JP2759520B2 - Positively chargeable toner for image formation - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positively chargeable toner for image formation for visualizing an electrostatic latent image in an image formation 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 finely pulverizing a dispersion of a colorant in a binder resin such as polystyrene to about 1 to 30 μm are used as the toner. As the magnetic toner, a toner containing magnetic particles such as magnetite is used. In the case of 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 the electric charge in the toner, it is possible to use the frictional charging property of the resin which is a component of the toner, but in this method, since the charging property of the toner is low, an image obtained by development is easily fogged and unclear. It will be.

Therefore, in order to impart an appropriate triboelectric charging property to the toner, a dye, a pigment for imparting the charging property, and a charge controlling agent have been added.

Today, as charge control agents known in the art, nigrosine dyes, azine dyes, triphenylmethane dyes, quaternary ammonium salts or polymers having a quaternary ammonium salt in the side chain are known. .

[Problems to be Solved by the Invention] However, since those containing these charge control agents easily contaminate the sleeve or carrier, the amount of triboelectricity of the toner using them decreases as the number of copies increases. Causes a reduction in image density. In addition, certain types of charge control agents have insufficient triboelectric charge and are susceptible to temperature and humidity, thus causing environmental fluctuations in image density. In addition, certain charge control agents have poor storage stability, and their triboelectric charging ability decreases during long-term storage. Further, since a certain type of charge control agent has poor dispersibility in a resin, the toner using the same has a non-uniform triboelectric charge amount between particles and is easily fogged.

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

That is, an object of the present invention is to provide a positively chargeable toner for image formation which has solved such a problem.

Means and Action for Solving the Problems According to the present invention, a toner image is formed by developing an electrostatic image with a positively chargeable toner, the formed toner image is transferred to a recording material, and the transferred toner is used. An image forming positively chargeable toner for use in an image forming method of heating and fixing an image to the recording material, wherein the positively chargeable toner has the following general formula [I] (However, R ¹ and R ² represent any one of an alkyl group, an aryl group, and an aralkyl group, and may be the same or different, and R ³ , R ⁴ , R ⁵ , and R ⁶ are hydrogen, an alkyl group , An alkoxy group, which may be the same or different,
X represents an anion. A) a colored fine powder containing at least a pyridinium salt derivative, a colorant, a binder resin and a waxy substance represented by
Positively-charged silica fine powder externally added to the colored fine powder, wherein the wax-like substance is contained in the colored fine powder in an amount of 0.5 to 5% by weight based on the weight of the toner. The present invention relates to a positively chargeable toner for forming an image.

Now, the compound obtained by dimerizing the pyridinium salt at the para position has a higher positive triboelectric charging property than other quaternary ammonium salts. In addition, as a result of investigations by the present inventors, it was found that the triboelectric charge of the present pyridinium salt derivative can be changed depending on the type of counter ion. However, since the pyridinium salt derivative slightly contaminates the toner carrier such as a carrier or a sleeve, the image density gradually decreases as the number of sheets increases. As a result of the examination,
In order to improve the contamination of the toner carrier with the pyridinium salt derivative, it has been found that the presence of finely triboelectrically chargeable silica fine powder on the toner surface has the least adverse effect and is effective. Further, since the present pyridinium salt derivative has a low triboelectric charging rate, a high-density image could not be obtained from the beginning.
However, this problem could also be solved by making the positive frictionally chargeable silica fine powder exist on the toner surface.

As described above, the present inventors have found that positively chargeable silica fine powder is indispensable in order to take advantage of the excellent properties as a positive charge control agent possessed by the compound obtained by dimerizing a pyridinium salt at the para position. We have found and completed the present invention.

Various structures are selected for the charge control agent according to the present invention. One example is as follows.

It is known from JP-A-59-177568 to include in a toner a compound obtained by dimerizing a pyridinium salt at the para position. However, they do not mention the effects of the positive triboelectrically chargeable silica fine powder of the present invention. There is no description about the effect of the counter ion. In the present invention, it is an essential component to use a combination of a special pyridinium salt derivative having excellent properties and a finely-charged silica fine powder as a charge control agent for a toner. No charge image developing toner is obtained.

