JPH0542673B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a carrier that constitutes an electrostatic developer together with a toner, and in particular to an electrostatic image development method in which durability is improved and triboelectric charging properties are stabilized by coating the carrier core material with a resin. related to carriers. [Prior Art] In electrophotography, a photoreceptor made of a photoconductive element is given a uniform surface charge in a dark place, an electrostatic charge image is formed by imagewise exposure, and this electrostatic charge 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 a fine powder, called a toner, which contains a colorant such as the following 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 charged toner particles contained in the developer adhere to the electrostatic charge 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. 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 triboelectricity of the toner is unstable, and the toner is formed by the developer. 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 triboelectric charging properties become 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 continuously ejected by an electronic copying device, the developer deteriorates after a few times, so it is 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, making it durable. Relatively good properties. 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 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 abrasion 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 abrasion resistance has not been significantly improved, resulting in poor durability and unstable triboelectric charging properties. It was hot. 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 this technology uses a high molecular weight polymer to increase the strength of the coating, it has insufficient adhesion and film forming properties, so the coating layer peels off during repeated use at high speeds and over long periods of time. The drawback was that the triboelectric charging properties became unstable, resulting in poor durability. In particular, it has been found that the peeling object that causes this is not one in which the coating layer peels off from the surface of the core material, but in which the coating layer peels off from the middle of the coating layer. [Object of the Invention] The object of the present invention is to provide an electrostatic charge image that has good film-forming and adhesion properties for the coating layer on the carrier core material, is durable even in high-speed and long-term use, and has stable triboelectric charging characteristics. The purpose is to provide a developing carrier. Other objects of the invention will become apparent from the following description of the specification. [Summary of the Invention] The carrier for developing electrostatic images according to the present invention is characterized in that a carrier core material is coated with a composition consisting of at least the following (a) and (b). (a) A copolymer whose essential main components are a monomer represented by the following general formula (1) and a monomer having a carboxylic acid group or carboxylic acid anhydride group in the side chain that can be copolymerized with the monomer. Combined. General formula (1) [In the formula, R represents a hydrogen atom or a methyl group, and
represents an oxygen atom, a COO group, or a CO group, and Rf represents a fluoroalkyl group. ] (b) A crosslinking agent selected from epoxy compounds, isocyanate compounds, hydroxy compounds, melamine resins, and urea resins. [Structure of the Invention] The composition of the present invention contains, as component a, a copolymer consisting of at least a monomer having a fluorine atom in its side chain and a monomer having a carboxylic acid group or a carboxylic acid anhydride group in its side chain. The composition further comprises at least a crosslinking agent capable of reacting with the side chain of the monomer having the carboxylic acid group or carboxylic anhydride group as component b. By bonding fluorine atoms to the side chains, it is possible to adjust solvent solubility, charging characteristics, film properties, etc., and it is easier to handle and has better properties than polymers in which fluorine atoms are directly bonded to the main chain. The top is also excellent. Structurally, it is necessary to use two or more atoms, preferably three or more atoms, from the main chain carbon atoms. For example, as the monomer having the nitrogen atom in its side chain, monomers listed in the following general formulas (2) to (15) can be used. General formula (2) General formula (3) General formula (4) General formula (5) General formula (6) General formula (7) General formula (8) General formula (9) General formula (10) General formula (11) General formula (12) General formula (13) General formula (14) General formula (15) In the formula, R ₁ represents a hydrogen atom or a methyl group, and R ₂
represents a fluoroalkyl group having 1 to 21 carbon atoms, preferably 2 to 12 carbon atoms, particularly preferably 2 to 8 carbon atoms, and R ₃
represents an alkyl group having 2 to 8 carbon atoms in which half or more of the hydrogen atoms are substituted with _fluorine ;
X ₂ and X ₃ are each selected from a halogen atom or hydrogen and always contain one or more fluorine atoms,
m represents 0, 1, 2, 3, and n represents 1 or 2. Among the monomers represented by the above general formulas, monomers of general formulas (2) to (5) are preferably used. As specific monomers, for example, those listed below can be used.

