non-adhesive fluorocarbon resin to the surface of the carrier core material, a cross-linking resin such as epoxy or polyurethane is blended and baked to bond it, and the surface of the carrier core material is bonded to the surface of the carrier core material. In the technique of using tetrafluoroethylene as a fluorocarbon resin and coating it with a brimer containing chromium or phosphoric acid as an adhesive (see Japanese Patent Application Laid-open No. 1983-90238), the adhesiveness is improved. It is coated with brimer containing chromium and phosphoric acid, and then coated with fluorine-based resin and fired.
It was necessary to bake at a high temperature of ~400°C, and there were drawbacks in manufacturing, such as the adhesion and the triboelectric charging characteristics of the developer changing depending on the temperature conditions. In contrast, the present invention does not have the above-mentioned drawbacks and can exhibit the various effects described above. [Example] Examples of the present invention will be described below, but the embodiments of the present invention are not limited thereto. Manufacture of carrier A coating solution was prepared by dissolving 15 g of each of exemplified polymers (1) to (2) in 500 ml of acetone-methyl ethyl ketone (1:1) mixed solvent. A carrier of the present invention having a film thickness of about 2 μm was produced by coating 1 kg of “DSP-135C” (manufactured by Dowa Iron Powder Industries Co., Ltd.) using a fluidizing bed device. These will be referred to as "carrier A" and "carrier B." On the other hand, using the following polymers (a) and (b) and using 1,1,2-trifluoro-1,2,2-trichloroethane or methyl ethyl ketone as a coating solvent,
A "comparative carrier A" and a "comparative carrier B" were produced in the same manner as the carrier of the present invention. Toner A 332g of terephthalic acid, 90g of polyoxypropylene (2,2)-2,2-bis(4-hydroxyphenyl)propane, and 587g of bisphenol A
into a round-bottomed flask equipped with a thermometer, a stainless steel stirrer, a glass nitrogen gas inlet tube, and a flow-down condenser, set the flask on a heating mantle, and introduce nitrogen gas through the nitrogen gas inlet tube. The temperature was raised while keeping the inside of the flask in an inert atmosphere. Then, 0.05 g of dibutyltin oxide was added, and the reaction was allowed to proceed at a temperature of 200° C. while monitoring the reaction at the softening point to produce a polyester resin. 100 parts by weight of this polyester resin, 10 parts by weight of carbon black "Regal 660R" (manufactured by Cabot), low molecular weight polypropylene "Viscol"
660P" (manufactured by Sanyo Chemical Industries, Ltd.) and 2 parts by weight of ethylene bisstearoylamide "Hoechst Wax C" (manufactured by Hoechst Corporation) were mixed in a ball mill, and after each process of kneading, pulverization, and classification, average particles were obtained. Toner A having a diameter of 10 μm was produced. Toner B 100 parts by weight of styrene/methyl methacrylate/n-butyl methacrylate copolymer obtained by reacting styrene, methyl methacrylate and n-butyl methacrylate at a molar ratio of 50:20:30, Carbon Black "Regal" 660R” (manufactured by Kyabot Co., Ltd.) 10 parts by weight, low molecular weight polypropylene “Viscol
660P'' (manufactured by Sanyo Chemical Industries, Ltd.) was mixed in a ball mill and subjected to the steps of kneading, pulverization, and classification to produce toner B having an average particle size of 11 μm. Examples and Comparative Examples Carriers A to B and toners A to B of the present invention were mixed in combinations shown in Table 1 at a toner concentration of 2% to prepare a total of two types of developers. On the other hand, for comparison, a total of two types of developers were prepared by combining comparative carriers A and B and toners A to B at a toner concentration of 2%. Next, the electrophotographic copying machine "U-
Using a modified machine called "Bix3000" (manufactured by Konishiroku Photo Industry Co., Ltd.), continuous copies of up to 20,000 sheets were made for each developer. The results are shown in Table 1.

[Table] In the table, "charge amount" is the amount of triboelectric charge per 1 g of toner measured by a known blow-off method, and "maximum image density" is the value of the developed image when the image density of the original image is 1.3. It is expressed by the relative density of the image, and "durability" is expressed by the number of copies made when fogging occurs and the image quality begins to deteriorate significantly. As is clear from Table 1 above, when the carrier of the present invention is used, the toner charge amount is also appropriate;
It is also found that the maximum image density is high and the durability is good. On the other hand, when using a comparison carrier,
Initially, both the toner charge amount and image density were satisfactory, but the durability deteriorated.

Claims (1)

[Scope of Claims] 1. Molecular weight/intrinsic viscosity [η] 0.01 obtained from a monomer mixture containing at least 50 wt% or more of the monomer represented by the following general formula (1) on the surface of the carrier core material.
2.0 or a composition containing the polymer. General formula (1) [In the formula, R ¹ represents a hydrogen atom or a methyl group,
n represents 1 or 2; m represents 1 or 2; ]