JPH056187B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic toner used in electrophotography, electrostatic recording, etc. Conventional electrophotographic methods include US Pat.
A number of methods are known, as described in Japanese Patent Publication No. 3666363) and Japanese Patent Publication No. 43-24748 (U.S. Pat. No. 4071361), but generally they utilize a photoconductive substance, An electrical latent image is formed on a photoreceptor by various means, and then the latent image is developed with toner to become a visible image, and if necessary, the toner image is transferred to a transfer material such as paper. , heat, pressure, etc. to obtain a copy. Various developing methods are also known in which an electrostatic latent image is visualized using toner. For example, US Patent No.
The magnetic brush method described in specification No. 2874063,
The cascade development method described in Specification No. 2618552, the powder cloud method and fur brush development method described in Specification No. 2221776,
A number of development methods are known, such as liquid development. Among these developing methods, a magnetic brush method, a cascade method, a liquid developing method, etc., which use a developer mainly consisting of toner and carrier, are in particular widely put into practical use. All of these methods are excellent methods in which good images can be obtained relatively stably, but on the other hand, they have common drawbacks associated with two-component developers, such as deterioration of the carrier and fluctuations in the mixing ratio of toner and carrier. In order to avoid such drawbacks, various development methods using a one-component developer made only of toner have been proposed, but among them, many methods using a developer made of magnetic toner particles are superior. . US Pat. No. 3,909,258 proposes a developing method using an electrically conductive magnetic toner. In this method, conductive magnetic toner is supported on a cylindrical conductive sleeve having magnetism inside, and is brought into contact with an electrostatic image to be developed. At this time, in the developing section, a conductive path is formed by the toner particles between the surface of the recording medium and the surface of the sleeve, and charges are guided from the sleeve to the toner particles through this conductive path, thereby creating a connection between the image area of the electrostatic image and the image area of the electrostatic image. Toner particles adhere to the image area due to Coulomb force and are developed. This developing method using conductive magnetic toner is an excellent method that avoids the problems associated with conventional two-component developing methods. Furthermore, as a developing method using a high-resistance magnetic toner, there is a developing method that utilizes dielectric polarization of toner particles. Another developing method using high-resistance magnetic toner is a method in which the toner particles are triboelectrified by friction between the toner particles or friction between the toner particles and a sleeve, etc., and the toner particles are brought into contact with an electrostatic image holding member for development. It has been known. Furthermore, in Japanese Patent Application Laid-open No. 55-18656, etc.,
A new development method has been proposed which eliminates the above-mentioned drawbacks. This involves applying a very thin layer of magnetic toner onto the sleeve, triboelectrically charging it, and then developing it in close proximity to the electrostatic image. This method increases the chances of contact between the sleeve and toner by applying an extremely thin layer of magnetic toner onto the sleeve, which enables sufficient frictional electrification, supports the toner by magnetic force, and connects the magnet and toner. By moving the toner particles relative to each other, mutual agglomeration is eliminated and sufficient friction with the sleeve is achieved, and the toner is supported by magnetic force and developed by facing the electrostatic image without coming into contact with it. Excellent images can be obtained by preventing background fog. The magnetic toner used in such a one-component development method is mainly composed of a binder resin and a magnetic material, and contains additives such as a colorant, a charge control agent, and a release agent to bring out the characteristics necessary for the toner. The biggest problem with this magnetic toner is the dispersion and adhesion of the binder resin and the magnetic material. If the magnetic material is poorly dispersed, transferability will be poor, and the content of the magnetic material will vary depending on the toner particles, resulting in differences in developability. In particular, when used as an insulating magnetic toner, a toner with a small amount of magnetic material has a high resistance and therefore a large amount of charge, whereas a toner with a large amount of magnetic material has a low resistance and therefore a small amount of charge. As a result, toners with less magnetic material are more likely to be developed, and when developing for a long time, only toner with a large amount of magnetic material and poor developability remains in the developing machine, resulting in an extremely low image density, and furthermore due to high humidity characteristics. This is the worst case scenario as it also worsens. In addition, when the adhesion between the binder resin and the magnetic material deteriorates, the magnetic material falls off from the toner particles, not only contaminating the image but also scratching the latent image holder, causing filsing, poor cleaning, etc. In the case of heat roller and pressure roller fusing, which are the most commonly used fusing devices,