【table】

【table】

[Exemplary compounds]

b-(1) b-(2) b-(3) Product name “Epon 1031” “ERRA-0153” (manufactured by UCC) b-(4) Product name “EPE-1359” (manufactured by Ciba Geigy) “QT-3476” (manufactured by Dow Chemical) b-(5) b-(6) Product name “DEN438” (n=1.3) “DEN439” “Epicote 152” (n=0-1) “Epicote 154” (n=1.5 or more) Above (manufactured by Ciel Chemical Co., Ltd.) b-(7) Tolylene diisocyanate ( TDI) b-(8) 3,3'-tolylene-4,4'-diisocyanate b-(9) Diphenylmethane-4,4'-diisocyanate (MDI) b-(10) Triphenylmethane-P,P',P''-triisocyanate (TM) b-(11) 2,4-trilene timer (TT) b-(12) Naphthalene-1,5-diisocyanate b-(13) Tris(4-phenyl isocyanate)
Thiophosphate Product name “Desmodur RF” (manufactured by Bayer) b-(14) Crude (MDI) b-(15) TDI trimer b-(16)dicyclohexamethane-4,4'-diisocyanate (HMDI) b-(17) Hydrogenated TDI (HTDI) b-(18) Metaxylene diisocyanate (XDI) b-(19) Hexahydrometa-xylene diisocyanate (HXDI) b-(20) Hexamethylene diisocyanate (HMDI) OCN-CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ CH ₂ -NCO b-(21) Trimethylpropane-1-methyl-2-
Isocyano-4-cababamate Product name: "Desmodur L" (manufactured by Bayer AG) b-(22) Polymethylene polyphenyl isocyanate Product name "PAPI"b-(23)3,3'-dimethoxy-4,4'-diphenyl diisocyanate Product name "DADI" b-(24) diphenyl ether-2,4,4'-triisocyanate b-(25) Product name "Desmodur TH" (manufactured by Bayer) b-(26) Product name: "Desmodur HH" (manufactured by Bayer AG) b-(27) Ethylene glycol HOCH ₂ CH ₂ OH b-(28) Diethylene glycol HO-CH ₂ CH ₂ -O-CH ₂ CH ₂ -OH b-(29) 1 ,2-propylene glycol b-(30) Dipropylene glycol b-(31) Hydrogenated bisphenol A b-(32)2,2-bis(4-oxyethoxyphenyl)propane b-(33)2,2-bis(4-oxypropoxyphenyl)propane When using a hydroxy compound among the above crosslinking agents, it is preferable to use a reaction accelerator (for example, thionyl chloride or benzoyl chloride) in combination, and in this case, it is necessary to fully consider corrosion of the reaction equipment and reaction environment. There is. The amount of the crosslinking agent to be added is desirably determined in consideration of the amount of functional groups present in the copolymer and the amount of functional groups of the crosslinking agent. In addition to the crosslinking agent, a low molecular weight acid, acid anhydride or amine may be added to the carrier coating layer composition. It is effective in stabilizing carrier performance by reacting excess unreacted crosslinking agent that could not contribute to three-dimensionalization. The reactive functional group of the crosslinking agent is used in a ratio of 0.05 to 10 times, preferably 0.5 to 2 times, per functional group of the copolymer. The blending ratio of the crosslinking agent is not necessarily 100% the functional group of the copolymer.
