JP2850016B2 - Positively chargeable magnetic developer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developer for developing a latent image in electrophotography, electrostatic recording, electrostatic printing, magnetic recording and the like. More specifically, the present invention relates to a magnetic developer for electrophotography, which is uniformly charged to a positive charge and visualizes a negative electrostatic latent image to provide a high quality image in a direct or indirect electrophotographic developing method.

[Prior Art] Conventionally, a number of methods are known as electrophotography, such as US Pat. No. 2,297,691, but generally, a photoconductive substance is used, and an electrophotographic method is applied to a photoreceptor by various means. Forming a latent image, and then developing the latent image with developing powder (hereinafter referred to as toner)
And then, if necessary, transferring the toner image to a transfer material such as paper, followed by fixing by heating, pressure or solvent vapor to obtain a copy. In the case where a step of transferring a toner image is provided, a step for removing residual toner on the photoconductor is usually provided.

A developing method for visualizing an electric latent image using toner is as follows.
For example, the magnetic brush method described in U.S. Pat.No. 2,874,063, the cascade developing method described in U.S. Pat. A method using a conductive magnetic toner described in the specification is known.

Conventionally, fine powders obtained by dispersing dyes and pigments in natural or synthetic resins have been used as toners applied to these developing methods. 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 toner. A magnetic toner containing magnetic particles such as magnetite is used.

Conventionally, a sufficient amount of triboelectricity is given to a toner (a developer before adding fine silica powder is hereinafter referred to as a toner), a transfer efficiency is increased, and a fluidity is improved. In order to prevent the bridging phenomenon and to smoothly supply the toner during development, it is known to add fine silica powder produced by a dry method or a wet method to the toner by dry mixing. However, since the silica fine powder itself is hydrophilic, it deteriorates the environmental characteristics of the developer, and particularly, under high temperature and high humidity, the image density is remarkably reduced, so that it cannot be used.

Therefore, in order to overcome this drawback, hydrophobization by surface treatment of fine silica powder has been proposed.
No. 16219, JP-A-55-120041, JP-A-58-186751
No. publication. In these, the surface treatment of the fine silica powder with various coupling agents has been proposed, and a developer containing the obtained fine hydrophobic silica powder has been proposed. In order to further improve the hydrophobicity and chargeability of the fine silica powder, Japanese Patent Application Laid-Open Nos. Sho 58-60754 and 59-201063 disclose various silicone oils or modified silicones. JP-A-59-45457 proposes a developer to which a silicic acid fine powder which has been subjected to a surface treatment using an oil is added, and further disclosed in JP-A-59-45457, a silica treated with a silane coupling agent and treated with a silicone oil. A developer to which an acid fine powder is added has been proposed.

However, when these surface-treated fine silica powders are subjected to long-term image durability using a conventional dry-type mixer using a developer contained in the vicinity of the toner surface, the silica powder may not be used. It has been found that the fine powder adheres and accumulates on the photoreceptor to form a filming state, and that fog, spots, and spots easily occur on the image.

FIG. 1 shows an example of a scanning electron micrograph of a state in which the fine silica powder has adhered to the photoreceptor and filming has occurred.

Although various causes can be considered as the cause of the filming, the present inventor has studied the above development and found that the main cause is a problem in the dispersion / adhesion state of the fine silica powder in the developer. This will be described below.

First, these surface-processed wet-processed synthetic silicate fine powders have a primary particle diameter of about 3 to 50 μm, but the state of the silicate fine powder before dry mixing with the toner is as follows. Aggregates (approximately 1.5 to 50μ) and cohesive aggregates are present as aggregates (approximately 30 to 300μ).

FIGS. 2 and 3 show scanning electron micrographs of the wet-processed synthetic silicate fine powder subjected to the surface treatment.

The silicic acid fine powder is mixed with the toner by dry mixing to form 1 powder.
The aggregates of the secondary particles and the aggregates of the aggregates must be loosely adhered to the vicinity of the developer surface while being loosened.
However, as a method of dry mixing, it is common to simply add or mix at a peripheral speed of about several m to 40 m / sec using a stirring blade or the like by a mixer such as a Henschel mixer or Papen Meyer.

