JPH0337676A - Magnetic toner for developing electrostatic images - Google Patents

Abstract

PURPOSE:To prevent staining of a toner carrier and to enhance storage stability by adding a positively chargeable fine silica powder to the outside of a fine colored powder comprising the metal compound of an imidazole derivative used as a charge controller and a magnetic material and a binder resin. CONSTITUTION:The positively chargeable fine silica powder is added to the outside of the fine powder comprising the metal compound of the imidazole derivative used as the charge controller and the magnetic material and the binder resin. The metal compound of the imidazole derivative is good in heat stability and does not degenerate at all from room temperature up to 250 deg.C. When this metal compound is incorporated in the toner, it is good in dispersibility in the binder resin, and an electrostatic charge quantity of the toner is high enough as compared with the case of using the imidazole compound alone, and the toner particles are uniformly charged among each particle, thus permitting the toner carrier to be prevented from staining, and storage stability to the enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a toner for visualizing electrostatic latent images in image forming methods such as electrophotography and electrostatic recording.

[Prior Art] Conventionally, as an electrophotographic method, U.S. Patent No. 2.297°69
1, Special Publication No. 42-23910, and Special Publication No. 4
Various methods are described in Japanese Patent No. 3-24748 and the like.

The developing methods applied to these electrophotographic methods include:
Broadly speaking, there are dry development methods and wet development methods. The former method is further divided into methods using a two-component developer and methods using a one-component developer.

As toners applied to these dry developing methods, fine powders in which dyes and pigments are dispersed in natural or synthetic resins have conventionally been used. For example, particles obtained by dispersing a colorant in a binder resin such as polystyrene and pulverizing the particles to about 1 to 30 μm are used as toner. As the magnetic toner, one containing magnetic particles such as magnetite is used. Further, in the case of a system using a two-component developer, the toner is usually mixed with carrier particles such as glass beads and iron powder.

Either toner must have a positive or negative charge depending on the polarity of the electrostatic latent image being developed.

In order to make the toner hold an electric charge, it is also possible to use the triboelectricity of the resin, which is a component of the toner, but with this method, the toner's chargeability is small, so the image obtained by development is prone to fogging and is unclear. Become something. Therefore, in order to impart desired triboelectric charging properties to toners, dyes, pigments, and even charge control agents that impart charging properties are added to the toners.

Charge control agents known in the technical field today include nigrosine dyes, azine dyes, triphenylmethane dyes and pigments, quaternary ammonium salts, or quaternary ammonium salts with side chains as positive triboelectric chargers. Polymers that have this are known.

However, since some of these charge control agents tend to contaminate the sleeve or carrier, toners using these agents have a reduced amount of triboelectric charge as the number of copies is increased, causing a reduction in image density.

Further, some charge control agents have an insufficient amount of triboelectric charge and are easily affected by temperature and humidity, which causes environmental fluctuations in image density. Furthermore, since some charge control agents have poor dispersibility in resins, toners using these agents tend to have non-uniform triboelectric charges between particles and are prone to fogging. Also,
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 a charge control agent that satisfies all of these requirements.

[Problem to be Solved by the Invention 1] An object of the present invention is to provide a novel toner that solves the above problems.

Another object of the present invention is to minimize contamination of toner carriers such as sleeves, to ensure that the amount of frictional charge between toner and toner carriers such as sleeves is stable without changes in temperature and humidity, and to maintain stability under environmental conditions. To provide a toner capable of reproducing stable images that are not easily affected by changes.

[Means and effects for solving the problem] The present inventors
As a result of intensive studies to solve the above-mentioned problems, we found that a toner in which positively chargeable silica fine powder is externally added to a colored fine powder using a metal compound of an imidazole derivative as a charge control agent has sufficient positive chargeability. It has been found that the toner carrier is less likely to contaminate toner carriers such as carriers, has good storage stability, and is less likely to fog.

