JPH10301319A - Magnetic developer and image forming method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic developer which produces high quality images. SOLUTION: This magnetic developer consists of toner particles and fine particles of fatty acid metal salt as an external additive. The toner particles consists of a styrene resin having <=200 ppm residual styrene monomer content and a magnetic powder having <=0.4 μm number average particle size in the resin. The fine particles satisfy the relation of Ds 50/Dt 50<=0.6 and Ds 84/Ds 16<=5, wherein Dt 50 is the volume average particle size of the toner particles, Ds 16, Ds 50 and Ds 84 are particle sizes corresponding to 16%, 50% and 84% volume particle size of the fine particles, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to a magnetic developer used for a laser beam printer, a digital copying machine of an electrophotographic system which has recently been receiving attention, and an electrophotographic image forming method using the same.

[0002]

2. Description of the Related Art Developers used in an electrophotographic image forming method include, as is well known, a one-component developer and a two-component developer. The use of a one-component developer makes it possible to reduce the size of the developing device and the image forming apparatus, and has the advantage that the reliability of maintenance is excellent. It is becoming active. It is expected that these small devices will be widely used in small offices and ordinary households in the future.

In an apparatus using a one-component developer, the one-component developer is quickly charged, and a thin layer of the developer is efficiently formed on the developing sleeve. A layer forming member is provided. In addition, a photoconductor using an organic photoconductor as a photosensitive material is often used as the photoconductor, and a blade made of an elastic material such as polyurethane is generally used for cleaning residual particles after image transfer. is there.

[0004] One-component developers include a magnetic developer containing a magnetic material therein and a non-magnetic developer containing no magnetic material. Magnetic developers are generally resins, magnetic materials,
It is manufactured by a so-called crushing method in which a colorant and a charge controlling agent are mixed and melt-kneaded, and then the kneaded material is cooled, crushed and classified to obtain toner particles. In order to improve the fluidity of the toner particles and facilitate the formation of a layer on the developing sleeve, silica particles and other fluidity improvers are externally added and used as a magnetic developer. Alternatively, a monomer composition obtained by dissolving or dispersing a polymerizable monomer, a magnetic material, a colorant, a charge controlling agent, and the like is subjected to suspension polymerization in an aqueous phase containing a suspension stabilizer. There is also a so-called polymerization method for obtaining toner particles.

[0005]

If volatile components such as residual monomers are contained in the resin forming the toner particles, odor is generated during the production process of the toner particles or during the use of the developer, which causes discomfort. It has been pointed out that there is such a problem. The problem of odor and discomfort during use is that the one-component developer is mainly used for devices used in relatively small rooms such as small offices and ordinary households as described above. Considering this, it is an increasingly important issue. Also, if the resin forming the toner particles contains a large amount of volatile components, the chargeability of the developer is reduced, and image defects such as a decrease in image quality density and fog on a white background of an image are generated. Problems such as copying and contamination of the apparatus due to scattering of the agent also occur. This problem is particularly likely to occur in a use environment under bad conditions such as high temperature and high humidity and low temperature and low humidity.

[0006] Since the charging mechanism of the magnetic developer is based on the contact with the developing sleeve, both the opportunity and the contact time for charging are shorter than those of the two-component developer having carrier particles. As a result, the charge amount of each particle is low, and the charge amount distribution is inevitably containing a large amount of the opposite polarity portion. Any of these causes the image density of the obtained image to be low and causes fogging, but the biggest problem is that the transferability in the transfer step is deteriorated, and the transferred image is likely to be hollow. is there. The void in the image makes the characters and lines in the image portion unclear, and is a fatal problem for image formation. In addition, when the magnetic developer is used for a long period of time, there is a problem that the initial charge amount is not maintained and the charge amount decreases. And the decrease in the charge amount due to this long-term use,
It will further promote the occurrence of the above problems. These problems are more likely to become more apparent as developer particles are reduced in size in response to recent market demands for higher image quality.