It is not necessary to add the amount that can achieve % crosslinking. If it is less than 0.05 times, crosslinking will be insufficient, and if it exceeds 10 times, the crosslinking agent itself will have adverse effects. Other additives conventionally known as carrier additives, such as natural or synthetic resins, dyes, pigments, plasticizers, fine magnetic materials, and surfactants, can be added to the coating composition. Various copolymers can be used as the component a, depending on the combination, and examples include the following. a-(1) The number at the bottom right of the parentheses indicates the polymerization ratio (the same applies hereinafter). a-(2) a-(3) a-(4) a-(5) a-(6) a-(7) a-(8) a-(9) a-(10) a-(11) a-(12) a-(13) a-(14) a-(15) a-(16) a-(17) a-(18) a-(19) a-(20) a-(21) a-(22) a-(23) a-(24) a-(25) The blending ratio of the fluorine-containing monomer component, carboxylic acid, carboxylic acid anhydride-containing monomer component, and optional third component is based on the fluorine-containing monomer component relative to the total weight of the copolymer. Body composition is 5-95% preferably 20
~80%, carboxylic acid or carboxylic acid anhydride-containing monomer component from 0.5 to 30%, preferably 1 to 20%, and third component from 0 to 90%, preferably 10 to 70%. In the production of the carrier of the present invention, a copolymer containing a fluorine-containing monomer component, a carboxylic acid-containing component, a carboxylic acid anhydride-containing component, and optionally a third component, a crosslinking agent, and other additives if necessary. A coating solution is prepared by dissolving the (preferable in terms of progress)
Alternatively, the carrier is crosslinked by leaving it to stand (crosslinking proceeds even without heating) to finally obtain the carrier of the present invention. 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 coating is repeated to form a coating layer in advance. Then, for example, an air circulation furnace (180℃
After heat treatment for 5 minutes or more, if any aggregated carriers are present, they are sieved to obtain the carriers of the present invention having a desired film thickness. The organic solvent used in the above production may be any organic solvent as long as it dissolves the above-mentioned substances, but examples include ketones such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, and methyl isobutyl ketone, ethyl acetate, and acetic acid. Acetate esters such as butyl, propyl acetate, cellosolve acetate, halogenated solvents such as tetrachloroethylene, trichloroethylene, methylene chloride, aromatic hydrocarbons such as toluene, xylene, methyl alcohol, ethyl alcohol, butyl alcohol, isopropyl alcohol, etc. Alcohols, ethers such as tetrahydrofuran and dioxane, 1,1,2-trifluorotrichloroethane, 1,2-difluorotetrachloroethane, hexafluorometa-xylene, 1,
Fluorine-containing solvents such as 1,2,3,3,4-hexafluorotetrachlorobutane, or a mixture of two or more of these solvents are 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,
For example, metals that exhibit ferromagnetism such as ferrite and magnetite, iron, cobalt, and nickel, or alloys or compounds containing these metals, and metals that do not contain ferromagnetic elements but exhibit ferromagnetism through appropriate heat treatment. Suitable examples include alloys of the type called Heusler alloys such as manganese-copper-aluminum or manganese-copper-tin, and chromium dioxide. The particle size of these carrier core materials is 30 to 1000 μm, preferably 50 to 500 μm. Further, the thickness of the carrier core material coating layer of the composition in the present invention is preferably 0.1 to 2 μm in terms of dry film thickness.
If it is thinner than 0.1 μm, it is not preferable in terms of durability. Furthermore, if the thickness is greater than 2 μm, there is a tendency for film peeling to occur easily. It is preferable that the glass transition temperature (Tg) of the resin after forming the coating layer is at least 60°C. If the glass transition temperature is low, heat will be generated due to friction between the carriers, friction between the carriers and the wall of the developing device, etc. In this case, the resin becomes sticky and its fluidity deteriorates. The carrier of the present invention is
It is preferable that the toner used therewith is provided with an electric charge of 5 to 40 microcoulombs/g in absolute value under normal usage conditions. The toner constituting the developer together with the carrier of the present invention is made by dispersing a colorant in a binder resin, and various thermoplastic resins are used as the binder resin. Specific examples include styrene, parachlorostyrene, α
- Styrenes such as methylstyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, butyl acrylate, lauryl acrylate,
2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, 2-methacrylate
α-methylene aliphatic monocarboxylic acid esters such as ethylhexyl; vinyl nitriles such as acrylonitrile and methacrylonitrile; vinylpyridines such as 2-vinylpyridine and 4-vinylpyridine; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether ; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and methyl isopropenyl ketone; Unsaturated hydrocarbons such as ethylene, propylene, isoprene, butadiene, and their halides; polymers, copolymers obtained by combining two or more of these monomers, and mixtures thereof, or, for example, rosin-modified phenol-formalin resins, oil-modified epoxy resins, polyester resins, polyurethane resins, polyimide resins. Examples include non-vinyl condensation resins such as cellulose resins, polyether resins, and mixtures of these and the above-mentioned vinyl resins. Further, as specific examples of the colorant, for example,
carbon black, nigrosine dye, aniline blue, calco oil blue, chrome yellow,
Mention may be made of ultramarine blue, methine blue, rose bengal, phthalocyanine blue, or mixtures thereof. The toner used in combination with the carrier of the present invention to produce a developer may contain external additives such as waxes, silica, and zinc stearate in addition to the above. When constituting a developer, the blending ratio of the carrier of the present invention and the toner is preferably 0.3 to 20 parts by weight of the toner to 100 parts by weight of the carrier of the present invention. [Effects of the Invention] The carrier of the present invention uses a copolymer containing a monomer having a side chain fluorine atom as a monomer component, as shown in the above general formula (1), as a material for its coating layer. Therefore, it has good negative triboelectrification characteristics, and because the carboxylic anhydride group or carboxylic acid group (functional group) in the copolymer reacts with the crosslinking agent to form a crosslink, it is difficult to form a film on the resin itself. It has the effect that it has a high adhesiveness to the carrier core material, and therefore has very stable triboelectric charging characteristics and high durability. In addition, since the copolymer of the present invention has high solubility in organic solvents, it also has the effect of being easy to manufacture since a dry spray method or a dipping method can be adopted. 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 was a drawback. For example, a technique for coating the surface of a carrier core material with a fluorocarbon resin, a copolymer of tetrafluoroethylene and hexafluoropropylene, and a modifier, such as an epoxy resin or polyurethane (Japanese Patent Application Laid-open No.