However, in this method, there is a large difference in peripheral speed between the vicinity of the rotation shaft in the center and the tip of the stirring blade.
Since there is no blade-shaped thing in the rotating shaft part, the stirring force and the dispersing force are partially different, and the dispersion state is likely to be uneven. Therefore, in such dry mixing, the aggregates of the primary particles of the silicic acid fine powder and the aggregates of the aggregates are hard to be loosened and easily remain in the developer as they are, and at the same time, the aggregates which are loosened and dispersed. Silicic acid fine powder also has a weak adhesive force to the developer surface and is easily detached. As a result, when a large number of copies were made using the developer, the aggregates of the primary particles of the silicic acid fine powder remaining in the developer and the aggregates of the aggregates were separated from the developer surface. Silicic acid fine powder adheres and accumulates on the surface of the photoreceptor and filming easily occurs.

In particular, silicic acid fine powder surface-treated with silicone oil system has strong cohesion between primary particles and aggregates.
The tendency of filming to occur is likely to be significant.

FIG. 4 shows a scanning electron micrograph of the developer in which the fine silica particles are in a state of poor dispersion as described above.

Further, in recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, their uses have been diversified, and requirements for image quality have become strict. Therefore, JP
Japanese Patent Publication No. 129437 aims to provide a developer having a smaller average particle diameter of deposition than a conventional developer and having a special particle size distribution, and to achieve high image quality of a copied image or the like. However, when a developer obtained by dry-mixing silicic acid fine powder with such a toner having a relatively smaller particle diameter than the conventional toner is used, the contact area on the photoreceptor increases. There is a problem that the fine powder adheres more to the photoreceptor and filming easily occurs.

Furthermore, a positively chargeable developer visualizes a negative electrostatic image, but as an electrophotographic photoreceptor holding a negative electrostatic image, low cost, light weight, high productivity, Organic photoconductive photoreceptors excellent in properties and the like are widely used. However, the organic photoconductive photoreceptor has a lower surface luminous intensity than the inorganic photoreceptor, and therefore, the photoreceptor is formed by aggregation of primary particles of silica fine powder or aggregates of aggregates in a developer. The surface is easily damaged, and the damaged portion further induces adhesion and deposition of fine silicic acid powder, which causes a problem that filming easily occurs.

[Problems to be Solved by the Invention] An object of the present invention is to provide a positively chargeable magnetic developer which solves the above-mentioned problems.

Further, an object of the present invention is to provide a positively chargeable magnetic developer which does not cause filming on the photoreceptor and can obtain a clear image without fog, spots, spots, etc. To provide.

It is a further object of the present invention to provide a positively chargeable magnetic developer having high image density, excellent fine line reproducibility and excellent gradation without causing filming on a photoreceptor.

It is a further object of the present invention to provide a positively chargeable magnetic developer which does not cause filming on the photoreceptor even when an organic photoconductive photoreceptor is used as the electrostatic latent image carrier.

[Means and Actions for Solving the Problems] Specifically, the present invention relates to (a) a method in which the volume average particle size is 4 to 10
a magnetic toner containing 12 to 60% by number of magnetic toner particles having a particle diameter of 5 μm or less, and (b) a bulk density of 60 g / or less and treated with a silane coupling agent or / and silicone oil. A positively-chargeable magnetic developer comprising a wet-processed synthetic silica fine powder.

The present inventors have conducted intensive studies and found that the aggregates of the primary particles of the wet-processed synthetic silicate fine powder treated with a silane coupling agent or / and silicone oil and the lumps in which the aggregates are further aggregated are reduced. It has been found that the bulk density of the silicic acid fine powder is reduced, and further, in a conventional general dry mixer, the bulk density of the silicic acid fine powder is not more than 60 g / No aggregates of the primary particles of the silicic acid fine powder in the developer and no lumps in which the aggregates are further aggregated are observed, and the fine silicic acid powder is uniformly and strongly dispersed and adhered to the toner surface. Was found. As a result, even with long term image durability, the fine silica particles in the developer do not adhere and accumulate on the photoreceptor and exhibit excellent filming resistance. is there.

In the present invention, the bulk density of the wet synthetic silicate fine powder treated with a silane coupling agent or a silicone oil is a value determined as follows. That is, 2.52
A 100 cm ³ cylindrical container with a height of 5.00 cm and a height of 5.00 cm was allowed to stand on a horizontal surface, and the sample was gently dropped from about 3 cm above the opening of the container, filled into the container, and raised above the horizontal surface of the opening. This is a value obtained by removing the excess and calculating the bulk density from the sample weight value in the container.