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

Furthermore, since carriers are less likely to be contaminated, image density decreases in durability tests tend to be less than with conventional charge control agents. Furthermore, it was found that this contamination could be almost completely resolved by externally adding positively charged silica fine powder.

Further, by externally adding positively chargeable silica fine powder, roughness of the image is improved, and a high-density image can be obtained from the initial stage. However, when positively chargeable silica powder is not externally added, the rise of the image density is poor and ground blurring occurs, making it difficult to put it to practical use. Based on these findings, it was discovered that positively chargeable silica fine powder is indispensable, and the present invention was completed.

The imidazole forming the metal compound of the imidazole derivative of the present invention includes all imidazole species, but considering the high charge imparting ability, the following formula [echo a, b, formula [+1] - a, b] The imidazole species shown are preferred.

In consideration of ease of production, the substituents R1 to R8 in the formula preferably have 24 or less carbon atoms, and more preferably have 6 or less carbon atoms.

[I] - (a) [r] - (b) [
111-(a) [11]-(b) Examples of the metal in the metal compound of the imidazole derivative include aluminum, chromium, manganese, iron, cobalt, nickel, copper, zinc, tin, lead, titanium, and the like. In consideration of the stability of the metal complex and the high charge amount, zinc, titanium, nickel, iron, and copper are preferable, and zinc is more preferable in consideration of ease of production and color. Further, the metal compound of the imidazole derivative of the present invention has a higher charge imparting ability than the imidazole derivative. The mechanism that provides this high charge-imparting ability is unknown, but it is thought to be due to the formation of a metal complex or metal salt via the nitrogen on imidazole.

Further, the metal compound of the imidazole derivative in the present invention has a counter ion as necessary. Counter anions in this case include inorganic anions and organic anions.

Inorganic anions include F-, CI, Br-, I-
rj which halogen ion, OH-, SOa'-, BF4
-, DFa-CR04-,5IF6- and [Mo, O
□4]6L[H2W+□042]10-[PlilO+
Examples include heteropolyacid ions such as z04°]'-, [pw, □04]'-, and the like.

Examples of organic ions include C1-C24 sulfonic acid ions, C1-C24 carboxylic acid ions, C1-C24 sulfuric acid monoalkyl ester anions, and tetraphenylboron ions.

The imidazole metal compound of the present invention is synthesized by adding the imidazole compound to a metal salt solution, and if necessary, adding a reagent for exchanging counterions, followed by purification to obtain the desired compound.

If the number of moles of metal per gram of the obtained product is M1, and the number of moles of imidazole species is L, then the ratio M/L is 0,
A value of 0.05 or more and 2 or less indicates good positive chargeability, and a value of 0.16 or more and 0.6 or less is preferable in consideration of the thermal stability of the compound and the durability stability in a copy durability test when used as a toner.

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

]1 C2115 C)13 The metal compound of the present invention may contain one or more of these imidazole species.

The toner of the present invention can be obtained by blending the above-mentioned imidazole metal compound into a toner (colored fine powder) containing a binder resin and a coloring component as essential components. As for the form of compounding, either a so-called internal addition form in which the additive is encapsulated uniformly or in a capsule form in the toner, or an external addition form in which it is mixed and attached to the toner can be adopted.

When internally added, the amount of imidazole metal compound used depends on the type of binder resin, the presence or absence of additives used as necessary,
It is determined by the toner production method including the dispersion method, and is preferably 0.1 to 20 parts by weight (more preferably 0.1 to 20 parts by weight, more preferably 0.1 to 20 parts by weight, based on 100 parts by weight of the binder resin), although the number is not limited. (5 to 10 parts by weight).

In addition, when externally added, 0.
01 to 10 parts by weight is desirable. As the external addition method, it is particularly preferable to fix by a mechanochemical method.

Note that, if necessary, a conventionally known charge control agent may be used in combination with the charge control agent of the present invention.

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

As the matrix for the positively chargeable silica fine powder, silica fine powder produced by a dry method or a wet method can be used.