In the present invention, the amount of the pyridinium salt derivative used is
The type of the binder resin, the presence or absence of additives used as necessary, is determined by the toner manufacturing method including the dispersion method, and is not limited to a specific one, but is preferably a binder resin 100. It is used in an amount of 0.1 to 10 parts by weight, more preferably 0.1 to 5 parts by weight based on parts by weight. In addition, the special pyridinium salt derivative of the present invention can be used in combination with a conventionally known charge control agent.

Further, as the fine silica powder constituting one component of the developer in the present invention, fine silica powder produced by a dry method and a wet method can be used.

Here, the dry method is a method for producing fine silica powder produced by vapor phase oxidation of a silicon halide derivative. 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 production process, for example, by using other metal halogen derivatives such as aluminum chloride and titanium chloride together with the silicon halogen derivative, a composite fine powder of silica and another metal oxide is obtained. It is also possible and encompasses them.

On the other hand, as a method for producing the 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 with an acid, as represented 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, etc., and ammonium salts or alkalis of sodium silicate Decomposition with salts, after producing an alkaline earth metal silicate from sodium silicate, a method of decomposing with an acid to silicic acid, a method of converting a sodium silicate solution to silicic acid with an 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 and the like 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 by nitrogen adsorption give good results.

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 oil having one or more organo groups, a method of treating with a nitrogen-containing silane coupling agent, or a method of treating with both.

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

As the silicone oil having a nitrogen atom in a side chain used for treating the silica fine powder, a silicone 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 aryl group, R ₅ Represents a nitrogen-containing heterocyclic group.) The above alkyl group, aryl group, alkylene group, and phenylene group may have an organo group having a nitrogen atom, and may be substituted with halogen or the like as long as chargeability is not impaired. It may have a group.

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 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 +
There is a relation of 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 each of them is applicable. 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, and monopropyltrimethoxysilane. Butylaminopropyltrimethoxysilane, dioctylaminopropyltrimethoxysilane, dibutylaminopropyldimethoxysilane, dibutylaminopropylmonomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-γ
-Propylphenylamine, trimethoxysilyl-γ-
Propylbenzylamine and the like, and nitrogen-containing heterocycles having the above-mentioned structure can be used. Examples of such derivatives include trimethoxysilyl-γ-propylpiperidine, trimethoxysilyl-γ-propylmorpholine, And trimethoxysilyl-γ-propylimidazole.

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.

In addition, 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 derivative for the purpose of hydrophobization, and a known method is also used. Is treated with the treating agent that reacts or physically adsorbs with the silica fine powder. Such treatment agents include, for example, 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
Diphenyltetramethyldisiloxane, and dimethylpolysiloxane having from 2 to 12 siloxane units per molecule, each containing one hydroxyl group bonded to Si at each terminal unit. These are one or two
Used in mixtures of more than one species.

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, in the methanol titration test, the degree of hydrophobicity of the silica fine powder having a hydrophobicized surface is confirmed.

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 as the entire amount of fine silica powder is suspended in the liquid, and the degree of hydrophobicity is expressed as the percentage of methanol in the liquid mixture of methanol and water when the end point is reached.

As the coloring agent used in the present invention, carbon black, lamp black, iron black, ultramarine, nigrosine dye, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, rhodamine 6G, calco oil blue, chrome yellow, quinacridone, Benzidine yellow, rose bengal, triarylmethane dyes, monoazo dyes, disazo dyes and pigments conventionally known can be used alone or in combination, but the hue changes with the pyridinium derivative.

Examples of the resin used in the present invention include styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyl toluene, and a homopolymer of a substituted product thereof; styrene-p
-Chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate 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 , Styrene-based copolymers such as styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenolic resin, natural modified phenolic resin, natural resin modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester Tree , Polyurethane, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, wheel of fortune resins, coumarone-indene resin, petroleum resin, or the like 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. Monocarboxylic acid having a double bond such as acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate A dicarboxylic acid having a double bond such as methyl, methyl maleate, dimethyl maleate and the like; and a vinyl ester such as vinyl chloride, vinyl acetate and vinyl benzoate;
Ethylene olefins such as 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; A single monomer or two or more monomers are used.

Here, as the cross-linking agent, a derivative having two or more polymerizable double bonds is mainly used, and examples thereof include aromatic divinyl derivatives such as divinylbenzene and divinylnaphthalene; for example, ethylene glycol diacrylate,
Carboxylic acid esters having two double bonds such as ethylene glycol dimethacrylate and 1,3-butanediol dimethacrylate; divinyl derivatives such as divinylaniline, divinyl ether, divinyl sulfide and divinyl sulfone; and three or more vinyls Derivatives having a group;
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.