This will scratch the roller, making it easier for toner to adhere to the roller, and causing offset and sticking phenomena. Furthermore, the more the development is repeated, the more the magnetic material that falls off remains in the developing machine, resulting in an extreme decrease in image density and deterioration in high humidity characteristics. Therefore, several methods have been proposed to improve the adhesiveness and dispersibility between the binder resin and the magnetic material. JP-A-54-84731 discloses a method of treating and using a magnetic material with a silane-based coupling agent, and JP-A-55-26519 and JP-A-55-28019 disclose a method of treating a magnetic material with a titanium-based coupling agent. and the method of using it, as well as Japanese Patent Application Laid-Open No. 122129/1983,
Publication No. 130130, Publication No. 55-6344, Publication No. 55-11218
The publication describes a method of using a magnetic material by coating it with a suitable coating material. However, although these methods achieve some results, they are not fully satisfactory in all respects. In particular, it is still not sufficient for long-term use and adaptation to high-speed development. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for producing a magnetic toner that can be used for a long period of time. Furthermore, the present invention provides a method for producing a magnetic toner for developing electrostatic images in which image density does not decrease even after repeated development. Furthermore, the present invention provides a method for producing a magnetic toner for developing electrostatic images that retains good images even after repeated development. Furthermore, the present invention provides a method for producing a magnetic toner for developing electrostatic images that does not damage or contaminate the latent image carrier even during repeated development. Furthermore, the present invention provides a method for producing a magnetic toner for developing electrostatic images whose high-humidity properties do not deteriorate even after repeated development. Furthermore, the present invention provides a method for producing a magnetic toner for developing electrostatic images that is suitable for high-speed development. Furthermore, the present invention provides a method for producing a magnetic toner for developing electrostatic images with good transferability. Specifically, the present invention uses a compound having a carboxylic acid group or a salt thereof and a weight average molecular weight of 300 to 10,000 and the -OH group on the surface of the magnetic material in a solvent, a drying agent, a dehydrating agent, or an esterification catalyst. The present invention relates to a method for producing a magnetic toner, which comprises treating the surface of a magnetic material by reacting in the presence of the magnetic material, heat-kneading the surface-treated magnetic material and a binder resin, and, after cooling, pulverizing and classifying. Furthermore, the present invention provides a method for combining a compound having a carboxylic acid group or a salt thereof and having a weight average molecular weight of 300 to 10,000 with -OH groups on the surface of a magnetic material in the presence of a solvent, a drying agent, a dehydrating agent, or an esterification catalyst. A method for producing a magnetic toner, which comprises treating the surface of a magnetic material by reaction, mixing the surface-treated magnetic material with a polymerizable monomer, and producing magnetic toner particles by a suspension polymerization method. . That is, the present invention can be achieved by using a magnetic material reacted with a compound containing a carboxylic acid or a salt thereof and having a weight average molecular weight of 300 to 10,000. Furthermore, it is preferable to use it in a toner manufactured by a suspension polymerization method. In the magnetic material reacted with the compound, the -OH groups on the surface of the magnetic material almost completely react with the compound and become hydrophobic. It can be said that coatings with conventional silane coupling agents, titanium coupling agents, and coating materials have not sufficiently rendered the toner hydrophobic in view of the toner properties. As for the reaction mechanism, when the -OH group on the surface of the magnetic material is expressed as M-OH, for example, M-OH+RCOOHH ⁺ ---→ +M-OOCR+
This reaction is considered to be in the form of H ₂ O, and since this reaction is an equilibrium reaction, in order to shift the equilibrium toward the production system, for example, using a large excess of the above compound, or using benzene, toluene, or xylene as a solvent, This includes separating and removing the water that is present. At this time, acidic ion exchange resin (e.g. ZeO-KarbH)
or using anhydrous magnesium sulfate or molecular sieves in a Soxhlet extractor.