In the present invention, as a method of obtaining a silane coupling agent having a bulk density of 60 g / or less, and a wet synthetic silica fine powder treated with silicone oil, for example, the surface-treated wet synthetic silica fine powder There is a method in which an aggregate of primary particles of the silicic acid fine powder and lumps of aggregates of the aggregates are crushed by using an impact type ultrafine crusher Cosmomiser (manufactured by Nara Machinery Co., Ltd.). Further, as another method, for example, by contacting the wet-process synthesized fine powder of untreated surface with a silane coupling agent and / or silicone oil, and simultaneously crushing the impact-type ultrafine crusher,
Silica fine powder having a bulk density of 60 g / or less and surface-treated with the treating agent can be obtained.

FIG. 5 shows a scanning electron micrograph of the silica fine powder after the surface-treated wet-processed synthetic silica fine powder shown in FIGS. 2 and 3 was crushed by a cosmomizer. FIG. 6 shows an example of the relationship between the bulk density of the surface-treated wet-processed synthetic silicate fine powder and the crushing time in a cosmomizer.

The wet-processed synthetic silicate fine powder having a bulk density of 60 g / or less and obtained as described above can be strongly adhered to the vicinity of the developer surface together with the toner by general dry mixing. FIG. 7 shows a scanning electron micrograph as an example of a developer obtained by mixing the surface-treated wet synthetic silica fine powder having a bulk density of 60 g / or less with a toner and a Henschel mixer.

Further, for the purpose of achieving high image quality of a copied image or the like, the toner having a smaller volume average particle diameter and a special particle size distribution than the conventional toner, and the surface treatment having a low bulk density obtained as described above are applied to the toner. Even when the wet-processed synthetic silicate fine powder is dry-mixed, the filming resistance of the obtained developer on the photoreceptor is not reduced.

For the purpose of achieving high image quality of a copied image or the like, a magnetic toner containing 12 to 60% by number of magnetic toner particles having a particle diameter of 5 μm or less and having a volume average particle diameter of 4 to 10 μm (preferably 8 to 10 μm) 1 to 33% by number of magnetic toner particles having a particle diameter of 12.7 μm, and a toner containing 2.0% by volume or less of magnetic toner particles having a particle diameter of 16 μm or more are preferable. The developer obtained by dry-mixing the surface-processed wet-processed synthetic silicate fine powder described below is, despite the large contact area with the photoconductor, the silicate fine powder in the developer is It is less likely to adhere to or accumulate on the photoreceptor and retains excellent filming resistance.

Further, in the developer containing the wet-processed synthetic fine powder having a bulk density of 60 g / or less, an aggregate of the primary particles of the silicic acid fine powder or a lump of aggregates of the aggregate is extremely contained in the developer. Because of the small amount, even if an organic photoconductive photoreceptor is used as the photoreceptor, the surface of the photoreceptor is not damaged, and the flawed portion does not induce adhesion and deposition of fine silica powder, thereby preventing filming. Can be.

In the present invention, a bulk density of 60 g / or less and a silane coupling agent or, and a wet-process synthetic silicic acid fine powder treated with silicone oil are used. Various conventionally known methods can be applied. For example, the decomposition of sodium silicate with an acid is represented by the following general reaction formula.

Na ₂ O ・ XSiO ₂ + HCl + H ₂ O → SiO ₂・ nH ₂ O + NaCl In addition, decomposition of sodium silicate with ammonium salts or alkali salts, formation of alkaline earth metal silicate from sodium silicate, and decomposition with acid Silicate, a method in which a sodium silicate solution is converted into silicate using an ion exchange resin, a method in which natural silicate or silicate is used, and the like.

As the silicic acid fine powder here, anhydrous silicon dioxide (silica) and other silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate and zinc silicate can be applied.

Commercially available fine silica powder synthesized by the wet method includes, for example, those commercially available under the following trade names.