The problem of insufficient chargeability of the developer particles can be ameliorated by providing a layer forming member for the developing sleeve so as to contact the developing sleeve. However, the problem of a decrease in the charge amount due to long-term use cannot be solved by this, and the problem that image quality deteriorates after long-term use remains. Further, in order to prevent image dropout, it has been considered to increase the output of a corona charger, a roller charger, or the like in the transfer process.
But there is a limit to improvement in this way, and produces a new problem that occurrence of ozone and NO _x is increased by raising the output. Ozone and NO _x is to degrade the organic photoconductor used in the photoreceptor, also adversely affect the human body and the environment to diffuse out of the apparatus.

As another problem of the magnetic developer, the degree of dispersion of the magnetic material inside has a great influence on its characteristics. For example, if the dispersion of the magnetic material is non-uniform and aggregates of the magnetic material are present in the magnetic developer, the organic photoconductive layer on the surface of the photoreceptor will be damaged, and the charging will be non-uniform and fog will worsen. Further, such a magnetic developer tends to aggregate when exposed to a high-temperature and high-humidity environment, and as a result, image quality and image density may be significantly reduced. As described above, the magnetic developer still has many problems to be solved. The present invention seeks to solve these problems.

[0009]

According to the present invention, there is provided a toner comprising a styrene resin having a residual styrene monomer content of 200 ppm or less and magnetic powder having a number average particle diameter of 0.4 μm or less dispersed therein. the particles, fine particles of the fatty acid metal salt are externally added, and the fine particles of the fatty acid metal salt, D _t 50 the volume average diameter of toner particles, a volume 16% diameter of the fine particles of the fatty acid metal salt, the 50% size and 84 % _S 1
6, when D _s 50 and D _s 84 are used, by using a magnetic developer characterized by simultaneously satisfying the following formulas (1) and (2), unpleasant odors are not emitted. An image with good image quality can be formed. _{D s 50 / D t 50 ≦} 0.6 ··· (1) D s 84 / D s 16 ≦ 5 ··· (2)

[0010]

DETAILED DESCRIPTION OF THE INVENTION The styrene resin used in the magnetic developer according to the present invention is styrene, chlorostyrene, α
A (co) polymer of a styrene-based monomer such as methylstyrene or a copolymer of such a styrene-based monomer and another vinyl monomer copolymerizable therewith. The ratio of the styrenic component in these copolymers is usually 50
% By weight or more, preferably 70% by weight or more. Monomers used for copolymerization with the styrene monomer include methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate,
Dodecyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-methacrylic acid
Unsaturated monocarboxylic acid esters such as ethylhexyl; vinyl chloride, vinyl bromide, vinyl fluoride; vinyl esters such as vinyl acetate; acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, and acrylamide; vinyl methyl ether; Vinyl ethers such as vinyl ethyl ether and vinyl isobutyl ether; vinyl naphthalenes; vinyl methyl ketone;
Vinyl ketones such as vinyl hexyl ketone; N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone. Two or more vinyl monomers can be used.

Among these, a combination of monomers that results in a styrene copolymer, a styrene-acrylic copolymer, and a styrene-methacrylic copolymer is preferred. Further, a copolymer crosslinked with a known crosslinking monomer such as divinylbenzene may be used. The production of styrenic resins from these monomers includes solution polymerization, bulk polymerization,
It can be carried out by a conventional polymerization method such as a suspension polymerization method and an emulsion polymerization method.

In the present invention, the amount of the residual styrene monomer in the styrene resin must be 200 ppm or less. The smaller the amount of the residual styrene monomer, the more effective the odor is, and more preferably 100 ppm or less.
If the amount of the residual styrene-based monomer exceeds 200 ppm, in addition to the problem of odor, the dispersibility of the magnetic powder and the charge controlling agent also deteriorates, and image defects such as filming and image density decrease become unfavorable.

As a method for reducing the amount of the residual styrene monomer in the styrene resin to 200 ppm or less, a monomer mixture constituting the styrene resin is synthesized by a polymerization method such as suspension polymerization, and then the resin dispersion is mixed with the resin glass. While heating to a temperature above the transition point, the amount of water in the dispersion is 5 to 50
There is a method of distilling out water of weight% as steam. If a large amount of air, nitrogen, or the like is blown in or the dispersion is heated to near the boiling point, the object can be achieved in a shorter time. Even if the above treatment is performed at a temperature not reaching the glass transition point, the amount of the residual styrene-based monomer in the resin is reduced to 2 because the remaining styrene-based monomer in the resin is hardly released to the outside.
It is difficult to make the content below 00 ppm. Further, even if the amount of evaporated water is further increased, the effect of reducing the residual styrene-based monomer is small, and conversely, problems such as secondary aggregation of the resin may occur. The amount of the residual styrene monomer can be determined by gas chromatography.