The dry method mentioned here is a method for producing fine silica powder produced by vapor phase oxidation of a silicon halide compound. For example, this method utilizes the thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen and hydrogen, and the basic reaction formula is as follows.

St(, j), + 282+ 02 → SiO, + 4
In addition, it is also possible to obtain a composite fine powder of silica and other metal oxides by using other metal halide compounds such as aluminum chloride or titanium chloride together with a silicon halide compound in this manufacturing process.
These are also included.

On the other hand, various conventionally known methods can be applied to produce the matrix of the silica fine powder used in the present invention by a wet method. For example, the decomposition of sodium silicate with an acid can be expressed as a general reaction formula (the reaction formula is omitted below): Na204Sf02+ HCJ' + 120 →
5IO2'n) 120 + NaCfOther methods include decomposition of sodium silicate with ammonia salts or alkali salts, a method of generating alkaline earth metal silicate from sodium silicate and then decomposing it with acid to produce silicic acid, silicic acid There are methods such as converting a sodium solution into silicic acid using an ion exchange resin, and methods using natural silicic acid or silicate.

As the silica fine powder referred to herein, any of anhydrous silicon dioxide (silica) and other silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate can be used.

Among the silica fine powders mentioned above, the specific surface area due to nitrogen adsorption measured by the BET method is 30 m'/g or more (especially 50 to 40 m'/g).
0m+27g) is preferable as the matrix silica.

As a method for obtaining positive 1F conductive silica fine powder, at least one nitrogen atom is attached to the side chain of the above-mentioned untreated silica fine powder.
There is a method of treatment with a silicone compound such as silicone oil, silicone varnish, silicone resin, etc. having more than one organo group, a method of treatment with a nitrogen-containing silane coupling agent, or a method of treatment with a plurality of these types.

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

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

R,R.

(In the formula, R1 represents hydrogen, an alkyl group, an aryl group, or an alkoxy group, R2 represents an alkylene group or a phenylene group, Rs, R4 represents hydrogen, an alkyl group, or an aryl group, and R5 represents a nitrogen-containing heterocyclic ring. The above alkyl group, aryl group, alkylene group, and phenylene group may have an organo group having a nitrogen atom,
Further, it may have a substituent such as halogen within a range that does not impair chargeability.

Furthermore, the nitrogen-containing silane coupling agent used in the present invention is
It generally has a structure shown by the following formula.

R,5iYn (R represents an alkoxy group or a halogen, Y represents an a) 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. Examples of the nitrogen-containing heterocyclic group include unsaturated heterocyclic groups and saturated heterocyclic groups, and known ones can be used. 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 five-membered ring or a six-membered ring in consideration of stability.

Examples of such treatment agents include aminopropyltrimethoxysilane, aminopropyltriethoxysilane, dimethylanobrobyltrimethoxysilane, diethylaminopropyltrimethoxysilane, dipropylaminopropyltrimethoxysilane, and dibutylaminopropyltrimethoxysilane. Propyltrimethoxysilane, monobutylaminopropyltrimethoxysilane, dioctylaminopropyltrimethoxysilane, dibutylaminopropyldimethoxysilane.

Dibutylaminopropylmonomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-γ-propylphenylamino.

Trimethoxysilyl-γ-propylbenzyladine, etc. can be used, and as the nitrogen-containing heterocycle, those having the above-mentioned structure can be used. Examples of such compounds include trimethoxysilyl-γ-propylbieridine, Trimethoxysilyl-γ-propylmorpholine, trimethoxysilyl-γ
- Propylimidazole, etc.

The applied amount of these treated silica fine powders exhibits an effect when the amount is 0.01 to 20% based on the weight of the developer, and particularly preferably when it is added in an amount of 0.03 to 5%, excellent stability is achieved. It exhibits positive chargeability. A preferred form of addition is that 0.01 to 3% by weight of treated silica fine powder based on the weight of the developer is attached to the surface of the toner particles.