There are methods to dehydrate by adding a desiccant such as 5A and refluxing the solvent, and methods to coexist with a dehydrating agent such as DDC. Further, in order to promote esterification, a method using a resin mixed with aluminum chloride as a catalyst is also used. Further, after these reactions, a reactive compound may be further reacted with a compound containing these carboxylic acids or salts thereof. When the magnetic material thus prepared is used in magnetic toner, it exhibits sufficiently satisfactory performance. The magnetic toner referred to here is produced by, for example, a pulverization method, that is, by mixing a magnetic material, a binder resin, a colorant, other additives, etc., and then heat-kneading the mixture.
After cooling, the toner is coarsely pulverized, finely pulverized, and classified if necessary to obtain a toner having a desired particle size and particle size distribution.Other methods include a capsule method, an emulsion polymerization method, and a spray dry method. In contrast, a suspension polymerization method is known. This involves dispersing polymerizable monomers, initiators, etc. in a dispersion medium,
This is a method of producing suspended particles with the required particle size and particle size distribution, and polymerizing them to obtain a toner. The magnetic material used in the present invention is particularly suitable for this suspension polymerization toner. Suspension polymerization creates suspended particles in a mostly aqueous dispersion medium. Therefore, if even a small amount of hydrophilic groups, such as -OH groups, remain on the surface of the magnetic material, those portions will be exposed to the aqueous dispersion medium, causing the magnetic material to gather on the particle surface. Therefore, the resistance of the toner is lowered due to the conductive portion, that is, the magnetic material, exposed on the surface. In the case of conductive magnetic toner, it seems that it can be used as a toner, but in reality, magnetic materials with hydrophilic groups have poor adhesion to binder resins, and most magnetic materials As a result, the magnetic material falls off the toner surface due to mechanical shear in the developing machine. Furthermore, such magnetic materials have poor dispersibility, resulting in non-uniform toner and poor developability. This tendency is greater than the previous pulverization method toner because there is no process of kneading the binder resin and magnetic material at high temperature, high viscosity, and high shear unlike the pulverization method toner. The advantages and disadvantages are that it is an energy-saving and low-cost manufacturing method. When this suspension polymerization method toner is used with a magnetic material made by reacting the reactive substance, the magnetic material is contained inside the toner and almost never comes out on the surface of the toner, which prevents mechanical shearing in the developing machine. In addition, the magnetic material is better dispersed in each toner particle, making the toner homogeneous and developing properties significantly improved. This toner has high resistance because almost no magnetic material is exposed on the surface of the toner, so it can be used as an insulating toner as is, or it can be made free by adding conductive fine powder such as carbon black. The resistance can be adjusted accordingly, making it suitable as a conductive magnetic toner. The carboxylic acid or its salt may be one in which an appropriate number of carboxylic acids or its salts are introduced into the side chain of a long polymer chain. If the weight average molecular weight is less than 300, the created magnetic material may not be sufficiently dispersed due to poor compatibility with the binder resin, and if it exceeds 10,000, the -OH groups on the surface of the magnetic material may not be completely dispersed. There may be cases where the product does not respond. This is probably because the molecular weight is so large that the molecules that react with the -OH group first protect the molecules that are about to react next. Compounds containing carboxylic acid or its salts include, for example, maleic acid resins, copolymers of maleic acid and other vinyl monomers, maleic acid half esters, copolymers of maleic acid half esters and other vinyl monomers, α , ω-polybutadiene dicarboxylic acid, acrylic acid, copolymers of acrylic acid and other vinyl monomers, methacrylic acid, copolymers of methacrylic acid and other vinyl monomers,
There are saturated fatty acids and unsaturated fatty acids. The magnetic powder used is a substance that becomes magnetized when placed in a magnetic field, and includes powders of ferromagnetic metals such as iron, cobalt, and nickel, and alloys and compounds such as magnetite, hematite, and ferrite. The content of this magnetic powder is 15% based on the weight of the toner.