As the magnetic powder, a ferromagnetic material exhibiting ferrimagnetism or ferromagnetism at a use environment temperature of a printer, a copying machine or the like, that is, around 0 to 60 ° C. is used.
For example, magnetite (Fe ₃ O ₄ ), maghemite (γ
-Fe ₂ O _3), an intermediate of magnetite and _{maghemite, M x Fe 3-x O} 4 (M is Mn, Fe, Co, Ni,
Spinel ferrites such as Cu, Mg, Zn, Cd, etc. or mixed crystal thereof, BaO.6Fe ₂ O ₃ , SrO.6
Hexagonal ferrites such as Fe ₂ O ₃ , Y ₃ Fe ₅ O ₁₂ ,
Garnet-type oxides such as Sm ₃ Fe ₅ O ₁₂ and ferromagnetic alloys are used. Among them, magnetite, maghemite, an intermediate between magnetite and maghemite, and the like are preferable, and magnetite is particularly preferable. The number average particle size of the magnetic powder must be 0.4 μm or less. Preferably, a magnetic powder having a number average particle size of 0.3 μm or less, particularly 0.2 μm or less is used. Two or more magnetic powders may be used in combination. The magnetic particles are preferably contained in the toner particles in an amount of 10 to 80% by weight, particularly 25 to 60% by weight. The number average particle size of the magnetic powder in the toner particles was determined by randomly selecting about 300 magnetic powder particles in a photograph of a thin section of the toner taken at a magnification of 20,000 times using a transmission electron microscope. It is calculated by actually measuring the diameter in the direction.

The toner particles contain a charge control agent for imparting negative chargeability. As the charge controlling agent, for example, Japanese Patent Publication No. 3-37183, Japanese Patent Publication No. 2-1691
No. 6, JP-A-61-155664, and the like, and metal-containing compounds such as metal complexes of salicylic acids described in JP-B-55-42752 are preferred. Among them, chromium, iron, metal-containing azo dye containing a metal such as cobalt has good dispersibility in the resin described above,
It is preferable because a stable high charge amount can be obtained.

The amount of charge control agent used is styrene resin 1
It is usually 0.1 to 10 parts by weight with respect to 00 parts by weight,
Preferably it is 0.5 to 5 parts by weight. As a colorant for coloring the toner, any suitable pigment or dye conventionally used can be used. For example, carbon black, titanium oxide, zinc white, alumina white, calcium carbonate, navy blue and other inorganic pigments, monoazo pigments, disazo pigments, copper phthalocyanine pigments, organic pigments such as quinacridone pigments, anthraquinone dyes, rhodamine dyes and the like. They can be used alone or in appropriate mixtures. The amount of the colorant to be used is preferably 20 to 200 parts by weight based on 100 parts by weight of the styrene resin, and particularly preferably 30 to 200 parts by weight.
It is desirable to use 120 parts by weight.

In addition, various known auxiliaries can be contained in the toner for the purpose of improving thermal characteristics and physical characteristics. For example, a polyalkylene wax, a paraffin wax, a higher fatty acid, a fatty acid amide, or the like is used as the release agent, and the addition amount thereof is preferably 0.1 to 10 parts by weight based on 100 parts by weight of the styrene resin. To produce toner particles from each of these components, first, a magnetic powder, a styrene-based resin, a colorant, a charge control agent, and the like are blended and mixed in a predetermined ratio. In this case, as a device, a V blender,
A gravity-flow mixer such as a ball mill, a high-speed fluid mixer such as a Henschel mixer (manufactured by Mitsui Miike Kakoki) or a super mixer (manufactured by Kawata) is used.