Furthermore, the silica fine powder used in the present invention may be treated with a treatment agent such as a silane coupling agent or an organosilicon compound for the purpose of hydrophobization, if necessary, and a known method may be used. , treated with the above-mentioned treatment agent that reacts with or physically adsorbs the silica fine powder. Examples of such treatment agents include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allyl phenyldichlorosilane, and benzyldimethylchlorosilane. , bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyl Dimethoxysilane, diphenyljethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and terminally located siloxane units with 2 to 12 siloxane units per molecule. Examples include dimethylpolysiloxane containing one hydroxyl group bonded to Si in each unit. These may be used alone or in a mixture of two or more.

Finally, the degree of hydrophobicity of the treated silica fine powder was determined to be 30 as measured by methanol titration test.
When the developer is hydrophobized so as to exhibit a value in the range of 80 to 80, the amount of triboelectric charge of the developer containing such fine silica powder becomes sharp and uniformly positive, which is preferable. Here, the methanol titration test confirms the degree of hydrophobization of the silica fine powder having a hydrophobized surface.

The "methanol titration test" specified herein for evaluating the degree of hydrophobicity of treated silica fine powder is conducted as follows. Sample silica fine powder 0.2g in capacity 250
Add to 50 mj+ of water in an 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 when the entire amount of fine silica powder is suspended in the liquid, and the degree of hydrophobization is expressed as the percentage of methanol in the liquid mixture of methanol and water when the end point is reached.

Examples of the resin used in the present invention include monopolymers of styrene and substituted products thereof such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene;
-Chlorstyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-methyl chloromethacrylate copolymer Polymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer , styrenic copolymers such as styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, naturally modified phenolic resins, natural resin-modified maleic resins, acrylic resins, methacrylic resins, polyvinyl acetate, silicone resins, polyesters Resin, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumaron indene resin,
Petroleum-based resins can be used.

Further, crosslinked styrenic copolymers are also preferred binder resins.

Examples of comonomers for the styrene monomer in the styrenic copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylate. Acid, monocarboxylic acid having a double bond such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, etc., or substitutes thereof; e.g., maleic acid, butyl maleate , methyl maleate, dimethyl maleate, etc., and their substituted dicarboxylic acids; for example, vinyl chloride, vinyl acetate,
Vinyl esters such as vinyl benzoate; ethylene olefins such as ethylene, propylene, butylene; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone; vinyl methyl ether, vinyl ethyl ether, Vinyl monomers such as vinyl ethers such as vinyl isobutyl ether may be used alone or in combination of two or more.

As the crosslinking agent, compounds having two or more polymerizable double bonds are mainly used, such as aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; for example, ethylene glycol diacrylate and ethylene glycol diacrylate. methacrylate, 1,3-butanediol dimethacrylate, etc.
Carboxylic acid esters having a divinyl compound such as divinylaniline, divinyl ether, divinyl sulfide, and divinyl sulfone; and compounds having three or more vinyl groups; are used alone or as a compound.

In addition, when using a pressure fixing method, it is possible to use a binder resin for pressure fixing toner, such as polyethylene,
Examples include polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, and paraffin.

Colorants include carbon black, lamp black,
Iron black, ultramarine, nigrosine dye, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa yellow G10-Damine 6G1 lake, calco oil blue, chrome yellow, quinacridone, benzidine yellow
Conventionally known dyes and pigments such as rose bengal, triarylmethane dyes, monoazo dyes, and disazo dyes and pigments can be used alone or in combination. The colorant is preferably used in an amount of 1 to 10 parts by weight per 100 parts by weight of the binder resin.

The toner of the present invention further contains a magnetic material.

The magnetic materials contained in the magnetic toner of the present invention include iron oxides such as magnetite, magnetite, and ferrite; metals such as iron, cobalt, and nickel, or these metals and aluminum, cobalt, copper, lead, magnesium, tin, Examples include alloys with metals such as zinc, antimony, beryllium, bismuth, cadmium, 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 0.1 μm to 2 μm. 1 to 1.0 μm is desirable, and the amount to be included in the toner is approximately 20 to 2 μm per 100 parts by weight of the resin component.
0G! i parts, particularly preferably 40 to 150 parts by weight per 100 parts by weight of the resin component.