~70% by weight is good. As the binder resin for the toner, homopolymers of styrene and its substituted products, such as polystyrene, poly-p-chlorostyrene, polyvinyltoluene, styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, and copolymers thereof; Coalescence: Styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-acrylic acid n-
Copolymers of styrene and acrylic esters such as butyl copolymers; styrene and methacrylates such as styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers, and styrene-n-butyl methacrylate copolymers Copolymers with acid esters; multi-component copolymers of styrene with acrylic esters and methacrylic esters; other styrene-acrylonitrile copolymers, styrene-vinyl methyl ether copolymers, styrene-butadiene copolymers, styrene- Styrenic copolymers of styrene and other vinyl monomers such as vinyl methyl ketone copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic ester copolymer; polymethyl methacrylate, polybutyl methacrylate, poly Vinyl acetate, polyester, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid, phenolic resin, aliphatic or alicyclic hydrocarbon resin, petroleum resin, chlorinated paraffin, etc. can be used alone or in combination. In particular, binder resins for toners used in pressure fixing systems include low molecular weight polyethylene, low molecular weight polypropylene, ethylene-vinyl acetate copolymers, ethylene-acrylic acid ester copolymers, higher fatty acids, polyamide resins, polyester resins, etc. can be used alone or in combination. The following monomers can be applied to the present invention when producing a toner by suspension polymerization. Styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene, 2,4- Dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n
- Styrene and its derivatives such as hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene; ethylenically unsaturated such as ethylene, propylene, butylene, isobutylene, etc. Monoolefins; Vinyl halides such as vinyl chloride, vinylidene chloride, vinyl bromide, and vinyl fluoride; Vinyl esters such as vinyl acetate, vinyl propionate, and vinyl benzoate; Methyl methacrylate, ethyl methacrylate, and methacrylic acid α such as propyl, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, etc. -Methylene aliphatic monocarboxylic acid esters; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, acrylic acid Acrylic acid esters such as stearyl, 2-chloroethyl acrylate, and phenyl acrylate; Vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone. ; N-vinyl compounds such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole, N-vinylpyrrolidone; vinylnaphthalenes; acrylonitrile, methacrylonitrile,
Examples include acrylic acid or methacrylic acid derivatives such as acrylamide. During polymerization, a crosslinked polymer may be obtained by polymerizing in the presence of the following crosslinking agent. Divinylbenzene, divinylnaphthalene, divinyl ether, divinyl sulfone, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate,
1,3-butylene glycol dimethacrylate,
1,6 hexane glycol dimethacrylate, neopentyl glycol dimethacrylate, dipropylene glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2'bis(4-methacryloxydiethoxyphenyl)propane, 2,2'bis(4- General crosslinking agents such as acryloxydiethoxyphenyl)propane, trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, tetramethylolmethanetetraacrylate, dibromneopentyl glycol dimethacrylate, and allyl phthalate can be used as appropriate. . If these crosslinking agents are used in large amounts, they will not dissolve and the fixing properties will be poor. Also, if the amount used is small, properties such as anti-blocking and durability required for toner will deteriorate, and during hot roll fixing, some of the toner will not completely adhere to the paper and will stick to the roller surface and transfer to the next paper. This makes it difficult to prevent the offset phenomenon. Therefore, the amount of these crosslinking agents used is based on the total amount of monomers.
It is preferably used in an amount of 0.001 to 15% by weight (more preferably 0.1 to 10% by weight). As the polymerization initiator, any suitable polymerization initiator, such as azobisisobutyronitrile (AIBN) benzoyl peroxide, methyl ethyl ketone peroxide, isopropyl peroxy carbonate, kyumene hydroperoxide, 2,4-dichloryl benzoyl Polymerization of monomers can be carried out using peroxide, lauroyl peroxide, and the like. Generally about 0.5 to 5% initiator by weight of monomer is sufficient. Suitable dispersion media used in the present invention include, for example, any suitable stabilizer, such as polyvinyl alcohol, gelatin, methyl cellulose, methyl hydropropyl cellulose, ethyl cellulose, sodium salt of carboxymethyl cellulose, polyacrylic acid, and the like. salts, starch, gum alginate, zein, casein, tricalcium phosphate, talc, barium sulfate, bentonite, aluminum hydroxide, ferric hydroxide, titanium hydroxide, thorium hydroxide, etc. are included in the aqueous phase. It can be used as The stabilizer is used in a stabilizing amount in the continuous phase, preferably in the range of about 0.1 to 10% by weight. Moreover, for fine dispersion of the inorganic dispersant,
