JP2704764B2 - Magnetic toner for developing electrostatic images - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a toner for visualizing a latent electrostatic image in an image forming method such as electrophotography and electrostatic recording.

[Prior Art] Conventionally, as an electrophotographic method, US Pat. No. 2,297,691,
Various methods are described in JP-B-42-23910 and JP-B-43-24748.

Developing methods applied to the electrophotographic method and the like are roughly classified into a dry developing method and a wet developing method. The former is further classified into a method using a two-component developer and a method using a one-component developer.

Conventional toners applied to these dry development methods include:
Fine powders in which dyes and pigments are dispersed in natural or synthetic resins are used. For example, particles obtained by dispersing a colorant in a binder resin such as polystyrene and finely pulverized to about 1 to 30 μm are used as toner. As the magnetic toner, a toner containing magnetic particles such as magnetite is used. In the case of a system using a two-component developer, the toner is usually used by being mixed with carrier particles such as glass beads and iron powder.

Any toner must have a positive or negative charge, depending on the polarity of the electrostatic latent image to be developed.

In order to retain charge in the toner, it is possible to use the triboelectricity of the resin which is a component of the toner.However, in this method, since the toner has a small chargeability, an image obtained by development is easily fogged and unclear. It will be. Accordingly, in order to impart a desired triboelectric charging property to the toner, a dye, a pigment for imparting the charging property, and a charge controlling agent have been added.

Today, the charge control agents known in the art include nigrosine dyes, azine dyes, triphenylmethane dyes and quaternary ammonium salts, or quaternary ammonium salts in the side chain as positive triboelectrification. Polymers having the same are known.

However, since some of these charge control agents easily contaminate the sleeve or carrier, the amount of triboelectricity of the toner using them decreases with the number of copies,
This causes a reduction in image density. In addition, some charge control agents have insufficient triboelectric charge and are susceptible to temperature and humidity, which causes environmental fluctuations in image density. Further, since a certain type of charge control agent has poor dispersibility in a resin, a toner using the same has a non-uniform triboelectric charge amount between particles and is easily fogged. In addition, certain charge control agents have poor storage stability, and their triboelectric charging ability decreases during long-term storage.

At present, there is a strong demand for the development of charge control agents that satisfy all of these.

[Problem to be Solved by the Invention] An object of the present invention is to provide a novel toner which has solved the above-mentioned problems.

Further, an object of the present invention is that the toner carrier such as a sleeve is less contaminated, the amount of triboelectricity between the toner and a toner carrier such as a sleeve is stable without being affected by changes in temperature and humidity, and environmental conditions are reduced. An object of the present invention is to provide a toner capable of reproducing a stable image which is hardly affected by a change.

[Means and Actions for Solving the Problems] The present invention provides positively chargeable fine powder particles containing at least a metal compound of an imidazole derivative having zinc, titanium, nickel, iron or copper, a magnetic material and a binder resin. The present invention relates to a magnetic toner for developing electrostatic images, wherein silica fine powder is externally added.

The present inventors have conducted intensive studies to solve the above problems, and as a result, a toner obtained by externally adding a positively chargeable silica fine powder to a colored fine powder using a metal compound of a specific imidazole derivative as a charge control agent has been developed. It has been found that the toner has a sufficient positive chargeability, does not easily contaminate the toner carrier, and has good storage stability and is hardly fogged.

The metal compound of the imidazole derivative used in the present invention has good thermal stability and does not deteriorate at all in the range from room temperature to 250 ° C. Further, when the metal compound of this specific imidazole derivative is contained in the toner, the dispersibility in the binder resin is also good, and the toner charge amount is higher and sufficient than when the imidazole compound is used alone, and The charge amount between the toner particles is uniform.

Further, since the toner carrier is less likely to be contaminated, the decrease in image density in the durable text tends to be smaller than that of a conventional charge control agent. Furthermore, it was found that this contamination can be almost completely solved by externally adding finely-charged silica fine powder.