The toner of the present invention may contain additives, if necessary. Examples of additives include lubricants such as zinc stearate, abrasives such as cerium oxide and silicon carbide, flow agents such as aluminum oxide, anti-caking agents, and conductive agents such as carbon black and tin oxide. There is a drug.

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

In addition, in order to improve mold releasability during hot roll fixing, waxy substances such as low molecular weight polyethylene, low molecular weight polypropylene, microcrystalline wax, carnauba wax, Sasol wax, paraffin wax, etc.
It is also one of the preferred embodiments of the present invention to add about 5 wt% to the toner.

In manufacturing the toner according to the present invention, the toner constituent materials as described above are sufficiently mixed using a ball main or other mixer, then thoroughly kneaded using a heat kneader such as a hot roll kneader or an extruder, and then cooled. After solidification, it is preferable to obtain the toner by mechanical crushing and classification; another method is to obtain the toner by dispersing the constituent materials in a binder resin solution and then spray drying; or by dispersing the constituent materials in a binder resin solution; Polymerization method toner production method, in which a specified material is mixed with the desired monomer to form an emulsified suspension, and then polymerized to obtain a toner; Alternatively, in a so-called microcapsule toner consisting of a core material and a shell material, material or shell material,
Or a method of containing a predetermined material in both;
The following methods can be applied. Furthermore, if necessary, desired additives are thoroughly mixed with a mixer such as a Henschel mixer,
A toner according to the present invention can be manufactured.

The toner of the present invention can be used in all conventionally known methods for developing electrostatic charge images in electrophotography, electrostatic recording, electrostatic printing, and the like.

[Examples] Hereinafter, the present invention will be specifically explained with reference to Examples, but these are not intended to limit the present invention in any way. Note that all parts in the following formulations are parts by weight.

Further, the ratio between the number of moles M of the metal in 1 g of the metal compound and the number of moles of the imidazole compound is expressed as M/L.

After thoroughly mixing the above materials in a blender, they were kneaded in a twin-screw kneading extruder set at 150°C.

The obtained kneaded material was cooled and coarsely pulverized using a cutter mill, and then finely pulverized using a pulverizer using a jet stream.
The obtained finely pulverized powder was classified using a fixed wall type wind classifier to refine the classified powder.

Furthermore, the obtained classified powder was strictly classified and removed at the same time to remove ultra-fine powder and coarse powder using a multi-division classifier that utilizes the Coanda effect (Elbowjet classifier manufactured by Nippon Steel Mining Co., Ltd.) to obtain a volume average particle size of 8.3 μm. A black fine powder (magnetic toner) was obtained.

0.8 parts of positively charged hydrophobic silica (BET specific surface area: 130 m'/g) treated with silicone oil having an amino group was mixed with 100 parts of this black fine powder to obtain a positively charged magnetic toner.

The obtained magnetic toner was transferred to a commercially available electrophotographic copying machine NP-1.
215 (manufactured by Canon ■), a copying test of 20,000 sheets was conducted. A clear image with an image density of 1.38 was obtained from the initial stage. The image after 20,000 copies was also clear with a density of 1.33.

In addition, when we measured the amount of triboelectric charge of the toner on the developing sleeve, it was +7.6 μc/g at the initial stage, 20,00 μc/g.
After copying 0 sheets, the charge was +7.0t1c/g, and almost no decrease in the amount of charge was observed.

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

When I did a copy test, the density was 1.3 in the initial stage.
Although a clear image of No. 3 was obtained, the density tended to decrease as the number of copies was increased, and after 1,000 copies, a clear image of No. 3 was obtained.
20 and fogging also occurred.