Surfactants in the range of 0.001 to 0.1% by weight may also be used. This is to promote the intended action of the above-mentioned dispersion stabilizer, and specific examples thereof include sodium dodecylbenzenesulfonate, sodium tetradecylsulfate, sodium pentadecylsulfate, sodium octylsulfate, and allyl-alkyl-polymers. Sodium ethersulfonate, sodium oleate, sodium laurate, sodium caprate, sodium caprylate, sodium caproate, potassium stearate, calcium oleate, 3,3-disulfone diphenyl urea-4,4-diazobis-amino- Sodium 8-naphthol-6-sulfonate,
Examples include ortho-carboxybenzene-azodimethylaniline, sodium 2,2,5,5-tetramethyl-triphenylmethane-4,4-diazobis-β-naphthol-disulfonate, and others. In addition, monomers that are easily soluble in water cause emulsion polymerization in water at the same time, and the resulting suspended polymer is contaminated with small emulsion polymer particles, so it is necessary to add a water-soluble polymerization inhibitor, such as a metal salt, to emulsify it in the aqueous phase. It is also good to prevent polymerization. In addition, glycerin, glycol, etc. may be added to the water in order to prevent coalescence of the particles as well as the clay medium. It is also possible to use salts such as NaCl, KCl, Na ₂ SO ₄ to reduce the solubility of easily soluble monomers in water. Known pigments or dyes can be used as the toner colorant. Examples of dyes include CI Direct Red 1, CI Direct Red 4, CI Assisted Red 1, CI Basic Red 1, CI Modern Red 30, CI Direct Blue-1, CI Direct Blue-2, CI Assisted Blue-9, and CI Assisted Blue-15. , CI Basic Blue 3, CI Basic Blue 5, CI Modern Blue 7, C.
I. Direct Green 6, CI Basic Green 4, CI Basic Green 6, etc. Pigments include yellow lead, cadmium yellow, mineral fast yellow, navel yellow, naphthol yellow S, Hansa yellow G, permanent yellow NCG, tartrazine lake, red yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, benzodine orange. G, Cadmium Red, Permanent Red 4R, Watching Red Calcium Salt, Eosin Lake, Brilliant Carmine 3B, Manganese Purple, Fast Violet B, Methyl Violet Lake, Deep Blue, Cobalt Blue, Alkaline Blue Lake, Victoria Blue Lake , Phthalocyanine Blue, Fast Sky Blue, Indanthrene Blue BC, Chrome Green, Chromium Oxide, Pigment Green B, Malachite Green Lake, Final Yellow Green G, etc. A charge control agent and a fluidity modifier may be added to the toner as necessary, and the charge control agent and fluidity modifier may be mixed (externally added) with the toner particles. Examples of the charge control agent include metal-containing dyes and nigrosine, and conventionally known dyes and pigments can be used as the colorant, and examples of the fluidity modifier include colloidal silica and fatty acid metal salts. There is. Further, for the purpose of increasing the amount, a filler such as calcium carbonate or finely powdered silica may be incorporated into the toner in an amount of 0.5 to 20 wt%. Furthermore, in order to prevent mutual aggregation of toner particles and improve their fluidity, a fluidity improver such as fine Teflon powder may be added, and this is for the purpose of improving mold releasability during hot roll fixing. It is also possible to add about 0.5 to 5 wt% of wax-like substances such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, and Sasol wax. In the suspension method, a monomer system in which a polymerization initiator, magnetic substance, monomer, and additives are uniformly dissolved or dispersed is stirred in an aqueous phase containing a suspension stabilizer, that is, a continuous phase. Disperse using a machine, homomixer, homogenizer, etc. Preferably, the stirring speed and time are adjusted so that the monomer droplets have the desired toner particle size, generally 30 μm or less, and thereafter this state is maintained substantially by the action of the dispersion stabilizer. Stirring may be carried out to the extent that sedimentation of particles is prevented. The polymerization temperature is set at 50°C or higher, generally 70 to 90°C. After the reaction is completed, the produced toner particles are recovered and dried by a suitable method such as washing, filtration, decantation, centrifugation, etc. Example 1 Xylene 2 and 20 g of cupric sulfate anhydride were mixed in the reaction vessel of Example 1 4, and 200 g of BL-200 (manufactured by Titan Kogyo) was added thereto, and the mixture was vigorously stirred to disperse the BL-200. The temperature was then raised to 60°C and maintained at that temperature. 50 g of lacelic acid was added thereto, and the whole was heated at 150° C. for 8 hours under reflux. The treated magnetite thus obtained was washed and dried, and then gently crushed to loosen agglomerations. A toner was prepared using this magnetite powder. The composition was as follows. Styrene-butyl acrylate copolymer (ratio 8:2, ω = 200,000) 100 parts Above-treated magnetite powder 50 parts Carbon black 5 parts Bontron E-81 (manufactured by Orient Chemical Co., Ltd.) 2 parts The compounding ratio used here is by weight The same shall apply hereinafter. After pre-mixing these materials, they are milled using a roll mill.