Carplex Shionogi Pharmaceutical Nip Seal Nippon Silica Tokuseal, Fine Seal Tokuyama Soda Vita Seal Takihito Shilton, Shirunex Mizusawa Chemical Starsil Kamijima Chemical Himezil Ehime Pharmaceutical Cyloid Fuji Devison Chemical Hi-sil Pittsburgh Plate Glass.Co. Durosil Ultorasil Fiillstoff-Gesellschaft Marquart Manosil Hardman and Holden Hoesch Chemische Fabrik Hoesch K-G Hesh) Sil-Stone (Sil-Stone) Stoner Rubber Co. (Stonener Rubber) Nalco (Narco) Nalco Chem. Co. (Narco Chemical) Quso (Kuso) Philadelphia Quartz Co. Radelphia Quartz) Imsil (Illinois Minerals Co.) (Illinois Minerals) Calcuim Silikat (Calcium Zilikat) (Fortafil) Imperial Chemical Industries. Ltd. (Imperial Chemical Industries) Microcal (Microcal) Joseph Crosfiels & Sons. Ltd. (Joseph Crossfield and Sands) Vulkasil (Vurkazir) Farbenfabriken Bryer.A.-G. (Bayer) Tufknit (Tafnit) Durham Chemicals. Ltd. (Doulham Chemicals) Silmos Shiraishi Kogyo Star Rex Kamishima Chemical Fricosyl Multi-wood fertilizer Of the above silicate fine powder, BET method Specific surface area by the boss was nitrogen adsorption in the range of 30 m ² / g or more (especially 50 to 400 m ² / g) gives good results.

Further, in the present invention, the fine powder of silicic acid synthesized by the water method is subjected to a surface treatment with a silane coupling agent or silicone oil, and is used in a reaction or physical adsorption state with these treating agents.

In the present invention, the silane coupling agent also includes an organosilicon compound, for example, hexamethyldisilazane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyl Trichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, Trimethylsilyl mercaptan, triorganosilyl acrylate, vinylmethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyl Ludiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, 1,3-diphenyltetramethyldisiloxane, and 2 to 12 siloxane units per molecule. There is a dimethylpolysiloxane containing a hydroxyl group bonded to one Si each.

Further, in the present invention, the citane coupling agent may be a nitrogen-containing silane coupling agent, and for example, generally has a structure represented by the following formula.

R _m -Si-Y _n (R represents an alkoxy group or a halogen, Y represents an organo group having at least one amino group or a nitrogen atom, m and n is an integer of 1 to 3 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, dibutylaminopropylmethoxysilane, dibutylaminopropylmonomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-γ
-Propylphenylamine, trimethoxysilyl-γ-
Propylbenzylamine and the like. Further, as a nitrogen-containing element environment, those having the above-mentioned structure can be used. Examples of such compounds include trimethoxysilyl-γ-propylpiperidine and trimethoxysilyl-γ-propylmorpholine. , Trimethoxysilyl-γ-propylimidazole and the like.

In the present invention, the silicone oil is generally represented by the following formula.

Preferred silicone oils are those having a viscosity of about 5 to 5000 centistokes at 25 ° C., such as methyl silicone oil, dimethyl silicone oil, phenyl methyl silicone oil, chlorophenyl methyl silicone oil, alkyl-modified silicone oil, and fatty acid-modified silicone oil. Silicone oil and polyoxyalkyl-modified silicone oil are preferred.

In the present invention, the silicone oil may be a modified silicone oil having an organo group having at least one nitrogen atom in a side chain. For example, 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 and 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, or may have a substituent such as halogen.

In the present invention, these silane coupling agents and silicone oils are used alone or as a mixture of two or more.

In the present invention, the applied amount of the wet-process synthetic silicic acid fine powder having a bulk density of 60 g / or less and treated with these silane coupling agents or silicone oil is based on 100 parts by weight of the developer. The fine silica powder is used in an amount of 0.01 to 8 parts by weight, preferably 0.1 to 5 parts by weight.

As the binder resin used in the developer of the present invention, when using a heat and pressure roller fixing device having a device for applying oil, the following binder resin for toner can be used, for example, polystyrene , Poly-p-chlorostyrene,
Styrenes such as polyvinyltoluene and their substituted homopolymers; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, styrene -Methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone Styrene-based copolymers such as copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, naturally-modified phenolic resins, and natural-resin-modified malees Acid resin, Acrylic Resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethane, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, terpene resin, coumarone-indene resins, and petroleum resins.