After thoroughly mixing the above materials in a blender, they were kneaded in a twin-screw kneading extruder set at 150°C.

The obtained kneaded material was cooled and coarsely pulverized using a cutter mill, and then finely pulverized using a pulverizer using a jet stream.
The obtained finely pulverized powder was classified using a fixed-wall type wind loosening machine to refine the classified powder.

Furthermore, the obtained classified powder is strictly classified and removed at the same time to remove ultrafine powder and coarse powder using a multi-division classifier (elbow jet classifier manufactured by 8 Iron Mining Co., Ltd.) that utilizes the Coanda effect to obtain a volume average particle size of 11,000 gm. A black fine powder magnetic toner was obtained.

Positively charged hydrophobic silica (BE) treated with dimethylaminopropyltrimethoxysilane was added to 100 parts of this black fine powder.
A positively charged magnetic toner was prepared by mixing 0.4 part of T (specific surface area: 200 m2/g).

The obtained magnetic toner was transferred to a commercially available electrophotographic copying machine NP-35.
25 (manufactured by Canon ■), a copying test of 20,000 sheets was conducted. A clear image with an image density of 1.37 was obtained from the initial stage. The image after 20,000 copies was also clear with a density of 1.31.

In addition, when we measured the amount of triboelectric charge of the toner on the developing sleeve, it was +7.1B/g at the initial stage and +6.0pc/g after copying 20,000 sheets, with almost no decrease in the charge amount observed. Ta.

The black fine powder obtained in Example 2 of Group L was used as it was as a -component magnetic toner without externally adding positively charged hydrophobic dry silica. When a copying test was carried out 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 fogging occurred.

A black fine powder having the above composition (volume average particle size: 1[), 9μff1] was obtained by the method of Example 1.

To 100 parts of the obtained black fine powder was added 0.5 part of positively charged hydrophobic silica (BET specific surface area 200 m2/g) treated with dimethylaminopropyltrimethoxysilane.
The components were made into magnetic toner.

The obtained magnetic toner was transferred to a commercially available electrophotographic copying machine NP-55.
40 (manufactured by Canon ■), a 20,000 copy test was conducted.

A good image with a density of 1.35 was obtained from the initial stage, and a density of 20.0
No deterioration in image quality was observed even after making 00 copies.

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

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

The obtained magnetic toner was transferred to a commercially available electrophotographic copying machine FC-5 (
A 3,000-sheet copying test was conducted using Canon ■.

A good image with a density of 1.31 was obtained from the beginning, and the density was 3.00.
No deterioration in image quality was observed even after copying 0 sheets.

[Effects of the Invention] As described above, the positively chargeable component-based magnetic toner of the present invention has a uniform amount of friction between toner particles, and provides a high-density, clear image without capri, scattering, or roughness. .

Furthermore, since there is little contamination of the toner carrier such as the sleeve, it has excellent durability, and even if the number of copies is increased, the friction ftf is stable and the '#l image density is also stable.

Claims (4)

[Claims] (1) A magnetic toner for developing an electrostatic image, characterized in that positively chargeable fine silica powder is externally added to fine powder particles comprising at least a metal compound of an imidazole derivative, a magnetic material, and a binder resin. (2) As the metal compound of the imidazole derivative, zinc,
2. The magnetic toner for developing electrostatic images according to claim 1, which contains an imidazole metal compound having titanium, nickel, iron, or copper as a central metal. (3) Positively chargeable silica fine powder has the formula R_
mSiY_n [wherein R represents an alkoxy group or halogen, m represents an integer of 1 to 3, Y represents an amino group or an organo group having at least one nitrogen atom,
n represents an integer of 1 to 3 such that m+n is 4. 2. The magnetic toner for developing electrostatic images according to claim 1, which is treated with a silane compound represented by: (4) The magnetic toner for developing electrostatic images according to claim 1, wherein the positively chargeable silica fine powder is obtained by treating the silica fine powder with a silicone oil having an organo group or an amino group having a nitrogen atom in a side chain. .