Further, by adding the positively chargeable silica fine powder externally, the roughness of the image is improved, and a high-density image can be obtained from the beginning. However, when the positively chargeable silica fine powder was not externally added, the rise in image density was poor, and ground fogging was generated, which was practically difficult. From these facts, it has been found that positively chargeable silica fine powder is indispensable, and the present invention has been completed.

The specific imidazole derivative metal compound used in the present invention specifically refers to a specific imidazole derivative metal complex or metal salt, as described later.

The imidazole which forms the metal compound of the specific imidazole derivative used in the present invention includes all kinds of imidazoles. In particular, considering the high charging ability, the following formulas [I] -a, b and formula [II] The imidazole species shown in -a and b are preferred.

The substituents R _{1 to} R ₆ in the formula are preferably substituents having 24 or less carbon atoms, more preferably substituents having 6 or less carbon atoms, in view of ease of production.

As the metal that the metal compound of the imidazole derivative has, zinc, titanium, nickel, iron, and copper are preferable in consideration of the stability of the metal compound and the high charge amount, and in consideration of ease of manufacture and color. Zinc is more preferred. Further, the metal compound of the imidazole derivative used in the present invention has higher charge-imparting ability than the imidazole derivative.
The mechanism for providing this high charge-imparting ability is unknown, but is presumed to be due to the formation of a metal complex or metal salt via nitrogen on imidazole.

In addition, the metal compound of the imidazole derivative in the present invention has a counter ion if necessary. In this case, the counter anion includes an inorganic anion and an organic anion.

The inorganic anions ^{F -, Cl -, Br -} , I - halogen, such as _{^{ion, OH -, SO 4 2-,}} BF 4 -, DF 6 -, ClO 4 -, SiF 6 -, also [Mo
₇ O ₂₄ ] ^6- , [H ₂ W ₁₂ O ₄₂ ] ^10- , [PMo ₁₂ O ₄₀ ] ^3- , [PW ₁₂ O ₄ ]
^And heteropolyacid ions such as ^3- .

Organic ions include C _{1 to} C ₂₄ sulfonate ions,
₁ -C ₂₄ carboxylic acid ions, C ₁ -C ₂₄ acid monoalkyl esters anions, such as tetraphenylborate ion.

The metal compound of the imidazole derivative used in the present invention is synthesized by adding an imidazole compound to a metal salt solution, and if necessary, adding a reagent for exchanging a counter ion, and then purifying the target compound by purification. obtain.

Assuming that the number of moles of the metal per 1 g of the obtained product is M and the number of moles of the imidazole species is L, the ratio M / L is 0.05 to 2 and shows good positive chargeability, and the thermal stability of the compound. In view of the durability stability in a copy durability test when the toner is used, it is preferably 0.16 or more and 0.6 or less.

Specific examples of the imidazole species forming the metal compound of the imidazole derivative used in the present invention are shown below.

The metal compound of the imidazole derivative used in the present invention may contain one or more of these imidazole species.

A metal compound of an imidazole derivative as described above,
By blending in a toner (colored fine powder) containing a binder resin and a coloring component as essential components, the toner of the present invention can be obtained. As a form of compounding, any of a so-called internal addition form in which the toner is included in a uniform or capsule form and a so-called external addition form in which the toner is mixed and adhered to the toner can be adopted.

In the case of internal addition, the amount of the metal compound of the imidazole derivative used is determined by the type of the binder resin, the presence or absence of additives used as necessary, and the toner production method including the dispersion method, and is generally used. Although not limited,
It is preferably used in an amount of 0.1 to 20 parts by weight (more preferably 0.5 to 10 parts by weight) based on 100 parts by weight of the binder resin.

When externally added, 0.01 parts by weight to 100 parts by weight of resin
~ 10 parts by weight is desirable. As the external addition method, it is particularly preferable to fix by a mechanochemical method.

In addition, if necessary, a conventionally known charge control agent can be used in combination with the metal compound of the imidazole derivative used in the present invention.

In the present invention, it is an essential component to use a combination of positively chargeable silica fine powder.