In the heat and pressure roller fixing method in which almost no oil is applied, so-called offset development in which a part of the developer image on the developer image support member is transferred to the roller, and the adhesion of the developer to the developer image support member is improved. This is an important issue.
Developers that fix with less thermal energy usually have the property of easily blocking or caking during storage or in a developing unit, and these problems must also be considered at the same time. In these developments, the physical properties of the binder resin in the developing agent are the most important, but according to the study of the present inventors, if the content of the magnetic substance in the developer is reduced, the developer is not fixed at the time of fixing. Although the adhesion of the developer to the image supporting member is improved, offset tends to occur, and blocking or caking tends to occur. Therefore, particularly in the present invention, the selection of the binder resin is more important, especially when using the heat and pressure roller fixing method in which almost no oil is applied.
Preferred binders include crosslinked styrenic copolymers or crosslinked polyesters.

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, a monocarboxylic acid having a double bond such as acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids having a double bond such as methyl maleate, dimethyl maleate and the like and their substituted products; 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 isobutyl ether and the like; alone or two or more vinyl monomers are used.

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 and the like; for example, ethylene glycol diacrylate, ethylene glycol dimethacrylate Double bonds such as 1,3-butanediol dimethacrylate, etc.
Carboxylic acid esters having two or more compounds; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide and divinyl sulfone; and compounds having three or more vinyl groups are used alone or as a mixture.

When the pressure fixing method is used, a binder resin for a pressure fixing developer can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer can be used. Examples include polymers, ionomer resins, styrene-butadiene copolymers, styrene-isoprene copolymers, linear saturated polyesters, and paraffins.

In the developer of the present invention, a positive charge control agent is preferably mixed (internally added) to the toner or mixed (externally added) with the toner particles.

Examples of positive charge control agents include denatured products such as nigrosine and fatty acid metal salts;
Quaternary ammonium salts such as -hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate; diorganotin oxides such as dibutyltin oxide, dioctyltin oxide and dicyclohexyltin oxide; dibutyltin borate, dioctyltin borate and dicyclohexyltin borate These diorganotin borates can be used alone or in combination of two or more. Among these, charge control agents such as nigrosine and quaternary ammonium salts are particularly preferably used.

Also, the general formula R ₁ : H, CH ₃ R ₂ , R ₃ : Monopolymer of a monomer represented by a substituted or unsubstituted alkyl group (preferably, C _{1 to} C ₄ ): or styrene or acrylate as described above; Copolymers with a polymerizable monomer such as methacrylic acid ester can be used as a positive charge control agent. In this case, these charge control agents also have an action as (all or part of) a binder resin.

The above-described positive charge control agent (having no action as a binder resin) is preferably used in the form of fine particles.
In this case, specifically, the number average particle diameter of the charge control agent is preferably 4 μm or less (more preferably 3 μm or less).

When internally added to the developer, such a positive charge control agent is used in an amount of 0.1 to 20 parts by weight (more preferably, 0.2 to 1 part by weight) based on 100 parts by weight of the binder resin.
0 parts by weight).

Various additives may be added internally or externally to the developer according to the present invention, if necessary.

As the coloring agent, conventionally known dyes and pigments can be used, and usually 0.5 to 100 parts by weight of the binder resin.
20 parts by weight may be used. Other additives include, for example, a lubricant such as zinc stearate, or an abrasive such as cerium oxide and silicon carbide, or a fluidity imparting agent such as fine resin particles, aluminum oxide, an anti-caking agent, or a carbon black, tin oxide, or the like. 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 developer is also one of the preferred embodiments of the present invention.

Further, the magnetic developer in the present invention may also serve as a colorant, but contains a magnetic material. Examples of the magnetic material include iron oxides such as magnetite, γ-iron oxide, ferrite, and iron-rich ferrite: metals such as iron, cobalt, and nickel, or these metals and aluminum, cobalt,
Examples include alloys with metals such as copper, lead, magnesium, tin, 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 about 0.1 to 1 μm, preferably about 0.1 to 0.5 μm, and the amount contained in the developer is 30 to 120 parts by weight, preferably 100 to 100 parts by weight of the resin component. It is 40 to 110 parts by weight based on 100 parts by weight of the component.

Preparation of the developer in the present invention is performed by adding a vinyl-based or non-vinyl-based thermoplastic resin, if necessary, a magnetic powder, a pigment or dye as a colorant, a charge control agent, and other additives, such as a ball mill. After sufficiently mixing with a mixer, the mixture is melted and kneaded using a heat kneader such as a heating roll, kneader, or extruder to make the resins compatible with each other, and the magnetic powder, the colorant, the positive charge control agent, After dispersing or dissolving other additives, and after pulverization and classification after cooling and solidifying, the bulk density is 60 g / or less and a silane coupling agent or / and a silicone oil-treated wet-processed synthetic silica fine powder, If necessary, other external additives and the like are externally added and mixed to obtain a positively chargeable magnetic developer according to the present invention.

