JPH02287459A - Negatively chargeable magnetic developer - Google Patents

Abstract

PURPOSE:To obtain a high-quality image by incorporating hydrophobic dry silica having a bulk density of <=25g/l and treated with a silicone oil or varnish. CONSTITUTION:The negatively chargeable magnetic toner contains the fine hydrophobic dry silica powder having a bulk density of <=25g/l and treated with the silicone oil. Such a powder is mixed in a general dry mixer with the developer and added to the vicinity of the surface of each developer particle. In such a developer, primary agglomerates of the fine silica powder, or further agglomerates are not found and the silica powder is uniformly dispersed and strongly attached to the surface of the developer particles, thus permitting the obtained developer to prevent occurrence of white spots due to secondary agglomerates of the silica powder, and accordingly, high-quality images to be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a developer for developing latent images in electrophotography, electrostatic recording, electrostatic printing, magnetic recording, and the like.

More specifically, in direct or indirect electrophotographic development methods, electrons are uniformly charged to a negative charge to visualize a positive electrostatic charge image, or to visualize a negative electrostatic charge image by reversal development to produce high-quality images. It relates to a photographic developer.

[Background technology]

As a conventional electrophotographic method, U.S. Patent No. 2,297,691
Although a number of methods are known, such as those described in the specification of No. After the toner image is transferred to a transfer material such as paper as necessary, it is fixed by heat, pressure, solvent vapor, etc. to obtain a copy. Furthermore, when a process for transferring a toner image is included, a process for removing residual toner on the photoreceptor is usually provided.

Development methods for visualizing electrical latent images using toner include, for example, the magnetic brush method described in U.S. Pat. No. 2,874,063, and the magnetic brush method described in U.S. Pat. No. 2,618,552. Cascade development method and 2.221, 7
Powder cloud method described in US Pat. No. 76, U.S. Pat.
, 909,258, which uses conductive magnetic toner, is known.

As toners applied to these 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 I to 30 μm are used as a toner. As the magnetic toner, one containing magnetic particles such as magnetite is used. In the case of a system using a so-called two-component developer, the toner is usually mixed with carrier particles such as glass beads and iron powder.

Furthermore, recently, electrophotographic systems have been used not only for obtaining copied images but also for printers used for computer output. In the case of printer applications, a light emitter (semiconductor laser, etc.) is turned on according to an image signal.
The light is turned off (ON-OFF) and projected onto the photoreceptor. In this case, the printing rate (ratio of printing area per page) is usually 30% or less, and the method of exposing the character portion (reversal development) is advantageous in terms of the life of the light emitter.

In addition, reversal development is used in devices that output positive and negative images from the same document (for example, microfilm output devices), and regular development is used to develop two or more colors in the same device. It has come to be used in devices that combine reversal development and reversal development.

However, reversal development has the following problems. The transfer electric field in normal development (hereinafter referred to as "normal development") has the same polarity as the -order charge, and even if the transfer electric field is applied onto the photoreceptor after passing through the image carrier (hereinafter referred to as paper, etc.), its influence will not be affected by erase exposure. It is erased at (6 in FIG. 1).

On the other hand, the transfer electric field in reversal development has the opposite polarity to the negative charge, and even after passing through the paper etc., when the transfer electric field is applied, a charge of the opposite polarity occurs on the photoreceptor, which cannot be erased by erase exposure, and the density of the image changes. It will come to you. This is a phenomenon called "paper trail."

As a countermeasure against paper traces, there are measures such as lowering the transfer current after the paper has passed, as shown in Japanese Patent Application Laid-Open No. 60-256173. This makes the apparatus complicated and increases the cost of the apparatus.Also, it is conceivable to reduce the transfer electric field to a range in which charging of the opposite polarity does not occur on the photoreceptor.

However, this method lowers the transfer efficiency, resulting in a reduction in image quality due to poor transfer. Another example of juxtaposition in the reversal development method is that the photoconductor and paper, etc. are charged with opposite polarities, so when charged with a strong electric field, the photoconductor and paper, etc. electrostatically attract each other, causing transfer. Even after the process is completed, the paper does not separate, and paper etc. enters the next process (cleaning process, etc.), causing paper jams. This is a phenomenon called "wrapping". As a countermeasure against wrapping, there is a means to prevent the photoreceptor from coming into close contact with paper, etc., as seen in Japanese Patent Laid-Open No. 56-60470. However, this method is not necessarily effective in reversal development. That is, this is considered to be because the close contact during separation in the transfer process of reversal development is stronger than that of normal development. Another method, as seen in U.S. Pat. No. 3,357,400, is an apparatus that includes separate charging or belt separation as an auxiliary means for separation. This results in
Although it is effective against the wrapping phenomenon, it is not effective against the paper trail phenomenon. This is because the separation charge is smaller than the transfer charge and does not affect the potential on the photoreceptor.