As a base of the positively chargeable silica fine powder, fine silica powder produced by a dry method and a wet method can be used.

The dry method referred to here is a method for producing silica fine powder generated by vapor phase oxidation of a silicon halide. For example, in a method utilizing the thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen-hydrogen, the basic reaction formula is as follows.

SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl In this manufacturing process, for example, by using another metal halide such as aluminum chloride or titanium chloride together with a silicon halide, a fine composite powder of silica and another metal oxide is obtained. It is also possible to obtain and include them.

On the other hand, as a method for producing the base of silica fine powder used in the present invention by a wet method, various conventionally known methods can be applied. For example, decomposition of sodium silicate by an acid, as shown by a general reaction formula (hereinafter, the reaction formula is abbreviated), Na ₂ O.XSiO ₂ + HCl + H ₂ O → SiO ₂ .nH ₂ O + NaCl In addition, ammonium silicate or alkali of sodium silicate Decomposition with salts, after producing an alkaline earth metal silicate from sodium silicate, a method of decomposing with an acid to produce silicic acid, a method of transforming sodium silicate solution into silicic acid with ion exchange resin, natural silicic acid or There is a method using a silicate.

Silica such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, zinc silicate, etc. can be applied to the silica fine powder here, in addition to anhydrous silicon dioxide (silica).

Among the above silica fine powders, those having a specific surface area of 30 m ² / g or more (particularly 50 to 400 m ² / g) measured by the BET method as measured by nitrogen adsorption are preferable as the base silica.

As a method for obtaining the positively chargeable silica fine powder, the untreated silica fine powder described above has at least one nitrogen atom as a side chain.
There is a method of treating with a silicone compound having at least one organo group, a silicone varnish, a silicone resin or the like, a method of treating with a nitrogen-containing silane coupling agent, or a method of treating with a plurality of these.

In the present invention, the positively chargeable silica refers to a silica having a positive triboelectric charge when measured by a blow-off method.

As the silicon oil having a nitrogen atom in the side chain used for treating the silica fine powder, a silicon oil having at least a partial structure represented by the following formula can be used.

(Wherein, R ₁ represents hydrogen, an alkyl group, an aryl group or an alkoxy group, R ₂ represents an alkylene group or a phenylene group, R _3, R ₄ represents hydrogen, an alkyl group or an aryl group,, R ₅ Represents a nitrogen-containing heterocyclic group) The above alkyl group,
The aryl group, alkylene group, and phenylene group may have an organo group having a nitrogen atom, or may have a substituent such as halogen as long as the chargeability is not impaired.

Further, the nitrogen-containing silane coupling agent used in the present invention generally has a structure represented by the following formula.

R _m SiY _n (R represents an alkoxy group or a halogen, Y represents an amino group or an organo group having at least one nitrogen atom, m and n are integers of 1 to 3, and m + n
= 4. Examples of the organo group having at least one nitrogen atom include an amino group having an organic group as a substituent, a nitrogen-containing heterocyclic group, or a group having a nitrogen-containing heterocyclic group. As the nitrogen-containing heterocyclic group, there is an unsaturated heterocyclic group or a saturated heterocyclic group, and known ones can be applied. Examples of the unsaturated heterocyclic group include the following.

Examples of the saturated heterocyclic group include the following.

The heterocyclic group used in the present invention is preferably a 5- or 6-membered ring in consideration of stability.

Examples of such treating agents include aminopropyltrimethoxysilane, aminopropyltriethoxysilane, dimethylaminopropyltrimethoxysilane, diethylaminopropyltrimethoxysilane, dipropylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane, Butylaminopropyltrimethoxysilane, dioctylaminopropyltrimethoxysilane, dibutylaminopropyldimethoxysilane, dibutylaminopropylmonomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-
γ-propylphenylamine, trimethoxysilyl-γ
And nitrogen-containing heterocycles having the above-mentioned structure. Examples of such compounds include trimethoxysilyl-γ-propylpiperidine and trimethoxysilyl-γ-propylmorpholine. , Trimethoxysilyl-γ-propylimidazole and the like.