Further, the toner of the present invention is used by being mixed with a carrier. As the carrier that can be used in the present invention, known carriers can be used, for example, iron powder, ferrite powder, powder having magnetic properties such as nickel powder, glass beads, and the like, and the surface thereof is treated with a resin or the like. What is done is raised.

Further, as the resin for coating the carrier surface, styrene-acrylate copolymer, styrene-methacrylate copolymer, acrylate copolymer,
A methacrylate copolymer, a silicone resin, a fluorine-containing resin, a polyamide resin, an ionomer resin, a polyphenylene sulfide resin, or a mixture thereof can be used.

Further, the toner for electrostatic charge development of the present invention may contain a magnetic material and be used as a magnetic toner. Examples of the magnetic material used include magnetite, γ-iron oxide, ferrite, iron oxides such as iron-rich ferrite; metals such as iron, cobalt, and nickel; or these metals and aluminum, cobalt, copper, lead, magnesium, tin, and the like. Examples thereof include alloys with metals such as zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof. These magnetic materials preferably have an average particle size of 0.1 to 1 μm, preferably about 0.1 to 0.5 μm. The amount contained in the magnetic toner is 40 to 150 parts by weight with respect to 100 parts by weight of the binder resin component. Preferably it is 60 to 120 parts by weight.

The toner of the present invention may optionally contain additives. Examples of the additive include a lubricant such as zinc stearate, a polishing agent such as cerium oxide and silicon carbide, a fluidity imparting agent such as aluminum oxide, an anti-caking agent, and a conductivity imparting agent such as carbon black and tin oxide. There are agents.

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

In addition, a wax-like substance such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sazol wax, and paraffin wax is added to the colored fine powder for the purpose of improving the releasability at the time of hot roll fixing. The content is 0.5 to 5% by weight on a weight basis.

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 kneader of a hot roll kneader or an extruder, and cooled and solidified. A method of obtaining a toner by mechanical pulverization and classification is preferable. Alternatively, a method of obtaining a toner by dispersing a constituent material in a binder resin solution and spray-drying; or forming a binder resin A polymerization method in which a predetermined material is mixed with a monomer to form an emulsified suspension and then polymerized to obtain a toner;
Alternatively, in a so-called microcapsule toner composed of a core material and a shell material, a method of including a predetermined material in the core material, the shell material, or both of them 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.

The pyridinium derivative dimerized at the para-position according to the present invention has good positive triboelectrification. Further, by externally adding the positively chargeable silica fine powder, contamination of the toner carrier by the present pyridinium derivative can be prevented, and the uniformity of density of a solid image can be improved.

Therefore, the toner of the present invention hardly causes image quality deterioration due to continuous copying and can provide an image having excellent density uniformity.

[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.

Example 1 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.

Further, the obtained classified powder is strictly classified and removed by a multi-division classifier utilizing a Coanda effect (an elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) at the same time to obtain a volume average particle size of 8.1 μm. A black fine powder was obtained.

100 parts of this black fine powder is mixed with positively charged hydrophobic dry silica (B
0.6 part of ET specific surface area (200 m ^{2 /} g) was added and mixed with a Henschel mixer to obtain a positively chargeable one-component magnetic toner.

The obtained magnetic toner was converted to a commercially available electrophotographic copying machine NP-3525.
(Manufactured by Canon Inc.), a 5,000 copy test was performed.

As a result, a clear image with an image density of 1.31 and a good resolution with little fog was obtained from the beginning. The image density after copying 5,000 sheets was as good as 1.28, and no reduction in density and no deterioration in image quality were observed.

Example 2 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 powder was purified.

Further, the obtained classified powder was strictly classified and removed simultaneously with a multi-division classifier using a Coanda effect (an elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) to obtain a volume average particle size of 11.2 μm. A black fine powder was obtained.

100 parts of this black fine powder is mixed with positively charged hydrophobic dry silica (B
0.4 parts of ET specific surface area (200 m ^{2 /} g) was added and mixed with a Henschel mixer to obtain a positively chargeable one-component magnetic toner.

The obtained magnetic toner was converted to a commercially available electrophotographic copying machine NP-5540.
(Manufactured by Canon Inc.), and a copy test of 10,000 sheets was performed.