47-17435), a non-adhesive fluororesin is bonded to the surface of the core material by blending a cross-linking resin such as epoxy or polyurethane and baking it. Also, in the technique of coating the surface of the carrier core material with a primer containing chromium or phosphoric acid as an adhesive using tetrafluoroethylene as a fluorocarbon resin (see Japanese Patent Application Laid-Open No. 48-90238), To improve adhesion, it is coated with a primer containing chromium and phosphoric acid, and then coated with a fluorine-based resin and fired. Both of these require firing at a high temperature of 300 to 400°C. There were drawbacks in manufacturing, as the adhesion and triboelectric properties of the developer changed depending on 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 present invention is not limited thereto. Example 1 2 parts by weight of the copolymer shown in exemplified compound a-(1) as a copolymer and 0.5 parts of exemplified compound b-(2) as a crosslinking agent
parts by weight in a mixed solvent of acetone and methyl ethyl ketone to prepare a coating liquid, and using this coating liquid, a spherical iron powder "DSP135C" (Dowa Iron Powder Industries Co., Ltd. made)
After coating 100 parts by weight and heat-treating in an air circulation oven at about 150° C. for 5 minutes, the aggregate was sieved to obtain a carrier of the present invention having a film thickness of about 2 μm. 100 parts by weight of the carrier of the present invention, 100 parts by weight of styrene-acrylic copolymer "HIMER SBM73" (manufactured by Sanyo Chemical Industries, Ltd.), 10 parts by weight of carbon black "Regal 660R" (manufactured by CABOT), and low molecular weight polypropylene "Viscol". A developer was prepared by mixing 3 parts by weight of "660P" (manufactured by Sanyo Chemical Industries, Ltd.) in a ball mill, and 2 parts by weight of toner having an average particle size of 10 μm obtained through the steps of kneading, pulverization, and classification. . Using this developer, an electrophotographic copy ``U'' was produced, which was equipped with an organic photoconductive photoreceptor having a negatively charged two-layer structure, using an anthrone pigment as a carrier-generating substance and a carbazole derivative as a carrier-transporting substance. -Bix3000” (manufactured by Konishiroku Photo Industry Co., Ltd.) A live-action test was conducted using a modified machine. As a result, a clear copy image without fog was obtained even after 50,000 continuous copies, and the maximum image density (relative density when the image density of the original image is 2) after this continuous copying was 1.3. . Further, the charge amount of this developer at the initial stage was 21.3 microcoulombs/g, and even after 50,000 copies, it remained 20.5 microcoulombs/g, showing almost no fluctuation and was found to be an excellent developer. Example 2 In Example 1, copolymer exemplified compound a-(1)
A carrier of the present invention was obtained in exactly the same manner as in Example 1, except that a copolymer of exemplified compound a-(2) was used instead. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 3 In Example 1, copolymer exemplified compound a-(1)
A carrier of the present invention was obtained in exactly the same manner as in Example 1, except that a copolymer of exemplified compound a-(3) was used instead. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 4 In Example 1, copolymer exemplified compound a-(1)
A carrier of the present invention was obtained in exactly the same manner as in Example 1, except that a copolymer of exemplified compound a-(4) was used instead of . Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 5 A carrier of the present invention was obtained in exactly the same manner as in Example 1, except that b-(21) was used instead of exemplified compound b-(2) used as a crosslinking agent in Example 1. . Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 6 In Example 1, except that b-(14) was used instead of exemplified compound b-(2) used as a crosslinking agent,
A carrier of the present invention was obtained in exactly the same manner as in Example 1. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, a good copy image was obtained. Example 7 A carrier of the present invention was obtained in exactly the same manner as in Example 1, except that b-(33) was used instead of exemplified compound b-(2) used as a crosslinking agent in Example 1. . Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, a good copy image was obtained. Example 8 In Example 1, copolymer exemplified compound a-(1)