Another method is to reduce the electrostatic adsorption force by lowering the transfer electric field, but this method is likely to cause image quality deterioration due to poor transfer as described above. In addition, lowering the transfer electric field results in a decrease in transfer efficiency, which is detrimental to the transfer of postcards and O.
Unable to meet diverse needs for HP films, etc. Furthermore, when the transfer electric field is lowered, "transfer voids", which are part of transfer defects, occur in areas where developer tends to concentrate (etch development areas), such as image outlines and line drawing areas. this is,
This is thought to be due to the fact that more developer is deposited in the etch development area than in the normal area, and developer aggregation is more likely to occur, reducing the response to the transfer electric field.As a result, it is difficult to obtain high-quality images that are faithful to the latent image. It has the problem of becoming.

In addition, in a method using dry toner, in order to form a visible image of good quality, the toner must have high fluidity.
It is also necessary to have uniform charging properties, and for this purpose, it has been conventionally practiced to include fine silica powder in the toner. However, since fine silica powder is hydrophilic as it is, toner containing fine silica powder may aggregate due to moisture in the air, resulting in decreased fluidity.
In severe cases, the silica fine powder absorbs moisture, which deteriorates the charging performance of the toner.

Therefore, in order to overcome this drawback, it has been proposed to make silicic acid fine powder hydrophobic by surface treatment.
No. 16219, Japanese Patent Application Laid-open No. 120041/1983,
There are Japanese Patent Laid-Open No. 58-186751, etc. In these studies, developers have proposed a developer containing hydrophobic silicic acid fine powder obtained by surface-treating silicic acid fine powder with various coupling agents. In addition, for the purpose of further hydrophobicizing silicic acid fine powder and controlling the chargeability, Japanese Patent Application Laid-Open No. 58-60754
In JP-A No. 59-201063, a developer to which fine silicic acid powder was surface-treated using various silicone oils or modified silicone oils was proposed, and JP-A-59-201063 also proposed No. 59-45457 proposes a developer to which fine silicic acid powder treated with a silane coupling agent and silicone oil is added.

However, fine silicic acid powder whose surface has been treated with silicone oil or a polymeric substance such as silicone oil is used in a conventional general dry mixer to form an image using a developer contained near the toner surface. If you make a withdrawal,
It has been found that white spots are likely to occur in the image area, especially in the early stages.

Analysis clearly shows that the white spots are caused by the development of silica clumps.

Normally, the surface-treated fine silicic acid powder has a primary particle diameter of about 10 to 20 μm, but the state of the fine silicic acid powder before being dry mixed into the toner is an aggregate of primary particles (about 5 to 20 μm).
150μ) and clumps (approximately 30~
300μ).

In addition, silica clumps contain 0.6 wt% of silica in the toner.
It becomes noticeable when more than 10% is added.

The silicic acid fine powder must strongly adhere to the vicinity of the developer surface while removing aggregates of primary particles and lumps of aggregates by dry mixing with the toner. However, as a general method of dry mixing, simple addition or a mixing machine such as a Henschel mixer or Papenmeyer using a stirring blade or the like is used at a circumferential speed of several m to 40 m/min.
Mixing of about sec is common.

However, with this method, there is a large difference in circumferential speed between the vicinity of the rotating shaft in the center and the tip of the stirring blade (also, since there is no blade-shaped part in the rotating shaft, the stirring force and dispersion force Therefore, in such dry mixing, aggregates of the primary particles of the silicic acid fine powder and clumps of aggregates may become separated, resulting in a non-uniform dispersion state. It tends to remain in the developer in this state, causing white spots on the image.

Furthermore, if a general mixer is used to apply enough shear to loosen these clumps, the already dispersed silicic acid fine powder will be driven into the toner surface and fixed, rendering it useless as a fluidizing agent.

In particular, silicic acid fine powder whose surface has been treated with silicone oil or a polymeric substance such as silicone oil has a tendency to strongly agglomerate, resulting in a marked tendency for white spots to occur in the image.