Next, the mixture is melt-kneaded. As a device used in the melt-kneading process, two or three rolls,
Examples include a Banbury mixer and a single or twin screw extruder. In this step, components having compatibility with the styrene-based resin are melted with the resin, and components such as magnetic powder and charge controlling agent having no compatibility are dispersed in the molten resin.

After the melt-kneaded product is cooled and solidified, toner particles are produced through the steps of pulverization, pulverization and classification. Hammer mills and cutter mills are used for coarse pulverization, and mechanical pulverizers such as high-speed rotary pulverizers and jet pulverizers such as impact-type jet mills and fluidized-bed jet mills are used for fine pulverization. For example, a forced vortex type centrifugal classifier or an inertial classifier is used.

The 50% volume diameter of the toner particles (D _t 50) is preferably 5 to 12 .mu.m. Volume of toner particles 5
If the 0% diameter is smaller than this, the toner tends to scatter,
Image fog tends to worsen. Conversely, if the volume 50% diameter is larger than this, the sharpness of the image tends to decrease. The particle size of the toner particles is measured using a Coulter counter (manufactured by Coulter, USA).

In the present invention, fine particles of a fatty acid metal salt are externally added to the toner particles. As the fatty acid metal salt, one satisfying the following conditions is used.

D _s 50 / D _t 50 ≦ 0.6 (1) D _s 84 / D _s 16 ≦ 5 (2)

Where D _s 16, D _s 50 and D _s 84
Represents the volume 16% diameter of the fatty acid metal salt particles (that is, the particle diameter at the point where the cumulative volume from particles having a small particle diameter is 16%), the volume 50% diameter, and the volume 84% diameter. In addition,
The measurement of the particle size of the fatty acid metal salt is performed by a laser diffraction particle size distribution measuring system Heros & Rodos (SYMPA, Germany).
(Manufactured by TEC) under the following conditions. Dispersion method: Flow type dispersion unit Dispersion air pressure: 2 bar Lens focal length: 100 mm Measurement time: 3 seconds

Conventionally, a fatty acid metal salt has been used for smoothing rubbing due to its friction-reducing action in a contact rubbing step between a photoreceptor and a cleaning blade in an electrophotographic process, for preventing adhesion of particles due to frictional heat and the like. It is known to be effective. However, in a magnetic developer obtained by externally adding a fatty acid metal salt satisfying the above conditions to the above toner particles, in addition to the above-described known functions, the chargeability of the developer is increased, and the charge amount distribution is increased. It has unexpected effects such as reducing the reverse polarity portion and improving the long-term stability of the charging property.

(1) Regarding the particle size of the above fatty acid metal salt
And (2) indicate that the particle size is small and the particle size distribution is narrow.
Means that. D_s50 / D_t50 exceeds 0.6
Fatty acid metal salts fall off the developer and easily scatter
No. If the fatty acid metal salt particles scatter, the equipment may be contaminated.
In addition, large-grain fog occurs on the image. Also D
_s84 / D_sThe fatty acid metal salt in which 16 exceeds 5 is a developer
Has a small effect of improving the long-term stability of the chargeability.

It is desirable that the particle size distribution of the fatty acid metal salt particles be a single-peak distribution. Examples of fatty acids of fatty acid metal salts include monovalent saturated fatty acids such as butyric acid, valeric acid, lauric acid, myristic acid, palmitic acid, stearic acid and montanic acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid, etc. Polyunsaturated fatty acids, monounsaturated fatty acids such as crotonic acid and oleic acid, and polyunsaturated fatty acids such as maleic acid and citraconic acid.

Preferably, saturated or unsaturated fatty acids having from 8 to 35 carbon atoms, in particular stearic acid, are used.
As the metal forming the salt, usually lithium, sodium, potassium, copper, rubinium, silver, zinc, magnesium, calcium, strontium, aluminum, iron,
Cobalt, nickel and the like are used, but zinc, magnesium, calcium, aluminum and the like are preferably used. One of the most preferred fatty acid metal salts is zinc stearate. Fatty acid metal salt is toner particles 1
0.01 to 3 parts by weight, especially 0.03 to 100 parts by weight
It is preferable to add 1 part by weight. The addition of the fatty acid metal salt to the toner particles is preferably performed using a high-speed fluid mixer or the like.