As a result, a clear image with an image density of 1.33 and little fog was obtained from the beginning. Further, the image density after copying 10,000 sheets was as good as 1.30, and no reduction in density and no deterioration in image quality were observed.

Example 3 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.

Further, the obtained classified powder is strictly classified and removed simultaneously and simultaneously with a multi-division classifier using a Coanda effect (elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) to obtain a volume average particle size of 12.4 μm. A black fine powder was obtained.

0.4% by weight of silica (140 m ² / g) treated with amino group-modified silicone oil was mixed with the black fine powder to obtain a toner.

For 100 parts of iron powder carrier with an average particle size of 50 to 80 μm,
The black fine powder was mixed at a ratio of 5 parts to prepare a developer. Next, a negative electrostatic charge image is formed on the OPC photoreceptor by a conventionally known electrophotography method, and the toner image is formed by developing the negative electrostatic charge image using the above-described developer by a magnetic brush method, and transferred to plain paper. And heat-fixed.

The obtained image had a sufficiently high density of 1.31 and was sharp. The density was 1.29 even after copying 5,000 sheets, and no reduction in density was observed. Further, the uniformity of density of the solid black image was excellent. When the triboelectric charge was measured by the blow-off method, the initial value was 10.1 μc / g and even after copying 5,000 sheets.
9.7 μc / g, which did not decrease.

Comparative Example 1 A copy test was performed in the same manner as in Example 1 except that the black fine powder obtained in Example 1 was used as a developer without externally adding positively charged hydrophobic fumed silica.

As a result, the image density was slightly low at 1.12 from the beginning, and fog was conspicuous. After continuous copying of 5,000 sheets, no increase in image density was observed, and the image density gradually decreased. When the amount of triboelectric charge of the toner on the sleeve was measured, 4.4
μc / g, which was slightly lower, and further decreased to 2.1 μc / g after 5,000 sheets.

Comparative Example 2 A toner was obtained in the same manner as in Example 3 except that 3 parts of benzylmethylhexadecyl ammonium chloride was used instead of 3 parts of the compound (1) used in Example 3. Using this toner, an image was obtained in the same manner as in Example 3.

As a result, the image density was slightly low at 1.15 from the beginning, and fog was conspicuous. After continuous copying of 5,000 sheets, no increase in image density was observed. The amount of triboelectric charge measured by the blow-off method was as low as 7.8 μc / g.

[Effects of the Invention] As described above, according to the positively chargeable toner for image formation of the present invention, there is no decrease in image density due to an increase in the number of copies, it is hardly affected by temperature and humidity, and high image quality without fog or the like is obtained. Can be stably obtained over a long period of time.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 9/097

Claims (4)

(57) [Claims] An image formed by developing an electrostatic image with a positively chargeable toner to form a toner image, transferring the formed toner image to a recording material, and heating and fixing the transferred toner image to the recording material. In a positively chargeable toner for forming an image for use in a forming method, the positively chargeable toner is represented by the following general formula [I] (However, R ¹ and R ² represent any one of an alkyl group, an aryl group, and an aralkyl group, and may be the same or different, and R ³ , R ⁴ , R ⁵ , and R ⁶ are hydrogen, an alkyl group , An alkoxy group, which may be the same or different,
X represents an anion. A) a colored fine powder containing at least a pyridinium salt derivative, a colorant, a binder resin and a waxy substance represented by
Positively-charged silica fine powder externally added to the colored fine powder, wherein the wax-like substance is contained in the colored fine powder in an amount of 0.5 to 5% by weight based on the weight of the toner. Characteristic positively chargeable toner for image formation. 2. The method according to claim 1, wherein the positively chargeable silica fine powder is obtained by treating the silica fine powder with a silane compound represented by the following general formula [II]. Positively chargeable toner for image formation. R _m SiY _n [II] (where R represents an alkoxy group or halogen, m is 1
Y is an amino group or an organo group having at least one nitrogen atom, and n is m + n = 4
Is an integer from 1 to 3 that satisfies ) 3. 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. Item 4. The positively chargeable toner for image formation according to Item 1. 4. The pyridinium salt derivative represented by the general formula [I], wherein X is , Mo ₈ O ₂₆ ^4-, and BF ₄ ^- positively chargeable toner for image formation according to any one of claims 1 to 3, characterized in that an anion selected from the group consisting of.