In addition, Japanese Patent Application Laid-Open No. 60-107036 discloses that the bulk density is 30.
A proposal has been made to add silica fine powder of m g/c rd or less to toner, but as a result of studies conducted by the present inventors, it has been found that it is difficult to simultaneously improve transferability in reversal development and prevent white spots on images. Met.

[Purpose of the invention]

An object of the present invention is to provide a negatively chargeable developer which solves the above-mentioned problems.

A further object of the present invention is to provide a negatively chargeable developer capable of producing high-quality images without white spots due to silica lumps during image formation. A further object of the present invention is to provide a negatively chargeable developer which has excellent impact resistance, does not cause aggregation, has excellent fluidity, and is durable. A further object of the present invention is to provide a negatively chargeable developer that maintains its initial characteristics even during long-term storage and has excellent storage stability.

[Summary of the invention]

The bulk density of the present invention is 25 g/i! The present invention relates to a negatively chargeable developer characterized by containing hydrophobic dry silicic acid fine powder treated with silicone oil as described below.

[Detailed description of the invention]

Furthermore, the silica according to the present invention is preferably treated with an organosilicon compound and then treated with silicone oil.

As a result of intensive research, the present inventors have found that by reducing the aggregates of primary particles of dry-synthesized silicic acid fine powder treated with a silane coupling agent or silicone oil, and by reducing the lumps formed by further agglomerating the aggregates, It has been discovered that the bulk density of fine silicic acid powder decreases, and furthermore, the fine silicic acid powder having a bulk density of 25 g/l or less is applied to the vicinity of the toner surface using a conventional general dry mixer. In the developer, there were no aggregates of primary particles of the silicic acid fine powder in the developer, and no lumps formed by further agglomeration of the aggregates, and the silicic acid fine powder was uniformly and strongly dispersed and adhered to the toner surface. I found something to do. As a result, with this toner, white spots due to silica clumps do not occur in the image area.

In the present invention, the bulk density of the dry-synthesized silicic acid fine powder treated with silicone oil is a value determined as follows. That is, a capacity 1 with an inner diameter of 2.52 cm and a height of 5,00 cm.
A cylindrical container of 00 crrf was placed on a horizontal surface, and a sample was gently dropped from about 3 cm above the opening of the container.
The bulk density is calculated from the weight of the sample in the container after filling the container with the sample in seconds, removing the excess that rose above the horizontal surface of the opening.

In the present invention, the bulk density is 25g/i! As a method for obtaining dry synthetic silicic acid fine powder treated with silicone oil as described below, for example, the treated dry synthetic silicic acid fine powder is passed through an impact type ultrafine grinder Costomizer (Nara Kikai Seisakusho Co., Ltd.). There is a method of crushing aggregates of primary particles of the silicic acid fine powder and clumps of aggregates.

An example of the relationship between the bulk density of the dry silicic acid fine powder surface-treated with the silicone oil of the present invention and the crushing time in a costomizer is shown in FIG.

Additionally, when using a toner with a special particle size distribution that has a smaller volume average particle diameter than conventional toners in order to achieve high quality copies, etc., a large amount of silica is added to improve fluidity. However, even in such cases, white spots due to silica lumps do not occur in the image area, and the effect of improving fluidity is significant.

For example, 5 μm for the purpose of achieving high image quality of copied images, etc.
17 to 60% by number of magnetic toner particles having the following particle size:
5 to 50% by number of magnetic toner particles having a particle size of 6.35 to 10.08 μm are contained, and 2.0% by volume or less of toner particles having a particle size of 12.7 μm or more; By dry mixing the surface-treated dry silicic acid fine powder with a bulk density of 25 g/f or less with a toner having a particle size distribution of 4.5 to 9 μm in diameter, it is possible to prevent white spots caused by silica clumps and to achieve excellent results. It is possible to ensure liquidity.

The degree of aggregation of the developer or toner in the present invention is measured and calculated as follows. The measurement was carried out using a powder tester manufactured by Hosokawa Micron Co., Ltd. and a three-tiered sieve in which a 20 mesh sieve, a 100 mesh sieve, and a 6 mesh sieve were sequentially stacked. As a measuring method, approximately 2g of powder made of toner or developer was placed on a 60-mesh sieve on the upper stage of a three-stage sieve, a voltage of 2.5V was applied to the powder tester, and the powder was passed through the three-stage sieve for 40 seconds. The weight of the powder remaining on the 60-mesh sieve is
g, and the weight Jl of the powder remaining on the 100 mesh sieve.
bg and powder type IC remaining on the 200 mesh sieve.
The degree of agglomeration is calculated from g using the following formula.