In the present invention, it is preferable that a fluidity improver is externally added to the toner particles in addition to the fatty acid metal salt. As the fluidity improver, it is preferable to use fine particles having an average particle size of 5 to 50 nm, and the shape is preferably spherical. Usually, fine particles of inorganic oxides such as silica, alumina and titania and fine particles of resins such as polymethyl methacrylate, Teflon and silicone resin are used. Among them, silica, alumina, and titania are preferably used alone or in combination, and it is particularly preferable to use silica alone. The silica fine particles may be produced by either a dry method or a wet method. Preferably, silica having a spherical shape and a surface subjected to a hydrophobic treatment is used. The magnetic developer with externally added spherical silica fine particles is compared to the magnetic developer with externally added irregular shaped and angular silica fine particles, and even when used in combination with a photoreceptor using an organic photoconductor for a long time, The surface is hardly scratched, so that it is possible to prevent the developer from adhering and solidifying to the photoreceptor. The shape of the silica fine particles can be determined by observing the primary shape of the silica fine particles using a transmission electron microscope. The spherical shape of the silica fine particles only needs to be substantially spherical, and the shape may be slightly distorted. In other words, the surface of most of the particles is formed as a continuous smooth curved surface and can be used without any trouble as long as it is almost spherical.

As the hydrophobizing agent, hexamethyldisilazane or silicone oil is preferably used. Silica that has been subjected to hydrophobizing treatment hardly forms aggregates, and therefore does not easily damage the photoreceptor. The fluidity improver is toner particles 10
0.05 to 3 parts by weight, especially 0.1 to 2 parts by weight per 0 parts by weight
It is preferable to externally add parts by weight, and the addition method may be performed using a high-speed fluid mixer as in the case of the fatty acid metal salt. If desired, a fatty acid metal salt and a fluidity improver can be mixed and externally added to the toner particles. In this case,
It is preferable to pulverize after mixing to remove coarse aggregates before adding to the toner particles.

The preferred embodiment of the image forming method using the magnetic developer according to the present invention will be described. FIG. 1 is a schematic view of a copying machine used in the method, and 1 is a developing sleeve. The developing sleeve 1 has a cylindrical or cylindrical shape, and a developer 6 is carried on the surface thereof. The developing sleeve is usually made of metal with a magnet inside,
The surface is formed to have an appropriate roughness in order to enhance the transportability of the developer 6. Reference numeral 2 denotes a layer forming member, which has its own elastic force, the elastic force of the developing sleeve 1 or an external force,
Alternatively, the toner is pressed against the developing sleeve 2 by a combination thereof. The layer forming member 2 may have various shapes such as a square rod-shaped rigid body, a projection-shaped elastic body, a leaf spring-shaped one using a surface or a tip, and a roller.
The layer forming member 2 is electrically made of an insulator, made of a conductor and capable of applying a voltage, or made of a conductor and electrically connected to any part. There can be various configurations, such as those that do not exist,
In the magnetic developer according to the present invention, the layer forming member is made of an insulator or a conductor but is not electrically connected, that is, no voltage is applied between the layer forming member and the developing sleeve 1. This is particularly effective in the case of a configuration. This is because, in the case of this configuration, fogging usually occurs due to the oppositely charged toner. By moving the developing sleeve 1 relative to the layer forming member 2 so as to slide, the developer particles pass while expanding the gap between them,
The developer layers are uniformly arranged on the developing sleeve 1 to form a developer layer. In general, the greater the pressure applied when passing through the gap, the thinner the developer layer and the larger the charge amount. However, the thickness and charge amount of the developer layer also depend on the materials and shapes of the developing sleeve 1 and the layer forming member 2 and the voltage applied between them.

Reference numeral 3 denotes a photoreceptor for holding an electrostatic latent image. In the present invention, an organic photoconductor using a polycarbonate resin, an acrylic resin, or the like as a binder is coated on a conductive substrate surface formed of a cylinder or a thin film of aluminum or the like. It is preferable to use a layer in which a photosensitive layer containing is formed by coating. The relative permittivity of the photosensitive layer is about 1 to 5, and the thickness of the photosensitive layer is usually 10 to 50.
It is about μm.