Cadmium sulfide, selenium, zinc oxide, organic photoconductor (OP)
C), amorphous silicon (α-Si) or the like is used.

When the developer of the present invention is used, a blade cleaning method, a fur brush cleaning method, a magnetic brush cleaning method, or the like is used as a method for cleaning the residual developer on the photosensitive member. In consideration of the excellent combination of the developer and the photoreceptor of the present invention, a blade cleaning system is preferable. In addition, a charge removing step or the like may be provided immediately before the cleaning step, if necessary, to facilitate developer cleaning.

EXAMPLES Hereinafter, the method of the present invention will be specifically described based on examples. However, this does not limit the embodiment of the present invention at all. All parts in the examples 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. A classified powder was produced. Further, the obtained classified powder was strictly classified and removed simultaneously by a multi-division classifier utilizing a Coanda effect (an elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) to obtain 35 toner particles of ≦ 5 μm. %, ≧ 16 μm toner particles 0.5% by volume,
13% by number of toner particles of 8 to 12.7 μm, volume average diameter of 8.0
A black fine powder (magnetic toner) of μm was obtained.

On the other hand, fine silica powder synthesized by a wet method as fine silica powder (trade name, Nip Seal E 200, specific surface area 110 m ² / g,
(Manufactured by Nippon Silica Kogyo Co., Ltd.) was placed in a closed Henschel mixer heated to 70 ° C., and the silane coupling agent was diluted with alcohol so as to give a processing amount of 5.0% by weight with respect to the fine silica powder. The mixture was stirred at high speed while adding -aminopropyltriethoxysilane dropwise. After completion of the dropwise addition, the temperature was dried to 120 ° C. while stirring in the same manner,
A silane coupling agent-treated fine silica powder (I) was obtained.

 The bulk density of the silica fine powder (I) was 79 g /.

Next, the silicic acid fine powder (I) was crushed by a cosmomizer to obtain a silicic acid fine powder (II) having a bulk density of 54 g /.

100 parts of the obtained magnetic toner and 0.6 fine silica powder (H)
Was charged into a Henschel mixer to obtain a developer (a).

Commercially available electrophotographic copying machine NP3525 (manufactured by Canon Inc.) equipped with an organic photoconductive photoreceptor without developer (a)
When the initial image was extracted using, the image density was 1.36.
As a result, a clear image with no fog and good resolution was obtained. Subsequently, after the image output test was continuously performed 20,000 times, the photoreceptor was taken out and observed. As a result, no deposit of fine silica powder (II) was found on the photoreceptor, and filming was not performed. It did not occur. Table 1 shows the results.

Comparative Example 1 100 parts of the magnetic toner obtained in the same manner as in Example 1 and 0.6 part of the fine silica powder (I) were charged into a Henschel mixer to obtain a developer (b).

When the developer (b) was evaluated for image formation in the same manner as in Example 1, as shown in Table 1, an excellent image was obtained in the initial stage. Black spots occurred on the upper surface due to filming of the photoconductor. Further, when the photoconductor was taken out and observed at 20,000 times, a large number of filming due to adhesion and deposition of the fine silica powder (I) was observed on the front side of the photoconductor.

Comparative Example 2 Instead of using the fine silica powder (I) in Example 1, a fine silica powder synthesized by a wet method as a fine silica powder (trade name, Nip Seal E 200A, specific surface area 130 m ² / g, Japan (Silica Industry Co., Ltd.)
Except for using a fine silica powder (III) which was sprayed with 20 parts of silicone oil having amine in the side chain (viscosity at 25 ° C 70 cps, amine equivalent 830) at 50 ° C and treated for 10 minutes, In the same manner as in Example 1, a developer (C) was obtained. The obtained silicone oil-treated fine silica powder (III)
Had a bulk density of 77 g /.

Using the developer (c), image evaluation was performed in the same manner as in Example 1. As a result, the image density was high, but fog was noticeable and the resolution was poor.

When image endurance was carried out, black spots were generated on the image from the filming of the photoreceptor after 70,000 times. Further, when the photoconductor was taken out and observed 20,000 times, a large number of adhered and deposited silica fine powder (III) were observed on the entire surface of the photoconductor.
Further, when the deposits and deposits were removed, many scratches were observed on the photoreceptor.