Also, the bulk density is 25g/I! In the following developer containing the surface-treated dry process synthetic fine powder, there are very few aggregates of primary particles of silicic acid fine powder or lumps of aggregates in the developer, so it cannot be used as a photoreceptor. Even when an organic photoconductive photoreceptor is used, the surface of the photoreceptor is less likely to be damaged.

In the present invention, a dry-process synthesized silicic acid fine powder having a bulk density of 25 g/f or less and appropriately treated with silicone oil is used. This is a method for producing acid fine powder. 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.

5iCI! 4+2H2+02→SiO2+4HCfAlso,
In this manufacturing process, for example, aluminum chloride or
It is also possible to obtain a composite fine powder of silicic acid and other metal oxides by using another metal halide compound such as titanium chloride together with a silicon halide compound, and these are also included.

Commercially available fine silicic acid powders produced by vapor phase oxidation of silicon halogen compounds used in the present invention include, for example, those commercially available under the following trade names.

AERO3IL (Aerosil) 130 (Japan Aerosil Co., Ltd.) 200x50 T600 0X80 0X170 0K84 Ca -0-SiL (Ca-0-SiL) M-5 (C
ABOTO Co., Ltd.) MS-
7S-5 H5 Wacker HDK N 20
V-15 (WACKER-CHEMIE (WACKER-CHEMIE) GMBH')
T-30D-CFine SiI! ica
(Fine Silica) (Dow Corning Co., Ltd.) Fransol (Fransol) In the present invention, the dry method synthesized silicic acid fine powder is surface-treated with silicone oil, and these treatment agents It is used in reaction with or physically adsorbed. It is also preferable to treat with an organosilicon compound before treating with silicone oil.

In the present invention, organosilicon compounds include, for example, hexamethyldisilazane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allyl Phenyldichlorosilane, benzyldimethylchlorosilane, bromomethyldimethylchlorosilane, α
-Chlorethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane,
Triorganosilyl mercaptan, trimethylsilyl mercaptan, triorganosilylacrylate, vinylmethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyljethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane, l, 3- Examples include diphenyltetramethyldisiloxane, and dimethylpolysiloxane which has 2 to 12 siloxane units per molecule and contains one Si-bonded hydroxyl group in each unit located at the end.

The silicone oil used in the present invention is generally represented by the following formula.

R: Alkyl group having 1 to 3 carbon atoms R': Alkyl, halogen-modified alkyl, phenyl, silicone oil modified group such as modified phenyl R': Represented by an alkyl group or alkoxy group having 1 to 3 carbon atoms, for example, Examples include dimethyl silicone oil, alkyl-modified silicone oil, γ-methylstyrene-modified silicone oil, chlorphenyl silicone oil, fluorine-modified silicone oil, but are not limited to the above.

The above silicone oil has a viscosity of 5 to 100 at 25℃.
0 centistoke is preferred.

In the present invention, these organosilicon compounds and silicone oils may be used alone or in a mixture of two or more.

In the present invention, the amount of the silicone oil-treated, dry-processed synthetic silicic acid fine powder having a bulk density of 25 g/l or less is as follows: 100 parts by weight of the toner. It is preferable to use 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, the following binder resins for toner can be used when a heating and pressure roller fixing device having an oil coating device is used.

For example, monopolymers of styrene and its substituted products such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene; styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers , styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-methyl chloromethacrylate copolymer, 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-acrylonitrile-indene Styrenic copolymers such as copolymers; polyvinyl chloride, phenolic resin, naturally modified phenolic resin, natural resin-modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin , furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumaron indene resin, petroleum resin, etc. can be used.

In the heating and pressure roller fixing method, in which almost no oil is applied, there is a so-called offset phenomenon 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 reduced. This is an important issue. Developers that require less thermal energy to fix tend to be prone to blocking or caking during storage or in a developing device, so these issues must also be taken into consideration. The physical properties of the binder resin in the developer are most responsible for these phenomena, but according to the research of the present inventors, reducing the content of magnetic material in the developer increases the The adhesion of the developer to the image supporting member is good (although offset is likely to occur, and blocking or caking is also likely to occur. Therefore, in the present invention, when using a heated pressure roller fixing method that does not apply much oil, The selection of the binder resin is more important. Preferred binder materials include crosslinked styrenic copolymers and crosslinked polyesters.