Reference numeral 4 denotes a contact member, which is provided upstream of the layer forming member 2 with respect to the moving direction of the developing sleeve 1. The contact member 4 is for positively attaching the developer 6 to the developing sleeve 1, and may be a sponge-like or brush-like one. That is, the developer is rubbed against the developing sleeve 1 by these. The charging of the developer can be promoted by utilizing the friction at this time. Alternatively, the contact member 4 may be formed of a conductive material, and a voltage may be applied between the contact member 4 and the developing sleeve so that the developer adheres to the developing sleeve 1 by electrostatic force. Further, it can also serve as a cleaning unit for removing the remaining developer from the developing sleeve 1 after developing the electrostatic latent image on the photoconductor 3 attached to the developing sleeve 1. In this case, a voltage may be applied so that a force in a direction in which the developer separates from the developing sleeve 1 is applied. When the cleaning and supply of the developer are performed at the same time, an alternating electric field can be applied to increase the charge amount of the developer. Note that the contact member 4 can be omitted, and if the developer according to the present invention is used, a remarkable effect that omission or fogging in an image hardly occurs even if the developer is omitted is achieved. Reference numeral 5 denotes a seal member for preventing the developer from leaking from a gap below the developing sleeve 1.

The formation of an image is performed according to the general principle of xerography. That is, the photoreceptor 3 is uniformly charged by a corona charger and other commonly used charging members 7, and an electrostatic latent image is formed on the photoreceptor 3 by exposure with a lamp or laser light. At this time, the maximum potential on the photoconductor 3 is set to about 100 to 1200 V, preferably about 300 to 900 V based on the conductive base material. Next, the photoconductor 3 is made to face the developer layer on the developing sleeve 1, and the developer is transferred to visualize the latent image.

At this time, in non-contact development such as flight development, a gap of 50 to 500 μm is formed, and the developer is transferred by electrostatic force. In the case of contact development, the developer is pressed to contact the developer layer, and the developer corresponding to the latent image pattern is transferred by electrostatic force. A general method is to keep the potential of the developing sleeve 1 at a potential between the potential of the latent image at which the developer is to be transferred and the potential of the latent image at which the developer is to be made white.

The developer transferred to the latent image pattern is further transferred to a transfer material such as paper or film by a transfer member 8 in the case of a usual copying machine or laser printer. In this transfer step, the material to be transferred is brought into contact with the photoreceptor,
A method of applying a charge from the back surface by corona discharge, a method of applying a voltage by pressing a conductive transfer roller, and the like are generally used. In the case of a transfer process that applies pressure such as roller transfer,
In general, image voids are likely to occur, but in this case, the present invention is also extremely effective.

After the transfer step, the developer remaining on the photoreceptor is removed by rubbing with a cleaning blade 9 made of polyurethane or the like in contact with the photoreceptor. At this time, in the photoreceptor using the organic photoreceptor layer, poor cleaning, polishing scratches on the photoreceptor surface, and adhesion and fixation of particles to the photoreceptor easily occur, and these cause fatal defects on an image. Occurs. The generation mechanism is presumed as follows. That is, the surface of the photoreceptor using the organic photosensitive layer is mainly made of a polymer material or the like. First, such a polymer material and the like tend to be easily elastically deformed by the pressure of the cleaning blade via the developer. In such a case, a phenomenon occurs in which the developer slips through, so that cleaning failure appears. Secondly, since its hardness is low, continuous rubbing with the cleaning blade through the particles causes scratches and polishing scratches on its surface, and the developer is rubbed into the scratches by frictional heat. It is considered that a point-like or film-like fusing phenomenon occurs and is detected as a stain on an image. The developer according to the present invention exerts a remarkable improvement effect on such a phenomenon. Further, the developer image on the transfer material passes through a heat fixing device 10 such as a hot roll system, and is thermally fused and fixed on the transfer material.

[0037]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. In the examples and comparative examples, “parts” simply means “parts by weight”.