The applied amount of these treated silica fine powders is effective when the amount is 0.01 to 20% with respect to the weight of the developer, and particularly preferable is a positively charged powder having excellent stability when added in an amount of 0.03 to 5%. Shows sex. According to a preferred embodiment of the addition form, it is preferable that 0.01 to 3% by weight of the treated silica fine powder based on the weight of the developer is attached to the surface of the toner particles.

Further, the silica fine powder used in the present invention may be treated with a silane coupling agent, if necessary, with a treating agent such as an organosilicon compound for the purpose of hydrophobization, and a known method is also used. Is treated with the treating agent which reacts or physically adsorbs with the silica fine powder. Examples of such a treating agent include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, benzyldimethylchlorosilane, Bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilyl acrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxy Silane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3- Examples include diphenyltetramethyldisiloxane and dimethylpolysiloxane having from 2 to 12 siloxane units per molecule, and the terminal units each containing one hydroxyl group bonded to Si. These are 1
It is used in a kind or a mixture of two or more kinds.

Finally, the degree of hydrophobicity of the treated silica fine powder was determined as a degree of hydrophobicity measured by a methanol titration test, 30
It is preferable that the developer containing such fine silica powder exhibits sharp and uniform positive chargeability when the toner is hydrophobicized so as to show a value in the range of from -80. Here, the methanol titration test confirms the degree of hydrophobicity of the silica fine powder having a hydrophobicized surface.

The "methanol titration test" defined herein for evaluating the degree of hydrophobicity of the treated silica fine powder is performed as follows. 0.2 g of the test silica fine powder is added to 50 ml of water in a 250 ml Erlenmeyer flask. Methanol is titrated from the burette until all of the silica is wetted.
At this time, the solution in the flask is constantly stirred with a magnetic stirrer. The end point is observed by the suspension of the entire amount of the fine silica powder in the liquid, and the degree of hydrophobicity is expressed as the percentage of methanol in the liquid mixture of methanol and water at the end point.

The resin used in the present invention includes, for example, styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyl toluene, and a homopolymer of a substituted product thereof;
p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene-methacrylate copolymer, styrene-α-chloromethacrylate Copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer,
Styrene-vinyl ethyl ether copolymer, styrene-
Styrene-based copolymers such as vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenolic resin, naturally modified phenolic resin, natural Resin-modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, cumarone indene resin, petroleum resin Etc. can be used.

Further, a crosslinked styrene copolymer is also a preferable binder resin.

Examples of the comonomer for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylic. Acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, monocarboxylic acid having a double bond such as acrylamide or the like; for example,
Dicarboxylic acids having a double bond such as maleic acid, butyl maleate, methyl maleate, dimethyl maleate and the like, and substituted products thereof; vinyl esters such as vinyl chloride, vinyl acetate and vinyl benzoate; Olefins such as ethylene, propylene and butylene; vinyl ketones such as vinyl methyl ketone and vinyl hexyl ketone; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether; Monomers may be used alone or in combination of two or more.

Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used, for example, an aromatic divinyl compound such as divinylbenzene, divinylnaphthalene, or the like; for example, ethylene glycol diacrylate, ethylene glycol diacrylate, or the like. Double bonds such as methacrylate, 1,3-butanediol dimethacrylate
Carboxylic acid esters having two or more divinyl compounds such as divinyl alline, divinyl ether, divinyl sulfide, and divinyl sulfone; and compounds having three or more vinyl groups are used alone or as a mixture.

When a pressure fixing method is used, a binder resin for a pressure fixing toner can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer can be used. Coalescent, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, paraffin and the like.

Coloring agents include carbon black, lamp black, iron black, ultramarine, nigrosine dye, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, rhodamine 6G, lake, calco oil blue, chrome yellow, quinacridone, benzidine yellow, and rose. Conventionally known dyes and pigments, such as bengal, triarylmethane dyes, monoazo and disazo dyes, can be used alone or in combination. The colorant is preferably used in an amount of 1 to 10 parts by weight based on 100 parts by weight of the binder resin.