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. acids, monocarboxylic acids having a double bond such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrinitrile, acrylamide, etc., or substituted products thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids with double bonds and substituted products thereof such as methyl maleate, dimethyl maleate, etc.; vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, etc.; e.g. ethylene, propylene, butylene, etc. vinyl monomers such as ethylene olefins; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether; More than one is used.

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,
Carboxylic acid esters having two double bonds such as ethylene glycol diacrylate and l,3-butadiol dimethacrylate; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide, and divinyl sulfone; and three or more vinyl Compounds having groups can be used alone or as a mixture.

In addition, when using a pressure fixing method, it is possible to use a binder resin for pressure fixing developer, 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.

Further, in the developer of the present invention, it is preferable to use a negative charge control agent by blending it into the toner (internal addition) or mixing it with toner particles (external addition).

For example, a negative charge control agent such as a metal complex salt of a monoazo dye; a metal complex salt of salicylic acid, alkyl salicylic acid, dialkyl salicylic acid, or naphthoic acid is used.

Further, it is preferable to use the above-mentioned negative charge control agent (one that does not act as a binder resin) in the form of fine particles. In this case, the number average particle diameter of the charge control agent is specifically preferably 4 μm or less (more preferably 3 μm or less).

When internally added to the developer, such a negative charge control agent is preferably used in an amount of 0.1 to 20 parts by weight (more preferably 0.2 to 10 parts by weight) based on 100 parts by weight of the binder resin.

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 0.00 parts by weight per 100 parts by weight of the binder resin.
5 to 20 parts by weight may be used. Other additives include
For example, a lubricant such as zinc stearate, an abrasive such as cerium oxide or silicon carbide, a fluidity imparting agent such as fine resin particles, aluminum oxide, an anti-caking agent, or a conductivity imparting agent such as carbon black or tin oxide. be.

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.
Adding about 5 wt % to the developer is also one of the preferred features of the present invention.

Further, the developer in the present invention may also serve as a colorant, but the effect is particularly significant when it contains a magnetic material. Magnetic materials used there include magnetite, γ
- Iron oxides such as iron oxides, ferrites, and iron-rich ferrites; metals such as iron, cobalt, and nickel, or these metals and aluminum, cobalt, copper, lead, magnesium,
Examples include alloys with metals such as tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, and vanadium, and mixtures thereof.

These magnetic substances preferably have an average particle size of about 0.1-1 μm, preferably about 0.01 to 0.5 μm, and are contained in the developer in an amount of 3 to 100 parts by weight of the resin component.
The amount is 0 to 120 parts by weight, preferably 40 to 110 parts by weight per 100 parts by weight of the resin component.

The developer in the present invention is produced by ball milling vinyl or non-vinyl thermoplastic resin, magnetic powder, pigment or dye as a coloring agent, charge control agent, other additives, etc. The magnetic powder, coloring agent, and positive charge control are mixed thoroughly using a mixer such as a mixer, and then melted and kneaded using a heat kneader such as a heated roll, niegoo, or extruder to make the resins mutually soluble. After dispersing or dissolving the additives and other additives, cooling and solidifying, pulverizing and classifying,
A negatively chargeable toner according to the present invention is prepared by mixing dry-process synthetic silicic acid fine powder with a bulk density of 25 g/f or less and treated with silicone oil, and other external additives as necessary. You can get it.

When using the toner of the present invention, photoreceptors include cadmium sulfide, selenium, zinc oxide, and organic photoconductors (OPC).
), amorphous silicon (α-5i), etc. are used.

Further, when the developer of the present invention is used, a blade cleaning method, a fur brush cleaning method, a magnetic brush cleaning method, etc. are used as a method for cleaning residual developer etc. on the photoreceptor, but in the present invention,
In consideration of the excellent combination of the developer of the present invention and the photoreceptor, the blade cleaning method is preferred. Also,
Immediately before the cleaning process, a static elimination process or the like may be provided as necessary to facilitate cleaning of the developer.

The method of the present invention will be specifically described below based on Examples. However, this does not limit the embodiments of the present invention in any way. All parts in the examples are parts by weight.