Comparative Example 3 The silicone oil-treated silicate fine powder (III) obtained in Comparative Example 2 was treated with a cosmomizer to give a bulk density of 65 g /
(IV) was obtained.

A developer (d) was prepared in the same manner as in Example 1, except that the fine silica powder (IV) was used instead of the fine silica powder (II).

When the developer (d) was evaluated for image formation in the same manner as in Example 1, as shown in Table 1, excellent images were initially obtained. Further, after 20,000 times of image output durability, a slight black spot due to filming of the photoreceptor was observed on the front side of the image. On the photoreceptor, adhesion and deposits of the fine silica powder (IV) were also found concentrated on the near side.

Example 2 The silicone oil-treated silicic acid fine powder (IV) obtained in Comparative Example 3 was further pulverized with a cosmomizer to give a bulk density of 60 g /
(V) was obtained.

A developer (e) was prepared in the same manner as in Example 1, except that the silica fine powder (V) was used instead of the silica fine powder (II).

Using the developer (e), image formation evaluation was performed in the same manner as in Example 1. As shown in Table 1, a clear high-quality initial image with high image density was obtained, and 20,000 images were obtained. Even after the endurance, no black spots occurred on the image due to filming. However, when the photoreceptor was removed and observed, slight adhesion and deposition of fine silica silicate powder (V) was observed in the non-image area at the front end of the photoreceptor.

Example 3 The silicone oil-treated silicic acid fine powder (V) obtained in Example 2 was further pulverized with a cosmomizer to obtain a bulk density of
57 g / silicic acid fine powder (VI) was obtained. A developer (f) was prepared in the same manner as in Example 1 except that the fine silica powder (VI) was used instead of the fine silica powder (II) in Example 1, and the image formation evaluation was performed. Was carried out, and as shown in Table 1, the filming was satisfactory, and no filming by the fine silica powder (VI) on the photoreceptor occurred at all even after the durability test for 20,000 times.

Example 4 The silicone oil-treated silica fine powder (VI) obtained in Example 3 was further pulverized with a cosmomizer to give a bulk density of 46 g /
(VII) was obtained. A developer (g) was prepared in the same manner as in Example 1 except that the fine silica powder (VII) was used instead of the fine silica powder (II) in Example 1, and the image formation evaluation was performed. As a result, as shown in Table 1, the film was good and no filming occurred.

[Effects of the Invention] According to the developer of the present invention having the above-described characteristics, even if long-term image endurance is performed, filming does not occur on the photoreceptor. Gives clear images without spots or spots.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing the state of the photoreceptor surface where filming is occurring due to the adhesion of fine silica powder in the developer, and FIGS. 2 and 3 are before dry mixing. FIG. 4 is a scanning electron micrograph showing the surface condition of the wet-processed synthetic silicate fine powder subjected to the surface treatment shown in FIG. 4. FIG. 4 is a scanning electron microscope photograph showing the surface condition of the developer in which the wet-processed synthetic silicate fine powder is in a poorly dispersed state. FIG. 5 is an electron micrograph, FIG. 5 is a scanning electron micrograph of the wet-processed synthetic silicate fine powder having been subjected to crushing with a cosmomizer, and FIG. FIG. 7 shows an example of the relationship between the bulk density of the finely synthesized silicic acid fine powder and the crushing time in a cosmomizer. FIG. 7 shows a developer containing the wet-processed finely synthesized silicic acid fine powder having a bulk density of 60 g / or less. 5 is a scanning electron micrograph of Example 1. The scanning electron micrograph is used instead of an X-ray photograph.

Claims (3)

(57) [Claims] (A) a volume average particle diameter of 4 to 10 μm;
A magnetic toner containing 12 to 60% by number of magnetic toner particles having a particle size of 5 μm or less, and (b) a wet-process synthesis having a bulk density of 60 g / or less and treated with a silane coupling agent and / or silicone oil. A positively-chargeable magnetic developer comprising fine silica powder. 2. The positively chargeable magnetic developer according to claim 1, wherein the silicone oil is a modified silicone oil. 3. The method according to claim 1, wherein 1 to 33% by number of magnetic toner particles having a particle diameter of 8 to 12.7 μm are contained, and 2.0% by volume or less of magnetic toner particles having a particle diameter of 16 μm or more. The positively-chargeable magnetic developer according to claim 1, wherein