Example 1 A magnetic developer was obtained according to the following compounding ratio. Styrene resin 100 parts (Monomer weight ratio: styrene / n-butyl methacrylate = 80/20) Charge control agent Chromium-containing azo dye 2 parts (Bontron S-34, manufactured by Orient Chemical Co.) Magnetite magnetic powder 70 parts Low molecular weight polypropylene 3 Department (Viscole 550P, manufactured by Sanyo Chemical)

The above-mentioned raw materials were mixed by a high-speed fluid mixer, and then melt-kneaded by a twin-screw extruder. After coarsely pulverized by a hammer mill, finely pulverized by a mechanical pulverizer (Cryptron; manufactured by Kawasaki Heavy Industries, Ltd.), and a zigzag classifier (Alpine)
Was classified. To 100 parts of the toner particles, hydrophobic fine silica particles and zinc stearate particles shown in Table 2 were added by a high-speed fluid mixer to prepare a magnetic developer.

In the evaluation, a commercially available magnetic one-component developing system printer was modified and used as an actual photographing evaluation device. The photoconductor of this printer is a drum-shaped laminated organic photoconductor having a diameter of 30 mm and a polycarbonate resin contained in the surface layer, and a urethane rubber cleaning blade as a cleaning member is pressed against the photoconductor. In the developing device, a urethane rubber blade is pressed against a stainless steel developing sleeve containing a magnet. About 7 in the developing tank of this printer
A magnetic developer was charged and evaluated so that printing on 000 sheets was possible.

The evaluation method is as follows.
C. and a relative humidity of 55%, a normal temperature and normal humidity atmosphere, a temperature of 35.degree. C. and a relative humidity of 85% in a high-temperature and high-humidity atmosphere, and a temperature of 10.degree. Table 3 shows the evaluation results.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

[0045]

[Table 4]

[0046]

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an example of an image forming apparatus that performs a method of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 developing sleeve 2 layer forming member 3 photoreceptor 4 contact member 5 seal member 6 developer 7 charging member 8 transfer member 9 cleaning blade 10 heat fixing machine

Claims (11)

[Claims] Claims: 1. The amount of a residual styrene monomer is 200 pp.
m or less in a styrene resin having a number average particle diameter of 0.4 μm
The toner particles following magnetic powder is contained dispersed, fatty particles of metallic salt are externally added, and the fine particles of the fatty acid metal salt, a volume-average diameter D _t 50 of toner particles, fatty acid metal salts 16% diameter, 50% diameter and 84
A magnetic developer characterized by satisfying the following expressions (1) and (2) at the same time, when the% diameters are D _s 16, D _s 50 and D _s 84, respectively. _{D s 50 / D t 50 ≦} 0.6 ··· (1) D s 84 / D s 16 ≦ 5 ··· (2) 2. The magnetic developer according to claim 1, wherein the number average particle diameter of the magnetic powder is 0.3 μm or less. 3. The magnetic developer according to claim 1, wherein 0.01 to 3 parts by weight of fine particles of a fatty acid metal salt is externally added to 100 parts by weight of the toner particles. 4. The magnetic developer according to claim 1, wherein the fatty acid metal salt is a metal stearate. 5. The magnetic developer according to claim 1, wherein a fluidity improver is externally added to the toner particles in addition to the fine particles of the fatty acid metal salt. 6. The fluidity improver has an average primary particle diameter of 5 to 5.
6. The magnetic developer according to claim 5, wherein the thickness is 0 nm. 7. The magnetic developer according to claim 5, wherein the fluidity improver is selected from the group consisting of silica, titania and alumina. 8. The magnetic developer according to claim 5, wherein the fluidity improver is silica that has been hydrophobized with an organosilicon compound. 9. The magnetic developer according to claim 5, wherein 0.05 to 3 parts by weight of a fluidity improver is externally added to 100 parts by weight of the toner particles. 10. An image forming apparatus comprising: a developing sleeve for holding a developer; and a layer forming member pressed against the developing sleeve. 10. An image forming method comprising a step of developing an electrostatic latent image, transferring a developer image on a photoreceptor to a transfer material, and then cleaning the photoreceptor with a cleaning blade, wherein the developer is used as a developer. An image forming method using the magnetic developer according to any one of the above. 11. The image forming method according to claim 10, wherein the photosensitive member has a photosensitive layer made of an organic photoconductor.