Completely the same as Example 1 except that a copolymer of exemplified compound a-(5) was used instead of , and b-(31) was used instead of exemplified compound b-(2) used as a crosslinking agent. Thus, the carrier of the present invention was obtained. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 9 In Example 1, copolymer exemplified compound a-(1)
Completely the same as Example 1 except that a copolymer of exemplified compound a-(6) was used instead of , and b-(9) was used instead of exemplified compound b-(2) used as a crosslinking agent. Thus, the carrier of the present invention was obtained. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 10 In Example 1, copolymer exemplified compound a-(1)
A copolymer of exemplified compound a-(7) was used instead of , and b-(4) (QT-3476, manufactured by Dow Chemical Company) was used instead of exemplified compound b-(2), which was used as a crosslinking agent. Except for the above, a carrier of the present invention was obtained in exactly the same manner as in Example 1. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 11 In Example 1, instead of the spherical iron powder "DSP135C" (manufactured by Dowa Iron Powder Kogyo Co., Ltd.) used as the carrier core material, spherical iron powder "Shinto 100M-1" (manufactured by Shinto Blater Co., Ltd.) was used. Except for the above, a carrier of the present invention was obtained in exactly the same manner as in Example 1. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Example 12 In Example 1, 2 parts by weight of the copolymer shown in a-(15) was used instead of exemplified compound a-(1) as a copolymer, and 2 parts by weight of the copolymer shown in a-(15) was used as a crosslinking agent instead of exemplified compound b-(2). A carrier of the present invention was obtained in exactly the same manner as in Example 1, except that 0.5 parts by weight of the urea resin was dissolved in an acetone-methanol mixed solvent. Using this carrier, a developer was prepared in the same manner as in Example 1, and a photocopying test was conducted. As in Example 1, good copied images were obtained. Comparative Example 1 A fluorine-containing monomer component and methyl methacrylate were polymerized to obtain the following copolymer (having no carboxy group). A coating solution was prepared by dissolving 2 parts by weight of the above copolymer in an acetone-methyl ethyl ketone mixed solvent,
Using this coating liquid, 100 parts by weight of spherical iron powder "DSP135C" (manufactured by Dowa Iron Powder Industries Co., Ltd.) was coated using a fluidized bed method to obtain a comparative carrier having a film thickness of about 2 μm. Using this carrier for comparison, a developer was prepared in the same manner as in the case of the carrier of the present invention in Example 1, and an actual photographic test was conducted. As a result, excellent images with no fog were obtained in the initial stage, and the maximum image density at this time was 1.4, but the number of copies was
From around 12,000 sheets, fogging was observed.
Image quality has significantly decreased. When this developer was observed under an electron microscope, it was found that the carrier film had peeled off. Comparative Example 2 A comparative carrier was obtained in exactly the same manner as in Example 1, except that exemplified compound b-(2) as a crosslinking agent was not added to the coating liquid. Using this carrier for comparison, a developer was prepared in the same manner as in the case of the carrier of the present invention in Example 1, and an actual photographic test was conducted. As a result, a clear image with no fog was obtained in the initial stage, with a maximum image density of 1.2, but fogging occurred after 50,000 continuous copies, and the maximum image density at that time was 0.7. It dropped to .

Claims (1)

[Scope of Claims] 1. A carrier for developing electrostatic images, comprising a carrier core material coated with a composition consisting of at least the following (a) and (b). (a) A copolymer whose essential main components are a monomer represented by the following general formula (1) and a monomer having a carboxylic acid group or carboxylic acid anhydride group in the side chain that can be copolymerized with the monomer. Combined. General formula (1) [In the formula, R represents a hydrogen atom or a methyl group, and
represents an oxygen atom, a COO group, or a CO group, and Rf represents a fluoroalkyl group. ] (b) A crosslinking agent selected from epoxy compounds, isocyanate compounds, hydroxy compounds, melamine resins, and urea resins.