The toner of the present invention further contains a magnetic material. Examples of the magnetic material contained in the magnetic toner of the present invention include iron oxides such as magnetite, maghemite, and ferrite; metals such as iron, cobalt, and nickel; or these metals and aluminum, cobalt, copper, lead, magnesium, tin, and the like. Zinc, antimony, beryllium, bismuth, cadmium,
Examples include alloys with metals such as calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof.

These ferromagnetic materials have an average particle size of about 0.1 to 2 μm, particularly
It is preferably from 0.1 to 1.0 μm, and the amount contained in the toner is about 20 to 200 parts by weight, particularly preferably 40 to 150 parts by weight, based on 100 parts by weight of the resin component.

The toner of the present invention may optionally contain additives. As an additive, for example, a lubricant such as zinc stearate, or a polishing agent such as cerium oxide or silicon carbide or a fluidity imparting agent such as aluminum oxide;
Anti-caking agent, or for example carbon black,
There is a conductivity imparting agent such as tin oxide.

Further, a fluorine-containing polymer fine powder such as a polyvinylidene fluoride fine powder is a preferable additive from the viewpoint of fluidity, abrasiveness, charge stability and the like.

Further, in order to improve the releasability at the time of hot roll fixing, a wax-like substance such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, paraffin wax, etc.
Addition of about 5 wt% to the toner is also a preferred embodiment of the present invention.

In producing the toner according to the present invention, the above-mentioned toner constituent materials are sufficiently mixed by a ball mill or other mixer, then kneaded well using a hot roll kneader or an extruder heat kneader, and cooled and solidified. , Mechanical pulverization, a method of obtaining a toner by classification, is preferred,
Another method is to obtain a toner by dispersing the constituent materials in a binder resin solution and then spray-drying; or a method of mixing a predetermined material with a monomer to form the binder resin and emulsifying a suspension. And then polymerizing the toner to obtain a toner; or a method in which a so-called microcapsule toner comprising a core material and a shell material contains a predetermined material in the core material, the shell material, or both. Method can be applied. Further, if necessary, the desired additive is sufficiently mixed with a mixer such as a Henschel mixer to produce the toner according to the present invention.

The toner of the present invention can be used for development for visualizing an electrostatic image in electrophotography, electrostatic recording, electrostatic printing, and the like, by a conventionally known means.

[Examples] Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. All parts in the following formulations are parts by weight.

The ratio of the number of moles of metal M to the number of moles of imidazole compound L in 1 g of the metal compound is represented by M / L.

After the above materials were mixed well in a blender, they were kneaded with a twin-screw kneading extruder set at 50 ° C. After cooling the obtained kneaded material and coarsely pulverizing with a cutter mill, finely pulverizing using a fine pulverizer using a jet stream, classifying the obtained finely pulverized powder with a fixed wall type air classifier. The classified powder was purified.

In addition, the obtained classified powder is strictly classified and removed simultaneously by a multi-division classifier using a Coanda effect (an elbow jet classifier manufactured by Nippon Steel Mining Co., Ltd.) to obtain a black powder with a volume average particle size of 8.3 μm. A fine powder (magnetic toner) was obtained.

Positively charged hydrophobic silica (BET specific surface area 1
30 m ^{2 /} g) was mixed to obtain a positively chargeable magnetic toner.

The obtained magnetic toner was used in a commercially available electrophotographic copying machine NP-12.
A 20,000 copy test was performed with 15 (manufactured by Canon Inc.). From the beginning, a clear image with an image density of 1.38 was obtained. Two
The image after copying 000 sheets was also clear with a density of 1.33.

Also, when the amount of triboelectric charge of the toner on the developing sleeve was measured, the initial value was +7.6 μc / g, and
At 7.0 μc / g, the charge amount was hardly reduced.

Comparative Example 1 Nigrosine base instead of 3 parts of zinc complex in Example 1
A magnetic toner having a volume average particle size of 7.6 μm was obtained in the same manner as in Example 1 except that 6 parts of EX was used.