[Example 1] - Styrene/butyl acrylate/divinylbenzene copolymer 100 parts (copolymerization weight ratio 80/19.510.5
．． Weight average molecular weight 320,000)・Magnetite (average particle size 0
．． 2μm) 100 parts Chromium complex of azo dye
1 part/Low molecular weight ethylene-propylene copolymer
4 parts The above materials were mixed in a blender (after mixing, kneaded in a twin-screw kneading extruder set at 150°C. The obtained kneaded product was cooled, coarsely pulverized in a cutter mill, and then kneaded using a jet stream. The resulting finely pulverized powder was classified using a fixed-wall wind classifier to produce classified powder.Furthermore, the obtained classified powder was subjected to multi-part classification using the Coanda effect. Ultra-fine powder and coarse powder were simultaneously strictly classified and removed using a device (Elbowjet classifier manufactured by Nippon Steel Mining Co., Ltd.), and magnetic toner particles with a size of ≦5 μm were 48% by number.12.
Magnetic toner particles of 70 μm or more are O volume %, 6.35 ~
A black fine powder (negatively charged insulating magnetic toner) containing 30% by number of magnetic toner particles of 10.08 μm and a volume average diameter of 6.5 μm was obtained.

On the other hand, silicic acid fine powder synthesized by dry method as silicic acid fine powder (trade name, Aerosil@200. Specific surface area and 2
00d/g, manufactured by Aerosil) was placed in a closed Henschel mixer heated to 70°C, and hexamethylsilazane diluted with alcohol was sprayed to give a treatment amount of 10% by weight to the silicic acid fine powder. while stirring at high speed.

After that, drying was carried out at a temperature of 120°C, and the temperature was again reduced to 70°C.
℃, and then stirred at high speed while spraying dimethylpolysiloxane (viscosity 80 ces at 25℃) diluted with alcohol to give a treatment amount of 20% by weight.The temperature was raised to 300℃ and heat treated for 2 hours. A negatively charged hydrophobic silicic acid fine powder (I) treated with methyldisilazane and silicone oil was obtained.

The bulk density of the silicic acid fine powder (I) was 38 g/f.

Next, the silicic acid fine powder (I) is crushed with a costomizer,
Fine silicic acid powders (■ to ■) having bulk densities shown in Table 1 were obtained. Of these, 2.0 parts of silicic acid fine powder (II) having a bulk density of 18 g/f was mixed with 100 parts of the aforementioned magnetic toner in a Henschel mixer to obtain a negatively chargeable developer A.

LB, a commercially available laser beam printer, uses developer A.
When initial plane exposure was performed using P-8II (manufactured by Canon), a clear image with an image density of 1.34 and no fog and high resolution was obtained, and no white spots were observed in the image area. The results are shown in Table 2 below.

[Example 2] The same procedure as in Example 1 was performed except that silicic acid fine powder (III) having a bulk density of 23 g/f was used instead of silicic acid fine powder (II), and a slight whiteness was observed in the image area. Although there were some spots, it was difficult to see with the naked eye, and it was difficult to see with the naked eye (there were no problems).

[Example 3] A fine silicic acid powder was prepared in the same manner as in Example 1 except that triethoxydecylsilane was used instead of hexamethyldisilazane, and the fine silicic acid powder was crushed using a costomizer. Fine silicic acid powder with a bulk density of 20 g/l (
IV) was obtained. When the same procedure as in Example 1 was carried out using this silicic acid fine powder (IV), good results were obtained with no white spots on the image.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the uncrushed silicic acid fine powder (I) shown in Table 1 was used instead of the silicic acid fine powder (n). As a result, 30-100 μm of silica agglomerates were formed in the initial image area.
A white spot of about 100 yen was generated, which was noticeable especially on solid black, but it was no longer noticeable to the naked eye due to the appearance of several dozen sheets.

Comparative Example 2 The silicic acid fine powder treated only with hexamethyldisilazane in Example 1 was crushed with a costomizer to give a bulk density of 18
A fine silicic acid powder (V) of g/j7 was obtained. When this silicic acid fine powder (V) was used in the same manner as in Example 1, the white spots in the image were good, but voids in the transfer occurred.

Also examples, Table 2 shows the results of the comparative example.

4,

[Brief explanation of drawings]

Figure 1 of the attached drawings shows Silica crushing time and bulk density It is a figure regarding the graph which shows a relationship. $1 Cos ε my? fq destination-i1

Claims (1)

[Claims] (1) A negatively chargeable developer characterized by containing hydrophobic dry silica having a bulk density of 25 g/l or less and treated with silicone oil or varnish.