The mixture was kneaded at 150°C, cooled, and then coarsely pulverized, finely pulverized, and classified to obtain a toner. The obtained toner has a number average particle size
The weight average diameter was 11.2μ, and the weight average diameter was 15.3μ. (Coulter counter type, using aperture diameter 100μ)
This toner was put into a Canon NP-500RE high-speed copying machine, and a 50,000-sheet image reproduction durability test was conducted. In addition, as a comparative example, untreated magnetite
BL-200 was made into a toner using the same blending ratio as above. The particle size of this toner was a number average diameter of 11.5μ and a weight average diameter of 15.5μ. The result will be:
The toners of Examples were particularly excellent. Furthermore, with the comparative toner, scratches appeared on the photoreceptor drum after about 40,000 sheets, but such a problem did not occur in the examples.

[Table] Evaluation 5=Excellent, 4=Good, 3=Practically usable 2=Practically bad
1 = Bad Example 2 60 parts of treated magnetite prepared in Example 1,
Added to next mixture. Styrene monomer 85 parts Butyl acrylate monomer 15 parts Initiator (V-65: Wako Pure Chemical Industries) 0.5 parts Paraffin 155F 3 parts Dimethylaminoethyl methacrylate monomer
5 parts These mixtures were kept at 60° C. and stirred and dispersed for 5 minutes using a TK homo mixer (Tokushu Kika Co., Ltd.). In a separately prepared container, 1,500 parts of water and 2.5 parts of tricalcium phosphate were dispersed, and the above monomer mixture was added thereto under stirring to carry out suspension polymerization. Tricalcium phosphate of this polymer was dissolved and removed with an acid, further washed with water and dried to obtain a toner powder. The obtained toner had a number average particle size of 10.5μ and a weight average particle size of 16.5μ. This toner is used in a Canon copier PC-20.
We conducted an image display durability test. As a comparative example, a toner was prepared in the same manner as in Example 2, using BL-200 magnetic material treated with 1% titanium coupling instead of the magnetite treated in Example 1.

[Table] Evaluation criteria are the same as in Example 1. In addition, the comparative toner had many scratches on the drum. In the toner of the comparative example, it was observed by microscopic observation that the magnetite powder had fallen off from the toner during the durability test. It is believed that this caused the toner properties to deteriorate and the drum to be scratched. With the toner of Example 2, no such problem occurred.

Claims (1)

[Claims] 1. A compound having a carboxylic acid group or a salt thereof and having a weight average molecular weight of 300 to 10,000 and an -OH group on the surface of a magnetic material in the presence of a solvent, a drying agent, a dehydrating agent, or an esterification catalyst. 1. A method for producing a magnetic toner, which comprises: treating the surface of a magnetic material by reacting with a binder resin; hot kneading the surface-treated magnetic material and a binder resin; and, after cooling, pulverizing and classifying. 2. Claim 1, in which benzene, toluene or xylene is used as a solvent, and the compound is reacted with the -OH group on the surface of the magnetic material under heating conditions.
2. Method for producing magnetic toner. 3 A magnetic material is produced by reacting a compound having a carboxylic acid group or a salt thereof and having a weight average molecular weight of 300 to 10,000 with the -OH group on the surface of the magnetic material in the presence of a solvent and a drying agent, a dehydrating agent, or an esterification catalyst. A method for producing a magnetic toner, which comprises treating the surface of a toner, mixing the surface-treated magnetic material with a polymerizable monomer, and producing magnetic toner particles by a suspension polymerization method. 4. Claim 3, in which benzene, toluene or xylene is used as a solvent, and the compound is reacted with the -OH group on the surface of the magnetic material under heating conditions.
2. Method for producing magnetic toner.