When a copy test was performed, the initial density was 1.33.
Although a clear image was obtained, the density tended to decrease as the number of copies increased, and after 10,000 copies, the density decreased to 1.20 and fog occurred.

After the above materials were mixed well in a blender, they were kneaded with a biaxial kneading extruder set at 150 ° C. The obtained kneaded material was cooled, coarsely pulverized by a cutter mill, and then finely pulverized using a fine pulverizer using a jet stream, and the obtained finely pulverized powder was classified by a fixed wall type air classifier. The classified powder was purified.

Furthermore, ultrafine powder and coarse powder are simultaneously strictly classified and removed by a multi-segmentation classifier (Nippon Mining Co., Ltd. Elbow Jet Classifier) utilizing the Coanda effect to obtain a black powder having a volume average particle size of 11.0 μm. A fine powder (magnetic toner) was obtained.

100 parts of this black fine powder was treated with dimethylaminopropyltrimethoxysilane to form a positively charged hydrophobic silica (BET
0.4 part of a specific surface area (200 m ^{2 /} g) was mixed to obtain a positively chargeable magnetic toner.

The obtained magnetic toner was converted to a commercially available electrophotographic copying machine NP-3525.
(Manufactured by Canon Inc.), a 20,000 copy test was performed. From the beginning, a clear image with an image density of 1.37 was obtained. Two
The image after copying 000 sheets was also clear with a density of 1.31.

When the triboelectric charge of the toner on the developing sleeve was measured, it was +7.1 μc / g in the initial stage, and +
At 6.0 μc / g, little decrease in charge was observed.

Comparative Example 2 The black fine powder obtained in Example 2 was directly used as a one-component magnetic toner without externally adding positively charged hydrophobic dry silica. When a copy test was performed using NP-3525 in the same manner as in Example 2, the initial image was rough and the image density was as low as 0.98. After 1,000 sheets, the image density increased to 1.23, but fog occurred.

Example 3 By the method of Example 1, a black fine powder having the above composition (volume average particle diameter 11.3 μm) was obtained.

Silica used in Example 2 was added to 100 parts of the obtained black fine powder.
0.5 part and 0.2 part of polyvinylidene fluoride were added to obtain a one-component magnetic toner.

The obtained magnetic toner is transferred to a commercially available electrophotographic copying machine FC-5.
(Manufactured by Canon Inc.), a 3,000 copy test was performed.

A good image with a density of 1.31 was obtained from the beginning, and no deterioration in image quality was observed even after copying 3,000 sheets.

[Effects of the Invention] As described above, the positively chargeable one-component magnetic toner of the present invention has a uniform triboelectric charge amount between toner particles, and gives a clear image with high density without fogging, scattering, or roughness. .

Further, since the toner carrier such as the sleeve is less contaminated, the durability is excellent, and the amount of triboelectric charge is stable and the image density is stable even when the number of copies is increased.

Claims (4)

(57) [Claims] 1. Finely chargeable silica fine powder is externally added to fine powder particles containing at least a metal compound of an imidazole derivative having zinc, titanium, nickel, iron or copper, a magnetic material and a binder resin. A magnetic toner for developing an electrostatic image, comprising: 2. The magnetic toner according to claim 1, wherein the metal compound is a metal complex or a metal salt. 3. The method of claim 1, wherein the positively chargeable silica fine powder is a silica fine powder of the formula R _m SiY _{n wherein} R is an alkoxy group or halogen, m is an integer of 1 to 3, Y is an amino group or It represents an organo group having at least one nitrogen atom, and n represents an integer of 1 to 3 where m + n is 4. The magnetic toner for developing an electrostatic image according to claim 1, wherein the magnetic toner has been treated with a silane compound represented by the formula: 4. The finely-charged silica fine powder is obtained by treating the fine silica powder with a silicone oil having an organo group or an amino group having a nitrogen atom in a side chain.
Or the magnetic toner for developing an electrostatic image according to 2.